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1

Introduction of a New Crossover Radius for Radial Heat Conduction, Part I: Cylindrical Systems

Use of the critical radius for radial heat conduction in thermal insu lation systems has been widely reported in the literature. When it is desirable to in crease heat dissipation, this critical radius can be used in a definitive manner to maxi mize the heat dissipation. However, if it is desirable to decrease heat gain or heat loss, the critical

M. R. Kulkarni

1998-01-01

2

Critical radius for radial heat conduction: a necessary criterion but not always sufficient

Use of the critical radius for radial heat conduction in thermal insulation systems has been widely reported in the literature. When it is desirable to increase heat dissipation in these systems, the critical radius can be used in a definitive manner to maximize the heat dissipation. However, if it is desirable to decrease heat gain or heat loss, the critical

M. R. Kulkarni

2004-01-01

3

Radial heat conduction in insulated pipes under external convection is usually dealt with great detail in several heat transfer publications. However, an analysis carried out through the graphical representation of the dimensionless characteristic parameters, will allow a better understanding of the phenomenon. Here the dependence of the convection coefficient on the external radius and external surface temperature, typical of forced

R. A. Figueiredo

2001-01-01

4

An improved local radial point interpolation method for transient heat conduction analysis

NASA Astrophysics Data System (ADS)

The smoothing thin plate spline (STPS) interpolation using the penalty function method according to the optimization theory is presented to deal with transient heat conduction problems. The smooth conditions of the shape functions and derivatives can be satisfied so that the distortions hardly occur. Local weak forms are developed using the weighted residual method locally from the partial differential equations of the transient heat conduction. Here the Heaviside step function is used as the test function in each sub-domain to avoid the need for a domain integral. Essential boundary conditions can be implemented like the finite element method (FEM) as the shape functions possess the Kronecker delta property. The traditional two-point difference method is selected for the time discretization scheme. Three selected numerical examples are presented in this paper to demonstrate the availability and accuracy of the present approach comparing with the traditional thin plate spline (TPS) radial basis functions.

Wang, Feng; Lin, Gao; Zheng, Bao-Jing; Hu, Zhi-Qiang

2013-06-01

5

NASA Astrophysics Data System (ADS)

The variations of thermal conductivities of solid phases versus temperature for pure Sn, pure Zn and Sn-9 wt.% Zn, Sn-14 wt.% Zn, Sn-50 wt.% Zn, Sn-80 wt.% Zn binary alloys were measured with a radial heat flow apparatus. The thermal conductivity ratios of liquid phase to solid phase for the pure Sn, pure Zn and eutectic Sn-9 wt.% Zn alloy at their melting temperature are found with a Bridgman-type directional solidification apparatus. Thus, the thermal conductivities of liquid phases for pure Sn, pure Zn and eutectic Sn-9 wt.% Zn binary alloy at their melting temperature were evaluated by using the values of solid phase thermal conductivities and the thermal conductivity ratios of liquid phase to solid phase.

Meydaneri, Fatma; Saatçi, Buket; Gündüz, Mehmet; Özdemir, Mehmet

2013-11-01

6

Stirling Engine With Radial Flow Heat Exchangers

NASA Technical Reports Server (NTRS)

Conflict between thermodynamical and structural requirements resolved. In Stirling engine of new cylindrical configuration, regenerator and acceptor and rejector heat exchangers channel flow of working gas in radial direction. Isotherms in regenerator ideally concentric cylinders, and gradient of temperature across regenerator radial rather than axial. Acceptor and rejector heat exchangers located radially inward and outward of regenerator, respectively. Enables substantial increase in power of engine without corresponding increase in diameter of pressure vessel.

Vitale, N.; Yarr, George

1993-01-01

7

Heat conduction in conducting polyaniline nanofibers

NASA Astrophysics Data System (ADS)

Thermal conductivity and specific heat of conducting polyaniline nanofibers are measured to identify the nature of heat carrying modes combined with their inhomogeneous structure. The low temperature thermal conductivity results reveal crystalline nature while the high temperature data confirm the amorphous nature of the material suggesting heterogeneous model for conducting polyaniline. Extended acoustic phonons dominate the low temperature (<100 K) heat conduction, while localized optical phonons hopping, assisted by the extended acoustic modes, account for the high temperature (>100 K) heat conduction.

Nath, Chandrani; Kumar, A.; Syu, K.-Z.; Kuo, Y.-K.

2013-09-01

8

NASA Technical Reports Server (NTRS)

Heat conduction plays an important role in the efficiency and life span of electronic components. To keep electronic components running efficiently and at a proper temperature, thermal management systems transfer heat generated from the components to thermal surfaces such as heat sinks, heat pipes, radiators, or heat spreaders. Thermal surfaces absorb the heat from the electrical components and dissipate it into the environment, preventing overheating. To ensure the best contact between electrical components and thermal surfaces, thermal interface materials are applied. In addition to having high conductivity, ideal thermal interface materials should be compliant to conform to the components, increasing the surface contact. While many different types of interface materials exist for varying purposes, Energy Science Laboratories, Inc. (ESLI), of San Diego, California, proposed using carbon velvets as thermal interface materials for general aerospace and electronics applications. NASA s Johnson Space Center granted ESLI a Small Business Innovation Research (SBIR) contract to develop thermal interface materials that are lightweight and compliant, and demonstrate high thermal conductance even for nonflat surfaces. Through Phase II SBIR work, ESLI created Vel-Therm for the commercial market. Vel-Therm is a soft, carbon fiber velvet consisting of numerous high thermal conductivity carbon fibers anchored in a thin layer of adhesive. The velvets are fabricated by precision cutting continuous carbon fiber tows and electrostatically flocking the fibers into uncured adhesive, using proprietary techniques.

2003-01-01

9

Effective Thermal Conductivity in a Radial-Flow Packed-Bed Reactor

In this work a theoretical and experimental study of the heat transfer process in a radial flow reactor was carried out under steady- and non-steady-state conditions in order to determine the effective thermal conductivity (ke). One of the mathematical models proposed was a pseudohomogeneous model in which the effective thermal conductivity varies with radial position. The second model studied was

J. Fuentes; F. Pironti; A. L. López de Ramos

1998-01-01

10

Conduction heat transfer solutions

This text is a collection of solutions to a variety of heat conduction problems found in numerous publications, such as textbooks, handbooks, journals, reports, etc. Its purpose is to assemble these solutions into one source that can facilitate the search for a particular problem solution. Generally, it is intended to be a handbook on the subject of heat conduction. There are twelve sections of solutions which correspond with the class of problems found in each. Geometry, state, boundary conditions, and other categories are used to classify the problems. Each problem is concisely described by geometry and condition statements, and many times a descriptive sketch is also included. The introduction presents a synopsis on the theory, differential equations, and boundary conditions for conduction heat transfer. Some discussion is given on the use and interpretation of solutions. Supplementary data such as mathematical functions, convection correlations, and thermal properties are included for aiding the user in computing numerical values from the solutions. 155 figs., 92 refs., 9 tabs.

VanSant, J.H.

1983-08-01

11

Radial heat transfer from a moving plasma

to design reactors. A good review of plasma jet technology has been prepared by Dennis? Smith, Gates, ard Bord (I). In th s research? the total heat flux in the radial direction was measured experimertaily from a moving plasma or plasma jet with a water... the advances made 'ri plasma generatior technology, John and Bade (4) suggested that the convective heat losses from a plasma gas stre am to the walls of the conf ining chamber may be represented by the equatior 0. 023 0 (Hs ? H ) qc = prO 60 Reo ~ 20 (II-2...

Johnson, James Randall

2012-06-07

12

Conduction heat transfer solutions

NASA Astrophysics Data System (ADS)

A collection of solutions to a variety of heat conduction problems found in numerous publications, such as textbooks, handbooks, journals, reports, etc., are presented. Its purpose is to assemble these solutions into one source that can facilitate the search for a particular problem solution. Generally, it is intended to be a handbook on the subject of heat conduction. This material is useful for engineers, scientists, technologists, and designers of all disciplines, particularly those who design thermal systems or estimate temperatures and heat transfer rates in structures. More than 500 problem solutions and relevant data are tabulated for easy retrieval. There are twelve sections of solutions which correspond with the class of problems found in each. Geometry, state, boundary conditions, and other categories are used to classify the problems. A case number is assigned to each problem for cross referencing, and also for future reference. Each problem is concisely described by geometry and condition statements, and many times a descriptive sketch is also included. At least one source reference is given so that the user can review the methods used to derive the solutions.

Vansant, J. H.

1980-03-01

13

Conduction heat transfer solutions

This text is a collection of solutions to a variety of heat conduction problems found in numerous publications, such as textbooks, handbooks, journals, reports, etc. Its purpose is to assemble these solutions into one source that can facilitate the search for a particular problem solution. Generally, it is intended to be a handbook on the subject of heat conduction. This material is useful for engineers, scientists, technologists, and designers of all disciplines, particularly those who design thermal systems or estimate temperatures and heat transfer rates in structures. More than 500 problem solutions and relevant data are tabulated for easy retrieval. There are twelve sections of solutions which correspond with the class of problems found in each. Geometry, state, boundary conditions, and other categories are used to classify the problems. A case number is assigned to each problem for cross-referencing, and also for future reference. Each problem is concisely described by geometry and condition statements, and many times a descriptive sketch is also included. At least one source reference is given so that the user can review the methods used to derive the solutions. Problem solutions are given in the form of equations, graphs, and tables of data, all of which are also identified by problem case numbers and source references.

VanSant, J.H.

1980-03-01

14

Variable conductance heat pipe technology

NASA Technical Reports Server (NTRS)

Research and development programs in variable conductance heat pipe technology were conducted. The treatment has been comprehensive, involving theoretical and/or experimental studies in hydrostatics, hydrodynamics, heat transfer into and out of the pipe, fluid selection, and materials compatibility, in addition to the principal subject of variable conductance control techniques. Efforts were not limited to analytical work and laboratory experimentation, but extended to the development, fabrication and test of spacecraft hardware, culminating in the successful flight of the Ames Heat Pipe Experiment on the OAO-C spacecraft.

Marcus, B. D.; Edwards, D. K.; Anderson, W. T.

1973-01-01

15

Effective heat conduction in a configuration with nonoverlapped magnetic islands

The effective radial heat conduction {kappa}{sub eff} in a plasma configuration with nonoverlapped magnetic island chains is assessed by applying an ''optimal path'' method. This approach implies that heat is transported predominantly along paths rendering the minimum temperature variation and is related to the principle of minimum entropy production. Paths combined of up to three radial sections and two segments aligned along magnetic field lines are considered. It is demonstrated that the enhancement of {kappa}{sub eff} over the level of perpendicular heat conduction {kappa}{sub perpendicular} arising due to flows along magnetic field lines is controlled only by the Chirikov parameter and by the value 4b{sub r}{sup 2}{kappa}{sub parallel}/{kappa}{sub perpendicular}, where b{sub r} is the relative amplitude of the radial field resonant harmonic and {kappa}{sub parallel} is the parallel heat conduction.

Gupta, A.; Tokar, M. Z. [Institut fuer Energieforschung - Plasmaphysik, Forschungszentrum Juelich, Association EURATOM-FZJ, Trilateral Euregio Cluster, Juelich (Germany)

2008-03-15

16

Heat transfer and combustion characteristics of an array of radial jet reattachment flames

Radial Jet Reattachment Combustion (RJRC) nozzle provided improved fuel\\/air mixing for use in impingement flame heating. Detailed heat transfer and combustion measurements are conducted to characterize the performance of the RJRC nozzles in an array configuration. The measurements indicated that the RJRC flames produce low NOx and CO emissions. However, their characteristics are highly dependent upon the between-nozzle spacing. At

J. WU; R. H. PAGE

2001-01-01

17

The use of the critical radius for radial heat conduction in thermal insulation systems has been widely reported in the literature. When it is desirable to increase heat dissipation, this critical radius can be used in a definitive manner to maximize the heat dissipation. However, if it is desirable to decrease heat gain or heat loss, the critical radius only

Manohar Kulkarni; Kristi Nelson

2006-01-01

18

Heat Transfer Experiments in the Internal Cooling Passages of a Cooled Radial Turbine Rotor

NASA Technical Reports Server (NTRS)

An experimental study was conducted (1) to experimentally measure, assess and analyze the heat transfer within the internal cooling configuration of a radial turbine rotor blade and (2) to obtain heat transfer data to evaluate and improve computational fluid dynamics (CFD) procedures and turbulent transport models of internal coolant flows. A 1.15 times scale model of the coolant passages within the NASA LERC High Temperature Radial Turbine was designed, fabricated of Lucite and instrumented for transient beat transfer tests using thin film surface thermocouples and liquid crystals to indicate temperatures. Transient heat transfer tests were conducted for Reynolds numbers of one-fourth, one-half, and equal to the operating Reynolds number for the NASA Turbine. Tests were conducted for stationary and rotating conditions with rotation numbers in the range occurring in the NASA Turbine. Results from the experiments showed the heat transfer characteristics within the coolant passage were affected by rotation. In general, the heat transfer increased and decreased on the sides of the straight radial passages with rotation as previously reported from NASA-HOST-sponsored experiments. The heat transfer in the tri-passage axial flow region adjacent to the blade exit was relatively unaffected by rotation. However, the heat transfer on one surface, in the transitional region between the radial inflow passage and axial, constant radius passages, decreased to approximately 20 percent of the values without rotation. Comparisons with previous 3-D numerical studies indicated regions where the heat transfer characteristics agreed and disagreed with the present experiment.

Johnson, B. V.; Wagner, J. H.

1996-01-01

19

Heat conduction in three dimensions

NASA Technical Reports Server (NTRS)

Multidimensional heat conduction program computes transient temperature history and steady state temperatures of complex body geometries in three dimensions. Emphasis is placed on type of problems associated with Space Shuttle thermal protection system, but program could be used in thermal analysis of most three dimensional systems.

Danza, T. M.; Fesler, L. W.; Mongan, R. D.

1980-01-01

20

Performance of a variable conductance heat pipe heat exchanger

The performance of an air to air heat exchanger in which heat is transferred to a finned evaporator and from a finned condenser via a heat pipe was evaluated. The variable conductance heat pipe is to the condenser fins a heat source and to the evaporator fins a heat sink. The principal advantage of the variable conductance heat pipe heat

P. D. Chancelor

1983-01-01

21

In this paper we derive a generalized fundamental solution for the BEM solution of problems of steady state heat conduction with arbitrarily spatially varying thermal conductivity. This is accomplished with the aid of a singular nonsymmetric generalized forcing function, D, with special sampling properties. Generalized fundamental solutions, E, are derived as locally radially symmetric responses to this nonsymmetric singular forcing

Alain J. Kassab; Eduardo Divo

1996-01-01

22

Heat conduction of symmetric lattices.

Heat conduction of symmetric Frenkel-Kontorova (FK) lattices with a coupling displacement was investigated. Through simplifying the model, we derived analytical expression of thermal current of the system in the overdamped case. By means of numerical calculations, the results indicate that: (i) As the coupling displacement d equals to zero, temperature oscillations of the heat baths linked with the lattices can control magnitude and direction of the thermal current; (ii) Whether there is a temperature bias or not, the thermal current oscillates periodically with d, whose amplitudes become greater and greater; (iii) As d is not equal to zero, the thermal current monotonically both increases and decreases with temperature oscillation amplitude of the heat baths, dependent on values of d; (iv) The coupling displacement also induces nonmonotonic behaviors of the thermal current vs spring constant of the lattice and coupling strength of the lattices; (v) These dynamical behaviors come from interaction of the coupling displacement with periodic potential of the FK lattices. Our results have the implication that the coupling displacement plays a crucial role in the control of heat current. PMID:23848662

Nie, Linru; Yu, Lilong; Zheng, Zhigang; Shu, Changzheng

2013-06-01

23

Optimization of a Radial Flow Heat Sink Under Natural Convection

NASA Astrophysics Data System (ADS)

A steady-state three-dimensional numerical model is developed to predict natural convection heat transfer from a radial flow heat sink. The considered medium is air. The effect of several design parameters, such as the fin length and height, number of fins, and the heat sink base radius, on heat transfer is investigated. The Taguchi method, known to be a very useful tool for selecting the best levels of control factors, is employed. Five factors and four levels for each factor are chosen. Sixteen kinds of models are analyzed, and the total heat transfer for each model is obtained. The results are used to estimate the optimum design values of the parameters affecting the heat sink performance. The reliability of these values is verified. The average heat transfer rate of the optimum model is shown to increase by 60% as compared to the reference model. Finally, the heat transfer data at different outer radii of the radial flow heat sink are correlated.

Bhowmik, Himangshu

2014-01-01

24

HEAT CONDUCTION NETWORKS: DISPOSITION OF HEAT BATHS AND INVARIANT MEASURE

HEAT CONDUCTION NETWORKS: DISPOSITION OF HEAT BATHS AND INVARIANT MEASURE ALAIN CAMANES Abstract linking existence and uniqueness of the invariant measure to the disposition of the heat baths. We consider a model of heat conduction networks consisting of oscillators in contact with heat baths

Paris-Sud XI, UniversitĂ© de

25

Microscale heat conduction in dielectric thin films

Starting from fundamental principles, it is shown that heat conduction by phonons can be analyzed in radiative transfer. A general theory of heat conduction is developed, showing that the Fourier law is a limiting case for steady-state macroscale heat transport. Two cases of heat transport across and along a thin film are considered. For the transient case, the theory shows

A. Majumdar

1993-01-01

26

Variable boundary II heat conduction

NASA Technical Reports Server (NTRS)

Computer program for solving both transient and steady-state heat transfer problems is presented. Specific applications of computer program are described. Formulation for individual nodes of solid medium for heat balance is presented. Diffusion equation is solved for all nodes simultaneously at finite increments of time.

Gramer, J.; Oneill, R. F.

1972-01-01

27

Heat transfer in NMR of conductive samples with radiofrequency decoupling

NASA Astrophysics Data System (ADS)

Under conditions of thermal and fluid mechanical equilibrium, heat transfer in a vortex-free liquid in an NMR tube spinning at about 30 Hz is evidently dominated by conduction, to first approximation. In contrast, heat transfer between the spinning tube and its stationary surroundings occurs primarily by convection. When high-power rf decoupling is used, lossy samples such as solutions of electrolytes or molecules having large electric dipole moments may exhibit large increases in average temperature as well as substantial radial temperature gradients, because of inductive dielectric heating. Equations for conduction of heat through such samples were applied to the case where chemical shift depends linearly on temperature, and the resulting expressions for the lineshape were fitted to 31P spectra of arylphosphine derivatives which were obtained using 100-MHz proton noise decoupling. For samples with ionic conductivity equal to that of 0.05 M aqueous NaCl, radial temperature gradients of 2.1 and 0.3 K were observed in 12- and 5-mm glass tubes, respectively, at 9 W radiated rf power and a maximum sample temperature of 302 K, 11 K above the temperatureof the thermostatted gas stream entering the NMR probe. Twelve-millimeter coaxial-cylinder sample tubes and coaxial inserts machined from polycrystalline beryllium oxide have thermal conductivities 250 times that of glass tubes and equilibrate rapidly in the probe. Heating effects and radial temperature gradients in BeO tubes equipped with coaxial BeO inserts were too small to measure. However, calculations suggest that the values should be close to 0.03 K for 9 W decoupling and other conditions as used for the conductive samples in glass tubes without inserts.

McNair, Douglas S.

28

Resistive Heating in Radial Geometry Diamond Anvil Cell

NASA Astrophysics Data System (ADS)

High temperature and pressure experiments are important for understanding deep Earth geodynamics. Radial x-ray diffraction from samples under high pressure within a diamond anvil cell(DAC) provide information on lattice strain and crystallite preferred orientation. Understanding the development of crystallographic preferred orientation is essential for identifying deformation mechanisms as well as assessing anisotropy of bulk physical properties. Many high pressure radial diffraction experiments in the diamond anvil cell are performed at room temperature. For high temperatures, laser heating can be used but this technique produces large temperature gradients. Resistive heating provides a more homogeneous temperature distribution and covers the inaccessible low temperature range (<~1400K) of laser heating. Another advantage of this technique is stability, allowing long time period in-situ temperature experiments to be possible. Applying both heating techniques simultaneously covers a wider temperature range while minimizing temperature gradients. We are developing a resistive heating system for diamond anvil cells in radial geometry (rDAC) at beamline 12.2.2 of the Advanced Light Source (ALS) of Lawrence Berkeley Laboratory to recreate deep Earth deformation conditions. The design is based on a previous one by Due et al., in revision. The heater is laser-milled from high-purity solid graphite, and designed to fit slightly displaced from the diamond culets. Due to the low inherent resistivity and small size of the graphite heater, 6x3x0.5mm, we can achieve temperatures at the cullet of 300 to >1300 K at relatively low power loads of ~ 200 watts. The laser machining produces very uniform heater geometry which allows us to obtain reproducible temperatures in the rDAC. The assembly is modular and self supporting which allows for ease of assembly a requirement if users are to install the heater in a cell themselves. We are currently applying this technique to study lattice preferred orientation changes during phase transformations. We study the transformation of coesite and stishovite that occurs in the deep crust, and olivine transforming to ringwoodite and then to magnesiowuestite and perovskite in the lower mantle.

Zepeda-Alarcon, E.; Knight, J. W.; MacDowell, A.; Miyagi, L. M.; Kaercher, P. M.; Kanitpanyacharoen, W.; Wenk, H.; Williams, Q. C.

2012-12-01

29

Heat conduction fronts in planetary nebulae

NASA Technical Reports Server (NTRS)

We present arguments which suggest that many of the x-ray, some optical, and some UV observations of planetary nebulae, can be explained by the presence of heat conduction fronts. The heat flows from the hot bubble formed by the shocked fast wind to the cool shell and halo. Heat conduction fronts are likely to account for emission of x rays from plasma at lower temperature than the expected temperature of the hot bubble. In the presence of magnetic fields, only a small fraction of the fast wind luminosity emerges as radiation. Heat conduction fronts can naturally produce some unusual line flux ratios, which are observed in some planetary nebulae. Heat conduction fronts may heat the halo and cause some material at the inner surface of the shell to expand slower than the rest of the shell. In the presence of an asymmetrical magnetic field, this flow, the x-ray intensity, and the emission lines, may acquire asymmetrical structure as well.

Soker, Noam

1994-01-01

30

Ballistic-Diffusive Heat-Conduction Equations

We present new heat-conduction equations, named ballistic-diffusive equations, which are derived from the Boltzmann equation. We show that the new equations are a better approximation than the Fourier law and the Cattaneo equation for heat conduction at the scales when the device characteristic length, such as film thickness, is comparable to the heat-carrier mean free path and\\/or the characteristic time,

Gang Chen; Gang

2001-01-01

31

Radial disk heating by more than one spiral density wave

We consider a differentially rotating, 2D stellar disk perturbed by two steady state spiral density waves moving at different patterns speeds. Our investigation is based on direct numerical integration of initially circular test-particle orbits. We examine a range of spiral strengths and spiral speeds and show that stars in this time dependent gravitational field can be heated (their random motions increased). This is particularly noticeable in the simultaneous propagation of a 2-armed spiral density wave near the corotation resonance (CR), and a weak 4-armed one near the inner and outer 4:1 Lindblad resonances. In simulations with 2 spiral waves moving at different pattern speeds we find: (1) the variance of the radial velocity, sigma_R^2, exceeds the sum of the variances measured from simulations with each individual pattern; (2) sigma_R^2 can grow with time throughout the entire simulation; (3) sigma_R^2 is increased over a wider range of radii compared to that seen with one spiral pattern; (4) particles diffuse radially in real space whereas they don't when only one spiral density wave is present. Near the CR with the stronger, 2-armed pattern, test particles are observed to migrate radially. These effects take place at or near resonances of both spirals so we interpret them as the result of stochastic motions. This provides a possible new mechanism for increasing the stellar velocity dispersion in galactic disks. If multiple spiral patterns are present in the Galaxy we predict that there should be large variations in the stellar velocity dispersion as a function of radius.

I. Minchev; A. C. Quillen

2005-10-28

32

Information filtering via biased heat conduction

NASA Astrophysics Data System (ADS)

The process of heat conduction has recently found application in personalized recommendation [Zhou , Proc. Natl. Acad. Sci. USA PNASA60027-842410.1073/pnas.1000488107107, 4511 (2010)], which is of high diversity but low accuracy. By decreasing the temperatures of small-degree objects, we present an improved algorithm, called biased heat conduction, which could simultaneously enhance the accuracy and diversity. Extensive experimental analyses demonstrate that the accuracy on MovieLens, Netflix, and Delicious datasets could be improved by 43.5%, 55.4% and 19.2%, respectively, compared with the standard heat conduction algorithm and also the diversity is increased or approximately unchanged. Further statistical analyses suggest that the present algorithm could simultaneously identify users' mainstream and special tastes, resulting in better performance than the standard heat conduction algorithm. This work provides a creditable way for highly efficient information filtering.

Liu, Jian-Guo; Zhou, Tao; Guo, Qiang

2011-09-01

33

Information filtering via biased heat conduction.

The process of heat conduction has recently found application in personalized recommendation [Zhou et al., Proc. Natl. Acad. Sci. USA 107, 4511 (2010)], which is of high diversity but low accuracy. By decreasing the temperatures of small-degree objects, we present an improved algorithm, called biased heat conduction, which could simultaneously enhance the accuracy and diversity. Extensive experimental analyses demonstrate that the accuracy on MovieLens, Netflix, and Delicious datasets could be improved by 43.5%, 55.4% and 19.2%, respectively, compared with the standard heat conduction algorithm and also the diversity is increased or approximately unchanged. Further statistical analyses suggest that the present algorithm could simultaneously identify users' mainstream and special tastes, resulting in better performance than the standard heat conduction algorithm. This work provides a creditable way for highly efficient information filtering. PMID:22060533

Liu, Jian-Guo; Zhou, Tao; Guo, Qiang

2011-09-01

34

Heat conduction controlled combustion for scramjet applications

NASA Technical Reports Server (NTRS)

The use of heat conduction flame generated in a premixed supersonic stream is discussed. It is shown that the flame is controlled initially by heat conduction and then by chemical reaction. Such a flame is shorter than the diffusion type of flame and therefore it requires a much shorter burner. The mixing is obtained by injecting the hydrogen in the inlet. Then the inlet can be cooled by film cooling.

Ferri, A.; Agnone, A. M.

1974-01-01

35

Cryogenic regenerator including sarancarbon heat conduction matrix

NASA Technical Reports Server (NTRS)

A saran carbon matrix is employed to conduct heat through the heat storing volume of a cryogenic regenerator. When helium is adsorbed into the saran carbon matrix, the combination exhibits a volumetric specific heat much higher than previously used lead balls. A helium adsorbed saran regenerator should allow much lower refrigerator temperatures than those practically obtainable with lead based regenerators for regenerator type refrigeration systems.

Jones, Jack A. (Inventor); Petrick, S. Walter (Inventor); Britcliffe, Michael J. (Inventor)

1989-01-01

36

Local effects of longitudinal heat conduction in plate heat exchangers

In a plate heat exchanger, heat transfer from the hot to the cold fluid is a multi-dimensional conjugate problem, in which longitudinal heat conduction (LHC) along the dividing walls often plays some role and can not be neglected. Large-scale, or end-to-end, LHC is always detrimental to the exchanger’s effectiveness. On the contrary, if significant non-uniformities exist in the distribution of

Michele Ciofalo

2007-01-01

37

Compact pulsed laser having improved heat conductance

NASA Technical Reports Server (NTRS)

A highly efficient, compact pulsed laser having high energy to weight and volume ratios is provided. The laser utilizes a cavity reflector that operates as a heat sink and is essentially characterized by having a high heat conductivity, by being a good electrical insulator and by being substantially immune to the deleterious effects of ultra-violet radiation. Manual portability is accomplished by eliminating entirely any need for a conventional circulating fluid cooling system.

Yang, L. C. (inventor)

1977-01-01

38

Measurement of heat conduction through stacked screens

NASA Technical Reports Server (NTRS)

This paper describes the experimental apparatus for the measurement of heat conduction through stacked screens as well as some experimental results taken with the apparatus. Screens are stacked in a fiberglass-epoxy cylinder, which is 24.4 mm in diameter and 55 mm in length. The cold end of the stacked screens is cooled by a Gifford-McMahon (GM) cryocooler at cryogenic temperature, and the hot end is maintained at room temperature. Heat conduction through the screens is determined from the temperature gradient in a calibrated heat flow sensor mounted between the cold end of the stacked screens and the GM cryocooler. The samples used for these experiments consisted of 400-mesh stainless steel screens, 400-mesh phosphor bronze screens, and two different porosities of 325-mesh stainless steel screens. The wire diameter of the 400-mesh stainless steel and phosphor bronze screens was 25.4 micrometers and the 325-mesh stainless steel screen wire diameters were 22.9 micrometers and 27.9 micrometers. Standard porosity values were used for the experimental data with additional porosity values used on selected experiments. The experimental results showed that the helium gas between each screen enhanced the heat conduction through the stacked screens by several orders of magnitude compared to that in vacuum. The conduction degradation factor is the ratio of actual heat conduction to the heat conduction where the regenerator material is assumed to be a solid rod of the same cross sectional area as the metal fraction of the screen. This factor was about 0.1 for the stainless steel and 0.022 for the phosphor bronze, and almost constant for the temperature range of 40 to 80 K at the cold end.

Lewis, M. A.; Kuriyama, T.; Kuriyama, F.; Radebaugh, R.

1998-01-01

39

Epiphytic plants in the Bromeliaceae known as tank bromeliads essentially lack stems and absorptive roots and instead take up water from reservoirs formed by their overlapping leaf bases. For such plants, leaf hydraulic conductance is plant hydraulic conductance. Their simple strap-shaped leaves and parallel venation make them suitable for modeling leaf hydraulic conductance based on vasculature and other anatomical and morphological traits. Plants of the tank bromeliad Guzmania lingulata were investigated in a lowland tropical forest in Costa Rica and a shaded glasshouse in Los Angeles, CA, USA. Stomatal conductance to water vapor and leaf anatomical variables related to hydraulic conductance were measured for both groups. Tracheid diameters and numbers of vascular bundles (veins) were used with the Hagen–Poiseuille equation to calculate axial hydraulic conductance. Measurements of leaf hydraulic conductance using the evaporative flux method were also made for glasshouse plants. Values for axial conductance and leaf hydraulic conductance were used in a model based on leaky cable theory to estimate the conductance of the radial pathway from the vein to the leaf surface and to assess the relative contributions of both axial and radial pathways. In keeping with low stomatal conductance, low stomatal density, low vein density, and narrow tracheid diameters, leaf hydraulic conductance for G. lingulata was quite low in comparison with most other angiosperms. Using the predicted axial conductance in the leaky cable model, the radial resistance across the leaf mesophyll was predicted to predominate; lower, more realistic values of axial conductance resulted in predicted radial resistances that were closer to axial resistance in their impact on total leaf resistance. Tracer dyes suggested that water uptake through the tank region of the leaf was not limiting. Both dye movement and the leaky cable model indicated that the leaf blade of G. lingulata was structurally and hydraulically well-suited to conserve water. PMID:23596446

North, Gretchen B.; Lynch, Frank H.; Maharaj, Franklin D. R.; Phillips, Carly A.; Woodside, Walter T.

2013-01-01

40

Heat Conductivity of Polyatomic and Polar Gases

The formal kinetic theory of Wang Chang and Uhlenbeck and of Taxman has been used to derive explicit expressions for the heat conductivity of polyatomic and polar gases. By systematic inclusion of terms involving inelastic collisions the usual modified Eucken expression is derived as a first approximation, and as a second approximation an expression involving the relaxation times for various

E. A. Mason; L. Monchick

1962-01-01

41

Large variable conductance heat pipe. Transverse header

NASA Technical Reports Server (NTRS)

The characteristics of gas-loaded, variable conductance heat pipes (VCHP) are discussed. The difficulties involved in developing a large VCHP header are analyzed. The construction of the large capacity VCHP is described. A research project to eliminate some of the problems involved in large capacity VCHP operation is explained.

Edelstein, F.

1975-01-01

42

Effects of anisotropic heat conduction on solidification

NASA Technical Reports Server (NTRS)

Two-dimensional solidification influenced by anisotropic heat conduction has been considered. The interfacial energy balance was derived to account for the heat transfer in one direction (x or y) depending on the temperature gradient in both the x and y directions. A parametric study was made to determine the effects of the Stefan number, aspect ratio, initial superheat, and thermal conductivity ratios on the solidification rate. Because of the imposed boundary conditions, the interface became skewed and sometimes was not a straight line between the interface position at the upper and lower adiabatic walls (spatially nonlinear along the height). This skewness depends on the thermal conductivity ratio k(yy)/k(yx). The nonlinearity of the interface is influenced by the solidification rate, aspect ratio, and k(yy/k(yx).

Weaver, J. A.; Viskanta, R.

1989-01-01

43

Shape factors in conductive heat transfer

: q e -k(~)ZT hT q = Heat flow, Btu/Hr k = Thexmal conductivity, -Btu Jk ~ Lrea, ZtB I ~ length of. heat flow path& Jt 6 T = Temperatux e di f f er ence, dp. R Resistance, (op Zt)pt. ln othex simple cases, such as the cylinder and, the sphex'e.... It has 'been shown bg Andrews 1 and Jacob d that. q = -k (S. Z. ) ~ T Where S. Z. = Shape abactor ~ ! - ~d dk dx (1S) Hence; S. P. ]~i (lSa) Sic. lariy the flow of d. irect current in an electrical circuit may be represented as: (S. X. ) h e S...

Faulkner, Richard Campbell

2012-06-07

44

NASA Technical Reports Server (NTRS)

Finite element method applied to heat conduction in solids with temperature dependent thermal conductivity, using nonlinear constitutive equation for heat ABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGH

Aguirre-Ramirez, G.; Oden, J. T.

1969-01-01

45

A localized radial basis function (RBF) meshless method is developed for coupled viscous fluid flow and convective heat transfer problems. The method is based on new localized radial-basis function (RBF) expansions using Hardy Multiquadrics for the sought-after unknowns. An efficient set of formulae are derived to compute the RBF interpolation in terms of vector products thus providing a substantial computational

Eduardo Divo; Alain J. Kassab

2007-01-01

46

A study aims to design an electroneuromyographic technique of radial nerve investigation and conduction block (CB) definition at the spiral groove level using surface electrodes. Eight healthy volunteers, 17 patients with focal radial nerve neuropathy in the spiral groove, 4 patients with a complete injury of the radial nerve aged from 22 to 54 years have been studied. The M-response was recorded from the extensor digitorum communis. Stimulation was performed at (1) the lateral brachium; (2) the Erb's point; (3) the medical brachium (stimulation of the median and ulnar nerves). Normal values have been determined. CB was calculated as follows: 100-A2/(A1+A3)*100%, where A1--a value of the M-response area amplitude at first point stimulation, A2--the second one, A3--the third one. The proximal M-response is the sum of motor unit action potentials of posterior and anterior groups of forearm muscles. Proximal M-response in patients with a complete injury of the radial nerve did not differ from the third one. The correlation between CB and the paresis degree as well as surface EMG were revealed in patients with radial neuropathy. Besides, there was correlation between CB and the percentage contribution of the third M-response in proximal one in this group. PMID:16921717

Khodulev, V I

2006-01-01

47

Parallelized solvers for heat conduction formulations

NASA Technical Reports Server (NTRS)

Based on multilevel partitioning, this paper develops a structural parallelizable solution methodology that enables a significant reduction in computational effort and memory requirements for very large scale linear and nonlinear steady and transient thermal (heat conduction) models. Due to the generality of the formulation of the scheme, both finite element and finite difference simulations can be treated. Diverse model topologies can thus be handled, including both simply and multiply connected (branched/perforated) geometries. To verify the methodology, analytical and numerical benchmark trends are verified in both sequential and parallel computer environments.

Padovan, Joe; Kwang, Abel

1991-01-01

48

Information filtering via weighted heat conduction algorithm

NASA Astrophysics Data System (ADS)

In this paper, by taking into account effects of the user and object correlations on a heat conduction (HC) algorithm, a weighted heat conduction (WHC) algorithm is presented. We argue that the edge weight of the user-object bipartite network should be embedded into the HC algorithm to measure the object similarity. The numerical results indicate that both the accuracy and diversity could be improved greatly compared with the standard HC algorithm and the optimal values reached simultaneously. On the Movielens and Netflix datasets, the algorithmic accuracy, measured by the average ranking score, can be improved by 39.7% and 56.1% in the optimal case, respectively, and the diversity could reach 0.9587 and 0.9317 when the recommendation list equals to 5. Further statistical analysis indicates that, in the optimal case, the distributions of the edge weight are changed to the Poisson form, which may be the reason why HC algorithm performance could be improved. This work highlights the effect of edge weight on a personalized recommendation study, which maybe an important factor affecting personalized recommendation performance.

Liu, Jian-Guo; Guo, Qiang; Zhang, Yi-Cheng

2011-06-01

49

Nonintegrability and the Fourier heat conduction law

NASA Astrophysics Data System (ADS)

We study in momentum-conserving systems, how nonintegrable dynamics may affect thermal transport properties. As illustrating examples, two one-dimensional (1D) diatomic chains, representing 1D fluids and lattices, respectively, are numerically investigated. In both models, the two species of atoms are assigned two different masses and are arranged alternatively. The systems are nonintegrable unless the mass ratio is one. We find that when the mass ratio is slightly different from one, the heat conductivity may keep significantly unchanged over a certain range of the system size and as the mass ratio tends to one, this range may expand rapidly. These results establish a new connection between the macroscopic thermal transport properties and the underlying dynamics.

Chen, Shunda; Wang, Jiao; Casati, Giulio; Benenti, Giuliano

2014-09-01

50

National Technical Information Service (NTIS)

The analytic solutions of the one-dimensional Fourier conductive heat flux law and corresponding transient heat transfer equation have been used to calculate temperature, conductive heat flux, and their trajectories due to radiant heating of opaque materi...

A. Cohen

2011-01-01

51

Are the Hot Coronae of Galaxies Heat Conductive

The effects of heat conductivity in the dynamics of hot X-ray coronae of galaxies are investigated by numerical integration of gas dynamics equations. Coronae are supposed to be confined by massive dark halos and\\/or hot intergalactic medium. The results are: (1) Coronae with zero heat conductivity can exist many Gyrs quasistationary. (2) Heat conductive coronae bound by dark halos rapidly

V. G. Berman; A. A. Suchkov

1986-01-01

52

The divertor heat flux footprint in tokamaks is often observed to be non-axisymmetric due to intrinsic error fields, applied 3D magnetic fields or during transients such as edge localized modes. Typically, only 1D radial heat flux profiles are analyzed; however, analysis of the full 2D divertor measurements provides opportunities to study the asymmetric nature of the deposited heat flux. To accomplish this an improved 3D Fourier analysis method has been successfully applied in a heat conduction solver (TACO) to determine the 2D heat flux distribution at the lower divertor surface in the National Spherical Torus Experiment (NSTX) tokamak. This advance enables study of helical heat deposition onto the divertor. In order to account for heat transmission through poorly adhered surface layers on the divertor plate, a heat transmission coefficient, defined as the surface layer thermal conductivity divided by the thickness of the layer, was introduced to the solution of heat conduction equation. This coefficient is denoted as ? and a range of values were tested in the model to ensure a reliable heat flux calculation until a specific value of ? led to the constant total deposited energy in the numerical solution after the end of discharge. A comparison between 1D heat flux profiles from TACO and from a 2D heat flux calculation code, THEODOR, shows good agreement. Advantages of 2D heat flux distribution over the conventional 1D heat flux profile are also discussed, and examples of 2D data analysis in the study of striated heat deposition pattern as well as the toroidal degree of asymmetry of peak heat flux and heat flux width are demonstrated. PMID:23464209

Gan, K F; Ahn, J-W; Park, J-W; Maingi, R; McLean, A G; Gray, T K; Gong, X; Zhang, X D

2013-02-01

53

NASA Astrophysics Data System (ADS)

The divertor heat flux footprint in tokamaks is often observed to be non-axisymmetric due to intrinsic error fields, applied 3D magnetic fields or during transients such as edge localized modes. Typically, only 1D radial heat flux profiles are analyzed; however, analysis of the full 2D divertor measurements provides opportunities to study the asymmetric nature of the deposited heat flux. To accomplish this an improved 3D Fourier analysis method has been successfully applied in a heat conduction solver (TACO) to determine the 2D heat flux distribution at the lower divertor surface in the National Spherical Torus Experiment (NSTX) tokamak. This advance enables study of helical heat deposition onto the divertor. In order to account for heat transmission through poorly adhered surface layers on the divertor plate, a heat transmission coefficient, defined as the surface layer thermal conductivity divided by the thickness of the layer, was introduced to the solution of heat conduction equation. This coefficient is denoted as ? and a range of values were tested in the model to ensure a reliable heat flux calculation until a specific value of ? led to the constant total deposited energy in the numerical solution after the end of discharge. A comparison between 1D heat flux profiles from TACO and from a 2D heat flux calculation code, THEODOR, shows good agreement. Advantages of 2D heat flux distribution over the conventional 1D heat flux profile are also discussed, and examples of 2D data analysis in the study of striated heat deposition pattern as well as the toroidal degree of asymmetry of peak heat flux and heat flux width are demonstrated.

Gan, K. F.; Ahn, J.-W.; Park, J.-W.; Maingi, R.; McLean, A. G.; Gray, T. K.; Gong, X.; Zhang, X. D.

2013-02-01

54

A small Radial Energy Analyzer (REA) was used on the Tandem Mirror Experiment-Upgrade (TMX-U), at Lawerence Livermore National Laboratory, to investigate the radial profiles of ion temperature, density, and plasma potential during Ion Cyclotron Resonance Heating (ICRH). The probe has been inserted into the central-cell plasma at temperatures of 200 eV and densities of 3 x 10/sup 12/cm/sup /minus 3// without damage to the probe, or major degradation of the plasma. This analyzer has indicated an increase in ion temperature from near 20 eV before ICRH to near 150 eV during ICRH, with about 60 kW of broadcast power. The REA measurements were cross-checked against other diagnostics on TMX-U and found to be consistent. The ion density measurement was compared to the line-density measured by microwave interferometry and found to agree within 10 to 20%. A radial intergral of n/sub i/T/sub i/ as measured by the REA shows good agreement with the diamagnetic loop measurement of plasma energy. The radial density profile is observed to broaden during the RF heating pulses, without inducing additional radial losses in the core plasma. The radial profile of plasma is seen to vary from axially peaked, to nearly flat as the plasma conditions carried over the series of experiments. To relate the increase in ion temperature to power absorbed by the plasma, a power balance as a function of radius was performed. The RF power absorbed is set equal to the sum of the losses during ICRH, minus those without ICRH. This method accounts for more than 70% of the broadcast power using a simple power balance model. The measured radial profile of the RF heating was compared to the calculations of two codes, ANTENA and GARFIELD, to test their effectiveness as predictors of power absorption profiles for TMX-U. 62 refs., 63 figs., 7 tabs.

Falabella, S.

1988-05-11

55

Heat Transfer from an ESF Radial Plate Clutch Surface Part II - Theory

In this paper half of a radial electro-structured fluid (ESF) clutch with vertical axis, consisting of a lower stationary disc and upper rotating disc is examined for constant speed of rotation. The narrow gap between the discs is filled with a viscous liquid, so electro-rheological effect is not taken into consideration. Frictional tangential forces in the fluid generate heat which

Vladimír Oravský

2003-01-01

56

Hierarchical Bayesian Models for Inverse Problems in Heat Conduction

Hierarchical Bayesian Models for Inverse Problems in Heat Conduction Jingbo Wang and Nicholas. Â§ Corresponding author: Nicholas Zabaras (zabaras@cornell.edu) #12;Bayesian model for inverse heat conduction 2 1 research. Very recently, a sequence of methods have been proposed to solve stochastic inverse heat transfer

Zabaras, Nicholas J.

