Darcy-Forchheimer flow with Cattaneo-Christov heat flux and homogeneous-heterogeneous reactions

PubMed Central

Hayat, Tasawar; Haider, Farwa; Alsaedi, Ahmed

2017-01-01

Here Darcy-Forchheimer flow of viscoelastic fluids has been analyzed in the presence of Cattaneo-Christov heat flux and homogeneous-heterogeneous reactions. Results for two viscoelastic fluids are obtained and compared. A linear stretching surface has been used to generate the flow. Flow in porous media is characterized by considering the Darcy-Forchheimer model. Modified version of Fourier's law through Cattaneo-Christov heat flux is employed. Equal diffusion coefficients are employed for both reactants and auto catalyst. Optimal homotopy scheme is employed for solutions development of nonlinear problems. Solutions expressions of velocity, temperature and concentration fields are provided. Skin friction coefficient and heat transfer rate are computed and analyzed. Here the temperature and thermal boundary layer thickness are lower for Cattaneo-Christov heat flux model in comparison to classical Fourier's law of heat conduction. Moreover, the homogeneous and heterogeneous reactions parameters have opposite behaviors for concentration field. PMID:28380014

Oscillating-flow loss test results in rectangular heat exchanger passages

NASA Technical Reports Server (NTRS)

Wood, J. Gary

1991-01-01

Test results of oscillating flow losses in rectangular heat exchanger passages of various aspect ratios are given. This work was performed in support of the design of a free-piston Stirling engine (FPSE) for a dynamic space power conversion system. Oscillating flow loss testing was performed using an oscillating flow rig, which was based on a variable stroke and variable frequency linear drive motor. Tests were run over a range of oscillating flow parameters encompassing the flow regimes of the proposed engine design. Test results are presented in both tabular and graphical form and are compared against analytical predictions.

Heat flow and heat generation in greenstone belts

NASA Technical Reports Server (NTRS)

Drury, M. J.

1986-01-01

Heat flow has been measured in Precambrian shields in both greenstone belts and crystalline terrains. Values are generally low, reflecting the great age and tectonic stability of the shields; they range typically between 30 and 50 mW/sq m, although extreme values of 18 and 79 mW/sq m have been reported. For large areas of the Earth's surface that are assumed to have been subjected to a common thermotectonic event, plots of heat flow against heat generation appear to be linear, although there may be considerable scatter in the data. The relationship is expressed as: Q = Q sub o + D A sub o in which Q is the observed heat flow, A sub o is the measured heat generation at the surface, Q sub o is the reduced heat flow from the lower crust and mantle, and D, which has the dimension of length, represents a scale depth for the distribution of radiogenic elements. Most authors have not used data from greenstone belts in attempting to define the relationship within shields, considering them unrepresentative and preferring to use data from relatively homogeneous crystalline rocks. A discussion follows.

A computational analysis subject to thermophysical aspects of Sisko fluid flow over a cylindrical surface

NASA Astrophysics Data System (ADS)

Awais, M.; Khalil-Ur-Rehman; Malik, M. Y.; Hussain, Arif; Salahuddin, T.

2017-09-01

The present analysis is devoted to probing the salient features of the mixed convection and non-linear thermal radiation effects on non-Newtonian Sisko fluid flow over a linearly stretching cylindrical surface. Properties of heat transfer are outlined via variable thermal conductivity and convective boundary conditions. The boundary layer approach is implemented to construct the mathematical model in the form of partial differential equations. Then, the requisite PDEs are transmuted into a complex ordinary differential system by invoking appropriate dimensionless variables. Solution of subsequent ODEs is obtained by utilizing the Runge-Kutta algorithm (fifth order) along with the shooting scheme. The graphical illustrations are presented to interpret the features of the involved pertinent flow parameters on concerning profiles. For a better description of the fluid flow, numerical variations in local skin friction coefficient and local Nusselt number are scrutinized in tables. From thorough analysis, it is inferred that the mixed convection parameter and the curvature parameter increase the velocity while temperature shows a different behavior. Additionally, both momentum and thermal distribution of fluid flow decrease with increasing values of the non-linearity index. Furthermore, variable thermal parameter and heat generation/absorption parameter amplify the temperature significantly. The skin friction is an increasing function of all momentum controlling parameters. The local Nusselt number also shows a similar behavior against heat radiation parameter and variable thermal conductivity parameter while it shows a dual nature for the heat generation/absorption parameter. Finally, the obtained results are validated by comparison with the existing literature and hence the correctness of the analysis is proved.

Unsteady Magnetized Flow and Heat Transfer of a Viscoelastic fluid over a Stretching Surface

NASA Astrophysics Data System (ADS)

Ghosh, Sushil Kumar

2017-12-01

This paper is to study the flow of heated ferro-fluid over a stretching sheet under the influence of magnetic field. The fluid considered in the present investigation is a mixture of blood as well as fluid-dispersed magnetic nano particles and under this context blood is found to be the appropriate choice of viscoelastic, Walter's B fluid. The objective of the present work is to study the effect of various parameters found in the mathematical analysis. Taking into account the blood has zero electrical conductivity, magnetization effect has been considered in the governing equation of the present study with the use of ferro-fluid dynamics principle. By introducing appropriate non-dimensional variables into the governing equations of unsteady two-dimensional flow of viscoelastic fluid with heat transfer are converted to a set of ordinary differential equations with appropriate boundary conditions. Newton's linearization technique has been employed for the solution of non-linear ordinary differential equations. Important results found in the present investigation are the substantial influence of ferro-magnetic parameter, Prandlt number and the parameter associated with the thermal conductivity on the flow and heat transfer. It is observed that the presence of magnetic dipole essentially reduces the flow velocity in the vertical direction and that helps to damage the cancer cells in the tumor region.

NEW MODEL AND MEASUREMENT PRINCIPLE OF FLOWING AND HEAT TRANSFER CHARACTERISTICS OF REGENERATOR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Y. Y.; Graduate University of the Chinese Academy of Sciences, Beijing, 100049; Luo, E. C.

2008-03-16

Regenerators play key role in oscillating-flow cryocoolers or thermoacoustic heat engine systems. However, their flowing and heat transfer mechanism is still not well understood. The complexities of the oscillating flow regenerator make traditional method of heat transfer research become difficult or helpless. In this paper, a model for porous media regenerator was given based on the linear thermoacoustic theory. Then the correlations for characteristic parameters were obtained by deducing universal expressions for thermoacoustic viscous function F{sub v} and thermal function F{sub T}. A simple acoustical method and experimental system to get F{sub v} and F{sub T} via measurements of isothermalmore » regenerators were presented. Some measurements of packed stainless screen regenerators were performed, and preliminary experimental results for flow and convective coefficients were derived, which showing flowing friction factor is approximately within 132/Re to 173/Re.« less

Thermal buoyancy on magneto hydrodynamic flow over a vertical saturated porous surface with viscous dissipation

NASA Astrophysics Data System (ADS)

Nirmala, P. H.; Saila Kumari, A.; Raju, C. S. K.

2018-04-01

In the present article, we studied the magnetohydro dynamic flow induced heat transfer from vertical surface embedded in a saturated porous medium in the presence of viscous dissipation. Appropriate similarity transformations are used to transmute the non-linear governing partial differential equations to non-linear ODE. To solve these ordinary differential equations (ODE) we used the well-known integral method of Von Karman type. A comparison has been done and originates to be in suitable agreement with the previous published results. The tabulated and graphical results are given to consider the physical nature of the problem. From this results we found that the magnetic field parameter depreciate the velocity profiles and improves the heat transfer rate of the flow.

Computational modeling of unsteady third-grade fluid flow over a vertical cylinder: A study of heat transfer visualization

NASA Astrophysics Data System (ADS)

Reddy, G. Janardhana; Hiremath, Ashwini; Kumar, Mahesh

2018-03-01

The present paper aims to investigate the effect of Prandtl number for unsteady third-grade fluid flow over a uniformly heated vertical cylinder using Bejan's heat function concept. The mathematical model of this problem is given by highly time-dependent non-linear coupled equations and are resolved by an efficient unconditionally stable implicit scheme. The time histories of average values of momentum and heat transport coefficients as well as the steady-state flow variables are displayed graphically for distinct values of non-dimensional control parameters arising in the system. As the non-dimensional parameter value gets amplified, the time taken for the fluid flow variables to attain the time-independent state is decreasing. The dimensionless heat function values are closely associated with an overall rate of heat transfer. Thermal energy transfer visualization implies that the heat function contours are compact in the neighborhood of the leading edge of the hot cylindrical wall. It is noticed that the deviations of flow-field variables from the hot wall for a non-Newtonian third-grade fluid flow are significant compared to the usual Newtonian fluid flow.

Physical aspects of heat generation/absorption in the second grade fluid flow due to Riga plate: Application of Cattaneo-Christov approach

NASA Astrophysics Data System (ADS)

Anjum, Aisha; Mir, N. A.; Farooq, M.; Javed, M.; Ahmad, S.; Malik, M. Y.; Alshomrani, A. S.

2018-06-01

The present article concentrates on thermal stratification in the flow of second grade fluid past a Riga plate with linear stretching towards a stagnation region. Heat transfer phenomenon is disclosed with heat generation/absorption. Riga plate is known as electromagnetic actuator which comprises of permanent magnets and alternating electrodes placed on a plane surface. Cattaneo-Christov heat flux model is implemented to analyze the features of heat transfer. This new heat flux model is the generalization of classical Fourier's law with the contribution of thermal relaxation time. For the first time heat generation/absorption effect is computed with non-Fourier's law of heat conduction (i.e., Cattaneo-Christov heat flux model). Transformations are used to obtain the governing non-linear ordinary differential equations. Approximate convergent solutions are developed for the non-dimensionalized governing problems. Physical features of velocity and temperature distributions are graphically analyzed corresponding to various parameters in 2D and 3D. It is noted that velocity field enhances with an increment of modified Hartman number while it reduces with increasing variable thickness parameter. Increment in modified heat generation parameter results in reduction of temperature field.

Effect of Cattaneo-Christov heat flux on buoyancy MHD nanofluid flow and heat transfer over a stretching sheet in the presence of Joule heating and thermal radiation impacts

NASA Astrophysics Data System (ADS)

Dogonchi, A. S.; Ganji, D. D.

2018-06-01

In this study, buoyancy MHD nanofluid flow and heat transfer over a stretching sheet in the presence of Joule heating and thermal radiation impacts, are studied. Cattaneo-Christov heat flux model instead of conventional Fourier's law of heat conduction is applied to investigate the heat transfer characteristics. A similarity transformation is used to transmute the governing momentum and energy equations into non-linear ordinary differential equations with the appropriate boundary conditions. The obtained non-linear ordinary differential equations are solved numerically. The impacts of diverse active parameters such as the magnetic parameter, the radiation parameter, the buoyancy parameter, the heat source parameter, the volume fraction of nanofluid and the thermal relaxation parameter are examined on the velocity and temperature profiles. In addition, the value of the Nusselt number is calculated and presented through figures. The results demonstrate that the temperature profile is lower in the case of Cattaneo-Christov heat flux model as compared to Fourier's law. Moreover, the Nusselt number raises with the raising volume fraction of nanofluid and it abates with the ascending the radiation parameter.

Understanding heat and fluid flow in linear GTA welds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharia, T.; David, S.A.; Vitek, J.M.

1992-01-01

A transient heat flow and fluid flow model was used to predict the development of gas tungsten arc (GTA) weld pools in 1.5 mm thick AISI 304 SS. The welding parameters were chosen so as to correspond to an earlier experimental study which produced high-resolution surface temperature maps. The motivation of the present study was to verify the predictive capability of the computational model. Comparison of the numerical predictions and experimental observations indicate good agreement.

Understanding heat and fluid flow in linear GTA welds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharia, T.; David, S.A.; Vitek, J.M.

1992-12-31

A transient heat flow and fluid flow model was used to predict the development of gas tungsten arc (GTA) weld pools in 1.5 mm thick AISI 304 SS. The welding parameters were chosen so as to correspond to an earlier experimental study which produced high-resolution surface temperature maps. The motivation of the present study was to verify the predictive capability of the computational model. Comparison of the numerical predictions and experimental observations indicate good agreement.

Oscillating flow loss test results in Stirling engine heat exchangers

NASA Technical Reports Server (NTRS)

Koester, G.; Howell, S.; Wood, G.; Miller, E.; Gedeon, D.

1990-01-01

The results are presented for a test program designed to generate a database of oscillating flow loss information that is applicable to Stirling engine heat exchangers. The tests were performed on heater/cooler tubes of various lengths and entrance/exit configurations, on stacked and sintered screen regenerators of various wire diameters and on Brunswick and Metex random fiber regenerators. The test results were performed over a range of oscillating flow parameters consistent with Stirling engine heat exchanger experience. The tests were performed on the Sunpower oscillating flow loss rig which is based on a variable stroke and variable frequency linear drive motor. In general, the results are presented by comparing the measured oscillating flow losses to the calculated flow losses. The calculated losses are based on the cycle integration of steady flow friction factors and entrance/exit loss coefficients.

A Comparative Study for Flow of Viscoelastic Fluids with Cattaneo-Christov Heat Flux.

PubMed

Hayat, Tasawar; Muhammad, Taseer; Alsaedi, Ahmed; Mustafa, Meraj

2016-01-01

This article examines the impact of Cattaneo-Christov heat flux in flows of viscoelastic fluids. Flow is generated by a linear stretching sheet. Influence of thermal relaxation time in the considered heat flux is seen. Mathematical formulation is presented for the boundary layer approach. Suitable transformations lead to a nonlinear differential system. Convergent series solutions of velocity and temperature are achieved. Impacts of various influential parameters on the velocity and temperature are sketched and discussed. Numerical computations are also performed for the skin friction coefficient and heat transfer rate. Our findings reveal that the temperature profile has an inverse relationship with the thermal relaxation parameter and the Prandtl number. Further the temperature profile and thermal boundary layer thickness are lower for Cattaneo-Christov heat flux model in comparison to the classical Fourier's law of heat conduction.

Dual solutions of three-dimensional flow and heat transfer over a non-linearly stretching/shrinking sheet

NASA Astrophysics Data System (ADS)

Naganthran, Kohilavani; Nazar, Roslinda; Pop, Ioan

2018-05-01

This study investigated the influence of the non-linearly stretching/shrinking sheet on the boundary layer flow and heat transfer. A proper similarity transformation simplified the system of partial differential equations into a system of ordinary differential equations. This system of similarity equations is then solved numerically by using the bvp4c function in the MATLAB software. The generated numerical results presented graphically and discussed in the relevance of the governing parameters. Dual solutions found as the sheet stretched and shrunk in the horizontal direction. Stability analysis showed that the first solution is physically realizable whereas the second solution is not practicable.

Investigation of pitchfork bifurcation phenomena effects on heat transfer of viscoelastic flow inside a symmetric sudden expansion

NASA Astrophysics Data System (ADS)

Shahbani-Zahiri, A.; Hassanzadeh, H.; Shahmardan, M. M.; Norouzi, M.

2017-11-01

In this paper, the inertial and non-isothermal flows of the viscoelastic fluid through a planar channel with symmetric sudden expansion are numerically simulated. Effects of pitchfork bifurcation phenomena on the heat transfer rate are examined for the thermally developing and fully developed flow of the viscoelastic fluid inside the expanded part of the planar channel with an expansion ratio of 1:3. The rheological model of exponential Phan Thien-Tanner is used to include both the effects of shear-thinning and elasticity in fluid viscosity. The properties of fluids are temperature-dependent, and the viscous dissipation and heat stored by fluid elasticity are considered in the heat transfer equation. For coupling the governing equations, the PISO algorithm (Pressure Implicit with Splitting of Operator) is applied and the system of equations is linearized using the finite volume method on the collocated grids. The main purpose of this study is to examine the pitchfork bifurcation phenomena and its influences on the temperature distribution, the local and mean Nusselt numbers, and the first and second normal stress differences at different Reynolds, elasticity, and Brinkman numbers. The results show that by increasing the Brinkman number for the heated flow of the viscoelastic fluid inside the expanded part of the channel, the value of the mean Nusselt number is almost linearly decreased. Also, the maximum values of the local Nusselt number for the thermally developing flow and the local Nusselt number of the thermally fully developed flow are decremented by enhancing the Brinkman number.

The Effects of Thermal Radiation on an Unsteady MHD Axisymmetric Stagnation-Point Flow over a Shrinking Sheet in Presence of Temperature Dependent Thermal Conductivity with Navier Slip

PubMed Central

Mondal, Sabyasachi; Haroun, Nageeb A. H.; Sibanda, Precious

2015-01-01

In this paper, the magnetohydrodynamic (MHD) axisymmetric stagnation-point flow of an unsteady and electrically conducting incompressible viscous fluid in with temperature dependent thermal conductivity, thermal radiation and Navier slip is investigated. The flow is due to a shrinking surface that is shrunk axisymmetrically in its own plane with a linear velocity. The magnetic field is imposed normally to the sheet. The model equations that describe this fluid flow are solved by using the spectral relaxation method. Here, heat transfer processes are discussed for two different types of wall heating; (a) a prescribed surface temperature and (b) a prescribed surface heat flux. We discuss and evaluate how the various parameters affect the fluid flow, heat transfer and the temperature field with the aid of different graphical presentations and tabulated results. PMID:26414006

Heat-flow measurements at shot points along the 1978 Saudi Arabia seismic deep-refraction line; Part I, Results of the measurements

USGS Publications Warehouse

Gettings, M.E.; Showail, Abdullah

1982-01-01

Heat-flow measurements were made at five onland shot points of the 1978 Saudi Arabian seismic deep-refraction line, which sample major tectonic elements of the Arabian Shield along a profile from Ar Riyad to the Farasan Islands. Because of the pattern drilling at each shot point, several holes (60 m deep) could be logged for temperature at each site and thus allow a better estimate of the geothermal gradient. Each site was mapped and sampled in detail, and modal and. chemical analyses of representative specimens were made in the laboratory. Thermal conductivities were computed from the modal analyses and single-mineral conductivity data. The resulting heat-flow values, combined with published values for the Red Sea and coastal plain, indicate a three-level pattern, with a heat flow of about 4.5 heat-flow unit (HFU) over the Red Sea axial trough, about 3.0 HFU over the shelf and coastal plain, and an essentially constant 1.0 HFU over the Arabian Shield at points well away from the suture zone with the oceanic crust. At three sites where the rocks are granitic, gamma-ray spectrometry techniques were employed to estimate thorium, potassium, and uranium concentrations. The resulting plot of heat generation versus heat flow suggests that in the Arabian Shield the relationship between heat flow and heat production is not linear. More heat-flow data are essential to establish or reject this conclusion.

Aero-thermal investigation of a highly loaded transonic linear turbine guide vane cascade. A test case for inviscid and viscous flow computations

NASA Astrophysics Data System (ADS)

Arts, T.; Lambertderouvroit, M.; Rutherford, A. W.

1990-09-01

An experimental aerothermal investigation of a highly loaded transonic turbine nozzle guide vane mounted in a linear cascade arrangement is presented. The measurements were performed in a short duration isentropic light piston compression tube facility, allowing a correct simulation of Mach and Reynolds numbers as well as of the gas to wall temperature ratio compared to the values currently observed in modern aeroengines. The experimental program consisted of the following: (1) flow periodicity checks by means of wall static pressure measurements and Schlieren flow visualizations; (2) blade velocity distribution measurements by means of static pressure tappings; (3) blade convective heat transfer measurements by means of static pressure tappings; (4) blade convective heat transfer measurements by means of platinium thin films; (5) downstream loss coefficient and exit flow angle determinations by using a new fast traversing mechanism; and (6) free stream turbulence intensity and spectrum measurements. These different measurements were performed for several combinations of the free stream flow parameters looking at the relative effects on the aerodynamic blade performance and blade convective heat transfer of Mach number, Reynolds number, and freestream turbulence intensity.

Three-phase flow? Consider helical-coil heat exchangers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haraburda, S.S.

1995-07-01

In recent years, chemical process plants are increasingly encountering processes that require heat exchange in three-phase fluids. A typical application, for example, is heating liquids containing solid catalyst particles and non-condensable gases. Heat exchangers designed for three-phase flow generally have tubes with large diameters (typically greater than two inches), because solids can build-up inside the tube and lead to plugging. At the same time, in order to keep heat-transfer coefficients high, the velocity of the process fluid within the tube should also be high. As a result, heat exchangers for three-phase flow may require less than five tubes -- eachmore » having a required linear length that could exceed several hundred feet. Given these limitations, it is obvious that a basic shell-and-tube heat exchanger is not the most practical solution for this purpose. An alternative for three-phase flow is a helical-coil heat exchanger. The helical-coil units offer a number of advantages, including perpendicular, counter-current flow and flexible overall dimensions for the exchanger itself. The paper presents equations for: calculating the tube-side heat-transfer coefficient; calculating the shell-side heat-transfer coefficient; calculating the heat-exchanger size; calculating the tube-side pressure drop; and calculating shell-side pressure-drop.« less

Thermally stratified flow of second grade fluid with non-Fourier heat flux and temperature dependent thermal conductivity

NASA Astrophysics Data System (ADS)

Khan, M. Ijaz; Zia, Q. M. Zaigham; Alsaedi, A.; Hayat, T.

2018-03-01

This attempt explores stagnation point flow of second grade material towards an impermeable stretched cylinder. Non-Fourier heat flux and thermal stratification are considered. Thermal conductivity dependents upon temperature. Governing non-linear differential system is solved using homotopic procedure. Interval of convergence for the obtained series solutions is explicitly determined. Physical quantities of interest have been examined for the influential variables entering into the problems. It is examined that curvature parameter leads to an enhancement in velocity and temperature. Further temperature for non-Fourier heat flux model is less than Fourier's heat conduction law.

Characteristics of melting heat transfer during flow of Carreau fluid induced by a stretching cylinder.

PubMed

Hashim; Khan, Masood; Saleh Alshomrani, Ali

2017-01-01

This article provides a comprehensive analysis of the energy transportation by virtue of the melting process of high-temperature phase change materials. We have developed a two-dimensional model for the boundary layer flow of non-Newtonian Carreau fluid. It is assumed that flow is caused by stretching of a cylinder in the axial direction by means of a linear velocity. Adequate local similarity transformations are employed to determine a set of non-linear ordinary differential equations which govern the flow problem. Numerical solutions to the resultant non-dimensional boundary value problem are computed via the fifth-order Runge-Kutta Fehlberg integration scheme. The solutions are captured for both zero and non-zero curvature parameters, i.e., for flow over a flat plate or flow over a cylinder. The flow and heat transfer attributes are witnessed to be prompted in an intricate manner by the melting parameter, the curvature parameter, the Weissenberg number, the power law index and the Prandtl number. We determined that one of the possible ways to boost the fluid velocity is to increase the melting parameter. Additionally, both the velocity of the fluid and the momentum boundary layer thickness are higher in the case of flow over a stretching cylinder. As expected, the magnitude of the skin friction and the rate of heat transfer decrease by raising the values of the melting parameter and the Weissenberg number.

Investigation of Heat Transfer in Straight and Curved Rectangular Ducts.

DTIC Science & Technology

1980-09-01

theoretical explanation of the heat transfer effects required that all non-linear terms be re- tained in the flow equations. R. Kahawita and R...112, February 1370. 2’. Kahawita , R. and Meroney, R., "The Inffluence of Heating on the Stability of Laminar Boundary Layers Along Con- cave Curved

Unsteady heat transfer performance of heat pipe with axially swallow-tailed microgrooves

NASA Astrophysics Data System (ADS)

Zhang, R. P.

2017-04-01

A mathematical model is developed for predicting the transient heat transfer and fluid flow of heat pipe with axially swallow-tailed microgrooves. The effects of liquid convective heat transfer in the microgrooves, liquid-vapor interfacial phase-change heat transfer and liquid-vapor interfacial shear stress are accounted for in the present model. The coupled non-linear control equations are solved numerically. Mass flow rate at the interface is obtained from the application of kinetic theory. Time variation of wall temperature is studied from the initial startup to steady state. The numerical results are verified by experiments. Time constants for startup and shutdown operation are defined to determine how fast a heat pipe responds to an applied input heat flux, which slightly decreases with increasing heat load.

Molecular shear heating and vortex dynamics in thermostatted two dimensional Yukawa liquids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, Akanksha; Ganesh, Rajaraman, E-mail: ganesh@ipr.res.in; Joy, Ashwin

2016-07-15

It is well known that two-dimensional macroscale shear flows are susceptible to instabilities leading to macroscale vortical structures. The linear and nonlinear fate of such a macroscale flow in a strongly coupled medium is a fundamental problem. A popular example of a strongly coupled medium is a dusty plasma, often modelled as a Yukawa liquid. Recently, laboratory experiments and molecular dynamics (MD) studies of shear flows in strongly coupled Yukawa liquids indicated the occurrence of strong molecular shear heating, which is found to reduce the coupling strength exponentially leading to the destruction of macroscale vorticity. To understand the vortex dynamicsmore » of strongly coupled molecular fluids undergoing macroscale shear flows and molecular shear heating, MD simulation has been performed, which allows the macroscopic vortex dynamics to evolve, while at the same time “removes” the microscopically generated heat without using the velocity degrees of freedom. We demonstrate that by using a configurational thermostat in a novel way, the microscale heat generated by shear flow can be thermostatted out efficiently without compromising the large scale vortex dynamics. In the present work, using MD simulations, a comparative study of shear flow evolution in Yukawa liquids in the presence and absence of molecular or microscopic heating is presented for a prototype shear flow, namely, Kolmogorov flow.« less

Interaction between mantle and crustal detachments: a non-linear system controlling lithospheric extension

NASA Astrophysics Data System (ADS)

Rosenbaum, G.; Regenauer-Lieb, K.; Weinberg, R. F.

2009-12-01

We use numerical modelling to investigate the development of crustal and mantle detachment faults during lithospheric extension. Our models simulate a wide range of rift systems with varying values of crustal thickness and heat flow, showing how strain localization in the mantle interacts with localization in the upper crust and controls the evolution of extensional systems. Model results reveal a richness of structures and deformation styles, which grow in response to a self-organized mechanism that minimizes the internal stored energy of the system by localizing deformation at different levels of the lithosphere. Crustal detachment faults are well developed during extension of overthickened (60 km) continental crust, even when the initial heat flow is relatively low (50 mW/m2). In contrast, localized mantle deformation is most pronounced when the extended lithosphere has a normal crustal thickness (30-40 km) and an intermediate (60-70 mW/m2) heat flow. Results show a non-linear response to subtle changes in crustal thickness or heat flow, characterized by abrupt and sometime unexpected switches in extension modes (e.g. from diffuse rifting to effective lithospheric-scale rupturing) or from mantle- to crust-dominated strain localization. We interpret this non-linearity to result from the interference of doming wavelengths. Disharmony of crust and mantle doming wavelengths results in efficient communication between shear zones at different lithospheric levels, leading to rupturing of the whole lithosphere. In contrast, harmonious crust and mantle doming inhibits interaction of shear zones across the lithosphere and results in a prolonged rifting history prior to continental breakup.

Solid state thermal rectifier

DOEpatents

None

2016-07-05

Thermal rectifiers using linear nanostructures as core thermal conductors have been fabricated. A high mass density material is added preferentially to one end of the nanostructures to produce an axially non-uniform mass distribution. The resulting nanoscale system conducts heat asymmetrically with greatest heat flow in the direction of decreasing mass density. Thermal rectification has been demonstrated for linear nanostructures that are electrical insulators, such as boron nitride nanotubes, and for nanostructures that are conductive, such as carbon nanotubes.

Unsteady boundary layer flow and heat transfer of a Casson fluid past an oscillating vertical plate with Newtonian heating.

PubMed

Hussanan, Abid; Zuki Salleh, Mohd; Tahar, Razman Mat; Khan, Ilyas

2014-01-01

In this paper, the heat transfer effect on the unsteady boundary layer flow of a Casson fluid past an infinite oscillating vertical plate with Newtonian heating is investigated. The governing equations are transformed to a systems of linear partial differential equations using appropriate non-dimensional variables. The resulting equations are solved analytically by using the Laplace transform method and the expressions for velocity and temperature are obtained. They satisfy all imposed initial and boundary conditions and reduce to some well-known solutions for Newtonian fluids. Numerical results for velocity, temperature, skin friction and Nusselt number are shown in various graphs and discussed for embedded flow parameters. It is found that velocity decreases as Casson parameters increases and thermal boundary layer thickness increases with increasing Newtonian heating parameter.

Combined effects of slip and convective boundary condition on MHD 3D stretched flow of nanofluid through porous media inspired by non-linear thermal radiation

NASA Astrophysics Data System (ADS)

Nayak, M. K.; Shaw, Sachin; Pandey, V. S.; Chamkha, Ali J.

2018-02-01

In the present study, the main concern is to investigate the magnetohydrodynamic nanofluid flow subject to porous matrix and convective heating past a permeable linear stretching sheet. In addition, the influence of velocity slip, viscous dissipation, Joule heating and non-linear thermal radiation are considered. A new micro-convection model known as the Patel model is implemented for considerable enhancement of the thermal conductivity and hence, the heat transfer capability of nanofluids. Moreover, a convective heat transfer model is introduced where the bottom surface of the sheet gets heated due to a convection mechanism from a hot fluid of particular temperature. The numerical results of the transformed governing differential equations have been obtained by using fourth-order Runge-Kutta method along with shooting approach and secant method is used for better approximation. In the present analysis, base fluids such as water and Ethylene glycol and Copper, Silver and Aluminum oxide nanoparticles are considered. Results of the present investigation show that inclusion of porous matrix contributes to slow down the fluid velocity and diminution of wall shear stress (axial as well as transverse). Drag force due to magnetic field strength, velocity slip and imposed fluid suction impede the fluid motion and upsurge the heat transfer rate from the surface. In addition, rise in viscous dissipation widens the thermal boundary layer.

Compressible Flow Toolbox

NASA Technical Reports Server (NTRS)

Melcher, Kevin J.

2006-01-01

The Compressible Flow Toolbox is primarily a MATLAB-language implementation of a set of algorithms that solve approximately 280 linear and nonlinear classical equations for compressible flow. The toolbox is useful for analysis of one-dimensional steady flow with either constant entropy, friction, heat transfer, or Mach number greater than 1. The toolbox also contains algorithms for comparing and validating the equation-solving algorithms against solutions previously published in open literature. The classical equations solved by the Compressible Flow Toolbox are as follows: The isentropic-flow equations, The Fanno flow equations (pertaining to flow of an ideal gas in a pipe with friction), The Rayleigh flow equations (pertaining to frictionless flow of an ideal gas, with heat transfer, in a pipe of constant cross section), The normal-shock equations, The oblique-shock equations, and The expansion equations.

Influence of thermal boundary conditions on heat transfer from a cylinder in cross flow

NASA Technical Reports Server (NTRS)

Papell, S. S.

1981-01-01

Local heat transfer data over the leading surface of a cylinder in crossflow were obtained for a Reynolds number range of 50,000. The cylinder was operated at both uniform-wall-temperature and uniform-heat-flux thermal ance of 80 deg from the front stagnation point, the uniform-wall-temperature heat transfer coefficients were as much as 66 percent lower than the uniform-heat-flux data. Between the stagnation point and 60 deg around the cylinder, there were no significant differences in the data. This region of the cylinder is within the cylindrical curvature region of the front end of a real turbine so it was concluded that either thermal boundary condition could be used to model turbine flow over that region of the blade. Results of evaluating the exponent x in the fundamental relationship Nu=f(Re) sup x, which is used in data correlation show the exponent varies as a function of local position on the cylinder even in the laminar flow region. The value of x increases linearly from 0.50 at the stagnation point to 0.59 at 60 deg around the cylinder. This linear trend continued into the separation region at 80 deg for the uniform-wall-temperature data, but x increased markedly in the separation region for the uniform-heat-flux data.

Influence of thermal boundary conditions on heat transfer from a cylinder in cross flow

NASA Astrophysics Data System (ADS)

Papell, S. S.

1981-08-01

Local heat transfer data over the leading surface of a cylinder in crossflow were obtained for a Reynolds number range of 50,000. The cylinder was operated at both uniform-wall-temperature and uniform-heat-flux thermal ance of 80 deg from the front stagnation point, the uniform-wall-temperature heat transfer coefficients were as much as 66 percent lower than the uniform-heat-flux data. Between the stagnation point and 60 deg around the cylinder, there were no significant differences in the data. This region of the cylinder is within the cylindrical curvature region of the front end of a real turbine so it was concluded that either thermal boundary condition could be used to model turbine flow over that region of the blade. Results of evaluating the exponent x in the fundamental relationship Nu=f(Re) sup x, which is used in data correlation show the exponent varies as a function of local position on the cylinder even in the laminar flow region. The value of x increases linearly from 0.50 at the stagnation point to 0.59 at 60 deg around the cylinder. This linear trend continued into the separation region at 80 deg for the uniform-wall-temperature data, but x increased markedly in the separation region for the uniform-heat-flux data.

Double stratification effects in chemically reactive squeezed Sutterby fluid flow with thermal radiation and mixed convection

NASA Astrophysics Data System (ADS)

Ahmad, S.; Farooq, M.; Javed, M.; Anjum, Aisha

2018-03-01

A current analysis is carried out to study theoretically the mixed convection characteristics in squeezing flow of Sutterby fluid in squeezed channel. The constitutive equation of Sutterby model is utilized to characterize the rheology of squeezing phenomenon. Flow characteristics are explored with dual stratification. In flowing fluid which contains heat and mass transport, the first order chemical reaction and radiative heat flux affect the transport phenomenon. The systems of non-linear governing equations have been modulating which then solved by mean of convergent approach (Homotopy Analysis Method). The graphs are reported and illustrated for emerging parameters. Through graphical explanations, drag force, rate of heat and mass transport are conversed for different pertinent parameters. It is found that heat and mass transport rate decays with dominant double stratified parameters and chemical reaction parameter. The present two-dimensional examination is applicable in some of the engineering processes and industrial fluid mechanics.

Photoacoustic thermal flowmetry with a single light source

NASA Astrophysics Data System (ADS)

Liu, Wei; Lan, Bangxin; Hu, Leo; Chen, Ruimin; Zhou, Qifa; Yao, Junjie

2017-09-01

We report a photoacoustic thermal flowmetry based on optical-resolution photoacoustic microscopy (OR-PAM) using a single laser source for both thermal tagging and photoacoustic excitation. When an optically absorbing medium is flowing across the optical focal zone of OR-PAM, a small volume of the medium within the optical focus is repeatedly illuminated and heated by a train of laser pulses with a high repetition rate. The average temperature of the heated volume at each laser pulse is indicated by the photoacoustic signal excited by the same laser pulse due to the well-established linear relationship between the Grueneisen coefficient and the local temperature. The thermal dynamics of the heated medium volume, which are closely related to the flow speed, can therefore be measured from the time course of the detected photoacoustic signals. Here, we have developed a lumped mathematical model to describe the time course of the photoacoustic signals as a function of the medium's flow speed. We conclude that the rising time constant of the photoacoustic signals is linearly dependent on the flow speed. Thus, the flow speed can be quantified by fitting the measured photoacoustic signals using the derived mathematical model. We first performed proof-of-concept experiments using defibrinated bovine blood flowing in a plastic tube. The experiment results have demonstrated that the proposed method has high accuracy (˜±6%) and a wide range of measurable flow speeds. We further validated the method by measuring the blood flow speeds of the microvasculature in a mouse ear in vivo.

A numerical analysis for non-linear radiation in MHD flow around a cylindrical surface with chemically reactive species

NASA Astrophysics Data System (ADS)

Khan, Junaid Ahmad; Mustafa, M.

2018-03-01

Boundary layer flow around a stretchable rough cylinder is modeled by taking into account boundary slip and transverse magnetic field effects. The main concern is to resolve heat/mass transfer problem considering non-linear radiative heat transfer and temperature/concentration jump aspects. Using conventional similarity approach, the equations of motion and heat transfer are converted into a boundary value problem whose solution is computed by shooting method for broad range of slip coefficients. The proposed numerical scheme appears to improve as the strengths of magnetic field and slip coefficients are enhanced. Axial velocity and temperature are considerably influenced by a parameter M which is inversely proportional to the radius of cylinder. A significant change in temperature profile is depicted for growing wall to ambient temperature ratio. Relevant physical quantities such as wall shear stress, local Nusselt number and local Sherwood number are elucidated in detail.

Internal friction between fluid particles of MHD tangent hyperbolic fluid with heat generation: Using coefficients improved by Cash and Karp

NASA Astrophysics Data System (ADS)

Salahuddin, T.; Khan, Imad; Malik, M. Y.; Khan, Mair; Hussain, Arif; Awais, Muhammad

2017-05-01

The present work examines the internal resistance between fluid particles of tangent hyperbolic fluid flow due to a non-linear stretching sheet with heat generation. Using similarity transformations, the governing system of partial differential equations is transformed into a coupled non-linear ordinary differential system with variable coefficients. Unlike the current analytical works on the flow problems in the literature, the main concern here is to numerically work out and find the solution by using Runge-Kutta-Fehlberg coefficients improved by Cash and Karp (Naseer et al., Alexandria Eng. J. 53, 747 (2014)). To determine the relevant physical features of numerous mechanisms acting on the deliberated problem, it is sufficient to have the velocity profile and temperature field and also the drag force and heat transfer rate all as given in the current paper.

Convection Heat and Mass Transfer in a Power Law Fluid with Non Constant Relaxation Time Past a Vertical Porous Plate in the Presence of Thermo and Thermal Diffusion

NASA Astrophysics Data System (ADS)

Olajuwon, B. I.; Oyelakin, I. S.

2012-12-01

The paper investigates convection heat and mass transfer in power law fluid flow with non relaxation time past a vertical porous plate in presence of a chemical reaction, heat generation, thermo diffu- sion and thermal diffusion. The non - linear partial differential equations governing the flow are transformed into ordinary differential equations using the usual similarity method. The resulting similarity equations are solved numerically using Runge-Kutta shooting method. The results are presented as velocity, temperature and concentration profiles for pseudo plastic fluids and for different values of parameters governing the prob- lem. The skin friction, heat transfer and mass transfer rates are presented numerically in tabular form. The results show that these parameters have significant effects on the flow, heat transfer and mass transfer.

Numerical Study of Hydrothermal Wave Suppression in Thermocapillary Flow Using a Predictive Control Method

NASA Astrophysics Data System (ADS)

Muldoon, F. H.

2018-04-01

Hydrothermal waves in flows driven by thermocapillary and buoyancy effects are suppressed by applying a predictive control method. Hydrothermal waves arise in the manufacturing of crystals, including the "open boat" crystal growth process, and lead to undesirable impurities in crystals. The open boat process is modeled using the two-dimensional unsteady incompressible Navier-Stokes equations under the Boussinesq approximation and the linear approximation of the surface thermocapillary force. The flow is controlled by a spatially and temporally varying heat flux density through the free surface. The heat flux density is determined by a conjugate gradient optimization algorithm. The gradient of the objective function with respect to the heat flux density is found by solving adjoint equations derived from the Navier-Stokes ones in the Boussinesq approximation. Special attention is given to heat flux density distributions over small free-surface areas and to the maximum admissible heat flux density.

Centrifugal and Coriolis Effects on Thermal Convection in a Rotating Vertical Cylinder

NASA Astrophysics Data System (ADS)

Lee, Hanjie; Pearlstein, Arne J.

1997-11-01

For a rotating vertical circular cylinder, we compute steady axisymmetric flows driven by heating from below, accounting for both centrifugal and Coriolis effects. We discuss the dependence of the flow and heat transfer on Rayleigh number and Ekman number for selected values of the Prandtl number and aspect ratio. For the case where the sidewall temperature varies linearly, the computed solutions include single- and multi-cell flows. We pay particular attention to deviations from rigid-body rotation, with emphasis on topological division of the flow by surfaces on which the azimuthal velocity is equal to the product of the angular velocity and the radius, or by surfaces on which the meridional flow vanishes.

Heat Transfer in Complex Fluids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mehrdad Massoudi

Amongst the most important constitutive relations in Mechanics, when characterizing the behavior of complex materials, one can identify the stress tensor T, the heat flux vector q (related to heat conduction) and the radiant heating (related to the radiation term in the energy equation). Of course, the expression 'complex materials' is not new. In fact, at least since the publication of the paper by Rivlin & Ericksen (1955), who discussed fluids of complexity (Truesdell & Noll, 1992), to the recently published books (Deshpande et al., 2010), the term complex fluids refers in general to fluid-like materials whose response, namely themore » stress tensor, is 'non-linear' in some fashion. This non-linearity can manifest itself in variety of forms such as memory effects, yield stress, creep or relaxation, normal-stress differences, etc. The emphasis in this chapter, while focusing on the constitutive modeling of complex fluids, is on granular materials (such as coal) and non-linear fluids (such as coal-slurries). One of the main areas of interest in energy related processes, such as power plants, atomization, alternative fuels, etc., is the use of slurries, specifically coal-water or coal-oil slurries, as the primary fuel. Some studies indicate that the viscosity of coal-water mixtures depends not only on the volume fraction of solids, and the mean size and the size distribution of the coal, but also on the shear rate, since the slurry behaves as shear-rate dependent fluid. There are also studies which indicate that preheating the fuel results in better performance, and as a result of such heating, the viscosity changes. Constitutive modeling of these non-linear fluids, commonly referred to as non-Newtonian fluids, has received much attention. Most of the naturally occurring and synthetic fluids are non-linear fluids, for example, polymer melts, suspensions, blood, coal-water slurries, drilling fluids, mud, etc. It should be noted that sometimes these fluids show Newtonian (linear) behavior for a given range of parameters or geometries; there are many empirical or semi-empirical constitutive equations suggested for these fluids. There have also been many non-linear constitutive relations which have been derived based on the techniques of continuum mechanics. The non-linearities oftentimes appear due to higher gradient terms or time derivatives. When thermal and or chemical effects are also important, the (coupled) momentum and energy equations can give rise to a variety of interesting problems, such as instability, for example the phenomenon of double-diffusive convection in a fluid layer. In Conclusion, we have studied the flow of a compressible (density gradient type) non-linear fluid down an inclined plane, subject to radiation boundary condition. The heat transfer is also considered where a source term, similar to the Arrhenius type reaction, is included. The non-dimensional forms of the equations are solved numerically and the competing effects of conduction, dissipation, heat generation and radiation are discussed. It is observed that the velocity increases rapidly in the region near the inclined surface and is slower in the region near the free surface. Since R{sub 7} is a measure of the heat generation due to chemical reaction, when the reaction is frozen (R{sub 7}=0.0) the temperature distributions would depend only on R{sub 1}, and R{sub 2}, representing the effects of the pressure force developed in the material due to the distribution, R{sub 3} and R{sub 4} viscous dissipation, R{sub 5} the normal stress coefficient, R{sub 6} the measure of the emissivity of the particles to the thermal conductivity, etc. When the flow is not frozen (RP{sub 7} > 0) the temperature inside the flow domain is much higher than those at the inclined and free surfaces. As a result, heat is transferred away from the flow toward both the inclined surface and the free surface with a rate that increases as R{sub 7} increases. For a given temperature, an increase in {zeta} implies that the activation energy is smaller and thus, the reaction rate is increased leading to an increase in the heat of the reaction. As a result the flow is chemically heated and its temperature increase. The results shown here indicate that for all values of {zeta} used the chemical effects are significant and the temperature is always higher than both the surface temperature and the free surface temperature. The heat transfer is always from the flow toward both the inclined surface and the free stream. It is also noticed that for all values of m chosen in this study, the temperature is higher than the surface and the free stream temperature. The heat transfer at the inclined surface and at the free stream increase slowly for negative values of m to about m=0.5, but it begins to significantly increase for m greater than 0.5.« less

Continued development of a semianalytical solution for two-phase fluid and heat flow in a porous medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doughty, C.; Pruess, K.

1991-06-01

Over the past few years the authors have developed a semianalytical solution for transient two-phase water, air, and heat flow in a porous medium surrounding a constant-strength linear heat source, using a similarity variable {eta} = r/{radical}t. Although the similarity transformation approach requires a simplified geometry, all the complex physical mechanisms involved in coupled two-phase fluid and heat flow can be taken into account in a rigorous way, so that the solution may be applied to a variety of problems of current interest. The work was motivated by adverse to predict the thermohydrological response to the proposed geologic repository formore » heat-generating high-level nuclear wastes at Yucca Mountain, Nevada, in a partially saturated, highly fractured volcanic formation. The paper describes thermal and hydrologic conditions near the heat source; new features of the model; vapor pressure lowering; and the effective-continuum representation of a fractured/porous medium.« less

Influence of thermal stratification and slip conditions on stagnation point flow towards variable thicked Riga plate

NASA Astrophysics Data System (ADS)

Anjum, A.; Mir, N. A.; Farooq, M.; Khan, M. Ijaz; Hayat, T.

2018-06-01

This article addresses thermally stratified stagnation point flow of viscous fluid induced by a non-linear variable thicked Riga plate. Velocity and thermal slip effects are incorporated to disclose the flow analysis. Solar thermal radiation phenomenon is implemented to address the characteristics of heat transfer. Variations of different physical parameters on the horizontal velocity and temperature distributions are described through graphs. Graphical interpretations of skin friction coefficient (drag force at the surface) and Nusselt number (rate of heat transfer) are also addressed. Modified Hartman number and thermal stratification parameter result in reduction of temperature distribution.

Heat flow and near-surface radioactivity in the Australian continental crust

USGS Publications Warehouse

Sass, J.H.; Jaeger, J.C.; Munroe, Robert J.

1976-01-01

Heat-flow data have been obtained at 44 sites in various parts of Australia. These include seven sites from the old (~ 2500 m.y.) Precambrian shield of Western Australia, seventeen from the younger (~ 600- 2000 m.y.) Precambrian rocks of South Australia, the Northern Territory, and Queensland, and twenty within the eastern Paleozoic and younger rocks. Thirty of the sites are located where no previous heat-flow data existed, and the remainder provide significant extensions or refinements of areas previously studied. Where the holes studied penetrated the crystalline basement rocks, or where the latter rocks were exposed within a few kilometers of the holes, the upper crustal radiogenic heat production has been estimated based on gamma-ray spectrometric determinations of U, Th, and K abundances. Three heat-flow provinces are recognized in Australia based on the linear relation (q = q* + DA0 ) between heat flow q and surface radioactivity A0. New data from the Western Australian shield support earlier studies showing that heat flow is low to normal with values ranging from 0.7 to 1.2 hfu and with the majority of values less than 1.0 hfu, and the parameters q* = 0.63 hfu and 0 = 4.5 km determined previously were confirmed. Heat flow in the Proterozoic shield of central Australia is quite variable, with values ranging between about l and 3 hfu. This variability is attributed mainly to variations in near-surface crustal radioactivity. The parameters of the heat-flow line are q* = 0.64 hfu and 0 = 11.1 km and moderately high temperatures are predicted for the lower crust and upper mantle. Previous suggestions of a band of l ow- to - normal heat flow near the coast in eastern Australia were confirmed in some areas, but the zone is interrupted in at least one region (the Sydney Basin), where heat flow is about 2.0 hfu over a large area. The reduced heat flow, q*, in the Paleozoic intrusive rocks of eastern Australia varies from about 0.8 to 2.0 hfu . This variability might be related to thermal transients associated with Late Tertiary and younger volcanic and tectonic activity, even though the relation between heat-flow values and the age of volcanism is not a simple one. Parts of the high heat-flow area in the southeast might be exploitable for geothermal energy.

Experimental analysis of R134a flow boiling inside a 5 PPI copper foam

NASA Astrophysics Data System (ADS)

Diani, A.; Mancin, S.; Rossetto, L.

2014-04-01

Heat dissipation is one of the most important issues for the reliability of electronic equipment. Boiling can be a very efficient heat transfer mechanism when used to face with the electronic technology needs of efficient and compact heat sinks. Recently, cellular structured materials both stochastic and periodic, particularly open cell metal foams, have been proposed as possible enhanced surfaces to lower the junction temperatures at high heat fluxes. Up today, most of the research on metal foams only regards single phase flow, whereas the two phase flow is still almost unexplored. This paper presents an experimental study on the heat transfer of R134a during flow boiling inside a 5 PPI (Pores Per linear Inch) copper foam, which is 5 mm high, 10 mm wide and 200 mm long, and it is brazed on a 10 mm thick copper plate. The experimental measurements were carried out by imposing three different heat fluxes (50, 75, and 100 kW m-2) and by varying the refrigerant mass velocity between 50 and 200 kg m-2 s-1 and the vapour quality from 0.2 to 0.90, at constant saturation temperature (30°C). The effects of the refrigerant mass flow rate, heat flux and vapour quality on the heat transfer coefficient, dry out phenomenon, and pressure drop are studied.

Non-linear isotope and fast ions effects: routes for low turbulence in DT plasmas

NASA Astrophysics Data System (ADS)

Garcia, Jeronimo

2017-10-01

The isotope effect, i.e. the fact that heat and particle fluxes do not follow the expected Gyro-Bohm estimate for turbulent transport when the plasma mass is changed, is one of the main challenges in plasma theory. Of particular interest is the isotope exchange between the fusion of deuterium (DD) and deuterium-tritium (DT) nuclei as there are no clear indications of what kind of transport difference can be expected in burning plasmas. The GENE code is therefore used for computing DD vs DT linear and nonlinear microturbulence characteristics in the core plasma region of a previously ITER hybrid scenario at high beta obtained in the framework of simplified integrated modelling. Scans on common turbulence related quantitates as external ExB flow shear, Parallel Velocity Gradient (PVG), plasma beta, colisionality or the number of ion species have been performed. Additionally, the role of energetic particles, known to reduce Ion Temperature Gradient (ITG) turbulence has been also addressed. It is obtained that the ITER operational point will be close to threshold and in these conditions turbulence is dominated by ITG modes. A purely weak non-linear isotope effect, absent in linear scans, can be found when separately adding moderate ExB flow shear or electromagnetic effects, whereas collisionality just modulates the intensity. The isotope effect, on the other hand, becomes very strong in conditions with simultaneously moderate ExB flow shear, beta and low q profile with significant reductions of ion heat transport from DD to DT. By analyzing the radial structure of the two point electrostatic potential correlation function it has been found that the inherent Gyro-Bohm scaling for plasma microturbulence, which increases the radial correlation length at short scales form DD to DT, is counteracted by the concomitant appearance of a complex nonlinear multiscale space interaction involving external ExB flow shear, zonal flow activity, magnetic geometry and electromagnetic effects. The number of ion species and the fast ion population is also found to play a role in this non-linear process whereas a symmetry breaking between D and T, with systematic reduced heat and particle transport for T, is always obtained.

Zonal flow dynamics and control of turbulent transport in stellarators.

PubMed

Xanthopoulos, P; Mischchenko, A; Helander, P; Sugama, H; Watanabe, T-H

2011-12-09

The relation between magnetic geometry and the level of ion-temperature-gradient (ITG) driven turbulence in stellarators is explored through gyrokinetic theory and direct linear and nonlinear simulations. It is found that the ITG radial heat flux is sensitive to details of the magnetic configuration that can be understood in terms of the linear behavior of zonal flows. The results throw light on the question of how the optimization of neoclassical confinement is related to the reduction of turbulence.

Heat-flow data and their relation to observed geothermal phenomena near Klamath Falls, Oregon

USGS Publications Warehouse

Sass, J.H.; Sammel, Edward A.

1976-01-01

Two holes were drilled to depths of about 180 m in the Lower Klamath Lake basin south of Klamath Falls, Oregon, to obtain heat flow data and to provide estimates of the thermal conductivity of the valley fill. Twenty-nine thermal conductivity determinations on eight cores give a mean conductivity of 1.82 mcal/cm s °C (0.75 W/m °K). Curvature in the upper 50 m of both terriperature profiles indicates a decrease in surface temperature of about 1.8°C, presumably resulting frorn reclamation of what was marshland in the early part of this century. A surprisingly low heat flow of 0.3 HFU (1 HFU = 10−6 cal/cm2 s = 41.8 mW/m2) was measured at site LS near the center of the basin. At site OC-1, 7 km east of LS and 2 km from the Klamath Hills geothermal zone, the heat flow was 1.44 HFU, also a low value in this setting. Temperature profiles in 15 unused water wells in the area had linear gradients ranging from 47° to 170°C/km. The corresponding lower limits of heat flow (conductivities measured at the two heat flow sites being used) range from 0.8 to 3.1 HFU. These variations in heat flow evidently are caused by temperature variations in a convecting system within the near-surface volcanic rocks and do not provide firm constraints on the nature of heat sources at depth.

Heat conductivity in graphene and related materials: A time-domain modal analysis

NASA Astrophysics Data System (ADS)

Gill-Comeau, Maxime; Lewis, Laurent J.

2015-11-01

We use molecular dynamics (MD) simulations to study heat conductivity in single-layer graphene and graphite. We analyze the MD trajectories through a time-domain modal analysis and show that this is essential for obtaining a reliable representation of the heat flow in graphene and graphite as it permits the proper treatment of collective vibrational excitations, in contrast to a frequency-domain formulation. Our temperature-dependent results are in very good agreement with experiment and, for temperatures in the range 300-1200 K, we find that the ZA branch allows more heat flow than all other branches combined while the contributions of the TA, LA, and ZO branches are comparable at all temperatures. Conductivity mappings reveal strong collective excitations associated with low-frequency ZA modes. We demonstrate that these collective effects are a consequence of the quadratic nature of the ZA branch as they also show up in graphite but are reduced in strained graphene, where the dispersion becomes linear, and are absent in diamond, where acoustic branches are linear. In general, neglecting collective excitations yields errors similar to those from the single-mode relaxation-time approximation.

Chemical reaction for Carreau-Yasuda nanofluid flow past a nonlinear stretching sheet considering Joule heating

NASA Astrophysics Data System (ADS)

Khan, Mair; Shahid, Amna; Malik, M. Y.; Salahuddin, T.

2018-03-01

Current analysis has been made to scrutinize the consequences of chemical response against magneto-hydrodynamic Carreau-Yasuda nanofluid flow induced by a non-linear stretching surface considering zero normal flux, slip and convective boundary conditions. Joule heating effect is also considered. Appropriate similarity approach is used to convert leading system of PDE's for Carreau-Yasuda nanofluid into nonlinear ODE's. Well known mathematical scheme namely shooting method is utilized to solve the system numerically. Physical parameters, namely Weissenberg number We , thermal slip parameter δ , thermophoresis number NT, non-linear stretching parameter n, magnetic field parameter M, velocity slip parameter k , Lewis number Le, Brownian motion parameter NB, Prandtl number Pr, Eckert number Ec and chemical reaction parameter γ upon temperature, velocity and concentration profiles are visualized through graphs and tables. Numerical influence of mass and heat transfer rates and friction factor are also represented in tabular as well as graphical form respectively. Skin friction coefficient reduces when Weissenberg number We is incremented. Rate of heat transfer enhances for large values of Brownian motion constraint NB. By increasing Lewis quantity Le rate of mass transfer declines.

Transverse thermopherotic MHD Oldroyd-B fluid with Newtonian heating

NASA Astrophysics Data System (ADS)

Mehmood, R.; Rana, S.; Nadeem, S.

2018-03-01

Hydromagnetic transverse flow of an Oldroyd-B type fluid with suspension of nanoparticles and Newtonian heating effects is conferred in this article. Relaxation and Retardation time effects are taken into consideration. Using suitable transformations physical problem is converted into non-linear ordinary differential equations which are tackled numerically via Runge-Kutta Fehlberg integration scheme. Illustration of embedded constraints on flow characteristics are extracted through graphs. The physical response of velocity, temperature and concentration are investigated computationally. Momentum boundary layer thickness decreases but local heat and mass flux rises for Deborah number and Hartman number. The results provide interesting insights into certain applicable transport phenomena involving hydromagnetic rheological fluids.

Cattaneo-Christov Heat Flux Model for MHD Three-Dimensional Flow of Maxwell Fluid over a Stretching Sheet.

PubMed

Rubab, Khansa; Mustafa, M

2016-01-01

This letter investigates the MHD three-dimensional flow of upper-convected Maxwell (UCM) fluid over a bi-directional stretching surface by considering the Cattaneo-Christov heat flux model. This model has tendency to capture the characteristics of thermal relaxation time. The governing partial differential equations even after employing the boundary layer approximations are non linear. Accurate analytic solutions for velocity and temperature distributions are computed through well-known homotopy analysis method (HAM). It is noticed that velocity decreases and temperature rises when stronger magnetic field strength is accounted. Penetration depth of temperature is a decreasing function of thermal relaxation time. The analysis for classical Fourier heat conduction law can be obtained as a special case of the present work. To our knowledge, the Cattaneo-Christov heat flux model law for three-dimensional viscoelastic flow problem is just introduced here.

Variation character of stagnation point heat flux for hypersonic pointed bodies from continuum to rarefied flow states and its bridge function study

NASA Astrophysics Data System (ADS)

Wang, Zhihui; Bao, Lin; Tong, Binggang

2009-12-01

This paper is a research on the variation character of stagnation point heat flux for hypersonic pointed bodies from continuum to rarefied flow states by using theoretical analysis and numerical simulation methods. The newly developed near space hypersonic cruise vehicles have sharp noses and wingtips, which desires exact and relatively simple methods to estimate the stagnation point heat flux. With the decrease of the curvature radius of the leading edge, the flow becomes rarefied gradually, and viscous interaction effects and rarefied gas effects come forth successively, which results in that the classical Fay-Riddell equation under continuum hypothesis will become invalid and the variation of stagnation point heat flux is characterized by a new trend. The heat flux approaches the free molecular flow limit instead of an infinite value when the curvature radius of the leading edge tends to 0. The physical mechanism behind this phenomenon remains in need of theoretical study. Firstly, due to the fact that the whole flow regime can be described by Boltzmann equation, the continuum and rarefied flow are analyzed under a uniform framework. A relationship is established between the molecular collision insufficiency in rarefied flow and the failure of Fourier’s heat conduction law along with the increasing significance of the nonlinear heat flux. Then based on an inspiration drew from Burnett approximation, control factors are grasped and a specific heat flux expression containing the nonlinear term is designed in the stagnation region of hypersonic leading edge. Together with flow pattern analysis, the ratio of nonlinear to linear heat flux W r is theoretically obtained as a parameter which reflects the influence of nonlinear factors, i.e. a criterion to classify the hypersonic rarefied flows. Ultimately, based on the characteristic parameter W r , a bridge function with physical background is constructed, which predicts comparative reasonable results in coincidence well with DSMC and experimental data in the whole flow regime.

Thermal Investigation in the Cappadocia Region, Central Anatolia-Turkey, Analyzing Curie Point Depth, Geothermal Gradient, and Heat-Flow Maps from the Aeromagnetic Data

NASA Astrophysics Data System (ADS)

Bilim, Funda; Kosaroglu, Sinan; Aydemir, Attila; Buyuksarac, Aydin

2017-12-01

In this study, curie point depth (CPD), heat flow, geothermal gradient, and radiogenic heat production maps of the Cappadocian region in central Anatolia are presented to reveal the thermal structure from the aeromagnetic data. The large, circular pattern in these maps matches with previously determined shallow (2 km in average) depression. Estimated CPDs in this depression filled with loose volcano-clastics and ignimbrite sheets of continental Neogene units vary from 7 to 12 km, while the geothermal gradient increases from 50 to 68 °C/km. Heat flows were calculated using two different conductivity coefficients of 2.3 and 2.7 Wm-1 K-1. The radiogenic heat production was also obtained between 0.45 and 0.70 μW m-3 in this area. Heat-flow maps were compared with the previous, regional heat-flow map of Turkey and significant differences were observed. In contrast to linear heat-flow increment through the northeast in the previous map in the literature, produced maps in this study include a large, caldera-like circular depression between Nevsehir, Aksaray, Nigde, and Yesilhisar cities indicating high geothermal gradient and higher heat-flow values. In addition, active deformation is evident with young magmatism in the Neogene and Quaternary times and a large volcanic cover on the surface. Boundaries of volcanic eruption centers and buried large intrusions are surrounded with the maxspots of the horizontal gradients of magnetic anomalies. Analytic signal (AS) map pointing-out exact locations of causative bodies is also presented in this study. Circular region in the combined map of AS and maxspots apparently indicates a possible caldera.

Oscillatory instability of a self-rewetting film driven by thermal modulation

NASA Astrophysics Data System (ADS)

Batson, William; Agnon, Yehuda; Oron, Alex

2016-11-01

Here we consider the self-rewetting fluids (SRWFs) that exhibit a well-defined minimum surface tension with respect to temperature, in contrast to those where surface tension decreases linearly. Utilization of SRWFs has grown significantly in the past decade, due to observations that heat transfer is enhanced in applications such as film boiling and pulsating heat pipes. With similar applications in mind, we investigate the dynamics of a thin SRWF film which is subjected to a temperature modulation in the bounding gas. A model is developed within the framework of the long-wave approximation, and a time-averaged thermocapillary driving force for destabilization is uncovered for SRWFs that results from the nonlinear surface tension. Linear analysis of the nonlinear PDE for the film thickness is used to determine the critical conditions at which this driving force destabilizes the film, and, numerical integration of this evolution equation reveals that linearly unstable perturbations saturate to regular periodic solutions (when the modulational frequency is set properly). Properties of these flows such as bifurcation and long-domain flows, where multiple unstable linear modes interact, will also be discussed.

Birch's Crustal Heat Production-Heat Flow Law: Key to Quantifying Mantle Heat Flow as a function of time

NASA Astrophysics Data System (ADS)

Blackwell, D. D.; Thakur, M.

2007-12-01

Birch (1968) first showed the linear correlation of surface heat flow and radioactive heat production (Qs = Qo + bAs ) in granites in New England, USA and discussed implications to the vertical scale of radioactive heat generation in the crust. Subsequently similar relationships have been found worldwide and numerous papers written describing more details and expanding the implications of Birch's Law. The results are a powerful contribution from heat flow research to the understanding of the lithosphere and its evolution. Models are both well constrained experimentally and simple in implications. However, there still exist thermal models of the crust and lithosphere that do not have the same firm foundation and involve unnecessary ad hoc assumptions. A main point of confusion has been that the several of the original relationships were so low in error as to be considered by some to be "fortuitous". Interestingly a "similar" relationship has been proposed based on regional scale averaging of Qs -As data. A second point of confusion is that one admissible crustal radioactivity distribution model (the constant heat generation to depth b) has been criticized as unrealistic for a number of reasons, including the effect of erosion. However, it is appropriate to refer to the Qs -As relationship as a law because in fact the relationship holds as long as the vertical distribution is "geologically realistic." as will be demonstrated in this paper. All geologic and geophysical models of the continental crust imply decreasing heat production as a function of depth (i.e. the seismic layering for example) except in very special cases. This general decrease with depth is the only condition required for the existence of a "linear" Qs -As relationship. A comparison of all the Qs -As relationships proposed for terrains not affected by thermal events over the last 150 to 200 Ma shows a remarkably uniformity in slope (10 ± 3 km) and intercept value (30 ± 5 mWm-2 ). Therefore these parameters of Birch's Law equation represent the starting place for discussions of lithospheric thermal regime and evolution. The stability of the values of intercept Qo for areas with thermal ages of Paleozoic and older prove that the lithosphere heat flow does not vary significantly with age as is demonstrated in the companion paper. The minimum mantle heat flow for preMesozoic thermal terrains is 20 - 25 mWm-2. This value is consistent with the lack of indication from xenolith data that lithosphere thickness changes with age and with theoretical models of mantle convection.

DSMC simulation of rarefied gas flows under cooling conditions using a new iterative wall heat flux specifying technique

NASA Astrophysics Data System (ADS)

Akhlaghi, H.; Roohi, E.; Myong, R. S.

2012-11-01

Micro/nano geometries with specified wall heat flux are widely encountered in electronic cooling and micro-/nano-fluidic sensors. We introduce a new technique to impose the desired (positive/negative) wall heat flux boundary condition in the DSMC simulations. This technique is based on an iterative progress on the wall temperature magnitude. It is found that the proposed iterative technique has a good numerical performance and could implement both positive and negative values of wall heat flux rates accurately. Using present technique, rarefied gas flow through micro-/nanochannels under specified wall heat flux conditions is simulated and unique behaviors are observed in case of channels with cooling walls. For example, contrary to the heating process, it is observed that cooling of micro/nanochannel walls would result in small variations in the density field. Upstream thermal creep effects in the cooling process decrease the velocity slip despite of the Knudsen number increase along the channel. Similarly, cooling process decreases the curvature of the pressure distribution below the linear incompressible distribution. Our results indicate that flow cooling increases the mass flow rate through the channel, and vice versa.

HST3D; a computer code for simulation of heat and solute transport in three-dimensional ground-water flow systems

USGS Publications Warehouse

Kipp, K.L.

1987-01-01

The Heat- and Soil-Transport Program (HST3D) simulates groundwater flow and associated heat and solute transport in three dimensions. The three governing equations are coupled through the interstitial pore velocity, the dependence of the fluid density on pressure, temperature, the solute-mass fraction , and the dependence of the fluid viscosity on temperature and solute-mass fraction. The solute transport equation is for only a single, solute species with possible linear equilibrium sorption and linear decay. Finite difference techniques are used to discretize the governing equations using a point-distributed grid. The flow-, heat- and solute-transport equations are solved , in turn, after a particle Gauss-reduction scheme is used to modify them. The modified equations are more tightly coupled and have better stability for the numerical solutions. The basic source-sink term represents wells. A complex well flow model may be used to simulate specified flow rate and pressure conditions at the land surface or within the aquifer, with or without pressure and flow rate constraints. Boundary condition types offered include specified value, specified flux, leakage, heat conduction, and approximate free surface, and two types of aquifer influence functions. All boundary conditions can be functions of time. Two techniques are available for solution of the finite difference matrix equations. One technique is a direct-elimination solver, using equations reordered by alternating diagonal planes. The other technique is an iterative solver, using two-line successive over-relaxation. A restart option is available for storing intermediate results and restarting the simulation at an intermediate time with modified boundary conditions. This feature also can be used as protection against computer system failure. Data input and output may be in metric (SI) units or inch-pound units. Output may include tables of dependent variables and parameters, zoned-contour maps, and plots of the dependent variables versus time. (Lantz-PTT)

Fundamental aspects of steady-state conversion of heat to work at the nanoscale

NASA Astrophysics Data System (ADS)

Benenti, Giuliano; Casati, Giulio; Saito, Keiji; Whitney, Robert S.

2017-06-01

In recent years, the study of heat to work conversion has been re-invigorated by nanotechnology. Steady-state devices do this conversion without any macroscopic moving parts, through steady-state flows of microscopic particles such as electrons, photons, phonons, etc. This review aims to introduce some of the theories used to describe these steady-state flows in a variety of mesoscopic or nanoscale systems. These theories are introduced in the context of idealized machines which convert heat into electrical power (heat-engines) or convert electrical power into a heat flow (refrigerators). In this sense, the machines could be categorized as thermoelectrics, although this should be understood to include photovoltaics when the heat source is the sun. As quantum mechanics is important for most such machines, they fall into the field of quantum thermodynamics. In many cases, the machines we consider have few degrees of freedom, however the reservoirs of heat and work that they interact with are assumed to be macroscopic. This review discusses different theories which can take into account different aspects of mesoscopic and nanoscale physics, such as coherent quantum transport, magnetic-field induced effects (including topological ones such as the quantum Hall effect), and single electron charging effects. It discusses the efficiency of thermoelectric conversion, and the thermoelectric figure of merit. More specifically, the theories presented are (i) linear response theory with or without magnetic fields, (ii) Landauer scattering theory in the linear response regime and far from equilibrium, (iii) Green-Kubo formula for strongly interacting systems within the linear response regime, (iv) rate equation analysis for small quantum machines with or without interaction effects, (v) stochastic thermodynamic for fluctuating small systems. In all cases, we place particular emphasis on the fundamental questions about the bounds on ideal machines. Can magnetic-fields change the bounds on power or efficiency? What is the relationship between quantum theories of transport and the laws of thermodynamics? Does quantum mechanics place fundamental bounds on heat to work conversion which are absent in the thermodynamics of classical systems?

Channel size influence on the heat flux density at zero net mass flow in the non-linear transport regime between 1.2 and 2.1 K

NASA Technical Reports Server (NTRS)

Frederking, T. H. K.; Yuan, S. W. K.; Lee, J. M.; Sun, G. S.

1987-01-01

Porous media and narrow ducts of simple shape at zero net mass flow (ZNMF) are used to investigate the influence of pore size on the entropy/heat convection rate at ZNMF. The study is relevant to the development of specific types of phase separators. Previous work on heat transport by convection is extended to porous media without mass loss. The experimental results show the influence of pore size on heat flux for permeabilities between 10 to the -8th and 10 to the -6th sq cm. ZNMF plug data are found to be similar to results obtained for vapor liquid phase separation.

General Reynolds analogy on curved surfaces in hypersonic rarefied gas flows with non-equilibrium chemical reactions

NASA Astrophysics Data System (ADS)

Xingxing, Chen; Zhihui, Wang; Yongliang, Yu

2016-11-01

Hypersonic chemical non-equilibrium gas flows around blunt nosed bodies are studied in the present paper to investigate the Reynolds analogy relation on curved surfaces. With a momentum and energy transfer model being applied through boundary layers, influences of molecular dissociations and recombinations on skin frictions and heat fluxes are separately modeled. Expressions on the ratio of Cf / Ch (skin friction coefficient to heat flux) are presented along the surface of circular cylinders under the ideal dissociation gas model. The analysis indicates that molecular dissociations increase the linear distribution of Cf / Ch, but the nonlinear Reynolds analogy relation could ultimately be obtained in flows with larger Reynolds numbers and Mach numbers, where the decrease of wall heat flux by molecular recombinations signifies. The present modeling and analyses are also verified by the DSMC calculations on nitrogen gas flows.

Development of a Linear Stirling Model with Varying Heat Inputs

NASA Technical Reports Server (NTRS)

Regan, Timothy F.; Lewandowski, Edward J.

2007-01-01

The linear model of the Stirling system developed by NASA Glenn Research Center (GRC) has been extended to include a user-specified heat input. Previously developed linear models were limited to the Stirling convertor and electrical load. They represented the thermodynamic cycle with pressure factors that remained constant. The numerical values of the pressure factors were generated by linearizing GRC s non-linear System Dynamic Model (SDM) of the convertor at a chosen operating point. The pressure factors were fixed for that operating point, thus, the model lost accuracy if a transition to a different operating point were simulated. Although the previous linear model was used in developing controllers that manipulated current, voltage, and piston position, it could not be used in the development of control algorithms that regulated hot-end temperature. This basic model was extended to include the thermal dynamics associated with a hot-end temperature that varies over time in response to external changes as well as to changes in the Stirling cycle. The linear model described herein includes not only dynamics of the piston, displacer, gas, and electrical circuit, but also the transient effects of the heater head thermal inertia. The linear version algebraically couples two separate linear dynamic models, one model of the Stirling convertor and one model of the thermal system, through the pressure factors. The thermal system model includes heat flow of heat transfer fluid, insulation loss, and temperature drops from the heat source to the Stirling convertor expansion space. The linear model was compared to a nonlinear model, and performance was very similar. The resulting linear model can be implemented in a variety of computing environments, and is suitable for analysis with classical and state space controls analysis techniques.

Effects of mantle rheologies on viscous heating induced by Glacial Isostatic Adjustment

NASA Astrophysics Data System (ADS)

Huang, PingPing; Wu, Patrick; van der Wal, Wouter

2018-04-01

It has been argued that viscous dissipation from mantle flow in response to surface loading during glacial cycles can result in short-term heating and thus trigger transient volcanism or changes in mantle properties, which may in turn affect mantle dynamics. Furthermore, heating near the Earth's surface can also affect the stability of ice sheets. We have studied the magnitude and spatial-temporal distribution of viscous heating induced in the mantle by the realistic ice model ICE-6G and gravitationally consistent ocean loads. Three types of mantle rheologies, including linear, non-linear and composite rheologies are considered to see if non-linear creep can induce larger viscous heating than linear rheology. We used the Coupled-Laplace-Finite-Element model of Glacial Isostatic Adjustment (GIA) to compute the strain, stress and shear heating during a glacial cycle. We also investigated the upper bound of temperature change and surface heat flux change due to viscous heating. We found that maximum viscous heating occurs near the end of deglaciation near the edge of the ice sheet with amplitude as high as 120 times larger than that of the chondritic radioactive heating. The maximum heat flux due to viscous heating can reach 30 mW m-2, but the area with large heat flux is small and the timescale of heating is short. As a result, the upper bound of temperature change due to viscous heating is small. Even if 30 glacial cycles are included, the largest temperature change can be of the order of 0.3 °C. Thus, viscous heating induced by GIA cannot induce volcanism and cannot significantly affect mantle material properties, mantle dynamics nor ice-sheet stability.

