Effect of squealer tip on rotor heat transfer and efficiency
Ameri, A.A.; Steinthorsson, E.; Rigby, D.L.
1998-10-01
Calculations were performed to simulate the tip flow and heat transfer on the GE-E{sup 3} first-stage turbine, which represents a modern gas turbine blade geometry. Cases considered were a smooth tip, 2 percent recess, and 3 percent recess. In addition, a two-dimensional cavity problem was calculated. Good agreement with experimental results was obtained for the cavity calculations, demonstrating that the {kappa}-{omega} turbulence model used is capable of representing flows of the present type. In the rotor calculations, two dominant flow structures were shown to exist within the recess. Also areas of large heat transfer rate were identified on the blade tip and the mechanisms of heat transfer enhancement were discussed. No significant difference in adiabatic efficiency was observed for the three tip treatments investigated.
Surface heat transfer coefficient, heat efficiency, and temperature of pulsed solid-state lasers
Mann, K.; Weber, H.
1988-08-01
The temperature of solid-state lasers is a critical parameter. Efficiency and output power are strongly influenced by it. The two parameters which determine the temperature are the heat generation efficiency (HGE) and the surface heat transfer coefficient (SHTC) of the laser rod. These parameters allow the scaling of the rod temperature up to high pumping powers. Moreover, from the temperature inside the rod, the temperature gradients and the mechanical stress can be evaluated. Using transient temperature measurements, the SHTC and the HGE were determined for air- and water-cooled Nd:YAG and alexandrite lasers. The SHTC can be confirmed by theoretical considerations.
NASA Astrophysics Data System (ADS)
Song, Hanjiang; Chen, Lingen; Sun, Fengrui
2008-09-01
Optimal configuration of a class of endoreversible heat engines with fixed duration, input energy and radiative heat transfer law ( q ∝ Δ( T 4)) is determined. The optimal cycle that maximizes the efficiency of the heat engine is obtained by using optimal-control theory, and the differential equations are solved by the Taylor series expansion. It is shown that the optimal cycle has eight branches including two isothermal branches, four maximum-efficiency branches, and two adiabatic branches. The interval of each branch is obtained, as well as the solutions of the temperatures of the heat reservoirs and the working fluid. A numerical example is given. The obtained results are compared with those obtained with the Newton’s heat transfer law for the maximum efficiency objective, those with linear phenomenological heat transfer law for the maximum efficiency objective, and those with radiative heat transfer law for the maximum power output objective.
Zhang, M.; Ibekwe, S.; Li, G.; Pang, S.S.; and Lian, K.
2006-07-01
The Pressurized Water Reactors (PWRs in Figure 1) were originally developed for naval propulsion purposes, and then adapted to land-based applications. It has three parts: the reactor coolant system, the steam generator and the condenser. The Steam generator (a yellow area in Figure 1) is a shell and tube heat exchanger with high-pressure primary water passing through the tube side and lower pressure secondary feed water as well as steam passing through the shell side. Therefore, a key issue in increasing the efficiency of heat exchanger is to improve the design of steam generator, which is directly translated into economic benefits. The past research works show that the presence of a pin-fin array in a channel enhances the heat transfer significantly. Hence, using microfabrication techniques, such as LIGA, micro-molding or electroplating, some special microstructures can be fabricated around the tubes in the heat exchanger to increase the heat-exchanging efficiency and reduce the overall size of the heat-exchanger for the given heat transfer rates. In this paper, micro-pin fins of different densities made of SU-8 photoresist are fabricated and studied to evaluate overall heat transfer efficiency. The results show that there is an optimized micro pin-fin configuration that has the best overall heat transfer effects.
A new method of efficient heat transfer and storage at very high temperatures
NASA Technical Reports Server (NTRS)
Shaw, D.; Bruckner, A. P.; Hertzberg, A.
1980-01-01
A unique, high temperature (1000-2000 K) continuously operating capacitive heat exchanger system is described. The system transfers heat from a combustion or solar furnace to a working gas by means of a circulating high temperature molten refractory. A uniform aggregate of beads of a glass-like refractory is injected into the furnace volume. The aggregate is melted and piped to a heat exchanger where it is sprayed through a counter-flowing, high pressure working gas. The refractory droplets transfer their heat to the gas, undergoing a phase change into the solid bead state. The resulting high temperature gas is used to drive a suitable high efficiency heat engine. The solidified refractory beads are delivered back to the furnace and melted to continue the cycle. This approach avoids the important temperature limitations of conventional tube-type heat exchangers, giving rise to the potential of converting heat energy into useful work at considerably higher efficiencies than currently attainable and of storing energy at high thermodynamic potential.
NASA Astrophysics Data System (ADS)
Laptev, A. G.; Lapteva, E. A.
2015-07-01
The efficiency of heat and mass transfer in the bubbling bed on the plate has been investigated with the use of the method of combined physical and mathematical modeling based on the representation of the physical process in the form of a combination of elementary phenomena having a hierarchy of scales that permits realizing a scale transition in designing a contact device. The mathematical modeling of the heat and mass transfer in the above bed is based on the idea that the structure of this bed is invariant with its size and the interaction of the phases in it. A parametric investigation of the interaction of various effects in the process of heat and mass transfer in the bubbling bed on the plate and their conjugation has been carried out on the basis of the variational formulation of the conservation laws. Examples of calculating the efficiencies of the heat and mass transfer processes on bubbling plates are given. The results of calculations were compared with the corresponding experimental data.
Effects of Tip Clearance and Casing Recess on Heat Transfer and Stage Efficiency in Axial Turbines
NASA Technical Reports Server (NTRS)
Ameri, A. A.; Steinthorsson, E.; Rigby, David L.
1998-01-01
Calculations were performed to assess the effect of the tip leakage flow on the rate of heat transfer to blade, blade tip and casing. The effect on exit angle and efficiency was also examined. Passage geometries with and without casing recess were considered. The geometry and the flow conditions of the GE-E 3 first stage turbine, which represents a modem gas turbine blade were used for the analysis. Clearance heights of 0%, 1%, 1.5% and 3% of the passage height were considered. For the two largest clearance heights considered, different recess depths were studied. There was an increase in the thermal load on all the heat transfer surfaces considered due to enlargement of the clearance gap. Introduction of recessed casing resulted in a drop in the rate of heat transfer on the pressure side but the picture on the suction side was found to be more complex for the smaller tip clearance height considered. For the larger tip clearance height the effect of casing recess was an orderly reduction in the suction side heat transfer as the casing recess height was increased. There was a marked reduction of heat load and peak values on the blade tip upon introduction of casing recess, however only a small reduction was observed on the casing itself. It was reconfirmed that there is a linear relationship between the efficiency and the tip gap height. It was also observed that the recess casing has a small effect on the efficiency but can have a moderating effect on the flow underturning at smaller tip clearances.
Effects of tip clearance and casing recess on heat transfer and stage efficiency in axial turbines
Ameri, A.A.; Steinthorsson, E.; Rigby, D.L.
1999-10-01
Calculations were performed to assess the effect of the tip leakage flow on the rate of heat transfer to blade, blade tip, and casing. The effect on exit angle and efficiency was also examined. Passage geometries with and without casing recess were considered. The geometry and the flow conditions of the GE-E{sup 3} first-stage turbine, which represents a modern gas turbine blade, were used for the analysis. Clearance heights of 0, 1, 1.5, and 3 percent of the passage height were considered. For the two largest clearance heights considered, different recess depths were studied. There was an increase in the thermal load on all the heat transfer surfaces considered due to enlargement of the clearance gap. Introduction, of recessed casing resulted in a drop in the rate of heat transfer on the pressure side, but the picture on the suction side was found to be more complex for the smaller tip clearance height considered. For the larger tip clearance height, the effect of casing recess was an orderly reduction in the suction side heat transfer as the casing recess height was increased. There was a marked reduction of heat load and peak values on the blade tip upon introduction of casing recess; however, only a small reduction was observed on the casing itself. It was reconfirmed that there is a linear relationship between the efficiency and tip gap height. It was also observed that the recess casing has a small effect on the efficiency but can have a moderating effect on the flow underturning at smaller tip clearances.
Zhao, Ye; Luo, Yuting; Zhu, Jie; Li, Juan; Gao, Xuefeng
2015-06-10
We report a type of copper-based ultrathin nickel nanocone films with high-efficiency dropwise condensation heat transfer (DCHT) performance, which can be fabricated by facile electrodeposition and low-surface-energy chemistry modification. Compared with flat copper samples, our nanosamples show condensate microdrop self-propelling (CMDSP) function and over 89% enhancement in the DCHT coefficient. Such remarkable enhancement may be ascribed to the cooperation of surface nanostructure-induced CMDSP function as well as in situ integration and ultrathin nature of nanofilms. These findings are very significant to design and develop advanced DCHT materials and devices, which help improve the efficiency of thermal management and energy utilization. PMID:26011021
Heat transfer in microwave heating
NASA Astrophysics Data System (ADS)
Peng, Zhiwei
Heat transfer is considered as one of the most critical issues for design and implement of large-scale microwave heating systems, in which improvement of the microwave absorption of materials and suppression of uneven temperature distribution are the two main objectives. The present work focuses on the analysis of heat transfer in microwave heating for achieving highly efficient microwave assisted steelmaking through the investigations on the following aspects: (1) characterization of microwave dissipation using the derived equations, (2) quantification of magnetic loss, (3) determination of microwave absorption properties of materials, (4) modeling of microwave propagation, (5) simulation of heat transfer, and (6) improvement of microwave absorption and heating uniformity. Microwave heating is attributed to the heat generation in materials, which depends on the microwave dissipation. To theoretically characterize microwave heating, simplified equations for determining the transverse electromagnetic mode (TEM) power penetration depth, microwave field attenuation length, and half-power depth of microwaves in materials having both magnetic and dielectric responses were derived. It was followed by developing a simplified equation for quantifying magnetic loss in materials under microwave irradiation to demonstrate the importance of magnetic loss in microwave heating. The permittivity and permeability measurements of various materials, namely, hematite, magnetite concentrate, wstite, and coal were performed. Microwave loss calculations for these materials were carried out. It is suggested that magnetic loss can play a major role in the heating of magnetic dielectrics. Microwave propagation in various media was predicted using the finite-difference time-domain method. For lossy magnetic dielectrics, the dissipation of microwaves in the medium is ascribed to the decay of both electric and magnetic fields. The heat transfer process in microwave heating of magnetite, which is a typical magnetic dielectric, was simulated by using an explicit finite-difference approach. It is demonstrated that the heat generation due to microwave irradiation dominates the initial temperature rise in the heating and the heat radiation heavily affects the temperature distribution, giving rise to a hot spot in the predicted temperature profile. Microwave heating at 915 MHz exhibits better heating homogeneity than that at 2450 MHz due to larger microwave penetration depth. To minimize/avoid temperature nonuniformity during microwave heating the optimization of object dimension should be considered. The calculated reflection loss over the temperature range of heating is found to be useful for obtaining a rapid optimization of absorber dimension, which increases microwave absorption and achieves relatively uniform heating. To further improve the heating effectiveness, a function for evaluating absorber impedance matching in microwave heating was proposed. It is found that the maximum absorption is associated with perfect impedance matching, which can be achieved by either selecting a reasonable sample dimension or modifying the microwave parameters of the sample.
Zhu, Jie; Luo, Yuting; Tian, Jian; Li, Juan; Gao, Xuefeng
2015-05-27
We report that the dropwise condensation heat transfer (DCHT) effectiveness of copper surfaces can be dramatically enhanced by in situ grown clustered ribbed-nanoneedles. Combined experiments and theoretical analyses reveal that, due to the microscopically rugged and low-adhesive nature of building blocks, the nanosamples can not only realize high-density nucleation but constrain growing condensates into suspended microdrops via the self-transport and/or self-expansion mode for subsequently self-propelled jumping, powered by coalescence-released excess surface energy. Consequently, our nanosample exhibits over 125% enhancement in DCHT coefficient. This work helps develop advanced heat-transfer materials and devices for efficient thermal management and energy utilization. PMID:25966966
Efficient heat-transfer surfaces assembled from partially finned flat-oval tubes
NASA Astrophysics Data System (ADS)
Pis'mennyi, E. N.
2011-04-01
The state of finned convective heat-transfer surfaces and prospects for using them in power engineering and industry are briefly reviewed. The characteristics of a heat-recovery economizer made of partially finned flat-oval tubes are presented by way of comparing them with design versions employing known types of finned tubes, and the results gained from its operation downstream of a PTVM-30M boiler are given.
McGuire, Joseph C.
1982-01-01
A heat transfer system for a nuclear reactor. Heat transfer is accomplished within a sealed vapor chamber which is substantially evacuated prior to use. A heat transfer medium, which is liquid at the design operating temperatures, transfers heat from tubes interposed in the reactor primary loop to spaced tubes connected to a steam line for power generation purposes. Heat transfer is accomplished by a two-phase liquid-vapor-liquid process as used in heat pipes. Condensible gases are removed from the vapor chamber through a vertical extension in open communication with the chamber interior.
Not Available
1980-03-07
A heat transfer system for a nuclear reactor is described. Heat transfer is accomplished within a sealed vapor chamber which is substantially evacuated prior to use. A heat transfer medium, which is liquid at the design operating temperatures, transfers heat from tubes interposed in the reactor primary loop to spaced tubes connected to a steam line for power generation purposes. Heat transfer is accomplished by a two-phase liquid-vapor-liquid process as used in heat pipes. Condensible gases are removed from the vapor chamber through a vertical extension in open communication with the chamber interior.
NASA Astrophysics Data System (ADS)
Yadav, R. K.; Gastine, T.; Christensen, U. R.; Duarte, L. D. V.; Reiners, A.
2016-02-01
We study rotating thermal convection in spherical shells as prototype for flow in the cores of terrestrial planets, gas planets or in stars. We base our analysis on a set of about 450 direct numerical simulations of the (magneto)hydrodynamic equations under the Boussinesq approximation. The Ekman number ranges from 10-3 to 10-5. The supercriticality of the convection reaches about 1000 in some models. Four sets of simulations are considered: non-magnetic simulations and dynamo simulations with either free-slip or no-slip flow boundary conditions. The non-magnetic setup with free-slip boundaries generates the strongest zonal flows. Both non-magnetic simulations with no-slip flow boundary conditions and self-consistent dynamos with free-slip boundaries have drastically reduced zonal-flows. Suppression of shear leads to a substantial gain in heat-transfer efficiency, increasing by a factor of 3 in some cases. Such efficiency enhancement occurs as long as the convection is significantly influenced by rotation. At higher convective driving the heat-transfer efficiency tends towards that of the classical non-rotating Rayleigh-Bénard system. Analysis of the latitudinal distribution of heat flow at the outer boundary reveals that the shear is most effective at suppressing heat-transfer in the equatorial regions. Simulations with convection zones of different thickness show that the zonal flows become less energetic in thicker shells, and, therefore, their effect on heat-transfer efficiency decreases. Furthermore, we explore the influence of the magnetic field on the non-zonal flow components of the convection. For this we compare the heat-transfer efficiency of no-slip non-magnetic cases with that of the no-slip dynamo simulations. We find that at E = 10-5 magnetic field significantly affects the convection and a maximum gain of about 30 per cent (as compared to the non-magnetic case) in heat-transfer efficiency is obtained for an Elsasser number of about 3. Our analysis motivates us to speculate that convection in the polar regions in dynamos at E = 10-5 is probably in a `magnetostrophic' regime.
Kurek, Harry; Wagner, John
2010-01-25
Direct Flame Impingement involves the use of an array of very high-velocity flame jets impinging on a work piece to rapidly heat the work piece. The predominant mode of heat transfer is convection. Because of the locally high rate of heat transfer at the surface of the work piece, the refractory walls and exhaust gases of a DFI furnace are significantly cooler than in conventional radiant heating furnaces, resulting in high thermal efficiency and low NOx emissions. A DFI furnace is composed of a successive arrangement of heating modules through or by which the work piece is conveyed, and can be configured for square, round, flat, and curved metal shapes (e.g., billets, tubes, flat bars, and coiled bars) in single- or multi-stranded applications.
NASA Technical Reports Server (NTRS)
Eaton, L. R. (Inventor)
1976-01-01
An improved heat transfer device particularly suited for use as an evaporator plate in a diffusion cloud chamber. The device is characterized by a pair of mutually spaced heat transfer plates, each being of a planar configuration, having a pair of opposed surfaces defining therebetween a heat pipe chamber. Within the heat pipe chamber, in contiguous relation with the pair of opposed surfaces, there is disposed a pair of heat pipe wicks supported in a mutually spaced relationship by a foraminous spacer of a planar configuration. A wick including a foraminous layer is contiguously related to the external surfaces of the heat transfer plates for uniformly wetting these surfaces.
Heat transfer equipment design
NASA Astrophysics Data System (ADS)
Shah, R. K.; Subbarao, Eleswarapu Chinna; Mashelkar, R. A.
A comprehensive presentation is made of state-of-the-art configurations and design methodologies for heat transfer devices applicable to industrial processes, automotive systems, air conditioning/refrigeration, cryogenics, and petrochemicals refining. Attention is given to topics in heat exchanger mechanical design, single-phase convection processes, thermal design, two-phase exchanger thermal design, heat-transfer augmentation, and rheological effects. Computerized analysis and design methodologies are presented for the range of heat transfer systems, as well as advanced methods for optimization and performance projection.
NASA Technical Reports Server (NTRS)
Burbach, T.
1985-01-01
The heat transfer from hot water to a cold copper pipe in laminar and turbulent flow condition is determined. The mean flow through velocity in the pipe, relative test length and initial temperature in the vessel were varied extensively during tests. Measurements confirm Nusselt's theory for large test lengths in laminar range. A new equation is derived for heat transfer for large starting lengths which agrees satisfactorily with measurements for large starting lengths. Test results are compared with the new Prandtl equation for heat transfer and correlated well. Test material for 200- and to 400-diameter test length is represented at four different vessel temperatures.
NASA Astrophysics Data System (ADS)
Jaluria, Yogesh; Torrance, Kenneth E.
Numerical approaches to heat-transfer problems are examined in an introductory text for senior and graduate engineering students. The emphasis is on the application of physical criteria in selecting the computational method. Chapters are devoted to the mathematics of the governing equations, finite differences, and finite elements; the simulation of transport processes; numerical methods for convective and radiative heat transfer; and combined modes and process applications. Graphs, diagrams, flow charts, problems, tables of material parameters, and sample computer programs are provided.
NASA Astrophysics Data System (ADS)
Shin, Sangwoo; Seok Kim, Beom; Choi, Geehong; Lee, Hwanseong; Hee Cho, Hyung
2012-12-01
Micro-nano hybrid structure (MNHS) that comprises of microcavities and nanowires is a specific class of MNHS that is considered to be ideal for two-phase boiling heat transfer applications. Realizing MNHS with electrodeposition is favorable in boiling heat transfer, but the realization has been very difficult and time-consuming to achieve. Here, we demonstrate a simple, robust, rapid, and photolithography-free route to fabricate MNHS that consists of individual microcavities and copper nanowires on a large area. We show that this MNHS can be extremely beneficial in boiling heat transfer compared to the state-of-the-art nanowire surface.
Heat transfer fluids containing nanoparticles
Singh, Dileep; Routbort, Jules; Routbort, A.J.; Yu, Wenhua; Timofeeva, Elena; Smith, David S.; France, David M.
2016-05-17
A nanofluid of a base heat transfer fluid and a plurality of ceramic nanoparticles suspended throughout the base heat transfer fluid applicable to commercial and industrial heat transfer applications. The nanofluid is stable, non-reactive and exhibits enhanced heat transfer properties relative to the base heat transfer fluid, with only minimal increases in pumping power required relative to the base heat transfer fluid. In a particular embodiment, the plurality of ceramic nanoparticles comprise silicon carbide and the base heat transfer fluid comprises water and water and ethylene glycol mixtures.
Thermal radiation heat transfer.
NASA Technical Reports Server (NTRS)
Siegel, R.; Howell, J. R.
1972-01-01
A comprehensive discussion of heat transfer by thermal radiation is presented, including the radiative behavior of materials, radiation between surfaces, and gas radiation. Among the topics considered are property prediction by electromagnetic theory, the observed properties of solid materials, radiation in the presence of other modes of energy transfer, the equations of transfer for an absorbing-emitting gas, and radiative transfer in scattering and absorbing media. Also considered are radiation exchange between black isothermal surfaces, radiation exchange in enclosures composed of diffuse gray surfaces and in enclosures having some specularly reflecting surfaces, and radiation exchange between nondiffuse nongray surfaces. The use of the Monte Carlo technique in solving radiant-exchange problems and problems of radiative transfer through absorbing-emitting media is explained.
ERIC Educational Resources Information Center
Knapp, Henry H., III
This module on heat transfer is one of six in a series intended for use as supplements to currently available materials on solar energy and energy conservation. Together with the recommended texts and references (sources are identified), these modules provide an effective introduction to energy conservation and solar energy technologies. The…
Nano materials for efficiently lowering the freezing point of heat transfer nanofluids
NASA Astrophysics Data System (ADS)
Hong, Haiping; Roy, Walter
2007-09-01
In this paper, we report, for the first time, the effect of the lowered freezing point in a 50% water / 50% antifreeze coolant (PAC) or 50% water / 50% ethylene glycol (EG) solution by the addition of carbon nanotubes and other particles. The experimental results indicated that the nano materials are much more efficient (hundreds fold) in lowering the freezing point than the regular ionic materials (e.g. NaCl). The possible explanation for this interesting phenomenon is the colligative property of fluid and relative small size of nano material. It is quite certain that the carbon nanotubes and metal oxide nano particles could be a wonderful candidate for the nano coolant application because they could not only increase the thermal conductivity, but also efficiently lower the freezing point of traditional coolants.
Methane heat transfer investigation
NASA Technical Reports Server (NTRS)
1984-01-01
Future high chamber pressure LOX/hydrocarbon booster engines require copper base alloy main combustion chamber coolant channels similar to the SSME to provide adequate cooling and reusable engine life. Therefore, it is of vital importance to evaluate the heat transfer characteristics and coking thresholds for LNG (94% methane) cooling, with a copper base alloy material adjacent to he fuel coolant. High pressure methane cooling and coking characteristics recently evaluated at Rocketdyne using stainless steel heated tubes at methane bulk temperatures and coolant wall temperatures typical of advanced engine operation except at lower heat fluxes as limited by the tube material. As expected, there was no coking observed. However, coking evaluations need be conducted with a copper base surface exposed to the methane coolant at higher heat fluxes approaching those of future high chamber pressure engines.
Gambill, W.R.; Greene, N.D.
1960-08-30
A method is given for increasing burn-out heat fluxes under nucleate boiling conditions in heat exchanger tubes without incurring an increase in pumping power requirements. This increase is achieved by utilizing a spinning flow having a rotational velocity sufficient to produce a centrifugal acceleration of at least 10,000 g at the tube wall. At this acceleration the heat-transfer rate at burn out is nearly twice the rate which can be achieved in a similar tube utilizing axial flow at the same pumping power. At higher accelerations the improvement over axial flow is greater, and heat fluxes in excess of 50 x 10/sup 6/ Btu/hr/sq ft can be achieved.
Methane heat transfer investigation
NASA Technical Reports Server (NTRS)
Cook, R. T.
1984-01-01
Future high chamber pressure LOX/hydrocarbon booster engines require copper-base alloy main combustion chamber coolant channels similar to the SSME to provide adequate cooling and resuable engine life. Therefore, it is of vital importance to evaluate the heat transfer characteristics and coking thresholds for LNG (94% methane) cooling, with a copper-base alloy material adjacent to the fuel coolant. High-pressure methane cooling and coking characteristics were recently evaluated using stainless-steel heated tubes at methane bulk temperatures and coolant wall temperatures typical of advanced engine operation except at lower heat fluxes as limited by the tube material. As expected, there was no coking observed. However, coking evaluations need be conducted with a copper-base surface exposed to the methane coolant at higher heat fluxes approaching those of future high chamber pressure engines.
Basmajian, V.V.
1986-01-28
This patent describes a heat transfer apparatus which consists of: heat exchanging means for orientation in the earth below ground substantially vertically, having a hollow conduit of length from top to bottom much greater than the span across the hollow conduit orthogonal to its length with a top, bottom and an intermediate portion contiguous and communicating with the top and bottom portions for allowing thermally conductive fluid to flow freely between the top, intermediate and bottom portions for immersion in thermally conductive fluid in the region around the heat exchanging means for increasing the heat flow between the latter and earth when inserted into a substantially vertical borehole in the earth with the top portion above the bottom portion. The heat exchanger consists of heat exchanging conduit means in the intermediate portion for carrying refrigerant. The heat exchanging conduit consisting of tubes of thermally conductive material for carrying the refrigerant and extending along the length of the hollow conduit for a tube length that is less than the length of the hollow conduit. The hollow conduit is formed with port means between the top and the plurality of tubes for allowing the thermally conductive fluid to pass in a flow path embracing the tubes, the bottom portion, an outer channel around the hollow conduit and the port means.
Fiebig, M.; Grosse-Gorgemann, A.; Chen, Y.; Mitra, N.K.
1995-08-01
The conjugate heat transfer in a high-performance finned-tube heat exchanger element was calculated for three-dimensional thermally and hydrodynamically developing laminar flows. The influence of Reynolds number Re and a fin efficiency parameter Fi (ratio of fin to fluid conductivity times fin thickness to fin pitch) on the heat transfer behavior has been studied. Flow patterns, pressure distribution, Nusselt number distribution, heat flux distribution, and fin efficiency are presented. The part of the fin upstream of the tube is much more efficient than the downstream part. A unique heat transfer phenomenon, a directional reversal of the heat transfer, occurred locally on the fin in the tube wake for small Fi and large Re. This can be interpreted as three-dimensional interaction of convection and the fin conduction in the tube wake, when the flow is dominated by a strong horseshoe vortex and a dead water zone with recirculation.
Transferring heat during a bounce
NASA Astrophysics Data System (ADS)
Shiri, Samira; Bird, James
2015-11-01
When a hot liquid drop impacts a cold non-wetting surface, the temperature difference drives heat transfer. If the drop leaves the surface before reaching thermal equilibrium, the amount of heat transfer may depend on the contact time. Past studies exploring finite-time heat exchange with droplets focus on the Leidenfrost condition where heat transfer is regulated by a thin layer of vapor. Here, we present systematic experiments to measure the heat transferred by a bouncing droplet in non-Leidenfrost conditions. We propose a physical model of this heat transfer and compare our model to the experiments.
Heat transfer in aeropropulsion systems
NASA Technical Reports Server (NTRS)
Simoneau, R. J.
1985-01-01
Aeropropulsion heat transfer is reviewed. A research methodology based on a growing synergism between computations and experiments is examined. The aeropropulsion heat transfer arena is identified as high Reynolds number forced convection in a highly disturbed environment subject to strong gradients, body forces, abrupt geometry changes and high three dimensionality - all in an unsteady flow field. Numerous examples based on heat transfer to the aircraft gas turbine blade are presented to illustrate the types of heat transfer problems which are generic to aeropropulsion systems. The research focus of the near future in aeropropulsion heat transfer is projected.
Heat transfer in aeropropulsion systems
NASA Astrophysics Data System (ADS)
Simoneau, R. J.
1985-07-01
Aeropropulsion heat transfer is reviewed. A research methodology based on a growing synergism between computations and experiments is examined. The aeropropulsion heat transfer arena is identified as high Reynolds number forced convection in a highly disturbed environment subject to strong gradients, body forces, abrupt geometry changes and high three dimensionality - all in an unsteady flow field. Numerous examples based on heat transfer to the aircraft gas turbine blade are presented to illustrate the types of heat transfer problems which are generic to aeropropulsion systems. The research focus of the near future in aeropropulsion heat transfer is projected.
Frank, Jeffrey I.; Rosengart, Axel J.; Kasza, Ken; Yu, Wenhua; Chien, Tai-Hsin; Franklin, Jeff
2006-10-10
Apparatuses, systems, methods, and computer code for, among other things, monitoring the health of samples such as the brain while providing local cooling or heating. A representative device is a heat transfer probe, which includes an inner channel, a tip, a concentric outer channel, a first temperature sensor, and a second temperature sensor. The inner channel is configured to transport working fluid from an inner inlet to an inner outlet. The tip is configured to receive at least a portion of the working fluid from the inner outlet. The concentric outer channel is configured to transport the working fluid from the inner outlet to an outer outlet. The first temperature sensor is coupled to the tip, and the second temperature sensor spaced apart from the first temperature sensor.
"Nanotechnology Enabled Advanced Industrial Heat Transfer Fluids"
Dr. Ganesh Skandan; Dr. Amit Singhal; Mr. Kenneth Eberts; Mr. Damian Sobrevilla; Prof. Jerry Shan; Stephen Tse; Toby Rossmann
2008-06-12
ABSTRACT Nanotechnology Enabled Advanced industrial Heat Transfer Fluids” Improving the efficiency of Industrial Heat Exchangers offers a great opportunity to improve overall process efficiencies in diverse industries such as pharmaceutical, materials manufacturing and food processing. The higher efficiencies can come in part from improved heat transfer during both cooling and heating of the material being processed. Additionally, there is great interest in enhancing the performance and reducing the weight of heat exchangers used in automotives in order to increase fuel efficiency. The goal of the Phase I program was to develop nanoparticle containing heat transfer fluids (e.g., antifreeze, water, silicone and hydrocarbon-based oils) that are used in transportation and in the chemical industry for heating, cooling and recovering waste heat. Much work has been done to date at investigating the potential use of nanoparticle-enhanced thermal fluids to improve heat transfer in heat exchangers. In most cases the effect in a commercial heat transfer fluid has been marginal at best. In the Phase I work, we demonstrated that the thermal conductivity, and hence heat transfer, of a fluid containing nanoparticles can be dramatically increased when subjected to an external influence. The increase in thermal conductivity was significantly larger than what is predicted by commonly used thermal models for two-phase materials. Additionally, the surface of the nanoparticles was engineered so as to have a minimal influence on the viscosity of the fluid. As a result, a nanoparticle-laden fluid was successfully developed that can lead to enhanced heat transfer in both industrial and automotive heat exchangers
Conduction heat transfer solutions
VanSant, J.H.
1980-03-01
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.
Conduction heat transfer solutions
VanSant, J.H.
1983-08-01
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.
Conjugate heat transfer of a finned oval tube. Part B: Heat transfer behaviors
Chen, Y.; Fiebig, M.; Mitra, N.K.
1998-03-01
Conjugate heat transfer in a high-performance finned oval tube heat exchanger element has been calculated for a thermally and hydrodynamically developing three-dimensional laminar flow. The influence of Reynolds number in the range 100--500 and of a fin parameter Fi, the product of the dimensionless fin thickness and its thermal conductivity, on the heat transfer behavior have been studied. In part 1, the computed velocity field was presented. Here the authors present the heat transfer behavior, including heat flux on the tube, fin temperatures, fin Nusselt numbers and heat flux distributions, fin efficiencies, Colburn j factor, and apparent friction factor f{sup app}. For the investigated configuration, the ratio of heat transfer on the tube to that on the fin remains under 10%. The fin temperature and fin efficiency depend weakly on Fi. Finned tube heat exchangers are used in air conditioners and the chemical industry.
Tubing for augmented heat transfer
Yampolsky, J.S.; Pavlics, P.
1983-08-01
The objectives of the program reported were: to determine the heat transfer and friction characteristics on the outside of spiral fluted tubing in single phase flow of water, and to assess the relative cost of a heat exchanger constructed with spiral fluted tubing with one using conventional smooth tubing. An application is examined where an isolation water/water heat exchanger was used to transfer the heat from a gaseous diffusion plant to an external system for energy recovery. (LEW)
Flow and heat transfer enhancement in tube heat exchangers
NASA Astrophysics Data System (ADS)
Sayed Ahmed, Sayed Ahmed E.; Mesalhy, Osama M.; Abdelatief, Mohamed A.
2015-11-01
The performance of heat exchangers can be improved to perform a certain heat-transfer duty by heat transfer enhancement techniques. Enhancement techniques can be divided into two categories: passive and active. Active methods require external power, such as electric or acoustic field, mechanical devices, or surface vibration, whereas passive methods do not require external power but make use of a special surface geometry or fluid additive which cause heat transfer enhancement. The majority of commercially interesting enhancement techniques are passive ones. This paper presents a review of published works on the characteristics of heat transfer and flow in finned tube heat exchangers of the existing patterns. The review considers plain, louvered, slit, wavy, annular, longitudinal, and serrated fins. This review can be indicated by the status of the research in this area which is important. The comparison of finned tubes heat exchangers shows that those with slit, plain, and wavy finned tubes have the highest values of area goodness factor while the heat exchanger with annular fin shows the lowest. A better heat transfer coefficient ha is found for a heat exchanger with louvered finned and thus should be regarded as the most efficient one, at fixed pumping power per heat transfer area. This study points out that although numerous studies have been conducted on the characteristics of flow and heat transfer in round, elliptical, and flat tubes, studies on some types of streamlined-tubes shapes are limited, especially on wing-shaped tubes (Sayed Ahmed et al. in Heat Mass Transf 50: 1091-1102, 2014; in Heat Mass Transf 51: 1001-1016, 2015). It is recommended that further detailed studies via numerical simulations and/or experimental investigations should be carried out, in the future, to put further insight to these fin designs.
Optimal thermodynamic heat transfer
Scenna, N.J. ); Aguirre, P.A. )
1989-06-01
This paper presents a set of heuristics useful for optimal design of heat-exchange networks and integrated heat and power systems. These heuristics consolidate other approaches reported in the literature in a formalism useful for design purposes.
Fraas, A.P.; Wislicenus, G.F.
1961-07-11
A heat exchanger is adapted to unifomly cool a spherical surface. Equations for the design of a spherical heat exchanger hav~g tubes with a uniform center-to-center spining are given. The heat exchanger is illustrated in connection with a liquid-fueled reactor.
Heat transfer and thermal control
NASA Astrophysics Data System (ADS)
Crosbie, A. L.
Radiation heat transfer is considered along with conduction heat transfer, heat pipes, and thermal control. Attention is given to the radiative properties of a painted layer containing nonspherical pigment, bidirectional reflectance measurements of specular and diffuse surfaces with a simple spectrometer, the radiative equilibrium in a general plane-parallel environment, and the application of finite-element techniques to the interaction of conduction and radiation in participating medium, a finite-element approach to combined conductive and radiative heat transfer in a planar medium. Heat transfer in irradiated shallow layers of water, an analytical and experimental investigation of temperature distribution in laser heated gases, numerical methods for the analysis of laser annealing of doped semiconductor wafers, and approximate solutions of transient heat conduction in a finite slab are also examined. Consideration is also given to performance testing of a hydrogen heat pipe, heat pipe performance with gravity assist and liquid overfill, vapor chambers for an atmospheric cloud physics laboratory, a prototype heat pipe radiator for the German Direct Broadcasting TV Satellite, free convection in enclosures exposed to compressive heating, and a thermal analysis of a multipurpose furnace for material processing in space.
Sphere Drag and Heat Transfer.
Duan, Zhipeng; He, Boshu; Duan, Yuanyuan
2015-01-01
Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body. PMID:26189698
Duan, Zhipeng; He, Boshu; Duan, Yuanyuan
2015-01-01
Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body. PMID:26189698
NASA Astrophysics Data System (ADS)
Duan, Zhipeng; He, Boshu; Duan, Yuanyuan
2015-07-01
Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body.
NASA Technical Reports Server (NTRS)
Widener, Edward L.
1992-01-01
The objective is to introduce some concepts of thermodynamics in existing heat-treating experiments using available items. The specific objectives are to define the thermal properties of materials and to visualize expansivity, conductivity, heat capacity, and the melting point of common metals. The experimental procedures are described.
Heat transfer, diffusion, and evaporation
NASA Technical Reports Server (NTRS)
Nusselt, Wilhelm
1954-01-01
Although it has long been known that the differential equations of the heat-transfer and diffusion processes are identical, application to technical problems has only recently been made. In 1916 it was shown that the speed of oxidation of the carbon in iron ore depends upon the speed with which the oxygen of the combustion air diffuses through the core of gas surrounding the carbon surface. The identity previously referred to was then used to calculate the amount of oxygen diffusing to the carbon surface on the basis of the heat transfer between the gas stream and the carbon surface. Then in 1921, H. Thoma reversed that procedure; he used diffusion experiments to determine heat-transfer coefficients. Recently Lohrisch has extended this work by experiment. A technically very important application of the identity of heat transfer and diffusion is that of the cooling tower, since in this case both processes occur simultaneously.
NASA Technical Reports Server (NTRS)
Friedell, M. V.; Anderson, A. J.
1974-01-01
Thermal switch maintains temperature of planetary lander, within definite range, by transferring heat. Switch produces relatively large stroke and force, uses minimum electrical power, is lightweight, is vapor pressure actuated, and withstands sterilization temperatures without damage.
Rotary Joint for Heat Transfer
NASA Technical Reports Server (NTRS)
Shauback, R.
1986-01-01
Rotary joint exchanges heat between two heat pipes - one rotating and one stationary. Joint accommodates varying heat loads with little temperature drop across interface. According to concept, heat pipe enters center of disklike stationary section of joint. There, wicks in central artery of heat pipe separate into multiple strands that lead to concentric channels on rotaryinterface side of stationary disk. Thin layer of liquid sodium/potassium alloy carries heat from one member of rotary joint to other. Liquid conducts heat efficiently while permitting relative motion between members. Polypropylene rings contain liquid without interfering with rotation.
Heat exchanger with heat transfer control
Wiard, M.R.
1986-11-18
This patent describes a multi-sided plate and fin type heat exchanger core in which plate elements, intermediately positioning spacer elements and fin strips are stacked in a layered assembly providing fluid passages for different fluids to flow in a segregated heat transfer relation to one another. The core is characterized in that at certain locations in a stacked assembly layers include spacer elements substantially closing all sides of the heat exchangers to define between adjacent fluid passages layers of increased heat transfer resistance. The fin strips are sheet-like elements corrugated to forms specifically identifiable in terms of fins per inch, there being fin strips in at least certain resistance layers differing in terms of fins per inch from other strips in certain resistance layers.
Heat transfer in damaged material
NASA Astrophysics Data System (ADS)
Kruis, J.
2013-10-01
Fully coupled thermo-mechanical analysis of civil engineering problems is studied. The mechanical analysis is based on damage mechanics which is useful for modeling of behaviour of quasi-brittle materials, especially in tension. The damage is assumed to be isotropic. The heat transfer is assumed in the form of heat conduction governed by the Fourier law and heat radiation governed by the Stefan-Boltzmann law. Fully coupled thermo-mechanical problem is formulated.
Enhanced heat transfer using nanofluids
Choi, Stephen U. S. (Lisle, IL); Eastman, Jeffrey A. (Naperville, IL)
2001-01-01
This invention is directed to a method of and apparatus for enhancing heat transfer in fluids such as deionized water. ethylene glycol, or oil by dispersing nanocrystalline particles of substances such as copper, copper oxide, aluminum oxide, or the like in the fluids. Nanocrystalline particles are produced and dispersed in the fluid by heating the substance to be dispersed in a vacuum while passing a thin film of the fluid near the heated substance. The fluid is cooled to control its vapor pressure.
Heat transfer characteristics for disk fans
NASA Astrophysics Data System (ADS)
Prikhodko, Yu. M.; Chekhov, V. P.; Fomichev, V. P.
2014-08-01
Multiple-disk fans belong to the class of friction machines; they can be designed in two variants: centrifugal disk fans and diametrical disk fans. Flow patterns in these two types of machines are different, and they possess different heat transfer characteristics. The paper presents results of experimental study for a centrifugal disk fan under atmospheric pressure with air taken as working gas. The radial temperature distribution for a disk was obtained at different rotation speed of the rotor and different heating of the disks. Heat transfer characteristics of a centrifugal disk fan and a diametrical disk fan were compared. The research results demonstrate a higher heat transfer efficiency for centrifugal design versus diametrical disk design.
Nanofluid impingement jet heat transfer
2012-01-01
Experimental investigation to study the heat transfer between a vertical round alumina-water nanofluid jet and a horizontal circular round surface is carried out. Different jet flow rates, jet nozzle diameters, various circular disk diameters and three nanoparticles concentrations (0, 6.6 and 10%, respectively) are used. The experimental results indicate that using nanofluid as a heat transfer carrier can enhance the heat transfer process. For the same Reynolds number, the experimental data show an increase in the Nusselt numbers as the nanoparticle concentration increases. Size of heating disk diameters shows reverse effect on heat transfer. It is also found that presenting the data in terms of Reynolds number at impingement jet diameter can take into account on both effects of jet heights and nozzle diameter. Presenting the data in terms of Peclet numbers, at fixed impingement nozzle diameter, makes the data less sensitive to the percentage change of the nanoparticle concentrations. Finally, general heat transfer correlation is obtained verses Peclet numbers using nanoparticle concentrations and the nozzle diameter ratio as parameters. PMID:22340669
Measurement of thermoacoustic convection heat transfer phenomenon
NASA Technical Reports Server (NTRS)
Parang, M.; Salah-Eddine, A.
1983-01-01
In this paper the results of an experimental investigation of thermoacoustic convection (TAC) heat transfer phenomenon in both zero-gravity and gravity environment are presented and compared with pure conduction heat transfer. The numerical solutions of the governing equations obtained by others for TAC heat transfer phenomenon are also discussed. The experimental results show that for rapid heating rate at a boundary, the contribution of TAC heat transfer to a gas could be significantly (one order of magnitude) higher than heat transfer rate from pure conduction. The results also show significantly reduced transient time in heat transfer processes involving thermoacoustic convective heat transfer mode in both space and gravity environment.
Examination of Liquid Fluoride Salt Heat Transfer
Yoder Jr, Graydon L
2014-01-01
The need for high efficiency power conversion and energy transport systems is increasing as world energy use continues to increase, petroleum supplies decrease, and global warming concerns become more prevalent. There are few heat transport fluids capable of operating above about 600oC that do not require operation at extremely high pressures. Liquid fluoride salts are an exception to that limitation. Fluoride salts have very high boiling points, can operate at high temperatures and low pressures and have very good heat transfer properties. They have been proposed as coolants for next generation fission reactor systems, as coolants for fusion reactor blankets, and as thermal storage media for solar power systems. In each case, these salts are used to either extract or deliver heat through heat exchange equipment, and in order to design this equipment, liquid salt heat transfer must be predicted. This paper discusses the heat transfer characteristics of liquid fluoride salts. Historically, heat transfer in fluoride salts has been assumed to be consistent with that of conventional fluids (air, water, etc.), and correlations used for predicting heat transfer performance of all fluoride salts have been the same or similar to those used for water conventional fluids an, water, etc). A review of existing liquid salt heat transfer data is presented, summarized, and evaluated on a consistent basis. Less than 10 experimental data sets have been found in the literature, with varying degrees of experimental detail and measured parameters provided. The data has been digitized and a limited database has been assembled and compared to existing heat transfer correlations. Results vary as well, with some data sets following traditional correlations; in others the comparisons are less conclusive. This is especially the case for less common salt/materials combinations, and suggests that additional heat transfer data may be needed when using specific salt eutectics in heat transfer equipment designs. All of the data discussed above were taken under forced convective conditions (both laminar and turbulent). Some recent data taken at ORNL under free convection conditions are also presented and results discussed. This data was taken using a simple crucible experiment with an instrumented nickel heater inserted in the salt to induce natural circulation within the crucible. The data was taken over a temperature range of 550oC to 650oC in FLiNaK salt. This data covers both laminar and turbulent natural convection conditions, and is compared to existing forms of natural circulation correlations.
Boost Process Heating Efficiency - PHAST
2005-05-01
Use the Process Heating Assessment and Survey Tool (PHAST) to survey all process heating equipment within a facility, select the equipment that uses the most energy, and identify ways to increase efficiency.
NASA Astrophysics Data System (ADS)
Chapman, K.; Ramadhyani, S.; Ramamurthy, H.; Viskanta, R.
1989-03-01
A simple two-dimensional mathematical model was developed to predict the steady state thermal performance and combustion characteristics of a natural gas indirectly fired once-through radiant tube. Different burner geometries were studied and a grid size analysis was performed to determine the optimum grid spacing for each case. The rate of fuel burn-up was correlated using the burner geometry, the equivalence ratio, the fuel firing rate and air preheat temperatures as variables for non-swirling diffusion flames in the radiant tube. The model predictions were also compared with available experimental data for the purpose of validating the model. The transient, zero-dimensional model was used to conduct a detailed parametric study of a directly-fired batch reheating furnace. The parameters that were investigated are the load and refractory emissivities, the air preheat temperature, the heat capacity of the load, and the height of the combustion space. A one-dimensional model of a directly-fired continuous reheating furnace was also developed. A parametric study was completed to examine the effect of the local throughput on the furnace performance.
NASA Astrophysics Data System (ADS)
Chapman, K. S.; Ramadhyani, S.; Ramamurthy, H.; Viskanta, R.
1990-04-01
One and two-dimensional mathematical models have been developed to predict the steady state thermal performance and combustion characteristics of a natural gas-fired straight-through radiant tube. The effects of burner geometry, equivalence ratio, and preheat temperature and fuel firing rate on fuel burn-up have been investigated. The one-dimensional models for straight-through and single-ended recuperative radiant tubes have been validated using available experimental data. Thermal system models have been developed for the continuous and batch indirectly fired (radiant tube) furnaces to identify opportunities for fuel savings and enhanced productivity. Extensive parametric investigations were performed to examine the effects of load and refractory emissivities, load throughput rate and thickness on the thermal performance of the furnaces. Batch and continuous direct-fired furnace thermal system models were developed to analyze the effect of various design and operation parameters on the furnace thermal performance. An attempt was made to validate the batch furnace model by using experimental data from a small experimental furnace. Due to the size of the furnace, the two-dimensional heat conduction effects near the corners and edges of the furnace walls were significant. Since the effects were neglected in the system model, which is intended to simulate a large industrial furnace, the validation was unsuccessful. The parametric study consisted of examining the effect of the load and refractory emissivities and other operating and load parameters on the thermal performance of the batch and continuous furnaces.
Coolant passage heat transfer with rotation
NASA Technical Reports Server (NTRS)
Hajek, T. J.; Wagner, J.; Johnson, B. V.
1986-01-01
In current and advanced gas turbine engines, increased speeds, pressures and temperatures are used to reduce specific fuel consumption and increase thrust/weight ratios. Hence, the turbine airfoils are subjected to increased heat loads escalating the cooling requirements to satisfy life goals. The efficient use of cooling air requires that the details of local geometry and flow conditions be adequately modeled to predict local heat loads and the corresponding heat transfer coefficients. The objective of this program is to develop a heat transfer and pressure drop data base, computational fluid dynamic techniques and correlations for multi-pass rotating coolant passages with and without flow turbulators. The experimental effort is focused on the simulation of configurations and conditions expected in the blades of advanced aircraft high pressure turbines. With the use of this data base, the effects of Coriolis and buoyancy forces on the coolant side flow can be included in the design of turbine blades.
Coolant passage heat transfer with rotation
NASA Astrophysics Data System (ADS)
Hajek, T. J.; Wagner, J.; Johnson, B. V.
1986-10-01
In current and advanced gas turbine engines, increased speeds, pressures and temperatures are used to reduce specific fuel consumption and increase thrust/weight ratios. Hence, the turbine airfoils are subjected to increased heat loads escalating the cooling requirements to satisfy life goals. The efficient use of cooling air requires that the details of local geometry and flow conditions be adequately modeled to predict local heat loads and the corresponding heat transfer coefficients. The objective of this program is to develop a heat transfer and pressure drop data base, computational fluid dynamic techniques and correlations for multi-pass rotating coolant passages with and without flow turbulators. The experimental effort is focused on the simulation of configurations and conditions expected in the blades of advanced aircraft high pressure turbines. With the use of this data base, the effects of Coriolis and buoyancy forces on the coolant side flow can be included in the design of turbine blades.
Heat transfer - A review of 1983 literature
NASA Astrophysics Data System (ADS)
Eckert, E. R. G.; Goldstein, R. J.; Patankar, S. V.; Pfender, E.; Ramsey, J. W.; Simon, T. W.; Decker, N.; Kuehn, T. H.
1984-12-01
Developments in heat transfer research during 1983 are reviewed. The topics addressed include: conduction, channel flow, boundary layer and external flows, flow with separated regions, heat transfer in porous media, internal and external flows in natural convection, convection from rotating surfaces, combined heat and mass transfer, boiling, condensation, freezing and melting, radiation, MHD, and applications to heat exchangers and heat pipes, to solar energy, to plasma heat transfer, and elsewhere.
Host turbine heat transfer overview
NASA Technical Reports Server (NTRS)
Rohde, J. E.
1984-01-01
Improved methods of predicting airfoil local metal temperatures require advances in the understanding of the physics and methods of analytically predicting the following four aerothermal loads: hot gas flow over airfoils, heat transfer rates on the gas-side of airfoils, cooling air flow inside airfoils, and heat transfer rates on the coolant-side of airfoils. A systematic building block research approach is being pursued to investigate these four areas of concern from both the experimental and analytical sides. Experimental approaches being pursued start with fundamental experiments using simple shapes and flat plates in wind tunnels, progress to more realistic cold and hot cascade tests using airfoils, continue to progress in large low-speed rigs and turbines and warm turbines, and finally, combine all the interactive effects in tests using real engines or real engine type turbine rigs. Analytical approaches being pursued also build from relatively simple steady two dimensional inviscid flow and boundary layer heat transfer codes to more advanced steady two and three dimensional viscous flow and heat transfer codes. These advanced codes provide more physics to model better the interactive effects and the true real-engine environment.
Enhancement of heat transfer in waste-heat heat exchangers
Not Available
1980-07-01
The Fluidfire shallow fluidized bed heat transfer facility was modified during this program to give increased air flow capacity and to allow testing with different distributor plates and with two-stage heat exchangers. Tests were conducted using this heat transfer facility to investigate the effect of reduced distributor plate pressure loss and amount and type of bed material on the heat transfer performance of a single-stage fluidized bed heat exchanger. Elutriation from the bed was measured for different bed materials and distributor plates; alternate heat exchanger surfaces having different fin spacings were also tested. Two types of two-stage fluidized bed heat exchangers were tested: one having a baffle (having almost no pressure loss) located between the stages and which allowed bed material to recirculate between upper and lower beds; the second having two distributor plates in series with no recirculation of the bed material. The results obtained in the experimental program were used in conceptual design studies of multi-stage fluidized bed heat exchangers for waste heat recovery from diesel engine exhaust gases. Information was obtained from the literature and from diesel engine manufacturers to determine allowable diesel engine operating back pressures. The costs were estimated for two- and three-stage designs and were compared with costs obtained previously for single-stage fluidized bed and conventional heat exchanger designs.
Urban, P; Hanzelka, P; Kralik, T; Musilova, V; Srnka, A; Skrbek, L
2012-10-12
The heat transfer efficiency in turbulent Rayleigh-Bénard convection is investigated experimentally, in a cylindrical cell of height 0.3 m, diameter 0.3 m. We show that for Rayleigh numbers 10(12) < or approximately equal to Ra < or approximately equal to 10(15) the Nusselt number closely follows Nu is proportional to Ra(1/3 if the mean temperature of the working fluid-cryogenic helium gas-is measured by small sensors directly inside the cell at about half of its height. In contrast, if the mean temperature is determined in a conventional way, as an arithmetic mean of the bottom and top plate temperatures, the Nu(Ra) is proportional to Ra(γ) displays spurious crossover to higher γ that might be misinterpreted as a transition to the ultimate Kraichnan regime. PMID:23102312
Heat transfer in granular beds in radiative heat supply
NASA Astrophysics Data System (ADS)
Teplitskii, Yu. S.; Kovenskii, V. I.
2010-07-01
The basic regularities of stationary heat transfer throughout the space of an infiltrated granular bed in radiative heat supply in cocurrent-flow (solar collector 1) and counterflow (solar collector 2) regimes have been investigated within the framework of a two-temperature model. The boundary layer of the third kind for the skeleton of particles at exit from the bed has been formulated; this condition allows for the degree of turbulence of the heat-transfer-agent flow. A quasihomogeneity criterion making it possible to evaluate the thermal state of a two-phase system has been introduced. The approximation dependences for calculation of the active-portion length, the bed’s resistance, the solar-collector efficiency, and the average relative phase-temperature difference have been established.
NASA Astrophysics Data System (ADS)
Boltenko, E. A.; Varava, A. N.; Dedov, A. V.; Zakharenkov, A. V.; Komov, A. T.; Malakhovskii, S. A.
2015-03-01
Results from systematic investigations of heat transfer and pressure drop for water flow in an annular channel using an efficient method for enhancing heat transfer on a convex heating surface are presented. The main technical data of the thermal-hydraulic experimental setup are given together with a brief description of the control, monitoring, and physical parameters measurement and recording systems, as well as primary experimental data processing and storage system. The test section, the enhancement method based on setting up swirl flows, the geometrical characteristics of intensifiers, their schematic design, and installation technology are described. The experimental data are obtained in a wide range of coolant flow parameters under the conditions of single-phase convection with using intensifiers having different shapes. The test measurements carried out on a smooth annular channel showed good agreement with the classic correlations both for heat transfer and pressure drop, thereby confirming reliability of the experimental data. A considerable improvement in heat removal efficiency on the convex heating surface is obtained. The value of heat transfer coefficient is a factor of 1.8 higher than it is for smooth annular channels. The region of the values of intensifier geometrical characteristics and Reynolds numbers for which the growth of heat transfer prevails over the growth of pressure drop is established. It is shown that the maximums of heat transfer and pressure drop are observed at quite definite values of intensifier geometrical characteristics. The primary experimental data are processed and presented as a dependence of the Nusselt number on the Reynolds number for different values of the intensifier's relative fin height ?. The value of ? at which heat transfer reaches its maximum is found. The experiments were carried out in the pressure range p = 3.0-10.0 MPa and at the constant temperature of liquid at the test section inlet equal to 100C. The influence of peripheral liquid flow swirling pitch on heat transfer and pressure drop is studied. An empirical correlation describing the dependence of heat transfer on the intensifier geometrical characteristics is obtained.