57

Experimental evidence of hyperbolic heat conduction in processed meat

The objective of this paper is to present experimental evidence of the wave nature of heat propagation in processed meat and to demonstrate that the hyperbolic heat conduction model is an accurate representation, on a macroscopic level, of the heat conduction process in such biological material. The value of the characteristic thermal time of a specific material, processed bologna meat,

K. Mitra; S. Kumar; A. Vedavarz; M. K. Moallemi

1995-01-01

58

Heat Conduction in Graphene Flakes of Arbitrary Geometry

It was reported that the values of the room temperature thermal conductivity of graphene exceed those of carbon nanotubes [1-2]. The measurements of the thermal conductivity of graphene utilized a technique where the excitation laser initiated a heat wave. The data extraction procedure assumed plane heat waves. Realistic graphene flakes have variations in their width, and the heat wave front

Samia Subrina; Dmitri Kotchetkov; Alexander Balandin

2009-01-01

59

Potential possibilities of an advanced approach based on the usage of DC cascade torch providing an axially symmetric plasma jet outflow, and continuous radial injection of powder into a plasma flow are discussed. Comparison is made of the results, obtained using two models of interphase heat and momentum exchange between polydisperse alumina particles and air plasma jet, other factors being the same. The widely used model of gradientless particles' heating was applied for computing the two-phase plasma jets' temperature and velocity fields. The model is compared with corresponding model of gradient particle heating computed by using an efficient numerical method developed. Calculations were conducted under different scales of dense loading conditions to estimate the maximum productivity of plasma spray process.

Solonenko, Oleg P.; Smirnov, Audrey V. [Institute of Theoretical and Applied Mechanics, Siberian Branch of Russian Academy of Sciences, 4/1 Institutskaya street, Novosibirsk, 630090 (Russian Federation); Sorokin, Anatoly L. [Institute of Thermophysics, Siberian Branch of Russian Academy of Sciences, 1 Lavrentieva Avenue, Novosibirsk, 630090 (Russian Federation)

2006-05-05

60

Methodology for comparison of inverse heat conduction methods

The inverse heat conduction problem involves the calculation of the surface heat flux from transient measured temperatures inside solids. The deviation of the estimated heat flux from the true heat flux due to stabilization procedures is called the deterministic bias. This paper defines two test problems that show the tradeoff between deterministic bias and sensitivity to measurement errors of inverse

M. Raynaud; J. V. Beck

1988-01-01

61

The effect of heat conduction on the interaction of disk and corona around black holes

Heat conduction plays an important role in the balance between heating and cooling in many astrophysical objects, e.g. cooling flows in clusters of galaxies. Here we investigate the effect of heat conduction on the interaction between a cool disk and a hot corona around black holes. Using the one-radial-zone approximation, we study the vertical structure of the disk corona and derive evaporation and coronal mass flow rates for various reduced thermal conductivities. We find lower evaporation rates and a shift in the evaporation maxima to smaller radii. This implies that the spectral state transition occurs at a lower mass flow rate and a disk truncation closer to the black hole. Reductions of thermal conductivity are thought to be magnetically caused and might vary from object to object by a different configuration of the magnetic fields.

E. Meyer-Hofmeister; F. Meyer

2005-12-21

62

Steady state Joule heating with temperature dependent conductivities

A general solution is given to the nonlinear steady state heat conduction equation for the case in which a metal is heated\\u000a by electrical conduction currents. The solution is valid for any temperature variation in the thermal and electrical conductivities\\u000a and is illustrated by application to a typical Joule heating situation in one dimension. Comparison of the case of temperature

John H. Young

1986-01-01

63

Statistical analysis as approach to conductive heat transfer modelling

NASA Astrophysics Data System (ADS)

The main inspiration for article was the problem of high investment into installation of the building insulation. The question of its effectiveness and reliability also after the period of 10 or 15 years was the topic of the international research project carried out at the University of Prešov in Prešov and Vienna University of Technology entitled "Detection and Management of Risk Processes in Building Insulation" and numbered SRDA SK-AT-0008-10. To detect especially the moisture problem as risk process in the space between the wall and insulation led to construction new measuring equipment to test the moisture and temperature without the insulation destruction and this way to describe real situation in old buildings too. The further investigation allowed us to analyse the range of data in the amount of 1680 measurements and express conductive heat transfer using the methods of statistical analysis. Modelling comprises relationships of the environment properties inside the building, in the space between the wall and insulation and in ambient surrounding of the building. Radial distribution function also characterizes the connection of the temperature differences.

Antonyová, A.; Antony, P.

2013-04-01

64

Transport of radial heat flux and second sound in fusion plasmas

Simple flux-gradient relations that involve time delay and radial coupling are discussed. Such a formulation leads to a rather simple description of avalanches and may explain breaking of gyroBohm transport scaling. The generalization of the flux-gradient relation (i.e., constitutive relation), which involve both time delay and spatial coupling, is derived from drift-kinetic equation, leading to kinetic definitions of constitutive elements such as the flux of radial heat flux. This allows numerical simulations to compute these cubic quantities directly. The formulation introduced here can be viewed as an extension of turbulence spreading to include the effect of spreading of cross-phase as well as turbulence intensity, combined in such a way to give the flux. The link between turbulence spreading and entropy production is highlighted. An extension of this formulation to general quasi-linear theory for the distribution function in the phase space of radial position and parallel velocity is also discussed.

Guercan, Oe. D.; Berionni, V.; Hennequin, P.; Morel, P.; Vermare, L. [Laboratoire de Physique des Plasmas, Ecole Polytechnique, CNRS, 91128 Palaiseau Cedex (France); Diamond, P. H. [WCI Center for Fusion Theory, NFRI, Daejeon (Korea, Republic of); CMTFO and CASS, UCSD, California 92093 (United States); Garbet, X.; Dif-Pradalier, G. [CEA, IRFM, F-13108 Saint Paul Lez Durance (France); Kosuga, Y. [WCI Center for Fusion Theory, NFRI, Daejeon (Korea, Republic of)

2013-02-15

65

E × B shear pattern formation by radial propagation of heat flux wavesa)

NASA Astrophysics Data System (ADS)

A novel theory to describe the formation of E ×B flow patterns by radially propagating heat flux waves is presented. A model for heat avalanche dynamics is extended to include a finite delay time between the instantaneous heat flux and the mean flux, based on an analogy between heat avalanche dynamics and traffic flow dynamics. The response time introduced here is an analogue of the drivers' response time in traffic dynamics. The microscopic foundation for the time delay is the time for mixing of the phase space density. The inclusion of the finite response time changes the model equation for avalanche dynamics from Burgers equation to a nonlinear telegraph equation. Based on the telegraph equation, the formation of heat flux jams is predicted. The growth rate and typical interval of jams are calculated. The connection of the jam interval to the typical step size of the E ×B staircase is discussed.

Kosuga, Y.; Diamond, P. H.; Dif-Pradalier, G.; Gürcan, Ă.-. D.

2014-05-01

66

Efficient Reformulation of HOTFGM: Heat Conduction with Variable Thermal Conductivity

NASA Technical Reports Server (NTRS)

Functionally graded materials (FGMs) have become one of the major research topics in the mechanics of materials community during the past fifteen years. FGMs are heterogeneous materials, characterized by spatially variable microstructure, and thus spatially variable macroscopic properties, introduced to enhance material or structural performance. The spatially variable material properties make FGMs challenging to analyze. The review of the various techniques employed to analyze the thermodynamical response of FGMs reveals two distinct and fundamentally different computational strategies, called uncoupled macromechanical and coupled micromechanical approaches by some investigators. The uncoupled macromechanical approaches ignore the effect of microstructural gradation by employing specific spatial variations of material properties, which are either assumed or obtained by local homogenization, thereby resulting in erroneous results under certain circumstances. In contrast, the coupled approaches explicitly account for the micro-macrostructural interaction, albeit at a significantly higher computational cost. The higher-order theory for functionally graded materials (HOTFGM) developed by Aboudi et al. is representative of the coupled approach. However, despite its demonstrated utility in applications where micro-macrostructural coupling effects are important, the theory's full potential is yet to be realized because the original formulation of HOTFGM is computationally intensive. This, in turn, limits the size of problems that can be solved due to the large number of equations required to mimic realistic material microstructures. Therefore, a basis for an efficient reformulation of HOTFGM, referred to as user-friendly formulation, is developed herein, and subsequently employed in the construction of the efficient reformulation using the local/global conductivity matrix approach. In order to extend HOTFGM's range of applicability, spatially variable thermal conductivity capability at the local level is incorporated into the efficient reformulation. Analytical solutions to validate both the user-friendly and efficient reformulations am also developed. Volume discretization sensitivity and validation studies, as well as a practical application of the developed efficient reformulation are subsequently carried out. The presented results illustrate the accuracy and implementability of both the user-friendly formulation and the efficient reformulation of HOTFGM.

Zhong, Yi; Pindera, Marek-Jerzy; Arnold, Steven M. (Technical Monitor)

2002-01-01

67

Phonon heat conduction in a semiconductor nanowire and Alexander Balandin

have been fabricated by regular electron beam lithography and wet etching.9 To date, there have beenPhonon heat conduction in a semiconductor nanowire Jie Zoua) and Alexander Balandin Department October 2000; accepted for publication 4 December 2000 A model for phonon heat conduction

68

Heat conduction through the Trombe wall

This paper aims to add to the theoretical understanding of Trombe walls, and to consider the most appropriate calculation methods for simulation purposes. Various control strategies can be used to improve the wall performance, but only movable insulation outside the wall produces any substantial improvement. In this case, total heat flow over a periodic cycle increases with thermal capacity to

C. Carter

1980-01-01

69

SPATIAL STATISTICS MODELS FOR STOCHASTIC INVERSE PROBLEMS IN HEAT CONDUCTION

A Bayesian statistical inference approach is presented herein for the solution of stochastic inverse problems in heat conduction. Spatial statistics models, in particular Markov random elds (MRF), are used to model the prior distributions of unknown thermal quantities (boundary heat ux or heat source). The posterior distribution of the unknown is derived from Bayes' formula and explored using Markov chain

J. Wang; N. Zabaras

2004-01-01

70

Hierarchical Bayesian models for inverse problems in heat conduction

Stochastic inverse problems in heat conduction with consideration of uncertainties in the measured temperature data, temperature sensor locations and thermophysical properties are addressed using a Bayesian statistical inference method. Both parameter estimation and thermal history reconstruction problems, including boundary heat flux and heat source reconstruction, are studied. Probabilistic specification of the unknown variables is deduced from temperature measurements. Hierarchical Bayesian

Jingbo Wang; Nicholas Zabaras

2005-01-01

71

Heat conduction errors and time lag in cryogenic thermometer installations

NASA Technical Reports Server (NTRS)

Installation practices are recommended that will increase rate of heat exchange between the thermometric sensing element and the cryogenic fluid and that will reduce the rate of undesired heat transfer to higher-temperature objects. Formulas and numerical data are given that help to estimate the magnitude of heat-conduction errors and of time lag in response.

Warshawsky, I.

1973-01-01

72

Comparison of some inverse heat conduction methods using experimental data

This paper compares several methods of finding the surface heat flux using transient temperature measurements inside a heat-conducting body. Experimental data is used with a known heat flux history. The methods include function specification with several future approximations, Tikhonov regularization, iterative regularization and specified functions over large time regions with Green's functions. The first three methods are used with the

A. Haji-Sheikh

1996-01-01

73

Manufacture of high heat conductivity resistant clay bricks containing perlite

Different methods have been investigated for achieving heat insulation in the buildings. Manufacturing of high heat conductivity resistant construction materials is an important part of these research efforts. Perlite is an extremely useful material for heat insulation and 70% of the world reserves are located in Turkey. Nearly 65% of the perlite produced today is consumed by the construction industry.

?lker Bekir Topçu; Burak I??kda?

2007-01-01

74

An inverse heat conduction method for simultaneously estimating spatially varying thermal conductivity and heat capacity per unit volume under the conditions of a flash method type of experiment is developed. The unknown thermal properties are assumed to vary only in the space dimension normal to the slab sample and are modeled with piecewise linear representations. Lacking in the literature are

G. P. Flach; M. N. Özi?ik

1989-01-01

75

Modeling Earth's Outer Radiation Belt Electron Dynamics---Radial Diffusion, Heating, and Loss

NASA Astrophysics Data System (ADS)

Earth's outer radiation belt is a relativistic electron environment that is hazardous to space systems. It is characterized by large variations in the electron flux, which are controlled by the competition between source, transport, and loss processes. One of the central questions in outer radiation belt research is to resolve the relative contribution of radial diffusion, wave heating, and loss to the enhancement and decay of the radiation belt electrons. This thesis studies them together and separately. Firstly, we develop an empirical Fokker-Planck model that includes radial diffusion, an internal source, and finite electron lifetimes parameterized as functions of geomagnetic indices. By simulating the observed electron variations, the model suggests that the required magnitudes of radial diffusion and internal heating for the enhancement of energetic electrons in the outer radiation belt vary from storm to storm, and generally internal heating contributes more to the enhancements of MeV energy electrons at L=4 (L is approximately the radial distance in Earth radii at the equator). However, since the source, transport, and loss terms in the model are empirical, the model results have uncertainties. To eliminate the uncertainty in the loss rate, both the precipitation and the adiabatic loss of radiation belt electrons are quantitatively studied. Based on the observations from Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX), a Drift-Diffusion model is applied to quantify electron precipitation loss, which is the dominant non-adiabatic loss mechanism for electrons in the heart of the outer radiation belt. Model results for a small storm, a moderate storm, and an intense storm indicate that fast precipitation losses of relativistic electrons, on the time scale of hours, persistently occur in the storm main phases and with more efficient losses at higher energies over wide range of L regions. Additionally, calculations of adiabatic effects on radiation belt electrons at low altitudes demonstrate that the adiabatic flux drop of electrons during the storm main phase is both altitude and storm dependent. During the main phase of a moderate geomagnetic storm, due solely to adiabatic effects a satellite at low altitude sees either zero electron flux or a fractional flux drop depending on its altitude. To physically quantify the radial diffusion rate, we use power spectral density and global mode structure of the Ultra-Low-Frequency (ULF) waves, which are derived from the Lyon-Fedder-Mobarry (LFM) MHD simulation and validated by field data from real satellites. The calculated total diffusion rate is shown to be dominated by the contribution from magnetic field perturbations, and much less from the electric field. Fast diffusion generally occurs when solar wind dynamic pressure is high or nightside geomagnetic activity is strong and with higher diffusion rates at higher L regions. Work performed in this thesis provides realistic loss rate and radial diffusion rate of radiation belt electrons, as well as a comprehensive Fokker-Planck model that can take the loss and radial diffusion rates as inputs and then determine the internal heating rate with less uncertainty. By this approach, we will be able to quantitatively understand the relative contribution of radial diffusion, wave heating, and loss to the variations of radiation belt electrons.

Tu, Weichao

76

A model of radial profiles of burnup, heat release, and accumulation of plutonium isotopes is described. The model was developed for use in the mechanistic RTOP fuel element code. The model is based on theoretical ideas about the mechanisms leading to the formation of the radial burnup profile and a simplified description of the neutron spectrum in the reactor, employing

S. Yu. Kurchatov; V. V. Likhanskii; A. A. Sorokin; O. V. Khoruzhii

2002-01-01

77

Heat conduction through the Trombe wall

NASA Astrophysics Data System (ADS)

This paper aims to add to the theoretical understanding of Trombe walls, and to consider the most appropriate calculation methods for simulation purposes. Various control strategies can be used to improve the wall performance, but only movable insulation outside the wall produces any substantial improvement. In this case, total heat flow over a periodic cycle increases with thermal capacity to an easily calculable upper limit which can be approached quite closely with practically realizable walls. An exact solution for a two-state Trombe wall is compared with approximate solutions obtained using finite difference methods and the author's modal expansion method. The Crank-Nicholson method has oscillatory errors in some problems, but adequate overall accuracy can be obtained using time steps up to four hours. The modal expansion method is generally very accurate and efficient.

Carter, C.

1980-07-01

78

NASA Astrophysics Data System (ADS)

Axial evolutions of radial heat flux profiles in argon and nitrogen plasma jets from an atmospheric pressure dc non-transferred arc plasma torch are determined using a double calorimetric technique. Results are presented for power levels suitable for the processing of high temperature ceramic oxides, where the heat flux data reported in the literature is rare. Variations of the profile widths and profile maxima are presented as a function of axial distance as well as power. Relatively uniform profile width over prolonged axial distance for nitrogen plasma compared to argon is an important observation which has the potential to offer a much longer dwell time of the injected particles inside the plasma, avoiding the problem of unmelts, especially for ceramics. A comparative study of the heat flux profiles for argon and nitrogen plasma is presented. The obtained results are compared with the data reported in literature.

Meher, K. C.; Tiwari, N.; Ghorui, S.; Sahasrabudhe, S. N.; Das, A. K.

2014-12-01

79

Enhanced anisotropic heat conduction in multi-walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Anisotropy of heat conduction in multi-walled carbon nanotubes (MWNTs) is investigated by measuring heat flows in a pristine MWNT and in a MWNT with defects. The in- and out-of-shell thermal conductivities of each MWNT graphite shell are determined, and differences of more than four orders of magnitude are obtained because of the inter-shell gaps. This enhanced anisotropy reduces the conductance by 74% compared with that of the pristine MWNT because of the presence of outer shell defects, which comprise only 2.8% volume ratio. Furthermore, the anisotropy-assisted length dependence of thermal conductivity is demonstrated, even though there is no ballistic phonon transport.

Hayashi, Hiroyuki; Ikuta, Tatsuya; Nishiyama, Takashi; Takahashi, Koji

2013-01-01

80

Heat Conduction in Homogeneous and Heterogeneous Billiard Systems

NASA Astrophysics Data System (ADS)

We investigate the heat conduction in a modified Lorentz gas with freely rotating disks periodically placed along one-dimensional channel. The heat conductivity is dependent on the moment of inertia ? of the disks, with a power-law decay when ? > 1. By plotting the Poincaré surface of the section, we observe a contraction of phase space over the range of ? > 1, which is sensitive to the initial condition. We find that the power-law decay of the heat conductivity is relevant to the mixing phase space. As a possible application, we model the heterostructure by connecting the segments of different ?, and predict the analytical results of the temperature profiles and the heat conductivity, which are in good agreement with the numerical ones.

Mao, Jun-Wen; Li, You-Quan; Deng, Ling-Yun

81

The influence of heat conduction on acoustic streaming

Summary The influence of heat conduction on acoustic streaming is considered including the effect of variable tube wall temperature. The calculations are carried out in the limiting case when the boundary layer is thin compared to the tube radius.

Nikolaus Rott

1974-01-01

82

Molecular Dynamics Simulations of Heat Conduction in Nanostructures: Effect of Heat Bath

may lead to non-physical results. In contrast, Langevin heat bath is recommended because it canMolecular Dynamics Simulations of Heat Conduction in Nanostructures: Effect of Heat Bath Jie CHEN1, 2010) We investigate systematically the impacts of heat bath used in molecular dynamics simulations

Li, Baowen

83

Ballistic heat conduction and mass disorder in one dimension

NASA Astrophysics Data System (ADS)

It is well-known that in the disordered harmonic chain, heat conduction is subballistic and the thermal conductivity (?) scales asymptotically as \\lim_{L\\rightarrow\\infty}\\kappa\\propto L^{0.5} where L is the chain length. However, using the nonequilibrium Green's function (NEGF) method and analytical modelling, we show that there exists a critical crossover length scale (LC) below which ballistic heat conduction (\\kappa\\propto L) can coexist with mass disorder. This ballistic-to-subballistic heat conduction crossover is connected to the exponential attenuation of the phonon transmittance function ? i.e. ?(?, L) = exp[?L/?(?)], where ? is the frequency-dependent attenuation length. The crossover length can be determined from the minimum attenuation length, which depends on the maximum transmitted frequency. We numerically determine the dependence of the transmittance on frequency and mass composition as well as derive a closed form estimate, which agrees closely with the numerical results. For the length-dependent thermal conductance, we also derive a closed form expression which agrees closely with numerical results and reproduces the ballistic to subballistic thermal conduction crossover. This allows us to characterize the crossover in terms of changes in the length, mass composition and temperature dependence, and also to determine the conditions under which heat conduction enters the ballistic regime. We describe how the mass composition can be modified to increase ballistic heat conduction.

Ong, Zhun-Yong; Zhang, Gang

2014-08-01

84

Ballistic heat conduction and mass disorder in one dimension.

It is well-known that in the disordered harmonic chain, heat conduction is subballistic and the thermal conductivity (?) scales asymptotically as lim(L--> ?) ? ? L(0.5) where L is the chain length. However, using the nonequilibrium Green's function (NEGF) method and analytical modelling, we show that there exists a critical crossover length scale (LC) below which ballistic heat conduction (? ? L) can coexist with mass disorder. This ballistic-to-subballistic heat conduction crossover is connected to the exponential attenuation of the phonon transmittance function ? i.e. ?(?, L) = exp[-L/?(?)], where ? is the frequency-dependent attenuation length. The crossover length can be determined from the minimum attenuation length, which depends on the maximum transmitted frequency. We numerically determine the dependence of the transmittance on frequency and mass composition as well as derive a closed form estimate, which agrees closely with the numerical results. For the length-dependent thermal conductance, we also derive a closed form expression which agrees closely with numerical results and reproduces the ballistic to subballistic thermal conduction crossover. This allows us to characterize the crossover in terms of changes in the length, mass composition and temperature dependence, and also to determine the conditions under which heat conduction enters the ballistic regime. We describe how the mass composition can be modified to increase ballistic heat conduction. PMID:25077430

Ong, Zhun-Yong; Zhang, Gang

2014-08-20

85

Radiative heat conduction and the magnetorotational instability

NASA Astrophysics Data System (ADS)

A photon or a neutrino gas, semicontained by a non-diffusive particle species through scattering, comprises a rather peculiar magnetohydrodynamic fluid where the magnetic field is truly frozen only to the comoving volume associated with the mass density. Although radiative diffusion precludes a formal adiabatic treatment of compressive perturbations, we cast the energy equation in quasi-adiabatic form by assuming a negligible rate of energy exchange among species on the time-scale of the perturbation. This leads to a simplified dispersion relation for toroidal, non-axisymmetric magnetorotational modes when the accretion disc has comparable stress contributions from diffusive and non-diffusive components. The properties of the modes of fastest growth are shown to depend strongly on the compressibility of the mode, with a reduction in growth rate consistent with the results of Blaes & Socrates for axisymmetric modes. A clumpy disc structure is anticipated on the basis of the polarization properties of the fastest-growing modes. This analysis is accurate in the near-hole region of locally cooled, hyper-accreting flows if the electron gas becomes moderately degenerate such that non-conductive, thermalizing processes with associated electron-positron release (i.e. neutrino annihilation and neutrino absorption on to nuclei) are effectively blocked by high occupation of the Fermi levels.

Araya-Góchez, Rafael A.; Vishniac, Ethan T.

2004-12-01

86

Thermal conductivity and specific heat of sorghum grain

diffusivity was able to calculate the value of specific heat for wheat, Table II (1). The apparatus which he used was the same as that described for thermal conductivity. The most useful reference was by Disney, who determined the specific heat of wheat... done with the same modified Bunsen ice calorimeter and method as described for Disney. None of these investigators made any determination of the specific heat of sorghum grain, and therefore the literature reviewed was only useful to indicate a...

Miller, Clinton Frank

2012-06-07

87

Unsteady droplet combustion with droplet heating. II. Conduction limit

The spherically-symmetric, thin-flame combustion of a pure component droplet is analyzed by assuming quasi-steady gas-phase processes and conduction being the only heat transfer mechanism within the droplet. Exact numerical, and an approximate analytical, solutions are presented. Results show that droplet heating is the dominant heat utilization mode for the initial 10 to 20 percent of the droplet lifetime, during which

C. K. Law; W. A. Sirignono

1977-01-01

88

Use of Spreadsheets in Solving Heat Conduction Problems in Fins

NSDL National Science Digital Library

Excel is an effective and inexpensive tool available on all computers equipped with Microsoft Office. This software has the necessary functions for solving a large class of engineering problems, including those related to heat transfer. This paper provides several examples to demonstrate the application of Excel in solving problems involving one-dimensional heat conduction in various fin configurations. It provides formulas for the temperature distribution and heat transfer for several different fin profiles.

Karimi, Amir

2011-04-04

89

Transient conduction and radiation heat transfer in porous thermal insulations

This paper analyzes transient radiation and conduction heat transfer through planar porous materials. The transient response considered is caused by a sudden increase of heat generation at the hot boundary. The objective was to establish the effect of radiation on the temperature rise of the hot wall. The problem investigated is relevant to the use of transient methods for measuring

T. W. Tong; D. L. McElroy; D. W. Yarbrough

1984-01-01

90

Transient Conduction and Radiation Heat Transfer in Porous Thermal Insulations

This paper analyzes transient radiation and conduction heat transfer through planar porous materials. The transient response considered is caused by a sudden increase of heat generation at the hot boundary. The objective was to establish the effect of radiation on the temperature rise of the hot wall. The problem investigated is relevant to the use of transient methods for measuring

T. W. Tong; D. L. McElroy; D. W. Yarbrough

1985-01-01

91

SPATIAL STATISTICS MODELS FOR STOCHASTIC INVERSE PROBLEMS IN HEAT CONDUCTION

A Bayesian statistical inference approach is presented herein for the solution of stochastic inverse problemsSPATIAL STATISTICS MODELS FOR STOCHASTIC INVERSE PROBLEMS IN HEAT CONDUCTION J. Wang and N. Zabaras (MRF), is presented in this study for the solution of stochastic inverse problems in heat conduc- tion

Zabaras, Nicholas J.

92

Efficient sequential solution of the nonlinear inverse heat conduction problem

A solution to the nonlinear inverse heat conduction problem is offered which employs a sequential procedure for the calculation of surface heat fluxes and temperatures from measured interior temperatures in opaque solids having temperature-variable thermal properties. The nonlinear problem is linearized, and through the elimination of iteration, computation time can be reduced by a factor of 3 or 4. The

J. V. Beck; B. Litkouhi; C. R. Saint Clair Jr.

1982-01-01

93

Heat conduction in relativistic systems: alternatives and perspectives

The non-equilibrium thermodynamics of relativistic systems have a rich phenomenology. The simplest phenomenon in the class of dissipative processes is that of heat. This letter presents a brief summary of the efforts made to tackle the problem of relativistic heat conduction. In particular, we focus on the multi-fluid approach to relativistic dissipation.

C. S. Lopez-Monsalvo

2010-11-30

94

An Experiment in Heat Conduction Using Hollow Cylinders

ERIC Educational Resources Information Center

An experimental apparatus was designed and built to allow students to carry out heat conduction experiments in hollow cylinders made of different materials, as well as to determine the thermal conductivity of these materials. The evolution of the temperature difference between the inner and outer walls of the cylinder as a function of time is…

Ortuno, M.; Marquez, A.; Gallego, S.; Neipp, C.; Belendez, A.

2011-01-01

95

Axial conduction in a thick-wall matrix heat exchanger

Solutions are developed for temperature distributions and ineffectiveness for a high Ntu matrix heat exchanger having simultaneous axial conduction in the single phase (matrix\\/fluid) flow channels and separating wall. A scale analysis of the governing equations shows a large disparity in length scales for the conduction and convection effects, thus indicating a singular perturbation problem. Solutions for both balanced and

G. F. Jones

1995-01-01

96

Fourier analysis of conductive heat transfer for glazed roofing materials

NASA Astrophysics Data System (ADS)

For low-rise buildings, roof is the most exposed surface to solar radiation. The main mode of heat transfer from outdoor via the roof is conduction. The rate of heat transfer and the thermal impact is dependent on the thermophysical properties of roofing materials. Thus, it is important to analyze the heat distribution for the various types of roofing materials. The objectives of this paper are to obtain the Fourier series for the conductive heat transfer for two types of glazed roofing materials, namely polycarbonate and polyfilled, and also to determine the relationship between the ambient temperature and the conductive heat transfer for these materials. Ambient and surface temperature data were collected from an empirical field investigation in the campus of Universiti Teknologi MARA Shah Alam. The roofing materials were installed on free-standing structures in natural ventilation. Since the temperature data are generally periodic, Fourier series and numerical harmonic analysis are applied. Based on the 24-point harmonic analysis, the eleventh order harmonics is found to generate an adequate Fourier series expansion for both glazed roofing materials. In addition, there exists a linear relationship between the ambient temperature and the conductive heat transfer for both glazed roofing materials. Based on the gradient of the graphs, lower heat transfer is indicated through polyfilled. Thus polyfilled would have a lower thermal impact compared to polycarbonate.

Roslan, Nurhana Lyana; Bahaman, Nurfaradila; Almanan, Raja Noorliyana Raja; Ismail, Razidah; Zakaria, Nor Zaini

2014-07-01

97

THERM3D -- A boundary element computer program for transient heat conduction problems

The computer code THERM3D implements the direct boundary element method (BEM) to solve transient heat conduction problems in arbitrary three-dimensional domains. This particular implementation of the BEM avoids performing time-consuming domain integrations by approximating a ``generalized forcing function`` in the interior of the domain with the use of radial basis functions. An approximate particular solution is then constructed, and the original problem is transformed into a sequence of Laplace problems. The code is capable of handling a large variety of boundary conditions including isothermal, specified flux, convection, radiation, and combined convection and radiation conditions. The computer code is benchmarked by comparisons with analytic and finite element results.

Ingber, M.S. [New Mexico Univ., Albuquerque, NM (United States). Dept. of Mechanical Engineering

1994-02-01

98

NASA Astrophysics Data System (ADS)

In the present study, laminar natural convection of nanofluids confined between two horizontal concentric cylinders with eight radial fins attached to the inner cylinder is studied. Governing equations are solved using the finite volume method. The computations are performed for various Rayleigh numbers, nanofluids and volume fractions of nanoparticles. From the results, it is found that the average Nusselt number enhances when volume fraction and thermal conductivity of nanoparticles increases. Also, it is observed that the average Nusselt number of Cu-water nanofluid is highest among the nanofluids of the present study. Moreover, it is seen that the temperature gradient and absolute value of stream function decrease by addition of nanoparticles.

Arbaban, M.; Salimpour, M. R.

2014-07-01

99

Heat Transfer Analysis for a Concentric Tube Heat Exchanger Including the Wall Axial Conduction

The effect of wall axial conduction on the heat transfer in a concentric tube heat exchanger is examined for the inner flow laminar flow regime. The procedure used for the current analysis combines the analytical solution for the inner fluid with a numerical approximation for the wall conduction and has the capability of handling the temperature variation for the outer

Mehmet Emin Arici

2010-01-01

100

Implicit continuum mechanics approach to heat conduction in granular materials

In this paper, we derive a properly frame-invariant implicit constitutive relationship for the heat flux vector for a granular medium (or a density-gradient-type fluid). The heat flux vector is commonly modeled by Fourier’s law of heat conduction, and for complex materials such as nonlinear fluids, porous media, or granular materials, the coefficient of thermal conductivity is generalized by assuming that it would depend on a host of material and kinematic parameters such as temperature, shear rate, porosity, concentration, etc. In this paper, we extend the approach of Massoudi [Massoudi, M. Math. Methods Appl. Sci. 2006, 29, 1585; Massoudi, M. Math. Methods Appl. Sci. 2006, 29, 1599], who provided explicit constitutive relations for the heat flux vector for flowing granular materials; in order to do so, we use the implicit scheme suggested by Fox [Fox, N. Int. J. Eng. Sci. 1969, 7, 437], who obtained implicit relations in thermoelasticity.

Massoudi, M.; Mehrabadi, M.

2010-01-01

101

Variable Conductance Heat Pipe Performance after Extended Periods of Freezing

NASA Astrophysics Data System (ADS)

Radiators operating in lunar or Martian environments must be designed to reject the maximum heat load at the maximum sink temperature, while maintaining acceptable temperatures at lower powers or sink temperatures. Variable Conductance Heat Pipe (VCHP) radiators can passively adjust to these changing conditions. Due to the presence of non-condensable gas (NCG) within each VCHP, the active condensing section adjusts with changes in either thermal load or sink temperature. In a Constant Conductance Heat Pipe (CCHP) without NCG, it is possible for all of the water to freeze in the condenser, by either sublimation or vaporization. With a dry evaporator, startup is difficult or impossible. Several previous studies have shown that adding NCG suppresses evaporator dryout when the condenser is frozen. These tests have been for relatively short durations, with relatively short condensers. This paper describes freeze/thaw experiments involving a VCHP with similar dimensions to the current reactor and cavity cooling radiator heat pipe designs.

Ellis, Michael C.; Anderson, William G.

2009-03-01

102

Heat capacity, magnetic susceptibility, EPR, and dc conductivity of some conducting polymers

NASA Astrophysics Data System (ADS)

Polyaniline doped with polystyrene-sulfonic-acid (PAN-PSSA), such that y =[sulfonate]/[aniline] = 1, exhibits a dc conductivity of 0.1 S/cm. On increasing the dopant concentration to y = 6, the conductivity drops by four orders of magnitude. Poly(3,4-ethylenedioxythiophene) doped with polystyrene-sulfonic-acid (PEDOT-PSSA) also exhibits a similar behavior on doping. The results of a study involving heat capacity, magnetic susceptibility, EPR, and dc conducting measurements will be reported.

Kahol, Pawan; Ho, James; Deterich, Stefania; Chen, Y. Y.; Wang, C. R.; Neeleshwar, S.; Tsai, C. B.; Wessling, B.

2004-03-01

103

Effect of crosslink formation on heat conduction in amorphous polymers

NASA Astrophysics Data System (ADS)

We performed molecular dynamics (MD) simulations on amorphous polyethylene (PE) and polystyrene (PS) in order to elucidate the effect of crosslinks between polymer chains on heat conduction. In each polymer system, thermal conductivities were measured for a range of crosslink concentration by using nonequilibrium MD techniques. PE comprised of 50 carbon atom long chains exhibited slightly higher conductivity than that of 250 carbon atom long chains at the standard state. In both cases for PE, crosslinking significantly increased conductivity and the increase was more or less proportional to the crosslink density. On the other hand, in the PS case, although the thermal conductivity increased with the crosslinking, the magnitude of change in thermal conductivity was relatively small. We attribute this difference to highly heterogeneous PS based network including phenyl side groups. In order to elucidate the mechanism for the increase of thermal conductivity with the crosslink concentration, we decomposed energy transfer into modes associated with various bonded and non-bonded interactions.

Kikugawa, Gota; Desai, Tapan G.; Keblinski, Pawel; Ohara, Taku

2013-07-01

104

Heat conduction induced by non-Gaussian athermal fluctuations.

We study the properties of heat conduction induced by non-Gaussian noises from athermal environments. We find that new terms should be added to the conventional Fourier law and the fluctuation theorem for the heat current, where its average and fluctuation are determined not only by the noise intensities but also by the non-Gaussian nature of the noises. Our results explicitly show the absence of the zeroth law of thermodynamics in athermal systems. PMID:23767504

Kanazawa, Kiyoshi; Sagawa, Takahiro; Hayakawa, Hisao

2013-05-01

105

Mechanical control of heat conductivity in molecular chains.

We discuss a possibility to control heat conductivity in molecular chains by means of external mechanical loads. To illustrate such possibilities we consider first well-studied one-dimensional chain with degenerate double-well potential of the nearest-neighbor interaction. We consider varying lengths of the chain with fixed number of particles. Number of possible energetically degenerate ground states strongly depends on the overall length of the chain, or, in other terms, on average length of the link between neighboring particles. These degenerate states correspond to mechanical equilibria; therefore, one can say that formation of such structures mimics a process of plastic deformation. We demonstrate that such modification of the chain length can lead to quite profound (almost fivefold) reduction of the heat conduction coefficient. Even more profound effect is revealed for a model with a single-well nonconvex potential. It is demonstrated that in a certain range of constant external forcing, this model becomes effectively double-well and has a multitude of possible states of equilibrium for fixed value of the external load. Due to this degeneracy, the heat-conduction coefficient can be reduced by two orders of magnitude. We suggest a mechanical model of a chain with periodic double-well potential, which allows control of the heat transport. The models considered may be useful for description of heat transfer in biological macromolecules and for control of the heat transport in microsystems. The possibility of the heat transport control in more realistic three-dimensional systems is illustrated by simulation of a three-dimensional model of polymer ?-helix. In this model, the mechanical stretching also brings about the structural inhomogeneity and, in turn, to essential reduction of the heat conductivity. PMID:24580199

Savin, A V; Gendelman, O V

2014-01-01

106

Heat conduction in one-dimensional aperiodic quantum Ising chains.

The heat conductivity of nonperiodic quantum Ising chains whose ends are connected with heat baths at different temperatures are studied numerically by solving the Lindblad master equation. The chains are subjected to a uniform transverse field h, while the exchange coupling J{m} between the nearest-neighbor spins takes the two values J{A} and J{B} arranged in Fibonacci, generalized Fibonacci, Thue-Morse, and period-doubling sequences. We calculate the energy-density profile and energy current of the resulting nonequilibrium steady states to study the heat-conducting behavior of finite but large systems. Although these nonperiodic quantum Ising chains are integrable, it is clearly found that energy gradients exist in all chains and the energy currents appear to scale as the system size ~N{?}. By increasing the ratio of couplings, the exponent ? can be modulated from ? > -1 to ? < -1 corresponding to the nontrivial transition from the abnormal heat transport to the heat insulator. The influences of the temperature gradient and the magnetic field to heat conduction have also been discussed. PMID:21517475

Li, Wenjuan; Tong, Peiqing

2011-03-01

107

Transient conduction and radiation heat transfer in porous thermal insulations

NASA Astrophysics Data System (ADS)

This paper analyzes transient radiation and conduction heat transfer through planar porous materials. The transient response considered is caused by a sudden increase of heat generation at the hot boundary. The objective was to establish the effect of radiation on the temperature rise of the hot wall. The problem investigated is relevant to the use of transient methods for measuring the thermal conductivity of porous insulations. It was found that, in cases such as when the porous material is a light-weight fiberglass insulation, neglecting radiation would result in serious errors in predicting the hot wall temperature rise.

Tong, T. W.; McElroy, D. L.; Yarbrough, D. W.

1984-12-01

108

A Mechanical Model for Fourier's Law of Heat Conduction

NASA Astrophysics Data System (ADS)

Nonequilibrium statistical mechanics close to equilibrium is a physically satisfactory theory centered on the linear response formula of Green-Kubo. This formula results from a formal first order perturbation calculation without rigorous justification. A rigorous derivation of Fourier's law for heat conduction from the laws of mechanics remains thus a major unsolved problem. In this note we present a deterministic mechanical model of a heat-conducting chain with nontrivial interactions, where kinetic energy fluctuations at the nodes of the chain are removed. In this model the derivation of Fourier's law can proceed rigorously.

Ruelle, David

2012-05-01

109

Neutrino Heat Conduction and Inhomogeneities in the Early Universe

NASA Technical Reports Server (NTRS)

Constraints on parameters of inhomogeneous nucteosynthesis, namely, the overdensity and size of baryon lumps, are found by calculatig the blackbody neutrino heat conduction into the lumps, which tends to inflate them away. The scale size for efficient heat conduction is determined by the mean free path lambda of the neutrino, and so we compute lambda in our case of a high-temperature plasma with low chemical potential, and find a general result that many-body effects are unimportant, simplifying the calculation. We find that in the region of interest for nucleosynthesis, neutrino inflation is important for overdensities greater than 10(exp 4).

Heckler, A.; Hogan, C. J.

1993-01-01

110

Application of genetic algorithms in nonlinear heat conduction problems.

Genetic algorithms are employed to optimize dimensionless temperature in nonlinear heat conduction problems. Three common geometries are selected for the analysis and the concept of minimum entropy generation is used to determine the optimum temperatures under the same constraints. The thermal conductivity is assumed to vary linearly with temperature while internal heat generation is assumed to be uniform. The dimensionless governing equations are obtained for each selected geometry and the dimensionless temperature distributions are obtained using MATLAB. It is observed that GA gives the minimum dimensionless temperature in each selected geometry. PMID:24695517

Kadri, Muhammad Bilal; Khan, Waqar A

2014-01-01

111

Molecular Dynamics Simulations of Heat Conduction in Nanostructures: Effect of Heat Bath

We investigate systematically the impacts of heat bath used in molecular dynamics simulations on heat conduction in nanostructures exemplified by silicon nanowires (SiNWs) and silicon\\/germanium nano junction. It is found that multiple layers of Nosé-Hoover heat bath are required to reduce the temperature jump at the boundary, while only a single layer of Langevin heat bath is sufficient to generate

Jie Chen; Gang Zhang; Baowen Li

2010-01-01

112

A heat conduction study at non-continuum scales

NASA Astrophysics Data System (ADS)

An extensive and detailed description of heat conduction at the micro- and nano-scale is presented. During the last two decades this phenomenon has become very attractive to study because of the shrinking in size of thermoelectric technologies and electronic devices. These newer technologies are at the micro- and nano-scale. Due to the small size, a power dissipation problem has presented itself in these applications. The proper thermal performance is related with the performance of the technology. Because of these facts a description of the thermal transport in different materials at these scales is required. This problem is important because understanding the energy transport will allow engineers to design faster electronic devices and more efficient thermoelectric applications. For macro-scale it is known that diffusive behavior is presented in heat conduction; here models that show different behavior than diffusive such as wave-like are presented. One extra tool to understand heat conduction is to calculate the thermal conductivity. Equilibrium molecular dynamics combined with the Green-Kubo formula can be used to calculate the thermal conductivity of materials such as germanium and carbon. The foundation of this calculation is extracting the heat current from the results, and implementing it into the Green-Kubo formula. This work considers all formulations from the literature that calculate the heat current for the Tersoff potential, the interatomic potential most applicable to semiconductor materials. The formulations for the heat current are described, and results for germanium and carbon are presented. The formulations are compared with respect to how well they capture the physics of the Tersoff potential and how well the calculated value of the thermal conductivity reflects the experimentally-measured value. The second part of this work deals with heat transport in low dimensions at the nano-scale. The energy transport in a two dimensional graphene sheet is studied and compared to that in a one dimensional chain. The equations of motion for each individual atom of the sheet are solved numerically to generate the distribution of kinetic energy in the structure. The distribution of kinetic energy in the sheet shows two different characteristics of the transport. The components of frequency of the kinetic energy in the graphene structure are identified. The components allow the identification under which potential more low frequency carriers are expected. The presence of chaos in the graphene sheet using the anharmonic potential is identified. Finally, conclusions and recommendations for the study of heat conduction at the nano-scale are presented.

Guajardo Cuellar, Alejandro

113

High Conductance Loop Heat Pipes for Space Application

NASA Astrophysics Data System (ADS)

Three high conductance Loop Heat Pipes (LHPs) for the Geostationary Imaging Fourier Transform Spectrometer (GIFTS) were designed, fabricated and thermal vacuum tested. One LHP with ammonia working fluid was designed for heat removal from a cryocooler cold head. Two ethane LHPs were designed to reject heat from the aft and fore optics to space. Thermal performance tests were performed in a vacuum chamber with attached masses simulating actual components. Thermal tests were also conducted on the bench and in an environmental chamber. The following features of the GIFTS LHPs were observed: (a) reliable startup and steady state operation with conductance as high as 83W/°C at various temperatures; (b) precision temperature control using compensation chamber heater during thermal cycling. Heat input power and condenser temperatures were varied periodically, while evaporator was maintained at a constant temperature. Temperature of the evaporator heat input surface fluctuated only by a fraction of a degree; (c) in addition there was no thermal performance degradation after 16 month of storage. The LHPs are installed on the instrument and waiting for a launch platform.

Semenov, Sergey Y.; Cho, Wei-Lin; Jensen, Scott M.

2006-01-01

114

A Numerical Procedure for Shock Problem Using Artificial Heat Conduction

A method for automatically taking into account the shock discontinuities in the flow problems whenever and wherever they occur was given by Von Neumann and Richtmyer by introducing an artificial viscosity term in the momentum and energy equations. In this paper, an alternative mechanism of artificial heat conduction is proposed. This alters only the energy equation and satisfies all conditions,

Purushottam Lal Sachdev; Phoolan Prasad

1966-01-01

115

Genetic Algorithm in Solution of Inverse Heat Conduction Problems

This report demonstrates the use of a genetic algorithm search in the solution of an inverse problem. The genetic algorithm is used to solve the one-dimensional inverse heat conduction problem using numerical data generated by solution of the corresponding direct problem. Both “pure” and noisy data are considered. If used with regularization, the method is shown to yield reasonable results

Miroslav Raudenský; Keith A. Woodbury; J. Kral; T. Brezina

1995-01-01

116

Equivalent inclusion method for steady state heat conduction in composites

The equivalent inclusion method is proposed to solve the steady state heat conduction problems in composites. This method is analogous to Eshelby's equivalent inclusion method in elasticity. Thus, the solution procedure by this method is very simple, involving only algebraic operations. The equivalent inclusion method developed here is also applicable to the case of high concentrations of ellipsoidal inhomogeneities. As

H Hiroshi; M. Taya

1986-01-01

117

Element-by-element factorization algorithms for heat conduction

NASA Technical Reports Server (NTRS)

Element-by-element solution strategies are developed for transient heat conduction problems. Results of numerical tests indicate the effectiveness of the procedures proposed. The small database requirements and attractive architectural features of the algorithms suggest considerable potential for solving large scale problems.