Numerical simulation of the heat transfer at cooling a high-temperature metal cylinder by a flow of a gas-liquid medium

NASA Astrophysics Data System (ADS)

Makarov, S. S.; Lipanov, A. M.; Karpov, A. I.

2017-10-01

The numerical modeling results for the heat transfer during cooling a metal cylinder by a gas-liquid medium flow in an annular channel are presented. The results are obtained on the basis of the mathematical model of the conjugate heat transfer of the gas-liquid flow and the metal cylinder in a two-dimensional nonstationary formulation accounting for the axisymmetry of the cooling medium flow relative to the cylinder longitudinal axis. To solve the system of differential equations the control volume approach is used. The flow field parameters are calculated by the SIMPLE algorithm. To solve iteratively the systems of linear algebraic equations the Gauss-Seidel method with under-relaxation is used. The results of the numerical simulation are verified by comparing the results of the numerical simulation with the results of the field experiment. The calculation results for the heat transfer parameters at cooling the high-temperature metal cylinder by the gas-liquid flow are obtained with accounting for evaporation. The values of the rate of cooling the cylinder by the laminar flow of the cooling medium are determined. The temperature change intensity for the metal cylinder is analyzed depending on the initial velocity of the liquid flow and the time of the cooling process.

Stability analysis on the flow and heat transfer of nanofluid past a stretching/shrinking cylinder with suction effect

NASA Astrophysics Data System (ADS)

Bakar, Nor Ashikin Abu; Bachok, Norfifah; Arifin, Norihan Md.; Pop, Ioan

2018-06-01

The steady boundary layer flow over a stretching/shrinking cylinder with suction effect is numerically studied. Using a similarity transformations, the governing partial differential equations are transformed into a set of nonlinear differential equations and have been solved numerically using a bvp4c code in Matlab software. The nanofluid model used is taking into account the effects of Brownian motion and thermophoresis. The influences of the governing parameters namely the curvature parameter γ, mass suction parameter S, Brownian motion parameter Nb and thermophoresis parameter Nt on the flow, heat and mass transfers characteristics are presented graphically. The numerical results obtained for the skin friction coefficient, local Nusselt number and local Sherwood number are thoroughly determined and presented graphically for several values of the governing parameters. From our investigation, it is found that the non-unique (dual) solutions exist for a certain range of mass suction parameter. It is observed that as curvature parameter increases, the skin friction coefficient and heat transfer rate decrease, meanwhile the mass transfer rates increase. Moreover, the stability analysis showed that the first solution is linearly stable, while the second solution is linearly unstable.

Two-phase magnetoconvection flow of magnetite (Fe3O4) nanoparticles in a horizontal composite porous annulus

NASA Astrophysics Data System (ADS)

Abbas, Zaheer; Hasnain, Jafar

A numerical study is performed to examine the two-phase magnetoconvection and heat transfer phenomena of Fe3O4 -kerosene nanofluid flow in a horizontal composite porous annulus with an external magnetic field. The annulus is filled with immiscible fluids flowing between two concentric cylinders. The governing equations of the flow problem are obtained using Darcy-Brinkman model. Heat transfer is analyzed in the presence of viscous and Darcian dissipation terms. The shooting method is used as a tool to solve the obtained non-linear ordinary differential equations for the velocity and temperature profiles. The velocity and temperature distributions are analyzed and discussed under the influence of involved flow parameters with the aid of graphs. It is found that both velocity and temperature of fluid are decreased with ferroparticle volume fraction. In addition to that, it is also presented that the existence of magnetic field decreases the benefit of ferrofluids in heat transfer progression.

Development of a Linear Stirling System Model with Varying Heat Inputs

NASA Technical Reports Server (NTRS)

Regan, Timothy F.; Lewandowski, Edward J.

2007-01-01

The linear model of the Stirling system developed by NASA Glenn Research Center (GRC) has been extended to include a user-specified heat input. Previously developed linear models were limited to the Stirling convertor and electrical load. They represented the thermodynamic cycle with pressure factors that remained constant. The numerical values of the pressure factors were generated by linearizing GRC's nonlinear System Dynamic Model (SDM) of the convertor at a chosen operating point. The pressure factors were fixed for that operating point, thus, the model lost accuracy if a transition to a different operating point were simulated. Although the previous linear model was used in developing controllers that manipulated current, voltage, and piston position, it could not be used in the development of control algorithms that regulated hot-end temperature. This basic model was extended to include the thermal dynamics associated with a hot-end temperature that varies over time in response to external changes as well as to changes in the Stirling cycle. The linear model described herein includes not only dynamics of the piston, displacer, gas, and electrical circuit, but also the transient effects of the heater head thermal inertia. The linear version algebraically couples two separate linear dynamic models, one model of the Stirling convertor and one model of the thermal system, through the pressure factors. The thermal system model includes heat flow of heat transfer fluid, insulation loss, and temperature drops from the heat source to the Stirling convertor expansion space. The linear model was compared to a nonlinear model, and performance was very similar. The resulting linear model can be implemented in a variety of computing environments, and is suitable for analysis with classical and state space controls analysis techniques.

Heat transfer characteristics within an array of impinging jets. Effects of crossflow temperature relative to jet temperature

NASA Technical Reports Server (NTRS)

Florschuetz, L. W.; Su, C. C.

1985-01-01

Spanwise average heat fluxes, resolved in the streamwise direction to one stream-wise hole spacing were measured for two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate. The jet flow, after impingement, was constrained to exit in a single direction along the channel formed by the jet orifice plate and heat transfer surface. The crossflow originated from the jets following impingement and an initial crossflow was present that approached the array through an upstream extension of the channel. The regional average heat fluxes are considered as a function of parameters associated with corresponding individual spanwise rows within the array. A linear superposition model was employed to formulate appropriate governing parameters for the individual row domain. The effects of flow history upstream of an individual row domain are also considered. The results are formulated in terms of individual spanwise row parameters. A corresponding set of streamwise resolved heat transfer characteristics formulated in terms of flow and geometric parameters characterizing the overall arrays is described.

Three-dimensional instabilities of natural convection between two differentially heated vertical plates: Linear and nonlinear complementary approaches

NASA Astrophysics Data System (ADS)

Gao, Zhenlan; Podvin, Berengere; Sergent, Anne; Xin, Shihe; Chergui, Jalel

2018-05-01

The transition to the chaos of the air flow between two vertical plates maintained at different temperatures is studied in the Boussinesq approximation. After the first bifurcation at critical Rayleigh number Rac, the flow consists of two-dimensional (2D) corotating rolls. The stability of the 2D rolls is examined, confronting linear predictions with nonlinear integration. In all cases the 2D rolls are destabilized in the spanwise direction. Efficient linear stability analysis based on an Arnoldi method shows competition between two eigenmodes, corresponding to different spanwise wavelengths and different types of roll distortion. Nonlinear integration shows that the lower-wave-number mode is always dominant. A partial route to chaos is established through the nonlinear simulations. The flow becomes temporally chaotic for Ra =1.05 Rac , but remains characterized by the spatial patterns identified by linear stability analysis. This highlights the complementary role of linear stability analysis and nonlinear simulation.

User Guide for Compressible Flow Toolbox Version 2.1 for Use With MATLAB(Registered Trademark); Version 7

NASA Technical Reports Server (NTRS)

Melcher, Kevin J.

2006-01-01

This report provides a user guide for the Compressible Flow Toolbox, a collection of algorithms that solve almost 300 linear and nonlinear classical compressible flow relations. The algorithms, implemented in the popular MATLAB programming language, are useful for analysis of one-dimensional steady flow with constant entropy, friction, heat transfer, or shock discontinuities. The solutions do not include any gas dissociative effects. The toolbox also contains functions for comparing and validating the equation-solving algorithms against solutions previously published in the open literature. The classical equations solved by the Compressible Flow Toolbox are: isentropic-flow equations, Fanno flow equations (pertaining to flow of an ideal gas in a pipe with friction), Rayleigh flow equations (pertaining to frictionless flow of an ideal gas, with heat transfer, in a pipe of constant cross section.), normal-shock equations, oblique-shock equations, and Prandtl-Meyer expansion equations. At the time this report was published, the Compressible Flow Toolbox was available without cost from the NASA Software Repository.

Nonlinear oscillatory rarefied gas flow inside a rectangular cavity

NASA Astrophysics Data System (ADS)

Wang, Peng; Zhu, Lianhua; Su, Wei; Wu, Lei; Zhang, Yonghao

2018-04-01

The nonlinear oscillation of rarefied gas flow inside a two-dimensional rectangular cavity is investigated on the basis of the Shakhov kinetic equation. The gas dynamics, heat transfer, and damping force are studied numerically via the discrete unified gas-kinetic scheme for a wide range of parameters, including gas rarefaction, cavity aspect ratio, and oscillation frequency. Contrary to the linear oscillation where the velocity, temperature, and heat flux are symmetrical and oscillate with the same frequency as the oscillating lid, flow properties in nonlinear oscillatory cases turn out to be asymmetrical, and second-harmonic oscillation of the temperature field is observed. As a consequence, the amplitude of the shear stress near the top-right corner of the cavity could be several times larger than that at the top-left corner, while the temperature at the top-right corner could be significantly higher than the wall temperature in nearly the whole oscillation period. For the linear oscillation with the frequency over a critical value, and for the nonlinear oscillation, the heat transfer from the hot to cold region dominates inside the cavity, which is contrary to the anti-Fourier heat transfer in a low-speed rarefied lid-driven cavity flow. The damping force exerted on the oscillating lid is studied in detail, and the scaling laws are developed to describe the dependency of the resonance and antiresonance frequencies (corresponding to the damping force at a local maximum and minimum, respectively) on the reciprocal aspect ratio from the near hydrodynamic to highly rarefied regimes. These findings could be useful in the design of the micro-electro-mechanical devices operating in the nonlinear-flow regime.

Three dimensional rotating flow of Powell-Eyring nanofluid with non-Fourier's heat flux and non-Fick's mass flux theory

NASA Astrophysics Data System (ADS)

Ibrahim, Wubshet

2018-03-01

This article numerically examines three dimensional boundary layer flow of a rotating Powell-Eyring nanofluid. In modeling heat transfer processes, non-Fourier heat flux theory and for mass transfer non-Fick's mass flux theory are employed. This theory is recently re-initiated and it becomes the active research area to resolves some drawback associated with the famous Fourier heat flux and mass flux theory. The mathematical model of the flow problem is a system of non-linear partial differential equations which are obtained using the boundary layer analysis. The non-linear partial differential equations have been transformed into non-linear high order ordinary differential equations using similarity transformation. Employing bvp4c algorithm from matlab software routine, the numerical solution of the transformed ordinary differential equations is obtained. The governing equations are constrained by parameters such as rotation parameter λ , the non-Newtonian parameter N, dimensionless thermal relaxation and concentration relaxation parameters δt and δc . The impacts of these parameters have been discussed thoroughly and illustrated using graphs and tables. The findings show that thermal relaxation time δt reduces the thermal and concentration boundary layer thickness. Further, the results reveal that the rotational parameter λ has the effect of decreasing the velocity boundary layer thickness in both x and y directions. Further examination pinpoints that the skin friction coefficient along x-axis is an increasing and skin friction coefficient along y-axis is a decreasing function of rotation parameter λ . Furthermore, the non-Newtonian fluid parameter N has the characteristic of reducing the amount of local Nusselt numbers -f″ (0) and -g″ (0) both in x and y -directions.

Magnetohydrodynamics Carreau nanofluid flow over an inclined convective heated stretching cylinder with Joule heating

NASA Astrophysics Data System (ADS)

Khan, Imad; Shafquatullah; Malik, M. Y.; Hussain, Arif; Khan, Mair

Current work highlights the computational aspects of MHD Carreau nanofluid flow over an inclined stretching cylinder with convective boundary conditions and Joule heating. The mathematical modeling of physical problem yields nonlinear set of partial differential equations. A suitable scaling group of variables is employed on modeled equations to convert them into non-dimensional form. The integration scheme Runge-Kutta-Fehlberg on the behalf of shooting technique is utilized to solve attained set of equations. The interesting aspects of physical problem (linear momentum, energy and nanoparticles concentration) are elaborated under the different parametric conditions through graphical and tabular manners. Additionally, the quantities (local skin friction coefficient, local Nusselt number and local Sherwood number) which are responsible to dig out the physical phenomena in the vicinity of stretched surface are computed and delineated by varying controlling flow parameters.

The inviscid stability of supersonic flow past heated or cooled axisymmetric bodies

NASA Technical Reports Server (NTRS)

Shaw, Stephen J.; Duck, Peter W.

1992-01-01

The inviscid, linear, nonaxisymmetric, temporal stability of the boundary layer associated with the supersonic flow past axisymmetric bodies (with particular emphasis on long thin, straight circular cylinders), subject to heated or cooled wall conditions is investigated. The eigenvalue problem is computed in some detail for a particular Mach number or 3.8, revealing that the effect of curvature and the choice of wall conditions both have a significant effect on the stability of the flow. Both the asymptotic, large azimuthal wavenumber solution and the asymptotic, far downstream solution are obtained for the stability analysis and compared with numerical results. Additionally, asymptotic analyses valid for large radii of curvature with cooled/heated wall conditions are presented. In general, important differences were found to exist between the wall temperature conditions imposed and the adiabatic wall conditions considered previously.

Finite-analytic numerical solution of heat transfer in two-dimensional cavity flow

NASA Technical Reports Server (NTRS)

Chen, C.-J.; Naseri-Neshat, H.; Ho, K.-S.

1981-01-01

Heat transfer in cavity flow is numerically analyzed by a new numerical method called the finite-analytic method. The basic idea of the finite-analytic method is the incorporation of local analytic solutions in the numerical solutions of linear or nonlinear partial differential equations. In the present investigation, the local analytic solutions for temperature, stream function, and vorticity distributions are derived. When the local analytic solution is evaluated at a given nodal point, it gives an algebraic relationship between a nodal value in a subregion and its neighboring nodal points. A system of algebraic equations is solved to provide the numerical solution of the problem. The finite-analytic method is used to solve heat transfer in the cavity flow at high Reynolds number (1000) for Prandtl numbers of 0.1, 1, and 10.

The inviscid stability of supersonic flow past heated or cooled axisymmetric bodies

NASA Technical Reports Server (NTRS)

Shaw, Stephen J.; Duck, Peter W.

1990-01-01

The inviscid, linear, nonaxisymmetric, temporal stability of the boundary layer associated with the supersonic flow past axisymmetric bodies (with particular emphasis on long thin, straight circular cylinders), subject to heated or cooled wall conditions is investigated. The eigenvalue problem is computed in some detail for a particular Mach number or 3.8, revealing that the effect of curvature and the choice of wall conditions both have a significant effect on the stability of the flow. Both the asymptotic, large azimuthal wavenumber solution and the asymptotic, far downstream solution are obtained for the stability analysis and compared with numerical results. Additionally, asymptotic analyses valid for large radii of curvature with cooled/heated wall conditions, are presented. In general, important differences were found to exist between the wall temperature conditions imposed and the adiabatic wall conditions considered previously.

Bifurcation physics of magnetic islands and stochasticity explored by heat pulse propagation studies in toroidal plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ida, K.; Kobayashi, T.; Yoshinuma, M.

Bifurcation physics of the magnetic island was investigated using the heat pulse propagation technique produced by the modulation of electron cyclotron heating. There are two types of bifurcation phenomena observed in LHD and DIII-D. One is a bifurcation of the magnetic topology between nested and stochastic fields. The nested state is characterized by the bi-directional (inward and outward) propagation of the heat pulse with slow propagation speed. The stochastic state is characterized by the fast propagation of the heat pulse with electron temperature flattening. The other bifurcation is between magnetic island with larger thermal diffusivity and that with smaller thermalmore » diffusivity. The damping of toroidal flow is observed at the O-point of the magnetic island both in helical plasmas and in tokamak plasmas during a mode locking phase with strong flow shears at the boundary of the magnetic island. Associated with the stochastization of the magnetic field, the abrupt damping of toroidal flow is observed in LHD. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. Lastly, this observation suggests that this flow damping is due to the change in the non-diffusive term of momentum transport.« less

Bifurcation physics of magnetic islands and stochasticity explored by heat pulse propagation studies in toroidal plasmas

DOE PAGES

Ida, K.; Kobayashi, T.; Yoshinuma, M.; ...

2016-07-29

Bifurcation physics of the magnetic island was investigated using the heat pulse propagation technique produced by the modulation of electron cyclotron heating. There are two types of bifurcation phenomena observed in LHD and DIII-D. One is a bifurcation of the magnetic topology between nested and stochastic fields. The nested state is characterized by the bi-directional (inward and outward) propagation of the heat pulse with slow propagation speed. The stochastic state is characterized by the fast propagation of the heat pulse with electron temperature flattening. The other bifurcation is between magnetic island with larger thermal diffusivity and that with smaller thermalmore » diffusivity. The damping of toroidal flow is observed at the O-point of the magnetic island both in helical plasmas and in tokamak plasmas during a mode locking phase with strong flow shears at the boundary of the magnetic island. Associated with the stochastization of the magnetic field, the abrupt damping of toroidal flow is observed in LHD. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. Lastly, this observation suggests that this flow damping is due to the change in the non-diffusive term of momentum transport.« less

Heat and mass transfer in MHD free convection from a moving permeable vertical surface by a perturbation technique

NASA Astrophysics Data System (ADS)

Abdelkhalek, M. M.

2009-05-01

Numerical results are presented for heat and mass transfer effect on hydromagnetic flow of a moving permeable vertical surface. An analysis is performed to study the momentum, heat and mass transfer characteristics of MHD natural convection flow over a moving permeable surface. The surface is maintained at linear temperature and concentration variations. The non-linear coupled boundary layer equations were transformed and the resulting ordinary differential equations were solved by perturbation technique [Aziz A, Na TY. Perturbation methods in heat transfer. Berlin: Springer-Verlag; 1984. p. 1-184; Kennet Cramer R, Shih-I Pai. Magneto fluid dynamics for engineers and applied physicists 1973;166-7]. The solution is found to be dependent on several governing parameter, including the magnetic field strength parameter, Prandtl number, Schmidt number, buoyancy ratio and suction/blowing parameter, a parametric study of all the governing parameters is carried out and representative results are illustrated to reveal a typical tendency of the solutions. Numerical results for the dimensionless velocity profiles, the temperature profiles, the concentration profiles, the local friction coefficient and the local Nusselt number are presented for various combinations of parameters.

Cattaneo-Christov based study of {TiO}_2 -CuO/EG Casson hybrid nanofluid flow over a stretching surface with entropy generation

NASA Astrophysics Data System (ADS)

Jamshed, Wasim; Aziz, Asim

2018-06-01

In the present research, a simplified mathematical model is presented to study the heat transfer and entropy generation analysis of thermal system containing hybrid nanofluid. Nanofluid occupies the space over an infinite horizontal surface and the flow is induced by the non-linear stretching of surface. A uniform transverse magnetic field, Cattaneo-Christov heat flux model and thermal radiation effects are also included in the present study. The similarity technique is employed to reduce the governing non-linear partial differential equations to a set of ordinary differential equation. Keller Box numerical scheme is then used to approximate the solutions for the thermal analysis. Results are presented for conventional copper oxide-ethylene glycol (CuO-EG) and hybrid titanium-copper oxide/ethylene glycol ({TiO}_2 -CuO/EG) nanofluids. The spherical, hexahedron, tetrahedron, cylindrical, and lamina-shaped nanoparticles are considered in the present analysis. The significant findings of the study is the enhanced heat transfer capability of hybrid nanofluids over the conventional nanofluids, greatest heat transfer rate for the smallest value of the shape factor parameter and the increase in Reynolds number and Brinkman number increases the overall entropy of the system.

Slip and frictional heating of extruded polyethylene melts

NASA Astrophysics Data System (ADS)

Pérez-González, José; Marín-Santibáñez, Benjamín M.; Zamora-López, Héctor S.; Rodríguez-González, Francisco

2017-05-01

Extrusion of polymer melts with slip at the die generates frictional heating. The relationship between slip flow and frictional heating during the continuous extrusion of a non-slipping linear low-density (LLDPE) and a slipping high-density polyethylene (HDPE), respectively, both pure as well as blended with a fluoropolymer processing aid (PA), was investigated in this work by Rheo-particle image velocimetry and thermal imaging. Significant rises in temperature were measured under slip and no slip conditions, being these much higher than the values predicted by the adiabatic flow assumption. Clear difference was made between viscous and frictional heating before the stick-slip regime for the LLDPE, even though they could not be distinguished from one another at higher stresses. Such a difference, however, could not be made for the slipping HDPE, since overall in the presence of slip, frictional and viscous heating act synergistically to increase the melt temperature.

Modeling Microscale Electro-thermally Induced Vortex Flows

NASA Astrophysics Data System (ADS)

Paul, Rajorshi; Tang, Tian; Kumar, Aloke

2017-11-01

In presence of a high frequency alternating electric field and a laser induced heat source, vortex flows are generated inside micro-channels. Such electro-thermally influenced micro-vortices can be used for manipulating nano-particles, programming colloidal assemblies, trapping biological cells as well as for fabricating designed bacterial biofilms. In this study, a theoretical model is developed for microscale electro-thermally induced vortex flows with multiple heat sources. Semi-analytical solutions are obtained, using Hankel transformation and linear superposition, for the temperature, pressure and velocity fields. The effect of material properties such as electrical and thermal conductivities, as well as experimental parameters such as the frequency and strength of the alternating electric field, and the intensity and heating profile of the laser source, are systematically investigated. Resolution for a pair of laser sources is determined by analyzing the strength of the micro-vortices under the influence of two heating sources. Results from this work will provide useful insights into the design of efficient optical tweezers and Rapid Electrokinetic Patterning techniques.

Influence of Lorentz force, Cattaneo-Christov heat flux and viscous dissipation on the flow of micropolar fluid past a nonlinear convective stretching vertical surface

NASA Astrophysics Data System (ADS)

Gnaneswara Reddy, Machireddy

2017-12-01

The problem of micropolar fluid flow over a nonlinear stretching convective vertical surface in the presence of Lorentz force and viscous dissipation is investigated. Due to the nature of heat transfer in the flow past vertical surface, Cattaneo-Christov heat flux model effect is properly accommodated in the energy equation. The governing partial differential equations for the flow and heat transfer are converted into a set of ordinary differential equations by employing the acceptable similarity transformations. Runge-Kutta and Newton's methods are utilized to resolve the altered governing nonlinear equations. Obtained numerical results are compared with the available literature and found to be an excellent agreement. The impacts of dimensionless governing flow pertinent parameters on velocity, micropolar velocity and temperature profiles are presented graphically for two cases (linear and nonlinear) and analyzed in detail. Further, the variations of skin friction coefficient and local Nusselt number are reported with the aid of plots for the sundry flow parameters. The temperature and the related boundary enhances enhances with the boosting values of M. It is found that fluid temperature declines for larger thermal relaxation parameter. Also, it is revealed that the Nusselt number declines for the hike values of Bi.

Evaluating geothermal and hydrogeologic controls on regional groundwater temperature distribution

USGS Publications Warehouse

Burns, Erick R.; Ingebritsen, Steven E.; Manga, Michael; Williams, Colin F.

2016-01-01

A one-dimensional (1-D) analytic solution is developed for heat transport through an aquifer system where the vertical temperature profile in the aquifer is nearly uniform. The general anisotropic form of the viscous heat generation term is developed for use in groundwater flow simulations. The 1-D solution is extended to more complex geometries by solving the equation for piece-wise linear or uniform properties and boundary conditions. A moderately complex example, the Eastern Snake River Plain (ESRP), is analyzed to demonstrate the use of the analytic solution for identifying important physical processes. For example, it is shown that viscous heating is variably important and that heat conduction to the land surface is a primary control on the distribution of aquifer and spring temperatures. Use of published values for all aquifer and thermal properties results in a reasonable match between simulated and measured groundwater temperatures over most of the 300 km length of the ESRP, except for geothermal heat flow into the base of the aquifer within 20 km of the Yellowstone hotspot. Previous basal heat flow measurements (∼110 mW/m2) made beneath the ESRP aquifer were collected at distances of >50 km from the Yellowstone Plateau, but a higher basal heat flow of 150 mW/m2 is required to match groundwater temperatures near the Plateau. The ESRP example demonstrates how the new tool can be used during preliminary analysis of a groundwater system, allowing efficient identification of the important physical processes that must be represented during more-complex 2-D and 3-D simulations of combined groundwater and heat flow.

The Madden-Julian Oscillation and the Indo-Pacific Warm Pool

NASA Astrophysics Data System (ADS)

Raymond, David J.; Fuchs, Željka

2018-04-01

A minimal model of the interaction of the Madden-Julian oscillation (MJO) with the Indo-Pacific warm pool is presented. This model is based on the linear superposition of the flow associated with a highly simplified treatment of the MJO plus the flow induced by the warm pool itself. Both of these components parameterize rainfall as proportional to the column water vapor, which in turn is governed by a linearized moisture equation in which WISHE (wind induced surface heat exchange) plays a governing role. The MJO component has maximum growth rate for planetary wavenumber 1 and is equatorially trapped with purely zonal winds. The warm pool component exhibits a complex flow pattern, differing significantly from the classical Gill model as a result of the mean easterly flow. The combination of the two produce a flow that reproduces many aspects of the observed global flow associated with the MJO.

Initial study of thermal energy storage in unconfined aquifers. [UCATES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haitjema, H.M.; Strack, O.D.L.

1986-04-01

Convective heat transport in unconfined aquifers is modeled in a semi-analytic way. The transient groundwater flow is modeled by superposition of analytic functions, whereby changes in the aquifer storage are represented by a network of triangles, each with a linearly varying sink distribution. This analytic formulation incorporates the nonlinearity of the differential equation for unconfined flow and eliminates numerical dispersion in modeling heat convection. The thermal losses through the aquifer base and vadose zone are modeled rather crudely. Only vertical heat conduction is considered in these boundaries, whereby a linearly varying temperature is assumed at all times. The latter assumptionmore » appears reasonable for thin aquifer boundaries. However, assuming such thin aquifer boundaries may lead to an overestimation of the thermal losses when the aquifer base is regarded as infinitely thick in reality. The approach is implemented in the computer program UCATES, which serves as a first step toward the development of a comprehensive screening tool for ATES systems in unconfined aquifers. In its present form, the program is capable of predicting the relative effects of regional flow on the efficiency of ATES systems. However, only after a more realistic heatloss mechanism is incorporated in UCATES will reliable predictions of absolute ATES efficiencies be possible.« less

Patterning of ultrathin polymethylmethacrylate films by in-situ photodirecting of the Marangoni flow

NASA Astrophysics Data System (ADS)

Elashnikov, Roman; Fitl, Premysl; Svorcik, Vaclav; Lyutakov, Oleksiy

2017-02-01

Laser heating and Marangoni flow result in the formation of surface structures with different geometries and shape on thin polymer films. By laser beam irradiation combined with a sample movement the solid polymethylmethacrylate (PMMA) films are heated and undergo phase transition which leads to a material flow. Since the laser beam has a non-linear distribution of energy, the PMMA film is heated inhomogeneously and a surface tension gradient in a lateral direction is introduced. During this procedure additional phenomena such as "reversible" or cyclic polymer flow also take place. The careful choice of experimental conditions enables the preparation of patterns with sophisticated geometries and with hierarchical pattern organization. Depending on initial PMMA film thickness and speed of the sample movement line arrays are created, which can subsequently be transformed into the crimped lines or system of circular holes. In addition, the introduction of a constant acceleration in the sample movement or a laser beam distortion enables the preparation of regularly crimped lines, ordered hexagonal holes or overlapped plates.

Radiated flow of chemically reacting nanoliquid with an induced magnetic field across a permeable vertical plate

NASA Astrophysics Data System (ADS)

Mahanthesh, B.; Gireesha, B. J.; Athira, P. R.

Impact of induced magnetic field over a flat porous plate by utilizing incompressible water-copper nanoliquid is examined analytically. Flow is supposed to be laminar, steady and two-dimensional. The plate is subjected to a regular free stream velocity as well as suction velocity. Flow formulation is developed by considering Maxwell-Garnetts (MG) and Brinkman models of nanoliquid. Impacts of thermal radiation, viscous dissipation, temperature dependent heat source/sink and first order chemical reaction are also retained. The subjected non-linear problems are non-dimensionalized and analytic solutions are presented via series expansion method. The graphs are plotted to analyze the influence of pertinent parameters on flow, magnetism, heat and mass transfer fields as well as friction factor, current density, Nusselt and Sherwood numbers. It is found that friction factor at the plate is more for larger magnetic Prandtl number. Also the rate of heat transfer decayed with increasing nanoparticles volume fraction and the strength of magnetism.

Method and apparatus for thermographically and quantitatively analyzing a structure for disbonds and/or inclusions

NASA Technical Reports Server (NTRS)

Heyman, Joseph S. (Inventor); Winfree, William P. (Inventor); Cramer, K. Elliott (Inventor); Zalamedia, Joseph N. (Inventor)

1996-01-01

A heat source such as a magnetic induction/eddy current generator remotely heats a region of a surface of a test structure to a desired depth. For example, the frequency of the heating source can be varied to heat to the desired depth. A thermal sensor senses temperature changes in the heated region as a function of time. A computer compares these sensed temperature changes with calibration standards of a similar sample having known disbond and/or inclusion geography(ies) to analyze the test structure. A plurality of sensors can be arranged linearly to sense vector heat flow.

Double slip effects of Magnetohydrodynamic (MHD) boundary layer flow over an exponentially stretching sheet with radiation, heat source and chemical reaction

NASA Astrophysics Data System (ADS)

Shaharuz Zaman, Azmanira; Aziz, Ahmad Sukri Abd; Ali, Zaileha Md

2017-09-01

The double slips effect on the magnetohydrodynamic boundary layer flow over an exponentially stretching sheet with suction/blowing, radiation, chemical reaction and heat source is presented in this analysis. By using the similarity transformation, the governing partial differential equations of momentum, energy and concentration are transformed into the non-linear ordinary equations. These equations are solved using Runge-Kutta-Fehlberg method with shooting technique in MAPLE software environment. The effects of the various parameter on the velocity, temperature and concentration profiles are graphically presented and discussed.

Laminar flow burner system with infrared heated spray chamber and condenser.

PubMed

Hell, A; Ulrich, W F; Shifrin, N; Ramírez-Muñoz, J

1968-07-01

A laminar flow burner is described that provides several advantages in atomic absorption flame photometry. Included in its design is a heated spray chamber followed by a condensing system. This combination improves the concentration level of the analyte in the flame and keeps solvent concentration low. Therefore, sensitivities are significantly improved for most elements relative to cold chamber burners. The burner also contains several safety features. These various design features are discussed in detail, and performance data are given on (a) signal size, (b) signal-to-noise ratio, (c) linearity, (d) working range, (e) precision, and (g) accuracy.

Numerical study for melting heat transfer and homogeneous-heterogeneous reactions in flow involving carbon nanotubes

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Muhammad, Khursheed; Alsaedi, Ahmed; Asghar, Saleem

2018-03-01

Present work concentrates on melting heat transfer in three-dimensional flow of nanofluid over an impermeable stretchable surface. Analysis is made in presence of porous medium and homogeneous-heterogeneous reactions. Single and multi-wall CNTs (carbon nanotubes) are considered. Water is chosen as basefluid. Adequate transformations yield the non-linear ordinary differential systems. Solution of emerging problems is obtained using shooting method. Impacts of influential variables on velocity and temperature are discussed graphically. Skin friction coefficient and Nusselt number are numerically discussed. The results for MWCNTs and SWCNTs are compared and examined.

Instability of water-ice interface under turbulent flow

NASA Astrophysics Data System (ADS)

Izumi, Norihiro; Naito, Kensuke; Yokokawa, Miwa

2015-04-01

It is known that plane water-ice interface becomes unstable to evolve into a train of waves. The underside of ice formed on the water surface of rivers are often observed to be covered with ice ripples. Relatively steep channels which discharge melting water from glaciers are characterized by beds covered with a series of steps. Though the flowing agent inducing instability is not water but gas including water vapor, a similar train of steps have been recently observed on the Polar Ice Caps on Mars (Spiral Troughs). They are expected to be caused by the instability of water-ice interface induced by flowing fluid on ice. There have been some studies on this instability in terms of linear stability analysis. Recently, Caporeale and Ridolfi (2012) have proposed a complete linear stability analysis in the case of laminar flow, and found that plane water-ice interface is unstable in the range of sufficiently large Reynolds numbers, and that the important parameters are the Reynolds number, the slope angle, and the water surface temperature. However, the flow inducing instability on water-ice interface in the field should be in the turbulent regime. Extension of the analysis to the case of fully developed turbulent flow with larger Reynolds numbers is needed. We have performed a linear stability analysis on the instability of water-ice interface under turbulent flow conditions with the use of the Reynolds-averaged Navier-Stokes equations with the mixing length turbulent model, the continuity equation of flow, the diffusion/dispersion equation of heat, and the Stefan equation. In order to reproduce the accurate velocity distribution and the heat transfer in the vicinity of smooth walls with the use of the mixing length model, it is important to take into account of the rapid decrease in the mixing length in the viscous sublayer. We employ the Driest model (1956) to the formulation. In addition, as the thermal boundary condition at the water surface, we describe the continuity of the heat fluxes from inside of water to the water surface and from the water surface to the surrounding air with the use of the heat transfer coefficient. The boundary condition then becomes the Robin boundary condition. It is found from the analysis, that the instability takes place in the range of large Froude numbers and small wavenumbers in the wavenumber-Froude number plane. It is also found that the unstable region does not show a significant difference when the Reynolds number is larger than somewhere around 5,000.

Axisymmetric Powell-Eyring fluid flow over a stretching sheet with a convective boundary condition and suction effects

NASA Astrophysics Data System (ADS)

Nasir, Nor Ain Azeany Mohd; Ishak, Anuar; Pop, Ioan

2018-04-01

In this paper, the heat and mass transfer of an axisymmetric Powell-Eyring fluid flow over a stretching sheet with a convective boundary condition and suction effects are investigated. An appropriate similarity transformation is used to reduce the highly non-linear partial differential equation into second and third order non-linear ordinary differential equations. Numerical solutions of the reduced governing equations are computed numerically by utilizing the MATLAB's built-in boundary value problem solver, bvp4c. The physical significance of various parameters such as Biot number, fluid parameters and Prandtl number on the velocity and temperature evolution profiles are illustrated graphically. The effects of these governing parameters on the skin friction coefficient and the local Nusselt number are also displayed graphically. It is noticed that the Powell-Eyring fluid parameter gives significant influence on the rates of heat and mass transfer of the fluid.

Effect of a crystal-melt interface on Taylor-vortex flow

NASA Technical Reports Server (NTRS)

Mcfadden, G. B.; Coriell, S. R.; Murray, B. T.; Glicksman, M. E.; Selleck, M. E.

1990-01-01

The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case that the stationary outer cylinder is a crystal-melt interface rather than a rigid surface. A radial temperature difference is maintained across the liquid gap, and equations for heat transport in the crystal and melt phases are included to extend the ordinary formulation of this problem. The stability of this two-phase system depends on the Prandtl number. For small Prandtl number the linear stability of the two-phase system is given by the classical results for a rigid-walled system. For increasing values of the Prandtl number, convective heat transport becomes significant and the system becomes increasingly less stable. Previous results in a narrow-gap approximation are extended to the case of a finite gap, and both axisymmetric and nonaxisymmetric disturbance modes are considered. The two-phase system becomes less stable as the finite gap tends to the narrow-gap limit. The two-phase system is more stable to nonaxisymmetric modes with azimuthal wavenumber n = 1; the stability of these n = 1 modes is sensitive to the latent heat of fusion.

Singularity computations

NASA Technical Reports Server (NTRS)

Swedlow, J. L.

1976-01-01

An approach is described for singularity computations based on a numerical method for elastoplastic flow to delineate radial and angular distribution of field quantities and measure the intensity of the singularity. The method is applicable to problems in solid mechanics and lends itself to certain types of heat flow and fluid motion studies. Its use is not limited to linear, elastic, small strain, or two-dimensional situations.

A computational study of entropy generation in magnetohydrodynamic flow and heat transfer over an unsteady stretching permeable sheet

NASA Astrophysics Data System (ADS)

Saeed Butt, Adnan; Ali, Asif

2014-01-01

The present article aims to investigate the entropy effects in magnetohydrodynamic flow and heat transfer over an unsteady permeable stretching surface. The time-dependent partial differential equations are converted into non-linear ordinary differential equations by suitable similarity transformations. The solutions of these equations are computed analytically by the Homotopy Analysis Method (HAM) then solved numerically by the MATLAB built-in routine. Comparison of the obtained results is made with the existing literature under limiting cases to validate our study. The effects of unsteadiness parameter, magnetic field parameter, suction/injection parameter, Prandtl number, group parameter and Reynolds number on flow and heat transfer characteristics are checked and analysed with the aid of graphs and tables. Moreover, the effects of these parameters on entropy generation number and Bejan number are also shown graphically. It is examined that the unsteadiness and presence of magnetic field augments the entropy production.

Probing Reliability of Transport Phenomena Based Heat Transfer and Fluid Flow Analysis in Autogeneous Fusion Welding Process

NASA Astrophysics Data System (ADS)

Bag, S.; de, A.

2010-09-01

The transport phenomena based heat transfer and fluid flow calculations in weld pool require a number of input parameters. Arc efficiency, effective thermal conductivity, and viscosity in weld pool are some of these parameters, values of which are rarely known and difficult to assign a priori based on the scientific principles alone. The present work reports a bi-directional three-dimensional (3-D) heat transfer and fluid flow model, which is integrated with a real number based genetic algorithm. The bi-directional feature of the integrated model allows the identification of the values of a required set of uncertain model input parameters and, next, the design of process parameters to achieve a target weld pool dimension. The computed values are validated with measured results in linear gas-tungsten-arc (GTA) weld samples. Furthermore, a novel methodology to estimate the overall reliability of the computed solutions is also presented.

A model of heat flow in the sheep exposed to high levels of solar radiation.

PubMed

Vera, R R; Koong, L J; Morris, J G

1975-08-01

The fleece is an important component in thermoregulation of sheep exposed to high levels of solar radiation. A model written in CSMP has been developed which represents the flow of energy between the sheep and its environment. This model is based on a set of differential equations which describe the flux of heat between the components of the system--fleece, tip, skin, body and environment. It requires as input parameters location, date, time of day, temperature, relative humidity, cloud cover, wind movement, animal weight and linear measurements and fleece length. At each integration interval incoming solar radiation and its components, the heat arising from the animal's metabolism and the heat exchange by long-wave radiation, convection, conduction and evaporative cooling are computed. Temperatures at the fleece tip, skin and body core are monitored.

Analytical study of Cattaneo-Christov heat flux model for a boundary layer flow of Oldroyd-B fluid

NASA Astrophysics Data System (ADS)

F, M. Abbasi; M, Mustafa; S, A. Shehzad; M, S. Alhuthali; T, Hayat

2016-01-01

We investigate the Cattaneo-Christov heat flux model for a two-dimensional laminar boundary layer flow of an incompressible Oldroyd-B fluid over a linearly stretching sheet. Mathematical formulation of the boundary layer problems is given. The nonlinear partial differential equations are converted into the ordinary differential equations using similarity transformations. The dimensionless velocity and temperature profiles are obtained through optimal homotopy analysis method (OHAM). The influences of the physical parameters on the velocity and the temperature are pointed out. The results show that the temperature and the thermal boundary layer thickness are smaller in the Cattaneo-Christov heat flux model than those in the Fourier’s law of heat conduction. Project supported by the Deanship of Scientific Research (DSR) King Abdulaziz University, Jeddah, Saudi Arabia (Grant No. 32-130-36-HiCi).

Systematic error of diode thermometer.

PubMed

Iskrenovic, Predrag S

2009-08-01

Semiconductor diodes are often used for measuring temperatures. The forward voltage across a diode decreases, approximately linearly, with the increase in temperature. The applied method is mainly the simplest one. A constant direct current flows through the diode, and voltage is measured at diode terminals. The direct current that flows through the diode, putting it into operating mode, heats up the diode. The increase in temperature of the diode-sensor, i.e., the systematic error due to self-heating, depends on the intensity of current predominantly and also on other factors. The results of systematic error measurements due to heating up by the forward-bias current have been presented in this paper. The measurements were made at several diodes over a wide range of bias current intensity.

Validity and reliability of temperature measurement by heat flow thermistors, flexible thermocouple probes and thermistors in a stirred water bath.

PubMed

Versey, Nathan G; Gore, Christopher J; Halson, Shona L; Plowman, Jamie S; Dawson, Brian T

2011-09-01

We determined the validity and reliability of heat flow thermistors, flexible thermocouple probes and general purpose thermistors compared with a calibrated reference thermometer in a stirred water bath. Validity (bias) was defined as the difference between the observed and criterion values, and reliability as the repeatability (standard deviation or typical error) of measurement. Data were logged every 5 s for 10 min at water temperatures of 14, 26 and 38 °C for ten heat flow thermistors and 24 general purpose thermistors, and at 35, 38 and 41 °C for eight flexible thermocouple probes. Statistical analyses were conducted using spreadsheets for validity and reliability, where an acceptable bias was set at ±0.1 °C. None of the heat flow thermistors, 17% of the flexible thermocouple probes and 71% of the general purpose thermistors met the validity criterion for temperature. The inter-probe reliabilities were 0.03 °C for heat flow thermistors, 0.04 °C for flexible thermocouple probes and 0.09 °C for general purpose thermistors. The within trial intra-probe reliability of all three temperature probes was 0.01 °C. The results suggest that these temperature sensors should be calibrated individually before use at relevant temperatures and the raw data corrected using individual linear regression equations.

Quantifying the evolution of flow boiling bubbles by statistical testing and image analysis: toward a general model.

PubMed

Xiao, Qingtai; Xu, Jianxin; Wang, Hua

2016-08-16

A new index, the estimate of the error variance, which can be used to quantify the evolution of the flow patterns when multiphase components or tracers are difficultly distinguishable, was proposed. The homogeneity degree of the luminance space distribution behind the viewing windows in the direct contact boiling heat transfer process was explored. With image analysis and a linear statistical model, the F-test of the statistical analysis was used to test whether the light was uniform, and a non-linear method was used to determine the direction and position of a fixed source light. The experimental results showed that the inflection point of the new index was approximately equal to the mixing time. The new index has been popularized and applied to a multiphase macro mixing process by top blowing in a stirred tank. Moreover, a general quantifying model was introduced for demonstrating the relationship between the flow patterns of the bubble swarms and heat transfer. The results can be applied to investigate other mixing processes that are very difficult to recognize the target.

Quantifying the evolution of flow boiling bubbles by statistical testing and image analysis: toward a general model

PubMed Central

Xiao, Qingtai; Xu, Jianxin; Wang, Hua

2016-01-01

A new index, the estimate of the error variance, which can be used to quantify the evolution of the flow patterns when multiphase components or tracers are difficultly distinguishable, was proposed. The homogeneity degree of the luminance space distribution behind the viewing windows in the direct contact boiling heat transfer process was explored. With image analysis and a linear statistical model, the F-test of the statistical analysis was used to test whether the light was uniform, and a non-linear method was used to determine the direction and position of a fixed source light. The experimental results showed that the inflection point of the new index was approximately equal to the mixing time. The new index has been popularized and applied to a multiphase macro mixing process by top blowing in a stirred tank. Moreover, a general quantifying model was introduced for demonstrating the relationship between the flow patterns of the bubble swarms and heat transfer. The results can be applied to investigate other mixing processes that are very difficult to recognize the target. PMID:27527065

Thermoconvective flow velocity in a high-speed magnetofluid seal after it has stopped

NASA Astrophysics Data System (ADS)

Krakov, M. S.; Nikiforov, I. V.

2012-09-01

Convective flow is investigated in the high-speed (linear velocity of the shaft seal is more than 1 m/s) magnetofluid shaft seal after it has been stopped. Magnetic fluid is preliminarily heated due to viscous friction in the moving seal. After the shaft has been stopped, nonuniform heated fluid remains under the action of a high-gradient magnetic field. Numerical analysis has revealed that in this situation, intense thermomagnetic convection is initiated. The velocity of magnetic fluid depends on its viscosity. For the fluid with viscosity of 2 × 10-4 m2/s the maximum flow velocity within the volume of magnetic fluid with a characteristic size of 1 mm can attain a value of 10 m/s.

Thermal elastoplastic structural analysis of non-metallic thermal protection systems

NASA Technical Reports Server (NTRS)

Chung, T. J.; Yagawa, G.

1972-01-01

An incremental theory and numerical procedure to analyze a three-dimensional thermoelastoplastic structure subjected to high temperature, surface heat flux, and volume heat supply as well as mechanical loadings are presented. Heat conduction equations and equilibrium equations are derived by assuming a specific form of incremental free energy, entropy, stresses and heat flux together with the first and second laws of thermodynamics, von Mises yield criteria and Prandtl-Reuss flow rule. The finite element discretization using the linear isotropic three-dimensional element for the space domain and a difference operator corresponding to a linear variation of temperature within a small time increment for the time domain lead to systematic solutions of temperature distribution and displacement and stress fields. Various boundary conditions such as insulated surfaces and convection through uninsulated surface can be easily treated. To demonstrate effectiveness of the present formulation a number of example problems are presented.

MHD Free Convective Boundary Layer Flow of a Nanofluid past a Flat Vertical Plate with Newtonian Heating Boundary Condition

PubMed Central

Uddin, Mohammed J.; Khan, Waqar A.; Ismail, Ahmed I.

2012-01-01

Steady two dimensional MHD laminar free convective boundary layer flows of an electrically conducting Newtonian nanofluid over a solid stationary vertical plate in a quiescent fluid taking into account the Newtonian heating boundary condition is investigated numerically. A magnetic field can be used to control the motion of an electrically conducting fluid in micro/nano scale systems used for transportation of fluid. The transport equations along with the boundary conditions are first converted into dimensionless form and then using linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order method with shooting technique. The effects of different controlling parameters, namely, Lewis number, Prandtl number, buoyancy ratio, thermophoresis, Brownian motion, magnetic field and Newtonian heating on the flow and heat transfer are investigated. The numerical results for the dimensionless axial velocity, temperature and nanoparticle volume fraction as well as the reduced Nusselt and Sherwood number have been presented graphically and discussed. It is found that the rate of heat and mass transfer increase as Newtonian heating parameter increases. The dimensionless velocity and temperature distributions increase with the increase of Newtonian heating parameter. The results of the reduced heat transfer rate is compared for convective heating boundary condition and found an excellent agreement. PMID:23166688

Flow behaviour and constitutive modelling of a ferritic stainless steel at elevated temperatures

NASA Astrophysics Data System (ADS)

Zhao, Jingwei; Jiang, Zhengyi; Zu, Guoqing; Du, Wei; Zhang, Xin; Jiang, Laizhu

2016-05-01

The flow behaviour of a ferritic stainless steel (FSS) was investigated by a Gleeble 3500 thermal-mechanical test simulator over the temperature range of 900-1100 °C and strain rate range of 1-50 s-1. Empirical and phenomenological constitutive models were established, and a comparative study was made on the predictability of them. The results indicate that the flow stress decreases with increasing the temperature and decreasing the strain rate. High strain rate may cause a drop in flow stress after a peak value due to the adiabatic heating. The Zener-Hollomon parameter depends linearly on the flow stress, and decreases with raising the temperature and reducing the strain rate. Significant deviations occur in the prediction of flow stress by the Johnson-Cook (JC) model, indicating that the JC model cannot accurately track the flow behaviour of the FSS during hot deformation. Both the multiple-linear and the Arrhenius-type models can track the flow behaviour very well under the whole hot working conditions, and have much higher accuracy in predicting the flow behaviour than that of the JC model. The multiple-linear model is recommended in the current work due to its simpler structure and less time needed for solving the equations relative to the Arrhenius-type model.

An external heat pulse method for measurement of sap flow through fruit pedicels, leaf petioles and other small-diameter stems.

PubMed

Clearwater, Michael J; Luo, Zhiwei; Mazzeo, Mariarosaria; Dichio, Bartolomeo

2009-12-01

The external heat ratio method is described for measurement of low rates of sap flow in both directions through stems and other plant organs, including fruit pedicels, with diameters up to 5 mm and flows less than 2 g h(-1). Calibration was empirical, with heat pulse velocity (v(h)) compared to gravimetric measurements of sap flow. In the four stem types tested (Actinidia sp. fruit pedicels, Schefflera arboricola petioles, Pittosporum crassifolium stems and Fagus sylvatica stems), v(h) was linearly correlated with sap velocity (v(s)) up to a v(s) of approximately 0.007 cm s(-1), equivalent to a flow of 1.8 g h(-1) through a 3-mm-diameter stem. Minimum detectable v(s) was approximately 0.0001 cm s(-1), equivalent to 0.025 g h(-1) through a 3-mm-diameter stem. Sensitivity increased with bark removal. Girdling had no effect on short-term measurements of in vivo sap flow, suggesting that phloem flows were too low to be separated from xylem flows. Fluctuating ambient temperatures increased variability in outdoor sap flow measurements. However, a consistent diurnal time-course of fruit pedicel sap flow was obtained, with flows towards 75-day-old kiwifruit lagging behind evaporative demand and peaking at 0.3 g h(-1) in the late afternoon.

Numerical marching techniques for fluid flows with heat transfer

NASA Technical Reports Server (NTRS)

Hornbeck, R. W.

1973-01-01

The finite difference formulation and method of solution is presented for a wide variety of fluid flow problems with associated heat transfer. Only a few direct results from these formulations are given as examples, since the book is intended primarily to serve a discussion of the techniques and as a starting point for further investigations; however, the formulations are sufficiently complete that a workable computer program may be written from them. In the appendixes a number of topics are discussed which are of interest with respect to the finite difference equations presented. These include a very rapid method for solving certain sets of linear algebraic equations, a discussion of numerical stability, the inherent error in flow rate for confined flow problems, and a method for obtaining high accuracy with a relatively small number of mesh points.

Numerical simulation of heat transfer in blood flow altered by electroosmosis through tapered micro-vessels.

PubMed

Prakash, J; Ramesh, K; Tripathi, D; Kumar, R

2018-07-01

A numerical simulation is presented to study the heat and flow characteristics of blood flow altered by electroosmosis through the tapered micro-vessels. Blood is assumed as non-Newtonian (micropolar) nanofluids. The flow regime is considered as asymmetric diverging (tapered) microchannel for more realistic micro-vessels which is produced by choosing the peristaltic wave train on the walls to have different amplitudes and phase. The Rosseland approximation is employed to model the radiation heat transfer and temperatures of the walls are presumed constants. The mathematical formulation of the present problem is simplified under the long-wavelength, low-Reynolds number and Debye-Hückel linearization approximations. The influence of various dominant physical parameters are discussed for axial velocity, microrotation distribution, thermal temperature distribution and nanoparticle volume fraction field. However, our foremost emphasis is to determine the effects of thermal radiation and coupling number on the axial velocity and microrotation distribution beneath electroosmotic environment. This analysis places a significant observation on the thermal radiation and coupling number which plays an influential role in hearten fluid velocity. This study is encouraged by exploring the nanofluid-dynamics in peristaltic transport as symbolized by heat transport in biological flows and also in novel pharmacodynamics pumps and gastro-intestinal motility enhancement. Copyright © 2018 Elsevier Inc. All rights reserved.

Enhanced styrene recovery from waste polystyrene pyrolysis using response surface methodology coupled with Box-Behnken design.

PubMed

Mo, Yu; Zhao, Lei; Wang, Zhonghui; Chen, Chia-Lung; Tan, Giin-Yu Amy; Wang, Jing-Yuan

2014-04-01

A work applied response surface methodology coupled with Box-Behnken design (RSM-BBD) has been developed to enhance styrene recovery from waste polystyrene (WPS) through pyrolysis. The relationship between styrene yield and three selected operating parameters (i.e., temperature, heating rate, and carrier gas flow rate) was investigated. A second order polynomial equation was successfully built to describe the process and predict styrene yield under the study conditions. The factors identified as statistically significant to styrene production were: temperature, with a quadratic effect; heating rate, with a linear effect; carrier gas flow rate, with a quadratic effect; interaction between temperature and carrier gas flow rate; and interaction between heating rate and carrier gas flow rate. The optimum conditions for the current system were determined to be at a temperature range of 470-505°C, a heating rate of 40°C/min, and a carrier gas flow rate range of 115-140mL/min. Under such conditions, 64.52% WPS was recovered as styrene, which was 12% more than the highest reported yield for reactors of similar size. It is concluded that RSM-BBD is an effective approach for yield optimization of styrene recovery from WPS pyrolysis. Copyright © 2014 Elsevier Ltd. All rights reserved.

Entropy generation minimization (EGM) of nanofluid flow by a thin moving needle with nonlinear thermal radiation

NASA Astrophysics Data System (ADS)

Waleed Ahmed Khan, M.; Ijaz Khan, M.; Hayat, T.; Alsaedi, A.

2018-04-01

Entropy generation minimization (EGM) and heat transport in nonlinear radiative flow of nanomaterials over a thin moving needle has been discussed. Nonlinear thermal radiation and viscous dissipation terms are merged in the energy expression. Water is treated as ordinary fluid while nanomaterials comprise titanium dioxide, copper and aluminum oxide. The nonlinear governing expressions of flow problems are transferred to ordinary ones and then tackled for numerical results by Built-in-shooting technique. In first section of this investigation, the entropy expression is derived as a function of temperature and velocity gradients. Geometrical and physical flow field variables are utilized to make it nondimensionalized. An entropy generation analysis is utilized through second law of thermodynamics. The results of temperature, velocity, concentration, surface drag force and heat transfer rate are explored. Our outcomes reveal that surface drag force and Nusselt number (heat transfer) enhanced linearly for higher nanoparticle volume fraction. Furthermore drag force decays for aluminum oxide and it enhances for copper nanoparticles. In addition, the lowest heat transfer rate is achieved for higher radiative parameter. Temperature field is enhanced with increase in temperature ratio parameter.

Regolith thermal property inversion in the LUNAR-A heat-flow experiment

NASA Astrophysics Data System (ADS)

Hagermann, A.; Tanaka, S.; Yoshida, S.; Fujimura, A.; Mizutani, H.

2001-11-01

In 2003, two penetrators of the LUNAR--A mission of ISAS will investigate the internal structure of the Moon by conducting seismic and heat--flow experiments. Heat-flow is the product of thermal gradient tial T / tial z, and thermal conductivity λ of the lunar regolith. For measuring the thermal conductivity (or dissusivity), each penetrator will carry five thermal property sensors, consisting of small disc heaters. The thermal response Ts(t) of the heater itself to the constant known power supply of approx. 50 mW serves as the data for the subsequent data interpretation. Horai et al. (1991) found a forward analytical solution to the problem of determining the thermal inertia λ ρ c of the regolith for constant thermal properties and a simplyfied geometry. In the inversion, the problem of deriving the unknown thermal properties of a medium from known heat sources and temperatures is an Identification Heat Conduction Problem (IDHCP), an ill--posed inverse problem. Assuming that thermal conductivity λ and heat capacity ρ c are linear functions of temperature (which is reasonable in most cases), one can apply a Kirchhoff transformation to linearize the heat conduction equation, which minimizes computing time. Then the error functional, i.e. the difference between the measured temperature response of the heater and the predicted temperature response, can be minimized, thus solving for thermal dissusivity κ = λ / (ρ c), wich will complete the set of parameters needed for a detailed description of thermal properties of the lunar regolith. Results of model calculations will be presented, in which synthetic data and calibration data are used to invert the unknown thermal diffusivity of the unknown medium by means of a modified Newton Method. Due to the ill-posedness of the problem, the number of parameters to be solved for should be limited. As the model calculations reveal, a homogeneous regolith allows for a fast and accurate inversion.

Simultaneous determination of the heat and the quantity of vapor sorption using a novel microcalorimetric method.

PubMed

Lehto, V P; Laine, E

2000-06-01

In this study, instrumentation for measuring vapor sorption enthalpies and sorption uptakes simultaneously with an isothermal microcalorimeter is introduced. Various pharmaceutical model substances undergoing phase transitions when exposed to humid conditions (25 degrees C), were employed to evaluate the usefulness and sensitivity of the constructed experimental method. The sample is placed in the sample vessel of a RH cell and the moisture content of the air flow is controlled. From the RH cell the air flow is conducted into a subsequent perfusion cell in which a saturated salt solution has been loaded. The RH cell and perfusion cells are positioned in the sample sides of two twin calorimetric units. Depending on the moisture content in the outlet flow leaving the preceding RH cell, the heat flow signal from the subsequent perfusion cell will vary. By means of blank measurement with identical settings, the rate of water sorption can be calculated and, by integration, the amount of sorbed water is obtained. Amorphous lactose and cefadroxil undergo recrystallization when the moisture level in the surroundings exceeds the threshold values specific to each compound. During the sorption phase, heat is evolved fairly linearly as a function of consumed moisture, and also after the recrystallization, the heats indicate linear behavior. The heat values for the desorption phase of amorphous lactose and the adsorption of crystalline lactose coincide. With the different anhydrous forms of theophylline, the hydration takes place more rapidly in the metastable form 1, and generally, the process is more energetic in form 1. In all cases, the gravimetric results agree with the water sorption uptakes calculated from the calorimetric data. The technique introduced offers a rapid and sensitive method to gain new insights into the transitions in which vapors are involved. In addition, different kinds of surfaces with various energetics can now be studied more closely.

Numerical simulations of sessile droplet evaporating on heated substrate

NASA Astrophysics Data System (ADS)

Chen, Xue; Chen, Paul G.; Ouazzani, Jalil; Liu, Qiusheng

2017-04-01

Motivated by the space project EFILE, a 2D axisymmetric numerical model in the framework of ALE method is developed to investigate the coupled physical mechanism during the evaporation of a pinned drop that partially wets on a heated substrate. The model accounts for mass transport in surrounding air, Marangoni convection inside the drop and heat conduction in the substrate as well as moving interface. Numerical results predict simple scaling laws for the evaporation rate which scales linearly with drop radius but follows a power-law with substrate temperature. It is highlighted that thermal effect of the substrate has a great impact on the temperature profile at the drop surface, which leads to a multicellular thermocapillary flow pattern. In particular, the structure of the multicellular flow behavior induced within a heated drop is mainly controlled by a geometric parameter (aspect ratio). A relationship between the number of thermal cells and the aspect ratio is proposed.

Unified nonlinear approach to both weak and strong-interaction problems. [heat transfer in hypersonic flow

NASA Technical Reports Server (NTRS)

Gupta, R. N.; Rodkiewicz, C. M.

1975-01-01

The numerical results are obtained for heat transfer, skin-friction, and viscous interaction induced pressure for a step-wise accelerated flat plate in hypersonic flow. In the unified approach here the results are presented for both weak and strong-interaction problems without employing any linearization scheme. With the help of the numerical method used in this work an accurate prediction of wall shear can be made for the problems with plate velocity changes of 1% or larger. The obtained results indicate that the transient contribution to the induced pressure for helium is greater than that for air.

Modified Chapman-Enskog moment approach to diffusive phonon heat transport.

PubMed

Banach, Zbigniew; Larecki, Wieslaw

2008-12-01

A detailed treatment of the Chapman-Enskog method for a phonon gas is given within the framework of an infinite system of moment equations obtained from Callaway's model of the Boltzmann-Peierls equation. Introducing no limitations on the magnitudes of the individual components of the drift velocity or the heat flux, this method is used to derive various systems of hydrodynamic equations for the energy density and the drift velocity. For one-dimensional flow problems, assuming that normal processes dominate over resistive ones, it is found that the first three levels of the expansion (i.e., the zeroth-, first-, and second-order approximations) yield the equations of hydrodynamics which are linearly stable at all wavelengths. This result can be achieved either by examining the dispersion relations for linear plane waves or by constructing the explicit quadratic Lyapunov entropy functionals for the linear perturbation equations. The next order in the Chapman-Enskog expansion leads to equations which are unstable to some perturbations. Precisely speaking, the linearized equations of motion that describe the propagation of small disturbances in the flow have unstable plane-wave solutions in the short-wavelength limit of the dispersion relations. This poses no problem if the equations are used in their proper range of validity.

Different nano-particles volume fraction and Hartmann number effects on flow and heat transfer of water-silver nanofluid under the variable heat flux

NASA Astrophysics Data System (ADS)

Forghani-Tehrani, Pezhman; Karimipour, Arash; Afrand, Masoud; Mousavi, Sayedali

2017-01-01

Nanofluid flow and heat transfer composed of water-silver nanoparticles is investigated numerically inside a microchannel. Finite volume approach (FVM) is applied and the effects of gravity are ignored. The whole length of Microchannel is considered in three sections as l1=l3=0.151 and l2=0.71. The linear variable heat flux affects the microchannel wall in the length of l2 while a magnetic field with strength of B0 is considered over the whole domain of it. The influences of different values of Hartmann number (Ha=0, 10, 20), volume fraction of the nanoparticles (ɸ=0, 0.02, 0.04) and Reynolds number (Re=10, 50, 200) on the hydrodynamic and thermal properties of flow are reported. The investigation of slip velocity variations under the effects of a magnetic field are presented for the first time (to the best knowledge of author) while the non-dimensional slip coefficient are selected as B=0.01, 0.05, 0.1 at different states.

Blade Heat Transfer Measurements and Prediction in a Transonic Turbine Cascade

NASA Technical Reports Server (NTRS)

Giel, P. W.; VanFossen, G. J.; Boyle, R. J.; Thurman, D. R.; Civinskas, K. C.

1999-01-01

Detailed heat transfer measurements and predictions are given for a turbine rotor with 136 deg of turning and an axial chord of 12.7 cm. Data were obtained for inlet Reynolds numbers of 0.5 and 1.0 x 10(exp 6), for isentropic exit Mach numbers of 1.0 and 1.3, and for inlet turbulence intensities of 0.25% and 7.0%. Measurements were made in a linear cascade having a highly three-dimensional flow field resulting from thick inlet boundary layers. The purpose of the work is to provide benchmark quality data for three-dimensional CFD code and model verification. Data were obtained by a steady-state technique using a heated, isothermal blade. Heat fluxes were determined from a calibrated resistance layer in conjunction with a surface temperature measured by calibrated liquid crystals. The results show the effects of strong secondary vortical flows, laminar-to-turbulent transition, shock impingement, and increased inlet turbulence on the surface heat transfer.

Three-dimensional flow of Prandtl fluid with Cattaneo-Christov double diffusion

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Aziz, Arsalan; Muhammad, Taseer; Alsaedi, Ahmed

2018-06-01

This research paper intends to investigate the 3D flow of Prandtl liquid in the existence of improved heat conduction and mass diffusion models. Flow is created by considering linearly bidirectional stretchable sheet. Thermal and concentration diffusions are considered by employing Cattaneo-Christov double diffusion models. Boundary layer approach has been used to simplify the governing PDEs. Suitable nondimensional similarity variables correspond to strong nonlinear ODEs. Optimal homotopy analysis method (OHAM) is employed for solutions development. The role of various pertinent variables on temperature and concentration are analyzed through graphs. The physical quantities such as surface drag coefficients and heat and mass transfer rates at the wall are also plotted and discussed. Our results indicate that the temperature and concentration are decreasing functions of thermal and concentration relaxation parameters respectively.

Subsurface temperatures and surface heat flow in the Michigan Basin and their relationships to regional subsurface fluid movement

USGS Publications Warehouse

Vugrinovich, R.

1989-01-01

Linear regression of 405 bottomhole temperature (BHT) measurements vs. associated depths from Michigan's Lower Peninsula results in the following equation relating BHT and depth: BHT(??C) = 14.5 + 0.0192 ?? depth(m) Temperature residuals, defined as (BHT measured)-(BHT calculated), were determined for each of the 405 BHT's. Areas of positive temperature residuals correspond to areas of regional groundwater discharge (determined from maps of equipotential surface) while areas of negative temperature residuals correspond to areas of regional groundwater recharge. These relationships are observed in the principal aquifers in rocks of Devonian and Ordovician age and in a portion of the principal aquifer in rocks of Silurian age. There is a similar correspondence between high surface heat flow (determined using the silica geothermometer) and regional groundwater discharge areas and low surface heat flow and regional groundwater recharge areas. Post-Jurassic depositional and tectonic histories suggest that the observed coupling of subsurface temperature and groundwater flow systems may have persisted since Jurassic time. Thus the higher subsurface palaeotemperatures (and palaeogeothermal gradients) indicated by recent studies most likely pre-date the Jurassic. ?? 1989.

Numerical analysis of steady and transient natural convection in an enclosed cavity

NASA Astrophysics Data System (ADS)

Mehedi, Tanveer Hassan; Tahzeeb, Rahat Bin; Islam, A. K. M. Sadrul

2017-06-01

The paper presents the numerical simulation of natural convection heat transfer of air inside an enclosed cavity which can be helpful to find out the critical width of insulation in air insulated walls seen in residential buildings and industrial furnaces. Natural convection between two walls having different temperatures have been simulated using ANSYS FLUENT 12.0 in both steady and transient conditions. To simulate different heat transfer and fluid flow conditions, Rayleigh number ranging from 103 to 105 has been maintained (i.e. Laminar flow.) In case of steady state analysis, the CFD predictions were in very good agreement with the reviewed literature. Transient simulation process has been performed by using User Defined Functions, where the temperature of the hot wall varies with time linearly. To obtain and compare the heat transfer properties, Nusselt number has been calculated at the hot wall at different conditions. The buoyancy driven flow characteristics have been investigated by observing the flow pattern in a graphical manner. The characteristics of the system at different temperature differences between the wall has been observed and documented.

Good News for Borehole Climatology

NASA Astrophysics Data System (ADS)

Rath, Volker; Fidel Gonzalez-Rouco, J.; Goosse, Hugues

2010-05-01

Though the investigation of observed borehole temperatures has proved to be a valuable tool for the reconstruction of ground surface temperature histories, there are many open questions concerning the significance and accuracy of the reconstructions from these data. In particular, the temperature signal of the warming after the Last glacial Maximum (LGM) is still present in borehole temperature profiles. It influences the relatively shallow boreholes used in current paleoclimate inversions to estimate temperature changes in the last centuries. This is shown using Monte Carlo experiments on past surface temperature change, using plausible distributions for the most important parameters, i.e.,amplitude and timing of the glacial-interglacial transition, the prior average temperature, and petrophysical properties. It has been argued that the signature of the last glacial-interglacial transition could be responsible for the high amplitudes of millennial temperature reconstructions. However, in shallow boreholes the additional effect of past climate can reasonably approximated by a linear variation of temperature with depth, and thus be accommodated by a "biased" background heat flow. This is good news for borehole climate, but implies that the geological heat flow values have to be interpreted accordingly. Borehole climate reconstructions from these shallow are most probably underestimating past variability due to the diffusive character of the heat conduction process, and the smoothness constraints necessary for obtaining stable solutions of this ill-posed inverse problem. A simple correction based on subtracting an appropriate prior surface temperature history shows promising results reducing these errors considerably, also with deeper boreholes, where the heat flow signal can not be approximated linearly, and improves the comparisons with AOGCM modeling results.

Extended-MHD Studies of Flow-Profile Effects on Edge Harmonic Oscillations in QH-mode Discharges

NASA Astrophysics Data System (ADS)

King, J. R.; Burrell, K. H.; Garofalo, A. M.; Jenkins, T. G.; Kruger, S. E.; Snyder, P. B.

2012-10-01

It is desirable to have an ITER H-mode regime that is quiescent to edge-localized modes (ELMs). ELMs deposit large, localized, impulsive, surface heat loads that can damage the divertor. One such quiescent regime with edge harmonic oscillations (EHO) is observed on DIII-D, JET, JT-60U, and ASDEX-U [1]. The physical mechanisms of EHO are not fully understood, but linear MHD calculations suggest EHO may be a saturated kink-peeling mode partially driven by flow-profile shear [2]. We present preliminary EHO computations using the extended-MHD NIMROD code. The model incorporates first-order FLR effects and parallel heat flows. Using reconstructed DIII-D profiles from discharges with EHO, we scan the ExB and polodial flow profiles and compute linear stability. The aim is to ascertain the role of the ExB flow shear, as motivated by experimental results [3], and to compare with theoretical predictions where the growth rate is enhanced at intermediate wavenumbers and cut-off at large wavenumbers by diamagnetic effects [4]. Initial nonlinear computations exploring the EHO saturation mechanism are presented.[4pt] [1] Phys. Plasmas, v19, p056117, 2012 (and refs. within).[0pt] [2] Nucl. Fusion, v47, p961, 2007.[0pt] [3] Nucl. Fusion, v51, p083018, 2011.[0pt] [4] Phys. Plasmas v10, p4405, 2003.

Theoretical analysis of non-linear Joule heating effects over an electro-thermal patterned flow

NASA Astrophysics Data System (ADS)

Sanchez, Salvador; Ascanio, Gabriel; Mendez, Federico; Bautista, Oscar

2017-11-01

In this work, non-linear Joule heating effects for electro-thermal patterned flows driven inside of a slit microchannel are analyzed. Here, the movement of fluids is controlled by placing electro-thermal forces, which are generated through an imposed longitudinal electric field, E0, and the wall electric potential produced by electrodes inserted along the surface of the microchannel wall, ζ. For this analysis, viscosity and electrical conductivity of fluids are included as known functions, which depend on the temperature; therefore, in order to determine the flow, temperature and electric potential fields together with its simultaneous interactions, the equations of continuity, momentum, energy, charges distribution and electrical current have to be solved in a coupled manner. The main results obtained in the study reveal that with the presence of thermal gradients along of the microchannel, local electro-thermal forces, Fχ, are affected in a sensible manner, and consequently, the flow field is modified substantially, causing the interruption or intensification of recirculations along of the microchannel. This work was supported by the Fondo SEP-CONACYT through research Grants No. 220900 and 20171181 from SIP-IPN. F. Mendez acknowledges support from PAPIIT-UNAM under Contract Number IN112215. S. Sanchez thanks to DGAPA-UNAM for the postdoctoral fellowship.

Separation and quantification of monoclonal-antibody aggregates by hollow-fiber-flow field-flow fractionation.

PubMed

Fukuda, Jun; Iwura, Takafumi; Yanagihara, Shigehiro; Kano, Kenji

2014-10-01

Hollow-fiber-flow field-flow fractionation (HF5) separates protein molecules on the basis of the difference in the diffusion coefficient, and can evaluate the aggregation ratio of proteins. However, HF5 is still a minor technique because information on the separation conditions is limited. We examined in detail the effect of different settings, including the main-flow rate, the cross-flow rate, the focus point, the injection amount, and the ionic strength of the mobile phase, on fractographic characteristics. On the basis of the results, we proposed optimized conditions of the HF5 method for quantification of monoclonal antibody in sample solutions. The HF5 method was qualified regarding the precision, accuracy, linearity of the main peak, and quantitation limit. In addition, the HF5 method was applied to non-heated Mab A and heat-induced-antibody-aggregate-containing samples to evaluate the aggregation ratio and the distribution extent. The separation performance was comparable with or better than that of conventional methods including analytical ultracentrifugation-sedimentation velocity and asymmetric-flow field-flow fractionation.

The cooling of terrestrial basaltic lava flows and implications for lava flow emplacement on Venus from surface morphology and radar data

NASA Astrophysics Data System (ADS)

Hultgrien, Lynn Kerrell

Basalt is the most common surface rock on the terrestrial planets. Understanding the emplacement mechanisms for basaltic lava flows facilitates study of the geologic history of a planet and in volcanic hazards assessment. Lava flow cooling is examined through two different models, one applicable to aa and the second to pahoehoe. Occurrence of these basaltic flow types is evaluated in an extensive global survey of lava flows on Venus using Magellan data. First, a basic heat balance model is considered for as flow cooling with terms for conduction, radiation, viscous dissipation and entrainment of cooler material. Pahoehoe cooling is modeled through three different analytic solutions to the one-dimensional, time-dependent heat conduction equation, with constant surface temperature, linear heat transfer at the surface, and surface radiation. The models are compared with thermal data from the Hawaiian 1984 Mauna Loa and 1990 Puu Oo-Kupaianaha, Kilauea eruptions, for as and pahoehoe, respectively. Although commonly omitted in other models, heat conduction is found here to be important in the cooling of both aa and pahoehoe. Equally important is entrainment in as flows and both radiation and atmospheric convection for pahoehoe cooling. Morphology measurements and surface properties are determined for ninety individual lava flows from forty-four volcanic features on Venus. Radar backscatter and rms slope values, relative to terrestrial studies, indicate Venusian lavas are predominately pahoehoe. Emissivities and dielectric constants are consistent with basalt as the principal lithology. Effusion rates and flow velocities, determined using Earth-calibrated parametric relationships, and lava flow dimensions are greater than those found on Earth. Modeling lava flows on the terrestrial planets should involve careful consideration of the type of lava flow being studied. This investigation finds that heat conduction is an important limitation in the ability of a basalt flow to cool. Some models underestimate cooling time and flow dimensions because of their failure to include such effects. Pahoehoe and aa flows are emplaced by different mechanisms and require individualized models. The prevalence of pahoehoe lava flows on both Earth and Venus is a major element for deciphering the past evolution of each planet.