Cueff, Sebastien; Labbe, Christophe; Cardin, Julien; Doualan, Jean-Louis; Khomenkova, Larysa; Hijazi, Khalil; Rizk, Richard
2010-09-15
This study investigates the influence of the deposition temperature T{sub d} on the Si-mediated excitation of Er ions within silicon-rich silicon oxide layers obtained by magnetron cosputtering. For T{sub d} exceeding 200 deg. C, an efficient indirect excitation of Er ions is observed for all as-deposited samples. The photoluminescence intensity improves gradually up to a maximum at T{sub d}=600 deg. C before decreasing for higher T{sub d} values. The effects of this ''growth-induced annealing'' are compared to those resulting from the same thermal budget used for the ''classical'' approach of postdeposition annealing performed after a room temperature deposition. It is demonstrated that the former approach is highly beneficial, not only in terms of saving time but also in the fourfold enhancement of the Er photoluminescence efficiency.
Heat transfer reviews 1976-1986
NASA Astrophysics Data System (ADS)
Eckert, Ernst Rudolf Georg; Goldstein, R. J.; Irvine, T. F., Jr.; Hartnett, J. P.
Theoretical and experimental investigations of heat-transfer phenomena are surveyed in a collection of annual review essays. The reviews were originally published in the International Journal of Heat and Mass Transfer. Cumulative author and subject indices are provided.
Heat transfer by thermovision and CFD methods
NASA Astrophysics Data System (ADS)
Kapjor, Andrej; Gressak, Tomas; Huzvar, Jozef; Vantuch, Martin
2014-08-01
The report deals with using of thermovision for analysis of heat transfer. It discusses the use of these methods to analysis of heat transfer in experimental measurement of floor convector and tubular heater with natural convection.
Boiling Heat Transfer to Halogenated Hydrocarbon Refrigerants
NASA Astrophysics Data System (ADS)
Yoshida, Suguru; Fujita, Yasunobu
The current state of knowledge on heat transfer to boiling refrigerants (halogenated hydrocarbons) in a pool and flowing inside a horizontal tube is reviewed with an emphasis on information relevant to the design of refrigerant evaporators, and some recommendations are made for future research. The review covers two-phase flow pattern, heat transfer characteristics, correlation of heat transfer coefficient, influence of oil, heat transfer augmentation, boiling from tube-bundle, influence of return bend, burnout heat flux, film boiling, dryout and post-dryout heat transfer.
Energy-efficient water heating
1995-01-01
This fact sheet describes how to reduce the amount of hot water used in faucets and showers, automatic dishwashers, and washing machines; how to increase water-heating system efficiency by lowering the water heater thermostat, installing a timer and heat traps, and insulating hot water pipes and the storage tank; and how to use off-peak power to heat water. A resource list for further information is included.
Heat transfer in GTA welding arcs
NASA Astrophysics Data System (ADS)
Huft, Nathan J.
Heat transfer characteristics of Gas Tungsten Arc Welding (GTAW) arcs with arc currents of 50 to 125 A and arc lengths of 3 to 11 mm were measured experimentally through wet calorimetry. The data collected were used to calculate how much heat reported to the cathode and anode and how much was lost from the arc column. A Visual Basic for Applications (VBA) macro was written to further analyze the data and account for Joule heating within the electrodes and radiation and convection losses from the arc, providing a detailed account of how heat was generated and dissipated within the system. These values were then used to calculate arc efficiencies, arc column voltages, and anode and cathode fall voltages. Trends were noted for variances in the arc column voltage, power dissipated from the arc column, and the total power dissipated by the system with changing arc length. Trends for variances in the anode and cathode fall voltages, total power dissipated, Joule heating within the torches and electrodes with changing arc current were also noted. In addition, the power distribution between the anode and cathode for each combination of arc length and arc current was examined. Keywords: Gas Tungsten Arc Welding, GTAW, anode fall, cathode fall, heat transfer, wet calorimetry
Nonlinear Heat Transfer 2d Structure
Energy Science and Technology Software Center (ESTSC)
1987-09-01
DOT-BPMD is a general-purpose, finite-element, heat-transfer program used to predict thermal environments. The code considers linear and nonlinear transient or steady-state heat conduction in two-dimensional planar or axisymmetric representations of structures. Capabilities are provided for modeling anisotropic heterogeneous materials with temperature-dependent thermal properties and time-dependent temperature, heat flux, convection and radiation boundary conditions, together with time-dependent internal heat generation. DOT-BPMD may be used in the evaluation of steady-state geothermal gradients as well as in themore » transient heat conduction analysis of repository and waste package subsystems. Strengths of DOT-BPMD include its ability to account for a wide range of possible boundary conditions, nonlinear material properties, and its efficient equation solution algorithm. Limitations include the lack of a three-dimensional analysis capability, no radiative or convective internal heat transfer, and the need to maintain a constant time-step in each program execution.« less
Heat Transfer in a Thermoacoustic Process
ERIC Educational Resources Information Center
Beke, Tamas
2012-01-01
Thermoacoustic instability is defined as the excitation of acoustic modes in chambers with heat sources due to the coupling between acoustic perturbations and unsteady heat addition. The major objective of this paper is to achieve accurate theoretical results in a thermoacoustic heat transfer process. We carry out a detailed heat transfer analysis…
Heat Transfer in a Thermoacoustic Process
ERIC Educational Resources Information Center
Beke, Tamas
2012-01-01
Thermoacoustic instability is defined as the excitation of acoustic modes in chambers with heat sources due to the coupling between acoustic perturbations and unsteady heat addition. The major objective of this paper is to achieve accurate theoretical results in a thermoacoustic heat transfer process. We carry out a detailed heat transfer analysis
Heat exchanger device and method for heat removal or transfer
Koplow, Jeffrey P.
2015-12-08
Systems and methods for a forced-convection heat exchanger are provided. In one embodiment, heat is transferred to or from a thermal load in thermal contact with a heat conducting structure, across a narrow air gap, to a rotating heat transfer structure immersed in a surrounding medium such as air.
Heat exchanger device and method for heat removal or transfer
Koplow, Jeffrey P.
2012-07-24
Systems and methods for a forced-convection heat exchanger are provided. In one embodiment, heat is transferred to or from a thermal load in thermal contact with a heat conducting structure, across a narrow air gap, to a rotating heat transfer structure immersed in a surrounding medium such as air.
Heat exchanger device and method for heat removal or transfer
Koplow, Jeffrey P
2013-12-10
Systems and methods for a forced-convection heat exchanger are provided. In one embodiment, heat is transferred to or from a thermal load in thermal contact with a heat conducting structure, across a narrow air gap, to a rotating heat transfer structure immersed in a surrounding medium such as air.
Heat exchanger device and method for heat removal or transfer
Koplow, Jeffrey P
2015-03-24
Systems and methods for a forced-convection heat exchanger are provided. In one embodiment, heat is transferred to or from a thermal load in thermal contact with a heat conducting structure, across a narrow air gap, to a rotating heat transfer structure immersed in a surrounding medium such as air.
Efficiency of Brownian heat engines.
Derényi, I; Astumian, R D
1999-06-01
We study the efficiency of one-dimensional thermally driven Brownian ratchets or heat engines. We identify and compare the three basic setups characterized by the type of the connection between the Brownian particle and the two heat reservoirs: (i) simultaneous, (ii) alternating in time, and (iii) position dependent. We make a clear distinction between the heat flow via the kinetic and the potential energy of the particle, and show that the former is always irreversible and it is only the third setup where the latter is reversible when the engine works quasistatically. We also show that in the third setup the heat flow via the kinetic energy can be reduced arbitrarily, proving that even for microscopic heat engines there is no fundamental limit of the efficiency lower than that of a Carnot cycle. PMID:11969723
Heat Transfer in Complex Fluids
Mehrdad Massoudi
2012-01-01
Amongst the most important constitutive relations in Mechanics, when characterizing the behavior of complex materials, one can identify the stress tensor T, the heat flux vector q (related to heat conduction) and the radiant heating (related to the radiation term in the energy equation). Of course, the expression 'complex materials' is not new. In fact, at least since the publication of the paper by Rivlin & Ericksen (1955), who discussed fluids of complexity (Truesdell & Noll, 1992), to the recently published books (Deshpande et al., 2010), the term complex fluids refers in general to fluid-like materials whose response, namely the stress tensor, is 'non-linear' in some fashion. This non-linearity can manifest itself in variety of forms such as memory effects, yield stress, creep or relaxation, normal-stress differences, etc. The emphasis in this chapter, while focusing on the constitutive modeling of complex fluids, is on granular materials (such as coal) and non-linear fluids (such as coal-slurries). One of the main areas of interest in energy related processes, such as power plants, atomization, alternative fuels, etc., is the use of slurries, specifically coal-water or coal-oil slurries, as the primary fuel. Some studies indicate that the viscosity of coal-water mixtures depends not only on the volume fraction of solids, and the mean size and the size distribution of the coal, but also on the shear rate, since the slurry behaves as shear-rate dependent fluid. There are also studies which indicate that preheating the fuel results in better performance, and as a result of such heating, the viscosity changes. Constitutive modeling of these non-linear fluids, commonly referred to as non-Newtonian fluids, has received much attention. Most of the naturally occurring and synthetic fluids are non-linear fluids, for example, polymer melts, suspensions, blood, coal-water slurries, drilling fluids, mud, etc. It should be noted that sometimes these fluids show Newtonian (linear) behavior for a given range of parameters or geometries; there are many empirical or semi-empirical constitutive equations suggested for these fluids. There have also been many non-linear constitutive relations which have been derived based on the techniques of continuum mechanics. The non-linearities oftentimes appear due to higher gradient terms or time derivatives. When thermal and or chemical effects are also important, the (coupled) momentum and energy equations can give rise to a variety of interesting problems, such as instability, for example the phenomenon of double-diffusive convection in a fluid layer. In Conclusion, we have studied the flow of a compressible (density gradient type) non-linear fluid down an inclined plane, subject to radiation boundary condition. The heat transfer is also considered where a source term, similar to the Arrhenius type reaction, is included. The non-dimensional forms of the equations are solved numerically and the competing effects of conduction, dissipation, heat generation and radiation are discussed. It is observed that the velocity increases rapidly in the region near the inclined surface and is slower in the region near the free surface. Since R{sub 7} is a measure of the heat generation due to chemical reaction, when the reaction is frozen (R{sub 7}=0.0) the temperature distributions would depend only on R{sub 1}, and R{sub 2}, representing the effects of the pressure force developed in the material due to the distribution, R{sub 3} and R{sub 4} viscous dissipation, R{sub 5} the normal stress coefficient, R{sub 6} the measure of the emissivity of the particles to the thermal conductivity, etc. When the flow is not frozen (RP{sub 7} > 0) the temperature inside the flow domain is much higher than those at the inclined and free surfaces. As a result, heat is transferred away from the flow toward both the inclined surface and the free surface with a rate that increases as R{sub 7} increases. For a given temperature, an increase in {zeta} implies that the activation energy is smaller and thus, the reaction rate is increased leading to an increase in the heat of the reaction. As a result the flow is chemically heated and its temperature increase. The results shown here indicate that for all values of {zeta} used the chemical effects are significant and the temperature is always higher than both the surface temperature and the free surface temperature. The heat transfer is always from the flow toward both the inclined surface and the free stream. It is also noticed that for all values of m chosen in this study, the temperature is higher than the surface and the free stream temperature. The heat transfer at the inclined surface and at the free stream increase slowly for negative values of m to about m=0.5, but it begins to significantly increase for m greater than 0.5.
Part B: Heat Transfer to Slush Hydrogen
NASA Technical Reports Server (NTRS)
Sindt, C. F.
1972-01-01
Heat transfer to slush hydrogen was measured at one atmosphere and at triple-point pressure. The data were compared with those for heat transfer to liquid hydrogen, and to classical heat transfer correlations for nucleate boiling. The slush data fit convective heat transfer correlations quite well. In general, the data show that for a given heat flux, the temperature difference between the wall and the bulk liquid is not as highly influenced by pressure as predicted by the core correlation for nucleate boiling.
Heat transfer in circulating fluidized bed combustor
Bucak, O.; Dogan, O.M.; Uysal, B.Z.
1999-07-01
The importance of fluidized bed combustion in utilizing the energy of especially low quality coals is widely accepted. Among various fluidized bed combustion technologies, circulating fluidized beds are preferred as a result of the efforts to get higher combustion efficiencies. The aim of the present research was to investigate the applicability of this technology to Turkish lignites. To achieve this object a 6.5 m tall pilot circulating fluidized bed combustor with 155 mm diameter and all the auxiliary equipment were designed, constructed and tested using Seyitomer lignite of 0.9--2.38 mm in size. Heat transfer from the bed to the water cooling jackets was examined to recover the combustion energy. The inside heat transfer coefficient was determined to be around 121 W/m{sup 2} K for the suspension density of 20--55 kg/m{sup 3}. The agreement of the experimental findings with theoretical estimations was also checked. Furthermore, the thermal efficiency of the system for the heat recovered was found to be 63%.
NASA Technical Reports Server (NTRS)
Garg, Vijay K.
2001-01-01
The turbine gas path is a very complex flow field. This is due to a variety of flow and heat transfer phenomena encountered in turbine passages. This manuscript provides an overview of the current work in this field at the NASA Glenn Research Center. Also, based on the author's preference, more emphasis is on the computational work. There is much more experimental work in progress at GRC than that reported here. While much has been achieved, more needs to be done in terms of validating the predictions against experimental data. More experimental data, especially on film cooled and rough turbine blades, are required for code validation. Also, the combined film cooling and internal cooling flow computation for a real blade is yet to be performed. While most computational work to date has assumed steady state conditions, the flow is clearly unsteady due to the presence of wakes. All this points to a long road ahead. However, we are well on course.
A literature survey on numerical heat transfer
NASA Astrophysics Data System (ADS)
Shih, T. M.
1982-12-01
Technical papers in the area of numerical heat transfer published from 1977 through 1981 are reviewed. The journals surveyed include: (1) ASME Journal of Heat Transfer, (2) International Journal of Heat and Mass Transfer, (3) AIAA Journal, (4) Numerical Heat Transfer, (5) Computers and Fluids, (6) International Journal for Numerical Methods in Engineering, (7) SIAM Journal of Numerical Analysis, and (8) Journal of Computational Physics. This survey excludes experimental work in heat transfer and numerical schemes that are not applied to equations governing heat transfer phenomena. The research work is categorized into the following areas: (A) conduction, (B) boundary-layer flows, (C) momentum and heat transfer in cavities, (D) turbulent flows, (E) convection around cylinders and spheres or within annuli, (F) numerical convective instability, (G) radiation, (H) combustion, (I) plumes, jets, and wakes, (J) heat transfer in porous media, (K) boiling, condensation, and two-phase flows, (L) developing and fully developed channel flows, (M) combined heat and mass transfer, (N) applications, (O) comparison and properties of numerical schemes, and (P) body-fitted coordinates and nonuniform grids.
Radiative heat transfer in porous uranium dioxide
Hayes, S.L.
1992-12-01
Due to low thermal conductivity and high emissivity of UO{sub 2}, it has been suggested that radiative heat transfer may play a significant role in heat transfer through pores of UO{sub 2} fuel. This possibility was computationally investigated and contribution of radiative heat transfer within pores to overall heat transport in porous UO{sub 2} quantified. A repeating unit cell was developed to model approximately a porous UO{sub 2} fuel system, and the heat transfer through unit cells representing a wide variety of fuel conditions was calculated using a finite element computer program. Conduction through solid fuel matrix as wekk as pore gas, and radiative exchange at pore surface was incorporated. A variety of pore compositions were investigated: porosity, pore size, shape and orientation, temperature, and temperature gradient. Calculations were made in which pore surface radiation was both modeled and neglected. The difference between yielding the integral contribution of radiative heat transfer mechanism to overall heat transport. Results indicate that radiative component of heat transfer within pores is small for conditions representative of light water reactor fuel, typically less than 1% of total heat transport. It is much larger, however, for conditions present in liquid metal fast breeder reactor fuel; during restructuring of this fuel type early in life, the radiative heat transfer mode was shown to contribute as much as 10-20% of total heat transport in hottest regions of fuel.
Low heat transfer oxidizer heat exchanger design and analysis
NASA Technical Reports Server (NTRS)
Kanic, P. G.; Kmiec, T. D.; Peckham, R. J.
1987-01-01
The RL10-IIB engine, a derivative of the RLIO, is capable of multi-mode thrust operation. This engine operates at two low thrust levels: tank head idle (THI), which is approximately 1 to 2 percent of full thrust, and pumped idle (PI), which is 10 percent of full thrust. Operation at THI provides vehicle propellant settling thrust and efficient engine thermal conditioning; PI operation provides vehicle tank pre-pressurization and maneuver thrust for log-g deployment. Stable combustion of the RL10-IIB engine at THI and PI thrust levels can be accomplished by providing gaseous oxygen at the propellant injector. Using gaseous hydrogen from the thrust chamber jacket as an energy source, a heat exchanger can be used to vaporize liquid oxygen without creating flow instability. This report summarizes the design and analysis of a United Aircraft Products (UAP) low-rate heat transfer heat exchanger concept for the RL10-IIB rocket engine. The design represents a second iteration of the RL10-IIB heat exchanger investigation program. The design and analysis of the first heat exchanger effort is presented in more detail in NASA CR-174857. Testing of the previous design is detailed in NASA CR-179487.
Asymmetric heat transfer from nanoparticles in lipid bilayers
NASA Astrophysics Data System (ADS)
Potdar, Dipti; Sammalkorpi, Maria
2015-12-01
Here, we use molecular dynamics simulations to characterize the heat transfer properties of lipid bilayer - gold nanoparticle systems in which the nanoparticle acts as a heat source. The focus is on dipalmitoylphosphatidylcholine (DPPC) lipid bilayers and thiolated alcohol and alkyl functionalized nanoparticles as prototype hydrophilic and hydrophobic nanoparticles. We find hydrophilic nanoparticles which are partly in contact with the surrounding water environment are more efficient in transferring heat to the system than hydrophobic ones which reside surrounded by the membrane. This is because of the hydrogen bonding capability of the hydroxy pentanethiol and the more efficient heat conductivity through water than the lipid bilayer. Additionally, we find the heat conductance is strongly asymmetric and has a discontinuity between the bilayer leaflets. In total, the findings provide understanding on heat transport from localized heat sources in lipid bilayers and could bear significance, e.g., in engineering and controlling photoactivated triggering of liposomal systems.
2011-12-05
HEATS Project: USF is developing low-cost, high-temperature phase-change materials (PCMs) for use in thermal energy storage systems. Heat storage materials are critical to the energy storage process. In solar thermal storage systems, heat can be stored in these materials during the day and released at night—when the sun is not out—to drive a turbine and produce electricity. In nuclear storage systems, heat can be stored in these materials at night and released to produce electricity during daytime peak-demand hours. Most PCMs do not conduct heat very well. Using an innovative, electroless encapsulation technique, USF is enhancing the heat transfer capability of its PCMs. The inner walls of the capsules will be lined with a corrosion-resistant, high-infrared emissivity coating, and the absorptivity of the PCM will be controlled with the addition of nano-sized particles. USF’s PCMs remain stable at temperatures from 600 to 1,000°C and can be used for solar thermal power storage, nuclear thermal power storage, and other applications.
Advanced turbine cooling, heat transfer, and aerodynamic studies
Je-Chin Han; Schobeiri, M.T.
1995-10-01
The contractual work is in three parts: Part I - Effect of rotation on enhanced cooling passage heat transfer, Part II - Effect on Thermal Barrier Coating (TBC) spallation on surface heat transfer, and Part III - Effect of surface roughness and trailing edge ejection on turbine efficiency under unsteady flow conditions. Each section of this paper has been divided into three parts to individually accommodate each part. Part III is further divided into Parts IIIa and IIIb.
Advanced turbine cooling, heat transfer, and aerodynamic studies
Han, Je-Chin; Schobeiri, M.T.
1995-12-31
The contractual work is in three parts: Part I - Effect of rotation on enhanced cooling passage heat transfer, Part II - Effect of Thermal Barrier Coating (TBC) spallation on surface heat transfer, and Part III - Effect of surface roughness and trailing edge ejection on turbine efficiency under unsteady flow conditions. Each section of this paper has been divided into three parts to individually accommodate each part. Part III is further divided into Parts IIIa and IIIb.
Containment condensing heat transfer. [PWR; BWR
Gido, R.G.; Koestel, A.
1983-01-01
This report presents a mechanistic heat-transfer model that is valid for large scale containment heat sinks. The model development is based on the determination that the condensation is controlled by mass diffusion through the vapor-air boundary layer, and the application of the classic Reynolds' analogy to formulate expressions for the transfer of heat and mass based on hydrodynamic measurements of the momentum transfer. As a result, the analysis depends on the quantification of the shear stress (momentum transfer) at the interface between the condensate film and the vapor-air boundary layer. In addition, the currently used Tagami and Uchida test observations and their range of applicability are explained.
Forced convective heat transfer in curved diffusers
NASA Technical Reports Server (NTRS)
Rojas, J.; Whitelaw, J. H.; Yianneskis, M.
1987-01-01
Measurements of the velocity characteristics of the flows in two curved diffusers of rectangular cross section with C and S-shaped centerlines are presented and related to measurements of wall heat transfer coefficients along the heated flat walls of the ducts. The velocity results were obtained by laser-Doppler anemometry in a water tunnel and the heat transfer results by liquid crystal thermography in a wind tunnel. The thermographic technique allowed the rapid and inexpensive measurement of wall heat transfer coefficients along flat walls of arbitrary boundary shapes with an accuracy of about 5 percent. The results show that an increase in secondary flow velocities near the heated wall causes an increase in the local wall heat transfer coefficient, and quantify the variation for maximum secondary-flow velocities in a range from 1.5 to 17 percent of the bulk flow velocity.
Phase Change Heat Transfer Device for Process Heat Applications
Piyush Sabharwall; Mike Patterson; Vivek Utgikar; Fred Gunnerson
2010-10-01
The next generation nuclear plant (NGNP) will most likely produce electricity and process heat, with both being considered for hydrogen production. To capture nuclear process heat, and transport it to a distant industrial facility requires a high temperature system of heat exchangers, pumps and/or compressors. The heat transfer system is particularly challenging not only due to the elevated temperatures (up to approx.1300 K) and industrial scale power transport (=50MW), but also due to a potentially large separation distance between the nuclear and industrial plants (100+m) dictated by safety and licensing mandates. The work reported here is the preliminary analysis of two-phase thermosyphon heat transfer performance with alkali metals. A thermosyphon is a thermal device for transporting heat from one point to another with quite extraordinary properties. In contrast to single-phased forced convective heat transfer via pumping a fluid, a thermosyphon (also called a wickless heat pipe) transfers heat through the vaporization/condensing process. The condensate is further returned to the hot source by gravity, i.e., without any requirement of pumps or compressors. With this mode of heat transfer, the thermosyphon has the capability to transport heat at high rates over appreciable distances, virtually isothermally and without any requirement for external pumping devices. Two-phase heat transfer by a thermosyphon has the advantage of high enthalpy transport that includes the sensible heat of the liquid, the latent heat of vaporization, and vapor superheat. In contrast, single-phase forced convection transports only the sensible heat of the fluid. Additionally, vapor-phase velocities within a thermosyphon are much greater than single-phase liquid velocities within a forced convective loop. Thermosyphon performance can be limited by the sonic limit (choking) of vapor flow and/or by condensate entrainment. Proper thermosyphon requires analysis of both.
Development of cryogenic rotatable heat transfer joints
NASA Astrophysics Data System (ADS)
Sadunas, J. A.; Backovsky, Z. F.; Wilson, D. E.
1992-07-01
A summary of cryogenic rotatable heat transfer joint technology development, at Rockwell International Space Division, is presented. Starting with the flight qualified radiative joint on the RM-20B IR sensor of the early 70's, leading to rotatable heat pipe joint, gas conductive joints, rolling-contact-conductance joints, and the more recent work on development and evaluation of cryogenic rotatable seals and mechanical interfaces. Potential applications, joint design optimization, heat transfer, seal leakage and torque test data are presented.
Enhanced Condensation Outside Horizontal Heat Transfer
NASA Astrophysics Data System (ADS)
Li, Tubes J.; Wang, H. F.; Sang, Z. F.
2010-03-01
Experimental investigation of heat transfer and friction characteristics was conducted on the out side of horizontal carbon steel heat transfer tubes under the pressure of saturated vapour 0.04 MP (gauge pressure). The test tubes included spiral-grooved tubes, corrugated tube and smooth tube. The use of water as test fluids has allowed to cover a wide range of turbulent fluid flow conditions: Reynolds number from 1104 to 5104. The heat transfer coefficients and amount of vapour condensation of spiral-grooved tube with different structure parameters are measured. The spiral-grooved tube has the best heat transfer performance compared with corrugated tube and smooth tube. The maximum heat transfer coefficients and amount of vapour condensation of spiralgroove tube is respectively 2.32 and 1.72 times as smooth tube. The maximum ? of spiral groove tube as comprehensive performance evaluation is 1.86. The corrugated tube increase heat transfer coefficients only in the Reynolds numbers lower than 1.5 104, but lower than spiralgroove tube, and transfer performance is worse than smooth tube with the Reynolds numbers grow. The structure parameters influence on spiral-grooved tube performance results show that the deeper of the groove, the better heat-exchange performance with the drag coefficient increased in the same Reynolds numbers. And the greater the fin pitch and trough radius, the poorer the heat exchange effectiveness with the drag coefficient decreased.
Fluid flow and heat transfer in polygonal micro heat pipes
NASA Astrophysics Data System (ADS)
Rao, Sai; Wong, Harris
2015-11-01
Micro heat pipes have been used to cool microelectronic devices, but their heat transfer coefficients are low compared with those of conventional heat pipes. We model heat and mass transfer in triangular, square, hexagonal, and rectangular micro heat pipes under small imposed temperature differences. A micro heat pipe is a closed microchannel filled with a wetting liquid and a long vapor bubble. When a temperature difference is applied across a micro heat pipe, the equilibrium vapor pressure at the hot end is higher than that at the cold end, and the difference drives a vapor flow. As the vapor moves, the vapor pressure at the hot end drops below the saturation pressure. This pressure drop induces continuous evaporation from the interface. Two dimensionless numbers emerge from the momentum and energy equations: the heat-pipe number H, and the evaporation exponent S. When H >> 1 and S >> 1, vapor-flow heat transfer dominates and a thermal boundary layer appears at the hot end, the thickness of which scales as L/S, where L is the half-length of the pipe. A similar boundary layer exists at the cold end. Outside the boundary layers, the temperature is uniform. We also find a dimensionless optimal pipe length Sm =Sm(H) for maximum evaporative heat transfer. Thus, our model suggests that micro heat pipes should be designed with H >> 1 and S =Sm. We calculate H and S for four published micro-heat-pipe experiments, and find encouraging support for our design criterion.
Heat transfer in a rotary kiln
Kirslis, S.J.; Watson, J.S.
1989-01-01
An improved heat transfer model has been developed for a direct-fired rotary kiln. The treatment of radiant heat transfer was based on the Reflection Method developed by Succec and applied by Gorog, and was extended to account for radiation from a flame. Some elements of the Resistive Network Method and Zone Method were incorporated in the model. This method results in a more straightforward and flexible treatment of radiant heat transfer than other methods of analysis. The model also accounts for conductive and convective heat transfer within the kiln and heat conducted through the kiln wall and lost from the outer kiln shell to the ambient surroundings. 25 refs., 9 figs., 2 tabs.
Conjugate heat transfer characterization in cooling channels
NASA Astrophysics Data System (ADS)
Cukurel, Beni; Arts, Tony; Selcan, Claudio
2012-06-01
Cooling technology of gas turbine blades, primarily ensured via internal forced convection, is aimed towards withdrawing thermal energy from the airfoil. To promote heat exchange, the walls of internal cooling passages are lined with repeated geometrical flow disturbance elements and surface non-uniformities. Raising the heat transfer at the expense of increased pressure loss; the goal is to obtain the highest possible cooling effectiveness at the lowest possible pressure drop penalty. The cooling channel heat transfer problem involves convection in the fluid domain and conduction in the solid. This coupled behavior is known as conjugate heat transfer. This experimental study models the effects of conduction coupling on convective heat transfer by applying iso-heat-flux boundary condition at the external side of a scaled serpentine passage. Investigations involve local temperature measurements performed by Infrared Thermography over flat and ribbed slab configurations. Nusselt number distributions along the wetted surface are obtained by means of heat flux distributions, computed from an energy balance within the metal domain. For the flat plate experiments, the effect of conjugate boundary condition on heat transfer is estimated to be in the order of 3%. In the ribbed channel case, the normalized Nusselt number distributions are compared with the basic flow features. Contrasting the findings with other conjugate and convective iso-heat-flux literature, a high degree of overall correlation is evident.
Pumped two-phase heat transfer loop
NASA Technical Reports Server (NTRS)
Edelstein, Fred
1988-01-01
A pumped loop two-phase heat transfer system, operating at a nearly constant temperature throughout, includes several independently operating grooved capillary heat exchanger plates supplied with working fluid through independent flow modulation valves connected to a liquid supply line, a vapor line for collecting vapor from the heat exchangers, a condenser between the vapor and the liquid lines, and a fluid circulating pump between the condenser and the heat exchangers.
Pumped two-phase heat transfer loop
NASA Technical Reports Server (NTRS)
Edelstein, Fred (Inventor)
1987-01-01
A pumped loop two-phase heat transfer system, operating at a nearly constant temperature throughout, includes a plurality of independently operating grooved capillary heat exchanger plates supplied with working fluid through independent flow modulation valves connected to a liquid supply line, a vapor line for collecting vapor from the heat exchangers, a condenser between the vapor and the liquid lines, and a fluid circulating pump between the condenser and the heat exchangers.
Prediction of Unshsrouded Rotor Blade Tip Heat Transfer
NASA Technical Reports Server (NTRS)
Ameri, A. A.; Steinthorsson, E.
1994-01-01
The rate of heat transfer on the tip of a turbine rotor blade and on the blade surface in the vicinity of the tip, was successfully predicted. The computations were performed with a multiblock computer code which solves the Reynolds Averaged Navier-Stokes equations using an efficient multigrid method. The case considered for the present calculations was the Space Shuttle Main Engine (SSME) high pressure fuel side turbine. The predictions of the blade tip heat transfer agreed reasonably well with the experimental measurements using the present level of grid refinement. On the tip surface, regions with high rate of heat transfer was found to exist close to the pressure side and suction side edges. Enhancement of the heat transfer was also observed on the blade surface near the tip. Further comparison of the predictions was performed with results obtained from correlations based on fully developed channel flow.
Heat transfer peculiarities in supersonic flows
NASA Astrophysics Data System (ADS)
Borovoi, V. Ia.; Brazhko, V. N.; Maikapar, G. I.; Skuratov, A. S.; Struminskaia, I. V.
1992-12-01
A method of heat transfer and gas flow investigation based on the application of thermal sensitive coatings or thermocouple sensors and various visualization techniques is described. The thermal sensitive coatings and visualization reveal heat transfer peculiarities, and the complex nature of the method contributes to understanding the processes and generalization of quantitative results. Data concerning heat transfer on the leeward side of a blunt cone in the regions of the shock-wave boundary layer and bow wave interaction, in gaps and cavities of the orbiter's thermal insulation, and in the vicinity of them, are presented.
HEAT TRANSFER AND TRITIUM PRODUCING SYSTEM
Johnson, E.F.
1962-06-01
This invention related to a circulating lithium-containing blanket system in a neution source hav'ing a magnetic field associated therewith. The blanket serves simultaneously and efficiently as a heat transfer mediunm and as a source of tritium. The blanket is composed of a lithium-6-enriched fused salt selected from the group consisting of lithium nitrite, lithium nitrate, a mixture of said salts, a mixture of each of said salts with lithium oxide, and a mixture of said salts with each other and with lithium oxide. The moderator, which is contained within the blanket in a separate conduit, can be water. A stellarator is one of the neutron sources which can be used in this invention. (AEC)
Passive heat transfer means for nuclear reactors
Burelbach, James P.
1984-01-01
An improved passive cooling arrangement is disclosed for maintaining adjacent or related components of a nuclear reactor within specified temperature differences. Specifically, heat pipes are operatively interposed between the components, with the vaporizing section of the heat pipe proximate the hot component operable to cool it and the primary condensing section of the heat pipe proximate the other and cooler component operable to heat it. Each heat pipe further has a secondary condensing section that is located outwardly beyond the reactor confinement and in a secondary heat sink, such as air ambient the containment, that is cooler than the other reactor component. Means such as shrouding normally isolated the secondary condensing section from effective heat transfer with the heat sink, but a sensor responds to overheat conditions of the reactor to open the shrouding, which thereby increases the cooling capacity of the heat pipe. By having many such heat pipes, an emergency passive cooling system is defined that is operative without electrical power.
Determination of the heat transfer coefficients in transient heat conduction
NASA Astrophysics Data System (ADS)
Nho Hào, Dinh; Thanh, Phan Xuan; Lesnic, D.
2013-09-01
The determination of the space- or time-dependent heat transfer coefficient which links the boundary temperature to the heat flux through a third-kind Robin boundary condition in transient heat conduction is investigated. The reconstruction uses average surface temperature measurements. In both cases of the space- or time-dependent unknown heat transfer coefficient the inverse problems are nonlinear and ill posed. Least-squares penalized variational formulations are proposed and new formulae for the gradients are derived. Numerical results obtained using the nonlinear conjugate gradient method combined with a boundary element direct solver are presented and discussed.
Coolant passage heat transfer with rotation
NASA Technical Reports Server (NTRS)
Hajek, T. J.; Wagner, J. H.; Johnson, B. V.
1987-01-01
The objective is to develop a heat transfer and pressure drop data base, computational fluid dynamic techniques and heat transfer correlations for rotating multipass coolant passages, with and without flow tabulators. The experimental effort is focused on the simulation of configurations and conditions expected in the blades of advanced aircraft high pressure turbines. With the use of this data base, the effects of Coriolis and buoyancy forces on the coolant side flow can be included in the design of turbine blades.
Condensation heat transfer in a microgravity environment
NASA Technical Reports Server (NTRS)
Chow, L. C.; Parish, R. C.
1986-01-01
In the present treatment of the condensation heat transfer process in a microgravity environment, two mechanisms for condensate removal are analyzed in light of two problems: (1) film condensation on a flat, porous plate, with condensate being removed by wall suction; and (2) the analytical prediction of the heat transfer coefficient of condensing annular flows, where the condensate film is driven by vapor shear. Both suction and vapor shear can effectively drain the condensate, ensuring continuous operation in microgravity.
Nanoparticle enhanced ionic liquid heat transfer fluids
Fox, Elise B.; Visser, Ann E.; Bridges, Nicholas J.; Gray, Joshua R.; Garcia-Diaz, Brenda L.
2014-08-12
A heat transfer fluid created from nanoparticles that are dispersed into an ionic liquid is provided. Small volumes of nanoparticles are created from e.g., metals or metal oxides and/or alloys of such materials are dispersed into ionic liquids to create a heat transfer fluid. The nanoparticles can be dispersed directly into the ionic liquid during nanoparticle formation or the nanoparticles can be formed and then, in a subsequent step, dispersed into the ionic liquid using e.g., agitation.
Prasad, B.G.S
1993-10-01
Regenerative heat in gas compressors diminishes performance, according to recent experiments. The results emphasize the importance of understanding and modeling the process to maximize operating efficiency. This paper presents results of experimental measurements done to determine regenerative heat transfer' contribution to suction gas heating and to compare its effect with earlier empirical models. These results form part of an ongoing research effort aimed at estimating heat transfer effect on compressor performance with a view to modeling such effects for improved prediction of compressor performance.
NASA Astrophysics Data System (ADS)
Wang, Yiping; Li, Shuai; Yang, Xue; Deng, Yadong; Su, Chuqi
2015-11-01
For vehicle thermoelectric exhaust energy recovery, the temperature difference between the heat exchanger and the coolant has a strong influence on the electric power generation, and ribs are often employed to enhance the heat transfer of the heat exchanger. However, the introduction of ribs will result in a large unwanted pressure drop in the exhaust system which is unfavorable for the engine's efficiency. Therefore, how to enhance the heat transfer and control the pressure drop in the exhaust system is quite important for thermoelectric generators (TEG). In the current study, a symmetrical arrangement of dimpled surfaces staggered in the upper and lower surfaces of the heat exchanger was proposed to augment heat transfer rates with minimal pressure drop penalties. The turbulent flow characteristics and heat transfer performance of turbulent flow over the dimpled surface in a flat heat exchanger was investigated by numerical simulation and temperature measurements. The heat transfer capacity in terms of Nusselt number and the pressure loss in terms of Fanning friction factors of the exchanger were compared with those of the flat plate. The pressure loss and heat transfer characteristics of dimples with a depth-to-diameter ratio (h/D) at 0.2 were investigated. Finally, a quite good heat transfer performance with minimal pressure drop heat exchanger in a vehicle TEG was obtained. And based on the area-averaged surface temperature of the heat exchanger and the Seeback effect, the power generation can be improved by about 15% at Re = 25,000 compared to a heat exchanger with a flat surface.
NASA Astrophysics Data System (ADS)
Wang, Yiping; Li, Shuai; Yang, Xue; Deng, Yadong; Su, Chuqi
2016-03-01
For vehicle thermoelectric exhaust energy recovery, the temperature difference between the heat exchanger and the coolant has a strong influence on the electric power generation, and ribs are often employed to enhance the heat transfer of the heat exchanger. However, the introduction of ribs will result in a large unwanted pressure drop in the exhaust system which is unfavorable for the engine's efficiency. Therefore, how to enhance the heat transfer and control the pressure drop in the exhaust system is quite important for thermoelectric generators (TEG). In the current study, a symmetrical arrangement of dimpled surfaces staggered in the upper and lower surfaces of the heat exchanger was proposed to augment heat transfer rates with minimal pressure drop penalties. The turbulent flow characteristics and heat transfer performance of turbulent flow over the dimpled surface in a flat heat exchanger was investigated by numerical simulation and temperature measurements. The heat transfer capacity in terms of Nusselt number and the pressure loss in terms of Fanning friction factors of the exchanger were compared with those of the flat plate. The pressure loss and heat transfer characteristics of dimples with a depth-to-diameter ratio ( h/D) at 0.2 were investigated. Finally, a quite good heat transfer performance with minimal pressure drop heat exchanger in a vehicle TEG was obtained. And based on the area-averaged surface temperature of the heat exchanger and the Seeback effect, the power generation can be improved by about 15% at Re = 25,000 compared to a heat exchanger with a flat surface.
Heat and mass transfer in materials processing
NASA Astrophysics Data System (ADS)
Tanasawa, Ichiro; Lior, Noam
Various papers on heat and mass transfer in materials processing are presented. The topics addressed include: heat transfer in plasma spraying, structure of ultrashort pulse plasma for CVD processing, heat flow and thermal contraction during plasma spray deposition, metal melting process by laser heating, improved electron beam weld design and control with beam current profile measurements, transport phenomena in laser materials processing, perspectives on integrated modeling of transport processes in semiconductor crystal growth, numerical simulation of natural convection in crystal growth in space and on the earth, conjugate heat transfer in crystal growth, effects of convection on the solidification of binary mixtures. Also discussed are: heat transfer in in-rotating-liquid-spinning process, thermal oscillations in materials processing, modeling and simulation of manufacturing processes of advanced composite materials, reaction engineering principles of combustion synthesis of advanced materials, numerical evaluation of the physical properties of magnetic fluids suitable for heat transfer control, and measurement techniques of thermophysical properties of high temperature melts. (For individual items see A93-10827 to A93-10843)
Heat transfer measurements for Stirling machine cylinders
NASA Technical Reports Server (NTRS)
Kornhauser, Alan A.; Kafka, B. C.; Finkbeiner, D. L.; Cantelmi, F. C.
1994-01-01
The primary purpose of this study was to measure the effects of inflow-produced heat turbulence on heat transfer in Stirling machine cylinders. A secondary purpose was to provide new experimental information on heat transfer in gas springs without inflow. The apparatus for the experiment consisted of a varying-volume piston-cylinder space connected to a fixed volume space by an orifice. The orifice size could be varied to adjust the level of inflow-produced turbulence, or the orifice plate could be removed completely so as to merge the two spaces into a single gas spring space. Speed, cycle mean pressure, overall volume ratio, and varying volume space clearance ratio could also be adjusted. Volume, pressure in both spaces, and local heat flux at two locations were measured. The pressure and volume measurements were used to calculate area averaged heat flux, heat transfer hysteresis loss, and other heat transfer-related effects. Experiments in the one space arrangement extended the range of previous gas spring tests to lower volume ratio and higher nondimensional speed. The tests corroborated previous results and showed that analytic models for heat transfer and loss based on volume ratio approaching 1 were valid for volume ratios ranging from 1 to 2, a range covering most gas springs in Stirling machines. Data from experiments in the two space arrangement were first analyzed based on lumping the two spaces together and examining total loss and averaged heat transfer as a function of overall nondimensional parameter. Heat transfer and loss were found to be significantly increased by inflow-produced turbulence. These increases could be modeled by appropriate adjustment of empirical coefficients in an existing semi-analytic model. An attempt was made to use an inverse, parameter optimization procedure to find the heat transfer in each of the two spaces. This procedure was successful in retrieving this information from simulated pressure-volume data with artificially generated noise, but it failed with the actual experimental data. This is evidence that the models used in the parameter optimization procedure (and to generate the simulated data) were not correct. Data from the surface heat flux sensors indicated that the primary shortcoming of these models was that they assumed turbulence levels to be constant over the cycle. Sensor data in the varying volume space showed a large increase in heat flux, probably due to turbulence, during the expansion stroke.
Interactive Heat Transfer Simulations for Everyone
ERIC Educational Resources Information Center
Xie, Charles
2012-01-01
Heat transfer is widely taught in secondary Earth science and physics. Researchers have identified many misconceptions related to heat and temperature. These misconceptions primarily stem from hunches developed in everyday life (though the confusions in terminology often worsen them). Interactive computer simulations that visualize thermal energy,…
Interactive Heat Transfer Simulations for Everyone
ERIC Educational Resources Information Center
Xie, Charles
2012-01-01
Heat transfer is widely taught in secondary Earth science and physics. Researchers have identified many misconceptions related to heat and temperature. These misconceptions primarily stem from hunches developed in everyday life (though the confusions in terminology often worsen them). Interactive computer simulations that visualize thermal energy,
Solving nonlinear heat transfer constant area fin problems
NASA Technical Reports Server (NTRS)
1968-01-01
Tables and graphs were compiled for solving nonlinear heat transfer constant area fin problems. The differential equation describing one-dimensional steady-state temperature distribution and heat flow under three modes of heat transfer with heat generation was investigated.
Heat transfer coefficient of nanofluids in minichannel heat sink
NASA Astrophysics Data System (ADS)
Utomo, Adi T.; Zavareh, Ashkan I. T.; Poth, Heiko; Wahab, Mohd; Boonie, Mohammad; Robbins, Phillip T.; Pacek, Andrzej W.
2012-09-01
Convective heat transfer in a heat sink consisting of rectangular minichannels and cooled with alumina and titania nanofluids has been investigated experimentally and numerically. Numerical simulations were carried out in a three dimensional domain employing homogeneous mixture model with effective thermo-physical properties of nanofluids. The predictions of base temperature profiles of the heat sink cooled with both water and nanofluids agree well with the experimental data. Experimental and numerical results show that the investigated nanofluids neither exhibits unusual enhancement of heat transfer coefficient nor decreases the heat sink base temperature. Although both nanofluids showed marginal thermal conductivity enhancements, the presence of solid nanoparticles lowers the specific heat capacity of nanofluids offseting the advantage of thermal conductivity enhancement. For all investigated flow rates, the Nusselt number of both nanofluids overlaps with that of water indicating that both nanofluids behave like single-phase fluids.
Optimizing Structure of LED Light Bulb for Heat Transfer
NASA Astrophysics Data System (ADS)
Kobayashi, T.; Itami, D.; Hashimoto, R.; Takashina, T.; Kanematsu, H.; Mizuta, K.; Utsumi, Y.
2013-04-01
In this paper, in order to optimize the heat transfer structure of LED light bulb, the effects of various parameters on the temperature of the LED device were systematically analyzed, and a design guideline was shown. Although LED device has become popular due to its high-efficiency and long life, the design issues on the heat transfer structure of LED light bulbs has still remained. Because the original efficiency and life of the LED device can not be obtained due to the local temperature rise of LED element and the surrounding polymer molding material. Therefore, heat transfer analysis by finite element method was conducted systematically by changing parameters such as the shape, number and thickness of the radiating fin of the LED. As a result, advantage of open type structure was shown, and the proper design guidance for the structure of the fin shape was obtained.
Heat transfer studies, quarterly report
Boehm, R.; Chen, Y.T.; Sathappan, A.K.
1996-01-19
Drying in subresidually-saturated systems at elevated temperatures has been studied for two different operating conditions. One condition started with flowing nitrogen gas through the test section and simultaneously heating up the porous medium at the same time (denoted in what follows as the ``transient heating case``). The other condition started initially with heating up the porous medium with no flow, and then running the nitrogen gas flow through the test section after a steady-state temperature distribution had been reached (denoted in what follows as the ``steady heating case``). A 90{degrees}C isothermal boundary condition was set on the aluminum wall. An average of 9% discrepancy in the mass balance calculation compared to the digital balance measurement has been found in the transient heating case. An average of 4.3% discrepancy in the mass balance calculation compared to the digital balance measurement has been found after the nitrogen gas flowed through test section for the steady heating case. A large discrepancy has also been found before the nitrogen gas admitted to the test section. This is because some of subresidual water in the test section has been drained out from the bottom due to the gravity effect and the strong convection flow in the porous medium before the nitrogen gas is admitted. This discrepancy may be reduced by closing the end tube at bottom before the nitrogen gas is admitted to the test section. The drying characteristics of this system are reported. A theoretical study has also been initiated in an attempt to supplement the experimental results, and this system is described in the report. A one-dimensional transient system is assumed in which a two-component (condensable and noncondensable) gas mixture flows through a porous medium with evaporation. The numerical calculation will be performed in the future work to compare to the experimental results.
Nonequilibrium Electromagnetic Fluctuations: Heat Transfer and Interactions
Krueger, Matthias; Kardar, Mehran; Emig, Thorsten
2011-05-27
The Casimir force between arbitrary objects in equilibrium is related to scattering from individual bodies. We extend this approach to heat transfer and Casimir forces in nonequilibrium cases where each body, and the environment, is at a different temperature. The formalism tracks the radiation from each body and its scatterings by the other objects. We discuss the radiation from a cylinder, emphasizing its polarized nature, and obtain the heat transfer between a sphere and a plate, demonstrating the validity of proximity transfer approximation at close separations and arbitrary temperatures.
Heat transfer studies. Quarterly report
Boehm, R.; Chen, Y.T.; Ma, L.
1995-04-20
Nitrogen gas has been replaced by room air in the extension of multi-phase models to sub-residual saturation experiments on drying. The TOUGH2 code has been used to simulate the same problem with the identical boundary conditions. A constant heat flux boundary condition on the heater has been performed in the repository drift experiment. The desired constant heat flux can produce a steady-state heater temperature ({approx}238{degrees}C) close to the constant heater surface temperature used before. What occurs in the air annulus and in the porous medium with the different thermal boundary conditions and water quantities is reported.
Code for Multiblock CFD and Heat-Transfer Computations
NASA Technical Reports Server (NTRS)
Fabian, John C.; Heidmann, James D.; Lucci, Barbara L.; Ameri, Ali A.; Rigby, David L.; Steinthorsson, Erlendur
2006-01-01
The NASA Glenn Research Center General Multi-Block Navier-Stokes Convective Heat Transfer Code, Glenn-HT, has been used extensively to predict heat transfer and fluid flow for a variety of steady gas turbine engine problems. Recently, the Glenn-HT code has been completely rewritten in Fortran 90/95, a more object-oriented language that allows programmers to create code that is more modular and makes more efficient use of data structures. The new implementation takes full advantage of the capabilities of the Fortran 90/95 programming language. As a result, the Glenn-HT code now provides dynamic memory allocation, modular design, and unsteady flow capability. This allows for the heat-transfer analysis of a full turbine stage. The code has been demonstrated for an unsteady inflow condition, and gridding efforts have been initiated for a full turbine stage unsteady calculation. This analysis will be the first to simultaneously include the effects of rotation, blade interaction, film cooling, and tip clearance with recessed tip on turbine heat transfer and cooling performance. Future plans call for the application of the new Glenn-HT code to a range of gas turbine engine problems of current interest to the heat-transfer community. The new unsteady flow capability will allow researchers to predict the effect of unsteady flow phenomena upon the convective heat transfer of turbine blades and vanes. Work will also continue on the development of conjugate heat-transfer capability in the code, where simultaneous solution of convective and conductive heat-transfer domains is accomplished. Finally, advanced turbulence and fluid flow models and automatic gridding techniques are being developed that will be applied to the Glenn-HT code and solution process.
Heat Transfer to Fuel Sprays Injected into Heated Gases
NASA Technical Reports Server (NTRS)
Selden, Robert F; Spencer, Robert C
1938-01-01
This report presents the results of a study made of the influence of several variables on the pressure decrease accompanying injection of a relatively cool liquid into a heated compressed gas. Indirectly, this pressure decrease and the time rate of change of it are indicative of the total heat transferred as well as the rate of heat transfer between the gas and the injected liquid. Air, nitrogen, and carbon dioxide were used as ambient gases; diesel fuel and benzene were the injected liquids. The gas densities and gas-fuel ratios covered approximately the range used in compression-ignition engines. The gas temperatures ranged from 150 degrees c. to 350 degrees c.
Indirect evaporative coolers with enhanced heat transfer
Kozubal, Eric; Woods, Jason; Judkoff, Ron
2015-09-22
A separator plate assembly for use in an indirect evaporative cooler (IEC) with an air-to-air heat exchanger. The assembly includes a separator plate with a first surface defining a dry channel and a second surface defining a wet channel. The assembly includes heat transfer enhancements provided on the first surface for increasing heat transfer rates. The heat transfer enhancements may include slit fins with bodies extending outward from the first surface of separator plate or may take other forms including vortex generators, offset strip fins, and wavy fins. In slit fin implementations, the separator plate has holes proximate to each of the slit fins, and the separator plate assembly may include a sealing layer applied to the second surface of the separator plate to block air flow through the holes. The sealing layer can be a thickness of adhesive, and a layer of wicking material is applied to the adhesive.
Modeling microscale heat transfer using Calore.
Gallis, Michail A.; Rader, Daniel John; Wong, Chung-Nin Channy; Bainbridge, Bruce L.; Torczynski, John Robert; Piekos, Edward Stanley
2005-09-01
Modeling microscale heat transfer with the computational-heat-transfer code Calore is discussed. Microscale heat transfer problems differ from their macroscopic counterparts in that conductive heat transfer in both solid and gaseous materials may have important noncontinuum effects. In a solid material, three noncontinuum effects are considered: ballistic transport of phonons across a thin film, scattering of phonons from surface roughness at a gas-solid interface, and scattering of phonons from grain boundaries within the solid material. These processes are modeled for polycrystalline silicon, and the thermal-conductivity values predicted by these models are compared to experimental data. In a gaseous material, two noncontinuum effects are considered: ballistic transport of gas molecules across a thin gap and accommodation of gas molecules to solid conditions when reflecting from a solid surface. These processes are modeled for arbitrary gases by allowing the gas and solid temperatures across a gas-solid interface to differ: a finite heat transfer coefficient (contact conductance) is imposed at the gas-solid interface so that the temperature difference is proportional to the normal heat flux. In this approach, the behavior of gas in the bulk is not changed from behavior observed under macroscopic conditions. These models are implemented in Calore as user subroutines. The user subroutines reside within Sandia's Source Forge server, where they undergo version control and regression testing and are available to analysts needing these capabilities. A Calore simulation is presented that exercises these models for a heated microbeam separated from an ambient-temperature substrate by a thin gas-filled gap. Failure to use the noncontinuum heat transfer models for the solid and the gas causes the maximum temperature of the microbeam to be significantly underpredicted.
Micro heat spreader enhanced heat transfer in MCMs
Shen, D.S.; Mitchell, R.T.; Dobranich, D.; Adkins, D.R.; Tuck, M.R.
1994-12-31
The peak thermal power generated in microelectronics assemblies has risen from less than 1 W/cm{sup 2} in 1980 to greater than 40 W/cm{sup 2} today, due primarily to increasing densities at both the IC and packaging levels. The authors have demonstrated enhanced heat transfer in a prototype Si substrate with a backside micro heat channel structure. Unlike conventional micro heat pipes, these channels are biaxial with a greater capacity for fluid transfer. Thermal modeling and preliminary experiments have shown an equivalent increase in substrate thermal conductivity to over 500 W/m{center_dot}K, or a four times improvement. Optimization of the structure and alternative liquids will further increase the thermal conductivity of the micro heat channel substrate with the objective being polycrystalline diamond, or about 1,200 W/m{center_dot}K. The crucial design parameters for the micro heat channel system and the thermal characteristics of the system will be covered.