Hughes, T. J. R.; Winget, J. M.; Park, K. C.

1983-01-01

118

Regularized numerical solution of nonlinear inverse heat-conduction problem

The construction of an algorithm for a numerical solution of the nonlinear inverse problem is discussed for the case of a generalized one-dimensional heat-conduction equation in a region with moving boundaries. The algorithm is regularized in the Tikhonov manner.

O. M. Alifanov; E. A. Artyukhin

1975-01-01

119

Group classification of heat conductivity equations with a nonlinear source

We suggest a systematic procedure for classifying partial differential equations (PDEs) invariant with respect to low-dimensional Lie algebras. This procedure is a proper synthesis of the infinitesimal Lie method, the technique of equivalence transformations and the theory of classification of abstract low-dimensional Lie algebras. As an application, we consider the problem of classifying heat conductivity equations in one variable with

R. Z. Zhdanov; V. I. Lahno

1999-01-01

120

Deterioration in Heat Transfer due to Axial Conduction of Heat in Open Cell Metal Foam

NASA Astrophysics Data System (ADS)

Cross-connection in the foam struts helps achieving augmentation in heat transfer. It is the same feature which adds the risk of promoting axial conduction. Fluid flow through a slice of open-cell foam, attached to a plate, has been considered for analysing the effect of axial conduction through the porous medium. A repetitive simple cubic structure model for the porous matrix has been assumed for simplicity. While, thermal gradient in the solid plate is always associated with axial flow of heat, existence of the same through the foam filaments becomes conditional. Axial heat flow through the foam-fibres has been found causing substantial deterioration in heat transfer.

Ghosh, Indranil

2010-05-01

121

Vacuum Induction Melting Unit Induction heating is a process wherein induced eddy currents heat conductive materials. This heating can be used to melt metals and make alloys. Vacuum Induction melting on the melting process. The induction melting facility (Figure 1) was established in the Symmetry Lab (WL-207

Subramaniam, Anandh

122

High temperature electrically conducting ceramic heating element and control system

NASA Technical Reports Server (NTRS)

Improvements were made in both electrode technology and ceramic conductor quality to increase significantly the lifetime and thermal cycling capability of electrically conducting ceramic heater elements. These elements were operated in vacuum, inert and reducing environments as well as oxidizing atmospheres adding to the versatility of the conducting ceramic as an ohmic heater. Using stabilized zirconia conducting ceramic heater elements, a furnace was fabricated and demonstrated to have excellent thermal response and cycling capability. The furnace was used to melt platinum-20% rhodium alloy (melting point 1904 C) with an isothermal ceramic heating element having a nominal working cavity size of 2.5 cm diameter by 10.0 cm long. The furnace was operated to 1940 C with the isothermal ceramic heating element. The same furnace structure was fitted with a pair of main heater elements to provide axial gradient temperature control over a working cavity length of 17.8 cm.

Halbach, C. R.; Page, R. J.

1975-01-01

123

Thermal conductivity, electrical conductivity and specific heat of copper-carbon fiber composite

NASA Technical Reports Server (NTRS)

A new material of copper/carbon fiber composite is developed which retains the properties of copper, i.e., its excellent electrical and thermal conductivity, and the property of carbon, i.e., a small thermal expansion coefficient. These properties of the composite are adjustable within a certain range by changing the volume and/or the orientation of the carbon fibers. The effects of carbon fiber volume and arrangement changes on the thermal and electrical conductivity, and specific heat of the composite are studied. Results obtained are as follows: the thermal and electrical conductivity of the composite decrease as the volume of the carbon fiber increases, and were influenced by the fiber orientation. The results are predictable from a careful application of the rule of mixtures for composites. The specific heat of the composite was dependent, not on fiber orientation, but on fiber volume. In the thermal fatigue tests, no degradation in the electrical conductivity of this composite was observed.

Kuniya, Keiichi; Arakawa, Hideo; Kanai, Tsuneyuki; Chiba, Akio

1988-01-01

124

Correlations and scaling in one-dimensional heat conduction.

We examine numerically the full spatiotemporal correlation functions for all hydrodynamic quantities for the random collision model introduced recently. The autocorrelation function of the heat current, through the Kubo formula, gives a thermal conductivity exponent of 1/3 in agreement with the analytical prediction and previous numerical work. Remarkably, this result depends crucially on the choice of boundary conditions: for periodic boundary conditions (as opposed to open boundary conditions with heat baths) the exponent is approximately 1/2. All primitive hydrodynamic quantities scale with the dynamic critical exponent predicted analytically. PMID:14682932

Deutsch, J M; Narayan, Onuttom

2003-10-01

125

Heat, Light, and Videotapes: Experiments in Heat Conduction Using Liquid Crystal Film.

ERIC Educational Resources Information Center

Presents a range of experiments in heat conduction suitable for upper-level undergraduate laboratories that make use of heat sensitive liquid crystal film to measure temperature contours. Includes experiments mathematically described by Laplace's equation, experiments theoretically described by Poisson's equation, and experiments that involve…

Bacon, Michael E.; And Others

1995-01-01

126

We consider three one-dimensional continuous-time Markov processes on a lattice, each of which models the conduction of heat: the family of Brownian Energy Processes with parameter $m$, a Generalized Brownian Energy Process, and the Kipnis-Marchioro-Presutti process. The hydrodynamic limit of each of these three processes is a parabolic equation, the linear heat equation in the case of the BEP$(m)$ and the KMP, and a nonlinear heat equation for the GBEP($a$). We prove the hydrodynamic limit rigorously for the BEP$(m)$, and give a formal derivation for the GBEP($a$). We then formally derive the pathwise large-deviation rate functional for the empirical measure of the three processes. These rate functionals imply gradient-flow structures for the limiting linear and nonlinear heat equations. We contrast these gradient-flow structures with those for processes describing the diffusion of mass, most importantly the class of Wasserstein gradient-flow systems. The linear and nonlinear heat-equation gradient-flow structures are each driven by entropy terms of the form $-\\log \\rho$; they involve dissipation or mobility terms of order $\\rho^2$ for the linear heat equation, and a nonlinear function of $\\rho$ for the nonlinear heat equation.

Mark A. Peletier; Frank Redig; Kiamars Vafayi

2014-03-19

127

NASA Astrophysics Data System (ADS)

We consider three one-dimensional continuous-time Markov processes on a lattice, each of which models the conduction of heat: the family of Brownian Energy Processes with parameter m (BEP(m)), a Generalized Brownian Energy Process, and the Kipnis-Marchioro-Presutti (KMP) process. The hydrodynamic limit of each of these three processes is a parabolic equation, the linear heat equation in the case of the BEP(m) and the KMP, and a nonlinear heat equation for the Generalized Brownian Energy Process with parameter a (GBEP(a)). We prove the hydrodynamic limit rigorously for the BEP(m), and give a formal derivation for the GBEP(a). We then formally derive the pathwise large-deviation rate functional for the empirical measure of the three processes. These rate functionals imply gradient-flow structures for the limiting linear and nonlinear heat equations. We contrast these gradient-flow structures with those for processes describing the diffusion of mass, most importantly the class of Wasserstein gradient-flow systems. The linear and nonlinear heat-equation gradient-flow structures are each driven by entropy terms of the form -log ?; they involve dissipation or mobility terms of order ?2 for the linear heat equation, and a nonlinear function of ? for the nonlinear heat equation.

Peletier, Mark A.; Redig, Frank; Vafayi, Kiamars

2014-09-01

128

Nanofluids, because of their enhanced heat transfer capability as compared to normal water\\/glycol\\/oil based fluids, offer the engineer opportunities for development in areas where high heat transfer, low temperature tolerance and small component size are required. In this present paper, the hydrodynamic and thermal fields of a water–?Al2O3 nanofluid in a radial laminar flow cooling system are considered. Results indicate

Gilles Roy; Cong Tam Nguyen; Paul-René Lajoie

2004-01-01

129

Dispersion of the conductance of quantum nanowires and Joule heating

NASA Astrophysics Data System (ADS)

The high-frequency ballistic conductance G(?) of a quantum wire connecting two classical reservoirs is discussed. It is supposed that the transverse size of the wire is on the order of the de Broglie wavelength of the conduction electrons. An expression for G(?) in a wide range of frequencies ? is given. The behavior of both active Re G(?) and reactive Im G(?) parts of the conductance is investigated. The frequency range is determined where the so-called kinetic inductance is dominant, i.e., Im G(?) is positive and larger than Re G(?). This range is defined by the condition that the time of flight of the conduction electrons along the wire length L exceeds the period of oscillation 2?/? of the electric potential. The Joule heat generation that accompanies the current flow through the quantum wire takes place in the reservoirs over a distance on the order of the mean free path of conduction electrons. The total rates of Joule heat generation are the same in both reservoirs.

Gurevich, V. L.

2013-01-01

130

An eigenvalue method for solving transient heat conduction problems

NASA Technical Reports Server (NTRS)

The eigenvalue method, which has been used by researchers in structure mechanics, is applied to problems in heat conduction. Its formulation is decribed in terms of an examination of transient heat conduction in a square slab. Taking advantage of the availability of the exact solution, we compare the accuracy and other numerical properties of the eigenvalue method with those of existing numerical schemes. The comparsion shows that, overall, the eigenvalue method appears to be fairly attractive. Furthermore, only a few dominant eigenvalues and their corresponding eigenvectors need to be computed and retained to yield reasonably high accuracy. Greater savings are attained in the computation time for a transient problem with long time duration and a large computational domain.

Shih, T. M.; Skladany, J. T.

1983-01-01

131

Non-steady state heat conduction in composite walls

The problem of heat conduction in one-dimensional piecewise homogeneous composite materials is examined by providing an explicit solution of the one-dimensional heat equation in each domain. The location of the interfaces is known, but neither temperature nor heat flux are prescribed there. Instead, the physical assumptions of their continuity at the interfaces are the only conditions imposed. The problem of two semi-infinite domains and that of two finite-sized domains are examined in detail. We indicate also how to extend the solution method to the setting of one finite-sized domain surrounded on both sides by semi-infinite domains, and on that of three finite-sized domains.

Bernard Deconinck; Beatrice Pelloni; Natalie Sheils

2014-02-12

132

Stochastic inverse heat conduction using a spectral approach

SUMMARY An adjoint based functional optimization technique in conjunction with the spectral stochastic nite element method is proposed for the solution of an inverse heat conduction problem in the presence of uncertainties in material data, process conditions and measurement noise. The ill-posed stochastic inverse problem is restated as a conditionally well-posed L2 optimization problem. The gradient of the objective function

Velamur Asokan Badri Narayanan; Nicholas Zabaras

2004-01-01

133

A general theory of heat conduction with finite wave speeds

The classical linear theory of heat conduction for homogeneous and isotropie media is based on the equation AO=b O0 where O=O(x, t) is the absolute temperature, 0=~T-, A is the Laplacian, and > 0 is a constant. This equation, which is parabolic, has a very unpleasant feature: a thermal disturbance at any point in the body is felt instantly at

Morton E. Gurtin; A. C. Pipkin

1968-01-01

134

Generalized thermoelastic diffusive waves in heat conducting materials

NASA Astrophysics Data System (ADS)

Keeping in view the applications of diffusion processes in geophysics and electronics industry, the aim of the present paper is to give a detail account of the plane harmonic generalized thermoelastic diffusive waves in heat conducting solids. According to the characteristic equation, three longitudinal waves namely, elastodiffusive (ED), mass diffusion (MD-mode) and thermodiffusive (TD-mode), can propagate in such solids in addition to transverse waves. The transverse waves get decoupled from rest of the fields and hence remain unaffected due to temperature change and mass diffusion effects. These waves travel without attenuation and dispersion. The other generalized thermoelastic diffusive waves are significantly influenced by the interacting fields and hence suffer both attenuation and dispersion. At low frequency mass diffusion and thermal waves do not exist but at high-frequency limits these waves propagate with infinite velocity being diffusive in character. Moreover, in the low-frequency regions, the disturbance is mainly dominant by mechanical process of transportation of energy and at high-frequency regions it is significantly dominated by a close to diffusive process (heat conduction or mass diffusion). Therefore, at low-frequency limits the waves like modes are identifiable with small amplitude waves in elastic materials that do not conduct heat. The general complex characteristic equation is solved by using irreducible case of Cardano's method with the help of DeMoivre's theorem in order to obtain phase speeds, attenuation coefficients and specific loss factor of energy dissipation of various modes. The propagation of waves in case of non-heat conducting solids is also discussed. Finally, the numerical solution is carried out for copper (solvent) and zinc (solute) materials and the obtained phase velocities, attenuation coefficients and specific loss factor of various thermoelastic diffusive waves are presented graphically.

Sharma, J. N.

2007-04-01

135

Fuzzy and interval finite element method for heat conduction problem

Traditional finite element method is a well-established method to solve various problems of science and engineering. Different authors have used various methods to solve governing differential equation of heat conduction problem. In this study, heat conduction in a circular rod has been considered which is made up of two different materials viz. aluminum and copper. In earlier studies parameters in the differential equation have been taken as fixed (crisp) numbers which actually may not. Those parameters are found in general by some measurements or experiments. So the material properties are actually uncertain and may be considered to vary in an interval or as fuzzy and in that case complex interval arithmetic or fuzzy arithmetic has to be considered in the analysis. As such the problem is discretized into finite number of elements which depend on interval/fuzzy parameters. Representation of interval/fuzzy numbers may give the clear picture of uncertainty. Hence interval/fuzzy arithmetic is applied in the finite element method to solve a steady state heat conduction problem. Application of fuzzy finite element method in the said problem gives fuzzy system of linear equations in general. Here new methods have also been proposed to handle such type of fuzzy system of linear equations. Corresponding results are computed and has been reported here.

Sarangam Majumdar; Sukanta Nayak; S. Chakraverty

2012-09-26

136

NASA Technical Reports Server (NTRS)

The paper describes the numerical simulation of hyperbolic heat conduction with convection boundary conditions. The effects of a step heat loading, a sudden pulse heat loading, and an internal heat source are considered in conjunction with convection boundary conditions. Two methods of solution are presened for predicting the transient behavior of the propagating thermal disturbances. In the first method, MacCormack's predictor-corrector method is employed for integrating the hyperbolic system of equations. Next, the transfinite element method, which employs specially tailored elements, is used for accurately representing the transient response of the propagating thermal wave fronts. The agreement between the results of various numerical test cases validate the representative behavior of the thermal wave fronts. Both methods represent hyperbolic heat conduction behavior by effectively modeling the sharp discontinuities of the propagating thermal disturbances.

Glass, David E.; Tamma, Kumar K.; Railkar, Sudhir B.

1989-01-01

137

NASA Technical Reports Server (NTRS)

Analysis of the effective thermal conductivity of ceramic coatings and its relation to the microstructure continued. Results (obtained in Task 1) for the three-dimensional problem of heat conduction in a solid containing an inclusion (or, in particular, cavity - thermal insulator) of the ellipsoidal shape, were further advanced in the following two directions: (1) closed form expressions of H tensor have been derived for special cases of ellipsoidal cavity geometry: spheroid, crack-like spheroidal cavity and needle shaped spheroidal cavity; (2) these results for one cavity have been incorporated to construct heat energy potential for a solid with many spheroidal cavities (in the approximation of non-interacting defects). This problem constitutes a basic building block for further analyses.

Kachanov, Mark

1998-01-01

138

Sodium Variable Conductance Heat Pipe for Radioisotope Stirling Systems

NASA Technical Reports Server (NTRS)

In a Stirling radioisotope system, heat must continually be removed from the General Purpose Heat Source (GPHS) modules to maintain the modules and surrounding insulation at acceptable temperatures. Normally, the Stirling convertor provides this cooling. If the converter stops in the current system, the insulation is designed to spoil, preventing damage to the GPHS, and also ending the mission. An alkali-metal Variable Conductance Heat Pipe (VCHP) has been designed to allow multiple stops and restarts of the Stirling convertor in an Advanced Stirling Radioisotope Generator (ASRG). When the Stirling convertor is turned off, the VCHP will activate when the temperatures rises 30 C above the setpoint temperature. A prototype VCHP with sodium as the working fluid was fabricated and tested in both gravity aided and against gravity conditions for a nominal heater head temperature of 790 C. The results show very good agreement with the predictions and validate the model. The gas front was located at the exit of the reservoir when heater head temperature was 790 C while cooling was ON, simulating an operating Advanced Stirling Converter (ASC). When cooling stopped, the temperature increased by 30 C, allowing the gas front to move past the radiator, which transferred the heat to the case. After resuming the cooling flow, the front returned at the initial location turning OFF the VCHP. The against gravity working conditions showed a colder reservoir and faster transients.

Tarau, Calin; Anderson, William G.; Walker, Kara

2009-01-01

139

Variable Conductance Heat Pipe Radiators for Lunar and Martian Environments

NASA Astrophysics Data System (ADS)

Long-term Lunar and Martian surface systems present challenges to thermal system design, including changes in thermal load, and large changes in the thermal environment between Lunar (or Martian) day and night. For example, the heat sink temperature at the Lunar equator can vary from 210 to 315 K. The radiator must be sized to reject the design power at the maximum temperature, but must also be able to accommodate both the changing heat sink temperature, as well as changes in power. Variable Conductance Heat Pipe (VCHP) radiators were examined for the main reactor of a fission surface power system, as well as the cavity cooling radiator. A VCHP radiator was designed for Lunar Equator that is capable of maintaining a 16 K temperature drop with a 4% addition to overall mass. Without the VCHP the radiator would experience a 43 K drop in temperature. This design is also capable of handling turndown on the power without an effect to the outlet temperature. At Shackleton Crater, the temperature drop for a conventional heat pipe radiator is small enough that a VCHP is not beneficial at constant power. However, a VCHP will allow turndown ratios of 5:1 or more. A conventional radiator can not be turned down more than 2:1, without valves to bypass part of the radiator. VCHPs are also easier to start than conventional radiators, since the gas-loading prevents sublimation from the evaporator when the condenser is frozen.

Anderson, William G.; Ellis, Michael C.; Walker, Kara L.

2009-03-01

140

Fabrication and test of a variable conductance heat pipe

NASA Technical Reports Server (NTRS)

A variable conductance heat pipe (VCHP) with feedback control was fabricated with a reservoir-condenser volume ratio of 10 and an axially grooved action section. Tests of the heat transport capability were greater than or equal to the analytical predictions for the no gas case. When gas was added, the pipe performance degraded by 18% at zero tilt as was expected. The placement of the reservoir heater and the test fixture cooling fins are believed to have caused a superheated vapor condition in the reservoir. Erroneously high reservoir temperature indications resulted from this condition. The observed temperature gradients in the reservoir lend support to this theory. The net result was higher than predicted reservoir temperatures. Also, significant increases in minimum heat load resulted for controller set point temperatures higher than 0 C. At 30 C, control within the tolerance band was maintained, but high reservoir heater power was required. Analyses showed that control is not possible for reasonably low reservoir heater power. This is supported by the observation of a significant reservoir heat leak through the condenser.

Lehtinen, A. M.

1978-01-01

141

Space-time nonlocal model for heat conduction

NASA Astrophysics Data System (ADS)

We consider a space-time nonlocal heat conduction model with balance laws in the form of integral equations (so-called strong nonlocality). The model identifies two internal parameters-the time ? and the space h scales of nonlocality. In going from the strong nonlocal model to its approximations of various accuracy in the form of partial differential equations, which correspond to weak nonlocality, we introduce two limiting relations between ? and h as ?,h-->0. In the diffusion limit, which preserves the thermal diffusivity a=h2/?=const as ?,h-->0, the strong nonlocal model gives a hierarchy of parabolic equations with an infinite speed of heat waves. In the wave limit, which preserves the ratio v=h/?=const as ?,h-->0, a hierarchy of hyperbolic equations has been obtained. The hyperbolic equations imply a finite speed of heat waves. These results suggest that for diffusion (low-k) and propagative (high-k) regimes distinct models are responsible for the space-time evolution of the temperature and heat flux. The connection with phonon hydrodynamic theory and applications to other problems are discussed.

Sobolev, S. L.

1994-10-01

142

Numerical Model for Conduction-Cooled Current Lead Heat Loads

Current leads are utilized to deliver electrical power from a room temperature junction mounted on the vacuum vessel to a superconducting magnet located within the vacuum space of a cryostat. There are many types of current leads used at laboratories throughout the world; however, conduction-cooled current leads are often chosen for their simplicity and reliability. Conduction-cooled leads have the advantage of using common materials, have no superconducting/normal state transition, and have no boil-off vapor to collect. This paper presents a numerical model for conduction-cooled current lead heat loads. This model takes into account varying material and fluid thermal properties, varying thicknesses along the length of the lead, heat transfer in the circumferential and longitudinal directions, electrical power dissipation, and the effect of thermal intercepts. The model is validated by comparing the numerical model results to ideal cases where analytical equations are valid. In addition, the XFEL (X-Ray Free Electron Laser) prototype current leads are modeled and compared to the experimental results from testing at DESY's XFEL Magnet Test Stand (XMTS) and Cryomodule Test Bench (CMTB).

White, M.J.; Wang, X.L.; /Fermilab; Brueck, H.D.; /DESY

2011-06-10

143

TOPAZ. 2D Finite Element Heat Conduction Code

TOPAZ and TOPAZ2D are two-dimensional implicit finite element computer codes for heat transfer analysis. TOPAZ2D can also be used to solve electrostatic and magnetostatic problems. The programs solve for the steady-state or transient temperature or electrostatic and magnetostatic potential field on two-dimensional planar or axisymmetric geometries. Material properties may be temperature or potential-dependent and either isotropic or orthotropic. A variety of time and temperature-dependent boundary conditions can be specified including temperature, flux, convection, and radiation. By implementing the user subroutine feature, users can model chemical reaction kinetics and allow for any type of functional representation of boundary conditions and internal heat generation. The programs can solve problems of diffuse and specular band radiation in an enclosure coupled with conduction in the material surrounding the enclosure. Additional features include thermal contact resistance across an interface, bulk fluids, phase change, and energy balances.

Shapiro, A.B. [Lawrence Livermore National Lab., CA (United States)

1985-01-01

144

Pseudo-updated constrained solution algorithm for nonlinear heat conduction

NASA Technical Reports Server (NTRS)

This paper develops efficiency and stability improvements in the incremental successive substitution (ISS) procedure commonly used to generate the solution to nonlinear heat conduction problems. This is achieved by employing the pseudo-update scheme of Broyden, Fletcher, Goldfarb and Shanno in conjunction with the constrained version of the ISS. The resulting algorithm retains the formulational simplicity associated with ISS schemes while incorporating the enhanced convergence properties of slope driven procedures as well as the stability of constrained approaches. To illustrate the enhanced operating characteristics of the new scheme, the results of several benchmark comparisons are presented.

Tovichakchaikul, S.; Padovan, J.

1983-01-01

145

Hierarchical Parallelism in Finite Difference Analysis of Heat Conduction

NASA Technical Reports Server (NTRS)

Based on the concept of hierarchical parallelism, this research effort resulted in highly efficient parallel solution strategies for very large scale heat conduction problems. Overall, the method of hierarchical parallelism involves the partitioning of thermal models into several substructured levels wherein an optimal balance into various associated bandwidths is achieved. The details are described in this report. Overall, the report is organized into two parts. Part 1 describes the parallel modelling methodology and associated multilevel direct, iterative and mixed solution schemes. Part 2 establishes both the formal and computational properties of the scheme.

Padovan, Joseph; Krishna, Lala; Gute, Douglas

1997-01-01

146

NASA Technical Reports Server (NTRS)

A research and development program in variable conductance heat pipe technology is reported. The project involved: (1) theoretical and/or experimental studies in hydrostatics, (2) hydrodynamics, (3) heat transfer into and out of the pipe, (4) fluid selection, and (5) materials compatibility. The development, fabrication, and test of the space hardware resulted in a successful flight of the heat pipe experiment on the OAO-3 satellite. A summary of the program is provided and a guide to the location of publications on the project is included.

Anderson, W. T.; Edwards, D. K.; Eninger, J. E.; Marcus, B. D.

1974-01-01

147

Homogeneous Thermal Cloak with Constant Conductivity and Tunable Heat Localization

Invisible cloak has long captivated the popular conjecture and attracted intensive research in various communities of wave dynamics, e.g., optics, electromagnetics, acoustics, etc. However, their inhomogeneous and extreme parameters imposed by transformation-optic method will usually require challenging realization with metamaterials, resulting in narrow bandwidth, loss, polarization-dependence, etc. In this paper, we demonstrate that thermodynamic cloak can be achieved with homogeneous and finite conductivity only employing naturally available materials. It is demonstrated that the thermal localization inside the coating layer can be tuned and controlled robustly by anisotropy, which enables an incomplete cloak to function perfectly. Practical realization of such homogeneous thermal cloak has been suggested by using two naturally occurring conductive materials, which provides an unprecedentedly plausible way to flexibly realize thermal cloak and manipulate heat flow with phonons. PMID:23549139

Han, Tiancheng; Yuan, Tao; Li, Baowen; Qiu, Cheng-Wei

2013-01-01

148

Homogeneous Thermal Cloak with Constant Conductivity and Tunable Heat Localization

NASA Astrophysics Data System (ADS)

Invisible cloak has long captivated the popular conjecture and attracted intensive research in various communities of wave dynamics, e.g., optics, electromagnetics, acoustics, etc. However, their inhomogeneous and extreme parameters imposed by transformation-optic method will usually require challenging realization with metamaterials, resulting in narrow bandwidth, loss, polarization-dependence, etc. In this paper, we demonstrate that thermodynamic cloak can be achieved with homogeneous and finite conductivity only employing naturally available materials. It is demonstrated that the thermal localization inside the coating layer can be tuned and controlled robustly by anisotropy, which enables an incomplete cloak to function perfectly. Practical realization of such homogeneous thermal cloak has been suggested by using two naturally occurring conductive materials, which provides an unprecedentedly plausible way to flexibly realize thermal cloak and manipulate heat flow with phonons.

Han, Tiancheng; Yuan, Tao; Li, Baowen; Qiu, Cheng-Wei

2013-04-01

149

A Direct Method for Measuring Heat Conductivity in Intracluster Medium

The inverse Compton scattering of the cosmic microwave background (CMB) radiation with electrons in the intracluster medium which has a temperature gradient, was examined by the third-order perturbation theory of the Compton scattering. A new type of the spectrum distortion of the CMB was found and named as gradient T Sunyaev-Zel'dovich effect (gradT SZE). The spectrum has an universal shape. The spectrum crosses over zero at 326GHz. The sign of the spectrum depends on the relative direction of the line-of-sight to the direction of the temperature gradient. This unique spectrum shape can be used to detect the gradT SZE signal by broad-band or multi-frequency observations of the SZE. The amplitude of the spectrum distortion does not depend on the electron density and is proportional to the heat conductivity. Therefore, the gradT SZE provides an unique opportunity to measure thermally nonequilibrium electron momentum distribution function when the ICM has a temperature gradient and the heat conductivity in the ICM. However, the expected amplitude of the signal is very small. The modifications to the thermal SZE spectrum due to variety of known effects, such as relativistic correction etc., can become problematic when using multi-frequency separation techniques to detect the gradT SZE signal.

Makoto Hattori; Nobuhiro Okabe

2005-02-09

150

High Temperature Variable Conductance Heat Pipes for Radioisotope Stirling Systems

NASA Technical Reports Server (NTRS)

In a Stirling radioisotope system, heat must continually be removed from the GPHS modules, to maintain the GPHS modules and surrounding insulation at acceptable temperatures. Normally, the Stirling convertor provides this cooling. If the Stirling convertor stops in the current system, the insulation is designed to spoil, preventing damage to the GPHS, but also ending the mission. An alkali-metal Variable Conductance Heat Pipe (VCHP) is under development to allow multiple stops and restarts of the Stirling convertor. The status of the ongoing effort in developing this technology is presented in this paper. An earlier, preliminary design had a radiator outside the Advanced Stirling Radioisotope Generator (ASRG) casing, used NaK as the working fluid, and had the reservoir located on the cold side adapter flange. The revised design has an internal radiator inside the casing, with the reservoir embedded inside the insulation. A large set of advantages are offered by this new design. In addition to reducing the overall size and mass of the VCHP, simplicity, compactness and easiness in assembling the VCHP with the ASRG are significantly enhanced. Also, the permanently elevated temperatures of the entire VCHP allows the change of the working fluid from a binary compound (NaK) to single compound (Na). The latter, by its properties, allows higher performance and further mass reduction of the system. Preliminary design and analysis shows an acceptable peak temperature of the ASRG case of 140 C while the heat losses caused by the addition of the VCHP are 1.8 W.

Tarau, Calin; Walker, Kara L.; Anderson, William G.

2009-01-01

151

High Temperature Variable Conductance Heat Pipes for Radioisotope Stirling Systems

NASA Astrophysics Data System (ADS)

In a Stirling radioisotope system, heat must continually be removed from the GPHS modules, to maintain the GPHS modules and surrounding insulation at acceptable temperatures. Normally, the Stirling converter provides this cooling. If the Stirling engine stops in the current system, the insulation is designed to spoil, preventing damage to the GPHS, but also ending the mission. An alkali-metal Variable Conductance Heat Pipe (VCHP) is under development to allow multiple stops and restarts of the Stirling engine. The status of the ongoing effort in developing this technology is presented in this paper. An earlier, preliminary design had a radiator outside the Advanced Stirling Radioisotope Generator (ASRG) casing, used NaK as the working fluid, and had the reservoir located on the cold side adapter flange. The revised design has an internal radiator inside the casing, with the reservoir embedded inside the insulation. A large set of advantages are offered by this new design. In addition to reducing the overall size and mass of the VCHP, simplicity, compactness and easiness in assembling the VCHP with the ASRG are significantly enhanced. Also, the permanently elevated temperatures of the entire VCHP allows the change of the working fluid from a binary compound (NaK) to single compound (Na). The latter, by its properties, allows higher performance and further mass reduction of the system. Preliminary design and analysis shows an acceptable peak temperature of the ASRG case of 140° C while the heat losses caused by the addition of the VCHP are 1.8 W.

Tarau, Calin; Walker, Kara L.; Anderson, William G.

2009-03-01

152

Variable Conductance Heat Pipes for Radioisotope Stirling Systems

NASA Astrophysics Data System (ADS)

In a Stirling radioisotope system, heat must continually be removed from the GPHS modules, to maintain the GPHS modules and surrounding insulation at acceptable temperatures. Normally, the Stirling convertor provides this cooling. If the Stirling engine stops in the current system, the insulation is designed to spoil, preventing damage to the GPHS, but also ending the mission. An alkali-metal Variable Conductance Heat Pipe (VCHP) was designed to allow multiple stops and restarts of the Stirling engine. A VCHP was designed for the Advanced Stirling Radioisotope Generator, with a 850 °C heater head temperature. The VCHP turns on with a ?T of 30 °C, which is high enough to not risk standard ASRG operation but low enough to save most heater head life. This VCHP has a low mass, and low thermal losses for normal operation. In addition to the design, a proof-of-concept NaK VCHP was fabricated and tested. While NaK is normally not used in heat pipes, it has an advantage in that it is liquid at the reservoir operating temperature, while Na or K alone would freeze. The VCHP had two condensers, one simulating the heater head, and the other simulating the radiator. The experiments successfully demonstrated operation with the simulated heater head condenser off and on, while allowing the reservoir temperature to vary over 40 to 120 °C, the maximum range expected. In agreement with previous NaK heat pipe tests, the evaporator ?T was roughly 70 °C, due to distillation of the NaK in the evaporator.

Anderson, William G.; Tarau, Calin

2008-01-01

153

Application of the boundary element method to transient heat conduction

NASA Technical Reports Server (NTRS)

An advanced boundary element method (BEM) is presented for the transient heat conduction analysis of engineering components. The numerical implementation necessarily includes higher-order conforming elements, self-adaptive integration and a multiregion capability. Planar, three-dimensional and axisymmetric analyses are all addressed with a consistent time-domain convolution approach, which completely eliminates the need for volume discretization for most practical analyses. The resulting general purpose algorithm establishes BEM as an attractive alternative to the more familiar finite difference and finite element methods for this class of problems. Several detailed numerical examples are included to emphasize the accuracy, stability and generality of the present BEM. Furthermore, a new efficient treatment is introduced for bodies with embedded holes. This development provides a powerful analytical tool for transient solutions of components, such as casting moulds and turbine blades, which are cumbersome to model when employing the conventional domain-based methods.

Dargush, G. F.; Banerjee, P. K.

1991-01-01

154

Efficient linear and nonlinear heat conduction with a quadrilateral element

NASA Technical Reports Server (NTRS)

A method is presented for performing efficient and stable finite element calculations of heat conduction with quadrilaterals using one-point quadrature. The stability in space is obtained by using a stabilization matrix which is orthogonal to all linear fields and its magnitude is determined by a stabilization parameter. It is shown that the accuracy is almost independent of the value of the stabilization parameter over a wide range of values; in fact, the values 3, 2, and 1 for the normalized stabilization parameter lead to the 5-point, 9-point finite difference, and fully integrated finite element operators, respectively, for rectangular meshes and have identical rates of convergence in the L2 norm. Eigenvalues of the element matrices, which are needed for stability limits, are also given. Numerical applications are used to show that the method yields accurate solutions with large increases in efficiency, particularly in nonlinear problems.

Liu, W. K.; Belytschko, T.

1983-01-01

155

Efficient linear and nonlinear heat conduction with a quadrilateral element

NASA Technical Reports Server (NTRS)

A method is presented for performing efficient and stable finite element calculations of heat conduction with quadrilaterals using one-point quadrature. The stability in space is obtained by using a stabilization matrix which is orthogonal to all linear fields and its magnitude is determined by a stabilization parameter. It is shown that the accuracy is almost independent of the value of the stabilization parameter over a wide range of values; in fact, the values 3, 2 and 1 for the normalized stabilization parameter lead to the 5-point finite difference, 9-point finite difference and fully integrated finite element operators, respectively, for rectangular meshes; numerical experiments reported here show that the three have identical rates of convergence in the L2 norm. Eigenvalues of the element matrices, which are needed for stability limits, are also given. Numerical applications are used to show that the method yields accurate solutions with large increases in efficiency, particularly in nonlinear problems.

Liu, W. K.; Belytschko, T.

1984-01-01

156

A finite element method for non-Fourier heat conduction in strong thermal shock environments

Non-Fourier effect is important in heat conduction in strong thermal environments. Currently, generally-purposed commercial\\u000a finite element code for non-Fourier heat conduction is not available. In this paper, we develop a finite element code based\\u000a on a hyperbolic heat conduction equation, which includes the non-Fourier effect in heat conduction. The finite element space\\u000a discretization is used to obtain a system of

Bao-Lin Wang; Jie-Cai Han

2010-01-01

157

Fixed conductance heat pipe performance with a liquid slug

NASA Astrophysics Data System (ADS)

Fixed conductance heat pipes (FCHPs) filled with working fluid at low or moderate temperatures develop a volume of excess liquid when operated at high temperatures. The excess liquid forms as either a puddle or a slug at the coldest end of the condenser and creates a temperature differential between the evaporator and the condenser end cap. Simple algebraic expressions are presented for predicting the thermal performance of an FCHP operating with a liquid slug formed by the combined influence of liquid density temperature dependence and meniscus depression. Both differential and two-node models are developed to account for condensation modeled either as a constant flux process or based on an isothermal vapor with a constant internal film coefficient. Numerical examples are included to illustrate the behavior of two axially grooved pipes operating over a range of heat loads with both real and ideal fluids. Prediction of evaporator temperature and liquid slug length is observed to have a weak dependence on the choice of model and mode of condensation and a strong dependence on real fluid effects.

Bobco, R. P.; Drolen, B. L.

1990-06-01

158

Heat conduction in nanoscale materials: A statistical-mechanics derivation of the local heat flux

NASA Astrophysics Data System (ADS)

We derive a coarse-grained model for heat conduction in nanoscale mechanical systems. Starting with an all-atom description, this approach yields a reduced model, in the form of conservation laws of momentum and energy. The model closure is accomplished by introducing a quasilocal thermodynamic equilibrium, followed by a linear response approximation. Of particular interest is the constitutive relation for the heat flux, which is expressed nonlocally in terms of the spatial and temporal variation of the temperature. Nanowires made of copper and silicon are presented as examples.

Li, Xiantao

2014-09-01

159

Diffusive-Ballistic Heat Conduction of Carbon Nanotubes and Nanographene Ribbons Junichiro Shiomi-3-5800-6983 Abstract Investigations of diffusive-ballistic heat conduction of finite-length single-walled carbon of the balance between ballistic and diffusive heat conduction. For both systems, the profile indicates

Maruyama, Shigeo

160

Numerical heat conduction in hydrodynamical models of colliding hypersonic flows

Hydrodynamical models of colliding hypersonic flows are presented which explore the dependence of the resulting dynamics and the characteristics of the derived X-ray emission on numerical conduction and viscosity. For the purpose of our investigation we present models of colliding flow with plane-parallel and cylindrical divergence. Numerical conduction causes erroneous heating of gas across the contact discontinuity which has implications for the rate at which the gas cools. We find that the dynamics of the shocked gas and the resulting X-ray emission are strongly dependent on the contrast in the density and temperature either side of the contact discontinuity, these effects being strongest where the postshock gas of one flow behaves quasi-adiabatically while the postshock gas of the other flow is strongly radiative. Introducing additional numerical viscosity into the simulations has the effect of damping the growth of instabilities, which in some cases act to increase the volume of shocked gas and can re-he...

Parkin, E R

2010-01-01

161

Incompressible Perturbations in Uniformally Stratified Viscous Heat-Conducting Fluid

NASA Astrophysics Data System (ADS)

One-component model of dissipative medium with two-parametric equation of state allows us to formulate a simple model of a stratified viscous heat-conducting fluid. At local thermodynamic equilibrium description and the simplifying assumption of constancy of the kinetic coefficients the complete system of equations of a viscous fluid can be written in the form of the equations of conservation of mass, momentum balance, entropy balance and state equation. Consequence of the equation of state is a linear relationship between changes in density and changes in pressure and entropy. In the case of an incompressible fluid change in the density does not occur when the pressure changes. This corresponds to an infinite speed of sound. As a result, change in the density is proportional to the temperature change and thermal expansion coefficient. Accordingly, the velocity of fluid flow is not solenoidal. At the constant heat capacity the entropy balance equation reduces to the heat equation, which in turn takes the form of the evolution equation of the density. This equation completes the equation of conservation of mass and the equation of fluid motion. We assume that fluid flow occurs in the gravity field and is caused by small external forces, a small source of mass and small thermal source. Let the initial state of the fluid is rest with the vertical coordinate-dependent density distribution. For simplicity it is assumed also that the stratification is uniform, i.e. the buoyancy frequency is constant. Then the weak current caused by the sources will be described by the linearized equations with constant coefficients in Boussinesq approximation. In this approximation, square of buoyancy frequency, the density at a fixed level and the transport coefficients are the basic constant coefficients of the equations. Gravity selects the vertical direction, and therefore it is convenient to divide vector characteristics of the perturbation in the horizontal and vertical parts. In turn, the horizontal components of vectors is conveniently represented by pairs of scalar potentials using the Helmholtz decomposition. Taking into account these relations complete system of equations for small perturbations can be reduced to separate equations for the characteristics of the perturbations. As a result, small perturbations of density, pressure and vectors of velocity and vorticity can be expressed in the form of various derivatives of the five quasipotentials. Four of these quasipotentials obey the same equation of sixth order with the mass, force and heat sources, respectively, on the right side. The operator left-hand side of these equations reflects the behavior of internal waves, as well as viscous and thermal relaxation. In addition to the viscosity this operator includes the kinetic coefficient, which is directly proportional to the coefficient of thermal conductivity and is inversely proportional to the specific heat. In this case the vertical componen

Gorodtsov, V. A.

2012-04-01

162

Theory and design of variable conductance heat pipes: Steady state and transient performance

NASA Technical Reports Server (NTRS)

Heat pipe technology pertinent to the design and application of self-controlled, variable conductance heat pipes for spacecraft thermal control is discussed. Investigations were conducted to: (1) provide additional confidence in existing design tools, (2) to generate new design tools, and (3) to develop superior variable conductance heat pipe designs. A computer program for designing and predicting the performance of the heat pipe systems was developed.

Edwards, D. K.; Fleischman, G. L.; Marcus, B. D.

1972-01-01

163

It is well known that a circular liquid jet impinging on a flat plate has high heat transfer efficiency. Because such a high heat transfer efficiency can be achieved without sophisticated apparatus, the impinging jet is applied to heating and cooling of a wide range of industrial apparatus, such as the quenching of steel during the rolling process or, conversely,

Kenji Katoh; Tsuneo Azuma; Shinji Kano

1995-01-01

164

The adventitious roots of Hordeum marinum grown in stagnant deoxygenated solution contain a barrier to radial O2 loss (ROL) in basal zones, whereas roots of plants grown in aerated solution do not. The present experi- ments assessed whether induction of the barrier to ROL influences root hydraulic conductivity (Lpr). Wheat (Triti- cum aestivum) was also studied since, like H. marinum,

Alaina J. Garthwaite; Ernst Steudle; Timothy D. Colmer; Universitaet Bayreuth

2006-01-01

165

Diffusive-Ballistic Heat Conduction along a Single-Walled Carbon Nanotube Shigeo Maruyama

Diffusive-Ballistic Heat Conduction along a Single-Walled Carbon Nanotube Shigeo Maruyama *E-mail address: maruyama@photon.t.u-tokyo.ac.jp The diffusive-ballistic heat conduction of finite at room temperature. A gradual transition from nearly pure ballistic to diffusive-ballistic heat

Maruyama, Shigeo

166

HEAT CONDUCTION AND ENTROPY PRODUCTION IN ANHARMONIC CRYSTALS WITH SELF-CONSISTENT

baths with which they can exchange energy. To obtain a heat flow between external reservoirs not hold when the "noise" is turned off (the heat conductivity then becoming infinite), one expectsHEAT CONDUCTION AND ENTROPY PRODUCTION IN ANHARMONIC CRYSTALS WITH SELF-CONSISTENT STOCHASTIC

Paris-Sud XI, UniversitĂ© de

167

The transient exact solution of heat conduction in a two-domain composite cylinder is developed using the separation of variables technique. The inner cylinder is isotropic and the outer cylindrical layer is orthotropic. Temperature solutions are obtained for boundary conditions of the first and second kinds at the outer surface of the orthotropic layer. These solutions are applied to heat flow calorimeters modeling assuming that there is heat generation due to nuclear reactions in the inner cylinder. Heat flow calorimeter simulations are carried out assuming that the inner cylinder is filled with plutonium oxide powder. The first objective in these simulations is to predict the onset of thermal equilibrium of the calorimeter with its environment. Two types of boundary conditions at the outer surface of the orthotropic layer are used to predict thermal equilibrium. The procedure developed to carry out these simulations can be used as a guideline for the design of calorimeters. Another important application of these solutions is on the estimation of thermophysical properties of orthotropic cylinders. The thermal conductivities in the vertical, radial and circumferential directions of the orthotropic outer layer can be estimated using this exact solution and experimental data. Simultaneous estimation of the volumetric heat capacity and thermal conductivities is also possible. Furthermore, this solution has potential applications to the solution of the inverse heat conduction problem in this cylindrical geometry. An interesting feature of the construction of this solution is that two different sets of eigenfunctions need to be considered in the eigenfunction expansion. These eigenfunctions sets depend on the relative values of the thermal diffusivity of the inner cylinder and the thermal diffusivity in the vertical direction of the outer cylindrical layer.