Transducer Workshop (12th) Held at Melbourne, Florida on 7-9 June 1983.

DTIC Science & Technology

1983-06-01

applications since above 200OF (930C) the heat treatment CES among others, history of the Manganin is changes and (*) The Specific products referenced the...linearization scheme is compromised. and manufacturers’ addresses are given Heat treatment history change means ind thebibliographyi add sesparate pa... pulsating (dynamic) flow, even ment with the Unified Approach to the when readings are averaged over a period Engineering of Measuring Systems on of the

Effects of Heat Source/Sink and Chemical Reaction on MHD Maxwell Nanofluid Flow Over a Convectively Heated Exponentially Stretching Sheet Using Homotopy Analysis Method

NASA Astrophysics Data System (ADS)

Sravanthi, C. S.; Gorla, R. S. R.

2018-02-01

The aim of this paper is to study the effects of chemical reaction and heat source/sink on a steady MHD (magnetohydrodynamic) two-dimensional mixed convective boundary layer flow of a Maxwell nanofluid over a porous exponentially stretching sheet in the presence of suction/blowing. Convective boundary conditions of temperature and nanoparticle concentration are employed in the formulation. Similarity transformations are used to convert the governing partial differential equations into non-linear ordinary differential equations. The resulting non-linear system has been solved analytically using an efficient technique, namely: the homotopy analysis method (HAM). Expressions for velocity, temperature and nanoparticle concentration fields are developed in series form. Convergence of the constructed solution is verified. A comparison is made with the available results in the literature and our results are in very good agreement with the known results. The obtained results are presented through graphs for several sets of values of the parameters and salient features of the solutions are analyzed. Numerical values of the local skin-friction, Nusselt number and nanoparticle Sherwood number are computed and analyzed.

Development and Validation of Computational Fluid Dynamics Models for Prediction of Heat Transfer and Thermal Microenvironments of Corals

PubMed Central

Ong, Robert H.; King, Andrew J. C.; Mullins, Benjamin J.; Cooper, Timothy F.; Caley, M. Julian

2012-01-01

We present Computational Fluid Dynamics (CFD) models of the coupled dynamics of water flow, heat transfer and irradiance in and around corals to predict temperatures experienced by corals. These models were validated against controlled laboratory experiments, under constant and transient irradiance, for hemispherical and branching corals. Our CFD models agree very well with experimental studies. A linear relationship between irradiance and coral surface warming was evident in both the simulation and experimental result agreeing with heat transfer theory. However, CFD models for the steady state simulation produced a better fit to the linear relationship than the experimental data, likely due to experimental error in the empirical measurements. The consistency of our modelling results with experimental observations demonstrates the applicability of CFD simulations, such as the models developed here, to coral bleaching studies. A study of the influence of coral skeletal porosity and skeletal bulk density on surface warming was also undertaken, demonstrating boundary layer behaviour, and interstitial flow magnitude and temperature profiles in coral cross sections. Our models compliment recent studies showing systematic changes in these parameters in some coral colonies and have utility in the prediction of coral bleaching. PMID:22701582

Steady Secondary Flows Generated by Periodic Compression and Expansion of an Ideal Gas in a Pulse Tube

NASA Technical Reports Server (NTRS)

Lee, Jeffrey M.

1999-01-01

This study establishes a consistent set of differential equations for use in describing the steady secondary flows generated by periodic compression and expansion of an ideal gas in pulse tubes. Also considered is heat transfer between the gas and the tube wall of finite thickness. A small-amplitude series expansion solution in the inverse Strouhal number is proposed for the two-dimensional axisymmetric mass, momentum and energy equations. The anelastic approach applies when shock and acoustic energies are small compared with the energy needed to compress and expand the gas. An analytic solution to the ordered series is obtained in the strong temperature limit where the zeroth-order temperature is constant. The solution shows steady velocities increase linearly for small Valensi number and can be of order I for large Valensi number. A conversion of steady work flow to heat flow occurs whenever temperature, velocity or phase angle gradients are present. Steady enthalpy flow is reduced by heat transfer and is scaled by the Prandtl times Valensi numbers. Particle velocities from a smoke-wire experiment were compared with predictions for the basic and orifice pulse tube configurations. The theory accurately predicted the observed steady streaming.

Effect of Running Parameters on Flow Boiling Instabilities in Microchannels.

PubMed

Zong, Lu-Xiang; Xu, Jin-Liang; Liu, Guo-Hua

2015-04-01

Flow boiling instability (FBI) in microchannels is undesirable because they can induce the mechanical vibrations and disturb the heat transfer characteristics. In this study, the synchronous optical visualization experimental system was set up. The pure acetone liquid was used as the working fluid, and the parallel triangle silicon microchannel heat sink was designed as the experimental section. With the heat flux ranging from 0-450 kW/m2 the microchannel demand average pressure drop-heater length (Δp(ave)L) curve for constant low mass flux, and the demand pressure drop-mass flux (Δp(ave)G) curve for constant length on main heater surface were obtained and studied. The effect of heat flux (q = 188.28, 256.00, and 299.87 kW/m2), length of main heater surface (L = 4.5, 6.25, and 8.00 mm), and mass flux (G = 188.97, 283.45, and 377.94 kg/m2s) on pressure drops (Ap) and temperatures at the central point of the main heater surface (Twc) were experimentally studied. The results showed that, heat flux, length of the main heater surface, and mass flux were identified as the important parameters to the boiling instability process. The boiling incipience (TBI) and critical heat flux (CHF) were early induced for the lower mass flux or the main heater surface with longer length. With heat flux increasing, the pressure drops were linearly and slightly decreased in the single liquid region but increased sharply in the two phase flow region, in which the flow boiling instabilities with apparent amplitude and long period were more easily triggered at high heat flux. Moreover, the system pressure was increased with the increase of the heat flux.

Hollow Fiber Ground Evaporator Unit Testing

NASA Technical Reports Server (NTRS)

Bue, Grant; Trevino, Luis; Tsioulos, Gus

2010-01-01

A candidate technology for 1-atmosphere suited heat rejection was developed and tested at NASA Johnson Space Center. The concept is to use a collection of microporous hydrophobic tubes potted between inlet and outlet headers with water as coolant. A pump provides flow between headers through the tubes which are subjected to fan driven cross flow of relatively dry air. The forced ventilation would sweep out the water vapor from the evaporation of the coolant rejecting heat from the coolant stream. The hollow fibers are obtained commercially (X50-215 Celgard) which are arranged in a sheet containing 5 fibers per linear inch. Two engineering development units were produced that vary the fold direction of the fiber sheets relative to the ventilation. These units were tested at inlet water temperatures ranging from 20 deg C to 30 deg C, coolant flow rates ranging from 10 to 90 kg/hr, and at three fan speeds. These results were used to size a system that could reject heat at a rate of 340 W.

Entropy Analysis in Mixed Convection MHD flow of Nanofluid over a Non-linear Stretching Sheet

NASA Astrophysics Data System (ADS)

Matin, Meisam Habibi; Nobari, Mohammad Reza Heirani; Jahangiri, Pouyan

This article deals with a numerical study of entropy analysis in mixed convection MHD flow of nanofluid over a non-linear stretching sheet taking into account the effects of viscous dissipation and variable magnetic field. The nanofluid is made of such nano particles as SiO2 with pure water as a base fluid. To analyze the problem, at first the boundary layer equations are transformed into non-linear ordinary equations using a similarity transformation. The resultant equations are then solved numerically using the Keller-Box scheme based on the implicit finite-difference method. The effects of different non-dimensional governing parameters such as magnetic parameter, nanoparticles volume fraction, Nusselt, Richardson, Eckert, Hartman, Brinkman, Reynolds and entropy generation numbers are investigated in details. The results indicate that increasing the nano particles to the base fluids causes the reduction in shear forces and a decrease in stretching sheet heat transfer coefficient. Also, decreasing the magnetic parameter and increasing the Eckert number result in improves heat transfer rate. Furthermore, the surface acts as a strong source of irreversibility due to the higher entropy generation number near the surface.

[Application of three heat pulse technique-based methods to determine the stem sap flow].

PubMed

Wang, Sheng; Fan, Jun

2015-08-01

It is of critical importance to acquire tree transpiration characters through sap flow methodology to understand tree water physiology, forest ecology and ecosystem water exchange. Tri-probe heat pulse sensors, which are widely utilized in soil thermal parameters and soil evaporation measurement, were applied to implement Salix matsudana sap flow density (Vs) measurements via heat-ratio method (HRM), T-Max method (T-Max) and single-probe heat pulse probe (SHPP) method, and comparative analysis was conducted with additional Grainer's thermal diffusion probes (TDP) measured results. The results showed that, it took about five weeks to reach a stable measurement stage after TPHP installation, Vs measured with three methods in the early stage after installation was 135%-220% higher than Vs in the stable measurement stage, and Vs estimated via HRM, T-Max and SHPP methods were significantly linearly correlated with Vs estimated via TDP method, with R2 of 0.93, 0.73 and 0.91, respectively, and R2 for Vs measured by SHPP and HRM reached 0.94. HRM had relatively higher precision in measuring low rates and reverse sap flow. SHPP method seemed to be very promising to measure sap flow for configuration simplicity and high measuring accuracy, whereas it couldn' t distinguish directions of flow. T-Max method had relatively higher error in sap flow measurement, and it couldn' t measure sap flow below 5 cm3 · cm(-2) · h(-1), thus this method could not be used alone, however it could measure thermal diffusivity for calculating sap flow when other methods were imposed. It was recommended to choose a proper method or a combination of several methods to measure stem sap flow, based on specific research purpose.

Analysis of ferrite nanoparticles in the flow of ferromagnetic nanofluid.

PubMed

Muhammad, Noor; Nadeem, Sohail; Mustafa, M T

2018-01-01

Theoretical analysis has been carried out to establish the heat transport phenomenon of six different ferromagnetic MnZnFe2O4-C2H6O2 (manganese zinc ferrite-ethylene glycol), NiZnFe2O4-C2H6O2 (Nickel zinc ferrite-ethylene glycol), Fe2O4-C2H6O2 (magnetite ferrite-ethylene glycol), NiZnFe2O4-H2O (Nickel zinc ferrite-water), MnZnFe2O4-H2O (manganese zinc ferrite-water), and Fe2O4-H2O (magnetite ferrite-water) nanofluids containing manganese zinc ferrite, Nickel zinc ferrite, and magnetite ferrite nanoparticles dispersed in a base fluid of ethylene glycol and water mixture. The performance of convective heat transfer is elevated in boundary layer flow region via nanoparticles. Magnetic dipole in presence of ferrites nanoparticles plays a vital role in controlling the thermal and momentum boundary layers. In perspective of this, the impacts of magnetic dipole on the nano boundary layer, steady, and laminar flow of incompressible ferromagnetic nanofluids are analyzed in the present study. Flow is caused by linear stretching of the surface. Fourier's law of heat conduction is used in the evaluation of heat flux. Impacts of emerging parameters on the magneto-thermomechanical coupling are analyzed numerically. Further, it is evident that Newtonian heating has increasing behavior on the rate of heat transfer in the boundary layer. Comparison with available results for specific cases show an excellent agreement.

Modeling 3D conjugate heat and mass transfer for turbulent air drying of Chilean papaya in a direct contact dryer

NASA Astrophysics Data System (ADS)

Lemus-Mondaca, Roberto A.; Vega-Gálvez, Antonio; Zambra, Carlos E.; Moraga, Nelson O.

2017-01-01

A 3D model considering heat and mass transfer for food dehydration inside a direct contact dryer is studied. The k- ɛ model is used to describe turbulent air flow. The samples thermophysical properties as density, specific heat, and thermal conductivity are assumed to vary non-linearly with temperature. FVM, SIMPLE algorithm based on a FORTRAN code are used. Results unsteady velocity, temperature, moisture, kinetic energy and dissipation rate for the air flow are presented, whilst temperature and moisture values for the food also are presented. The validation procedure includes a comparison with experimental and numerical temperature and moisture content results obtained from experimental data, reaching a deviation 7-10 %. In addition, this turbulent k- ɛ model provided a better understanding of the transport phenomenon inside the dryer and sample.

Stirling System Modeling for Space Nuclear Power Systems

NASA Technical Reports Server (NTRS)

Lewandowski, Edward J.; Johnson, Paul K.

2008-01-01

A dynamic model of a high-power Stirling convertor has been developed for space nuclear power systems modeling. The model is based on the Component Test Power Convertor (CTPC), a 12.5-kWe free-piston Stirling convertor. The model includes the fluid heat source, the Stirling convertor, output power, and heat rejection. The Stirling convertor model includes the Stirling cycle thermodynamics, heat flow, mechanical mass-spring damper systems, and the linear alternator. The model was validated against test data. Both nonlinear and linear versions of the model were developed. The linear version algebraically couples two separate linear dynamic models; one model of the Stirling cycle and one model of the thermal system, through the pressure factors. Future possible uses of the Stirling system dynamic model are discussed. A pair of commercially available 1-kWe Stirling convertors is being purchased by NASA Glenn Research Center. The specifications of those convertors may eventually be incorporated into the dynamic model and analysis compared to the convertor test data. Subsequent potential testing could include integrating the convertors into a pumped liquid metal hot-end interface. This test would provide more data for comparison to the dynamic model analysis.

Heat And Mass Transfer Analysis of a Film Evaporative MEMS Tunable Array

NASA Astrophysics Data System (ADS)

O'Neill, William J.

This thesis details the heat and mass transfer analysis of a MEMs microthruster designed to provide propulsive, attitude control and thermal control capabilities to a cubesat. This thruster is designed to function by retaining water as a propellant and applying resistive heating in order to increase the temperature of the liquid-vapor interface to either increase evaporation or induce boiling to regulate mass flow. The resulting vapor is then expanded out of a diverging nozzle to produce thrust. Because of the low operating pressure and small length scale of this thruster, unique forms of mass transfer analysis such as non-continuum gas flow were modeled using the Direct Simulation Monte Carlo method. Continuum fluid/thermal simulations using COMSOL Multiphysics have been applied to model heat and mass transfer in the solid and liquid portions of the thruster. The two methods were coupled through variables at the liquid-vapor interface and solved iteratively by the bisection method. The simulations presented in this thesis confirm the thermal valving concept. It is shown that when power is applied to the thruster there is a nearly linear increase in mass flow and thrust. Thus, mass flow can be regulated by regulating the applied power. This concept can also be used as a thermal control device for spacecraft.

TACT1- TRANSIENT THERMAL ANALYSIS OF A COOLED TURBINE BLADE OR VANE EQUIPPED WITH A COOLANT INSERT

NASA Technical Reports Server (NTRS)

Gaugler, R. E.

1994-01-01

As turbine-engine core operating conditions become more severe, designers must develop more effective means of cooling blades and vanes. In order to design reliable, cooled turbine blades, advanced transient thermal calculation techniques are required. The TACT1 computer program was developed to perform transient and steady-state heat-transfer and coolant-flow analyses for cooled blades, given the outside hot-gas boundary condition, the coolant inlet conditions, the geometry of the blade shell, and the cooling configuration. TACT1 can analyze turbine blades, or vanes, equipped with a central coolant-plenum insert from which coolant-air impinges on the inner surface of the blade shell. Coolant-side heat-transfer coefficients are calculated with the heat transfer mode at each station being user specified as either impingement with crossflow, forced convection channel flow, or forced convection over pin fins. A limited capability to handle film cooling is also available in the program. The TACT1 program solves for the blade temperature distribution using a transient energy equation for each node. The nodal energy balances are linearized, one-dimensional, heat-conduction equations which are applied at the wall-outer-surface node, at the junction of the cladding and the metal node, and at the wall-inner-surface node. At the mid-metal node a linear, three-dimensional, heat-conduction equation is used. Similarly, the coolant pressure distribution is determined by solving the set of transfer momentum equations for the one-dimensional flow between adjacent fluid nodes. In the coolant channel, energy and momentum equations for one-dimensional compressible flow, including friction and heat transfer, are used for the elemental channel length between two coolant nodes. The TACT1 program first obtains a steady-state solution using iterative calculations to obtain convergence of stable temperatures, pressures, coolant-flow split, and overall coolant mass balance. Transient calculations are based on the steady-state solutions obtained. Input to the TACT1 program includes a geometrical description of the blade and insert, the nodal spacing to be used, and the boundary conditions describing the outside hot-gas and the coolant-inlet conditions. The program output includes the value of nodal temperatures and pressures at each iteration. The final solution output includes the temperature at each coolant node, and the coolant flow rates and Reynolds numbers. This program is written in FORTRAN IV for batch execution and has been implemented on an IBM 360 computer with a central memory requirement of approximately 480K of 8 bit bytes. The TACT1 program was developed in 1978.

Effect of thermal radiation on laminar boundary layer flow over a permeable flat plate with Newtonian heating

NASA Astrophysics Data System (ADS)

Khairul Anuar Mohamed, Muhammad; Zuki Salleh, Mohd; Noar, Nor Aida Zuraimi Md; Ishak, Anuar

2017-09-01

The laminar boundary layer flow over a permeable flat plat with the presence of thermal radiation and Newtonian heating is numerically studied. The non linear partial differential equations that governed the model are transformed to ordinary differential equations before being solved numerically by Runge-Kutta-Fehlberg (RKF) method using Maple software. The influenced and characteristic of pertinent parameters which are the Prandtl number, the suction/blowing parameter, the thermal radiation parameter and the conjugate parameter are analyzed and discussed. It is found that the presence of thermal radiation and blowing parameter has increased the value of wall temperature. Meanwhile, the trend is contrary with the suction effect.

A study of two cases of comma-cloud cyclogenesis using a semigeostrophic model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Craig, G.C.; Cho, Hanru

1992-12-01

The linear stability of two atmospheric flows is studied, with basic-state data taken from environments where comma clouds are observed to flow. Each basic state features a baroclinic zone associated with an upper-level jet, with conditional instability on the north side. The semigeostrophic approximation is utilized, along with a simple parameterization for cumulus heating, and the eigenvalue problem is solved employing a Chebyshev spectral technique. 47 refs.

Heat flow in the flanks of the Oceanographer-Hayes segment of the Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Le Gal, V.; Lucazeau, F.; Cannat, M.; Battani, A.; Poort, J.; Guichet, X.; Monnin, C.; Fontaine, F. J.; Leroy, S. D.

2016-12-01

It is currently estimated that a third of the oceanic heat loss is due to fluid circulation in the oceanic crust. Besides high and low temperature fluid discharge at ridge axis, off-axis low temperature fluid circulations can affect large volumes of the oceanic crust. Long term investigations of the Eastern Juan de Fuca ridge flank (Hutnak et al.2006) have established a circulation pattern where hydrothermal discharge and recharge occur at basement outcrops and where sediment is mostly impermeable. Here, we present results from the recent Oceanograflu cruise (2013), on the Oceanographer-Hayes segment ridge flanks of the Mid-Atlantic ridge in crust 5 and 12 myrs in age. On both flanks, we obtained 185 temperature gradients and conductivities in-situ, 30 Küllenberg cores (3 to 5 meters long) coupled with temperature gradients in-situ and conductivity measurements onboard. These data are interpreted in terms of heat flow values and are generally lower than the conductive cooling model. Several temperature-depth profiles don't show linear gradients, but rather sigmoid shapes or inverse gradients suggesting superficial circulations through the first meters of sediments. The corresponding heat flow pattern is not similar to the one observed at Juan de Fuca. No systematic links have been observed between basement outcrops and lower or higher heat flow which would point to discharge or recharge sites. Instead, the pattern recalls studies in the North Pond area (Langseth et al.1992), with a clear predominance of low heat flow values over the site. We propose that the North Pond circulation model is applicable to large portions of slow-spreading ridge flanks such as the Atlantic. In this model, seawater cools the uppermost crust below sediments in basins that are typically tens of kms wide, reducing the surface heat flow under cooling model values. Based on subsidence rates, these shallow hydrothermal circulations have a minor impact on the cooling of the diverging plates.

Investigation of Instabilities and Heat Transfer Phenomena in Supercritical Fuels at High Heat Flux and Temperatures

NASA Technical Reports Server (NTRS)

Linne, Diane L.; Meyer, Michael L.; Braun, Donald C.; Keller, Dennis J.

2000-01-01

A series of heated tube experiments was performed to investigate fluid instabilities that occur during heating of supercritical fluids. In these tests, JP-7 flowed vertically through small diameter tubes at supercritical pressures. Test section heated length, diameter, mass flow rate, inlet temperature, and heat flux were varied in an effort to determine the range of conditions that trigger the instabilities. Heat flux was varied up to 4 BTU/sq in./s, and test section wall temperatures reached as high as 1950 F. A statistical model was generated to explain the trends and effects of the control variables. The model included no direct linear effect of heat flux on the occurrence of the instabilities. All terms involving inlet temperature were negative, and all terms involving mass flow rate were positive. Multiple tests at conditions that produced instabilities provided inconsistent results. These inconsistencies limit the use of the model as a predictive tool. Physical variables that had been previously postulated to control the onset of the instabilities, such as film temperature, velocity, buoyancy, and wall-to-bulk temperature ratio, were evaluated here. Film temperatures at or near critical occurred during both stable and unstable tests. All tests at the highest velocity were stable, but there was no functional relationship found between the instabilities and velocity, or a combination of velocity and temperature ratio. Finally, all of the unstable tests had significant buoyancy at the inlet of the test section, but many stable tests also had significant buoyancy forces.

Source model of volcanic tremor: two-phase flow instability in a pipe-valve system

NASA Astrophysics Data System (ADS)

Fujita, E.

2003-12-01

Volcanic tremor at a shallow depth beneath the volcano is inferred to link to hydrothermal activities powered by heat supply from magma. In this study, we developed numerical simulations of the instabilities of the water-steam two-phase flow in a pipe-valve system and considered the source mechanism of volcanic tremor. The experiments of two-phase flow by Veziroglu and Lee [1968] revealed the two kinds of oscillating modes, density wave oscillation with the period of a few seconds and pressure drop oscillation with the period of dozens of seconds. These modes were mainly controlled by the pressure difference between inlet and outlet, flux rate of fluid and heat supply rate. Especially, the former mode appears when the flux rate is small and the latter does when the pressure difference and heat supply rate are larger. We performed some preliminary numerical simulation of these oscillations in water-steam flow in a cylindrical conduit. As an example, we assume the flow in conduit of 4 m length with the valves at inlet and outlet with the conditions of non-slip at the wall. As initial conditions, the inlet and outlet pressures are fixed to be 1.2E5 Pa and 1.0E5 Pa, respectively, water temperature of 370 K, heat supply of 1.0E6 - 2.0E7W/m3. The friction except the valve area is assumed to be 1000kg/m3. After the heating condition becomes stable, we shut the valve at the outlet and detect the significant oscillation. In case of the heat supply of 1.1E7W/m3, density drop oscillation with the period of 0.16s has appeared. In this model, the oscillation originates from the density change due to vaporization, and its information arrives at the outlet with the velocity of two-phase flow. The cycle of heating and boiling controls the interval of the tremor occurrence and the period is determined by the length of the pipe and the flow velocity. The shut of valve physically corresponds to geometrical narrowing, choking, and non-linear effect of flow and/or surrounding medium.

Prediction of free turbulent mixing using a turbulent kinetic energy method

NASA Technical Reports Server (NTRS)

Harsha, P. T.

1973-01-01

Free turbulent mixing of two-dimensional and axisymmetric one- and two-stream flows is analyzed by a relatively simple turbulent kinetic energy method. This method incorporates a linear relationship between the turbulent shear and the turbulent kinetic energy and an algebraic relationship for the length scale appearing in the turbulent kinetic energy equation. Good results are obtained for a wide variety of flows. The technique is shown to be especially applicable to flows with heat and mass transfer, for which nonunity Prandtl and Schmidt numbers may be assumed.

Feasibility Study on a Segmented Ferrofluid Flow Linear Generator for Increasing the Time-Varying Magnetic Flux.

PubMed

Lee, Won-Ho; Lee, Se-Hee; Lee, Sangyoup; Lee, Jong-Chul

2018-09-01

Nanoparticles and nanofluids have been implemented in energy harvesting devices, and energy harvesting based on magnetic nanofluid flow was recently achieved by using a layer-built magnet and micro-bubble injection to induce a voltage on the order of 10-1 mV. However, this is not yet suitable for some commercial purpose. In order to further increase the amount of electric voltage and current from this energy harvesting the air bubbles must be segmented in the base fluid, and the magnetic flux of the segmented flow should be materially altered over time. The focus of this research is on the development of a segmented ferrofluid flow linear generator that would scavenge electrical power from waste heat. Experiments were conducted to obtain the induced voltage, which was generated by moving a ferrofluid-filled capsule inside a multi-turn coil. Computations were then performed to explain the fundamental physical basis of the motion of the segmented flow of the ferrofluids and the air-layers.

Nonlinear radiative peristaltic flow of hydromagnetic fluid through porous medium

NASA Astrophysics Data System (ADS)

Hussain, Q.; Latif, T.; Alvi, N.; Asghar, S.

2018-06-01

The radiative heat and mass transfer in wall induced flow of hydromagnetic fluid through porous medium in an asymmetric channel is analyzed. The fluid viscosity is considered temperature dependent. In the theory of peristalsis, the radiation effects are either ignored or taken as linear approximation of radiative heat flux. Such approximation is only possible when there is sufficiently small temperature differences in the flow field; however, nonlinear radiation effects are valid for large temperature differences as well (the new feature added in the present study). Mathematical modeling of the problems include the complicated system of highly nonlinear differential equations. Semi-analytical solutions are established in the wave reference frame. Results are displayed graphically and discussed in detail for the variation of various physical parameters with the special attention to viscosity, radiation, and temperature ratio parameters.

Turbulent heat transfer prediction method for application to scramjet engines

NASA Technical Reports Server (NTRS)

Pinckney, S. Z.

1974-01-01

An integral method for predicting boundary layer development in turbulent flow regions on two-dimensional or axisymmetric bodies was developed. The method has the capability of approximating nonequilibrium velocity profiles as well as the local surface friction in the presence of a pressure gradient. An approach was developed for the problem of predicting the heat transfer in a turbulent boundary layer in the presence of a high pressure gradient. The solution was derived with particular emphasis on its applicability to supersonic combustion; thus, the effects of real gas flows were included. The resulting integrodifferential boundary layer method permits the estimation of cooling reguirements for scramjet engines. Theoretical heat transfer results are compared with experimental combustor and noncombustor heat transfer data. The heat transfer method was used in the development of engine design concepts which will produce an engine with reduced cooling requirements. The Langley scramjet engine module was designed by utilizing these design concepts and this engine design is discussed along with its corresponding cooling requirements. The heat transfer method was also used to develop a combustor cooling correlation for a combustor whose local properties are computed one dimensionally by assuming a linear area variation and a given heat release schedule.

Vibration effect on the Soret-induced convection of ternary mixture in a rectangular cavity heated from below

NASA Astrophysics Data System (ADS)

Lyubimova, T. P.; Zubova, N. A.

2017-06-01

This paper presents the results of numerical simulation of the Soret-induced convection of ternary mixture in the rectangular cavity elongated in horizontal direction in gravity field. The cavity has rigid impermeable boundaries. It is heated from the bellow and undergoes translational linearly polarized vibrations of finite amplitude and frequency in the horizontal direction. The problem is solved by finite difference method in the framework of full unsteady non-linear approach. The procedure of diagonalization of the molecular diffusion coefficient matrix is applied, allowing to eliminate cross-diffusion components in the equations and to reduce the number of the governing parameters. The calculations are performed for model ternary mixture with positive separation ratios of the components. The data on the vibration effect on temporal evolution of instantaneous and average fields and integral characteristics of the flow and heat and mass transfer at different levels of gravity are obtained.

Multi-foci beamforming for thermal strain imaging using a single ultrasound linear array transducer

PubMed Central

Nguyen, Man M; Ding, Xuan; Leers, Steven A.; Kim, Kang

2017-01-01

Ultrasound-induced thermal strain imaging (TSI) has been used to successfully identify lipid and water-based tissues in atherosclerotic plaques in some research settings. However, TSI faces several challenges to be realized in clinics. These challenges include motion artifacts, displacement tracking accuracy as well as limited heating capability which contributes to low thermal strain signal-to-noise ratio and a limited field of view. The goal of this paper is to address the challenge in heating tissue in TSI. Current TSI systems use separate heating and imaging transducers, which require physically aligning the heating and imaging beams and result in a bulky setup that limits in vivo operation. This paper proposes and evaluates a new design for heating beams that can be implemented on a linear array imaging transducer and can provide an improved heating area and efficiency as compared to previous implementations. The designed heating beams were implemented with a clinical linear array imaging transducer connected to a research ultrasound platform. In-vitro experiments using tissue mimicking phantoms with no blood flow showed that the new design resulted in an effective heating area of approximately 0.85 cm2 and a 0.3°C temperature rise in 2 seconds of heating, which compared well with in- silico finite element simulations. With the new heating beams, TSI was shown to be able to detect a lipid-mimicking rubber inclusion with a diameter of 1 cm from the water-based gelatin background, with a strain contrast of 2.3 (+0.14% strain in the rubber inclusion and −0.06% strain in the gelatin background). Lastly, lipid-based tissue in a 1-cm diameter human carotid endarterectomy (CEA) sample was identified with good agreement to histology. PMID:28318887

User's guide of TOUGH2-EGS-MP: A Massively Parallel Simulator with Coupled Geomechanics for Fluid and Heat Flow in Enhanced Geothermal Systems VERSION 1.0

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiong, Yi; Fakcharoenphol, Perapon; Wang, Shihao

2013-12-01

TOUGH2-EGS-MP is a parallel numerical simulation program coupling geomechanics with fluid and heat flow in fractured and porous media, and is applicable for simulation of enhanced geothermal systems (EGS). TOUGH2-EGS-MP is based on the TOUGH2-MP code, the massively parallel version of TOUGH2. In TOUGH2-EGS-MP, the fully-coupled flow-geomechanics model is developed from linear elastic theory for thermo-poro-elastic systems and is formulated in terms of mean normal stress as well as pore pressure and temperature. Reservoir rock properties such as porosity and permeability depend on rock deformation, and the relationships between these two, obtained from poro-elasticity theories and empirical correlations, are incorporatedmore » into the simulation. This report provides the user with detailed information on the TOUGH2-EGS-MP mathematical model and instructions for using it for Thermal-Hydrological-Mechanical (THM) simulations. The mathematical model includes the fluid and heat flow equations, geomechanical equation, and discretization of those equations. In addition, the parallel aspects of the code, such as domain partitioning and communication between processors, are also included. Although TOUGH2-EGS-MP has the capability for simulating fluid and heat flows coupled with geomechanical effects, it is up to the user to select the specific coupling process, such as THM or only TH, in a simulation. There are several example problems illustrating applications of this program. These example problems are described in detail and their input data are presented. Their results demonstrate that this program can be used for field-scale geothermal reservoir simulation in porous and fractured media with fluid and heat flow coupled with geomechanical effects.« less

Effect of Material Property Variations at Near Critical Thermodynamic Conditions on Pipe Flow Heat Transfer

NASA Astrophysics Data System (ADS)

Barney, Rebecca; Nourgaliev, Robert; Delplanque, Jean-Pierre; McCallen, Rose

2017-11-01

Heat transfer is quantified and contrasted for the Poiseuille flow of a fluid at both subcritical and supercritical thermodynamic conditions in a circular pipe subject to a uniform wall heat flux. The conditions considered are relevant to Supercritical Water Reactor (SCWR) applications. In the supercritical thermodynamic regime, a fluid can exhibit large density variations of density, thermal conductivity, and viscosity, which will affect flow and heat transfer characteristics significantly. An advanced equation of state for supercritical water was implemented in a 2D and 3D Arbitrary Lagrangian-Eurlerian multi-physics simulation tool called ALE3D developed at Lawrence Livermore National Laboratory. A newly developed, robust, high-order in space and time, fully implicit reconstructed discontinuous Galerkin (rDG) method is used to enable the numerical simulation of convective heat transfer with supercritical water. Results demonstrate the capability of this approach to accurately capture the non-linear behavior and enhanced heat transfer with supercritical water. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Information management release number LLNL-ABS-736004. Work is supported by the Integrated University Program Graduate Fellowship. Opinions, findings, conclusions or recommendations expressed are of the authors and do not necessarily reflect the views of DOE office of NE.

Gradient-driven flux-tube simulations of ion temperature gradient turbulence close to the non-linear threshold

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peeters, A. G.; Rath, F.; Buchholz, R.

2016-08-15

It is shown that Ion Temperature Gradient turbulence close to the threshold exhibits a long time behaviour, with smaller heat fluxes at later times. This reduction is connected with the slow growth of long wave length zonal flows, and consequently, the numerical dissipation on these flows must be sufficiently small. Close to the nonlinear threshold for turbulence generation, a relatively small dissipation can maintain a turbulent state with a sizeable heat flux, through the damping of the zonal flow. Lowering the dissipation causes the turbulence, for temperature gradients close to the threshold, to be subdued. The heat flux then doesmore » not go smoothly to zero when the threshold is approached from above. Rather, a finite minimum heat flux is obtained below which no fully developed turbulent state exists. The threshold value of the temperature gradient length at which this finite heat flux is obtained is up to 30% larger compared with the threshold value obtained by extrapolating the heat flux to zero, and the cyclone base case is found to be nonlinearly stable. Transport is subdued when a fully developed staircase structure in the E × B shearing rate forms. Just above the threshold, an incomplete staircase develops, and transport is mediated by avalanche structures which propagate through the marginally stable regions.« less

Numerical study of MHD nanofluid flow and heat transfer past a bidirectional exponentially stretching sheet

NASA Astrophysics Data System (ADS)

Ahmad, Rida; Mustafa, M.; Hayat, T.; Alsaedi, A.

2016-06-01

Recent advancements in nanotechnology have led to the discovery of new generation coolants known as nanofluids. Nanofluids possess novel and unique characteristics which are fruitful in numerous cooling applications. Current work is undertaken to address the heat transfer in MHD three-dimensional flow of magnetic nanofluid (ferrofluid) over a bidirectional exponentially stretching sheet. The base fluid is considered as water which consists of magnetite-Fe3O4 nanoparticles. Exponentially varying surface temperature distribution is accounted. Problem formulation is presented through the Maxwell models for effective electrical conductivity and effective thermal conductivity of nanofluid. Similarity transformations give rise to a coupled non-linear differential system which is solved numerically. Appreciable growth in the convective heat transfer coefficient is observed when nanoparticle volume fraction is augmented. Temperature exponent parameter serves to enhance the heat transfer from the surface. Moreover the skin friction coefficient is directly proportional to both magnetic field strength and nanoparticle volume fraction.

Mercury Thermal Hydraulic Loop (MTHL) Summary Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Felde, David K.; Crye, Jason Michael; Wendel, Mark W.

2017-03-01

The Spallation Neutron Source (SNS) is a high-power linear accelerator built at Oak Ridge National Laboratory (ORNL) which incorporates the use of a flowing liquid mercury target. The Mercury Thermal Hydraulic Loop (MTHL) was constructed to investigate and verify the heat transfer characteristics of liquid mercury in a rectangular channel. This report provides a compilation of previously reported results from the water-cooled and electrically heated straight and curved test sections that simulate the geometry of the window cooling channel in the target nose region.

A study of nonlinear dynamics of single- and two-phase flow oscillations

NASA Astrophysics Data System (ADS)

Mawasha, Phetolo Ruby

The dynamics of single- and two-phase flows in channels can be contingent on nonlinearities which are not clearly understood. These nonlinearities could be interfacial forces between the flowing fluid and its walls, variations in fluid properties, growth of voids, etc. The understanding of nonlinear dynamics of fluid flow is critical in physical systems which can undergo undesirable system operating scenarios such an oscillatory behavior which may lead to component failure. A nonlinear lumped mathematical model of a surge tank with a constant inlet flow into the tank and an outlet flow through a channel is derived from first principles. The model is used to demonstrate that surge tanks with inlet and outlet flows contribute to oscillatory behavior in laminar, turbulent, single-phase, and two-phase flow systems. Some oscillations are underdamped while others are self-sustaining. The mechanisms that are active in single-phase oscillations with no heating are presented using specific cases of simplified models. Also, it is demonstrated how an external mechanism such as boiling contributes to the oscillations observed in two-phase flow and gives rise to sustained oscillations (or pressure drop oscillations). A description of the pressure drop oscillation mechanism is presented using the steady state pressure drop versus mass flow rate characteristic curve of the heated channel, available steady state pressure drop versus mass flow rate from the surge tank, and the transient pressure drop versus mass flow rate limit cycle. Parametric studies are used to verify the theoretical pressure drop oscillations model using experimental data by Yuncu's (1990). The following contributions are unique: (1) comparisons of nonlinear pressure drop oscillation models with and without the effect of the wall thermal heat capacity and (2) comparisons of linearized pressure drop oscillation models with and without the effect of the wall thermal heat capacity to identify stability boundaries.

Analysis of ferrite nanoparticles in the flow of ferromagnetic nanofluid

PubMed Central

Nadeem, Sohail; Mustafa, M. T.

2018-01-01

Theoretical analysis has been carried out to establish the heat transport phenomenon of six different ferromagnetic MnZnFe2O4—C2H6O2 (manganese zinc ferrite-ethylene glycol), NiZnFe2O4—C2H6O2 (Nickel zinc ferrite-ethylene glycol), Fe2O4—C2H6O2 (magnetite ferrite-ethylene glycol), NiZnFe2O4—H2O (Nickel zinc ferrite-water), MnZnFe2O4—H2O (manganese zinc ferrite-water), and Fe2O4—H2O (magnetite ferrite-water) nanofluids containing manganese zinc ferrite, Nickel zinc ferrite, and magnetite ferrite nanoparticles dispersed in a base fluid of ethylene glycol and water mixture. The performance of convective heat transfer is elevated in boundary layer flow region via nanoparticles. Magnetic dipole in presence of ferrites nanoparticles plays a vital role in controlling the thermal and momentum boundary layers. In perspective of this, the impacts of magnetic dipole on the nano boundary layer, steady, and laminar flow of incompressible ferromagnetic nanofluids are analyzed in the present study. Flow is caused by linear stretching of the surface. Fourier’s law of heat conduction is used in the evaluation of heat flux. Impacts of emerging parameters on the magneto—thermomechanical coupling are analyzed numerically. Further, it is evident that Newtonian heating has increasing behavior on the rate of heat transfer in the boundary layer. Comparison with available results for specific cases show an excellent agreement. PMID:29320488

User's Guide of TOUGH2-EGS. A Coupled Geomechanical and Reactive Geochemical Simulator for Fluid and Heat Flow in Enhanced Geothermal Systems Version 1.0

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fakcharoenphol, Perapon; Xiong, Yi; Hu, Litang

TOUGH2-EGS is a numerical simulation program coupling geomechanics and chemical reactions for fluid and heat flows in porous media and fractured reservoirs of enhanced geothermal systems. The simulator includes the fully-coupled geomechanical (THM) module, the fully-coupled geochemical (THC) module, and the sequentially coupled reactive geochemistry (THMC) module. The fully-coupled flow-geomechanics model is developed from the linear elastic theory for the thermo-poro-elastic system and is formulated with the mean normal stress as well as pore pressure and temperature. The chemical reaction is sequentially coupled after solution of flow equations, which provides the flow velocity and phase saturation for the solute transportmore » calculation at each time step. In addition, reservoir rock properties, such as porosity and permeability, are subjected to change due to rock deformation and chemical reactions. The relationships between rock properties and geomechanical and chemical effects from poro-elasticity theories and empirical correlations are incorporated into the simulator. This report provides the user with detailed information on both mathematical models and instructions for using TOUGH2-EGS for THM, THC or THMC simulations. The mathematical models include the fluid and heat flow equations, geomechanical equation, reactive geochemistry equations, and discretization methods. Although TOUGH2-EGS has the capability for simulating fluid and heat flows coupled with both geomechanical and chemical effects, it is up to the users to select the specific coupling process, such as THM, THC, or THMC in a simulation. There are several example problems illustrating the applications of this program. These example problems are described in details and their input data are presented. The results demonstrate that this program can be used for field-scale geothermal reservoir simulation with fluid and heat flow, geomechanical effect, and chemical reaction in porous and fractured media.« less

Relationship between level of forage intake, blood flow and oxygen consumption by splanchnic tissues of sheep fed a tropical grass forage.

PubMed

Hentz, F; Kozloski, G V; Zeni, D; Brun, M V; Stefanello, S

2017-02-01

Four Polwarth castrated male sheep (42 ± 4.4 kg live weight (LW) surgically implanted with chronic indwelling catheters into the mesenteric, portal and hepatic veins, housed in metabolism cages and offered Cynodon sp. hay at rates (g of dry matter (DM)/kg LW) of 7, 14, 21 or ad libitum, were used in a 4 × 4 Latin square experiment to evaluate the effect of the level of forage intake on blood flow and oxygen consumption by the portal-drained viscera (PDV), liver and total splanchnic tissues (ST). The portal blood flow and the oxygen consumption by PDV linearly increased at increased organic matter (OM) intake. No effect of level of OM intake was obtained for the hepatic artery blood flow and oxygen consumption by liver. As a consequence, the level of OM intake only tended to directly affect hepatic blood flow and oxygen consumption by total ST. Oxygen consumption was linearly and positively related to blood flow across PDV, liver and total ST. The heat production by PDV and total ST, as proportion of metabolizable energy (ME) intake, decreased curvilinearly at increased ME intake. In conclusion, the oxygen consumption by PDV, but not by liver, was directly related to the level of forage intake by sheep. Moreover, when ingested at levels below maintenance, most of ME was spent as heat produced by ST. Journal of Animal Physiology and Animal Nutrition © 2016 Blackwell Verlag GmbH.

Numerical simulation for aspects of homogeneous and heterogeneous reactions in forced convection flow of nanofluid

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Shah, Faisal; Khan, Muhammad Ijaz; Alsaedi, Ahmed

2018-03-01

Mixed convection stagnation point flow of nanofluid by a vertical permeable circular cylinder has been addressed. Water is treated as ordinary liquid while nanoparticles include aluminium oxide, copper and titanium dioxide. Homogeneous-heterogeneous reactions are considered. The nonlinear higher order expressions are changed into first ordinary differential equations and then solved by built-in-Shooting method in mathematica. The results of velocity, temperature, concentration, skin friction and local Nusselt number are discussed. Our results demonstrate that surface drag force and heat transfer rate are enhanced linearly for higher estimation of curvature parameter. Further surface drag force decays for aluminium oxide and it enhances for copper nanoparticle. Heat transfer rate enhances with increasing all three types of nanoparticles. In addition, the lowest heat transfer rate is obtained in case of titanium dioxide when compared with copper and aluminium oxide.

Analytical exploration of a TiO2 nanofluid along a rotating disk with homogeneous-heterogeneous chemical reactions and non-uniform heat source/sink

NASA Astrophysics Data System (ADS)

Das, Kalidas; Chakraborty, Tanmoy; Kumar Kundu, Prabir

2017-12-01

Comparative flow features of two different nanofluids containing TiO2 nanoparticles along a rotating disk near a stagnation point are theoretically addressed here. The primary fluids are presumed as ethylene glycol and water. The influences of non-uniform heat absorption/generation with homogeneous and heterogeneous chemical reactions have been integrated to modify the energy and concentration profiles. By virtue of similarity conversions, the leading partial differential system has been standardized into non-linear ODEs and then cracked analytically by NDM and numerically by RK-4 based shooting practice. Impressions of emerging parameters on the flow regime have been reported by tables and graphs coupled with required discussions. One of our results predicts that, with the augmentation of TiO2 nanoparticles concentration, the rate of heat transport for ethylene glycol nanofluid becomes 30-36% higher compared to that of a water nanofluid.

Heat Budget of Large Rivers: Sensitivity to Stream Morphology

NASA Astrophysics Data System (ADS)

Lancaster, S. T.; Haggerty, R.

2014-12-01

In order to assess the feasibility of effecting measurable changes in the heat budget of a large river through restoration, we use a numerical model to analyze the sensitivity of that heat budget to morphological manipulations, specifically those resulting in a narrower main channel with more alcoves. We base model parameters primarily on the gravel-bedded middle Snake River near Marsing, Idaho. The heat budget is represented by an advection-dispersion-reaction equation with, in addition to radiative, evaporative, and sensible heat fluxes, a hyporheic flux term that models lateral flow from the main stream, through bars, and into alcoves and side channels. This term effectively introduces linear dispersion of water temperatures with respect to time, so that the magnitude of the hyporheic term in the heat budget is expected to scale with the ``hyporheic number," defined as , where is dimensionless hyporheic flow rate and is dimensionless mean residence time of water entering the hyporheic zone. Simulations varying the parameters for channel width and hyporheic flow indicate that, for a large river such as the middle Snake River, feasible changes in channel width would produce downstream changes in heat flux an order of magnitude larger than would relatively extreme changes in hyporheic number. Changes, such as reduced channel width and increased hyporheic number, that tend to reduce temperatures in the summer, when temperatures are increasing with time and downstream distance, actually tend to increase temperatures in the fall, when temperatures are decreasing with time and distance.

Stably stratified canopy flow in complex terrain

NASA Astrophysics Data System (ADS)

Xu, X.; Yi, C.; Kutter, E.

2015-07-01

Stably stratified canopy flow in complex terrain has been considered a difficult condition for measuring net ecosystem-atmosphere exchanges of carbon, water vapor, and energy. A long-standing advection error in eddy-flux measurements is caused by stably stratified canopy flow. Such a condition with strong thermal gradient and less turbulent air is also difficult for modeling. To understand the challenging atmospheric condition for eddy-flux measurements, we use the renormalized group (RNG) k-ϵ turbulence model to investigate the main characteristics of stably stratified canopy flows in complex terrain. In this two-dimensional simulation, we imposed persistent constant heat flux at ground surface and linearly increasing cooling rate in the upper-canopy layer, vertically varying dissipative force from canopy drag elements, buoyancy forcing induced from thermal stratification and the hill terrain. These strong boundary effects keep nonlinearity in the two-dimensional Navier-Stokes equations high enough to generate turbulent behavior. The fundamental characteristics of nighttime canopy flow over complex terrain measured by the small number of available multi-tower advection experiments can be reproduced by this numerical simulation, such as (1) unstable layer in the canopy and super-stable layers associated with flow decoupling in deep canopy and near the top of canopy; (2) sub-canopy drainage flow and drainage flow near the top of canopy in calm night; (3) upward momentum transfer in canopy, downward heat transfer in upper canopy and upward heat transfer in deep canopy; and (4) large buoyancy suppression and weak shear production in strong stability.

A local heat transfer analysis of lava cooling in the atmosphere: application to thermal diffusion-dominated lava flows

NASA Astrophysics Data System (ADS)

Neri, Augusto

1998-05-01

The local cooling process of thermal diffusion-dominated lava flows in the atmosphere was studied by a transient, one-dimensional heat transfer model taking into account the most relevant processes governing its behavior. Thermal diffusion-dominated lava flows include any type of flow in which the conductive-diffusive contribution in the energy equation largely overcomes the convective terms. This type of condition is supposed to be satisfied, during more or less extended periods of time, for a wide range of lava flows characterized by very low flow-rates, such as slabby and toothpaste pahoehoe, spongy pahoehoe, flow at the transition pahoehoe-aa, and flows from ephemeral vents. The analysis can be useful for the understanding of the effect of crust formation on the thermal insulation of the lava interior and, if integrated with adequate flow models, for the explanation of local features and morphologies of lava flows. The study is particularly aimed at a better knowledge of the complex non-linear heat transfer mechanisms that control lava cooling in the atmosphere and at the estimation of the most important parameters affecting the global heat transfer coefficient during the solidification process. The three fundamental heat transfer mechanisms with the atmosphere, that is radiation, natural convection, and forced convection by the wind, were modeled, whereas conduction and heat generation due to crystallization were considered within the lava. The magma was represented as a vesiculated binary melt with a given liquidus and solidus temperature and with the possible presence of a eutectic. The effects of different morphological features of the surface were investigated through a simplified description of their geometry. Model results allow both study of the formation in time of the crust and the thermal mushy layer underlying it, and a description of the behavior of the temperature distribution inside the lava as well as radiative and convective fluxes to the atmosphere. The analysis, performed by using parameters typical of Etnean lavas, particularly focuses on the non-intuitive relations between superficial cooling effects and inner temperature distribution as a function of the major variables involved in the cooling process. Results integrate recent modelings and measurements of the cooling process of Hawaiian pahoehoe flow lobes by Hon et al. (1994) and Keszthelyi and Denlinger (1996) and highlight the critical role played by surface morphology, lava thermal properties, and crystallization dynamics. Furthermore, the reported description of the various heat fluxes between lava and atmosphere can be extended to any other type of lava flows in which atmospheric cooling is involved.

A Few New 2+1-Dimensional Nonlinear Dynamics and the Representation of Riemann Curvature Tensors

NASA Astrophysics Data System (ADS)

Wang, Yan; Zhang, Yufeng; Zhang, Xiangzhi

2016-09-01

We first introduced a linear stationary equation with a quadratic operator in ∂x and ∂y, then a linear evolution equation is given by N-order polynomials of eigenfunctions. As applications, by taking N=2, we derived a (2+1)-dimensional generalized linear heat equation with two constant parameters associative with a symmetric space. When taking N=3, a pair of generalized Kadomtsev-Petviashvili equations with the same eigenvalues with the case of N=2 are generated. Similarly, a second-order flow associative with a homogeneous space is derived from the integrability condition of the two linear equations, which is a (2+1)-dimensional hyperbolic equation. When N=3, the third second flow associative with the homogeneous space is generated, which is a pair of new generalized Kadomtsev-Petviashvili equations. Finally, as an application of a Hermitian symmetric space, we established a pair of spectral problems to obtain a new (2+1)-dimensional generalized Schrödinger equation, which is expressed by the Riemann curvature tensors.

Heat Flow and Hydrologic Characteristics at the AND-1B borehole, ANDRILL McMurdo Ice Shelf Project, Antarctica

USGS Publications Warehouse

Morin, Roger H.; Williams, Trevor; Henry, Stuart; ,; Hansaraj, Dhiresh

2010-01-01

The Antarctic Drilling Program (ANDRILL) successfully drilled and cored a borehole, AND-1B, beneath the McMurdo Ice Shelf and into a flexural moat basin that surrounds Ross Island. Total drilling depth reached 1285 m below seafloor (mbsf) with 98 percent core recovery for the detailed study of glacier dynamics. With the goal of obtaining complementary information regarding heat flow and permeability, which is vital to understanding the nature of marine hydrogeologic systems, a succession of three temperature logs was recorded over a five-day span to monitor the gradual thermal recovery toward equilibrium conditions. These data were extrapolated to true, undisturbed temperatures, and they define a linear geothermal gradient of 76.7 K/km from the seafloor to 647 mbsf. Bulk thermal conductivities of the sedimentary rocks were derived from empirical mixing models and density measurements performed on core, and an average value of 1.5 W/mK ± 10 percent was determined. The corresponding estimate of heat flow at this site is 115 mW/m2. This value is relatively high but is consistent with other elevated heat-flow data associated with the Erebus Volcanic Province. Information regarding the origin and frequency of pathways for subsurface fluid flow is gleaned from drillers' records, complementary geophysical logs, and core descriptions. Only two prominent permeable zones are identified and these correspond to two markedly different features within the rift basin; one is a distinct lithostratigraphic subunit consisting of a thin lava flow and the other is a heavily fractured interval within a single thick subunit.

Influence of Non-linear Radiation Heat Flux on Rotating Maxwell Fluid over a Deformable Surface: A Numerical Study

NASA Astrophysics Data System (ADS)

Mustafa, M.; Mushtaq, A.; Hayat, T.; Alsaedi, A.

2018-04-01

Mathematical model for Maxwell fluid flow in rotating frame induced by an isothermal stretching wall is explored numerically. Scale analysis based boundary layer approximations are applied to simplify the conservation relations which are later converted to similar forms via appropriate substitutions. A numerical approach is utilized to derive similarity solutions for broad range of Deborah number. The results predict that velocity distributions are inversely proportional to the stress relaxation time. This outcome is different from that observed for the elastic parameter of second grade fluid. Unlike non-rotating frame, the solution curves are oscillatory decaying functions of similarity variable. As angular velocity enlarges, temperature rises and significant drop in the heat transfer coefficient occurs. We note that the wall slope of temperature has an asymptotically decaying profile against the wall to ambient ratio parameter. From the qualitative view point, temperature ratio parameter and radiation parameter have similar effect on the thermal boundary layer. Furthermore, radiation parameter has a definite role in improving the cooling process of the stretching boundary. A comparative study of current numerical computations and those from the existing studies is also presented in a limiting case. To our knowledge, the phenomenon of non-linear radiation in rotating viscoelastic flow due to linearly stretched plate is just modeled here.

Scrutinization of thermal radiation, viscous dissipation and Joule heating effects on Marangoni convective two-phase flow of Casson fluid with fluid-particle suspension

NASA Astrophysics Data System (ADS)

Mahanthesh, B.; Gireesha, B. J.

2018-03-01

The impact of Marangoni convection on dusty Casson fluid boundary layer flow with Joule heating and viscous dissipation aspects is addressed. The surface tension is assumed to vary linearly with temperature. Physical aspects of magnetohydrodynamics and thermal radiation are also accounted. The governing problem is modelled under boundary layer approximations for fluid phase and dust particle phase and then Runge-Kutta-Fehlberg method based numeric solutions are established. The momentum and heat transport mechanisms are focused on the result of distinct governing parameters. The Nusselt number is also calculated. It is established that the rate of heat transfer can be enhanced by suspending dust particles in the base fluid. The temperature field of fluid phase and temperature of dust phase are quite reverse for thermal dust parameter. The radiative heat, viscous dissipation and Joule heating aspects are constructive for thermal fields of fluid and dust phases. The velocity of dusty Casson fluid dominates the velocity of dusty fluid while this trend is opposite in the case of temperature. Moreover qualitative behaviour of fluid phase and dust phase temperature/velocity are similar.

Revisiting Gill's Circulation. Dynamic Response to Diabatic Heating of Different Horizontal Extents

NASA Astrophysics Data System (ADS)

Reboredo, B.; Bellon, G.

2017-12-01

The horizontal extent of diabatic heating associated with the MJO is thought to be crucial to its development, and the inability of GCMs to simulate the spatial, horizontal organization of clouds is considered a leading hypothesis to explain their limited capacity to simulate MJO events. This prevents the MJO large-circulation response from developing and feeding back on the development of clouds. We apply mid-tropospheric heating of different size in simple linear and non-linear models of the tropical atmosphere following Gill's seminal work on heat-induced tropical circulations. Results show that there is a scale for which the characteristic circulation {Γ c} for the vertical advection of moisture to produce the latent heat mean {Q} gives a rough estimate of the real world MJO scale. Overturning circulation flow rates above {Γ c} account for a circulation that transports more moisture than necessary to be maintained, and below {Γ c}, circulation would not transport enough moisture to maintain circulation. This dynamic scale might constrain the size of the spatially-organised convection necessary to the development of an MJO event. However, other effects are expected to modulate this scale, such as vertical advection of moisture anomalies, horizontal advection, evaporation, radiative heating, and sensible heat fluxes.

Single-bubble boiling under Earth's and low gravity

NASA Astrophysics Data System (ADS)

Khusid, Boris; Elele, Ezinwa; Lei, Qian; Tang, John; Shen, Yueyang

2017-11-01

Miniaturization of electronic systems in terrestrial and space applications is challenged by a dramatic increase in the power dissipation per unit volume with the occurrence of localized hot spots where the heat flux is much higher than the average. Cooling by forced gas or liquid flow appears insufficient to remove high local heat fluxes. Boiling that involves evaporation of liquid in a hot spot and condensation of vapor in a cold region can remove a significantly larger amount of heat through the latent heat of vaporization than force-flow cooling can carry out. Traditional methods for enhancing boiling heat transfer in terrestrial and space applications focus on removal of bubbles from the heating surface. In contrast, we unexpectedly observed a new boiling regime of water under Earth's gravity and low gravity in which a bubble was pinned on a small heater up to 270°C and delivered a heat flux up to 1.2 MW/m2 that was as high as the critical heat flux in the classical boiling regime on Earth .Low gravity measurements conducted in parabolic flights in NASA Boeing 727. The heat flux in flight and Earth's experiments was found to rise linearly with increasing the heater temperature. We will discuss physical mechanisms underlying heat transfer in single-bubble boiling. The work supported by NASA Grants NNX12AM26G and NNX09AK06G.

Darcy-Forchheimer flow of Maxwell nanofluid flow with nonlinear thermal radiation and activation energy

NASA Astrophysics Data System (ADS)

Sajid, T.; Sagheer, M.; Hussain, S.; Bilal, M.

2018-03-01

The present article is about the study of Darcy-Forchheimer flow of Maxwell nanofluid over a linear stretching surface. Effects like variable thermal conductivity, activation energy, nonlinear thermal radiation is also incorporated for the analysis of heat and mass transfer. The governing nonlinear partial differential equations (PDEs) with convective boundary conditions are first converted into the nonlinear ordinary differential equations (ODEs) with the help of similarity transformation, and then the resulting nonlinear ODEs are solved with the help of shooting method and MATLAB built-in bvp4c solver. The impact of different physical parameters like Brownian motion, thermophoresis parameter, Reynolds number, magnetic parameter, nonlinear radiative heat flux, Prandtl number, Lewis number, reaction rate constant, activation energy and Biot number on Nusselt number, velocity, temperature and concentration profile has been discussed. It is viewed that both thermophoresis parameter and activation energy parameter has ascending effect on the concentration profile.

Model and Comparative Study for Flow of Viscoelastic Nanofluids with Cattaneo-Christov Double Diffusion

PubMed Central

Hayat, Tasawar; Aziz, Arsalan; Muhammad, Taseer; Alsaedi, Ahmed

2017-01-01

Here two classes of viscoelastic fluids have been analyzed in the presence of Cattaneo-Christov double diffusion expressions of heat and mass transfer. A linearly stretched sheet has been used to create the flow. Thermal and concentration diffusions are characterized firstly by introducing Cattaneo-Christov fluxes. Novel features regarding Brownian motion and thermophoresis are retained. The conversion of nonlinear partial differential system to nonlinear ordinary differential system has been taken into place by using suitable transformations. The resulting nonlinear systems have been solved via convergent approach. Graphs have been sketched in order to investigate how the velocity, temperature and concentration profiles are affected by distinct physical flow parameters. Numerical values of skin friction coefficient and heat and mass transfer rates at the wall are also computed and discussed. Our observations demonstrate that the temperature and concentration fields are decreasing functions of thermal and concentration relaxation parameters. PMID:28046011

Thermally induced rarefied gas flow in a three-dimensional enclosure with square cross-section

NASA Astrophysics Data System (ADS)

Zhu, Lianhua; Yang, Xiaofan; Guo, Zhaoli

2017-12-01

Rarefied gas flow in a three-dimensional enclosure induced by nonuniform temperature distribution is numerically investigated. The enclosure has a square channel-like geometry with alternatively heated closed ends and lateral walls with a linear temperature distribution. A recently proposed implicit discrete velocity method with a memory reduction technique is used to numerically simulate the problem based on the nonlinear Shakhov kinetic equation. The Knudsen number dependencies of the vortices pattern, slip velocity at the planar walls and edges, and heat transfer are investigated. The influences of the temperature ratio imposed at the ends of the enclosure and the geometric aspect ratio are also evaluated. The overall flow pattern shows similarities with those observed in two-dimensional configurations in literature. However, features due to the three-dimensionality are observed with vortices that are not identified in previous studies on similar two-dimensional enclosures at high Knudsen and small aspect ratios.

Numerical Study of Buoyancy and Different Diffusion Effects on the Structure and Dynamics of Triple Flames

NASA Technical Reports Server (NTRS)

Chen, Jyh-Yuan; Echekki, Tarek

2001-01-01

Numerical simulations of 2-D triple flames under gravity force have been implemented to identify the effects of gravity on triple flame structure and propagation properties and to understand the mechanisms of instabilities resulting from both heat release and buoyancy effects. A wide range of gravity conditions, heat release, and mixing widths for a scalar mixing layer are computed for downward-propagating (in the same direction with the gravity vector) and upward-propagating (in the opposite direction of the gravity vector) triple flames. Results of numerical simulations show that gravity strongly affects the triple flame speed through its contribution to the overall flow field. A simple analytical model for the triple flame speed, which accounts for both buoyancy and heat release, is developed. Comparisons of the proposed model with the numerical results for a wide range of gravity, heat release and mixing width conditions, yield very good agreement. The analysis shows that under neutral diffusion, downward propagation reduces the triple flame speed, while upward propagation enhances it. For the former condition, a critical Froude number may be evaluated, which corresponds to a vanishing triple flame speed. Downward-propagating triple flames at relatively strong gravity effects have exhibited instabilities. These instabilities are generated without any artificial forcing of the flow. Instead disturbances are initiated by minute round-off errors in the numerical simulations, and subsequently amplified by instabilities. A linear stability analysis on mean profiles of stable triple flame configurations have been performed to identify the most amplified frequency in spatially developed flows. The eigenfunction equations obtained from the linearized disturbance equations are solved using the shooting method. The linear stability analysis yields reasonably good agreements with the observed frequencies of the unstable triple flames. The frequencies and amplitudes of disturbances increase with the magnitude of the gravity vector. Moreover, disturbances appear to be most amplified just downstream of the premixed branches. The effects of mixing width and differential diffusion are investigated and their roles on the flame stability are studied.

On radiative heat transfer in stagnation point flow of MHD Carreau fluid over a stretched surface

NASA Astrophysics Data System (ADS)

Khan, Masood; Sardar, Humara; Mudassar Gulzar, M.

2018-03-01

This paper investigates the behavior of MHD stagnation point flow of Carreau fluid in the presence of infinite shear rate viscosity. Additionally heat transfer analysis in the existence of non-linear radiation with convective boundary condition is performed. Moreover effects of Joule heating is observed and mathematical analysis is presented in the presence of viscous dissipation. The suitable transformations are employed to alter the leading partial differential equations to a set of ordinary differential equations. The subsequent non-straight common ordinary differential equations are solved numerically by an effective numerical approach specifically Runge-Kutta Fehlberg method alongside shooting technique. It is found that the higher values of Hartmann number (M) correspond to thickening of the thermal and thinning of momentum boundary layer thickness. The analysis further reveals that the fluid velocity is diminished by increasing the viscosity ratio parameter (β∗) and opposite trend is observed for temperature profile for both hydrodynamic and hydromagnetic flows. In addition the momentum boundary layer thickness is increased with velocity ratio parameter (α) and opposite is true for thermal boundary layer thickness.

Kelvin-Helmholtz instability for flow in porous media under the influence of oblique magnetic fields: A viscous potential flow analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moatimid, Galal M.; Obied Allah, M. H.; Hassan, Mohamed A.

2013-10-15

In this paper, the Kelvin-Helmholtz instability of viscous incompressible magnetic fluid fully saturated porous media is achieved through the viscous potential theory. The flow is considered to be through semi-permeable boundaries above and below the fluids through which the fluid may either be blown in or sucked out, in a direction normal to the main streaming direction of the fluid flow. An oblique magnetic field, mass, heat transfer, and surface tension are present across the interface. Through the linear stability analysis, a general dispersion relation is derived and the natural curves are plotted. Therefore, the linear stability condition is discussedmore » in some depth. In view of the multiple time scale technique, the Ginzburg–Landau equation, which describes the behavior of the system in the nonlinear approach, is obtained. The effects of the orientation of the magnetic fields on the stability configuration in linear, as well as nonlinear approaches, are discussed. It is found that the Darcy's coefficient for the porous layers plays a stabilizing role. The injection of the fluids at both boundaries has a stabilizing effect, in contrast with the suction at both boundaries.« less

Smart catheter flow sensor for real-time continuous regional cerebral blood flow monitoring

NASA Astrophysics Data System (ADS)

Li, Chunyan; Wu, Pei-Ming; Hartings, Jed A.; Wu, Zhizhen; Ahn, Chong H.; LeDoux, David; Shutter, Lori A.; Narayan, Raj K.

2011-12-01

We present a smart catheter flow sensor for real-time, continuous, and quantitative measurement of regional cerebral blood flow using in situ temperature and thermal conductivity compensation. The flow sensor operates in a constant-temperature mode and employs a periodic heating and cooling technique. This approach ensures zero drift and provides highly reliable data with microelectromechanical system-based thin film sensors. The developed flow sensor has a sensitivity of 0.973 mV/ml/100 g/min in the range from 0 to 160 ml/100 g/min with a linear correlation coefficient of R2 = 0.9953. It achieves a resolution of 0.25 ml/100 g/min and an accuracy better than 5 ml/100 g/min.

Combined Lorentz force and ultrasound Doppler velocimetry in a vertical convection liquid metal flow

NASA Astrophysics Data System (ADS)

Zürner, Till; Vogt, Tobias; Resagk, Christian; Eckert, Sven; Schumacher, Jörg

2017-11-01

We report experimental studies on turbulent vertical convection flow in the liquid metal alloy gallium-indium-tin. Flow measurements were conducted by a combined use of local Lorentz force velocimetry (LLFV) and ultrasound Doppler velocimetry (UDV). It is known that the forced convection flow in a duct generates a force on the LLFV magnet system, that grows proportional to the flow velocity. We show that for the slower flow of natural convection LLFV retains this linear dependence in the range of micronewtons. Furthermore experimental results on the scaling of heat and momentum transport with the thermal driving are presented. The results cover a range of Rayleigh numbers 3 ×105 < Ra < 3 ×107 at a Prandtl number Pr 0.032 . The Nusselt number Nu is found to scale as Nu Ra0.31 . A Reynolds number Rez based on the vertical velocities close the heated and cooled side walls scales with Rez Ra0.45 . Additionally a Reynolds number based on the horizontal flow component is scaling as Rex Ra0.67 . These results agree well with numerical simulations and theoretical predictions. This work is funded by the Deutsche Forschungsgemeinschaft under Grant No. GRK 1567.

Progress Toward Improving Jet Noise Predictions in Hot Jets

NASA Technical Reports Server (NTRS)

Khavaran, Abbas; Kenzakowski, Donald C.

2007-01-01

An acoustic analogy methodology for improving noise predictions in hot round jets is presented. Past approaches have often neglected the impact of temperature fluctuations on the predicted sound spectral density, which could be significant for heated jets, and this has yielded noticeable acoustic under-predictions in such cases. The governing acoustic equations adopted here are a set of linearized, inhomogeneous Euler equations. These equations are combined into a single third order linear wave operator when the base flow is considered as a locally parallel mean flow. The remaining second-order fluctuations are regarded as the equivalent sources of sound and are modeled. It is shown that the hot jet effect may be introduced primarily through a fluctuating velocity/enthalpy term. Modeling this additional source requires specialized inputs from a RANS-based flowfield simulation. The information is supplied using an extension to a baseline two equation turbulence model that predicts total enthalpy variance in addition to the standard parameters. Preliminary application of this model to a series of unheated and heated subsonic jets shows significant improvement in the acoustic predictions at the 90 degree observer angle.

Joule heating effects on electromagnetohydrodynamic flow through a peristaltically induced micro-channel with different zeta potential and wall slip

NASA Astrophysics Data System (ADS)

Ranjit, N. K.; Shit, G. C.

2017-09-01

This paper aims to develop a mathematical model for magnetohydrodynamic flow of biofluids through a hydrophobic micro-channel with periodically contracting and expanding walls under the influence of an axially applied electric field. The velocity slip effects have been taken into account at the channel walls by employing different slip lengths due to hydrophobic gating. Different temperature jump factors have also been used to investigate the thermomechanical interactions at the fluid-solid interface. The electromagnetohydrodynamic flow in a microchannel is simplified under the framework of Debye-Hückel linearization approximation. We have derived the closed-form solutions for the linearized dimensionless boundary value problem under the assumptions of long wave length and low Reynolds number. The axial velocity, temperature, pressure distribution, stream function, wall shear stress and the Nusselt number have been appraised for diverse values of the parameters approaching into the problem. Our main focus is to determine the effects of different zeta potential on the axial velocity and temperature distribution under electromagnetic environment. This study puts forward an important observation that the different zeta potential plays an important role in controlling fluid velocity. The study further reveals that the temperature increases significantly with the Joule heating parameter and the Brinkman number (arises due to the dissipation of energy).

Turbulent Friction in the Boundary Layer of a Flat Plate in a Two-Dimensional Compressible Flow at High Speeds

NASA Technical Reports Server (NTRS)

Frankl, F.; Voishel, V.

1943-01-01

In the present report an investigation is made on a flat plate in a two-dimensional compressible flow of the effect of compressibility and heating on the turbulent frictional drag coefficient in the boundary layer of an airfoil or wing radiator. The analysis is based on the Prandtl-Karman theory of the turbulent boundary later and the Stodola-Crocco, theorem on the linear relation between the total energy of the flow and its velocity. Formulas are obtained for the velocity distribution and the frictional drag law in a turbulent boundary later with the compressibility effect and heat transfer taken into account. It is found that with increase of compressibility and temperature at full retardation of the flow (the temperature when the velocity of the flow at a given point is reduced to zero in case of an adiabatic process in the gas) at a constant R (sub x), the frictional drag coefficient C (sub f) decreased, both of these factors acting in the same sense.

Heat current through an artificial Kondo impurity beyond linear response

NASA Astrophysics Data System (ADS)

Sierra, Miguel A.; Sánchez, David

2018-03-01

We investigate the heat current of a strongly interacting quantum dot in the presence of a voltage bias in the Kondo regime. Using the slave-boson mean-field theory, we discuss the behavior of the energy flow and the Joule heating. We find that both contributions to the heat current display interesting symmetry properties under reversal of the applied dc bias. We show that the symmetries arise from the behavior of the dot transmission function. Importantly, the transmission probability is a function of both energy and voltage. This allows us to analyze the heat current in the nonlinear regime of transport. We observe that nonlinearities appear already for voltages smaller than the Kondo temperature. Finally, we suggest to use the contact and electric symmetry coefficients as a way to measure pure energy currents.

Non-equilibrium thermodynamics, heat transport and thermal waves in laminar and turbulent superfluid helium

NASA Astrophysics Data System (ADS)

Mongiovì, Maria Stella; Jou, David; Sciacca, Michele

2018-01-01

This review paper puts together some results concerning non equilibrium thermodynamics and heat transport properties of superfluid He II. A one-fluid extended model of superfluid helium, which considers heat flux as an additional independent variable, is presented, its microscopic bases are analyzed, and compared with the well known two-fluid model. In laminar situations, the fundamental fields are density, velocity, absolute temperature, and heat flux. Such a theory is able to describe the thermomechanical phenomena, the propagation of two sounds in liquid helium, and of fourth sound in superleak. It also leads in a natural way to a two-fluid model on purely macroscopical grounds and allows a small amount of entropy associated with the superfluid component. Other important features of liquid He II arise in rotating situations and in superfluid turbulence, both characterized by the presence of quantized vortices (thin vortex lines whose circulation is restricted by a quantum condition). Such vortices have a deep influence on the transport properties of superfluid helium, as they increase very much its thermal resistance. Thus, heat flux influences the vortices which, in turn, modify the heat flux. The dynamics of vortex lines is the central topic in turbulent superfluid helium. The model is generalized to take into account the vortices in different cases of physical interest: rotating superfluids, counterflow superfluid turbulence, combined counterflow and rotation, and mass flow in addition to heat flow. To do this, the averaged vortex line density per unit volume L, is introduced and its dynamical equations are considered. Linear and non-linear evolution equations for L are written for homogeneous and inhomogeneous, isotropic and anisotropic situations. Several physical experiments are analyzed and the influence of vortices on the effective thermal conductivity of turbulent superfluid helium is found. Transitions from laminar to turbulent flows, from diffusive to ballistic regimes, from isotropic to anisotropic situations, are analyzed, thus providing a wide range of practical applications. Besides the steady-state effective thermal conductivity, the propagation of harmonic waves is also studied, motivated by the fact that vortex line density is experimentally detected via the attenuation of second sound and because it provides dynamical information on heat transport and thermal waves which complement the static information of the thermal conductivity.