Experimental and numerical investigation of HyperVapotron heat transfer
NASA Astrophysics Data System (ADS)
Wang, Weihua; Deng, Haifei; Huang, Shenghong; Chu, Delin; Yang, Bin; Mei, Luoqin; Pan, Baoguo
2014-12-01
The divertor first wall and neutral beam injection (NBI) components of tokamak devices require high heat flux removal up to 20-30 MW m-2 for future fusion reactors. The water cooled HyperVapotron (HV) structure, which relies on internal grooves or fins and boiling heat transfer to maximize the heat transfer capability, is the most promising candidate. The HV devices, that are able to transfer large amounts of heat (1-20 MW m-2) efficiently, have therefore been developed specifically for this application. Until recently, there have been few attempts to observe the detailed bubble characteristics and vortex evolvement of coolant flowing inside their various parts and understand of the internal two-phase complex heat transfer mechanism behind the vapotron effect. This research builds the experimental facilities of HyperVapotron Loop-I (HVL-I) and Pressure Water HyperVapotron Loop-II (PWHL-II) to implement the subcooled boiling principle experiment in terms of typical flow parameters, geometrical parameters of test section and surface heat flux, which are similar to those of the ITER-like first wall and NBI components (EAST and MAST). The multiphase flow and heat transfer phenomena on the surface of grooves and triangular fins when the subcooled water flowed through were observed and measured with the planar laser induced fluorescence (PLIF) and high-speed photography (HSP) techniques. Particle image velocimetry (PIV) was selected to reveal vortex formation, the flow structure that promotes the vapotron effect during subcooled boiling. The coolant flow data for contributing to the understanding of the vapotron phenomenon and the assessment of how the design and operational conditions that might affect the thermal performance of the devices were collected and analysed. The subcooled flow boiling model and methods of HV heat transfer adopted in the considered computational fluid dynamics (CFD) code were evaluated by comparing the calculated wall temperatures with the experimentally measured values. It was discovered that the bubble and vortex characteristics in the HV are clearly heavily dependent on the internal geometry, flow conditions and input heat flux. The evaporation latent heat is the primary heat transfer mechanism of HV flow under the condition of high heat flux, and the heat transfer through convection is very limited. The percentage of wall heat flux going into vapour production is almost 70%. These relationships between the flow phenomena and thermal performance of the HV device are essential to study the mechanisms for the flow structure alterations for design optimization and improvements of the ITER-like devices' water cooling structure and plasma facing components for future fusion reactors.
Heat transfer performance of Al2O3/water nanofluids in a mini channel heat sink.
Dominic, A; Sarangan, J; Suresh, S; Sai, Monica
2014-03-01
The high density heat removal in electronic packaging is a challenging task of modern days. Finding compact, energy efficient and cost effective methods of heat removal is being the interest of researchers. In the present work, mini channel with forced convective heat transfer in simultaneously developing regime is investigated as the heat transfer coefficient is inversely proportional to hydraulic diameter. Mini channel heat sink is made from the aluminium plate of 30 mm square with 8 mm thickness. It has 15 mini channel of 0.9 mm width, 1.3 mm height and 0.9 mm of pitch. DI water and water based 0.1% and 0.2% volume fractions of Al2O3/water nanofluids are used as coolant. The flow rates of the coolants are maintained in such a way that it is simultaneously developing. Reynolds number is varied from 400 to 1600 and heat input is varied from 40 W to 70 W. The results showed that heat transfer coefficient is more than the heat transfer coefficient of fully developed flow. Also the heat transfer is more for nanofluids compared to DI water. PMID:24745233
Characteristics of Transient Boiling Heat Transfer
Liu, Wei; Monde, Masanori; Mitsutake, Y.
2002-07-01
In this paper, one dimensional inverse heat conduction solution is used for a measurement of pool boiling curve. The experiments are performed under atmospheric pressure for copper, brass, carbon steel and gold. Boiling curves, including unsteady transition boiling region, are found can be traced fairly well from a simple experiment system by solving inverse heat conduction solution. Boiling curves for steady heating and transient heating, for heating process and cooling process are compared. Surface behavior around CHF point, transition boiling and film-boiling regions are observed by using a high-speed camera. The results show the practicability of the inverse heat conduction solution in tracing boiling curve and thereby supply us a new way in boiling heat transfer research. (authors)
Heat transfer in pressurized circulating fluidized beds
Wirth, K.E.
1997-12-31
The wall-to-suspension heat transfer in circulating fluidized beds (CFBs) operated at almost atmospheric pressure depends on the fluid mechanics immediately near the wall and on the thermal properties of the gas used. No influence of the superficial gas velocity adjusted is present. Consequently, the wall-to-suspension heat transfer coefficient in the form of the Nusselt number can be described by the Archimedes number of the gas-solid-system and the pressure drop number. The last number relates the cross-sectional average solids concentration to the solids concentration at minimum fluidization condition. However, with pressurized CFBs an influence of the superficial gas velocity on the wall-to-suspension heat transfer can be observed. Normalizing the superficial gas velocity in the form of the particle Froude number, two cases for the heat transfer in pressurized CFBs can be detected: with small particle Froude numbers (smaller than four) the same flow behavior and consequently the same heat transfer correlation is valid as it is for CFBs operated at almost atmospheric conditions; and with high particle Froude numbers (for example higher than four) the flow behavior immediately near the heat exchanger surface (CFB wall) can change. Instead of curtains of solids falling down with almost atmospheric pressure swirls of gas and solids can occur in the vicinity of the CFB wall when the static pressure is increased. With the change of the flow pattern near the CFB wall, i.e., the heat exchanger surface, a change of the heat transfer coefficient takes place. For the same Archimedes number, i.e., the same gas-solid system, and the same pressure drop number, i.e., the same cross-sectional average solids concentration, the Nusselt number, i.e., the heat transfer coefficient, increases when the flow pattern near the CFB wall changes from the curtain-type flow to that of the swirl-type flow. From experimentally obtained data in a cold running CFB a very simple correlation was obtained for the heat transfer coefficient.
Gopal, M.R.; Murthy, S.S.
1995-07-01
Metal hydride heat transformers are very promising energy conservation devices because they are compact, environmentally sound, and energy efficient and offer wide operating temperature ranges. Metal hydride heat transformers are considered as the most cost effective means to generate electric power or high-pressure steam from industrial waste heat with temperatures lower than 100 C for which no conventional process exists which can compete with metal hydride systems. The performance of a metal hydride heat transformer is predicted based on heat transfer and reaction kinetics of the paired hydride beds. Results are computed for a heat transformer working with a ZrCrFe{sub 1.4}/LaNi{sub 5} pair. The results show that due to the low effective thermal conductivity of the hydride beds, the performance of the system is controlled initially by heat transfer. However, when the effective thermal conductivity and overall heat transfer coefficient exceed a certain value, the reaction kinetics assume importance. The performance of the system improves significantly with input temperature as heat is supplied in both the half cycles. The performance also improves as the output and heat rejection temperatures decrease. For the ZrCrFe{sub 1.4}/LaNi{sub 5} system the coefficient of performance lies between 0.27 and 0.30 and the second-law efficiency lies between 0.37 and 0.44.
Fluid dynamics at transition regions of enhanced heat transfer channels
NASA Astrophysics Data System (ADS)
Case, Jennifer C.; Pohlman, Nicholas A.
2012-11-01
Helical wire coil inserts are used to enhance heat transfer in high heat flux cooling channels. Past research using temperature probes has sufficiently proven that wire coils increase heat transfer by factors of three to five through the disruption of the boundary layer in the channels. The coils are passive devices that are inexpensive to manufacture and easily integrate into existing heat exchangers given the limited pressure drop they produce. Most of the fluid mechanics research in flow over helical coils has focused on the dynamics and vortex structure in fully developed regions rather than the short transition region where the enhanced heat transfer is often expected. Understanding how the development of the flow occurs over the axial length of the cooling channel will determine minimum dimensions necessary for enhanced heat transfer. Results of particle-shadow velocimetry (PSV) measurements report on the flow velocities and turbulence that occurs in the transition regions at the beginning of wire coil inserts. The ability to relate parameters such as flow rate, wire diameter, coil pitch, and the total tube length will increase fundamental knowledge and will allow for more efficient heat exchanger designs. Funding provided by NIU's Undergraduate Special Opportunities in Artistry & Research grant program.
Progress in direct numerical simulation of turbulent heat transfer
Kasagi, Nobuhide; Iida, Oaki
1999-07-01
With high performance computers, reliable numerical methods and efficient post-processing environment, direct numerical simulation (DNS) offers valuable numerical experiments for turbulent heat transfer research. In particular, one can extensively study the turbulence dynamics and transport mechanism by visualizing any physical variable in space and time. It is also possible to establish detailed database of various turbulence statistics of turbulent transport phenomena, while systematically changing important flow and scalar field parameters. The present paper illustrates these novelties of DNS by introducing several examples in recent studies. Future directions of DNS for turbulence and heat transfer research are also discussed.
Heat transfer on accreting ice surfaces
NASA Technical Reports Server (NTRS)
Yamaguchi, Keiko; Hansman, R. John, Jr.
1990-01-01
Based on previous observations of glaze ice accretion, a 'Multi-Zone' model with distinct zones of different surface roughness is demonstrated. The use of surface roughness in the LEWICE ice accretion prediction code is examined. It was found that roughness is used in two ways: to determine the laminar to turbulent transition location and to calculate the turbulent heat transfer coefficient. A two zone version of the Multi-Zone model is implemented in the LEWICE code, and compared with experimental heat transfer coefficient and ice accretin results. The analysis of the boundary layer transition, surface roughness, and viscous flow field effects significantly increased the accuracy in predicting heat transfer coefficients. The Multi-Zone model was found to greatly improve the ice accretion prediction for the cases compared.
Heat transfer on accreting ice surfaces
NASA Technical Reports Server (NTRS)
Yamaguchi, Keiko; Hansman, R. John, Jr.
1993-01-01
Based on previous observations of glaze ice accretion on aircraft surfaces, a multizone model with distinct zones of different surface roughness is demonstrated. The use of surface roughness in the LEWICE ice accretion prediction code is examined. It was found that roughness is used in two ways: (1) to determine the laminar to turbulent boundary-layer transition location; and (2) to calculate the convective turbulent heat-transfer coefficient. A two-zone version of the multizone model is implemented in the LEWICE code, and compared with experimental convective heat-transfer coefficient and ice accretion results. The analysis of the boundary-layer transition, surface roughness, and viscous flowfield effects significantly increased the accuracy in predicting heat-transfer coefficients. The multizone model was found to significantly improve the ice accretion prediction for the cases compared.
Condensation heat transfer under a microgravity environment
NASA Technical Reports Server (NTRS)
Chow, L. C.
1986-01-01
A description of the condensation heat transfer process in microgravity is given. A review of the literature is also reported. The most essential element of condensation heat transfer in microgravity is the condensate removal mechanism. Two mechanisms for condensate removal are analyzed by looking into two problems. The first problem is concerned with film condensation on a flat porous plate with the condensate being removed by suction at the wall. The second problem is an analytical prediction of the heat transfer coefficient for condensing annular flows with the condensate film driven by the vapor shear. It is concluded that both suction and vapor shear can effectively drain the condensate to ensure continuous operation of the condensers operated under a microgravity environment. It is recommended that zero-g flight experiments be carried out to verify the prediction made in the present report. The results contained in this report should also aid in the design of future space condensers.
Gondrexon, N; Cheze, L; Jin, Y; Legay, M; Tissot, Q; Hengl, N; Baup, S; Boldo, P; Pignon, F; Talansier, E
2015-07-01
This paper aims to illustrate the interest of ultrasound technology as an efficient technique for both heat and mass transfer intensification. It is demonstrated that the use of ultrasound results in an increase of heat exchanger performances and in a possible fouling monitoring in heat exchangers. Mass transfer intensification was observed in the case of cross-flow ultrafiltration. It is shown that the enhancement of the membrane separation process strongly depends on the physico-chemical properties of the filtered suspensions. PMID:25216897
Self supporting heat transfer element
Story, Grosvenor Cook; Baldonado, Ray Orico
2002-01-01
The present invention provides an improved internal heat exchange element arranged so as to traverse the inside diameter of a container vessel such that it makes good mechanical contact with the interior wall of that vessel. The mechanical element is fabricated from a material having a coefficient of thermal conductivity above about 0.8 W cm.sup.-1.degree. K.sup.-1 and is designed to function as a simple spring member when that member has been cooled to reduce its diameter to just below that of a cylindrical container or vessel into which it is placed and then allowed to warm to room temperature. A particularly important application of this invention is directed to a providing a simple compartmented storage container for accommodating a hydrogen absorbing alloy.
Enhanced boiling heat transfer using radial fins
NASA Astrophysics Data System (ADS)
Razelos, P.; Das, S.; Krikkis, R. N.
2008-04-01
A numerical bifurcation analysis is carried out in order to determine the solution structure of radial fins subjected to multi-boiling heat transfer mode. One-dimensional conduction is employed throughout the thermal analysis. The fluid heat transfer coefficient is temperature dependent on the three regimes of phase-change of the fluid. Six fin profiles, defined in the text, are considered. Multiplicity structure is obtained to determine different types of bifurcation diagrams, which describe the dependence of a state variable of the system like the temperature or the heat dissipation on the fin design parameters, conduction convection parameter (CCP) or base temperature difference (Δ T). Specifically, the effects of Δ T, CCP and Biot number are analyzed. The results are presented graphically, showing the significant behavioral features of the heat rejection mechanism.
Heat transfer in slagging MHD radiant boilers
NASA Astrophysics Data System (ADS)
Im, K. H.; Ahluwalia, R. K.; Berry, G.
1981-01-01
A combined convection-radiation model is formulated to study heat transfer characteristics of slagging MHD radiant boilers. The model includes the contributions of carbon dioxide, water vapor, potassium atoms, and slag particles to gas radiation; it also accounts for the presence of slag layer on the wall of the radiant boiler. In order to determine the slag layer dynamics, the mechanism of slag particle deposition by thermophoresis and by fluid turbulence is investigated. The role of a slag layer in moderating the influence of refractory thickness on heat transfer is illustrated. The calculations indicate that an adequately slow cooling rate of the combustion gas can be realized in the radiant boiler.
Splice connector with internal heat transfer jacket
Silva, Frank A.; Mayer, Robert W.
1977-01-01
A heat transfer jacket is placed over the terminal portions of the conductors of a pair of high voltage cables which are connected in a splice connection wherein a housing surrounds the connected conductor portions, the heat transfer jacket extending longitudinally between the confronting ends of a pair of adaptor sleeves placed upon the insulation of the cables to engage and locate the adaptor sleeves relative to one another, and laterally between the conductors and the housing to provide a path of relatively high thermal conductivity between the connected conductor portions and the housing.
Heat transfer characteristics of an emergent strand
NASA Technical Reports Server (NTRS)
Simon, W. E.; Witte, L. C.; Hedgcoxe, P. G.
1974-01-01
A mathematical model was developed to describe the heat transfer characteristics of a hot strand emerging into a surrounding coolant. A stable strand of constant efflux velocity is analyzed, with a constant (average) heat transfer coefficient on the sides and leading surface of the strand. After developing a suitable governing equation to provide an adequate description of the physical system, the dimensionless governing equation is solved with Laplace transform methods. The solution yields the temperature within the strand as a function of axial distance and time. Generalized results for a wide range of parameters are presented, and the relationship of the results and experimental observations is discussed.
Microscale surface modifications for heat transfer enhancement.
Bostanci, Huseyin; Singh, Virendra; Kizito, John P; Rini, Daniel P; Seal, Sudipta; Chow, Louis C
2013-10-01
In this experimental study, two surface modification techniques were investigated for their effect on heat transfer enhancement. One of the methods employed the particle (grit) blasting to create microscale indentations, while the other used plasma spray coating to create microscale protrusions on Al 6061 (aluminum alloy 6061) samples. The test surfaces were characterized using scanning electron microscopy (SEM) and confocal scanning laser microscopy. Because of the surface modifications, the actual surface area was increased up to 2.8× compared to the projected base area, and the arithmetic mean roughness value (Ra) was determined to vary from 0.3 μm for the reference smooth surface to 19.5 μm for the modified surfaces. Selected samples with modified surfaces along with the reference smooth surface were then evaluated for their heat transfer performance in spray cooling tests. The cooling system had vapor-atomizing nozzles and used anhydrous ammonia as the coolant in order to achieve heat fluxes up to 500 W/cm(2) representing a thermal management setting for high power systems. Experimental results showed that the microscale surface modifications enhanced heat transfer coefficients up to 76% at 500 W/cm(2) compared to the smooth surface and demonstrated the benefits of these practical surface modification techniques to enhance two-phase heat transfer process. PMID:24003985
Experimental determination of stator endwall heat transfer
NASA Technical Reports Server (NTRS)
Boyle, Robert J.; Russell, Louis M.
1989-01-01
Local Stanton numbers were experimentally determined for the endwall surface of a turbine vane passage. A six vane linear cascade having vanes with an axial chord of 13.81 cm was used. Results were obtained for Reynolds numbers based on inlet velocity and axial chord between 73,000 and 495,000. The test section was connected to a low pressure exhaust system. Ambient air was drawn into the test section, inlet velocity was controlled up to a maximum of 59.4 m/sec. The effect of the inlet boundary layer thickness on the endwall heat transfer was determined for a range of test section flow rates. The liquid crystal measurement technique was used to measure heat transfer. Endwall heat transfer was determined by applying electrical power to a foil heater attached to the cascade endwall. The temperature at which the liquid crystal exhibited a specific color was known from a calibration test. Lines showing this specific color were isotherms, and because of uniform heat generation they were also lines of nearly constant heat transfer. Endwall static pressures were measured, along with surveys of total pressure and flow angles at the inlet and exit of the cascade.
Experimental determination of stator endwall heat transfer
NASA Technical Reports Server (NTRS)
Boyle, Robert J.; Russell, Louis M.
1989-01-01
Local Stanton numbers were experimentally determined for the endwall surface of a turbine vane possage. A six vane linear cascade having vanes with an axial chord of 13.81 cm was used. Resutls were obtained for Reynolds numbers based on inlet velocity and axial chord between 75,000 and 495,000. The test section was connected to a low pressure exhaust system. Ambient air was drawn into the test section, inlet velocity was controlled up to a maximum of 59.4 m/sec. The effect of the inlet boundary layer thickness on the endwall heat transfer was determined for a range of test section flow rates. The liquid crystal measurement technique was used to measure heat transfer. Endwall heat transfer was determined by applying electrical power to a foil heater attached to the cascade endwall. The temperature at which the liquid crystal exhibited a specific color was known from a calibration test. Lines showing this specific color were isotherms, and because of uniform heat generation they were also lines of nearly constant heat transfer. Endwall static pressures were measured, along with surveys of total pressure and flow angles at the inlet and exit of the cascade.
Heat transfer mechanisms in pulsating heat-pipes with nanofluid
NASA Astrophysics Data System (ADS)
Gonzalez, Miguel; Kelly, Brian; Hayashi, Yoshikazu; Kim, Yoon Jo
2015-01-01
In this study, the effect of silver nanofluid on a pulsating heat-pipe (PHP) thermal performance was experimentally investigated to figure out how nanofluid works with PHP. A closed loop PHP was built with 3 mm diameter tubes. Thermocouples and pressure transducers were installed for fluid and surface temperature and pressure measurements. The operating temperature of the PHP varied from 30-100 °C, with power rates of 61 W and 119 W. The fill ratio of 30%, 50%, and 70% were tested. The results showed that the evaporator heat transfer performance was degraded by the addition of nanoparticles due to increased viscosity at high power rate, while the positive effects of high thermal conductivity and enhanced nucleate boiling worked better at low power rate. In the condenser section, owing to the relatively high liquid content, nanofluid more effectively improved the heat transfer performance. However, since the PHP performance was dominantly affected by evaporator heat transfer performance, the overall benefit of enhanced condenser section performance was greatly limited. It was also observed that the poor heat transfer performance with nanofluid at the evaporator section led to lower operating pressure of PHP.
Axial flow heat exchanger devices and methods for heat transfer using axial flow devices
Koplow, Jeffrey P.
2016-02-16
Systems and methods described herein are directed to rotary heat exchangers configured to transfer heat to a heat transfer medium flowing in substantially axial direction within the heat exchangers. Exemplary heat exchangers include a heat conducting structure which is configured to be in thermal contact with a thermal load or a thermal sink, and a heat transfer structure rotatably coupled to the heat conducting structure to form a gap region between the heat conducting structure and the heat transfer structure, the heat transfer structure being configured to rotate during operation of the device. In example devices heat may be transferred across the gap region from a heated axial flow of the heat transfer medium to a cool stationary heat conducting structure, or from a heated stationary conducting structure to a cool axial flow of the heat transfer medium.
Heat transfer characteristics of porous media
NASA Technical Reports Server (NTRS)
Singh, B. S.; Dybbs, A.
1974-01-01
An investigation was conducted regarding the relative effects of conduction and convection in a saturated porous medium. A method reported by Singh et al. (1973) is used to determine the effective thermal conductivity of the saturated porous material. Heat transfer measurements are conducted under conditions of forced convection of the saturated liquid parallel and countercurrent to the flow of heat. The results are compared with the data obtained with the aid of an analytical model.
Heat transfer studies. Quarterly report
Boehm, R.; Chen, Y.; Izzeldin, A.; Kuharic, W.; Manuel, D.
1994-07-20
The experiments on determination of the wavelength corresponding to the equality of the refractive indices and how this varies with temperature have been completed. This was accomplished using the calibration setup of a 2-inch-long test cell filled with 2 mm diameter soda-lime glass beads. Some good images result, but these are not very clear. Therefore, a 1-inch long test cell has now been built. The modified test cell is shown. A 30-gauge type K thermocouple is placed at the center inside the test cell. A model 450 AET Omega thermocouple thermometer is used to indicate the temperature from the thermocouple. A polyurethane foam insulator covered the test cell circular wall to approximate an adiabatic condition. The organic chemical liquid and glass beads are heated up by the mica band heater. A variable transformer is used to the control power to the heater and, thus, the temperature in the cell. The temperature is slowly increased from ambient to try to maintain a generally homogeneous temperature inside the cell. If the indices of refraction of the glass beads and the organic liquid are the same, the image of glass beads then can be found. Chlorobenzene (C{sub 6}H{sub 5}Cl) with a refractive index of about 1.52 at 25{degrees}C (boiling point of 131.6{degrees}C), has been used as the organic chemical liquid. A 5 W argon-ion laser has been used as the light source to visualize the image generated by the Christiansen effect. Two optical grade prisms are used to separate the three wavelengths (green, teal, and blue) of the beam. 80 {mu}m and 200 {mu}m apertures are used to select a single wavelength portion of the beam (either 488 nm blue or 514.5 nm green).
Heat Flux Sensors for Infrared Thermography in Convective Heat Transfer
Carlomagno, Giovanni Maria; de Luca, Luigi; Cardone, Gennaro; Astarita, Tommaso
2014-01-01
This paper reviews the most dependable heat flux sensors, which can be used with InfraRed (IR) thermography to measure convective heat transfer coefficient distributions, and some of their applications performed by the authors' research group at the University of Naples Federico II. After recalling the basic principles that make IR thermography work, the various heat flux sensors to be used with it are presented and discussed, describing their capability to investigate complex thermo-fluid-dynamic flows. Several applications to streams, which range from natural convection to hypersonic flows, are also described. PMID:25386758
Heat flux sensors for infrared thermography in convective heat transfer.
Carlomagno, Giovanni Maria; de Luca, Luigi; Cardone, Gennaro; Astarita, Tommaso
2014-01-01
This paper reviews the most dependable heat flux sensors, which can be used with InfraRed (IR) thermography to measure convective heat transfer coefficient distributions, and some of their applications performed by the authors' research group at the University of Naples Federico II. After recalling the basic principles that make IR thermography work, the various heat flux sensors to be used with it are presented and discussed, describing their capability to investigate complex thermo-fluid-dynamic flows. Several applications to streams, which range from natural convection to hypersonic flows, are also described. PMID:25386758
Yutaka Abe; Yujiro Kawamoto; Chikako Iwaki; Tadashi Narabayashi; Michitsugu Mori; Shuichi Ohmori
2006-07-01
Next-generation nuclear reactor systems have been under development aiming at simplified system and improvement of safety and credibility. One of the innovative technologies is the supersonic steam injector, which has been investigated as one of the most important component of the next-generation nuclear reactor. The steam injector has functions of a passive pump without large motor or turbo-machinery and a high efficiency heat exchanger. The performances of the supersonic steam injector as a pump and a heat exchanger are dependent on direct contact condensation phenomena between a supersonic steam and a sub-cooled water jet. In previous studies of the steam injector, there are studies about the operating characteristics of steam injector and about the direct contact condensation between static water pool and steam in atmosphere. However, there is a little study about the turbulent heat transfer and flow behavior under the great shear stress. In order to examine the heat transfer and flow behavior in supersonic steam injector, it is necessary to measure the spatial temperature distribution and velocity in detail. The present study, visible transparent supersonic steam injector is used to obtain the axial pressure distributions in the supersonic steam injector, as well as high speed visual observation of water jet and steam interface. The experiments are conducted with and without non-condensable gas. The experimental results of the interfacial flow behavior between steam and water jet are obtained. It is experimentally clarified that an entrainment exists on the water jet surface. It is also clarified that discharge pressure is depended on the steam supply pressure, the inlet water flow rate, the throat diameter and non-condensable flow rate. Finally a heat flux is estimated about 19 MW/m{sup 2} without non-condensable gas condition in steam. (authors)
Information highway and numerical heat transfer
Shih, T.M.; Minkowycz, W.J.
1996-11-22
It is proposed that researchers in the numerical heat transfer community need to realize the trend of the information highway and agree to use a protocol or a module that constitutes the core of a computer program solving heat transfer problems. This will avoid duplicate programming and accelerate the technology advancement of numerical heat transfer. The module for two-dimensional incompressible Navier-Stokes flows is presented and explained. It is further demonstrated that, using this module as the foundation, the user can straightforwardly build up an entire personal computer code by inputting the data, specifying boundary conditions, and outputting the result. Other modules for slightly more complicated problems, such as transient flows with variable viscosity in irregular geometries, are also presented. Other than zoning matches for problems with multizones, the programming task for a user becomes minimal and simple: input, prescribe the boundary conditions, and output. The availability of Navier-Stokes modules is particularly helpful for less experienced numerical researchers, newcomers, and graduate students who have just entered the area of heat transfer and fluid flows.
Computational Aspects of Heat Transfer in Structures
NASA Technical Reports Server (NTRS)
Adelman, H. M. (Compiler)
1982-01-01
Techniques for the computation of heat transfer and associated phenomena in complex structures are examined with an emphasis on reentry flight vehicle structures. Analysis methods, computer programs, thermal analysis of large space structures and high speed vehicles, and the impact of computer systems are addressed.
Forced Convection Heat Transfer in Circular Pipes
ERIC Educational Resources Information Center
Tosun, Ismail
2007-01-01
One of the pitfalls of engineering education is to lose the physical insight of the problem while tackling the mathematical part. Forced convection heat transfer (the Graetz-Nusselt problem) certainly falls into this category. The equation of energy together with the equation of motion leads to a partial differential equation subject to various…
Heat Transfer and Thermodynamics: a Compilation
NASA Technical Reports Server (NTRS)
1974-01-01
A compilation is presented for the dissemination of information on technological developments which have potential utility outside the aerospace and nuclear communities. Studies include theories and mechanical considerations in the transfer of heat and the thermodynamic properties of matter and the causes and effects of certain interactions.
Forced Convection Heat Transfer in Circular Pipes
ERIC Educational Resources Information Center
Tosun, Ismail
2007-01-01
One of the pitfalls of engineering education is to lose the physical insight of the problem while tackling the mathematical part. Forced convection heat transfer (the Graetz-Nusselt problem) certainly falls into this category. The equation of energy together with the equation of motion leads to a partial differential equation subject to various
Heat transfer in a nuclear rocket engine
Konyukhov, G.V.; Petrov, A.I.
1995-02-01
Special features of heat transfer in the reactor of a nuclear rocket engine (NRE) are dealt with. It is shown that the design of the cooling system of the NRE reactor is governed by its stability to small deviations of the parameters from the corresponding calculated values and the possibility of compensating for effects due to nonuniformities and distrubances of various types and scales.
FED. Zoning for TRUMP Heat Transfer Code
Elrod, D.
1987-10-23
FED reduces the effort required to obtain the necessary geometric input for problems which are to be solved using the heat-transfer code, TRUMP. TRUMP calculates transient and steady-state temperature distributions in multidimensional systems. FED can properly zone any body of revolution in one, two, or three dimensions.
NASA Technical Reports Server (NTRS)
Pohner, John A.; Dempsey, Brian P.; Herold, Leroy M.
1990-01-01
Space Station elements and advanced military spacecraft will require rejection of tens of kilowatts of waste heat. Large space radiators and two-phase heat transport loops will be required. To minimize radiator size and weight, it is critical to minimize the temperature drop between the heat source and sink. Under an Air Force contract, a unique, high-performance heat exchanger is developed for coupling the radiator to the transport loop. Since fluid flow through the heat exchanger is driven by capillary forces which are easily dominated by gravity forces in ground testing, it is necessary to perform microgravity thermal testing to verify the design. This contract consists of an experiment definition phase leading to a preliminary design and cost estimate for a shuttle-based flight experiment of this heat exchanger design. This program will utilize modified hardware from a ground test program for the heat exchanger.
NASA Astrophysics Data System (ADS)
Pohner, John A.; Dempsey, Brian P.; Herold, Leroy M.
1990-07-01
Space Station elements and advanced military spacecraft will require rejection of tens of kilowatts of waste heat. Large space radiators and two-phase heat transport loops will be required. To minimize radiator size and weight, it is critical to minimize the temperature drop between the heat source and sink. Under an Air Force contract, a unique, high-performance heat exchanger is developed for coupling the radiator to the transport loop. Since fluid flow through the heat exchanger is driven by capillary forces which are easily dominated by gravity forces in ground testing, it is necessary to perform microgravity thermal testing to verify the design. This contract consists of an experiment definition phase leading to a preliminary design and cost estimate for a shuttle-based flight experiment of this heat exchanger design. This program will utilize modified hardware from a ground test program for the heat exchanger.
An experimental study of premixed flame impingement heat transfer
Mizuno, K.; Mital, R.; Viskanta, R.
1996-12-31
This paper reports results of an experimental study to determine the flame structure and heat transfer characteristics of a premixed methane-air flame impinging on a calorimeter. The flame structure is studied photographically and through temperature measurements. The convection and radiation heat transfer contributions of the flame are separated using a black and a highly reflecting water cooled calorimeter. The effects of nozzle-to-plate spacing, firing rate and equivalence ratio on the flame structure and average heat flux are reported. The axial temperature profiles are found to be a strong function of the gap between burner and calorimeter. The radial temperature profiles show a sharp decline near the burner edge. The photographs reveal that multiple jets, arranged in a circular configuration, exit between the cup-shaped ceramic burner and the calorimeter plate. The length of the flame increases with both the firing rate and the equivalence ratio. The heat flux is highest when the burner is closest to the calorimeter, except for the high firing rates when quenching occurs. Even though the heat flux increases, the heat transfer efficiency decreases with increasing firing rate. Heat flux is also found to increase as the flame becomes air rich in the range of parameters investigated.
Cooperative heat transfer and ground coupled storage system
Metz, Philip D.
1982-01-01
A cooperative heat transfer and ground coupled storage system wherein collected solar heat energy is ground stored and permitted to radiate into the adjacent ground for storage therein over an extended period of time when such heat energy is seasonally maximally available. Thereafter, when said heat energy is seasonally minimally available and has propagated through the adjacent ground a substantial distance, the stored heat energy may be retrieved by a circumferentially arranged heat transfer means having a high rate of heat transfer.
Cooperative heat transfer and ground coupled storage system
Metz, P.D.
A cooperative heat transfer and ground coupled storage system wherein collected solar heat energy is ground stored and permitted to radiate into the adjacent ground for storage therein over an extended period of time when such heat energy is seasonally maximally available. Thereafter, when said heat energy is seasonally minimally available and has propagated through the adjacent ground a substantial distance, the stored heat energy may be retrieved by a circumferentially arranged heat transfer means having a high rate of heat transfer.
Numerical Modeling of Ablation Heat Transfer
NASA Technical Reports Server (NTRS)
Ewing, Mark E.; Laker, Travis S.; Walker, David T.
2013-01-01
A unique numerical method has been developed for solving one-dimensional ablation heat transfer problems. This paper provides a comprehensive description of the method, along with detailed derivations of the governing equations. This methodology supports solutions for traditional ablation modeling including such effects as heat transfer, material decomposition, pyrolysis gas permeation and heat exchange, and thermochemical surface erosion. The numerical scheme utilizes a control-volume approach with a variable grid to account for surface movement. This method directly supports implementation of nontraditional models such as material swelling and mechanical erosion, extending capabilities for modeling complex ablation phenomena. Verifications of the numerical implementation are provided using analytical solutions, code comparisons, and the method of manufactured solutions. These verifications are used to demonstrate solution accuracy and proper error convergence rates. A simple demonstration of a mechanical erosion (spallation) model is also provided to illustrate the unique capabilities of the method.
Heat transfer in bioengineering and medicine
Chato, J.C.; Diller, T.E.; Diller, K.R.; Roemer, R.B.
1987-01-01
This book contains the following papers: New ideas in heat transfer for agricultural animals; Issues in heat transfer and tumor blood flow in localized hyperthermia treatments of cancer; Ultrasound enhances adriamycin toxicity in vitro; Scanned, focused ultrasound hyperthermia treatment of brain tumors; Mathematical prediction and phantom studies of the clinical target ''hot spot'' using a three applicator phased array system (TRIPAS); Development of an endoscopic RF hyperthermia system for deep tumor therapy; Simultaneous measurement of intrinsic and effective thermal conductivity; Determination of the transport of thermal energy by conduction in perfused tissue; A whole body thermal model of man with a realistic circulatory system; and Canine muscle blood flow changes in response to initial heating rates.
Heat transfer in a real engine environment
NASA Technical Reports Server (NTRS)
Gladden, Herbert J.
1985-01-01
The hot section facility at the Lewis Research Center was used to demonstrate the capability of instruments to make required measurements of boundary conditions of the flow field and heat transfer processes in the hostile environment of the turbine. The results of thermal scaling tests show that low temperature and pressure rig tests give optimistic estimates of the thermal performance of a cooling design for high pressure and temperature application. The results of measuring heat transfer coefficients on turbine vane airfoils through dynamic data analysis show good comparison with measurements from steady state heat flux gauges. In addition, the data trends are predicted by the STAN5 boundary layer code. However, the magnitude of the experimental data was not predicted by the analysis, particularly in laminar and transitional regions near the leading edge. The infrared photography system was shown capable of providing detailed surface thermal gradients and secondary flow features on a turbine vane and endwell.
Increase of unit efficiency by improved waste heat recovery
Bauer, G.; Lankes, F.
1998-07-01
For coal-fired power plants with flue gas desulfurization by wet scrubbing and desulfurized exhaust gas discharge via cooling tower, a further improvement of new power plant efficiency is possible by exhaust gas heat recovery. The waste heat of exhaust gas is extracted in a flue gas cooler before the wet scrubber and recovered for combustion air and/or feedwater heating by either direct or indirect coupling of heat transfer. Different process configurations for heat recovery system are described and evaluated with regard to net unit improvement. For unite firing bituminous coal an increase of net unit efficiency of 0.25 to 0.7 percentage points and for lignite 0.7 to 1.6 percentage points can be realized depending on the process configurations of the heat recovery systems.
Evaporative Heat Transfer Mechanisms within a Heat Melt Compactor
NASA Technical Reports Server (NTRS)
Golliher, Eric L.; Gotti, Daniel J.; Rymut, Joseph Edward; Nguyen, Brian K; Owens, Jay C.; Pace, Gregory S.; Fisher, John W.; Hong, Andrew E.
2013-01-01
This paper will discuss the status of microgravity analysis and testing for the development of a Heat Melt Compactor (HMC). Since fluids behave completely differently in microgravity, the evaporation process for the HMC is expected to be different than in 1-g. A thermal model is developed to support the design and operation of the HMC. Also, low-gravity aircraft flight data is described to assess the point at which water may be squeezed out of the HMC during microgravity operation. For optimum heat transfer operation of the HMC, the compaction process should stop prior to any water exiting the HMC, but nevertheless seek to compact as much as possible to cause high heat transfer and therefore shorter evaporation times.
Microscale Heat Transfer Transduced by Surface Plasmon Resonant Gold Nanoparticles
Roper, D. Keith; Ahn, W.; Hoepfner, M.
2008-01-01
Visible radiation at resonant frequencies is transduced to thermal energy by surface plasmons on gold nanoparticles. Temperature in ≤10-microliter aqueous suspensions of 20-nanometer gold particles irradiated by a continuous wave Ar+ ion laser at 514 nm increased to a maximum equilibrium value. This value increased in proportion to incident laser power and in proportion to nanoparticle content at low concentration. Heat input to the system by nanoparticle transduction of resonant irradiation equaled heat flux outward by conduction and radiation at thermal equilibrium. The efficiency of transducing incident resonant light to heat by microvolume suspensions of gold nanoparticles was determined by applying an energy balance to obtain a microscale heat-transfer time constant from the transient temperature profile. Measured values of transduction efficiency were increased from 3.4% to 9.9% by modulating the incident continuous wave irradiation. PMID:19011696
Wildemeersch, S; Jamin, P; Orban, P; Hermans, T; Klepikova, M; Nguyen, F; Brouyère, S; Dassargues, A
2014-11-15
Geothermal energy systems, closed or open, are increasingly considered for heating and/or cooling buildings. The efficiency of such systems depends on the thermal properties of the subsurface. Therefore, feasibility and impact studies performed prior to their installation should include a field characterization of thermal properties and a heat transfer model using parameter values measured in situ. However, there is a lack of in situ experiments and methodology for performing such a field characterization, especially for open systems. This study presents an in situ experiment designed for estimating heat transfer parameters in shallow alluvial aquifers with focus on the specific heat capacity. This experiment consists in simultaneously injecting hot water and a chemical tracer into the aquifer and monitoring the evolution of groundwater temperature and concentration in the recovery well (and possibly in other piezometers located down gradient). Temperature and concentrations are then used for estimating the specific heat capacity. The first method for estimating this parameter is based on a modeling in series of the chemical tracer and temperature breakthrough curves at the recovery well. The second method is based on an energy balance. The values of specific heat capacity estimated for both methods (2.30 and 2.54MJ/m(3)/K) for the experimental site in the alluvial aquifer of the Meuse River (Belgium) are almost identical and consistent with values found in the literature. Temperature breakthrough curves in other piezometers are not required for estimating the specific heat capacity. However, they highlight that heat transfer in the alluvial aquifer of the Meuse River is complex and contrasted with different dominant process depending on the depth leading to significant vertical heat exchange between upper and lower part of the aquifer. Furthermore, these temperature breakthrough curves could be included in the calibration of a complex heat transfer model for estimating the entire set of heat transfer parameters and their spatial distribution by inverse modeling. PMID:25201639
NASA Astrophysics Data System (ADS)
Wildemeersch, S.; Jamin, P.; Orban, P.; Hermans, T.; Klepikova, M.; Nguyen, F.; Brouyère, S.; Dassargues, A.
2014-11-01
Geothermal energy systems, closed or open, are increasingly considered for heating and/or cooling buildings. The efficiency of such systems depends on the thermal properties of the subsurface. Therefore, feasibility and impact studies performed prior to their installation should include a field characterization of thermal properties and a heat transfer model using parameter values measured in situ. However, there is a lack of in situ experiments and methodology for performing such a field characterization, especially for open systems. This study presents an in situ experiment designed for estimating heat transfer parameters in shallow alluvial aquifers with focus on the specific heat capacity. This experiment consists in simultaneously injecting hot water and a chemical tracer into the aquifer and monitoring the evolution of groundwater temperature and concentration in the recovery well (and possibly in other piezometers located down gradient). Temperature and concentrations are then used for estimating the specific heat capacity. The first method for estimating this parameter is based on a modeling in series of the chemical tracer and temperature breakthrough curves at the recovery well. The second method is based on an energy balance. The values of specific heat capacity estimated for both methods (2.30 and 2.54 MJ/m3/K) for the experimental site in the alluvial aquifer of the Meuse River (Belgium) are almost identical and consistent with values found in the literature. Temperature breakthrough curves in other piezometers are not required for estimating the specific heat capacity. However, they highlight that heat transfer in the alluvial aquifer of the Meuse River is complex and contrasted with different dominant process depending on the depth leading to significant vertical heat exchange between upper and lower part of the aquifer. Furthermore, these temperature breakthrough curves could be included in the calibration of a complex heat transfer model for estimating the entire set of heat transfer parameters and their spatial distribution by inverse modeling.
Combined heat and mass transfer device for improving separation process
Tran, Thanh Nhon
1999-01-01
A two-phase small channel heat exchange matrix simultaneously provides for heat transfer and mass transfer between the liquid and vapor phases of a multi-component mixture at a single, predetermined location within a separation column, significantly improving the thermodynamic efficiency of the separation process. The small channel heat exchange matrix is composed of a series of channels having a hydraulic diameter no greater than 5.0 millimeters for conducting a two-phase coolant. In operation, the matrix provides the liquid-vapor contacting surfaces within the separation column, such that heat and mass are transferred simultaneously between the liquid and vapor phases. The two-phase coolant allows for a uniform heat transfer coefficient to be maintained along the length of the channels and across the surface of the matrix. Preferably, a perforated, concave sheet connects each channel to an adjacent channel to facilitate the flow of the liquid and vapor phases within the column and to increase the liquid-vapor contacting surface area.
Combined heat and mass transfer device for improving separation process
Tran, T.N.
1999-08-24
A two-phase small channel heat exchange matrix simultaneously provides for heat transfer and mass transfer between the liquid and vapor phases of a multi-component mixture at a single, predetermined location within a separation column, significantly improving the thermodynamic efficiency of the separation process. The small channel heat exchange matrix is composed of a series of channels having a hydraulic diameter no greater than 5.0 millimeters for conducting a two-phase coolant. In operation, the matrix provides the liquid-vapor contacting surfaces within the separation column, such that heat and mass are transferred simultaneously between the liquid and vapor phases. The two-phase coolant allows for a uniform heat transfer coefficient to be maintained along the length of the channels and across the surface of the matrix. Preferably, a perforated, concave sheet connects each channel to an adjacent channel to facilitate the flow of the liquid and vapor phases within the column and to increase the liquid-vapor contacting surface area. 12 figs.
Analysis of a heat transfer device for measuring film coefficients
NASA Technical Reports Server (NTRS)
Medrow, R. A.; Johnson, R. L.; Loomis, W. R.; Wedeven, L. D.
1975-01-01
A heat transfer device consisting of a heated rotating cylinder in a bath was analyzed for its effectiveness to determine heat transfer coefficient of fluids. A time dependent analysis shows that the performance is insensitive to the value of heat transfer coefficient with the given rig configuration.
Microconvection heat transfer in electrorheological fluids in rotating electric field
NASA Astrophysics Data System (ADS)
Mokeev, A. A.; Gubarev, S. A.; Korobko, E. V.; Bedik, N. A.
2013-02-01
This work is dedicated to the study of heat transfer characteristics of electrorheological fluids in rotating electric fields. The problem of heat transfer in the electrosensitive heat carrier considering the microconvection transport mechanism is formulated and numerically solved. It is shown on the example of a flat layer, that internal rotations of elementary particles intensify heat transfer in ERF.
Unsteady heat transfer during subcooled film boiling
NASA Astrophysics Data System (ADS)
Yagov, V. V.; Zabirov, A. R.; Lexin, M. A.
2015-11-01
Cooling of high-temperature bodies in subcooled liquid is of importance for quenching technologies and also for understanding the processes initiating vapor explosion. An analysis of the available experimental information shows that the mechanisms governing heat transfer in these processes are interpreted ambiguously; a more clear-cut definition of the Leidenfrost temperature notion is required. The results of experimental observations (Hewitt, Kenning, and previous investigations performed by the authors of this article) allow us to draw a conclusion that there exists a special mode of intense heat transfer during film boil- ing of highly subcooled liquid. For revealing regularities and mechanisms governing intense transfer of energy in this process, specialists of Moscow Power Engineering Institute's (MPEI) Department of Engineering Thermal Physics conduct systematic works aimed at investigating the cooling of high-temperature balls made of different metals in water with a temperature ranging from 20 to 100°C. It has been determined that the field of temperatures that takes place in balls with a diameter of more than 30 mm in intense cooling modes loses its spherical symmetry. An approximate procedure for solving the inverse thermal conductivity problem for calculating the heat flux density on the ball surface is developed. During film boiling, in which the ball surface temperature is well above the critical level for water, and in which liquid cannot come in direct contact with the wall, the calculated heat fluxes reach 3-7 MW/m2.
Heterogeneous nanofluids: natural convection heat transfer enhancement
2011-01-01
Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case. PMID:21711755
Analysis of natural convective heat transfer of nano coated aluminium fins using Taguchi method
NASA Astrophysics Data System (ADS)
Senthilkumar, R.; Nandhakumar, A. J. D.; Prabhu, S.
2013-01-01
Rectangular aluminium fins were preferred for analysis and coated by carbon nano tubes using PVD to enhance the heat transfer rate of fins. Convective heat transfer rates for coated and non-coated surfaces were calculated and compared. The temperature and heat transfer characteristics were investigated using Nusselt, Grashof, Prandtl and Rayleigh numbers and also optimized by Taguchi method and ANOVA analysis. The average percentage of increase in fin efficiency is 5 %.
Local nucleation propagation on heat transfer uniformity during subcooled convective boiling
NASA Astrophysics Data System (ADS)
Kim, Beom Seok; Yang, Gang Mo; Shin, Sangwoo; Choi, Geehong; Cho, Hyung Hee
2015-01-01
Convective boiling heat transfer is an efficient cooling mechanism to dissipate amount of thermal energy by accompanying the phase transition of the working fluids. Particularly, the amount of heat dissipation capacity can be readily extensible by increasing the degree of subcooling due to initial demands requiring for coolant saturation. Under severely subcooled condition of 60°, we investigate boiling heat transfer phenomena regarding spatial heat transfer uniformity and stability on a planar surface. Severe subcooling can induce locally concentrated thermal loads due to poor spatial uniformity of the heat transfer. For reliable cooling, a high degree of spatial uniformity of the heat transfer should be guaranteed with minimized spatial deviation of heat transfer characteristics. Under pre-requisite safeguards below CHF, we experimentally elucidate the principal factors affecting the spatial uniformity of the heat transfer for a flow/thermal boundary layer considering heat transfer domains from a single-phase regime to a fully-developed boiling regime. Based on the local heat transfer evaluation, we demonstrate that full nucleation boiling over the entire heat transfer surface under subcooling conditions is favorable in terms of the uniformity of heat dissipation through the phase-change of the working fluid.
Reversible and irreversible heat transfer by radiation
NASA Astrophysics Data System (ADS)
del Río, Fernando; de la Selva, Sara María Teresa
2015-05-01
The theme of heat transfer by radiation is absent from most textbooks on thermodynamics, and its treatment in the applied literature presents some basic discrepancies concerning the validity of the Clausius relation between the quantity of heat exchanged, δ Q, and the accompanying entropy change, dS. We review the reversible and irreversible heat transfers by radiation to clarify the validity of the Clausius relation, and we show that in both cases, the Clausius relation is obeyed, as it should be. We also deal with radiation diluted by the presence of matter, introducing a dilution coefficient, ϕ, and an irreversibility factor, χ (φ ). This treatment requires the use of the correct relation between energy and heat fluxes, the spectral fluxes of energy and entropy, and Planck’s equation for the entropy of monochromatic radiation. For the irreversible case of diluted radiation, we recover the ratio between the fluxes of heat and entropy that agree with Clausius’ inequality, including an irreversibility factor, (4/3)χ (φ ). An improved modification for the explicit function χ (φ ) is given. As an illustration, the fluxes of energy and entropy from the Sun to the Earth are obtained. We also calculate the fluxes re-emitted by the Earth, taking into account the greenhouse effect. We find the value of 1.258 W{{m}-2}{{K}-1} for the re-emitted entropy flux after the radiation has been thermalized, which is much larger than the incident flux, in agreement with other authors.
Regenerative heat transfer in rotary kilns
NASA Astrophysics Data System (ADS)
Gorog, J. P.; Adams, T. N.; Brimacombe, J. K.
1982-06-01
A mathematical model has been developed to determine the temperature distribution in the wall of a rotary kiln. The model, which incorporates a detailed formulation of the radiative and convective heat-transfer coefficients in a kiln, has been employed to examine the effect of different kiln variables on both the regenerative and the overall heat transfer to the solids. The variables include rotational speed, pct loading, temperature of gas and solids, emissivity of wall and solids, convective heattransfer coefficients at the exposed and covered wall, and thermal diffusivity of the wall. The model shows that the regenerative heat flow is most important in the cold end of a rotary kiln, but that generally the temperature distribution and heat flows are largely independent of these variables. Owing to this insensitivity it has been possible to simplify the model with the aid of a resistive analog. Calculations are presented indicating that both the shell loss and total heat flow to the bed may be estimated to within 5 pct using this simplified model.
Full Eulerian lattice Boltzmann model for conjugate heat transfer.
Hu, Yang; Li, Decai; Shu, Shi; Niu, Xiaodong
2015-12-01
In this paper a full Eulerian lattice Boltzmann model is proposed for conjugate heat transfer. A unified governing equation with a source term for the temperature field is derived. By introducing the source term, we prove that the continuity of temperature and its normal flux at the interface is satisfied automatically. The curved interface is assumed to be zigzag lines. All physical quantities are recorded and updated on a Cartesian grid. As a result, any complicated treatment near the interface is avoided, which makes the proposed model suitable to simulate the conjugate heat transfer with complex interfaces efficiently. The present conjugate interface treatment is validated by several steady and unsteady numerical tests, including pure heat conduction, forced convection, and natural convection problems. Both flat and curved interfaces are also involved. The obtained results show good agreement with the analytical and/or finite volume results. PMID:26764851
Full Eulerian lattice Boltzmann model for conjugate heat transfer
NASA Astrophysics Data System (ADS)
Hu, Yang; Li, Decai; Shu, Shi; Niu, Xiaodong
2015-12-01
In this paper a full Eulerian lattice Boltzmann model is proposed for conjugate heat transfer. A unified governing equation with a source term for the temperature field is derived. By introducing the source term, we prove that the continuity of temperature and its normal flux at the interface is satisfied automatically. The curved interface is assumed to be zigzag lines. All physical quantities are recorded and updated on a Cartesian grid. As a result, any complicated treatment near the interface is avoided, which makes the proposed model suitable to simulate the conjugate heat transfer with complex interfaces efficiently. The present conjugate interface treatment is validated by several steady and unsteady numerical tests, including pure heat conduction, forced convection, and natural convection problems. Both flat and curved interfaces are also involved. The obtained results show good agreement with the analytical and/or finite volume results.
NASA Astrophysics Data System (ADS)
Benelmir, Riad; Mokraoui, Salim
2012-04-01
A simulation model of a fin-and-tube heat exchanger is presented. The effect of the relative humidity, air speed, fin base temperature, and inlet air temperature on the estimation of the overall heat-transfer coefficient and fin efficiency under wet conditions is also investigated. This model considers a non-uniform airflow velocity as well as a variable sensible heat transfer coefficient.
Acquisition systems for heat transfer measurement
De Witt, R.J.
1983-01-01
Practical heat transfer data acquisition systems are normally characterized by the need for high-resolution, low-drift, low-speed recording devices. Analog devices such as strip chart or circular recorders and FM analog magnetic tape have excellent resolution and work well when data will be presented in temperature versus time format only and need not be processed further. Digital systems are more complex and require an understanding of the following components: digitizing devices, interface bus types, processor requirements, and software design. This paper discusses all the above components of analog and digital data acquisition, as they are used in current practice. Additional information on thermocouple system analysis will aid the user in developing accurate heat transfer measuring systems.
A diffuser heat transfer and erosion code
NASA Astrophysics Data System (ADS)
Buzzard, G. H.
1985-10-01
A computer code for diffuser heat transfer and erosion analysis (DHTE) has been developed which improves upon the earlier Rocket Engine Diffuser Thermal Analysis Program (REDTAP). Improvements contained within DHTE include provision for a radial temperature gradient within the diffuser wall, an improved model for the particle impingement accommodation coefficient, a model for particle debris shielding, and a model for wall erosion by particle impact. DHTE differs from an earlier diffuser heat transfer code (DHT) to the extent that it incorporates a simple erosion model and utilizes a more recent diffuser version of the JANNAF Standardized Plume Flow Field Model (SCP2ND). The 77-inch diffuser was instrumented to record the water side wall temperature and water jacket temperature at selected sites along the initial seven feet of the diffuser during routine test firings. Data is presented that supports the predictions of DHTE but is inadequate to validate the code.
Dust as a Working Fluid for Heat Transfer Project
NASA Technical Reports Server (NTRS)
Mantovani, James G.
2015-01-01
The project known as "Dust as a Working Fluid" demonstrates the feasibility of a dust-based system for transferring heat radiatively into space for those space applications requiring higher efficiency, lower mass, and the need to operate in extreme vacuum and thermal environments - including operating in low or zero gravity conditions in which the dust can be conveyed much more easily than on Earth.