C. AVILES-RAMOS; C. RUDY

2000-11-01

168

The primary objective of the work is to evaluate the performance of an air to air variable conductance heat pipe heat exchanger (VCHPHX). This type of heat exchanger is of particular interest to the commercial aircraft industry because of its unique control system. The results from this research will help to provide the engineer with experimental data necessary to design

Chancelor

1983-01-01

169

A flexible variable conductance heat pipe design for temperature control of spacecraft equipment

The paper describes a variable conductance heat pipe design with a flexible joint. The heat pipe is developed for temperature control of high power electronics using a deployable space radiator. The evaporator section of the heat pipe is attached to the baseplate of the electronics. The condenser section of the heat pipe and the reservoir of noncondensible gas are attached

Han Hwangbo; T. E. Joost

1988-01-01

170

Constructal-theory network of conducting paths for cooling a heat generating volume

This paper develops a solution to the fundamental problem of how to collect and ‘channel’ to one point the heat generated volumetrically in a low conductivity volume of given size. The amount of high conductivity material that is available for building channels (high conductivity paths) through the volume is fixed. The total heat generation rate is also fixed. The solution

Adrian Bejan

1997-01-01

171

Isotope Effects on Heat Conduction of Carbon Nanotubes Shigeo Maruyama, Yuki Taniguchi and Yasushi that the inclusion of only 1 % of 13 C natural isotope dramatically reduces the thermal conductivity of diamond. However, isotope effects on heat conduction of SWNTs have not been elucidated. We estimated isotope

Maruyama, Shigeo

172

Transient heat conduction in one-dimensional composite slab. A ‘natural’ analytic approach

The transient response of one-dimensional multilayered composite conducting slabs to sudden variations of the temperature of the surrounding fluid is analysed. The solution is obtained applying the method of separation of variables to the heat conduction partial differential equation. In separating the variables, the thermal diffusivity is retained on the side of the modified heat conduction equation where the time-dependent

F. de Monte

2000-01-01

173

In this paper, two modified types of polypropylene (PP) with high thermal conductivity up to 2.3 W/m K and 16.5 W/m K are used to manufacture the finned-tube heat exchangers, which are prospected to be used in liquid desiccant air conditioning, heat recovery, water source heat pump, sea water desalination, etc. A third plastic heat exchanger is also manufactured with ordinary PP for validation and comparison. Experiments are carried out to determine the thermal performance of the plastic heat exchangers. It is found that the plastic finned-tube heat exchanger with thermal conductivity of 16.5 W/m K can achieve overall heat transfer coefficient of 34 W/m{sup 2} K. The experimental results are compared with calculation and they agree well with each other. Finally, the effect of material thermal conductivity on heat exchanger thermal performance is studied in detail. The results show that there is a threshold value of material thermal conductivity. Below this value improving thermal conductivity can considerably improve the heat exchanger performance while over this value improving thermal conductivity contributes very little to performance enhancement. For the finned-tube heat exchanger designed in this paper, when the plastic thermal conductivity can reach over 15 W/m K, it can achieve more than 95% of the titanium heat exchanger performance and 84% of the aluminum or copper heat exchanger performance with the same dimension. (author)

Chen, Lin; Li, Zhen; Guo, Zeng-Yuan [Department of Engineering Mechanics, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084 (China)

2009-07-15

174

An Experimental Study of a Radially Arranged Thin Film Heat Flux Gauge

NASA Technical Reports Server (NTRS)

A new thin-film heat-flux gauge was designed and fabricated on three different substrate materials. Forty pairs of Pt-Pt/10% Rh thermocouple junctions were deposited in a circular pattern on the same plane of the substrate. Over the thermocouples, 5 and 10 micron thick thermal resistance layers were deposited to create a temperature gradient across those layers. Calibration and testing of these gauges were carried out in an arc-lamp calibration facility. The heat flux calculated from the gauge output is in good agreement with the value obtained from the pre-calibrated standard sensor. A CO2 laser was also used to test the steady-state and dynamic responses of the heat-flux gauge. During the steady-state test, the time constant for the heating period was 30 s. The frequency response of the heat-flux gauge was measured in the frequency domain using a CO2 laser and a chopper. The responses from an infrared detector and the heat-flux gauge were measured simultaneously and compared. It was found that the thin-film heat-flux gauge has a dynamic frequency response of 3 kHz.

Cho, Christoper S. K.; Fralick, Gustave C.; Bhatt, Hemanshu D.

1997-01-01

175

We present a new mathematical method for the analysis of heat capacity and thermal conductivity measurements by the heat pulse\\u000a technique for the case of samples of finite length with a one-dimensional heat flow. In these experiments a heat pulse is\\u000a produced by a heater, and the temperature is measured as a function of time at a different location on

M. Gershenson; S. Alterovitz

1975-01-01

176

Effect of flow maldistribution and axial conduction on compact microchannel heat exchanger

NASA Astrophysics Data System (ADS)

When a compact microchannel heat exchanger is operated at cryogenic environments, it has potential problems of axial conduction and flow maldistribution. To analyze these detrimental effects, the heat exchanger model that includes both axial conduction and flow maldistribution effect is developed in consideration of the microchannel heat exchanger geometry. A dimensionless axial conduction parameter (?) is used to describe the axial conduction effect, and the coefficient of variation (CoV) is introduced to quantify the flow maldistribution condition. The effectiveness of heat exchanger is calculated according to the various values of the axial conduction parameter and the CoV. The analysis results show that the heat exchanger effectiveness is insensitive when ? is less than 0.005, and effectiveness is degraded with the large value of CoV. Three microchannel heat exchangers are fabricated with printed circuit heat exchanger (PCHE) technology for validation purpose of the heat exchanger model. The first heat exchanger is a conventional heat exchanger, the second heat exchanger has the modified cross section to eliminate axial conduction effect, and the third heat exchanger has the modified cross section and the cross link in parallel channel to mitigate flow maldistribution effect. These heat exchangers are tested in cryogenic single-phase, and two-phase environments. The third heat exchanger shows the ideal thermal characteristic, while the other two heat exchangers experience some performance degradation due to axial conduction or flow maldistribution. The impact of axial conduction and flow maldistribution effects are verified by the simulation results and compared with the experimental results.

Baek, Seungwhan; Lee, Cheonkyu; Jeong, Sangkwon

2014-03-01

177

Nonstationary heat conduction in a single-walled carbon nanotube was investigated by applying a local heat pulse with duration of subpicoseconds. The investigation was based on classical molecular dynamics simulations, where the heat pulse was generated as coherent fluctuations by connecting a thermostat to the local cell for a short duration. The heat conduction through the nanotube was observed in terms of spatiotemporal temperature profiles. Results of the simulations exhibit non-Fourier heat conduction where a distinct amount of heat is transported in a wavelike form. The geometry of carbon nanotubes allows us to observe such a phenomenon in the actual scale of the material. The resulting spatiotemporal profile was compared with the available macroscopic equations, the so-called non-Fourier heat conduction equations, in order to investigate the applicability of the phenomenological models to a quasi-one-dimensional system. The conventional hyperbolic diffusion equation fails to predict the heat conduction due to the lack of local diffusion. It is shown that this can be remedied by adopting a model with dual relaxation time. Further modal analyses using wavelet transformations reveal a significant contribution of the optical phonon modes to the observed wavelike heat conduction. The result suggests that, in carbon nanotubes with finite length where the long-wavelength acoustic phonons behave ballistically, even optical phonons can play a major role in the non-Fourier heat conduction.

Shiomi, Junichiro; Maruyama, Shigeo [Department of Mechanical Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

2006-05-15

178

In this paper, we describe the thermal conductivity measurement of single-walled carbon nanotubes thin film using a laser point source-based steady state heat conduction method. A high precision micropipette thermal sensor fabricated with a sensing tip size varying from 2 ?m to 5 ?m and capable of measuring thermal fluctuation with resolution of ±0.01 K was used to measure the temperature gradient across the suspended carbon nanotubes (CNT) film with a thickness of 100 nm. We used a steady heat conduction model to correlate the temperature gradient to the thermal conductivity of the film. We measured the average thermal conductivity of CNT film as 74.3 ± 7.9 W m(-1) K(-1) at room temperature. PMID:23556837

Shrestha, R; Lee, K M; Chang, W S; Kim, D S; Rhee, G H; Choi, T Y

2013-03-01

179

In this paper, we describe the thermal conductivity measurement of single-walled carbon nanotubes thin film using a laser point source-based steady state heat conduction method. A high precision micropipette thermal sensor fabricated with a sensing tip size varying from 2 ?m to 5 ?m and capable of measuring thermal fluctuation with resolution of ±0.01 K was used to measure the temperature gradient across the suspended carbon nanotubes (CNT) film with a thickness of 100 nm. We used a steady heat conduction model to correlate the temperature gradient to the thermal conductivity of the film. We measured the average thermal conductivity of CNT film as 74.3 ± 7.9 W m?1 K?1 at room temperature. PMID:23556837

Shrestha, R.; Lee, K. M.; Chang, W. S.; Kim, D. S.; Rhee, G. H.; Choi, T. Y.

2013-01-01

180

of the finite thermal conductivity kT of individual nanotubes on the conductivity k of the CNT materials. The physical origin of this effect is explained in a theoretical analysis of systems composed of straight.1063/1.4737903] Experimental measurements of thermal conductivity of individual CNTs, kT, reveal exceptionally high room

Zhigilei, Leonid V.

181

NASA Astrophysics Data System (ADS)

Subcooled flow boiling is generally characterized by high heat transfer capacity and low wall superheat, which is essential for cooling applications requiring high heat transfer rate, such as nuclear reactors and fossil boilers. In this study, subcooled flow boiling on copper and stainless steel heating surfaces was experimentally investigated from both macroscopic and microscopic points of view. Flow boiling heat flux and heat transfer coefficient were experimentally measured on both surfaces under different conditions, such as pressure, flow rate and inlet subcooling. Significant boiling heat transfer coefficient differences were found between the copper and the stainless steel heating surfaces. To explain the different flow boiling behaviors on these two heating surfaces, nucleation site density and bubble dynamics were visually observed and measured at different experimental conditions utilizing a high-speed digital video camera. These two parameters are believed to be keys in determining flow boiling heat flux. Wall superheat, critical cavity size and wall heat flux were used to correlate with nucleation site density data. Among them, wall heat flux shows the best correlation for eliminating both pressure and surface property effects. The observed nucleation site distribution shows a random distribution. When compared to the spatial Poisson distribution, similarity between them was found, while the measured nucleation site distribution is more uniform. From experimental observations, for the two surface materials investigated, which have similar surface wettability but sharply different thermal properties, bubble dynamics displayed fairly similar behavior. The obtained experimental results indicate that thermal conductivity of heating surface material plays an important role in boiling heat transfer. This is due to thermal conductivity having a significant impact on the lateral heat conduction at the heating surface and consequently temperature uniformity of the heating surface. A model was then developed and solved numerically for heat conduction at the heating surface when bubbles are present. Several key parameters which impact lateral heat conduction and surface temperature profile were studied. These parameters include material thermal conductivity, bubble size, heating surface thickness, etc. Numerical results show that, temperature profile on the heating surface tends to be more uniform and have a lower average value on a heating surface with higher thermal conductivity, which agrees well with the experimental observation.

Zou, Ling

182

EFFECT OF A CENTERED CONDUCTING BODY ON NATURAL CONVECTION HEAT TRANSFER IN AN ENCLOSURE

The effect of a centered, square, heat-conducting body on natural convection in a vertical square enclosure was examined numerically. The analysis reveals that the fluid flow and heat transfer processes are governed by the Rayleigh and Prandtl numbers, the dimensionless body size, and the ratio of the thermal conductivity of the body to that of the fluid. For Pr =

John M. House; Christoph Beckermann; Theodore F. Smith

1990-01-01

183

Nonballistic heat conduction in an integrable random-exchange Ising chain studied with quantum numerically investigate the heat conduction in a random-exchange Ising spin chain by using the quantum master equation. The chain is subject to a uniform transverse field h, while the exchange couplings Qn between

Li, Baowen

184

Solving an inverse heat conduction problem using a non-integer identified model

An inverse heat conduction problem in a system is solved using a non-integer identified model as the direct model for the estimation procedure. This method is efficient when some governing parameters of the heat transfer equations, such as thermal conductivity or thermal resistance, are not known precisely. Reliability of the inversion depends on the precision of the identified model. From

J.-L. Battaglia; O. Cois; L. Puigsegur; A. Oustaloup

2001-01-01

185

Numerical Modeling of Combined Radiation and Conduction Heat Transfer in Mineral Wool Insulations

This article addresses numerical modeling of coupled heat conduction and radiation in mineral wools under steady-state condition for prediction of its effective thermal conductivity. The radiative heat transfer is modeled using the Monte Carlo Ray-Trace Method. The radiation model is based on a random distribution of fibers in the media. The radiation distribution factor is employed in order to compute

Sohrab Veiseh; Ali Hakkaki-Fard

2009-01-01

186

An AC conductance technique for measuring self-heating in SOI MOSFET's

In this paper, we present a new technique for isolating the electrical behavior of an SOI MOSFET's from the self-heating effect using an AC conductance method. This method reconstructs an I-V curve by integrating high frequency output conductance data. The heating effect is eliminated when the frequency is much higher than the inverse of the thermal time constant of the

Robert H. Tu; Clement Wann; Joseph C. King; Ping K. KO; Chenming Hu

1995-01-01

187

An Input Estimation Approach to On-Line Two-Dimensional Inverse Heat Conduction Problems

An on-line methodology to solve two-dimensional inverse heat conduction problems (IHCP) is presented. A new input estimation approach based on the Kalman filtering technique is developed to estimate the two separate unknown heat flux inputs on the two boundaries in real time. A recursive relation between the observed value of the residual sequence with unknown heat flux and the theoretical

Pan-Chio Tuan; Ching-China Ji; Li-Wei Fong; Wen-Tang Huang

1996-01-01

188

Thermal conductivity and diffusivity of biomaterials measured with self-heated thermistors

This paper presents an experimental method to measure the thermal conductivity and thermal diffusivity of biomaterials. Self-heated thermistor probes, inserted into the tissue of interest, are used to deliver heat as well as to monitor the rate of heat removal. An empirical calibration procedure allows accurate thermal-property measurements over a wide range of tissue temperatures. Operation of the instrument in

J. W. Valvano; J. R. Cochran; K. R. Diller

1985-01-01

189

Dissipative Particle Dynamics with Energy Conservation: Heat Conduction

We study by means of numerical simulations the model of dissipative particle dynamics with energy conservation for the simple case of thermal conduction. It is shown that the model displays correct equilibrium fluctuations and reproduces Fourier law. The connection between \\

Marisol Ripoll; Pep Espańol; Matthieu H. Ernst

1999-01-01

190

Variable Conductance Heat Pipe Cooling of Stirling Convertor and General Purpose Heat Source

NASA Technical Reports Server (NTRS)

In a Stirling Radioisotope Power System (RPS), heat must be continuously removed from the General Purpose Heat Source (GPHS) modules to maintain the modules and surrounding insulation at acceptable temperatures. The Stirling convertor normally provides this cooling. If the Stirling convertor stops in the current system, the insulation is designed to spoil, preventing damage to the GPHS at the cost of an early termination of the mission. An alkali-metal Variable Conductance Heat Pipe (VCHP) can be used to passively allow multiple stops and restarts of the Stirling convertor. In a previous NASA SBIR Program, Advanced Cooling Technologies, Inc. (ACT) developed a series of sodium VCHPs as backup cooling systems for Stirling RPS. The operation of these VCHPs was demonstrated using Stirling heater head simulators and GPHS simulators. In the most recent effort, a sodium VCHP with a stainless steel envelope was designed, fabricated and tested at NASA Glenn Research Center (GRC) with a Stirling convertor for two concepts; one for the Advanced Stirling Radioisotope Generator (ASRG) back up cooling system and one for the Long-lived Venus Lander thermal management system. The VCHP is designed to activate and remove heat from the stopped convertor at a 19 degC temperature increase from the nominal vapor temperature. The 19 degC temperature increase from nominal is low enough to avoid risking standard ASRG operation and spoiling of the Multi-Layer Insulation (MLI). In addition, the same backup cooling system can be applied to the Stirling convertor used for the refrigeration system of the Long-lived Venus Lander. The VCHP will allow the refrigeration system to: 1) rest during transit at a lower temperature than nominal; 2) pre-cool the modules to an even lower temperature before the entry in Venus atmosphere; 3) work at nominal temperature on Venus surface; 4) briefly stop multiple times on the Venus surface to allow scientific measurements. This paper presents the experimental results from integrating the VCHP with an operating Stirling convertor and describes the methodology used to achieve their successful combined operation.

Tarau, Calin; Schwendeman, Carl; Anderson William G.; Cornell, Peggy A.; Schifer, Nicholas A.

2013-01-01

191

Glasslike Heat Conduction in High-Mobility Crystalline Semiconductors

The thermal conductivity of polycrystalline semiconductors with type-I\\u000aclathrate hydrate crystal structure is reported. Ge clathrates (doped with Sr\\u000aand\\/or Eu) exhibit lattice thermal conductivities typical of amorphous\\u000amaterials. Remarkably, this behavior occurs in spite of the well-defined\\u000acrystalline structure and relatively high electron mobility ($\\\\sim 100\\u000acm^2\\/Vs$). The dynamics of dopant ions and their interaction with the\\u000apolyhedral cages

J. L. Cohn; G. S. Nolas; V. Fessatidis; T. H. Metcalf; G. A. Slack

1999-01-01

192

Non-linear vibrations of heated non-homogeneous circular plates with radially varying rigidity

The field equation of the vertical motion of heated non-homogeneous elastic circular plates with varying rigidity are derived by Berger approach. Assuming the non-homogeneous Young` s modulus, for a circular clamped plate due to a temperature distribution as seen in aerodynamic heating and prevented from inplane motions on the boundary, the governing time equation is derived by means of a Galerkin procedure applied to the field equation of the vertical motion. It is solved for free vibration and also for forced vibration by Ritz`s method. The influence of non-homogeneous Young`s modulus and temperature change on the period of free and forced vibration are shown in the graphs.

Ohnabe, H. [Ishikawajima-Harima Heavy Industries, Tanashi (Japan); Mizuguchi, F. [Japan Maritime Safety Academy, Kure (Japan)

1994-12-31

193

Heat conduction in a symmetric body subjected to a current flow of symmetric input and output

Steady heat conduction in symmetrical electro-thermal problems is analyzed under the influence of a steady direct current passing through symmetrical regions of the boundary. In the present approach, solution is obtained by dividing the temperature field of the electro-thermal problem into two fields—one is related to the heat conduction problem without Joule heating and the other corresponds to a symmetric

M. Saka; Y. X. Sun; S. Reaz Ahmed

2009-01-01

194

Hyperbolic Heat Conduction in a Cracked Thermoelastic Half-Plane Bonded to a Coating

NASA Astrophysics Data System (ADS)

In this paper, the transient temperature field around a thermally insulated crack in a substrate bonded to a coating is obtained using the hyperbolic heat conduction model. Fourier and Laplace transforms are applied, and the thermal conduction problem is reduced to solving a singular integral equation. Numerical results show that the hyperbolic heat conduction parameters, the heat conductivity of the substrate and coating, and the geometric size of the composite have significant influence on the transient temperature field. In the case of very small time scales, the results predicted by the hyperbolic model are more conservative than that by the parabolic model.

Chen, Z. T.; Hu, K. Q.

2012-05-01

195

NASA Technical Reports Server (NTRS)

In the present investigation of crystalline phase internal radiation and heat conduction during the vertical Bridgman growth of a YAG-like oxide crystal, where transport through the melt is dominated by convection and conduction, heat is also noted to be conducted through ampoule walls via natural convection and enclosure radiation. The results of a quasi-steady-state axisymmetric Galerkin FEM indicate that heat transfer through the system is powerfully affected by the optical absorption coefficient of the crystal. The coupling of internal radiation through the crystal with conduction through the ampoule walls promotes melt/crystal interface shapes that are highly reflected near the ampoule wall.

Brandon, S.; Derby, J. J.

1992-01-01

196

Heat conduction in cooling flows. [in clusters of galaxies

NASA Technical Reports Server (NTRS)

It has been suggested that electron conduction may significantly reduce the accretion rate (and star foramtion rate) for cooling flows in clusters of galaxies. A numerical hydrodynamics code was used to investigate the time behavior of cooling flows with conduction. The usual conduction coefficient is modified by an efficiency factor, mu, to realize the effects of tangled magnetic field lines. Two classes of models are considered, one where mu is independent of position and time, and one where inflow stretches the field lines and changes mu. In both cases, there is only a narrow range of initial conditions for mu in which the cluster accretion rate is reduced while a significant temperature gradient occurs. In the first case, no steady solution exists in which both conditions are met. In the second case, steady state solutions occur in which both conditions are met, but only for a narrow range of initial values where mu = 0.001.

Bregman, Joel N.; David, L. P.

1988-01-01

197

The radial velocity curves of optical components in X-ray binary systems can differ from the radial velocity curves of their barycenters due to tidal distortion, gravitational darkening, X-ray heating, etc. This motivated us to investigate how the semiamplitudes of the radial velocity curves of these optical components can depend on the binary-system parameters in a Roche model. The K-correction is taken to be the ratio of the radial velocity semiamplitude for a star in the Roche model to the corresponding value for the stellar barycenter. K-corrections are tabulated for the optical stars in the massive X-ray binaries Cen X-3, LMC X-4, SMC X-1, Vela X-1, and 4U 1538-52.

Petrov, V S; Cherepashchuk, A M

2013-01-01

198

Guaranteed Verification of Finite Element Solutions of Heat Conduction

, and 4 respectively. . . . . . . . . . . . . . . . . . 67 4.2 Heat transition problem in one dimension. The effectivity indices ? based on the exact solution u? and ?Sp+k?h? = ESp+k?h? /||eh||C based on the finite element solution u?Sp+k?h? (k = 1... dimensional synthetic problem. The effectivity indices ? based on the exact solution u? and ?Sp+k?h? = ESp+k?h? /||eh||C based on the finite element solution u?Sp+k?h? (k = 1, 2, 3, and ?h? from the nest subdivision of the original mesh ?h) of elliptic...

Wang, Delin

2012-07-16

199

NASA Technical Reports Server (NTRS)

The phenomenon of hyperbolic heat conduction in contrast to the classical (parabolic) form of Fourier heat conduction involves thermal energy transport that propagates only at finite speeds, as opposed to an infinite speed of thermal energy transport. To accommodate the finite speed of thermal wave propagation, a more precise form of heat flux law is involved, thereby modifying the heat flux originally postulated in the classical theory of heat conduction. As a consequence, for hyperbolic heat conduction problems, the thermal energy propagates with very sharp discontinuities at the wave front. Accurate solutions are found for a class of one-dimensional hyperbolic heat conduction problems involving non-Fourier effects that can be used effectively for representative benchmark tests and for validating alternate schemes. Modeling/analysis formulations via specially tailored hybrid computations are provided for accurately modeling the sharp discontinuities of the propagating thermal wave front. Comparative numerical test models are presented for various hyperbolic heat conduction models involving non-Fourier effects to demonstrate the present formulations.

Tamma, Kumar K.; Railkar, Sudhir B.

1989-01-01

200

Effect of sand addition on the specific heat and thermal conductivity of cement

Sand addition was found to decrease the specific heat and increase the thermal conductivity of cement, in contrast to the opposite effects of silica fume addition. The thermal conductivity increase due to sand addition was much greater when silica fume was present. The thermal conductivity decrease due to silica fume addition was much smaller when sand was present.

Xu, Y.; Chung, D.D.L.

2000-01-01

201

Heat conductivity in the beta-FPU lattice. Solitons and breathers as energy carriers

This paper consists of two parts. The first part proposes a new methodological framework within which the heat conductivity in 1D lattices can be studied. The total process of heat conductivity is decomposed into two contributions where the first one is the equilibrium process at equal temperatures T of both lattice ends and the second -- non-equilibrium process with the temperature \\Delta T of one end and zero temperature of the other. The heat conductivity in the limit \\Delta T \\to 0 is reduced to the heat conductivity of harmonic lattice. A threshold temperature T_{thr} scales T_{thr}(N) \\sim N^{-3} with the lattice size N. Some unusual properties of heat conductivity can be exhibited on nanoscales at low temperatures. The thermodynamics of the \\beta-FPU lattice can be adequately approximated by the harmonic lattice. The second part testifies in the favor of the soliton and breather contribution to the heat conductivity in contrast to [N. Li, B. Li, S. Flach, PRL 105 (2010) 054102]. In the continuum limit the \\beta-FPU lattice is reduced to the modified Korteweg - de Vries equation with soliton and breather solutions. Numerical simulations demonstrate their high stability. New method for the visualization of moving solitons and breathers is suggested. An accurate expression for the dependence of the sound velocity on temperature is also obtained. Our results support the conjecture on the solitons and breathers contribution to the heat conductivity.

T. Yu. Astakhova; V. N. Likhachev; G. A. Vinogradov

2011-03-18

202

Phonon Transport in Graphene: Umklapp Quenching and Heat Conduction

NASA Astrophysics Data System (ADS)

Since its exfoliation, graphene attracted tremendous attention of the research community. Graphene, which consists of a single atomic plane of carbon atoms, revealed many unique properties including extremely high electron mobility. In this talk I will show that unusual properties of graphene are not limited to electrons alone. Phonons also behave differently in two-dimensional (2D) system such as graphene. We have recently discovered experimentally that thermal conductivity of suspended graphene layers is extremely high and exceeds that of diamond or graphite [2-3]. We explained our results theoretically by considering the Umklapp and edge scattering of phonons in graphene [3]. Unlike in bulk graphite, the phonon transport in graphene is pure 2D for all phonon energies. As a result, the thermal conductivity of graphene can become extremely high. The extraordinary high thermal conductivity of graphene can be used for thermal management of nanoscale electronic devices. This work was supported by SRC-DARPA Functional Engineered Nano Architectonics (FENA) center and Interconnect Focus Center (IFC). [1] A.A. Balandin, et al. Nano Letters, 8, 902 (2008); S. Ghosh, et al., Appl. Phys. Lett., 92, 151911 (2008). [2] D.L. Nika, et al., Phys. Rev. B, 79, 155413 (2009); D.L. Nika et al., Appl. Phys. Lett., 94, 203103 (2009)

Balandin, Alexander

2009-11-01

203

Tables for solution of the heat-conduction equation with a time-dependent heating rate

Tables are presented for the solution of the transient onedimensional heat flow in a solid body of constant material properties with the heating rate at one boundary dependent on time. These tables allow convenient and ...

Bergles A. E.

1962-01-01

204

Plate Fin Heat Exchanger Model with Axial Conduction and Variable Properties

Future superconducting radio frequency (SRF) cavities, as part of Project X at Fermilab, will be cooled to superfluid helium temperatures by a cryogenic distribution system supplying cold supercritical helium. To reduce vapor fraction during the final Joule-Thomson (J-T) expansion into the superfluid helium cooling bath, counter-flow, plate-fin heat exchangers will be utilized. Due to their compact size and ease of fabrication, plate-fin heat exchangers are an effective option. However, the design of compact and high-effectiveness cryogenic heat exchangers operating at liquid helium temperatures requires consideration of axial heat conduction along the direction of flow, in addition to variable fluid properties. Here we present a numerical model that includes the effects of axial conduction and variable properties for a plate fin heat exchanger. The model is used to guide design decisions on heat exchanger material choice and geometry. In addition, the J-T expansion process is modeled with the heat exchanger ...

Hansen, B J; Klebaner, A; 10.1063/1.4706971

2012-01-01

205

A Multiscale Model for Coupled Heat Conduction and Deformations of Viscoelastic Composites

formulation is implemented within the ABAQUS, general purpose displacement based FE software, allowing for analyzing coupled heat conduction and deformations of composite structures. Experimental data on the effective thermal properties and time dependent...

Khan, Kamran Ahmed

2012-07-16

206

Some Analogies from Classical Analysis in the Theory of Heat Conduction.

National Technical Information Service (NTIS)

The theory of heat conduction exhibits many analogies with the theory of functions of a complex variable (or alternatively with potential theory). The analogies are emphasized to illuminate the structure of the former theory and to indicate directions for...

D. V. Widder

1965-01-01

207

Molecular dynamics analysis of spectral characteristics of phonon heat conduction in silicon

Due to the technological significance of silicon, its heat conduction mechanisms have been studied extensively. However, there have been some lingering questions surrounding the phonon mean free path and importance of ...

Henry, Asegun Sekou Famake

2006-01-01

208

NASA Technical Reports Server (NTRS)

The theory of sound propagation is examined in a viscous, heat-conducting fluid, initially at rest and in a uniform state, and contained in a rigid, impermeable duct with isothermal walls. Topics covered include: (1) theoretical formulation of the small amplitude fluctuating motions of a viscous, heat-conducting and compressible fluid; (2) sound propagation in a two dimensional duct; and (3) perturbation study of the inplane modes.

Huerre, P.; Karamcheti, K.

1976-01-01

209

NASA Technical Reports Server (NTRS)

A numerical procedure is presented for analyzing a wide variety of heat conduction problems in multilayered bodies having complex geometry. The method is based on a finite difference solution of the heat conduction equation using a body fitted coordinate system transformation. Solution techniques are described for steady and transient problems with and without internal energy generation. Results are found to compare favorably with several well known solutions.

Masiulaniec, K. C.; Keith, T. G., Jr.; Dewitt, K. J.

1984-01-01

210

The importance of electron heat conduction in the energy balance of the F-region

NASA Technical Reports Server (NTRS)

Taking into account heat conduction in the analysis of electron temperature data acquired by the AE-C satellite during the daytime at middle latitudes is shown to bring theoretical electron temperature profiles in good agreement with experimental ones. Middle latitude passes were chosen because in this region the horizontal electron temperature gradient is negligible and the height variation can be approximated by the satellite data. Inclusion of heat conduction is shown to have little effect on low-latitude data.

Hoegy, W. R.; Brace, L. H.

1978-01-01

211

Effect of heat treatment on the thermal conductivity of plasma-sprayed thermal barrier coatings

The effect of heat treatment on the thermal conductivity of plasma-sprayed Y2O3 stabilized ZrO2 (YSZ) and Al2O3 coatings was investigated. A heat treatment of 1300 °C in flowing argon for 50 h was found to significantly increase the\\u000a thermal conductivity of the coatings when compared to measurements in the assprayed condition. Transmission electron microscopy\\u000a (TEM) examination of the microstructures of

Rollie Dutton; Robert Wheeler; K. S. Ravichandran; K. An

2000-01-01

212

Numerical approach based on the spectral collocation method has been utilized for analyzing heat convection and conduction\\u000a in eccentric annuli. An eccentric instead of concentric annular duct is sometimes used as a fluid-flow and heat-transfer device\\u000a especially in nuclear power plants. The hydrodynamically and thermally fully developed laminar flow with uniform heat flux\\u000a through the inner and outer walls has

Woo Gun Sim; Jong Min Kim

1996-01-01

213

The theory and the equations governing the temperature distribution, resistance, and heat flow in a tungsten filament as affected by its leads are given for the low temperature range (<600°K), both for the general case and for several special cases. A low temperature vs. current scale for tungsten is calculated from these equations using measurements of heat conductivity given in

Irving Langmuir; John Bradshaw Taylor

1936-01-01

214

Effect of sidewall conductance on heat-transport measurements for turbulent Rayleigh, California 93106 Received 31 July 2000; published 27 December 2000 For measurements of turbulent heat or based on measurements or estimates for the empty cell. It is argued that the lateral thermal coupling

Fygenson, Deborah Kuchnir

215

Finite element formulation for two-dimensional inverse heat conduction analysis

This paper presents a finite element algorithm for two-dimensional nonlinear inverse heat conduction analysis. The proposed method is capable of handling both unknown surface heat flux and unknown surface temperature of solids using temperature histories measured at a few discrete points. The proposed algorithms were used in the study of the thermofracture behavior of leaking pipelines with experimental verifications.

T. R. Hsu; N. S. Sun; G. G. Chen; Z. L. Gong

1992-01-01

216

Hyperbolic heat conduction equation for materials with a nonhomogeneous inner structure

The physical meaning of the constant Ď in Cattaneo and Vernotte's equation for materials with a nonhomogeneous inner structure has been considered. An experimental determination of the constant Ď has been proposed and some values for selected products have been given. The range of differences in the description of heat transfer by parabolic and hyperbolic heat conduction equations has been

W. Kaminski

1990-01-01

217

An analysis is carried out to study the flow and heat transfer characteristics in an electrically conducting fluid near an isothermal sheet. The sheet is linearly stretched in the presence of a uniform free stream of constant velocity and temperature. The effects of free convection and internal heat generation or absorption are also considered. The resulting coupled nonlinear differential equations

K. Vajravelu; A. Hadjinicolaou

1997-01-01

218

NASA Astrophysics Data System (ADS)

In this paper, we undertake the thermodynamical analysis of the diffusive transport to wave propagation transition in heat conducting thin films. Several constitutive equations have been conceived to describe heat transport but most fail at the nanometric length scales, where size effects must be taken into account or at time scales in the order of magnitude of heat carriers relaxation time, as for example when a laser pulse is applied to the system. The analysis is based on Jeffrey's model since it allows a jointed description of Fourier and Cattaneo heat conduction mechanisms. Jeffrey's model is complemented with a size dependent heat conductivity derived from Boltzmann transport equation. We study the diffusive transport to wave propagation transition in terms of the group and phase velocity of propagating modes, the system's effective thermodynamic susceptibility, the statistical properties of heat flux fluctuations, and the entropy produced in a thin heat conducting film. Jeffrey's model predicts a kind of discontinuity in the entropy production for thickness film of the order of magnitude of heat carrier mean free path which is corroborated by simulations results from the literature.

Vázquez, F.; del Río, J. A.

2012-12-01

219

A new mathematical model for numerical simulation of two dimensional food freezing due to natural convection is presented. Fluid mechanics and heat transfer by natural convection between air and a solid food in a freezer are predicted along with the heat conduction inside a plate shaped food. The mathematical model used includes continuity, linear momentum and energy partial differential equations

Nelson O. Moraga; Hernán G. Barraza

2003-01-01

220

Problems in the mathematical modeling of heat-distribution processes on the basis of more general equations than parabolic equations are considered. We study the general structure of the relations between solutions of various approximations to the generalized heat-conductivity equations. We introduce a notion of singularly perturbed dissipative structures and analyze singularly, perturbed blow-up regimes.

Makarenko, A.S. [Kiev State Univ. (Russian Federation)

1994-06-01

221

Homogenization of a Conductive, Convective and Radiative Heat Transfer Problem in a Heterogeneous in the homogenization of heat transfer in periodic porous media where the fluid part is made of long thin parallel. To obtain the homogenized problem we first use a formal two-scale asymptotic expansion method. The resulting

Paris-Sud XI, UniversitĂ© de

222

In the present study a three-dimensional (3-D) transient inverse heat conduction problem is solved using the conjugate gradient method (CGM) and the general purpose commercial code CFX4.2-based inverse algorithm to estimate the unknown boundary heat flux in any 3-D irregular domain.The advantage of calling CFX4.2 as a subroutine in the present inverse calculation lies in that many difficult but practical

Cheng-Hung Huang; Shao-Pei Wang

1999-01-01

223

Effects of anisotropic conduction and heat pipe interaction on minimum mass space radiators

NASA Technical Reports Server (NTRS)

Equations are formulated for the two dimensional, anisotropic conduction of heat in space radiator fins. The transverse temperature field was obtained by the integral method, and the axial field by numerical integration. A shape factor, defined for the axial boundary condition, simplifies the analysis and renders the results applicable to general heat pipe/conduction fin interface designs. The thermal results are summarized in terms of the fin efficiency, a radiation/axial conductance number, and a transverse conductance surface Biot number. These relations, together with those for mass distribution between fins and heat pipes, were used in predicting the minimum radiator mass for fixed thermal properties and fin efficiency. This mass is found to decrease monotonically with increasing fin conductivity. Sensitivities of the minimum mass designs to the problem parameters are determined.

Baker, Karl W.; Lund, Kurt O.

1991-01-01

224

NASA Astrophysics Data System (ADS)

Melting anomalies in the Earth's upper mantle have often been attributed to the presence of mantle plumes that may originate in the lower mantle, possibly from the core-mantle boundary. Globally, mantle plumes exhibit a large range in buoyancy flux that which is proportional to their temperature and volume. Plumes with higher buoyancy fluxes should have higher temperatures and experience higher degrees of partial melting. Excess heat in mantle plumes could reflect either a) an enrichment of the heat producing elements (HPE: U, Th, K) in their mantle source leading to an increase of heat production by radioactive decay or b) advective or conductive heat transport across the core-mantle boundary. The advective transport of heat may result in a physical contribution of material from the core to the lower mantle. If core material is incorporated into the lower mantle, mantle plumes with a higher buoyancy flux should have higher core tracers, e.g. increased 186Os and Fe concentrations. Geophysical and dynamic modelling indicate that at least Afar, Easter, Hawaii, Louisville and Samoa may all originate at the core-mantle boundary. These plumes encompass the whole range of known buoyancy fluxes from 1.2 Mgs -1(Afar) to 6.5 Mgs -1 (Hawaii) providing evidence that the buoyancy flux is largely independent of other geophysical parameters. In an effort to explore whether the heat producing elements are the cause of excess heat we looked for correlations between fractionation corrected concentrations of the HPE and buoyancy flux. Our results suggest that there is no correlation between HPE concentrations and buoyancy flux (with and without an additional correction for variable degrees of partial melting). As anticipated, K, Th and U are positively correlated with each other (e.g. Hawaii, Iceland and Galapagos have significantly lower concentrations than e.g. Tristan da Cunha, the Canary Islands and the Azores). We also find no correlation between currently available Fe concentration data and buoyancy flux. The apparent lack of correlation suggests that excess heat may be a result of conductive heat contribution from the core. Additional precise 186Os and Fe data are needed to further assess these conclusions.

Rushmer, T.; Beier, C.; Turner, S.

2007-12-01

225

Numerical simulation of a latent heat thermal energy storage system with enhanced heat conduction

A latent heat storage system has been designed to take advantage of the off-peak electrical energy for space heating. Using an enthalpy formation and a fully implicit finite difference method, the thermal performance of such a storage system with and without fins has been analysed. For the one-dimensional simulation model, calculations have been made for the melt fraction and energy

M. Costa; D. Buddhi; A. Oliva

1998-01-01

226

Microwave absorption in powders of small conducting particles for heating applications.

In microwave chemistry there is a common misconception that small, highly conducting particles heat profusely when placed in a large microwave electric field. However, this is not the case; with the simple physical explanation that the electric field (which drives the heating) within a highly conducting particle is highly screened. Instead, it is the magnetic absorption associated with induction that accounts for the large experimental heating rates observed for small metal particles. We present simple principles for the effective heating of particles in microwave fields from calculations of electric and magnetic dipole absorptions for a range of practical values of particle size and conductivity. For highly conducting particles, magnetic absorption dominates electric absorption over a wide range of particle radii, with an optimum absorption set by the ratio of mean particle radius a to the skin depth ? (specifically, by the condition a = 2.41?). This means that for particles of any conductivity, optimized magnetic absorption (and hence microwave heating by magnetic induction) can be achieved by simple selection of the mean particle size. For weakly conducting samples, electric dipole absorption dominates, and is maximized when the conductivity is approximately ? ? 3??(0) ? 0.4 S m(-1), independent of particle radius. Therefore, although electric dipole heating can be as effective as magnetic dipole heating for a powder sample of the same volume, it is harder to obtain optimized conditions at a fixed frequency of microwave field. The absorption of sub-micron particles is ineffective in both magnetic and electric fields. However, if the particles are magnetic, with a lossy part to their complex permeability, then magnetic dipole losses are dramatically enhanced compared to their values for non-magnetic particles. An interesting application of this is the use of very small magnetic particles for the selective microwave heating of biological samples. PMID:23321957

Porch, Adrian; Slocombe, Daniel; Edwards, Peter P

2013-02-28

227

Joule-heating induced conductance-switching is studied in VO2 , a Mott insulator. Complementary in situ techniques including optical characterization, blackbody microscopy, scanning transmission X-ray microscopy (STXM) and numerical simulations are used. Abrupt redistribution in local temperature is shown to occur upon conductance-switching along with a structural phase transition, at the same current. PMID:23868142

Kumar, Suhas; Pickett, Matthew D; Strachan, John Paul; Gibson, Gary; Nishi, Yoshio; Williams, R Stanley

2013-11-13

228

Combined radiation and conduction heat transfer in high temperature fiber thermal insulation

Three different approaches for describing combined radiation and conduction heat transfer in fiber thermal insulation at high temperatures are analyzed and compared. The considered approaches include the radiation transfer equation or its approximations, approximation of radiation thermal conductivity and the radiation diffusion approximation for radiation transfer. The first causes difficulties due to the need for experimental measurement of optical properties,

Vadim A. Petrov

1997-01-01

229

Molecular Dynamics Simulations of Heat Conduction of Peapods Shigeo Maruyama, Yuki Taniguchi conductivity of Peapods was slightly higher than empty (10,10) tubes. [1]S. Maruyama and S.-H. Choi, Therm. Sci. Eng., 9-3, (2001), 17-24. [2]S. Maruyama, Physica B, (2002), in print. [3]S. Maruyama, Micro

Maruyama, Shigeo

230

ERIC Educational Resources Information Center

This study proposes a multi-dimensional approach to investigate, represent, and categorize students' in-depth understanding of complex physics concepts. Clinical interviews were conducted with 30 undergraduate physics students to probe their understanding of heat conduction. Based on the data analysis, six aspects of the participants' responses…

Chiou, Guo-Li; Anderson, O. Roger

2010-01-01

231

A generalized boundary integral equation (BIE) is formulated for heat conduction problems in anisotropic media with spatially varying thermal conductivities arising from material heterogeneity. The generalized integral equation is expressed in terms of contour integrals only. This is accomplished with the aid of a generalized fundamental solution E and with the definition of a singular nonsymmetric generalized forcing function, D.

Eduardo Divo; Alain Kassab

1997-01-01

232

NASA Astrophysics Data System (ADS)

Shocks are often simulated using the classical molecular dynamics (MD) method in which the electrons are not included explicitly and the interatomic interaction is described by an effective potential. As a result, the fast electronic heat conduction in metals and the coupling between the lattice vibrations and the electronic degrees of freedom can not be represented. Under conditions of steep temperature gradients that can form near the shock front, however, the electronic heat conduction can play an important part in redistribution of the thermal energy in the shocked target. We present the first atomistic simulation of a shock propagation including the electronic heat conduction and electron-phonon coupling. The computational model is based on the two-temperature model (TTM) that describes the time evolution of the lattice and electron temperatures by two coupled non-linear differential equations. In the combined TTM-MD method, MD substitutes the TTM equation for the lattice temperature. Simulations are performed with both MD and TTM-MD models for an EAM Al target shocked at 300 kbar. The target includes a tilt grain boundary, which provides a region where shock heating is more pronounced and, therefore, the effect of the electronic heat conduction is expected to be more important. We find that the differences between the predictions of the MD and TTM-MD simulations are significantly smaller as compared to the hydrodynamics calculations performed at similar conditions with and without electronic heat conduction.

Ivanov, Dmitriy S.; Zhigilei, Leonid V.; Bringa, Eduardo M.; De Koning, Maurice; Remington, Bruce A.; Caturla, Maria Jose; Pollaine, Stephen M.

2004-07-01

233

Fourier Heat Conduction as a phenomenon described within the scope of the Second Law

The historical development of the Carnot cycle necessitated the construction of isothermal and adiabatic pathways within the cycle that were also mechanically "reversible" which lead eventually to the Kelvin-Clausius development of the entropy function where the heat absorption is for the diathermal (isothermal) paths of the cycle only. It is deduced from traditional arguments that Fourier heat conduction involves mechanically "reversible" heat transfer with irreversible entropy increase. Here we model heat conduction as a thermodynamically reversible but mechanically irreversible process. The MD simulations conducted shows excellent agreement with the theory. Such views and results as these, if developed to a successful conclusion could imply that the Carnot cycle be viewed as describing a local process of energy-work conversion and that irreversible local processes might be brought within the scope of this cycle, implying a unified treatment of thermodynamically (i) irreversible, (ii) reversible, (iii) isot...

Jesudason, Christopher G

2014-01-01

234

Fourier Heat Conduction as a phenomenon described within the scope of the Second Law

The historical development of the Carnot cycle necessitated the construction of isothermal and adiabatic pathways within the cycle that were also mechanically "reversible" which lead eventually to the Kelvin-Clausius development of the entropy function where the heat absorption is for the diathermal (isothermal) paths of the cycle only. It is deduced from traditional arguments that Fourier heat conduction involves mechanically "reversible" heat transfer with irreversible entropy increase. Here we model heat conduction as a thermodynamically reversible but mechanically irreversible process. The MD simulations conducted shows excellent agreement with the theory. Such views and results as these, if developed to a successful conclusion could imply that the Carnot cycle be viewed as describing a local process of energy-work conversion and that irreversible local processes might be brought within the scope of this cycle, implying a unified treatment of thermodynamically (i) irreversible, (ii) reversible, (iii) isothermal and (iv) adiabatic processes.