Artificial neural network analysis based on genetic algorithm to predict the performance characteristics of a cross flow cooling tower

NASA Astrophysics Data System (ADS)

Wu, Jiasheng; Cao, Lin; Zhang, Guoqiang

2018-02-01

Cooling tower of air conditioning has been widely used as cooling equipment, and there will be broad application prospect if it can be reversibly used as heat source under heat pump heating operation condition. In view of the complex non-linear relationship of each parameter in the process of heat and mass transfer inside tower, In this paper, the BP neural network model based on genetic algorithm optimization (GABP neural network model) is established for the reverse use of cross flow cooling tower. The model adopts the structure of 6 inputs, 13 hidden nodes and 8 outputs. With this model, the outlet air dry bulb temperature, wet bulb temperature, water temperature, heat, sensible heat ratio and heat absorbing efficiency, Lewis number, a total of 8 the proportion of main performance parameters were predicted. Furthermore, the established network model is used to predict the water temperature and heat absorption of the tower at different inlet temperatures. The mean relative error MRE between BP predicted value and experimental value are 4.47%, 3.63%, 2.38%, 3.71%, 6.35%,3.14%, 13.95% and 6.80% respectively; the mean relative error MRE between GABP predicted value and experimental value are 2.66%, 3.04%, 2.27%, 3.02%, 6.89%, 3.17%, 11.50% and 6.57% respectively. The results show that the prediction results of GABP network model are better than that of BP network model; the simulation results are basically consistent with the actual situation. The GABP network model can well predict the heat and mass transfer performance of the cross flow cooling tower.

Two distinct groups within the Bacillus subtilis group display significantly different spore heat resistance properties.

PubMed

Berendsen, Erwin M; Zwietering, Marcel H; Kuipers, Oscar P; Wells-Bennik, Marjon H J

2015-02-01

The survival of bacterial spores after heat treatment and the subsequent germination and outgrowth in a food product can lead to spoilage of the food product and economical losses. Prediction of time-temperature conditions that lead to sufficient inactivation requires access to detailed spore thermal inactivation kinetics of relevant model strains. In this study, the thermal inactivation kinetics of spores of fourteen strains belonging to the Bacillus subtilis group were determined in detail, using both batch heating in capillary tubes and continuous flow heating in a micro heater. The inactivation data were fitted using a log linear model. Based on the spore heat resistance data, two distinct groups (p < 0.001) within the B. subtilis group could be identified. One group of strains had spores with an average D120 °C of 0.33 s, while the spores of the other group displayed significantly higher heat resistances, with an average D120 °C of 45.7 s. When comparing spore inactivation data obtained using batch- and continuous flow heating, the z-values were significantly different, hence extrapolation from one system to the other was not justified. This study clearly shows that heat resistances of spores from different strains in the B. subtilis group can vary greatly. Strains can be separated into two groups, to which different spore heat inactivation kinetics apply. Copyright © 2014 Elsevier Ltd. All rights reserved.

Investigating the use of a rational Runge Kutta method for transport modelling

NASA Astrophysics Data System (ADS)

Dougherty, David E.

An unconditionally stable explicit time integrator has recently been developed for parabolic systems of equations. This rational Runge Kutta (RRK) method, proposed by Wambecq 1 and Hairer 2, has been applied by Liu et al.3 to linear heat conduction problems in a time-partitioned solution context. An important practical question is whether the method has application for the solution of (nearly) hyperbolic equations as well. In this paper the RRK method is applied to a nonlinear heat conduction problem, the advection-diffusion equation, and the hyperbolic Buckley-Leverett problem. The method is, indeed, found to be unconditionally stable for the linear heat conduction problem and performs satisfactorily for the nonlinear heat flow case. A heuristic limitation on the utility of RRK for the advection-diffusion equation arises in the Courant number; for the second-order accurate one-step two-stage RRK method, a limiting Courant number of 2 applies. First order upwinding is not as effective when used with RRK as with Euler one-step methods. The method is found to perform poorly for the Buckley-Leverett problem.

Finite element computation of multi-physical micropolar transport phenomena from an inclined moving plate in porous media

NASA Astrophysics Data System (ADS)

Shamshuddin, MD.; Anwar Bég, O.; Sunder Ram, M.; Kadir, A.

2018-02-01

Non-Newtonian flows arise in numerous industrial transport processes including materials fabrication systems. Micropolar theory offers an excellent mechanism for exploring the fluid dynamics of new non-Newtonian materials which possess internal microstructure. Magnetic fields may also be used for controlling electrically-conducting polymeric flows. To explore numerical simulation of transport in rheological materials processing, in the current paper, a finite element computational solution is presented for magnetohydrodynamic, incompressible, dissipative, radiative and chemically-reacting micropolar fluid flow, heat and mass transfer adjacent to an inclined porous plate embedded in a saturated homogenous porous medium. Heat generation/absorption effects are included. Rosseland's diffusion approximation is used to describe the radiative heat flux in the energy equation. A Darcy model is employed to simulate drag effects in the porous medium. The governing transport equations are rendered into non-dimensional form under the assumption of low Reynolds number and also low magnetic Reynolds number. Using a Galerkin formulation with a weighted residual scheme, finite element solutions are presented to the boundary value problem. The influence of plate inclination, Eringen coupling number, radiation-conduction number, heat absorption/generation parameter, chemical reaction parameter, plate moving velocity parameter, magnetic parameter, thermal Grashof number, species (solutal) Grashof number, permeability parameter, Eckert number on linear velocity, micro-rotation, temperature and concentration profiles. Furthermore, the influence of selected thermo-physical parameters on friction factor, surface heat transfer and mass transfer rate is also tabulated. The finite element solutions are verified with solutions from several limiting cases in the literature. Interesting features in the flow are identified and interpreted.

A numerical solution for the diffusion equation in hydrogeologic systems

USGS Publications Warehouse

Ishii, A.L.; Healy, R.W.; Striegl, Robert G.

1989-01-01

The documentation of a computer code for the numerical solution of the linear diffusion equation in one or two dimensions in Cartesian or cylindrical coordinates is presented. Applications of the program include molecular diffusion, heat conduction, and fluid flow in confined systems. The flow media may be anisotropic and heterogeneous. The model is formulated by replacing the continuous linear diffusion equation by discrete finite-difference approximations at each node in a block-centered grid. The resulting matrix equation is solved by the method of preconditioned conjugate gradients. The conjugate gradient method does not require the estimation of iteration parameters and is guaranteed convergent in the absence of rounding error. The matrixes are preconditioned to decrease the steps to convergence. The model allows the specification of any number of boundary conditions for any number of stress periods, and the output of a summary table for selected nodes showing flux and the concentration of the flux quantity for each time step. The model is written in a modular format for ease of modification. The model was verified by comparison of numerical and analytical solutions for cases of molecular diffusion, two-dimensional heat transfer, and axisymmetric radial saturated fluid flow. Application of the model to a hypothetical two-dimensional field situation of gas diffusion in the unsaturated zone is demonstrated. The input and output files are included as a check on program installation. The definition of variables, input requirements, flow chart, and program listing are included in the attachments. (USGS)

Return current instability driven by a temperature gradient in ICF plasmas

DOE PAGES

Rozmus, W.; Brantov, A. V.; Sherlock, M.; ...

2017-10-12

Here, hot plasmas with strong temperature gradients in inertial confinement fusion (ICF) experiments are examined for ion acoustic instabilities produced by electron heat flow. The return current instability (RCI) due to a neutralizing current of cold electrons arising in response to a large electron heat flux has been considered. First, the linear threshold and growth rates are derived in the nonlocal regime of thermal transport. They are compared with the results of Vlasov-Fokker-Planck (VFP) simulations in one spatial dimension. Very good agreement has been found between kinetic VFP simulations and the linear theory of the RCI. A quasi-stationary state ofmore » ion acoustic turbulence produced by the RCI is achieved in the VFP simulations. Saturation of the RCI involves heating of ions in the tail of the ion distribution function and convection of the enhanced ion acoustic fluctuations from the unstable region of the plasma. Further evolution of the ion acoustic turbulence and its effects on absorption and transport are also discussed.« less

Analytical analysis of solar thermal collector with glass and Fresnel lens glazing

NASA Astrophysics Data System (ADS)

Zulkifle, Idris; Ruslan, Mohd Hafidz Hj; Othman, Mohd Yusof Hj; Ibarahim, Zahari

2018-04-01

Solar thermal collector is a system that converts solar radiation to heat. The heat will raise the temperature higher than the ambient temperature. Absorber and glazing are two important components in order to increase the temperature of the collector. The thermal absorber will release heat by convection and as radiation to the surrounding. These losses will be reduced by glazing. Other than that, glazing is beneficial for protecting the collector from dust and water. This study discusses about modelling of solar thermal collector effects of different mass flow rates with different glazing for V-groove flat plate solar collectors. The glazing used was the glass and linear Fresnel lens. Concentration ratio in this modelling was 1.3 for 0.1m solar collector thickness. Results show that solar collectors with linear Fresnel lens has the highest efficiency value of 71.18% compared to solar collectors with glass which has efficiency 54.10% with same operation conditions.

Return current instability driven by a temperature gradient in ICF plasmas

NASA Astrophysics Data System (ADS)

Rozmus, W.; Brantov, A. V.; Sherlock, M.; Bychenkov, V. Yu

2018-01-01

Hot plasmas with strong temperature gradients in inertial confinement fusion experiments are examined for ion acoustic instabilities produced by electron heat flow. The return current instability (RCI) due to a neutralizing current of cold electrons arising in response to a large electron heat flux has been considered. First, the linear threshold and growth rates are derived in the non-local regime of thermal transport. They are compared with the results of Vlasov-Fokker-Planck (VFP) simulations in one spatial dimension. Very good agreement has been found between kinetic VFP simulations and the linear theory of the RCI. A quasi-stationary state of ion acoustic turbulence (IAT) produced by the RCI is achieved in the VFP simulations. Saturation of the RCI involves heating of ions in the tail of the ion distribution function and convection of the enhanced ion acoustic fluctuations from the unstable region of the plasma. Further evolution of the IAT and its effects on absorption and transport are also discussed.

Unsteady MHD free convection flow of casson fluid over an inclined vertical plate embedded in a porous media

NASA Astrophysics Data System (ADS)

Manideep, P.; Raju, R. Srinivasa; Rao, T. Siva Nageswar; Reddy, G. Jithender

2018-05-01

This paper deals, an unsteady magnetohydrodynamic heat transfer natural convection flow of non-Newtonian Casson fluid over an inclined vertical plate embedded in a porous media with the presence of boundary conditions such as oscillating velocity, constant wall temperature. The governing dimensionless boundary layer partial differential equations are reduced to simultaneous algebraic linear equation for velocity, temperature of Casson fluid through finite element method. Those equations are solved by Thomas algorithm after imposing the boundary conditions through MATLAB for analyzing the behavior of Casson fluid velocity and temperature with various physical parameters. Also analyzed the local skin-friction and rate of heat transfer. Compared the present results with earlier reported studies, the results are comprehensively authenticated and robust FEM.

Oceanic lithosphere and asthenosphere - Thermal and mechanical structure

NASA Technical Reports Server (NTRS)

Schubert, G.; Yuen, D. A.; Froidevaux, C.

1976-01-01

A coupled thermomechanical subsolidus model of the oceanic lithosphere and asthenosphere is developed which includes vertical heat conduction, a temperature-dependent thermal conductivity, heat advection by a horizontal and vertical mass flow that depends on depth and age, contributions of viscous dissipation or shear heating, a linear or nonlinear deformation law relating shear stress and strain rate, as well as a temperature- and pressure-dependent viscosity. The model requires a constant horizontal velocity and temperature at the surface, but zero horizontal velocity and constant temperature at great depths. The depth- and age-dependent temperature, horizontal and vertical velocities, and viscosity structure of the lithosphere and asthenosphere are determined along with the age-dependent shear stress in those two zones. The ocean-floor topography, oceanic heat flow, and lithosphere thickness are deduced as functions of ocean-floor age; seismic velocity profiles which exhibit a marked low-velocity zone are constructed from the age-dependent geotherms and assumed values of the elastic parameters. It is found that simple boundary-layer cooling determines the thermal structure at young ages, while effects of viscous dissipation become more important at older ages.

Performance of Flow and Heat Transfer in a Hot-Dip Round Coreless Galvanizing Bath

NASA Astrophysics Data System (ADS)

Yue, Qiang; Zhang, Chengbo; Xu, Yong; Zhou, Li; Kong, Hui; Wang, Jia

2017-04-01

Flow field in a coreless hot-dip galvanizing pot was investigated through a water modeling experiment. The corresponding velocity vector was measured using an acoustic Doppler velocimeter. The flow field of molten zinc in the bath was also analyzed. Steel strip velocities from 1.7 to 2.7 m/s were adopted to determine the effect of steel strip velocity on the molten zinc flow in the bath. A large vortex filled the space at the right side of the sink roll, under linear speed from 1.0 to 2.7 m/s and width from 1.0 to 1.3 m of the steel strip, because of the effects of wall and shear stress. The results of the water modeling experiment were compared with those of numerical simulations. In the simulation, Maxwell equations were solved using finite element method to obtain magnetic flux density, electromagnetic force, and Joule heating. The Joule heating rate reached the maximum and minimum values near the side wall and at the core of the bath, respectively, because of the effect of skin and proximity. In an industrial-sized model, the molten zinc flow and temperature fields driven by electromagnetic force and Joule heating in the inductor of a coreless galvanizing bath were numerically simulated. The results indicated that the direction of electromagnetic force concentrated at the center of the galvanizing pot horizontal planes and exerted a pinch effect on molten zinc. Consequently, molten zinc in the pot was stirred by electromagnetic force. Under molten zinc flow and electromagnetic force stirring, the temperature of the molten zinc became homogeneous throughout the bath. This study provides a basis for optimizing electromagnetic fields in coreless induction pot and fine-tuning the design of steel strip parameters.

Numerical Study of Mixed Convective Peristaltic Flow through Vertical Tube with Heat Generation for Moderate Reynolds and Wave Numbers

NASA Astrophysics Data System (ADS)

Javed, Tariq; Ahmed, B.; Sajid, M.

2018-04-01

The current study focuses on the numerical investigation of the mixed convective peristaltic mechanism through a vertical tube for non-zero Reynolds and wave number. In the set of constitutional equations, energy equation contains the term representing heat generation parameter. The problem is formulated by dropping the assumption of lubrication theory that turns the model mathematically into a system of the nonlinear partial differential equations. The results of the long wavelength in a creeping flow are deduced from the present analysis. Thus, the current study explores the neglected features of peristaltic heat flow in the mixed convective model by considering moderate values of Reynolds and wave numbers. The finite element based on Galerkin’s weighted residual scheme is applied to solve the governing equations. The computed solution is presented in the form of contours of streamlines and isothermal lines, velocity and temperature profiles for variation of different involved parameters. The investigation shows that the strength of circulation for stream function increases by increasing the wave number and Reynolds number. Symmetric isotherms are reported for small values of time-mean flow. Linear behavior of pressure is noticed by vanishing inertial forces while the increase in pressure is observed by amplifying the Reynolds number.

Plasma flow measurements in the Prototype-Material Plasma Exposure eXperiment (Proto-MPEX) and comparison with B2.5-Eirene modeling

NASA Astrophysics Data System (ADS)

Kafle, N.; Owen, L. W.; Caneses, J. F.; Biewer, T. M.; Caughman, J. B. O.; Donovan, D. C.; Goulding, R. H.; Rapp, J.

2018-05-01

The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) at Oak Ridge National Laboratory is a linear plasma device that combines a helicon plasma source with additional microwave and radio frequency heating to deliver high plasma heat and particle fluxes to a target. Double Langmuir probes and Thomson scattering are being used to measure local electron temperature and density at various radial and axial locations. A recently constructed Mach-double probe provides the added capability of simultaneously measuring electron temperatures ( T e), electron densities ( n e), and Mach numbers (M). With this diagnostic, it is possible to infer the plasma flow, particle flux, and heat flux at different locations along the plasma column in Proto-MPEX. Preliminary results show Mach numbers of 0.5 (towards the dump plate) and 1.0 (towards the target plate) downstream from the helicon source, and a stagnation point (no flow) near the source for the case where the peak magnetic field was 1.3 T. Measurements of particle flow and ne and Te profiles are discussed. The extensive coverage provided by these diagnostics permits data-constrained B2.5-Eirene modeling of the entire plasma column, and comparison with results of modeling in the high-density helicon plasmas will be presented.

On the dynamical basis for the Asian summer monsoon rainfall-El Nino relationship

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nigam, S.

The dynamical basis for the Asian summer monsoon rainfall-El Nino linkage is explored through diagnostic calculations with a linear steady-state multilayer primitive equation model. The contrasting monsoon circulation during recent El Nino (1987) and La Nina (1988) years is first simulated using orography and the residually diagnosed heating (from the thermodynamic equation and the uninitialized, but mass-balanced, ECMWF analysis) as forcings, and then analyzed to provide insight into the importance of various regional forcings, such as the El Nino-related heating anomalies over the tropical Indian and Pacific Oceans. The striking simulation of the June-August (1987-1988) near-surface and upper-air tropical circulationmore » anomalies indicates that tropical anomaly dynamics during northern summer is essentially linear even at the 150-mb level. The vertical structure of the residually diagnosed heating anomaly that contributes to this striking simulation differs significantly from the specified canonical vertical structure (used in generating 3D heating from OLR/precipitation distributions) near the tropical tropopause. The dynamical diagnostic analysis of the anomalous circulation during 1987 and 1988 March-May and June-August periods shows the orographically forced circulation anomaly (due to changes in the zonally averaged basic-state flow) to be quite dominant in modulating the low-level moisture-flux convergence and hence monsoon rainfall over Indochina. The El Nino-related persistent (spring-to-summer) heating anomalies over the tropical Pacific and Indian Ocean basins, on the other hand, mostly regulate the low-level westerly monsoon flow intensity over equatorial Africa and the northern Indian Ocean and, thereby, the large-scale moisture flux into Sahel and Indochina. 38 refs., 12 figs.« less

The link between Tibetan Plateau monsoon and Indian summer precipitation: a linear diagnostic perspective

NASA Astrophysics Data System (ADS)

Ge, Fei; Sielmann, Frank; Zhu, Xiuhua; Fraedrich, Klaus; Zhi, Xiefei; Peng, Ting; Wang, Lei

2017-12-01

The thermal forcing of the Tibetan Plateau (TP) is analyzed to investigate the formation and variability of Tibetan Plateau Summer Monsoon (TPSM), which affects the climates of the surrounding regions, in particular the Indian summer monsoon precipitation. Dynamic composites and statistical analyses indicate that the Indian summer monsoon precipitation is less/greater than normal during the strong/weak TPSM. Strong (weak) TPSM is associated with an anomalous near surface cyclone (anticyclone) over the western part of the Tibetan Plateau, enhancing (reducing) the westerly flow along its southern flank, suppressing (favoring) the meridional flow of warm and moist air from the Indian ocean and thus cutting (providing) moisture supply for the northern part of India and its monsoonal rainfall. These results are complemented by a dynamic and thermodynamic analysis: (i) A linear thermal vorticity forcing primarily describes the influence of the asymmetric heating of TP generating an anomalous stationary wave flux. Composite analysis of anomalous stationary wave flux activity (after Plumb in J Atmos Sci 42:217-229, 1985) strongly indicate that non-orographic effects (diabatic heating and/or interaction with transient eddies) of the Tibetan Plateau contribute to the generation of an anomalous cyclone (anti-cyclone) over the western TP. (ii) Anomalous TPSM generation shows that strong TPSM years are related to the positive surface sensible heating anomalies over the eastern TP favoring the strong diabatic heating in summer. While negative TPSM years are associated with the atmospheric circulation anomalies during the preceding spring, enhancing northerly dry-cold air intrusions into TP, which may weaken the condensational heat release in the middle and upper troposphere, leading to a weaker than normal summer monsoon over the TP in summer.

Study of ion-gyroscale fluctuations in low-density L-mode plasmas heated by NBI on KSTAR

NASA Astrophysics Data System (ADS)

Lee, W.; Ko, S. H.; Leem, J.; Yun, G. S.; Park, H. K.; Wang, W. X.; Budny, R. V.; Kim, K. W.; Luhmann, N. C., Jr.; The KSTAR Team

2018-04-01

Broadband density fluctuations with peak frequency ranging from 150 to 400 kHz were measured using a multichannel microwave imaging reflectometer in core region of the low-density L-mode plasmas heated by neutral beam injection on KSTAR. These fluctuations have been studied by comparing the dominant mode scales estimated from the measurement with those predicted from linear gyrokinetic simulation. The measured poloidal wavenumbers are qualitatively comparable to those of the ‘fastest growing modes’ from simulations, whereas they are larger than those of the ‘transport-dominant modes’ by about a factor of three. The agreement on wavenumbers between the measurement and linear simulation (for the fastest growing modes) is probably due to sufficiently weak E × B flow shear compared to the maximum linear growth rate. Meanwhile, the transport-dominant modes seem to be related to the fluctuations in lower frequencies (˜80-150 kHz) observed in some of the measurement.

Multi-Focus Beamforming for Thermal Strain Imaging Using a Single Ultrasound Linear Array Transducer.

PubMed

Nguyen, Man M; Ding, Xuan; Leers, Steven A; Kim, Kang

2017-06-01

Ultrasound-induced thermal strain imaging (TSI) has been used successfully to identify lipid- and water-based tissues in atherosclerotic plaques in some research settings. However, TSI faces several challenges to be realized in clinics. These challenges include motion artifacts and displacement tracking accuracy, as well as limited heating capability, which contributes to low thermal strain signal-to-noise ratio, and a limited field of view. Our goal was to address the challenge in heating tissue in TSI. Current TSI systems use separate heating and imaging transducers, which require physical alignment of the heating and imaging beams and result in a bulky setup that limits in vivo operation. We evaluated a new design for heating beams that can be implemented on a linear array imaging transducer and can provide improved heating area and efficiency as compared with previous implementations. The heating beams designed were implemented with a clinical linear array imaging transducer connected to a research ultrasound platform. In vitro experiments using tissue-mimicking phantoms with no blood flow revealed that the new design resulted in an effective heating area of approximately 0.85 cm 2 and a 0.3°C temperature rise in 2 s of heating, which compared well with in silico finite-element simulations. With the new heating beams, TSI was found to be able to detect a lipid-mimicking rubber inclusion with a diameter of 1 cm from the water-based gelatin background, with a strain contrast of 2.3 (+0.14% strain in the rubber inclusion and -0.06% strain in the gelatin background). Lastly, lipid-based tissue in a 1-cm-diameter human carotid endarterectomy (CEA) sample was identified in good agreement with histology. Copyright © 2017 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Acute cell death rate of vascular smooth muscle cells during or after short heating up to 20s ranging 50 to 60°C as a basic study of thermal angioplasty

NASA Astrophysics Data System (ADS)

Shinozuka, Machiko; Shimazaki, Natsumi; Ogawa, Emiyu; Machida, Naoki; Arai, Tsunenori

2014-02-01

We studied the relations between the time history of smooth muscle cells (SMCs) death rate and heating condition in vitro to clarify cell death mechanism in heating angioplasty, in particular under the condition in which intimal hyperplasia growth had been prevented in vivo swine experiment. A flow heating system on the microscope stage was used for the SMCs death rate measurement during or after the heating. The cells were loaded step-heating by heated flow using a heater equipped in a Photo-thermo dynamic balloon. The heating temperature was set to 37, 50-60°C. The SMCs death rate was calculated by a division of PI stained cell number by Hoechst33342 stained cell number. The SMCs death rate increased 5-10% linearly during 20 s with the heating. The SMCs death rate increased with duration up to 15 min after 5 s heating. Because fragmented nuclei were observed from approximately 5 min after the heating, we defined that acute necrosis and late necrosis were corresponded to within 5 min after the heating and over 5 min after the heating, respectively. This late necrosis is probably corresponding to apoptosis. The ratio of necrotic interaction divided the acute necrosis rate by the late necrosis was calculated based on this consideration as 1.3 under the particular condition in which intimal hyperplasia growth was prevented in vivo previous porcine experiment. We think that necrotic interaction rate is larger than expected rate to obtain intimal hyperplasia suppression.

Tunneling of heat: Beyond linear response regime

NASA Astrophysics Data System (ADS)

Walczak, Kamil; Saroka, David

2018-02-01

We examine nanoscale processes of heat (energy) transfer as carried by electrons tunneling via potential barriers and molecular interconnects between two heat reservoirs (thermal baths). For that purpose, we use Landauer-type formulas to calculate thermal conductance and quadratic correction to heat flux flowing via quantum systems. As an input, we implement analytical expressions for transmission functions related to simple potential barriers and atomic bridges. Our results are discussed with respect to energy of tunneling electrons, temperature, the presence of resonant states, and specific parameters characterizing potential barriers as well as heat carriers. The simplicity of semi-analytical models developed by us allows to fit experimental data and extract crucial information about the values of model parameters. Further investigations are expected for more realistic transmission functions, while time-dependent aspects of nanoscale heat transfer may be addressed by using the concept of wave packets scattered on potential barriers and point-like defects within regular (periodic) nanostructures.

Near-field three-terminal thermoelectric heat engine

NASA Astrophysics Data System (ADS)

Jiang, Jian-Hua; Imry, Yoseph

2018-03-01

We propose a near-field inelastic thermoelectric heat engine where quantum dots are used to effectively rectify the charge flow of photocarriers. The device converts near-field heat radiation into useful electrical power. Heat absorption and inelastic transport can be enhanced by introducing two continuous spectra separated by an energy gap. The thermoelectric transport properties of the heat engine are studied in the linear-response regime. Using a small band-gap semiconductor as the absorption material, we show that the device achieves very large thermopower and thermoelectric figure of merit, as well as considerable power factor. By analyzing thermal-photocarrier generation and conduction, we reveal that the Seebeck coefficient and the figure of merit have oscillatory dependence on the thickness of the vacuum gap. Meanwhile, the power factor, the charge, and thermal conductivity are significantly improved by near-field radiation. Conditions and guiding principles for powerful and efficient thermoelectric heat engines are discussed in details.

Flow field measurements for cylindrical configurations in a hypersonic wind tunnel: Windward and leeward flow fields

NASA Technical Reports Server (NTRS)

Bertin, J. J.; Lamb, J. P.; Center, K. R.; Graumann, B. W.

1971-01-01

Windward and leeward measurements were made for a variety of simulated infinite cylinders exposed to hypersonic streams over an angle of attack from 30 deg to 90 deg. For the range of conditions included in the study, the following conclusions are made: (1) Swept cylinder theory provides a reasonable correlation of the measured laminar heat transfer rates from the plane of symmetry. (2) The boundary layer transition criteria in the plane of symmetry are a function of the transverse curvature. (3) Relaminarization of the circumferential boundary layer for a right circular cylinder was observed at the highest Reynolds number tested. (4) The effect of leeside geometry on the average heat transfer rate can be correlated with a single geometric parameter which is dependent on the location of separation. (5) The relationship of leeward heating to angle of attack is virtually linear for each cross section. (6) No systematic effect of free stream Reynolds number was observed.

Heat and mass transfer rates during flow of dissociated hydrogen gas over graphite surface

NASA Technical Reports Server (NTRS)

Nema, V. K.; Sharma, O. P.

1986-01-01

To improve upon the performance of chemical rockets, the nuclear reactor has been applied to a rocket propulsion system using hydrogen gas as working fluid and a graphite-composite forming a part of the structure. Under the boundary layer approximation, theoretical predictions of skin friction coefficient, surface heat transfer rate and surface regression rate have been made for laminar/turbulent dissociated hydrogen gas flowing over a flat graphite surface. The external stream is assumed to be frozen. The analysis is restricted to Mach numbers low enough to deal with the situation of only surface-reaction between hydrogen and graphite. Empirical correlations of displacement thickness, local skin friction coefficient, local Nusselt number and local non-dimensional heat transfer rate have been obtained. The magnitude of the surface regression rate is found low enough to ensure the use of graphite as a linear or a component of the system over an extended period without loss of performance.

Thermal Marangoni convection in two-phase flow of dusty Casson fluid

NASA Astrophysics Data System (ADS)

Mahanthesh, B.; Gireesha, B. J.

2018-03-01

This paper deals with the thermal Marangoni convection effects in magneto-Casson liquid flow through suspension of dust particles. The transpiration cooling aspect is accounted. The surface tension is assumed to be fluctuating linearly with temperature. The fluid and dust particle's temperature of the interface is chosen as a quadratic function of interface arc length. The governing problem is modelled by conservation laws of mass, momentum and energy for fluid and dust particle phase. Stretching transformation technique is utilized to form ordinary differential equations from the partial differential equations. Later, the numerical solutions based on Runge-Kutta-Fehlberg method are established. The momentum and heat transport distributions are focused on the outcome of distinct governing parameters. The results of Nusselt number is also presented and discussed. It is established that the heat transfer rate is higher in the case of dusty non-Newtonian fluid than dusty Newtonian fluid. The rate of heat transfer can be enhanced by suspending dust particles in a base liquid.

Dissipative models of colliding stellar winds - I. Effects of thermal conduction in wide binary systems

NASA Astrophysics Data System (ADS)

Myasnikov, A. V.; Zhekov, S. A.

1998-11-01

The influence of electron thermal conduction on the 2D gas dynamics of colliding stellar winds is investigated. It is shown that, as a result of the non-linear dependence of the electron thermal flux on the temperature, the pre-heating zones (in which the hot gas in the interaction region heats the cool winds in front of the shocks) have finite sizes. The dependence of the problem of the structure of the flow in the interaction region on the dimensionless parameters is studied, and a simple expression is derived for the size of the pre-heating zones at the axis of symmetry. It is shown that small values of the thermal conductivity do not suppress the Kelvin-Helmholtz instability if the adiabatic flow is subject to it. Further studies, both numerical and analytical, in this direction will be of great interest. The influence of thermal conduction on the X-ray emission from the interaction region is also estimated.

Endwall Heat Transfer Measurements in a Transonic Turbine Cascade

NASA Technical Reports Server (NTRS)

Giel, P. W.; Thurman, D. R.; VanFossen, G. J.; Hippensteele, S. A.; Boyle, R. J.

1996-01-01

Turbine blade endwall heat transfer measurements are given for a range of Reynolds and Mach numbers. Data were obtained for Reynolds numbers based on inlet conditions of 0.5 and 1.0 x 106, for isentropic exit Mach numbers of 1.0 and 1.3, and for freestream turbulence intensities of 0.25% and 7.0%. Tests were conducted in a linear cascade at the NASA Lewis Transonic Turbine Blade Cascade Facility. The test article was a turbine rotor with 136' of turning and an axial chord of 12.7 cm. The large scale allowed for very detailed measurements of both flow field and surface phenomena. The intent of the work is to provide benchmark quality data for computational fluid dynamics (CFD) code and model verification. The flow field in the cascade is highly three-dimensional as a result of thick boundary layers at the test section inlet. Endwall heat transfer data were obtained using a steady-state liquid crystal technique.

Autothermal and partial oxidation reformer-based fuel processor, method for improving catalyst function in autothermal and partial oxidation reformer-based processors

DOEpatents

Ahmed, Shabbir; Papadias, Dionissios D.; Lee, Sheldon H. D.; Ahluwalia, Rajesh K.

2013-01-08

The invention provides a fuel processor comprising a linear flow structure having an upstream portion and a downstream portion; a first catalyst supported at the upstream portion; and a second catalyst supported at the downstream portion, wherein the first catalyst is in fluid communication with the second catalyst. Also provided is a method for reforming fuel, the method comprising contacting the fuel to an oxidation catalyst so as to partially oxidize the fuel and generate heat; warming incoming fuel with the heat while simultaneously warming a reforming catalyst with the heat; and reacting the partially oxidized fuel with steam using the reforming catalyst.

Unsteady convection in tin in a Bridgman configuration

NASA Technical Reports Server (NTRS)

Knuteson, David J.; Fripp, Archibald L.; Woodell, Glenn A.; Debnam, William J., Jr.; Narayanan, Ranga

1991-01-01

When a quiescent fluid is heated sufficiently from below, steady convection will begin. Further heating will cause oscillatory and then turbulent flow. Theoretical results predict that the frequency of oscillation will depend on the square root of the Rayleigh number in the fluid. In the current work, liquid tin was heated from below for three aspect ratios, h/R = 3.4, 5.3, and 7.0. The experimental results are curve-fit for the square-root relation and also for a linear relation. The fit of the expression is evaluated using a correlation coefficient. An estimate for the first critical Rayleigh number (onset of steady convection) is obtained for both expressions. These values are compared to previous experimental results.

A possible closure relation for heat transport in the solar wind

NASA Technical Reports Server (NTRS)

Feldman, W. C.; Asbridge, J. R.; Bame, S. J.; Gosling, J. T.; Lemons, D. S.

1979-01-01

The objective of the present paper is to search for an empirical closure relation for solar wind heat transport that applies to a microscopic scale. This task is approached by using the quasi-linear wave-particle formalism proposed by Perkins (1973) as a guide to derive an equation relating the relative drift speed between core-electron and proton populations to local bulk flow conditions. The resulting relationship, containing one free parameter, is found to provide a good characterization of Los Alamos Imp electron data measuring during the period from March 1971 through August 1974. An empirical closure relation is implied by this result because of the observed proportionality between heat flux and relative drift speed.

Is thermal dispersivity significant for the use of heat as a tracer?

NASA Astrophysics Data System (ADS)

Rau, G. C.; Andersen, M. S.; Acworth, I.

2011-12-01

Heat profiles are regularly used to estimate sediment thermal parameters and to quantify vertical water flow velocity in fully saturated porous media. However, it has been pointed out by several authors that there is disagreement regarding the use of thermal dispersivity in heat transport models [e.g. Anderson, 2005]. Some researchers argue that this term should be treated analogous to solute transport [e.g. de Marsily, 1986], whilst others state that because heat diffusion is much faster than solute diffusion the dispersivity term can be neglected [e.g. Ingebritsen and Sanford, 1998]. This issue has never been properly addressed experimentally for environmentally relevant conditions. In order to address this question a hydraulic laboratory experiment was designed to investigate heat transport for different steady-state uniform flow velocities in the Darcy range (between 0 and 100 m/d) through homogeneous sand. For each flow velocity a point heat source at the center of the tank was instantaneously activated, and the thermal response was measured at 27 different locations using high resolution temperature probes. For the same flow velocities, a solute slug was injected in the center of the tank and the solute slug breakthrough was measured using 3 fluid EC sensors at different distances downstream of the injection point. This enabled direct comparison of solute and heat transport under identical conditions. The recorded temperature time-series data were used to calculate the thermal properties of the sand for conduction only, and estimate water flow velocity and thermal dispersion. The recorded EC time-series data were used to independently estimate water flow velocity but also solute dispersivity. The analytical solution for the solute transport case [Hunt, 1978] was adapted for heat transport and extended to account for slightly non-ideal experiment conditions. Velocity results independently derived from solute and heat show a discrepancy of up to 20%. The reason for this is not clear. Furthermore, the results show that thermal dispersivity can best be approximated with a square dependency on flow velocity. This agrees with earlier experiments in ideal materials by Green et al. [1964] as well as theoretical derivations [Kaviany, 1995]. However, this is in contrast to the linear dispersion model which has been adapted from solute transport and is commonly used in groundwater studies. The experimental results can be visualized in a conceptual plot devised by Bear [1972] for solute dispersion data (Figure 1). From this it becomes clear that the heat and solute transport Peclet numbers differs by several orders of magnitude for the same flow velocity and material because diffusion of heat is much faster than solute diffusion. As a result, the same Darcy flow range covers a different Peclet number range in heat transport and solute transport. This explains the controversy in the hydrologic community regarding the use of thermal dispersivity in transport models. In summary, for this experiment thermal dispersivity can be neglected when thermal Pe < 0.5, but should be considered for Pe > 0.5 with a square dependency on velocity.

Entropy generation in a second grade magnetohydrodynamic nanofluid flow over a convectively heated stretching sheet with nonlinear thermal radiation and viscous dissipation

NASA Astrophysics Data System (ADS)

Sithole, Hloniphile; Mondal, Hiranmoy; Sibanda, Precious

2018-06-01

This study addresses entropy generation in magnetohydrodynamic flow of a second grade nanofluid over a convectively heated stretching sheet with nonlinear thermal radiation and viscous dissipation. The second grade fluid is assumed to be electrically conducting and is permeated by an applied non-uniform magnetic field. We further consider the impact on the fluid properties and the Nusselt number of homogeneous-heterogeneous reactions and a convective boundary condition. The mathematical equations are solved using the spectral local linearization method. Computations for skin-friction coefficient and local Nusselt number are carried out and displayed in a table. It is observed that the effects of the thermophoresis parameter is to increase the temperature distributions throughout the boundary layer. The entropy generation is enhanced by larger magnetic parameters and increasing Reynolds number. The aim of this manuscript is to pay more attention of entropy generation analysis with heat and fluid flow on second grade nanofluids to improve the system performance. Also the fluid velocity and temperature in the boundary layer region rise significantly for increasing the values of the second grade nanofluid parameter.

Numerical study of heat transfer and fluid flow for steady crystal growth in a vertical Bridgman device

NASA Astrophysics Data System (ADS)

Pohlman, Matthew Michael

The study of heat transfer and fluid flow in a vertical Bridgman device is motivated by current industrial difficulties in growing crystals with as few defects as possible. For example, Gallium Arsenide (GaAs) is of great interest to the semiconductor industry but remains an uneconomical alternative to silicon because of the manufacturing problems. This dissertation is a two dimensional study of the fluid in an idealized Bridgman device. The model nonlinear PDEs are discretized using second order finite differencing. Newton's method solves the resulting nonlinear discrete equations. The large sparse linear systems involving the Jacobian are solved iteratively using the Generalized Minimum Residual method (GMRES). By adapting fast direct solvers for elliptic equations with simple boundary conditions, a good preconditioner is developed which is essential for GMRES to converge quickly. Trends of the fluid flow and heat transfer for typical ranges of the physical parameters are determined. Also, the size of the terms in the mathematical model are found by numerical investigation, in order to find what terms are in balance as the physical parameters vary. The results suggest the plausibility of simpler asymptotic solutions.

Heat Transfer Measurements and Predictions on a Power Generation Gas Turbine Blade

NASA Technical Reports Server (NTRS)

Giel, Paul W.; Bunker, Ronald S.; VanFossen, G. James; Boyle, Robert J.

2000-01-01

Detailed heat transfer measurements and predictions are given for a power generation turbine rotor with 129 deg of nominal turning and an axial chord of 137 mm. Data were obtained for a set of four exit Reynolds numbers comprised of the design point of 628,000, -20%, +20%, and +40%. Three ideal exit pressure ratios were examined including the design point of 1.378, -10%, and +10%. Inlet incidence angles of 0 deg and +/-2 deg were also examined. Measurements were made in a linear cascade with highly three-dimensional blade passage flows that resulted from the high flow turning and thick inlet boundary layers. Inlet turbulence was generated with a blown square bar grid. The purpose of the work is the extension of three-dimensional predictive modeling capability for airfoil external heat transfer to engine specific conditions including blade shape, Reynolds numbers, and Mach numbers. Data were obtained by a steady-state technique using a thin-foil heater wrapped around a low thermal conductivity blade. Surface temperatures were measured using calibrated liquid crystals. The results show the effects of strong secondary vortical flows, laminar-to-turbulent transition, and also show good detail in the stagnation region.

An optimal analysis for Darcy-Forchheimer 3D flow of Carreau nanofluid with convectively heated surface

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Aziz, Arsalan; Muhammad, Taseer; Alsaedi, Ahmed

2018-06-01

Darcy-Forchheimer three dimensional flow of Carreau nanoliquid induced by a linearly stretchable surface with convective boundary condition has been analyzed. Buongiorno model has been employed to elaborate thermophoresis and Brownian diffusion effects. Zero nanoparticles mass flux and convective surface conditions are implemented at the boundary. The governing problems are nonlinear. Optimal homotopic procedure has been used to tackle the governing mathematical system. Graphical results clearly depict the outcome of temperature and concentration fields. Surface drag coefficients and local Nusselt number are also plotted and discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Isfahani, RN; Moghaddam, S

An experimental study on absorption characteristics of water vapor into a thin lithium bromide (LiBr) solution flow is presented. The LiBr solution flow is constrained between a superhydrophobic vapor permeable wall and a solid surface that removes the heat of absorption. As opposed to conventional falling film absorbers, in this configuration, the solution film thickness and velocity can be controlled independently to enhance the absorption rate. The effects of water vapor pressure, cooling surface temperature, solution film thickness, and solution flow velocity on the absorption rate are studied. An absorption rate of approximately 0.006 kg/m(2) s was measured at amore » LiBr solution channel thickness and flow velocity of 100 mu m and 5 mm/s, respectively. The absorption rate increased linearly with the water vapor driving potential at the test conditions of this study. It was demonstrated that decreasing the solution film thickness and increasing the solution velocity enhance the absorption rate. The high absorption rate and the inherently compact form of the proposed,absorber facilitate development of compact small-scale waste heat or solar-thermal driven cooling systems. Published by Elsevier Ltd.« less

Application of Multivariable Model Predictive Advanced Control for a 2×310T/H CFB Boiler Unit

NASA Astrophysics Data System (ADS)

Weijie, Zhao; Zongllao, Dai; Rong, Gou; Wengan, Gong

When a CFB boiler is in automatic control, there are strong interactions between various process variables and inverse response characteristics of bed temperature control target. Conventional Pill control strategy cannot deliver satisfactory control demand. Kalman wave filter technology is used to establish a non-linear combustion model, based on the CFB combustion characteristics of bed fuel inventory, heating values, bed lime inventory and consumption. CFB advanced combustion control utilizes multivariable model predictive control technology to optimize primary and secondary air flow, bed temperature, air flow, fuel flow and heat flux. In addition to providing advanced combustion control to 2×310t/h CFB+1×100MW extraction condensing turbine generator unit, the control also provides load allocation optimization and advanced control for main steam pressure, combustion and temperature. After the successful implementation, under 10% load change, main steam pressure varied less than ±0.07MPa, temperature less than ±1°C, bed temperature less than ±4°C, and air flow (O2) less than ±0.4%.

Generalized Fluid System Simulation Program (GFSSP) - Version 6

NASA Technical Reports Server (NTRS)

Majumdar, Alok; LeClair, Andre; Moore, Ric; Schallhorn, Paul

2015-01-01

The Generalized Fluid System Simulation Program (GFSSP) is a finite-volume based general-purpose computer program for analyzing steady state and time-dependent flow rates, pressures, temperatures, and concentrations in a complex flow network. The program is capable of modeling real fluids with phase changes, compressibility, mixture thermodynamics, conjugate heat transfer between solid and fluid, fluid transients, pumps, compressors, flow control valves and external body forces such as gravity and centrifugal. The thermo-fluid system to be analyzed is discretized into nodes, branches, and conductors. The scalar properties such as pressure, temperature, and concentrations are calculated at nodes. Mass flow rates and heat transfer rates are computed in branches and conductors. The graphical user interface allows users to build their models using the 'point, drag, and click' method; the users can also run their models and post-process the results in the same environment. The integrated fluid library supplies thermodynamic and thermo-physical properties of 36 fluids, and 24 different resistance/source options are provided for modeling momentum sources or sinks in the branches. Users can introduce new physics, non-linear and time-dependent boundary conditions through user-subroutine.

Nonlinear Upshift of Trapped Electron Mode Critical Density Gradient: Simulation and Experiment

NASA Astrophysics Data System (ADS)

Ernst, D. R.

2012-10-01

A new nonlinear critical density gradient for pure trapped electron mode (TEM) turbulence increases strongly with collisionality, saturating at several times the linear threshold. The nonlinear TEM threshold appears to limit the density gradient in new experiments subjecting Alcator C-Mod internal transport barriers to modulated radio-frequency heating. Gyrokinetic simulations show the nonlinear upshift of the TEM critical density gradient is associated with long-lived zonal flow dominated states [1]. This introduces a strong temperature dependence that allows external RF heating to control TEM turbulent transport. During pulsed on-axis heating of ITB discharges, core electron temperature modulations of 50% were produced. Bursts of line-integrated density fluctuations, observed on phase contrast imaging, closely follow modulations of core electron temperature inside the ITB foot. Multiple edge fluctuation measurements show the edge response to modulated heating is out of phase with the core response. A new limit cycle stability diagram shows the density gradient appears to be clamped during on-axis heating by the nonlinear TEM critical density gradient, rather than by the much lower linear threshold. Fluctuation wavelength spectra will be quantitatively compared with nonlinear TRINITY/GS2 gyrokinetic transport simulations, using an improved synthetic diagnostic. In related work, we are implementing the first gyrokinetic exact linearized Fokker Planck collision operator [2]. Initial results show short wavelength TEMs are fully stabilized by finite-gyroradius collisional effects for realistic collisionalities. The nonlinear TEM threshold and its collisionality dependence may impact predictions of density peaking based on quasilinear theory, which excludes zonal flows.[4pt] In collaboration with M. Churchill, A. Dominguez, C. L. Fiore, Y. Podpaly, M. L. Reinke, J. Rice, J. L. Terry, N. Tsujii, M. A. Barnes, I. Bespamyatnov, R. Granetz, M. Greenwald, A. Hubbard, J. W. Hughes, M. Landreman, B. Li, Y. Ma, P. Phillips, M. Porkolab, W. Rowan, S. Wolfe, and S. Wukitch.[4pt] [1] D. R. Ernst et al., Proc. 21st IAEA Fusion Energy Conference, Chengdu, China, paper IAEA-CN-149/TH/1-3 (2006). http://www-pub.iaea.org/MTCD/Meetings/FEC200/th1-3.pdf[0pt] [2] B. Li and D.R. Ernst, Phys. Rev. Lett. 106, 195002 (2011).

Effects of Tip Clearance and Casing Recess on Heat Transfer and Stage Efficiency in Axial Turbines

NASA Technical Reports Server (NTRS)

Ameri, A. A.; Steinthorsson, E.; Rigby, David L.

1998-01-01

Calculations were performed to assess the effect of the tip leakage flow on the rate of heat transfer to blade, blade tip and casing. The effect on exit angle and efficiency was also examined. Passage geometries with and without casing recess were considered. The geometry and the flow conditions of the GE-E 3 first stage turbine, which represents a modem gas turbine blade were used for the analysis. Clearance heights of 0%, 1%, 1.5% and 3% of the passage height were considered. For the two largest clearance heights considered, different recess depths were studied. There was an increase in the thermal load on all the heat transfer surfaces considered due to enlargement of the clearance gap. Introduction of recessed casing resulted in a drop in the rate of heat transfer on the pressure side but the picture on the suction side was found to be more complex for the smaller tip clearance height considered. For the larger tip clearance height the effect of casing recess was an orderly reduction in the suction side heat transfer as the casing recess height was increased. There was a marked reduction of heat load and peak values on the blade tip upon introduction of casing recess, however only a small reduction was observed on the casing itself. It was reconfirmed that there is a linear relationship between the efficiency and the tip gap height. It was also observed that the recess casing has a small effect on the efficiency but can have a moderating effect on the flow underturning at smaller tip clearances.

Effects of variable properties on MHD heat and mass transfer flow near a stagnation point towards a stretching sheet in a porous medium with thermal radiation

NASA Astrophysics Data System (ADS)

M. Salem, A.; Rania, Fathy

2012-05-01

The effect of variable viscosity and thermal conductivity on steady magnetohydrodynamic (MHD) heat and mass transfer flow of viscous and incompressible fluid near a stagnation point towards a permeable stretching sheet embedded in a porous medium are presented, taking into account thermal radiation and internal heat genberation/absorbtion. The stretching velocity and the ambient fluid velocity are assumed to vary linearly with the distance from the stagnation point. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing fundamental equations are first transformed into a system of ordinary differential equations using a scaling group of transformations and are solved numerically by using the fourth-order Rung—Kutta method with the shooting technique. A comparison with previously published work has been carried out and the results are found to be in good agreement. The results are analyzed for the effect of different physical parameters, such as the variable viscosity and thermal conductivity, the ratio of free stream velocity to stretching velocity, the magnetic field, the porosity, the radiation and suction/injection on the flow, and the heat and mass transfer characteristics. The results indicate that the inclusion of variable viscosity and thermal conductivity into the fluids of light and medium molecular weight is able to change the boundary-layer behavior for all values of the velocity ratio parameter λ except for λ = 1. In addition, the imposition of fluid suction increases both the rate of heat and mass transfer, whereas fluid injection shows the opposite effect.

A Si/Glass Bulk-Micromachined Cryogenic Heat Exchanger for High Heat Loads: Fabrication, Test, and Application Results.

PubMed

Zhu, Weibin; White, Michael J; Nellis, Gregory F; Klein, Sanford A; Gianchandani, Yogesh B

2010-02-01

This paper reports on a micromachined Si/glass stack recuperative heat exchanger with in situ temperature sensors. Numerous high-conductivity silicon plates with integrated platinum resistance temperature detectors (Pt RTDs) are stacked, alternating with low-conductivity Pyrex spacers. The device has a 1 x 1-cm(2) footprint and a length of up to 3.5 cm. It is intended for use in Joule-Thomson (J-T) coolers and can sustain pressure exceeding 1 MPa. Tests at cold-end inlet temperatures of 237 K-252 K show that the heat exchanger effectiveness is 0.9 with 0.039-g/s helium mass flow rate. The integrated Pt RTDs present a linear response of 0.26%-0.30%/K over an operational range of 205 K-296 K but remain usable at lower temperatures. In self-cooling tests with ethane as the working fluid, a J-T system with the heat exchanger drops 76.1 K below the inlet temperature, achieving 218.7 K for a pressure of 835.8 kPa. The system reaches 200 K in transient state; further cooling is limited by impurities that freeze within the flow stream. In J-T self-cooling tests with an external heat load, the system reaches 239 K while providing 1 W of cooling. In all cases, there is an additional parasitic heat load estimated at 300-500 mW.

Experimental results from plasma transport on Prototype-Material Plasma Exposure eXperiment and comparison with B2-Eirene modeling

NASA Astrophysics Data System (ADS)

Kafle, N.; Caneses, J. F.; Biewer, T. M.; Owen, L.; Showers, M.; Donovan, D.; Caughman, J. B.; Goulding, R. H.; Rapp, Juergen

2017-10-01

Proto-MPEX at ORNL is a linear plasma device that combines a helicon plasma source with additional microwave and RF heating to deliver high plasma heat and particle fluxes to a target. Double Langmuir probes and Thomson scattering are being used to measure local Te and ne at various radial and axial locations. A recently constructed Mach- double probe provides the added capability of simultaneously measuring Te, ne, and Mach number. With this diagnostic, it is possible to infer the plasma flow, particle flux, and convective heat flux at different locations along the plasma column in Proto-MPEX. Preliminary results show Mach numbers of 0.6 and 0.8 in either direction away from the helicon source, and no flow near the source for the case where the peak magnetic field was 1.0 T. In addition, the Thomson Scattering system has been upgraded to measure ne and Te profiles at two axial locations, upstream at the electron heating location and downstream close to the target. Measurements of particle flow and flux profiles, heat flux, and profiles of ne and Te will be discussed. The extensive coverage provided by these diagnostics permits data-constrained B2-Eirene modeling of the entire plasma column, and comparison with results of modeling of high density mode plasmas will be presented. Supported by the US. D.O.E. contract DE-AC05-00OR22725.

Seasonal thermal energy storage in aquifers: Mathematical modeling studies in 1979

NASA Technical Reports Server (NTRS)

Tsang, C. F.

1980-01-01

A numerical model of water and heat flow in geologic media was developed, verified, and tested. The hydraulic parameters (transmittivity and storativity) and the location of a linear hydrologic barrier were simulated and compared with results from field experiments involving two injection-storage-recovery cycles. For both cycles, the initial simulated and observed temperatures agree (55c).

Flow and Heat Transfer in Sisko Fluid with Convective Boundary Condition

PubMed Central

Malik, Rabia; Khan, Masood; Munir, Asif; Khan, Waqar Azeem

2014-01-01

In this article, we have studied the flow and heat transfer in Sisko fluid with convective boundary condition over a non-isothermal stretching sheet. The flow is influenced by non-linearly stretching sheet in the presence of a uniform transverse magnetic field. The partial differential equations governing the problem have been reduced by similarity transformations into the ordinary differential equations. The transformed coupled ordinary differential equations are then solved analytically by using the homotopy analysis method (HAM) and numerically by the shooting method. Effects of different parameters like power-law index , magnetic parameter , stretching parameter , generalized Prandtl number Pr and generalized Biot number are presented graphically. It is found that temperature profile increases with the increasing value of and whereas it decreases for . Numerical values of the skin-friction coefficient and local Nusselt number are tabulated at various physical situations. In addition, a comparison between the HAM and exact solutions is also made as a special case and excellent agreement between results enhance a confidence in the HAM results. PMID:25285822

Numerical solution of mixed convection flow of an MHD Jeffery fluid over an exponentially stretching sheet in the presence of thermal radiation and chemical reaction

NASA Astrophysics Data System (ADS)

Shateyi, Stanford; Marewo, Gerald T.

2018-05-01

We numerically investigate a mixed convection model for a magnetohydrodynamic (MHD) Jeffery fluid flowing over an exponentially stretching sheet. The influence of thermal radiation and chemical reaction is also considered in this study. The governing non-linear coupled partial differential equations are reduced to a set of coupled non-linear ordinary differential equations by using similarity functions. This new set of ordinary differential equations are solved numerically using the Spectral Quasi-Linearization Method. A parametric study of physical parameters involved in this study is carried out and displayed in tabular and graphical forms. It is observed that the velocity is enhanced with increasing values of the Deborah number, buoyancy and thermal radiation parameters. Furthermore, the temperature and species concentration are decreasing functions of the Deborah number. The skin friction coefficient increases with increasing values of the magnetic parameter and relaxation time. Heat and mass transfer rates increase with increasing values of the Deborah number and buoyancy parameters.

Probing heat transfer, fluid flow and microstructural evolution during fusion welding of alloys

NASA Astrophysics Data System (ADS)

Zhang, Wei

The composition, geometry, structure and properties of the welded joints are affected by the various physical processes that take place during fusion welding. Understanding these processes has been an important goal in the contemporary welding research to achieve structurally sound and reliable welds. In the present thesis research, several important physical processes including the heat transfer, fluid flow and microstructural evolution in fusion welding were modeled based on the fundamentals of transport phenomena and phase transformation theory. The heat transfer and fluid flow calculation is focused on the predictions of the liquid metal convection in the weld pool, the temperature distribution in the entire weldment, and the shape and size of the fusion zone (FZ) and heat affected zone (HAZ). The modeling of microstructural evolution is focused on the quantitative understanding of phase transformation kinetics during welding of several important alloys under both low and high heating and cooling conditions. Three numerical models were developed in the present thesis work: (1) a three-dimensional heat transfer and free surface flow model for the gas metal arc (GMA) fillet welding considering the complex weld joint geometry, (2) a phase transformation model based on the Johnson-Mehl-Avrami (JMA) theory, and (3) a one-dimensional numerical diffusion model considering multiple moving interfaces. To check the capabilities of the developed models, several cases were investigated, in which the predictions from the models were compared with the experimental results. The cases studied are the follows. For the modeling of heat transfer and fluid flow, the welding processes studied included gas tungsten arc (GTA) linear welding, GTA transient spot welding, and GMA fillet welding. The calculated weldment geometry and thermal cycles was validated against the experimental data under various welding conditions. For the modeling of microstructural evolution, the welded materials investigated included AISI 1005 low-carbon steel, 1045 medium-carbon steel, 2205 duplex stainless steel (DSS) and Ti-6Al-4V alloy. The calculated phase transformation kinetics were compared with the experimental results obtained using an x-ray diffraction technique by Dr. John W. Elmer of Lawrence Livermore National Laboratory. (Abstract shortened by UMI.)

Climate reconstruction from borehole temperatures influenced by groundwater flow

NASA Astrophysics Data System (ADS)

Kurylyk, B.; Irvine, D. J.; Tang, W.; Carey, S. K.; Ferguson, G. A. G.; Beltrami, H.; Bense, V.; McKenzie, J. M.; Taniguchi, M.

2017-12-01

Borehole climatology offers advantages over other climate reconstruction methods because further calibration steps are not required and heat is a ubiquitous subsurface property that can be measured from terrestrial boreholes. The basic theory underlying borehole climatology is that past surface air temperature signals are reflected in the ground surface temperature history and archived in subsurface temperature-depth profiles. High frequency surface temperature signals are attenuated in the shallow subsurface, whereas low frequency signals can be propagated to great depths. A limitation of analytical techniques to reconstruct climate signals from temperature profiles is that they generally require that heat flow be limited to conduction. Advection due to groundwater flow can thermally `contaminate' boreholes and result in temperature profiles being rejected for regional climate reconstructions. Although groundwater flow and climate change can result in contrasting or superimposed thermal disturbances, groundwater flow will not typically remove climate change signals in a subsurface thermal profile. Thus, climate reconstruction is still possible in the presence of groundwater flow if heat advection is accommodated in the conceptual and mathematical models. In this study, we derive a new analytical solution for reconstructing surface temperature history from borehole thermal profiles influenced by vertical groundwater flow. The boundary condition for the solution is composed of any number of sequential `ramps', i.e. periods with linear warming or cooling rates, during the instrumented and pre-observational periods. The boundary condition generation and analytical temperature modeling is conducted in a simple computer program. The method is applied to reconstruct climate in Winnipeg, Canada and Tokyo, Japan using temperature profiles recorded in hydrogeologically active environments. The results demonstrate that thermal disturbances due to groundwater flow and climate change must be considered in a holistic manner as opposed to isolating either perturbation as was done in prior analytical studies.

A Low-Power Thermal-Based Sensor System for Low Air Flow Detection

PubMed Central

Arifuzzman, AKM; Haider, Mohammad Rafiqul; Allison, David B.

2016-01-01

Being able to rapidly detect a low air flow rate with high accuracy is essential for various applications in the automotive and biomedical industries. We have developed a thermal-based low air flow sensor with a low-power sensor readout for biomedical applications. The thermal-based air flow sensor comprises a heater and three pairs of temperature sensors that sense temperature differences due to laminar air flow. The thermal-based flow sensor was designed and simulated by using laminar flow, heat transfer in solids and fluids physics in COMSOL MultiPhysics software. The proposed sensor can detect air flow as low as 0.0064 m/sec. The readout circuit is based on a current- controlled ring oscillator in which the output frequency of the ring oscillator is proportional to the temperature differences of the sensors. The entire readout circuit was designed and simulated by using a 130-nm standard CMOS process. The sensor circuit features a small area and low-power consumption of about 22.6 µW with an 800 mV power supply. In the simulation, the output frequency of the ring oscillator and the change in thermistor resistance showed a high linearity with an R2 value of 0.9987. The low-power dissipation, high linearity and small dimensions of the proposed flow sensor and circuit make the system highly suitable for biomedical applications. PMID:28435186

Numerical investigation of heat transfer in parallel channels with water at supercritical pressure.

PubMed

Shitsi, Edward; Kofi Debrah, Seth; Yao Agbodemegbe, Vincent; Ampomah-Amoako, Emmanuel

2017-11-01

Thermal phenomena such as heat transfer enhancement, heat transfer deterioration, and flow instability observed at supercritical pressures as a result of fluid property variations have the potential to affect the safety of design and operation of Supercritical Water-cooled Reactor SCWR, and also challenge the capabilities of both heat transfer correlations and Computational Fluid Dynamics CFD physical models. These phenomena observed at supercritical pressures need to be thoroughly investigated. An experimental study was carried out by Xi to investigate flow instability in parallel channels at supercritical pressures under different mass flow rates, pressures, and axial power shapes. Experimental data on flow instability at inlet of the heated channels were obtained but no heat transfer data along the axial length was obtained. This numerical study used 3D numerical tool STAR-CCM+ to investigate heat transfer at supercritical pressures along the axial lengths of the parallel channels with water ahead of experimental data. Homogeneous axial power shape HAPS was adopted and the heating powers adopted in this work were below the experimental threshold heating powers obtained for HAPS by Xi. The results show that the Fluid Centre-line Temperature FCLT increased linearly below and above the PCT region, but flattened at the PCT region for all the system parameters considered. The inlet temperature, heating power, pressure, gravity and mass flow rate have effects on WT (wall temperature) values in the NHT (normal heat transfer), EHT (enhanced heat transfer), DHT (deteriorated heat transfer) and recovery from DHT regions. While variation of all other system parameters in the EHT and PCT regions showed no significant difference in the WT and FCLT values respectively, the WT and FCLT values respectively increased with pressure in these regions. For most of the system parameters considered, the FCLT and WT values obtained in the two channels were nearly the same. The numerical study was not quantitatively compared with experimental data along the axial lengths of the parallel channels, but it was observed that the numerical tool STAR-CCM+ adopted was able to capture the trends for NHT, EHT, DHT and recovery from DHT regions. The heating powers used for the various simulations were below the experimentally observed threshold heating powers, but heat transfer deterioration HTD was observed, confirming the previous finding that HTD could occur before the occurrence of unstable behavior at supercritical pressures. For purposes of comparing the results of numerical simulations with experimental data, the heat transfer data on temperature oscillations obtained at the outlet of the heated channels and instability boundary results obtained at the inlet of the heated channels were compared. The numerical results obtained quite well agree with the experimental data. This work calls for provision of experimental data on heat transfer in parallel channels at supercritical pressures for validation of similar numerical studies.

Stability and sensitivity analysis of hypersonic flow past a blunt cone

NASA Astrophysics Data System (ADS)

Nichols, Joseph W.; Cook, David; Brock, Joseph M.; Candler, Graham V.

2017-11-01

We investigate the effects of nosetip bluntness and low-level distributed roughness on instabilities leading to transition on a 7 degree half-angle blunt cone at Mach 10. To study the sensitivity of boundary layer instabilities to bluntness and roughness, we numerically extract Jacobian matrices directly from the unstructured hypersonic flow solver US3D. These matrices govern the dynamics of small perturbations about otherwise laminar base flows. We consider the frequency response of the resulting linearized dynamical system between different input and output locations along the cone, including close to the nosetip. Using adjoints, our method faithfully captures effects of complex geometry such as strong curvature and roughness that lead to flow acceleration and localized heating in this region. These effects violate the assumption of a slowly-varying base flow that underpins traditional linear stability analyses. We compare our results, which do not rely upon this assumption, to experimental measurements of a Mach 10 blunt cone taken at the AEDC Hypervelocity Ballistic Range G facility. In particular, we assess whether effects of complex geometry can explain discrepancies previously noted between traditional stability analysis and observations. This work is supported by the Office of Naval Research through Grant Number N00014-17-1-2496.

3D CFD ELECTROCHEMICAL AND HEAT TRANSFER MODEL OF AN INTERNALLY MANIFOLDED SOLID OXIDE ELECTROLYSIS CELL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grant L. Hawkes; James E. O'Brien; Greg Tao

2011-11-01

A three-dimensional computational fluid dynamics (CFD) electrochemical model has been created to model high-temperature electrolysis cell performance and steam electrolysis in an internally manifolded planar solid oxide electrolysis cell (SOEC) stack. This design is being evaluated at the Idaho National Laboratory for hydrogen production from nuclear power and process heat. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT. A solid-oxide fuel cell (SOFC) model adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. The FLUENT SOFC user-defined subroutine was modified formore » this work to allow for operation in the SOEC mode. Model results provide detailed profiles of temperature, operating potential, steam-electrode gas composition, oxygen-electrode gas composition, current density and hydrogen production over a range of stack operating conditions. Single-cell and five-cell results will be presented. Flow distribution through both models is discussed. Flow enters from the bottom, distributes through the inlet plenum, flows across the cells, gathers in the outlet plenum and flows downward making an upside-down ''U'' shaped flow pattern. Flow and concentration variations exist downstream of the inlet holes. Predicted mean outlet hydrogen and steam concentrations vary linearly with current density, as expected. Effects of variations in operating temperature, gas flow rate, oxygen-electrode and steam-electrode current density, and contact resistance from the base case are presented. Contour plots of local electrolyte temperature, current density, and Nernst potential indicate the effects of heat transfer, reaction cooling/heating, and change in local gas composition. Results are discussed for using this design in the electrolysis mode. Discussion of thermal neutral voltage, enthalpy of reaction, hydrogen production, cell thermal efficiency, cell electrical efficiency, and Gibbs free energy are discussed and reported herein.« less

Linear temporal and spatio-temporal stability analysis of a binary liquid film flowing down an inclined uniformly heated plate

NASA Astrophysics Data System (ADS)

Hu, Jun; Hadid, Hamda Ben; Henry, Daniel; Mojtabi, Abdelkader

Temporal and spatio-temporal instabilities of binary liquid films flowing down an inclined uniformly heated plate with Soret effect are investigated by using the Chebyshev collocation method to solve the full system of linear stability equations. Seven dimensionless parameters, i.e. the Kapitza, Galileo, Prandtl, Lewis, Soret, Marangoni, and Biot numbers (Ka, G, Pr, L, ) are used to control the flow system. In the case of pure spanwise perturbations, thermocapillary S- and P-modes are obtained. It is found that the most dangerous modes are stationary for positive Soret numbers (0), and oscillatory for =0 remains so for >0 and even merges with the long-wave S-mode. In the case of streamwise perturbations, a long-wave surface mode (H-mode) is also obtained. From the neutral curves, it is found that larger Soret numbers make the film flow more unstable as do larger Marangoni numbers. The increase of these parameters leads to the merging of the long-wave H- and S-modes, making the situation long-wave unstable for any Galileo number. It also strongly influences the short-wave P-mode which becomes the most critical for large enough Galileo numbers. Furthermore, from the boundary curves between absolute and convective instabilities (AI/CI) calculated for both the long-wave instability (S- and H-modes) and the short-wave instability (P-mode), it is shown that for small Galileo numbers the AI/CI boundary curves are determined by the long-wave instability, while for large Galileo numbers they are determined by the short-wave instability.

A hierarchy for modeling high speed propulsion systems

NASA Technical Reports Server (NTRS)

Hartley, Tom T.; Deabreu, Alex

1991-01-01

General research efforts on reduced order propulsion models for control systems design are overviewed. Methods for modeling high speed propulsion systems are discussed including internal flow propulsion systems that do not contain rotating machinery such as inlets, ramjets, and scramjets. The discussion is separated into four sections: (1) computational fluid dynamics model for the entire nonlinear system or high order nonlinear models; (2) high order linearized model derived from fundamental physics; (3) low order linear models obtained from other high order models; and (4) low order nonlinear models. Included are special considerations on any relevant control system designs. The methods discussed are for the quasi-one dimensional Euler equations of gasdynamic flow. The essential nonlinear features represented are large amplitude nonlinear waves, moving normal shocks, hammershocks, subsonic combustion via heat addition, temperature dependent gases, detonation, and thermal choking.

Numerical investigation of laminar forced convection in Newtonian and non-Newtonian flows in eccentric annuli

NASA Astrophysics Data System (ADS)

Fang, Pingping

1998-12-01

An extended numerical investigation of fully developed, forced convective laminar flows with heat transfer in eccentric annuli has been carried out. Both Newtonian and non-Newtonian (power-law or Ostwald-de Waele) fluids are studied, representing typical applications in petrochemical, bio-chemical, personal care products, polymer/plastic extrusion and food industries. For the heat transfer problem, with an insulated outer surface, two types of thermal boundary conditions have been considered: Constant wall temperature (T), and uniform axial heat flux with constant peripheral temperature (H1) on the inner surface of the annulus. The governing differential equations for momentum and energy conservation are solved by finite-difference methods. Velocity and temperature distributions in the flow cross section, the wall shear-stress distribution, and isothermal f Re, Nu i,T and Nu i,H1 values for different eccentric annuli (0/leɛ/*/le0.6,/ 0.2/le r/sp/*/le0.8) are presented. In Newtonian flows, the eccentricity is found to have a very strong influence on the flow and temperature fields. In an annulus with relatively large inner cylinder eccentricity, the flow tends to stagnate in the narrow section and has higher peak velocities in the wide section of the annulus. There is considerable flow maldistribution in the azimuthal direction, which in turn produces greater nonuniformity in the temperature field and a consequent degradation in the average heat transfer. Also, the H1 wall condition sustains higher heat transfer coefficients relative to the T boundary condition on the inner surface. For viscous, power-law type non-Newtonian flows, both shear thinning (n<1) and shear thickening (n>1) fluids are considered. Here, the non-linear shear behavior of the fluid is found to further aggravate the flow and temperature maldistribution, and once again the eccentricity is seen to exhibit a very strong influence on the friction and heat transfer behavior. Finally, the hydrodynamic characteristics of fully developed axial laminar flow of Newtonian fluids in eccentric annuli with a rotating inner cylinder are investigated. These are of significant importance to the design and operation of oil and gas drilling wells. Using finite-difference method to solve the governing flow equations in bipolar coordinates, computational results for a wide range of annulus geometry (0/le r/sp/*/le1,/ 0/le/varepsilon/sp/*/le0.8), and rotational Reynolds number (0/le Rer/le150) are presented, where the rotational speeds are restricted to the sub-critical Taylor number regime. The results delineate the effects of annuli r/sp/* and ɛsp/*, and inner cylinder rotation speed on the flow structure and frictional losses.

Thermal management optimization of an air-cooled Li-ion battery module using pin-fin heat sinks for hybrid electric vehicles

NASA Astrophysics Data System (ADS)

Mohammadian, Shahabeddin K.; Zhang, Yuwen

2015-01-01

Three dimensional transient thermal analysis of an air-cooled module that contains prismatic Li-ion cells next to a special kind of aluminum pin fin heat sink whose heights of pin fins increase linearly through the width of the channel in air flow direction was studied for thermal management of Lithium-ion battery pack. The effects of pin fins arrangements, discharge rates, inlet air flow velocities, and inlet air temperatures on the battery were investigated. The results showed that despite of heat sinks with uniform pin fin heights that increase the standard deviation of the temperature field, using this kind of pin fin heat sink compare to the heat sink without pin fins not only decreases the bulk temperature inside the battery, but also decreases the standard deviation of the temperature field inside the battery as well. Increasing the inlet air temperature leads to decreasing the standard deviation of the temperature field while increases the maximum temperature of the battery. Furthermore, increasing the inlet air velocity first increases the standard deviation of the temperature field till reaches to the maximum point, and after that decreases. Also, increasing the inlet air velocity leads to decrease in the maximum temperature of the battery.

Double Diffusive Convection in Materials Processing

NASA Technical Reports Server (NTRS)

Ramachandra, Narayanan; Leslie, Fred W.

1999-01-01

A great number of crystals grown in space are plagued by convective motions which contribute to structural flaws. The character of these instabilities is not well understood but is associated with density variations in the presence of residual gravity (g-jitter). As a specific example, past HgCdTe crystal growth space experiments by Lehoczky and co-workers indicate radial compositional asymmetry in the grown crystals. In the case of HgCdTe the rejected component into the melt upon solidification is HgTe which is denser than the melt. The space grown crystals indicate the presence of three dimensional flow with the heavier HgTe-rich material clearly aligned with the residual gravity (0.55-1.55 micro g) vector. This flow stems from double-diffusive convection, namely, thermal and solutal buoyancy driven flow in the melt. The study of double-diffusive convection is multi-faceted and rather vast. In our investigation, we seek to focus on one specific aspect of this discipline that is of direct relevance to materials processing especially crystal growth, namely, the side ways heating regime. This problem has been widely studied, both experimentally and numerically, in the context of solar ponds wherein the system is characterized by a linear salt (solutal) gradient with an imposed lateral temperature gradient. The induced flow instabilities arise from the wide disparity between the fluid thermal diffusivity and the solute diffusivity. The extension of the analysis to practical crystal growth applications has however not been rigorously made and understood. One subtle but important difference in crystal growth systems is the fact that die system solute gradient is non-linear (typically exponential). Besides, the crystal growth problem has the added complexities of solidification, both lateral and longitudinal thermal gradients and segregation phenomena in systems where binary and ternary compounds are being grown. This paper treats the side ways heating problem alone in a model fluid system. Results from detailed numerical calculations, mainly two dimensional are provided. The interactions between a non-linear solute gradient and an imposed transverse thermal gradient are investigated. The buoyancy effects are treated in the traditional Boussinesq approximation and also in a more complete density formulation to address recent concerns of the first approach especially in simulations of the system response in a reduced gravity environment. Detailed flow, temperature and solute field plots along with heat and mass transfer results are presented in the paper. Implications to practical crystal growth systems as discerned from the modeling results are also explored and reported.

Microgravity Flammability of PMMA Rods in Concurrent Flow

NASA Technical Reports Server (NTRS)

Olson, Sandra L.; Ferkul, Paul V.