Coolant passage heat transfer with rotation
NASA Technical Reports Server (NTRS)
Hajek, T. J.; Higgins, A. W.
1985-01-01
The objective is to develop a heat transfer and pressure drop data base, computational fluid dynamic techniques, and correlations for multi-pass rotating coolant passages with and without flow turbulators. The experimental effort is focused on the simulation of configurations and conditions expected in the blades of advanced aircraft high pressure turbines. With the use of this data base, the effects of Coriolis and buoyancy forces on the coolant side flow can be included in the design of turbine blades.
Modeling heat transfer within porous multiconstituent materials
NASA Astrophysics Data System (ADS)
Niezgoda, Mathieu; Rochais, Denis; Enguehard, Franck; Rousseau, Benoit; Echegut, Patrick
2012-06-01
The purpose of our work has been to determine the effective thermal properties of materials considered heterogeneous at the microscale but which are regarded as homogenous in the macroscale environment in which they are used. We have developed a calculation code that renders it possible to simulate thermal experiments over complex multiconstituent materials from their numerical microstructural morphology obtained by volume segmentation through tomography. This modeling relies on the transient solving of the coupled conductive and radiative heat transfer in these voxelized structures.
Heat Transfer in a Superelliptic Transition Duct
NASA Technical Reports Server (NTRS)
Poinsatte, Philip; Thurman, Douglas; Hippensteele, Steven
2008-01-01
Local heat transfer measurements were experimentally mapped using a transient liquid-crystal heat transfer technique on the surface of a circular-to-rectangular transition duct. The transition duct had a length-to-diameter ratio of 1.5 and an exit-plane aspect ratio of 3. The crosssectional geometry was defined by the equation of a superellipse. The cross-sectional area was the same at the inlet and exit but varied up to 15 percent higher through the transition. The duct was preheated to a uniform temperature (nominally 64 C) before allowing room temperature air to be suddenly drawn through it. As the surface cooled, the resulting isothermal contours on the duct surface were revealed using a surface coating of thermochromic liquid crystals that display distinctive colors at particular temperatures. A video record was made of the surface temperature and time data for all points on the duct surfaces during each test. Using this surface temperature-time data together with the temperature of the air flowing through the model and the initial temperature of the model wall, the heat transfer coefficient was calculated by employing the classic one-dimensional, semi-infinite wall heat transfer conduction model. Test results are reported for inlet diameter-based Reynolds numbers ranging from 0.4x106 to 2.4x106 and two grid-generated freestream turbulence intensities of about 1 percent, which is typical of wind tunnels, and up to 16 percent, which may be more typical of real engine conditions.
Radiation heat transfer shapefactors for combustion systems
NASA Technical Reports Server (NTRS)
Emery, A. F.; Johansson, O.; Abrous, A.
1987-01-01
The computation of radiation heat transfer through absorbing media is commonly done through the zoning method which relies upon values of the geometric mean transmittance and absorptance. The computation of these values is difficult and expensive, particularly if many spectral bands are used. This paper describes the extension of a scan line algorithm, based upon surface-surface radiation, to the computation of surface-gas and gas-gas radiation transmittances.
Coolant passage heat transfer with rotation
NASA Astrophysics Data System (ADS)
Hajek, T. J.; Higgins, A. W.
1985-10-01
The objective is to develop a heat transfer and pressure drop data base, computational fluid dynamic techniques, and correlations for multi-pass rotating coolant passages with and without flow turbulators. The experimental effort is focused on the simulation of configurations and conditions expected in the blades of advanced aircraft high pressure turbines. With the use of this data base, the effects of Coriolis and buoyancy forces on the coolant side flow can be included in the design of turbine blades.
Low-melting point heat transfer fluid
Cordaro, Joseph Gabriel; Bradshaw, Robert W.
2010-11-09
A low-melting point, heat transfer fluid made of a mixture of five inorganic salts including about 29.1-33.5 mol % LiNO.sub.3, 0-3.9 mol % NaNO.sub.3, 2.4-8.2 mol % KNO.sub.3, 18.6-19.9 mol % NaNO.sub.2, and 40-45.6 mol % KNO.sub.2. These compositions can have liquidus temperatures below 80.degree. C. for some compositions.
Radiation heat transfer in catalytic monoliths
Boehman, A.L.
1998-12-01
Numerical simulations of heat- and mass-transfer and heterogeneous reactions in catalytic monoliths are reported with the focus on the influence of radiation heat transfer on the thermal behavior of the monolith. Appropriate heterogeneous kinetics and boundary conditions were calculated for two cases including: an automobile catalytic converter in which carbon monoxide is oxidized over a platinum (Pt) catalyst and a catalytic combustor for gas turbine power generation in which methane is oxidized over a palladium oxide (PdO) catalyst. Surface oxidation rates of carbon monoxide are based on measurements of Pt catalyst activity in a catalytic flow reactor, and rates for methane oxidation are based on reaction kinetics for a supported PdO catalyst assigned from differential reactor measurements. These simulations show that in the high aspect ratio passageways (length to diameter) in catalytic monoliths, radiation heat transfer can play a major role in the energy balance on the catalytic surfaces, which determines the transient warm-up behavior and the steady-state location of catalyst light-off. For gray surfaces, however, the predicted steady-state and transient behaviors are not sensitive to the emissivity of the monolith walls.
HOST turbine heat transfer subproject overview
NASA Technical Reports Server (NTRS)
Gladden, Herbert J.
1986-01-01
The experimental part of the turbine heat transfer subproject consists of six large experiments, which are highlighted in this overview, and three of somewhat more modest scope. One of the initial efforts was the stator airfoil heat transfer program. The non-film cooled and the showerhead film cooled data have already been reported. The gill region film cooling effort is currently underway. The investigation of secondary flows in a 90 deg curved duct, was completed. The first phase examined flows with a relatively thin inlet boundary layer and low free stream turbulence. The second phase studied a thicker inlet boundary layer and higher free stream turbulence. A comparison of analytical and experimental cross flow velocity vectors is shown for the 60 deg plane. Two experiments were also conducted in the high pressure facility. One examined full coverage film cooled vanes, and the other, advanced instrumentation. The other three large experimental efforts were conducted in a rotation reference frame. An experiment to obtain gas path airfoil heat transfer coefficients in the large, low speed turbine was completed. Single-stage data with both high and low-inlet turbulence were taken. The second phase examined a one and one-half stage turbine and focused on the second vane row. Under phase 3 aerodynamic quantities such as interrow time-averaged and rms values of velocity, flow angle, inlet turbulence, and surface pressure distribution were measured.
Heat transfer at interfaces with graphene
NASA Astrophysics Data System (ADS)
Xu, Zhiping
2012-02-01
Graphene has an ultrahigh in-plane thermal conductivity (5500 W/mK), but simultaneously a much lower conductivity along the c-axis in graphite or at the interfaces with other materials. As graphene finds more and more applications in nanoelectronics and high-performance composites, these interfaces become critically important in defining their heat dissipation and conduction performance. Unlike conventional interfaces in materials such as grain boundaries, the interfaces with graphene can be tuned by chemically modifying the graphene monolayer or intercalating the interfaces. These nano-engineering proposals require fundamental understanding of the heat transfer mechanisms. In order to obtain some insights on the transfer processes of mechanical and thermal energy across these interfaces, we perform series of molecular dynamics simulations, in combination with theoretical analysis by considering the quasi-ballistic nature of phonon transport at nanoscale. The result shows that heat dissipation or transport can be divided into two stages, beginning with an interface-controlled process. The effects of interface structures and binding properties on the whole process will be covered in this talk, with several examples showing how the interfacial thermal transfer can be engineered.
Enhanced condensation heat transfer with wettability patterning
NASA Astrophysics Data System (ADS)
Sinha Mahapatra, Pallab; Ghosh, Aritra; Ganguly, Ranjan; Megaridis, Constantine
2015-11-01
Condensation of water vapor on metal surfaces is useful for many engineering applications. A facile and scalable method is proposed for removing condensate from a vertical plate during dropwise condensation (DWC) in the presence of non-condensable gases (NCG). We use wettability-patterned superhydrophilic tracks (filmwise condensing domains) on a mirror-finish (hydrophilic) aluminum surface that promotes DWC. Tapered, horizontal ``collection'' tracks are laid to create a Laplace pressure driven flow, which collects condensate from the mirror-finish domains and sends it to vertical ``drainage tracks'' for gravity-induced shedding. An optimal design is achieved by changing the fractional area of superhydrophilic tracks with respect to the overall plate surface, and augmenting capillary-driven condensate-drainage by adjusting the track spatial layout. The design facilitates pump-less condensate drainage and enhances DWC heat transfer on the mirror-finish regions. The study highlights the relative influences of the promoting and retarding effects of dropwise and filmwise condensation zones on the overall heat transfer improvement on the substrate. The study demonstrated ~ 34% heat transfer improvement on Aluminum surface for the optimized design.
Liquid crystal thermography in boiling heat transfer
Klausner, J.F.; Mei, R.; Chen, W.C.
1995-12-31
The utilization of liquid crystal thermography to study heterogeneous boiling phenomena has gained popularity in recent years. In order not to disturb the nucleation process, which occurs in the microstructure of the heating surface, the crystals are applied to the backside of a thin heater. This work critically examines the ability of liquid crystal thermography to quantitatively capture the thermal field on the boiling surface. The thermal field identified experimentally through liquid crystal thermography is compared against that computed in the vicinity of a growing vapor bubble using a simulation which considers the simultaneous heat transfer between three phases: the solid heater, the liquid microlayer, and the growing vapor bubble. The temperature history beneath a growing vapor bubble elucidates the high frequency response required to capture the transient thermal fields commonly encountered in boiling experiments. Examination of the governing equations and numerical results reveal that due to the heater thermal inertia, the temperature variation on the bottom of the heater is significantly different than that on the boiling surface. In addition, the crystals themselves have a finite spatial resolution and frequency response which filter out much of the microscale phenomenon associated with boiling heat transfer. Analysis of existing pool and flow boiling liquid crystal thermographs indicate that the typical spacial resolution is on the order of 0.25 mm and the response time is on the order of 5 ms which are insufficient to resolve the fine spacial and temporal details of the heating surface thermal field. Thus the data obtained from liquid crystal thermography applied to boiling heat transfer must be cautiously interpreted.
High efficiency pump for space helium transfer
NASA Technical Reports Server (NTRS)
Hasenbein, Robert; Izenson, Michael G.; Swift, Walter L.; Sixsmith, Herbert
1991-01-01
A centrifugal pump was developed for the efficient and reliable transfer of liquid helium in space. The pump can be used to refill cryostats on orbiting satellites which use liquid helium for refrigeration at extremely low temperatures. The pump meets the head and flow requirements of on-orbit helium transfer: a flow rate of 800 L/hr at a head of 128 J/kg. The overall pump efficiency at the design point is 0.45. The design head and flow requirements are met with zero net positive suction head, which is the condition in an orbiting helium supply Dewar. The mass transfer efficiency calculated for a space transfer operation is 0.99. Steel ball bearings are used with gas fiber-reinforced teflon retainers to provide solid lubrication. These bearings have demonstrated the longest life in liquid helium endurance tests under simulated pumping conditions. Technology developed in the project also has application for liquid helium circulation in terrestrial facilities and for transfer of cryogenic rocket propellants in space.
Pressure loss and heat transfer in a toothed finned heat transfer medium
NASA Astrophysics Data System (ADS)
Ebeling, W. D.; Leidinger, B. J. G.
Thermohydraulic investigation was carried out in a special toothed-finned geometry, which was provided for increasing heat transfer in an evaporator cooler. The evaporator cooler has applications in space navigation. The toothed-finned heat carrier was used in a counter current, with a view to simplifying the heat transfer coefficient evaluation, from the temperature and volume flows measured. Test results obtained confirmed the suitability of this test arrangement. Relationships were derived from test results, for the pressure loss coefficient and the Nusselt number, with regard to the Reynolds number for this determined finned geometry.
Visualization study on pool boiling heat transfer
NASA Astrophysics Data System (ADS)
Kamei, Shuya; Hirata, Masaru
1991-04-01
The visualized boiling phenomena were observed by means of high speed photographic shadowgraphy using a rotating prism camera (nac HIGH SPEED CAMERA model-16HD) with the speed of about 3500 frames per second. The photographs show that pool boiling heat transfer phenomena are varied for the boiling curve based on the experiments. Experiments have been carried out to investigate pool boiling heat transfer phenomena on a horizontal thin filament in subcooled and saturated distilled water. The experiments were performed for atmospheric pressure,for filament diameters of about 0.3 mm, for region of natural convection to film boiling. The color-film made by high speed movie camera are converted to high speed color video-tape. It is convenient to edit and show the tape for visualization with teaching the students. The high speed color video showed that the successive motion and shape of bubbles during their process of detachment varied with increasing heat flux on the heated surface of a filament. From these results, it was confirmed that the high speed phenomena of boiling by the slow motion video pictures could be estimated clearly.
Two Heat-Transfer Improvements for Gas Liquefiers
NASA Technical Reports Server (NTRS)
Martin, Jerry L.
2005-01-01
Two improvements in heat-transfer design have been investigated with a view toward increasing the efficiency of refrigerators used to liquefy gases. The improvements could contribute to the development of relatively inexpensive, portable oxygen liquefiers for medical use. A description of the heat-transfer problem in a pulse-tube refrigerator is prerequisite to a meaningful description of the first improvement. In a pulse-tube refrigerator in particular, one of in-line configuration heat must be rejected from two locations: an aftercooler (where most of the heat is rejected) and a warm heat exchanger (where a small fraction of the total input power must be rejected as heat). Rejection of heat from the warm heat exchanger can be problematic because this heat exchanger is usually inside a vacuum vessel. When an acoustic-inertance tube is used to provide a phase shift needed in the pulse-tube cooling cycle, another problem arises: Inasmuch as the acoustic power in the acoustic-inertance tube is dissipated over the entire length of the tube, the gas in the tube must be warmer than the warm heat exchanger in order to reject heat at the warm heat exchanger. This is disadvantageous because the increase in viscosity with temperature causes an undesired increase in dissipation of acoustic energy and an undesired decrease in the achievable phase shift. Consequently, the overall performance of the pulse-tube refrigerator decreases with increasing temperature in the acoustic-inertance tube. In the first improvement, the acoustic-inertance tube is made to serve as the warm heat exchanger and to operate in an approximately isothermal condition at a lower temperature, thereby increasing the achievable phase shift and the overall performance of the refrigerator. This is accomplished by placing the acoustic-inertance tube inside another tube and pumping a cooling fluid (e.g., water) in the annular space between the tubes. Another benefit of this improvement is added flexibility of design to locate the warm heat-rejection components outside the vacuum vessel. The second improvement is the development of a compact radial-flow condenser characterized by a very high heat transfer coefficient and a small pressure drop.
High heat transfer oxidizer heat exchanger design and analysis. [RL10-2B engine
NASA Technical Reports Server (NTRS)
Kmiec, Thomas D.; Kanic, Paul G.; Peckham, Richard J.
1987-01-01
The RL10-2B engine, a derivative of the RL10, is capable of multimode thrust operation. This engine operates at two low thrust levels: tank head idle (THI), which is approximately 1 to 2% of full thrust, and pumped idle (PI), which is 10% of full thrust. Operation at THI provides vehicle propellant settling thrust and efficient engine thermal conditioning; PI operation provides vehicle tank pre-pressurization and maneuver thrust for low-g deployment. Stable combustion of the RL10-2B engine during the low thrust operating modes can be accomplished by using a heat exchanger to supply gaseous oxygen to the propellant injector. The oxidizer heat exchanger (OHE) vaporizes the liquid oxygen using hydrogen as the energy source. The design, concept verification testing and analysis for such a heat exchanger is discussed. The design presented uses a high efficiency compact core to vaporize the oxygen, and in the self-contained unit, attenuates any pressure and flow oscillations which result from unstable boiling in the core. This approach is referred to as the high heat transfer design. An alternative approach which prevents unstable boiling of the oxygen by limiting the heat transfer is referred to as the low heat transfer design and is reported in Pratt & Whitney report FR-19135-2.
Supercritical oxygen heat transfer. [regenerative cooling
NASA Technical Reports Server (NTRS)
Spencer, R. G.; Rousar, D. C.
1977-01-01
Heat transfer to supercritical oxygen was experimentally measured in electrical heated tubes. Experimental data were obtained for pressures ranging from 17 to 34.5 MPa (2460 to 5000 psia), and heat fluxes from 2 to 90 million w/sq cm (1.2 to 55 Btu/(sq in. sec)). Bulk temperatures ranged from 96 to 217 K (173 to 391 R). Experimental data obtained by other investigators were added to this to increase the range of pressure down to 2 MPa (290 psia) and increase the range of bulk temperature up to 566 K (1019 R). From this compilation of experimental data a correlating equation was developed which predicts over 95% of the experimental data within + or - 30%.
Thermal Storage and Advanced Heat Transfer Fluids (Fact Sheet)
Not Available
2010-08-01
Fact sheet describing NREL CSP Program capabilities in the area of thermal storage and advanced heat transfer fluids: measuring thermophysical properties, measuring fluid flow and heat transfer, and simulating flow of thermal energy and fluid.
Radiative heat transfer between two dielectric-filled metal gratings
NASA Astrophysics Data System (ADS)
Dai, J.; Dyakov, S. A.; Yan, M.
2016-04-01
Nanoscale surface corrugation is known to be able to drastically enhance radiative heat transfer between two metal plates. Here we numerically calculate the radiative heat transfer between two dielectric-filled metal gratings at dissimilar temperatures based on a scattering approach. It is demonstrated that, compared to unfilled metal gratings, the heat flux for a fixed geometry can be further enhanced, by up to 650% for the geometry separated by a vacuum gap of g =1 μ m and temperature values concerned in our study. The enhancement in radiative heat transfer is found to depend on refractive index of the filling dielectric, the specific grating temperatures, and naturally the gap size between the two gratings. The enhancement can be understood through examining the transmission factor spectra, especially the spectral locations of the spoof surface plasmon polariton modes. Of more practical importance, it's shown that the radiative heat flux can exceed that between two planar SiC plates with same thickness, separation, and temperature settings over a wide temperature range. This reaffirms that one can harness rich electromagnetic modal properties in nanostructured materials for efficient thermal management at nanoscale.
Heat and mass transfer over slippery, superhydrophobic surfaces
NASA Astrophysics Data System (ADS)
Haase, A. Sander; Lammertink, Rob G. H.
2016-04-01
The classical Graetz-Nusselt problem is extended to describe heat and mass transfer over heterogeneously slippery, superhydrophobic surfaces. The cylindrical wall consists of segments with a constant temperature/concentration and areas that are insulating/impermeable. Only in the case of mass transport do the locations of hydrodynamic slip and mass exchange coincide. This makes advection near the mass exchanging wall segments larger than near the heat exchanging regions. Also the direction of radial fluid flow is reversed for heat and mass transport, which has an influence on the location where the concentration or temperature boundary layer is compressed or extended. As a result, mass transport is more efficient than heat transfer. Also the influence of axial diffusion on the Nusselt and Sherwood numbers is investigated for various Péclet numbers Pe. When Pe < 102, which is characteristic for heat transfer over superhydrophobic surfaces, axial conduction should be taken into account. For Pe ≥ 102, which are typical numbers for mass transport in microfluidic systems, axial diffusion can be neglected.
Simulation of contact heat and mass transfer in spray and bubbling apparatuses
NASA Astrophysics Data System (ADS)
Shilyaev, Michael; Khromova, Helen; Tolstykh, Alexander
2014-08-01
The results of numerical implementation of mathematical models of heat and mass transfer and complex condensation-absorption dust- and gas cleaning of the vapor-gas flows are compared with the known empirical data for HSS, VS, FA, and CBA on heat and mass transfer characteristics and efficiency of dust catching.
Measuring Furnace/Sample Heat-Transfer Coefficients
NASA Technical Reports Server (NTRS)
Rosch, William R.; Fripp, Archibald L., Jr.; Debnam, William J., Jr.; Woodell, Glenn A.
1993-01-01
Complicated, inexact calculations now unnecessary. Device called HTX used to simulate and measure transfer of heat between directional-solidification crystal-growth furnace and ampoule containing sample of crystalline to be grown. Yields measurement data used to calculate heat-transfer coefficients directly, without need for assumptions or prior knowledge of physical properties of furnace, furnace gas, or specimen. Determines not only total heat-transfer coefficients but also coefficients of transfer of heat in different modes.
Various methods to improve heat transfer in exchangers
NASA Astrophysics Data System (ADS)
Pavel, Zitek; Vaclav, Valenta
2015-05-01
The University of West Bohemia in Pilsen (Department of Power System Engineering) is working on the selection of effective heat exchangers. Conventional shell and tube heat exchangers use simple segmental baffles. It can be replaced by helical baffles, which increase the heat transfer efficiency and reduce pressure losses. Their usage is demonstrated in the primary circuit of IV. generation MSR (Molten Salt Reactors). For high-temperature reactors we consider the use of compact desk heat exchangers, which are small, which allows the integral configuration of reactor. We design them from graphite composites, which allow up to 1000°C and are usable as exchangers: salt-salt or salt-acid (e.g. for the hydrogen production). In the paper there are shown thermo-physical properties of salts, material properties and principles of calculations.
Heat Transfer Through Turbulent Friction Layers
NASA Technical Reports Server (NTRS)
Reichardt, H.
1943-01-01
The "general Prandtl number" Pr(exp 1) - A(sub q)/A Pr, aside from the Reynolds number determines the ratio of turbulent to molecular heat transfer, and the temperature distribution in turbulent friction layers. A(sub q) = exchange coefficient for heat; A = exchange coefficient for momentum transfer. A formula is derived from the equation defining the general Prandtl number which describes the temperature as a function of the velocity. For fully developed thermal boundary layers all questions relating to heat transfer to and from incompressible fluids can be treated in a simple manner if the ratio of the turbulent shear stress to the total stress T(sub t)/T in the layers near the wall is known, and if the A(sub q)/A can be regarded as independent of the distance from the wall. The velocity distribution across a flat smooth channel and deep into the laminar sublayer was measured for isothermal flow to establish the shear stress ratio T(sub t)/T and to extend the universal wall friction law. The values of T(sub t)/T which resulted from these measurements can be approximately represented by a linear function of the velocity in the laminar-turbulent transition zone. The effect of the temperature relationship of the material values on the flow near the wall is briefly analyzed. It was found that the velocity at the laminar boundary (in contrast to the thickness of the laminar layer) is approximately independent of the temperature distribution. The temperature gradient at the wall and the distribution of temperature and heat flow in the turbulent friction layers were calculated on the basis of the data under two equations. The derived formulas and the figures reveal the effects of the Prandtl number, the Reynolds number, the exchange quantities and the temperature relationship of the material values.
NASA Astrophysics Data System (ADS)
Shokati, Naser; Mohammadkhani, Farzad; Farrokhi, Navid; Ranjbar, Faramarz
2014-12-01
During manufacture of engines, evaluation of engine performance is essential. This is accomplished in test cells. During the test, a significant portion of heat energy released by the fuel is wasted. In this study, in order to recover these heat losses, Organic Rankine Cycle (ORC) is recommended. The study has been conducted assuming the diesel oil to be composed of a single hydrocarbon such as C12H26. The composition of exhaust gases (products of combustion) have been computed (and not determined experimentally) from the stoichiometric equation representing the combustion reaction. The test cell heat losses are recovered in three separate heat exchangers (preheater, evaporator and superheater). These heat exchangers are separately designed, and the whole system is analyzed from energy and exergy viewpoints. Finally, a parametric study is performed to investigate the effect of different variables on the system performance characteristics such as the ORC net power, heat exchangers effectiveness, the first law efficiency, exergy destruction and heat transfer surfaces. The results of the study show that by utilizing ORC, heat recovery equivalent to 8.85 % of the engine power is possible. The evaporator has the highest exergy destruction rate, while the pump has the lowest among the system components. Heat transfer surfaces are calculated to be 173.6, 58.7, and 11.87 m2 for the preheater, evaporator and superheater, respectively.
7 CFR 3201.54 - Heat transfer fluids.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 7 Agriculture 15 2014-01-01 2014-01-01 false Heat transfer fluids. 3201.54 Section 3201.54... Designated Items § 3201.54 Heat transfer fluids. (a) Definition. Products with high thermal capacities used to facilitate the transfer of heat from one location to another, including coolants or...
7 CFR 3201.54 - Heat transfer fluids.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 7 Agriculture 15 2012-01-01 2012-01-01 false Heat transfer fluids. 3201.54 Section 3201.54... Designated Items § 3201.54 Heat transfer fluids. (a) Definition. Products with high thermal capacities used to facilitate the transfer of heat from one location to another, including coolants or...
7 CFR 3201.54 - Heat transfer fluids.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 7 Agriculture 15 2013-01-01 2013-01-01 false Heat transfer fluids. 3201.54 Section 3201.54... Designated Items § 3201.54 Heat transfer fluids. (a) Definition. Products with high thermal capacities used to facilitate the transfer of heat from one location to another, including coolants or...
7 CFR 2902.54 - Heat transfer fluids.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 7 Agriculture 15 2011-01-01 2011-01-01 false Heat transfer fluids. 2902.54 Section 2902.54... Items § 2902.54 Heat transfer fluids. (a) Definition. Products with high thermal capacities used to facilitate the transfer of heat from one location to another, including coolants or refrigerants for use...
Heat Transfer in Glass, Aluminum, and Plastic Beverage Bottles
ERIC Educational Resources Information Center
Clark, William M.; Shevlin, Ryan C.; Soffen, Tanya S.
2010-01-01
This paper addresses a controversy regarding the effect of bottle material on the thermal performance of beverage bottles. Experiments and calculations that verify or refute advertising claims and represent an interesting way to teach heat transfer fundamentals are described. Heat transfer coefficients and the resistance to heat transfer offered
Film-Cooling Heat-Transfer Measurements Using Liquid Crystals
NASA Technical Reports Server (NTRS)
Hippensteele, Steven A.
1997-01-01
The following topics are discussed: (1) The Transient Liquid-Crystal Heat-Transfer Technique; (2) 2-D Film-Cooling Heat-Transfer on an AlliedSignal Vane; and (3) Effects of Tab Vortex Generators on Surface Heat Transfer. Downstream of a Jet in Crossflow.
Heat Transfer in Glass, Aluminum, and Plastic Beverage Bottles
ERIC Educational Resources Information Center
Clark, William M.; Shevlin, Ryan C.; Soffen, Tanya S.
2010-01-01
This paper addresses a controversy regarding the effect of bottle material on the thermal performance of beverage bottles. Experiments and calculations that verify or refute advertising claims and represent an interesting way to teach heat transfer fundamentals are described. Heat transfer coefficients and the resistance to heat transfer offered…
NASA Astrophysics Data System (ADS)
Yankovskii, A. P.
2015-07-01
The author has obtained equations describing thermal conductivity of composite bodies spatially reinforced with a system of smooth tubes in which an incompressible liquid heat-transfer agent is pumped in a developed turbulent regime. The corresponding boundary-value heat-conduction problem was formulated and its qualitative analysis was made. Specific calculations were performed for steady-state temperature fields in cylindrical concrete shells spirally reinforced with steel tubes through which a heat-transfer agent (air) is pumped. A study has been made of the influence of the reinforcement parameters and of the velocity and direction of the heat-transfer agent in the tubes and the dimensions of their cross sections on the temperature field. It has been established that variation of these characteristics enables one to substantially change the intensity of heat removal from the shells, opening up wide opportunities for efficient control of the heat transfer in them.
Enhancement of heat and mass transfer by cavitation
NASA Astrophysics Data System (ADS)
Zhang, Y. N.; Zhang, Y. N.; Du, X. Z.; Xian, H. Z.
2015-01-01
In this paper, a brief summary of effects of cavitation on the heat and mass transfer are given. The fundamental studies of cavitation bubbles, including its nonlinearity, rectified heat and mass diffusion, are initially introduced. Then selected topics of cavitation enhanced heat and mass transfer were discussed in details including whales stranding caused by active sonar activity, pool boiling heat transfer, oscillating heat pipe and high intensity focused ultrasound treatment.
Liquid metal heat exchanger for efficient heating of soils and geologic formations
DeVault, Robert C. [Knoxville, TN; Wesolowski, David J. [Kingston, TN
2010-02-23
Apparatus for efficient heating of subterranean earth includes a well-casing that has an inner wall and an outer wall. A heater is disposed within the inner wall and is operable within a preselected operating temperature range. A heat transfer metal is disposed within the outer wall and without the inner wall, and is characterized by a melting point temperature lower than the preselected operating temperature range and a boiling point temperature higher than the preselected operating temperature range.
NASA Astrophysics Data System (ADS)
Kaminaga, Fumito; Okamoto, Yoshizo
1992-08-01
A correlation for the boiling heat transfer coefficient in the heating section of a two-phase thermosyphon heat pipe is developed in comparison with experimental data. The experiments are conducted for a vertically oriented thermosyphon pipe using three kinds of working fluid, water, Feron R 113, and ethanol, at a wide pressure range of 0.1 to 20 bar and a fill charge rate of 0.3 to 0.9. The correlation is obtained by modification of Kutateladze's nucleate boiling correlation in terms of an additional two parameters, the density ratio of liquid and vapor and the surface roughness. The correlation is shown to be in good agreement with the experimental data at a system pressure above 1 bar. The experiments also indicate that the adiabatic wall temperature is less than the saturation temperature corresponding to the system pressure in the pipe.
Thermochromic liquid crystals in heat transfer research
NASA Astrophysics Data System (ADS)
Stasiek, Jan A.; Kowalewski, Tomasz A.
2002-06-01
In recent years Thermochromic Liquid Crystals (TLC) have been successfully used in non-intrusive heat transfer and fluid mechanics studies. Thin coatings of TLC's at surfaces is utilized to obtain detailed heat transfer data of steady or transient process. Application of TLC tracers allows instantaneous measurement of the temperature and velocity fields for two-dimensional cross-section of flow. Computerized flow visualization techniques allow automatic quantification of temperature of the analyzed surface or the visualized flow cross-section. Here we describe our experience in applying the method to selected problems studied in our laboratory. They include modeling flow configurations in the differentially heated inclined cavity with vertical temperature gradient simulating up-slope flow as well as thermal convection under freezing surface. The main aim of these experimental models is to generate reliable experimental database on velocity and temperature fields for specific flow. The methods are based on computerized true-color analysis of digital images for temperature measurements and modified Particle Image Velocimetry and Thermometry (PIVT) used to obtain the flow field velocity.
Transient Heat Transfer in Zero Gravity Environment
NASA Technical Reports Server (NTRS)
Giarratano, P. G.; Arp, V. D.; Kumakawa, A.
1985-01-01
The objective is to provide computer codes and/or correlations for application in the design of transient heat transfer systems. The mathematical models in the computer codes are being tested by experimental data obtained in the laboratory using optical techniques. The elimination of natural convection (buoyancy) in the experimental data obtained in zero-g (KC-135) facilitates the study of thermal expansion effects which is of interest in the development and testing of the mathematical models of the transient heat transfer. Initial flight in the KC 135 (June 1983) suggested some modifications to the experimental apparatus and the data acquisition technique (high speed video will replace high speed movies for recording optical records generated during the experiments). A series of KC-135 flights with this experiment on board are scheduled for summer/fall 1984. The acquisition of the aforementioned data using interferometry and beam deflection optical techniques is anticipated. The measurements provide time dependent temperature fields above a horizontal heater surface submerged in a static fluid (Freon 13). The heater surface is electrically heated for a time interval approximately 0.100 sec. during which the data are optically recorded.
Heat transfer to a supercritical hydrocarbon fuel with endothermic reaction.
Yu, W.; France, D. M.; Wambsganss, M. W.; Energy Technology; Univ. of Illinois at Chicago
2000-01-01
Supercritical fuel reforming is being studied as a technology for reducing emissions of industrial gas turbine engines. In this study, experiments were performed in a 2.67-mm-inside-diameter stainless steel tube with a heated length of 0.610 m for the purpose of investigating the characteristics of supercritical heat transfer with endothermic fuel reforming. Thermocouples were positioned along the tube both in the fluid stream and on the heated wall for local heat transfer measurements. Both heat transfer coefficients and endotherms were calculated from the measured results. State-of-the-art correlations for heat transfer were evaluated, and a correlation for supercritical heat transfer to hydrocarbon fuel has been developed. The results provide a basis for supercritical fuel heat-exchanger/reactor design and its practical applications, in an area that has received relatively little attention in the engineering literature, viz., supercritical forced convection heat transfer with endothermic chemical reaction.
On the efficiency of solar heating in the middle atmosphere
NASA Technical Reports Server (NTRS)
Mlynczak, Martin G.; Solomon, Susan
1991-01-01
The efficiency at which solar ultraviolet radiation absorbed in the Hartley band of ozone is directly converted to heat in the terrestrial mesosphere and lower thermosphere (50-110 km) is calculated. The ozone molecule undergoes photolysis to yield the excited species O(1D) and O2(1Delta) with a quantum yield of about 0.9. Spontaneous emission from O2(1Delta) and from O2(1Sigma) (excited by energy transfer from O/1D/) significantly decreases the amount of energy available for heat. Similarly, the efficiency at which solar ultraviolet radiation absorbed by O2 in the Schumann-Runge continuum is directly converted to heat in the lower thermosphere (95-110 km) is calculated. The O2 undergoes photolysis and the excited product O(1D) is generated. Spontaneous emission from O2(1Sigma) (excited by energy transfer from O/1D/) reduces the amount of energy available for heat in the lower thermosphere. The consideration of these energy transfer and loss processes results in significantly reduced heating rates as compared to those conventionally calculated in models of the middle atmosphere.
A Model of Respiratory Heat Transfer in a Small Mammal
Collins, J. C.; Pilkington, T. C.; Schmidt-Nielsen, K.
1971-01-01
A steady-state model of the heat and water transfer occurring in the upper respiratory tract of the kangaroo rat, Dipodomys spectabilis, is developed and tested. The model is described by a steady-state energy balance equation in which the rate of energy transfer from a liquid stream (representing the flow of heat and blood from the body core to the nasal region) is equated with the rate of energy transfer by thermal conduction from the nose tip to the environment. All of the variables in the equation except the flow rate of the liquid stream can be either measured directly or estimated from physiological measurements, permitting the solution of the equation for the liquid stream flow rate. After solving for the liquid stream flow rate by using data from three animals, the energy balance equation is used to compute values of energy transfer, expired air temperature, rates of water loss, and efficiency of vapor recovery for a variety of ambient conditions. These computed values are compared with values measured or estimated from physiological measurements on the same three animals, and the equation is thus shown to be internally consistent. To evaluate the model's predictive value, calculated expired air temperatures are compared with measured expired air temperatures of eight additional animals. Finally, the model is used to examine the general dependence of expired air temperature, of rates of water loss, and of efficiency of vapor recovery on ambient conditions. PMID:5113001
Heat transfer in He I for industrially manufactured aluminium plate heat exchangers
NASA Astrophysics Data System (ADS)
Jager, B.; Bon Mardion, G.; Claudet, G.; Desmaris, M.
The heat transfer characteristics in boiling helium for commercially available aluminium plate heat exchangers, with and without fins, are given. In nucleate boiling both surfaces present the same heat transfer characteristics. For film boiling, the presence of fins improves heat transfer. It was also verified that for surfaces without fins, the peak nucleate boiling flux follows a Kutateladze law.
Investigation of heat transfer in the petal detector structure
NASA Astrophysics Data System (ADS)
Lávička, David; Kňourek, Jindřich
2016-03-01
This paper describes the CFD numerical simulation of heat transfer in the petal complex structure. Petal consists of core structure and detectors designed to improve the detection capabilities of the ATLAS detector and take advantage of operating at the High Luminosity LHC (HL-LHC). New generation silicon detectors in the petal require more efficient cooling of the front-end electronics and the silicon sensors themselves. To minimize reverse annealing of the silicon sensors the operating temperatures need to be reduced. In this case the evaporative CO2 cooling medium is used as it is ideal for this purpose. This work describes the flow simulation setup and results for the current prototype and heat transfer behavior for different operating states.
A review of turbine blade tip heat transfer.
Bunker, R S
2001-05-01
This paper presents a review of the publicly available knowledge base concerning turbine blade tip heat transfer, from the early fundamental research which laid the foundations of our knowledge, to current experimental and numerical studies utilizing engine-scaled blade cascades and turbine rigs. Focus is placed on high-pressure, high-temperature axial-turbine blade tips, which are prevalent in the majority of today's aircraft engines and power generating turbines. The state of our current understanding of turbine blade tip heat transfer is in the transitional phase between fundamentals supported by engine-based experience, and the ability to a priori correctly predict and efficiently design blade tips for engine service. PMID:11460670
Glycol coolants improve heat transfer and corrosion control
Holfield, R.
1995-03-01
Various liquids from plain water to exotic fluids have been used as coolants in large stationary diesel engines that drive compressors on natural gas pipeline distribution systems. Although water is an efficient heat transfer medium, its drawbacks of freezing at {minus}32 F and boiling at 212 F seriously limit its usefulness. Special glycol-based heat transfer fluids are available and refined specifically for long-term needs of gas compressor engines. Appropriate corrosion inhibitors have been formulated for metallurgy and operating conditions encountered with these engines. Propylene glycol was developed as an alternative for use in environmentally sensitive areas. Glycol-based fluids must be specifically inhibited for industrial applications because uninhibited or improperly inhibited coolants can seriously damage reciprocating engines.
Van der Waals interaction-tuned heat transfer in nanostructures.
Sun, Tao; Wang, Jianxiang; Kang, Wei
2013-01-01
Interfaces usually impede heat transfer in heterogeneous structures. Recent experiments show that van der Waals (vdW) interactions can significantly enhance thermal conductivity parallel to the interface of a bundle of nanoribbons compared to a single layer of freestanding nanoribbon. In this paper, by simulating heat transfer in nanostructures based on a model of nonlinear one-dimensional lattices interacting via van der Waals interactions, we show that the vdW interface interaction can adjust the thermal conductivity parallel to the interface. The efficiency of the adjustment depends on the intensity of interactions and temperature. The nonlinear dependence of the conductivity on the intensity of interactions agrees well with experimental results for carbon nanotube bundles, multi-walled carbon nanotubes, multi-layer graphene, and nanoribbons. PMID:23147396
Rocket engine thrust chamber heat transfer calculation and analysis
NASA Technical Reports Server (NTRS)
Saha, H.
1974-01-01
A parametric study of the heat transfer rate along the wall of a rocket nozzle is presented. The influences of different parameters; laminar and turbulent Lewis number, mixture ratio, initial wall temperature distribution, and eddy viscosity, were considered. The numerical evaluation of these influences on heat transfer rate was done by using three different compressible, reacting laminar and turbulent boundary layer computer programs; MABL (Mass Addition Boundary Layer Program), MABL-KE (MABL program is modified to include turbulent kinetic energy equation), and BLIMP (Boundary Layer Integral Matrix Procedure). This study also provided an excellent opportunity to evaluate the efficiencies of these three computer programs and to suggest one of them for future computational purposes.
Beasley, D.E.; Hassan, Y.A.; Cheung, F.B.; Yang, B.; Presser, C.; Olsen, D.A.; Tong, W.; Phelan, P.; Swanson, L.W.; McEligot, D.W.; Bogard, D.G.
1997-07-01
This volume contains a portion of the over 240 ASME papers which were presented at the conference. For over 40 years, the National Heat Transfer Conference has been the premiere forum for the presentation and dissemination of the latest advances in heat transfer. The work contained in these volumes range from studies of fundamental phenomena to applications in the latest heat transfer equipment. Topics covered in this volume are: Fundamental experiment techniques in heat transfer; thermal hydraulics of advanced nuclear reactors; heat and mass transfer in supercritical fluid systems; heat transfer in energy conversion; heat transfer equipment; and heat transfer in gas turbine systems. Separate abstracts were prepared for most papers in this volume.
3-D Finite Element Heat Transfer
Energy Science and Technology Software Center (ESTSC)
1992-02-01
TOPAZ3D is a three-dimensional implicit finite element computer code for heat transfer analysis. TOPAZ3D can be used to solve for the steady-state or transient temperature field on three-dimensional geometries. Material properties may be temperature-dependent and either isotropic or orthotropic. A variety of time-dependent 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 functionalmore » representation of boundary conditions and internal heat generation. TOPAZ3D 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.« less
Advances in refrigeration and heat transfer engineering
Bansal, Pradeep; Cremaschi, Prof. Lorenzo
2015-01-01
This special edition of Science and Technology for the Built Environment (STBE) presents selected high quality papers that were presented at the 15th International Refrigeration and Air Conditioning Conference held at Purdue University during July 14-17 2014. All papers went through the additional review before being finally accepted for publication in this special issue of Science and Technology and the Built Environment. Altogether 20 papers made to this special issue that cover a wide range of topics, including advancements in alternative refrigerants, heat exchangers/heat transfer, nano-fluids, systems design and optimization and modeling approaches. Although CO2 may perhaps have been the most researched and popular refrigerant in the past decade, R32 is being seriously considered lately as an alternative and environmentally friendly refrigerant for small systems due to its low Global Warming Potential (GWP).
Advances in refrigeration and heat transfer engineering
Bansal, Pradeep; Cremaschi, Prof. Lorenzo
2015-05-13
This special edition of Science and Technology for the Built Environment (STBE) presents selected high quality papers that were presented at the 15th International Refrigeration and Air Conditioning Conference held at Purdue University during July 14-17 2014. All papers went through the additional review before being finally accepted for publication in this special issue of Science and Technology and the Built Environment. Altogether 20 papers made to this special issue that cover a wide range of topics, including advancements in alternative refrigerants, heat exchangers/heat transfer, nano-fluids, systems design and optimization and modeling approaches. Although CO2 may perhaps have been themore » most researched and popular refrigerant in the past decade, R32 is being seriously considered lately as an alternative and environmentally friendly refrigerant for small systems due to its low Global Warming Potential (GWP).« less
Advances in refrigeration and heat transfer engineering
Bansal, Pradeep; Cremaschi, Prof. Lorenzo
2015-05-13
This special edition of Science and Technology for the Built Environment (STBE) presents selected high quality papers that were presented at the 15th International Refrigeration and Air Conditioning Conference held at Purdue University during July 14-17 2014. All papers went through the additional review before being finally accepted for publication in this special issue of Science and Technology and the Built Environment. Altogether 20 papers made to this special issue that cover a wide range of topics, including advancements in alternative refrigerants, heat exchangers/heat transfer, nano-fluids, systems design and optimization and modeling approaches. Although CO_{2} may perhaps have been the most researched and popular refrigerant in the past decade, R32 is being seriously considered lately as an alternative and environmentally friendly refrigerant for small systems due to its low Global Warming Potential (GWP).
Heat transfer augmentation in nanofluids via nanofins.
Vadasz, Peter
2011-01-01
Theoretical results derived in this article are combined with experimental data to conclude that, while there is no improvement in the effective thermal conductivity of nanofluids beyond the Maxwell's effective medium theory (J.C. Maxwell, Treatise on Electricity and Magnetism, 1891), there is substantial heat transfer augmentation via nanofins. The latter are formed as attachments on the hot wire surface by yet an unknown mechanism, which could be related to electrophoresis, but there is no conclusive evidence yet to prove this proposed mechanism. PMID:21711695
Heat transfer augmentation in nanofluids via nanofins
2011-01-01
Theoretical results derived in this article are combined with experimental data to conclude that, while there is no improvement in the effective thermal conductivity of nanofluids beyond the Maxwell's effective medium theory (J.C. Maxwell, Treatise on Electricity and Magnetism, 1891), there is substantial heat transfer augmentation via nanofins. The latter are formed as attachments on the hot wire surface by yet an unknown mechanism, which could be related to electrophoresis, but there is no conclusive evidence yet to prove this proposed mechanism. PMID:21711695
Heat transfer analysis in rotating sphericall shells
NASA Astrophysics Data System (ADS)
Cabello, Ares; Avila, Ruben
2015-11-01
The study of flow patterns within rotating spherical annular geometries with natural convection, is essential to understand the internal dynamics of the planets. We investigate the convective flows and the heat transfer rate in an spherical gap in which a temperature difference between the inner sphere and the outer sphere is present. A self gravity field which varies as a function of 1 /rn (where r is the radial position and the integer exponent n has the values 2,3,4,5) is assumed. The Boussinesq fluid equations are solved by using a spectral element method (SEM). To avoid the singularity at the poles, the cubed-sphere algorithm is used to generate the spherical mesh. Heat fluxes at the surface of both spheres are analyzed. We find, for several Ekman and Rayleigh numbers, that there exists a high correlation between the azimuthal motion of both the Busse cells and the zones where the maximum surface heat fluxes occur. The azimuthal position, as a function of time, of the maximum heat flux zones (which are located symmetrically with respect to the equator), allows to speculate on the nature of the phenomena occurring (in geological times) on the surface of the terrestrial planets. Thanks to DGAPA-PAPIIT project: IN117314-3.
NASA Astrophysics Data System (ADS)
Inaba, Hideo; Komatsu, Fujio; Horibe, Akihiko; Haruki, Naoto; Machida, Akito
2008-09-01
This paper describes heat and mass transfer characteristics of organic sorbent coated on heat transfer surface of a fin-tube heat exchanger. The experiments in which the moist air was passed into the heat exchanger coated with sorption material were conducted under various conditions of air flow rate (0.5 1.0 m/s) and the temperature of brine (14 20C) that was the heat transfer fluid to cool the air flow in the dehumidifying process. It is found that the sorption rate of vapor is affected by the air flow rate and the brine temperature. Meanwhile, the attempt of clarifying the sorption mechanism is also conducted. Finally the average mass transfer coefficient of the organic sorbent coated on heat transfer surface of a fin-tube heat exchanger is non-dimensionalzed as a function of Reynolds number and non-dimensional temperature, and it is found that the effect of non-dimensional temperature on them is larger than Reynolds number .
Optimizing transfer efficiency in spray painting
Darvin, C.H.
1987-01-01
This paper describes an extensive program to define the effects of operating and maintenance practices on the transfer efficiency of spray painting. Three spray painting systems were used: air-atomized conventional, air-atomized electrostatic, and airless conventional. More than 30 operating variables were initially identified and evaluated. Eight were found to be most important and received intensive testing: restricted air lines, booth air rate, gun cleanliness, restricted paint lines, fan or shaping air, gun tip erosion, electrode position, and tip voltage.
NASA Astrophysics Data System (ADS)
Wang, C.; Zhu, J. G.; Sang, Z. F.
2010-03-01
In this study, the heat transfer and tube frictional characteristics of the helixchangers (shell-and-tube heat exchanger with helical baffles) with spirally corrugated and smooth tubes and the conventional shell-and-tube heat exchanger with smooth tubes were experimentally obtained. The results show that the helixchangers with the spirally corrugated tube and the smooth tubes enhance the total heat transfer coefficient about 26% and 7% on the average than the segmental baffled heat exchanger. In the tube side, the spirally corrugated tube leads to about 28% average increase on convective heat transfer performance and about 24% average increase on pressure drop than the smooth tube, but its conversion efficiency is still higher. The helical baffle could enhance the shell-side condensation coefficient by 13%, and the spirally corrugated tube could help the helixchanger with it enhance remarkably the condensation performance by 53% than the segmental baffled heat exchanger.
NASA Astrophysics Data System (ADS)
Volosencu, Constantin; Curiac, Daniel-Ioan
2013-12-01
This paper gives a technical solution to improve the efficiency in multi-sensor wireless network based estimation for distributed parameter systems. A complex structure based on some estimation algorithms, with regression and autoregression, implemented using linear estimators, neural estimators and ANFIS estimators, is developed for this purpose. The three kinds of estimators are working with precision on different parts of the phenomenon characteristic. A comparative study of three methods - linear and nonlinear based on neural networks and adaptive neuro-fuzzy inference system - to implement these algorithms is made. The intelligent wireless sensor networks are taken in consideration as an efficient tool for measurement, data acquisition and communication. They are seen as a "distributed sensor", placed in the desired positions in the measuring field. The algorithms are based on regression using values from adjacent and also on auto-regression using past values from the same sensor. A modelling and simulation for a case study is presented. The quality of estimation is validated using a quadratic criterion. A practical implementation is made using virtual instrumentation. Applications of this complex estimation system are in fault detection and diagnosis of distributed parameter systems and discovery of malicious nodes in wireless sensor networks.
Heat Transfer Characterization Using Heat and Solute Tracer Tests in a Shallow Alluvial Aquifer
NASA Astrophysics Data System (ADS)
Dassargues, A.
2013-12-01
Very low enthalpy geothermal systems are increasingly considered for heating or cooling using groundwater energy combined with heat pumps. The design and the impact of shallow geothermal systems are often assessed in a semi-empirical way. It is accepted by most of the private partners but not by environmental authorities deploring a lack of rigorous evaluation of the mid- to long-term impact on groundwater. In view of a more rigorous methodology, heat and dye tracers are used for estimating simultaneously heat transfer and solute transport parameters in an alluvial aquifer. The experimental field site, is equipped with 21 piezometers drilled in alluvial deposits composed of a loam layer overlying a sand and gravel layer constituting the alluvial aquifer. The tracing experiment consisted in injecting simultaneously heated water and a dye tracer in a piezometer and monitoring evolution of groundwater temperature and tracer concentration in 3 control panels set perpendicularly to the main groundwater flow. Results showed drastic differences between heat transfer and solute transport due to the main influence of thermal capacity of the saturated porous medium. The tracing experiment was then simulated using a numerical model and the best estimation of heat transfer and solute transport parameters is obtained by calibrating this numerical model using inversion tools. The developed concepts and tests may lead to real projects of various extents that can be now optimized by the use of a rigorous and efficient methodology at the field scale. On the field: view from the injection well in direction of the pumping well through the three monitoring panels Temperature monitoring in the pumping well and in the piezometers of the three panels: heat transfer is faster in the lower part of the aquifer (blue curves) than in the upper part (red curves). Breakthrough curves are also more dispersed in the upper part with longer tailings.
Nanoscale heat transfer and phase transformation surrounding intensely heated nanoparticles
NASA Astrophysics Data System (ADS)
Sasikumar, Kiran
Over the last decade there has been significant ongoing research to use nanoparticles for hyperthermia-based destruction of cancer cells. In this regard, the investigation of highly non-equilibrium thermal systems created by ultrafast laser excitation is a particularly challenging and important aspect of nanoscale heat transfer. It has been observed experimentally that noble metal nanoparticles, illuminated by radiation at the plasmon resonance wavelength, can act as localized heat sources at nanometer-length scales. Achieving biological response by delivering heat via nanoscale heat sources has also been demonstrated. However, an understanding of the thermal transport at these scales and associated phase transformations is lacking. A striking observation made in several laser-heating experiments is that embedded metal nanoparticles heated to extreme temperatures may even melt without an associated boiling of the surrounding fluid. This unusual phase stability is not well understood and designing experiments to understand the physics of this phenomenon is a challenging task. In this thesis, we will resort to molecular dynamics (MD) simulations, which offer a powerful tool to investigate this phenomenon, without assumptions underlying continuum-level model formulations. We present the results from a series of steady state and transient non-equilibrium MD simulations performed on an intensely heated nanoparticle immersed in a model liquid. For small nanoparticles (1-10 nm in diameter) we observe a stable liquid phase near the nanoparticle surface, which can be at a temperature well above the boiling point. Furthermore, we report the existence of a critical nanoparticle size (4 nm in diameter) below which we do not observe formation of vapor even when local fluid temperatures exceed the critical temperature. Instead, we report the existence of a stable fluid region with a density much larger than that of the vapor phase. We explain this stability in terms of the Laplace pressure associated with the formation of a vapor nanocavity and the associated effect on the Gibbs free energy. Separately, we also demonstrate the role of extreme temperature gradients (108-1010 K/m) in elevating the boiling point of liquids. We show that, assuming local thermal equilibrium, the observed elevation of the boiling point is associated with the interplay between the "bulk" driving force for the phase change and surface tension of the liquid-vapor interface that suppresses the transformation. In transient simulations that mimic laser-heating experiments we observe the formation and collapse of vapor bubbles around the nanoparticles beyond a threshold. Detailed analysis of the cavitation dynamics indicates adiabatic formation followed by an isothermal final stage of growth and isothermal collapse.
Heat Transfer in High Temperature Multilayer Insulation
NASA Technical Reports Server (NTRS)
Daryabeigi, Kamran; Miller, Steve D.; Cunnington, George R.
2007-01-01
High temperature multilayer insulations have been investigated as an effective component of thermal-protection systems for atmospheric re-entry of reusable launch vehicles. Heat transfer in multilayer insulations consisting of thin, gold-coated, ceramic reflective foils and Saffil(TradeMark) fibrous insulation spacers was studied both numerically and experimentally. A finite volume numerical thermal model using combined conduction (gaseous and solid) and radiation in porous media was developed. A two-flux model with anisotropic scattering was used for radiation heat transfer in the fibrous insulation spacers between the reflective foils. The thermal model was validated by comparison with effective thermal conductivity measurements in an apparatus based on ASTM standard C201. Measurements were performed at environmental pressures in the range from 1x10(exp -4) to 760 torr over the temperature range from 300 to 1300 K. Four multilayer samples with nominal densities of 48 kg/cu m were tested. The first sample was 13.3 mm thick and had four evenly spaced reflective foils. The other three samples were 26.6 mm thick and utilized either one, two, or four reflective foils, located near the hot boundary with nominal foil spacing of 1.7 mm. The validated thermal model was then used to study relevant design parameters, such as reflective foil spacing and location in the stack-up and coating of one or both sides of foils.