Christopher G. Jesudason

2014-07-29

235

Variable thermal properties and thermal relaxation time in hyperbolic heat conduction

NASA Technical Reports Server (NTRS)

Numerical solutions were obtained for a finite slab with an applied surface heat flux at one boundary using both the hyperbolic (MacCormack's method) and parabolic (Crank-Nicolson method) heat conduction equations. The effects on the temperature distributions of varying density, specific heat, and thermal relaxation time were calculated. Each of these properties had an effect on the thermal front velocity (in the hyperbolic solution) as well as the temperatures in the medium. In the hyperbolic solutions, as the density or specific heat decreased with temperature, both the temperatures within the medium and the thermal front velocity increased. The value taken for the thermal relaxation time was found to determine the 'hyperbolicity' of the heat conduction model. The use of a time dependent relaxation time allowed for solutions where the thermal energy propagated as a high temperature wave initially, but approached a diffusion process more rapidly than was possible with a constant large relaxation time.

Glass, David E.; Mcrae, D. Scott

1989-01-01

236

Heat conductivity of liquid ternary mixtures of various compositions at various pressures and temperatures was experimentally studied. Dependence of heat conductivities of ternary mixtures on concentration of components was established. An equation linking the heat conductivities of ternary mixtures through those of pure components and appropriate binary mixtures was proposed.

Naziev, D.Ya. [Azerbaidzhan State Oil Academy, Baku (Russian Federation)

1994-03-20

237

Analysis of a Bayonet-Type Counterflow Heat Exchanger with Axial Conduction and Radiative Heat Loss

A counterflow heat exchanger model, based on a bayonet-type configuration, has been developed for predicting the performance of small-scale thermal systems. The purpose of the model is to predict how well a counterflow heat exchanger works for isolating high temperatures for devices that might act as miniature combustors, fuel reformers, or micro-reactors. Three thermal loss mechanisms are considered: (1) flow

Richard B. Peterson; John A. Vanderhoff

2001-01-01

238

NASA Astrophysics Data System (ADS)

This study aims to investigate the role of aggregation of the hybrid nanocomposite particles on thermal conductivity and heat transfer of the phase change colloidal suspensions. It is observed that the incorporation of the hybrid nanocomposite particles substantially enhances thermal conductivity of such suspensions up to 42.4% and effectively reduces their freezing time by 19.5%. The predictions and the experimental results supports the fact that the aggregation of the hybrid nanocomposite particles largely involve in the eventual thermal conductivity enhancements and heat transfer of the phase change colloidal suspensions, with a sufficiently lesser effects realized from the nanoparticles Brownian motion.

Parameshwaran, R.; Kalaiselvam, S.

2013-11-01

239

On Energy and Entropy Influxes in the Green-Naghdi Type III Theory of Heat Conduction

The energy-influx/entropy-influx relation in the Green-Naghdi Type III theory of heat conduction is examined within a thermodynamical framework \\`a la Mueller-Liu, where that relation is not specified a priori irrespectively of the constitutive class under attention. It is shown that the classical assumption, i.e., that the entropy influx and the energy influx are proportional via the absolute temperature, holds true if heat conduction is, in a sense that is made precise, isotropic. In addition, it is proven that the standard assumption does not hold in case of transversely isotropic conduction.

Swantje Bargmann; Antonino Favata; Paolo Podio-Guidugli

2012-09-13

240

Plate Fin Heat Exchanger Model with Axial Conduction and Variable Properties

Future superconducting radio frequency (SRF) cavities, as part of Project X at Fermilab, will be cooled to superfluid helium temperatures by a cryogenic distribution system supplying cold supercritical helium. To reduce vapor fraction during the final Joule-Thomson (J-T) expansion into the superfluid helium cooling bath, counter-flow, plate-fin heat exchangers will be utilized. Due to their compact size and ease of fabrication, plate-fin heat exchangers are an effective option. However, the design of compact and high-effectiveness cryogenic heat exchangers operating at liquid helium temperatures requires consideration of axial heat conduction along the direction of flow, in addition to variable fluid properties. Here we present a numerical model that includes the effects of axial conduction and variable properties for a plate fin heat exchanger. The model is used to guide design decisions on heat exchanger material choice and geometry. In addition, the J-T expansion process is modeled with the heat exchanger to analyze the effect of heat load and cryogenic supply parameters. A numerical model that includes the effects of axial conduction and variable properties for a plate fin heat exchanger was developed and the effect of various design parameters on overall heat exchanger size was investigated. It was found that highly conductive metals should be avoided in the design of compact JT heat exchangers. For the geometry considered, the optimal conductivity is around 3.5 W/m-K and can range from 0.3-10 W/m-K without a large loss in performance. The model was implemented with an isenthalpic expansion process. Increasing the cold side inlet temperature from 2K to 2.2 K decreased the liquid fraction from 0.856 to 0.839 which corresponds to a 0.12 g/s increase in supercritical helium supply needed to maintain liquid level in the cooling bath. Lastly, it was found that the effectiveness increased when the heat load was below the design value. Therefore, the heat exchanger should be sized on the high end of the required heat load.

Hansen, B.J.; White, M.J.; Klebaner, A.; /Fermilab

2011-06-10

241

The upper crustal-scale convection of fluids is one of the main factors distorting the conductive geothermal field. Geothermal anomalies caused by water circulation, as a rule, exceed the contributions from other factors (relief, sedimentation, structural and climatic effects). The measured temperature gradient has to be corrected before being used for calculation of the heat flow. In the present work, certain

Bertalan Bodri

1995-01-01

242

Conductivity heating a subterranean oil shale to create permeability and subsequently produce oil

This patent describes an improvement in a process in which oil is produced from a subterranean oil shale deposit by extending at least one each of heat-injecting and fluid-producing wells into the deposit, establishing a heat-conductive fluid-impermeable barrier between the interior of each heat-injecting well and the adjacent deposit, and then heating the interior of each heat-injecting well at a temperature sufficient to conductively heat oil shale kerogen and cause pyrolysis products to form fractures within the oil shale deposit through which the pyrolysis products are displaced into at least one production well. The improvement is for enhancing the uniformity of the heat fronts moving through the oil shale deposit. Also described is a process for exploiting a target oil shale interval, by progressively expanding a heated treatment zone band from about a geometric center of the target oil shale interval outward, such that the formation or extension of vertical fractures from the heated treatment zone band to the periphery of the target oil shale interval is minimized.

Van Meurs, P.; DeRouffignac, E.P.; Vinegar, H.J.; Lucid, M.F.

1989-12-12

243

NASA Technical Reports Server (NTRS)

A numerical analysis is presented for the overall performance of heat pipes with single or multiple heat sources. The analysis includes the heat conduction in the wall and liquid-wick regions as well as the compressibility effect of the vapor inside the heat pipe. The two-dimensional elliptic governing equations in conjunction with the thermodynamic equilibrium relation and appropriate boundary conditions are solved numerically. The solutions are in agreement with existing experimental data for the vapor and wall temperatures at both low and high operating temperatures.

Chen, Ming-Ming; Faghri, Amir

1990-01-01

244

NASA Astrophysics Data System (ADS)

A simple heat treatment was used to fabricate carbonaceous layer-coated electrodes: micro-ring electrodes and conductive stainless steel. Substrates of sharpened quartz capillaries or type-316 stainless steel plates were put in an alumina boat with powder of petroleum pitch A240F separately and heated at 1073-1273 K in a flow of nitrogen or argon. By this treatment, both of the substrates were coated with a uniform carbonaceous layer of several hundred nano-meters in thickness. The electric conductivity of the layer was improved by increases in temperature and period of the heating. The quartz glass-capillary covered with the conductive layer was modified to a needle-type microelectrode by coating with an insulating polymer and baring the tip. At least a dozen carbon micro-ring electrodes with an outer radius of about 1 ?m were successfully prepared by the simple heat treatment. On the other hand, the carbonaceous layer formed on type-316 stainless steel showed relatively poor conductivity due to the formation of oxides in the layer. However, the conductivity was improved by electroplating of nickel on the substrate before the heating. The carbonaceous layer-coated stainless steel showed good corrosion resistance in sulphuric acid.

Fushimi, K.; Ono, A.; Matsushita, K.; Kumagai, H.; Konno, H.

2011-07-01

245

For bulk thermoelectrics, figure-of-merit, ZT, still needs to improve from the current value of 1.0 - 1.5 to above 2 to be competitive to other alternative technologies. In recent years, the most significant improvements in ZT were mainly due to successful reduction of thermal conductivity. However, thermal conductivity cannot be measured directly at high temperatures. The combined measurements of thermal diffusivity and specific heat and density are required. It has been shown that thermal conductivity is the property with the greatest uncertainty and has a direct influence on the accuracy of the figure of merit. The International Energy Agency (IEA) group under the implementing agreement for Advanced Materials for Transportation (AMT) has conducted two international round-robins since 2009. This paper is Part II of the international round-robin testing of transport properties of bulk bismuth telluride. The main focuses in Part II are on thermal diffusivity, specific heat and thermal conductivity.

Wang, Hsin [ORNL; Porter, Wallace D [ORNL; Bottner, Harold [Fraunhofer-Institute, Freiburg, Germany; Konig, Jan [Fraunhofer-Institute, Freiburg, Germany; Chen, Lidong [Chinese Academy of Sciences; Bai, Shengqiang [Chinese Academy of Sciences; Tritt, Terry M. [Clemson University; Mayolett, Alex [Corning, Inc; Senawiratne, Jayantha [Corning, Inc; Smith, Charlene [Corning, Inc; Harris, Fred [ZT-Plus; Gilbert, Partricia [Marlow Industries, Inc; Sharp, J [Marlow Industries, Inc; Lo, Jason [CANMET - Materials Technology Laboratory, Natural Resources of Canada; Keinke, Holger [University of Waterloo, Canada; Kiss, Laszlo I. [University of Quebec at Chicoutimi

2013-01-01

246

Radiative heat exchange of a meteor body in the approximation of radiant heat conduction

The problem of the thermal and dynamic destruction of large meteor bodies moving in planetary atmospheres is fundamental for the clarification of optical observations and anomalous phenomena in the atmosphere, the determination of the physicochemical properties of meteoroids, and the explanation of the fall of remnants of large meteorites. Therefore, it is important to calculate the coefficient of radiant heat exchange (which is the determining factor under these conditions) for large meteor bodies as they move with hypersonic velocities in an atmosphere. The solution of this problem enables one to find the ablation of a meteorite during its aerodynamic heating and to determine the initial conditions for the solution of problems of the breakup of large bodies and their subsequent motion and ablation. Hypersonic flow of an inviscid gas stream over an axisymmetric blunt body is analyzed with allowance for radiative transfer in a thick-thin approximation. The gas-dynamic problem of the flow of an optically thick gas over a large body is solved by the method of asymptotic joined expansions, using a hypersonic approximation and local self-similarity. An equation is obtained for the coefficient of radiant heat exchange and the peculiarities of such heat exchange for meteor bodies of large size are noted.

Pilyugin, N.N.; Chernova, T.A.

1986-07-01

247

NASA Astrophysics Data System (ADS)

Controlling heat flow by phononic nanodevices has received significant attention recently because of its fundamental and practical implications. Elementary phononic devices such as thermal rectifiers, transistors, and logic gates are essentially based on two intriguing properties: heat diode effect and negative differential thermal conductance. However, little is known about these heat transfer properties across metal-dielectric interfaces, especially at nanoscale. Here we analytically resolve the microscopic mechanism of the nonequilibrium nanoscale energy transfer across metal-dielectric interfaces, where the inelastic electron-phonon scattering directly assists the energy exchange. We demonstrate the emergence of heat diode effect and negative differential thermal conductance in nanoscale interfaces and explain why these novel thermal properties are usually absent in bulk metal-dielectric interfaces. These results will generate exciting prospects for the nanoscale interfacial energy transfer, which should have important implications in designing hybrid circuits for efficient thermal control and open up potential applications in thermal energy harvesting with low-dimensional nanodevices.

Ren, Jie; Zhu, Jian-Xin

2013-06-01

248

NASA Technical Reports Server (NTRS)

This paper describes the evaluation of mixed implicit-explicit finite element formulations for hyperbolic heat conduction problems involving non-Fourier effects. In particular, mixed implicit-explicit formulations employing the alpha method proposed by Hughes et al. (1987, 1990) are described for the numerical simulation of hyperbolic heat conduction models, which involves time-dependent relaxation effects. Existing analytical approaches for modeling/analysis of such models involve complex mathematical formulations for obtaining closed-form solutions, while in certain numerical formulations the difficulties include severe oscillatory solution behavior (which often disguises the true response) in the vicinity of the thermal disturbances, which propagate with finite velocities. In view of these factors, the alpha method is evaluated to assess the control of the amount of numerical dissipation for predicting the transient propagating thermal disturbances. Numerical test models are presented, and pertinent conclusions are drawn for the mixed-time integration simulation of hyperbolic heat conduction models involving non-Fourier effects.

Tamma, Kumar K.; D'Costa, Joseph F.

1991-01-01

249

The effects of 50-hour heat treatments at 1000°C, 1200°C, and 1400°C on air plasma-sprayed coatings of 7 wt% Y2O3-ZrO2 (YSZ) have been investigated. Changes in the phase stability and microstructure were investigated using x-ray diffraction and transmission electron microscopy, respectively. Changes in the thermal conductivity of the coating that occurred during heat treatment were interpreted with respect to microstructural evolution.

R. W. Trice; Y. Jennifer Su; J. R. Mawdsley; K. T. Faber; A. R. De Arellano-López; Hsin Wang; W. D. Porter

2002-01-01

250

Numerical techniques used in thermal-hydraulic computer analysis codes must be fast to enable modeling of complex transients and accurate to provide a high degree of fidelity. In an attempt to satisfy these conflicting requirements, the best-estimate code TRAC-PF1 uses a semi-implicit technique to couple heat transfer between a flow field and a conduction slab. To test the accuracy of the current semi-implicit method used in TRAC-PF1, a series of simple tube experiments were modeled with TRAC-PF1 version 3.9B. To overcome identified problems, fully implicit techniques were developed and incorporated into TRAC-PF1. The new methods treat the heat transfer coefficient and wall temperature in the energy source term of both the convection and the conduction equation implicitly. One method uses a linear extrapolation and the other a nonlinear iterative technique. In general, both methods produced higher wall temperature and a lattice quench in better agreement with the experimental data. These methods also eliminated the double-valued results obtained for the other experiments. In general, these techniques have given more accurate results and saved computer time in the film boiling heat transfer regime.

Wang, L.C.; Baratta, A.J.; Mahaffy, J.H. (Pennsylvania State Univ. University Park (USA))

1990-01-01

251

NASA Astrophysics Data System (ADS)

In semi-solid die-casting, a metallic billet is first heated in an induction furnace until it reaches a semi-solid state (partially liquid and partially solid). Then, it is injected into a die and kept there until it is solidified. Subsequently, the die opens, the part is ejected and the cycle starts again. The liquid-solid fraction and its spatial distribution within the billet at the end of the heating phase are of prime importance for the success of the process and the quality of the final product. These parameters are strongly correlated with temperature gradients within the billet and their evolution in time through the heating cycle. There is presently no inspection method that could reasonably be used to control the billet temperature in a production environment. In this work, we investigate the suitability of using infrared thermography to meet the heating requirements. With this technique, it is possible to non-intrusively monitor the temperature distribution on the entire surface of the billet and to obtain information on how thermal energy is dissipated. Moreover, with the combination of surface infrared measurements and inverse heat conduction formalism, it is also possible to recover some information about the temperature distribution inside the billet. Effects of some process operating conditions such as heating power magnitude, power input cycles, location of the billet inside the induction coil, and the coil overhang are considered and discussed.

Bendada, A.; Zheng, C. Q.; Nardini, N.

2004-04-01

252

Electrical conductivity of carbonaceous chondrites and electric heating of meteorite parent bodies

NASA Technical Reports Server (NTRS)

Electromagnetic heating of rock-forming materials most probably was an important process in the early history of the solar system. Electrical conductivity experiments of representative materials such as carbonaceous chondrites are necessary to obtain data for use in electromagnetic heating models. With the assumption that carbon was present at grain boundaries in the material that comprised the meteorite parent bodies, the electrical heating of such bodies was calculated as a function of body size and solar distance using the T-Tauri model of Sonett and Herbert (1977). The results are discussed.

Duba, AL

1987-01-01

253

Heat conductivity in small quantum systems: Kubo formula in Liouville space

We consider chains consisting of several identical subsystems weakly coupled by various types of next neighbor interactions. At both ends the chain is coupled to a respective heat bath with different temperature modeled by a Lindblad formalism. The temperature gradient introduced by this environment is then treated as an external perturbation. We propose a method to evaluate the heat current and the local temperature profile of the resulting stationary state as well as the heat conductivity in such systems. This method is similar to Kubo techniques used e.g. for electrical transport but extended here to the Liouville space.

Mathias Michel; Jochen Gemmer; Guenter Mahler

2005-03-22

254

NASA Technical Reports Server (NTRS)

Continuing efforts in large gains in heat-pipe performance are reported. It was found that gas-controlled variable-conductance heat pipes can perform reliably for long periods in space and effectively provide temperature stabilization for spacecraft electronics. A solution was formulated that allows the control gas to vent through arterial heat-pipe walls, thus eliminating the problem of arterial failure under load, due to trace impurities of noncondensable gas trapped in an arterial bubble during priming. This solution functions well in zero gravity. Another solution was found that allows priming at a much lower fluid charge. A heat pipe with high capacity, with close temperature control of the heat source and independent of large variations in sink temperature was fabricated.

Enginer, J. E.; Luedke, E. E.; Wanous, D. J.

1976-01-01

255

Estimating thermal diffusivity and specific heat from needle probe thermal conductivity data

Thermal diffusivity and specific heat can be estimated from thermal conductivity measurements made using a standard needle probe and a suitably high data acquisition rate. Thermal properties are calculated from the measured temperature change in a sample subjected to heating by a needle probe. Accurate thermal conductivity measurements are obtained from a linear fit to many tens or hundreds of temperature change data points. In contrast, thermal diffusivity calculations require a nonlinear fit to the measured temperature change occurring in the first few tenths of a second of the measurement, resulting in a lower accuracy than that obtained for thermal conductivity. Specific heat is calculated from the ratio of thermal conductivity to diffusivity, and thus can have an uncertainty no better than that of the diffusivity estimate. Our thermal conductivity measurements of ice Ih and of tetrahydrofuran (THF) hydrate, made using a 1.6 mm outer diameter needle probe and a data acquisition rate of 18.2 pointss, agree with published results. Our thermal diffusivity and specific heat results reproduce published results within 25% for ice Ih and 3% for THF hydrate. ?? 2006 American Institute of Physics.

Waite, W. F.; Gilbert, L. Y.; Winters, W. J.; Mason, D. H.

2006-01-01

256

Laser high heat flux test approaches have been established to obtain critical properties of ceramic thermal barrier coatings\\u000a (TBCs) under near-realistic temperature and thermal gradients that may be encountered in advanced engine systems. Thermal\\u000a conductivity change kinetics of a thin ceramic coating were continuously monitored in real time at various test temperatures.\\u000a A significant thermal conductivity increase was observed during

Dongming Zhu; Robert A. Miller

2000-01-01

257

Preparation of flexible and heat-resisting conductive transparent film by the pyrosol process

A pyrosol process was successfully applied for the preparation of a flexible, conductive, and transparent inorganic film, a tin-doped indium oxide (ITO) film lined with a thin mica layer. This flexible heat-resistant ITO-mica film exhibited high conductivity and transparency, comparable to ITO deposited on glass substrate. The minimum radius of bending for the film, without any recognizable change in the

Hisanao Usami; Akihiko Nakasa; Mami Adachi; Eiji Suzuki; Hitoshi Fujimatsu; Tatsuya Ohashi; Shigeo Yamada; Kouhei Tsugita; Yoshio Taniguchi

2006-01-01

258

While window frames typically represent 20-30% of the overall window area, their impact on the total window heat transfer rates may be much larger. This effect is even greater in low-conductance (highly insulating) windows that incorporate very low-conductance glazing. Developing low-conductance window frames requires accurate simulation tools for product research and development. Based on a literature review and an evaluation of current methods of modeling heat transfer through window frames, we conclude that current procedures specified in ISO standards are not sufficiently adequate for accurately evaluating heat transfer through the low-conductance frames. We conclude that the near-term priorities for improving the modeling of heat transfer through low-conductance frames are: (1) Add 2D view-factor radiation to standard modeling and examine the current practice of averaging surface emissivity based on area weighting and the process of making an equivalent rectangular frame cavity. (2) Asses 3D radiation effects in frame cavities and develop recommendation for inclusion into the design fenestration tools. (3) Assess existing correlations for convection in vertical cavities using CFD. (4) Study 2D and 3D natural convection heat transfer in frame cavities for cavities that are proven to be deficient from item 3 above. Recommend improved correlations or full CFD modeling into ISO standards and design fenestration tools, if appropriate. (5) Study 3D hardware short-circuits and propose methods to ensure that these effects are incorporated into ratings. (6) Study the heat transfer effects of ventilated frame cavities and propose updated correlations.

Gustavsen, Arild; Arasteh, Dariush; Jelle, Bjorn Petter; Curcija, Charlie; Kohler, Christian

2008-09-11

259

NASA Astrophysics Data System (ADS)

Due to fine grain-size and high Fe contents, radiative transfer in the outer layers of the Earth is low compared to heat transport via lattice vibrations. We constrain the latter from laser flash measurements of diverse minerals, basalts, rocks, glasses and melts. High porosity reduces thermal diffusivity (D) from that of the matrix, and also thermal conductivity (k = D X density X heat capacity). Melting significantly reduces D and k. Our method was benchmarked against NIST standards and shows that conventional measurements of minerals, which involve physical contact with thermocouples, contain substantial and opposing errors due to interface losses and spurious radiative transfer. Field determinations may be similarly affected. To independently ascertain heat flux we utilize the fact that heat emitted from the mantle is carried conductively across the oceanic lithosphere, except possibly where magma forms. The conductive gradient is obtained from a surface temperature of 298 K and basalt solidus (1300 K) at the base of plates that average 100 km thick. From our data on D, average lithosphere carries 57 mW/m2 by conduction, which equals the average flux measured from oceanic floor away from ridges. Near the ridges, plates are much thinner (~10 km) with a smaller temperature difference (600 K) and lower D (0.5 mm2/s) due to melting, providing a conductive flux at the ridges of 100 mW/m2, which is similar to field data. These results indicate global power is 30 TW. Latent heat released during crystallization MORBs of ca 1 TW is within uncertainty of any estimates. MORs are edge effects of weak mantle convection cells and correlated with stress fractures on the lithosphere arising from self-compression of a triaxial Earth. Copious upwelling of heat are not needed for magma production due to near solidus temperatures of the lowest lithosphere, and runaway melting promoted by low D of melts.

Hofmeister, A. M.; Whittington, A. G.; Galenas, M.; Branlund, J. M.; Criss, R. E.

2008-05-01

260

Temperature Profiles in Hamiltonian Heat Conduction Jean-Pierre Eckmann1,2 and Lai-Sang Young3

says that heat flux is proportional to temperature gradient times heat conductivity. Ever since Fourier that by Fourier's law, the temperature profile is lin- ear. This seems to be the predominant thinking behind muchTemperature Profiles in Hamiltonian Heat Conduction Jean-Pierre Eckmann1,2 and Lai-Sang Young3 1D

Young, Lai-Sang

261

. This law describes phenomenologically that the heat current is proportional to the temperature gradient) harmonic oscillator model shows [2] that there is no well-defined temperature gradient, the thermal. The detailed ato- mistic theories of heat conduction appeared only much later. For heat conduction in gas

Li, Baowen

262

A peridynamic formulation for transient heat conduction in bodies with evolving discontinuities

NASA Astrophysics Data System (ADS)

We introduce a multidimensional peridynamic formulation for transient heat-transfer. The model does not contain spatial derivatives and uses instead an integral over a region around a material point. By construction, the formulation converges to the classical heat transfer equations in the limit of the horizon (the nonlocal region around a point) going to zero. The new model, however, is suitable for modeling, for example, heat flow in bodies with evolving discontinuities such as growing insulated cracks. We introduce the peridynamic heat flux which exists even at sharp corners or when the isotherms are not smooth surfaces. The peridynamic heat flux coincides with the classical one in simple cases and, in general, it converges to it in the limit of the peridynamic horizon going to zero. We solve test problems and compare results with analytical solutions of the classical model or with other numerical solutions. Convergence to the classical solutions is seen in the limit of the horizon going to zero. We then solve the problem of transient heat flow in a plate in which insulated cracks grow and intersect thus changing the heat flow patterns. We also model heat transfer in a fiber-reinforced composite and observe transient but steep thermal gradients at the interfaces between the highly conductive fibers and the low conductivity matrix. Such thermal gradients can lead to delamination cracks in composites from thermal fatigue. The formulation may be used to, for example, evaluate effective thermal conductivities in bodies with an evolving distribution of insulating or permeable, possibly intersecting, cracks of arbitrary shapes.

Bobaru, Florin; Duangpanya, Monchai

2012-04-01

263

Transport of heat in caloric vestibular stimulation. Conduction, convection or radiation?

Experiments in temporal bone specimens were carried out under strictly controlled conditions: temperature (37 degrees C) and humidity kept constant; standardized irrigation of the external ear canal by an automated system (in 15 s, 50 ml of water, 11 degrees C above temperature of specimen), thermistor probes of 0.2 mm diameter placed in different parts of the specimens. In the intact temporal bone such an irrigation causes a rise in temperature with a gradient from the external ear canal across the bony bridge to the lateral semicircular canal as expected with heat conduction. After removal of the bony bridge, which is the main route for heat conduction, the rise in temperature in the lateral semicircular canal is greater and faster than in the intact specimen. This effect again is drastically reduced by placing a reflecting shield between tympanic membrane and labyrinth. In the intact middle ear inserting a reflecting shield or filling the cavity with gel also reduces the heat transfer to the labyrinth, although the bony routes for heat conduction are left untouched. The experiments prove that radiation plays an important part in heat transfer in caloric stimulation. PMID:2068898

Feldmann, H; Hüttenbrink, K B; Delank, K W

1991-01-01

264

Enhancement and reduction of one-dimensional heat conduction with correlated mass disorder

NASA Astrophysics Data System (ADS)

Short-range order in strongly disordered structures plays an important role in their heat conduction property. Using numerical and analytical methods, we show that short-range spatial correlation (with a correlation length of ?m) in the mass distribution of the one-dimensional (1D) alloylike random binary lattice leads to a dramatic enhancement of the high-frequency phonon transmittance but also increases the low-frequency phonon opacity. High-frequency semiextended states are formed while low-frequency modes become more localized. This results in ballistic heat conduction at finite lengths but also paradoxically higher thermal resistance that scales as ?{?m} in the L ?? limit. We identify an emergent crossover length (Lc) below which the onset of thermal transparency appears. The crossover length is linearly dependent on but is two orders of magnitude larger than ?m. Our results suggest that the phonon transmittance spectrum and heat conduction in a disordered 1D lattice can be controlled via statistical clustering of the constituent component atoms into domains. They also imply that the detection of ballistic heat conduction in disordered 1D structures may be a signature of the intrinsic mass correlation at a much smaller length scale.

Ong, Zhun-Yong; Zhang, Gang

2014-10-01

265

The form of Abstract Molecular dynamics simulations of diffusive-ballistic heat conduction

The form of Abstract Molecular dynamics simulations of diffusive-ballistic heat conduction carbon bonds and quasi-one-dimensional confinement of phonons. As a consequence, the ballistic phonon, phonon transport exhibits complex diffusive-ballistic feature, which gives rise to unique steady

Maruyama, Shigeo

266

SUMMARY The identification and quantification of conductive and convective components in the heat transfer of a sedimentary basin is demonstrated for the Rheingraben. Three different methods of varying complexity as well as three independent data sets are employed: (1) energy budget considerations based on hydraulically perturbed thermal data from shallow boreholes (<500m), (2) 1-D vertical Peclet number analysis of thermal

C. Clauser; H. Villinger

1990-01-01

267

size. For example, a 1 cm copper sphere centered in a cube with a solid material of TC as water, or 10 mixtures if exposed to "over-all unidirectional" boundary conditions. This approach has been used to model conductivity, unidirectional heat transfer, heterogeneous mixtures, nanofluids, cubic model, Maxwell model 1

Kostic, Milivoje M.

268

Using the finite element method for solving heat conductivity problems for cooled gas-turbine blades

A finite element procedure for solving stationary and nonstationary heat conductivity problems for bodies of arbitrary shape has been developed and implemented in computer software. The usefulness of the procedure is demonstrated by using it to calculate the stationary temperature field of a gas-turbine blade with longitudinal cooling ducts. The results are then compared with results obtained by integral and

A. S. Sakharov; A. L. Kozak; S. M. Chornyi; B. D. Bileka; S. M. Chepaskina

1985-01-01

269

INSTABILITIES ASSOCIATED WITH HEAT CONDUCTION IN THE SOLAR WIND AND THEIR CONSEQUENCES

Associated with the large heat conduction in the solar wind is a skewing of the ion and electron distribution functions. It is shown that this collisional skewing of the electron distribution function can linearly excite collisionless ion-acoustic, electrostatic ion cyclotron, magnetoacoustic, and ion cyclotron waves in the steady-state solar wind even though the net equilibrium current parallel to B is

D. W. Forslund

1970-01-01

270

LOCAL THEORY IN CRITICAL SPACES FOR COMPRESSIBLE VISCOUS AND HEAT-CONDUCTIVE GASES

We are concerned with local existence and uniqueness of solutions for a general model of viscous and heat-conductive gases with low regularity assumptions on the initial data (the velocity and the temperature may be discontinuous). Local well-posedness is showed to hold in spaces which are critical with respect to the scaling of the equations, provided that the initial density is

Raphaël Danchin

2001-01-01

271

A boundary element approach is used to solve inverse heat conduction problems in multidimensional and nonlinear situations. In stationary and transient cases, discretized boundary integral equations are expressed and, to obtain satisfying results, are associated with regularization procedures over space and time (transient case). The efficiency of the method, which depends on the accuracy of the measurements, is explored through

R. Pasquetti; C. Le Niliot

1991-01-01

272

The Spontaneous Magnetic Field Generation and Suppression of Heat Conduction in Clusters of Galaxies

We show that magnetic fields are spontaneously generated in the plasmas which have the temperature inhomogeneity and the heat conduction is spontaneously suppressed. This is based on the microscopic plasma instability that the anisotropic velocity distribution induced by the temperature gradient derives the low frequency growing transverse magnetic waves. We have shown that the physical mechanism for this growth is

Nobuhiro Okabe; Makoto Hattori

2004-01-01

273

Collisional Joule dissipation in the ionosphere of Venus: The importance of electron heat conduction

The ionosphere of an unmagnetized planet, such as Venus, is characterized by rel- atively high Pedersen conductivity in comparison to the terrestrial ionosphere because of the weak magnetic field. Collisional Joule dissipation of plasma waves might therefore be an important source of heat within the Venus ionosphere. However, any assessment of the importance of colli- sional Joule dissipation must take

R. J. Strangeway

1996-01-01

274

Review and Comparison of Nanofluid Thermal Conductivity and Heat Transfer Enhancements

This study provides a detailed literature review and an assessment of results of the research and development work forming the current status of nanofluid technology for heat transfer applications. Nanofluid technology is a relatively new field, and as such, the supporting studies are not extensive. Specifically, experimental results were reviewed in this study regarding the enhancement of the thermal conductivity

Wenhua Yu; David M. France; Jules L. Routbort

2008-01-01

275

Piston problem with allowance for finite rate of exothermic reactions and nonlinear heat conduction

One-dimensional nonstationary flows of a combustible mixture of gases are considered with allowance for nonlinear heat conduction. The possible existence of similarity solutions is studied, and conditions are found under which such solutions do exist. The results are given of a numerical calculation of the similarity problems of a piston and self-sustaining thermal wave.

A. S. Leibenzon

1979-01-01

276

Fuzzy finite element analysis of heat conduction problems with uncertain parameters

In this article we have used four different global optimisation algorithms for interval finite element analysis of (non)linear heat conduction problems: (i) sequential quadratic programming (SQP), (ii) a scatter search method (SSm), (iii) the vertex algorithm, and (iv) the response surface method (RSM). Their performance was compared based on a thermal sterilisation problem and a food freezing problem. The vertex

Bart M. Nicolaď; Jose A. Egea; Nico Scheerlinck; Julio R. Banga; Ashim K. Datta

2011-01-01

277

Spatial statistics models for stochastic inverse problems in heat conduction Jingbo Wanga

Spatial statistics models for stochastic inverse problems in heat conduction Jingbo Wanga due to the ill-posed nature of such problems. However, there is a rich statistical information) are computed in probabilistic spaces. A Bayesian statistical inference approach is presented here

Zabaras, Nicholas J.

278

TOPAZ - a finite element heat conduction code for analyzing 2-D solids

TOPAZ is a two-dimensional implicit finite element computer code for heat conduction analysis. This report provides a user's manual for TOPAZ and a description of the numerical algorithms used. Sample problems with analytical solutions are presented. TOPAZ has been implemented on the CRAY and VAX computers.

Shapiro, A.B.

1984-03-01

279

Thermal conductivity and heat transfer through the snow on the ice of the Beaufort Sea

measurements have been widely available for the Arctic Ocean [Vowinkel and Orvig, 1970; Radionov et al., 1997; Colony et al., 1998; Warren et al., 1999], but textural descriptions and thermal conductivity of the Beaufort Sea. These were made during project SHEBA (Surface HEat Budget of the Arctic Ocean) [Perovich et

Sturm, Matthew

280

Heat conduction in systems with Kolmogorov-Arnold-Moser phase space structure

NASA Astrophysics Data System (ADS)

We study heat conduction in a billiard channel formed by two sinusoidal walls and the diffusion of particles in the corresponding channel of infinite length; the latter system has an infinite horizon, i.e., a particle can travel an arbitrary distance without colliding with the rippled walls. For small ripple amplitudes, the dynamics of the heat carriers is regular and analytical results for the temperature profile and heat flux are obtained using an effective potential. The study also proposes a formula for the temperature profile that is valid for any ripple amplitude. When the dynamics is regular, ballistic conductance and ballistic diffusion are present. The Poincaré plots of the associated dynamical system (the infinitely long channel) exhibit the generic transition to chaos as ripple amplitude is increased. When no Kolmogorov-Arnold-Moser (KAM) curves are present to forbid the connection of all chaotic regions, the mean square displacement grows asymptotically with time t as tln(t).

Herrera-González, I. F.; Pérez-Aguilar, H. I.; Mendoza-Suárez, A.; Tututi, E. S.

2012-09-01

281

Equilibrium molecular dynamics combined with the Green-Kubo formula can be used to calculate the thermal conductivity of materials such as germanium and carbon. The foundation of this calculation is extracting the heat current from the results and implementing it into the Green-Kubo formula. This work considers all formulations from the literature that calculate the heat current for the Tersoff potential, the interatomic potential most applicable to semiconductor materials. The formulations for the heat current are described, and results for germanium and carbon are presented. The formulations are compared with respect to how well they capture the physics of the Tersoff potential and how well the calculated value of the thermal conductivity reflects the experimentally measured value. PMID:20232951

Guajardo-Cuéllar, Alejandro; Go, David B; Sen, Mihir

2010-03-14

282

NASA Technical Reports Server (NTRS)

The present paper describes the applicability of hybrid transfinite element modeling/analysis formulations for nonlinear heat conduction problems involving phase change. The methodology is based on application of transform approaches and classical Galerkin schemes with finite element formulations to maintain the modeling versatility and numerical features for computational analysis. In addition, in conjunction with the above, the effects due to latent heat are modeled using enthalpy formulations to enable a physically realistic approximation to be dealt computationally for materials exhibiting phase change within a narrow band of temperatures. Pertinent details of the approach and computational scheme adapted are described in technical detail. Numerical test cases of comparative nature are presented to demonstrate the applicability of the proposed formulations for numerical modeling/analysis of nonlinear heat conduction problems involving phase change.

Tamma, Kumar K.; Railkar, Sudhir B.

1988-01-01

283

Heat conduction in a turbulent magnetic field, with application to solar-wind electrons.

NASA Technical Reports Server (NTRS)

Consideration of random, long-wavelength fluctuations in a turbulent magnetic field, showing that they can appreciably decrease the heat conductivity of a plasma along the magnetic field. In simple cases of interest, the reduction along the average field is approximately by the factor (cos delta theta) squared, where delta theta is the angle of the local magnetic field relative to the average field. Application to solar-wind electrons indicates that this reduction in heat conductivity due to observed fluctuations in the interplanetary magnetic field may be of the order of a factor of 2. This may help to explain recent measurements which indicate a rather low electron heat flux in the solar wind.

Hollweg, J. V.; Jokipii, J. R.

1972-01-01

284

A theoretical study of heat exchange during the cooling of a rotating cylinder by an im- pinging jet is carried out. The temperature eld is bidimensional - the longitudinal heat conduction being neglected - and is obtained by solving the heat equation using Laplace and Fourier transforms. In order to assess the external heat ux condition, an inverse method using

F. VOLLE; M. LEBOUCHE; M. GRADECK; D. MAILLET

285

NASA Astrophysics Data System (ADS)

To extend the range of high-temperature, high-pressure studies within the diamond anvil cell, a Liermann-type diamond anvil cell with radial diffraction geometry (rDAC) was redesigned and developed for synchrotron X-ray diffraction experiments at beamline 12.2.2 of the Advanced Light Source. The rDAC, equipped with graphite heating arrays, allows simultaneous resistive and laser heating while the material is subjected to high pressure. The goals are both to extend the temperature range of external (resistive) heating and to produce environments with lower temperature gradients in a simultaneously resistive- and laser-heated rDAC. Three different geomaterials were used as pilot samples to calibrate and optimize conditions for combined resistive and laser heating. For example, in Run#1, FeO was loaded in a boron-mica gasket and compressed to 11 GPa then gradually resistively heated to 1007 K (1073 K at the diamond side). The laser heating was further applied to FeO to raise temperature to 2273 K. In Run#2, Fe-Ni alloy was compressed to 18 GPa and resistively heated to 1785 K (1973 K at the diamond side). The combined resistive and laser heating was successfully performed again on (Mg0.9Fe0.1)O in Run#3. In this instance, the sample was loaded in a boron-kapton gasket, compressed to 29 GPa, resistive-heated up to 1007 K (1073 K at the diamond side), and further simultaneously laser-heated to achieve a temperature in excess of 2273 K at the sample position. Diffraction patterns obtained from the experiments were deconvoluted using the Rietveld method and quantified for lattice preferred orientation of each material under extreme conditions and during phase transformation.

Miyagi, Lowell; Kanitpanyacharoen, Waruntorn; Raju, Selva Vennila; Kaercher, Pamela; Knight, Jason; MacDowell, Alastair; Wenk, Hans-Rudolf; Williams, Quentin; Alarcon, Eloisa Zepeda

2013-02-01

286

To extend the range of high-temperature, high-pressure studies within the diamond anvil cell, a Liermann-type diamond anvil cell with radial diffraction geometry (rDAC) was redesigned and developed for synchrotron X-ray diffraction experiments at beamline 12.2.2 of the Advanced Light Source. The rDAC, equipped with graphite heating arrays, allows simultaneous resistive and laser heating while the material is subjected to high pressure. The goals are both to extend the temperature range of external (resistive) heating and to produce environments with lower temperature gradients in a simultaneously resistive- and laser-heated rDAC. Three different geomaterials were used as pilot samples to calibrate and optimize conditions for combined resistive and laser heating. For example, in Run1, FeO was loaded in a boron-mica gasket and compressed to 11 GPa then gradually resistively heated to 1007 K (1073 K at the diamond side). The laser heating was further applied to FeO to raise temperature to 2273 K. In Run2, Fe-Ni alloy was compressed to 18 GPa and resistively heated to 1785 K (1973 K at the diamond side). The combined resistive and laser heating was successfully performed again on (Mg{sub 0.9}Fe{sub 0.1})O in Run3. In this instance, the sample was loaded in a boron-kapton gasket, compressed to 29 GPa, resistive-heated up to 1007 K (1073 K at the diamond side), and further simultaneously laser-heated to achieve a temperature in excess of 2273 K at the sample position. Diffraction patterns obtained from the experiments were deconvoluted using the Rietveld method and quantified for lattice preferred orientation of each material under extreme conditions and during phase transformation.

Miyagi, Lowell [Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112 (United States); Department of Earth Sciences, Montana State University, Bozeman, Montana 59717 (United States); Kanitpanyacharoen, Waruntorn; Kaercher, Pamela; Wenk, Hans-Rudolf; Alarcon, Eloisa Zepeda [Department of Earth and Planetary Science, University of California, Berkeley, California 94720 (United States); Raju, Selva Vennila [Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States); HiPSEC, Department of Physics, University of Nevada, Las Vegas, Nevada 89154 (United States); Knight, Jason; MacDowell, Alastair [Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States); Williams, Quentin [Department of Earth and Planetary Science, University of California, Santa Cruz, California 95064 (United States)

2013-02-15

287

The coupling of mass and heat fluxes is responsible for the Soret effect in fluid mixtures containing particles of dissimilar mass and/or size. We investigate using equilibrium and non-equilibrium molecular dynamics simulations the relevance of these coupling effects in determining the thermal transport in fluids consisting of binary mixtures where the individual components feature significant mass, 1?:?8, or size, 1?:?3, asymmetries. We quantify the thermal transport by using both boundary driven molecular dynamics simulations (NEMD) and the equilibrium Green-Kubo (GK) approach and investigate the impact of different heat flux definitions, relevant in kinetic theory and experiments, in the quantification of the thermal conductivity. We find that the thermal conductivities obtained from the different definitions agree within numerical accuracy, suggesting that the Soret coefficient does not lead to significant changes in the thermal conduction, even for the large asymmetries considered here, which lead to significant Soret coefficients (?10(-2) K(-1)). The asymmetry in size and mass introduces large differences in the specific enthalpy of the individual components that must be carefully considered to compute accurate thermal conductivities using the GK approach. Neglecting the enthalpic contributions, results in large overestimations of the thermal conductivity, typically between 20% and 50%. Further, we quantify the time dependent behavior of the internal energy and mass flux correlation functions and propose a microscopic mechanism for the heat transport in these asymmetric mixtures. PMID:24818599

Armstrong, Jeff; Bresme, Fernando

2014-06-28

288

Thermal conductance measures the ease with which heat leaves or enters an organism's body. Although the analysis of this physiological variable in relation to climatic and ecological factors can be traced to studies by Scholander and colleagues, only small advances have occurred ever since. Here, we analyse the relationship between minimal thermal conductance estimated during summer (Cmin) and several ecological, climatic and geographical factors for 127 rodent species, in order to identify the exogenous factors that have potentially affected the evolution of thermal conductance. In addition, we evaluate whether there is compensation between Cmin and basal metabolic rate (BMR)—in such a way that a scale-invariant ratio between both variables is equal to one—as could be expected from the Scholander–Irving model of heat transfer. Our major findings are (i) annual mean temperature is the best single predictor of mass-independent Cmin. (ii) After controlling for the effect of body mass, there is a strong positive correlation between log10 (Cmin) and log10 (BMR). Further, the slope of this correlation is close to one, indicating an almost perfect compensation between both physiological variables. (iii) Structural equation modelling indicated that Cmin values are adjusted to BMR values and not the other way around. Thus, our results strongly suggest that BMR and thermal conductance integrate a coordinated system for heat regulation in endothermic animals and that summer conductance values are adjusted (in an evolutionary sense) to track changes in BMRs. PMID:23902915

Naya, Daniel E.; Spangenberg, Lucia; Naya, Hugo; Bozinovic, Francisco

2013-01-01

289

NASA Astrophysics Data System (ADS)

Nanofluids, the fluid suspensions of nonmaterials, have shown many interesting properties and the unique features offer unprecedented potential for many applications. Research on nanofluids has progressed rapidly since its enhanced thermal conductivity was first noted, about a decade ago, though much debate and inconsistency have been reported. Insufficient understanding of the formulation, mechanism of nanofluids further limits their applications [1-34]. Inconsistent data have been presented in the literature on the effect that nanofluids have on the boiling heat-transfer coefficient; however, almost all researchers [35-43] have noted an enhancement in the critical heat flux during nanofluid boiling. Some researchers have observed nanoparticle deposition at the heater surface, which they have related back to the critical heat flux augmentation. In the review, the future developments of these technologies are discussed. In order to be able to put the nanofluid heat transfer technologies into practice, fundamental of these studies are greatly needed to comprehend the physical mechanisms.