2015-01-01

Microgravity experiments burning cast PMMA cylindrical rods in axial flow have been conducted aboard the International Space Station in the Microgravity Science Glovebox (MSG) facility using the Burning and Suppression of Solids (BASS) flow duct, as part of the BASS-II experiment. Twenty-four concurrent-flow tests were performed, focusing on finding flammability limits as a function of oxygen and flow speed. The oxygen was varied by using gaseous nitrogen to vitiate the working volume of the MSG. The speed of the flow parallel to the rod was varied using a fan at the entrance to the duct. Both blowoff and quenching limits were obtained at several oxygen concentrations. Each experiment ignited the rod at the initially hemispherical stagnation tip of the rod, and allowed the flame to develop and heat the rod at a sufficient flow to sustain burning. For blowoff limit tests, the astronaut quickly turned up the flow to obtain extinction. Complementary 5.18-second Zero Gravity Facility drop tests were conducted to compare blowoff limits in short and long duration microgravity. For quenching tests, the flow was incrementally turned down and the flame allowed to stabilize at the new flow condition for at least the solid-phase response time before changing it again. Quenching was observed when the flow became sufficiently weak that the flame could no longer provide adequate heat flux to compensate for the heat losses (conduction into the rod and radiation). A surface energy balance is presented that shows the surface radiative loss exceeds the conductive loss into the rod near the limit. The flammability boundary is shown to represent a critical Damkohler number, expressed in terms of the reaction rate divided by the stretch rate. For the blowoff branch, the boundary exhibits a linear dependence on oxygen concentration and stretch rate, indicating that the temperature at blowoff must be fairly constant. For the quenching branch, the dominance of the exponential nature of the Arrhenius kinetics reaction rate indicates that the temperature is critical.

Efficient simulation of press hardening process through integrated structural and CFD analyses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palaniswamy, Hariharasudhan; Mondalek, Pamela; Wronski, Maciek

Press hardened steel parts are being increasingly used in automotive structures for their higher strength to meet safety standards while reducing vehicle weight to improve fuel consumption. However, manufacturing of sheet metal parts by press hardening process to achieve desired properties is extremely challenging as it involves complex interaction of plastic deformation, metallurgical change, thermal distribution, and fluid flow. Numerical simulation is critical for successful design of the process and to understand the interaction among the numerous process parameters to control the press hardening process in order to consistently achieve desired part properties. Until now there has been no integratedmore » commercial software solution that can efficiently model the complete process from forming of the blank, heat transfer between the blank and tool, microstructure evolution in the blank, heat loss from tool to the fluid that flows through water channels in the tools. In this study, a numerical solution based on Altair HyperWorks® product suite involving RADIOSS®, a non-linear finite element based structural analysis solver and AcuSolve®, an incompressible fluid flow solver based on Galerkin Least Square Finite Element Method have been utilized to develop an efficient solution for complete press hardening process design and analysis. RADIOSS is used to handle the plastic deformation, heat transfer between the blank and tool, and microstructure evolution in the blank during cooling. While AcuSolve is used to efficiently model heat loss from tool to the fluid that flows through water channels in the tools. The approach is demonstrated through some case studies.« less

A kinetic study of solar wind electrons in the transition region from collision dominated to collisionless flow

NASA Technical Reports Server (NTRS)

Lie-Svendsen, O.; Leer, E.

1995-01-01

We have studied the evolution of the velocity distribution function of a test population of electrons in the solar corona and inner solar wind region, using a recently developed kinetic model. The model solves the time dependent, linear transport equation, with a Fokker-Planck collision operator to describe Coulomb collisions between the 'test population' and a thermal background of charged particles, using a finite differencing scheme. The model provides information on how non-Maxwellian features develop in the distribution function in the transition region from collision dominated to collisionless flow. By taking moments of the distribution the evolution of higher order moments, such as the heat flow, can be studied.

Thermocapillary effect on the dynamics of viscous beads on vertical fiber

NASA Astrophysics Data System (ADS)

Liu, Rong; Liu, Qiu Sheng

2014-09-01

The gravity-driven flow of a thin liquid film down a uniformly heated vertical fiber is considered. This is an unstable open flow that exhibits rich dynamics including the formation of droplets, or beads, driven by a Rayleigh-Plateau mechanism modified by the presence of gravity as well as the variation of surface tension induced by temperature disturbance at the interface. A linear stability analysis and a nonlinear simulation are performed to investigate the dynamic of axisymmetric disturbances. The results showed that the Marangoni instability and the Rayleigh-Plateau instability reinforce each other. With the increase of the thermocapillary effect, the fiber flow has a tendency to break up into smaller droplets.

Condensation heat transfer correlation for water-ethanol vapor mixture flowing through a plate heat exchanger

NASA Astrophysics Data System (ADS)

Zhou, Weiqing; Hu, Shenhua; Ma, Xiangrong; Zhou, Feng

2018-04-01

Condensation heat transfer coefficient (HTC) as a function of outlet vapor quality was investigated using water-ethanol vapor mixture of different ethanol vapor concentrations (0%, 1%, 2%, 5%, 10%, 20%) under three different system pressures (31 kPa, 47 kPa, 83 kPa). A heat transfer coefficient was developed by applying multiple linear regression method to experimental data, taking into account the dimensionless numbers which represents the Marangoni condensation effects, such as Re, Pr, Ja, Ma and Sh. The developed correlation can predict the condensation performance within a deviation range from -22% to 32%. Taking PHE's characteristic into consideration and bringing in Ma number and Sh number, a new correlation was developed, which showed a much more accurate prediction, within a deviation from -3.2% to 7.9%.

Validation of Supersonic Film Cooling Modeling for Liquid Rocket Engine Applications

NASA Technical Reports Server (NTRS)

Morris, Christopher I.; Ruf, Joseph H.

2010-01-01

Topics include: upper stage engine key requirements and design drivers; Calspan "stage 1" results, He slot injection into hypersonic flow (air); test articles for shock generator diagram, slot injector details, and instrumentation positions; test conditions; modeling approach; 2-d grid used for film cooling simulations of test article; heat flux profiles from 2-d flat plate simulations (run #4); heat flux profiles from 2-d backward facing step simulations (run #43); isometric sketch of single coolant nozzle, and x-z grid of half-nozzle domain; comparison of 2-d and 3-d simulations of coolant nozzles (run #45); flowfield properties along coolant nozzle centerline (run #45); comparison of 3-d CFD nozzle flow calculations with experimental data; nozzle exit plane reduced to linear profile for use in 2-d film-cooling simulations (run #45); synthetic Schlieren image of coolant injection region (run #45); axial velocity profiles from 2-d film-cooling simulation (run #45); coolant mass fraction profiles from 2-d film-cooling simulation (run #45); heat flux profiles from 2-d film cooling simulations (run #45); heat flux profiles from 2-d film cooling simulations (runs #47, #45, and #47); 3-d grid used for film cooling simulations of test article; heat flux contours from 3-d film-cooling simulation (run #45); and heat flux profiles from 3-d and 2-d film cooling simulations (runs #44, #46, and #47).

Analysis of key factors influencing the evaporation performances of an oriented linear cutting copper fiber sintered felt

NASA Astrophysics Data System (ADS)

Pan, Minqiang; Zhong, Yujian

2018-01-01

Porous structure can effectively enhance the heat transfer efficiency. A kind of micro vaporizer using the oriented linear cutting copper fiber sintered felt is proposed in this work. Multiple long cutting copper fibers are firstly fabricated with a multi-tooth tool and then sintered together in parallel to form uniform thickness metal fiber sintered felts that provided a characteristic of oriented microchannels. The temperature rise response and thermal conversion efficiency are experimentally investigated to evaluate the influences of porosity, surface structure, feed flow rate and input power on the evaporation characteristics. It is indicated that the temperature rise response of water is mainly affected by input power and feed flow rate. High input power and low feed flow rate present better temperature rise response of water. Porosity rather than surface structure plays an important role in the temperature rise response of water at a relatively high input power. The thermal conversion efficiency is dominated by the input power and surface structure. The oriented linear cutting copper fiber sintered felts for three kinds of porosities show better thermal conversion efficiency than that of the oriented linear copper wire sintered felt when the input power is less than 115 W. All the sintered felts have almost the same performance of thermal conversion at a high input power.

Linear models for sound from supersonic reacting mixing layers

NASA Astrophysics Data System (ADS)

Chary, P. Shivakanth; Samanta, Arnab

2016-12-01

We perform a linearized reduced-order modeling of the aeroacoustic sound sources in supersonic reacting mixing layers to explore their sensitivities to some of the flow parameters in radiating sound. Specifically, we investigate the role of outer modes as the effective flow compressibility is raised, when some of these are expected to dominate over the traditional Kelvin-Helmholtz (K-H) -type central mode. Although the outer modes are known to be of lesser importance in the near-field mixing, how these radiate to the far-field is uncertain, on which we focus. On keeping the flow compressibility fixed, the outer modes are realized via biasing the respective mean densities of the fast (oxidizer) or slow (fuel) side. Here the mean flows are laminar solutions of two-dimensional compressible boundary layers with an imposed composite (turbulent) spreading rate, which we show to significantly alter the growth of instability waves by saturating them earlier, similar to in nonlinear calculations, achieved here via solving the linear parabolized stability equations. As the flow parameters are varied, instability of the slow modes is shown to be more sensitive to heat release, potentially exceeding equivalent central modes, as these modes yield relatively compact sound sources with lesser spreading of the mixing layer, when compared to the corresponding fast modes. In contrast, the radiated sound seems to be relatively unaffected when the mixture equivalence ratio is varied, except for a lean mixture which is shown to yield a pronounced effect on the slow mode radiation by reducing its modal growth.

Optical analysis and thermal management of 2-cell strings linear concentrating photovoltaic system

NASA Astrophysics Data System (ADS)

Reddy, K. S.; Kamnapure, Nikhilesh R.

2015-09-01

This paper presents the optical and thermal analyses for a linear concentrating photovoltaic/thermal collector under different operating conditions. Linear concentrating photovoltaic system (CPV) consists of a highly reflective mirror, a receiver and semi-dual axis tracking mechanism. The CPV receiver embodies two strings of triple-junction cells (100 cells in each string) adhered to a mild steel circular tube mounted at the focal length of trough. This system provides 560 W of electricity and 1580 W of heat which needs to be dissipated by active cooling. The Al2O3/Water nanofluid is used as heat transfer fluid (HTF) flowing through circular receiver for CPV cells cooling. Optical analysis of linear CPV system with 3.35 m2 aperture and geometric concentration ratio (CR) of 35 is carried out using Advanced System Analysis Program (ASAP) an optical simulation tool. Non-uniform intensity distribution model of solar disk is used to model the sun in ASAP. The impact of random errors including slope error (σslope), tracking error (σtrack) and apparent change in sun's width (σsun) on optical performance of collector is shown. The result from the optical simulations shows the optical efficiency (ηo) of 88.32% for 2-cell string CPV concentrator. Thermal analysis of CPV receiver is carried out with conjugate heat transfer modeling in ANSYS FLUENT-14. Numerical simulations of Al2O3/Water nanofluid turbulent forced convection are performed for various parameters such as nanoparticle volume fraction (φ), Reynolds number (Re). The addition of the nanoparticle in water enhances the heat transfer in the ranges of 3.28% - 35.6% for φ = 1% - 6%. Numerical results are compared with literature data which shows the reasonable agreement.

Ion heating and flows in a high power helicon source

NASA Astrophysics Data System (ADS)

Thompson, Derek S.; Agnello, Riccardo; Furno, Ivo; Howling, Alan; Jacquier, Rémy; Plyushchev, Gennady; Scime, Earl E.

2017-06-01

We report experimental measurements of ion temperatures and flows in a high power, linear, magnetized, helicon plasma device, the Resonant Antenna Ion Device (RAID). Parallel and perpendicular ion temperatures on the order of 0.6 eV are observed for an rf power of 4 kW, suggesting that higher power helicon sources should attain ion temperatures in excess of 1 eV. The unique RAID antenna design produces broad, uniform plasma density and perpendicular ion temperature radial profiles. Measurements of the azimuthal flow indicate rigid body rotation of the plasma column of a few kHz. When configured with an expanding magnetic field, modest parallel ion flows are observed in the expansion region. The ion flows and temperatures are derived from laser induced fluorescence measurements of the Doppler resolved velocity distribution functions of argon ions.

Including geological information in the inverse problem of palaeothermal reconstruction

NASA Astrophysics Data System (ADS)

Trautner, S.; Nielsen, S. B.

2003-04-01

A reliable reconstruction of sediment thermal history is of central importance to the assessment of hydrocarbon potential and the understanding of basin evolution. However, only rarely do sedimentation history and borehole data in the form of present day temperatures and vitrinite reflectance constrain the past thermal evolution to a useful level of accuracy (Gallagher and Sambridge,1992; Nielsen,1998; Trautner and Nielsen,2003). This is reflected in the inverse solutions to the problem of determining heat flow history from borehole data: The recent heat flow is constrained by data while older values are governed by the chosen a prior heat flow. In this paper we reduce this problem by including geological information in the inverse problem. Through a careful analysis of geological and geophysical data the timing of the tectonic processes, which may influence heat flow, can be inferred. The heat flow history is then parameterised to allow for the temporal variations characteristic of the different tectonic events. The inversion scheme applies a Markov chain Monte Carlo (MCMC) approach (Nielsen and Gallagher, 1999; Ferrero and Gallagher,2002), which efficiently explores the model space and futhermore samples the posterior probability distribution of the model. The technique is demonstrated on wells in the northern North Sea with emphasis on the stretching event in Late Jurassic. The wells are characterised by maximum sediment temperature at the present day, which is the worst case for resolution of the past thermal history because vitrinite reflectance is determined mainly by the maximum temperature. Including geological information significantly improves the thermal resolution. Ferrero, C. and Gallagher,K.,2002. Stochastic thermal history modelling.1. Constraining heat flow histories and their uncertainty. Marine and Petroleum Geology, 19, 633-648. Gallagher,K. and Sambridge, M., 1992. The resolution of past heat flow in sedimentary basins from non-linear inversion of geochemical data: the smoothest model approach, with synthetic examples. Geophysical Journal International, 109, 78-95. Nielsen, S.B, 1998. Inversion and sensitivity analysis in basin modelling. Geoscience 98. Keele University, UK, Abstract Volume, 56. Nielsen, S.B. and Gallagher, K., 1999. Efficient sampling of 3-D basin modelling scenarios. Extended Abstracts Volume, 1999 AAPG International Conference &Exhibition, Birmingham, England, September 12-15, 1999, p. 369 - 372. Trautner S. and Nielsen, S.B., 2003. 2-D inverse thermal modelling in the Norwegian shelf using Fast Approximate Forward (FAF) solutions. In R. Marzi and Duppenbecker, S. (Ed.), Multi-Dimensional Basin Modeling, AAPG, in press.

Nonlinear stability of non-stationary cross-flow vortices in compressible boundary layers

NASA Technical Reports Server (NTRS)

Gajjar, J. S. B.

1995-01-01

The nonlinear evolution of long wavelength non-stationary cross-flow vortices in a compressible boundary layer is investigated and the work extends that of Gajjar (1994) to flows involving multiple critical layers. The basic flow profile considered in this paper is that appropriate for a fully three-dimensional boundary layer with O(1) Mach number and with wall heating or cooling. The governing equations for the evolution of the cross-flow vortex are obtained and some special cases are discussed. One special case includes linear theory where exact analytic expressions for the growth rate of the vortices are obtained. Another special case is a generalization of the Bassom & Gajjar (1988) results for neutral waves to compressible flows. The viscous correction to the growth rate is derived and it is shown how the unsteady nonlinear critical layer structure merges with that for a Haberman type of viscous critical layer.

A THEORETICAL TREATMENT OF THE STEADY-FLOW, LINEAR, CROSSED-FIELD, DIRECT- CURRENT PLASMA ACCELERATOR FOR INVISCID, ADIABATIC, ISOTHERMAL, CONSTANTAREA FLOW

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wood, G.P.; Carter, A.F.; Lintz, H.K.

1961-01-01

The theory is developed from the individual equations fo motion of the three componenets of the plasma. The effect of the ion cyclotron angle omega tau, which is the product of the ion cyclotron frequency and the ion mean free time between collisions with neutral particles and which is proportional to the axial component of the ion slip velocity, on both Joule heating rate and accelerator length is included in the results and is shown to be small only for values of about 10/sup -3/ radian or less. (auth)

Thermal and Mechanical Non-equilibrium Effects on Turbulent Flows Fundamental Studies of Energy Exchanges Through Direct Numerical Simulations and Experiments

DTIC Science & Technology

2013-10-21

AFOSR-2012-0001, 2012. Chu, B., and Kovásznay, L . S . G ., “Non-linear Interactions in a Viscous Heat-Conducting Compressible Gas,” Journal of Fluid...229-247. Kovásznay, L . S . G ., “Turbulence in Supersonic Flow,” Journal of the Aeronautical Sciences, Vol. 20, No. 10, 1953, pp. 657-674, 682. Larsson...Interactions,” Annual Review of Fluid Mechanics, Vol. 32, 2000, pp. 309-345. Barre, S ., Alem, D., and Bonnet, J. P ., “Experimental Study of a Normal Shock

A Theoretical Treatment of the Steady-Flow, Linear, Crossed-Field, Direct-Current Plasma Accelerator for Inviscid, Adiabatic, Isothermal, Constant-Area Flow

NASA Technical Reports Server (NTRS)

Wood, George P.; Carter, Arlen F.; Lintz, Hubert K.; Pennington, J. Byron

1961-01-01

The theory is developed from the individual equations of motion of the three components of the plasma. The effect of the ion cyclotron angle (omega tau), which is the product of the ion cyclotron frequency and the ion mean free time between collisions with neutral particles and which is proportional to the axial component of the ion slip velocity, on both Joule heating rate and accelerator length is included in the results and is shown to be small only for values of about 10(exp -3) radian or less.

MHD effects and heat transfer for the UCM fluid along with Joule heating and thermal radiation using Cattaneo-Christov heat flux model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shah, S., E-mail: sajidshah313@yahoo.com; Hussain, S.; Sagheer, M.

2016-08-15

Present study examines the numerical analysis of MHD flow of Maxwell fluid with thermal radiation and Joule heating by considering the recently developed Cattaneo-Christov heat flux model which explains the time relaxation characteristics for the heat flux. The objective is to analyze the governing parameters such as viscoelastic fluid parameter, Magnetic parameter, Eckert and Prandtl number’s impact on the velocity and temperature profiles through graphs and tables. Suitable similarity transformations have been used to reduce the formulated PDEs into a system of coupled non-linear ODEs. Shooting technique has been invoked for finding the numerical solutions of the dimensionless velocity andmore » temperature profiles. Additionally, the MATLAB built-in routine bvp4c has also been used to verify and strengthen the results obtained by shooting method. From some special cases of the present work, a comparison with the previously published results has been presented.« less

On the calculation of turbulent heat transport downstream from an abrupt pipe expansion

NASA Technical Reports Server (NTRS)

Chieng, C. C.; Launder, B. E.

1980-01-01

A numerical study is reported of flow and heat transfer in the separated flow region created by an abrupt pipe expansion. Computations employed an adaptation of the TEACH-2E computer program with the standard model of turbulence. Emphasis is given to the simulation, from both a physical and numerical viewpoint, of the region in the immediate vicinity of the wall where turbulent transport gives way to molecular conduction and diffusion. Wall resistance laws or wall functions used to bridge this near-wall region are based on the idea that, beyond the viscous sublayer, the turbulent length scale is universal, increasing linearly with distance from the wall. Predictions of expermental data for a diameter ratio of 0.54 show generally encouraging agreement with experiment. At a diameter of 0.43 different trends are discernible between measurement and calculation though this appears to be due to effects unconnected with the wall region studied.

Study of Periodical Flow Heat Transfer in an Internal Combustion Engine

NASA Astrophysics Data System (ADS)

Luo, Xi

In-cylinder heat transfer is one of the most critical physical behaviors which has a direct influence on engine out emission and thermal efficiency for IC engine. In-cylinder wall temperature has to be precisely controlled to achieve high efficiency and low emission. However, this cannot be done without knowing gas-to-wall heat flux. This study reports on the development of a technique suitable for engine in-cylinder surface temperature measurement, as the traditional method is "hard to reach." A laser induced phosphorescence technique was used to study in-cylinder wall temperature effects on engine out unburned hydrocarbons during the engine transitional period (warm up). A linear correlation was found between the cylinder wall surface temperature and the unburned hydrocarbons at mediate and high charge densities. At low charge density, no clear correlation was observed because of miss-fire events. A new auto background correction infrared (IR) diagnostic was developed to measure the instantaneous in-cylinder surface temperature at 0.1 CAD resolution. A numerical mechanism was designed to suppress relatively low-frequency background noise and provide an accurate in-cylinder surface temperature measurements with an error of less than 1.4% inside the IC engine. In addition, a proposed optical coating reduced time delay errors by 50% compared to more conventional thermocouple techniques. A new cycle-averaged Res number was developed for an IC engine to capture the characteristics of engine flow. Comparison and scaling between different engine flow parameters are available by matching the averaged Res number. From experimental results, the engine flow motion was classified as intermittently turbulent, and it is different from the original fully developed turbulent assumption, which has previously been used in almost all engine simulations. The intermittent turbulence could have a great impact on engine heat transfer because of the transitional turbulence effect. Engine 3D CFD model further proves the existence of transitional turbulence flow. A new multi zone heat transfer model is proposed for IC engines only. The model includes pressure work effects and improved heat transfer prediction compared to the standard Law of the wall model.

A Si/Glass Bulk-Micromachined Cryogenic Heat Exchanger for High Heat Loads: Fabrication, Test, and Application Results

PubMed Central

Zhu, Weibin; White, Michael J.; Nellis, Gregory F.; Klein, Sanford A.; Gianchandani, Yogesh B.

2010-01-01

This paper reports on a micromachined Si/glass stack recuperative heat exchanger with in situ temperature sensors. Numerous high-conductivity silicon plates with integrated platinum resistance temperature detectors (Pt RTDs) are stacked, alternating with low-conductivity Pyrex spacers. The device has a 1 × 1-cm2 footprint and a length of up to 3.5 cm. It is intended for use in Joule–Thomson (J–T) coolers and can sustain pressure exceeding 1 MPa. Tests at cold-end inlet temperatures of 237 K–252 K show that the heat exchanger effectiveness is 0.9 with 0.039-g/s helium mass flow rate. The integrated Pt RTDs present a linear response of 0.26%–0.30%/K over an operational range of 205 K–296 K but remain usable at lower temperatures. In self-cooling tests with ethane as the working fluid, a J–T system with the heat exchanger drops 76.1 K below the inlet temperature, achieving 218.7 K for a pressure of 835.8 kPa. The system reaches 200 K in transient state; further cooling is limited by impurities that freeze within the flow stream. In J–T self-cooling tests with an external heat load, the system reaches 239 K while providing 1 W of cooling. In all cases, there is an additional parasitic heat load estimated at 300–500 mW. PMID:20490284

Configurational Heat Capacity of Na- and Ca-bearing Aluminosilicate Melts

NASA Astrophysics Data System (ADS)

Webb, S. L.

2006-12-01

The Na2O-Al2O3-SiO2 and CaO-Al2O3-SiO2 systems are used as analogs for the more complex natural magmatic systems of the Earth in studies of the physical properties, structure and flow mechanisms of silicate melts. Although the description of flow in binary alkali-silicate melts is clear; that for multi-oxide compositions quickly becomes very complex. The addition of aluminium to melts creates the need for a charge-balancing cation for the tetrahedrally co-ordinated Al3+. With the presence of both mono- and di-valent ions there are questions about which atom is preferred as the charge balancer and which will create non-bridging oxygens. This study addresses the structure of peraluminous and peralkaline/metaluminous Na2O-CaO-Al2O3-SiO2 melts and the change in structure with composition via determination of their shear viscosity and heat capacity. Viscosity has been determined using the micropenetration technique and the heat capacity and configurational heat capacity have been determined by differential scanning calorimetry. While the viscosity of these melts indicates structural changes at the condition where there are no longer enough Na+ or Ca2+ to charge balance all of the Al3+ in tetrahedral co-ordination, it is the heat capacity data which provides more information about the energy required for flow to occur in the melts as the structure changes due to changing composition. The configurational heat capacity can be determined from the difference between the liquid (cpl) and the glass (cpg) heat capacity at the glass transition temperature. To a first approximation cpg can be calculated from a linear summation of the cps of the oxide components. Similarly, if there are no anomalous changes in melt structure upon heating through Tg, the cpl will be a linear sum of the contributions of the component oxides. Configurational entropy Sconf(Tg) has been calculated from the viscosity data using the Adam-Gibbs equation for viscosity as a function of configurational entropy and temperature. In addition to the change in structure implied from changes in the trends of the viscosity and heat capacity data when there are no longer enough charge balancers for all of the Al3+ in tetrahedral co-ordination, there also appears to be a change in structure at the composition where there are no longer enough Ca2+ in the melt that each Al3+ tetrahedron has its own charge balancer that is the composition at which pairs of Al3+ tetrahedra must share a Ca2+ as charge balancer.

Flow and heat transfer of nanofluid over a stretching sheet with non-linear velocity in the presence of thermal radiation and chemical reaction

NASA Astrophysics Data System (ADS)

Madaki, A. G.; Roslan, R.; Kandasamy, R.; Chowdhury, M. S. H.

2017-04-01

In this paper, the effects of Brownian motion, thermophoresis, chemical reaction, heat generation, magnetohydrodynamic and thermal radiation has been included in the model of nanofluid flow and heat transfer over a moving surface with variable thickness. The similarity transformation is used to transform the governing boundary layer equations into ordinary differential equations (ODE). Both optimal homotopy asymptotic method (OHAM) and Runge-Kutta fourth order method with shooting technique are employed to solve the resulting ODEs. For different values of the pertinent parameters on the velocity, temperature and concentration profiles have been studied and details are given in tables and graphs respectively. A comparison with the previous study is made, where an excellent agreement is achieved. The results demonstrate that the radiation parameter N increases, with the increase in both the temperature and the thermal boundary layer thickness respectively. While the nanoparticles concentration profiles increase with the influence of generative chemical reaction γ < 0, while it decreases with destructive chemical reaction γ > 0.

A New Similarity theory for Strongly Unstable Atmospheric Surface Layer

NASA Astrophysics Data System (ADS)

Ji, Yong; She, Zhen-Su

2017-11-01

We apply the structural ensemble dynamics (SED) theory to analyze mean velocity and streamwise turbulence intensity distribution in unstable atmospheric surface layer (ASL). The turbulent kinetic energy balance equation in ASL asserts that above a critical height zL, the buoyancy production cannot be neglected. The SED theory predicts that a stress length function displays a generalized scaling law from z to z 4 / 3. The zL derived from observational data show a two-regime form with Obukhov length L , including a linear dependence for moderate heat flux and a constant regime for large heat flux, extending the Monin-Obukhov similarity theory which is only valid for large | L | . This two-regime description is further extended to model turbulent intensity, with a new similarity coordinate Lz such that the observational data collapse for all L. Finally, we propose a phase diagram for characterizing different ASL flow regimes, and the corresponding flow structures are discussed. In summary, a new similarity theory for unstable atmosphere is constructed, and validated by observational data of the mean velocity and streamwise turbulence intensity distribution for all heat flux regimes.

Numerical study of laminar magneto-convection in a differentially heated square duct

NASA Astrophysics Data System (ADS)

Tassone, A.; Giannetti, F.; Caruso, G.

2017-01-01

Magnetohydrodynamic pressure drops are one of the main issues for liquid metal blanket in fusion reactors. Minimize the fluid velocity at few millimeters per second is one strategy that can be employed to address the problem. For such low velocities, buoyant forces can effectively contribute to drive the flow and therefore must be considered in the blanket design. In order to do so, a CFD code able to represent magneto-convective phenomena is required. This work aims to gauge the capability of ANSYS© CFX-15 to solve such cases. The laminar flow in a differentially heated duct was selected as validation benchmark. A horizontal and uniform magnetic field was imposed over a square duct with a linear and constant temperature gradient perpendicular to the field. The fully developed flow was analyzed for Gr = 105 and Hartmann number (M) ranging from 102 to 103. Both insulating and conducting duct walls were considered. Strong dampening of the flow in the center of the duct was observed, whereas high velocity jets appeared close to the walls parallel to the magnetic field. The numerical results were validated against theoretical and numerical results founding an excellent agreement.

Numerical study of steady dissipative mixed convection optically-thick micropolar flow with thermal radiation effects

NASA Astrophysics Data System (ADS)

Gupta, Diksha; Kumar, Lokendra; Bég, O. Anwar; Singh, Bani

2017-10-01

The objective of this paper is to study theoretically and numerically the effect of thermal radiation on mixed convection boundary layer flow of a dissipative micropolar non-Newtonian fluid from a continuously moving vertical porous sheet. The governing partial differential equations are transformed into a set of non-linear differential equations by using similarity transformations. These equations are solved iteratively with the Bellman-Kalaba quasi-linearization algorithm. This method converges quadratically and the solution is valid for a large range of parameters. The effects of transpiration (suction or injection) parameter, buoyancy parameter, radiation parameter and Eckert number on velocity, microrotation and temperature functions have been studied. Under a special case comparison of the present numerical results is made with the results available in the literature and an excellent agreement is found. Additionally skin friction and rate of heat transfer have also been computed. The study has applications in polymer processing.

Thermal Rayleigh-Marangoni convection in a three-layer liquid-metal-battery model.

PubMed

Köllner, Thomas; Boeck, Thomas; Schumacher, Jörg

2017-05-01

The combined effects of buoyancy-driven Rayleigh-Bénard convection (RC) and surface tension-driven Marangoni convection (MC) are studied in a triple-layer configuration which serves as a simplified model for a liquid metal battery (LMB). The three-layer model consists of a liquid metal alloy cathode, a molten salt separation layer, and a liquid metal anode at the top. Convection is triggered by the temperature gradient between the hot electrolyte and the colder electrodes, which is a consequence of the release of resistive heat during operation. We present a linear stability analysis of the state of pure thermal conduction in combination with three-dimensional direct numerical simulations of the nonlinear turbulent evolution on the basis of a pseudospectral method. Five different modes of convection are identified in the configuration, which are partly coupled to each other: RC in the upper electrode, RC with internal heating in the molten salt layer, and MC at both interfaces between molten salt and electrode as well as anticonvection in the middle layer and lower electrode. The linear stability analysis confirms that the additional Marangoni effect in the present setup increases the growth rates of the linearly unstable modes, i.e., Marangoni and Rayleigh-Bénard instability act together in the molten salt layer. The critical Grashof and Marangoni numbers decrease with increasing middle layer thickness. The calculated thresholds for the onset of convection are found for realistic current densities of laboratory-sized LMBs. The global turbulent heat transfer follows scaling predictions for internally heated RC. The global turbulent momentum transfer is comparable with turbulent convection in the classical Rayleigh-Bénard case. In summary, our studies show that incorporating Marangoni effects generates smaller flow structures, alters the velocity magnitudes, and enhances the turbulent heat transfer across the triple-layer configuration.

Thermal Rayleigh-Marangoni convection in a three-layer liquid-metal-battery model

NASA Astrophysics Data System (ADS)

Köllner, Thomas; Boeck, Thomas; Schumacher, Jörg

2017-05-01

The combined effects of buoyancy-driven Rayleigh-Bénard convection (RC) and surface tension-driven Marangoni convection (MC) are studied in a triple-layer configuration which serves as a simplified model for a liquid metal battery (LMB). The three-layer model consists of a liquid metal alloy cathode, a molten salt separation layer, and a liquid metal anode at the top. Convection is triggered by the temperature gradient between the hot electrolyte and the colder electrodes, which is a consequence of the release of resistive heat during operation. We present a linear stability analysis of the state of pure thermal conduction in combination with three-dimensional direct numerical simulations of the nonlinear turbulent evolution on the basis of a pseudospectral method. Five different modes of convection are identified in the configuration, which are partly coupled to each other: RC in the upper electrode, RC with internal heating in the molten salt layer, and MC at both interfaces between molten salt and electrode as well as anticonvection in the middle layer and lower electrode. The linear stability analysis confirms that the additional Marangoni effect in the present setup increases the growth rates of the linearly unstable modes, i.e., Marangoni and Rayleigh-Bénard instability act together in the molten salt layer. The critical Grashof and Marangoni numbers decrease with increasing middle layer thickness. The calculated thresholds for the onset of convection are found for realistic current densities of laboratory-sized LMBs. The global turbulent heat transfer follows scaling predictions for internally heated RC. The global turbulent momentum transfer is comparable with turbulent convection in the classical Rayleigh-Bénard case. In summary, our studies show that incorporating Marangoni effects generates smaller flow structures, alters the velocity magnitudes, and enhances the turbulent heat transfer across the triple-layer configuration.

Transition to turbulence and noise radiation in heated coaxial jet flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gloor, Michael, E-mail: gloor@ifd.mavt.ethz.ch; Bühler, Stefan; Kleiser, Leonhard

2016-04-15

Laminar-turbulent transition and noise radiation of a parametrized set of subsonic coaxial jet flows with a hot primary (core) stream are investigated numerically by Large-Eddy Simulation (LES) and direct noise computation. This study extends our previous research on local linear stability of heated coaxial jet flows by analyzing the nonlinear evolution of initially laminar flows disturbed by a superposition of small-amplitude unstable eigenmodes. First, a baseline configuration is studied to shed light on the flow dynamics of coaxial jet flows. Subsequently, LESs are performed for a range of Mach and Reynolds numbers to systematically analyze the influences of the temperaturemore » and the velocity ratios between the primary and the secondary (bypass) stream. The results provide a basis for a detailed analysis of fundamental flow-acoustic phenomena in the considered heated coaxial jet flows. Increasing the primary-jet temperature leads to an increase of fluctuation levels and to an amplification of far-field noise, especially at low frequencies. Strong mixing between the cold bypass stream and the hot primary stream as well as the intermittent character of the flow field at the end of the potential core lead to a pronounced noise radiation at an aft angle of approximately 35{sup ∘}. The velocity ratio strongly affects the shear-layer development and therefore also the noise generation mechanisms. Increasing the secondary-stream velocity amplifies the dominance of outer shear-layer perturbations while the disturbance growth rates in the inner shear layer decrease. Already for r{sub mic} > 40R{sub 1}, where r{sub mic} is the distance from the end of the potential core and R{sub 1} is the core-jet radius, a perfect 1/r{sub mic} decay of the sound pressure amplitudes is observed. The potential-core length increases for higher secondary-stream velocities which leads to a shift of the center of the dominant acoustic radiation in the downstream direction.« less

Triaxial thermopile array geo-heat-flow sensor

DOEpatents

Carrigan, C.R.; Hardee, H.C.; Reynolds, G.D.; Steinfort, T.D.

1990-01-01

A triaxial thermopile array geothermal heat flow sensor is designed to measure heat flow in three dimensions in a reconstituted or unperturbed subsurface regime. Heat flow can be measured in conductive or permeable convective media. The sensor may be encased in protective pvc tubing and includes a plurality of thermistors and an array of heat flow transducers produce voltage proportional to heat flux along the subsurface regime and permit direct measurement of heat flow in the subsurface regime. The presence of the thermistor array permits a comparison to be made between the heat flow estimates obtained from the transducers and heat flow calculated using temperature differences and Fourier's Law. The device is extremely sensitive with an accuracy of less than 0.1 Heat Flow Units (HFU) and may be used for long term readings. 6 figs.

Techniques in Linear and Nonlinear Partial Differential Equations

DTIC Science & Technology

1991-10-21

theory. J. Grotowski (a student) studied the heat flow approach to harmonic maps betv:een manifolds: between spheres. and from the ball B’ in R 3 into...T. Yau; S. Kichenessamy: F. H. Lin. L. Sadun: Wu. Sigue; Yi. Fang. Also these graduate students: Li, Cong Ming, received Ph.D. in 1989. J. Grotowski . received Ph.D. in 1990. I. Birindelli, working on Ph.D. thesis. 5

Linear Algebraic Modeling of Power Flow in the HMPT500-3 Transmission

DTIC Science & Technology

2012-08-01

BFV ) family and Multiple Launch Rocket System (MLRS). It is also proposed for use in the Paladin Integrated Management (PIM) self-propelled...howitzer and BFV derived Armored Multipurpose Vehicle (AMPV). Weight growth of these vehicles is exceeding the capacity of the current HMPT500-3...reduce the heat-rejection burden to the cooling system also makes efficiency improvements desirable. Automotive performance models of the BFV to

Linear Algebraic Modeling of Power Flow in the HMP500-3 Transmission

DTIC Science & Technology

2012-08-01

BFV ) family and Multiple Launch Rocket System (MLRS). It is also proposed for use in the Paladin Integrated Management (PIM) self-propelled...howitzer and BFV derived Armored Multipurpose Vehicle (AMPV). Weight growth of these vehicles is exceeding the capacity of the current HMPT500-3...reduce the heat-rejection burden to the cooling system also makes efficiency improvements desirable. Automotive performance models of the BFV to date

Annual Research Briefs - 2006

DTIC Science & Technology

2006-12-01

IACCARINO AND Q. WANG 3 Strain and stress analysis of uncertain engineering systems . D. GHOSH, C. FARHAT AND P. AVERY 17 Separated flow in a three...research in predictive science in complex systems , CTR has strived to maintain a critical mass in numerical analysis , computer science and physics based... analysis for a linear problem: heat conduction The design and analysis of complex engineering systems is challenging not only be- cause of the physical

Numerical simulation for flow and heat transfer to Carreau fluid with magnetic field effect: Dual nature study

NASA Astrophysics Data System (ADS)

Hashim; Khan, Masood; Alshomrani, Ali Saleh

2017-12-01

This article considers a realistic approach to examine the magnetohydrodynamics (MHD) flow of Carreau fluid induced by the shrinking sheet subject to the stagnation-point. This study also explores the impacts of non-linear thermal radiation on the heat transfer process. The governing equations of physical model are expressed as a system of partial differential equations and are transformed into non-linear ordinary differential equations by introducing local similarity variables. The economized equations of the problem are numerically integrated using the Runge-Kutta Fehlberg integration scheme. In this study, we explore the condition of existence, non-existence, uniqueness and dual nature for obtaining numerical solutions. It is found that the solutions may possess multiple natures, upper and lower branch, for a specific range of shrinking parameter. Results indicate that due to an increment in the magnetic parameter, range of shrinking parameter where a dual solution exists, increases. Further, strong magnetic field enhances the thickness of the momentum boundary layer in case of the second solution while for first solution it reduces. We further note that the fluid suction diminishes the fluid velocity and therefore the thickness of the hydrodynamic boundary layer decreases as well. A critical analysis with existing works is performed which shows that outcome are benchmarks with these works.

Numerical simulation for heat transfer performance in unsteady flow of Williamson fluid driven by a wedge-geometry

NASA Astrophysics Data System (ADS)

Hamid, Aamir; Hashim; Khan, Masood

2018-06-01

The main concern of this communication is to investigate the two-layer flow of a non-Newtonian rheological fluid past a wedge-shaped geometry. One remarkable aspect of this article is the mathematical formulation for two-dimensional flow of Williamson fluid by incorporating the effect of infinite shear rate viscosity. The impacts of heat transfer mechanism on time-dependent flow field are further studied. At first, we employ the suitable non-dimensional variables to transmute the time-dependent governing flow equations into a system of non-linear ordinary differential equations. The converted conservation equations are numerically integrated subject to physically suitable boundary conditions with the aid of Runge-Kutta Fehlberg integration procedure. The effects of involved pertinent parameters, such as, moving wedge parameter, wedge angle parameter, local Weissenberg number, unsteadiness parameter and Prandtl number on the non-dimensional velocity and temperature distributions have been evaluated. In addition, the numerical values of the local skin friction coefficient and the local Nusselt number are compared and presented through tables. The outcomes of this study indicate that the rate of heat transfer increases with the growth of both wedge angle parameter and unsteadiness parameter. Moreover, a substantial rise in the fluid velocity is observed with enhancement in the viscosity ratio parameter while an opposite trend is true for the non-dimensional temperature field. A comparison is presented between the current study and already published works and results found to be in outstanding agreement. Finally, the main findings of this article are highlighted in the last section.

Numerical study of transitional flow in fractures: the role of roughness on the road to turbulence

NASA Astrophysics Data System (ADS)

Linga, G.; Mathiesen, J.

2017-12-01

In aquifers and petroleum reservoirs, fractures are ubiquitous, and the majority of the fluid transport in such systems often occurs through fracture networks. Knowledge of the flow properties in the single fractures that together form the networks is hence necessary for safe operation downhole. Non-linear, high-velocity flow in such systems is of particular importance for geothermics, since turbulent mixing is known to increase heat conduction by several orders of magnitude. This is of importance both in terms of storing and recovering heat from aquifers. On the other hand, flow in rough fractures is interesting from a turbulence perspective. The onset of turbulence in pipes and channels is a phenomenon that historically has received broad attention since the early experiments by Reynolds, and only during the last decades, the phenomenon is beginning to be fully understood. However, in the presence of roughness, much less is known. In this work, we present comprehensive numerical simulations of flow in synthetic rough channels, representing single fracture joints. Using the finite element method, we solve the full-fledged, time-dependent Navier-Stokes equations for flow in the channels, from laminar flow, through transitional, to turbulent flow. We link the descriptions of microscopic to macroscopic properties, using geometric properties such as effective aperture, paying particular attention to the role of inertia and roughness for the transport properties of the channels. Finally, we discuss implications of our study for the transition to turbulence in the presence of roughness.

A heat receiver design for solar dynamic space power systems

NASA Technical Reports Server (NTRS)

Baker, Karl W.; Dustin, Miles O.; Crane, Roger

1990-01-01

An advanced heat pipe receiver designed for a solar dynamic space power system is described. The power system consists of a solar concentrator, solar heat receiver, Stirling heat engine, linear alternator and waste heat radiator. The solar concentrator focuses the sun's energy into a heat receiver. The engine and alternator convert a portion of this energy to electric power and the remaining heat is rejected by a waste heat radiator. Primary liquid metal heat pipes transport heat energy to the Stirling engine. Thermal energy storage allows this power system to operate during the shade portion of an orbit. Lithium fluoride/calcium fluoride eutectic is the thermal energy storage material. Thermal energy storage canisters are attached to the midsection of each heat pipe. The primary heat pipes pass through a secondary vapor cavity heat pipe near the engine and receiver interface. The secondary vapor cavity heat pipe serves three important functions. First, it smooths out hot spots in the solar cavity and provides even distribution of heat to the engine. Second, the event of a heat pipe failure, the secondary heat pipe cavity can efficiently transfer heat from other operating primary heat pipes to the engine heat exchanger of the defunct heat pipe. Third, the secondary heat pipe vapor cavity reduces temperature drops caused by heat flow into the engine. This unique design provides a high level of reliability and performance.

Measuring Joule heating and strain induced by electrical current with Moire interferometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen Bicheng; Basaran, Cemal

2011-04-01

This study proposes a new method to locate and measure the temperature of the hot spots caused by Joule Heating by measuring the free thermal expansion in-plane strain. It is demonstrated that the hotspot caused by the Joule heating in a thin metal film/plate structure can be measured by Phase shifting Moire interferometry with continuous wavelet transform (PSMI/CWT) at the microscopic scale. A demonstration on a copper film is conducted to verify the theory under different current densities. A correlation between the current density and strain in two orthogonal directions (one in the direction of the current flow) is proposed.more » The method can also be used for the measurement of the Joule heating in the microscopic solid structures in the electronic packaging devices. It is shown that a linear relationship exists between current density squared and normal strains.« less

Convective heat transfer in MHD slip flow over a stretching surface in the presence of carbon nanotubes

NASA Astrophysics Data System (ADS)

Ul Haq, Rizwan; Nadeem, Sohail; Khan, Z. H.; Noor, N. F. M.

2015-01-01

In the present study, thermal conductivity and viscosity of both single-wall and multiple-wall Carbon Nanotubes (CNT) within the base fluids (water, engine oil and ethylene glycol) of similar volume have been investigated when the fluid is flowing over a stretching surface. The magnetohydrodynamic (MHD) and viscous dissipation effects are also incorporated in the present phenomena. Experimental data consists of thermo-physical properties of each base fluid and CNT have been considered. The mathematical model has been constructed and by employing similarity transformation, system of partial differential equations is rehabilitated into the system of non-linear ordinary differential equations. The results of local skin friction and local Nusselt number are plotted for each base fluid by considering both Single Wall Carbon Nanotube (SWCNT) and Multiple-Wall Carbon Nanotubes (MWCNT). The behavior of fluid flow for water based-SWCNT and MWCNT are analyzed through streamlines. Concluding remarks have been developed on behalf of the whole analysis and it is found that engine oil-based CNT have higher skin friction and heat transfer rate as compared to water and ethylene glycol-based CNT.

The Coupling of Macrosegregation with Grain Nucleation, Growth and Motion in DC Cast Aluminum Alloy Ingots

NASA Astrophysics Data System (ADS)

Založnik, Miha; Kumar, Arvind; Combeau, Hervé; Bedel, Marie; Jarry, Philippe; Waz, Emmanuel

The phenomena responsible for the formation of macrosegregations, and grain structures during solidification are closely intertwined. We present a model study of the formation of macrosegregation and grain structure in an industrial sized (350 mm thick) direct chill (DC) cast aluminum alloy slab. The modeling of these phenomena in DC casting is a challenging problem mainly due to the size of the products, the variety of the phenomena to be accounted for, and the non-linearities involved. We used a volume-averaged multiscale model that describes nucleation on grain refiner particles and grain growth, coupled with macroscopic transport: fluid flow driven by natural convection and shrinkage, transport of free-floating globular equiaxed grains, heat transfer, and solute transport. We analyze the heat and mass transfer in the slurry moving-grain zone that is a result of the coupling of the fluid flow and of the grain nucleation, growth and motion. We discuss the impact of the flow structure in the slurry zone and of the grain packing fraction on the macrosegregation.

Wind-US Code Physical Modeling Improvements to Complement Hypersonic Testing and Evaluation

NASA Technical Reports Server (NTRS)

Georgiadis, Nicholas J.; Yoder, Dennis A.; Towne, Charles S.; Engblom, William A.; Bhagwandin, Vishal A.; Power, Greg D.; Lankford, Dennis W.; Nelson, Christopher C.

2009-01-01

This report gives an overview of physical modeling enhancements to the Wind-US flow solver which were made to improve the capabilities for simulation of hypersonic flows and the reliability of computations to complement hypersonic testing. The improvements include advanced turbulence models, a bypass transition model, a conjugate (or closely coupled to vehicle structure) conduction-convection heat transfer capability, and an upgraded high-speed combustion solver. A Mach 5 shock-wave boundary layer interaction problem is used to investigate the benefits of k- s and k-w based explicit algebraic stress turbulence models relative to linear two-equation models. The bypass transition model is validated using data from experiments for incompressible boundary layers and a Mach 7.9 cone flow. The conjugate heat transfer method is validated for a test case involving reacting H2-O2 rocket exhaust over cooled calorimeter panels. A dual-mode scramjet configuration is investigated using both a simplified 1-step kinetics mechanism and an 8-step mechanism. Additionally, variations in the turbulent Prandtl and Schmidt numbers are considered for this scramjet configuration.

Effects of Variable Thermal Conductivity and Non-linear Thermal Radiation Past an Eyring Powell Nanofluid Flow with Chemical Reaction

NASA Astrophysics Data System (ADS)

Ramzan, M.; Bilal, M.; Kanwal, Shamsa; Chung, Jae Dong

2017-06-01

Present analysis discusses the boundary layer flow of Eyring Powell nanofluid past a constantly moving surface under the influence of nonlinear thermal radiation. Heat and mass transfer mechanisms are examined under the physically suitable convective boundary condition. Effects of variable thermal conductivity and chemical reaction are also considered. Series solutions of all involved distributions using Homotopy Analysis method (HAM) are obtained. Impacts of dominating embedded flow parameters are discussed through graphical illustrations. It is observed that thermal radiation parameter shows increasing tendency in relation to temperature profile. However, chemical reaction parameter exhibits decreasing behavior versus concentration distribution. Supported by the World Class 300 Project (No. S2367878) of the SMBA (Korea)

Overview of the GRC Stirling Convertor System Dynamic Model

NASA Technical Reports Server (NTRS)

Lewandowski, Edward J.; Regan, Timothy F.

2004-01-01

A Stirling Convertor System Dynamic Model has been developed at the Glenn Research Center for controls, dynamics, and systems development of free-piston convertor power systems. It models the Stirling cycle thermodynamics, heat flow, gas, mechanical, and mounting dynamics, the linear alternator, and the controller. The model's scope extends from the thermal energy input to thermal, mechanical dynamics, and electrical energy out, allowing one to study complex system interactions among subsystems. The model is a non-linear time-domain model containing sub-cycle dynamics, allowing it to simulate transient and dynamic phenomena that other models cannot. The model details and capability are discussed.

Triaxial thermopile array geo-heat-flow sensor

DOEpatents

Carrigan, Charles R.; Hardee, Harry C.; Reynolds, Gerald D.; Steinfort, Terry D.

1992-01-01

A triaxial thermopile array geothermal heat flow sensor is designed to measure heat flow in three dimensions in a reconstituted or unperturbed subsurface regime. Heat flow can be measured in conductive or permeable convective media. The sensor may be encased in protective pvc tubing and includes a plurality of thermistors and an array of heat flow transducers arranged in a vertical string. The transducers produce voltage proportional to heat flux along the subsurface regime and permit direct measurement of heat flow in the subsurface regime. The presence of the thermistor array permits a comparison to be made between the heat flow estimates obtained from the transducers and heat flow calculated using temperature differences and Fourier's Law. The device is extremely sensitive with an accuracy of less than 0.1 Heat Flow Units (HFU) and may be used for long term readings.

Modeling highly transient flow, mass, and heat transport in the Chattahoochee River near Atlanta, Georgia

USGS Publications Warehouse

Jobson, Harvey E.; Keefer, Thomas N.

1979-01-01

A coupled flow-temperature model has been developed and verified for a 27.9-km reach of the Chattahoochee River between Buford Dam and Norcross, Ga. Flow in this reach of the Chattahoochee is continuous but highly regulated by Buford Dam, a flood-control and hydroelectric facility located near Buford, Ga. Calibration and verification utilized two sets of data collected under highly unsteady discharge conditions. Existing solution techniques, with certain minor improvements, were applied to verify the existing technology of flow and transport modeling. A linear, implicit finite-difference flow model was coupled with implicit, finite-difference transport and temperature models. Both the conservative and nonconservative forms of the transport equation were solved, and the difference in the predicted concentrations of dye were found to be insignificant. The temperature model, therefore, was based on the simpler nonconservative form of the transport equation. (Woodard-USGS)

Numerical simulation of aerothermal loads in hypersonic engine inlets due to shock impingement

NASA Technical Reports Server (NTRS)

Ramakrishnan, R.

1992-01-01

The effect of shock impingement on an axial corner simulating the inlet of a hypersonic vehicle engine is modeled using a finite-difference procedure. A three-dimensional dynamic grid adaptation procedure is utilized to move the grids to regions with strong flow gradients. The adaptation procedure uses a grid relocation stencil that is valid at both the interior and boundary points of the finite-difference grid. A linear combination of spatial derivatives of specific flow variables, calculated with finite-element interpolation functions, are used as adaptation measures. This computational procedure is used to study laminar and turbulent Mach 6 flows in the axial corner. The description of flow physics and qualitative measures of heat transfer distributions on cowl and strut surfaces obtained from the analysis are compared with experimental observations. Conclusions are drawn regarding the capability of the numerical scheme for enhanced modeling of high-speed compressible flows.

Magnetic Heat Pump Containing Flow Diverters

NASA Technical Reports Server (NTRS)

Howard, Frank S.

1995-01-01

Proposed magnetic heat pump contains flow diverters for suppression of undesired flows. If left unchecked, undesired flows mix substantial amounts of partially heated and partially cooled portions of working fluid, effectively causing leakage of heat from heated side to cooled side. By reducing leakage of heat, flow diverters increase energy efficiency of magnetic heat pump, potentially offering efficiency greater than compressor-driven refrigerator.

MHD Forced Convective Laminar Boundary Layer Flow from a Convectively Heated Moving Vertical Plate with Radiation and Transpiration Effect

PubMed Central

Uddin, Md. Jashim; Khan, Waqar A.; Ismail, A. I. Md.

2013-01-01

A two-dimensional steady forced convective flow of a Newtonian fluid past a convectively heated permeable vertically moving plate in the presence of a variable magnetic field and radiation effect has been investigated numerically. The plate moves either in assisting or opposing direction to the free stream. The plate and free stream velocities are considered to be proportional to whilst the magnetic field and mass transfer velocity are taken to be proportional to where is the distance along the plate from the leading edge of the plate. Instead of using existing similarity transformations, we use a linear group of transformations to transform the governing equations into similarity equations with relevant boundary conditions. Numerical solutions of the similarity equations are presented to show the effects of the controlling parameters on the dimensionless velocity, temperature and concentration profiles as well as on the friction factor, rate of heat and mass transfer. It is found that the rate of heat transfer elevates with the mass transfer velocity, convective heat transfer, Prandtl number, velocity ratio and the magnetic field parameters. It is also found that the rate of mass transfer enhances with the mass transfer velocity, velocity ratio, power law index and the Schmidt number, whilst it suppresses with the magnetic field parameter. Our results are compared with the results existing in the open literature. The comparisons are satisfactory. PMID:23741295

Mantle-driven geodynamo features - accounting for non-thermal lower mantle features

NASA Astrophysics Data System (ADS)

Choblet, G.; Amit, H.

2011-12-01

Lower mantle heterogeneity responsible for spatial variations of the CMB heat flux could control long term geodynamo properties such as deviations from axial symmetry in the magnetic field and the core flow, frequency of geomagnetic reversals and anisotropic growth of the inner core. In this context, a classical interpretation of tomographic mapping of the lowermost mantle is to correlate linearly seismic velocities to heat flux anomalies. This implicitly assumes that temperature alone controls the tomographic anomalies. In addition, the limited spatial resolution of tomographic images precludes modeling sharp CMB heat flux structures.. There has been growing evidence however that non-thermal origins are also be expected for seismic velocity anomalies: the three main additional control parameters are (i) compositional anomalies possibly associated to the existence of a deep denser layer, (ii) the phase transition in magnesium perovskite believed to occur in the lowermost mantle and (iii) the possible presence of partial melts. Numerical models of mantle dynamics have illustrated how the first two parameters could distort the linear relationship between shear wave velocity anomalies and CMB heat flux (Nakagawa and Tackley, 2008). In this presentation we will consider the effect of such alternative interpretations of seismic velocity anomalies in order to prescribe CMB heat flux as an outer boundary for dynamo simulations. We first focus on the influence of post-perovskite. Taking into account this complexity could result in an improved agreement between the long term average properties of simulated dynamos and geophysical observations, including the Atlantic/Pacific hemispherical dichotomy in core flow activity, the single intense paleomagnetic field structure in the southern hemisphere, and possibly degree 1 dominant mode of inner-core seismic heterogeneity. We then account for sharp anomalies that are not resolved by the global tomographic probe. For instance, Ultra Low Velocity Zones (ULVZs) have been identified by dedicated seismic tools that cannot be observed by global tomographic models. These are likely associated to the hottest regions in the lowermost mantle. We thus model anomalies of the CMB heat flux where narrow ridges with low heat flux are juxtaposed to a large scale degree 2 pattern which represents the dominant component of tomographic observations. We find that hot ridges located with a large-scale positive heat flux anomaly to the east produce a time-average narrow elongated upwelling which acts as a flow barrier at the top of the core and results in intensified low-latitudes magnetic flux patches. This is found to have a clear signature on the meridional component of the thermal wind balance. Based on the lower mantle seismic tomography pattern, time average intense geomagnetic flux patches are expected below east Asia and Oceania and below the Americas.

Diffusion Flame Extinction in a Low Strain Flow

NASA Technical Reports Server (NTRS)

Sutula, Jason; Jones, Joshua; Torero, Jose L.; Borlik, Jeffrey; Ezekoye, Ofodike A.

1997-01-01

Diffusion flames are of great interest in fire safety and many industrial processes. Many parameters significantly affect the flame structure, shape and stability, of particular importance are the constraints imposed by geometrical boundaries. Physical boundaries determine the characteristics of the flow, affect heat, fuel, and oxidizer transport from and towards the flame and can act as heat sinks or heat sources. As a result, the existence of a flame, its shape and nature are intimately related to the geometrical characteristics of the environment that surrounds it. The counter-flow configuration provides a constant strain flow, therefore, is ideal to study the structure of diffusion flames. Most studies have concentrated on the high velocity, high strain limit, since buoyantly induced instabilities will disintegrate the planar flame as the velocity decreases. Only recently, experimental studies in micro-gravity conditions have begun to explore the low strain regimes. The main objective of these on-going studies is to determine the effect of radiative heat losses and variable strain on the structure and radiation-induced extinction of diffusion flames. For these programs, size, geometry, and experimental conditions have been chosen to keep the flame unaffected by the physical boundaries. Whether is the burning of condensed or gaseous fuels, for most real situations the boundaries impose a significant effect on the nature of the flame. There is, therefore, a need to better understand the effect that geometrical constraints (i.e. flow nonperpendicular to a fuel surface, heat losses to the boundaries, etc.) might have on the final characteristics of a diffusion flame. Preliminary experiments have shown that, in the absence of gravity, and depending on the distance from the flame to the boundary, three characteristically different regimes can be observed. Close to the boundary, the flame is parabolic, very thin and blue, almost soot-less. Diffusion is the main mechanism controlling fuel transport to the reaction zone, conduction towards the inlets is the main source of heat losses. As the distance increases the flame becomes linear and thickens, remaining blue at the oxidizer side and turning yellow at the fuel side. Here, convection brings fuel and oxidizer together and the reaction occurs in the viscous layer formed between the fuel and oxidizer streams. This region corresponds to the characteristic counter-flow flame where conduction and convection become negligible forms of heat losses and radiation becomes dominant. The flame in the third (mixed) region, between the two others, results from the combination of the scenarios presented above.

Continuous Flow Chemistry: Reaction of Diphenyldiazomethane with p-Nitrobenzoic Acid.

PubMed

Aw, Alex; Fritz, Marshall; Napoline, Jonathan W; Pollet, Pamela; Liotta, Charles L

2017-11-15

Continuous flow technology has been identified as instrumental for its environmental and economic advantages leveraging superior mixing, heat transfer and cost savings through the "scaling out" strategy as opposed to the traditional "scaling up". Herein, we report the reaction of diphenyldiazomethane with p-nitrobenzoic acid in both batch and flow modes. To effectively transfer the reaction from batch to flow mode, it is essential to first conduct the reaction in batch. As a consequence, the reaction of diphenyldiazomethane was first studied in batch as a function of temperature, reaction time, and concentration to obtain kinetic information and process parameters. The glass flow reactor set-up is described and combines two types of reaction modules with "mixing" and "linear" microstructures. Finally, the reaction of diphenyldiazomethane with p-nitrobenzoic acid was successfully conducted in the flow reactor, with up to 95% conversion of the diphenyldiazomethane in 11 min. This proof of concept reaction aims to provide insight for scientists to consider flow technology's competitiveness, sustainability, and versatility in their research.

Plasma rotation and transport in MAST spherical tokamak

NASA Astrophysics Data System (ADS)

Field, A. R.; Michael, C.; Akers, R. J.; Candy, J.; Colyer, G.; Guttenfelder, W.; Ghim, Y.-c.; Roach, C. M.; Saarelma, S.; MAST Team

2011-06-01

The formation of internal transport barriers (ITBs) is investigated in MAST spherical tokamak plasmas. The relative importance of equilibrium flow shear and magnetic shear in their formation and evolution is investigated using data from high-resolution kinetic- and q-profile diagnostics. In L-mode plasmas, with co-current directed NBI heating, ITBs in the momentum and ion thermal channels form in the negative shear region just inside qmin. In the ITB region the anomalous ion thermal transport is suppressed, with ion thermal transport close to the neo-classical level, although the electron transport remains anomalous. Linear stability analysis with the gyro-kinetic code GS2 shows that all electrostatic micro-instabilities are stable in the negative magnetic shear region in the core, both with and without flow shear. Outside the ITB, in the region of positive magnetic shear and relatively weak flow shear, electrostatic micro-instabilities become unstable over a wide range of wave numbers. Flow shear reduces the linear growth rates of low-k modes but suppression of ITG modes is incomplete, which is consistent with the observed anomalous ion transport in this region; however, flow shear has little impact on growth rates of high-k, electron-scale modes. With counter-NBI ITBs of greater radial extent form outside qmin due to the broader profile of E × B flow shear produced by the greater prompt fast-ion loss torque.

Entropy production in a photovoltaic cell

NASA Astrophysics Data System (ADS)

Ansari, Mohammad H.

2017-05-01

We evaluate entropy production in a photovoltaic cell that is modeled by four electronic levels resonantly coupled to thermally populated field modes at different temperatures. We use a formalism recently proposed, the so-called multiple parallel worlds, to consistently address the nonlinearity of entropy in terms of density matrix. Our result shows that entropy production is the difference between two flows: a semiclassical flow that linearly depends on occupational probabilities, and another flow that depends nonlinearly on quantum coherence and has no semiclassical analog. We show that entropy production in the cells depends on environmentally induced decoherence time and energy detuning. We characterize regimes where reversal flow of information takes place from a cold to hot bath. Interestingly, we identify a lower bound on entropy production, which sets limitations on the statistics of dissipated heat in the cells.

Finite Element Modelling of the Apollo Heat Flow Experiments

NASA Astrophysics Data System (ADS)

Platt, J.; Siegler, M. A.; Williams, J.

2013-12-01

The heat flow experiments sent on Apollo missions 15 and 17 were designed to measure the temperature gradient of the lunar regolith in order to determine the heat flux of the moon. Major problems in these experiments arose from the fact that the astronauts were not able to insert the probes below the thermal skin depth. Compounding the problem, anomalies in the data have prevented scientists from conclusively determining the temperature dependent conductivity of the soil, which enters as a linear function into the heat flow calculation, thus stymieing them in their primary goal of constraining the global heat production of the Moon. Different methods of determining the thermal conductivity have yielded vastly different results resulting in downward corrections of up to 50% in some cases from the original calculations. Along with problems determining the conductivity, the data was inconsistent with theoretical predictions of the temperature variation over time, leading some to suspect that the Apollo experiment itself changed the thermal properties of the localised area surrounding the probe. The average temperature of the regolith, according to the data, increased over time, a phenomenon that makes calculating the thermal conductivity of the soil and heat flux impossible without knowing the source of error and accounting for it. The changes, possibly resulting from as varied sources as the imprint of the Astronauts boots on the lunar surface, compacted soil around the bore stem of the probe or even heat radiating down the inside of the tube, have convinced many people that the recorded data is unusable. In order to shed some light on the possible causes of this temperature rise, we implemented a finite element model of the probe using the program COMSOL Multi-physics as well as Matlab. Once the cause of the temperature rise is known then steps can be taken to account for the failings of the experiment and increase the data's utility.

Heat Flow, Regional Geophysics and Lithosphere Structure In The Czech Republic

NASA Astrophysics Data System (ADS)

Safanda, J.; Cermak, V.; Kresl, M.; Dedecek, P.

Paper summarises and critically revises heat flow data that have been collected in the Czech Republic to date. The regional heat flow density map was prepared in view of all existing heat flow data completed with the similar in the surrounding countries and taking into consideration also temperature measurements in deep boreholes. Crustal temperature profiles were calculated by using the available geological information, results of deep seismic sounding and the laboratory data on radiogenic heat produc- tion and thermal conductivity. Special attention was paid to numerous temperature logs in two sedimentary basins, namely in the Cheb and Ostrava-Karvina coal basins, for which detailed heat flow patterns were proposed. Relationships between heat flow distribution and the crustal/lithosphere evolution, between heat flow and the heat pro- duction of the crustal rocks, heat flow and crustal thickness and the steady-state vs. transient heat transport are discussed.

Theoretical simulation of the dual-heat-flux method in deep body temperature measurements.

PubMed

Huang, Ming; Chen, Wenxi

2010-01-01

Deep body temperature reveals individual physiological states, and is important in patient monitoring and chronobiological studies. An innovative dual-heat-flux method has been shown experimentally to be competitive with the conventional zero-heat-flow method in its performance, in terms of measurement accuracy and step response to changes in the deep temperature. We have utilized a finite element method to model and simulate the dynamic process of a dual-heat-flux probe in deep body temperature measurements to validate the fundamental principles of the dual-heat-flux method theoretically, and to acquire a detailed quantitative description of the thermal profile of the dual-heat-flux probe. The simulation results show that the estimated deep body temperature is influenced by the ambient temperature (linearly, at a maximum rate of 0.03 °C/°C) and the blood perfusion rate. The corresponding depth of the estimated temperature in the skin and subcutaneous tissue layer is consistent when using the dual-heat-flux probe. Insights in improving the performance of the dual-heat-flux method were discussed for further studies of dual-heat-flux probes, taking into account structural and geometric considerations.

Internal transport barrier triggered by non-linear lower hybrid wave deposition under condition of beam-driven toroidal rotation

NASA Astrophysics Data System (ADS)

Gao, Q. D.; Budny, R. V.

2015-03-01

By using gyro-Landau fluid transport model (GLF23), time-dependent integrated modeling is carried out using TRANSP to explore the dynamic process of internal transport barrier (ITB) formation in the neutral beam heating discharges. When the current profile is controlled by LHCD (lower hybrid current drive), with appropriate neutral beam injection, the nonlinear interplay between the transport determined gradients in the plasma temperature (Ti,e) and toroidal velocity (Vϕ) and the E×B flow shear (including q-profile) produces transport bifurcations, generating spontaneously a stepwise growing ITB. In the discharge, the constraints imposed by the wave propagation condition causes interplay of the LH driven current distribution with the plasma configuration modification, which constitutes non-linearity in the LH wave deposition. The non-linear effects cause bifurcation in LHCD, generating two distinct quasi-stationary reversed magnetic shear configurations. The change of current profile during the transition period between the two quasi-stationary states results in increase of the E×B shearing flow arising from toroidal rotation. The turbulence transport suppression by sheared E×B flow during the ITB development is analysed, and the temporal evolution of some parameters characterized the plasma confinement is examined. Ample evidence shows that onset of the ITB development is correlated with the enhancement of E×B shearing rate caused by the bifurcation in LHCD. It is suggested that the ITB triggering is associated with the non-linear effects of the LH power deposition.

Dual Rate Adaptive Control for an Industrial Heat Supply Process Using Signal Compensation Approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chai, Tianyou; Jia, Yao; Wang, Hong

The industrial heat supply process (HSP) is a highly nonlinear cascaded process which uses a steam valve opening as its control input, the steam flow-rate as its inner loop output and the supply water temperature as its outer loop output. The relationship between the heat exchange rate and the model parameters, such as steam density, entropy, and fouling correction factor and heat exchange efficiency are unknown and nonlinear. Moreover, these model parameters vary in line with steam pressure, ambient temperature and the residuals caused by the quality variations of the circulation water. When the steam pressure and the ambient temperaturemore » are of high values and are subjected to frequent external random disturbances, the supply water temperature and the steam flow-rate would interact with each other and fluctuate a lot. This is also true when the process exhibits unknown characteristic variations of the process dynamics caused by the unexpected changes of the heat exchange residuals. As a result, it is difficult to control the supply water temperature and the rates of changes of steam flow-rate well inside their targeted ranges. In this paper, a novel compensation signal based dual rate adaptive controller is developed by representing the unknown variations of dynamics as unmodeled dynamics. In the proposed controller design, such a compensation signal is constructed and added onto the control signal obtained from the linear deterministic model based feedback control design. Such a compensation signal aims at eliminating the unmodeled dynamics and the rate of changes of the currently sample unmodeled dynamics. A successful industrial application is carried out, where it has been shown that both the supply water temperature and the rate of the changes of the steam flow-rate can be controlled well inside their targeted ranges when the process is subjected to unknown variations of its dynamics.« less

A THC Simulator for Modeling Fluid-Rock Interactions

NASA Astrophysics Data System (ADS)

Hamidi, Sahar; Galvan, Boris; Heinze, Thomas; Miller, Stephen

2014-05-01

Fluid-rock interactions play an essential role in many earth processes, from a likely influence on earthquake nucleation and aftershocks, to enhanced geothermal system, carbon capture and storage (CCS), and underground nuclear waste repositories. In THC models, two-way interactions between different processes (thermal, hydraulic and chemical) are present. Fluid flow influences the permeability of the rock especially if chemical reactions are taken into account. On one hand solute concentration influences fluid properties while, on the other hand, heat can affect further chemical reactions. Estimating heat production from a naturally fractured geothermal systems remains a complex problem. Previous works are typically based on a local thermal equilibrium assumption and rarely consider the salinity. The dissolved salt in fluid affects the hydro- and thermodynamical behavior of the system by changing the hydraulic properties of the circulating fluid. Coupled thermal-hydraulic-chemical models (THC) are important for investigating these processes, but what is needed is a coupling to mechanics to result in THMC models. Although similar models currently exist (e.g. PFLOTRAN), our objective here is to develop algorithms for implementation using the Graphics Processing Unit (GPU) computer architecture to be run on GPU clusters. To that aim, we present a two-dimensional numerical simulation of a fully coupled non-isothermal non-reactive solute flow. The thermal part of the simulation models heat transfer processes for either local thermal equilibrium or nonequilibrium cases, and coupled to a non-reactive mass transfer described by a non-linear diffusion/dispersion model. The flow process of the model includes a non-linear Darcian flow for either saturated or unsaturated scenarios. For the unsaturated case, we use the Richards' approximation for a mixture of liquid and gas phases. Relative permeability and capillary pressure are determined by the van Genuchten relations. Permeability of rock is controlled by porosity, which is itself related to effective stress. The theoretical model is solved using explicit finite differences, and runs in parallel mode with OpenMP. The code is fully modular so that any combination of current THC processes, one- and two-phase, can be chosen. Future developments will include dissolution and precipitation of chemical components in addition to chemical erosion.

Poiseuille, thermal transpiration and Couette flows of a rarefied gas between plane parallel walls with nonuniform surface properties in the transverse direction and their reciprocity relations

NASA Astrophysics Data System (ADS)

Doi, Toshiyuki

2018-04-01

Slow flows of a rarefied gas between two plane parallel walls with nonuniform surface properties are studied based on kinetic theory. It is assumed that one wall is a diffuse reflection boundary and the other wall is a Maxwell-type boundary whose accommodation coefficient varies periodically in the direction perpendicular to the flow. The time-independent Poiseuille, thermal transpiration and Couette flows are considered. The flow behavior is numerically studied based on the linearized Bhatnagar-Gross-Krook-Welander model of the Boltzmann equation. The flow field, the mass and heat flow rates in the gas, and the tangential force acting on the wall surface are studied over a wide range of the gas rarefaction degree and the parameters characterizing the distribution of the accommodation coefficient. The locally convex velocity distribution is observed in Couette flow of a highly rarefied gas, similarly to Poiseuille flow and thermal transpiration. The reciprocity relations are numerically confirmed over a wide range of the flow parameters.

Heat Transfer Through Turbulent Friction Layers

NASA Technical Reports Server (NTRS)

Reichardt, H.

1943-01-01

The "general Prandtl number" Pr(exp 1) - A(sub q)/A Pr, aside from the Reynolds number determines the ratio of turbulent to molecular heat transfer, and the temperature distribution in turbulent friction layers. A(sub q) = exchange coefficient for heat; A = exchange coefficient for momentum transfer. A formula is derived from the equation defining the general Prandtl number which describes the temperature as a function of the velocity. For fully developed thermal boundary layers all questions relating to heat transfer to and from incompressible fluids can be treated in a simple manner if the ratio of the turbulent shear stress to the total stress T(sub t)/T in the layers near the wall is known, and if the A(sub q)/A can be regarded as independent of the distance from the wall. The velocity distribution across a flat smooth channel and deep into the laminar sublayer was measured for isothermal flow to establish the shear stress ratio T(sub t)/T and to extend the universal wall friction law. The values of T(sub t)/T which resulted from these measurements can be approximately represented by a linear function of the velocity in the laminar-turbulent transition zone. The effect of the temperature relationship of the material values on the flow near the wall is briefly analyzed. It was found that the velocity at the laminar boundary (in contrast to the thickness of the laminar layer) is approximately independent of the temperature distribution. The temperature gradient at the wall and the distribution of temperature and heat flow in the turbulent friction layers were calculated on the basis of the data under two equations. The derived formulas and the figures reveal the effects of the Prandtl number, the Reynolds number, the exchange quantities and the temperature relationship of the material values.

Combining CFD simulations with blockoriented heatflow-network model for prediction of photovoltaic energy-production

NASA Astrophysics Data System (ADS)

Haber, I. E.; Farkas, I.