Micro-grooved heat transfer combustor wall
NASA Technical Reports Server (NTRS)
Ward, Steven D. (Inventor)
1994-01-01
A gas turbine engine hot section combustor liner is provided a non-film cooled portion of a heat transfer wall having a hot surface and a plurality of longitudinally extending micro-grooves disposed in the portion of the wall along the hot surface in a direction parallel to the direction of the hot gas flow. The depth of the micro-grooves is very small and on the order of magnitude of a predetermined laminar sublayer of a turbulent boundary layer. The micro-grooves are sized so as to inhibit heat transfer from the hot gas flow to the hot surface of the wall while reducing NOx emissions of the combustor relative to an otherwise similar combustor having a liner wall portion including film cooling apertures. In one embodiment the micro-grooves are about 0.001 inches deep and have a preferred depth range of from about 0.001 inches to 0.005 inches and which are square, rectangular, or triangular in cross-section and the micro-grooves are spaced about one width apart.
Liquid-metal heat transfer in a cocurrent- flow, double-pipe heat exchanger is investigated
NASA Technical Reports Server (NTRS)
Merriam, R. L.
1969-01-01
Analysis of liquid-metal heat transfer in cocurrent-flow, double-pipe heat exchangers shows that heat-transfer coefficients depend upon the operating conditions of the heat exchanger and that use of the customary design equation to predict heat-exchanger performance leads to significant errors.
Manufacture of a biporous nickel wick and its effect on LHP heat transfer performance enhancement
NASA Astrophysics Data System (ADS)
Wu, S. C.; Hsieh, B. H.; Wang, D.; Chen, Y. M.
2015-11-01
This work describes a mixed powder sintering method that uses polymer as sacrificial substance to manufacture wicks for LHPs to improve the heat transfer performance of a conventional monoporous wick during high heat flux in LHP. The proposed porous manufacturing method is simple, efficient, structurally sound, and easily managed. Compared to findings in literatures for LHPs with monoporous wicks, the heat transfer performance of the proposed method is enhanced by nearly 80 %.
Turbulence convective heat transfer for cooling the photovoltaic cells
NASA Astrophysics Data System (ADS)
Arianmehr, Iman
Solar PV (photovoltaic) is a rapidly advancing renewable energy technology which converts sunlight directly into electricity. One of the outstanding challenges of the current PV technology is the reduction in its conversion efficiency with increasing PV panel temperature, which is closely associated with the increase in solar intensity and the ambient temperature surrounding the PV panels. To more effectively capture the available energy when the sun is most intense, significant efforts have been invested in active and passive cooling research over the last few years. While integrated cooling systems can lead to the highest total efficiencies, they are usually neither the most feasible nor the most cost effective solutions. This work examines some simple passive means of manipulating the prevailing wind turbulence to enhance convective heat transfer over a heated plate in a wind tunnel.
NASA Astrophysics Data System (ADS)
Chen, Kaifeng; Santhanam, Parthiban; Fan, Shanhui
2015-08-01
We consider a near-field thermophotovoltaic device with metal as the emitter and semiconductor as the photovoltaic cell. We show that when the cell is a III-V semiconductor, such as GaSb, parasitic phonon-polariton heat transfer reduces efficiency in the near-field regime, especially when the temperature of the emitter is not high enough. We further propose ways to avoid the phonon-polariton heat transfer by replacing the III-V semiconductor with a non-polar semiconductor such as Ge. Our work provides practical guidance on the design of near-field thermophotovoltaic systems for efficient harvesting of low-quality waste heat.
Inelastic Heat Transfer in Molecular Quantum Dots
NASA Astrophysics Data System (ADS)
Dyrkacz, Joanna; Walczak, Kamil
We examine electronic heat conduction via molecular complexes in the presence of local electron-phonon coupling effects. In off-resonance transport regime, even weak electron-phonon interactions lead to phonon-mediated changes of transport characteristics. In the nearly resonance conditions, the strong electron-phonon coupling reduces the height of the main conductance peak, generating additional satellites (phonon sidebands) in transport characteristics and shifting molecular energy spectrum via reorganization (polaron) energy. In the past, it was shown that inclusion of electron-phonon coupling effects into computational scheme reduces discrepancy between theoretical results and experimental data. The aim of this project is to study electron-phonon coupling effects on electronic heat transfer at molecular level. For that purpose, we use non-perturbative computational scheme based on inelastic version of Landauer formula, where the Green's functions technique combined with polaron transformation was used to calculate multi-channel transmission probability function, while accessibility of individual conduction channels is governed by Boltzmann statistics. Our analysis is based on the hypothesis that the dynamics created by electron-phonon interaction onto the molecular quantum dot asymmetrically connected to two thermal reservoirs will lead to thermal rectification effect. Our results will be discussed in a few aspects: electron-phonon coupling strength, phonon dispersion relationship, and heat fluxes generated by temperature difference as well as bias voltage.
Transient critical heat flux and blowdown heat-transfer studies
Leung, J.C.
1980-05-01
Objective of this study is to give a best-estimate prediction of transient critical heat flux (CHF) during reactor transients and hypothetical accidents. To accomplish this task, a predictional method has been developed. Basically it involves the thermal-hydraulic calculation of the heated core with boundary conditions supplied from experimental measurements. CHF predictions were based on the instantaneous ''local-conditions'' hypothesis, and eight correlations (consisting of round-tube, rod-bundle, and transient correlations) were tested against most recent blowdown heat-transfer test data obtained in major US facilities. The prediction results are summarized in a table in which both CISE and Biasi correlations are found to be capable of predicting the early CHF of approx. 1 s. The Griffith-Zuber correlation is credited for its prediction of the delay CHF that occurs in a more tranquil state with slowly decaying mass velocity. In many instances, the early CHF can be well correlated by the x = 1.0 criterion; this is certainly indicative of an annular-flow dryout-type crisis. The delay CHF occurred at near or above 80% void fraction, and the success of the modified Zuber pool-boiling correlation suggests that this CHF is caused by flooding and pool-boiling type hydrodynamic crisis.
NASA Astrophysics Data System (ADS)
Okamoto, Akio; Arima, Hirofumi; Kim, Jeong-Hun; Akiyama, Hirokuni; Ikegami, Yasuyuki; Monde, Masanori
Ocean thermal energy conversion (OTEC) and discharged thermal energy conversion (DTEC) are expected to be the next generation energy production systems. Both systems use a plate type evaporator, and ammonia or ammonia/water mixture as a working fluid. It is important to clarify heat transfer characteristic for designing efficient power generation systems. Measurements of local boiling heat transfer coefficients and visualization were performed for ammonia /water mixture (z = 0.9) on a vertical flat plate heat exchanger in a range of mass flux (7.5 - 15 kg/m2s), heat flux (15 - 23 kW/m2), and pressure (0.7 - 0.9 MPa). The result shows that in the case of ammonia /water mixture, the local heat transfer coefficients increase with an increase of vapor quality and mass flux, and decrease with an increase of heat flux, and the influence of the flow pattern on the local heat transfer coefficient is observed.
Boiling local heat transfer enhancement in minichannels using nanofluids
2013-01-01
This paper reports an experimental study on nanofluid convective boiling heat transfer in parallel rectangular minichannels of 800 μm hydraulic diameter. Experiments are conducted with pure water and silver nanoparticles suspended in water base fluid. Two small volume fractions of silver nanoparticles suspended in water are tested: 0.000237% and 0.000475%. The experimental results show that the local heat transfer coefficient, local heat flux, and local wall temperature are affected by silver nanoparticle concentration in water base fluid. In addition, different correlations established for boiling flow heat transfer in minichannels or macrochannels are evaluated. It is found that the correlation of Kandlikar and Balasubramanian is the closest to the water boiling heat transfer results. The boiling local heat transfer enhancement by adding silver nanoparticles in base fluid is not uniform along the channel flow. Better performances and highest effect of nanoparticle concentration on the heat transfer are obtained at the minichannels entrance. PMID:23506445
Heat transfer assembly for a fluorescent lamp and fixture
Siminovitch, M.J.; Rubenstein, F.M.; Whitman, R.E.
1992-12-29
In a lighting fixture including a lamp and a housing, a heat transfer structure is disclosed for reducing the minimum lamp wall temperature of a fluorescent light bulb. The heat transfer structure, constructed of thermally conductive material, extends from inside the housing to outside the housing, transferring heat energy generated from a fluorescent light bulb to outside the housing where the heat energy is dissipated to the ambient air outside the housing. Also disclosed is a method for reducing minimum lamp wall temperatures. Further disclosed is an improved lighting fixture including a lamp, a housing and the aforementioned heat transfer structure. 11 figs.
Heat transfer assembly for a fluorescent lamp and fixture
Siminovitch, Michael J.; Rubenstein, Francis M.; Whitman, Richard E.
1992-01-01
In a lighting fixture including a lamp and a housing, a heat transfer structure is disclosed for reducing the minimum lamp wall temperature of a fluorescent light bulb. The heat transfer structure, constructed of thermally conductive material, extends from inside the housing to outside the housing, transferring heat energy generated from a fluorescent light bulb to outside the housing where the heat energy is dissipated to the ambient air outside the housing. Also disclosed is a method for reducing minimum lamp wall temperatures. Further disclosed is an improved lighting fixture including a lamp, a housing and the aforementioned heat transfer structure.
Study and Analysis of Heat Transfer Limitation of Separated Heat Pipe
NASA Astrophysics Data System (ADS)
Mou, Qizheng; Mou, Kai
2002-01-01
satellite and spacecraft. evaporator, heat isolation and condenser along the axial direction. The working fluid absorbs heat and evaporates in evaporator, and then the vapor flows to condenser and gives out heat. The condensed liquid is pumped to evaporator by wick. By the circulation, the heat can by transferred continuously. heat pipe as follow: - Vapor-liquid two phase flow inside pipe; - The manner of latent heat to transfer heat; - Automatic circulation by working fluid flowing - A certain extent of vacuum. and the traditional heat pipe, that is, the vapor fluid and liquid fluid flow along the same direction. So it is obviously that the separated heat pipe has special internal heat transfer characteristic and crisis. This paper has regard for the heat transfer crisis of the separated heat pipe, and meanwhile relevant calculation and analysis have been done. 1. FLOW TYPE OF THE WORKING FLUID IN SEPARATED HEAT PIPE 2. HEAT TRANSFER CRISIS IN THE EVAPORATOR 3. CARRYING PHENOMENON INSIDE SEPARATED HEAT PIPE 4. THE STAGNANT FLOW PHENOMENON AND THE BACKWARD FLOW PHENOMENON IN EVAPORATOR CONCLUSION transfer limitation of location burn-out, and the heat transfer limitation of flow unconventionality in erective pipe. The carrying phenomenon can occurs not only in evaporator but also in condenser of separated heat pipe. It is in the evaporator that should take place the heat transfer limitation of liquid film dry-out at first. Then with the increasing of heat flux, the heat transfer limitation of location burn-out would happen. In order to avoid the heat transfer limitation of flow unconventionality in erective pipe, the length and diameter of the outflow tube and inflow tube must be reasonably calculated to control the flow velocity of the working fluid inside pipe. Key words:Separated Heat PipeHeat Transfer LimitationDry-OutCarryingStagnancy
Efficiency bounds for nonequilibrium heat engines
Mehta, Pankaj; Polkovnikov, Anatoli
2013-05-15
We analyze the efficiency of thermal engines (either quantum or classical) working with a single heat reservoir like an atmosphere. The engine first gets an energy intake, which can be done in an arbitrary nonequilibrium way e.g. combustion of fuel. Then the engine performs the work and returns to the initial state. We distinguish two general classes of engines where the working body first equilibrates within itself and then performs the work (ergodic engine) or when it performs the work before equilibrating (non-ergodic engine). We show that in both cases the second law of thermodynamics limits their efficiency. For ergodic engines we find a rigorous upper bound for the efficiency, which is strictly smaller than the equivalent Carnot efficiency. I.e. the Carnot efficiency can be never achieved in single reservoir heat engines. For non-ergodic engines the efficiency can be higher and can exceed the equilibrium Carnot bound. By extending the fundamental thermodynamic relation to nonequilibrium processes, we find a rigorous thermodynamic bound for the efficiency of both ergodic and non-ergodic engines and show that it is given by the relative entropy of the nonequilibrium and initial equilibrium distributions. These results suggest a new general strategy for designing more efficient engines. We illustrate our ideas by using simple examples. -- Highlights: ► Derived efficiency bounds for heat engines working with a single reservoir. ► Analyzed both ergodic and non-ergodic engines. ► Showed that non-ergodic engines can be more efficient. ► Extended fundamental thermodynamic relation to arbitrary nonequilibrium processes.
Heat transfer mechanisms in poplar wood undergoing torrefaction
NASA Astrophysics Data System (ADS)
Sule, Idris O.; Mahmud, Shohel; Dutta, Animesh; Tasnim, Syeda Humaira
2016-03-01
Torrefaction, a thermal treatment process of biomass, has been proved to improve biomass combustible properties. Torrefaction is defined as a thermochemical process in reduced oxygen condition and at temperature range from 200 to 300 °C for shorter residence time whereby energy yield is maximized, can be a bridging technology that can lead the conventional system (e.g. coal-fired plants) towards a sustainable energy system. In efforts to develop a commercial operable torrefaction reactor, the present study examines the minimum input condition at which biomass is torrefied and explores the heat transfer mechanisms during torrefaction in poplar wood samples. The heat transfer through the wood sample is numerically modeled and analyzed. Each poplar wood is torrefied at temperature of 250, 270, and 300 °C. The experimental study shows that the 270 °C-treatment can be deduced as the optimal input condition for torrefaction of poplar wood. A good understanding of heat transfer mechanisms can facilitate the upscaling and downscaling of torrefaction process equipment to fit the feedstock input criteria and can help to develop treatment input specifications that can maximize process efficiency.
Heat transfer mechanisms in poplar wood undergoing torrefaction
NASA Astrophysics Data System (ADS)
Sule, Idris O.; Mahmud, Shohel; Dutta, Animesh; Tasnim, Syeda Humaira
2015-04-01
Torrefaction, a thermal treatment process of biomass, has been proved to improve biomass combustible properties. Torrefaction is defined as a thermochemical process in reduced oxygen condition and at temperature range from 200 to 300 C for shorter residence time whereby energy yield is maximized, can be a bridging technology that can lead the conventional system (e.g. coal-fired plants) towards a sustainable energy system. In efforts to develop a commercial operable torrefaction reactor, the present study examines the minimum input condition at which biomass is torrefied and explores the heat transfer mechanisms during torrefaction in poplar wood samples. The heat transfer through the wood sample is numerically modeled and analyzed. Each poplar wood is torrefied at temperature of 250, 270, and 300 C. The experimental study shows that the 270 C-treatment can be deduced as the optimal input condition for torrefaction of poplar wood. A good understanding of heat transfer mechanisms can facilitate the upscaling and downscaling of torrefaction process equipment to fit the feedstock input criteria and can help to develop treatment input specifications that can maximize process efficiency.
Analysis of Heat Transfer in Ancient Inuit Fur Parka Ruffs
NASA Astrophysics Data System (ADS)
Cotel, Aline
2000-11-01
Arctic people living throughout the circumpolar region have time tested their caribou skin clothing ensembles for 3000 to 8000 years (Stefansson 1944 and 1955). The traditional clothing system developed and used by the Inuit is the most effective cold weather clothing developed to date (Oakes et al. 1995). One of the key elements used by the Inuit is a fur ruff attached to the hood, hem, and cuffs of their parkas. This paper determines why the fur ruff is so critical to the effectiveness of cold weather clothing, especially in protecting the face, without impeding movement or view, so essential to the Inuit hunter. The effectiveness of this clothing is established using both traditional and scientific knowledge. To quantify the effectiveness of this clothing, the heat transfer was measured on a model, placed into a wind tunnel. The wind velocity and angle to the wind were varied. A boundary layer forms on the face, the heat transfer was measured across that layer using thermocouples. It is essential to minimize that heat transfer for survival and frostbite prevention. Different fur ruffs geometries were examined to determine the most efficient one. This information was combined with data collected using ethno-historical methods. Data for this portion of the research has been collected since 1970 and 1983 by two of the co-researchers. This unique combination of scientific and traditional Aboriginal knowledge provides a wholistic perspective on new insights on the effectiveness of cold weather clothing systems.
Radiative heat transfer in rotary kilns
NASA Astrophysics Data System (ADS)
Gorog, J. P.; Brimacombe, J. K.; Adams, T. N.
1981-03-01
Radiative heat transfer between a nongray freeboard gas and the interior surfaces of a rotary kiln has been studied by evaluating the fundamental radiative exchange integrals using numerical methods. Direct gas-to-surface exchange, reflection of the gas radiation by the kiln wall, and kiln wall-to-solids exchange have been considered. Graphical representations of the results have been developed which facilitate the determination of the gas mean beamlength and the total heat flux to the wall and to the solids. These charts can be used to account for both kiln size and solids fill ratio as well as composition and temperature of the gas. Calculations using these charts and an equimolar CO2-H2O mixture at 1110 K indicate that gas-to-surface exchange is a very localized phenomenon. Radiation to a surface element from gas more than half a kiln diameter away is quite small and, as a result, even large axial gas temperature gradients have a negligible effect on total heat flux. Results are also presented which show that the radiant energy either reflected or emitted by a surface element is limited to regions less than 0.75 kiln diameters away. The radiative exchange integrals have been used, together with a modified reflection method, to develop a model for the net heat flux to the solids and to the kiln wall from a nongray gas. This model is compared to a simple resistive network/gray-gas model and it is shown that substantial errors may be incurred by the use of the simple models.
Multiscale simulations of heat transfer in nanocomposites
NASA Astrophysics Data System (ADS)
Bui, Khoa Nguyen Dang
The field of nanotechnology has been expanded by the discovery of fullerenes and carbon nanotubes (CNTs) in the 20th century. Geim and Novoselov won the Nobel prize in 2010 for their work on graphene sheets (GSs). Those materials with their outstanding properties have been suggested as reinforcement fillers in a variety of composite materials. By incorporating these nanomaterials into a polymer matrix, or dispersing them into a solution, the effective thermal conductivity of the resulting composite (Keff) can be increased. For example, this enhancement can range from 80% to 125% at 1.0wt% of CNTs over pure polymer for the case of epoxy composites or by a factor of almost 4 in the case of high concentration of single-walled carbon nanotubes (SWNTs) in poly-styrene. However, based on the properties of pristine CNTs and GSs, one would expect a much higher value of Keff of such composites, more than one order of magnitude according to the classical theory of Maxwell. The presence of resistance to heat transfer at the nanoinclusion-polymer interface, known as the interfacial thermal resistance or Kapitza resistance, is the reason for this difference. Experimentally measuring and characterizing heat transport at the nanoscale are not trivial tasks and current theory in this area is limited to simple cases only. The acoustic mismatch theory and the effective medium theory provide a rough estimation of Kapitza resistance and Keff of the composites, respectively. However, the effect of dispersion pattern and the orientation of nanoinclusions inside the polymer matrix on Keff is still an open question. For the case of multi-walled carbon nanotubes (MWCNTs) embedded in polymer matrix, it is unknown whether thermal transfer occurs solely via the outermost wall or through the center of the tube. In this work, Monte Carlo (MC) simulations were developed to investigate heat transfer in nanocomposites. This approach is capable of taking into account the effect of different geometries, realistic orientations, and dispersion patterns of nanoinclusions on Keff. Furthermore, molecular dynamics (MD) simulations were employed coherently with MC simulations to characterize interfacial thermal resistance. Results from this work provide suggestions for producing superior thermal nanocomposites through the controll of Kapitza resistance and the configurations of nanoinclusions inside the polymer matrix.
Increasing Boiling Heat Transfer using Low Conductivity Materials
Mahamudur Rahman, Md; Pollack, Jordan; McCarthy, Matthew
2015-01-01
We report the counterintuitive mechanism of increasing boiling heat transfer by incorporating low-conductivity materials at the interface between the surface and fluid. By embedding an array of non-conductive lines into a high-conductivity substrate, in-plane variations in the local surface temperature are created. During boiling the surface temperature varies spatially across the substrate, alternating between high and low values, and promotes the organization of distinct liquid and vapor flows. By systematically tuning the peak-to-peak wavelength of this spatial temperature variation, a resonance-like effect is seen at a value equal to the capillary length of the fluid. Replacing ~18% of the surface with a non-conductive epoxy results in a greater than 5x increase in heat transfer rate at a given superheat temperature. This drastic and counterintuitive increase is shown to be due to optimized bubble dynamics, where ordered pathways allow for efficient removal of vapor and the return of replenishing liquid. The use of engineered thermal gradients represents a potentially disruptive approach to create high-efficiency and high-heat-flux boiling surfaces which are naturally insensitive to fouling and degradation as compared to other approaches. PMID:26281890
Increasing Boiling Heat Transfer using Low Conductivity Materials
NASA Astrophysics Data System (ADS)
Mahamudur Rahman, Md; Pollack, Jordan; McCarthy, Matthew
2015-08-01
We report the counterintuitive mechanism of increasing boiling heat transfer by incorporating low-conductivity materials at the interface between the surface and fluid. By embedding an array of non-conductive lines into a high-conductivity substrate, in-plane variations in the local surface temperature are created. During boiling the surface temperature varies spatially across the substrate, alternating between high and low values, and promotes the organization of distinct liquid and vapor flows. By systematically tuning the peak-to-peak wavelength of this spatial temperature variation, a resonance-like effect is seen at a value equal to the capillary length of the fluid. Replacing ~18% of the surface with a non-conductive epoxy results in a greater than 5x increase in heat transfer rate at a given superheat temperature. This drastic and counterintuitive increase is shown to be due to optimized bubble dynamics, where ordered pathways allow for efficient removal of vapor and the return of replenishing liquid. The use of engineered thermal gradients represents a potentially disruptive approach to create high-efficiency and high-heat-flux boiling surfaces which are naturally insensitive to fouling and degradation as compared to other approaches.
Heat Sponge: A Concept for Mass-Efficient Heat Storage
NASA Technical Reports Server (NTRS)
Splinter, Scott C.; Blosser, Max L.; Gifford, Andrew R.
2008-01-01
The heat sponge is a device for mass-efficient storage of heat. It was developed to be incorporated in the substructure of a re-entry vehicle to reduce thermal- protection-system requirements. The heat sponge consists of a liquid/vapor mixture contained within a number of miniature pressure vessels that can be embedded within a variety of different types of structures. As temperature is increased, pressure in the miniature pressure vessels also increases so that heat absorbed through vaporization of the liquid is spread over a relatively large temperature range. Using water as a working fluid, the heat-storage capacity of the liquid/vapor mixture is many times higher than that of typical structural materials and is well above that of common phase change materials over a temperature range of 200 F to 700 F. The use of pure ammonia as the working fluid provides a range of application between 432 deg R and 730 deg R, or the use of the more practical water-ammonia solution provides a range of application between 432 deg R and 1160 deg R or in between that of water and pure ammonia. Prototype heat sponges were fabricated and characterized. These heat sponges consisted of 1.0-inch-diameter, hollow, stainless-steel spheres with a wall thickness of 0.020 inches which had varying percentages of their interior volumes filled with water and a water-ammonia solution. An apparatus to measure the heat stored in these prototype heat sponges was designed, fabricated, and verified. The heat-storage capacity calculated from measured temperature histories is compared to numerical predictions.
46 CFR 153.430 - Heat transfer systems; general.
Code of Federal Regulations, 2014 CFR
2014-10-01
... 46 Shipping 5 2014-10-01 2014-10-01 false Heat transfer systems; general. 153.430 Section 153.430... Temperature Control Systems § 153.430 Heat transfer systems; general. Each cargo cooling system required by... separated from all other cooling and heating systems; and (c) Allow manual regulation of the system's...
46 CFR 153.430 - Heat transfer systems; general.
Code of Federal Regulations, 2012 CFR
2012-10-01
... 46 Shipping 5 2012-10-01 2012-10-01 false Heat transfer systems; general. 153.430 Section 153.430... Temperature Control Systems § 153.430 Heat transfer systems; general. Each cargo cooling system required by... separated from all other cooling and heating systems; and (c) Allow manual regulation of the system's...
46 CFR 153.430 - Heat transfer systems; general.
Code of Federal Regulations, 2013 CFR
2013-10-01
... 46 Shipping 5 2013-10-01 2013-10-01 false Heat transfer systems; general. 153.430 Section 153.430... Temperature Control Systems § 153.430 Heat transfer systems; general. Each cargo cooling system required by... separated from all other cooling and heating systems; and (c) Allow manual regulation of the system's...
46 CFR 153.430 - Heat transfer systems; general.
Code of Federal Regulations, 2011 CFR
2011-10-01
... 46 Shipping 5 2011-10-01 2011-10-01 false Heat transfer systems; general. 153.430 Section 153.430... Temperature Control Systems § 153.430 Heat transfer systems; general. Each cargo cooling system required by... separated from all other cooling and heating systems; and (c) Allow manual regulation of the system's...
The heat transfer of cooling fins on moving air
NASA Technical Reports Server (NTRS)
Doetsch, Hans
1935-01-01
The present report is a comparison of the experimentally defined temperature and heat output of cooling fins in the air stream with theory. The agreement is close on the basis of a mean coefficient of heat transfer with respect to the total surface. A relationship is established between the mean coefficient of heat transfer, the dimensions of the fin arrangement, and the air velocity.
Heat exchanger efficiently operable alternatively as evaporator or condenser
Ecker, Amir L.
1981-01-01
A heat exchanger adapted for efficient operation alternatively as evaporator or condenser and characterized by flexible outer tube having a plurality of inner conduits and check valves sealingly disposed within the outer tube and connected with respective inlet and outlet master flow conduits and configured so as to define a parallel flow path for a first fluid such as a refrigerant when flowed in one direction and to define a serpentine and series flow path for the first fluid when flowed in the opposite direction. The flexible outer tube has a heat exchange fluid, such as water, flowed therethrough by way of suitable inlet and outlet connections. The inner conduits and check valves form a package that is twistable so as to define a spiral annular flow path within the flexible outer tube for the heat exchange fluid. The inner conduits have thin walls of highly efficient heat transfer material for transferring heat between the first and second fluids. Also disclosed are specific materials and configurations.
Nucleate Boiling Heat Transfer Studied Under Reduced-Gravity Conditions
NASA Technical Reports Server (NTRS)
Chao, David F.; Hasan, Mohammad M.
2000-01-01
Boiling is known to be a very efficient mode of heat transfer, and as such, it is employed in component cooling and in various energy-conversion systems. In space, boiling heat transfer may be used in thermal management, fluid handling and control, power systems, and on-orbit storage and supply systems for cryogenic propellants and life-support fluids. Recent interest in the exploration of Mars and other planets and in the concept of in situ resource utilization on the Martian and Lunar surfaces highlights the need to understand how gravity levels varying from the Earth's gravity to microgravity (1g = or > g/g(sub e) = or > 10(exp -6)g) affect boiling heat transfer. Because of the complex nature of the boiling process, no generalized prediction or procedure has been developed to describe the boiling heat transfer coefficient, particularly at reduced gravity levels. Recently, Professor Vijay K. Dhir of the University of California at Los Angeles proposed a novel building-block approach to investigate the boiling phenomena in low-gravity to microgravity environments. This approach experimentally investigates the complete process of bubble inception, growth, and departure for single bubbles formed at a well-defined and controllable nucleation site. Principal investigator Professor Vijay K. Dhir, with support from researchers from the NASA Glenn Research Center at Lewis Field, is performing a series of pool boiling experiments in the low-gravity environments of the KC 135 microgravity aircraft s parabolic flight to investigate the inception, growth, departure, and merger of bubbles from single- and multiple-nucleation sites as a function of the wall superheat and the liquid subcooling. Silicon wafers with single and multiple cavities of known characteristics are being used as test surfaces. Water and PF5060 (an inert liquid) were chosen as test liquids so that the role of surface wettability and the magnitude of the effect of interfacial tension on boiling in reduced gravity can be investigated.
Heat transfer investigations in a slurry bubble column
Saxena, S.C.; Rao, N.S.; Vadivel, R.; Shrivastav, S.; Saxena, A.C.; Patel, B.B.; Thimmapuram, P.R.; Kagzi, M.Y.; Khan, I.A.; Verma, A.K.
1991-02-01
Slurry bubble columns, for use in Fischer-Tropsch synthesis, have been investigated. Two bubble columns (0.108 and 0.305 m internal diameter) were set up and experiments were conducted to determine gas holdup and heat transfer coefficients. These columns were equipped with either single heat transfer probes of different diameters, or bundles of five-, seven-, or thirty-seven tubes. the experiments were conducted for two- and three phase systems; employing for gas phase: air and nitrogen, liquid phase: water and Therminol-66, and solid phase: red iron oxide (1.02, 1.70 and 2.38 {mu}m), glass beads (50.0, 90.0, 119.0 and 143.3 {mu}m), silica sand (65 {mu}m), and magnetite (28.0, 35.7, 46.0, 58.0, 69.0, 90.5, 115.5 and 137.5 {mu}m). The column temperature was varied between 298--523 K, gas velocity between 0--40 cm/s, and solids concentration between 0--50 weight percent. The holdup and heat transfer data as a function of operating and system parameters were employed to assess the available correlations and semitheoretical models, and to develop new correlations. Information concerning the design and scale-up of larger units is presented. Specific research work that need to be undertaken to understand the phenomena of heat transfer and gas holdup is outlined so that efficient gas conversion and catalyst usage may be accomplished in slurry bubble columns. 28 refs., 102 figs., 42 tabs.
Convective heat transfer in building energy analysis
Gadgil, A.J.
1980-05-01
In the ongoing efforts to study energy consumption in buildings through computer simulations, practically no attention has been given to modeling natural convective heat transfer in buildings. The main reason for this neglect is due to the difficulty of solving the problem numerically. This paper makes a contribution towards the solution of this difficulty by presenting a numerical code for modeling natural convection in rectangular enclosures at Rayleigh numbers up to 10/sup 10/. Chapter 2 develops the general equations of motion to be solved. Chapter 3 is devoted to simplification of these equations and description of the numerical scheme. Chapter 4 describes the comparisons of the predictions of the computer program based on the numerical scheme with various published experimental and numerical results of other investigators. Chapter 5 illustrates an application of the computer program to investigate the soundness of an assumption commonly made by all the building energy analysis programs.
Investigation of heat transfer in porous duct
NASA Astrophysics Data System (ADS)
Athani, Abdulgaphur; Khan, T. M. Yunus
2016-05-01
Investigation of heat transfer in a square porous duct is carried out. The porous medium is sandwiched between inner and outer surface of a square duct. The flow is assumed to follow the Darcy law. The governing momentum and energy equations are non-dimensionalised and then converted to algebraic form of equations using finite element method. Galerkin method is used to transform the partial differential equations into simpler algebraic equations then solved in a iterative manner to arrive at the solution. The results are presented with respect to various geometric and physical parameters such as depth of porous medium, Rayleigh number etc. It is found that the isotherms and the streamlines take symmetrical position along the vertical central line of square duct. The isotherms are penetrated into deeper area at upper half of duct as compared to lower half.
Heat and mass transfer in flames
NASA Technical Reports Server (NTRS)
Faeth, G. M.
1986-01-01
Heat- and mass-transfer processes in turbulent diffusion flames are discussed, considering turbulent mixing and the structure of single-phase flames, drop processes in spray flames, and nonluminous and luminous flame radiation. Interactions between turbulence and other phenomena are emphasized, concentrating on past work of the author and his associates. The conserved-scalar formalism, along with the laminar-flamelet approximation, is shown to provide reasonable estimates of the structure of gas flames, with modest levels of empiricism. Extending this approach to spray flames has highlighted the importance of drop/turbulence interactions; e.g., turbulent dispersion of drops, modification of turbulence by drops, etc. Stochastic methods being developed to treat these phenomena are yielding encouraging results.
Submersible pumping system with heat transfer mechanism
Hunt, Daniel Francis Alan; Prenger, F. Coyne; Hill, Dallas D; Jankowski, Todd Andrew
2014-04-15
A submersible pumping system for downhole use in extracting fluids containing hydrocarbons from a well. In one embodiment, the pumping system comprises a rotary induction motor, a motor casing, one or more pump stages, and a cooling system. The rotary induction motor rotates a shaft about a longitudinal axis of rotation. The motor casing houses the rotary induction motor such that the rotary induction motor is held in fluid isolation from the fluid being extracted. The pump stages are attached to the shaft outside of the motor casing, and are configured to impart fluid being extracted from the well with an increased pressure. The cooling system is disposed at least partially within the motor casing, and transfers heat generated by operation of the rotary induction motor out of the motor casing.
Low-melting point heat transfer fluid
Cordaro, Joseph G.; Bradshaw, Robert W.
2011-04-12
A low-melting point, heat transfer fluid comprising a mixture of LiNO.sub.3, NaNO.sub.3, KNO.sub.3, NaNO.sub.2 and KNO.sub.2 salts where the Li, Na and K cations are present in amounts of about 20-33.5 mol % Li, about 18.6-40 mol % Na, and about 40-50.3 mol % K and where the nitrate and nitrite anions are present in amounts of about 36-50 mol % NO.sub.3, and about 50-62.5 mol % NO.sub.2. These compositions can have liquidus temperatures between 70.degree. C. and 80.degree. C. for some compositions.
Heat and mass transfer in the gas tungsten and gas metal arc welding processes
Watkins, A.D; Smartt, H.B.; Einerson, C.J.; Watkins, J.A.
1990-01-01
The heat transferred from an electrode negative, argon gas tungsten arc to an anode was measured for a wide range of conditions suitable for mechanized welding. The results are given as (1) the arc efficiency and (2) the anode heat and current input distributions for various anode materials over a range of current and voltage. The nominal arc is Gaussian, {approximately}4 mm in diameter, with {approximately}75{percent}heat transfer efficiency. Variations from these values are discussed in terms of the electrical and thermal energy transport mechanisms. Heat transferred to the workpiece (cathode) during direct current, electrode positive gas metal arc welding (GMAW) was measured for various parameters applicable to machine welding. The results are presented as a function of electrode speed for changing voltages and contact tip to workpiece distances. The total heat transfer efficiency was nominally 85{percent} for a 0.89 mm diameter steel electrode using an argon-2{percent} oxygen shielding gas; the nominal heat transfer efficiency of the droplet component was 40{percent}. The average droplet temperatures ranged from 2400 to 3100 K, depending on the process parameters. A new method of measuring the heat transferred from the arc to the workpiece, using a boiling liquid nitrogen calorimeter, has been developed that gives rapid, accurate values. 20 refs., 8 figs., 2 tabs.
Heat Transfer Analysis of a Closed Brayton Cycle Space Radiator
NASA Technical Reports Server (NTRS)
Juhasz, Albert J.
2007-01-01
This paper presents a mathematical analysis of the heat transfer processes taking place in a radiator for a closed cycle gas turbine (CCGT), also referred to as a Closed Brayton Cycle (CBC) space power system. The resulting equations and relationships have been incorporated into a radiator sub-routine of a numerical triple objective CCGT optimization program to determine operating conditions yielding maximum cycle efficiency, minimum radiator area and minimum overall systems mass. Study results should be of interest to numerical modeling of closed cycle Brayton space power systems and to the design of fluid cooled radiators in general.
Personalized recommendation based on heat bidirectional transfer
NASA Astrophysics Data System (ADS)
Ma, Wenping; Feng, Xiang; Wang, Shanfeng; Gong, Maoguo
2016-02-01
Personalized recommendation has become an increasing popular research topic, which aims to find future likes and interests based on users' past preferences. Traditional recommendation algorithms pay more attention to forecast accuracy by calculating first-order relevance, while ignore the importance of diversity and novelty that provide comfortable experiences for customers. There are some levels of contradictions between these three metrics, so an algorithm based on bidirectional transfer is proposed in this paper to solve this dilemma. In this paper, we agree that an object that is associated with history records or has been purchased by similar users should be introduced to the specified user and recommendation approach based on heat bidirectional transfer is proposed. Compared with the state-of-the-art approaches based on bipartite network, experiments on two benchmark data sets, Movielens and Netflix, demonstrate that our algorithm has better performance on accuracy, diversity and novelty. Moreover, this method does better in exploiting long-tail commodities and cold-start problem.
NASA Technical Reports Server (NTRS)
Fink, Richard
2015-01-01
The increasing use of power electronics, such as high-current semiconductor devices and modules, within space vehicles is driving the need to develop specialty thermal management materials in both the packaging of these discrete devices and the packaging of modules consisting of these device arrays. Developed by Applied Nanotech, Inc. (ANI), CarbAl heat transfer material is uniquely characterized by its low density, high thermal diffusivity, and high thermal conductivity. Its coefficient of thermal expansion (CTE) is similar to most power electronic materials, making it an effective base plate substrate for state-of-the-art silicon carbide (SiC) super junction transistors. The material currently is being used to optimize hybrid vehicle inverter packaging. Adapting CarbAl-based substrates to space applications was a major focus of the SBIR project work. In Phase I, ANI completed modeling and experimentation to validate its deployment in a space environment. Key parameters related to cryogenic temperature scaling of CTE, thermal conductivity, and mechanical strength. In Phase II, the company concentrated on improving heat sinks and thermally conductive circuit boards for power electronic applications.
Convective heat transfer for fluids passing through aluminum foams
NASA Astrophysics Data System (ADS)
Dyga, Roman; Troniewski, Leon
2015-03-01
This paper analyses the experimental findings within heat transfer when heating up air, water and oil streams which are passed through a duct with internal structural packing elements in the form of metal foams. Three types of aluminum foams with different cell sizes, porosity specifications and thermal conductivities were used in the study. The test data were collected and they made it possible to establish the effect of the foam geometry, properties of fluids and flow hydrodynamic conditions on the convective heat transfer process from the heating surface to the fluid flowing by (wetting) that surface. The foam was found to be involved in heat transfer to a limited extent only. Heat is predominantly transferred directly from the duct wall to a fluid, and intensity of convective heat transfer is controlled by the wall effects. The influence of foam structural parameters, like cell size and/or porosity, becomes more clearly apparent under laminar flow conditions.
Sensitivity Analysis of the Gap Heat Transfer Model in BISON.
Swiler, Laura Painton; Schmidt, Rodney C.; Williamson, Richard; Perez, Danielle
2014-10-01
This report summarizes the result of a NEAMS project focused on sensitivity analysis of the heat transfer model in the gap between the fuel rod and the cladding used in the BISON fuel performance code of Idaho National Laboratory. Using the gap heat transfer models in BISON, the sensitivity of the modeling parameters and the associated responses is investigated. The study results in a quantitative assessment of the role of various parameters in the analysis of gap heat transfer in nuclear fuel.
Nonlinear Transient Problems Using Structure Compatible Heat Transfer Code
NASA Technical Reports Server (NTRS)
Hou, Gene
2000-01-01
The report documents the recent effort to enhance a transient linear heat transfer code so as to solve nonlinear problems. The linear heat transfer code was originally developed by Dr. Kim Bey of NASA Largely and called the Structure-Compatible Heat Transfer (SCHT) code. The report includes four parts. The first part outlines the formulation of the heat transfer problem of concern. The second and the third parts give detailed procedures to construct the nonlinear finite element equations and the required Jacobian matrices for the nonlinear iterative method, Newton-Raphson method. The final part summarizes the results of the numerical experiments on the newly enhanced SCHT code.
Heat Transfer Variation on Protuberances and Surface Roughness Elements
NASA Technical Reports Server (NTRS)
Henry, Robert C.; Hansman, R. John, Jr.; Breuer, Kenneth S.
1995-01-01
In order to determine the effect of surface irregularities on local convective heat transfer, the variation in heat transfer coefficients on small (2-6 mm diam) hemispherical roughness elements on a flat plate has been studied in a wind funnel using IR techniques. Heat transfer enhancement was observed to vary over the roughness elements with the maximum heat transfer on the upstream face. This heat transfer enhancement increased strongly with roughness size and velocity when there was a laminar boundary layer on the plate. For a turbulent boundary layer, the heat transfer enhancement was relatively constant with velocity, but did increase with element size. When multiple roughness elements were studied, no influence of adjacent roughness elements on heat transfer was observed if the roughness separation was greater than approximately one roughness element radius. As roughness separation was reduced, less variation in heat transfer was observed on the downstream elements. Implications of the observed roughness enhanced heat transfer on ice accretion modeling are discussed.
Heat Transfer in Regions of Separated and Reattached Flows
NASA Technical Reports Server (NTRS)
Crawford, Davis H; Rumsey, Charles B
1957-01-01
Past experimental work has indicated that separated flow can greatly increase the heat transfer to a surface; whereas, some theoretical studies have indicated a possible decrease. Recent investigations have helped to clarify the effects of separation on heat transfer and have indicated a method of reducing separation. This paper considers the results of some of these investigations and shows the heat transfer in regions of separation and reattachment for a few specific shapes. These results show that the heat transfer in a separated region is strongly affected by the extent of separation, the location of the reattachment point, and the location of transition along the separated boundary.
NASA Technical Reports Server (NTRS)
Daryabeigi, Kamran; Cunnington, George R.; Miller, Steve D.; Knutson, Jeffry R.
2010-01-01
Combined radiation and conduction heat transfer through various high-temperature, high-porosity, unbonded (loose) fibrous insulations was modeled based on first principles. The diffusion approximation was used for modeling the radiation component of heat transfer in the optically thick insulations. The relevant parameters needed for the heat transfer model were derived from experimental data. Semi-empirical formulations were used to model the solid conduction contribution of heat transfer in fibrous insulations with the relevant parameters inferred from thermal conductivity measurements at cryogenic temperatures in a vacuum. The specific extinction coefficient for radiation heat transfer was obtained from high-temperature steady-state thermal measurements with large temperature gradients maintained across the sample thickness in a vacuum. Standard gas conduction modeling was used in the heat transfer formulation. This heat transfer modeling methodology was applied to silica, two types of alumina, and a zirconia-based fibrous insulation, and to a variation of opacified fibrous insulation (OFI). OFI is a class of insulations manufactured by embedding efficient ceramic opacifiers in various unbonded fibrous insulations to significantly attenuate the radiation component of heat transfer. The heat transfer modeling methodology was validated by comparison with more rigorous analytical solutions and with standard thermal conductivity measurements. The validated heat transfer model is applicable to various densities of these high-porosity insulations as long as the fiber properties are the same (index of refraction, size distribution, orientation, and length). Furthermore, the heat transfer data for these insulations can be obtained at any static pressure in any working gas environment without the need to perform tests in various gases at various pressures.
Boiling heat transfer of refrigerant R-21 in upward flow in plate-fin heat exchanger
NASA Astrophysics Data System (ADS)
Kuznetsov, V. V.; Shamirzaev, A. S.
2015-11-01
The article presents the results of experimental investigation of boiling heat transfer of refrigerant R-21 in upward flow in a vertical plate-fin heat exchanger with transverse size of the channels that is smaller than the capillary constant. The heat transfer coefficients obtained in ranges of small mass velocities and low heat fluxes, which are typical of the industry, have been poorly studied yet. The characteristic patterns of the upward liquid-vapor flow in the heat exchanger channels and the regions of their existence are detected. The obtained data show a weak dependence of heat transfer coefficient on equilibrium vapor quality, mass flow rate, and heat flux density and do not correspond to calculations by the known heat transfer models. A possible reason for this behavior is a decisive influence of evaporation of thin liquid films on the heat transfer at low heat flux.
Efficient Three-dimensional NLTE Dust Radiative Transfer with SKIRT
NASA Astrophysics Data System (ADS)
Baes, Maarten; Verstappen, Joris; De Looze, Ilse; Fritz, Jacopo; Saftly, Waad; Vidal Pérez, Edgardo; Stalevski, Marko; Valcke, Sander
2011-10-01
We present an updated version of SKIRT, a three-dimensional (3D) Monte Carlo radiative transfer code developed to simulate dusty galaxies. The main novel characteristics of the SKIRT code are the use of a stellar foam to generate random positions, an efficient combination of eternal forced scattering and continuous absorption, and a new library approach that links the radiative transfer code to the DustEM dust emission library. This approach enables a fast, accurate, and self-consistent calculation of the dust emission of arbitrary mixtures of transiently heated dust grains and polycyclic aromatic hydrocarbons, even for full 3D models containing millions of dust cells. We have demonstrated the accuracy of the SKIRT code through a set of simulations based on the edge-on spiral galaxy UGC 4754. The models we ran were gradually refined from a smooth, two-dimensional, local thermal equilibrium (LTE) model to a fully 3D model that includes non-LTE (NLTE) dust emission and a clumpy structure of the dusty interstellar medium. We find that clumpy models absorb UV and optical radiation less efficiently than smooth models with the same amount of dust, and that the dust in clumpy models is on average both cooler and less luminous. Our simulations demonstrate that, given the appropriate use of optimization techniques, it is possible to efficiently and accurately run Monte Carlo radiative transfer simulations of arbitrary 3D structures of several million dust cells, including a full calculation of the NLTE emission by arbitrary dust mixtures.
Effects of Solar Photovoltaic Panels on Roof Heat Transfer
NASA Technical Reports Server (NTRS)
Dominguez, A.; Klessl, J.; Samady, M.; Luvall, J. C.
2010-01-01
Building Heating, Ventilation and Air Conditioning (HVAC) is a major contributor to urban energy use. In single story buildings with large surface area such as warehouses most of the heat enters through the roof. A rooftop modification that has not been examined experimentally is solar photovoltaic (PV) arrays. In California alone, several GW in residential and commercial rooftop PV are approved or in the planning stages. With the PV solar conversion efficiency ranging from 5-20% and a typical installed PV solar reflectance of 16-27%, 53-79% of the solar energy heats the panel. Most of this heat is then either transferred to the atmosphere or the building underneath. Consequently solar PV has indirect effects on roof heat transfer. The effect of rooftop PV systems on the building roof and indoor energy balance as well as their economic impacts on building HVAC costs have not been investigated. Roof calculator models currently do not account for rooftop modifications such as PV arrays. In this study, we report extensive measurements of a building containing a flush mount and a tilted solar PV array as well as exposed reference roof. Exterior air and surface temperature, wind speed, and solar radiation were measured and thermal infrared (TIR) images of the interior ceiling were taken. We found that in daytime the ceiling surface temperature under the PV arrays was significantly cooler than under the exposed roof. The maximum difference of 2.5 C was observed at around 1800h, close to typical time of peak energy demand. Conversely at night, the ceiling temperature under the PV arrays was warmer, especially for the array mounted flat onto the roof. A one dimensional conductive heat flux model was used to calculate the temperature profile through the roof. The heat flux into the bottom layer was used as an estimate of the heat flux into the building. The mean daytime heat flux (1200-2000 PST) under the exposed roof in the model was 14.0 Watts per square meter larger than under the tilted PV array. The maximum downward heat flux was 18.7 Watts per square meters for the exposed roof and 7.0 Watts per square meters under the tilted PV array, a 63% reduction due to the PV array. This study is unique as the impact of tilted and flush PV arrays could be compared against a typical exposed roof at the same roof for a commercial uninhabited building with exposed ceiling and consisting only of the building envelope. Our results indicate a more comfortable indoor environment in PV covered buildings without HVAC both in hotter and cooler seasons.
High thermal power density heat transfer. [thermionic converters
NASA Technical Reports Server (NTRS)
Morris, J. F. (Inventor)
1980-01-01
Heat from a high temperature heat pipe is transferred through a vacuum or a gap filled with electrically nonconducting gas to a cooler heat pipe. The heat pipe is used to cool the nuclear reactor while the heat pipe is connected thermally and electrically to a thermionic converter. If the receiver requires greater thermal power density, geometries are used with larger heat pipe areas for transmitting and receiving energy than the area for conducting the heat to the thermionic converter. In this way the heat pipe capability for increasing thermal power densities compensates for the comparatively low thermal power densities through the electrically non-conducting gap between the two heat pipes.
In - line determination of heat transfer coefficients in a plate heat exchanger
NASA Astrophysics Data System (ADS)
Sotelo, S. Silva; Domínguez, R. J. Romero
This paper shows an in - line determination of heat transfer coefficients in a plate heat exchanger. Water and aqueous working solution of lithium bromide + ethylene glycol are considered. Heat transfer coefficients are calculated for both fluids. "Type T" thermocouples were used for monitoring the wall temperature in a plate heat exchanger, which is one of the main components in an absorption system. Commercial software Agilent HP Vee Pro 7.5 was used for monitoring the temperatures and for the determination of the heat transfer coefficients. There are not previous works for heat transfer coefficients for the working solution used in this work.
Convective heat transfer enhancement inside tubes using inserted helical coils
NASA Astrophysics Data System (ADS)
Ali, R. K.; Sharafeldeen, M. A.; Berbish, N. S.; Moawed, M. A.
2016-01-01
Convective heat transfer was experimentally investigated in tubes with helical coils inserts in turbulent flow regime within Reynolds number range of 14400 ≤ Re ≤ 42900. The present work aims to extend the experimental data available on wire coil inserts to cover wire diameter ratio from 0.044 to 0.133 and coil pitch ratio from 1 to 5. Uniform heat flux was applied to the external surface of the tube and air was selected as fluid. The effects of Reynolds number and wire diameter and coil pitch ratios on the Nusselt number and friction factor were studied. The enhancement efficiency and performance criteria ranges are of (46.9-82.6%) and (100.1-128%) within the investigated range of the different parameters, respectively. Correlations are obtained for the average Nusselt number and friction factor utilizing the present measurements within the investigated range of geometrical parameters and Re.
Methods for increasing the efficiency of heating scrap metal in electric arc furnaces
NASA Astrophysics Data System (ADS)
Raile, V.
2013-06-01
The type of heating, which determines heat transfer from an external energy source to a metallic charge, plays a key role in the process of preliminary heating of scrap metal. The type of charge heating during preliminary heating of scrap metal mainly determines the average scrap metal heating temperature and the formation of harmful substances. This article considers the existing types of charge heating in EAF baths and shaft heaters. The types of scrap metal heating that increase the energy efficiency and weaken the ecological problems related to this process in electric furnace steelmaking units are found.
Investigations on the heat transfer performance of edge-shaped finned-tubes
NASA Astrophysics Data System (ADS)
Wang, Xiao-wu; Wan, Zhen-ping; Tang, Yong
2014-09-01
The third generation enhanced heat transfer technologies, such as three-dimensional fin and dimple, are still important means of improving energy efficiency and will continue to be challenging issues. This paper concentrates on the analysis of the condensation heat transfer performance of an edge-shaped finned-tube fabricated by extrusion-ploughing process. Experimental results show that the overall heat transfer coefficient increases with increases of volumetric flow rate of cold water and heat flux whereas the shell side heat transfer coefficient decreases with volumetric flow rate and heat flux increasing. At the similar volumetric flow rate, the shell side heat transfer coefficient of the edge-shaped finned-tube is 4-6 times larger than that of the smooth tube. At the similar volumetric flow rate, the shell side heat transfer coefficient of edge-shaped finned-tube increases with ploughing depth increasing. At the same temperature difference between wall and vapor, the shell side heat transfer coefficient is also higher than what had been reported in the literature.
Generator-absorber-heat exchange heat transfer apparatus and method and use thereof in a heat pump
Phillips, Benjamin A.; Zawacki, Thomas S.
1996-12-03
Numerous embodiments and related methods for generator-absorber heat exchange (GAX) are disclosed, particularly for absorption heat pump systems. Such embodiments and related methods use the working solution of the absorption system for the heat transfer medium. A combination of weak and rich liquor working solution is used as the heat transfer medium.
An experimental procedure to determine heat transfer properties of turbochargers
NASA Astrophysics Data System (ADS)
Serrano, J. R.; Olmeda, P.; Páez, A.; Vidal, F.
2010-03-01
Heat transfer phenomena in turbochargers have been a subject of investigation due to their importance for the correct determination of compressor real work when modelling. The commonly stated condition of adiabaticity for turbochargers during normal operation of an engine has been revaluated because important deviations from adiabatic behaviour have been stated in many studies in this issue especially when the turbocharger is running at low rotational speeds/loads. The deviations mentioned do not permit us to assess properly the turbine and compressor efficiencies since the pure aerodynamic effects cannot be separated from the non-desired heat transfer due to the presence of both phenomena during turbocharger operation. The correction of the aforesaid facts is necessary to properly feed engine models with reliable information and in this way increase the quality of the results in any modelling process. The present work proposes a thermal characterization methodology successfully applied in a turbocharger for a passenger car which is based on the physics of the turbocharger. Its application helps to understand the thermal behaviour of the turbocharger, and the results obtained constitute vital information for future modelling efforts which involve the use of the information obtained from the proposed methodology. The conductance values obtained from the proposed methodology have been applied to correct a procedure for measuring the mechanical efficiency of the tested turbocharger.
Generator-absorber-heat exchange heat transfer apparatus and method and use thereof in a heat pump
Phillips, Benjamin A.; Zawacki, Thomas S.; Marsala, Joseph
1994-11-29
Numerous embodiments and related methods for generator-absorber heat exchange (GAX) are disclosed, particularly for absorption heat pump systems. Such embodiments and related methods use the working solution of the absorption system for the heat transfer medium.
Study of a high performance evaporative heat transfer surface
NASA Technical Reports Server (NTRS)
Saaski, E. W.; Hamasaki, R. H.