Kshirsagar, Jagdeep M.; Shrivastava, Ramakant

2014-08-01

290

Heat conductivities of insulation mats based on water glass bonded non-textile hemp or flax fibres

Heat insulation mats based on water glass bonded non-textile flax and hemp fibres were fabricated via a pilot plant, and their heat conductivities investigated. Under the influence of various factors like moisture content, water sorption and diffusion processes, fibre characteristics and heat radiation as well as thickness and apparent density, heat conductivities in the range of 0.0392–0.0484 W\\/mK for flax fibre

B. Grohe

2004-01-01

291

Quasi-Static Heat Transfer in an Experimental Device with a Radial Electro-Structured Fluid Clutch

In the paper an experimental device with upper half of a radial electro-structured fluid (ESF) clutch with vertical axis (consisting of a lower stationary disc and upper rotating disc) is examined for constant speed of rotation. The narrow gap between the discs is filled with a viscous liquid, so electro-structural effect is not taken into consideration. Frictional tangential forces in

Vladimir Oravsky

2002-01-01

292

Baroclinic waves in a rotating fluid annulus with a downward sloping bottom in the radial direction and with a free upper surface have been studied experimentally. Dispersive wave flows due to the effect of the depth variation (the topographic beta-effect) have been observed and analyzed with special attention to the interactions among the wave components. The internal structure, the upper

Katsumi TAMAKI; Kazuo UKAJI

2003-01-01

293

, UMR 6294 CNRS Â UniversitÂ´e du Havre 53, rue de Prony Â 76058 Le Havre Cedex, France (Dated: 20 annulus with a radial temperature gradient has been performed. Depending on values of control parameters number against the temperature gradient but not against any dimensionless control parameter

Paris-Sud XI, UniversitĂ© de

294

The main driver for small scale turbomachinery in domestic heat pumps is the potential for reaching higher efficiencies than volumetric compressors currently used and the potential for making the compressor oil-free, bearing a considerable advantage in the design of advanced multi-stage heat pump cycles. An appropriate turbocompressor for driving domestic heat pumps with a high temperature lift requires the ability

J. Schiffmann; D. Favrat

2010-01-01

295

NASA Astrophysics Data System (ADS)

A novel method is proposed for the simultaneous calculation of thermal conductivity ? and specific heat capacity C. The new method is a combination of two established techniques. One is the photopyroelectric method for thermal diffusivity ? and the other is the front-heat front-detection photothermoreflectance method for thermal effusivity b. After ?, b, and density ? measurements, C and ? are easily calculated as C = b ? -1/2 ? -1 and ? = ? 1/2 b. Test measurements on a commercial Si single-crystal wafer were performed to demonstrate that the method is sufficiently accurate.

Okamoto, Yoichi; Okada, Ryo; Nemoto, Takashi; Ohta, Hiromichi; Takiguchi, Hiroaki

2012-07-01

296

The formal solutions of problems involving transient heat conduction in infinite internally bounded cylindrical solids may be obtained by the Laplace transform method. Asymptotic series representing the solutions for large values of time are given in terms of functions related to the derivatives of the reciprocal gamma function. The results are applied to the case of the internally bounded infinite cylindrical medium with, (a) the boundary held at constant temperature; (b) with constant heat flow over the boundary; and (c) with the "radiation" boundary condition. A problem in the flow of gas through a porous medium is considered in detail.

Ritchie, R. H.; Sakakura, A. Y.

1956-01-01

297

In temperature measurement of non-isothermal fluid flows by a contact-type temperature sensor, heat conduction along the sensor body can cause significant measurement error which is called "heat-conduction error." The conventional formula for estimating the heat-conduction error was derived under the condition that the fluid temperature to be measured is uniform. Thus, if we apply the conventional formula to a thermal field with temperature gradient, the heat-conduction error will be underestimated. In the present study, we have newly introduced a universal physical model of a temperature-measurement system to estimate accurately the heat-conduction error even if a temperature gradient exists in non-isothermal fluid flows. Accordingly, we have been able to successfully derive a widely applicable estimation and/or evaluation formula of the heat-conduction error. Then, we have verified experimentally the effectiveness of the proposed formula using the two non-isothermal fields-a wake flow formed behind a heated cylinder and a candle flame-whose fluid-dynamical characteristics should be quite different. As a result, it is confirmed that the proposed formula can represent accurately the experimental behaviors of the heat-conduction error which cannot be explained appropriately by the existing formula. In addition, we have analyzed theoretically the effects of the heat-conduction error on the fluctuating temperature measurement of a non-isothermal unsteady fluid flow to derive the frequency response of the temperature sensor to be used. The analysis result shows that the heat-conduction error in temperature-fluctuation measurement appears only in a low-frequency range. Therefore, if the power-spectrum distribution of temperature fluctuations to be measured is sufficiently away from the low-frequency range, the heat-conduction error has virtually no effect on the temperature-fluctuation measurements even by the temperature sensor accompanying the heat-conduction error in the mean-temperature measurements. PMID:23635222

Khine, Soe Minn; Houra, Tomoya; Tagawa, Masato

2013-04-01

298

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site]

The ejecta surrounding the crater (off image to the left) in this image has undergone significant erosion by the wind. The wind has stripped the surface features from the ejecta and has started to winnow away the ejecta blanket. Near the margin of the ejecta the wind is eroding along a radial pattern -- taking advantage of radial emplacement. Note the steep margin of the ejecta blanket. Most, if not all, of the fine ejecta material has been removed and the wind in now working on the more massive continuous ejecta blanket.

Image information: VIS instrument. Latitude 12.5, Longitude 197.4 East (162.6 West). 37 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

2005-01-01

299

Coupled Ablation, Heat Conduction, Pyrolysis, Shape Change and Spallation of the Galileo Probe

NASA Technical Reports Server (NTRS)

The Galileo probe enters the atmosphere of Jupiter in December 1995. This paper presents numerical methodology and detailed results of our final pre-impact calculations for the heat shield response. The calculations are performed using a highly modified version of a viscous shock layer code with massive radiation coupled with a surface thermochemical ablation and spallation model and with the transient in-depth thermal response of the charring and ablating heat shield. The flowfield is quasi-steady along the trajectory, but the heat shield thermal response is dynamic. Each surface node of the VSL grid is coupled with a one-dimensional thermal response calculation. The thermal solver includes heat conduction, pyrolysis, and grid movement owing to surface recession. Initial conditions for the heat shield temperature and density were obtained from the high altitude rarefied-flow calculations of Haas and Milos. Galileo probe surface temperature, shape, mass flux, and element flux are all determined as functions of time along the trajectory with spallation varied parametrically. The calculations also estimate the in-depth density and temperature profiles for the heat shield. All this information is required to determine the time-dependent vehicle mass and drag coefficient which are necessary inputs for the atmospheric reconstruction experiment on board the probe.

Milos, Frank S.; Chen, Y.-K.; Rasky, Daniel J. (Technical Monitor)

1995-01-01

300

The polymer matrix composite through-thickness thermal conductivity is particularly important in applications such as composite space borne electronics enclosures where the heat dissipation is entirely dependent on thermal conduction to a heat sink. The spreading of heat at the composite surface and subsequent localized conduction in the through-thickness direction down to high thermal conductivity fiber may be the key to designing a lightweight, thermally efficient enclosure. A finite element model was constructed of a composite with heat applied to a central area. The laminate consisted of a hybrid of high thermal conductivity pitch fiber/epoxy (K1100/ERL 1939-3) on the outside surfaces interlaminated with low thermal conductivity carbon fabric/epoxy (HMF-322D/7714AC) in a [{+-}10{degree}, (45{degree}), {+-}10{degree}, ({ovr 45}{degree})]{sub s} configuration. Three configurations were modeled: (A) a heat source in the middle, (B) Cu plating under the central heat source and (C) Cu plating under the heat source with a centrally located hole that was also Cu plated. The model with Cu on the surface under the heat source had a maximum surface temperature 35% lower than the model with no Cu to spread the heat. The model with a central Cu plated hole had a maximum surface temperature 58% lower than that with no Cu plating on the surface. Therefore, the surface Cu plating with Cu plated hole spreads the heat and increases the through-thickness thermal conductivity.

Roberts, J.C.; Luesse, M.H.; Magee, T.C. [Johns Hopkins University, Baltimore, MD (United States)

1994-12-31

301

This study aims to assess for a Stirling engine the influence of the overall heat transfer coefficient variation on the optimum state and on the optimum distribution of the heat transfer surface conductance or area among the machine heat exchangers. The analysis is based on a Stirling machine optimization method, previously elaborated, which is now applied to a cycle with

M. Costea; M. Feidt

1998-01-01

302

Calculating heat conduction transfer function through multi-layer slab using model reduction method

Heat conduction transfer function (CTF) method is suitable to deal with the transient heat-conduction through multi-layer slabs encountered in engineering practice frequently. To determine the CTF efficiently, a model reduction approach combining Routh and Pade approximations is developed. Firstly, the transfer function in frequency domain is expanded in the form of power series with infinite terms. Secondly, the Routh approximation is used to determine the denominator coefficients of the reduced CTF. Thirdly, the numerator coefficients of the reduced CFT are evaluated by the Pade approximation. Finally, a direct way from the reduced CTF in frequency domain to that in z-domain is presented. Case study demonstrates that high precision can be obtained by the reduced model in fairly low order.

Zhang, C.; Ding, G.; Li, H.; Chen, Z.

1999-07-01

303

NASA Technical Reports Server (NTRS)

The particular problems investigated in the present study arise from nonlinear transient heat conduction. One of two types of nonlinearities considered is related to a material temperature dependence which is frequently needed to accurately model behavior over the range of temperature of engineering interest. The second nonlinearity is introduced by radiation boundary conditions. The finite element equations arising from the solution of nonlinear transient heat conduction problems are formulated. The finite element matrix equations are temporally discretized, and a nonlinear iterative solution algorithm is proposed. Algorithms for solving the linear problem are discussed, taking into account the form of the matrix equations, Gaussian elimination, cost, and iterative techniques. Attention is also given to approximate factorization, implementational aspects, and numerical results.

Winget, J. M.; Hughes, T. J. R.

1985-01-01

304

Specific heat and thermal conductivity of ferromagnetic magnons in Yttrium Iron Garnet

NASA Astrophysics Data System (ADS)

The specific heat and thermal conductivity of an insulating ferrimagnet Y3Fe5O12 (Yttrium Iron Garnet, YIG) single crystal were measured down to 50 mK. The ferromagnetic magnon specific heat Cm shows a characteristic T1.5-dependence down to 0.77 K. Below 0.77 K, a downward deviation is observed, which is attributed to the magnetic dipole-dipole interaction with typical magnitude of 10^{-4}\\ \\text{eV} . The ferromagnetic magnon thermal conductivity \\kappa_m does not show the characteristic T2-dependence below 0.8 K. To fit the \\kappa_m data, both magnetic defect scattering effect and dipole-dipole interaction are taken into account. These results provide a complete picture of the thermodynamic and thermal transport properties of the low-lying ferromagnetic magnons.

Pan, B. Y.; Guan, T. Y.; Hong, X. C.; Zhou, S. Y.; Qiu, X.; Zhang, H.; Li, S. Y.

2013-08-01

305

Two-Gradient Convection in a Vertical Slot with Maxwell-Cattaneo Heat Conduction

We study the effect of the Maxwell-Cattaneo law of heat conduction (MCHC) on the 1D flow in a vertical slot subject to both vertical and horizontal temperature gradients. The gravitational acceleration is allowed to oscillate, which provides an opportunity to investigate the quantitative contribution of thermal inertia as epitomized by MCHC. The addition of the time derivative in MCHC increases the order of the system. We use a spectral expansion with Rayleigh's beam functions as the basis set, which is especially suited to fourth order boundary value problems (BVP). We show that the time derivative (relaxation of the thermal flux) has a dissipative nature and leads to the appearance of purely real negative eigenvalues. Yet it also increases the absolute value of the imaginary part and decreases the absolute value of the real part of the complex eigenvalues. Thus, the system has a somewhat more oscillatory behavior than the one based on Fourier's heat conduction law (FHC)

Papanicolaou, N. C. [Department of Computer Science, University of Nicosia, P.O. Box 24005, 1700 Nicosia (Cyprus); Christov, C. I. [Department of Mathematics, University of Louisiana at Lafayette, LA 70504-1010 (United States); Jordan, P. M. [Entropy Reversal Consultants (L.L.C), P. O. Box 691, Abita Springs, LA 70420 (United States); Code 7181, Naval Research Lab., Stennis Space Ctr., MS 39529 (United States)

2009-10-29

306

Analysis and solution of the ill-posed inverse heat conduction problem

The inverse conduction problem arises when experimental measurements are taken in the interior of a body, and it is desired to calculate temperature and heat flux values on the surface. The problem is shown to be ill-posed, as the solution exhibits unstable dependence on the given data functions. A special solution procedure is developed for the one-dimensional case which replaces the heat conduction equation with an approximating hyperbolic equation. If viewed from a new perspective, where the roles of the spatial and time variables are interchanged, then an initial value problem for the damped wave equation is obtained. Since this formulation is well-posed, both analytic and numerical solution procedures are readily available. Sample calculations confirm that this approach produces consistent, reliable results for both linear and nonlinear problems.

Weber, C.F.

1981-01-01

307

Hamiltonian dynamics of thermostated systems: two-temperature heat-conducting phi4 chains.

We consider and compare four Hamiltonian formulations of thermostated mechanics, three of them kinetic, and the other one configurational. Though all four approaches "work" at equilibrium, their application to many-body nonequilibrium simulations can fail to provide a proper flow of heat. All the Hamiltonian formulations considered here are applied to the same prototypical two-temperature "phi4" model of a heat-conducting chain. This model incorporates nearest-neighbor Hooke's-Law interactions plus a quartic tethering potential. Physically correct results, obtained with the isokinetic Gaussian and Nose-Hoover thermostats, are compared with two other Hamiltonian results. The latter results, based on constrained Hamiltonian thermostats, fail to model correctly the flow of heat. PMID:17477595

Hoover, Wm G; Hoover, Carol G

2007-04-28

308

NASA Technical Reports Server (NTRS)

An explicit and unconditionally stable finite difference method for the solution of the transient inverse heat conduction problem in a semi-infinite or finite slab mediums subject to nonlinear radiation boundary conditions is presented. After measuring two interior temperature histories, the mollification method is used to determine the surface transient heat source if the energy radiation law is known. Alternatively, if the active surface is heated by a source at a rate proportional to a given function, the nonlinear surface radiation law is then recovered as a function of the interface temperature when the problem is feasible. Two typical examples corresponding to Newton cooling law and Stefan-Boltzmann radiation law respectively are illustrated. In all cases, the method predicts the surface conditions with an accuracy suitable for many practical purposes.

Murio, Diego A.

1991-01-01

309

CTS-type variable conductance heat pipes for SEP FM/PPU

NASA Technical Reports Server (NTRS)

The development effort for, and the fabrication and testing of, six CTS-type variable conductance heat pipes is described. The heat pipes are constructed of stainless steel, use methanol as a working fluid, and a nitrogen/helium mixture as the control gas. The wicking structure consists of interior wall grooves, a metal-felt diametral slab wick, and two wire-mesh arteries. The heat pipes are used to cool two Functional Model/Power Processing Units in a Solar Electric Propulsion prototype BIMOD thruster subsystem assembly. The Power Processing Units convert the electric power from a spacecraft solar array system to the voltages required to operate the electric thrusters which are part of the BIMOD assembly.

Antoniuk, D.; Luedke, E. E.

1978-01-01

310

Through field studies in large commercial buildings and reviews of building plans, we investigated the effective leakage areas (ELAs), air-leakage rates, and conduction heat gains of duct systems. Different methods for measuring air-leakage rates were also compared. ELAs of supply ducts ranged from 0.4 to 2.0 cm2 per square meter of floor area served, and from 1.0 to 4.8 cm2

William J. Fisk; Woody Delp; Rick Diamond; Darryl Dickerhoff; Ronnen Levinson; Mark Modera; Matty Nematollahi; Duo Wang

2000-01-01

311

Transient conductive, radiative heat transfer coupled with moisture transport in attic insulations

A transient, one-dimensional thermal model that incorporates combined conduction, radiation heat transfer, and moisture transport for residential attic insulations has been developed. The governing equations are the energy equation, the radiative transport equation for volumetric radiation within the insulation batt, and the species equations for bound H2O and vapor H2O. A simultaneous solution procedure with a Eulerian control volume-based finite

R. Gorthala; K. T. Harris; J. A. Roux; T. A. Mccarty

1994-01-01

312

On heat conduction in multicomponent, non-Maxwellian spherically symmetric solar wind plasmas

NASA Technical Reports Server (NTRS)

A generalized expression for the steady-state heat flux in multicomponent, moderately non-Maxwellian spherically symmetric plasmas is presented and discussed. The work was motivated by the inability of the simple, Fourier-type formula for the thermal conductivity to explain the observed correlations in the solar wind. The results hold for situations not far from local thermodynamic equilibrium. The generalized expression includes not only correlations that have been observed but also correlations not sought for previously.

Cuperman, S.; Dryer, M.

1985-01-01

313

Analysis of heat conduction in deep penetration welding with a time-modulated laser beam

The heat conduction model of a cylinder-type source in laser keyhole welding is extended to a time-modulated laser beam with a prescribed energy flux density instead of a prescribed temperature at the wall of the cylinder. A new non-dimensional parameter Omega = omega r02\\/ kappa ( omega denotes the frequency of the time-modulated laser beam, r0 the focus radius and

G. Simon; U. Gratzke; J. Kroos

1993-01-01

314

A direct approach to finding unknown boundary conditions in steady heat conduction

NASA Technical Reports Server (NTRS)

The capability of the boundary element method (BEM) in determining thermal boundary conditions on surfaces of a conducting solid where such quantities are unknown was demonstrated. The method uses a non-iterative direct approach in solving what is usually called the inverse heat conduction problem (IHCP). Given any over-specified thermal boundary conditions such as a combination of temperature and heat flux on a surface where such data is readily available, the algorithm computes the temperature field within the object and any unknown thermal boundary conditions on surfaces where thermal boundary values are unavailable. A two-dimensional, steady-state BEM program was developed and was tested on several simple geometries where the analytic solution was known. Results obtained with the BEM were in excellent agreement with the analytic values. The algorithm is highly flexible in treating complex geometries, mixed thermal boundary conditions, and temperature-dependent material properties and is presently being extended to three-dimensional and unsteady heat conduction problems. The accuracy and reliability of this technique was very good but tended to deteriorate when the known surface conditions were only slightly over-specified and far from the inaccessible surface.

Martin, Thomas J.; Dulikravich, George S.

1993-01-01

315

Conditions for Aeronomic Applicability of the Classical Electron Heat Conduction Formula

NASA Technical Reports Server (NTRS)

Conditions for the applicability of the classical formula for heat conduction in the electrons in ionized gas are investigated. In a fully ionised gas ( V(sub en) much greater than V(sub ei)), when the mean free path for electron-electron (or electron-ion) collisions is much larger than the characteristic thermal scale length of the observed system, the conditions for applicability break down. In the case of the Venus ionosphere this breakdown is indicated for a large fraction of the electron temperature data from altitudes greater than 180 km, for electron densities less than 10(exp 4)/cc cm. In a partially ionised gas such that V(sub en) much greater than V(sub ei) there is breakdown of the formula not only when the mean free path of electrons greatly exceeds the thermal scale length, but also when the gradient of neutral particle density exceeds the electron thermal gradient. It is shown that electron heat conduction may be neglected in estimating the temperature of joule heated electrons by observed strong 100 Hz electric fields when the conduction flux is limited by the saturation flux. The results of this paper support our earlier aeronomical arguments against the hypothesis of planetary scale whistlers for the 100 Hz electric field signal. In turn this means that data from the 100 Hz signal may not be used to support the case for lightning on Venus.

Cole, K. D.; Hoegy, W. R.

1998-01-01

316

The effect of heat conduction on the realization of the primary standard for sound pressure

NASA Astrophysics Data System (ADS)

Pressure reciprocity calibration of microphones provides the basis for primary measurement standards for sound pressure in air. At low frequencies, reciprocity calibration requires that a heat conduction correction be employed to account for energy transfer to and from the bounding surfaces of the close-coupled microphone arrangement. The standard governing reciprocity calibration, IEC 61094-2?:?2009, provides two models for the heat conduction correction: the Low Frequency Solution, and the Broadband Solution. Analysis has revealed significant and unexplained differences in behaviour between the models at very low frequencies, leading to inconsistency in calibration results, which has been quantified. Additionally, both heat conduction solutions given in IEC 61094-2 are simplifications that strictly apply only above their respective lower limiting frequencies. An international comparison on microphone calibration is currently underway that includes measurements below the lower limiting frequencies of the models. In this paper, the origin and nature of the Broadband simplifications have been identified, and estimates of the error given. A flaw in the Broadband theory is identified and its effect quantified. Simplification error for the Low Frequency solution is evaluated, and the full spectrum solution is given. This paper urges caution in the application of the models at low frequency and provides data useful for assessing the contribution to the measurement uncertainty.

Jackett, Richard J.

2014-10-01

317

We introduce a new method of solution for the convective heat transfer under forced laminar flow that is confined by two parallel plates with a distance of 2a or by a circular tube with a radius of a. The advection-conduction equation is first mapped onto the boundary. The original problem of solving the unknown field T(x,r,t) is reduced to seek the solutions of T at the boundary (r = a or r = 0, r is the distance from the centerline shown in Fig. 1), i.e., the boundary functions T{sub a}(x,t) {triple_bond} T(x,r=a,t) and/or T{sub 0}(x,t) {triple_bond} T(x,r=0,t). In this manner, the original problem is significantly simplified by reducing the problem dimensionality from 3 to 2. The unknown field T(x,r,t) can be eventually solved in terms of these boundary functions. The method is applied to the convective heat transfer with uniform wall temperature boundary condition and with heat exchange between flowing fluids and its surroundings that is relevant to the geothermal applications. Analytical solutions are presented and validated for the steady-state problem using the proposed method.

Zhijie Xu

2012-07-01

318

Heat, chloride, and specific conductance as ground water tracers near streams

Commonly measured water quality parameters were compared to heat as tracers of stream water exchange with ground water. Temperature, specific conductance, and chloride were sampled at various frequencies in the stream and adjacent wells over a 2-year period. Strong seasonal variations in stream water were observed for temperature and specific conductance. In observation wells where the temperature response correlated to stream water, chloride and specific conductance values were similar to stream water values as well, indicating significant stream water exchange with ground water. At sites where ground water temperature fluctuations were negligible, chloride and/or specific conductance values did not correlate to stream water values, indicating that ground water was not significantly influenced by exchange with stream water. Best-fit simulation modeling was performed at two sites to derive temperature-based estimates of hydraulic conductivities of the alluvial sediments between the stream and wells. These estimates were used in solute transport simulations for a comparison of measured and simulated values for chloride and specific conductance. Simulation results showed that hydraulic conductivities vary seasonally and annually. This variability was a result of seasonal changes in temperature-dependent hydraulic conductivity and scouring or clogging of the streambed. Specific conductance fits were good, while chloride data were difficult to fit due to the infrequent (quarterly) stream water chloride measurements during the study period. Combined analyses of temperature, chloride, and specific conductance led to improved quantification of the spatial and temporal variability of stream water exchange with shallow ground water in an alluvial system. ?? 2007 National Ground Water Association.

Cox, M. H.; Su, G. W.; Constantz, J.

2007-01-01

319

The Green's function for three-dimensional transient heat conduction (diffusion equation) for functionally graded materials (FGMs) is derived. The thermal conductivity and heat capacitance both vary exponentially in one coordinate. In the process of solving this diffusion problem numerically, a Laplace transform (LT) approach is used to eliminate the dependence on time. The fundamental solution in Laplace space is derived and

Alok Sutradhar; Glaucio H. Paulino; L. J. Gray

2002-01-01

320

Transient conductive, radiative heat transfer coupled with moisture transport in attic insulations

NASA Astrophysics Data System (ADS)

A transient, one-dimensional thermal model that incorporates combined conduction, radiation heat transfer, and moisture transport for residential attic insulations has been developed. The governing equations are the energy equation, the radiative transport equation for volumetric radiation within the insulation batt, and the species equations for bound H2O and vapor H2O. A simultaneous solution procedure with a Eulerian control volume-based finite difference method was used to solve the energy equation and the species equations. The method of discrete ordinates was used in solving the radiative transport equation. For H2O transport, both diffusion of vapor H2O and bound H2O and moisture adsorption/desorption within the insulation binder are included in the model. The experimental data measured at an occupied North Mississippi residence for R19STD (standard R19 fiberglass insulation batt without a foil radiant barrier) were used to validate the model which predicted heat fluxes for summer, spring, winter, and fall seasonal conditions. These predictions were compared with the measured heat flux data and the predictions from the dry model (without the moisture transport). Various profiles such as temperature-time histories, relative humidity time histories, spatial H2O concentrations, spatial temperatures, and spatial heat fluxes are presented to explain the overall heat transfer behavior.

Gorthala, R.; Harris, K. T.; Roux, J. A.; McCarty, T. A.

1994-01-01

321

Review and comparison of nanofluid thermal conductivity and heat transfer enhancements.

This study provides a detailed literature review and an assessment of results of the research and development work forming the current status of nanofluid technology for heat transfer applications. Nanofluid technology is a relatively new field, and as such, the supporting studies are not extensive. Specifically, experimental results were reviewed in this study regarding the enhancement of the thermal conductivity and convective heat transfer of nanofluids relative to conventional heat transfer fluids, and assessments were made as to the state-of-the-art of verified parametric trends and magnitudes. Pertinent parameters of particle volume concentration, particle material, particle size, particle shape, base fluid material, temperature, additive, and acidity were considered individually, and experimental results from multiple research groups were used together when assessing results. To this end, published research results from many studies were recast using a common parameter to facilitate comparisons of data among research groups and to identify thermal property and heat transfer trends. The current state of knowledge is presented as well as areas where the data are presently inconclusive or conflicting. Heat transfer enhancement for available nanofluids is shown to be in the 15-40% range, with a few situations resulting in orders of magnitude enhancement.

Yu, W.; France, D. M.; Routbort, J. L.; Choi, S. U.S.; Energy Systems; Univ. of Illinois at Chicago; Korea Inst. of Energy Research

2008-05-01

322

NaK Variable Conductance Heat Pipe for Radioisotope Stirling Systems

NASA Technical Reports Server (NTRS)

In a Stirling radioisotope power system, heat must continually be removed from the General Purpose Heat Source (GPHS) modules to maintain the modules and surrounding insulation at acceptable temperatures. The Stirling convertor normally provides most of this cooling. If the Stirling convertor stops in the current system, the insulation is designed to spoil, preventing damage to the GPHS, but also ending use of that convertor for the mission. An alkali-metal Variable Conductance Heat Pipe (VCHP) was designed to allow multiple stops and restarts of the Stirling convertor. In the design of the VCHP for the Advanced Stirling Radioisotope Generator, the VCHP reservoir temperature can vary between 40 and 120 C. While sodium, potassium, or cesium could be used as the working fluid, their melting temperatures are above the minimum reservoir temperature, allowing working fluid to freeze in the reservoir. In contrast, the melting point of NaK is -12 C, so NaK can't freeze in the reservoir. One potential problem with NaK as a working fluid is that previous tests with NaK heat pipes have shown that NaK heat pipes can develop temperature non-uniformities in the evaporator due to NaK's binary composition. A NaK heat pipe was fabricated to measure the temperature non-uniformities in a scale model of the VCHP for the Stirling Radioisotope system. The temperature profiles in the evaporator and condenser were measured as a function of operating temperature and power. The largest delta T across the condenser was 2S C. However, the condenser delta T decreased to 16 C for the 775 C vapor temperature at the highest heat flux applied, 7.21 W/ square cm. This decrease with increasing heat flux was caused by the increased mixing of the sodium and potassium in the vapor. This temperature differential is similar to the temperature variation in this ASRG heat transfer interface without a heat pipe, so NaK can be used as the VCHP working fluid.

Tarau, Calin; Anderson, William G.; Walker, Kara

2008-01-01

323

Surface roughness and three-dimensional heat conduction in thermophysical models

NASA Astrophysics Data System (ADS)

A thermophysical model is presented that considers surface roughness, cast shadows, multiple or single scattering of radiation, visual and thermal infrared self heating, as well as heat conduction in one or three dimensions. The code is suitable for calculating infrared spectral energy distributions for spatially resolved or unresolved minor Solar System bodies without significant atmospheres or sublimation, such as the Moon, Mercury, asteroids, irregular satellites or inactive regions on comet nuclei. It is here used to explore the effects of surface roughness on spatial scales small enough for heat conduction to erase lateral temperature gradients. Analytically derived corrections to one-dimensional models that reproduce the results of three-dimensional modeling are presented. We find that the temperature of terrains with such small-scale roughness is identical to that of smooth surfaces for certain types of topographies and non-scattering material. However, systematic differences between smooth and rough terrains are found for scattering materials, or topographies with prominent positive relief. Contrary to common beliefs, the roughness on small spatial scales may therefore affect the thermal emission of Solar System bodies.

Davidsson, Björn J. R.; Rickman, Hans

2014-11-01

324

Thermal conductivity, thermal diffusivity and specific heat of sI methane hydrate were measured as functions of temperature and pressure using a needle probe technique. The temperature dependence was measured between -20??C and 17??C at 31.5 MPa. The pressure dependence was measured between 31.5 and 102 MPa at 14.4??C. Only weak temperature and pressure dependencies were observed. Methane hydrate thermal conductivity differs from that of water by less than 10 per cent, too little to provide a sensitive measure of hydrate content in water-saturated systems. Thermal diffusivity of methane hydrate is more than twice that of water, however, and its specific heat is about half that of water. Thus, when drilling into or through hydrate-rich sediment, heat from the borehole can raise the formation temperature more than 20 per cent faster than if the formation's pore space contains only water. Thermal properties of methane hydrate should be considered in safety and economic assessments of hydrate-bearing sediment. ?? 2007 The Authors Journal compilation ?? 2007 RAS.

Waite, W. F.; Stern, L. A.; Kirby, S. H.; Winters, W. J.; Mason, D. H.

2007-01-01

325

Deicing heating layers are frequently used in covers of large radio-frequency (RF) equipment, such as radar, to remove ice that could damage the structures or make them unstable. Typically, the deicers are made using a metal framework and inorganic insulator; commercial resistive heating materials are often nontransparent to RF waves. The preparation of a sub-skin-depth thin film, whose thickness is very small relative to the RF skin (or penetration) depth, is the key to minimizing the RF absorption. The skin depth of typical metals is on the order of a micrometer at the gigahertz frequency range. As a result, it is very difficult for conventional conductive materials (such as metals) to form large-area sub-skin-depth films. In this report, we disclose a new deicing heating layer composite made using graphene nanoribbons (GNRs). We demonstrate that the GNR film is thin enough to permit RF transmission. This metal-free, ultralight, robust, and scalable graphene-based RF-transparent conductive coating could significantly reduce the size and cost of deicing coatings for RF equipment covers. This is important in many aviation and marine applications. This is a demonstration of the efficacy and applicability of GNRs to afford performances unattainable by conventional materials. PMID:24328320

Volman, Vladimir; Zhu, Yu; Raji, Abdul-Rahman O; Genorio, Bostjan; Lu, Wei; Xiang, Changsheng; Kittrell, Carter; Tour, James M

2014-01-01

326

The thermal conductivity of electron beam-physical vapor deposited (EB-PVD) ZrO2–8 wt.%Y2O3 thermal barrier coatings was determined by a steady-state laser heat flux technique. Thermal conductivity change kinetics of the EB-PVD ceramic coatings were also obtained in real time, at high temperatures, under the laser high heat flux, long-term test conditions. The thermal conductivity increase due to micro-pore sintering and the

Dongming Zhu; Robert A. Miller; Ben A. Nagaraj; Robert W. Bruce

2001-01-01

327

Cooling performance of a nanofluid flow in a heat sink microchannel with axial conduction effect

NASA Astrophysics Data System (ADS)

In this work, the forced convection of a nanofluid flow in a microscale duct has been investigated numerically. The governing equations have been solved utilizing the finite volume method. Two different conjugated domains for both flow field and substrate have been considered in order to solve the hydrodynamic and thermal fields. The results of the present study are compared to those of analytical and experimental ones, and a good agreement has been observed. The effects of Reynolds number, thermal conductivity and thickness of substrate on the thermal and hydrodynamic indexes have been studied. In general, considering the wall affected the thermal parameter while it had no impact on the hydrodynamics behavior. The results show that the effect of nanoparticle volume fraction on the increasing of normalized local heat transfer coefficient is more efficient in thick walls. For higher Reynolds number, the effect of nanoparticle inclusion on axial distribution of heat flux at solid-fluid interface declines. Also, less end losses and further uniformity of axial heat flux lead to an increase in the local normalized heat transfer coefficient.

Izadi, M.; Shahmardan, M. M.; Norouzi, M.; Rashidi, A. M.; Behzadmehr, A.

2014-09-01

328

An implicit-iterative solution of the heat conduction equation with a radiation boundary condition

NASA Technical Reports Server (NTRS)

For the problem of predicting one-dimensional heat transfer between conducting and radiating mediums by an implicit finite difference method, four different formulations were used to approximate the surface radiation boundary condition while retaining an implicit formulation for the interior temperature nodes. These formulations are an explicit boundary condition, a linearized boundary condition, an iterative boundary condition, and a semi-iterative boundary method. The results of these methods in predicting surface temperature on the space shuttle orbiter thermal protection system model under a variety of heating rates were compared. The iterative technique caused the surface temperature to be bounded at each step. While the linearized and explicit methods were generally more efficient, the iterative and semi-iterative techniques provided a realistic surface temperature response without requiring step size control techniques.

Williams, S. D.; Curry, D. M.

1977-01-01

329

The gravitational heat conduction and the hierarchical structure in solar interior

With the assumption of local Tsallis equilibrium, the newly defined gravitational temperature is calculated in the solar interior, whose distribution curve can be divided into three parts, the solar core region, radiation region and convection region, in excellent agreement with the solar hierarchical structure. By generalizing the Fourier law, one new mechanism of heat conduction, based on the gradient of the gravitational temperature, is introduced into the astrophysical system. This mechanism is related to the self-gravity of such self-gravitating system whose characteristic scale is large enough. It perhaps plays an important role in the astrophysical system which, in the solar interior, leads to the heat accumulation at the bottom of the convection layer and then motivates the convection motion.

Zheng Yahui; Du Jiulin

2014-03-07

330

The gravitational heat conduction and the hierarchical structure in solar interior

With the assumption of local Tsallis equilibrium, the newly defined gravitational temperature is calculated in the solar interior, whose distribution curve can be divided into three parts, the solar core region, radiation region and convection region, in excellent agreement with the solar hierarchical structure. By generalizing the Fourier law, one new mechanism of heat conduction, based on the gradient of the gravitational temperature, is introduced into the astrophysical system. This mechanism is related to the self-gravity of such self-gravitating system whose characteristic scale is large enough. It perhaps plays an important role in the astrophysical system which, in the solar interior, leads to the heat accumulation at the bottom of the convection layer and then motivates the convection motion.

Yahui, Zheng

2014-01-01

331

NASA Technical Reports Server (NTRS)

Efforts in integrated circuit (IC) packaging technologies have recently been focused on management of increasing heat density associated with high frequency and high density circuit designs. While current flip-chip package designs can accommodate relatively high amounts of heat density, new materials need to be developed to manage thermal effects of next-generation integrated circuits. Multiwall carbon nanotubes (MWNT) have been shown to significantly enhance thermal conduction in the axial direction and thus can be considered to be a candidate for future thermal interface materials by facilitating efficient thermal transport. This work focuses on fabrication and characterization of a robust MWNT-copper composite material as an element in IC package designs. We show that using vertically aligned MWNT arrays reduces interfacial thermal resistance by increasing conduction surface area, and furthermore, the embedded copper acts as a lateral heat spreader to efficiently disperse heat, a necessary function for packaging materials. In addition, we demonstrate reusability of the material, and the absence of residue on the contacting material, both novel features of the MWNT-copper composite that are not found in most state-of-the-art thermal interface materials. Electrochemical methods such as metal deposition and etch are discussed for the creation of the MWNT-Cu composite, detailing issues and observations with using such methods. We show that precise engineering of the composite surface affects the ability of this material to act as an efficient thermal interface material. A thermal contact resistance measurement has been designed to obtain a value of thermal contact resistance for a variety of different thermal contact materials.

Ngo, Quoc; Cruden, Brett A.; Cassell, Alan M.; Sims, Gerard; Li, Jun; Meyyappa, M.; Yang, Cary Y.

2005-01-01

332

Wavelets in the domain decomposition method for transient heat conduction equation

NASA Astrophysics Data System (ADS)

We solve the transient heat conduction equation in an L- shaped region using domain decomposition and boundary integrals. The iterations need to be carried out only on the interfaces between the subdomains unlike finite difference or finite element methods where the iterations are to be performed in the entire domain. Numerically, the problem reduces to the multiplication of dense matrices by vectors of boundary or initial values. The DAUB4 wavelet transform is used to compress the matrices which leads to computational advantage without loss of accuracy. This procedure, capable of parallel implementation, is an extension of the work of Zarantonello and Elton for Laplace equation in overlapping circular discs.

Avudainayagam, A.; Vani, C.

1999-10-01

333

Heat conductivity from molecular chaos hypothesis in locally confined billiard systems.

We study the transport properties of a large class of locally confined Hamiltonian systems, in which neighboring particles interact through hard-core elastic collisions. When these collisions become rare and the systems large, we derive a Boltzmann-like equation for the evolution of the probability densities. We solve this equation in the linear regime and compute the heat conductivity from a Green-Kubo formula. The validity of our approach is demonstrated by comparing our predictions with the results of numerical simulations performed on a new class of high-dimensional defocusing chaotic billiards. PMID:19113325

Gilbert, Thomas; Lefevere, Raphaël

2008-11-14

334

Effects of friction and heat conduction on sound propagation in ducts

NASA Technical Reports Server (NTRS)

A theoretical formulation of the propagation of sound in a viscous and heat conducting medium is presented. The problem is reduced to the determination of two scalar potentials related to pressure and entropy fluctuations respectively, and a vector potential related to vorticity fluctuations. The particular case of a two-dimensional duct of constant width is thoroughly investigated in the low, high, and very high frequency ranges. It is shown that three distinct families of modes may propagate along the duct axis, namely, pressure, entropy, and vorticity dominated modes. Perturbation methods are used to study the variations of attenuation rates, phase velocities, and mode shapes, as a function of frequency and duct width.

Huerre, P.; Karamcheti, K.

1975-01-01

335

Multiply scaled constrained nonlinear equation solvers. [for nonlinear heat conduction problems

NASA Technical Reports Server (NTRS)

To improve the numerical stability of nonlinear equation solvers, a partitioned multiply scaled constraint scheme is developed. This scheme enables hierarchical levels of control for nonlinear equation solvers. To complement the procedure, partitioned convergence checks are established along with self-adaptive partitioning schemes. Overall, such procedures greatly enhance the numerical stability of the original solvers. To demonstrate and motivate the development of the scheme, the problem of nonlinear heat conduction is considered. In this context the main emphasis is given to successive substitution-type schemes. To verify the improved numerical characteristics associated with partitioned multiply scaled solvers, results are presented for several benchmark examples.

Padovan, Joe; Krishna, Lala

1986-01-01

336

Mathematical equations for heat conduction in the fins of air-cooled engines

NASA Technical Reports Server (NTRS)

The problem considered in this report is that of reducing actual geometrical area of fin-cooling surface, which is, of course, not uniform in temperature, to equivalent cooling area at one definite temperature, namely, that prevailing on the cylinder wall at the point of attachment of the fin. This makes it possible to treat all the cooling surface as if it were part of the cylinder wall and 100 per cent effective. The quantities involved in the equations are the geometrical dimensions of the fin, thermal conductivity of the material composing it, and the coefficient of surface heat dissipation between the fin and the air streams.

Harper, R R; Brown, W B

1923-01-01

337

Subsurface Temperature, Moisture, Thermal Conductivity and Heat Flux, Barrow, Area A, B, C, D

Subsurface temperature data are being collected along a transect from the center of the polygon through the trough (and to the center of the adjacent polygon for Area D). Each transect has five 1.5m vertical array thermistor probes with 16 thermistors each. This dataset also includes soil pits that have been instrumented for temperature, water content, thermal conductivity, and heat flux at the permafrost table. Area C has a shallow borehole of 2.5 meters depth is instrumented in the center of the polygon.

Cable, William; Romanovsky, Vladimir

338

Coupled heat conduction and thermal stress formulation using explicit integration. [LMFBR

The formulation needed for the conductance of heat by means of explicit integration is presented. The implementation of these expressions into a transient structural code, which is also based on explicit temporal integration, is described. Comparisons of theoretical results with code predictions are given both for one-dimensional and two-dimensional problems. The coupled thermal and structural solution of a concrete crucible, when subjected to a sudden temperature increase, shows the history of cracking. The extent of cracking is compared with experimental data.

Marchertas, A.H.; Kulak, R.F.

1982-06-01

339

Specific heat and thermal conductivity of HoN and ErN at cryogenic temperatures

NASA Astrophysics Data System (ADS)

The rare earth nitrides, HoN and ErN, were synthesized by the hot isostatic pressing method. Their specific heat CH(T) and the thermal conductivity ? were measured at cryogenic temperatures. In zero field, the peak values of the C0(T) of HoN and ErN are larger than those of the magnetic regenerators such as Er3Ni. The peak values of the adiabatic temperature change ?T(T) of HoN and ErN showed similar or larger values compared with those of the candidate materials for the magnetic refrigerants such as ErAl2. The thermal conductivity of HoN and ErN are comparable to those of the magnetic regenerators such as Er3Ni. The present results indicate that HoN and ErN are promising materials as the magnetic refrigerant and regenerator for the cryogenic refrigeration system.

Nishio, Shohei; Nakagawa, Takashi; Arakawa, Takayuki; Tomioka, Naoto; Yamamoto, Takao A.; Kusunose, Takafumi; Niihara, Koichi; Numazawa, Takenori; Kamiya, Koji

2006-04-01

340

NASA Technical Reports Server (NTRS)

Experimental measurements of thermal conductivity and thermal diffusivity obtained with a transient hot-wire apparatus are reported for three mixtures of nitrogen, oxygen, and argon. Values of the specific heat, Cp, are calculated from these measured values and the density calculated with an equation of state. The measurements were made at temperatures between 65 and 303 K with pressures between 0.1 and 70 MPa. The data cover the vapor, liquid, and supercritical gas phases for the three mixtures. The total reported points are 1066 for the air mixture (78.11 percent nitrogen, 20.97 percent oxygen, and 0.92 percent argon), 1058 for the 50 percent nitrogen, 50 percent oxygen mixture, and 864 for the 25 percent nitrogen, 75 oxygen mixture. Empirical thermal conductivity correlations are provided for the three mixtures.

Perkins, R. A.; Cieszkiewicz, M. T.

1991-01-01

341

NASA Technical Reports Server (NTRS)

Laser high heat flux test approaches have been established to obtain critical properties of ceramic thermal barrier coatings (TBCs) under near-realistic temperature and thermal gradients that may he encountered in advanced engine systems. Thermal conductivity change kinetics of a thin ceramic coating were continuously monitored in real time at various test temperatures. A significant thermal conductivity increase was observed during the laser simulated engine heat flux tests. For a 0.25 mm thick ZrO2-8%Y2O3 coating system, the overall thermal conductivity increased from the initial value of 1.0 W/m-K to 1. 15 W/m-K, 1. 19 W/m-K and 1.5 W/m-K after 30 hour testing at surface temperatures of 990C, 1100C, and 1320C. respectively. Hardness and modulus gradients across a 1.5 mm thick TBC system were also determined as a function of laser testing time using the laser sintering/creep and micro-indentation techniques. The coating Knoop hardness values increased from the initial hardness value of 4 GPa to 5 GPa near the ceramic/bond coat interface, and to 7.5 GPa at the ceramic coating surface after 120 hour testing. The ceramic surface modulus increased from an initial value of about 70 GPa to a final value of 125 GPa. The increase in thermal conductivity and the evolution of significant hardness and modulus gradients in the TBC systems are attributed to sintering-induced micro-porosity gradients under the laser-imposed high thermal gradient conditions. The test techniques provide a viable means for obtaining coating data for use in design, development, stress modeling, and life prediction for various thermal barrier coating applications.