2011-01-01

The exterior factors which influencing the working circumstances of photovoltaic modules are the irradiation, the optical air layer (Air Mass - AM), the irradiation angle, the environmental temperature and the cooling effect of the wind. The efficiency of photovoltaic (PV) devices is inversely proportional to the cell temperature and therefore the mounting of the PV modules can have a big affect on the cooling, due to wind flow-around and naturally convection. The construction of the modules could be described by a heatflow-network model, and that can define the equation which determines the cells temperature. An equation like this can be solved as a block oriented model with hybrid-analogue simulator such as Matlab-Simulink. In view of the flow field and the heat transfer, witch was calculated numerically, the heat transfer coefficients can be determined. Five inflow rates were set up for both pitched and flat roof cases, to let the trend of the heat transfer coefficient know, while these functions can be used for the Matlab/Simulink model. To model the free convection flows, the Boussinesq-approximation were used, integrated into the Navier-Stokes equations and the energy equation. It has been found that under a constant solar heat gain, the air velocity around the modules and behind the pitched-roof mounted module is increasing, proportionately to the wind velocities, and as result the heat transfer coefficient increases linearly, and can be described by a function in both cases. To the block based model the meteorological parameters and the results of the CFD simulations as single functions were attached. The final aim was to make a model that could be used for planning photovoltaic systems, and define their accurate performance for better sizing of an array of modules.

Cutaneous heat flow during heating and cooling in Alligator mississipiensis.

PubMed

Smith, E N

1976-05-01

Direct in vivo measurement of heat flow across the skin of the American alligator (Alligator mississipiensis) showed increased heat flow during warming. Mean values at 25 degrees C during warming (15-35 degrees C) in air (airspeed 300 cm/s) were 17.9 +/- 92 SE cal/cm2 per h (mean alligator wt 3.27 kg). Cooling heat flow at the same temperature was 13.6 +/- 0.57 cal/cm2 per h. Subdermal heat flow was reduced during warming and was not significantly different from cutaneous heat flow during cooling. This indicated that the alligator was able to control its rate of heat exchange with the environment by altering cutaneous perfusion. Atropine, phenoxybenzamine, nitroglycerin, and Xylocaine did not affect cutaneous heat flow or heating and cooling rates. Atropine blocked bradycardia during cooling.

Rotary magnetic heat pump

DOEpatents

Kirol, Lance D.

1988-01-01

A rotary magnetic heat pump constructed without flow seals or segmented rotor accomplishes recuperation and regeneration by using split flow paths. Heat exchange fluid pumped through heat exchangers and returned to the heat pump splits into two flow components: one flowing counter to the rotor rotation and one flowing with the rotation.

Rotary magnetic heat pump

DOEpatents

Kirol, L.D.

1987-02-11

A rotary magnetic heat pump constructed without flow seals or segmented rotor accomplishes recuperation and regeneration by using split flow paths. Heat exchange fluid pumped through heat exchangers and returned to the heat pump splits into two flow components: one flowing counter to the rotor rotation and one flowing with the rotation. 5 figs.

Variations and controls on crustal thermal regimes in Southeastern Australia

NASA Astrophysics Data System (ADS)

Mather, Ben; McLaren, Sandra; Taylor, David; Roy, Sukanta; Moresi, Louis

2018-01-01

The surface heat flow field in Australia has for many years been poorly constrained compared to continental regions elsewhere. 182 recent heat flow determinations and 66 new heat production measurements for Southeastern Australia significantly increase our understanding of local and regional lithospheric thermal regimes and allow for detailed thermal modelling. The new data give a mean surface heat flow for Victoria of 71 ± 15 mW m- 2 which fits within the 61-77 mW m- 2 range reported for Phanerozoic-aged crust globally. These data reveal three new thermally and compositionally distinct heat flow sub-provinces within the previously defined Eastern Heat Flow Province: the Delamerian heat flow sub-province (average surface heat flow 60 ± 9 mW m- 2); the Lachlan heat flow sub-province (average surface heat flow 74 ± 13 mW m- 2); and the Newer Volcanics heat flow sub-province (average surface heat flow 72 ± 16 mW m- 2) which includes extreme values that locally exceed 100 mW m- 2. Inversions of reduced heat flow and crustal differentiation find that the Delamerian sub-province has experienced significant crustal reworking compared to the Lachlan and Newer Volcanics sub-provinces. The latter has experienced volcanism within the last 8 Ma and the degree of variability observed in surface heat flow points (up to 8 mW m- 2 per kilometre laterally) cannot be replicated with steady-state thermal models through this sub-province. In the absence of a strong palaeoclimate signal, aquifer disturbances, or highly enriched granites, we suggest that this high variability arises from localised transient perturbations to the upper crust associated with recent intraplate volcanism. This is supported by a strong spatial correlation of high surface heat flow and known eruption points within the Newer Volcanics heat flow sub-province.

An Experimental and Numerical Investigation of Endwall Aerodynamics and Heat Transfer in a Gas Turbine Nozzle Guide Vane with Slot Film Cooling

NASA Astrophysics Data System (ADS)

Alqefl, Mahmood Hasan

In many regions of the high-pressure gas turbine, film cooling flows are used to protect the turbine components from the combustor exit hot gases. Endwalls are challenging to cool because of the complex system of secondary flows that disturb surface film coolant coverage. The secondary flow vortices wash the film coolant from the surface into the mainstream significantly decreasing cooling effectiveness. In addition to being effected by secondary flow structures, film cooling flow can also affect these structures by virtue of their momentum exchange. In addition, many studies in the literature have shown that endwall contouring affects the strength of passage secondary flows. Therefore, to develop better endwall cooling schemes, a good understanding of passage aerodynamics and heat transfer as affected by interactions of film cooling flows with secondary flows is required. This experimental and computational study presents results from a linear, stationary, two-passage cascade representing the first stage nozzle guide vane of a high-pressure gas turbine with an axisymmetrically contoured endwall. The sources of film cooling flows are upstream combustor liner coolant and endwall slot film coolant injected immediately upstream of the cascade passage inlet. The operating conditions simulate combustor exit flow features, with a high Reynolds number of 390,000 and approach flow turbulence intensity of 11% with an integral length scale of 21% of the chord length. Measurements are performed with varying slot film cooling mass flow to mainstream flow rate ratios (MFR). Aerodynamic effects are documented with five-hole probe measurements at the exit plane. Heat transfer is documented through recovery temperature measurements with a thermocouple. General secondary flow features are observed. Total pressure loss measurements show that varying the slot film cooling MFR has some effects on passage loss. Velocity vectors and vorticity distributions show a very thin, yet intense, cross-pitch flow on the contoured endwall side. Endwall adiabatic effectiveness values and coolant distribution thermal fields show minimal effects of varying slot film coolant MFR. This suggests the dominant effects of combustor liner coolant. show dominant effects of combustor liner coolant on cooling the endwall. A coolant vorticity correlation presenting the advective mixing of the coolant due to secondary flow vorticity at the exit plane is also discussed.

Investigations on cooling with forced flow of He II. Part 2

NASA Astrophysics Data System (ADS)

Srinivasan, R.; Hofmann, A.

The measurements described in Part 1 of this Paper have been extended to a pressure of 7 bar . The value of the conductivity function, f( T), at a temperature greater than Tmax, at which it exhibits a maximum, drops rapidly with increasing pressure. Below Tmax the change in f( T) with pressure is less drastic. The Gorter-Mellink constant, AGM, increases linearly with pressure in the range 1.5-2 K and its pressure coefficient at 1 bar is 0.038 ± 0.01 per bar, independent of temperature. The superfilter is tested at 1.8 K. The flow through the superfilter is Gorter-Mellink flow. The maximum flow rate decreases as the pressure increases. The temperature distribution in the test section with and without flow is adequately described by the one-dimensional model discussed in Part 1. It is concluded that for heat transfer to He II in forced flow there is no advantage in working at pressures > 1 bar. 1 bar = 100 kPa

Axial flow heat exchanger devices and methods for heat transfer using axial flow devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koplow, Jeffrey P.

Systems and methods described herein are directed to rotary heat exchangers configured to transfer heat to a heat transfer medium flowing in substantially axial direction within the heat exchangers. Exemplary heat exchangers include a heat conducting structure which is configured to be in thermal contact with a thermal load or a thermal sink, and a heat transfer structure rotatably coupled to the heat conducting structure to form a gap region between the heat conducting structure and the heat transfer structure, the heat transfer structure being configured to rotate during operation of the device. In example devices heat may be transferredmore » across the gap region from a heated axial flow of the heat transfer medium to a cool stationary heat conducting structure, or from a heated stationary conducting structure to a cool axial flow of the heat transfer medium.« less

Tidal Dissipation Within the Jupiter Moon Io - A Numerical Approach

NASA Astrophysics Data System (ADS)

Steinke, Teresa; van der Wal, Wouter; Hu, Haiyang; Vermeersen, Bert

2017-04-01

Satellite images and recent Earth-based observations of the innermost of the Galilean moons reveal a conspicuous pattern of volcanic hotspots and paterae on its surface. This pattern is associated with the heat flux originating from tidal dissipation in Io's mantle and asthenosphere. As shown by many analytical studies [e.g. Segatz et al. 1988], the local heat flux pattern depends on the rheology and structure of the satellite's interior and therefore could reveal constraints on Io's present interior. However, non-linear processes, different rheologies, and in particular lateral variations arising from the spatial heating pattern are difficult to incorporate in analytical 1D models but might be crucial. This motivates the development of a 3D finite element model of a layered body disturbed by a tidal potential. As a first step of this project we present a 3D finite element model of a spherically stratified body of linear viscoelastic rheology. For validation, we compare the resulting tidal deformation and local heating patterns with the results obtained by analytical models. Numerical errors increase with lower values of the asthenosphere viscosity. Currently, the numerical model allows realistic simulation down to viscosities of 1018 Pa s. Furthermore, we investigate an adequate way to deal with the relaxation of false modes that arise at the onset of the periodic tidal potential series in the numerical approach. Segatz, M., Spohn, T., Ross, M. N., Schubert, G. (1988). Tidal dissipation, surface heat flow, and figure of viscoelastic models of Io. Icarus, 75(2), 187-206.

A novel investigation of a micropolar fluid characterized by nonlinear constitutive diffusion model in boundary layer flow and heat transfer.

PubMed

Sui, Jize; Zhao, Peng; Cheng, Zhengdong; Zheng, Liancun; Zhang, Xinxin

2017-02-01

The rheological and heat-conduction constitutive models of micropolar fluids (MFs), which are important non-Newtonian fluids, have been, until now, characterized by simple linear expressions, and as a consequence, the non-Newtonian performance of such fluids could not be effectively captured. Here, we establish the novel nonlinear constitutive models of a micropolar fluid and apply them to boundary layer flow and heat transfer problems. The nonlinear power law function of angular velocity is represented in the new models by employing generalized " n -diffusion theory," which has successfully described the characteristics of non-Newtonian fluids, such as shear-thinning and shear-thickening fluids. These novel models may offer a new approach to the theoretical understanding of shear-thinning behavior and anomalous heat transfer caused by the collective micro-rotation effects in a MF with shear flow according to recent experiments. The nonlinear similarity equations with a power law form are derived and the approximate analytical solutions are obtained by the homotopy analysis method, which is in good agreement with the numerical solutions. The results indicate that non-Newtonian behaviors involving a MF depend substantially on the power exponent n and the modified material parameter [Formula: see text] introduced by us. Furthermore, the relations of the engineering interest parameters, including local boundary layer thickness, local skin friction, and Nusselt number are found to be fitted by a quadratic polynomial to n with high precision, which enables the extraction of the rapid predictions from a complex nonlinear boundary-layer transport system.

A novel investigation of a micropolar fluid characterized by nonlinear constitutive diffusion model in boundary layer flow and heat transfer

PubMed Central

Zhao, Peng; Cheng, Zhengdong; Zheng, Liancun; Zhang, Xinxin

2017-01-01

The rheological and heat-conduction constitutive models of micropolar fluids (MFs), which are important non-Newtonian fluids, have been, until now, characterized by simple linear expressions, and as a consequence, the non-Newtonian performance of such fluids could not be effectively captured. Here, we establish the novel nonlinear constitutive models of a micropolar fluid and apply them to boundary layer flow and heat transfer problems. The nonlinear power law function of angular velocity is represented in the new models by employing generalized “n-diffusion theory,” which has successfully described the characteristics of non-Newtonian fluids, such as shear-thinning and shear-thickening fluids. These novel models may offer a new approach to the theoretical understanding of shear-thinning behavior and anomalous heat transfer caused by the collective micro-rotation effects in a MF with shear flow according to recent experiments. The nonlinear similarity equations with a power law form are derived and the approximate analytical solutions are obtained by the homotopy analysis method, which is in good agreement with the numerical solutions. The results indicate that non-Newtonian behaviors involving a MF depend substantially on the power exponent n and the modified material parameter K0 introduced by us. Furthermore, the relations of the engineering interest parameters, including local boundary layer thickness, local skin friction, and Nusselt number are found to be fitted by a quadratic polynomial to n with high precision, which enables the extraction of the rapid predictions from a complex nonlinear boundary-layer transport system. PMID:28344433

Open-loop heat-recovery dryer

DOEpatents

TeGrotenhuis, Ward Evan

2013-11-05

A drying apparatus is disclosed that includes a drum and an open-loop airflow pathway originating at an ambient air inlet, passing through the drum, and terminating at an exhaust outlet. A passive heat exchanger is included for passively transferring heat from air flowing from the drum toward the exhaust outlet to air flowing from the ambient air inlet toward the drum. A heat pump is also included for actively transferring heat from air flowing from the passive heat exchanger toward the exhaust outlet to air flowing from the passive heat exchanger toward the drum. A heating element is also included for further heating air flowing from the heat pump toward the drum.

Numerical investigation of the onset of centrifugal buoyancy in a rotating cavity

NASA Astrophysics Data System (ADS)

Pitz, Diogo B.; Marxen, Olaf; Chew, John

2016-11-01

Buoyancy-induced flows in a differentially heated rotating annulus present a multitude of dynamics when control parameters such as rotation rate, temperature difference and Prandtl number are varied. Whilst most of the work in this area has been motivated by applications involving geophysics, the problem of buoyancy-induced convection in rotating systems is also relevant in industrial applications such as the flow between rotating disks of turbomachinery internal air systems, in which buoyancy plays a major role and poses a challenge to accurately predict temperature distributions and heat transfer rates. In such applications the rotational speeds involved are very large, so that the centrifugal accelerations induced are much higher than gravity. In this work we perform direct numerical simulations and linear stability analysis of flow induced by centrifugal buoyancy in a sealed rotating annulus of finite gap with flat end-walls, using a canonical setup representative of an internal air system rotating cavity. The analysis focuses on the behaviour of small-amplitude disturbances added to the base flow, and how those affect the onset of Rossby waves and, ultimately, the transition to a fully turbulent state where convection columns no longer have a well-defined structure. Diogo B. Pitz acknowledges the financial support from the Capes foundation through the Science without Borders program.

Flow and heat transfer in water based liquid film fluids dispensed with graphene nanoparticles

NASA Astrophysics Data System (ADS)

Zuhra, Samina; Khan, Noor Saeed; Khan, Muhammad Altaf; Islam, Saeed; Khan, Waris; Bonyah, Ebenezer

2018-03-01

The unsteady flow and heat transfer characteristics of electrically conducting water based thin liquid film non-Newtonian (Casson and Williamson) nanofluids dispensed with graphene nanoparticles past a stretching sheet are considered in the presence of transverse magnetic field and non-uniform heat source/sink. Embedding the graphene nanoparticles effectively amplifies the thermal conductivity of Casson and Williamson nanofluids. Ordinary differential equations together with the boundary conditions are obtained through similarity variables from the governing equations of the problem, which are solved by the HAM (Homotopy Analysis Method). The solution is expressed through graphs and illustrated which show the influences of all the parameters. The convergence of the HAM solution for the linear operators is obtained. Favorable comparison with previously published research paper is performed to show the correlation for the present work. Skin friction coefficient and Nusselt number are presented through Tables and graphs which show the validation for the achieved results demonstrating that the thin liquid films results from this study are in close agreement with the results reported in the literature. Results achieved by HAM and residual errors are evaluated numerically, given in Tables and also depicted graphically which show the accuracy of the present work.

Submarine hydrogeology of the Hawaiian archipelagic apron: 2. Numerical simulations of coupled heat transport and fluid flow

NASA Astrophysics Data System (ADS)

Harris, Robert N.; Garven, Grant; Georgen, Jennifer; McNutt, Marcia K.; Christiansen, Lizet; von Herzen, Richard P.

2000-09-01

We perform numerical simulations of buoyancy-driven, pore fluid flow in the Hawaiian archipelagic apron and underlying oceanic crust in order to determine the extent to which heat redistributed by such flow might cause conductive heat flow measurements to underrepresent the true mantle heat flux. We also seek an understanding of undulations observed in finely spaced heat flow measurements acquired north of Oahu and Maro Reef with wavelengths of 10 to 100 km and amplitudes of 2 to 7 mW m-2. We find that pore fluid flow can impart significant perturbations to seafloor heat flow from the value expected assuming a constant mantle flux. In the simplest scenario, moat-wide circulation driven by bathymetric relief associated with the volcanic edifice recharges a fluid system over the moat and discharges the geothermally heated water through the volcanic edifice. The existing heat flow data are unable to confirm the existence of such a flow regime, in that it produces prominent heat flow anomalies only on the steep flanks of the volcano where heat flow probes cannot penetrate. However, this flow system does not significantly mask the mantle flux for reasonable permeabilities and flow rates. Another numerical simulation in which the upper oceanic basement acts as a aquifer for a flow loop recharged at basement outcrops on the flexural arch and discharged within a permeable volcanic edifice is capable of almost uniformly depressing conductive heat flow across the entire moat by ˜15%. Large heat flow anomalies (>20 mW m-2) are located over the recharge and discharge zones but are beyond the area sampled by our data. Presumably finely spaced heat flow measurements over the flexural arch could test for the existence of the predicted recharge zone. We demonstrate that the prominent, shorter-wave undulations in heat flow across the Oahu and Maro Reef moats are too large to be explained solely by relief in the upper oceanic basement. More likely, shallower large-scale turbidites or debris flows also serve as aquifers within the less permeable moat sediments. With our limited information on the structural geology of the moat, permeability structure of its major geologic units, and their variations in the third dimension, we are not able to exactly match the spatial distribution of heat flow anomalies in our data, but spectral comparisons look promising.

Heat transfer in gas turbine engines and three-dimensional flows; Proceedings of the Symposium, ASME Winter Annual Meeting, Chicago, IL, Nov. 27-Dec. 2, 1988

NASA Technical Reports Server (NTRS)

Elovic, E. (Editor); O'Brien, J. E. (Editor); Pepper, D. W. (Editor)

1988-01-01

The present conference on heat transfer characteristics of gas turbines and three-dimensional flows discusses velocity-temperature fluctuation correlations at the flow stagnation flow of a circular cylinder in turbulent flow, heat transfer across turbulent boundary layers with pressure gradients, the effect of jet grid turbulence on boundary layer heat transfer, and heat transfer characteristics predictions for discrete-hole film cooling. Also discussed are local heat transfer in internally cooled turbine airfoil leading edges, secondary flows in vane cascades and curved ducts, three-dimensional numerical modeling in gas turbine coal combustor design, numerical and experimental results for tube-fin heat exchanger airflow and heating characteristics, and the computation of external hypersonic three-dimensional flow field and heat transfer characteristics.

Heat transfer in gas turbine engines and three-dimensional flows; Proceedings of the Symposium, ASME Winter Annual Meeting, Chicago, IL, Nov. 27-Dec. 2, 1988

NASA Astrophysics Data System (ADS)

Elovic, E.; O'Brien, J. E.; Pepper, D. W.

The present conference on heat transfer characteristics of gas turbines and three-dimensional flows discusses velocity-temperature fluctuation correlations at the flow stagnation flow of a circular cylinder in turbulent flow, heat transfer across turbulent boundary layers with pressure gradients, the effect of jet grid turbulence on boundary layer heat transfer, and heat transfer characteristics predictions for discrete-hole film cooling. Also discussed are local heat transfer in internally cooled turbine airfoil leading edges, secondary flows in vane cascades and curved ducts, three-dimensional numerical modeling in gas turbine coal combustor design, numerical and experimental results for tube-fin heat exchanger airflow and heating characteristics, and the computation of external hypersonic three-dimensional flow field and heat transfer characteristics.

Stability investigation in nominally two-dimensional laminar boundary layers by means of heat pulsing

NASA Astrophysics Data System (ADS)

Zhou, Ming De; Liu, Tian Shu

The effects of heat pulses from surface-mounted wires on the laminar boundary-layer flow on an 800 x 300 x 32-mm flat wooden plate with a 6:1 elliptical nose are investigated experimentally in the 1.5 x 0.3-m working section of the DFVLR-AVA Goettingen low-turbulence wind tunnel at maximum free-stream velocity 45 m/s and longitudinal turbulence intensity about 0.05 percent. The results of flow visualization and hot-film measurements are presented in extensive graphs and photographs and analyzed. It is found that the initial amplification of disturbances is accurately predicted by two-dimensional linear stability theory, even when the disturbances include significant three-dimensional components. Subharmonic paths to turbulence are shown to begin from lower initial-disturbance fluctuation levels or at lower Reynolds numbers than predicted by the 'K' mechanism (Klebanoff et al., 1962), and the oblique wave angles at which maximum amplification occurs are seen as consistent with the resonant triad model of Craik (1971).

Fluid dynamic propagation of initial baryon number perturbations on a Bjorken flow background

DOE PAGES

Floerchinger, Stefan; Martinez, Mauricio

2015-12-11

Baryon number density perturbations offer a possible route to experimentally measure baryon number susceptibilities and heat conductivity of the quark gluon plasma. We study the fluid dynamical evolution of local and event-by-event fluctuations of baryon number density, flow velocity, and energy density on top of a (generalized) Bjorken expansion. To that end we use a background-fluctuation splitting and a Bessel-Fourier decomposition for the fluctuating part of the fluid dynamical fields with respect to the azimuthal angle, the radius in the transverse plane, and rapidity. Here, we examine how the time evolution of linear perturbations depends on the equation of statemore » as well as on shear viscosity, bulk viscosity, and heat conductivity for modes with different azimuthal, radial, and rapidity wave numbers. Finally we discuss how this information is accessible to experiments in terms of the transverse and rapidity dependence of correlation functions for baryonic particles in high energy nuclear collisions.« less

THE FLOW AROUND A COSMIC STRING. I. HYDRODYNAMIC SOLUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beresnyak, Andrey; Nordita, KTH Royal Institute of Technology and Stockholm University, SE-10691

2015-05-10

Cosmic strings are linear topological defects which are hypothesized to be produced during inflation. Most searches for strings have relied on the string’s lensing of background galaxies or the cosmic microwave background. In this paper, I obtained a solution for the supersonic flow of collisional gas past the cosmic string which has two planar shocks with a shock compression ratio that depends on the angle defect of the string and its speed. The shocks result in the compression and heating of the gas and, given favorable conditions, particle acceleration. Gas heating and over-density in an unusual wedge shape can bemore » detected by observing the Hi line at high redshifts. Particle acceleration can occur in the present-day universe when the string crosses the hot gas contained in galaxy clusters and, since the consequences of such a collision persist for cosmological timescales, could be located by looking at unusual large-scale radio sources situated on a single spatial plane.« less

Electrical resistivity and thermal conductivity of hcp Fe-Ni alloys under high pressure: Implications for thermal convection in the Earth's core

NASA Astrophysics Data System (ADS)

Gomi, Hitoshi; Hirose, Kei

2015-10-01

We measured the electrical resistivity of Fe-Ni alloys (iron with 5, 10, and 15 wt.% nickel) using four-terminal method in a diamond-anvil cell up to 70 GPa at 300 K. The results demonstrate that measured resistivity increases linearly with increasing nickel impurity concentration, as predicted by the Matthiessen's rule. The impurity resistivity is predominant at ambient temperature; the incorporation of 5 wt.% nickel into iron doubles the electrical resistivity at 60 GPa. Such impurity effect becomes minor at high temperature of the Earth's core because of the resistivity "saturation". We also calculated that >0.9 TW heat flow is necessary at the top of the inner core for thermal convection in the inner core. It requires the CMB heat flow of ∼30 TW, which is much higher than recent estimates of 5-15 TW. This means that purely thermal convection does not occur in the inner core.

Two-phase flows within systems with ambient pressure

NASA Technical Reports Server (NTRS)

Hendricks, R. C.; Braun, M. J.; Wheeler, R. L., III; Mullen, R. L.

1985-01-01

In systems where the design inlet and outlet pressures are maintained above the thermodynamic critical pressure, it is often assumed that two phase flows within the system cannot occur. Designers rely on this simple rule of thumb to circumvent problems associated with a highly compressible two phase flow occurring within the supercritical pressure system along with the uncertainties in rotordynamics, load capacity, heat transfer, fluid mechanics, and thermophysical property variations. The simple rule of thumb is adequate in many low power designs but is inadequate for high performance turbomachines and linear systems, where two phase regions can exist even though outlet pressure is greater than critical pressure. Rotordynamic-fluid-mechanic restoring forces depend on momentum differences, and those for a two phase zone can differ significantly from those for a single-phase zone. Using the Reynolds equation the angular velocity, eccentricity, geometry, and ambient conditions are varied to determine the point of two phase flow incipience.

Multifarious slips perception on unsteady Casson nanofluid flow impinging on a stretching cylinder in the presence of solar radiation

NASA Astrophysics Data System (ADS)

Kundu, Prabir Kumar; Sarkar, Amit

2017-03-01

In the present work, a study is prepared for unsteady axisymmetric Casson-type nanofluid flow as a result of a contracting impermeable cylinder under the influence of solar radiation. The model of multifarious slip is included. The governing system of equations takes the form of non-linear ODEs by employing appropriate transformation and then resolve it numerically by RK-Fehlberg scheme in Maple 18 symbolic software. The effects of leading parameters on the flow characteristics are presented through tables and graphs coupled with necessary discussion and physical insinuation. Strong effects of various slip parameters on the physical quantities of interest are found here. The upsurge of surface slip is spotted to boost up temperature profile whereas it slows the flow down. However, thermal slip conducts to drop the temperature but enhancing the heat transfer rate.

Magnetic heat pump flow director

NASA Technical Reports Server (NTRS)

Howard, Frank S. (Inventor)

1995-01-01

A fluid flow director is disclosed. The director comprises a handle body and combed-teeth extending from one side of the body. The body can be formed of a clear plastic such as acrylic. The director can be used with heat exchangers such as a magnetic heat pump and can minimize the undesired mixing of fluid flows. The types of heat exchangers can encompass both heat pumps and refrigerators. The director can adjust the fluid flow of liquid or gas along desired flow directions. A method of applying the flow director within a magnetic heat pump application is also disclosed where the comb-teeth portions of the director are inserted into the fluid flow paths of the heat pump.

A Global Assessment of Oceanic Heat Loss: Conductive Cooling and Hydrothermal Redistribution of Heat

NASA Astrophysics Data System (ADS)

Hasterok, D. P.; Chapman, D. S.; Davis, E. E.

2011-12-01

A new dataset of ~15000 oceanic heat flow measurements is analyzed to determine the conductive heat loss through the seafloor. Many heat flow values in seafloor younger than 60 Ma are lower than predicted by models of conductively cooled lithosphere. This heat flow deficit is caused by ventilated hydrothermal circulation discharging at crustal outcrops or through thin sedimentary cover. Globally filtering of heat flow data to retain sites with sediment cover >400 m thick and located >60 km from the nearest seamount minimizes the effect of hydrothermal ventilation. Filtered heat flow exhibit a much higher correlation coefficient with seafloor age (up to 0.95 for filtered data in contrast to 0.5 for unfiltered data) and lower variability (reduction by 30%) within an age bin. A small heat flow deficit still persists at ages <25 Ma, possibly as a result of global filtering limitations and incomplete thermal rebound following sediment burial. Detailed heat flow surveys co-located with seismic data can identify environments favoring conductive heat flow; heat flow collected in these environments is higher than that determined by the global dataset, and is more consistent with conductive cooling of the lithosphere. The new filtered data analysis and a growing number of site specific surveys both support estimates of global heat loss in the range 40-47 TW. The estimated hydrothermal deficit is consistent with estimates from geochemical studies ~7 TW, but is a few TW lower than previous estimates derived from heat flow determinations.

Thermal Analysis of a Carbon Fiber Rope Barrier for Use in the Reusable Solid Rocket Motor Nozzle Joint-2

NASA Technical Reports Server (NTRS)

Clayton, J. Louie

2002-01-01

This study provides development and verification of analysis methods used to assess performance of a carbon fiber rope (CFR) thermal barrier system that is currently being qualified for use in Reusable Solid Rocket Motor (RSRM) nozzle joint-2. Modeled geometry for flow calculations considers the joint to be vented with the porous CFR barriers placed in the 'open' assembly gap. Model development is based on a 1-D volume filling approach where flow resistances (assembly gap and CFRs) are defined by serially connected internal flow and the porous media 'Darcy' relationships. Combustion gas flow rates are computed using the volume filling code by assuming a lumped distribution total joint fill volume on a per linear circumferential inch basis. Gas compressibility, friction and heat transfer are included in the modeling. Gas-to-wall heat transfer is simulated by concurrent solution of the compressible flow equations and a large thermal 2-D finite element (FE) conduction grid. The derived numerical technique loosely couples the FE conduction matrix with the compressible gas flow equations. Free constants that appear in the governing equations are calibrated by parametric model comparison to hot fire subscale test results. The calibrated model is then used to make full-scale motor predictions using RSRM aft dome environments. Model results indicate that CFR thermal barrier systems will provide a thermally benign and controlled pressurization environment for the RSRM nozzle joint-2 primary seal activation.

Thermal Analysis of a Carbon Fiber Rope Barrier for Use in the Reusable Solid Rocket Motor Nozzle Joint-2

NASA Technical Reports Server (NTRS)

Clayton, J. Louie; Phelps, Lisa (Technical Monitor)

2001-01-01

This study provides for development and verification of analysis methods used to assess performance of a carbon fiber rope (CFR) thermal barrier system that is currently being qualified for use in Reusable Solid Rocket Motor (RSRM) nozzle joint-2. Modeled geometry for flow calculations considers the joint to be vented with the porous CFR barriers placed in the "open' assembly gap. Model development is based on a 1-D volume filling approach where flow resistances (assembly gap and CFRs) are defined by serially connected internal flow and the porous media "Darcy" relationships. Combustion gas flow rates are computed using the volume filling code by assuming a lumped distribution total joint fill volume on a per linear circumferential inch basis. Gas compressibility, friction and heat transfer are included in the modeling. Gas-to-wall heat transfer is simulated by concurrent solution of the compressible flow equations and a large thermal 2-D finite element (FE) conduction grid. The derived numerical technique loosely couples the FE conduction matrix with the compressible gas flow equations, Free constants that appear in the governing equations are calibrated by parametric model comparison to hot fire subscale test results. The calibrated model is then used to make full-scale motor predictions using RSRM aft dome environments. Model results indicate that CFR thermal barrier systems will provide a thermally benign and controlled pressurization environment for the RSRM nozzle joint-2 primary seal activation.

Correcting Borehole Temperture Profiles for the Effects of Postglacial Warming

NASA Astrophysics Data System (ADS)

Rath, V.; Gonzalez-Rouco, J. F.

2010-09-01

Though the investigation of observed borehole temperatures has proved to be a valuable tool for the reconstruction of ground surface temperature histories, there are many open questions concerning the signifcance and accuracy of the reconstructions from these data. In particular, the temperature signal of the warming after the Last glacial Maximum (LGM) is still present in borehole temperature proiles. It also influences the relatively shallow boreholes used in current paleoclimate inversions to estimate temperature changes in the last centuries. This is shown using Monte Carlo experiments on past surface temperature change, using plausible distributions for the most important parameters, i.e.,amplitude and timing of the glacial-interglacial transition, the prior average temperature, and petrophysical properties. It has been argued that the signature of the last glacial-interglacial transition could be responsible for the high amplitudes of millennial temperature reconstructions. However, in shallow boreholes the additional effect of past climate can reasonably approximated by a linear variation of temperature with depth, and thus be accommodated by a "biased" background heat flow. This is good news for borehole climatology. A simple correction based on subtracting an appropriate prior surface temperature history shows promising results reducing these errors considerably, in particular with deeper boreholes, where the warming signal in heat flow can no longer be approximated linearly. We will show examples from North America and Eurasia, comparing temperatures reduced the proposed algoritm with AOGCM modeling results.

Lightning energetics: Estimates of energy dissipation in channels, channel radii, and channel-heating risetimes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borovsky, J.E.

1998-05-01

In this report, several lightning-channel parameters are calculated with the aid of an electrodynamic model of lightning. The electrodynamic model describes dart leaders and return strokes as electromagnetic waves that are guided along conducting lightning channels. According to the model, electrostatic energy is delivered to the channel by a leader, where it is stored around the outside of the channel; subsequently, the return stroke dissipates this locally stored energy. In this report this lightning-energy-flow scenario is developed further. Then the energy dissipated per unit length in lightning channels is calculated, where this quantity is now related to the linear chargemore » density on the channel, not to the cloud-to-ground electrostatic potential difference. Energy conservation is then used to calculate the radii of lightning channels: their initial radii at the onset of return strokes and their final radii after the channels have pressure expanded. Finally, the risetimes for channel heating during return strokes are calculated by defining an energy-storage radius around the channel and by estimating the radial velocity of energy flow toward the channel during a return stroke. In three appendices, values for the linear charge densities on lightning channels are calculated, estimates of the total length of branch channels are obtained, and values for the cloud-to-ground electrostatic potential difference are estimated. {copyright} 1998 American Geophysical Union« less

Study on Gas-liquid Falling Film Flow in Internal Heat Integrated Distillation Column

NASA Astrophysics Data System (ADS)

Liu, Chong

2017-10-01

Gas-liquid internally heat integrated distillation column falling film flow with nonlinear characteristics, study on gas liquid falling film flow regulation control law, can reduce emissions of the distillation column, and it can improve the quality of products. According to the distribution of gas-liquid mass balance internally heat integrated distillation column independent region, distribution model of heat transfer coefficient of building internal heat integrated distillation tower is obtained liquid distillation falling film flow in the saturated vapour pressure of liquid water balance, using heat transfer equation and energy equation to balance the relationship between the circulating iterative gas-liquid falling film flow area, flow parameter information, at a given temperature, pressure conditions, gas-liquid flow falling film theory makes the optimal parameters to achieve the best fitting value with the measured values. The results show that the geometric gas-liquid internally heat integrated distillation column falling film flow heat exchange area and import column thermostat, the average temperature has significant. The positive correlation between the heat exchanger tube entrance due to temperature difference between inside and outside, the heat flux is larger, with the increase of internal heat integrated distillation column temperature, the slope decreases its temperature rise, which accurately describes the internal gas-liquid heat integrated distillation tower falling film flow regularity, take appropriate measures to promote the enhancement of heat transfer. It can enhance the overall efficiency of the heat exchanger.

Understanding heat and groundwater flow through continental flood basalt provinces: insights gained from alternative models of permeability/depth relationships for the Columbia Plateau, USA

USGS Publications Warehouse

Burns, Erick R.; Williams, Colin F.; Ingebritsen, Steven E.; Voss, Clifford I.; Spane, Frank A.; DeAngelo, Jacob

2015-01-01

Heat-flow mapping of the western USA has identified an apparent low-heat-flow anomaly coincident with the Columbia Plateau Regional Aquifer System, a thick sequence of basalt aquifers within the Columbia River Basalt Group (CRBG). A heat and mass transport model (SUTRA) was used to evaluate the potential impact of groundwater flow on heat flow along two different regional groundwater flow paths. Limited in situ permeability (k) data from the CRBG are compatible with a steep permeability decrease (approximately 3.5 orders of magnitude) at 600–900 m depth and approximately 40°C. Numerical simulations incorporating this permeability decrease demonstrate that regional groundwater flow can explain lower-than-expected heat flow in these highly anisotropic (kx/kz ~ 104) continental flood basalts. Simulation results indicate that the abrupt reduction in permeability at approximately 600 m depth results in an equivalently abrupt transition from a shallow region where heat flow is affected by groundwater flow to a deeper region of conduction-dominated heat flow. Most existing heat-flow measurements within the CRBG are from shallower than 600 m depth or near regional groundwater discharge zones, so that heat-flow maps generated using these data are likely influenced by groundwater flow. Substantial k decreases at similar temperatures have also been observed in the volcanic rocks of the adjacent Cascade Range volcanic arc and at Kilauea Volcano, Hawaii, where they result from low-temperature hydrothermal alteration.

Colorado Heat Flow Data from IHFC

DOE Data Explorer

Richard E. Zehner

2012-02-01

This layer contains the heat flow sites and data of the State of Colorado compiled from the International Heat Flow Commission (IHFC) of the International Association of Seismology and Physics of the Earth's Interior (IASPEI) global heat flow database (www.heatflow.und.edu/index2.html). The data include different items: Item number, descriptive code, name of site, latitude and longitude, elevation, depth interval, number of temperature data, temperature gradient, number of conductivity measurement, average conductivity, number of heat generation measurements, average heat production, heat flow, number of individual sites, references, and date of publication.

The relationship of temperature rise to specific absorption rate and current in the human leg for exposure to electromagnetic radiation in the high frequency band.

PubMed

Wainwright, P R

2003-10-07

Of the biological effects of human exposure to radiofrequency and microwave radiation, the best-established are those due to elevation of tissue temperature. To prevent harmful levels of heating, restrictions have been proposed on the specific absorption rate (SAR). However, the relationship between SAR and temperature rise is not an invariant, since not only the heat capacity but also the efficiency of heat dissipation varies between different tissues and exposure scenarios. For small enough SAR, the relationship is linear and may be characterized by a 'heating factor' deltaT/SAR. Under whole-body irradiation the SAR may be particularly high in the ankles due to the concentration of current flowing through a relatively small cross-sectional area. In a previous paper, the author has presented calculations of the SAR distribution in a human leg in the high frequency (HF) band. In this paper, the heating factor for this situation is derived using a finite element approximation of the Pennes bioheat equation. The sensitivity of the results to different blood perfusion rates is investigated, and a simple local thermoregulatory model is applied. Both time-dependent and steady-state solutions are considered. Results confirm the appropriateness of the ICNIRP reference level of 100 mA on current through the leg, but suggest that at higher currents significant thermoregulatory adjustments to muscle blood flow will occur.

A hierarchy for modeling high speed propulsion systems

NASA Technical Reports Server (NTRS)

Hartley, Tom T.; Deabreu, Alex

1991-01-01

General research efforts on reduced order propulsion models for control systems design are overviewed. Methods for modeling high speed propulsion systems are discussed including internal flow propulsion systems that do not contain rotating machinery, such as inlets, ramjets, and scramjets. The discussion is separated into four areas: (1) computational fluid dynamics models for the entire nonlinear system or high order nonlinear models; (2) high order linearized models derived from fundamental physics; (3) low order linear models obtained from the other high order models; and (4) low order nonlinear models (order here refers to the number of dynamic states). Included in the discussion are any special considerations based on the relevant control system designs. The methods discussed are for the quasi-one-dimensional Euler equations of gasdynamic flow. The essential nonlinear features represented are large amplitude nonlinear waves, including moving normal shocks, hammershocks, simple subsonic combustion via heat addition, temperature dependent gases, detonations, and thermal choking. The report also contains a comprehensive list of papers and theses generated by this grant.

Computational manipulation of a radiative MHD flow with Hall current and chemical reaction in the presence of rotating fluid

NASA Astrophysics Data System (ADS)

Alias Suba, Subbu; Muthucumaraswamy, R.

2018-04-01

A numerical analysis of transient radiative MHD(MagnetoHydroDynamic) natural convective flow of a viscous, incompressible, electrically conducting and rotating fluid along a semi-infinite isothermal vertical plate is carried out taking into consideration Hall current, rotation and first order chemical reaction.The coupled non-linear partial differential equations are expressed in difference form using implicit finite difference scheme. The difference equations are then reduced to a system of linear algebraic equations with a tri-diagonal structure which is solved by Thomas Algorithm. The primary and secondary velocity profiles, temperature profile, concentration profile, skin friction, Nusselt number and Sherwood Number are depicted graphically for a range of values of rotation parameter, Hall parameter,magnetic parameter, chemical reaction parameter, radiation parameter, Prandtl number and Schmidt number.It is recognized that rate of heat transfer and rate of mass transfer decrease with increase in time but they increase with increasing values of radiation parameter and Schmidt number respectively.

Numerical treatment for Carreau nanofluid flow over a porous nonlinear stretching surface

NASA Astrophysics Data System (ADS)

Eid, Mohamed R.; Mahny, Kasseb L.; Muhammad, Taseer; Sheikholeslami, Mohsen

2018-03-01

The impact of magnetic field and nanoparticles on the two-phase flow of a generalized non-Newtonian Carreau fluid over permeable non-linearly stretching surface has been analyzed in the existence of all suction/injection and thermal radiation. The governing PDEs with congruous boundary condition are transformed into a system of non-linear ODEs with appropriate boundary conditions by using similarity transformation. It solved numerically by using 4th-5th order Runge-Kutta-Fehlberg method based on shooting technique. The impacts of non-dimensional controlling parameters on velocity, temperature, and nanoparticles volume concentration profiles are scrutinized with aid of graphs. The Nusselt and the Sherwood numbers are studied at the different situations of the governing parameters. The numerical computations are in excellent consent with previously reported studies. It is found that the heat transfer rate is reduced with an increment of thermal radiation parameter and on contrary of the rising of magnetic field. The opposite trend happens in the mass transfer rate.

First Simulations of a Collisional Two-Stream Instability in the Chromosphere

NASA Astrophysics Data System (ADS)

Oppenheim, Meers; Dimant, Yakov; Madsen, Chad Allen; Fontenla, Juan

2014-06-01

Observations and modeling shows that immediately above the temperature minimum in the solar atmosphere, a steep rise from below 4,000 K to over 6,000K occurs. Recent papers show that a collisional two-stream plasma instability called the Farley-Buneman Instability can develop at the altitudes where this increase occurs. This instability may play an important role in transferring energy from turbulent neutral flows originating in the photosphere to the mid-chromosphere in the form of heat. Plasma turbulence resulting from this instability could account for some or most of this intense chromospheric heating. This paper presents a set of simulations showing the development and evolution of the Farley-Buneman Instability (FBI) applicable to the chromosphere. It compares these results with the better-understood ionospheric FBI. It examines the linear behavior and the dependence of growth rates for a range of altitudes and driving flows. It also presents the first study of FBI driven plasma nonlinearities and turbulence in the chromosphere. This research should help us evaluate the FBI as a mechanism to convert neutral flow and turbulence energy into electron thermal energy in the quiet Sun.

Present-day heat flow model of Mars

PubMed Central

Parro, Laura M.; Jiménez-Díaz, Alberto; Mansilla, Federico; Ruiz, Javier

2017-01-01

Until the acquisition of in-situ measurements, the study of the present-day heat flow of Mars must rely on indirect methods, mainly based on the relation between the thermal state of the lithosphere and its mechanical strength, or on theoretical models of internal evolution. Here, we present a first-order global model for the present-day surface heat flow for Mars, based on the radiogenic heat production of the crust and mantle, on scaling of heat flow variations arising from crustal thickness and topography variations, and on the heat flow derived from the effective elastic thickness of the lithosphere beneath the North Polar Region. Our preferred model finds heat flows varying between 14 and 25 mW m−2, with an average value of 19 mW m−2. Similar results (although about ten percent higher) are obtained if we use heat flow based on the lithospheric strength of the South Polar Region. Moreover, expressing our results in terms of the Urey ratio (the ratio between total internal heat production and total heat loss through the surface), we estimate values close to 0.7–0.75, which indicates a moderate contribution of secular cooling to the heat flow of Mars (consistent with the low heat flow values deduced from lithosphere strength), unless heat-producing elements abundances for Mars are subchondritic. PMID:28367996

Internal transport barrier triggered by non-linear lower hybrid wave deposition under condition of beam-driven toroidal rotation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Q. D., E-mail: qgao@swip.ac.cn; Budny, R. V.

2015-03-15

By using gyro-Landau fluid transport model (GLF23), time-dependent integrated modeling is carried out using TRANSP to explore the dynamic process of internal transport barrier (ITB) formation in the neutral beam heating discharges. When the current profile is controlled by LHCD (lower hybrid current drive), with appropriate neutral beam injection, the nonlinear interplay between the transport determined gradients in the plasma temperature (T{sub i,e}) and toroidal velocity (V{sub ϕ}) and the E×B flow shear (including q-profile) produces transport bifurcations, generating spontaneously a stepwise growing ITB. In the discharge, the constraints imposed by the wave propagation condition causes interplay of the LHmore » driven current distribution with the plasma configuration modification, which constitutes non-linearity in the LH wave deposition. The non-linear effects cause bifurcation in LHCD, generating two distinct quasi-stationary reversed magnetic shear configurations. The change of current profile during the transition period between the two quasi-stationary states results in increase of the E×B shearing flow arising from toroidal rotation. The turbulence transport suppression by sheared E×B flow during the ITB development is analysed, and the temporal evolution of some parameters characterized the plasma confinement is examined. Ample evidence shows that onset of the ITB development is correlated with the enhancement of E×B shearing rate caused by the bifurcation in LHCD. It is suggested that the ITB triggering is associated with the non-linear effects of the LH power deposition.« less

Two-phase flow patterns of a top heat mode closed loop oscillating heat pipe with check valves (THMCLOHP/CV)

NASA Astrophysics Data System (ADS)

Thongdaeng, S.; Bubphachot, B.; Rittidech, S.

2016-11-01

This research is aimed at studying the two-phase flow pattern of a top heat mode closed loop oscillating heat pipe with check valves. The working fluids used are ethanol and R141b and R11 coolants with a filling ratio of 50% of the total volume. It is found that the maximum heat flux occurs for the R11 coolant used as the working fluid in the case with the inner diameter of 1.8 mm, inclination angle of -90°, evaporator temperature of 125°C, and evaporator length of 50 mm. The internal flow patterns are found to be slug flow/disperse bubble flow/annular flow, slug flow/disperse bubble flow/churn flow, slug flow/bubble flow/annular flow, slug flow/disperse bubble flow, bubble flow/annular flow, and slug flow/annular flow.

Effects of microscale inertia on heat or mass transfer from a drop

NASA Astrophysics Data System (ADS)

Krishnamurthy, Deepak; Subramanian, Ganesh

2012-11-01

Heat or mass transport from suspensions of solid particles or drops is ubiquitous in many industrial processes. In the zero inertia limit the transport is diffusion limited owing to the presence of closed streamlines around each particle. A small but finite amount of inertia though, results in a vastly different picture, greatly enhancing transport by destroying the closed streamline configuration. We develop a theoretical formulation to study the effects of weak inertia on transport from a density-matched drop in a 2D linear flow. It is shown that, unlike a solid particle, the near-surface streamlines are closed only when the viscosity ratio (λ) exceeds a critical value λc = 2 α / (1- α) , where α is the linear flow parameter measuring relative magnitudes of extension and vorticity. The velocity field on the drop surface can be characterized using a complex-valued analogue of the (C, τ) coordinate system used to describe Jeffrey orbits of an axisymmetric particle. In the open-streamline case (λ < λ c) , convective transport occurs even with zero inertia, and for large Peclet number (Pe) (the relative magnitude of convective to diffusive transport), the Nusselt number (dimensionless rate of heat transfer) is expected to scale as F(α, λ) Pe1/2 and is determined via a boundary layer analysis in the (C, τ) coordinate system. In the closed streamline case (λ > λ c) , similar to the solid particle, inertia plays a crucial role, and the Nusselt number must scale as G(α, λ)Re1/2Pe1/2. A methodology is developed to analyze the convection along spiraling streamlines using a physically motivated choice of coordinate system on the drop surface.

Coupled thermal stresses analysis in the composite elastic-plastic cylinder

NASA Astrophysics Data System (ADS)

Murashkin, E. V.; Dats, E. P.

2018-04-01

The present study is devoted to the set of boundary value problems in the frameworks of coupled thermoelastoplasticity under axial symmetry conditions for a composite circular cylinder. Throughout the paper the conventional Prandtl–Reuss elastic–plastic model generalised on the thermal effects is used. The yield stress is assumed by linear function of the temperature. The plastic potential is chosen in the form of Tresca yield criterion and the associated plastic flow rule is derived. The adding process of a heated cylinder to another is simulated. The coupled thermal stresses are calculated during processes of cooling and material unloading. The elastic-plastic borders positions are calculated and plastic flow domains are localized. Numerical results are graphically analysed.

Optimizing parameters of GTU cycle and design values of air-gas channel in a gas turbine with cooled nozzle and rotor blades

NASA Astrophysics Data System (ADS)

Kler, A. M.; Zakharov, Yu. B.

2012-09-01

The authors have formulated the problem of joint optimization of pressure and temperature of combustion products before gas turbine, profiles of nozzle and rotor blades of gas turbine, and cooling air flow rates through nozzle and rotor blades. The article offers an original approach to optimization of profiles of gas turbine blades where the optimized profiles are presented as linear combinations of preliminarily formed basic profiles. The given examples relate to optimization of the gas turbine unit on the criterion of power efficiency at preliminary heat removal from air flows supplied for the air-gas channel cooling and without such removal.

Oceanic lithosphere and asthenosphere: The thermal and mechanical structure

NASA Technical Reports Server (NTRS)

Schubert, G.; Froidevaux, C.; Yuen, D. A.

1976-01-01

A coupled thermal and mechanical solid state model of the oceanic lithosphere and asthenosphere is presented. The model includes vertical conduction of heat with a temperature dependent thermal conductivity, horizontal and vertical advection of heat, viscous dissipation or shear heating, and linear or nonlinear deformation mechanisms with temperature and pressure dependent constitutive relations between shear stress and strain rate. A constant horizontal velocity u sub 0 and temperature t sub 0 at the surface and zero horizontal velocity and constant temperature t sub infinity at great depth are required. In addition to numerical values of the thermal and mechanical properties of the medium, only the values of u sub 0, t sub 0 and t sub infinity are specified. The model determines the depth and age dependent temperature horizontal and vertical velocity, and viscosity structures of the lithosphere and asthenosphere. In particular, ocean floor topography, oceanic heat flow, and lithosphere thickness are deduced as functions of the age of the ocean floor.

Passive containment cooling system

DOEpatents

Conway, Lawrence E.; Stewart, William A.

1991-01-01

A containment cooling system utilizes a naturally induced air flow and a gravity flow of water over the containment shell which encloses a reactor core to cool reactor core decay heat in two stages. When core decay heat is greatest, the water and air flow combine to provide adequate evaporative cooling as heat from within the containment is transferred to the water flowing over the same. The water is heated by heat transfer and then evaporated and removed by the air flow. After an initial period of about three to four days when core decay heat is greatest, air flow alone is sufficient to cool the containment.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burns, Erick R.; Williams, Colin F.; Ingebritsen, Steven E.

Heat-flow mapping of the western USA has identified an apparent low-heat-flow anomaly coincident with the Columbia Plateau Regional Aquifer System, a thick sequence of basalt aquifers within the Columbia River Basalt Group (CRBG). A heat and mass transport model (SUTRA) was used to evaluate the potential impact of groundwater flow on heat flow along two different regional groundwater flow paths. Limited in situ permeability (k) data from the CRBG are compatible with a steep permeability decrease (approximately 3.5 orders of magnitude) at 600–900 m depth and approximately 40°C. Numerical simulations incorporating this permeability decrease demonstrate that regional groundwater flow canmore » explain lower-than-expected heat flow in these highly anisotropic (kx/kz ~ 104) continental flood basalts. Simulation results indicate that the abrupt reduction in permeability at approximately 600 m depth results in an equivalently abrupt transition from a shallow region where heat flow is affected by groundwater flow to a deeper region of conduction-dominated heat flow. Most existing heat-flow measurements within the CRBG are from shallower than 600 m depth or near regional groundwater discharge zones, so that heat-flow maps generated using these data are likely influenced by groundwater flow. Substantial k decreases at similar temperatures have also been observed in the volcanic rocks of the adjacent Cascade Range volcanic arc and at Kilauea Volcano, Hawaii, where they result from low-temperature hydrothermal alteration.« less

Heat Transfer and Flow on the Squealer Tip of a Gas Turbine Blade

NASA Technical Reports Server (NTRS)

Azad, Gm S.; Han, Je-Chin; Boyle, Robert J.

2000-01-01

Experimental investigations are performed to measure the detailed heat transfer coefficient and static pressure distributions on the squealer tip of a gas turbine blade in a five-bladed stationary linear cascade. The blade is a 2-dimensional model of a modem first stage gas turbine rotor blade with a blade tip profile of a GE-E(sup 3) aircraft gas turbine engine rotor blade. A squealer (recessed) tip with a 3.77% recess is considered here. The data on the squealer tip are also compared with a flat tip case. All measurements are made at three different tip gap clearances of about 1%, 1.5%, and 2.5% of the blade span. Two different turbulence intensities of 6.1% and 9.7% at the cascade inlet are also considered for heat transfer measurements. Static pressure measurements are made in the mid-span and near-tip regions, as well as on the shroud surface opposite to the blade tip surface. The flow condition in the test cascade corresponds to an overall pressure ratio of 1.32 and an exit Reynolds number based on the axial chord of 1.1 x 10(exp 6). A transient liquid crystal technique is used to measure the heat transfer coefficients. Results show that the heat transfer coefficient on the cavity surface and rim increases with an increase in tip clearance. 'Me heat transfer coefficient on the rim is higher than the cavity surface. The cavity surface has a higher heat transfer coefficient near the leading edge region than the trailing edge region. The heat transfer coefficient on the pressure side rim and trailing edge region is higher at a higher turbulence intensity level of 9.7% over 6.1 % case. However, no significant difference in local heat transfer coefficient is observed inside the cavity and the suction side rim for the two turbulence intensities. The squealer tip blade provides a lower overall heat transfer coefficient when compared to the flat tip blade.

Visualization of various working fluids flow regimes in gravity heat pipe

NASA Astrophysics Data System (ADS)

Nemec, Patrik

Heat pipe is device working with phase changes of working fluid inside hermetically closed pipe at specific pressure. The phase changes of working fluid from fluid to vapour and vice versa help heat pipe to transport high heat flux. Amount of heat flux transferred by heat pipe, of course depends on kind of working fluid. The article deal about visualization of various working fluids flow regimes in glass gravity heat pipe by high speed camera and processes casing inside during heat pipe operation. Experiment working fluid flow visualization is performed with two glass heat pipes with different inner diameter (13 mm and 22 mm) filled with water, ethanol and fluorinert FC 72. The working fluid flow visualization explains the phenomena as a working fluid boiling, nucleation of bubbles, and vapour condensation on the wall, vapour and condensate flow interaction, flow down condensate film thickness on the wall occurred during the heat pipe operation.

Earthquake Cycle Simulations with Rate-and-State Friction and Linear and Nonlinear Viscoelasticity

NASA Astrophysics Data System (ADS)

Allison, K. L.; Dunham, E. M.

2016-12-01

We have implemented a parallel code that simultaneously models both rate-and-state friction on a strike-slip fault and off-fault viscoelastic deformation throughout the earthquake cycle in 2D. Because we allow fault slip to evolve with a rate-and-state friction law and do not impose the depth of the brittle-to-ductile transition, we are able to address: the physical processes limiting the depth of large ruptures (with hazard implications); the degree of strain localization with depth; the relative partitioning of fault slip and viscous deformation in the brittle-to-ductile transition zone; and the relative contributions of afterslip and viscous flow to postseismic surface deformation. The method uses a discretization that accommodates variable off-fault material properties, depth-dependent frictional properties, and linear and nonlinear viscoelastic rheologies. All phases of the earthquake cycle are modeled, allowing the model to spontaneously generate earthquakes, and to capture afterslip and postseismic viscous flow. We compare the effects of a linear Maxwell rheology, often used in geodetic models, with those of a nonlinear power law rheology, which laboratory data indicates more accurately represents the lower crust and upper mantle. The viscosity of the Maxwell rheology is set by power law rheological parameters with an assumed a geotherm and strain rate, producing a viscosity that exponentially decays with depth and is constant in time. In contrast, the power law rheology will evolve an effective viscosity that is a function of the temperature profile and the stress state, and therefore varies both spatially and temporally. We will also integrate the energy equation for the thermomechanical problem, capturing frictional heat generation on the fault and off-fault viscous shear heating, and allowing these in turn to alter the effective viscosity.

Ion Heating and Flows in a High Power Helicon Source

NASA Astrophysics Data System (ADS)

Scime, Earl; Agnello, Riccardo; Furno, Ivo; Howling, Alan; Jacquier, Remy; Plyushchev, Gennady; Thompson, Derek

2017-10-01

We report experimental measurements of ion temperatures and flows in a high power, linear, magnetized, helicon plasma device, the Resonant Antenna Ion Device (RAID). RAID is equipped with a high power helicon source. Parallel and perpendicular ion temperatures on the order of 0.6 eV are observed for an rf power of 4 kW, suggesting that higher power helicon sources should attain ion temperatures in excess of 1 eV. The unique RAID antenna design produces broad, uniform plasma density and perpendicular ion temperature radial profiles. Measurements of the azimuthal flow indicate rigid body rotation of the plasma column of a few kHz. When configured with an expanding magnetic field, modest parallel ion flows are observed in the expansion region. The ion flows and temperatures are derived from laser induced fluorescence measurements of the Doppler resolved velocity distribution functions of argon ions. This work supported by U.S. National Science Foundation Grant No. PHY-1360278.

Non-linear dual-phase-lag model for analyzing heat transfer phenomena in living tissues during thermal ablation.

PubMed

Kumar, P; Kumar, Dinesh; Rai, K N

2016-08-01

In this article, a non-linear dual-phase-lag (DPL) bio-heat transfer model based on temperature dependent metabolic heat generation rate is derived to analyze the heat transfer phenomena in living tissues during thermal ablation treatment. The numerical solution of the present non-linear problem has been done by finite element Runge-Kutta (4,5) method which combines the essence of Runge-Kutta (4,5) method together with finite difference scheme. Our study demonstrates that at the thermal ablation position temperature predicted by non-linear and linear DPL models show significant differences. A comparison has been made among non-linear DPL, thermal wave and Pennes model and it has been found that non-linear DPL and thermal wave bio-heat model show almost same nature whereas non-linear Pennes model shows significantly different temperature profile at the initial stage of thermal ablation treatment. The effect of Fourier number and Vernotte number (relaxation Fourier number) on temperature profile in presence and absence of externally applied heat source has been studied in detail and it has been observed that the presence of externally applied heat source term highly affects the efficiency of thermal treatment method. Copyright © 2016 Elsevier Ltd. All rights reserved.

Capillary hydrodynamics and transport processes during phase change in microscale systems

NASA Astrophysics Data System (ADS)

Kuznetsov, V. V.

2017-09-01

The characteristics of two-phase gas-liquid flow and heat transfer during flow boiling and condensing in micro-scale heat exchangers are discussed in this paper. The results of numerical simulation of the evaporating liquid film flowing downward in rectangular minichannel of the two-phase compact heat exchanger are presented and the peculiarities of microscale heat transport in annular flow with phase changes are discussed. Presented model accounts the capillarity induced transverse flow of liquid and predicts the microscale heat transport processes when the nucleate boiling becomes suppressed. The simultaneous influence of the forced convection, nucleate boiling and liquid film evaporation during flow boiling in plate-fin heat exchangers is considered. The equation for prediction of the flow boiling heat transfer at low flux conditions is presented and verified using experimental data.

Three-dimensional analysis for liquid hydrogen in a cryogenic storage tank with heat pipe pump system

NASA Astrophysics Data System (ADS)

Ho, Son H.; Rahman, Muhammad M.

2008-01-01

This paper presents a study on fluid flow and heat transfer of liquid hydrogen in a zero boil-off cryogenic storage tank in a microgravity environment. The storage tank is equipped with an active cooling system consisting of a heat pipe and a pump-nozzle unit. The pump collects cryogen at its inlet and discharges it through its nozzle onto the evaporator section of the heat pipe in order to prevent the cryogen from boiling off due to the heat leaking through the tank wall from the surroundings. A three-dimensional (3-D) finite element model is employed in a set of numerical simulations to solve for velocity and temperature fields of liquid hydrogen in steady state. Complex structures of 3-D velocity and temperature distributions determined from the model are presented. Simulations with an axisymmetric model were also performed for comparison. Parametric study results from both models predict that as the speed of the cryogenic fluid discharged from the nozzle increases, the mean or bulk cryogenic fluid speed increases linearly and the maximum temperature within the cryogenic fluid decreases.

Heat and fluid flow characteristics of an oval fin-and-tube heat exchanger with large diameters for textile machine dryer

NASA Astrophysics Data System (ADS)

Bae, Kyung Jin; Cha, Dong An; Kwon, Oh Kyung

2016-11-01

The objectives of this paper are to develop correlations between heat transfer and pressure drop for oval finned-tube heat exchanger with large diameters (larger than 20 mm) used in a textile machine dryer. Numerical tests using ANSYS CFX are performed for four different parameters; tube size, fin pitch, transverse tube pitch and longitudinal tube pitch. The numerical results showed that the Nusselt number and the friction factor are in a range of -16.2 ~ +3.1 to -7.7 ~ +3.9 %, respectively, compared with experimental results. It was found that the Nusselt number linearly increased with increasing Reynolds number, but the friction factor slightly decreased with increasing Reynolds number. It was also found that the variation of longitudinal tube pitch has little effect on the Nusselt number and friction factor than other parameters (below 2.0 and 2.5 %, respectively). This study proposed a new Nusselt number and friction factor correlation of the oval finned-tube heat exchanger with large diameters for textile machine dryer.

An experimental study of the validity of the heat-field concept for sonic-boom alleviation

NASA Technical Reports Server (NTRS)

Swigart, R. J.

1974-01-01

An experimental program was carried out in the NASA-Langley 4 ft x 4 ft supersonic pressure tunnel to investigate the validity of the heat-field concept for sonic boom alleviation. The concept involves heating the flow about a supersonic aircraft in such a manner as to obtain an increase in effective aircraft length and yield an effective aircraft shape that will result in a shock-free pressure signature on the ground. First, a basic body-of-revolution representing an SST configuration with its lift equivalence in volume was tested to provide a baseline pressure signature. Second, a model having a 5/2-power area distribution which, according to theory, should yield a linear pressure rise with no front shock wave was tested. Third, the concept of providing the 5/2-power area distribution by using an off-axis slender fin below the basic body was investigated. Then a substantial portion (approximately 40 percent) of the solid fin was replaced by a heat field generated by passing heated nitrogen through the rear of the fin.

Ballistic vs. diffusive heat transfer across nanoscopic films of layered crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shen, Meng; Keblinski, Pawel, E-mail: keblip@rpi.edu

2014-04-14

We use non-equilibrium molecular dynamics to study the heat transfer mechanism across sandwich interfacial structures of Si/n-atomic-layers/Si, with 1 ≤ n ≤ 20 and atomic layers composed of WSe{sub 2} and/or graphene. In the case of WSe{sub 2} sheets, we observe that the thermal resistance of the sandwich structure is increasing almost linearly with the number of WSe{sub 2} sheets, n, indicating a diffusive phonon transport mechanism. By contrast in the case of n graphene layers, the interfacial thermal resistance is more or less independent on the number of layers for 1 ≤ n ≤ 10, and is associated with ballistic phonon transport mechanism. We attribute the diffusivemore » heat transfer mechanism across WSe{sub 2} sheets to abundant low frequency and low group velocity optical modes that carry most of the heat across the interface. By contrast, in graphene, acoustic modes dominate the thermal transport across the interface and render a ballistic heat flow mechanism.« less

Method for the determination of lignin content of a sample by flash pyrolysis in an atmosphere of hydrogen or helium and method therefor

NASA Technical Reports Server (NTRS)

Shakkottai, Parthasarathy (Inventor); Kwack, Eug Y. (Inventor); Lawson, Daniel D. (Inventor)

1991-01-01

The lignin content of wood, paper pulp or other material containing lignin (such as filter paper soaked in black liquor) is more readily determined by flash pyrolysis of the sample at approximately 550.degree. C. in a reducing atmosphere of hydrogen or in an inert atmosphere of helium followed by a rapid analysis of the product gas by a mass spectrometer. The heated pyrolysis unit as fabricated comprises a small platinum cup welded to an electrically-heated stainless steel ribbon with control means for programmed short duration (1.5 sec, approximately) heating and means for continuous flow of hydrogen or helium. The pyrolysis products enter an electron-ionization mode mass spectrometer for spectral evaluation. Lignin content is obtained from certain ratios of integrated ion currents of many mass spectral lines, the ratios being linearly related to the Kappa number of Klason lignin.

Conceptual design for spacelab pool boiling experiment

NASA Technical Reports Server (NTRS)

Lienhard, J. H.; Peck, R. E.

1978-01-01

A pool boiling heat transfer experiment to be incorporated with a larger two-phase flow experiment on Spacelab was designed to confirm (or alter) the results of earth-normal gravity experiments which indicate that the hydrodynamic peak and minimum pool boiling heat fluxes vanish at very low gravity. Twelve small sealed test cells containing water, methanol or Freon 113 and cylindrical heaters of various sizes are to be built. Each cell will be subjected to one or more 45 sec tests in which the surface heat flux on the heaters is increased linearly until the surface temperature reaches a limiting value of 500 C. The entire boiling process will be photographed in slow-motion. Boiling curves will be constructed from thermocouple and electric input data, for comparison with the motion picture records. The conduct of the experiment will require no more than a few hours of operator time.

Topographically driven groundwater flow and the San Andreas heat flow paradox revisited

USGS Publications Warehouse

Saffer, D.M.; Bekins, B.A.; Hickman, S.

2003-01-01

Evidence for a weak San Andreas Fault includes (1) borehole heat flow measurements that show no evidence for a frictionally generated heat flow anomaly and (2) the inferred orientation of ??1 nearly perpendicular to the fault trace. Interpretations of the stress orientation data remain controversial, at least in close proximity to the fault, leading some researchers to hypothesize that the San Andreas Fault is, in fact, strong and that its thermal signature may be removed or redistributed by topographically driven groundwater flow in areas of rugged topography, such as typify the San Andreas Fault system. To evaluate this scenario, we use a steady state, two-dimensional model of coupled heat and fluid flow within cross sections oriented perpendicular to the fault and to the primary regional topography. Our results show that existing heat flow data near Parkfield, California, do not readily discriminate between the expected thermal signature of a strong fault and that of a weak fault. In contrast, for a wide range of groundwater flow scenarios in the Mojave Desert, models that include frictional heat generation along a strong fault are inconsistent with existing heat flow data, suggesting that the San Andreas Fault at this location is indeed weak. In both areas, comparison of modeling results and heat flow data suggest that advective redistribution of heat is minimal. The robust results for the Mojave region demonstrate that topographically driven groundwater flow, at least in two dimensions, is inadequate to obscure the frictionally generated heat flow anomaly from a strong fault. However, our results do not preclude the possibility of transient advective heat transport associated with earthquakes.

Terrestrial heat flow in east and southern Africa

NASA Astrophysics Data System (ADS)

Nyblade, Andrew A.; Pollack, Henry N.; Jones, D. L.; Podmore, Francis; Mushayandebvu, Martin

1990-10-01

We report 26 new heat flow and 13 radiogenic heat production measurements from Zimbabwe, Zambia and Tanzania, together with details and some revisions of 18 previous heat flow measurements by other investigators from Kenya and Tanzania. These measurements come from Archean cratons, Proterozoic mobile belts, and Mesozoic and Cenozoic rifts. Heat flow data from eight new sites in the Archean Zimbabwe Craton are consistent with previous measurements in the Archean Kaapvaal-Zimbabwe Craton and Limpopo Belt (Kalahari Craton) and do not change the mean heat flow of 47±2 mW m-2 (standard error of the mean) in the Kalahari Craton based on 53 previous measurements. Eight new sites in the Archean Tanzania Craton give a mean heat flow of 34±4 mW m-2. The mean heat flow from nine sites in the Proterozoic Mozambique Belt to the east of the Tanzania Craton in Kenya and Tanzania is 47±4 mW m-2. Twelve measurements in the Mesozoic rifted continental margin in east Africa give a mean heat flow of 68±4 mW m-2; four measurements in the Mesozoic Luangwa and Zambezi Rifts range from 44 to 110 mW m-2 with a mean of 76±14 mW m-2. In comparing heat flow in east and southern Africa, we observe a common heat flow pattern of increasing heat flow away from the centers of the Archean cratons. This pattern suggests a fundamental difference in lithospheric thermal structure between the Archean cratons and the Proterozoic and early Paleozoic mobile belts which surround them. Superimposed on this common pattern are two regional variations in heat flow. Heat flow in the Tanzania Craton is lower by about 13 mW m-2 than in the Kalahari Craton, and in the Mozambique Belt in east Africa heat flow is somewhat lower than in the southern African mobile belts at similar distances from the Archean cratonic margin. The two regional variations can be explained in several ways, none of which can as yet be elevated to a preferred status: (1) by variations in crustal heat production, (2) by thin-skinned thrusting of the Mozambique Belt over the Tanzania Cratonic margin, (3) by lateral heat transfer from beneath the rift flanks into the rifts, or (4) by lower mantle heat flow beneath all of eastern Africa prior to the Cenozoic development of the East African rift system.

Interpretation of lunar heat flow data. [for estimating bulk uranium abundance

NASA Technical Reports Server (NTRS)

Conel, J. E.; Morton, J. B.

1975-01-01

Lunar heat flow observations at the Apollo 15 and 17 sites can be interpreted to imply bulk U concentrations for the moon of 5 to 8 times those of normal chondrites and 2 to 4 times terrestrial values inferred from the earth's heat flow and the assumption of thermal steady state between surface heat flow and heat production. A simple model of nearsurface structure that takes into account the large difference in (highly insulating) regolith thickness between mare and highland provinces is considered. This model predicts atypically high local values of heat flow near the margins of mare regions - possibly a factor of 10 or so higher than the global average. A test of the proposed model using multifrequency microwave techniques appears possible wherein heat flow traverse measurements are made across mare-highland contacts. The theoretical considerations discussed here urge caution in attributing global significance to point heat-flow measurements on the moon.

A Preliminary Study on the Circulation of an ocean covering a Synchronously Rotating Planet

NASA Astrophysics Data System (ADS)

Matsuo, H.; Ishiwatari, M.; Takehiro, S.; Hayashi, Y.; Nakajima, K.

2012-12-01

Recently, nearly 800 extrasolar planets have been detected. It seems that some of them present into habitable zone, in which planets can have ocean, and such planets rotate synchronously with their central stars. Ocean is necessary for life, and the circulation makes climate mild by heat transport on the earth. The earth is the only planet that has ocean in the solar system so that it has not been understood what oceanic circulation is like in another planets. The purpose of this study is prediction of oceanic circulation on extrasolar planets by using numerical simulation. As a first step, elementary consideration is made. The planet is almost entirely covered with ocean and whose rotation period corresponds with its orbital period. On synchronously rotating planets, the thermal contrast between day-hemisphere and night-hemisphere would be extreme. However, it may be lessend if there is significant zonal heat transport. The circulation in such conditions has not been known well. We performed a numerical experiment based on the linear shallow water equation, assuming that both the evaporation and the precipitation occur only on day-hemisphere (Noda et al., 2011). With these distributions of the evaporation and the precipitation, one may anticipate the circulation occurs in only day-hemisphere. However, the resulting calculation is characterized with zonally uniform zonal flow, which also covers night hemisphere. In addition, the intensity of the flow increases with time. That behavior can be understood by constructing asymptotic solution which is first degree in time. The importance of Coriolis force, which bends meridional flow to zonal flow, is identified. It is implied that, even when only day-hemisphere has the evaporation and precipitation, there may be significant amount of heat can be transported from the day-hemisphere to the night-hemisphere by the strong zonal flow. The growth of zonal flow would be stopped when the evaporation and the precipitation are balanced with mass transport in the bottom Ekman layer.

Testing paleointensity determinations on recent lava flows and scorias from Miyakejima, Japan

NASA Astrophysics Data System (ADS)

Fukuma, K.