1977-01-01
An evaporative surface is described for heat pipes and other two-phase heat transfer applications that consists of a hybrid composition of V-grooves and capillary wicking. Characteristics of the surface include both a high heat transfer coefficient and high heat flux capability relative to conventional open-faced screw thread surfaces. With a groove density of 12.6 cm/1 and ammonia working fluid, heat transfer coefficients in the range of 1 to 2 W/sq cm have been measured along with maximum heat flux densities in excess of 20 W/sq cm. A peak heat transfer coefficient in excess of 2.3 W/sq cm was measured with a 37.8 cm/1 hybrid surface.
Concurrent implementation of the Crank-Nicolson method for heat transfer analysis
NASA Technical Reports Server (NTRS)
Ransom, J. B.; Fulton, R. E.
1985-01-01
To exploit the significant gains in computing speed provided by Multiple Instruction Multiple Data (MIMD) computers, concurrent methods for practical problems need to be investigated and test problems implemented on actual hardware. One such problem class is heat transfer analysis which is important in many aerospace applications. This paper compares the efficiency of two alternate implementations of heat transfer analysis on an experimental MIMD computer called the Finite Element Machine (FEM). The implicit Crank-Nicolson method is used to solve concurrently the heat transfer equations by both iterative and direct methods. Comparison of actual timing results achieved for the two methods and their significance relative to more complex problems are discussed.
Double tube heat exchanger with novel enhancement: part II—single phase convective heat transfer
NASA Astrophysics Data System (ADS)
Tiruselvam, R.; Chin, W. M.; Raghavan, Vijay R.
2012-08-01
The study is conducted to evaluate the heat transfer characteristics of two new and versatile enhancement configurations in a double tube heat exchanger annulus. The novelty is that they are usable in single phase forced convection, evaporation and condensation. Heat transfer coefficients are determined by the Wilson Plot technique in laminar and turbulent flow and correlations are proposed for Nusselt numbers. Comparisons are then made between heat transfer and flow friction.
Heat transfer and flow in solar energy and bioenergy systems
NASA Astrophysics Data System (ADS)
Xu, Ben
The demand for clean and environmentally benign energy resources has been a great concern in the last two decades. To alleviate the associated environmental problems, reduction of the use of fossil fuels by developing more cost-effective renewable energy technologies becomes more and more significant. Among various types of renewable energy sources, solar energy and bioenergy take a great proportion. This dissertation focuses on the heat transfer and flow in solar energy and bioenergy systems, specifically for Thermal Energy Storage (TES) systems in Concentrated Solar Power (CSP) plants and open-channel algal culture raceways for biofuel production. The first part of this dissertation is the discussion about mathematical modeling, numerical simulation and experimental investigation of solar TES system. First of all, in order to accurately and efficiently simulate the conjugate heat transfer between Heat Transfer Fluid (HTF) and filler material in four different solid-fluid TES configurations, formulas of an e?ective heat transfer coe?cient were theoretically developed and presented by extending the validity of Lumped Capacitance Method (LCM) to large Biot number, as well as verifications/validations to this simplified model. Secondly, to provide design guidelines for TES system in CSP plant using Phase Change Materials (PCM), a general storage tank volume sizing strategy and an energy storage startup strategy were proposed using the enthalpy-based 1D transient model. Then experimental investigations were conducted to explore a novel thermal storage material. The thermal storage performances were also compared between this novel storage material and concrete at a temperature range from 400 °C to 500 °C. It is recommended to apply this novel thermal storage material to replace concrete at high operating temperatures in sensible heat TES systems. The second part of this dissertation mainly focuses on the numerical and experimental study of an open-channel algae culture raceway for biofuel production. According to the proposed flow field design of ARID-HV algal raceway, experiments and numerical simulation have been conducted to understand the enhancement of flow mixing in the flow field of ARID-HV raceway by cutting slots on top of the dam near the dead zones. A new method was proposed to quantitatively evaluate the flow mixing by using the statistics of temporal and spatial distribution of the massless fluid particles (centered in each cell at the inlet surface) in the raceway collecting the data of path-lines of fluid particles from CFD results. It is hoped that this method can be applied to assist the algal raceway flow field design as well as other engineering applications. The third part introduces the details about the construction work of a high temperature molten salt test loop. Because of the limited operating temperature of conventional synthetic oils, in order to obtain higher energy conversion efficiency, higher operating temperature is always desirable in a CSP plant which leads to the requirement of new generation of HTF. Currently, a halide salt eutectic mixture (NaCl-KCl-ZnCl2) as a potential HTF for future CSP applications has been proposed by a multi-institute research team, led by University of Arizona. The thermophysical properties of the halide eutectic salt have been measured. However, this new developed halide eutectic salt has not been tested in a circulating loop at a high operating temperature for the measurement of heat transfer coefficient. It is a significant effort to build such a test system due to extremely high operating temperature. As a consequence, in the third part of this dissertation, details about the design of the lab-scale test system and all the equipment items will be introduced. The investigations included in this dissertation for the heat transfer and flow in solar energy and bioenergy systems are of particular interest to the renewable energy engineering community. It is expected that the proposed methods can provide useful information for engineers and researchers.
NASA Astrophysics Data System (ADS)
Cleveland, Mathew A.
We investigate several aspects of the numerical solution of the radiative transfer equation in the context of coal combustion: the parallel efficiency of two commonly-used opacity models, the sensitivity of turbulent radiation interaction (TRI) effects to the presence of coal particulate, and an improvement of the order of temporal convergence using the coarse mesh finite difference (CMFD) method. There are four opacity models commonly employed to evaluate the radiative transfer equation in combustion applications; line-by-line (LBL), multigroup, band, and global. Most of these models have been rigorously evaluated for serial computations of a spectrum of problem types [1]. Studies of these models for parallel computations [2] are limited. We assessed the performance of the Spectral-Line-Based weighted sum of gray gasses (SLW) model, a global method related to K-distribution methods [1], and the LBL model. The LBL model directly interpolates opacity information from large data tables. The LBL model outperforms the SLW model in almost all cases, as suggested by Wang et al. [3]. The SLW model, however, shows superior parallel scaling performance and a decreased sensitivity to load imbalancing, suggesting that for some problems, global methods such as the SLW model, could outperform the LBL model. Turbulent radiation interaction (TRI) effects are associated with the differences in the time scales of the fluid dynamic equations and the radiative transfer equations. Solving on the fluid dynamic time step size produces large changes in the radiation field over the time step. We have modified the statistically homogeneous, non-premixed flame problem of Deshmukh et al. [4] to include coal-type particulate. The addition of low mass loadings of particulate minimally impacts the TRI effects. Observed differences in the TRI effects from variations in the packing fractions and Stokes numbers are difficult to analyze because of the significant effect of variations in problem initialization. The TRI effects are very sensitive to the initialization of the turbulence in the system. The TRI parameters are somewhat sensitive to the treatment of particulate temperature and the particulate optical thickness, and this effect are amplified by increased particulate loading. Monte Carlo radiative heat transfer simulations of time-dependent combustion processes generally involve an explicit evaluation of emission source because of the expense of the transport solver. Recently, Park et al. [5] have applied quasi-diffusion with Monte Carlo in high energy density radiative transfer applications. We employ a Crank-Nicholson temporal integration scheme in conjunction with the coarse mesh finite difference (CMFD) method, in an effort to improve the temporal accuracy of the Monte Carlo solver. Our results show that this CMFD-CN method is an improvement over Monte Carlo with CMFD time-differenced via Backward Euler, and Implicit Monte Carlo [6] (IMC). The increase in accuracy involves very little increase in computational cost, and the figure of merit for the CMFD-CN scheme is greater than IMC.
Coupling radiative heat transfer in participating media with other heat transfer modes
Tencer, John; Howell, John R.
2015-09-28
The common methods for finding the local radiative flux divergence in participating media through solution of the radiative transfer equation are outlined. The pros and cons of each method are discussed in terms of their speed, ability to handle spectral properties and scattering phenomena, as well as their accuracy in different ranges of media transport properties. The suitability of each method for inclusion in the energy equation to efficiently solve multi-mode thermal transfer problems is discussed. Lastly, remaining topics needing research are outlined.
Summary of NASA aerodynamic and heat transfer studies in turbine vanes and blades
NASA Technical Reports Server (NTRS)
Moffitt, T. P.; Stepka, F. S.; Rohlik, H. E.
1976-01-01
Aerodynamic effects of trailing edge geometry, hole size, angle, spacing, and shape have been studied in two- and three-dimensional cascades and in a warm turbine test series. Heat transfer studies have been carried out in various two- and three-dimensional test facilities in order to provide corresponding heat transfer data. Results are shown in terms of cooling effectiveness and aerodynamic efficiency for various coolant fractions, coolant-primary temperature ratios, and cooling configurations.
Summary of NASA aerodynamic and heat transfer studies in turbine vanes and blades
NASA Technical Reports Server (NTRS)
Moffitt, T. P.; Stepka, F. S.; Rohlik, H. E.
1976-01-01
Aerodynamic effects of trailing edge geometry, hole size, angle, spacing, and shape were studied in two- and three-dimensional cascades and in a warm turbine test series. Heat transfer studies were carried out in various two- and three-dimensional test facilities in order to provide corresponding heat transfer data. Results are shown in terms of cooling effectiveness and aerodynamic efficiency for various coolant fractions, coolant-primary temperature ratios, and cooling configurations.
SIMULATION OF BOILING HEAT TRANSFER AROUND MICRO PIN-FIN HEAT EXCHANGER: PROGRESS AND CHALLENGES
Tyagi, M.; Maha, A.; Singh, K. V.; Li, G.; and Pang, S.S.
2006-07-01
Boiling at microscales is a challenging problem for the computational models as well as the resources. During boiling, the formation and departure of vapor bubbles from the heated surface involves the physics from nano/micro level to the macro level. Therefore, a hierarchical methodology is needed to incorporate the nano/microscale physics with the macroscale system performance. Using micro-fabrication techniques, microstructures (micropin-fins) can be fabricated around the tubes in the heat exchanger of Pressurized Water Reactors (PWRs) to increase the heat-exchanging efficiency and reduce the overall size of the heat-exchanger for the given heat transfer rates. Combined with high fidelity simulations of the thermal transport in the entire system, optimal design of microstructure patterns and layouts can be worked out pragmatically. Properly patterned microstructures on the pipe in the steam generation zone should create more nuclei for bubble to form and result in a reduced average bubble size and shorter retention time, i.e. the time for the vapor phase sticking on the pipe surface. The smaller average steam bubble size and shorter bubble retention time will enhance the overall thermal efficiency. As a preliminary step, a periodic arrangement of micropin-fins containing four in-line cylindrical fins was modeled. The governing equations for the mass, momentum and energy transport were solved in the fluid in a conjugate heat transfer mode. In the future, several studies will be conducted to simulate different geometric arrangements, different fin cross-sections, and realistic operating conditions including phase-change with boiling by adding complexities in simple steps.
Takeishi, K; Aoki, S
2001-05-01
The improvement of the heat transfer coefficient of the 1st row blades in high temperature industrial gas turbines is one of the most important issues to ensure reliable performance of these components and to attain high thermal efficiency of the facility. This paper deals with the contribution of heat transfer to increase the turbine inlet temperature of such gas turbines in order to attain efficient and environmentally benign engines. Following the experiments described in Part 1, a set of trials was conducted to clarify the influence of the blade's rotating motion on the heat transfer coefficient for internal serpentine flow passages with turbulence promoters. Test results are shown and discussed in this second part of the contribution. PMID:11460663
Improving Heat Transfer Performance of Printed Circuit Boards
NASA Technical Reports Server (NTRS)
Schatzel, Donald V.
2009-01-01
This paper will explore the ability of printed circuit boards laminated with a Carbon Core Laminate to transfer heat vs. standard printed circuit boards that use only thick layers of copper. The paper will compare the differences in heat transfer performance of printed circuit boards with and without CCL.
Effects of simulated combustor turbulence on boundary layer heat transfer
NASA Technical Reports Server (NTRS)
Ames, F. E.; Moffat, R. J.
1990-01-01
A simulated combustor flow field has been generated in order to study the effects of high intensity large scale turbulence on boundary layer heat transfer. Turbulence intensities of up to 19 percent and integral lengths scales of 4 to 6 centimeters have been generated. Heat transfer has been augmented by up to 28 percent for the flat plate constant velocity turbulent boundary layer.
NASA Astrophysics Data System (ADS)
Ahn, Ho Seon; Kim, Jin Man; Kim, Taejoo; Park, Su Cheong; Kim, Ji Min; Park, Youngjae; Yu, Dong In; Hwang, Kyoung Won; Jo, Hangjin; Park, Hyun Sun; Kim, Hyungdae; Kim, Moo Hwan
2014-09-01
Boiling heat transfer (BHT) is a particularly efficient heat transport method because of the latent heat associated with the process. However, the efficiency of BHT decreases significantly with increasing wall temperature when the critical heat flux (CHF) is reached. Graphene has received much recent research attention for applications in thermal engineering due to its large thermal conductivity. In this study, graphene films of various thicknesses were deposited on a heated surface, and enhancements of BHT and CHF were investigated via pool-boiling experiments. In contrast to the well-known surface effects, including improved wettability and liquid spreading due to micron- and nanometer-scale structures, nanometer-scale folded edges of graphene films provided a clue of BHT improvement and only the thermal conductivity of the graphene layer could explain the dependence of the CHF on the thickness. The large thermal conductivity of the graphene films inhibited the formation of hot spots, thereby increasing the CHF. Finally, the provided empirical model could be suitable for prediction of CHF.
Ahn, Ho Seon; Kim, Jin Man; Kim, TaeJoo; Park, Su Cheong; Kim, Ji Min; Park, Youngjae; Yu, Dong In; Hwang, Kyoung Won; Jo, HangJin; Park, Hyun Sun; Kim, Hyungdae; Kim, Moo Hwan
2014-01-01
Boiling heat transfer (BHT) is a particularly efficient heat transport method because of the latent heat associated with the process. However, the efficiency of BHT decreases significantly with increasing wall temperature when the critical heat flux (CHF) is reached. Graphene has received much recent research attention for applications in thermal engineering due to its large thermal conductivity. In this study, graphene films of various thicknesses were deposited on a heated surface, and enhancements of BHT and CHF were investigated via pool-boiling experiments. In contrast to the well-known surface effects, including improved wettability and liquid spreading due to micron- and nanometer-scale structures, nanometer-scale folded edges of graphene films provided a clue of BHT improvement and only the thermal conductivity of the graphene layer could explain the dependence of the CHF on the thickness. The large thermal conductivity of the graphene films inhibited the formation of hot spots, thereby increasing the CHF. Finally, the provided empirical model could be suitable for prediction of CHF. PMID:25182076
Mixed convection heat transfer in concave and convex channels
Moukalled, F.; Doughan, A.; Acharya, S.
1997-07-01
Mixed convection heat transfer studies in the literature have been primarily confined to pipe and rectangular channel geometry's. In some applications, however, heat transfer in curved channels may be of interest (e.g., nozzle and diffuser shaped passages in HVAC systems, fume hoods, chimneys, bell-shaped or dome-shaped chemical reactors, etc.). A numerical investigation of laminar mixed convection heat transfer of air in concave and convex channels is presented. Six different channel aspects ratios (R/L = 1.04, 1.25, 2.5, 5, 10, and {infinity}) and five different values of Gr/Re{sup 2} (Gr/Re{sup 2} = 0, 0.1, 1, 3, 5) are considered. Results are displayed in terms of streamline and isotherm plots, velocity and temperature profiles, and local and average Nusselt number estimates. Numerical predictions reveal that compared to straight channels of equal height, concave channels of low aspect ratio have lower heat transfer at relatively low values of Gr/Re{sup 2} and higher heat transfer at high values of Gr/Re{sup 2}. When compared to straight channels of equal heated length, concave channels are always found to have lower heat transfer and for all values of Gr/Re{sup 2}. On the other hand, predictions for convex channels revealed enhancement in heat transfer compared to straight channels of equal height and/or equal heated length for all values of Gr/Re{sup 2}.
Micro-scale drop dynamics for heat transfer enhancement
NASA Astrophysics Data System (ADS)
Francois, Marianne; Shyy, Wei
2002-05-01
With rapid advances in micro-device fabrication, computational techniques, and diagnostic tools, there is a significant interest in applying micro-scale fluid dynamics and heat transfer to flow control, flight vehicle protection, and thermal management. Utilizing energy transfer associated with phase change, multiphase systems offer many new opportunities. To elucidate the main scientific issues and technical implications, recent research addressing the interplay between capillarity, moving boundaries, fluid dynamics, heat transfer, and phase change of micro-scale multiphase systems is reviewed. The parametric variations in contact angle, surface tension, impact velocity, and liquid viscosity related to drop impingement and heat transfer are discussed.
NASA Astrophysics Data System (ADS)
Pronobis, M.; Kalisz, S.; Wejkowski, R.
The paper presents the results of an investigation concerning heat transfer and pressure loss in air crossflow of diagonally shaped membrane heating surfaces. The heat and mass transfer analogy by means of naphthalene sublimation technique is used in order to evaluate mean Nusselt number values in such tube banks. The effect of tube bank arrangement on heat transfer coefficients and flow resistance is discussed. Convective heat transfer and pressure loss characteristics of diagonally shaped membrane tube banks, plain tube banks and ordinary membrane tube banks are compared.
A review of NASA combustor and turbine heat transfer research
NASA Technical Reports Server (NTRS)
Rudey, R. A.; Graham, R. W.
1984-01-01
The thermal design of the combustor and turbine of a gas turbine engine poses a number of difficult heat transfer problems. The importance of improved prediction techniques becomes more critical in anticipation of future generations of gas turbine engines which will operate at higher cycle pressure and temperatures. Research which addresses many of the complex heat transfer processes holds promise for yielding significant improvements in prediction of metal temperatures. Such research involves several kinds of program including: (1) basic experiments which delineate the fundamental flow and heat transfer phenomena that occur in the hot sections of the gas turbine but at low enthalpy conditions; (2) analytical modeling of these flow and heat transfer phenomena which results from the physical insights gained in experimental research; and (3) verification of advanced prediction techniques in facilities which operate near the real engine thermodynamic conditions. In this paper, key elements of the NASA program which involves turbine and combustor heat transfer research will be described and discussed.
Heat transfer between immiscible liquids enhanced by gas bubbling
NASA Astrophysics Data System (ADS)
Greene, G. A.; Schwarz, C. E.; Klages, J.; Klein, J.
1982-08-01
The phenomena of core-concrete interactions impact upon containment integrity of light water reactors (LWR) following postulated complete meltdown of the core by containment pressurization, production of combustible gases, and basemat penetration. Experiments were performed with nonreactor materials to investigate one aspect of this problem, heat transfer between overlying immiscible liquids whose interface is disturbed by a transverse non-condensable gas flux emanating from below. Hydrodynamic studies were performed to test a criterion for onset of entrainment due to bubbling through the interface and subsequent heat transfer studies were performed to assess the effect of bubbling on interfacial heat transfer rates, both with and without bubble induced entrainment. Non entraining interfacial heat transfer data with mercury-water/oil fluid pairs were observed to be bounded from below within a factor of two to three by the Szekeley surface renewal heat transfer model.
Measurement of airfoil heat transfer coefficients on a turbine stage
NASA Astrophysics Data System (ADS)
Dring, Robert P.; Blair, Michael F.; Joslyn, H. David
1986-10-01
The Primary basis for heat transfer analysis of turbine airfoils is experimental data obtained in linear cascades. These data were very valuable in identifying the major heat transfer and fluid flow features of a turbine airfoil. The first program objective is to obtain a detailed set of heat transfer coefficients along the midspan of a stator and a rotor in a rotating turbine stage. The data are to be compared to some standard analysis of blade boundary layer heat transfer which is in use today. A second program objective is to obtain a detailed set of heat transfer coefficients along the midspan of a stator located in the wake of an upstream turbine stage.
Condensation Heat Transfer Performance of Nano- Engineered Cu Surfaces
NASA Astrophysics Data System (ADS)
Kim, Hyunsik; Nam, Youngsuk
2014-11-01
We investigated condensate mobility and resulting heat transfer performance on Cu based water repellent surfaces including hydrophobic, superhydrophobic and oil-infused surfaces. We observed the transient microscale condensation behaviours up to 3 hours with controlling the supersaturation level at 1.64. We experimentally characterized the nucleation density, droplet size distribution and growth rate, and then incorporated them into the developed condensation heat transfer model to compare the condensation heat transfer performance of each surface. Due to the spontaneous coalescence induced jumping, superhydrophobic surface can maintain the high heat transfer performance while other surfaces show a gradual decrease in heat transfer performance due to the increase in the thermal resistance across the growing droplets. We also quantified each thermal resistance values from the vapor to the surface through the droplets to find out the relative importance of each thermal resistance term.
Quantitative Global Heat Transfer in a Mach-6 Quiet Tunnel
NASA Technical Reports Server (NTRS)
Sullivan, John P.; Schneider, Steven P.; Liu, Tianshu; Rubal, Justin; Ward, Chris; Dussling, Joseph; Rice, Cody; Foley, Ryan; Cai, Zeimin; Wang, Bo; Woodiga, Sudesh
2012-01-01
This project developed quantitative methods for obtaining heat transfer from temperature sensitive paint (TSP) measurements in the Mach-6 quiet tunnel at Purdue, which is a Ludwieg tube with a downstream valve, moderately-short flow duration and low levels of heat transfer. Previous difficulties with inferring heat transfer from TSP in the Mach-6 quiet tunnel were traced to (1) the large transient heat transfer that occurs during the unusually long tunnel startup and shutdown, (2) the non-uniform thickness of the insulating coating, (3) inconsistencies and imperfections in the painting process and (4) the low levels of heat transfer observed on slender models at typical stagnation temperatures near 430K. Repeated measurements were conducted on 7 degree-half-angle sharp circular cones at zero angle of attack in order to evaluate the techniques, isolate the problems and identify solutions. An attempt at developing a two-color TSP method is also summarized.
Heat Transfer Performance of Absorber of Absorption Refrigerating Machine
NASA Astrophysics Data System (ADS)
Kunugi, Yoshifumi; Ouchi, Tomihisa; Usui, Sanpei; Fukuda, Tamio
Experimental studies on heat transfer performance of absorber for lithium bromide-water absorption refrigerating machine are presented in this paper. Experimental apparatus for 35 kW evaporator and absorber, and outer grooved tubes are used. As a result, over-al1 coefficient of heat transmission of absorber has a maximum value, in the case of heat transfer area ratio of absorber to evaporator, is about 0.8. Heat transfer rate of absorber is increased by 60% by using the outer grooved tube compared with the plane surfaced tube.
Boyer, B.D.; Parlatan, Y.; Slovik, G.C.
1995-09-01
RELAP5 MOD3.1.1 is being used to simulate Loss of Coolant Accidents (LOCA) for the Simplified Boiling Water Reactor (SBWR) being proposed by General Electric (GE). One of the major components associated with the SBWR is the Passive Containment Cooling System (PCCS) which provides the long-term heat sink to reject decay heat. The RELAP5 MOD3.1.1 code is being assessed for its ability to represent accurately the PCCS. Data from the Phase 1, Step 1 Heat Transfer Tests performed at Toshiba`s Gravity-Driven Integral Full-Height Test for Passive Heat Removal (GIRAFFE) facility will be used for assessing the ability of RELAP5 to model condensation in the presence of noncondensables. The RELAP5 MOD3.1.1 condensation model uses the University of California at Berkeley (UCB) correlation developed by Vierow and Schrock. The RELAP5 code uses this heat transfer coefficient with the gas velocity effect multiplier being limited to 2. This heat transfer option was used to analyze the condensation heat transfer in the GIRAFFE PCCS heat exchanger tubes in the Phase 1, Step 1 Heat Transfer Tests which were at a pressure of 3 bar and had a range of nitrogen partial pressure fractions from 0.0 to 0.10. The results of a set of RELAP5 calculations at these conditions were compared with the GIRAFFE data. The effects of PCCS cell noding on the heat transfer process were also studied. The UCB correlation, as implemented in RELAP5, predicted the heat transfer to {plus_minus}5% of the data with a three--node model. The three-node model has a large cell in the entrance region which smeared out the entrance effects on the heat transfer, which tend to overpredict the condensation. Hence, the UCB correlation predicts condensation heat transfer correlation implemented in the code must be removed to allow for accurate calculations with smaller cell sizes.
NASA Astrophysics Data System (ADS)
Kanzaka, Mitsuo; Iwabuchi, Makio
1992-11-01
The heat transfer performance of the actual heat exchangers obtained from the experimental results of the test Stirling engine is presented. The heater for the test engine has 120 heat transfer tubes that consist of a bare-tube part and a fin-tube part. These tubes are located around the combustion chamber and heated by the combustion gas. The cooler is the shell-and-tube-type heat exchanger and is chilled by water. It is shown that the experimental results of heat transfer performance of the heater and cooler of the test Stirling engine are in good agreement with the results calculated by the correlation proposed in our previous heat transfer study under the periodically reversing flow condition. Our correlation is thus confirmed to be applicable to the evaluation of the heat transfer coefficient and the thermal design of the heat exchangers in the Stirling engine.
Laser Measurement Of Convective-Heat-Transfer Coefficient
NASA Technical Reports Server (NTRS)
Porro, A. Robert; Hingst, Warren R.; Chriss, Randall M.; Seablom, Kirk D.; Keith, Theo G., Jr.
1994-01-01
Coefficient of convective transfer of heat at spot on surface of wind-tunnel model computed from measurements acquired by developmental laser-induced-heat-flux technique. Enables non-intrusive measurements of convective-heat-transfer coefficients at many points across surfaces of models in complicated, three-dimensional, high-speed flows. Measurement spot scanned across surface of model. Apparatus includes argon-ion laser, attenuator/beam splitter electronic shutter infrared camera, and subsystem.
Unsteady transonic heat transfer in a transient facility
NASA Technical Reports Server (NTRS)
Lagraff, J. E.
1985-01-01
A facility for making heat transfer measurements on solid surfaces using transient techniques is constructed. The facility being constructed is a Ludweig tube with isentropic compression heating (LICH tube). The work completed is detailed as is the work remaining in order to complete the facility and make useful heat transfer measurements. The scope of the project is briefly discussed along with an overall appraisal of the progress.
Heat transfer of dilute viscoelastic solutions in helical exchangers
NASA Astrophysics Data System (ADS)
Ismail, Z.; Karim, R.
2013-05-01
The study examined heat transfer of two dilute viscoelastic solutions in helical exchangers of circular cross-section. Ten helical coil heat exchangers with diameter ratios ranging from 4 to 50 were constructed. Results showed doubling the concentrations of polymer increased heat transfer performance by 12 %. The results were expressed in forms of some existing equations and were found to be in fair agreement to previous results.
Studies of heat transfer in complex internal flows
NASA Astrophysics Data System (ADS)
Sparrow, E. M.
1983-01-01
Experiments have been performed to determine the heat transfer and pressure drop response of heat exchange devices subject to highly complex fluid flows. Three research problems were undertaken and completed, each dealing with a different aspect of heat exchanger performance. In one case, per-tube transfer coefficients were measured in a tube bank in the presence of abrupt upstream enlargement of the flow cross section. Enhancement of the heat transfer was found to occur as a result of the flow disturbance caused by the enlargement. In the second research problem, the effect on heat transfer of the competition between tubes which draw air from a common plenum was investigated. This competition resulted in a skewing of the flow entering the tubes. Significant effects of the skewing occurred when the tubes were relatively close together (pitch approx. 1.5 tube diameters), but for larger spacings the heat transfer coefficients were virtually identical to those for a single tube. In the last of the problems, the effects of flow maldistribution caused by partial blockage of the inlet of a flat rectangular duct were investigated. Large spanwise nonuniformities of the local heat transfer coefficient were induced by the maldistributed flow. The spanwise average heat transfer coefficients in the downstream portion of the duct were found to be enhanced due to flow maldistribution, whereas at more upstream locations a reduction of the coefficients occurred.
CFD Extraction of Heat Transfer Coefficient in Cryogenic Propellant Tanks
NASA Technical Reports Server (NTRS)
Yang, H. Q.; West, Jeff
2015-01-01
Current reduced-order thermal model for cryogenic propellant tanks is based on correlations built for flat plates collected in the 1950's. The use of these correlations suffers from inaccurate geometry representation; inaccurate gravity orientation; ambiguous length scale; and lack of detailed validation. This study uses first-principles based CFD methodology to compute heat transfer from the tank wall to the cryogenic fluids and extracts and correlates the equivalent heat transfer coefficient to support reduced-order thermal model. The CFD tool was first validated against available experimental data and commonly used correlations for natural convection along a vertically heated wall. Good agreements between the present prediction and experimental data have been found for flows in laminar as well turbulent regimes. The convective heat transfer between the tank wall and cryogenic propellant, and that between the tank wall and ullage gas were then simulated. The results showed that the commonly used heat transfer correlations for either vertical or horizontal plate over-predict heat transfer rate for the cryogenic tank, in some cases by as much as one order of magnitude. A characteristic length scale has been defined that can correlate all heat transfer coefficients for different fill levels into a single curve. This curve can be used for the reduced-order heat transfer model analysis.
Enhanced two phase flow in heat transfer systems
Tegrotenhuis, Ward E; Humble, Paul H; Lavender, Curt A; Caldwell, Dustin D
2013-12-03
A family of structures and designs for use in devices such as heat exchangers so as to allow for enhanced performance in heat exchangers smaller and lighter weight than other existing devices. These structures provide flow paths for liquid and vapor and are generally open. In some embodiments of the invention, these structures can also provide secondary heat transfer as well. In an evaporate heat exchanger, the inclusion of these structures and devices enhance the heat transfer coefficient of the evaporation phase change process with comparable or lower pressure drop.
Droplet Evaporator For High-Capacity Heat Transfer
NASA Technical Reports Server (NTRS)
Valenzuela, Javier A.
1993-01-01
Proposed heat-exchange scheme boosts heat transfer per unit area. Key component is generator that fires uniform size droplets of subcooled liquid at hot plate. On impact, droplets spread out and evaporate almost instantly, removing heat from plate. In practice, many generator nozzles arrayed over evaporator plate.
46 CFR 153.430 - Heat transfer systems; general.
Code of Federal Regulations, 2010 CFR
2010-10-01
... Temperature Control Systems § 153.430 Heat transfer systems; general. Each cargo cooling system required by this part and each cargo heating system must: (a) Meet the standards of Subchapters F (Marine... separated from all other cooling and heating systems; and (c) Allow manual regulation of the system's...
Radiation Heat Transfer in 3 Dimensions for Semi-Transparent Materials....
Energy Science and Technology Software Center (ESTSC)
2010-12-02
The RAD3D software solves the critical heat transfer mechanisms that occur in production glass furnaces. The code includes state-of-the-art solution algorithms for efficient radiant interaction of the heating elements, furnace walls and internal furnace components. The code specifically solves the coupled radiative and conductive heating of semi-transparent materials such as glass to calculate the temperature distribution in the glass during processing.
Efficient Transfer of Images over Networks
NASA Astrophysics Data System (ADS)
Percival, J. W.; White, R. L.
1993-01-01
Effective remote observing requires sending large images over long distances. The usual approach to the transfer problem is to require high bandwidth transmission links, which are expensive to install and operate. An alternative approach is to use existing low-bandwidth connections, such as phone lines or the Internet, in a highly efficient manner by compressing the images. The combined use of existing low-cost infrastructure and standard networking software means that remote observing can be made practical even for small observatories with limited network resources. We have implemented such a scheme based on the H-transform compression method developed by White (1992) for astronomical images, which are often resistant to compression because they are noisy. The H-transform can be used for either lossy or lossless compression, and compression factors of at least 10 can be achieved with no noticeable losses in the astrometric or photometric properties of the compressed images. The H-transform allows us to organize the information in an image so that the ``useful'' information can be sent first, followed by the noise, which makes up the bulk of the transmission. The receiver can invert a partially received set of H-coefficients, creating an image that improves with time. The H-transform is particularly well-suited to this style of incremental reconstruction, because the spatially localized nature of the basis functions of the H-transform prevents the appearance of artifacts such as ringing around point sources and edges. Our implementation uses the WIYN Telescope Control System's TCP-based communications protocol. We sent an 800x800 16-bit astronomical image over a 2400 baud connection, which would normally take about 71 minutes; after only 60 seconds, the partially received H-transform produced an image that did not differ appreciably from the original. This paper presents a quantification of the efficiencies, as well as examples of images reconstructed from partial data.
Flow and heat transfer measurements in a swirl chamber with different outlet geometries
NASA Astrophysics Data System (ADS)
Biegger, Christoph; Weigand, Bernhard
2015-04-01
In technical applications, an efficient cooling is necessary for high thermal load components such as turbine blades. One potential and promising technique is a swirling tube flow in comparison with an axial flow. The additional circumferential velocity and enhanced turbulent mixing increase the heat transfer. But the complex flow field and heat transfer mechanisms are still under research. Furthermore, the reliability of a swirl chamber regarding different outlet conditions is of great interest for a robust cooling design. Therefore, we investigated the influence of a straight, a tangential and a bend outlet. To gain understanding of the flow phenomena, we measured the velocity field by means of stereo-PIV (particle image velocimetry). We experimentally studied the cooling capability measuring the heat transfer coefficients using thermochromic liquid crystals. For an accurate cooling design, we used the local adiabatic wall temperature as the correct reference temperature for calculating the heat transfer coefficients. We will show the velocity field, the pressure loss and the heat transfer results for realistic Reynolds numbers from 10,000 to 40,000 and for swirl numbers between and . The obtained heat transfer is more than four times higher compared to an axial tube flow. Our measurements indicate that the here investigated outlet redirection has no significant influence on the flow field and the heat transfer coefficients.
Local heat transfer behavior and its impact on a single-row, annularly finned tube heat exchanger
Hu, X.; Jacobi, A.M. )
1993-02-01
Experimental studies of the local mass transfer characteristics of annularly finned tubes in crossflow are presented. Variations due to boundary layer development, forward-edge separation, the tube wake, horseshoe vortices, and tip vortices are discussed. In addition, regularly located local maxima in mass transfer rates associated with the horseshoe vortex system are found, and conjecture as to their mechanism is offered. Inferring heat transfer behavior from the mass transfer results, we find that the true fin efficiency is always less than that obtained with an assumed constant convective heat transfer coefficient. The difference is 3-7 percent for high-conductivity materials such as aluminum alloys, and 9-17 percent for low-conductivity materials such as mild steels. 26 refs., 7 refs., 2 tabs.
Conjugate Compressible Fluid Flow and Heat Transfer in Ducts
NASA Technical Reports Server (NTRS)
Cross, M. F.
2011-01-01
A computational approach to modeling transient, compressible fluid flow with heat transfer in long, narrow ducts is presented. The primary application of the model is for analyzing fluid flow and heat transfer in solid propellant rocket motor nozzle joints during motor start-up, but the approach is relevant to a wide range of analyses involving rapid pressurization and filling of ducts. Fluid flow is modeled through solution of the spatially one-dimensional, transient Euler equations. Source terms are included in the governing equations to account for the effects of wall friction and heat transfer. The equation solver is fully-implicit, thus providing greater flexibility than an explicit solver. This approach allows for resolution of pressure wave effects on the flow as well as for fast calculation of the steady-state solution when a quasi-steady approach is sufficient. Solution of the one-dimensional Euler equations with source terms significantly reduces computational run times compared to general purpose computational fluid dynamics packages solving the Navier-Stokes equations with resolved boundary layers. In addition, conjugate heat transfer is more readily implemented using the approach described in this paper than with most general purpose computational fluid dynamics packages. The compressible flow code has been integrated with a transient heat transfer solver to analyze heat transfer between the fluid and surrounding structure. Conjugate fluid flow and heat transfer solutions are presented. The author is unaware of any previous work available in the open literature which uses the same approach described in this paper.
Radiative heat transfer in the extreme near field.
Kim, Kyeongtae; Song, Bai; Fernández-Hurtado, Víctor; Lee, Woochul; Jeong, Wonho; Cui, Longji; Thompson, Dakotah; Feist, Johannes; Reid, M T Homer; García-Vidal, Francisco J; Cuevas, Juan Carlos; Meyhofer, Edgar; Reddy, Pramod
2015-12-17
Radiative transfer of energy at the nanometre length scale is of great importance to a variety of technologies including heat-assisted magnetic recording, near-field thermophotovoltaics and lithography. Although experimental advances have enabled elucidation of near-field radiative heat transfer in gaps as small as 20-30 nanometres (refs 4-6), quantitative analysis in the extreme near field (less than 10 nanometres) has been greatly limited by experimental challenges. Moreover, the results of pioneering measurements differed from theoretical predictions by orders of magnitude. Here we use custom-fabricated scanning probes with embedded thermocouples, in conjunction with new microdevices capable of periodic temperature modulation, to measure radiative heat transfer down to gaps as small as two nanometres. For our experiments we deposited suitably chosen metal or dielectric layers on the scanning probes and microdevices, enabling direct study of extreme near-field radiation between silica-silica, silicon nitride-silicon nitride and gold-gold surfaces to reveal marked, gap-size-dependent enhancements of radiative heat transfer. Furthermore, our state-of-the-art calculations of radiative heat transfer, performed within the theoretical framework of fluctuational electrodynamics, are in excellent agreement with our experimental results, providing unambiguous evidence that confirms the validity of this theory for modelling radiative heat transfer in gaps as small as a few nanometres. This work lays the foundations required for the rational design of novel technologies that leverage nanoscale radiative heat transfer. PMID:26641312
Calculation of heat transfer in a radially rotating coolant passage
Tolpadi, A.K. )
1994-12-01
The three-dimensional flow field and heat transfer in a radially rotating coolant passage are studied numerically. The passage chosen has a square cross section with smooth isothermal walls of finite length. The axis rotation is normal to the flow direction with the flow radially outward. The effects of Coriolis forces, centrifugal buoyancy, and fluid Reynolds number on the flow and heat transfer have all been considered. The analysis has been performed by using a fully elliptic, three-dimensional, body-fitted computational fluid dynamics code based on pressure correction techniques. The numerical technique employs a multigrid iterative solution procedure and the standard k [minus] [epsilon] turbulence model for both the hydrodynamics and heat transfer. The effect of rotation is included by considering the governing equations of motion in a relative frame of reference that moves with the passage. The consequence of rotation is to bring higher velocity fluid from the core to the trailing surface, thereby increasing both the friction and heat transfer at this face. At the same time, the heat transfer is predicted to decrease along the leading surface. The effect of buoyancy is to increase the radial velocity of the fluid, thus generally increasing the heat transfer along both the leading and trailing surfaces. These effects and trends that have been predicted are in agreement with experimental heat transfer data available in the literature. The quantitative agreement with the data was also found to be quite satisfactory.
Radiation Heat Transfer Procedures for Space-Related Applications
NASA Technical Reports Server (NTRS)
Chai, John C.
2000-01-01
Over the last contract year, a numerical procedure for combined conduction-radiation heat transfer using unstructured grids has been developed. As a result of this research, one paper has been published in the Numerical Heat Transfer Journal. One paper has been accepted for presentation at the International Center for Heat and Mass Transfer's International Symposium on Computational Heat Transfer to be held in Australia next year. A journal paper is under review by my NASA's contact. A conference paper for the ASME National Heat Transfer conference is under preparation. In summary, a total of four (4) papers (two journal and two conference) have been published, accepted or are under preparation. There are two (2) to three (3) more papers to be written for the project. In addition to the above publications, one book chapter, one journal paper and six conference papers have been published as a result of this project. Over the last contract year, the research project resulted in one Ph.D. thesis and partially supported another Ph.D. student. My NASA contact and myself have formulated radiation heat transfer procedures for materials with different indices of refraction and for combined conduction-radiation heat transfer. We are trying to find other applications for the procedures developed under this grant.
Radiative heat transfer in the extreme near field
NASA Astrophysics Data System (ADS)
Kim, Kyeongtae; Song, Bai; Fernández-Hurtado, Víctor; Lee, Woochul; Jeong, Wonho; Cui, Longji; Thompson, Dakotah; Feist, Johannes; Reid, M. T. Homer; García-Vidal, Francisco J.; Cuevas, Juan Carlos; Meyhofer, Edgar; Reddy, Pramod
2015-12-01
Radiative transfer of energy at the nanometre length scale is of great importance to a variety of technologies including heat-assisted magnetic recording, near-field thermophotovoltaics and lithography. Although experimental advances have enabled elucidation of near-field radiative heat transfer in gaps as small as 20-30 nanometres (refs 4, 5, 6), quantitative analysis in the extreme near field (less than 10 nanometres) has been greatly limited by experimental challenges. Moreover, the results of pioneering measurements differed from theoretical predictions by orders of magnitude. Here we use custom-fabricated scanning probes with embedded thermocouples, in conjunction with new microdevices capable of periodic temperature modulation, to measure radiative heat transfer down to gaps as small as two nanometres. For our experiments we deposited suitably chosen metal or dielectric layers on the scanning probes and microdevices, enabling direct study of extreme near-field radiation between silica-silica, silicon nitride-silicon nitride and gold-gold surfaces to reveal marked, gap-size-dependent enhancements of radiative heat transfer. Furthermore, our state-of-the-art calculations of radiative heat transfer, performed within the theoretical framework of fluctuational electrodynamics, are in excellent agreement with our experimental results, providing unambiguous evidence that confirms the validity of this theory for modelling radiative heat transfer in gaps as small as a few nanometres. This work lays the foundations required for the rational design of novel technologies that leverage nanoscale radiative heat transfer.
Heat transfer and flow characteristics on a gas turbine shroud.
Obata, M; Kumada, M; Ijichi, N
2001-05-01
The work described in this paper is an experimental investigation of the heat transfer from the main flow to a turbine shroud surface, which may be applicable to ceramic gas turbines. Three kinds of turbine shrouds are considered with a flat surface, a taper surface and a spiral groove surface opposite to the blades in an axial flow turbine of actual turbo-charger. Heat transfer measurements were performed for the experimental conditions of a uniform heat flux or a uniform wall temperature. The effects of the inlet flow angle, rotational speed, and tip clearance on the heat transfer coefficient were clarified under on- and off-design flow conditions. The mean heat transfer coefficient was correlated to the blade Reynolds number and tip clearance, and compared with an experimental correlation and measurements of a flat surface. A comparison was also made for the measurement of static pressure distributions. PMID:11460639
Flow and heat transfer of petal shaped double tube
NASA Astrophysics Data System (ADS)
Shakouchi, Toshihiko; Kawashima, Yuki; Tsujimoto, Koichi; Ando, Toshitake
2014-06-01
In this study, the flow and heat transfer characteristics of petal-shaped double tube with 6 petals are examined experimentally for a compact heat exchanger. As results, the heat transfer rate, Q, of the 6 petal shaped double tube (6-p tube) is much larger than that, Qp, of conventional circular double tube in all Reynolds number Rein,h (where, the reference length is hydraulic diameter) ranges. For example, at Rein,h =(0.5～1.0)× 104 it is about 4 times of Qp. The heat transfer enhancement of 6-p tube is by the increase of heat transfer area, wetting perimeter, and a highly fluctuating flow, and Q of the 6-p tube can be expressed by Q [kW/m] = 0.54Rein,h + 2245.
Radiative heat transfer in low-dimensional systems -- microscopic mode
NASA Astrophysics Data System (ADS)
Woods, Lilia; Phan, Anh; Drosdoff, David
2013-03-01
Radiative heat transfer between objects can increase dramatically at sub-wavelength scales. Exploring ways to modulate such transport between nano-systems is a key issue from fundamental and applied points of view. We advance the theoretical understanding of radiative heat transfer between nano-objects by introducing a microscopic model, which takes into account the individual atoms and their atomic polarizabilities. This approach is especially useful to investigate nano-objects with various geometries and give a detailed description of the heat transfer distribution. We employ this model to study the heat exchange in graphene nanoribbon/substrate systems. Our results for the distance separations, substrates, and presence of extended or localized defects enable making predictions for tailoring the radiative heat transfer at the nanoscale. Financial support from the Department of Energy under Contract No. DE-FG02-06ER46297 is acknowledged.
Heat Transfer in a Flash Fuser.
NASA Astrophysics Data System (ADS)
Baumann, Gerald Walter
Flash fusing is used in high speed electrophotographic computer printers to melt the thermoplastic printed image on the paper surface. This technology is not yet well understood, even though it has been used in several different machines. Consequently current fusers may be far from optimum. The aim of this research is to formulate and confirm mathematical models of the fuser. The fusing process was modelled by transient thermal conduction. The toner was assumed to fuse to the paper when its lower surface, against the paper, reached its melting point. The temperature depends on the power input to the toner from the flash tube. Hence, mathematical models were developed to describe both the electrical conduction and radiation characteristics of the flash tube. These models were coupled to the equations describing the electrical drive circuits, and the instantaneous output of the flash was computed. These results were then used in the transient heat conduction model of the toner and paper. A ballistic integrating radiometer was built to measure the total output energy of the flash tube. The electrical input power to the flash tube was measured and compared to the model. These experiments were used to support the computed power input to the toner surface. Unfused prints were exposed to a multitude of pulse shapes, pulse widths, and energies. A standard adhesion test was used to measure the degree of fusing. The temperature of the toner/paper interface was computed. The toner had significant porosity and its heat capacity varied greatly with temperature. The adsorbed water in the paper influenced the temperature profile. The experiments confirmed the melting model. The degree of fusing correlated well with computed interface temperature, and not with input energy or surface temperature. Toner porosity and flash pulse shape are potential design parameters, and they were studied in detail. Modelling results indicate that modest reductions in porosity can significantly reduce both the fuser energy consumption and the maximum toner temperature. A departure from the present RLC flash drive circuit to a terminated RC circuit improves both the lamp efficiency and the circuit losses.
NASA Astrophysics Data System (ADS)
Stein, R. P.
Aspects of direct contact heat transfer are considered along with transport phenomena in fusion reactors, enhanced nucleate boiling, flow boiling, heat transfer in non-Newtonian systems, two-phase systems, heat transfer in fossil fuel conversion systems, process heat transfer, thermal and hydraulic behavior in rod and tube bundles, and two-phase systems in rod and tube bundles. Attention is also given to solar energy heat transfer, heat transfer in fluidized beds, and fire and combustion fundamentals, taking into account thermal stress oscillations induced by dynamic instabilities in radiation-heated boiler tubes, convection losses from a cavity receiver, numerical solutions of turbulent models for flow over a flat plate with angle of attack, and the heat transfer from smooth horizontal tubes immersed in gas fluidized beds. A description is provided of aspects of turbulent combustion modelling, the exhaust gas emission from a swirl stabilized combustor, the analytical solution for diffusion in the core of a droplet with internal circulation, and the radiant ignition of a thin combustible solid.
Nanoscale heat transfer and thermoelectrics for alternative energy
NASA Astrophysics Data System (ADS)
Robinson, Richard
2011-03-01
In the area of alternative energy, thermoelectrics have experienced an unprecedented growth in popularity because of their ability to convert waste heat into electricity. Wired in reverse, thermoelectrics can act as refrigeration devices, where they are promising because they are small in size and lightweight, have no moving parts, and have rapid on/off cycles. However, due to their low efficiencies bulk thermoelectrics have historically been a niche market. Only in the last decade has thermoelectric efficiency exceeded ~ 20 % due to fabrication of nanostructured materials. Nanoscale materials have this advantage because electronic and acoustic confinement effects can greatly increase thermoelectric efficiency beyond bulk values. In this talk, I will introduce our work in the area of nanoscale heat transfer with the goal of more efficient thermoelectrics. I will discuss our experiments and methods to study acoustic confinement in nanostructures and present some of our new nanostructured thermoelectric materials. To study acoustic confinement we are building a nanoscale phonon spectrometer. The instrument can excite phonon modes in nanostructures in the ~ 100 s of GHz. Ballistic phonons from the generator are used to probe acoustic confinement and surface scattering effects. Transmission studies using this device will help optimize materials and morphologies for more efficient nanomaterial-based thermoelectrics. For materials, our group has synthesized nano-layer superlattices of Na x Co O2 . Sodium cobaltate was recently discovered to have a high Seebeck coeficent and is being studied as an oxide thermoelectric material. The thickness of our nano-layers ranges from 5 nm to 300 nm while the lengths can be varied between 10 μ m and 4 mm. Typical aspect ratios are 40 nm: 4 mm, or 1:100,000. Thermoelectric characterization of samples with tilted multiple-grains along the measurement axis indicate a thermoelectric efficiency on par with current polycrystalline samples. Due to phonon confinement in nano-structures, it is expected that the thermoelectric efficiency of these sheets will be much higher than that of single crystalline Na 0.7 Co O2 , when the nanosheets have single grains along the heat transport path. This work is supported by KAUST (KUS-C1-018-02), NSF (DMR 0520404), and the DOE (DE-SC0001086).
Cryogenic apparatus for study of near-field heat transfer.
Kralik, T; Hanzelka, P; Musilova, V; Srnka, A; Zobac, M
2011-05-01
For bodies spaced in vacuum at distances shorter than the wavelength of the thermal radiation, radiative heat transfer substantially increases due to the contribution of evanescent electromagnetic waves. Experimental data on heat transfer in near-field regime are scarce. We have designed a cryogenic apparatus for the study of heat transfer over microscopic distances between metallic and non-metallic surfaces. Using a mechanical positioning system, a planeparallel gap between the samples, concentric disks, each 35 mm in diameter, is set and varied from 10(0) to 10(3) μm. The heat transferred from the hot (10 - 100 K) to the cold sample (∼5 K) sinks into a liquid helium bath through a thermal resistor, serving as a heat flux meter. Transferred heat power within ∼2 nW∕cm(2) and ∼30 μW∕cm(2) is derived from the temperature drop along the thermal resistor. For tungsten samples, the distance of the near-field effect onset was inversely proportional to temperature and the heat power increase was observed up to three orders of magnitude greater than the power of far-field radiative heat transfer. PMID:21639537
Simulation Approach for Microscale Noncontinuum Gas-Phase Heat Transfer
NASA Astrophysics Data System (ADS)
Torczynski, J. R.; Gallis, M. A.
2008-11-01
In microscale thermal actuators, gas-phase heat transfer from the heated beams to the adjacent unheated substrate is often the main energy-loss mechanism. Since the beam-substrate gap is comparable to the molecular mean free path, noncontinuum gas effects are important. A simulation approach is presented in which gas-phase heat transfer is described by Fourier's law in the bulk gas and by a wall boundary condition that equates the normal heat flux to the product of the gas-solid temperature difference and a heat transfer coefficient. The dimensionless parameters in this heat transfer coefficient are determined by comparison to Direct Simulation Monte Carlo (DSMC) results for heat transfer from beams of rectangular cross section to the substrate at free-molecular to near-continuum gas pressures. This simulation approach produces reasonably accurate gas-phase heat-transfer results for wide ranges of beam geometries and gas pressures. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Wall-to-suspension heat transfer in circulating fluidized beds
Wirth, K.E.
1995-12-31
The wall-to-suspension heat transfer in circulating fluidized beds depends on the fluid mechanics immediately near the wall and on the thermal properties of the gas used. Experimental investigations of circulating fluidized beds of low dimensionless pressure gradients with different solid particles like bronze, glass and polystyrene at ambient temperatures showed no influence of the conductivity and the heat capacity of the solids on the heat transfer coefficient. Consequently the heat transfer coefficient in the form of the dimensionless Nusselt number can be described by the dimensionless numbers which characterize the gas-solid-flow near the wall. These numbers are the Archimedes number and the pressure drop-number. The last number relates the cross-sectional average solids concentration to the solids concentration at minimum fluidization condition. With the aid of a model of segregated vertical gas-solid flow, the flow pattern in the wall region can be calculated and thus the wall heat transfer which depends only on heat conduction in the gas and on the convective heat transfer by the gas. With elevated suspension temperatures, radiation contributes additionally to the heat transfer. When the solids concentration is low, the effect of the radiation on the heat transfer is high. Increasing solids concentration results in a decrease of the radiation effect due to the wall being shielded from the radiation of the hot particles in the core region by the cold solids clusters moving down the wall. A simple correlation is presented for calculating the wall-to-suspension heat transfer in circulating fluidized beds.
Heat and Mass Transfer Processes in Scrubber of Flue Gas Heat Recovery Device
NASA Astrophysics Data System (ADS)
Veidenbergs, Ivars; Blumberga, Dagnija; Vigants, Edgars; Kozuhars, Grigorijs
2010-01-01
The paper deals with the heat and mass transfer process research in a flue gas heat recovery device, where complicated cooling, evaporation and condensation processes are taking place simultaneously. The analogy between heat and mass transfer is used during the process of analysis. In order to prepare a detailed process analysis based on heat and mass process descriptive equations, as well as the correlation for wet gas parameter calculation, software in the
Determination of the heat transfer coefficients in porous media
Kim, L.V.
1994-06-01
The process of transpiration cooling is considered. Methods are suggested for estimating the volumetric coefficient of heat transfer with the use of a two-temperature model and the surface heat transfer coefficient at entry into a porous wall. The development of new technology under conditions of increasing heat loads puts the search for effective methods of heat transfer enhancement in the forefront of theoretical investigations. One of the promising trends in the solution of this problem is the use of porous materials (PM) in the elements of power units. For thermal protection against convective or radiative heat fluxes, the method of transpiration cooling is successfully used. The mechanism operative in the thermal protection involves the injection of a coolant through a porous medium to produce a screen over the contour of a body in a flow for removing heat energy from the skeleton of the porous material.
Concepts and realization of microstructure heat exchangers for enhanced heat transfer
Brandner, J.J.; Anurjew, E.; Bohn, L.; Hansjosten, E.; Henning, T.; Schygulla, U.; Wenka, A.; Schubert, K.