Zhu, Dongming; Miller, Robert A.

1999-01-01

342

A radial engine is described comprising: a housing; equally spaced openings disposed in ring-like arrangement on the periphery of the housing; a piston and cylinder arrangement in each of the opening, a piston rod for each arrangement fixed to and extending radially inwardly from its respective piston and through its respective opening; shoe means pivotally attached at the other end of each of the piston rod; radial guide means extending in the housing in line with each of the piston rods, and the shoe means provided with guide means followers to ensure radial reciprocal movement of the piston rods and shoe means; and a connecting ring journaled on a crankshaft for circular translation motion in the housing, the ring including a circular rim. Each shoe means includes an arcuate follower member being slidably connected to the rim of the connecting ring.

Kmicikiewicz, M.A.

1988-03-01

343

Variation in Conductivity of Cadmium Sulfo-Selenide Sintered Films with Vacuum Heat Treatment

NASA Astrophysics Data System (ADS)

The conductivity of CdS-Se sintered film increases irreversibly about 109-fold with vacuum heat treatment from 100° C to 200° C. The mechanism of such a large variation has been studied using highly sensitive Hall effect and conductivity measurements. The obtained results can be analyzed by the grain-boundary potential-barrier model with the aid of the charge neutrality condition for the grains, the maximum allowable values of surface potential and potential barrier height, and the density of interface states. Increase in conductivity of 8 orders of magnitude is brought about by increase in the free electron density, which occurs in two steps: in the low-temperature region, the release of trapped electrons from the surface state occurs due to desorption of chemisorbed oxygen; in the high-temperature region, the increase in effective doping density through the decrease in acceptor density occurs due to the release of occluded oxygen from the bulk crystallites near the surface. The mobility of free electrons contributes to an increase of one order of magnitude in conductivity, which decreases once to a minimum and then increases. The variation in mobility is attributed to the barrier height at the grain boundary which is produced by trapped electrons at the intrinsic interface state.

Abdulla, Aniwar; Kasai, Akinari; Takenaga, Mitsuru; Nakamura, Akira

1995-05-01

344

Quantized thermal conductance via phononic heat transport in nanoscale devices at low temperatures

NASA Astrophysics Data System (ADS)

We study phononic heat transport in nanoscale devices. In the nonequilibrium Green's function formalism, an analytical small-frequency expansion of the phonon current transmission is derived for an arbitrary oscillator chain with typical contact-device-contact structure. Applying this expansion in a Landauer formula, it is possible to construct a systematic low-temperature expansion of the thermal conductance. It follows that quantized thermal conductance occurs as a plateau of the thermal conductance divided by the temperature within second order of the temperature expansion for completely heterogeneous systems as long as the product of force constant and oscillator mass is identical in both contacts, independent of the scattering area. Beyond this plateau, the higher-order terms of the low-temperature expansion yield a finite-temperature correction exhibiting the form of a cubic power law depending on the details of the scattering area. These findings are in agreement with experiments and numerical calculations. Our general results are applied to a double junction chain, where we find as the first phenomenon beyond our low-temperature expansion a second plateau. This plateau is associated with a thermal phase averaging of the phonon transmission, which leads for increasing temperatures to an independence of the thermal conductance from the device length.

Käso, M.; Wulf, U.

2014-04-01

345

NASA Astrophysics Data System (ADS)

The separator is a critical, multi-functional component of a Li-ion cell that plays a key role in performance and safety during energy conversion and storage processes. Heat flow through the separator is important for minimizing cell temperature and avoiding thermal runaway. Despite the critical nature of thermal conduction through the separator, very little research has been reported on understanding and measuring the thermal conductivity and heat capacity of the separator. This paper presents first-ever measurements of thermal conductivity and heat capacity of the separator material. These measurements are based on thermal response to an imposed DC heating within a time period during which an assumption of a thermally semi-infinite domain is valid. Experimental data are in excellent agreement with the analytical model. Comparison between the two results in measurement of the in-plane thermal conductivity and heat capacity of the separator. Results indicate very low thermal conductivity of the separator. Measurements at an elevated temperature indicate that thermal conductivity and heat capacity do not change much with increasing temperature. Experimental measurements of previously unavailable thermal properties reported here may facilitate a better fundamental understanding of thermal transport in a Li-ion cell, and enhanced safety due to more accurate thermal prediction.

Vishwakarma, V.; Jain, A.

2014-12-01

346

On the dynamical Rayleigh-Taylor instability in compressible viscous flows without heat conductivity

We investigate the instability of a smooth Rayleigh-Taylor steady-state solution to compressible viscous flows without heat conductivity in the presence of a uniform gravitational field in a bounded domain $\\Omega\\subset{\\mathbb R}^3$ with smooth boundary $\\partial\\Omega$. We show that the steady-state is linearly unstable by constructing a suitable energy functional and exploiting arguments of the modified variational method. Then, based on the constructed linearly unstable solutions and a local well-posedness result of classical solutions to the original nonlinear problem, we further reconstruct the initial data of linearly unstable solutions to be the one of the original nonlinear problem and establish an appropriate energy estimate of Gronwall-type. With the help of the established energy estimate, we show that the steady-state is nonlinearly unstable in the sense of Hadamard by a careful bootstrap argument. As a byproduct of our analysis, we find that the compressibility has no stabilizing effect in the linearized problem for compressible viscous flows without heat conductivity.

Fei Jiang; Song Jiang

2014-03-20

347

Advanced development of the boundary element method for steady-state heat conduction

NASA Technical Reports Server (NTRS)

Considerable progress has been made in recent years toward advancing the state-of-the-art in solid mechanics boundary element technology. In the present work, much of this new technology is applied in the development of a general-purpose boundary element method (BEM) for steady-state heat conduction. In particular, the BEM implementation involves the use of higher-order conforming elements, self-adaptive integration and multi-region capability. Two- and three-dimensional, as well as axisymmetric analysis, are incorporated within a unified framework. In addition, techniques are introduced for the calculation of boundary flux, and for the inclusion of thermal resistance across interfaces. As a final extension, an efficient formulation is developed for the analysis of solid three-dimensional bodies with embedded holes. For this last class of problems, the new BEM formulation is particularly attractive, since use of the alternatives (i.e. finite element or finite difference methods) is not practical. A number of detailed examples illustrate the suitability and robustness of the present approach for steady-state heat conduction.

Dargush, G. F.; Banerjee, Prasanta K.

1989-01-01

348

NASA Technical Reports Server (NTRS)

This research investigates residual-based a posteriori error estimates for finite element approximations of heat conduction in single-layer and multi-layered materials. The finite element approximation, based upon hierarchical modelling combined with p-version finite elements, is described with specific application to a two-dimensional, steady state, heat-conduction problem. Element error indicators are determined by solving an element equation for the error with the element residual as a source, and a global error estimate in the energy norm is computed by collecting the element contributions. Numerical results of the performance of the error estimate are presented by comparisons to the actual error. Two methods are discussed and compared for approximating the element boundary flux. The equilibrated flux method provides more accurate results for estimating the error than the average flux method. The error estimation is applied to multi-layered materials with a modification to the equilibrated flux method to approximate the discontinuous flux along a boundary at the material interfaces. A directional error indicator is developed which distinguishes between the hierarchical modeling error and the finite element error. Numerical results are presented for single-layered materials which show that the directional indicators accurately determine which contribution to the total error dominates.

Lang, Christapher G.; Bey, Kim S. (Technical Monitor)

2002-01-01

349

We explore the consequences of a deterministic microscopic thermostat-reservoir contact mechanism. With different temperature reservoirs at each end of a two-dimensional system, a heat current is produced and the system has an anomalous thermal conductivity. The microscopic form for the local heat flux vector is derived and both the kinetic and potential contributions are calculated. The total heat flux vector is shown to satisfy the continuity equation. The properties of this nonequilibrium steady state are studied as functions of system size and temperature gradient, identifying key scaling relations for the local fluid properties and separating bulk and boundary effects. The local entropy density calculated from the local equilibrium distribution is shown to be a very good approximation to the entropy density calculated directly from the velocity distribution even for systems that are far from equilibrium. The dissipation and kinetic entropy production and flux are compared quantitatively and the differing mechanisms discussed within the Bhatnagar-Gross-Krook approximation. For equal-temperature reservoirs the entropy production near the reservoir walls is shown to be proportional to the local phase space contraction calculated from the tangent space dynamics. However, for unequal temperatures, the connection between local entropy production and local phase space contraction is more complicated. PMID:23848664

Morriss, Gary P; Truant, Daniel P

2013-06-01

350

The thermal conductivities of three plasma-sprayed cermets have been determined over the temperature range 23-630 degrees C from the measurement of the specific heat, thermal diffusivity, and density. These cermets are mixtures of Al and SiC prepared by plasma spray deposition and are being considered for various applications in magnetic confinement fusion devices. The samples consisted of three compositions: 61 vol% Al/39 vol% SiC, 74 vol% Al/26 vol% SiC, and 83 vol% Al/17 vol% SiC. The specific heat was determined by differential scanning calorimetry through the Al melt transition up to 720/sup 0/C, while the thermal diffusivity was determined using the laser flash technique up to 630/sup 0/C. The linear thermal expansion was measured and used to correct the diffusivity and density values. The thermal diffusivity showed a significant increase after thermal cycling due to a reduction in the intergrain contact resistance, increasing from 0.4 to 0.6 cm /SUP 2./ S/sup -1/ at 160/sup 0/C. However, effective medium theory calculations indicated that the thermal conductivities of both the Al and the SiC were below the ideal defect-free limit even after high-temperature cycling. The specific heat measurements showed suppressed melting points in the plasmasprayed cermets. The 39 vol% SiC began a melt endotherm at 577/sup 0/C, which peaked in the 640-650/sup 0/C range depending on the sample thermal history. Chemical and X-ray diffraction analysis indicated the presence of free silicon in the cermet and in the SiC powder, which resulted in a eutectic Al/Si alloy.

Roth, E.P.; Smith, M.F.; Hanley, H.J.M.; Cezairliyan, A.

1986-03-01

351

NASA Astrophysics Data System (ADS)

The thermal conductivities of three plasma-sprayed cermets have been determined over the temperature range 23 630°C from the measurement of the specific heat, thermal diffusivity, and density. These cermets are mixtures of Al and SiC prepared by plasma spray deposition and are being considered for various applications in magnetic confinement fusion devices. The samples consisted of three compositions: 61 vol% Al/39 vol% SiC, 74vol% Al/26vol% SiC, and 83 vol% Al/17 vol% SiC. The specific heat was determined by differential scanning calorimetry through the Al melt transition up to 720°C, while the thermal diffusivity was determined using the laser flash technique up to 630°C. The linear thermal expansion was measured and used to correct the diffusivity and density values. The thermal diffusivity showed a significant increase after thermal cycling due to a reduction in the intergrain contact resistance, increasing from 0.4 to 0.6 cm2·-1 at 160°C. However, effective medium theory calculations indicated that the thermal conductivities of both the Al and the SiC were below the ideal defect-free limit even after high-temperature cycling. The specific heat measurements showed suppressed melting points in the plasmasprayed cermets. The 39 vol% SiC began a melt endotherm at 577°C, which peaked in the 640 650°C range depending on the sample thermal history. Chemical and X-ray diffraction analysis indicated the presence of free silicon in the cermet and in the SiC powder, which resulted in a eutectic Al/Si alloy.

Roth, E. P.; Smith, M. F.

1986-03-01

352

The lack of a centre of inversion in a cholesteric liquid crystal allows linear cross couplings between thermodynamic forces and fluxes that are polar vectors and pseudovectors, respectively. This makes it possible for a temperature gradient parallel to the cholesteric axis to induce a torque that rotates the director, a phenomenon known as the Lehmann effect or thermomechanical coupling. The converse is also possible: a torque applied parallel to the cholesteric axis rotates the director and drives a heat flow. In order to study this phenomenon, nonequilibrium molecular dynamics simulation algorithms and Green-Kubo relations evaluated by equilibrium molecular dynamics simulation have been used to calculate the Leslie coefficient, i.e. the cross coupling coefficient between the temperature gradient and the director angular velocity, for a model system composed of soft prolate ellipsoids of revolution interacting via the Gay-Berne potential augmented by a chiral interaction potential causing the formation of a cholesteric phase. It is found that the Leslie coefficient is two orders of magnitudes smaller than other transport coefficients such as the heat conductivity and the twist viscosity, so that very long simulations are required to evaluate it. The Leslie coefficient decreases with the pitch but it has not been possible to determine the exact functional dependence of this coefficient on the pitch. Since very long simulations have been performed to evaluate the Leslie coefficient, very accurate values have been obtained for the twist viscosity and the heat conductivity as a by-product and it is found that they are very similar to the values of the corresponding quantities in the achiral nematic phase that arises when the pitch goes to infinity. PMID:23223192

Sarman, Sten; Laaksonen, Aatto

2013-03-14

353

In this paper the composition and thermal property of soil are discussed. The main factors that impact the soil thermal conductivity and several commonly-used pipe materials are studied. A model of heat exchanger with horizontal pipes of ground...

Song, Y.; Yao, Y.; Na, W.

2006-01-01

354

We consider unsteady flows of inhomogeneous, incompressible, shear-thickening and heat-conducting fluids where the viscosity depends on the density, the temperature and the shear rate, and the heat conductivity depends on the temperature and the density. For any values of initial total mass and initial total energy we establish the long-time existence of weak solution to internal flows inside an arbitrary

Jens Frehse; Josef Málek; Michael R?ži?ka

2010-01-01

355

Heat capacity, enthalpy of mixing, and thermal conductivity of Hg(1-x)Cd(x)Te pseudobinary melts

NASA Technical Reports Server (NTRS)

Heat capacity and enthalpy of mixing of Hg(1-x)Cd(x)Te pseudobinary melts were calculated assuming an associated solution model for the liquid phase. The thermal conductivity of the pseudobinary melts for x = 0, 0.05, 0.1, and 0.2 was then calculated from the heat capacity values and the experimental values of thermal diffusivity and density for these melts. The thermal conductivity for the pseudobinary solid solution is also discussed.

Su, Ching-Hua

1986-01-01

356

Network simulation method (NSM) is used to solve the laminar heat and mass transfer of an electrically-conducting, heat generating\\/absorbing\\u000a fluid past a perforated horizontal surface in the presence of viscous and Joule heating problem. The governing partial differential\\u000a equations are non-dimensionalized and transformed into a system of nonlinear ordinary differential similarity equations, in\\u000a a single independent variable, ?. The resulting

Joaquín Zueco; O. Anwar Bég; L. M. López-Ochoa

2011-01-01

357

In this work the uncopled thermoelastic model based on the Dual Phase Lag (DPL) heat conduction equation is used to investigate the thermoelastic properties of a semi-infinite medium induced by a homogeneously illuminating ultrashort pulsed laser heating. The exact solution for the temperature, the displacement and the stresses distributions ob- tained analytically using the separation of variables method (SVM) hybrid

Ibrahim A. Abdallah

358

Bottom-simulating reflectors (BSRs) represent the base of the stability field for gas hydrates in shallow oceanic sediments. A simple conductive model is used to calculate surface heat flow through the Hikurangi and southwest Fiordland continental margins of New Zealand, based on the depths of BSRs. The results indicate mean uncorrected heat flows through the two regions of 37 ± 8

John Townend

1997-01-01

359

With the advent of lasers with very short pulse durations and their use in materials processing, the effect of thermal wave propagation velocity becomes important. Also, localized heating in laser-aided materials processing causes significant variations in the material properties. To account for these two effects, hyperbolic heat conduction is studied in this paper by considering all the thermophysical properties, except

A. Kar; C. L. Chan; J. Mazumder

1992-01-01

360

In this article, we investigate the thermal decomposition of a stockpile of reactive material undergoing a steady-state exothermic chemical reaction inside a long pipe with heat loss characteristics at its surface. It is assumed that the thermal conductivity (k) of the material varies exponentially with temperature and the pipe surface exchanges heat with the ambient following Newton's law of cooling.

O. D. Makinde

2012-01-01

361

Results are reported of a numerical analysis of conduction heat loss from a parabolic trough solar receiver with controlled pressure within the annular gap between the tubular absorber and the glass vacuum jacket. A direct simulation Monte Carlo (DSMC)model of rarefied gas within the annular gap is coupled to radiation heat transfer for directional- and spectral-dependent concentrated incident solar radiation.

Matthew Roesle; Philipp Good; Volkan Coskun; Aldo Steinfeld

2012-01-01

362

NASA Astrophysics Data System (ADS)

A self-similar solution for the propagation of a shock wave driven by a cylindrical piston moving according to exponential temporal law in a nonideal rotating gas with heat conduction and radiation heat fluxes is investigated. The density and angular velocity of the ambient medium are assumed to be constant. Heat conduction is expressed in terms of the Fourier law, and radiation is considered to be of diffusion type for an optically thick gray gas model. The thermal conductivity and absorption coefficient are assumed to vary with temperature and density. Similarity solutions are obtained, and the effects of variations in the heat transfer parameters and gas nonidealness on the flow variables in the region behind the shock are investigated.

Singh, K. K.; Nath, B.

2014-07-01

363

Due to their poor conductivity, latex (20--30% by weight of cement), methylcellulose (0.4--0.8% by weight of cement), and silica fume (15% by weight of cement) decreased the thermal conductivity of cement paste by up to 46%. In addition, these admixtures increased the specific heat of cement paste by up to 10%. The thermal conductivity decreased and the specific heat increased with increasing latex or methylcellulose content. Short carbon fibers (0.5--1.0% by weight of cement) either did not change or decreased the thermal conductivity of cement paste, such that the thermal conductivity decreased with increasing fiber content due to the increase in air void content. The fibers increased the specific heat due to the contribution of the fiber-matrix interface to vibration.

Fu, X.; Chung, D.D.L. [State Univ. of New York, Buffalo, NY (United States). Composite Materials Research Lab.] [State Univ. of New York, Buffalo, NY (United States). Composite Materials Research Lab.

1997-12-01

364

A steady-state solution for heat transfer from an isothermal, spherical magma chamber, with an imposed regional geothermal gradient far from the chamber, is developed. The extensive published heat-flow data set for Mount Hood, Oregon, is dominated by conductive heat transfer in the deeper parts of most drill holes and provides an ideal application of such a model. Magma-chamber volumes or depths needed to match the distribution of heat-flow data are larger or shallower than those inferred from geologic evidence.

Nathenson, Menuel; Tilling, Robert I.

1993-01-01

365

NASA Technical Reports Server (NTRS)

Reduced gravity does not significantly affect the thermal histories in the M551 specimen, even if molten metal flow pattern is different from that in terrestrial conditions. Thermal histories corresponding to terrestrial experimental conditions were calculated by use of the computer programs. Heat conduction through brazing alloy (M552 experiment) is improved in the Skylab conditions, because of the increased extent, rate and uniformity of braze spreading in space. Effects of reduced gravity on heat flow in the M553 specimen are insignificant, because convection effects appear instantaneously and conduction is a governing factor on the heat flow.

Muraki, T.; Masubuchi, K.

1974-01-01

366

The need for the engineering analysis of systems in which the transport of thermal energy occurs primarily through a conduction process is a common situation. For all but the simplest geometries and boundary conditions, analytic solutions to heat conduction problems are unavailable, thus forcing the analyst to call upon some type of approximate numerical procedure. A wide variety of numerical packages currently exist for such applications, ranging in sophistication from the large, general purpose, commercial codes, such as COMSOL, COSMOSWorks, ABAQUS and TSS to codes written by individuals for specific problem applications. The original purpose for developing the finite element code described here, COYOTE, was to bridge the gap between the complex commercial codes and the more simplistic, individual application programs. COYOTE was designed to treat most of the standard conduction problems of interest with a user-oriented input structure and format that was easily learned and remembered. Because of its architecture, the code has also proved useful for research in numerical algorithms and development of thermal analysis capabilities. This general philosophy has been retained in the current version of the program, COYOTE, Version 5.0, though the capabilities of the code have been significantly expanded. A major change in the code is its availability on parallel computer architectures and the increase in problem complexity and size that this implies. The present document describes the theoretical and numerical background for the COYOTE program. This volume is intended as a background document for the user's manual. Potential users of COYOTE are encouraged to become familiar with the present report and the simple example analyses reported in before using the program. The theoretical and numerical background for the finite element computer program, COYOTE, is presented in detail. COYOTE is designed for the multi-dimensional analysis of nonlinear heat conduction problems. A general description of the boundary value problems treated by the program is presented. The finite element formulation and the associated numerical methods used in COYOTE are also outlined. Instructions for use of the code are documented in SAND2010-0714.

Glass, Micheal W.; Hogan, Roy E., Jr.; Gartling, David K.

2010-03-01

367

NASA Astrophysics Data System (ADS)

Longitudinal heat conduction from surface to inside of solid material could be used to evaluate the subsurface defects. Considering that the skin depth of high frequency eddy current in metal is quite small, this paper proposed logarithmic analysis of eddy current thermography (ECT) to quantify the depth of subsurface defects. The proposed method was verified through numerical and experimental studies. In numerical study, ferromagnetic material and non-ferromagnetic material were both considered. Results showed that the temperature-time curve in the logarithm domain could be used to detect subsurface defects. Separation time was defined as the characteristic feature to measure the defect's depth based on their linear relationships. The thermograms reconstructed by logarithm of temperature can improve defect detectability.

Yang, Ruizhen; He, Yunze

2014-11-01

368

Response-coefficient method for heat-conduction transients with time-dependent inputs

NASA Technical Reports Server (NTRS)

A theoretical overview of the response coefficient method for heat conduction transients with time-dependent input forcing functions is presented with a number of illustrative applications. The method may be the most convenient and economical if the same problem is to be solved many times with different input-time histories or if the solution time is relatively long. The method is applicable to a wide variety of problems, including irregular geometries, position-dependent boundary conditions, position-dependent physical properties, and nonperiodic irregular input histories. Nonuniform internal energy generation rates within the structure can also be handled by the method. The area of interest is long-time solutions, in which initial condition is unimportant, and not the early transient period. The method can be applied to one dimensional problems in cartesian, cylindrical, and spherical coordinates as well as to two dimensional problems in cartesian and cylindrical coordinates.

Ceylan, Tamer

1993-01-01

369

Effect of the time window on the heat-conduction information filtering model

NASA Astrophysics Data System (ADS)

Recommendation systems have been proposed to filter out the potential tastes and preferences of the normal users online, however, the physics of the time window effect on the performance is missing, which is critical for saving the memory and decreasing the computation complexity. In this paper, by gradually expanding the time window, we investigate the impact of the time window on the heat-conduction information filtering model with ten similarity measures. The experimental results on the benchmark dataset Netflix indicate that by only using approximately 11.11% recent rating records, the accuracy could be improved by an average of 33.16% and the diversity could be improved by 30.62%. In addition, the recommendation performance on the dataset MovieLens could be preserved by only considering approximately 10.91% recent records. Under the circumstance of improving the recommendation performance, our discoveries possess significant practical value by largely reducing the computational time and shortening the data storage space.

Guo, Qiang; Song, Wen-Jun; Hou, Lei; Zhang, Yi-Lu; Liu, Jian-Guo

2014-05-01

370

NASA Technical Reports Server (NTRS)

The development of low conductivity and high temperature capable thermal barrier coatings requires advanced testing techniques that can accurately and effectively evaluate coating thermal conductivity under future high-performance and low-emission engine heat-flux conditions. In this paper, a unique steady-state CO2 laser (wavelength 10.6 microns) heat-flux approach is described for determining the thermal conductivity and conductivity deduced cyclic durability of ceramic thermal and environmental barrier coating systems at very high temperatures (up to 1700 C) under large thermal gradients. The thermal conductivity behavior of advanced thermal and environmental barrier coatings for metallic and Si-based ceramic matrix composite (CMC) component applications has also been investigated using the laser conductivity approach. The relationships between the lattice and radiation conductivities as a function of heat flux and thermal gradient at high temperatures have been examined for the ceramic coating systems. The steady-state laser heat-flux conductivity approach has been demonstrated as a viable means for the development and life prediction of advanced thermal barrier coatings for future turbine engine applications.

Zhu, Dong-Ming; Miller, Robert A.

2004-01-01

371

Steady-state heat conduction in multilayered composite plates and shells

NASA Technical Reports Server (NTRS)

A study is made of a predictor-corrector procedure for the accurate determination of the temperature and heat flux distributions in thick multilayered composite plates and shells. A linear through-the-thickness temperature distribution is used in the predictor phase. The functional dependence of temperature on the thickness coordinate is then calculated a posteriori and used in the corrector phase. Extensive numerical results are presented for linear steady-state heat conduction problems, showing the effects of variation in the geometric and lamination parameters on the accuracy of the thermal response predictions of the predictor-corrector approach. Both antisymmetrically laminated anisotropic plates and multilayered orthotropic cylinders are considered. The solutions are assumed to be periodic in the surface coordinates. For each problem the standard of comparison is taken to be the analytic three-dimensional solution based on treating each layer as a homogeneous anisotropic medium. The potential of the predictor-corrector approach for predicting the thermal response of multilayered plates and shells with complicated geometry is discussed.

Noor, A. K.; Burton, W. S.

1991-01-01

372

Shortened version: The fate of IS clouds embedded in a hot tenuous medium depends on whether the clouds suffer from evaporation or whether material condensates onto them. Analytical solutions for the rate of evaporative mass loss from an isolated spherical cloud embedded in a hot tenuous gas are deduced by Cowie & McKee (1977). In order to test the validity of the analytical results for more realistic IS conditions the full hydrodynamical equations must be treated. Therefore, 2D numerical simulations of the evolution of IS clouds %are performed with different internal density structures and surrounded by a hot plasma reservoir. Self-gravity, interstellar heating and cooling effects and heat conduction by electrons are added. Classical thermal conductivity of a fully ionized hydrogen plasma and saturated heat flux are considered. Using pure hydrodynamics and classical heat flux we can reproduce the analytical results. Heat flux saturation reduces the evaporation rate by one order of magnitude below the analytical value. The evolution changes totally for more realistic conditions when interstellar heating and cooling effects stabilize the self-gravity. Evaporation then turns into condensation, because the additional energy by heat conduction can be transported away from the interface and radiated off efficiently from the cloud's inner parts. I.e. that the saturated heat flux consideration is inevitable for IS clouds embedded in hot tenuous gas. Various consequences are discussed in the paper.

W. Vieser; G. Hensler

2007-09-05

373

NASA Astrophysics Data System (ADS)

For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current values of 1.0 to 1.5 would enhance their competitiveness with alternative technologies. In recent years, the most significant improvements in ZT have mainly been due to successful reduction of thermal conductivity. However, thermal conductivity is difficult to measure directly at high temperatures. Combined measurements of thermal diffusivity, specific heat, and mass density are a widely used alternative to direct measurement of thermal conductivity. In this work, thermal conductivity is shown to be the factor in the calculation of ZT with the greatest measurement uncertainty. The International Energy Agency (IEA) group, under the implementing agreement for Advanced Materials for Transportation (AMT), has conducted two international round-robins since 2009. This paper, part II of our report on the international round-robin testing of transport properties of bulk bismuth telluride, focuses on thermal diffusivity, specific heat, and thermal conductivity measurements.

Wang, Hsin; Porter, Wallace D.; Böttner, Harald; König, Jan; Chen, Lidong; Bai, Shengqiang; Tritt, Terry M.; Mayolet, Alex; Senawiratne, Jayantha; Smith, Charlene; Harris, Fred; Gilbert, Patricia; Sharp, Jeff; Lo, Jason; Kleinke, Holger; Kiss, Laszlo

2013-06-01

374

NASA Astrophysics Data System (ADS)

In this paper, we report that the thermal conductivity (TC) of heat transfer nanofluids containing Ni coated single wall carbon nanotube can be enhanced by applied magnetic field. A reasonable explanation for these interesting results is that Ni coated nanotubes form aligned chains under applied magnetic field, which improves thermal conductivity via increased contacts. On longer holding in magnetic field, the nanotubes gradually move and form large clumps of nanotubes, which eventually decreases the TC. When we reduce the magnetic field strength and maintain a smaller field right after TC reaches the maximum, the TC value can be kept longer compared to without magnetic field. We attribute gradual magnetic clumping to the gradual cause of the TC decrease in the magnetic field. We also found that the time to reach the maximum peak value of TC is increased as the applied magnetic field is reduced. Scanning electron microscopy images show that the Ni coated nantubes are aligned well under the influence of a magnetic field. Transmission electron microscopy images indicate that nickel remains attached onto the nanotubes after the magnetic field exposure.

Wright, Brian; Thomas, Dustin; Hong, Haiping; Groven, Lori; Puszynski, Jan; Duke, Edward; Ye, Xiangrong; Jin, Sungho

2007-10-01

375

Nanoparticle synergies in modifying thermal conductivity for heat exchanger in condensing boilers

NASA Astrophysics Data System (ADS)

The heat exchanger we are using for condensing boilers is mainly made from aluminum alloys and stainless steel. However, the metal is relatively expensive and corrosion together with maintenance is also a big problem. Therefore, we have developed a new design and material which contain carbon black, carbon nanotube, aluminum oxide and graphene as additives in polypropylene. When multiple types of particles can be melt blended simultaneously and synergies can be achieved, imparting particles to the nanocomposite, achieved much higher thermal conductivity rather than single additive. Here we show the flame retardant nanocomposite which can pass the UL-94-V0 vertical burning test, perform nice in Cone Calorimetry Test and has relatively good mechanical properties. SEM images of the blend show that the Carbon nanobute and other additives well dispersed within the polymer matrix which match our computational calculation for getting the percolation to achieve thermal conductivity around 1.5W/m.K rather than 0.23W/m.K as pure polypropylene.

Yang, Kai; He, Shan; Butcher, Thomas; Trojanowski, Rebecca; Sun, Ning; Gersappe, Dilip; Rafailovich, Miriam

2013-03-01

376

Belmont Hyperthermia Pump in the conduct of intra-operative heated chemotherapy.

Intra-operative heated chemotherapy (IOHC) has been performed in the Thoracic surgical department of Brigham and Women's Hospital (BWH, Boston, MA, USA) for over a decade. A "home-grown" system was developed for this purpose with limited improvements made to it through the years. This technology is used for neo-adjuvant therapy in the conduct of extra-pleural pneumonectomy and pleurectomy for treatment of mesothelioma. Improvements to the traditional BWH system were sought due to the hazardous nature of the chemotherapy solution and the relative complexity of the IOHC circuit. Belmont Instrument (Belmont Instrument Corporation, Billerica, MA, USA) applied their proprietary infusion/warming technology to develop the Belmont Hyperthermia Pump. The Hyperthermia Pump was designed to recirculate large volumes of fluid while maintaining perfusate temperatures up to 46oC at a flow rate of up to 750 ml/min. Approval from the FDA for clinical use of this device was granted June 2007. Parameters were defined and investigated to determine if the Hyperthermia Pump would meet or exceed the performance characteristics of the traditional BWH system. Our investigation resulted in the replacement of the traditional BWH circuit. The Belmont Hyperthermia Pump is a compact, easy to use, extremely safe means to deliver intra-operative hyperthermic chemotherapy in the conduct of surgical treatment of mesothelioma. PMID:19654155

Riley, W

2009-03-01

377

NASA Technical Reports Server (NTRS)

The thermal conductivity of electron beam-physical vapor deposited (EB-PVD) Zr02-8wt%Y2O3 thermal barrier coatings was determined by a steady-state heat flux laser technique. Thermal conductivity change kinetics of the EB-PVD ceramic coatings were also obtained in real time, at high temperatures, under the laser high heat flux, long term test conditions. The thermal conductivity increase due to micro-pore sintering and the decrease due to coating micro-delaminations in the EB-PVD coatings were evaluated for grooved and non-grooved EB-PVD coating systems under isothermal and thermal cycling conditions. The coating failure modes under the high heat flux test conditions were also investigated. The test technique provides a viable means for obtaining coating thermal conductivity data for use in design, development, and life prediction for engine applications.

Zhu, Dongming; Miller, Robert A.; Nagaraj, Ben A.; Bruce, Robert W.

2000-01-01

378

Earth's magnetic field is sustained by magnetohydrodynamic convection within the metallic liquid core. In a thermally advecting core, the fraction of heat available to drive the geodynamo is reduced by heat conducted along the core geotherm, which depends sensitively on the thermal conductivity of liquid iron and its alloys with candidate light elements. The thermal conductivity for Earth's core is very poorly constrained, with current estimates based on a set of scaling relations that were not previously tested at high pressures. We perform first-principles electronic structure computations to determine the thermal conductivity and electrical resistivity for Fe, Fe-Si, and Fe-O liquid alloys. Computed resistivity agrees very well with existing shock compression measurements and shows strong dependence on light element concentration and type. Thermal conductivity at pressure and temperature conditions characteristic of Earth's core is higher than previous extrapolations. Conductive heat flux near the core-mantle boundary is comparable to estimates of the total heat flux from the core but decreases with depth, so that thermally driven flow would be constrained to greater depths in the absence of an inner core. PMID:22375035

de Koker, Nico; Steinle-Neumann, Gerd; Vlcek, Vojtech

2012-03-13

379

Earth’s magnetic field is sustained by magnetohydrodynamic convection within the metallic liquid core. In a thermally advecting core, the fraction of heat available to drive the geodynamo is reduced by heat conducted along the core geotherm, which depends sensitively on the thermal conductivity of liquid iron and its alloys with candidate light elements. The thermal conductivity for Earth’s core is very poorly constrained, with current estimates based on a set of scaling relations that were not previously tested at high pressures. We perform first-principles electronic structure computations to determine the thermal conductivity and electrical resistivity for Fe, Fe–Si, and Fe–O liquid alloys. Computed resistivity agrees very well with existing shock compression measurements and shows strong dependence on light element concentration and type. Thermal conductivity at pressure and temperature conditions characteristic of Earth’s core is higher than previous extrapolations. Conductive heat flux near the core–mantle boundary is comparable to estimates of the total heat flux from the core but decreases with depth, so that thermally driven flow would be constrained to greater depths in the absence of an inner core. PMID:22375035

de Koker, Nico; Steinle-Neumann, Gerd; Vlcek, Vojtech

2012-01-01

380

Non-Fourier heat conduction model with dual phase lag wave-diffusion model was analyzed by using well-conditioned asymptotic wave evaluation (WCAWE) and finite element method (FEM). The non-Fourier heat conduction has been investigated where the maximum likelihood (ML) and Tikhonov regularization technique were used successfully to predict the accurate and stable temperature responses without the loss of initial nonlinear/high frequency response. To reduce the increased computational time by Tikhonov WCAWE using ML (TWCAWE-ML), another well-conditioned scheme, called mass effect (ME) T-WCAWE, is introduced. TWCAWE with ME (TWCAWE-ME) showed more stable and accurate temperature spectrum in comparison to asymptotic wave evaluation (AWE) and also partial Pade AWE without sacrificing the computational time. However, the TWCAWE-ML remains as the most stable and hence accurate model to analyze the fast transient thermal analysis of non-Fourier heat conduction model. PMID:25019096

Rana, Sohel; Kanesan, Jeevan; Reza, Ahmed Wasif; Ramiah, Harikrishnan

2014-01-01

381

This study aimed determination of proper amount of paraffin (n-docosane) absorbed into expanded graphite (EG) to obtain form-stable composite as phase change material (PCM), examination of the influence of EG addition on the thermal conductivity using transient hot-wire method and investigation of latent heat thermal energy storage (LHTES) characteristics of paraffin such as melting time, melting temperature and latent heat

Ahmet Sar?; Ali Karaipekli

2007-01-01

382

NASA Astrophysics Data System (ADS)

A mathematical model of data transmission from the site of self-warming in a dispersed system with distributed parameters is suggested which allows one to perform systematic calculations of the parameters of the process of heat propagation in a silo tower. The inverse heat conduction problem is solved allowing one, by using information signals on the current temperature of a granular bed, to promptly guard against the occurrence of local sites of self-warming under conditions of grain storage.

Shevtsov, A. A.; Pavlov, I. O.; Voronova, E. V.; Britikov, D. A.

2012-07-01

383

Steady-State and Transient Boundary Element Methods for Coupled Heat Conduction

NASA Technical Reports Server (NTRS)

Boundary element algorithms for the solution of steady-state and transient heat conduction are presented. The algorithms are designed for efficient coupling with computational fluid dynamic discretizations and feature piecewise linear elements with offset nodal points. The steady-state algorithm employs the fundamental solution approach; the integration kernels are computed analytically based on linear shape functions, linear elements, and variably offset nodal points. The analytic expressions for both singular and nonsingular integrands are presented. The transient algorithm employs the transient fundamental solution; the temporal integration is performed analytically and the nonsingular spatial integration is performed numerically using Gaussian quadrature. A series solution to the integration is derived for the instance of a singular integrand. The boundary-only character of the algorithm is maintained by integrating the influence coefficients from initial time. Numerical results are compared to analytical solutions to verify the current boundary element algorithms. The steady-state and transient algorithms are numerically shown to be second-order accurate in space and time, respectively.

Kontinos, Dean A.

1997-01-01

384

A lot of different approaches have been performed in the literature to estimate the surface heat flow on Venus. Estimates based on parameterized convection solutions resulted in values between 15 and 50 mW m-2, in contrast to global scaling from Earth, which results in a distinctively higher amount of heat loss (between ca. 60 and 70 mW m-2) as shown

J. J. Leitner; M. G. Firneis

2005-01-01

385

An experimental study was carried out to investigate the effects of inlet pressure, sample thickness, initial sample temperature, and temperature sensor location on the surface heat flux, surface temperature, and surface ultrafast cooling rate using stainless steel samples of diameter 27 mm and thickness (mm) 8.5, 13, 17.5, and 22, respectively. Inlet pressure was varied from 0.2 MPa to 1.8 MPa, while sample initial temperature varied from 600°C to 900°C. Beck's sequential function specification method was utilized to estimate surface heat flux and surface temperature. Inlet pressure has a positive effect on surface heat flux (SHF) within a critical value of pressure. Thickness of the sample affects the maximum achieved SHF negatively. Surface heat flux as high as 0.4024 MW/m(2) was estimated for a thickness of 8.5 mm. Insulation effects of vapor film become apparent in the sample initial temperature range of 900°C causing reduction in surface heat flux and cooling rate of the sample. A sensor location near to quenched surface is found to be a better choice to visualize the effects of spray parameters on surface heat flux and surface temperature. Cooling rate showed a profound increase for an inlet pressure of 0.8 MPa. PMID:24977219

Aamir, Muhammad; Liao, Qiang; Zhu, Xun; Aqeel-ur-Rehman; Wang, Hong; Zubair, Muhammad

2014-01-01

386

An experimental study was carried out to investigate the effects of inlet pressure, sample thickness, initial sample temperature, and temperature sensor location on the surface heat flux, surface temperature, and surface ultrafast cooling rate using stainless steel samples of diameter 27?mm and thickness (mm) 8.5, 13, 17.5, and 22, respectively. Inlet pressure was varied from 0.2?MPa to 1.8?MPa, while sample initial temperature varied from 600°C to 900°C. Beck's sequential function specification method was utilized to estimate surface heat flux and surface temperature. Inlet pressure has a positive effect on surface heat flux (SHF) within a critical value of pressure. Thickness of the sample affects the maximum achieved SHF negatively. Surface heat flux as high as 0.4024?MW/m2 was estimated for a thickness of 8.5?mm. Insulation effects of vapor film become apparent in the sample initial temperature range of 900°C causing reduction in surface heat flux and cooling rate of the sample. A sensor location near to quenched surface is found to be a better choice to visualize the effects of spray parameters on surface heat flux and surface temperature. Cooling rate showed a profound increase for an inlet pressure of 0.8?MPa. PMID:24977219

Aamir, Muhammad; Liao, Qiang; Zhu, Xun; Aqeel-ur-Rehman; Wang, Hong

2014-01-01

387

A numerical analysis of an adsorptive heat pump system with thermal wave heat regeneration is presented, using a two-dimensional model taking into account axial heat transfer in the circulating fluid and radial heat conduction in the adsorbent bed. The axial heat conduction in the adsorbent bed is neglected, allowing the two-dimensional model to be solved as a one-dimensional one. The

L. M. Sun; Y. Feng; M. Pons

1997-01-01

388

Yucca Mountain, Nevada has been designated as the nation's high-level radioactive waste repository and the U.S. Department of Energy has been approved to apply to the U.S. Nuclear Regulatory Commission for a license to construct a repository. Heat transfer in the Yucca Mountain Project (YMP) drift enclosures is an important aspect of repository waste emplacement. Canisters containing radioactive waste are to be emplaced in tunnels drilled 500 m below the ground surface. After repository closure, decaying heat is transferred from waste packages to the host rock by a combination of thermal radiation, natural convection and conduction heat transfer mechanism?. Current YMP mountain-scale and drift-scale numerical models often use a simplified porous medium code to model fluid and heat flow in the drift openings. To account for natural convection heat transfer, the thermal conductivity of the air was increased in the porous medium model. The equivalent thermal conductivity, defined as the ratio of total heat flow to conductive heat flow, used in the porous media models was based on horizontal concentric cylinders. Such modeling does not effectively capture turbulent natural convection in the open spaces as discussed by Webb et al. (2003) yet the approach is still widely used on the YMP project. In order to mechanistically model natural convection conditions in YMP drifts, the computational fluid dynamics (CFD) code FLUENT (Fluent, Incorporated, 2001) has been used to model natural convection heat transfer in the YMP emplacement drifts. A two-dimensional (2D) model representative of YMP geometry (e.g., includes waste package, drip shield, invert and drift wall) has been developed and numerical simulations made (Francis et al., 2003). Using CFD simulation results for both natural convection and conduction-only heat transfer in a single phase, single component fluid, equivalent thermal conductivities have been calculated for different Rayleigh numbers. Correlation equations for equivalent thermal conductivity as a function of Rayleigh number were developed for the Yucca Mountain geometry and comparisons were made to experimental data and correlations found in the literature on natural convection in horizontal concentric cylinders, a geometry similar to YMP. The objective of this work is to compare the results of CFD natural convection simulations and conduction-only calculations that used the equivalent thermal conductivity to represent heat transfer by turbulent natural convection. The FLUENT code was used for both simulations with heat generation boundary condition at the waste package and constant temperature boundary condition 5 meters into the host rock formation. Comparisons are made of temperature contours in the drift air and temperature profiles at surfaces of the different engineered components using the two approaches. The results show that for the two-dimensional YMP geometry considered, the average surface temperatures of the CFD natural convection and conduction-only using the equivalent thermal conductivity are similar and the maximum local temperature differences for the different surfaces were within two 2 C. The differences in temperature profiles reflect the use of a constant equivalent thermal conductivity. The effect of the differences is discussed.

T. Hadgu; S. Webb; M. Itamura

2004-02-12

389

Unsteady heat conduction in the soil layers above underground repository for spent nuclear fuel

Due to radioactivity of spent nuclear fuel, a repository is expected to act as a heat source of exponentially decreasing intensity over hundreds of years. In case of underground emplacement of such a heat source, the temperature changes in the soil layers surrounding the heat source may have important implications such as evaporation of the water contained in the soil

N. K. Talukder

2000-01-01

390

In the present study, the effect of presence and type of reinforcing particulates (C and SiC) on the electrical conductivity of 99.5% non heat treatable aluminum was investigated. The synthesis of the unreinforced and reinforced samples was carried out using disintegrated melt deposition route. Microstructural characterization studies conducted on the unreinforced and reinforced samples revealed the presence of columnar-equiaxed microstructure

M. Gupta; G. Karunasiri; M. O. Lai

1996-01-01

391

NASA Technical Reports Server (NTRS)

The solution of the inverse problem of nonsteady heat conduction is discussed, based on finding the coefficient of the heat conduction and the coefficient of specific volumetric heat capacity. These findings are included in the equation used for the electrical model of this phenomenon.

Kozdoba, L. A.; Krivoshei, F. A.