2013-12-01

Still no consensus has been reached on paleointensity method. Even the classical Thellier method has not been fully tested on recent lava flows with known geomagnetic field intensity based on a systematic sampling scheme. In this study, Thellier method was applied for 1983, 1962 and 1940 basaltic lava flows and scorias from Miyakejima, Japan. Several vertical lava sections and quenched scorias, which are quite variable in magnetic mineralogy and grain size, provide an unparalleled opportunity to test paleointensity methods. Thellier experiments were conducted on a completely automated three-component spinner magnetometer with thermal demagnetizer 'tspin'. Specimens were heated in air, applied laboratory field was 45 microT, and pTRM checks were performed at every two heating steps. Curie points and hysteresis properties were obtained on small fragments removed from cylindrical specimens. For lava flows sigmoidal curves were commonly observed on the Arai diagrams. Especially the interior part of lava flows always revealed sigmoidal patterns and sometimes resulted in erroneously blurred behaviors. The directions after zero-field heating were not necessarily stable in the course of the Thellier experiments. It was very difficult, for the interior part, to ascertain linear segments on Arai diagrams corresponding to the geomagnetic field intensity at the eruption. Upper and lower clinker samples also generally revealed sigmoidal or upward concave curves on Arai diagrams. Neither lower nor higher temperature portions of the sigmoids or concaves gave the expected geomagnetic field intensities. However, there were two exceptional cases of lava flows giving correct field intensities: upper clinkers with relatively low unblocking temperatures (< 400 deg.C) and lower clinkers with broad unblocking temperature ranges from room temperature to 600 deg.C. A most promising target for paleointensity experiments within the volcanic rocks is scoria. Scoria samples always carry single Curie temperatures higher than 500 deg.C, and the ratios of saturation remanence to saturation magnetization (Mr/Ms) of about 0.5 are indicative of truly single-domain low-titanium titanomagnetite. Unambiguous straight lines were always observed on Arai diagrams covering broad temperature ranges like the lower clinker samples, and the gradients gave the expected field values within a few percent errors. Thellier experiments applied for the recent lava flows did not successfully recover the expected field intensity from most samples. No linear segment was recognized or incorrect paleointensity values were obtained from short segments with limited temperature ranges. In Thellier or other types of paleointensity experiments laboratory alteration is checked in details, but if a sample once passed the alteration check, the TRM/NRM ratios of any limited temperature or field ranges were accepted as reflecting paleointensity. Previously published paleointensity data from lava flows should include much of such dubious data. Generally lava flows are not suitable for paleointensity determinations in light of its large grain-size and mixed magnetic mineralogy, except for scoria and clinker.

Fluid-cooled heat sink with improved fin areas and efficiencies for use in cooling various devices

DOEpatents

Bharathan, Desikan; Bennion, Kevin; Kelly, Kenneth; Narumanchi, Sreekant

2015-04-21

The disclosure provides a fluid-cooled heat sink having a heat transfer base and a plurality of heat transfer fins in thermal communication with the heat transfer base, where the heat transfer base and the heat transfer fins form a central fluid channel through which a forced or free cooling fluid may flow. The heat transfer pins are arranged around the central fluid channel with a flow space provided between adjacent pins, allowing for some portion of the central fluid channel flow to divert through the flow space. The arrangement reduces the pressure drop of the flow through the fins, optimizes average heat transfer coefficients, reduces contact and fin-pin resistances, and reduces the physical footprint of the heat sink in an operating environment.

Suppression of the sonic heat transfer limit in high-temperature heat pipes

NASA Astrophysics Data System (ADS)

Dobran, Flavio

1989-08-01

The design of high-performance heat pipes requires optimization of heat transfer surfaces and liquid and vapor flow channels to suppress the heat transfer operating limits. In the paper an analytical model of the vapor flow in high-temperature heat pipes is presented, showing that the axial heat transport capacity limited by the sonic heat transfer limit depends on the working fluid, vapor flow area, manner of liquid evaporation into the vapor core of the evaporator, and lengths of the evaporator and adiabatic regions. Limited comparisons of the model predictions with data of the sonic heat transfer limits are shown to be very reasonable, giving credibility to the proposed analytical approach to determine the effect of various parameters on the axial heat transport capacity. Large axial heat transfer rates can be achieved with large vapor flow cross-sectional areas, small lengths of evaporator and adiabatic regions or a vapor flow area increase in these regions, and liquid evaporation in the evaporator normal to the main flow.

Fundamental Studies and Device Development in Beta Silicon Carbide.

DTIC Science & Technology

1987-08-31

2 and Cr exhibited nonlinear I - V characteristics; however, the resistivity to current flow in either voltage direction was small, as seen in the...this material. The nonlinear I - V characteristics previously noted and shown in Fig. 1 for the as-deposited TaSi 2, became linear upon annealing at 1123K...for these three materials. Even after heating at 1473K for 1800 s, the Au-Ta-Al alloy contact showed nonlinear I - V characteristics and possessed a high

Development of an Experimental Test Section for Forcing Unsteady Flow in a Linear Compressor Cascade using Circular Rods

DTIC Science & Technology

2003-03-01

to be moved while the tunnel was running, reducing the need for tunnel shut-down and allowing for thermal equilibrium to be maintained during the high ...rather quickly. However, for the high speed runs, the tunnel heats up greatly, so data cannot be taken until the tunnel reaches thermal steady-state...January 1992. 10. Wilson, David G. and Korakianitis, Theodosius. The Design of High - Efficiency Turbo- machinery and Gas Turbines , 317—322. Upper Saddle

Error compensation for thermally induced errors on a machine tool

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krulewich, D.A.

1996-11-08

Heat flow from internal and external sources and the environment create machine deformations, resulting in positioning errors between the tool and workpiece. There is no industrially accepted method for thermal error compensation. A simple model has been selected that linearly relates discrete temperature measurements to the deflection. The biggest problem is how to locate the temperature sensors and to determine the number of required temperature sensors. This research develops a method to determine the number and location of temperature measurements.

Modelling of the rotational moulding process for the manufacture of plastic products

NASA Astrophysics Data System (ADS)

Khoon, Lim Kok

The present research is mainly focused on two-dimensional non-linear thermal modelling, numerical procedures and software development for the rotational moulding process. The RotoFEM program is developed for the rotational moulding process using finite element procedures. The program is written in the MATLAB environment. The research includes the development of new slip flow models, phase change study, warpage study and process analyses. A new slip flow methodology is derived for the heat transfer problem inside the enclosed rotating mould during the heating stage of the tumbling powder. The methodology enables the discontinuous powder to be modelled by the continuous-based finite element method. The Galerkin Finite Element Method is incorporated with the lumped-parameter system and the coincident node technique in finding the multi-interacting heat transfer solutions inside the mould. Two slip flow models arise from the slip flow methodology; they are SDM (single-layered deposition method) and MDM (multi-layered deposition method). These two models have differences in their thermal description for the internal air energy balance and the computational procedure for the deposition of the molten polymer. The SDM model assumes the macroscopic deposition of the molten polymer bed exists only between the bed and the inner mould surface. On the other hand, the MDM model allows the layer-by-layer deposition of the molten polymer bed macroscopically. In addition, the latter has a more detailed heat transfer description for the internal air inside the mould during the powder heating cycle. In slip flow models, the semi-implicit approach has been introduced to solve the final quasi-equilibrium internal air temperature during the heating cycle. A notable feature of this slip flow methodology is that the slip flow models are capable of producing good results for the internal air at the heating powder stage, without the consideration of the powder movement and changeable powder mass. This makes the modelling of the rotational moulding process much simpler. In the simulation of the cooling stage in rotational moulding, the thermal aspects of the inherent warpage problem and external-internal cooling method have been explored. The predicted internal air temperature profiles have shown that the less apparent crystallization plateau in the experimental internal air in practice could be related to warpage. Various phase change algorithms have been reviewed and compared, and thus the most convenient and considerable effective algorithm is proposed. The dimensional analysis method, expressed by means of dimensionless combinations of physical, boundary, and time variables, is utilized to study the dependence of the key thermal parameters on the processing times of rotational moulding. Lastly, the predicted results have been compared with the experimental results from two different external resources. The predicted temperature profiles of the internal air, oven times and other process conditions are consistent with the available data.

Characterization of Single Phase and Two Phase Heat and Momentum Transport in a Spiraling Radial Inow Microchannel Heat Sink

NASA Astrophysics Data System (ADS)

Ruiz, Maritza

Thermal management of systems under high heat fluxes on the order of hundreds of W/cm2 is important for the safety, performance and lifetime of devices, with innovative cooling technologies leading to improved performance of electronics or concentrating solar photovoltaics. A novel, spiraling radial inflow microchannel heat sink for high flux cooling applications, using a single phase or vaporizing coolant, has demonstrated enhanced heat transfer capabilities. The design of the heat sink provides an inward swirl flow between parallel, coaxial disks that form a microchannel of 1 cm radius and 300 micron channel height with a single inlet and a single outlet. The channel is heated on one side through a conducting copper surface, and is essentially adiabatic on the opposite side to simulate a heat sink scenario for electronics or concentrated photovoltaics cooling. Experimental results on the heat transfer and pressure drop characteristics in the heat sink, using single phase water as a working fluid, revealed heat transfer enhancements due to flow acceleration and induced secondary flows when compared to unidirectional laminar fully developed flow between parallel plates. Additionally, thermal gradients on the surface are small relative to the bulk fluid temperature gain, a beneficial feature for high heat flux cooling applications. Heat flux levels of 113 W/cm2 at a surface temperature of 77 deg C were reached with a ratio of pumping power to heat rate of 0.03%. Analytical models on single phase flow are used to explore the parametric trends of the flow rate and passage geometry on the streamlines and pressure drop through the device. Flow boiling heat transfer and pressure drop characteristics were obtained for this heat sink using water at near atmospheric pressure as the working fluid for inlet subcooling levels ranging from 20 to 80 deg C and mean mass flux levels ranging from 184-716 kg/m. 2s. Flow enhancements similar to singlephase flow were expected, as well as enhancements due to increased buoyant forces on vapor bubbles resulting from centripetal acceleration in the flow which will tend to draw the vapor towards the outlet. This can also aid in the reduction of vapor obstruction of the flow. The flow was identified as transitioning through three regimes as the heat rate was increased: partial subcooled flow boiling, oscillating boiling and fully developed flow boiling. During partial subcooled flow boiling, both forced convective and nucleate boiling effects are important. During oscillating boiling, the system fluctuated between partial subcooled flow boiling and fully developed nucleate boiling. Temperature and pressure oscillations were significant in this regime and are likely due to bubble constriction of flow in the microchannel. This regime of boiling is generally undesirable due to the large oscillations in temperatures and pressure and design constraints should be established to avoid large oscillations from occurring. During fully developed flow boiling, water vapor rapidly leaves the surface and the flow does not sustain large oscillations. Reducing inlet subcooling levels was found to reduce the magnitude of oscillations in the oscillating boiling regime. Additionally, reduced inlet subcooling levels reduced the average surface temperature at the highest heat flux levels tested when heat transfer was dominated by nucleate boiling, yet increased the average surface temperatures at low heat flux levels when heat transfer was dominated by forced convection. Experiments demonstrated heat fluxes up to 301 W/cm. 2at an average surface temperature of 134 deg C under partial subcooled flow boiling conditions. At this peak heat flux, the system required a pumping power to heat rate ratio of 0.01%. This heat flux is 2.4 times the typical values for critical heat flux in pool boiling under similar conditions.

Shape effects of nanoparticles on the squeezed flow between two Riga plates in the presence of thermal radiation

NASA Astrophysics Data System (ADS)

Ahmed, Naveed; Adnan; Khan, Umar; Tauseef Mohyud-Din, Syed; Waheed, Asif

2017-07-01

This paper aims to explore the flow of water saturated with copper nanoparticles of different shapes between parallel Riga plates. The plates are placed horizontally in the coordinate axis. Influence of the linear thermal radiation is also taken into account. The equations governing the flow have been transformed into a nondimensional form by employing a set of similarity transformations. The obtained system is solved analytically (variation-of-parameters method) and numerically (Runge-Kutta scheme). Under certain conditions, a special case of the model is also explored. Furthermore, influences of the physical quantities on velocity and thermal fields are discussed with the graphical aid over the domain of interest. The quantities of engineering and practical interest (skin friction coefficient and local rate of heat transfer) are also explored graphically.

The Sap Flow Dynamics and Response of Hedysarum scoparium to Environmental Factors in Semiarid Northwestern China.

PubMed

Deng, Jifeng; Ding, Guodong; Gao, Guanglei; Wu, Bin; Zhang, Yuqing; Qin, Shugao; Fan, Wenhui

2015-01-01

Hedysarum scoparium is an important, fast-growing and drought-resistant shrub that has been extensively used for grassland restoration and preventing desertification in semiarid regions of northwestern China. The primary objective of this study was to investigate the diurnal and seasonal variations in stem sap flow (Js) and its relation to environmental factors. The stem heat balance method was applied to plants that were approximately 17 years old (with diameters of 25, 16, 13, and 9 mm at ground level and heights of 3.1, 1.8, 1.7 and 1.4 m) and growing under natural conditions. The vertical soil temperature profile (ST), soil surface heat flux (SoilG), volumetric soil moisture content (SWC) and meteorological variables such as solar radiation (Rn), air temperature (Ta), vapour pressure deficit (VPD), wind speed (Ws) relative humidity (RH) and precipitation (P) were simultaneously measured at a meteorological station on site. Results indicated that Js varied regularly during the diurnal and seasonal term. The nocturnal Js was substantial, with a seasonal variation similar to the patterns of daytime Js. The magnitude of Js changed considerably between sunny and rainy days. Redundancy (RDA) and Kendall's tau analysis suggested that daily Js in large plants was more sensitive to environmental factors, and the variation in daily Js during the growing season could be described by a multiple linear regression against environmental variables including Ta, VPD, Ws, RH, ST, and SoilG. While the nocturnal Js in smaller plants was more sensitive to meteorological factors. Ta, VPD, and Ws were significantly correlated with nighttime Js. The hourly nighttime sap flow rate of H. scoparium corresponded closely to Ta and VPD following a non-linear pattern. The results of this study can be used to estimate the transpiration of H. scoparium.

Crustal heat production and estimate of terrestrial heat flow in central East Antarctica, with implications for thermal input to the East Antarctic ice sheet

NASA Astrophysics Data System (ADS)

Goodge, John W.

2018-02-01

Terrestrial heat flow is a critical first-order factor governing the thermal condition and, therefore, mechanical stability of Antarctic ice sheets, yet heat flow across Antarctica is poorly known. Previous estimates of terrestrial heat flow in East Antarctica come from inversion of seismic and magnetic geophysical data, by modeling temperature profiles in ice boreholes, and by calculation from heat production values reported for exposed bedrock. Although accurate estimates of surface heat flow are important as an input parameter for ice-sheet growth and stability models, there are no direct measurements of terrestrial heat flow in East Antarctica coupled to either subglacial sediment or bedrock. As has been done with bedrock exposed along coastal margins and in rare inland outcrops, valuable estimates of heat flow in central East Antarctica can be extrapolated from heat production determined by the geochemical composition of glacial rock clasts eroded from the continental interior. In this study, U, Th, and K concentrations in a suite of Proterozoic (1.2-2.0 Ga) granitoids sourced within the Byrd and Nimrod glacial drainages of central East Antarctica indicate average upper crustal heat production (Ho) of about 2.6 ± 1.9 µW m-3. Assuming typical mantle and lower crustal heat flux for stable continental shields, and a length scale for the distribution of heat production in the upper crust, the heat production values determined for individual samples yield estimates of surface heat flow (qo) ranging from 33 to 84 mW m-2 and an average of 48.0 ± 13.6 mW m-2. Estimates of heat production obtained for this suite of glacially sourced granitoids therefore indicate that the interior of the East Antarctic ice sheet is underlain in part by Proterozoic continental lithosphere with an average surface heat flow, providing constraints on both geodynamic history and ice-sheet stability. The ages and geothermal characteristics of the granites indicate that crust in central East Antarctica resembles that in the Proterozoic Arunta and Tennant Creek inliers of Australia but is dissimilar to other areas like the Central Australian Heat Flow Province that are characterized by anomalously high heat flow. Age variation within the sample suite indicates that central East Antarctic lithosphere is heterogeneous, yet the average heat production and heat flow of four age subgroups cluster around the group mean, indicating minor variation in the thermal contribution to the overlying ice sheet from upper crustal heat production. Despite these minor differences, ice-sheet models may favor a geologically realistic input of crustal heat flow represented by the distribution of ages and geothermal characteristics found in these glacial clasts.

Lead Coolant Test Facility Systems Design, Thermal Hydraulic Analysis and Cost Estimate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soli Khericha; Edwin Harvego; John Svoboda

2012-01-01

The Idaho National Laboratory prepared a preliminary technical and functional requirements (T&FR), thermal hydraulic design and cost estimate for a lead coolant test facility. The purpose of this small scale facility is to simulate lead coolant fast reactor (LFR) coolant flow in an open lattice geometry core using seven electrical rods and liquid lead or lead-bismuth eutectic coolant. Based on review of current world lead or lead-bismuth test facilities and research needs listed in the Generation IV Roadmap, five broad areas of requirements were identified as listed: (1) Develop and Demonstrate Feasibility of Submerged Heat Exchanger; (2) Develop and Demonstratemore » Open-lattice Flow in Electrically Heated Core; (3) Develop and Demonstrate Chemistry Control; (4) Demonstrate Safe Operation; and (5) Provision for Future Testing. This paper discusses the preliminary design of systems, thermal hydraulic analysis, and simplified cost estimate. The facility thermal hydraulic design is based on the maximum simulated core power using seven electrical heater rods of 420 kW; average linear heat generation rate of 300 W/cm. The core inlet temperature for liquid lead or Pb/Bi eutectic is 4200 C. The design includes approximately seventy-five data measurements such as pressure, temperature, and flow rates. The preliminary estimated cost of construction of the facility is $3.7M (in 2006 $). It is also estimated that the facility will require two years to be constructed and ready for operation.« less

Experimental determination of the key heat transfer mechanisms in pharmaceutical freeze-drying.

PubMed

Ganguly, Arnab; Nail, Steven L; Alexeenko, Alina

2013-05-01

The study is aimed at quantifying the relative contribution of key heat transfer modes in lyophilization. Measurements of vial heat transfer rates in a laboratory-scale freeze-dryer were performed using pure water, which was partially sublimed under various conditions. The separation distance between the shelf and the vial was systematically varied, and sublimation rates were determined gravimetrically. The heat transfer rates were observed to be independent of separation distance between the vial and the shelf and linearly dependent on pressure in the free molecular flow limit, realized at low pressures (<50 mTorr). However, under higher pressures (>120 mTorr), heat transfer rates were independent of pressure and inversely proportional to separation distance. Previous heat transfer studies in conventional freeze-drying cycles have attributed a dominant portion of the total heat transfer to radiation, the rest to conduction, whereas convection has been found to be insignificant. Although the measurements reported here confirm the significance of the radiative and gas conduction components, the convective component has been found to be comparable to the gas conduction contribution at pressures greater than 100 mTorr. The current investigation supports the conclusion that the convective component of the heat transfer cannot be ignored in typical laboratory-scale freeze-drying conditions. Copyright © 2013 Wiley Periodicals, Inc.

Rapid heat-flowing surveying of geothermal areas, utilizing individual snowfalls as calorimeters

USGS Publications Warehouse

White, Donald E.

1969-01-01

Local differences in rate of heat transfer in vapor and by conduction through the ground in hot spring areas are difficult and time-consuming to measure quantitatively. Individual heavy snowfalls provide a rapid low-cost means of measuring total heat flow from such ground. After a favorable snowfall (heavy, brief duration, little wind, air temperature near 0°C), contacts between snow-covered and snow-free ground are mapped on a suitable base. Each mapped contact, as time elapses after a specific snowfall, is a heat-flow contour representing a decreasing rate of flow. Calibration of each mapped contact or snow line is made possible by the fact that snow remains on insulated surfaces (such as the boardwalks of Yellowstone's thermal areas) long after it has melted on adjacent warm ground. Heat-flow contours mapped to date range from 450 to 5500 μcal/cm2 sec, or 300 to 3700 times the world average of conductive heat flow. The very high rates of heat flow (2000 to > 10,000 μcal/cm2 sec) are probably too high, and the lower heat flows determinable by the method (2 sec) may be too low. Values indicated by the method are, however, probably within a factor of 2 of the total conductive and convective heat flow. Thermal anomalies from infrared imagery are similar in shape to heat-flow contours of a test area near Old Faithful geyser. Snowfall calorimetry provides a rapid means for evaluating the imagery and computer-derived products of the infrared data in terms of heat flow.

Systematic heat flow measurements across the Wagner Basin, northern Gulf of California

NASA Astrophysics Data System (ADS)

Neumann, Florian; Negrete-Aranda, Raquel; Harris, Robert N.; Contreras, Juan; Sclater, John G.; González-Fernández, Antonio

2017-12-01

A primary control on the geodynamics of rifting is the thermal regime. To better understand the geodynamics of rifting in the northern Gulf of California we systematically measured heat-flow across the Wagner Basin, a tectonically active basin that lies near the southern terminus of the Cerro Prieto fault. The heat flow profile is 40 km long, has a nominal measurement spacing of ∼1 km, and is collocated with a seismic reflection profile. Heat flow measurements were made with a 6.5-m violin-bow probe. Although heat flow data were collected in shallow water, where there are significant temporal variations in bottom water temperature, we use CTD data collected over many years to correct our measurements to yield accurate values of heat flow. After correction for bottom water temperature, the mean and standard deviation of heat flow across the western, central, and eastern parts of the basin are 220 ± 60, 99 ± 14, 889 ± 419 mW m-2, respectively. Corrections for sedimentation would increase measured heat flow across the central part of basin by 40 to 60%. We interpret the relatively high heat flow and large variability on the western and eastern flanks in terms of upward fluid flow at depth below the seafloor, whereas the lower and more consistent values across the central part of the basin are suggestive of conductive heat transfer. Moreover, heat flow across the central basin is consistent with gabbroic underplating at a depth of 15 km and suggests that continental rupture here has not gone to completion.

Comparison of forced-air warming systems with upper body blankets using a copper manikin of the human body.

PubMed

Bräuer, A; English, M J M; Steinmetz, N; Lorenz, N; Perl, T; Braun, U; Weyland, W

2002-09-01

Forced-air warming with upper body blankets has gained high acceptance as a measure for the prevention of intraoperative hypothermia. However, data on heat transfer with upper body blankets are not yet available. This study was conducted to determine the heat transfer efficacy of eight complete upper body warming systems and to gain more insight into the principles of forced-air warming. Heat transfer of forced-air warmers can be described as follows: Qdot;=h. DeltaT. A, where Qdot;= heat flux [W], h=heat exchange coefficient [W m-2 degrees C-1], DeltaT=temperature gradient between the blanket and surface [ degrees C], and A=covered area [m2]. We tested eight different forced-air warming systems: (1) Bair Hugger and upper body blanket (Augustine Medical Inc. Eden Prairie, MN); (2) Thermacare and upper body blanket (Gaymar Industries, Orchard Park, NY); (3) Thermacare (Gaymar Industries) with reusable Optisan upper body blanket (Willy Rüsch AG, Kernen, Germany); (4) WarmAir and upper body blanket (Cincinnati Sub-Zero Products, Cincinnati, OH); (5) Warm-Gard and single use upper body blanket (Luis Gibeck AB, Upplands Väsby, Sweden); (6) Warm-Gard and reusable upper body blanket (Luis Gibeck AB); (7) WarmTouch and CareDrape upper body blanket (Mallinckrodt Medical Inc., St. Luis, MO); and (8) WarmTouch and reusable MultiCover trade mark upper body blanket (Mallinckrodt Medical Inc.) on a previously validated copper manikin of the human body. Heat flux and surface temperature were measured with 11 calibrated heat flux transducers. Blanket temperature was measured using 11 thermocouples. The temperature gradient between the blanket and surface (DeltaT) was varied between -8 and +8 degrees C, and h was determined by linear regression analysis as the slope of DeltaT vs. heat flux. Mean DeltaT was determined for surface temperatures between 36 and 38 degrees C, as similar mean skin surface temperatures have been found in volunteers. The covered area was estimated to be 0.35 m2. Total heat flow from the blanket to the manikin was different for surface temperatures between 36 and 38 degrees C. At a surface temperature of 36 degrees C the heat flows were higher (4-26.6 W) than at surface temperatures of 38 degrees C (2.6-18.1 W). The highest total heat flow was delivered by the WarmTouch trade mark system with the CareDrape trade mark upper body blanket (18.1-26.6 W). The lowest total heat flow was delivered by the Warm-Gard system with the single use upper body blanket (2.6-4 W). The heat exchange coefficient varied between 15.1 and 36.2 W m-2 degrees C-1, and mean DeltaT varied between 0.5 and 3.3 degrees C. We found total heat flows of 2.6-26.6 W by forced-air warming systems with upper body blankets. However, the changes in heat balance by forced-air warming systems with upper body blankets are larger, as these systems are not only transferring heat to the body but are also reducing heat losses from the covered area to zero. Converting heat losses of approximately 37.8 W to heat gain, results in a 40.4-64.4 W change in heat balance. The differences between the systems result from different heat exchange coefficients and different mean temperature gradients. However, the combination of a high heat exchange coefficient with a high mean temperature gradient is rare. This fact offers some possibility to improve these systems.

Post-Dryout Heat Transfer to a Refrigerant Flowing in Horizontal Evaporator Tubes

NASA Astrophysics Data System (ADS)

Mori, Hideo; Yoshida, Suguru; Kakimoto, Yasushi; Ohishi, Katsumi; Fukuda, Kenichi

Studies of the post-dryout heat transfer were made based on the experimental data for HFC-134a flowing in horizontal smooth and spiral1y grooved (micro-fin) tubes and the characteristics of the post-dryout heat transfer were c1arified. The heat transfer coefficient at medium and high mass flow rates in the smooth tube was lower than the single-phase heat transfer coefficient of the superheated vapor flow, of which mass flow rate was given on the assumption that the flow was in a thermodynamic equilibrium. A prediction method of post-dryout heat transfer coefficient was developed to reproduce the measurement satisfactorily for the smooth tube. The post dryout heat transfer in the micro-fin tube can be regarded approximately as a superheated vapor single-phase heat transfer.

Fluid-cooled heat sink for use in cooling various devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bharathan, Desikan; Bennion, Kevin; Kelly, Kenneth

The disclosure provides a fluid-cooled heat sink having a heat transfer base, a shroud, and a plurality of heat transfer fins in thermal communication with the heat transfer base and the shroud, where the heat transfer base, heat transfer fins, and the shroud form a central fluid channel through which a forced or free cooling fluid may flow. The heat transfer pins are arranged around the central fluid channel with a flow space provided between adjacent pins, allowing for some portion of the central fluid channel flow to divert through the flow space. The arrangement reduces the pressure drop ofmore » the flow through the fins, optimizes average heat transfer coefficients, reduces contact and fin-pin resistances, and reduces the physical footprint of the heat sink in an operating environment.« less

Study of the heat-transfer crisis on heat-release surfaces of annular channels with swirl and transit flows

NASA Astrophysics Data System (ADS)

Boltenko, E. A.

2016-10-01

The results of the experimental study of the heat-transfer crisis on heat-release surfaces of annular channels with swirl and transit flow are presented. The experiments were carried out using electric heated annular channels with one and (or) two heat-release surfaces. For the organization of transit flow on a convex heat-release surface, four longitudinal ribs were installed uniformly at its perimeter. Swirl flow was realized using a capillary wound tightly (without gaps) on the ribs. The ratio between swirl and transit flows in the annular gap was varied by applying longitudinal ribs of different height. The experiments were carried out using a closed-type circulatory system. The experimental data were obtained in a wide range of regime parameters. Both water heated to the temperature less than the saturation temperature and water-steam mixture were fed at the inlet of the channels. For the measurement of the temperature of the heat-release surfaces, chromel-copel thermocouples were used. It was shown that the presence of swirl flow on a convex heatrelease surface led to a significant decrease in critical heat flows (CHF) compared to a smooth surface. To increase CHF, it was proposed to use the interaction of swirl flows of the heat carrier. The second swirl flow was transit flow, i.e., swirl flow with the step equal to infinity. It was shown that CHF values for a channel with swirl and transit flow in all the studied range of regime parameters was higher than CHF values for both a smooth annular channel and a channel with swirl. The empirical ratios describing the dependence of CHF on convex and concave heat-release surfaces of annular channels with swirl and transit flow on the geometrical characteristics of channels and the regime parameters were obtained. The experiments were carried out at the pressure p = 3.0-16.0 MPa and the mass velocity ρw = 250-3000 kg/(m2s).

Solid-Solid Phase Transition Kinetics of FOX-7

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burnham, A K; Weese, R K; Wang, R

Since it was developed in the late 1990s, 1,1-diamino-2,2-dinitroethene (FOX-7), with lower sensitivity and comparable performance to RDX, has received increasing interest. This paper will present our results for the phase changes of FOX-7 using DSC and HFC (Heat Flow Calorimetry). DSC thermal curves recorded at linear heating rates of 0.10, 0.35 and 1.0 C min{sup -1} show two endothermic peaks and two exothermic peaks. The two endothermic peaks represent solid-solid phase transitions, which have been observed in the literature at 114 C ({beta}-{gamma}) and 159 C ({gamma}-{delta}) by both DSC and XPD (X-ray powder diffraction) measurements. The first transitionmore » shifts from 114.5 to 115.8 C as the heating rate increases from 0.10 to 1.0 C min{sup -1}, while the second transition shifts from 158.5 to 160.4 C. Cyclical heating experiments show the endotherms and exotherms for a first heating through the {gamma} phase to the {delta} phase, a cooling and reversion to the {alpha} or {beta} phase, and a second heating to the {gamma} and {delta} phases. The data are interpreted using kinetic models with thermodynamic constraints.« less

Metal ions induced heat shock protein response by elevating superoxide anion level in HeLa cells transformed by HSE-SEAP reporter gene.

PubMed

Yu, Zhanjiang; Yang, Xiaoda; Wang, Kui

2006-06-01

The aim of this work is to define the relationship between heat shock protein (HSP) and reactive oxygen species (ROS) in the cells exposed to different concentrations of metal ions, and to evaluate a new method for tracing the dynamic levels of cellular reactive oxygen species using a HSE-SEAP reporter gene. The expression of heat shock protein was measured using a secreted alkaline phosphatase (SEAP) reporter gene transformed into HeLa cell strain, the levels of superoxide anion (O(2)(-)) and hydrogen peroxide (H(2)O(2)) were determined by NBT reduction assay and DCFH staining flow cytometry (FCM), respectively. The experimental results demonstrated that the expression of heat shock protein induced by metal ions was linearly related to the cellular superoxide anion level before cytotoxic effects were observed, but not related to the cellular hydrogen peroxide level. The experimental results suggested that metal ions might induce heat shock protein by elevating cellular superoxide anion level, and thus the expression of heat shock protein indicated by the HSE-SEAP reporter gene can be an effective model for monitoring the dynamic level of superoxide anion and early metal-induced oxidative stress/cytotoxicity.

Shielded regeneration heating element for a particulate filter

DOEpatents

Gonze, Eugene V [Pinckney, MI; Ament, Frank [Troy, MI

2011-01-04

An exhaust system includes a particulate filter (PF) that is disposed downstream from an engine. The PF filters particulates within an exhaust from the engine. A heating element heats particulate matter in the PF. A catalyst substrate or a flow converter is disposed upstream from said heating element. The catalyst substrate oxidizes the exhaust prior to reception by the heating element. The flow converter converts turbulent exhaust flow to laminar exhaust flow prior to reception by the heating element.

Characteristics of turbulence transport for momentum and heat in particle-laden turbulent vertical channel flows

NASA Astrophysics Data System (ADS)

Liu, Caixi; Tang, Shuai; Shen, Lian; Dong, Yuhong

2017-10-01

The dynamic and thermal performance of particle-laden turbulent flow is investigated via direction numerical simulation combined with the Lagrangian point-particle tracking under the condition of two-way coupling, with a focus on the contributions of particle feedback effect to momentum and heat transfer of turbulence. We take into account the effects of particles on flow drag and Nusselt number and explore the possibility of drag reduction in conjunction with heat transfer enhancement in particle-laden turbulent flows. The effects of particles on momentum and heat transfer are analyzed, and the possibility of drag reduction in conjunction with heat transfer enhancement for the prototypical case of particle-laden turbulent channel flows is addressed. We present results of turbulence modification and heat transfer in turbulent particle-laden channel flow, which shows the heat transfer reduction when large inertial particles with low specific heat capacity are added to the flow. However, we also found an enhancement of the heat transfer and a small reduction of the flow drag when particles with high specific heat capacity are involved. The present results show that particles, which are active agents, interact not only with the velocity field, but also the temperature field and can cause a dissimilarity in momentum and heat transport. This demonstrates that the possibility to increase heat transfer and suppress friction drag can be achieved with addition of particles with different thermal properties.

Minnowbrook IV: 2003 Workshop on Transition and Unsteady Aspects of Turbomachinery Flows

NASA Technical Reports Server (NTRS)

LaGraff, John E. (Editor); Ashpis, David E.

2004-01-01

This Minnowbrook IV 2003 workshop on Transition and Unsteady Aspects of Turbomachinery Flows includes the following topics: 1) Current Issues in Unsteady Turbomachinery Flows; 2) Global Instability and Control of Low-Pressure Turbine Flows; 3) Influence of End Wall Leakage on Secondary Flow Development in Axial Turbines; 4) Active and Passive Flow Control on Low Pressure Turbine Airfoils; 5) Experimental and Numerical Investigation of Transitional Flows as Affected by Passing Wakes; 6) Effects of Freestream Turbulence on Turbine Blade Heat Transfer; 7) Bypass Transition Via Continuous Modes and Unsteady Effects on Film Cooling; 8) High Frequency Surface Heat Flux Imaging of Bypass Transition; 9) Skin Friction and Heat Flux Oscillations in Upstream Moving Wave Packets; 10) Transition Mechanisms and Use of Surface Roughness to Enhance the Benefits of Wake Passing in LP Turbines; 11) Transient Growth Approach to Roughness-Induced Transition; 12) Roughness- and Freestream-Turbulence-Induced Transient Growth as a Bypass Transition Mechanism; 13) Receptivity Calculations as a Means to Predicting Transition; 14) On Streamwise Vortices in a Curved Wall Jet and Their Effect on the Mean Flow; 15) Plasma Actuators for Separation Control of Low Pressure Turbine Blades; 16) Boundary-Layer Separation Control Under Low-Pressure-Turbine Conditions Using Glow-Discharge Plasma Actuators; 17) Control of Separation for Low Pressure Turbine Blades: Numerical Simulation; 18) Effects of Elevated Free-Stream Turbulence on Active Control of a Separation Bubble; 19) Wakes, Calming and Transition Under Strong Adverse Pressure Gradients; 20) Transitional Bubble in Periodic Flow Phase Shift; 21) Modelling Spots: The Calmed Region, Pressure Gradient Effects and Background; 22) Modeling of Unsteady Transitional Flow on Axial Compressor Blades; 23) Challenges in Predicting Component Efficiencies in Turbomachines With Low Reynolds Number Blading; 24) Observations on the Causal Relationship Between Blade Count and Developing Rotating Stall in a Four Stage Axial Compressor; 25) Experimental and Numerical Study of Non-Linear Interactions in Transonic Nozzle Flow; 26) Clocking Effects on a Modern Stage and One-Half Transonic Turbine; 27) DNS and LES of Transition on Turbine Blades; 28) The Use of Cellular Automata in Modeling the Transition; 29) Predicting Unsteady Buffet Onset Using RANS Solutions; 30) Transition Modelling With the SST Turbulence Model and an Intermittency Transport; and 31) Equation Workshop Summary Transcript

The turbulence structure of katabatic flows below and above wind-speed maximum

NASA Astrophysics Data System (ADS)

Grachev, Andrey; Leo, Laura; Di Sabatino, Silvana; Fernando, Harindra; Pardyjak, Eric; Fairall, Christopher

2015-04-01

Measurements of atmospheric small-scale turbulence made over the complex-terrain at the US Army Dugway Proving Grounds in Utah during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program are used to describe the turbulence structure of katabatic flows. Turbulent and mean meteorological data were continuously measured at multiple levels (up to seven) on four towers deployed along East lower slope (2-4 degrees) of Granite Mountain. The multi-level, multi-tower observations obtained during a 30-day long MATERHORN-Fall field campaign in September-October 2102 allow studying temporal and spatial structure of nocturnal slope flows in detail. In this study, we focus on the various statistics (fluxes, variances, spectra, cospectra, etc.) of the small-scale turbulence of katabatic winds. Observed vertical profiles of velocity, turbulent fluxes, and other quantities show steep gradients near the surface but in the layer above the slope jet these variables vary with height more slowly than near the surface. It is found that vertical momentum flux and horizontal heat (buoyancy) flux in a slope-following coordinate system change their sign below and above the wind maximum of a katabatic flow. The vertical momentum flux is directed downward (upward) whereas the horizontal heat flux is downslope (upslope) below (above) the wind maximum. Our study, therefore, suggests that a position of the jet speed maximum can be derived from linear interpolation between positive and negative values of the momentum flux (or the horizontal heat flux) and determination of a height where a flux becomes zero. It is shown that the standard deviations of all wind speed components (and therefore the turbulent kinetic energy) and the dissipation rate of turbulent kinetic energy have a local minimum, whereas the standard deviation of air temperature has an absolute maximum at the height of wind speed maximum. We report several cases when the destructive effect of vertical heat (buoyancy) flux is completely cancelled by the generation of turbulence due to the horizontal heat (buoyancy) flux. Turbulence in the layer above the wind-speed maximum is decoupled from the surface and it is consistent with the classical local z-less predictions for stably stratified boundary layer.

Microwave heating of aqueous samples on a micro-optical-electro-mechanical system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beer, Neil Reginald

2016-04-12

Apparatus for heating a sample includes a microchip; a microchannel flow channel in the microchip, the microchannel flow channel containing the sample; a microwave source that directs microwaves onto the sample for heating the sample; a wall section of the microchannel flow channel that receives the microwaves and enables the microwaves to pass through wall section of the microchannel flow channel, the wall section the microchannel flow channel being made of a material that is not appreciably heated by the microwaves; a carrier fluid within the microchannel flow channel for moving the sample in the microchannel flow channel, the carriermore » fluid being made of a material that is not appreciably heated by the microwaves; wherein the microwaves pass through wall section of the microchannel flow channel and heat the sample.« less

Microwave heating of aqueous samples on a micro-optical-electro-mechanical system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beer, Neil Reginald

Apparatus for heating a sample includes a microchip; a microchannel flow channel in the microchip, the microchannel flow channel containing the sample; a microwave source that directs microwaves onto the sample for heating the sample; a wall section of the microchannel flow channel that receives the microwaves and enables the microwaves to pass through wall section of the microchannel flow channel, the wall section the microchannel flow channel being made of a material that is not appreciably heated by the microwaves; a carrier fluid within the microchannel flow channel for moving the sample in the microchannel flow channel, the carriermore » fluid being made of a material that is not appreciably heated by the microwaves; wherein the microwaves pass through wall section of the microchannel flow channel and heat the sample.« less

Tuning near field radiative heat flux through surface excitations with a metal insulator transition.

PubMed

van Zwol, P J; Ranno, L; Chevrier, J

2012-06-08

The control of heat flow is a formidable challenge due to lack of good thermal insulators. Promising new opportunities for heat flow control were recently theoretically discovered for radiative heat flow in near field, where large heat flow contrasts may be achieved by tuning electronic excitations on surfaces. Here we show experimentally that the phase transition of VO2 entails a change of surface polariton states that significantly affects radiative heat transfer in near field. In all cases the Derjaguin approximation correctly predicted radiative heat transfer in near field, but it underestimated the far field limit. Our results indicate that heat flow contrasts can be realized in near field that can be larger than those obtained in far field.

Reaction Kernel Structure of a Slot Jet Diffusion Flame in Microgravity

NASA Technical Reports Server (NTRS)

Takahashi, F.; Katta, V. R.

2001-01-01

Diffusion flame stabilization in normal earth gravity (1 g) has long been a fundamental research subject in combustion. Local flame-flow phenomena, including heat and species transport and chemical reactions, around the flame base in the vicinity of condensed surfaces control flame stabilization and fire spreading processes. Therefore, gravity plays an important role in the subject topic because buoyancy induces flow in the flame zone, thus increasing the convective (and diffusive) oxygen transport into the flame zone and, in turn, reaction rates. Recent computations show that a peak reactivity (heat-release or oxygen-consumption rate) spot, or reaction kernel, is formed in the flame base by back-diffusion and reactions of radical species in the incoming oxygen-abundant flow at relatively low temperatures (about 1550 K). Quasi-linear correlations were found between the peak heat-release or oxygen-consumption rate and the velocity at the reaction kernel for cases including both jet and flat-plate diffusion flames in airflow. The reaction kernel provides a stationary ignition source to incoming reactants, sustains combustion, and thus stabilizes the trailing diffusion flame. In a quiescent microgravity environment, no buoyancy-induced flow exits and thus purely diffusive transport controls the reaction rates. Flame stabilization mechanisms in such purely diffusion-controlled regime remain largely unstudied. Therefore, it will be a rigorous test for the reaction kernel correlation if it can be extended toward zero velocity conditions in the purely diffusion-controlled regime. The objectives of this study are to reveal the structure of the flame-stabilizing region of a two-dimensional (2D) laminar jet diffusion flame in microgravity and develop a unified diffusion flame stabilization mechanism. This paper reports the recent progress in the computation and experiment performed in microgravity.

Results from On-Board CSA-CP and CDM Sensor Readings During the Burning and Suppression of Solids II (BASS-II) Experiment in the Microgravity Science Glovebox (MSG)

NASA Technical Reports Server (NTRS)

Olson, Sandra L.; Ferkul, Paul V.; Bhattacharjee, Subrata; Miller, Fletcher J.; Fernandez-Pello, Carlos; Link, Shmuel; T'ien, James S.; Wichman, Indrek

2015-01-01

For the first time on ISS, BASS-II utilized MSG working volume dilution with gaseous nitrogen (N2). We developed a perfectly stirred reactor model to determine the N2 flow time and flow rate to obtain the desired reduced oxygen concentration in the working volume for each test. We calibrated the model with CSA-CP oxygen readings offset using the Mass Constituents Analyzer reading of the ISS ambient atmosphere data for that day. This worked out extremely well for operations, and added a new vital variable, ambient oxygen level, to our test matrices. The main variables tested in BASS-II were ambient oxygen concentration, ventilation flow velocity, and fuel type, thickness, and geometry. BASS-II also utilized the on-board CSA-CP for oxygen and carbon monoxide readings, and the CDM for carbon dioxide readings before and after each test. Readings from these sensors allow us to evaluate the completeness of the combustion. The oxygen and carbon dioxide readings before and after each test were analyzed and compared very well to stoichiometric ratios for a one step gas-phase reaction. The CO versus CO2 followed a linear trend for some datasets, but not for all the different geometries of fuel and flow tested. Lastly, we calculated the heat release rates during each test from the oxygen consumption and burn times, using the constant 13.1 kJ of heat released per gram of oxygen consumed. The results showed that the majority of the tests had heat release rates well below 100 Watts.

Direct Simulation Monte Carlo for astrophysical flows - II. Ram-pressure dynamics

NASA Astrophysics Data System (ADS)

Weinberg, Martin D.

2014-03-01

We use the Direct Simulation Monte Carlo method combined with an N-body code to study the dynamics of the interaction between a gas-rich spiral galaxy and intracluster or intragroup medium, often known as the ram pressure scenario. The advantage of this gas kinetic approach over traditional hydrodynamics is explicit treatment of the interface between the hot and cold, dense and rarefied media typical of astrophysical flows and the explicit conservation of energy and momentum and the interface. This approach yields some new physical insight. Owing to the shock and backward wave that forms at the point intracluster medium (ICM)-interstellar medium (ISM) contact, ICM gas is compressed, heated and slowed. The shock morphology is Mach disc like. In the outer galaxy, the hot turbulent post-shock gas flows around the galaxy disc while heating and ablating the initially cool disc gas. The outer gas and angular momentum are lost to the flow. In the inner galaxy, the hot gas pressurizes the neutral ISM gas causing a strong two-phase instability. As a result, the momentum of the wind is no longer impulsively communicated to the cold gas as assumed in the Gunn-Gott formula, but oozes through the porous disc, transferring its linear momentum to the disc en masse. The escaping gas mixture has a net positive angular momentum and forms a slowly rotating sheath. The shear flow caused by the post-shock ICM flowing through the porous multiphase ISM creates a strong Kelvin-Helmholtz instability in the disc that results in Cartwheel-like ring and spoke morphology.

Entropy Generation in Regenerative Systems

NASA Technical Reports Server (NTRS)

Kittel, Peter

1995-01-01

Heat exchange to the oscillating flows in regenerative coolers generates entropy. These flows are characterized by oscillating mass flows and oscillating temperatures. Heat is transferred between the flow and heat exchangers and regenerators. In the former case, there is a steady temperature difference between the flow and the heat exchangers. In the latter case, there is no mean temperature difference. In this paper a mathematical model of the entropy generated is developed for both cases. Estimates of the entropy generated by this process are given for oscillating flows in heat exchangers and in regenerators. The practical significance of this entropy is also discussed.

A review of surface heat-flow data of the northern Middle Atlas (Morocco)

NASA Astrophysics Data System (ADS)

Chiozzi, Paolo; Barkaoui, Alae-Eddine; Rimi, Abdelkrim; Verdoya, Massimo; Zarhloule, Yassine

2017-12-01

We revised thermal data available from water and oil wells in the northern sector of the Middle Atlas region. To avoid biased estimation of surface heat flow caused by advection likely occurring in shallow aquifers, temperature measurements in water boreholes were carefully inspected and selected. The heat flow in the oil wells was inferred by taking into account the porosity variation with depth, the temperature effect on thermal conductivity of the matrix and the pore fluid, together with the contribution of the radiogenic heat production. Moreover, the possible bias in heat flow caused by convection occurring in confined carbonate aquifers was evaluated. The results of heat flow slightly modify the picture reported in previous investigations. The heat flow value over the investigated region is rather uniform (about 80 mW m-2) and is similar in oil wells and in water boreholes. Geothermal calculations indicate that such a surface heat flow is compatible with a ∼70 km thick thermal lithosphere and normal thermal conditions in the asthenospheric mantle.

Nonlinear Stability and Structure of Compressible Reacting Mixing Layers

NASA Technical Reports Server (NTRS)

Day, M. J.; Mansour, N. N.; Reynolds, W. C.

2000-01-01

The parabolized stability equations (PSE) are used to investigate issues of nonlinear flow development and mixing in compressible reacting shear layers. Particular interest is placed on investigating the change in flow structure that occurs when compressibility and heat release are added to the flow. These conditions allow the 'outer' instability modes- one associated with each of the fast and slow streams-to dominate over the 'central', Kelvin-Helmholtz mode that unaccompanied in incompressible nonreacting mixing layers. Analysis of scalar probability density functions in flows with dominant outer modes demonstrates the ineffective, one-sided nature of mixing that accompany these flow structures. Colayer conditions, where two modes have equal growth rate and the mixing layer is formed by two sets of vortices, offer some opportunity for mixing enhancement. Their extent, however, is found to be limited in the mixing layer's parameter space. Extensive validation of the PSE technique also provides a unique perspective on central- mode vortex pairing, further supporting the view that pairing is primarily governed perspective sheds insight on how linear stability theory is able to provide such an accurate prediction of experimentally-observed, fully nonlinear flow phenomenon.

Surface treatment with linearly polarized laser beam at oblique incidence

NASA Astrophysics Data System (ADS)

Gutu, I.; Petre, C.; Mihailescu, I. N.; Taca, M.; Alexandrescu, E.; Ivanov, I.

2002-07-01

An effective method for surface heat treatment with 10.6 μm linear polarized laser beam at oblique incidence is reported. A circular focused laser spot on the workpiece surface, simultaneously with 2.2-4 times increasing of the absorption are obtained in the 70-80° range of the incidence angle. The main element of the experimental setup is the astigmatic focusing head which focalize the laser beam into an elliptical spot of ellipticity ɛ>3 at normal incidence. At a proper incidence angle (obtained by the focusing head tilting) the focused laser spot on the work piece surface gets a circular form and p-state of polarization is achieved. We performed laser heat treatment (transformation hardening, surface remelting) of the uncoated surface, as well as the alloying and cladding processes by powder injection. An enhancement of the processing efficiency was obtained; in this way the investment and operation costs for surface treatment with CO 2 laser can be significantly reduced. Several technical advantages concerning the pollution of the focusing optical components, powder jet flowing and reflected radiation by the work piece surface are obtained.

Effect of a resistive load on the starting performance of a standing wave thermoacoustic engine: A numerical study.

PubMed

Ma, Lin; Weisman, Catherine; Baltean-Carlès, Diana; Delbende, Ivan; Bauwens, Luc

2015-08-01

The influence of a resistive load on the starting performance of a standing-wave thermoacoustic engine is investigated numerically. The model used is based upon a low Mach number assumption; it couples the two-dimensional nonlinear flow and heat exchange within the thermoacoustic active cell with one-dimensional linear acoustics in the loaded resonator. For a given engine geometry, prescribed temperatures at the heat exchangers, prescribed mean pressure, and prescribed load, results from a simulation in the time domain include the evolution of the acoustic pressure in the active cell. That signal is then analyzed, extracting growth rate and frequency of the dominant modes. For a given load, the temperature difference between the two sides is then varied; the most unstable mode is identified and so is the corresponding critical temperature ratio between heater and cooler. Next, varying the load, a stability diagram is obtained, potentially with a predictive value. Results are compared with those derived from Rott's linear theory as well as with experimental results found in the literature.

Determination of the temperature distribution in a minichannel using ANSYS CFX and a procedure based on the Trefftz functions

NASA Astrophysics Data System (ADS)

Maciejewska, Beata; Błasiak, Sławomir; Piasecka, Magdalena

This work discusses the mathematical model for laminar-flow heat transfer in a minichannel. The boundary conditions in the form of temperature distributions on the outer sides of the channel walls were determined from experimental data. The data were collected from the experimental stand the essential part of which is a vertical minichannel 1.7 mm deep, 16 mm wide and 180 mm long, asymmetrically heated by a Haynes-230 alloy plate. Infrared thermography allowed determining temperature changes on the outer side of the minichannel walls. The problem was analysed numerically through either ANSYS CFX software or special calculation procedures based on the Finite Element Method and Trefftz functions in the thermal boundary layer. The Trefftz functions were used to construct the basis functions. Solutions to the governing differential equations were approximated with a linear combination of Trefftz-type basis functions. Unknown coefficients of the linear combination were calculated by minimising the functional. The results of the comparative analysis were represented in a graphical form and discussed.

Re-evaluation of heat flow data near Parkfield, CA: Evidence for a weak San Andreas Fault

USGS Publications Warehouse

Fulton, P.M.; Saffer, D.M.; Harris, Reid N.; Bekins, B.A.

2004-01-01

Improved interpretations of the strength of the San Andreas Fault near Parkfield, CA based on thermal data require quantification of processes causing significant scatter and uncertainty in existing heat flow data. These effects include topographic refraction, heat advection by topographically-driven groundwater flow, and uncertainty in thermal conductivity. Here, we re-evaluate the heat flow data in this area by correcting for full 3-D terrain effects. We then investigate the potential role of groundwater flow in redistributing fault-generated heat, using numerical models of coupled heat and fluid flow for a wide range of hydrologic scenarios. We find that a large degree of the scatter in the data can be accounted for by 3-D terrain effects, and that for plausible groundwater flow scenarios frictional heat generated along a strong fault is unlikely to be redistributed by topographically-driven groundwater flow in a manner consistent with the 3-D corrected data. Copyright 2004 by the American Geophysical Union.

Transport Phenomena in Fluid Dynamics: Matrix Heat Exchangers and Their Applications in Energy Systems

DTIC Science & Technology

2009-07-01

presented a summary of recent research on boiling in microchannels . He addressed the topics of macro scale versus micro scale heat transfer , two phase...flow regime, flow boiling 14 heat transfer results for microchannels , heat transfer mechanisms in microchannels , and flow boiling models for... Heat Transfer Boiling In Minichannel And Microchannel Flow Passages Of Compact Evaporators, Keynote Lecture Presented at the Engineering Foundation

Numerical simulation of hydrothermal circulation in the Cascade Range, north-central Oregon

USGS Publications Warehouse

Ingebritsen, S.E.; Paulson, K.M.

1990-01-01

Alternate conceptual models to explain near-surface heat-flow observations in the central Oregon Cascade Range involve (1) an extensive mid-crustal magmatic heat source underlying both the Quaternary arc and adjacent older rocks or (2) a narrower deep heat source which is flanked by a relatively shallow conductive heat-flow anomaly caused by regional ground-water flow (the lateral-flow model). Relative to the mid-crustal heat source model, the lateral-flow model suggests a more limited geothermal resource base, but a better-defined exploration target. We simulated ground-water flow and heat transport through two cross sections trending west from the Cascade range crest in order to explore the implications of the two models. The thermal input for the alternate conceptual models was simulated by varying the width and intensity of a basal heat-flow anomaly and, in some cases, by introducing shallower heat sources beneath the Quaternary arc. Near-surface observations in the Breitenbush Hot Springs area are most readily explained in terms of lateral heat transport by regional ground-water flow; however, the deep thermal structure still cannot be uniquely inferred. The sparser thermal data set from the McKenzie River area can be explained either in terms of deep regional ground-water flow or in terms of a conduction-dominated system, with ground-water flow essentially confined to Quaternary rocks and fault zones.

From Finite Time to Finite Physical Dimensions Thermodynamics: The Carnot Engine and Onsager's Relations Revisited

NASA Astrophysics Data System (ADS)

Feidt, Michel; Costea, Monica

2018-04-01

Many works have been devoted to finite time thermodynamics since the Curzon and Ahlborn [1] contribution, which is generally considered as its origin. Nevertheless, previous works in this domain have been revealed [2], [3], and recently, results of the attempt to correlate Finite Time Thermodynamics with Linear Irreversible Thermodynamics according to Onsager's theory were reported [4]. The aim of the present paper is to extend and improve the approach relative to thermodynamic optimization of generic objective functions of a Carnot engine with linear response regime presented in [4]. The case study of the Carnot engine is revisited within the steady state hypothesis, when non-adiabaticity of the system is considered, and heat loss is accounted for by an overall heat leak between the engine heat reservoirs. The optimization is focused on the main objective functions connected to engineering conditions, namely maximum efficiency or power output, except the one relative to entropy that is more fundamental. Results given in reference [4] relative to the maximum power output and minimum entropy production as objective function are reconsidered and clarified, and the change from finite time to finite physical dimension was shown to be done by the heat flow rate at the source. Our modeling has led to new results of the Carnot engine optimization and proved that the primary interest for an engineer is mainly connected to what we called Finite Physical Dimensions Optimal Thermodynamics.

Onset of fractional-order thermal convection in porous media

NASA Astrophysics Data System (ADS)

Karani, Hamid; Rashtbehesht, Majid; Huber, Christian; Magin, Richard L.

2017-12-01

The macroscopic description of buoyancy-driven thermal convection in porous media is governed by advection-diffusion processes, which in the presence of thermophysical heterogeneities fail to predict the onset of thermal convection and the average rate of heat transfer. This work extends the classical model of heat transfer in porous media by including a fractional-order advective-dispersive term to account for the role of thermophysical heterogeneities in shifting the thermal instability point. The proposed fractional-order model overcomes limitations of the common closure approaches for the thermal dispersion term by replacing the diffusive assumption with a fractional-order model. Through a linear stability analysis and Galerkin procedure, we derive an analytical formula for the critical Rayleigh number as a function of the fractional model parameters. The resulting critical Rayleigh number reduces to the classical value in the absence of thermophysical heterogeneities when solid and fluid phases have similar thermal conductivities. Numerical simulations of the coupled flow equation with the fractional-order energy model near the primary bifurcation point confirm our analytical results. Moreover, data from pore-scale simulations are used to examine the potential of the proposed fractional-order model in predicting the amount of heat transfer across the porous enclosure. The linear stability and numerical results show that, unlike the classical thermal advection-dispersion models, the fractional-order model captures the advance and delay in the onset of convection in porous media and provides correct scalings for the average heat transfer in a thermophysically heterogeneous medium.

Numerical analysis of inertance pulse tube cryocooler with a modified reservoir

NASA Astrophysics Data System (ADS)

Abraham, Derick; Damu, C.; Kuzhiveli, Biju T.

2017-12-01

Pulse tube cryocoolers are used for cooling applications, where very high reliability is required as in space applications. These cryocoolers require a buffer volume depending on the temperature to be maintained and cooling load. A miniature single stage coaxial Inertance Pulse Tube Cryocooler is proposed which operates at 80 K to provide a cooling effect of at least 2 W. In this paper a pulse tube cryocooler, with modified reservoir is suggested, where the reverse fluctuation in compressor case is used instead of a steady pressure in the reservoir to bring about the desired phase shift between the pressure and the mass flow rate in the cold heat exchanger. Therefore, the large reservoir of the cryocooler is replaced by the crank volume of the hermetically sealed linear compressor, and hence the cryocooler is simplified and compact in size. The components of the cryocooler consist of a connecting tube, aftercooler, regenerator, cold heat exchanger, flow straightener, pulse tube, warm heat exchanger, inertance tube and the modified reservoir along with the losses were designed and analyzed. Each part of the cryocooler was analysed using SAGE v11 and verified with ANSYS Fluent. The simulation results clearly show that there is 50% reduction in the reservoir volume for the modified Inertance pulse tube cryocooler.

[INVITED] Coupling of polarisation of high frequency electric field and electronic heat conduction in laser created plasma

NASA Astrophysics Data System (ADS)

Gamaly, Eugene G.; Rode, Andrei V.

2016-08-01

Powerful short laser pulse focused on a surface swiftly transforms the solid into the thermally and electrically inhomogeneous conductive plasma with the large temperature and dielectric permeability gradients across the focal spot. The laser-affected spot becomes thermally inhomogeneous with where temperature has maximum in the centre and gradually decreasing to the boundaries of the spot in accord to the spatial intensity distribution of the Gaussian pulse. Here we study the influence of laser polarisation on ionization and absorption of laser radiation in the focal spot. In this paper we would like to discuss new effect in thermally inhomogeneous plasma under the action of imposed high frequency electric field. We demonstrate that high-frequency (HF) electric field is coupled with the temperature gradient generating the additional contribution to the conventional electronic heat flow. The additional heat flow strongly depends on the polarisation of the external field. It appears that effect has maximum when the imposed electric field is collinear to the thermal gradient directed along the radius of a circular focal spot. Therefore, the linear polarised field converts the circular laser affected spot into an oval with the larger oval's axis parallel to the field direction. We compare the developed theory to the available experiments, discuss the results and future directions.

Present heat flow and paleo-geothermal regime in the Canadian Arctic margin: analysis of industrial thermal data and coalification gradients

NASA Astrophysics Data System (ADS)

Majorowicz, Jacek A.; Embry, Ashton F.

1998-06-01

Calculations of the present geothermal gradient and terrestrial heat flow were made on 156 deep wells of the Canadian Arctic Archipelago. Corrected bottom hole temperature (BHT) data and drill stem test (DST) temperatures were used to determine the thermal gradients for sites for which the quality of data was sufficient. Thermal gradients evaluated for depths below the base of permafrost for the onshore wells and below sea bottom for the offshore wells were combined with the estimates of effective thermal conductivity to approximate heat flow for these sites. The present geothermal gradient is in the 15-50 mK/m range (mean = 31 ± 7 mK/m). Present heat flow is mainly in the 35-90 mW/m 2 range (mean = 53 ± 12 mW/m 2). Maps of the present geothermal gradient and present heat flow have been constructed for the basin. The analysis of vitrinite reflectance profiles and the calculation of logarithmic coalification gradients for 101 boreholes in the Sverdrup Basin showed large variations related in many cases to regional variations of present terrestrial heat flow. Paleo-geothermal gradients estimated from these data are mostly in the range of 15-50 mK/m (mean = 28 ± 9 mK/m) and paleo-heat flow is in the 40-90 mW/m 2 range (mean = 57 ± 18 mW/m 2) related to the time of maximum burial in the Early Tertiary. Mean values of the present heat flow and paleo-heat flow for the Sverdrup Basin are almost identical considering the uncertainties of the methods used (53 ± 12 versus 57 ± 18 mW/m 2, respectively). Present geothermal gradients and paleo-geothermal gradients are also close when means are compared (31 ± 7 versus 28 ± 9 mK/m respectively). A zone of high present heat flow and a paleo-heat flow zone coincide in places with the northeastern-southwestern incipient rift landward of the Arctic margin first described by Balkwill and Fox (1982). Correlation between present heat flow and paleo-heat flow for the time of maximum burial in the earliest Tertiary suggests that the high heat flow zone has prevailed since that time.

Flow and Pollutant Transport in Urban Street Canyons of Different Aspect Ratios with Ground Heating: Large-Eddy Simulation

NASA Astrophysics Data System (ADS)

Li, Xian-Xiang; Britter, Rex E.; Norford, Leslie K.; Koh, Tieh-Yong; Entekhabi, Dara

2012-02-01

A validated large-eddy simulation model was employed to study the effect of the aspect ratio and ground heating on the flow and pollutant dispersion in urban street canyons. Three ground-heating intensities (neutral, weak and strong) were imposed in street canyons of aspect ratio 1, 2, and 0.5. The detailed patterns of flow, turbulence, temperature and pollutant transport were analyzed and compared. Significant changes of flow and scalar patterns were caused by ground heating in the street canyon of aspect ratio 2 and 0.5, while only the street canyon of aspect ratio 0.5 showed a change in flow regime (from wake interference flow to skimming flow). The street canyon of aspect ratio 1 does not show any significant change in the flow field. Ground heating generated strong mixing of heat and pollutant; the normalized temperature inside street canyons was approximately spatially uniform and somewhat insensitive to the aspect ratio and heating intensity. This study helps elucidate the combined effects of urban geometry and thermal stratification on the urban canyon flow and pollutant dispersion.

Experimental study on heat transfer performance of fin-tube exchanger and PSHE for waste heat recovery

NASA Astrophysics Data System (ADS)

Chen, Ting; Bae, Kyung Jin; Kwon, Oh Kyung

2018-02-01

In this paper, heat transfer characteristics of fin-tube heat exchanger and primary surface heat exchanger (PSHE) used in waste heat recovery were investigated experimentally. The flow in the fin-tube heat exchanger is cross flow and in PSHE counter flow. The variations of friction factor and Colburn j factor with air mass flow rate, and Nu number with Re number are presented. Various comparison methods are used to evaluate heat transfer performance, and the results show that the heat transfer rate of the PSHE is on average 17.3% larger than that of fin-tube heat exchanger when air mass flow rate is ranging from 1.24 to 3.45 kg/min. However, the PSHE causes higher pressure drop, and the fin-tube heat exchanger has a wider application range which leads to a 31.7% higher value of maximum heat transfer rate compared to that of the PSHE. Besides, under the same fan power per unit frontal surface, a higher heat transfer rate value is given in the fin-tube heat exchanger.

Exhaust bypass flow control for exhaust heat recovery

DOEpatents

Reynolds, Michael G.

2015-09-22

An exhaust system for an engine comprises an exhaust heat recovery apparatus configured to receive exhaust gas from the engine and comprises a first flow passage in fluid communication with the exhaust gas and a second flow passage in fluid communication with the exhaust gas. A heat exchanger/energy recovery unit is disposed in the second flow passage and has a working fluid circulating therethrough for exchange of heat from the exhaust gas to the working fluid. A control valve is disposed downstream of the first and the second flow passages in a low temperature region of the exhaust heat recovery apparatus to direct exhaust gas through the first flow passage or the second flow passage.

Flow Regime Identification of Horizontal Two Phase Refrigerant R-134a Flow Using Neural Networks (Postprint)

DTIC Science & Technology

2013-11-01

Flows in Microchannels ," Heat Transfer Engineering, Vol. 27, No. 9, 2006, pp. 4-19. 2Kandlikar, S. G., " Heat Transfer Mechanisms During Flow...Boiling in Microchannels ," Journal of Heat Transfer , Vol. 126, No. 1, 2004, pp. 8-16. 3Kreitzer, P. J., Byrd, L., and Willebrand, B. J., "Initial...an integral aspect of modeling two phase flows as most pressure drop and heat transfer correlations rely on a priori knowledge of the flow regime for

Thermal radiation and mass transfer effects on unsteady MHD free convection flow past a vertical oscillating plate

NASA Astrophysics Data System (ADS)

Rana, B. M. Jewel; Ahmed, Rubel; Ahmmed, S. F.

2017-06-01

Unsteady MHD free convection flow past a vertical porous plate in porous medium with radiation, diffusion thermo, thermal diffusion and heat source are analyzed. The governing non-linear, partial differential equations are transformed into dimensionless by using non-dimensional quantities. Then the resultant dimensionless equations are solved numerically by applying an efficient, accurate and conditionally stable finite difference scheme of explicit type with the help of a computer programming language Compaq Visual Fortran. The stability and convergence analysis has been carried out to establish the effect of velocity, temperature, concentration, skin friction, Nusselt number, Sherwood number, stream lines and isotherms line. Finally, the effects of various parameters are presented graphically and discussed qualitatively.

Heat flow in relation to hydrothermal activity in the southern Black Rock Desert, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sass, J.H.; Zoback, M.L.; Galanis, S.P. Jr.

1979-01-01

As part of an investigation of the Gerlach NE KGRA (Known Geothermal Resource Area) a number of heat-flow measurements were made in playa sediments of the southern Black Rock Desert, northwestern Nevada. These data together with additional previously unpublished heat-flow values reveal a complex pattern of heat flow with values ranging between 1.0 to 5.0 HFU (40 to 100 mWm/sup -2/) outside of the hot springs area. The mean heat flow for the 13 reported sites in the southern Black Rock Desert is 1.8 +- 0.15 HFU (75 +- 6 mWm/sup -2/). The complexity of the pattern of heat flowmore » is believed to arise from hydrothermal circulation supporting the numerous hot springs throughout the region. The fact that the lowest observed heat flow occurs in the deepest part of the basin strongly suggests that fluid movement within the basin represents part of the recharge for the hydrothermal system. A thermal balance for the system incorporating both anomalous conductive heat loss and convective heat loss from the spring systems indicate a total energy loss of about 8.0 Mcal/sec or 34 megawatts over an estimated 1000 km/sup 2/ region. Consideration of this additional heat loss yields a mean regional heat flow of 2.5 + HFU (100 + mWm/sup -2/) and warrants inclusion of this region in the Battle Mountain heat-flow high (Lachenbruch and Sass, 1977, 1978).« less

Time variability in Cenozoic reconstructions of mantle heat flow: plate tectonic cycles and implications for Earth's thermal evolution.

PubMed

Loyd, S J; Becker, T W; Conrad, C P; Lithgow-Bertelloni, C; Corsetti, F A

2007-09-04

The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by approximately 0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past.

Time variability in Cenozoic reconstructions of mantle heat flow: Plate tectonic cycles and implications for Earth's thermal evolution

PubMed Central

Loyd, S. J.; Becker, T. W.; Conrad, C. P.; Lithgow-Bertelloni, C.; Corsetti, F. A.

2007-01-01

The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by ∼0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past. PMID:17720806

Modelling fully-coupled Thermo-Hydro-Mechanical (THM) processes in fractured reservoirs using GOLEM: a massively parallel open-source simulator

NASA Astrophysics Data System (ADS)

Jacquey, Antoine; Cacace, Mauro

2017-04-01

Utilization of the underground for energy-related purposes have received increasing attention in the last decades as a source for carbon-free energy and for safe storage solutions. Understanding the key processes controlling fluid and heat flow around geological discontinuities such as faults and fractures as well as their mechanical behaviours is therefore of interest in order to design safe and sustainable reservoir operations. These processes occur in a naturally complex geological setting, comprising natural or engineered discrete heterogeneities as faults and fractures, span a relatively large spectrum of temporal and spatial scales and they interact in a highly non-linear fashion. In this regard, numerical simulators have become necessary in geological studies to model coupled processes and complex geological geometries. In this study, we present a new simulator GOLEM, using multiphysics coupling to characterize geological reservoirs. In particular, special attention is given to discrete geological features such as faults and fractures. GOLEM is based on the Multiphysics Object-Oriented Simulation Environment (MOOSE). The MOOSE framework provides a powerful and flexible platform to solve multiphysics problems implicitly and in a tightly coupled manner on unstructured meshes which is of interest for the considered non-linear context. Governing equations in 3D for fluid flow, heat transfer (conductive and advective), saline transport as well as deformation (elastic and plastic) have been implemented into the GOLEM application. Coupling between rock deformation and fluid and heat flow is considered using theories of poroelasticity and thermoelasticity. Furthermore, considering material properties such as density and viscosity and transport properties such as porosity as dependent on the state variables (based on the International Association for the Properties of Water and Steam models) increase the coupling complexity of the problem. The GOLEM application aims therefore at integrating more physical processes observed in the field or in the laboratory to simulate more realistic scenarios. The use of high-level nonlinear solver technology allow us to tackle these complex multiphysics problems in three dimensions. Basic concepts behing the GOLEM simulator will be presented in this study as well as a few application examples to illustrate its main features.

Simulation of interior ballistics flows in a shock tube

NASA Astrophysics Data System (ADS)

Seiler, F.

1983-07-01

The flow in front of and behind a projectile was investigated in a interior ballistics shock tube simulator. Flow patterns and heat flow were examined for flows with and without gas leakage. The boundary layers behind the piston can clearly be shown by differential interferograms. The dependence of the heat flow into the measuring tube wall on the base form is smaller than the signal perturbations. Flow patterns show no appreciable effect of gas leakage on the flow behind the piston; strong flow effects arise in front of the piston. The same effects are shown by heat flow measurements. In case of gas leakage heat flows into the tube wall before the piston reaches the wall. In the slit between piston and wall a maximum heat flow is found. High temperature gradients, due to the fact that hot gases come closer to the tube wall than in the boundary layer flow behind the piston, lead to high thermal loading of the wall materials which can cause cracks.

Heat exchanger with transpired, highly porous fins

DOEpatents

Kutscher, Charles F.; Gawlik, Keith

2002-01-01

The heat exchanger includes a fin and tube assembly with increased heat transfer surface area positioned within a hollow chamber of a housing to provide effective heat transfer between a gas flowing within the hollow chamber and a fluid flowing in the fin and tube assembly. A fan is included to force a gas, such as air, to flow through the hollow chamber and through the fin and tube assembly. The fin and tube assembly comprises fluid conduits to direct the fluid through the heat exchanger, to prevent mixing with the gas, and to provide a heat transfer surface or pathway between the fluid and the gas. A heat transfer element is provided in the fin and tube assembly to provide extended heat transfer surfaces for the fluid conduits. The heat transfer element is corrugated to form fins between alternating ridges and grooves that define flow channels for directing the gas flow. The fins are fabricated from a thin, heat conductive material containing numerous orifices or pores for transpiring the gas out of the flow channel. The grooves are closed or only partially open so that all or substantially all of the gas is transpired through the fins so that heat is exchanged on the front and back surfaces of the fins and also within the interior of the orifices, thereby significantly increasing the available the heat transfer surface of the heat exchanger. The transpired fins also increase heat transfer effectiveness of the heat exchanger by increasing the heat transfer coefficient by disrupting boundary layer development on the fins and by establishing other beneficial gas flow patterns, all at desirable pressure drops.

Heat transport in the Red Lake Bog, Glacial Lake Agassiz Peatlands

USGS Publications Warehouse

McKenzie, J.M.; Siegel, D.I.; Rosenberry, D.O.; Glaser, P.H.; Voss, C.I.

2007-01-01

We report the results of an investigation on the processes controlling heat transport in peat under a large bog in the Glacial Lake Agassiz Peatlands. For 2 years, starting in July 1998, we recorded temperature at 12 depth intervals from 0 to 400 cm within a vertical peat profile at the crest of the bog at sub-daily intervals. We also recorded air temperature 1 m above the peat surface. We calculate a peat thermal conductivity of 0.5 W m-1 ??C-1 and model vertical heat transport through the peat using the SUTRA model. The model was calibrated to the first year of data, and then evaluated against the second year of collected heat data. The model results suggest that advective pore-water flow is not necessary to transport heat within the peat profile and most of the heat is transferred by thermal conduction alone in these waterlogged soils. In the spring season, a zero-curtain effect controls the transport of heat through shallow depths of the peat. Changes in local climate and the resulting changes in thermal transport still may cause non-linear feedbacks in methane emissions related to the generation of methane deeper within the peat profile as regional temperatures increase. Copyright ?? 2006 John Wiley & Sons, Ltd.

A New Determination of Io's Heat Flow Using Diurnal Heat Balance Constraints

NASA Technical Reports Server (NTRS)

Spencer, J. R.; Rathbun, J. A.; McEwen, A. S.; Pearl, J. C.; Bastos, A.; Andrade, J.; Correia, M.; Barros, S.

2002-01-01

We use heat balance arguments to obtain a new estimate of Io's heat flow that does not depend on assumptions about the temperatures of its thermal anomalies. Our estimated heat flow is somewhat less than 2.2 +/- 0.9 W/sq m. Additional information is contained in the original extended abstract.

Self-sustained flow oscillations and heat transfer in radial flow through co-rotating parallel disks

NASA Astrophysics Data System (ADS)

Mochizuki, S.; Inoue, T.

1990-03-01

An experimental study was conducted to determine the fluid flow and heat transfer characteristics in a passage formed by two parallel rotating disks. The local heat transfer coefficients along the disk radius were measured in detail and the flow patterns between the two rotating disks were visualized by using paraffin mist and a laser-light sheet. It was disclosed that: (1) the self-sustained laminar flow separation which is characteristic of the stationary disks still exists even when the disks are set in motion, giving significant influence to the heat transfer; (2) for small source flow Reynolds number, Re, and large rotational Reynolds number, Re(omega), rotating stall dominates the heat transfer; and (3) heat transfer for steady laminar flow occurs only when Re is less than 1200 and Re(omega) is less than 20.