2006-08-15
Microstructure heat exchangers have unique properties that make them useful for numerous scientific and industrial applications. The power transferred per unit volume is mainly a function of the distance between heat source and heat sink-the smaller this distance, the better the heat transfer. Another parameter governing for the heat transfer is the lateral characteristic dimension of the heat transfer structure; in the case of microchannels, this is the hydraulic diameter. Decreasing this characteristic dimension into the range of several 10s of micrometers leads to very high values for the heat transfer rate. Another possible way of increasing the heat transfer rate of a heat exchanger is changing the flow regime. Microchannel devices usually operate within the laminar flow regime. By changing from microchannels to three dimensional structures, or to planar geometries with microcolumn arrays, a significant increase of the heat transfer rate can be achieved. Microheat exchangers in the form of both microchannel devices (with different hydraulic diameters) and microcolumn array devices (with different microcolumn layouts) are presented and compared. Electrically heated microchannel devices are presented, and industrial applications are briefly described. (author)
Experimental measurements of heat transfer in an internally finned tube
Huq, M.; Huq, A.M.A.; Rahman, M.M.
1998-07-01
This paper reports new experimental data for turbulent fluid flow and heat transfer in a tube having internal fins. An experimental set-up was designed to study the heat transfer performance in the entrance region as well as in the fully-developed region. The tube and the fin assembly was cast from aluminum to avoid any thermal contact resistance. The length of the test section was 15.2 m. The inner diameter of the tube was 70 mm. The tube contained six equally spaced fins of height 15 mm. Air was used as the working fluid in all experiments. The Reynolds number based on hydraulic diameter ranged from 2.6 {times} 10{sup 4} to 7.9 {times} 10{sup 4}. Heat was supplied from an electrical heating system providing an uniform heat flux around the tube periphery over the entire length of the test section. Results exhibited high pressure gradients and high heat transfer coefficients in the entrance region, approaching the fully developed values away from the entrance section. Nusselt numbers of the finned tube were compared with those for an unfinned (smooth) tube for both constant Reynolds number and constant pumping power. The enhancement of heat transfer rate due to integral fins was found to be very significant over the entire range of flow rates studied in this experiment. Heat transfer coefficient, based on inside diameter and nominal area of finned tube exceeded unfinned tube values by as much as 112%. When compared at constant pumping power, an improvement as high as 52% was observed for the overall heat transfer rate. The results of this study indicates that significant enhancement of heat transfer is possible by using internal fins without sacrificing any additional pumping power. The experimental results are expected to be very useful for the design of pipelines and heat exchanger tubes.
Heat transfer performance of an external receiver pipe under unilateral concentrated solar radiation
Jianfeng, Lu; Jing, Ding; Jianping, Yang
2010-11-15
The heat transfer and absorption characteristics of an external receiver pipe under unilateral concentrated solar radiation are theoretically investigated. Since the heat loss ratio of the infrared radiation has maximum at moderate energy flux, the heat absorption efficiency will first increase and then decrease with the incident energy flux. The local absorption efficiency will increase with the flow velocity, while the wall temperature drops quickly. Because of the unilateral concentrated solar radiation and different incident angle, the heat transfer is uneven along the circumference. Near the perpendicularly incident region, the wall temperature and absorption efficiency slowly approaches to the maximum, while the absorption efficiency sharply drops near the parallelly incident region. The calculation results show that the heat transfer parameters calculated from the average incident energy flux have a good agreement with the average values of the circumference under different boundary conditions. For the whole pipe with coating of Pyromark, the absorption efficiency of the main region is above 85%, and only the absorption efficiency near the parallelly incident region is below 80%. In general, the absorption efficiency of the whole pipe increases with flow velocity rising and pipe length decreasing, and it approaches to the maximum at optimal concentrated solar flux. (author)
Design code verification of external heat transfer coefficients
NASA Astrophysics Data System (ADS)
Soechting, F. O.; Sharma, O. P.
1988-07-01
A comparative study is conducted for measured and predicted heat-transfer coefficients of air-cooled turbine blade airfoils. A modified version of the STAN-5 boundary layer code was used to obtain analytical predictions of the heat transfer levels for the cascade test conditions. A two-dimensional cascade test was conducted at engine-level Mach number and Reynolds number distributions in order to obtain baseline data that can be used with engine data in order to quantify the effects of environmental conditions on heat transfer levels and distributions.
Heat transfer during the boiling of liquids in heat pipe wicks
NASA Technical Reports Server (NTRS)
Gontarev, Yu. K.; Navruzov, Yu. V.; Prisnyakov, V. F.; Serebryanskiy, N.
1987-01-01
Data in the literature on heat transfer in the case of nucleate boiling of various liquids in the wicks of heat pipes are reviewed. It is shown that none of the known analytical relationships can be used to generalize, with sufficient accuracy, the experimental data found in the literature. It is further shown that the exponent of the specific heat flux in the heat transfer law changes as a function of the liquid and wick properties. A relationship is obtained which generalizes experimental data for heat transfer agents of moderate temperatures (water, acetone, ethanol, and R-11 and R-113 coolants) and ammonia.
Transient Heat Transfer in TCAP Coils
Steimke, J.L.
1999-03-09
The Thermal Cycling Absorption Process (TCAP) is used to separate isotopes of hydrogen. TCAP involves passing a stream of mixed hydrogen isotopes through palladium deposited on kieselguhr (Pd/k) while cycling the temperature of the Pd/k. Kieselguhr is a silica mineral also called diatomite. To aid in the design of a full scale facility, the Thermal Fluids Laboratory was used by the Chemical and Hydrogen Technology Section to compare the heat transfer properties of three different configurations of stainless steel coils containing kieselguhr and helium. Testing of coils containing Pd/k and hydrogen isotopes would have been more prototypical but would have been too expensive. Three stainless steel coils filled with kieselguhr were tested; one made from 2.0 inch diameter tubing, one made from 2.0 inch diameter tubing with foam copper embedded in the kieselguhr and one made from 1.25 inch diameter tubing. It was known prior to testing that increasing the tubing diameter from 1.25 inch to 2.0 inch would slow the rate of temperature change. The primary purpose of the testing was to measure to what extent the presence of copper foam in a 2.0 tubing coil would compensate for the effect of larger diameter. Each coil was connected to a pressure gage and the coil was evacuated and backfilled with helium gas. Helium was used instead of a mixture of hydrogen isotopes for reasons of safety. Each coil was quickly immersed in a stirred bath of ethylene glycol at a temperature of approximately 100 degrees Celsius. The coil pressure increased, reflecting the increase in average temperature of its contents. The pressure transient was recored as a function of time after immersion. Because of the actual process will use Pd/k instead of kieselguhr, additional tests were run to determine the differences in thermal properties between the two materials. The method was to position a thermocouple at the center of a hollow sphere and pack the sphere with Pd/k. The sphere was sealed, quickly submerged in a bath of boiling water and the temperature transient was recorded. There sphere was then opened, the Pd/k was replaced with kieselguhr and the transient was repeated. The response was a factor of 1.4 faster for Pd/k than for kieselguhr, implying a thermal diffusivity approximately 40 percent higher than for kieselguhr. Another implication is that the transient tests with the coils would have proceeded faster if the coils had been filled with Pd/k rather than kieselguhr.
Transient Heat Transfer in TCAP Coils
Steimke, J.L.
1999-03-09
The Thermal Cycling Absorption Process (TCAP) is used to separate isotopes of hydrogen. TCAP involves passing a stream of mixed hydrogen isotopes through palladium deposited on kieselguhr (Pd/k) while cycling the temperature of the Pd/k. Kieselguhr is a silica mineral also called diatomite. To aid in the design of a full scale facility, the Thermal Fluids Laboratory was used by the Chemical and Hydrogen Technology Section to compare the heat transfer properties of three different configurations of stainless steel coils containing kieselguhr and helium. Testing of coils containing Pd/k and hydrogen isotopes would have been more prototypical but would have been too expensive. Three stainless steel coils filled with kieselguhr were tested; one made from 2.0 inch diameter tubing, one made from 2.0 inch diameter tubing with foam copper embedded in the kieselguhr and one made from 1.25 inch diameter tubing. It was known prior to testing that increasing the tubing diameter from 1.25 inch to 2.0 inch would slow the rate of temperature change. The primary purpose of the testing was to measure to what extent the presence of copper foam in a 2.0" tubing coil would compensate for the effect of larger diameter. Each coil was connected to a pressure gage and the coil was evacuated and backfilled with helium gas. Helium was used instead of a mixture of hydrogen isotopes for reasons of safety. Each coil was quickly immersed in a stirred bath of ethylene glycol at a temperature of approximately 100 degrees Celsius. The coil pressure increased, reflecting the increase in average temperature of its contents. The pressure transient was recored as a function of time after immersion. Because of the actual process will use Pd/k instead of kieselguhr, additional tests were run to determine the differences in thermal properties between the two materials. The method was to position a thermocouple at the center of a hollow sphere and pack the sphere with Pd/k. The sphere was sealed, quickly submerged in a bath of boiling water and the temperature transient was recorded. There sphere was then opened, the Pd/k was replaced with kieselguhr and the transient was repeated. The response was a factor of 1.4 faster for Pd/k than for kieselguhr, implying a thermal diffusivity approximately 40 percent higher than for kieselguhr. Another implication is that the transient tests with the coils would have proceeded faster if the coils had been filled with Pd/k rather than kieselguhr.
Nanoscale heat transfer in the head-disk interface for heat assisted magnetic recording
NASA Astrophysics Data System (ADS)
Wu, Haoyu; Xiong, Shaomin; Canchi, Sripathi; Schreck, Erhard; Bogy, David
2016-02-01
Laser heating has been introduced in heat-assisted magnetic recording in order to reduce the magnetic coercivity and enable data writing. However, the heat flow inside a couple of nanometers head-disk gap is still not well understood. An experimental stage was built for studying heat transfer in the head-disk interface (HDI) and the heat-induced instability of the HDI. A laser heating system is included to produce a heated spot on the disk at the position of the slider. A floating air bearing slider is implemented in the stage for sensing the temperature change of the slider due to the heat transfer from the disk by the use of an embedded contact sensor, and the gap between the two surfaces is controlled by the use of a thermal fly-height control actuator. By using this system, we explore the dependency of the heat transfer on the gap spacing as well as the disk temperature.
Enhancement of natural-convection heat transfer from a horizontal heated plate using grid fins
Kitamura, Kenzo; Nagae, Naoyuki; Kimura, Fumiyoshi
1996-01-01
An enhancement technique was developed for natural-convection heat transfer from a horizontal heated plate. In order to enhance the heat transfer, grid fins made of copper plates were soldered to the copper base plate. These grid fins function not only as an extended surface but also as a heat-transfer promoter. The apparent heat-transfer coefficient of the above enhanced plate were measured and compared with those of a nontreated, smooth plate and a conventional plate with vertical straight fins. It was found that the highest performance is achieved by the present plate. By adopting grid fins with appropriate size and height, the heat-transfer coefficient at the central portion of the present plate is increased by 35% compared to that of the conventional finned plate with the same fin area of fin height.
A flux correction method for the conjugate heat transfer problem
He, M.; Bishop, P.J.; Minardi, A.; Kassab, A.J.
1995-12-31
A computational method, the flux correction method, is proposed to deal with the conjugate heat transfer problem, which uses a coupled FDM/BEM iteration scheme. The convective heat transfer in the fluid is solved using the BEM. The two solutions are coupled by enforcing continuity of temperature and heat flux at the solid-fluid interfaces. The proposed method is tested using available experimental data. For the considered cases of flow in a parallel plate channel subjected to constant heat flux or constant temperature, good agreements are observed.
Enhanced heat transfer with full circumferential ribs in helical pipe
NASA Astrophysics Data System (ADS)
Chang, S. W.; Su, L. M.; Yang, T. L.
2002-08-01
This paper describes an experimental study of heat transfers in the smooth-walled and rib-roughened helical pipes with reference to the design of enhanced cooling passages in the cylinder head and liner of a marine propulsive diesel engine. The manner in which the repeated ribs modify the forced heat convection in the helical pipe is considered for the case where the flow is turbulent upon entering the coil but laminar in further downstream. A selection of experimental results illustrates the individual and interactive effects of Dean vortices and rib-flows on heat transfer along the inner and outer helixes of coils. The experimental-based observations reveal that the centrifugal force modifies the heat transfer in a manner to generate circumferential heat transfer variation with better cooling performance on the outer edge relative to its inner counterpart even with the agitated flow field caused by the repeated ribs. Heat transfer augmentation factor in the range of 1.3 - 3 times of the smooth-walled level is achieved using the present ribbing geometry. A set of empirical correlations based on the experimental data has been developed to permit the evaluation of heat transfers along the inner and outer helixes of the smooth-walled and rib-roughened helical pipes.
Fourier analysis of conductive heat transfer for glazed roofing materials
NASA Astrophysics Data System (ADS)
Roslan, Nurhana Lyana; Bahaman, Nurfaradila; Almanan, Raja Noorliyana Raja; Ismail, Razidah; Zakaria, Nor Zaini
2014-07-01
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.
Measurement of surface heat transfer due to particle impact
Sun, J.G.; Chen, M.M.
1995-11-01
Heat transfer coefficients for a surface continuously impacted by a stream of falling particles in air and in helium were measured as functions of particle flux and particle velocity. The purpose was to provide well-controlled data to clarify the mechanisms of heat transfer in particle suspension flows. The particles were spherical glass beads with mean diameters of 0.5, 1.13, and 2.6 mm. The distribution of the particle impact flux on the surface was determined by deconvolution from the measurement of the total solid masses collected at both sides of a movable splitter plate. The particle velocity was calculated from a simple, well-established model. The experimental results showed that in air, the heat transfer coefficient increases approximately linearly with particle impact flux. At high impact fluxes, the heat transfer coefficient decreases with particle impact velocity, and at low impact fluxes, it increases with particle impact velocity. Furthermore, the heat transfer coefficient decreases drastically with the particle size. In helium gas, it was found that at low particle impact fluxes, the difference between the coefficients in helium and in air is small, whereas at high fluxes, the difference becomes large. A length scale, V/nd{sup 2}{sub p}, was used to correlate the data. At low particle Reynolds numbers, gas-mediated heat conduction was identified as the dominant particle/surface heat transfer mechanism, whereas at high particle Reynolds numbers, induced gas convection was the dominant mechanism. 23 refs., 10 figs.
Percolation induced heat transfer in deep unsaturated zones
Lu, N.; LeCain, G.D.
2003-01-01
Subsurface temperature data from a borehole located in a desert wash were measured and used to delineate the conductive and advective heat transfer regimes, and to estimate the percolation quantity associated with the 1997-1998 El Ni??no precipitation. In an arid environment, conductive heat transfer dominates the variation of shallow subsurface temperature most of the time, except during sporadic precipitation periods. The subsurface time-varying temperature due to conductive heat transfer is highly correlated with the surface atmospheric temperature variation, whereas temperature variation due to advective heat transfer is strongly correlated with precipitation events. The advective heat transfer associated with precipitation and infiltration is the focus of this paper. Disruptions of the subsurface conductive temperature regime, associated with the 1997-1998 El Ni??no precipitation, were detected and used to quantify the percolation quantity. Modeling synthesis using a one-dimensional coupled heat and unsaturated flow model indicated that a percolation per unit area of 0.7 to 1.3 m height of water in two weeks during February 1998 was responsible for the observed temperature deviations down to a depth of 35.2 m. The reported study demonstrated quantitatively, for the first time, that the near surface temperature variation due to advective heat transfer can be significant at a depth greater than 10 m in unsaturated soils and can be used to infer the percolation amount in thick unsaturated soils.
Wake-induced unsteady stagnation-region heat transfer measurements
Magari, P.J.; LaGraff, L.E. . Dept. of Mechanical and Aerospace Engineering)
1994-01-01
An experimental investigation of wake-induced unsteady heat transfer in the stagnation region of a cylinder was conducted. The objective of the study was to create a quasi-steady representation of the stator/rotor interaction in a gas turbine using two stationary cylinders in crossflow. In this simulation, a larger cylinder, representing the leading-edge region of a rotor blade, was immersed in the wake of a smaller cylinder, representing the trailing-edge region of a stator vane. Time-averaged and time-resolved heat transfer results were obtained over a wide range of Reynolds number at two Mach number: one incompressible and one transonic. The tests were conducted at Reynolds numbers, Mach numbers, and gas-to-wall temperature ratios characteristic of turbine engine conditions in an isentropic compression-heated transient wind tunnel (LICH tube). The augmentation of the heat transfer in the stagnation region due to wake unsteadiness was documented by comparison with isolated cylinder tests. It was found that the time-averaged heat transfer rate at the stagnation line, expressed in terms of the Frossling number (Nu/[radical]RE), reached a maximum independent of the Reynolds number. The power spectra and cross-correlation of the heat transfer signals in the stagnation region revealed the importance of large vortical structures shed from upstream wake generator. These structures caused large positive and negative excursions about the mean heat transfer rate in the stagnation region.
Fourier analysis of conductive heat transfer for glazed roofing materials
Roslan, Nurhana Lyana; Bahaman, Nurfaradila; Almanan, Raja Noorliyana Raja; Ismail, Razidah; Zakaria, Nor Zaini
2014-07-10
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.
Nere, Nandkishor K; Allen, Kimberley C; Marek, James C; Bordawekar, Shailendra V
2012-10-01
Drying an early stage active pharmaceutical ingredient candidate required excessively long cycle times in a pilot plant agitated filter dryer. The key to faster drying is to ensure sufficient heat transfer and minimize mass transfer limitations. Designing the right mixing protocol is of utmost importance to achieve efficient heat transfer. To this order, a composite model was developed for the removal of bound solvent that incorporates models for heat transfer and desolvation kinetics. The proposed heat transfer model differs from previously reported models in two respects: it accounts for the effects of a gas gap between the vessel wall and solids on the overall heat transfer coefficient, and headspace pressure on the mean free path length of the inert gas and thereby on the heat transfer between the vessel wall and the first layer of solids. A computational methodology was developed incorporating the effects of mixing and headspace pressure to simulate the drying profile using a modified model framework within the Dynochem software. A dryer operational protocol was designed based on the desolvation kinetics, thermal stability studies of wet and dry cake, and the understanding gained through model simulations, resulting in a multifold reduction in drying time. PMID:22753308
Heat Transfer of Airfoils and Plates
NASA Technical Reports Server (NTRS)
Seibert, Otto
1943-01-01
The few available test data on the heat dissipation of wholly or partly heated airfoil models are compared with the corresponding data for the flat plate as obtained by an extension of Prandtl's momentum theory, with differentiation between laminar and turbulent boundary layer and transitional region between both, the extent and appearance of which depend upon certain critical factors. The satisfactory agreement obtained justifies far-reaching conclusions in respect to other profile forms and arrangements of heated surface areas. The temperature relationship of the material quantities in its effect on the heat dissipation is discussed as far as is possible at tk.e present state of research, and it is shown that the profile drag of heated wing surfaces can increase or decrease with the temperature increase depending upon the momentarily existent structure of the boundary layer.
Performance and heat transfer characteristics of a carbon monoxide/oxygen rocket engine
NASA Technical Reports Server (NTRS)
Linne, Diane L.
1993-01-01
The combustion and heat transfer characteristics of a carbon monoxide and oxygen rocket engine were evaluated. The test hardware consisted of a calorimeter combustion chamber with a heat sink nozzle and an eighteen element concentric tube injector. Experimental results are given at chamber pressures of 1070 and 3070 kPa, and over a mixture ratio range of 0.3 to 1.0. Experimental C efficiency was between 95 and 96.5 percent. Heat transfer results are discussed both as a function of mixture ratio and axial distance in the chamber. They are also compared to a Nusselt number correlation for fully developed turbulent flow.
Integrated finite element thermal-structural analysis with radiation heat transfer
NASA Technical Reports Server (NTRS)
Thornton, E. A.; Dechaumphai, P.; Wieting, A. R.
1982-01-01
An integrated approach for efficiently coupling thermal and stress analyses of structures with radiation heat transfer is presented. A new integrated one dimensional element based on a nodeless variable formulation is introduced. Lumped and consistent formulations of the nonlinear radiation heat transfer matrix are presented. The accuracy of the integrated approach is assessed by comparisons with analytical solutions and conventional finite element thermal-structural analyses. Results show that the nodeless variable thermal element yields accuracy equivalent to a higher order element but permits a common discretization with a lower order congruent structural element. The integrated element thus provides improved accuracy and efficiency of thermal stress analysis for structures with complex temperature distributions.
Vapordynamic thermosyphon - heat transfer two-phase device for wide applications
NASA Astrophysics Data System (ADS)
Vasiliev, Leonard; Vasiliev, Leonid; Zhuravlyov, Alexander; Shapovalov, Aleksander; Rodin, Aleksei
2015-12-01
Vapordynamic thermosyphon (VDT) is an efficient heat transfer device. The two-phase flow generation and dynamic interaction between the liquid slugs and vapor bubbles in the annular minichannel of the VDT condenser are the main features of such thermosyphon, which allowed to increase its thermodynamic efficiency. VDT can transfer heat in horizontal position over a long distance. The condenser is nearly isothermal with the length of tens of meters. The VDT evaporators may have different forms. Some practical applications of VDT are considered.
Nonlinear aspects of high heat flux nucleate boiling heat transfer. Part 1, Formulation
Sadasivan, P.; Unal, C.; Nelson, R.
1994-04-01
This paper outlines the essential details of the formulation and numerical implementation of a model used to study nonlinear aspects of the macrolayer-controlled heat transfer process associated with high heat flux nucleate boiling and the critical heat flux. The model addresses the three-dimensional transient conduction heat transfer process within the problem domain comprised of the macrolayer and heater. Heat dissipation from the heater is modeled as the sum of transient transport into the macrolayer, and the heat loss resulting from evaporation of menisci associated with vapor stems.
Efficient near-field energy transfer and relieved Casimir stiction between sub-wavelength gratings
NASA Astrophysics Data System (ADS)
Liu, Xianglei; Zhao, Bo; Zhang, Zhuomin
2015-03-01
The promising applications of near-field heat transfer in thermophotovoltaic devices, thermal imaging, thermal rectifiers, and local thermal management have motivated the search for nanostructures capable of supporting higher efficiency or greater heat flux than simple planar substances. In this work, efficient and delocalized radiative heat transfer between two aligned 1D sub-wavelength gratings is demonstrated based on the scattering theory using the rigorous coupled-wave analysis (RCWA). It is shown that the heat flux can be greatly enhanced and the accurate prediction may differ significantly from that of the geometry-based Derjaguin's proximity approximation (PA). The underlying mechanism is attributed to the excitation of hyperbolic modes that increase the energy transmission by supporting propagation of waves with large parallel wavevectors and. Besides efficient energy transport, the performance is robust, insensitive to the relative lateral shift. In addition, the Casimir stiction considering both quantum and thermal fluctuations is found to be relieved compared with bulks.
Kaji, N. ); Mori, Y.H. ); Tochitani, Y. )
1988-08-01
The heat transfer enhancement caused by the application of a low-frequency (1 {approximately} 16 Hz) alternating field having the sinusoidal waveform has been studied experimentally with water drops in a medium of silicone oil. The heat transfer coefficients has been found to peak at three particular frequencies. The data newly obtained with the sinusoidal waveform are compared with earlier results obained with electric fields having other waveforms. The waveform and the frequency that yield the largest enhancement of heat transfer are sought.
A high-efficiency double quantum dot heat engine
NASA Astrophysics Data System (ADS)
Liu, Y. S.; Yang, X. F.; Hong, X. K.; Si, M. S.; Chi, F.; Guo, Y.
2013-08-01
High-efficiency heat engine requires a large output power at the cost of less input heat energy as possible. Here we propose a heat engine composed of serially connected two quantum dots sandwiched between two metallic electrodes. The efficiency of the heat engine can approach the maximum allowable Carnot efficiency ηC. We also find that the strong intradot Coulomb interaction can induce additional work regions for the heat engine, whereas the interdot Coulomb interaction always suppresses the efficiency. Our results presented here indicate a way to fabricate high-efficiency quantum-dot thermoelectric devices.
Volume-energy parameters for heat transfer to supercritical fluids
NASA Technical Reports Server (NTRS)
Kumakawa, A.; Niino, M.; Hendricks, R. C.; Giarratano, P. J.; Arp, V. D.
1986-01-01
Reduced Nusselt numbers of supercritical fluids from different sources were grouped by several volume-energy parameters. A modified bulk expansion parameter was introduced based on a comparative analysis of data scatter. Heat transfer experiments on liquefied methane were conducted under near-critical conditions in order to confirm the usefulness of the parameters. It was experimentally revealed that heat transfer characteristics of near-critical methane are similar to those of hydrogen. It was shown that the modified bulk expansion parameter and the Gibbs-energy parameter grouped the heat transfer data of hydrogen, oxygen and methane including the present data on near-critical methane. It was also indicated that the effects of surface roughness on heat transfer were very important in grouping the data of high Reynolds numbers.
Enhancement of laminar convective heat transfer using microparticle suspensions
NASA Astrophysics Data System (ADS)
Zhu, Jiu Yang; Tang, Shiyang; Yi, Pyshar; Baum, Thomas; Khoshmanesh, Khashayar; Ghorbani, Kamran
2016-04-01
This paper investigates the enhancement of convective heat transfer within a sub-millimetre diameter copper tube using Al2O3, Co3O4 and CuO microparticle suspensions. Experiments are conducted at different particle concentrations of 1.0, 2.0 and 5.0 wt% and at various flow rates ranging from 250 to 1000 µl/min. Both experimental measurements and numerical analyses are employed to obtain the convective heat transfer coefficient. The results indicate a significant enhancement in convective heat transfer coefficient due to the implementation of microparticle suspensions. For the case of Al2O3 microparticle suspension with 5.0 wt% concentration, a 20.3 % enhancement in convective heat transfer coefficient is obtained over deionised water. This is comparable to the case of Al2O3 nanofluid at the same concentration. Hence, there is a potential for the microparticle suspensions to be used for cooling of compact integrated systems.
Navier-Stokes analysis of turbine blade heat transfer
NASA Technical Reports Server (NTRS)
Boyle, R. J.
1990-01-01
Comparisons with experimental heat transfer and surface pressures were made for seven turbine vane and blade geometries using a quasi-three-dimensional thin-layer Navier-Stokes analysis. Comparisons are made for cases with both separated and unseparated flow over a range of Reynolds numbers and freestream turbulence intensities. The analysis used a modified Baldwin-Lomax turbulent eddy viscosity mode. Modifications were made to account for the effects of: (1) freestream turbulence on both transition and leading edge heat transfer; (2) strong favorable pressure gradients on relaminarization; and (3) variable turbulent Prandtl number heat transfer. In addition, the effect of heat transfer on the near wall model of Deissler is compared with the Van Driest model.
Heat transfer in serpentine flow passages with rotation
NASA Astrophysics Data System (ADS)
Mochizuki, S.; Takamura, J.; Yamawaki, S.; Yang, Wen-Jei
1992-06-01
Results are reported of an experimental study tracing heat transfer performance in a rotating serpentine flow passage of a square cross section. The test section is preceded by a hydrodynamic calming region. The test model is a blow-up (by seven times) of actual winding flow passages in rotor blades. It is concluded that the flow in the 180-deg bends exhibits strong 3D structure. The heat transfer coefficient in the bend is substantially higher than in the straight flow passages. The average heat transfer characteristics over the entire flow passage is greatly affected by flow at the 180-deg bends. Due to secondary flow induced by the Coriolis force, the heat transfer coefficient in the radially outward flow passages diminish on the leading surface, but increase on the trailing surface, with an increase in rotational speed. The trend is reversed in the radially inward flow passages.
Heat Transfer at Supercritical Pressures and the Onset of Deterioration
Kirillov, Pavel L.; Grabezhnaya, Vera A.
2006-07-01
The comparison of the data on heat transfer at supercritical pressures (SCP) demonstrates that they have a considerable spread, which shows a complex nature of the process and a probable inaccuracy in the methods of data processing caused by a sharp change in thermophysical properties near the pseudo-critical point. The recent experimental data at SCP for upward flow of water are compared with some correlations applicable to engineering analysis. The correlations for the onset of heat transfer deterioration against the experimental data were analyzed. The heat transfer deterioration in this data was far from test section inlet The generalization of data on the onset of heat transfer deterioration for various coolants (water, CO{sub 2}, R12) was proposed. (authors)
Boyer, B.D.; Parlatan, Y.; Slovik, G.C.; Rohatgi, U.S.
1995-09-01
RELAP5 MOD3.1.1 is being used to simulate Loss of Coolant Accidents (LOCA) for the Simplified Boiling Water Reactor (SBWR) being proposed by General Electric (GE). One of the major components associated with the SBWR is the Passive Containment Cooling System (PCCS) which provides the long-term heat sink to reject decay heat. The RELAP5 MOD3.1.1 code is being assessed for its ability to represent accurately the PCCS. Data from the Phase 1, Step 1 Heat Transfer Tests performed at Toshiba`s Gravity-Driven Integral Full-Height Test for Passive Heat Removal (GIRAFFE) facility will be used for assessing the ability of RELAP5 to model condensation in the presence of noncondensables. The RELAP5 MOD3.1.1 condensation model uses the University of California at Berkeley (UCB) correlation developed by Vierow and Schrock. The RELAP5 code uses this heat transfer coefficient with the gas velocity effect multiplier being limited to 2. This heat transfer option was used to analyze the condensation heat transfer in the GIRAFFE PCCS heat exchanger tubes in the Phase 1, Step 1 Heat Transfer Tests which were at a pressure of 3 bar and had a range of nitrogen partial pressure fractions from 0.0 to 0.10. The results of a set of RELAP5 calculations al these conditions were compared with the GIRAFFE data. The effects of PCCS cell nodings on the heat transfer process were also studied. The UCB correlation, as implemented in RELAP5, predicted the heat transfer to {+-}5% of the data with a three-node model. The three-node model has a large cell in the entrance region which smeared out the entrance effects on the heat transfer, which tend to overpredict the condensation. Hence, the UCB correlation predicts condensation heat transfer in the presence of noncondensable gases with only a coarse mesh. The cell length term in the condensation heat transfer correlation implemented in the code must be removed to allow for accurate calculations with smaller cell sizes.
Spray Cooling Modeling: Liquid Film Thickness Effect on Heat Transfer
NASA Astrophysics Data System (ADS)
Selvam, R. Panneer; Hamilton, Matthew; Silk, Eric A.
2007-01-01
Spray cooling is a novel solution for high heat flux applications, whose need is becoming apparent with the advance of high power density electronic systems (lasers, radars, etc). The aim of this investigation is to explore thermal management solutions for space-based systems and the effects of varying gravity on heat transfer. Previous modeling done by Selvam, Lin, and Ponnappan (2006) used a liquid film thickness of ≈ 40 μm on the heater wall. The two-phase flow modeling is done using the level set method to identify the interface of vapor and liquid as explained in Selvam, Lin, and Ponnappan (2005; 2006). Modifications to the incompressible Navier-Stokes equations for surface tension, viscosity, gravity and phase change are discussed in detail. The equations are solved using finite difference method. The computed heat flux in thick layers is compared with previous thin layer heat flux. The computed liquid and vapor interface and temperature distributions are also visualized for better understanding of the heat removal process. To understand the heat transfer mechanisms in thick liquid layer, droplet impact on a growing vapor bubble is used to study heat transfer in the liquid layer. The thickness has been varied from 100 μm to 200 μm. Also the impact of initial temperature distribution on heat flux is investigated. This will help us to know how to improve the heat transfer in spray cooling.
Heat transfer across the interface between nanoscale solids and gas.
Cheng, Chun; Fan, Wen; Cao, Jinbo; Ryu, Sang-Gil; Ji, Jie; Grigoropoulos, Costas P; Wu, Junqiao
2011-12-27
When solid materials and devices scale down in size, heat transfer from the active region to the gas environment becomes increasingly significant. We show that the heat transfer coefficient across the solid-gas interface behaves very differently when the size of the solid is reduced to the nanoscale, such as that of a single nanowire. Unlike for macroscopic solids, the coefficient is strongly pressure dependent above ∼10 Torr, and at lower pressures it is much higher than predictions of the kinetic gas theory. The heat transfer coefficient was measured between a single, free-standing VO(2) nanowire and surrounding air using laser thermography, where the temperature distribution along the VO(2) nanowire was determined by imaging its domain structure of metal-insulator phase transition. The one-dimensional domain structure along the nanowire results from the balance between heat generation by the focused laser and heat dissipation to the substrate as well as to the surrounding gas, and thus serves as a nanoscale power-meter and thermometer. We quantified the heat loss rate across the nanowire-air interface, and found that it dominates over all other heat dissipation channels for small-diameter nanowires near ambient pressure. As the heat transfer across the solid-gas interface is nearly independent of the chemical identity of the solid, the results reveal a general scaling relationship for gaseous heat dissipation from nanostructures of all solid materials, which is applicable to nanoscale electronic and thermal devices exposed to gaseous environments. PMID:22070645
Heat transfer intensification by increasing vapor flow rate in flat heat pipes
NASA Astrophysics Data System (ADS)
Sprinceana, Silviu; Mihai, Ioan; Beniuga, Marius; Suciu, Cornel
2015-02-01
Flat heat pipes have various technical applications, one of the most important being the cooling of electronic components[9]. Their continuous development is due to the fact that these devices permit heat transfer without external energetic contribution. The practical exploitation of flat heat pipes however is limited by the fact that dissipated power can only reach a few hundred watts. The present paper aims to advance a new method for the intensification of convective heat transfer. A centrifugal mini impeller, driven by a turntable which incorporates four permanent magnets was designed. These magnets are put in motion by another rotor, which in its turn includes two permanent magnets and is driven by a mini electrical motor. Rotation of the centrifugal blades generates speed and pressure increase of the cooling agent brought to vapor state within the flat micro heat pipe. It's well known that the liquid suffers biphasic transformations during heat transfer inside the heat pipe. Over the hotspot (the heat source being the electronic component) generated at one end of the heat pipe, convective heat transfer occurs, leading to sudden vaporization of the liquid. Pressures generated by newly formed vapors push them towards the opposite end of the flat heat pipe, where a finned mini heat sink is usually placed. The mini-heat exchanger is air-cooled, thus creating a cold spot, where vapors condensate. The proposed method contributes to vapor flow intensification by increasing their transport speed and thus leading to more intense cooling of the heat pipe.
Enhanced heat transfer in partially-saturated hydrothermal systems
Bixler, N.E.; Carrigan, C.R.
1986-01-01
The role of capillarity is potentially important for determining heat transfer in hydrothermal regions. Capillarity allows mixing of phases in liquid/vapor systems and results in enhanced two-phase convection. Comparisons involving a numerical model with capillarity and analytical models without indicate that heat transfer can be enhanced by about an order of magnitude. Whether capillarity can be important for a particular hydrothermal region will depend on the nature of mineral precipitation as well as pore and fracture size distributions.
Heat transfer additives for adsorption cooling system fluids, phase 2
NASA Astrophysics Data System (ADS)
Chandler, T.
1993-11-01
The objectives of the project are the following: to increase the available information on heat and mass transfer additives used in liquid-vapor absorption equipment so that meaningful analysis of additive function is possible; to analyze the experimental results with respect to various postulated heat and mass transfer mechanisms; to develop reasonable alternate hypotheses for mechanisms that are consistent with known data; to dismiss those which exhibit no significant impact; and to note and refine those that have a major influence.
Radiative heat transfer between nanoparticles enhanced by intermediate particle
NASA Astrophysics Data System (ADS)
Wang, Yanhong; Wu, Jingzhi
2016-02-01
Radiative heat transfer between two polar nanostructures at different temperatures can be enhanced by resonant tunneling of surface polaritons. Here we show that the heat transfer between two nanoparticles is strongly varied by the interactions with a third nanoparticle. By controlling the size of the third particle, the time scale of thermalization toward the thermal bath temperature can be modified over 5 orders of magnitude. This effect provides control of temperature distribution in nanoparticle aggregation and facilitates thermal management at nanoscale.
Comparison of Methods for Calculating Radiative Heat Transfer
Schock, Alfred; Abbate, M J
2012-01-19
Various approximations for calculating radioactive heat transfer between parallel surfaces are evaluated. This is done by applying the approximations based on total emissivities to a special case of known spectral emissivities, for which exact heat transfer calculations are possible. Comparison of results indicates that the best approximation is obtained by basing the emissivity of the receiving surface primarily on the temperature of the emitter. A specific model is shown to give excellent agreement over a very wide range of values.
High-Power Liquid-Metal Heat-Transfer Loop
NASA Technical Reports Server (NTRS)
Bhandari, Pradeep; Fujita, Toshio
1991-01-01
Proposed closed-loop system for transfer of thermal power operates at relatively high differential pressure between vapor and liquid phases of liquid-metal working fluid. Resembles "capillary-pumped" liquid-metal heat-transfer loop except electric field across permselective barrier of beta alumina keeps liquid and vapor separate at heat-input end. Increases output thermal power, contains no moving parts, highly reliable and well suited to long-term unattended operation.
One dimensional lunar ash flow with and without heat transfer
NASA Technical Reports Server (NTRS)
Pai, S. I.; Hsieh, T.
1971-01-01
The characteristics of lunar ash flow are discussed in terms of the two phase flow theory of a mixture of a gas and small solid particles. A model is developed to present the fundamental equations and boundary conditions. Numerical solutions for special ash flow with and without heat transfer are presented. In the case of lunar ash flow with small initial velocity, the effect of the heat transfer makes the whole layer of ash flow more compacted together than the corresponding isothermal case.
Magnetohydrodynamic Phenomena and Heat Transfer Near a Rotating Disk
NASA Astrophysics Data System (ADS)
Borisevich, V. D.; Potanin, E. P.
2015-11-01
We propose an approach that permits constructing an analytical solution of the problem of flow and heat transfer in a viscous compressible conducting medium near an infinite dielectric disk rotating in a homogeneous magnetic field. The influence of the magnetic field on the process of heat transfer near the disk surface has been investigated. It has been shown that Joule energy dissipation prevails over viscous dissipation at moderate magnetic fields.
Heat transfer from fail-safe magnetorheological fluid dampers
NASA Astrophysics Data System (ADS)
Dogruoz, M. Baris; Gordaninejad, Faramarz; Wang, Eric L.; Stipanovich, Arthur J.
2001-07-01
This study focuses on an experimental study of heat transfer from magneto-rheological fluid (MRF) dampers. Two semi- active automotive size MRF dampers, one with fins and the other without fins, were constructed and tested. The experimental results were compared with those of a previously developed theoretical model. It is demonstrate that especially at high peak velocities, the temperature rise is significant and heat transfer from these devices can be enhanced considerably by utilizing fins.
Application of ray tracing in radiation heat transfer
NASA Technical Reports Server (NTRS)
Baumeister, Joseph F.
1993-01-01
This collection of presentation figures displays the capabilities of ray tracing for radiation propagation calculations as compared to an analytical approach. The goal is to introduce the terminology and solution process used in ray tracing, and provide insight into radiation heat transfer principles and analysis tools. A thermal analysis working environment is introduced that solves demanding radiation heat transfer problems based on ray tracing. This information may serve as a reference for designing and building ones own analysis environment.
Heat transfer and oil displacement models for tar sands reservoirs
Ward, C.E.; Ward, G.D.
1984-09-01
A convective heat transfer model and one dimensional displacement model applicable to tar sands and heavy oils for use with a microcomputer are presented. The convective heat transfer model describes the temperature profiles in a thermal operation. The displacement model offers insight into the effect of process variables on the steam/oil or air/oil ratio of thermal operations. A method is presented for predicting the fuel burn in a fireflood.
Numerical Modeling of Conjugate Heat Transfer in Fluid Network
NASA Technical Reports Server (NTRS)
Majumdar, Alok
2004-01-01
Fluid network modeling with conjugate heat transfer has many applications in Aerospace engineering. In modeling unsteady flow with heat transfer, it is important to know the variation of wall temperature in time and space to calculate heat transfer between solid to fluid. Since wall temperature is a function of flow, a coupled analysis of temperature of solid and fluid is necessary. In cryogenic applications, modeling of conjugate heat transfer is of great importance to correctly predict boil-off rate in propellant tanks and chill down of transfer lines. In TFAWS 2003, the present author delivered a paper to describe a general-purpose computer program, GFSSP (Generalized Fluid System Simulation Program). GFSSP calculates flow distribution in complex flow circuit for compressible/incompressible, with or without heat transfer or phase change in all real fluids or mixtures. The flow circuit constitutes of fluid nodes and branches. The mass, energy and specie conservation equations are solved at the nodes where as momentum conservation equations are solved at the branches. The proposed paper describes the extension of GFSSP to model conjugate heat transfer. The network also includes solid nodes and conductors in addition to fluid nodes and branches. The energy conservation equations for solid nodes solves to determine the temperatures of the solid nodes simultaneously with all conservation equations governing fluid flow. The numerical scheme accounts for conduction, convection and radiation heat transfer. The paper will also describe the applications of the code to predict chill down of cryogenic transfer line and boil-off rate of cryogenic propellant storage tank.
Heat Transfer to Longitudinal Laminar Flow Between Cylinders
NASA Technical Reports Server (NTRS)
Sparrow, Ephraim M.; Loeffler, Albert L. Jr.; Hubbard, H. A.
1960-01-01
Consideration is given to the fully developed heat transfer characteristics for longitudinal laminar flow between cylinders arranged in an equilateral triangular array. The analysis is carried out for the condition of uniform heat transfer per unit length. Solutions are obtained for the temperature distribution, and from these, Nusselt numbers are derived for a wide range of spacing-to-diameter ratios. It is found that as the spacing ratio increases, so also does the wall-to-bulk temperature difference for a fixed heat transfer per unit length. Corresponding to a uniform surface temperature around the circumference of a cylinder, the circumferential variation of the local heat flux is computed. For spacing ratios of 1.5 - 2.0 and greater, uniform peripheral wall temperature and uniform peripheral heat flux are simultaneously achieved. A simplified analysis which neglects circumferential variations is also carried out, and the results are compared with those from the more exact formulation.
NASA Technical Reports Server (NTRS)
Rule, T. D.; Kim, J.; Kalkur, T. S.
1998-01-01
Boiling heat transfer is an efficient means of heat transfer because a large amount of heat can be removed from a surface using a relatively small temperature difference between the surface and the bulk liquid. However, the mechanisms that govern boiling heat transfer are not well understood. Measurements of wall temperature and heat flux near the wall would add to the database of knowledge which is necessary to understand the mechanisms of nucleate boiling. A heater array has been developed which contains 96 heater elements within a 2.5 mm square area. The temperature of each heater element is held constant by an electronic control system similar to a hot-wire anemometer. The voltage that is being applied to each heater element can be measured and digitized using a high-speed A/D converter, and this digital information can be compiled into a series of heat-flux maps. Information for up to 10,000 heat flux maps can be obtained each second. The heater control system, the A/D system and the heater array construction are described in detail. Results are presented which show that this is an effective method of measuring the local heat flux during nucleate and transition boiling. Heat flux maps are obtained for pool boiling in FC-72 on a horizontal surface. Local heat flux variations are shown to be three to six times larger than variations in the spatially averaged heat flux.
NASA Astrophysics Data System (ADS)
Wu, Yan-Qiu
2015-07-01
In this paper, an endoreversible Carnot heat engine with irreversible heat transfer processes is analyzed based on generalized heat transfer law. The applicability of the entropy generation minimization, exergy analyses method, and entransy theory to the analyses is discussed. Three numerical cases are presented. It is shown that the results obtained from the entransy theory are different from those from the entropy generation minimization, which is equivalent to the exergy analyses method. For the first case in which the application preconditions of the entropy generation minimization and entransy loss maximization are satisfied, both smaller entropy generation rate and larger entransy loss rate lead to larger output power. For the second and third cases in which the preconditions are not satisfied, the entropy generation minimization does not lead to the maximum output power, while larger entransy loss rate still leads to larger output power in the third case. For the discussed cases, the concept of entransy dissipation is not applicable for the analyses of output power. The problems in the negative comments on the entransy theory are pointed out and discussed. The related researchers are advised to focus on some new specific application cases to show if the entransy theory is the same as some other theories. Project supported by the Youth Programs of Chongqing Three Gorges University, China (Grant No. 13QN18).
Heat transfer in geometrically similar cylinders
NASA Technical Reports Server (NTRS)
Riekert, P; Held, A
1941-01-01
The power and heat-stress conditions of geometrically similar engines are discussed. The advantages accruing from smaller cylinder dimensions are higher specific horsepower, lower weight per horsepower, lower piston temperature, and less frontal area, with reduced detonation tendency.
Heat transfer in a finned dehumidifier coil under partially wet condition
Rosario, L.; Rahman, M.M.
1999-07-01
The aim of this paper is the analysis of heat transfer in a radial fin assembly during the process of dehumidification. A numerical simulation of the fin with dry, wet, and partially wet boundary conditions have been carried out using a control volume based finite-difference method and compared with past analytical studies. The augmentation of heat transfer due to fin was calculated by comparing heat transfer rate with and without fins under the same operating conditions. In addition, the fin efficiency was calculated. The parameters that influenced the heat transfer rate in the finned tube structure are ratio of fin and wall thermal conductivities, ratio of fin thickness to fin pitch, ratio of wall thickness to fin pitch, ratio of fin length to fin pitch, cold fluid Biot number, ambient Biot number, the relative humidity and dry bulb temperature of the incoming air, and the cold fluid temperature inside the coil. Numerical calculations were carried out to study the performance of the heat exchanger for various combinations of these parameters. It was found that the heat transfer increased with increment in both dry bulb temperature and the relative humidity of the air. The results suggested that fin efficiency can be very significantly altered by the condensation phenomenon on the fin surface and designs with dry fin data may result in serious over or under prediction of coil performance. The present results are expected to be very useful for the design of dehumidifier (cooling) coils for air conditioning applications.
Revealing the complex conduction heat transfer mechanism of nanofluids.
Sergis, A; Hardalupas, Y
2015-12-01
Nanofluids are two-phase mixtures consisting of small percentages of nanoparticles (sub 1-10 %vol) inside a carrier fluid. The typical size of nanoparticles is less than 100 nm. These fluids have been exhibiting experimentally a significant increase of thermal performance compared to the corresponding carrier fluids, which cannot be explained using the classical thermodynamic theory. This study deciphers the thermal heat transfer mechanism for the conductive heat transfer mode via a molecular dynamics simulation code. The current findings are the first of their kind and conflict with the proposed theories for heat transfer propagation through micron-sized slurries and pure matter. The authors provide evidence of a complex new type of heat transfer mechanism, which explains the observed abnormal heat transfer augmentation. The new mechanism appears to unite a number of popular speculations for the thermal heat transfer mechanism employed by nanofluids as predicted by the majority of the researchers of the field into a single one. The constituents of the increased diffusivity of the nanoparticle can be attributed to mismatching of the local temperature profiles between parts of the surface of the solid and the fluid resulting in increased local thermophoretic effects. These effects affect the region surrounding the solid manifesting interfacial layer phenomena (Kapitza resistance). In this region, the activity of the fluid and the interactions between the fluid and the nanoparticle are elevated. Isotropic increased nanoparticle mobility is manifested as enhanced Brownian motion and diffusion effects. PMID:26058515
Heat Transfer Modeling for Rigid High-Temperature Fibrous Insulation
NASA Technical Reports Server (NTRS)
Daryabeigi, Kamran; Cunnington, George R.; Knutson, Jeffrey R.
2012-01-01
Combined radiation and conduction heat transfer through a high-temperature, high-porosity, rigid multiple-fiber fibrous insulation was modeled using a thermal model previously used to model heat transfer in flexible single-fiber fibrous insulation. The rigid insulation studied was alumina enhanced thermal barrier (AETB) at densities between 130 and 260 kilograms per cubic meter. The model consists of using the diffusion approximation for radiation heat transfer, a semi-empirical solid conduction model, and a standard gas conduction model. The relevant parameters needed for the heat transfer model were estimated from steady-state thermal measurements in nitrogen gas at various temperatures and environmental pressures. The heat transfer modeling methodology was evaluated by comparison with standard thermal conductivity measurements, and steady-state thermal measurements in helium and carbon dioxide gases. The heat transfer model is applicable over the temperature range of 300 to 1360 K, pressure range of 0.133 to 101.3 x 10(exp 3) Pa, and over the insulation density range of 130 to 260 kilograms per cubic meter in various gaseous environments.
Heat transfer coefficients for staggered arrays of short pin fins
NASA Technical Reports Server (NTRS)
Vanfossen, G. J.
1981-01-01
Short pin fins are often used to increase that heat transfer to the coolant in the trailing edge of a turbine blade. Due primarily to limits of casting technology, it is not possible to manufacture pins of optimum length for heat transfer purposes in the trailing edge region. In many cases the pins are so short that they actually decrease the total heat transfer surface area compared to a plain wall. A heat transfer data base for these short pins is not available in the literature. Heat transfer coefficients on pin and endwall surfaces were measured for several staggered arrays of short pin fins. The measured Nusselt numbers when plotted versus Reynolds numbers were found to fall on a single curve for all surfaces tested. The heat transfer coefficients for the short pin fins (length to diameter ratios of 1/2 and 2) were found to be about a factor of two lower than data from the literature for longer pin arrays (length to diameter ratios of about 8).
Heat transfer coefficients for staggered arrays of short pin fins
NASA Technical Reports Server (NTRS)
Vanfossen, G. J.
1981-01-01
Short pin fins are often used to increase the heat transfer to the coolant in the trailing edge of a turbine blade. Due primarily to limits of casting technology, it is not possible to manufacture pins of optimum length for heat transfer purposes in the trailing edge region. In many cases the pins are so short that they actually decrease the total heat transfer surface area compared to a plain wall. A heat transfer data base for these short pins is not available in the literature. Heat transfer coefficients on pin and endwall surfaces were measured for several staggered arrays of short pin fins. The measured Nusselt numbers when plotted versus Reynolds numbers were found to fall on a single curve for all surfaces tested. The heat transfer coefficients for the short pin fins (length to diameter ratios of 1/2 and 2) were found to be about a factor of two lower than data from the literature for longer pin arrays (length to diameter ratios of about 8).
Literature survey of heat transfer enhancement techniques in refrigeration applications
Jensen, M.K.; Shome, B.
1994-05-01
A survey has been performed of the technical and patent literature on enhanced heat transfer of refrigerants in pool boiling, forced convection evaporation, and condensation. Extensive bibliographies of the technical literature and patents are given. Many passive and active techniques were examined for pure refrigerants, refrigerant-oil mixtures, and refrigerant mixtures. The citations were categorized according to enhancement technique, heat transfer mode, and tube or shell side focus. The effects of the enhancement techniques relative to smooth and/or pure refrigerants were illustrated through the discussion of selected papers. Patented enhancement techniques also are discussed. Enhanced heat transfer has demonstrated significant improvements in performance in many refrigerant applications. However, refrigerant mixtures and refrigerant-oil mixtures have not been studied extensively; no research has been performed with enhanced refrigerant mixtures with oil. Most studies have been of the parametric type; there has been inadequate examination of the fundamental processes governing enhanced refrigerant heat transfer, but some modeling is being done and correlations developed. It is clear that an enhancement technique must be optimized for the refrigerant and operating condition. Fundamental processes governing the heat transfer must be examined if models for enhancement techniques are to be developed; these models could provide the method to optimize a surface. Refrigerant mixtures, with and without oil present, must be studied with enhancement devices; there is too little known to be able to estimate the effects of mixtures (particularly NARMs) with enhanced heat transfer. Other conclusions and recommendations are offered.
Revealing the complex conduction heat transfer mechanism of nanofluids
NASA Astrophysics Data System (ADS)
Sergis, A.; Hardalupas, Y.
2015-06-01
Nanofluids are two-phase mixtures consisting of small percentages of nanoparticles (sub 1-10 %vol) inside a carrier fluid. The typical size of nanoparticles is less than 100 nm. These fluids have been exhibiting experimentally a significant increase of thermal performance compared to the corresponding carrier fluids, which cannot be explained using the classical thermodynamic theory. This study deciphers the thermal heat transfer mechanism for the conductive heat transfer mode via a molecular dynamics simulation code. The current findings are the first of their kind and conflict with the proposed theories for heat transfer propagation through micron-sized slurries and pure matter. The authors provide evidence of a complex new type of heat transfer mechanism, which explains the observed abnormal heat transfer augmentation. The new mechanism appears to unite a number of popular speculations for the thermal heat transfer mechanism employed by nanofluids as predicted by the majority of the researchers of the field into a single one. The constituents of the increased diffusivity of the nanoparticle can be attributed to mismatching of the local temperature profiles between parts of the surface of the solid and the fluid resulting in increased local thermophoretic effects. These effects affect the region surrounding the solid manifesting interfacial layer phenomena (Kapitza resistance). In this region, the activity of the fluid and the interactions between the fluid and the nanoparticle are elevated. Isotropic increased nanoparticle mobility is manifested as enhanced Brownian motion and diffusion effects
Two phase heat transfer in tubes, rod bundles and blockages
Drucker, M.I.; Dhir, V.K.; Duffey, R.B.; Ford, G.; Hagemeyer, B.