1985-01-01

392

The material used in this study was a carbon-carbon fiber composite manufactured from precursor yarn and petroleum based pitch through a process of repetitive densification of a woven preform. The resultant high temperature-high strength material exhibits relatively high thermal conductivity and is thus of interest to the fusion energy, plasma materials interactions (PMI) and plasma facing components (PFC) communities. Carbon-carbon fiber composite manufacture involves two distinct processes, preform weaving and component densification. In this study three samples were subjected to an additional heat treatment of 2550, 2750 or 3000{degree}C at Oak Ridge National Laboratory (ORNL) subsequent to their fourth graphitization at 2400{degree}C. It should be noted that no effort was made to optimize the composite for thermal conductivity, but rather only to provide a material with which to evaluate the effect of the final heat treatment temperature on the thermal conductivity. The fiber is the primary source of heat conduction in the composite. Consequently, increasing the fiber volume fraction, and/or the fiber thermal conductivity is expected to increase the composite thermal conductivity. 3 refs., 1 fig.

Dinwiddie, R.B.; Burchell, T.D. (Oak Ridge National Lab., TN (USA)); Baker, C.F. (Fiber Materials, Inc., Biddeford, ME (USA))

1991-01-01

393

On the stability of the exact solutions of the dual-phase lagging model of heat conduction.

The dual-phase lagging (DPL) model has been considered as one of the most promising theoretical approaches to generalize the classical Fourier law for heat conduction involving short time and space scales. Its applicability, potential, equivalences, and possible drawbacks have been discussed in the current literature. In this study, the implications of solving the exact DPL model of heat conduction in a three-dimensional bounded domain solution are explored. Based on the principle of causality, it is shown that the temperature gradient must be always the cause and the heat flux must be the effect in the process of heat transfer under the dual-phase model. This fact establishes explicitly that the single- and DPL models with different physical origins are mathematically equivalent. In addition, taking into account the properties of the Lambert W function and by requiring that the temperature remains stable, in such a way that it does not go to infinity when the time increases, it is shown that the DPL model in its exact form cannot provide a general description of the heat conduction phenomena. PMID:21711850

Ordonez-Miranda, Jose; Alvarado-Gil, Juan Jose

2011-01-01

394

NASA Technical Reports Server (NTRS)

A computer program (Program SPHERE) solving the inhomogeneous equation of heat conduction with radiation boundary condition on a thermally homogeneous sphere is described. The source terms are taken to be exponential functions of the time. Thermal properties are independent of temperature. The solutions are appropriate to studying certain classes of planetary thermal history. Special application to the moon is discussed.

Conel, J. E.

1975-01-01

395

A finite-dlfference method is presented for solving threedimensional ; transient heat conduction problems. The method is a modification of the method ; of Douglas and Rachford which achieves the higher-order accuracy of a Crank-; Nicholson formulation while preserving the advantages of the Douglas-Rachford ; method: unconditional stability and simplicity of solving the equations at each ; time level. Although the

P. L. T. Brian; P. L. T

1961-01-01

396

The initial value problem associated with the equations of motion for isotropic Newtonian fluids is investigated. The fluids are compressible, viscous and heat-conductive. It is proved that there exists a unique global solution in time, for the small initial data, and the solution has the decay rate of (1 - t) to 3\\/4 power as t approaches positive infinity. The

Akitaka Matsumura; Takaaki Nishida

1979-01-01

397

The equations of motion of compressible viscous and heat-conductive fluids are investigated for initial boundary value problems on the half space and on the exterior domain of any bounded region. The global solution in time is proved to exist uniquely and approach the stationary state ast?8, provided the prescribed initial data and the external force are sufficiently small.

Akitaka Matsumura; Takaaki Nishida

1983-01-01

398

Heat stress is associated with increased fatigue perception and decrements in function for individuals with multiple sclerosis (MS). Similarly, healthy individuals experience decrements in exercise performance during hyperthermia. Alterations in central nervous system (CNS) function during hyperthermia include reduced voluntary activation of muscle and increased effort perception. The purpose of this investigation was to test the hypothesis that passive heat exposure in MS patients will produce increased subjective fatigue and impairments in physiological measures of central conduction and cortical excitability compared with healthy individuals. Eleven healthy individuals and 11 MS patients completed a series of transcranial magnetic stimulation studies to examine central conduction and cortical excitability under thermoneutral and heat-stressed (HS) conditions at rest and after a fatiguing thumb abduction task. Passive heat stress resulted in significantly greater fatigue perception and impairments in force production in MS patients. Central motor conduction time was significantly shorter during HS in controls; however, in MS patients normal increases in conduction velocity with increased temperature were not observed centrally. MS patients also exhibited decreased cortical excitability during HS, evidenced by significant increases in resting motor threshold, decreased MEP amplitude, and decreased recruitment curve slope. Both groups exhibited postexercise depression of MEP amplitude, but the magnitude of these decrements was amplified in MS patients during HS. Taken together, these results suggest that CNS pathology in MS patients played a substantial role in reducing cortical excitability during HS. PMID:23599395

White, Andrea T; Vanhaitsma, Timothy A; Vener, Jamie; Davis, Scott L

2013-06-15

399

Nonhomogeneous materials, such as functionally gradient materials (FGM), have special characteristics due to arbitrarily distributed and continuously varied material properties. For such nonhomogeneous materials, the heat conduction equation is presented in a nonlinear form. In this paper, the temperature solution for such a nonlinear system is formulated approximately, and the solution of the integral form of nonuniform thermal material constants

Y. Tanigawa; T. Akai; R. Kawamura; N. Oka

1996-01-01

400

Heat stress is associated with increased fatigue perception and decrements in function for individuals with multiple sclerosis (MS). Similarly, healthy individuals experience decrements in exercise performance during hyperthermia. Alterations in central nervous system (CNS) function during hyperthermia include reduced voluntary activation of muscle and increased effort perception. The purpose of this investigation was to test the hypothesis that passive heat exposure in MS patients will produce increased subjective fatigue and impairments in physiological measures of central conduction and cortical excitability compared with healthy individuals. Eleven healthy individuals and 11 MS patients completed a series of transcranial magnetic stimulation studies to examine central conduction and cortical excitability under thermoneutral and heat-stressed (HS) conditions at rest and after a fatiguing thumb abduction task. Passive heat stress resulted in significantly greater fatigue perception and impairments in force production in MS patients. Central motor conduction time was significantly shorter during HS in controls; however, in MS patients normal increases in conduction velocity with increased temperature were not observed centrally. MS patients also exhibited decreased cortical excitability during HS, evidenced by significant increases in resting motor threshold, decreased MEP amplitude, and decreased recruitment curve slope. Both groups exhibited postexercise depression of MEP amplitude, but the magnitude of these decrements was amplified in MS patients during HS. Taken together, these results suggest that CNS pathology in MS patients played a substantial role in reducing cortical excitability during HS. PMID:23599395

VanHaitsma, Timothy A.; Vener, Jamie; Davis, Scott L.

2013-01-01

401

The design and use of a marine heat probe with capability for measuring thermal conductivity insitu with high accuracy, and providing digital acoustic transmission of data to the ship, is described. The instrument employs the ‘violin bow’ strength member and parallel sensor string configuration suggested by C. R. B. Lister. Several hundred measurements have been made in the deep ocean

R. D. Hyndman; E. E. Davis; J. A. Wright

1979-01-01

402

This paper develops a parallel domain decomposition Laplace transform BEM algorithm for the solution of large-scale transient heat conduction problems. In order to tackle large problems the original domain is decomposed into a number of sub-domains, and a Laplace transform method is utilized to avoid time marching. A procedure is described which provides a good initial guess for the domain

Kevin Erhart; Eduardo Divo; Alain J. Kassab

2006-01-01

403

In this paper, we address concerns which were raised with respect to the sifting property of the forcing function D which is crucial in deriving an integral equation for heat conduction in non-homogeneous media. The error in the sifting property (which we neglected in our previous papers) is expanded in a series which leads to evaluation of the error in

Eduardo Divo; Alain J. Kassab

1998-01-01

404

Thermal conductivity of a highly porous carbon\\/carbon composite, known as carbon bonded carbon fiber (CBCF) and used as thermal insulation, was measured and related to the structure investigated by optical microscopy, x-ray diffraction and Raman spectroscopy. It was found that halogen purification of CBCF, that involves heat treatment in chlorine atmosphere, did not result in a greater extent of structural

R. I. Baxter; N. Iwashita; Y. Sawada

2000-01-01

405

NASA Astrophysics Data System (ADS)

Consideration is given to the problem of heat conduction in a thick wall exposed to a constant radiative flux density on one face with convective and radiative boundary conditions. The equation of heat conduction within the wall with the appropriate boundary conditions taking into account the three most common regimes of convective flow is solved numerically using a second-order implicit finite difference scheme and an alternating direction method. It is found that the effects of longitudinal convection remain constant for wall height/thickness ratios greater than 3, allowing the problem to be reduced one depending on five parameters. Results may be used in the optimization of vertical solar heat collection and storage walls.

Yguel, F.; Peube, J.-L.

1981-03-01

406

NASA Technical Reports Server (NTRS)

A steady-state laser heat flux technique has been developed at the NASA Glenn Research Center at Lewis Field to obtain critical thermal conductivity data of ceramic thermal barrier coatings under the temperature and thermal gradients that are realistically expected to be encountered in advanced engine systems. In this study, thermal conductivity change kinetics of a plasma-sprayed, 254-mm-thick ZrO2-8 wt % Y2O3 ceramic coating were obtained at high temperatures. During the testing, the temperature gradients across the coating system were carefully measured by the surface and back pyrometers and an embedded miniature thermocouple in the substrate. The actual heat flux passing through the coating system was determined from the metal substrate temperature drop (measured by the embedded miniature thermocouple and the back pyrometer) combined with one-dimensional heat transfer models.

Zhu, Dongming; Miller, Robert A.

2000-01-01

407

Unsteady heat conduction in the soil layers above underground repository for spent nuclear fuel

Due to radioactivity of spent nuclear fuel, a repository is expected to act as a heat source of exponentially decreasing\\u000a intensity over hundreds of years. In case of underground emplacement of such a heat source, the temperature changes in the\\u000a soil layers surrounding the heat source may have important implications such as evaporation of the water contained in the\\u000a soil

N. K. Talukder

2000-01-01

408

NASA Astrophysics Data System (ADS)

Accurate knowledge of thermophysical properties is needed to predict and optimize the thermal performance of microsystems. Thermal conductivity is experimentally determined by measuring quantities such as voltage or temperature and then inferring a thermal conductivity from a thermal model. Thermal models used for data analysis contain inherent assumptions, and the resultant thermal conductivity value is sensitive to how well the actual experimental conditions match the model assumptions. In this paper, a modified data analysis procedure for the steady state Joule heating technique is presented that accounts for bond pad effects including thermal resistance, electrical resistance, and Joule heating. This new data analysis method is used to determine the thermal conductivity of polycrystalline silicon (polysilicon) microbridges fabricated using the Sandia National Laboratories SUMMiT V™ micromachining process over the temperature range of 77-350 K, with the value at 300 K being 71.7 ± 1.5 W/(m K). It is shown that making measurements on beams of multiple lengths is useful, if not essential, for inferring the correct thermal conductivity from steady state Joule heating measurements.

Sayer, Robert A.; Piekos, Edward S.; Phinney, Leslie M.

2012-12-01

409

This paper utilizes non-Fourier two-temperature heat conduction model to investigate the temperature field in nanometer-sized thin films irradiated by an ultrashort-pulse laser. Ultrashort-pulse laser processing for nanometer-sized devices is usually applied in MEMS and nanotechnology. For ultrashort-pulse laser interaction with metals, the two-temperature model was proposed to describe the heat transport in metals due to a substantial nonequilibrium between the electron and lattice temperature. For heat conduction in nanoscale devices, Fourier law is inadequate for describing the heat conduction in nanoscale due to the boundary scattering and the finite relaxation time of heat carriers. Therefore, in this work, the Non-Fourier two-temperature heat conduction model used to analyze ultrashort-pulse laser processing of nanoscale metal film. The result obtained from non-Fourier heat conduction equations is compared with the available experimental data. The parametric effects are also discussed. PMID:24758069

Ho, Ching-Yen; Wen, Mao-Yu; Chen, Bor-Chyuan; Tsai, Yu-Hsiang

2014-07-01

410

Method for processing an article comprising mixed conducting metal oxide material. The method comprises contacting the article with an oxygen-containing gas and either reducing the temperature of the oxygen-containing gas during a cooling period or increasing the temperature of the oxygen-containing gas during a heating period; during the cooling period, reducing the oxygen activity in the oxygen-containing gas during at least a portion of the cooling period and increasing the rate at which the temperature of the oxygen-containing gas is reduced during at least a portion of the cooling period; and during the heating period, increasing the oxygen activity in the oxygen-containing gas during at least a portion of the heating period and decreasing the rate at which the temperature of the oxygen-containing gas is increased during at least a portion of the heating period.

Carolan, Michael Francis (Allentown, PA); Bernhart, John Charles (Fleetwood, PA)

2012-08-21

411

NASA Technical Reports Server (NTRS)

A variable-conductance heat-pipe system (VCHPS) with methanol as the working fluid and a nitrogen and helium mixture as the control gas was used for the thermal control of a 200 W RF traveling wave tube of the Communication Technology Satellite. Three stainless steel heat pipes (one redundant) and an aluminum radiator were designed to transfer 196 watts for an evaporator temperature of 50 C. The system has operated for three years with no noticeable change in performance. On four occasions the heat pipes apparently deprimed. A short time after reducing the tube power, the heat pipes reprimed and the system continued to operate normally. The description, qualification testing, and orbit data of the VCHPS are presented.

Gedeon, L.

1979-01-01

412

NASA Astrophysics Data System (ADS)

We report thermal conductivities, thermal diffusivities, and volumetric heat capacities determined by a transient plane heat source method for four whole-round core samples obtained by the Japan Trench Fast Drilling Project/Integrated Ocean Drilling Program Expedition 343. These thermal properties are necessary for the interpretation of a temperature anomaly detected in the vicinity of the plate boundary fault that ruptured during the 2011 Tohoku-Oki earthquake and other thermal processes observed within the Japan Trench Fast Drilling Project temperature observatory. Results of measured thermal conductivities are consistent with those independently measured using a transient line source method and a divided bar technique. Our measurements indicate no significant anisotropy in either thermal conductivity or thermal diffusivity.

Lin, Weiren; Fulton, Patrick M.; Harris, Robert N.; Tadai, Osamu; Matsubayashi, Osamu; Tanikawa, Wataru; Kinoshita, Masataka

2014-12-01

413

In semi-solid die-casting, a metallic billet is first heated in an induction furnace until it reaches a semi-solid state (partially liquid and partially solid). Then, it is injected into a die and kept there until it is solidified. Subsequently, the die opens, the part is ejected and the cycle starts again. The liquid-solid fraction and its spatial distribution within the

A. Bendada; C. Q. Zheng; N. Nardini

2004-01-01

414

NSDL National Science Digital Library

Describes main features of students' thinking about heat and temperature (developed before formal science teaching) and results of a study that shows that many notions about heat/temperature used by younger children are still apparent in the thinking of older students. The study involved interviews with 84 students in three age groups.

Clough, Elizabeth; Driver, Rosalind

2005-11-02

415

Geothermal setting and simple heat conduction models for the Long Valley caldera

Heat flow and heat production measurements have been made in the vicinity of Long Valley from 0-30 km from the rim of the caldera and up to 30 km on either side of the boundary of the Basin and Range province at the eastern scarp of the Sierra Nevada. The data show no conspicuous effect of the province transition, possibly

Arthur H. Lachenbruch; J. H. Sass; Robert J. Munroe; T. H. Jr. Moses

1976-01-01

416

Rigorous thermodynamic treatment of heat generation and conduction in semiconductor device modeling

Not only in power electronics but in particular in the field of VLSI and ULSI, the influence of self-heating on the performance of a semiconductor device proves to be more and more crucial as the power density dissipated within the device increases in consequence of en- hanced functional integration. Device modeling allows for such self- heating effects by the coupled

Gerhard K. M. Wachutka

1990-01-01

417

ERIC Educational Resources Information Center

Describes main features of students' thinking about heat and temperature (developed before formal science teaching) and results of a study that shows that many notions about heat/temperature used by younger children are still apparent in the thinking of older students. The study involved interviews with 84 students in three age groups. (JN)

Clough, Elizabeth Engel; Driver, Rosalind

1985-01-01

418

Local thermal equilibrium refers to the state in which a single temperature can be used to describe a heat transfer process in a multiphase system. When this condition occurs, a one-equation model can be used and the analysis of the heat transfer process is greatly simplified. In this paper we first develop the constraints that must be satisfied in order

Stephen Whitaker

1995-01-01

419

Measuring the Thermal Conductive Property of Protective Fabrics to Radiant Heat Exposure

A novel experimental apparatus called thermal simulating box is designed to evaluate the heat transmission of protective fabrics subject to radiation\\/ convection heat flux representative of typical high temperature occupational environments. The cold side of the test sample is maintained around human body skin temperature as high as 36°C, however, the hot side was exposed to dry hot air. An

Zhu Fanglong; Zhang Weiyuan

2007-01-01

420

Effect of structural conduction and heat loss on combustion in micro-channels

This paper presents a simple analytical model for the effects of heat exchange within the structure of a micro-channel combustor, and heat loss from the structure to the environment. This is accomplished by extending reasoning similar to that employed by Mallard and Le Chatelier in their thermal theory for flame propagation. The model is used to identify some of the

T. T. Leach; C. P. Cadou; G. S. Jackson

2006-01-01

421

Design and testing of a passive, feedback-controlled, variable conductance heat pipe

NASA Technical Reports Server (NTRS)

A passive feedback system, which stabilizes the heat source temperature (T sub s) of a gas loaded heat pipe, was designed and tested. The control of T sub s is accomplished by an auxiliary liquid that senses the heat source and actuates a metal bellows system due to the liquid's thermal expansion. The movement of the bellows varies the gas reservoir volume and leads to a corresponding change of the condensation area of the heat pipe. With methanol as the heat pipe working fluid and perfluoro-n-pentane as the auxiliary liquid, the control capability was found to be T sub s = 31.5 + or - 1.5 C in a power range from 3 to 30 W, compared to T sub s = 33 + or - 3 C with methanol as auxiliary liquid. The change in T sub s was 35 + or - 5.5 C with the bellows held in the closed position.

Schlitt, K. R.

1973-01-01

422

Construction and testing of a gas-loaded, passive-control, variable-conductance heat pipe

NASA Technical Reports Server (NTRS)

A methanol heat pipe using nitrogen gas for temperature control has been constructed and tested. The system was run over a power ratio of 15 (2 to 30 watts) with the heat source near ambient temperature and with the heat sink at a nominal value of 32 F. Control was obtained with a metal bellows gas reservoir which was actuated by an internal liquid-filled bellows. The liquid bellows was pressurized by expanding liquid methanol which was contained in an auxiliary reservoir in the evaporator heater block. It was demonstrated that the temperature variation of the heat source was reduced from 36 F for the heat pipe with no control to 7 F with the actuated bellows control.

Depew, C. A.; Sauerbrey, W. J.; Benson, B. A.

1973-01-01

423

-conductance (highly insulating) windows which incorporate very low conductance glazings. Developing low Introduction Low U-value (highly insulating) windows require low-conductance frames. Design and development and radiation through hollow cavities within a frame (typically extruded vinyl, fiberglass, or alu

424

This paper presents a thermal analysis and experimental validation of natural convective heat transfer of a high-brightness light-emitting diode (LED) package assembly. The substrate materials used in the LED package assembly were filled and doped using boron nitride (BN) filler. The thermal conductivity of the BN-filled substrate was measured. The temperature distribution and heat flow of the LED package were assessed by thermal profile measurement using an infrared (IR) camera and thermocouples. In addition, the heat transfer process of the LED package assembly in natural convection was also simulated using the computational fluid dynamics method. The optical performance of the LED package was monitored and investigated with various filler contents. The heat conduction mechanism in the substrate was analyzed. IR thermogram showed that the BN-doped substrate could effectively lower the surface temperature of the LED package by 21.5°C compared with the traditional FR4 substrate. According to the IESNA LM 80 lifetime testing method, reduction in LED temperature can prolong the LED's lifetime by 19,000 h. The optical performance of the LED package assembly was also found to be improved significantly in lighting power by 10%. As a result, the overall heat dissipation capability of the LED package to the surrounding is enhanced, which improves the LED's efficacy. PMID:24513891

Yung, K C; Liem, H; Choy, H S

2013-12-10

425

Temperature histories obtained from transient heat-conduction theory are applicable to most dikes despite potential complicating effects related to magma flow during emplacement, groundwater circulation, and metamorphic reaction during cooling. Here. machine-independent FORTRAN 77 programs are presented to calculate temperatures in and around dikes as they cool conductively. Analytical solutions can treat thermal-property contrasts between the dike and host rocks, but cannot address the release of magmatic heat of crystallization after the early stages of cooling or the appreciable temperature dependence of thermal conductivity and diffusivity displayed by most rock types. Numerical solutions can incorporate these additional factors. The heat of crystallization can raise the initial temperature at the dike contact, ??c1, about 100??C above that which would be estimated if it were neglected, and can decrease the rate at which the front of solidified magma moves to the dike center by a factor of as much as three. Thermal conductivity and diffusivity of rocks increase with decreasing temperature and, at low temperatures, these properties increase more if the rocks are saturated with water. Models that treat these temperature dependencies yield estimates of ??c1 that are as much as 75??C beneath those which would be predicted if they were neglected. ?? 1988.

Delaney, P.T.

1988-01-01

426

NASA Astrophysics Data System (ADS)

The present paper deals with the determination of the displacement and thermal stresses in a thin circular plate defined as 0 ? r ? b, 0 ? z ? h under a steady temperature field, due to a constant rate of heat generation within it. A thin circular plate is insulated at the fixed circular boundary ( r = b), and the remaining boundary surfaces ( z = 0, z = h) are kept at zero temperature. The governing heat conduction equation has been solved by using an integral transform technique. The results are obtained in series form in terms of modified Bessel functions. The results for displacement and stresses have been computed numerically and are illustrated graphically.

Deshmukh, K. C.; Warbhe, S. D.; Kulkarni, V. S.

2009-10-01

427

Some aspects of the computer simulation of conduction heat transfer and phase change processes

Various aspects of phase change processes in materials are discussd including computer modeling, validation of results and sensitivity. In addition, the possible incorporation of cognitive activities in computational heat transfer is examined.

Solomon, A. D.

1982-04-01

428

An experimental study of conductive heating using a concentric double-electrode applicator

With hyperthermia for treatment of superficial tumors in mind, a prototype applicator with two electrodes arranged concentrically\\u000a on a disk was designed for efficient local heating, and a basic heating test was carried out. Frequencies as low as 200 kHz\\u000a were used in order to simplify the configuration of the power device. The applicator consists of two electrodes, a circular

Takashi Tanaka; Tadaoki Morimoto; Yohsuke Kinouchi; Tadamitsu Iritani; Yasumasa Monden

1995-01-01

429

Measurements of Terahertz Electrical Conductivity of Intense Laser-Heated Dense Aluminum Plasmas

We report the electrical conductivity of laser-produced warm dense aluminum plasmas measured using single-shot ultrafast terahertz (THz) frequency spectroscopy. In contrast with experiments performed at optical frequencies, measurements based upon THz probe reflectivity directly determine a quasi-dc electrical conductivity, and therefore the analysis does not require a free-electron Drude model based extrapolation to recover the near zero frequency conductivity. In

K. Y. Kim; B. Yellampalle; J. H. Glownia; A. J. Taylor; G. Rodriguez

2008-01-01

430

NASA Technical Reports Server (NTRS)

Solutions are presented for the conduction of beat through a semi-infinite gas medium having a uniform initial temperature and a constant boundary temperature. The coefficients of thermal conductivity and diffusivity are treated as variables, and the solutions are extended to the case of air at temperatures where oxygen dissociation occurs. These solutions are used together with shock-tube measurements to evaluate the integral of thermal conductivity for air as a function of temperature.

Hansen, C. Frederick; Early, Richard A.; Alzofon, Frederick E.; Witteborn, Fred C.

1959-01-01

431

Non-adiabatic radial-flow reactor for styrene production

A non-adiabatic radial reactor is proposed to carry out the dehydrogenation of ethylbenzene to styrene. Radial flow and continuous heating (using superheated steam) are the main features of the new design. Steam used as heating medium flows through tubes, which are radially installed in the catalyst bed. By means of steady-state simulations, this new design has been compared with two

A. A. Savoretti; D. O. Borio; V. Bucalá; J. A. Porras

1999-01-01

432

Heat conduction in metal-filled polymers - The role of particle size, shape, and orientation

NASA Technical Reports Server (NTRS)

This paper presents a new type of analysis for predicting the thermal conductivity of disperse composites from the properties of the component phases and elementary characterizations of particle shapes and orientation. This analysis successfully predicted the sensitivity to particle shape which was confirmed by experiments also reported in this paper. These results suggest that highly elongated particles may be used to achieve dramatic modifications of thermal conductivity and the analysis presented here may be a useful tool in the design or development of disperse composites of specific thermal conductivity. The analysis may also apply to other properties such as electrical conductivity or magnetic permeability.

Hansen, D.; Tomkiewicz, R.

1975-01-01

433

NASA Astrophysics Data System (ADS)

A modified pulse-heating method is proposed to improve the accuracy of measurement of the hemispherical total emissivity, specific heat capacity, and electrical resistivity of electrically conductive materials at high temperatures. The proposed method is based on the analysis of a series of rapid resistive self-heating experiments on a sample heated at different temperature rates. The method is used to measure the three properties of the IG-110 grade of isotropic graphite at temperatures from 850 to 1800 K. The problem of the extrinsic heating-rate effect, which reduces the accuracy of the measurements, is successfully mitigated by compensating for the generally neglected experimental error associated with the electrical measurands (current and voltage). The results obtained by the proposed method can be validated by the linearity of measured quantities used in the property determinations. The results are in reasonably good agreement with previously published data, which demonstrate the suitability of the proposed method, in particular, to the resistivity and total emissivity measurements. An interesting result is the existence of a minimum in the emissivity of the isotropic graphite at around 1120 K, consistent with the electrical resistivity results.

Watanabe, Hiromichi; Yamashita, Yuichiro

2012-01-01

434

A modified pulse-heating method is proposed to improve the accuracy of measurement of the hemispherical total emissivity, specific heat capacity, and electrical resistivity of electrically conductive materials at high temperatures. The proposed method is based on the analysis of a series of rapid resistive self-heating experiments on a sample heated at different temperature rates. The method is used to measure the three properties of the IG-110 grade of isotropic graphite at temperatures from 850 to 1800 K. The problem of the extrinsic heating-rate effect, which reduces the accuracy of the measurements, is successfully mitigated by compensating for the generally neglected experimental error associated with the electrical measurands (current and voltage). The results obtained by the proposed method can be validated by the linearity of measured quantities used in the property determinations. The results are in reasonably good agreement with previously published data, which demonstrate the suitability of the proposed method, in particular, to the resistivity and total emissivity measurements. An interesting result is the existence of a minimum in the emissivity of the isotropic graphite at around 1120 K, consistent with the electrical resistivity results. PMID:22299976

Watanabe, Hiromichi; Yamashita, Yuichiro

2012-01-01

435

NASA Technical Reports Server (NTRS)

The design and testing of a heat pipe for spacecraft application is presented. The application in mind calls for heat loads up to 20 watts, a set-point temperature of 294K, and a sink that varies from -220K to nearly as high as the set-point. The overall heat pipe length is 137 cm. Two basically different mechanisms of achieving variable conductance in the pipe by vapor-flow throttling were studied. In one, the thermal resistance between the heat source and sink is due to a saturation-temperature drop corresponding to the vapor-pressure drop developed across the valve. In the other, the pressure difference across the valve induces capillary groove and wick dry out in an evaporation region, and thus results in an increased thermal resistance. This mechanism was selected for fabrication and testing. The pipe is a stainless-steel/methanol two-heat-pipe system. Results are presented and discussed. Engineering drawings and specifications of the pipe are shown.

Eninger, J. E.; Fleischman, G. L.; Luedke, E. E.

1975-01-01

436

NASA Astrophysics Data System (ADS)

An improved technique employing the photopyroelectric effect to measure thermal conductivity and heat capacity simultaneously near solid state phase transitions is reported. A calibration procedure adaptable to the use of a pyroelectric detector on a thermally thick backing medium is described in detail. A quantitative comparison of the predictions of the theory with experimental results on selected known samples is used to test the applicability of the method as a practical technique. The variations of the thermal diffusivity (?s), thermal effusivity (es), thermal conductivity (Ks) and heat capacity (cps) near the para-ferroelectric phase transition in single-crystalline triglycine sulphate at 49.4 °C cut along various axes are reported and compared with available experimental data. The method can be adapted to the measurement of these parameters during any kind of phase transition in solids, the only limitation being the temperature range over which the sensitivity of the pyroelectric detector remains sufficiently high.

Preethy Menon, C.; Philip, J.

2000-12-01

437

A semi-implicit coupling technique (treating only the fluid temperature in the energy source term implicitly) of fluid heat-transfer to conduction slabs is presently used in TRAC-PF1. In this study, a fully implicit coupling scheme between the flow field and conduction slab for the one-dimensional capability of TRAC-PF1 has been developed. The new methods treat the heat-transfer coefficient and wall temperature in the energy source term of both the convection and the conduction equation implicitly. In order to test the accuracy of the standard TRAC coupling method and the new methods used in TRAC-PF1, a series of simple tube experiments were modeled with TRAC-PF1 version 3.9B. Additional studies showed the current TRAC-PF1 convergence variables (pressure fraction change and temperature change) and the current convergence criteria are not appropriate for obtaining an accurate result. Use of these values would produce non-physical double values or would adversely affect results in the reflood calculation. Another study also had been done to determine the importance of each HTC variable on computational accuracy and speed by using the non-linear oterative method. It is found that the heat-transfer correlations have a strong dependency on the local void fraction rather than on fluid velocity, fluid temperature, and wall surface temperature in the film boiling heat-transfer regime. At the beginning of a cooldown transient, the old time void fraction is always higher than the new time void fraction in the same time step. The old time void fraction evaluates a lower heat-transfer coefficient for that cell and initiates cooldown later and more slowly. This then leads to a longer quench time and lowers the fluid temperature and the wall temperature plateau for the downstream control volumes.

Wang, Lang Chen.

1990-01-01

438

Thick deposits of evaporitic hydrates can markedly influence heat flow due to the anomalous low thermal conductivity of hydrated salts and the high conductivity of anhydrous salts. The regulation or oscillation of hydration states and generation or freezing of saturated brines can be effected by interactive feedbacks between hydration states, volumes, thermal conductivities, and conductive regimes of hydrated materials. Tens

J. S. Kargel; J. Crowley; S. Hook; R. Furfaro; O. Prieto-Ballesteros; J. A. Palmero-Rodriguez; G. Marion; A. Baldridge

2007-01-01

439

The time dependent heat conduction equation in the x-y Cartesian geometry is formulated in terms of a nine-point finite difference relation using a Taylor series expansion technique. The accuracy of the nine-point formulation over the five-point formulation has been tested and evaluated for various reactor fuel-cladding plate configurations using a computer program. The results have been checked against analytical solutions

Kadri

1983-01-01

440

Lithium bis(trifluoromethylsulfone)imide (LiTFSI) is a promising electrolyte for high-energy lithium batteries due to its high solubility in most solvents and electrochemical stability. To characterize this electrolyte in solution, its conductance and apparent molar volume and heat capacity were measured over a wide range of concentration in glymes, tetraethylsulfamide (TESA), acetonitrile, ?-butyrolactone, and propylene carbonate at 25°C and were compared with

Dany Brouillette; Gérald Perron; Jacques E. Desnoyers

1998-01-01

441

NASA Technical Reports Server (NTRS)

The condensation-mode growth rate of the thermal instability in an empirically motivated sheared field is shown to depend upon the existence of perpendicular thermal conduction. This typically very small effect (perpendicular conductivity/parallel conductivity less than about 10 to the -10th for the solar corona) increases the spatial-derivative order of the compressible temperature-perturbation equation, and thereby eliminates the singularities which appear when perpendicular conductivity = 0. The resulting growth rate is less than 1.5 times the controlling constant-density radiation rate, and has a clear maximum at a cross-field length of order 100 times and a width of about 0.1 the magnetic shear scale for solar conditions. The profiles of the observable temperature and density perturbations are independent of the thermal conductivity, and thus agree with those found previously. An analytic solution to the short-wavelength incompressible case is also given.

Van Hoven, G.; Mok, Y.

1984-01-01

442

NASA Astrophysics Data System (ADS)

We present a C-language program, THERMIC, that solves the 2-dimensional (pseudo 3D for axi-symmetric cases) conductive and advective heat-transfer equation. THERMIC uses a finite-element method that takes into account realistic geometries, heterogeneous material properties and various boundary and initial conditions. As it also allows for latent heat (heat production due to crystallisation) and for thermal properties, such as thermal conductivity, to be dependent on temperature, it is particularly suited to heat transfer problems encountered in the Earth Sciences. We present sample applications from the various problems already treated by THERMIC (cooling of magma chambers and dykes, the study of a granitic magma ascent or of pore water flow in sedimentary basins). Successfully tested on SUN® and SGI® UNIX workstations and on Microsoft Windows 95®, 98® and NT® 4.0 system based PCs, the THERMIC package can be downloaded from the web (THERMIC home page: http://www.ipgp.jussieu.fr/UFP/thermic/html/Thermic_home.html) and contains source files, makefiles and environment files as well as executable files for both systems and an html directory with help and example files.

Bonneville, Alain; Capolsini, Patrick

1999-12-01

443

This paper describes an investigation of the axial heat transfer within a thermal transient anemometer probe. A previous study, evaluated the performance characteristics of a thermal transient anemometer system. The study revealed discrepancies between a simplified theory and test results in the development of a universal calibration curve for probes of varying diameters. Although the cause of these discrepancies were left uncertain due to an inadequate theoretical model, the study suggested that axial conduction within the probe could account for the deviations. In this paper, computer simulations are used to further investigate axial heat conduction within the probes. The effect on calibration of axial variations of material properties along the probes is also discussed. Results from the computer simulation are used in lieu of the theoretical model used in the previous study to develop a satisfactory universal calibration curve. The computer simulations provide evidence that there is significant axial heat conduction within the probes, and that this was the cause of the discrepancies noted in the previous study.

Bailey, J.L.; Page, R.J. [Argonne National Lab., IL (United States); Acharya, M. [Illinois Inst. of Technology, Chicago, IL (United States). Fluid Dynamics Research Center

1995-07-01

444

Molecular Dynamics of Diffusive-Ballistic Heat Conduction in Single-Walled Carbon Nanotubes towards their thermal and electric device applications. In this study, diffusive-ballistic heat conduction-lengths up to a micrometer at room temperature. A gradual transition from nearly pure ballistic to diffusive-ballistic

Maruyama, Shigeo

445

We use nonequilibrium molecular dynamics to analyze and illustrate the qualitative differences between the one-thermostat and two-thermostat versions of equilibrium and nonequilibrium (heat-conducting) harmonic oscillators. Conservative nonconducting regions can coexist with dissipative heat conducting regions in phase space with exactly the same imposed temperature field. PMID:24827320

Sprott, Julien Clinton; Hoover, William Graham; Hoover, Carol Griswold

2014-04-01

446

NASA Astrophysics Data System (ADS)

We use nonequilibrium molecular dynamics to analyze and illustrate the qualitative differences between the one-thermostat and two-thermostat versions of equilibrium and nonequilibrium (heat-conducting) harmonic oscillators. Conservative nonconducting regions can coexist with dissipative heat conducting regions in phase space with exactly the same imposed temperature field.

Sprott, Julien Clinton; Hoover, William Graham; Hoover, Carol Griswold

2014-04-01

447

Advancement of EGS requires improved prediction of fracture development and growth during reservoir stimulation and long-term operation. This, in turn, requires better understanding of the dynamics of the strongly coupled thermo-hydro-mechanical (THM) processes within fractured rocks. We have developed a physically based rock deformation and fracture propagation simulator by using a quasi-static discrete element model (DEM) to model mechanical rock deformation and fracture propagation induced by thermal stress and fluid pressure changes. We also developed a network model to simulate fluid flow and heat transport in both fractures and porous rock. In this paper, we describe results of simulations in which the DEM model and network flow & heat transport model are coupled together to provide realistic simulation of the changes of apertures and permeability of fractures and fracture networks induced by thermal cooling and fluid pressure changes within fractures. Various processes, such as Stokes flow in low velocity pores, convection-dominated heat transport in fractures, heat exchange between fluid-filled fractures and solid rock, heat conduction through low-permeability matrices and associated mechanical deformations are all incorporated into the coupled model. The effects of confining stresses, developing thermal stress and injection pressure on the permeability evolution of fracture and fracture networks are systematically investigated. Results are summarized in terms of implications for the development and evolution of fracture distribution during hydrofracturing and thermal stimulation for EGS.

Huang, Hai; Plummer, Mitchell; Podgorney, Robert

2013-02-01

448

Nonlinear unsteady contact heat conduction of two-layer shells in the presence of thermal radiation

NASA Technical Reports Server (NTRS)

A technique is proposed for calculating the complex heat transfer of mated shells with the surrounding medium which also takes into account the temperature dependence of the contact thermal resistance between the shells. This technique can be used for thermal calculations and for calculations of the temperature stresses in two-layer space structure shells.

Novikov, V. S.; Chumakov, V. L.

1974-01-01

449

Students' Design of Experiments: An Inquiry Module on the Conduction of Heat

ERIC Educational Resources Information Center

This article examines secondary students' design of experiments after engagement in an innovative and inquiry-oriented module on heat transfer. The module consists of an integration of hands-on experiments, simulated experiments and microscopic model simulations, includes a structured series of guided investigative tasks and was implemented for a…

Hatzikraniotis, E.; Kallery, M.; Molohidis, A.; Psillos, D.

2010-01-01

450

is anticipated [15] with the new generation technique using high-pressure and high-temperature CO gas [16 the measured temperature gradient and the heat flux obtained by the integration of the additional force reported for randomly oriented [7] or magnetically aligned [8] conditions. Comparing with the temperature

Maruyama, Shigeo

451

sound, i.e. the sound propagation in phonon gas, but with relaxation and dissipation due to the excess simulations Junichiro Shiomi and Shigeo Maruyama* Department of Mechanical Engineering, The University-picoseconds. The investigation was based on classical molecular dynamics simulations, where the heat pulse was generated

Maruyama, Shigeo

452

Radial head fracture - aftercare

Elbow fracture - radial head ... the radial bone, just below your elbow. A fracture is a break in your bone. The most common cause of a radial head fracture is breaking a fall with an outstretched arm.

453

We report on scaling behavior of the thermal conductivity of width-modulated nanowires and nanofilms that have been studied with the phonon Monte Carlo technique. It has been found that the reduction of the thermal conductivity scales with the nanostructure transmissivity, a property entirely determined by the modulation geometry, irrespectively of the material choice. Tuning of the thermal conductivity is possible by the nanostructure width-modulation without strict limitations for the modulation profile. In addition, a very significant constriction thermal resistance due to width-discontinuity has been identified, in analogy to the contact thermal resistance between two dissimilar materials. The constriction thermal resistance also scales with the modulated nanostructure transmissivity. Our conclusions are generic indicating that a wide range of materials can be used for the modulated nanostructures. Direct heat flow control can be provided by designing the nanostructure width-modulation. PMID:25360881

Zianni, Xanthippi; Jean, Valentin; Termentzidis, Konstantinos; Lacroix, David

2014-11-21

454

Effect of wall conduction on heat transfer for turbulent flow in a circular tube

on interfacial temperature and local Nusselt number(constant heat flux at outer surface of tube, Fr=0. 01, Re=200000, Nu =13. 6891, r, /L=0. 05) 30 1. 0 0. 9 K= 1 0. 7 so 0. 6 0. 5 -=0. 05 0. 4 0. 3 0. 1 50 500 10 constant temperature at interface... on interfacial temperature and local Nusselt number(constant heat flux at outer surface of tube, Fr=0. 01, Re=200000, Nu =13. 6891, r /L=0. 05) 32 0. 35 0. 30 0. 25 for s=0. 05 ~ 0. 0001 so o 0. 20 K Q r K=10 0. 15 0. 10 0. 05 100 constant...

Lin, Yie-Kuang

2012-06-07

455

NASA Astrophysics Data System (ADS)

The dynamics of heat transfer in stripe GaAlAs laser diodes is investigated by solving the linear diffusion equation for a quasitwo-dimensional multilayer structure. The calculations are rationalized drastically by the transfer matrix method and also using for the first time the asymptotes of the decay constants. Special attention is given to the convergence of the Fourier series. A comparison with experimental results reveals however that this is essentially the Stefan problem (with moving boundary conditions).

Enders, P.; Galley, J.

1988-11-01

456

Two-phase numerical model for thermal conductivity and convective heat transfer in nanofluids

Due to the numerous applications of nanofluids, investigating and understanding of thermophysical properties of nanofluids\\u000a has currently become one of the core issues. Although numerous theoretical and numerical models have been developed by previous\\u000a researchers to understand the mechanism of enhanced heat transfer in nanofluids; to the best of our knowledge these models\\u000a were limited to the study of either

Sasidhar Kondaraju; Joon Sang Lee

2011-01-01

457

NASA Astrophysics Data System (ADS)

Some examples of high rate sputtered low refractive index metal-oxy-fluorine materials, in particular aluminium-oxy-fluorine and tin-oxy-fluorine, have been evaluated as antireflection layers for two commercially available sputtered multilayer heat mirrors on glass, commercially available sputtered indium-tin-oxide film on polyester and laboratory produced evaporated indium-tin-oxide on glass. Improvements of approximately 9 percent in luminous transmittance, approximately 8 percent in solar transmittance, and considerably reduced luminous reflectance were achieved for the heat mirrors, with considerably less color, particularly in the reflected light. The increases achieved for the luminous transmittance of high quality laboratory produced ITO depend on the thickness of the ITO film, and range from 3 to 9 percent. Larger improvements (not less than 15 percent) are obtained for the commercially produced ITO on polyester. The thermal emittances of the heat mirrors are not affected significantly by the antireflection layers, and preliminary tests indicate that the coatings are stable under exposure to uv radiation.

Harding, G. L.; Hamberg, I.; Granqvist, C. G.

1985-08-01

458

A non-local model of fractional heat conduction in rigid bodies

NASA Astrophysics Data System (ADS)

In recent years several applications of fractional differential calculus have been proposed in physics, chemistry as well as in engineering fields. Fractional order integrals and derivatives extend the well-known definitions of integer-order primitives and derivatives of the ordinary differential calculus to real-order operators. Engineering applications of fractional operators spread from viscoelastic models, stochastic dynamics as well as with thermoelasticity. In this latter field one of the main actractives of fractional operators is their capability to interpolate between the heat flux and its time-rate of change, that is related to the well-known second sound effect. In other recent studies a fractional, non-local thermoelastic model has been proposed as a particular case of the non-local, integral, thermoelasticity introduced at the mid of the seventies. In this study the autors aim to introduce a different non-local model of extended irreverible thermodynamics to account for second sound effect. Long-range heat flux is defined and it involves the integral part of the spatial Marchaud fractional derivatives of the temperature field whereas the second-sound effect is accounted for introducing time-derivative of the heat flux in the transport equation. It is shown that the proposed model does not suffer of the pathological problems of non-homogenoeus boundary conditions. Moreover the proposed model coalesces with the Povstenko fractional models in unbounded domains.

Borino, G.; di Paola, M.; Zingales, M.

2011-03-01

459

Electron heat conduction under non-Maxwellian distribution in hohlraum simulation

NASA Astrophysics Data System (ADS)

An electron transport model based on the non-Maxwellian distribution f0?e-?m (NM model), caused by the inverse bremsstrahlung heating, is used in 1-D plane target and 2-D hohlraum simulations. In the NM model, the electron heat flux depends not only on the gradient of electron temperature Te but also on the gradients of electron number density and the index m. From 1-D simulations, the spatial distribution of Te is dune-like and Te decreases obviously in the flux-heated region, which is very different from the flat profile obtained by using the flux limit model (FL model) but similar to the experimental observations [Gregori et al., Phys. Rev. Lett. 92, 205006 (2004)] and the nonlocal results [Rosen et al., High Energy Density Phys. 7, 180 (2011)]. The reason which causes the dune-like profile of Te is discussed in the paper. From 2-D hohlraum simulations, the NM results of the plasma status, the emission peak and profile inside hohlraum are very different from the FL model results. Finally, it is hard to use an average flux limiter in the FL model to obtain the same hohlraum plasma status and emission with those under the NM model.

Yi Huo, Wen; Lan, Ke; Jun Gu, Pei; Yong, Heng; Hong Zeng, Qing

2012-01-01