Modeling heat loss from the udder of a dairy cow.

PubMed

Gebremedhin, Kifle G; Wu, Binxin

2016-07-01

A mechanistic model that predicts sensible and latent heat fluxes from the udder of a dairy cow was developed. The prediction of the model was spot validated against measured data from the literature, and the result agreed within 7% of the measured value for the same ambient temperature. A dairy cow can lose a significant amount of heat (388W/m(2)) from the udder. This suggests that the udder could be considered as a heat sink. The temperature profile through the udder tissue (core to skin) approached the core temperature for an air temperature ≥37°C whereas the profile decreased linearly from the core to skin surface for an air temperature less than 37°C. Sensible heat loss was dominant when ambient air temperature was less than 37.5°C but latent heat loss was greater than sensible heat loss when air temperature was ≥37.5°C. The udder could lose a total (sensible + latent) heat flux of 338W/m(2) at an ambient temperature of 35°C and blood-flow rate of 3.2×10(-3)m(3)/(sm(3) tissue). The results of this study suggests that, in time of heat stress, a dairy cow could be cooled by cooling the udder only (e.g., using an evaporative cooling jacket). Copyright © 2016 Elsevier Ltd. All rights reserved.

Heat flow in eastern Egypt - The thermal signature of a continental breakup

NASA Technical Reports Server (NTRS)

Morgan, P.; Boulos, F. K.; Hennin, S. F.; El-Sherif, A. A.; El-Sayed, A. A.

1985-01-01

Data on the heat flow in eastern Egypt were collected to provide information related to the mode and the mechanism of the Red Sea opening. The data indicate a general increase in heat flow towards the Red Sea (75-100 mW/sq m in a zone within 40 km of the coast compared with 35-55 mW/sq m inland). Moderately high heat flow (about 70 mW/sq m) was found for the Gulf of Suez. Heat production data indicate that the coastal thermal anomaly is not primarily related to crustal radiogenic heat production. Possible causes of the anomaly (one of which could be a high mantle heat flow causing a lithospheric thinning centered beneath the Red Sea) are discussed.

Thaw flow control for liquid heat transport systems

DOEpatents

Kirpich, Aaron S.

1989-01-01

In a liquid metal heat transport system including a source of thaw heat for use in a space reactor power system, the thaw flow throttle or control comprises a fluid passage having forward and reverse flow sections and a partition having a plurality of bleed holes therein to enable fluid flow between the forward and reverse sections. The flow throttle is positioned in the system relatively far from the source of thaw heat.

Direct Numerical Simulation of turbulent heat transfer up to Reτ = 2000

NASA Astrophysics Data System (ADS)

Hoyas, Sergio; Pérez-Quiles, Jezabel; Lluesma-Rodríguez, Federico

2017-11-01

We present a new set of direct numerical simulations of turbulent heat transfer in a channel flow for a Prandtl number of 0.71 and a friction Reynolds number of 2000. Mixed boundary conditions, i.e., wall temperature is time independent and varies linearly along streamwise component, have been used as boundary conditions for the thermal field. The effect of the size of the box in the one point statistics of the thermal field, and the kinetic energy, dissipation and turbulent budgets has been studied, showing that a domain with streamwise and spanwise sizes of 4 πh and 2 πh, where h is the channel half-height, is large enough to reproduce the one point statistics of larger boxes. The scaling of the previous quantities with respect to the Reynolds number has been also studied using a new dataset of simulations at smaller Reynolds number, finding two different scales for the inner and outer layers of the flow. Funded by project ENE2015-71333-R of the Spanish Ministerio de Economía y Competitividad.

Thermodiffusion as a means to manipulate liquid film dynamics on chemically patterned surfaces

PubMed Central

Kalpathy, Sreeram K.; Shreyes, Amrita Ravi

2017-01-01

The model problem examined here is the stability of a thin liquid film consisting of two miscible components, resting on a chemically patterned solid substrate and heated from below. In addition to surface tension gradients, the temperature variations also induce gradients in the concentration of the film by virtue of thermodiffusion/Soret effects. We study the stability and dewetting behaviour due to the coupled interplay between thermal gradients, Soret effects, long-range van der Waals forces, and wettability gradient-driven flows. Linear stability analysis is first employed to predict growth rates and the critical Marangoni number for chemically homogeneous surfaces. Then, nonlinear simulations are performed to unravel the interfacial dynamics and possible locations of the film rupture on chemically patterned substrates. Results suggest that appropriate tuning of the Soret parameter and its direction, in conjunction with either heating or cooling, can help manipulate the location and time scales of the film rupture. The Soret effect can either potentially aid or oppose film instability depending on whether the thermal and solutal contributions to flow are cooperative or opposed to each other. PMID:28595391

Validation of a CFD Methodology for Variable Speed Power Turbine Relevant Conditions

NASA Technical Reports Server (NTRS)

Ameri, Ali A.; Giel, Paul W.; McVetta, Ashlie B.

2013-01-01

Analysis tools are needed to investigate aerodynamic performance of Variable-Speed Power Turbines (VSPT) for rotorcraft applications. The VSPT operates at low Reynolds numbers (transitional flow) and over a wide range of incidence. Previously, the capability of a published three-equation turbulence model to predict accurately the transition location for three-dimensional heat transfer problems was assessed. In this paper, the results of a post-diction exercise using a three-dimensional flow in a transonic linear cascade comprising VSPT blading are presented. The measured blade pressure distributions and exit total pressure and flow angles for two incidence angles corresponding to cruise (i = 5.8deg) and takeoff (i = -36.7deg) were used for this study. For the higher loading condition of cruise and the negative incidence condition of takeoff, overall agreement with data may be considered satisfactory but areas of needed improvement are also indicated.

The effects of magnetic fields on the growth of thermal instabilities in cooling flows

NASA Technical Reports Server (NTRS)

David, Laurence P.; Bregman, Joel N.

1989-01-01

The effects of heat conduction and magnetic fields on the growth of thermal instabilities in cooling flows are examined using a time-dependent hydrodynamics code. It is found that, for magnetic field strengths of roughly 1 micro-Gauss, magnetic pressure forces can completely suppress shocks from forming in thermally unstable entropy perturbations with initial length scales as large as 20 kpc, even for initial amplitudes as great as 60 percent. Perturbations with initial amplitudes of 50 percent and initial magnetic field strengths of 1 micro-Gauss cool to 10,000 K on a time scale which is only 22 percent of the initial instantaneous cooling time. Nonlinear perturbations can thus condense out of cooling flows on a time scale substantially less than the time required for linear perturbations and produce significant mass deposition of cold gas while the accreting intracluster gas is still at large radii.

Response mechanisms of attached premixed flames subjected to harmonic forcing

NASA Astrophysics Data System (ADS)

Shreekrishna

The persistent thrust for a cleaner, greener environment has prompted air pollution regulations to be enforced with increased stringency by environmental protection bodies all over the world. This has prompted gas turbine manufacturers to move from nonpremixed combustion to lean, premixed combustion. These lean premixed combustors operate quite fuel-lean compared to the stochiometric, in order to minimize CO and NOx productions, and are very susceptible to oscillations in any of the upstream flow variables. These oscillations cause the heat release rate of the flame to oscillate, which can engage one or more acoustic modes of the combustor or gas turbine components, and under certain conditions, lead to limit cycle oscillations. This phenomenon, called thermoacoustic instabilities, is characterized by very high pressure oscillations and increased heat fluxes at system walls, and can cause significant problems in the routine operability of these combustors, not to mention the occasional hardware damages that could occur, all of which cumulatively cost several millions of dollars. In a bid towards understanding this flow-flame interaction, this research works studies the heat release response of premixed flames to oscillations in reactant equivalence ratio, reactant velocity and pressure, under conditions where the flame preheat zone is convectively compact to these disturbances, using the G-equation. The heat release response is quantified by means of the flame transfer function and together with combustor acoustics, forms a critical component of the analytical models that can predict combustor dynamics. To this end, low excitation amplitude (linear) and high excitation amplitude (nonlinear) responses of the flame are studied in this work. The linear heat release response of lean, premixed flames are seen to be dominated by responses to velocity and equivalence ratio fluctuations at low frequencies, and to pressure fluctuations at high frequencies which are in the vicinity of typical screech frequencies in gas turbine combustors. The nonlinear response problem is exclusively studied in the case of equivalence ratio coupling. Various nonlinearity mechanisms are identified, amongst which the crossover mechanisms, viz., stoichiometric and flammability crossovers, are seen to be responsible in causing saturation in the overall heat release magnitude of the flame. The response physics remain the same across various preheat temperatures and reactant pressures. Finally, comparisons between the chemiluminescence transfer function obtained experimentally and the heat release transfer functions obtained from the reduced order model (ROM) are performed for lean, CH4/Air swirl-stabilized, axisymmetric V-flames. While the comparison between the phases of the experimental and theoretical transfer functions are encouraging, their magnitudes show disagreement at lower Strouhal number gains show disagreement.

Heat flow, heat production, and crustal temperatures in the Archaean Bundelkhand craton, north-central India: Implications for thermal regime beneath the Indian shield

NASA Astrophysics Data System (ADS)

Podugu, Nagaraju; Ray, Labani; Singh, S. P.; Roy, Sukanta

2017-07-01

Heat flow and heat production data sets constrain the crustal thermal structure in the 2.5-3.5 Ga Bundelkhand craton, the oldest cratonic core in northern Indian shield, for the first time and allow comparisons with the southern Indian shield. Temperature measurements carried out in 10 boreholes at five sites in the craton, combined with systematic thermal conductivity measurements on major rock types, yield low heat flow in the range of 32-41 mW m-2, which is distinct from the generally high heat flow reported from other parts of the northern Indian shield. Radioelemental measurements on 243 samples of drill cores and outcrops reveal both large variability and high average heat production for the Neo-Archaean to Palaeo-Proterozoic granites (4.0 ± 2.1 (SD) μW m-3) relative to the Meso-Archaean tonalite-trondhjemite-granodiorite (TTG) gneisses (2.0 ± 1.0 (SD) μW m-3). On the basis of new heat flow and heat production data sets combined with available geological and geophysical information, a set of steady state, heat flow-crustal heat production models representative of varying crustal scenarios in the craton are envisaged. Mantle heat flow and Moho temperatures are found to be in the range of 12-22 mW m-2 and 290-420°C, respectively, not much different from those reported for the similar age Dharwar craton in southern India. This study reveals similar mantle thermal regimes across the northern and southern parts of the Indian shield, in spite of varying surface heat flow regimes, implying that much of the intraprovince and interprovince variations in the Indian shield are explained by variations in upper crustal heat production.

Dynamical criterion for a marginally unstable, quasi-linear behavior in a two-layer model

NASA Technical Reports Server (NTRS)

Ebisuzaki, W.

1988-01-01

A two-layer quasi-geostrophic flow forced by meridional variations in heating can be in regimes ranging from radiative equilibrium to forced geostrophic turbulence. Between these extremes is a regime where the time-mean (zonal) flow is marginally unstable. Using scaling arguments, it is concluded that such a marginally unstable state should occur when a certain parameter, measuring the strength of wave-wave interactions relative to the beta effect and advection by the thermal wind, is small. Numerical simulations support this proposal. A transition from the marginally unstable regime to a more nonlinear regime is then examined through numerical simulations with different radiative forcings. It is found that transition is not caused by secondary instability of waves in the marginally unstable regime. Instead, the time-mean flow can support a number of marginally unstable normal modes. These normal modes interact with each other, and if they are of sufficient amplitude, the flow enters a more nonlinear regime.

Uncertainty and Sensitivity Analysis of Afterbody Radiative Heating Predictions for Earth Entry

NASA Technical Reports Server (NTRS)

West, Thomas K., IV; Johnston, Christopher O.; Hosder, Serhat

2016-01-01

The objective of this work was to perform sensitivity analysis and uncertainty quantification for afterbody radiative heating predictions of Stardust capsule during Earth entry at peak afterbody radiation conditions. The radiation environment in the afterbody region poses significant challenges for accurate uncertainty quantification and sensitivity analysis due to the complexity of the flow physics, computational cost, and large number of un-certain variables. In this study, first a sparse collocation non-intrusive polynomial chaos approach along with global non-linear sensitivity analysis was used to identify the most significant uncertain variables and reduce the dimensions of the stochastic problem. Then, a total order stochastic expansion was constructed over only the important parameters for an efficient and accurate estimate of the uncertainty in radiation. Based on previous work, 388 uncertain parameters were considered in the radiation model, which came from the thermodynamics, flow field chemistry, and radiation modeling. The sensitivity analysis showed that only four of these variables contributed significantly to afterbody radiation uncertainty, accounting for almost 95% of the uncertainty. These included the electronic- impact excitation rate for N between level 2 and level 5 and rates of three chemical reactions in uencing N, N(+), O, and O(+) number densities in the flow field.

Boundary Layer Transition in the Leading Edge Region of a Swept Cylinder in High Speed Flow

NASA Technical Reports Server (NTRS)

Coleman, Colin P.

1998-01-01

Experiments were conducted on a 76 degree swept cylinder to establish the behavior of the attachment line transition process in a low-disturbance level, Mach number 1.6 flow. For a near adiabatic wall condition, the attachment-line boundary layer remained laminar up to the highest attainable Reynolds number. The attachment-line boundary layer transition under the influence of trip wires depended on wind tunnel disturbance level, and a transition onset condition for this flow is established. Internal heating raised the surface temperature of the attachment line to induce boundary layer instabilities. This was demonstrated experimentally for the first time and the frequencies of the most amplified disturbances were determined over a range of temperature settings. Results were in excellent agreement to those predicted by a linear stability code, and provide the first experimental verification of theory. Transition onset along the heated attachment line at an R-bar of 800 under quiet tunnel conditions was found to correlate with an N factor of 13.2. Increased tunnel disturbance levels caused the transition onset to occur at lower cylinder surface temperatures and was found to correlate with an approximate N factor of 1 1.9, so demonstrating that the attachment-line boundary layer is receptive to increases in the tunnel disturbance level.

Heat transfer and pressure drop characteristics of the tube bank fin heat exchanger with fin punched with flow redistributors and curved triangular vortex generators

NASA Astrophysics Data System (ADS)

Liu, Song; Jin, Hua; Song, KeWei; Wang, LiangChen; Wu, Xiang; Wang, LiangBi

2017-10-01

The heat transfer performance of the tube bank fin heat exchanger is limited by the air-side thermal resistance. Thus, enhancing the air-side heat transfer is an effective method to improve the performance of the heat exchanger. A new fin pattern with flow redistributors and curved triangular vortex generators is experimentally studied in this paper. The effects of the flow redistributors located in front of the tube stagnation point and the curved vortex generators located around the tube on the characteristics of heat transfer and pressure drop are discussed in detail. A performance comparison is also carried out between the fins with and without flow redistributors. The experimental results show that the flow redistributors stamped out from the fin in front of the tube stagnation points can decrease the friction factor at the cost of decreasing the heat transfer performance. Whether the combination of the flow redistributors and the curved vortex generators will present a better heat transfer performance depends on the size of the curved vortex generators. As for the studied two sizes of vortex generators, the heat transfer performance is promoted by the flow redistributors for the fin with larger size of vortex generators and the performance is suppressed by the flow redistributors for the fin with smaller vortex generators.

Size effects in non-linear heat conduction with flux-limited behaviors

NASA Astrophysics Data System (ADS)

Li, Shu-Nan; Cao, Bing-Yang

2017-11-01

Size effects are discussed for several non-linear heat conduction models with flux-limited behaviors, including the phonon hydrodynamic, Lagrange multiplier, hierarchy moment, nonlinear phonon hydrodynamic, tempered diffusion, thermon gas and generalized nonlinear models. For the phonon hydrodynamic, Lagrange multiplier and tempered diffusion models, heat flux will not exist in problems with sufficiently small scale. The existence of heat flux needs the sizes of heat conduction larger than their corresponding critical sizes, which are determined by the physical properties and boundary temperatures. The critical sizes can be regarded as the theoretical limits of the applicable ranges for these non-linear heat conduction models with flux-limited behaviors. For sufficiently small scale heat conduction, the phonon hydrodynamic and Lagrange multiplier models can also predict the theoretical possibility of violating the second law and multiplicity. Comparisons are also made between these non-Fourier models and non-linear Fourier heat conduction in the type of fast diffusion, which can also predict flux-limited behaviors.

Heat flow in the SAFOD pilot hole and implications for the strength of the San Andreas Fault

USGS Publications Warehouse

Williams, C.F.; Grubb, F.V.; Galanis, S.P.

2004-01-01

Detailed thermal measurements have been acquired in the 2.2-km-deep SAFOD pilot hole, located 1.8 km west of the SAF near Parkfield, California. Heat flow from the basement section of the borehole (770 to 2160 m) is 91 mW m-2, higher than the published 74 mW m -2 average for the Parkfield area. Within the resolution of the measurements, heat flow is constant across faults that intersect the borehole, suggesting that fluid flow does not alter the conductive thermal regime. Reanalysis of regional heat flow reveals an increase in heat flow along the SAF northwest of Parkfield. This transition corresponds to a shallowing base of seismicity and a change in fault behavior near the northern terminus of the M6 1966 Parkfield earthquake rupture. The persistence of elevated heat flow in the Coast Ranges to the west appears to rule out frictional heating on the SAF as the source of the SAFOD value.

Measurement and simulation of thermoelectric efficiency for single leg

NASA Astrophysics Data System (ADS)

Hu, Xiaokai; Yamamoto, Atsushi; Ohta, Michihiro; Nishiate, Hirotaka

2015-04-01

Thermoelectric efficiency measurements were carried out on n-type bismuth telluride legs with the hot-side temperature at 100 and 150 °C. The electric power and heat flow were measured individually. Water coolant was utilized to maintain the cold-side temperature and to measure heat flow out of the cold side. Leg length and vacuum pressure were studied in terms of temperature difference across the leg, open-circuit voltage, internal resistance, and heat flow. Finite-element simulation on thermoelectric generation was performed in COMSOL Multiphysics, by inputting two-side temperatures and thermoelectric material properties. The open-circuit voltage and resistance were in good agreement between the measurement and simulation. Much larger heat flows were found in measurements, since they were comprised of conductive, convective, and radiative contributions. Parasitic heat flow was measured in the absence of bismuth telluride leg, and the conductive heat flow was then available. Finally, the maximum thermoelectric efficiency was derived in accordance with the electric power and the conductive heat flow.

Map of Io Volcanic Heat Flow

NASA Image and Video Library

2015-09-15

This frame from an animation shows Jupiter volcanic moon Io as seen by NASA Voyager and Galileo spacecraft (at left) and the pattern of heat flow from 242 active volcanoes (at right). The red and yellow areas are places where local heat flow is greatest -- the result of magma erupting from Io's molten interior onto the surface. The map is the result of analyzing decades of observations from spacecraft and ground-based telescopes. It shows Io's usual volcanic thermal emission, excluding the occasional massive but transient "outburst" eruption; in other words, this is what Io looks like most of the time. This heat flow map will be used to test models of interior heating. The map shows that areas of enhanced volcanic heat flow are not necessarily correlated with the number of volcanoes in a particular region and are poorly correlated with expected patterns of heat flow from current models of tidal heating -- something that is yet to be explained. This research is published in association with a 2015 paper in the journal Icarus by A. Davies et al., titled "Map of Io's Volcanic Heat Flow," (http://dx.doi.org/10.1016/j.icarus.2015.08.003.) http://photojournal.jpl.nasa.gov/catalog/PIA19655

Evaluation of correlations of flow boiling heat transfer of R22 in horizontal channels.

PubMed

Zhou, Zhanru; Fang, Xiande; Li, Dingkun

2013-01-01

The calculation of two-phase flow boiling heat transfer of R22 in channels is required in a variety of applications, such as chemical process cooling systems, refrigeration, and air conditioning. A number of correlations for flow boiling heat transfer in channels have been proposed. This work evaluates the existing correlations for flow boiling heat transfer coefficient with 1669 experimental data points of flow boiling heat transfer of R22 collected from 18 published papers. The top two correlations for R22 are those of Liu and Winterton (1991) and Fang (2013), with the mean absolute deviation of 32.7% and 32.8%, respectively. More studies should be carried out to develop better ones. Effects of channel dimension and vapor quality on heat transfer are analyzed, and the results provide valuable information for further research in the correlation of two-phase flow boiling heat transfer of R22 in channels.

Evaluation of Correlations of Flow Boiling Heat Transfer of R22 in Horizontal Channels

PubMed Central

Fang, Xiande; Li, Dingkun

2013-01-01

The calculation of two-phase flow boiling heat transfer of R22 in channels is required in a variety of applications, such as chemical process cooling systems, refrigeration, and air conditioning. A number of correlations for flow boiling heat transfer in channels have been proposed. This work evaluates the existing correlations for flow boiling heat transfer coefficient with 1669 experimental data points of flow boiling heat transfer of R22 collected from 18 published papers. The top two correlations for R22 are those of Liu and Winterton (1991) and Fang (2013), with the mean absolute deviation of 32.7% and 32.8%, respectively. More studies should be carried out to develop better ones. Effects of channel dimension and vapor quality on heat transfer are analyzed, and the results provide valuable information for further research in the correlation of two-phase flow boiling heat transfer of R22 in channels. PMID:23956695

Spectral Attenuation of Sound in Dilute Suspensions with Nonlinear Particle Relaxation

NASA Technical Reports Server (NTRS)

Kandula, Max

2008-01-01

Previous studies on the sound attenuation in particle-laden flows under Stokesian drag and conduction-controlled heat transfer have been extended to accommodate the nonlinear drag and heat transfer. It has been shown that for large particle-to-fluid density ratio, the particle Reynolds number bears a cubic relationship with (omega(tau))(sub d) (where omega is the circular frequency and (tau)(sub d) the Stokesian particle relaxation time). This dependence leads to the existence of a peak value in the linear absorption coefficient occurring at a finite value of(omega(tau))(sub d). Comparison of the predictions with the test data for the spectral attenuation of sound with water injection in a perfectly expanded supersonic air jet shows a satisfactory trend of the theory accounting for nonlinear particle relaxation processes.

Thermal Fault Tolerance Analysis of Carbon Fiber Rope Barrier Systems for Use in the Reusable Solid Rocket Motor ( RSRM) Nozzle Joints

NASA Technical Reports Server (NTRS)

Clayton, J. Louie; Phelps, Lisa (Technical Monitor)

2001-01-01

Carbon Fiber Rope (CFR) thermal barrier systems are being considered for use in several RSRM (Reusable Solid Rocket Motor) nozzle joints as a replacement for the current assembly gap close-out process/design. This study provides for development and test verification of analysis methods used for flow-thermal modeling of a CFR thermal barrier subject to fault conditions such as rope combustion gas blow-by and CFR splice failure. Global model development is based on a 1-D (one dimensional) transient volume filling approach where the flow conditions are calculated as a function of internal 'pipe' and porous media 'Darcy' flow correlations. Combustion gas flow rates are calculated for the CFR on a per-linear inch basis and solved simultaneously with a detailed thermal-gas dynamic model of a local region of gas blow by (or splice fault). Effects of gas compressibility, friction and heat transfer are accounted for the model. Computational Fluid Dynamic (CFD) solutions of the fault regions are used to characterize the local flow field, quantify the amount of free jet spreading and assist in the determination of impingement film coefficients on the nozzle housings. Gas to wall heat transfer is simulated by a large thermal finite element grid of the local structure. The employed numerical technique loosely couples the FE (Finite Element) solution with the gas dynamics solution of the faulted region. All free constants that appear in the governing equations are calibrated by hot fire sub-scale test. The calibrated model is used to make flight predictions using motor aft end environments and timelines. Model results indicate that CFR barrier systems provide a near 'vented joint' style of pressurization. Hypothetical fault conditions considered in this study (blow by, splice defect) are relatively benign in terms of overall heating to nozzle metal housing structures.

Numerical modeling of the thermoelectric cooler with a complementary equation for heat circulation in air gaps

NASA Astrophysics Data System (ADS)

Fang, En; Wu, Xiaojie; Yu, Yuesen; Xiu, Junrui

2017-03-01

In this paper, a numerical model is developed by combining thermodynamics with heat transfer theory. Taking inner and external multi-irreversibility into account, it is with a complementary equation for heat circulation in air gaps of a steady cooling system with commercial thermoelectric modules operating in refrigeration mode. With two modes concerned, the equation presents the heat flowing through air gaps which forms heat circulations between both sides of thermoelectric coolers (TECs). In numerical modelling, a TEC is separated as two temperature controlled constant heat flux reservoirs in a thermal resistance network. In order to obtain the parameter values, an experimental apparatus with a commercial thermoelectric cooler was built to characterize the performance of a TEC with heat source and sink assembly. At constant power dissipation, steady temperatures of heat source and both sides of the thermoelectric cooler were compared with those in a standard numerical model. The method displayed that the relationship between Φf and the ratio Φ_{c}'/Φ_{c} was linear as expected. Then, for verifying the accuracy of proposed numerical model, the data in another system were recorded. It is evident that the experimental results are in good agreement with simulation(proposed model) data at different heat transfer rates. The error is small and mainly results from the instabilities of thermal resistances with temperature change and heat flux, heat loss of the device vertical surfaces and measurements.

Heat exchanger with oscillating flow

NASA Technical Reports Server (NTRS)

Scotti, Stephen J. (Inventor); Blosser, Max L. (Inventor); Camarda, Charles J. (Inventor)

1992-01-01

Various heat exchange apparatuses are described in which an oscillating flow of primary coolant is used to dissipate an incident heat flux. The oscillating flow may be imparted by a reciprocating piston, a double action twin reciprocating piston, fluidic oscillators, or electromagnetic pumps. The oscillating fluid flows through at least one conduit in either an open loop or a closed loop. A secondary flow of coolant may be used to flow over the outer walls of at least one conduit to remove heat transferred from the primary coolant to the walls of the conduit.

Heat exchanger with oscillating flow

NASA Technical Reports Server (NTRS)

Scotti, Stephen J. (Inventor); Blosser, Max L. (Inventor); Camarda, Charles J. (Inventor)

1993-01-01

Various heat exchange apparatuses are described in which an oscillating flow of primary coolant is used to dissipate an incident heat flux. The oscillating flow may be imparted by a reciprocating piston, a double action twin reciprocating piston, fluidic oscillators or electromagnetic pumps. The oscillating fluid flows through at least one conduit in either an open loop or a closed loop. A secondary flow of coolant may be used to flow over the outer walls of at least one conduit to remove heat transferred from the primary coolant to the walls of the conduit.

Experimental and Numerical Analysis of Air Flow, Heat Transfer and Thermal Comfort in Buildings with Different Heating Systems

NASA Astrophysics Data System (ADS)

Sabanskis, A.; Virbulis, J.

2016-04-01

Monitoring of temperature, humidity and air flow velocity is performed in 5 experimental buildings with the inner size of 3×3×3 m3 located in Riga, Latvia. The buildings are equipped with different heating systems, such as an air-air heat pump, air-water heat pump, capillary heating mat on the ceiling and electric heater. Numerical simulation of air flow and heat transfer by convection, conduction and radiation is carried out using OpenFOAM software and compared with experimental data. Results are analysed regarding the temperature and air flow distribution as well as thermal comfort.

Aerodynamic pressure and heating-rate distributions in tile gaps around chine regions with pressure gradients at a Mach number of 6.6

NASA Technical Reports Server (NTRS)

Hunt, L. Roane; Notestine, Kristopher K.

1990-01-01

Surface and gap pressures and heating-rate distributions were obtained for simulated Thermal Protection System (TPS) tile arrays on the curved surface test apparatus of the Langley 8-Foot High Temperature Tunnel at Mach 6.6. The results indicated that the chine gap pressures varied inversely with gap width because larger gap widths allowed greater venting from the gap to the lower model side pressures. Lower gap pressures caused greater flow ingress from the surface and increased gap heating. Generally, gap heating was greater in the longitudinal gaps than in the circumferential gaps. Gap heating decreased with increasing gap depth. Circumferential gap heating at the mid-depth was generally less than about 10 percent of the external surface value. Gap heating was most severe at local T-gap junctions and tile-to-tile forward-facing steps that caused the greatest heating from flow impingement. The use of flow stoppers at discrete locations reduced heating from flow impingement. The use of flow stoppers at discrete locations reduced heating in most gaps but increased heating in others. Limited use of flow stoppers or gap filler in longitudinal gaps could reduce gap heating in open circumferential gaps in regions of high surface pressure gradients.

Heating and cooling system for an on-board gas adsorbent storage vessel

DOEpatents

Tamburello, David A.; Anton, Donald L.; Hardy, Bruce J.; Corgnale, Claudio

2017-06-20

In one aspect, a system for controlling the temperature within a gas adsorbent storage vessel of a vehicle may include an air conditioning system forming a continuous flow loop of heat exchange fluid that is cycled between a heated flow and a cooled flow. The system may also include at least one fluid by-pass line extending at least partially within the gas adsorbent storage vessel. The fluid by-pass line(s) may be configured to receive a by-pass flow including at least a portion of the heated flow or the cooled flow of the heat exchange fluid at one or more input locations and expel the by-pass flow back into the continuous flow loop at one or more output locations, wherein the by-pass flow is directed through the gas adsorbent storage vessel via the by-pass line(s) so as to adjust an internal temperature within the gas adsorbent storage vessel.

Modeling of Compressible Flow with Friction and Heat Transfer Using the Generalized Fluid System Simulation Program (GFSSP)

NASA Technical Reports Server (NTRS)

Bandyopadhyay, Alak; Majumdar, Alok

2007-01-01

The present paper describes the verification and validation of a quasi one-dimensional pressure based finite volume algorithm, implemented in Generalized Fluid System Simulation Program (GFSSP), for predicting compressible flow with friction, heat transfer and area change. The numerical predictions were compared with two classical solutions of compressible flow, i.e. Fanno and Rayleigh flow. Fanno flow provides an analytical solution of compressible flow in a long slender pipe where incoming subsonic flow can be choked due to friction. On the other hand, Raleigh flow provides analytical solution of frictionless compressible flow with heat transfer where incoming subsonic flow can be choked at the outlet boundary with heat addition to the control volume. Nonuniform grid distribution improves the accuracy of numerical prediction. A benchmark numerical solution of compressible flow in a converging-diverging nozzle with friction and heat transfer has been developed to verify GFSSP's numerical predictions. The numerical predictions compare favorably in all cases.

The Characteristics of Heat Flow in the Ryukyu Trench-Arc-Basin System: Constraints on Thermal Structure and Evolution of the Okinawa Trough

NASA Astrophysics Data System (ADS)

Zhang, L.

2017-12-01

Heat flow is an important constraint to study the thermal structure and evolution in modeling experiments. Based on the surface heat flow map and recent geochemistry results, a 2D transient heat conduction-advection model is used to investigate how the effects of sedimentation rate, magmatic intrusion, extension duration and rate on the surface heat flow distribution of the Okinawa Trough. Surface heat flow distribution map is interpolated based on a data set with 664 measurements in the Ryukyu trench-arc-basin system. The map shows an obviously correspondence between heat flows and tectonic zones, characterized by belts in E-W and blocks in S-N. The heat flow is extremely high and variable in the central Okinawa Trough (COT). The lowest heat values are distributed in the northwest of West Philippine Sea near the Ryukyu Trench. This phenomenon is likely related to increasing hydrothermal circulation of cold water into the upper portion of the incoming plate because of bend-faulting and little sediment coverage. Simulation results show that (1) High sedimentation rate can reduce heat flow by 30-35 % in the southern OT. (2) The sedimentation-corrected heat flow indicates that mantle upwelling occurred in the whole OT. The isotherm of 1000°C reaches to the depth of 19 km in the axil of the COT after 10 Ma. (3) The heat flow can be improved drastically by dyke intrusion along normal faults, but subsequent decreases rapidly about 15% after 0.1 Ma, which indicates the age of dyke intrusion under the Iheya area is younger than 0.5 Ma, and the depth is shallower than 2 km. Moreover, the magma fluid upward migrated along the magma conduits is required for the extremely high heat flow and its Darcy velocity can reach to 9 cm/yr. Based on the distribution of heat flow, we suggest that there is a different evolution model between the central- northern OT and the southern. The time of rifting in the NOT-COT began at 10 Ma with the mean rate of 0.4 cm/yr, while the rifting of the SOT started from 6 Ma with higher rate of 0.6 cm/yr.

Laser heating of aqueous samples on a micro-optical-electro-mechanical system

DOEpatents

Beer, Neil Reginald; Kennedy, Ian

2013-12-17

A system of heating a sample on a microchip includes the steps of providing a microchannel flow channel in the microchip; positioning the sample within the microchannel flow channel, providing a laser that directs a laser beam onto the sample for heating the sample; providing the microchannel flow channel with a wall section that receives the laser beam and enables the laser beam to pass through wall section of the microchannel flow channel without being appreciably heated by the laser beam; and providing a carrier fluid in the microchannel flow channel that moves the sample in the microchannel flow channel wherein the carrier fluid is not appreciably heated by the laser beam.

Laser heating of aqueous samples on a micro-optical-electro-mechanical system

DOEpatents

Beer, Neil Reginald; Kennedy, Ian

2013-02-05

A system of heating a sample on a microchip includes the steps of providing a microchannel flow channel in the microchip; positioning the sample within the microchannel flow channel, providing a laser that directs a laser beam onto the sample for heating the sample; providing the microchannel flow channel with a wall section that receives the laser beam and enables the laser beam to pass through wall section of the microchannel flow channel without being appreciably heated by the laser beam; and providing a carrier fluid in the microchannel flow channel that moves the sample in the microchannel flow channel wherein the carrier fluid is not appreciably heated by the laser beam.

Weld pool development during GTA and laser beam welding of Type 304 stainless steel; Part I - theoretical analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharia, T.; David, S.A.; Vitek, J.M.

1989-12-01

A computational and experimental study was carried out to quantitatively understand the influence of the heat flow and the fluid flow in the transient development of the weld pool during gas tungsten arc (GTA) and laser beam welding of Type 304 stainless steel. Stationary gas tungsten arc and laser beam welds were made on two heats of Type 304 austenitic stainless steels containing 90 ppm sulfur and 240 ppm sulfur. A transient heat transfer model was utilized to simulate the heat flow and fluid flow in the weld pool. In this paper, the results of the heat flow and fluidmore » flow analysis are presented.« less

A mechanistic model of heat transfer for gas-liquid flow in vertical wellbore annuli.

PubMed

Yin, Bang-Tang; Li, Xiang-Fang; Liu, Gang

2018-01-01

The most prominent aspect of multiphase flow is the variation in the physical distribution of the phases in the flow conduit known as the flow pattern. Several different flow patterns can exist under different flow conditions which have significant effects on liquid holdup, pressure gradient and heat transfer. Gas-liquid two-phase flow in an annulus can be found in a variety of practical situations. In high rate oil and gas production, it may be beneficial to flow fluids vertically through the annulus configuration between well tubing and casing. The flow patterns in annuli are different from pipe flow. There are both casing and tubing liquid films in slug flow and annular flow in the annulus. Multiphase heat transfer depends on the hydrodynamic behavior of the flow. There are very limited research results that can be found in the open literature for multiphase heat transfer in wellbore annuli. A mechanistic model of multiphase heat transfer is developed for different flow patterns of upward gas-liquid flow in vertical annuli. The required local flow parameters are predicted by use of the hydraulic model of steady-state multiphase flow in wellbore annuli recently developed by Yin et al. The modified heat-transfer model for single gas or liquid flow is verified by comparison with Manabe's experimental results. For different flow patterns, it is compared with modified unified Zhang et al. model based on representative diameters.

An efficient direct solver for rarefied gas flows with arbitrary statistics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Diaz, Manuel A., E-mail: f99543083@ntu.edu.tw; Yang, Jaw-Yen, E-mail: yangjy@iam.ntu.edu.tw; Center of Advanced Study in Theoretical Science, National Taiwan University, Taipei 10167, Taiwan

2016-01-15

A new numerical methodology associated with a unified treatment is presented to solve the Boltzmann–BGK equation of gas dynamics for the classical and quantum gases described by the Bose–Einstein and Fermi–Dirac statistics. Utilizing a class of globally-stiffly-accurate implicit–explicit Runge–Kutta scheme for the temporal evolution, associated with the discrete ordinate method for the quadratures in the momentum space and the weighted essentially non-oscillatory method for the spatial discretization, the proposed scheme is asymptotic-preserving and imposes no non-linear solver or requires the knowledge of fugacity and temperature to capture the flow structures in the hydrodynamic (Euler) limit. The proposed treatment overcomes themore » limitations found in the work by Yang and Muljadi (2011) [33] due to the non-linear nature of quantum relations, and can be applied in studying the dynamics of a gas with internal degrees of freedom with correct values of the ratio of specific heat for the flow regimes for all Knudsen numbers and energy wave lengths. The present methodology is numerically validated with the unified treatment by the one-dimensional shock tube problem and the two-dimensional Riemann problems for gases of arbitrary statistics. Descriptions of ideal quantum gases including rotational degrees of freedom have been successfully achieved under the proposed methodology.« less

[The value of the thermocouple in the measurement of the gastric mucosal blood-flow. The influence of the occlusion of the celiac artery and prostaglandin E1 on the gastric mucosal blood flow. An experimental study in animals (author's transl)].

PubMed

Koch, H; Demling, L

1976-02-27

The study has been carried out to ensure the positive evidence of the measurement of the gastric mucosal blood-flow with the aid of the thermocouple (heat-clearance technique). The experiments have shown that the suction pressure of 600 mm mercury column which was used to fix the Thermocouple to the mucosa was indispensable in order to assess the blood-flow in the entire depth of the mucosa. Changes in the mucosal blood-flow are measuured at the same rate in all quadrants of the gastric corpus. The measuring of the blood-flow of a well circumscribed area of the mucosa is therefore representative for the entire corpus. Vasopressin led to a significant reduction of the gastric mucosal blood-flow measured with heat-clearance as well aminopyrine-clearance. There was a linear correlation between the results of both methods. Vasopressin selectively reduces the blood-flow of the gastric mucosa but not of the submucosa, the muscular layer and the serosa. Therefore it seems to be probable that changes in mucosal blood-flow selectively can be measured with the aid of the thermocouple. After previous stimulation with pentagastrin neither mucosal blood-flow nor acid secretion of the stomach were influenced by the occlusion of the celiac artery by 25 %. The occlusion of the celiac artery by 50 % reduced significantly the pentagastrin-stimulated gastric mucosal blood-flow whereas the acid secretion was not influenced. Prostaglandin E1 at a dose rate of 2 mug/kg-h increased significantly arterial and mucosal blood-flow as well as acid secretion of the stomach. In comparison PGE1 administered at a dose rate of 4 mug/kg-h reduced significantly gastric mucosal blood-flow and gastric secretion. PGE1 at a dose rate of 8 mug/kg-h did not produce any significant changes in blood-flow and secretion. The results suggested that the changes of gastric secretion observed with PGE1 were the consequence of primary changes in the gastric mucosal blood-flow.

Improving crystal size distribution by internal seeding combined cooling/antisolvent crystallization with a cooling/heating cycle

NASA Astrophysics Data System (ADS)

Lenka, Maheswata; Sarkar, Debasis

2018-03-01

This work investigates the effect of internal seeding and an initial cooling/heating cycle on the final crystal size distribution (CSD) during a combined cooling/antisolvent crystallization of L-asparagine monohydrate from it's aqueous solution using isopropyl-alcohol as antisolvent. Internal seeds were generated by one-pot addition of various amounts of antisolvent to the crystallizer. It was then followed by a cooling/heating cycle to dissolve the fines produced and thus obtain a suitable initial seed. A combined cooling/antisolvent crystallization was then followed by employing a linear cooling profile with simultaneous addition of antisolvent with a constant mass flow rate to promote the growth of the internally generated seeds. The amount of initial antisolvent influences the characteristics of the internal seeds generated and the effect of initial amount of antisolvent on the final CSD is investigated. It was found that the introduction of a single cooling/heating cycle significantly improves the reproducibility of final CSD as well as the mean size. Overall, the study indicates that the application of internal seeding with a single cooling/heating cycle for fines dissolution is an effective technique to tailor crystal size distribution.

The sudden coalescene model of the boiling crisis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carrica, P.M.; Clausse, A.

1995-09-01

A local two-phase flow integral model of nucleate boiling and crisis is presented. The model is based on average balances on a control volume, yielding to a set of three nonlinear differential equations for the local void fraction, bubble number density and velocity. Boiling crisis as critical heat flux is interpreted as a dynamic transition caused by the coalescence of bubbles near the heater. The theoretical dynamic model is compared with experimental results obtained for linear power ramps in a horizontal plate heater in R-113, showing an excellent qualitative agreement.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nabeel, A.; Khan, T.A.; Sharma, D.K.

The kinetics of co-combustion/co-cracking of Topa coal with polystyrene, poly(vinyl chloride), and bakelite have been studied by theromogravimetric analysis at a linear heating rate of 20C/min in a stream of air for combustion and in nitrogen for cracking with a flow rate of 20 cm{sup 3}/min up to the temperature of 900C under non-isothermal conditions. The order of reaction and overall activation energy of the reactions have been calculated. These studies may help in synergistic production of value-added organic compounds and spatiality chemicals from coal and plastics.

Power dependence of reflectivity of metallic films.

PubMed

Yeh, Y C; Stafsudd, O M

1976-01-01

The reflectivity of vacuum-deposited gold films on quartz glass substrates was studied as a function of 10.6-microm radiation power density. A simple linear model of the temperature dependence of the absorptivity of the gold film is developed. This temperature dependence is coupled with a three-dimensional heat flow analysis and fits the experimental data well. The absorptivity alpha is written as alpha(0)(1 + betaT) and the values of alpha(0) and beta are determined, respectively, as (0.88 +/- 0.01) x 10(-2) and 12 x 10(-4)/ degrees C.

Pneumatic Proboscis Heat-Flow Probe

NASA Technical Reports Server (NTRS)

Zacny, Kris; Hedlund, Magnus; Mumm, Eric; Shasho, Jeffrey; Chu, Philip; Kumar, Nishant

2013-01-01

Heat flow is a fundamental property of a planet, and provides significant constraints on the abundance of radiogenic isotopes, the thermal evolution and differentiation history, and the mechanical properties of the lithosphere. Heat-flow measurements are also essential in achieving at least four of the goals set out by the National Research Council for future lunar exploration. The heat-flow probe therefore directly addresses the goal of the Lunar Geophysical Network, which is to understand the interior structure and composition of the Moon. A key challenge for heat flow measurement is to install thermal sensors to the depths approximately equal to 3 m that are not influenced by the diurnal, annual, and longer-term fluctuations of the surface thermal environment. In addition, once deployed, the heat flow probe should cause little disturbance to the thermal regime of the surrounding regolith. A heat-flow probe system was developed that has two novel features: (1) it utilizes a pneumatic (gas) approach, excavates a hole by lofting the lunar soil out of the hole, and (2) deploys the heat flow probe, which utilizes a coiled up tape as a thermal probe to reach greater than 3-meter depth. The system is a game-changer for small lunar landers as it exhibits extremely low mass, volume, and simple deployment. The pneumatic system takes advantage of the helium gas used for pressurizing liquid propellant of the lander. Normally, helium is vented once the lander is on the surface, but it can be utilized for powering pneumatic systems. Should sufficient helium not be available, a simple gas delivery system may be taken specifically for the heat flow probe. Either way, the pneumatic heat flow probe system would be much lighter than other systems that entirely rely on the electrical power of the lander.

New Marine Heat Flow measurements at the Costa Rica Rift, Panama Basin

NASA Astrophysics Data System (ADS)

Harris, R. N.; Kolandaivelu, K. P.; Gregory, E. P. M.; Alshafai, R.; Lowell, R. P.; Hobbs, R. W.

2016-12-01

We report new heat flow measurements collected along the southern flank of the Costa Rica ridge. This ridge flank has been the site of numerous seismic, heat flow, and ocean drilling experiments and has become an important type location for investigations of off-axis hydrothermal processes. These data were collected as part of an interdisciplinary NERC and NSF-funded collaboration entitled: Oceanographic and Seismic Characterization of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge (OSCAR), to better understand links between crustal evolution, hydrothermal heat loss and the impact of this heat loss and fluid mass discharge on deep ocean circulation. The heat flow measurements are collocated with a newly acquired high-resolution seismic profile collected using a GI-gun source to image the sedimentary and upper crustal section. The profile is tied to ODP Hole 504B and provides robust estimates of the sediment thickness as well as its internal structure. In total five heat flow stations consisting of 67 new heat flow measurements were made, spanning crustal ages between 1.3 and 5.4 Myr. The full spreading rate of 66 mm/yr gives rise to abyssal hill basement relief between 500 and 250 m. Sediment cover is relatively incomplete in this region and varies between 0 and 290 m. The majority of heat flow values fall below half-space cooling models indicating that significant amounts of heat are removed by hydrothermal circulation. Low heat flow values are observed in sediment ponds between abyssal hill relief and high values are generally associated with ridge-ward dipping faults bounding abyssal hills. These faults are likely high permeability pathways where heated fluids are discharging, providing an example where large-scale faulting and block rotation plays a major role in ventilated ridge flank fluid circulation. The heat flow fraction (qobs/qpred) varies between varies between 0.01 and 4.1 and has a mean of 0.3 indicating that on average 70% of the expected heat is advected. The mass flux associated with this heat advection is 5 x 10-6 kg/m2-s assuming temperature discharge on the ridge flank is 10° C above ambient.

Periodic unsteady effects on turbulent boundary layer transport and heat transfer: An experimental investigation in a cylinder-wall junction flow

NASA Astrophysics Data System (ADS)

Xie, Qi

Heat transfer in a turbulent boundary layer downstream of junction with a cylinder has many engineering applications including controlling heat transfer to the endwall in gas turbine passages and cooling of protruding electronic chips. The main objective of this research is to study the fundamental process of heat transport and wall heat transfer in a turbulent three-dimensional flow superimposed with local large-scale periodic unsteadiness generated by vortex shedding from the cylinder. Direct measurements of the Reynolds heat fluxes (/line{utheta},\\ /line{vtheta}\\ and\\ /line{wtheta}) and time-resolved wall heat transfer rate will provide insight into unsteady flow behavior and data for advanced turbulence models for numerical simulation of complex engineering flows. Experiments were conducted in an open-circuit, low-speed wind tunnel. Reynolds stresses and heat fluxes were obtained from turbulent heat-flux probes which consisted of two hot wires, arranged in an X-wire configuration, and a cold wire located in front of the X-wire. Thin-film surface heat flux sensors were designed for measuring time-resolved wall heat flux. A reference probe and conditional-sampling technique connected the flow field dynamics to wall heat transfer. An event detecting and ensemble-averaging method was developed to separate effects of unsteadiness from those of background turbulence. Results indicate that unsteadiness affects both heat transport and wall heat transfer. The flow behind the cylinder can be characterized by three regions: (1) Wake region, where unsteadiness is observed to have modest effect; (2) Unsteady region, where the strongest unsteadiness effect is found; (3) Outer region, where the flow approaches the two-dimensional boundary-layer behavior. Vortex shedding from both sides of the cylinder contributes to mixing enhancement in the wake region. Unsteadiness contributes up to 51% of vertical and 59% of spanwise turbulent heat fluxes in the unsteady region. The instantaneous wall Stanton number increased up to 100% compared with an undisturbed flow. Large-scale fluctuations of wall Stanton number were due to the periodic thinning and thickening of the thermal layer caused by periodic vertical velocity fluctuations. This suggests that the outerlayer motion affects near-wall flow behavior and wall heat transfer.

AEROELASTIC SIMULATION TOOL FOR INFLATABLE BALLUTE AEROCAPTURE

NASA Technical Reports Server (NTRS)

Liever, P. A.; Sheta, E. F.; Habchi, S. D.

2006-01-01

A multidisciplinary analysis tool is under development for predicting the impact of aeroelastic effects on the functionality of inflatable ballute aeroassist vehicles in both the continuum and rarefied flow regimes. High-fidelity modules for continuum and rarefied aerodynamics, structural dynamics, heat transfer, and computational grid deformation are coupled in an integrated multi-physics, multi-disciplinary computing environment. This flexible and extensible approach allows the integration of state-of-the-art, stand-alone NASA and industry leading continuum and rarefied flow solvers and structural analysis codes into a computing environment in which the modules can run concurrently with synchronized data transfer. Coupled fluid-structure continuum flow demonstrations were conducted on a clamped ballute configuration. The feasibility of implementing a DSMC flow solver in the simulation framework was demonstrated, and loosely coupled rarefied flow aeroelastic demonstrations were performed. A NASA and industry technology survey identified CFD, DSMC and structural analysis codes capable of modeling non-linear shape and material response of thin-film inflated aeroshells. The simulation technology will find direct and immediate applications with NASA and industry in ongoing aerocapture technology development programs.

Pāhoehoe flow cooling, discharge, and coverage rates from thermal image chronometry

USGS Publications Warehouse

Dehn, Jonathan; Hamilton, Christopher M.; Harris, A. J. L.; Herd, Richard A.; James, M.R.; Lodato, Luigi; Steffke, Andrea

2007-01-01

Theoretically- and empirically-derived cooling rates for active pāhoehoe lava flows show that surface cooling is controlled by conductive heat loss through a crust that is thickening with the square root of time. The model is based on a linear relationship that links log(time) with surface cooling. This predictable cooling behavior can be used assess the age of recently emplaced sheet flows from their surface temperatures. Using a single thermal image, or image mosaic, this allows quantification of the variation in areal coverage rates and lava discharge rates over 48 hour periods prior to image capture. For pāhoehoe sheet flow at Kīlauea (Hawai`i) this gives coverage rates of 1–5 m2/min at discharge rates of 0.01–0.05 m3/s, increasing to ∼40 m2/min at 0.4–0.5 m3/s. Our thermal chronometry approach represents a quick and easy method of tracking flow advance over a three-day period using a single, thermal snap-shot.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chandra, Mani; Gammie, Charles F.; Foucart, Francois, E-mail: manic@illinois.edu, E-mail: gammie@illinois.edu, E-mail: fvfoucart@lbl.gov

Hot, diffuse, relativistic plasmas such as sub-Eddington black-hole accretion flows are expected to be collisionless, yet are commonly modeled as a fluid using ideal general relativistic magnetohydrodynamics (GRMHD). Dissipative effects such as heat conduction and viscosity can be important in a collisionless plasma and will potentially alter the dynamics and radiative properties of the flow from that in ideal fluid models; we refer to models that include these processes as Extended GRMHD. Here we describe a new conservative code, grim, that enables all of the above and additional physics to be efficiently incorporated. grim combines time evolution and primitive variablemore » inversion needed for conservative schemes into a single step using an algorithm that only requires the residuals of the governing equations as inputs. This algorithm enables the code to be physics agnostic as well as flexibility regarding time-stepping schemes. grim runs on CPUs, as well as on GPUs, using the same code. We formulate a performance model and use it to show that our implementation runs optimally on both architectures. grim correctly captures classical GRMHD test problems as well as a new suite of linear and nonlinear test problems with anisotropic conduction and viscosity in special and general relativity. As tests and example applications, we resolve the shock substructure due to the presence of dissipation, and report on relativistic versions of the magneto-thermal instability and heat flux driven buoyancy instability, which arise due to anisotropic heat conduction, and of the firehose instability, which occurs due to anisotropic pressure (i.e., viscosity). Finally, we show an example integration of an accretion flow around a Kerr black hole, using Extended GRMHD.« less

Heat flow in Oklahoma

NASA Astrophysics Data System (ADS)

Cranganu, Constantin

Twenty new heat flow values are incorporated, along with 40 previously published data, into a heat flow map of Oklahoma. The new heat flow data were estimated using previous temperature measurements in boreholes made by American Petroleum Institute researchers and 1,498 thermal conductivity measurements on drill cuttings. The mean of 20 average thermal gradients is 30.50sp°C/km. In general, thermal gradients increase from SW (14.11sp°C/km) to NE (42.24sp°C/km). The range of 1,498 in situ thermal conductivity measurements (after corrections for anisotropy, in situ temperature, and porosity) is 0.90-6.1 W/m-K; the average is 1.68 W/m-K. Estimated near-surface heat flow (±20%) at 20 new sites in Oklahoma varies between 22 ± 4 mW/msp2 and 86 ± 17 mW/msp2; the average is 50 mW/msp2. Twenty-seven new heat-generation estimates, along with 22 previously published data, are used to create a heat generation map of Oklahoma. The range of heat production estimates is 1.1-3.5 muW/msp3, with an average of 2.5 muW/msp3. The heat flow regime in Oklahoma is primarily conductive in nature, except for a zone in northeast. Transient effects due to sedimentary processes and metamorphic/igneous activity, as well as past climatic changes, do not significantly influence the thermal state of the Oklahoma crust. Heat flow near the margins of the Arkoma and Anadarko Basins may be depressed or elevated by 5-13 mW/msp2 by refraction of heat from sedimentary rocks of relatively low thermal conductivity (1-2 W/m-K) into crystalline basement rocks of relatively high thermal conductivity (˜3-4 W/m-K). The heat generation-heat flow relationship shows a modest correlation. The relatively high heat flow (˜70-80 mW/msp2) in part of northeastern Oklahoma suggests that the thermal regime there may be perturbed by regional groundwater flow originating in the fractured outcrops of the Arbuckle-Simpson aquifer in the Arbuckle Mountains.

Heat Pipe Planets

NASA Technical Reports Server (NTRS)

Moore, William B.; Simon, Justin I.; Webb, A. Alexander G.

2014-01-01

When volcanism dominates heat transport, a terrestrial body enters a heat-pipe mode, in which hot magma moves through the lithosphere in narrow channels. Even at high heat flow, a heat-pipe planet develops a thick, cold, downwards-advecting lithosphere dominated by (ultra-)mafic flows and contractional deformation at the surface. Heat-pipes are an important feature of terrestrial planets at high heat flow, as illustrated by Io. Evidence for their operation early in Earth's history suggests that all terrestrial bodies should experience an episode of heat-pipe cooling early in their histories.

Frictional strength and heat flow of southern San Andreas Fault

NASA Astrophysics Data System (ADS)

Zhu, P. P.

2016-01-01

Frictional strength and heat flow of faults are two related subjects in geophysics and seismology. To date, the investigation on regional frictional strength and heat flow still stays at the stage of qualitative estimation. This paper is concentrated on the regional frictional strength and heat flow of the southern San Andreas Fault (SAF). Based on the in situ borehole measured stress data, using the method of 3D dynamic faulting analysis, we quantitatively determine the regional normal stress, shear stress, and friction coefficient at various seismogenic depths. These new data indicate that the southern SAF is a weak fault within the depth of 15 km. As depth increases, all the regional normal and shear stresses and friction coefficient increase. The former two increase faster than the latter. Regional shear stress increment per kilometer equals 5.75 ± 0.05 MPa/km for depth ≤15 km; regional normal stress increment per kilometer is equal to 25.3 ± 0.1 MPa/km for depth ≤15 km. As depth increases, regional friction coefficient increment per kilometer decreases rapidly from 0.08 to 0.01/km at depths less than ~3 km. As depth increases from ~3 to ~5 km, it is 0.01/km and then from ~5 to 15 km, and it is 0.002/km. Previously, frictional strength could be qualitatively determined by heat flow measurements. It is difficult to obtain the quantitative heat flow data for the SAF because the measured heat flow data exhibit large scatter. However, our quantitative results of frictional strength can be employed to investigate the heat flow in the southern SAF. We use a physical quantity P f to describe heat flow. It represents the dissipative friction heat power per unit area generated by the relative motion of two tectonic plates accommodated by off-fault deformation. P f is called "fault friction heat." On the basis of our determined frictional strength data, utilizing the method of 3D dynamic faulting analysis, we quantitatively determine the regional long-term fault friction heat at various seismogenic depths in the southern SAF. The new data show that as depth increases, regional friction stress increases within the depth of 15 km; its increment per kilometer equals 5.75 ± 0.05 MPa/km. As depth increases, regional long-term fault friction heat increases; its increment per kilometer is equal to 3.68 ± 0.03 mW/m2/km. The values of regional long-term fault friction heat provided by this study are always lower than those from heat flow measurements. The difference between them and the scatter existing in the measured heat flow data are mainly caused by the following processes: (i) heat convection, (ii) heat advection, (iii) stress accumulation, (iv) seismic bursts between short-term lull periods in a long-term period, and (v) influence of seismicity in short-term periods upon long-term slip rate and heat flow. Fault friction heat is a fundamental parameter in research on heat flow.

A prototype heat pipe heat exchanger for the capillary pumped loop flight experiment

NASA Technical Reports Server (NTRS)

Ku, Jentung; Yun, Seokgeun; Kroliczek, Edward J.

1992-01-01

A Capillary Pumped Two-Phase Heat Transport Loop (CAPL) Flight Experiment, currently planned for 1993, will provide microgravity verification of the prototype capillary pumped loop (CPL) thermal control system for EOS. CAPL employs a heat pipe heat exchanger (HPHX) to couple the condenser section of the CPL to the radiator assembly. A prototype HPHX consisting of a heat exchanger (HX), a header heat pipe (HHP), a spreader heat pipe (SHP), and a flow regulator has been designed and tested. The HX transmits heat from the CPL condenser to the HHP, while the HHP and SHP transport heat to the radiator assembly. The flow regulator controls flow distribution among multiple parallel HPHX's. Test results indicated that the prototype HPHX could transport up to 800 watts with an overall heat transfer coefficient of more than 6000 watts/sq m-deg C. Flow regulation among parallel HPHX's was also demonstrated.

Using hydrogeologic data to evaluate geothermal potential in the eastern Great Basin

USGS Publications Warehouse

Masbruch, Melissa D.; Heilweil, Victor M.; Brooks, Lynette E.

2012-01-01

In support of a larger study to evaluate geothermal resource development of high-permeability stratigraphic units in sedimentary basins, this paper integrates groundwater and thermal data to evaluate heat and fluid flow within the eastern Great Basin. Previously published information from a hydrogeologic framework, a potentiometric-surface map, and groundwater budgets was compared to a surficial heat-flow map. Comparisons between regional groundwater flow patterns and surficial heat flow indicate a strong spatial relation between regional groundwater movement and surficial heat distribution. Combining aquifer geometry and heat-flow maps, a selected group of subareas within the eastern Great Basin are identified that have high surficial heat flow and are underlain by a sequence of thick basin-fill deposits and permeable carbonate aquifers. These regions may have potential for future geothermal resources development.

Survey of literature on convective heat transfer coefficients and recovery factors for high atmosphere thermometry

NASA Technical Reports Server (NTRS)

Chung, S.

1973-01-01

Heat transfer phenomena of rarefied gas flows is discussed based on a literature survey of analytical and experimental rarefied gas dynamics. Subsonic flows are emphasized for the purposes of meteorological thermometry in the high atmosphere. The heat transfer coefficients for three basic geometries are given in the regimes of free molecular flow, transition flow, slip flow, and continuum flow. Different types of heat phenomena, and the analysis of theoretical and experimental data are presented. The uncertainties calculated from the interpolation rule compared with the available experimental data are discussed. The recovery factor for each geometry in subsonic rarefied flows is also given.

Advective and Conductive Heat Flow Budget Across the Wagner Basin, Northern Gulf of California

NASA Astrophysics Data System (ADS)

Neumann, F.; Negrete-Aranda, R.; Contreras, J.; Müller, C.; Hutnak, M.; Gonzalez-Fernandez, A.; Harris, R. N.; Sclater, J. G.

2015-12-01

In May 2015, we conducted a cruise across the northern Gulf of California, an area of continental rift basin formation and rapid deposition of sediments. The cruise was undertaken aboard the R/V Alpha Helix; our goal was to study variation in superficial conductive heat flow, lateral changes in the shallow thermal conductivity structure, and advective transport of heat across the Wagner basin. We used a Fielax heat flow probe with 22 thermistors that can penetrate up to 6 m into the sediment cover. The resulting data set includes 53 new heat flow measurements collected along three profiles. The longest profile (42 km) contains 30 measurements spaced 1-2 km apart. The western part of the Wagner basin (hanging wall block) exhibit low to normal conductive heat flow whereas the eastern part of the basin (foot wall block) heat flow is high to very high (up to 2500 mWm-2). Two other short profiles (12 km long each) focused on resolving an extremely high heat flow anomaly up to 15 Wm-2 located near the intersection between the Wagner bounding fault system and the Cerro Prieto fault. We hypothesize that the contrasting heat flow values observed across the Wagner basin are due to horizontal water circulation through sand layers and fault pathways of high permeability. Circulation appears to be from west (recharge zone) to east (discharge zone). Additionally, our results reveal strong vertical advection of heat due to dehydration reactions and compaction of fine grained sediments.

Complex Heat Exchangers for Improved Performance

NASA Astrophysics Data System (ADS)

Bran, Gabriela Alejandra

After a detailed literature review, it was determined that there was a need for a more comprehensive study on the transient behavior of heat exchangers. Computational power was not readily available when most of the work on transient heat exchangers was done (1956 - 1986), so most of these solutions have restrictions, or very specific assumptions. More recently, authors have obtained numerical solutions for more general problems (2003 - 2013), but they have investigated very specific conditions, and cases. For a more complex heat exchanger (i.e. with heat generation), the transient solutions from literature are no longer valid. There was a need to develop a numerical model that relaxes the restrictions of current solutions to explore conditions that have not been explored. A one dimensional transient heat exchanger model was developed. There are no restrictions on the fluids and wall conditions. The model is able to obtain a numerical solution for a wide range of fluid properties and mass flow rates. Another innovative characteristic of the numerical model is that the boundary and initial conditions are not limited to constant values. The boundary conditions can be a function of time (i.e. sinusoidal signal), and the initial conditions can be a function of position. Four different cases were explored in this work. In the first case, the start-up of a system was investigated where the whole system is assumed to be at the same temperature. In the second case, the new steady state in case one gets disrupted by a smaller inlet temperature step change. In the third case, the new steady state in case one gets disrupted by a step change in one of the mass flow rates. The response of these three cases show that there are different transient behaviors, and they depend on the conditions imposed on the system. The fourth case is a system that has a sinusoidal time varying inlet temperature for one of the flows. The results show that the sinusoidal behavior at the inlet propagates along the channel. However, the sinusoidal behavior on one of the fluids does not fully translate to the other gets damped by the wall and the heat transfer coefficients that can be barely seen on the other flow. A scaling analysis and a parametric study were performed to determine the influence the different parameters on the system have on the time a heat exchanger takes to reach steady state. The results show the dependency of tst* (time a system takes to reach steady state) on the dimensionless parameters M, C, NTUh, NTUc, and Cw. t st* depends linearly on C and Cw, and it is a power function of M. It was also shown that tst* has a logarithmic dependency on NTUh and NTUc. A correlation was generated to approximate the time a system takes to reach steady state for systems where C w << 1. A more complex heat exchanger with the specific application of solar energy storage was also investigated. This application involves a counter-flow heat exchanger with a reacting flow in one of the channels, and it includes varying properties, heat generation, varying heat transfer coefficient, and axial conduction. The application for this reactor heat exchanger is on solar energy storage, and the goals is to heat up steam to 650 °C by using the ammonia synthesis heat of reaction. One of the concerns for this system is the start-up time and also how disturbances in reacting flow can affect the steam outlet temperature. The transient behavior during the system start-up was presented. In order to achieve the desired outlet steam temperature at a reasonable time, the system must operate at high gas mass flow rates. If the inlet temperature of the gas suffers a step change, it affects the reaction rate as well as the outlet steam temperature. A small perturbation on the gas mass flow rate has an effect on the profile shape. However, the maximum temperature reached by the gas due to reaction is not affected, and consequently, it has little effect on the steam temperature. Axial conduction in the reactor heat exchanger was also investigated, specifically in the gas section. Axial conduction cannot be assumed to be negligible in the reactor heat exchanger because of the iron-based catalytic bed. Results in this section show that axial conduction is detrimental for the system. It was found that for Peclet number greater than 100, axial conduction can be neglected. An alternative solution to address axial conduction was proposed, namely to include a well-insulated non-reacting section (without a catalytic bed) upstream of the reactor. The modified reactor heat exchanger was a novel solution to avoid the negative effect of axial conduction. Results show that by having a non-reacting section, axial conduction becomes unimportant.

Experiment of flow regime map and local condensing heat transfer coefficients inside three dimensional inner microfin tubes

NASA Astrophysics Data System (ADS)

Du, Yang; Xin, Ming Dao

1999-03-01

This paper developed a new type of three dimensional inner microfin tube. The experimental results of the flow patterns for the horizontal condensation inside these tubes are reported in the paper. The flow patterns for the horizontal condensation inside the new made tubes are divided into annular flow, stratified flow and intermittent flow within the test conditions. The experiments of the local heat transfer coefficients for the different flow patterns have been systematically carried out. The experiments of the local heat transfer coefficients changing with the vapor dryness fraction have also been carried out. As compared with the heat transfer coefficients of the two dimensional inner microfin tubes, those of the three dimensional inner microfin tubes increase 47-127% for the annular flow region, 38-183% for the stratified flow and 15-75% for the intermittent flow, respectively. The enhancement factor of the local heat transfer coefficients is from 1.8-6.9 for the vapor dryness fraction from 0.05 to 1.

Development of Modal Analysis for the Study of Global Modes in High Speed Boundary Layer Flows

NASA Astrophysics Data System (ADS)

Brock, Joseph Michael

Boundary layer transition for compressible flows remains a challenging and unsolved problem. In the context of high-speed compressible flow, transitional and turbulent boundary-layers produce significantly higher surface heating caused by an increase in skin-friction. The higher heating associated with transitional and turbulent boundary layers drives thermal protection systems (TPS) and mission trajectory bounds. Proper understanding of the mechanisms that drive transition is crucial to the successful design and operation of the next generation spacecraft. Currently, prediction of boundary-layer transition is based on experimental efforts and computational stability analysis. Computational analysis, anchored by experimental correlations, offers an avenue to assess/predict stability at a reduced cost. Classical methods of Linearized Stability Theory (LST) and Parabolized Stability Equations (PSE) have proven to be very useful for simple geometries/base flows. Under certain conditions the assumptions that are inherent to classical methods become invalid and the use of LST/PSE is inaccurate. In these situations, a global approach must be considered. A TriGlobal stability analysis code, Global Mode Analysis in US3D (GMAUS3D), has been developed and implemented into the unstructured solver US3D. A discussion of the methodology and implementation will be presented. Two flow configurations are presented in an effort to validate/verify the approach. First, stability analysis for a subsonic cylinder wake is performed and results compared to literature. Second, a supersonic blunt cone is considered to directly compare LST/PSE analysis and results generated by GMAUS3D.

Design and fabrication of a 3-D printable counter-low/precipitation heat exchanger for use with a novel off-grid solid state refrigeration system

NASA Astrophysics Data System (ADS)

Ryan, Sean Thomas

Off-grid refrigeration technologies are currently limited to either vapor-compression cycles driven by photovoltaics or solar thermal absorption cycles. Rebound Technologies has recently developed a novel off-grid refrigeration system called Sunchill(TM) for agricultural applications in humid environments in the developing world. The Sunchill(TM) refrigeration system utilizes the daily high and low temperatures to drive a 24 hour refrigeration cycle. Cooling is provided by the dissolution of an endothermic salt, sodium carbonate decahydrate. Once the salt is solvated and cooling is delivered to freshly harvest crops, the system is "recharged" in a multi-step process that relies on a solar collector, an air-gap membrane unit and a heat exchanger. The heat exchanger, which is the focus of this thesis, is required to remove 36.6 MJ of heat over a twelve hour period in order to "recharge" the system. The heat exchanger is also required to transfer heat from a fresh water stream to a cold brine solution to generate the cold water necessary to submerse and cool harvested crops. To provide a sustainable technology to the target community, the feasibility of fabricating the heat exchanger via the low cost 3-D printing method of fused filament fabrication (FFF) was examined. This thesis presents the design, development, and manufacturing considerations that were performed in support of developing a waterproof, counter-flow, 3-D printable heat exchanger. Initial geometries and performance were modeled by constructing a linear thermal resistance network with truncating temperatures of 30°C (saturated brine temperature) and 18°C (average daily low temperature). The required surface area of the heat exchanger was found to be 20.46 m2 to remove the required 36.6 MJ of heat. Iterative print tests were conducted to arrive at the wall thickness, hexagon shape, and double wall structure of the heat exchanger. A laboratory-scale heat exchanger was fabricated using a Lulzbot Taz 4 printer from acrylonitrile butadiene styrene (ABS) polymer. Performance was verified empirically for the laboratory-scale unit. A heat transfer rate of 22.8 W was obtained at a flow rate of 0.00075 kg/s. The results of this thesis demonstrate the feasibility of manufacturing low cost heat exchangers using additive manufacturing techniques.

The Constrained Vapor Bubble Experiment - Interfacial Flow Region

NASA Technical Reports Server (NTRS)

Kundan, Akshay; Wayner, Peter C., Jr.; Plawsky, Joel L.

2015-01-01

Internal heat transfer coefficient of the CVB correlated to the presence of the interfacial flow region. Competition between capillary and Marangoni flow caused Flooding and not a Dry-out region. Interfacial flow region growth is arrested at higher power inputs. 1D heat model confirms the presence of interfacial flow region. 1D heat model confirms the arresting phenomena of interfacial flow region Visual observations are essential to understanding.

Overview of Recent Alcator C-Mod Highlights

NASA Astrophysics Data System (ADS)

Marmar, Earl; C-Mod Team

2013-10-01

Analysis and modeling of recent C-Mod experiments has yielded significant results across multiple research topics. I-mode provides routine access to high confinement plasma (H98 up to 1.2) in quasi-steady state, without large ELMs; pedestal pressure and impurity transport are regulated by short-wavelength EM waves, and core turbulence is reduced. Multi-channel transport is being investigated in Ohmic and RF-heated plasmas, using advanced diagnostics to validate non-linear gyrokinetic simulations. Results from the new field-aligned ICRF antenna, including significantly reduced high-Z metal impurity contamination, and greatly improved load-tolerance, are being understood through antenna-plasma modeling. Reduced LHCD efficiency at high density correlates with parametric decay and enhanced edge absorption. Strong flow drive and edge turbulence suppression are seen from LHRF, providing new approaches for plasma control. Plasma density profiles directly in front of the LH coupler show non-linear modifications, with important consequences for wave coupling. Disruption-mitigation experiments using massive gas injection at multiple toroidal locations show unexpected results, with potentially significant implications for ITER. First results from a novel accelerator-based PMI diagnostic are presented. What would be the world's first actively-heated high-temperature advanced tungsten divertor is designed and ready for construction. Conceptual designs are being developed for an ultra-advanced divertor facility, Alcator DX, to attack key FNSF and DEMO heat-flux challenges integrated with a high-performance core. Supported by USDOE.

The frequency response of a coupled ice sheet-ice shelf-ocean system to climate forcing variability

NASA Astrophysics Data System (ADS)

Goldberg, D.; Snow, K.; Jordan, J. R.; Holland, P.; Arthern, R. J.

2017-12-01

Changes at the West Antarctic ice-ocean boundary in recent decades has triggered significant increases in the regions contribution to global sea-level rise, coincident with large scale, and in some cases potentially unstable, grounding line retreat. Much of the induced change is thought to be driven by fluctuations in the oceanic heat available at the ice-ocean boundary, transported on-shelf via warm Circumpolar Deep Water (CDW). However, the processes in which ocean heat drives ice-sheet loss remains poorly understood, with observational studies routinely hindered by the extreme environment notorious to the Antarctic region. In this study we apply a novel synchronous coupled ice-ocean model, developed within the MITgcm, and are thus able to provide detailed insight into the impacts of short time scale (interannual to decadal) climate variability and feedbacks within the ice-ocean system. Feedbacks and response are assessed in an idealised ice-sheet/ocean-cavity configuration in which the far field ocean condition is adjusted to emulate periodic climate variability patterns. We reveal a non-linear response of the ice-sheet to periodic variations in thermocline depth. These non-linearities illustrate the heightened sensitivity of fast flowing ice-shelves to periodic perturbations in heat fluxes occurring at interannual and decadal time scales. The results thus highlight how small perturbations in variable climate forcing, like that of ENSO, may trigger large changes in ice-sheet response.

Development of Flow Boiling and Condensation Experiment on the International Space Station- Normal and Low Gravity Flow Boiling Experiment Development and Test Results

NASA Technical Reports Server (NTRS)

Nahra, Henry K.; Hall, Nancy R.; Hasan, Mohammad M.; Wagner, James D.; May, Rochelle L.; Mackey, Jeffrey R.; Kolacz, John S.; Butcher, Robert L.; Frankenfield, Bruce J.; Mudawar, Issam;