1982-01-01
Available two-component two phase heat transfer data in tubes have been reviewed. Based on momentum transfer considerations and the important influence of turbulence in the continuous phase, two phase heat transfer data in tubes for liquid Reynolds number varying from 600-190,000 and void fraction varying from 0.01-0.35 have been correlated. New two phase data obtained on rod bundles are also correlated by the above expression when the empirical constant is increased to 3.25. Further, the correlation is modified and extended to account for the enhancement in heat transfer downstream of blockages. Although the correlation is developed for bubbly flows, it should be applicable to entrained flows in which droplets do not wet the heated surface. Data for heat transfer in the vicinity of blockages was obtained on a four rod bundle with rods arranged in a square grid. Sleeve type blockages mounted on all the rods had a length to diameter ratio of 2.5 and blocked about 60% of the flow area of the inner channel while providing an effectively infinite flow bypass. The local heat transfer coefficients were determined for single and two phase flows in which water and nitrogen gas flow rates were varied parametrically.
Spinodal turbulence enhances heat transfer in micro devices
NASA Astrophysics Data System (ADS)
Farisé, Stefano; Poesio, Pietro; Beretta, Gian Paolo
2012-11-01
We experimentally prove the possibility of using spinodal mixtures to increase heat transfer in micro devices as a consequence of an evenly distributed micro agitation, which increases the effective diffusivity. Despite the Re -number is as low as 5, turbulence-like mixing can be achieved by mass transfer effects. A mixture of acetone-hexadecane is quenched in a micro heat exchanger to induce spinodal decomposition. The heat transfer rate is enhanced by self-induced convective motion (spinodal turbulence) because the drops of one phase move against each others under the influence of non-equilibrium capillary forces, Korteweg stresses,which are sustained by the free energy liberated during phase separation. The heat transfer is increased up to the 200% and the effect become larger as the bulk Re decreses, while no dramatic increase in the pressure drop is observed. We built two different experimental set-ups: in the first we measure the heat transfer with a feedback method and in the second we measure the pressure drop and we visualize the induced convection. High-speed camera visualization,pressure drop and temperature measurements allow a complete characterization of the phenomenon, with a special attention to the quantification of the heat transfer coefficent enhancement.
NASA Astrophysics Data System (ADS)
Chen, Kaifeng; Santhanam, Parthiban; Sandhu, Sunil; Zhu, Linxiao; Fan, Shanhui
2015-04-01
We consider near-field heat transfer with nonzero chemical potential for photons, as can occur between two semiconductor bodies, held at different temperatures with at least one of the bodies under external bias. We show that the dependence of radiative heat flux on chemical potential enables electronic control of both the direction and magnitude of near-field heat transfer between the two bodies. Moreover such a configuration can operate as a solid-state cooling device whose efficiency can approach the Carnot limit in the ideal case. Significant cooling can also be achieved in the presence of inherent nonidealities including Auger recombination and parasitic phonon-polariton heat transfer.
Piyush Sabharwall; Fred Gunnerson; Akira Tokuhiro; Vivek Utgiker; Kevan Weaver; Steven Sherman
2007-10-01
The work reported here is the preliminary analysis of two-phase Thermosyphon heat transfer performance with various alkali metals. Thermosyphon is a device for transporting heat from one point to another with quite extraordinary properties. Heat transport occurs via evaporation and condensation, and the heat transport fluid is re-circulated by gravitational force. With this mode of heat transfer, the thermosyphon has the capability to transport heat at high rates over appreciable distances, virtually isothermally and without any requirement for external pumping devices. For process heat, intermediate heat exchangers (IHX) are required to transfer heat from the NGNP to the hydrogen plant in the most efficient way possible. The production of power at higher efficiency using Brayton Cycle, and hydrogen production requires both heat at higher temperatures (up to 1000oC) and high effectiveness compact heat exchangers to transfer heat to either the power or process cycle. The purpose for selecting a compact heat exchanger is to maximize the heat transfer surface area per volume of heat exchanger; this has the benefit of reducing heat exchanger size and heat losses. The IHX design requirements are governed by the allowable temperature drop between the outlet of the NGNP (900oC, based on the current capabilities of NGNP), and the temperatures in the hydrogen production plant. Spiral Heat Exchangers (SHE’s) have superior heat transfer characteristics, and are less susceptible to fouling. Further, heat losses to surroundings are minimized because of its compact configuration. SHEs have never been examined for phase-change heat transfer applications. The research presented provides useful information for thermosyphon design and Spiral Heat Exchanger.
Forced convection heat transfer from pin fin arrays
Maudgal, V.K.
1992-01-01
Extended surfaces in the form of fins are widely used to enhance heat dissipation from a surface. A review of the literature revealed that there exists considerable experience in experimental and numerical analysis for retangular fins, but there is a scarcity of information on pin fins. This dissertation presents the findings of a comprehensive literature search on the state-of-the-art of pin fins, detailed experimental investigation of forced convection heat transfer from pin fin arrays involving complex flow fields that are caused by orientation of the find arrays at various angle of inclination an fin tip clearances, and a simplified numerical analysis. An experimental investigation was conducted to study the forced convection/radiation heat transfer characteristics of three staggered and in-line pin fin arrays that had different fin diameter in interfin spacing ratios. The experiments were performed for two tip clearances, four to seven heat inputs to the array baseplate, two or three flow rates, two fin orientations and five different angles of natural convection experiments were performed on one of the arrays. The combined mode rate of heat transfer was measured and the contribution of the radiation heat transfer was determined analytically. The flow field was studied through flow visualization, velocity and pressure measurements. The heat transfer results were used to establish an empirical correlation to evaluate and predict the performance of pin fin arrays subjected to complex boundary conditions. A simplified numerical analysis was performed for an in-line fin array with simple boundary conditions.
Full coverage impingement heat transfer at high temperatures
NASA Astrophysics Data System (ADS)
Abdul Husain, R. A. A.; Andrews, G. E.
1990-06-01
Transient cooling techniques were developed for the direct simultaneous measurement of full coverage multijet impingement heat transfer coefficient and cooling effectiveness under high temperature combustion convective wall heating conditions. A step change in the impingement coolant flow rate was made and the change in temperature recorded as a function of time, from which the heat transfer coefficient was calculated. A comparison between steady state and transient techniques was also made on a conventional low temperature electrically heated test facility and good agreement was found. There was reasonable agreement between the high temperature heat transfer coefficients and the low temperature results, using similar transient cooling techniques. There was little influence of the coolant to wall temperature ratio on the impingement heat transfer coefficient or the cooling effectiveness obtained from the high temperature test rig. The transient technique was used to study the influence of crossflow in the impingement gap on both the cooling effectiveness and the heat transfer coefficient for a range of low pressure loss impingement walls with an X/D of 1.9 - 11.
Sliding bubble dynamics and the effects on surface heat transfer
NASA Astrophysics Data System (ADS)
Donnelly, B.; Robinson, A. J.; Delauré, Y. M. C.; Murray, D. B.
2012-11-01
An investigation into the effects of a single sliding air bubble on heat transfer from a submerged, inclined surface has been undertaken. Existing literature has shown that both vapour and gas bubbles can increase heat transfer rates from adjacent heated surfaces. However, the mechanisms involved are complex and dynamic and in some cases poorly understood. The present study utilises high speed, high resolution, infrared thermography and video photography to measure two dimensional surface heat transfer and three dimensional bubble position and shape. This provides a unique insight into the complex interactions at the heated surface. Bubbles of volume 0.05, 0.1, 0.2 and 0.4 ml were released onto a surface inclined at 30 degrees to horizontal. Results confirmed that sliding bubbles can enhance heat transfer rates up to a factor of 9 and further insight was gained about the mechanisms behind this phenomenon. The enhancement effects were observed over large areas and persisted for a long duration with the bubble exhibiting complex shape and path oscillations. It is believed that the periodic wake structure present behind the sliding bubble affects the bubble motion and is responsible for the heat transfer effects observed. The nature of this wake is proposed to be that of a chain of horseshoe vortices.
NASA Astrophysics Data System (ADS)
Kandlikar, S. G.
2013-02-01
Evaporation momentum force arises due to the difference in liquid and vapor densities at an evaporating interface. The resulting rapid interface motion increases the microconvection heat transfer around a nucleating bubble in pool boiling. Microstructure features are developed on the basis of this hypothesis to control the bubble trajectory for (i) enhancing the heat transfer coefficient, and (ii) creating separate liquid and vapor pathways that result in an increased critical heat flux (CHF). An eightfold higher heat transfer coefficient (629 000 W/m2 °C) and two-and-half times higher CHF (3 MW/m2) over a plain copper surface were achieved with water.
Heat transfer measurements of the 1983 kilauea lava flow.
Hardee, H C
1983-10-01
Convective heat flow measurements of a basaltic lava flow were made during the 1983 eruption of Kilauea volcano in Hawaii. Eight field measurements of induced natural convection were made, giving heat flux values that ranged from 1.78 to 8.09 kilowatts per square meter at lava temperatures of 1088 and 1128 degrees Celsius, respectively. These field measurements of convective heat flux at subliquidus temperatures agree with previous laboratory measurements in furnace-melted samples of molten lava, and are useful for predicting heat transfer in magma bodies and for estimating heat extraction rates for magma energy. PMID:17810087
Heat-transfer measurements of the 1983 Kilauea lava flow
Hardee, H.C.
1983-10-07
Convective heat flow measurements of a basaltic lava flow were made during the 1983 eruption of Kilauea volcano in Hawaii. Eight field measurements of induced natural convection were made, giving heat flux values that ranged from 1.78 to 8.09 kilowatts per square meter at lava temperatures of 1088 and 1128 degrees Celsius, respectively. These field measurements of convective heat flux at subliquidus temperatures agree with previous laboratory measurements in furnace-melted samples of molten lava, and are useful for predicting heat transfer in magma bodies and for estimating heat extraction rates for magma energy.
Students' Misconceptions about Heat Transfer Mechanisms and Elementary Kinetic Theory
ERIC Educational Resources Information Center
Pathare, S. R.; Pradhan, H. C.
2010-01-01
Heat and thermodynamics is a conceptually rich area of undergraduate physics. In the Indian context in particular there has been little work done in this area from the point of view of misconceptions. This prompted us to undertake a study in this area. We present a study of students' misconceptions about heat transfer mechanisms, i.e. conduction,…
Heat Transfer from Finned Metal Cylinders in an Air Stream
NASA Technical Reports Server (NTRS)
Biermann, Arnold, E; Pinkel, Benjamin
1935-01-01
This report presents the results of tests made to supply design information for the construction of metal fins for the cooling of heated cylindrical surfaces by an air stream. A method is given for determining fin dimensions for a maximum heat transfer with the expenditure of a given amount of material for a variety of conditions of air flow and metals.
Rocket engine heat transfer and material technology for commercial applications
NASA Technical Reports Server (NTRS)
Hiltabiddle, J.; Campbell, J.
1974-01-01
Liquid fueled rocket engine combustion, heat transfer, and material technology have been utilized in the design and development of compact combustion and heat exchange equipment intended for application in the commercial field. An initial application of the concepts to the design of a compact steam generator to be utilized by electrical utilities for the production of peaking power is described.
Students' Misconceptions about Heat Transfer Mechanisms and Elementary Kinetic Theory
ERIC Educational Resources Information Center
Pathare, S. R.; Pradhan, H. C.
2010-01-01
Heat and thermodynamics is a conceptually rich area of undergraduate physics. In the Indian context in particular there has been little work done in this area from the point of view of misconceptions. This prompted us to undertake a study in this area. We present a study of students' misconceptions about heat transfer mechanisms, i.e. conduction,
Heat transfer enhancement in fin-tube heat exchangers by winglet type vortex generators
NASA Astrophysics Data System (ADS)
Biswas, G.; Mitra, N. K.; Fiebig, M.
1994-01-01
Numerical investigations of the flow structure and heat transfer enhancement in a channel with a built-in-circular tube and a winglet type vortex generator are presented. The geometrical configuration represents an element of a gas-liquid fin-tube crossflow heat exchanger. In the absence of the winglet type vortex generator, relatively little heat transfer takes place in the downstream of the circular tube which is a recirculation region with low velocity fluid. However, in the presence of a winglet type longitudinal vortex generator in the wake region behind the cylinder, heat transfer in this region can be enhanced as high as 240%. Results show a marked increase in overall channel heat transfer. The enhancement shows great promise in reducing the size of the heat exchangers.
NASA Astrophysics Data System (ADS)
Piasecka, Magdalena; Strąk, Kinga
2016-03-01
The aim of the paper is to estimate effect of the heating surface enhancement on FC-72 flow boiling heat transfer for a vertical minichannel 1.7 mm deep, 24 mm wide and 360 mm long. Two types of enhanced heating surfaces were used: one with minicavities distributed unevenly, and the other with capillary metal fibrous structure. It was to measure temperature field on the plain side of the heating surface by means of the infrared thermography and to observe the two-phase flow patterns on the enhanced foil side. The paper analyses mainly the impact of the microstructured heating surface on the heat transfer coefficient. The results are presented as heat transfer coefficient dependences on the distance along the minichannel length. The data obtained using two types of enhanced heating surfaces in experiments was compared with the data when smooth foil as the heating surface was used. The highest local values of heat transfer coefficient were obtained using enhanced foil with minicavities - in comparison to other cases. Local values of heat transfer coefficient received for capillary fibrous structure were the lowest, even compared with data obtained for smooth foil. Probably this porous structure caused local flow disturbances.
Overview of NASA Glenn Research Center Programs in Aero-Heat Transfer and Future Needs
NASA Technical Reports Server (NTRS)
Gaugler, Raymond E.
2002-01-01
This presentation concentrates on an overview of the NASA Glenn Research Center and the projects that are supporting Turbine Aero-Heat Transfer Research. The principal areas include the Ultra Efficient Engine Technology (UEET) Project, the Advanced Space Transportation Program (ASTP) Revolutionary Turbine Accelerator (RTA) Turbine Based Combined Cycle (TBCC) project, and the Propulsion & Power Base R&T - Smart Efficient Components (SEC), and Revolutionary Aeropropulsion Concepts (RAC) Projects. In addition, highlights are presented of the turbine aero-heat transfer work currently underway at NASA Glenn, focusing on the use of the Glenn-HT Navier- Stokes code as the vehicle for research in turbulence & transition modeling, grid topology generation, unsteady effects, and conjugate heat transfer.
The influence of oil on nucleate pool boiling heat transfer
NASA Astrophysics Data System (ADS)
Spindler, Klaus; Hahne, Erich
2009-05-01
The influence of various oil contents in R134a is investigated for nucleate pool boiling on copper tubes either sandblasted or with enhanced heating surfaces (GEWA-B tube). Polyolester oils (POE) (Reniso Triton) with medium viscosity 55 cSt (SE55) and high viscosity 170 cSt (SE170) were used. Heat transfer coefficients were obtained for boiling temperatures between -28.6 and +20.1°C. The oil content varied from 0 to 5% mass fraction. For the sandblasted tube and the SE55 oil the heat transfer coefficients for the refrigerant/oil-mixture can be higher or lower than those for the pure refrigerant, depending on oil mass fraction, boiling temperature and heat flux. In some cases the highest heat transfer coefficients were obtained at a mass fraction of 3%. For the 170 cSt oil there is a clear decrease in heat transfer for all variations except for a heat flux 4,000 W/m2 and -10.1°C at 0.5% oil content. The heat transfer coefficients are compared to those in the literature for a smooth stainless steel tube and a platinum wire. For the enhanced tube and 55 cSt oil the heat transfer coefficients are clearly below those for pure refrigerant in all cases. The experimental results for the sandblasted tube are compared with the correlation by Jensen and Jackman. The calculated values are within +20 and -40% for the medium viscosity oil and between +50% and -40% for the high viscosity oil. A correlation for predicting oil-degradation effects on enhanced surfaces does not exist.
Finite Element Heat & Mass Transfer Code
Energy Science and Technology Software Center (ESTSC)
1996-10-10
FEHM is a numerical simulation code for subsurface transport processes. It models 3-D, time-dependent, multiphase, multicomponent, non-isothermal, reactive flow through porous and fractured media. It can accurately represent complex 3-D geologic media and structures and their effects on subsurface flow and transport. Its capabilities include flow of gas, water, and heat; flow of air, water, and heat; multiple chemically reactive and sorbing tracers; finite element/finite volume formulation; coupled stress module; saturated and unsaturated media; andmore » double porosity and double porosity/double permeability capabilities.« less
Fiebig, M.; Chen, Y.; Grosse-Gorgemann, A.; Mitra, N.K.
1995-08-01
Numerical investigations of three-dimensional flow and heat transfer in a finned tube with punched longitudinal vortex generators (LVG`s) are carried out for Reynolds number of 250 and 300. Air with a Prandtl number of 0.7 is used as the fluid. The flow is both thermally and hydrodynamically developing. The LVG is a delta winglet pair (DWP) punched out of the fin and is located directly behind the tube, symmetrically separated by one tube diameter. The DWP generates longitudinal vortices in the wake of the tube, defers flow separation on the tube, deflects the main stream into the tube wake, and strong reduces the ``dead water zone.`` Heat transfer reversal is avoided by the DWP. Comparison of the span-averaged Nusselt numbers for the fin with and without DWP shows significant local heat transfer enhancement of several hundred percent in the tube wake. For Re = 300 and Fi = 200 the global heat transfer augmentation by a DWP, which amounts to only 2.5% of the fin area, is 31%.
Nanoscale Radiative Heat Transfer between Graphene Ribbon Arrays
NASA Astrophysics Data System (ADS)
Zhang, Zhuomin; Liu, Xianglei
Near-field radiative heat transfer between two graphene sheets can exceed that between blackbodies due to surface plasmons excited by the graphene sheet. This study shows that, by patterning a single layer of graphene sheet into ribbons, a giant enhancement of the near-field radiative heat flux, by more than one order of magnitude higher than that between two graphene sheets, can be achieved. The mechanism lies in that when the graphene sheet is patterned into an array of ribbons, the closed circular dispersion of graphene plasmons is opened to become hyperbolic, leading to broadband singularities of density of states. Extremely high-k evanescent waves can now couple with hyperbolic graphene plasmons. Exact numerical simulations are used by combining the scattering theory and rigorous coupled-wave analysis. Furthermore, effective medium calculations are used to support the arguments and provide clear physical insights. The findings from this study may open promising pathways for highly efficient thermal management, energy harvesting, and subwavelength thermal imaging. This work was supported by the Department of Energy, Office of Science, Basic Energy Sciences (DE-FG02-06ER46343).
Gas flow and heat transfer in nanotube and nanowire arrays
NASA Astrophysics Data System (ADS)
Martin, Michael J.
2012-03-01
Gas flow through arrays of nanotube or nanowire structures is modeled by combining the one-dimensional equations for conservation of mass, momentum, and energy with the linearized free-molecular drag and heat transfer for a cylinder. The results show that the pressure gradient, temperature, and local velocity of the gas are governed by coupled ordinary differential equations. Three cases are considered: an isothermal system, a constant wall temperature, and a constant wall heat flux. While the coupled momentum, heat transfer, and continuity equations are nonlinear, the relatively low velocities encountered in these systems cause the nonlinear portions of pressure drops and thermal phenomena to be relatively small.
Unsteady heat transfer from a thick hot-film sensor
NASA Astrophysics Data System (ADS)
Park, Chong H.; Cole, Kevin D.
1994-10-01
This study is aimed at developing numerical and analytical models of thick hot-film sensor that include thermal storage in the sensor. Transient conjugate heat transfer analysis is carried out with the unsteady surface element (USE) method. The temperature response of the sensor is determined from analysis of three bodies (air, hot film, and polymer substrate). The average temperature of the hot-film sensor is determined, with known heat flux input to the hot film and with known air velocity. This work, which involves steady airflow with transient heat transfer, is a first step toward transient airflow analysis of these sensors.
Heat transfer in serpentine passages with turbulence promoters
NASA Technical Reports Server (NTRS)
Boyle, R. J.
1984-01-01
Local heat transfer rates and overall pressure losses were determined for serpentine passages of square cross section. The flow entered an inlet leg, turned 180 deg and then passed through an outlet leg. Results were obtained for a passage with smooth walls for three different bend geometries and the effect of turbulence promoters was investigated. Turbulence promoters between 0.6 and 15% of the passage height were tested. Local heat transfer rates are determined from thermocouple measurements on a thin electrically heated Inconel foil and pressure drop is measured along the flow path.
Heat and mass transfer performances on plate fin and tube heat exchangers with dehumidification
Seshimo, Y.; Ogawa, K.; Marumoto, K.; Fujii, M. )
1990-09-01
The authors discuss how they conducted an experimental study on the air side performance of a single-row plate fin and tube heat exchanger in moist air where mass transfer exist under a relatively low driving potential. The results are as follows: The heat transfer with dehumidification is about 20% greater than that with only sensible heat transfer. Also the air side pressure drop is about 30-40% greater. The reason, as clarified by visual observations, comes from the condensate effect. To study how the condensate film affects performance, the presence of the stagnant condensate in the heat exchanger was modeled as an apparent change of the heat exchanger geometry, and the equivalent thickness of the condensate film was calculated from the increase in the air side pressure drop. As a result, if the presence of condensate in the heat exchanger is considered, then the heat transfer with dehumidification can be treated in the same way as with only sensible heat transfer. The analogy between heat and mass transfer does not strictly hold, the experimental results being closed to the Lewis Law.
Heat Transfer Over the Circumference of a Heated Cylinder in Transverse Flow
NASA Technical Reports Server (NTRS)
Schmidt, Ernst; Wenner, Karl
1943-01-01
A method for recording the local heat-transfer coefficients on bodies in flow was developed. The cylinder surface was kept at constant temperature by the condensation of vapor except for a narrow strip which is heated separately to the same temperature by electricity. The heat-transfer coefficient at each point was determined from the electric heat output and the temperature increase. The distribution of the heat transfer along the circumference of cylinders was recorded over a range of Reynolds numbers of from 5000 to 426,000. The pressure distribution was measured at the same time. At Reynolds numbers up to around 100,000 high maximums of the heat transfer occurred in the forward stagnation point at and on the rear side at 180C, while at around 80 the heat-transfer coefficient on both sides of the cylinder behind the forward stagnation point manifested distinct minimums. Two other maximums occurred at around 115 C behind the forward stagnation point between 170,000 and 426,000. At 426,000 the heat transfer at the location of those maximums was almost twice as great as in the forward stagnation point, and the rear half of the cylinder diffused about 60 percent of the entire heat, The tests are compared with the results of other experimental and theoretical investigations.
Power density of piezoelectric transformers improved using a contact heat transfer structure.
Shao, Wei Wei; Chen, Li Juan; Pan, Cheng Liang; Liu, Yong Bin; Feng, Zhi Hua
2012-01-01
Based on contact heat transfer, a novel method to increase power density of piezoelectric transformers is proposed. A heat transfer structure is realized by directly attaching a dissipater to the piezoelectric transformer plate. By maintaining the vibration mode of the transformer and limiting additional energy losses from the contact interface, an appropriate design can improve power density of the transformer on a large scale, resulting from effective suppression of its working temperature rise. A prototype device was fabricated from a rectangular piezoelectric transformer, a copper heat transfer sheet, a thermal grease insulation pad, and an aluminum heat radiator. The experimental results show the transformer maintains a maximum power density of 135 W/cm(3) and an efficiency of 90.8% with a temperature rise of less than 10 °C after more than 36 h, without notable changes in performance. PMID:22293737
Research Strategy for Modeling the Complexities of Turbine Heat Transfer
NASA Technical Reports Server (NTRS)
Simoneau, Robert J.
1996-01-01
The subject of this paper is a NASA research program, known as the Coolant Flow Management Program, which focuses on the interaction between the internal coolant channel and the external film cooling of a turbine blade and/or vane in an aircraft gas turbine engine. The turbine gas path is really a very complex flow field. The combination of strong pressure gradients, abrupt geometry changes and intersecting surfaces, viscous forces, rotation, and unsteady blade/vane interactions all combine to offer a formidable challenge. To this, in the high pressure turbine, we add the necessity of film cooling. The ultimate goal of the turbine designer is to maintain or increase the high level of turbine performance and at the same time reduce the amount of coolant flow needed to achieve this end. Simply stated, coolant flow is a penalty on the cycle and reduces engine thermal efficiency. Accordingly, understanding the flow field and heat transfer associated with the coolant flow is a priority goal. It is important to understand both the film cooling and the internal coolant flow, particularly their interaction. Thus, the motivation for the Coolant Flow Management Program. The paper will begin with a brief discussion of the management and research strategy, will then proceed to discuss the current attack from the internal coolant side, and will conclude by looking at the film cooling effort - at all times keeping sight of the primary goal the interaction between the two. One of the themes of this paper is that complex heat transfer problems of this nature cannot be attacked by single researchers or even groups of researchers, each working alone. It truly needs the combined efforts of a well-coordinated team to make an impact. It is important to note that this is a government/industry/university team effort.
A Conceptual Change Model for Teaching Heat Energy, Heat Transfer and Insulation
ERIC Educational Resources Information Center
Lee, C. K.
2014-01-01
This study examines the existing knowledge that pre-service elementary teachers (PSETs) have regarding heat energy, heat transfer and insulation. The PSETs' knowledge of heat energy was initially assessed by using an activity: determining which container would be best to keep hot water warm for the longest period of time. Results showed that…
Heat Transfer Enhancement in Separated and Vortex Flows
Richard J. Goldstein
2004-05-27
This document summarizes the research performance done at the Heat Transfer Laboratory of the University of Minnesota on heat transfer and energy separation in separated and vortex flow supported by DOE in the period September 1, 1998--August 31, 2003. Unsteady and complicated flow structures in separated or vortex flows are the main reason for a poor understanding of heat transfer under such conditions. The research from the University of Minnesota focused on the following important aspects of understanding such flows: (1) Heat/mass transfer from a circular cylinder; (2) study of energy separation and heat transfer in free jet flows and shear layers; and (3) study of energy separation on the surface and in the wake of a cylinder in crossflow. The current study used three different experimental setups to accomplish these goals. A wind tunnel and a liquid tunnel using water and mixtures of ethylene glycol and water, is used for the study of prandtl number effect with uniform heat flux from the circular cylinder. A high velocity air jet is used to study energy separation in free jets. A high speed wind tunnel, same as used for the first part, is utilized for energy separation effects on the surface and in the wake of the circular cylinder. The final outcome of this study is a substantial advancement in this research area.
Heat Transfer Characteristics of Slush Nitrogen in Turbulent Pipe Flows
NASA Astrophysics Data System (ADS)
Ohira, K.; Ishimoto, J.; Nozawa, M.; Kura, T.; Takahashi, N.
2008-03-01
Slush fluids, such as slush hydrogen and slush nitrogen, are two-phase (solid-liquid) single-component cryogenic fluids containing solid particles in a liquid, and consequently their density and refrigerant capacity are greater than for liquid state fluid alone. This paper reports on the experimental results of the forced convection heat transfer characteristics of slush nitrogen flowing in a pipe. Heat was supplied to slush nitrogen by a heater wound around the copper pipe wall. The local heat transfer coefficient was measured in conjunction with changes in the velocity and the solid fraction. The differences in heat transfer characteristics between two-phase slush and single phase liquid nitrogen were obtained, and the decrease in heat transfer to slush nitrogen caused by the previously observed pressure drop reduction was confirmed by this study. Furthermore, for the purpose of establishing the thermal design criteria for slush nitrogen in the case of pressure drop reduction, the heat transfer correlation between the experimental results and the Sieder-Tate Equation was obtained.
Turbulent heat transfer prediction method for application to scramjet engines
NASA Technical Reports Server (NTRS)
Pinckney, S. Z.
1974-01-01
An integral method for predicting boundary layer development in turbulent flow regions on two-dimensional or axisymmetric bodies was developed. The method has the capability of approximating nonequilibrium velocity profiles as well as the local surface friction in the presence of a pressure gradient. An approach was developed for the problem of predicting the heat transfer in a turbulent boundary layer in the presence of a high pressure gradient. The solution was derived with particular emphasis on its applicability to supersonic combustion; thus, the effects of real gas flows were included. The resulting integrodifferential boundary layer method permits the estimation of cooling reguirements for scramjet engines. Theoretical heat transfer results are compared with experimental combustor and noncombustor heat transfer data. The heat transfer method was used in the development of engine design concepts which will produce an engine with reduced cooling requirements. The Langley scramjet engine module was designed by utilizing these design concepts and this engine design is discussed along with its corresponding cooling requirements. The heat transfer method was also used to develop a combustor cooling correlation for a combustor whose local properties are computed one dimensionally by assuming a linear area variation and a given heat release schedule.
Experimental Investigation of Entrance-region Heat-transfer Coefficients
NASA Technical Reports Server (NTRS)
Joyner, Upshur T
1943-01-01
Experimental results of tests made at the Langley Memorial Aeronautical Laboratory are presented to show how heat-transfer coefficients can he increased by a method utilizing the high rate of heat transfer known to exist on any heat-transfer surface in the region adjacent to the edge on which the cooling or heating fluid impinges. The results show that, for the same pressure drop, the average surface heat-transfer.coefficient can be increased 50 to 100 percent when a cooling surface having a length of four inches in the direction of fluid flow is cut to form twenty fins with a length of 0.2 inch in the direction of fluid flow and the fins are sharpened and staggered in the air stream. The percentage of increase in the surface heat-transfer coefficient obtained as a result of shortening the length of the cooling surface varies with the pressure drop of the cooling fluid in passing the surface, the increase being largest when small pressure drop is used and smallest when high pressure drop is used.
Heat, mass, and momentum transfer about arbitrary groups of particles
Dwyer, H.A.; Nirschl, H.; Kerschl, P.; Denk, V.
1994-12-31
The flow over groups of particles with heat and mass transfer has been numerically simulated at intermediate Reynolds numbers, and the flow characteristics have been studied and documented. The method of approach consisted of using a new overset mesh technique and a numerical solution of the Navier-Stokes equations. Group behavior has been observed for all the particle configurations studied, and significant changes in drag and heat transfer have been documented for particles within a group. The influence of surface mass transfer has been analyzed with the changes in skin friction and heat transfer, as in single particle flows. The methods used in this paper are new to particle dynamics, and they can be extended to arbitrary-shaped particles in arbitrary configurations. The methods developed in this paper can be extended to reacting spray flows to offer detailed knowledge in the near future.
Advanced two-phase heat transfer systems
NASA Technical Reports Server (NTRS)
Swanson, Theodore D.
1992-01-01
Future large spacecraft, such as the Earth Observing System (EOS) platforms, will require a significantly more capable thermal control system than is possible with current 'passive' technology. Temperatures must be controlled much more tightly over a larger surface area. Numerous heat load sources will often be located inside the body of the spacecraft without a good view to space. Power levels and flux densities may be higher than can be accommodated with traditional technology. Integration and ground testing will almost certainly be much more difficult with such larger, more complex spacecraft. For these and similar reasons, the Goddard Space Flight Center (GSFC) has been developing a new, more capable thermal control technology called capillary pumped loops (CPL's). CPL's represent an evolutionary improvement over heat pipes; they can transport much greater quantities of heat over much longer distances and can serve numerous heat load sources. In addition, CPL's can be fabricated into large cold plates that can be held to tight thermal gradients. Development of this technology began in the early 1980's and is now reaching maturity. CPL's have recently been baselined for the EOS-AM platform (1997 launch) and the COMET spacecraft (1992 launch). This presentation describes this new technology and its applications. Most of the viewgraphs are self descriptive. For those that are less clear additional comments are provided.
Field Measurements of Heating System Efficiency in Nine Electrically-Heated Manufactured Homes.
Davis, Bob; Siegel, J.; Palmiter, L.; Baylon, D.
1996-07-01
This report presents the results of field measurements of heating efficiency performed on nine manufactured homes sited in the Pacific Northwest. The testing procedure collects real-time data on heating system energy use and heating zone temperatures, allowing direct calculation of heating system efficiency.
Boiling heat transfer enhancement in subsurface horizontal and vertical tunnels
Pastuszko, Robert
2008-09-15
Complex experimental investigations of boiling heat transfer on structured surfaces covered with perforated foil were taken up. Experimental data were discussed for two kinds of enhanced surfaces formed by joined horizontal and vertical tunnels: tunnel structures (TS) and narrow tunnel structures (NTS). The experiments were carried out with water, ethanol and R-123 at atmospheric pressure. The TS and NTS surfaces were manufactured out of perforated copper foil of 0.05 mm thickness (hole diameters: 0.3, 0.4, 0.5 mm) sintered with the mini-fins, formed on the vertical side of the 5 mm high rectangular fins and horizontal inter-fin surface. The effects of hole (pore) diameters, tunnel pitch for TS and tunnel width for NTS on nucleate pool boiling were examined. Substantial enhancement of heat transfer coefficient was observed. The investigated surfaces showed boiling heat transfer coefficients similar to those of existing structures with subsurface tunnels, but at higher heat fluxes range. (author)
Forced flow heat transfer of supercritical hydrogen for superconductor cooling
NASA Astrophysics Data System (ADS)
Shiotsu, M.; Shirai, Y.; Tatsumoto, H.; Hata, K.; Kobayashi, H.; Naruo, Y.; Inatani, H.
2014-01-01
Heat transfer from inner side of a vertical tube to forced flow of hydrogen was measured at the pressure of 1.5 MPa. The test tubes were made of stainless steel 316L with the inner diameters from 3 mm to 9 mm and lengths from 100 mm to 250 mm. Heat transfer curves were obtained by gradually increasing the heating current to the test tube and raising the surface temperature up to around 200 K. Inlet fluid temperature and flow velocity were varied from 21 to 30 K and 0.5 to 12 m/s, respectively. Effects of inlet temperature, flow velocity and tube dimension were clearly observed. The heat transfer curve for each flow velocity consists of a lower temperature region with a higher gradient and higher temperature region with a lower gradient. The experimental results were compared with the authors' correlation presented formerly. It was confirmed that this correlation can describe the experimental results obtained here.
Effect of boiling surface vibration on heat transfer
NASA Astrophysics Data System (ADS)
Alangar, Sathyabhama
2016-03-01
Experimental investigation of effect of forced vertical surface vibration on nucleate pool boiling heat transfer of saturated water at atmospheric pressure is presented in this paper. Vertical vibration was induced externally to the circular copper test surface on which boiling took place, using a vibration exciter. Frequency was varied in the range 0-25 Hz and amplitude of vibration was varied in the range 0-5 mm. Boiling takes place at much lower superheats for the same heat flux, slope of boiling curve decreases remarkably, when the surface is given external excitation. High frequency and high amplitude oscillations lead to more intensive heat transfer. There are some combinations of frequency and vibration amplitude, which cause up to two times increase in heat transfer coefficients.
Heat transfer from cylinders in subsonic slip flows
NASA Technical Reports Server (NTRS)
Nagabushana, K. A.; Stainback, P. C.
1992-01-01
The heat transfer in heated wires was measured using a constant temperature anemometer over a Mach number range from 0.05 to 0.4 and pressures from 0.5 to 8.0 atmospheres. The total temperature ranged from 80 to 120 F and the wire diameters were 0.00015, 0.00032, and 0.00050 inch. The heat transfer data is presented in the form of a corrected Nusselt number. Based on suggested criteria, much of the data was obtained in the slip flow regime. Therefore, the data is compared with data having comparable flow conditions. The possible application of the heat transfer data to hot wire anemometry is discussed. To this end, the sensitivity of the wires to velocity, density, and total temperature is computed and compared using two different types of correlations.
Modelling of heat and mass transfer processes in neonatology.
Ginalski, Maciej K; Nowak, Andrzej J; Wrobel, Luiz C
2008-09-01
This paper reviews some of our recent applications of computational fluid dynamics (CFD) to model heat and mass transfer problems in neonatology and investigates the major heat and mass transfer mechanisms taking place in medical devices such as incubators and oxygen hoods. This includes novel mathematical developments giving rise to a supplementary model, entitled infant heat balance module, which has been fully integrated with the CFD solver and its graphical interface. The numerical simulations are validated through comparison tests with experimental results from the medical literature. It is shown that CFD simulations are very flexible tools that can take into account all modes of heat transfer in assisting neonatal care and the improved design of medical devices. PMID:18708705
Takeishi, K; Aoki, S
2001-05-01
This paper deals with the contribution of heat transfer to increase the turbine inlet temperature of industrial gas turbines in order to attain efficient and environmentally benign engines. High efficiency film cooling, in the form of shaped film cooling and full coverage film cooling, is one of the most important cooling technologies. Corresponding heat transfer tests to optimize the film cooling effectiveness are shown and discussed in this first part of the contribution. PMID:11460641
Effect of Channel Configurations for Tritium Transfer in Printed Circuit Heat Exchangers
Chang Oh; Eung Kim; Robert Shrake; Mike Patterson
2009-05-01
The Next Generation Nuclear Plant (NGNP), a very High temperature Gas-Cooled Reactor (VHTR) concept, will provide the first demonstration of a closed-loop Brayton cycle at a commercial scale of a few hundred megawatts electric and hydrogen production. The power conversion system (PCS) for the NGNP will take advantage of the significantly higher reactor outlet temperatures of the VHTR to provide higher efficiencies than can be achieved in the current generation of light water reactors. Besides demonstrating a system design that can be used directly for subsequent commercial deployment, the NGNP will demonstrate key technology elements that can be used in subsequent advanced power conversion systems for other Generation IV reactors. In anticipation of the design, development and procurement of an advanced power conversion system for the NGNP, the system integration of the NGNP and hydrogen plant was initiated to identify the important design and technology options that must be considered in evaluating the performance of the proposed NGNP. In the VHTR system, an intermediate heat exchanger (IHX), which transfers heat from the reactor core to the electricity or hydrogen production system is one key component, and its effectiveness is directly related to the system overall efficiency. In the VHTRs, the gas fluids used for coolant generally have poor heat transfer capability, so it requires very large surface area for a given condition. For this reason, a compact heat exchanger (CHE), which is widely used in industry especially for gasto-gas or gas-to-liquid heat exchange is considered as a potential candidate for an IHX replacing the classical shell and tube type heat exchanger. A compact heat exchanger is arbitrary referred to be a heat exchanger having a surface area density greater than 700 m2/m3. The compactness is usually achieved by fins and micro-channels, and leads to the enormous heat transfer enhancement and size reduction. The surface area density is the total heat transfer area divided by the volume of the heat exchanger. In the case of PCHE units, the heat transfer surface area density may be as high as 2,500 m2/m3. This high compactness implies an appreciable reduction in material reducing cost. In this study, heat transfer and tritium penetration analyses have been performed for two different channel configurations of the PCHE; (1) standard and (2) off-set. One of the goals of this study was to determine whether offsetting the hot and cold streams would significantly reduce the tritium flux, and whether or not it would affect the heat transfer significantly.
O'Brien, James Edward; Sohal, Manohar Singh; Huff, George Albert
2002-08-01
A combined experimental and numerical investigation is under way to investigate heat transfer enhancement techniques that may be applicable to large-scale air-cooled condensers such as those used in geothermal power applications. The research is focused on whether air-side heat transfer can be improved through the use of finsurface vortex generators (winglets,) while maintaining low heat exchanger pressure drop. A transient heat transfer visualization and measurement technique has been employed in order to obtain detailed distributions of local heat transfer coefficients on model fin surfaces. Pressure drop measurements have also been acquired in a separate multiple-tube row apparatus. In addition, numerical modeling techniques have been developed to allow prediction of local and average heat transfer for these low-Reynolds-number flows with and without winglets. Representative experimental and numerical results presented in this paper reveal quantitative details of local fin-surface heat transfer in the vicinity of a circular tube with a single delta winglet pair downstream of the cylinder. The winglets were triangular (delta) with a 1:2 height/length aspect ratio and a height equal to 90% of the channel height. Overall mean fin-surface Nusselt-number results indicate a significant level of heat transfer enhancement (average enhancement ratio 35%) associated with the deployment of the winglets with oval tubes. Pressure drop measurements have also been obtained for a variety of tube and winglet configurations using a single-channel flow apparatus that includes four tube rows in a staggered array. Comparisons of heat transfer and pressure drop results for the elliptical tube versus a circular tube with and without winglets are provided. Heat transfer and pressure-drop results have been obtained for flow Reynolds numbers based on channel height and mean flow velocity ranging from 700 to 6500.
Visualization of heat transfer for impinging swirl flow
Bakirci, K.; Bilen, K.
2007-10-15
The objective of the experimental study was to visualize the temperature distribution and evaluate heat transfer rate on the impingement surface kept at a constant wall temperature boundary condition for the swirling (SIJ), multi-channel (MCIJ) and conventional impinging jet (CIJ) using liquid crystal technique. The swirling jet assembly consisted of a housing tube and a solid swirl generator insert which had four narrow slots machined on its surface. The swirl angle, {theta}, was set as 0 , 22.5 , 41 , 50 to change the direction and strength of the swirl in the air flow exiting the housing tube. The local Nusselt numbers of the MCIJ ({theta} = 0 ) were generally much higher than those of CIJ and SIJs. As the swirl angle increased, the radial uniformity of the heat transfer was seen compared to MCIJ and SIJ; the best results were for {theta} = 50 and the jet-to-surface distance of H/D = 14. The location of the distance of the maximum heat transfer for the swirl angles of {theta} = 41 and 50 was shifted away from the stagnation point in a radial distance of nearly r/D = 2.5. Increasing Reynolds number for same swirler angle increased the heat transfer rate on the entire surface, and increased saddle shape heat transfer distribution on the surface, but had no significant effect on the position of the individual impingement regions, but increased saddle shape heat transfer distribution on the surface. The lower Reynolds number (Re = 10 000) and the highest H/D = 14 gave much more uniform local and average heat transfer distribution on the surface, but decreased their values on the entire surface. (author)
Methamphetamine residue dermal transfer efficiencies from household surfaces.
Van Dyke, Mike; Martyny, John W; Serrano, Kate A
2014-01-01
Methamphetamine contamination from illegal production operations poses a potential health concern for emergency responders, child protective services, law enforcement, and children living in contaminated structures. The objective of this study was to evaluate dermal transfer efficiencies of methamphetamine from contaminated household surfaces. These transfer efficiencies are lacking for methamphetamine, and would be beneficial for use in exposure models. Surfaces were contaminated using a simulated smoking method in a stainless steel chamber. Household surfaces were carpet, painted drywall, and linoleum. Dermal transfer efficiencies were obtained using cotton gloves for two hand conditions, dry or saliva moistened (wet). In addition, three contact scenarios were evaluated for both hand conditions: one, two, or three contacts with contaminated surfaces. Dermal transfer efficiencies were calculated for both hand conditions and used as inputs in a Stochastic Human Exposure and Dose Simulation model (SHEDS-Multimedia, Office of Research and Development, United States Environmental Protection Agency, Research Triangle Park, N.C.). Results of this study showed that average dermal transfer efficiencies of methamphetamine ranged from 11% for dry hands to 26% for wet hands. There was a significantly higher wet transfer as compared to dry transfer for all surfaces. For wet hands, dermal transfer depended on surface type with higher transfer from carpet and linoleum as compared to drywall. Based on our estimates of dermal transfer efficiency, a surface contamination clearance level of 1.5 μg/100 cm(2) may not ensure absorbed doses remain below the level associated with adverse health effects in all cases. Additional dermal transfer studies should be performed using skin surrogates that may better predict actual skin transfer. PMID:24579754
Laboratory Investigations of Lava Flow Heat Transfer
NASA Astrophysics Data System (ADS)
Fagents, S. A.; Rumpf, M. E.; Hamilton, C. W.
2011-12-01
To investigate the effectiveness with which lava can heat substrates of different types, we conducted a suite of experiments in which molten basalt was poured onto solid or particulate materials, and the downward propagation of the heat pulse was measured. The motivation for this work lies in seeking to understand how lava flows on the Moon would have heated the underlying regolith, and thus to determine the depths at which solar wind particles implanted in the regolith would have been protected from the heat of the overlying flow. Extraction and analysis of ancient solar wind samples would provide a wealth of information on the evolution and fate of the Sun. Our experimental device consists of a box constructed from 1"-thick calcium silicate sheeting with interior dimensions of 20 x 20 x 25 cm. The substrate material (a particulate lunar regolith simulant or solid basalt) occupies the lower 15 cm of the box, which is embedded with an array of 8 thermocouples. Up to 6 kg of crushed basalt collected from the 2010 Kilauea lava flows is heated to supraliquidus temperatures and poured directly onto the substrate. The evolution of the temperature profile within the lava flow and substrate is recorded as the basalt cools, and the surface temperature distribution is recorded using a Forward Looking Infrared Radiometer (FLIR) video camera. We have been using the experimental data sets to validate a numerical model of substrate heating. If the physics is appropriately formulated, the model will accurately predict both surface and internal temperature distribution as a function of time. A key issue has been incorporation of valid temperature-dependent thermophysical properties, because particulate materials are not well characterized at elevated temperatures. Regolith thermal conductivity in particular exerts a strong control over the depth of penetration of the thermal wave, so its accurate description is essential for a robust model. Comparison of experimental vs. modeled temperature distributions has allowed for refinement of thermophysical properties. The numerical simulations closely approximate the temperature profile within the regolith simulant and confirm an elevated thermal conductivity that varies with temperature. Full validation of the model under a range of conditions will permit its application to the lunar environment to determine conditions favorable for the preservation of ancient solar wind deposits.
Energy Efficient Storage and Transfer of Cryogens
NASA Technical Reports Server (NTRS)
Fesmire, James E.
2013-01-01
Cryogenics is globally linked to energy generation, storage, and usage. Thermal insulation systems research and development is an enabling part of NASA's technology goals for Space Launch and Exploration. New thermal testing methodologies and materials are being transferred to industry for a wide range of commercial applications.
Effect of geometry of film flow passage in superfluid heat pipe on heat transfer
NASA Astrophysics Data System (ADS)
Takada, Suguru; Ishii, Soh; Murakami, Masahide
2014-01-01
A superfluid heat pipe is one of the excellent heat transfer devices below 2.17 K. The overall heat conductance of this type of heat pipe is extremely high below the critical heat flow. In this study, the critical heat flow rates through the heat pipes with different internal structures of superfluid film flow passage were measured. In the case of the heat pipe where straight stainless steel wires were inserted, the critical heat flow was proportional to the wetted perimeter as far as the porosity is high enough. On the other hand, for the heat pipe with inside porous structure composed of glass beads, the critical heat flow doesn't follow the simple linear equation.
Heat transfer by fluids in granulite metamorphism
NASA Technical Reports Server (NTRS)
Morgan, Paul; Ashwal, Lewis D.
1988-01-01
The thermal role of fluids in granulite metamorphism was presented. It was shown that for granulites to be formed in the middle crust, heat must be advected by either magma or by volatile fluids, such as water or CO2. Models of channelized fluid flow indicate that there is little thermal difference between channelized and pervasive fluid flow, for the same total fluid flux, unless the channel spacing is of the same order or greater than the thickness of the layer through which the fluids flow. The volumes of volatile fluids required are very large and are only likely to be found associated with dehydration of a subducting slab, if volatile fluids are the sole heat source for granulite metamorphism.
NASA Astrophysics Data System (ADS)
Huang, S. D.; Li, Z. Q.; Li, Y.
2014-05-01
Generally, for the magnetic resonance coupling wireless power transfer (WPT) system, the transfer efficiency and the transmission distance are contradictory. In order to simultaneously achieve the high transfer efficiency and the far transmission distance, some researchers have successfully proposed to use intermediate coils system to improve efficiency of WPT. In this paper, the expression for the efficiency of intermediate WPT system is obtained by applying coupled-mode theory. System efficiency is improved by optimizing key parameters of system. The intermediate WPT system via magnetic resonance coupling is designed. Simulation and experimental results validate the proposed optimization method.
Characterization of Heat Transfer in Superhydrophobic Microchannels under Different Wetting Modes
NASA Astrophysics Data System (ADS)
Kim, Tae Jin; Hidrovo, Carlos
2013-11-01
Slip flow in microchannels is known to reduce the wall friction and consequently decreases the pumping power to drive the flow. One method to achieve slip flow is by trapping gas bubbles in the microchannel wall that is highly corrugated. While the use of rough walls to induce friction reduction is attractive, many microfluidic applications involve coupling of heat source in the microchip: the gas pockets may affect the heat transfer from the heaters to the microchannel walls. The purpose of this research is to explore the heat transfer efficiency of microchannels with corrugated surfaces heated from the side walls. The microchannel walls are modified to have an array of micro-trenches arranged transverse to the fluid flow along the axial direction, and a constant water pressure source is used to drive the flow and control the air pocket size. Advective heat transfer is then analyzed between the microchannel inlet and outlet using laser induced thermometry technique. Under identical flow rate conditions, it is expected that 1) the advective efficiency is affected by the degree of wetting of the corrugated walls and that 2) the advective heat transfer is lower for superhydrophobic microchannels with gas pockets trapped in the corrugated walls than those filled with water.
NASA Astrophysics Data System (ADS)
Galindo, P.
1984-06-01
Heat transfer coefficients, pressure distributions, and fluid flow patterns on the shell side of shell and tube heat exchangers are discussed. The main focus was to quantify the effect of the size of the baffle window on the heat transfer coefficient, which was measured at each tube in the bundle and at three Reynolds numbers. Pressure drops were obtained by measuring detailed pressure distributions within the exchangers. The flow visualizations provided fluid flow patterns adjacent to the shell wall, to the baffle plates, and at each tube of the array. Performance comparisons among the exchangers were carried out holding the heat transfer surface area fixed together with either the pumping power, the mass flow rate, or the pressure drop. Numerical evaluations of commonly employed design procedures are presented using the present data as a means for rank ordering their validity. Tinker's design method provided the best predictions of the present heat transfer and pressure drop results, which are unaffected by leakage and bypass.
Heat transfer and flow characteristics around a finned-tube bank heat exchanger in fluidized bed
NASA Astrophysics Data System (ADS)
Honda, Ryosuke; Umekawa, Hisashi; Ozawa, Mamoru
2009-06-01
Principal heat transfer mechanisms in a fluidized bed have been classified into three categories, i.e. solid convection, gas convection and radiation. Among these mechanisms, the solid convection is a dominant mechanism in the bubbling fluidized bed. This solid convection is substantially caused by the bubble movement, thus the visualization of the void fraction distribution becomes a very useful method to understand the characteristics of the fluidized-bed heat exchanger. In this study, the heat transfer coefficient and the void fraction around the heat transfer tube with annuler fin were measured. For the quantitative measurement of the void fraction, neutron radiography and image processing technique were employed. Owing to the existence of the annuler fin, the restriction of the particle movements was put. This restriction suppressed the disturbance caused by tubes, and the influence of the tube arrangement on the flow and heat transfer characteristics could be clearly expressed.
Particle shape effect on heat transfer performance in an oscillating heat pipe.
Ji, Yulong; Wilson, Corey; Chen, Hsiu-Hung; Ma, Hongbin
2011-01-01
The effect of alumina nanoparticles on the heat transfer performance of an oscillating heat pipe (OHP) was investigated experimentally. A binary mixture of ethylene glycol (EG) and deionized water (50/50 by volume) was used as the base fluid for the OHP. Four types of nanoparticles with shapes of platelet, blade, cylinder, and brick were studied, respectively. Experimental results show that the alumina nanoparticles added in the OHP significantly affect the heat transfer performance and it depends on the particle shape and volume fraction. When the OHP was charged with EG and cylinder-like alumina nanoparticles, the OHP can achieve the best heat transfer performance among four types of particles investigated herein. In addition, even though previous research found that these alumina nanofluids were not beneficial in laminar or turbulent flow mode, they can enhance the heat transfer performance of an OHP. PMID:21711830
NASA Astrophysics Data System (ADS)
Sheng, Shiqi; Tu, Z. C.
2013-10-01
A unified χ-criterion for heat devices (including heat engines and refrigerators), which is defined as the product of the energy conversion efficiency and the heat absorbed per unit time by the working substance (de Tomás et al 2012 Phys. Rev. E 85 010104), is optimized for tight-coupling heat engines and refrigerators operating between two heat baths at temperatures Tc and Th( > Tc). By taking a new convention on the thermodynamic flux related to the heat transfer between two baths, we find that for a refrigerator tightly and symmetrically coupled with two heat baths, the coefficient of performance (i.e., the energy conversion efficiency of refrigerators) at maximum χ asymptotically approaches \\sqrt{\\varepsilon _C} when the relative temperature difference between two heat baths \\varepsilon _C^{-1}\\equiv (T_h-T_c)/T_c is sufficiently small. Correspondingly, the efficiency at maximum χ (equivalent to maximum power) for a heat engine tightly and symmetrically coupled with two heat baths is proved to be \\eta _C/2+\\eta _C^2/8 up to the second order term of ηC ≡ (Th - Tc)/Th, which reverts to the universal efficiency at maximum power for tight-coupling heat engines operating between two heat baths at small temperature difference in the presence of left-right symmetry (Esposito et al 2009 Phys. Rev. Lett. 102 130602).
Heat transfer evaluation in a plasma core reactor
NASA Technical Reports Server (NTRS)
Smith, D. E.; Smith, T. M.; Stoenescu, M. L.
1976-01-01
Numerical evaluations of heat transfer in a fissioning uranium plasma core reactor cavity, operating with seeded hydrogen propellant, was performed. A two-dimensional analysis is based on an assumed flow pattern and cavity wall heat exchange rate. Various iterative schemes were required by the nature of the radiative field and by the solid seed vaporization. Approximate formulations of the radiative heat flux are generally used, due to the complexity of the solution of a rigorously formulated problem. The present work analyzes the sensitivity of the results with respect to approximations of the radiative field, geometry, seed vaporization coefficients and flow pattern. The results present temperature, heat flux, density and optical depth distributions in the reactor cavity, acceptable simplifying assumptions, and iterative schemes. The present calculations, performed in cartesian and spherical coordinates, are applicable to any most general heat transfer problem.
Probing Heat Transfer in the Nanoscale Using Optomechanical Sensors.
NASA Astrophysics Data System (ADS)
Burg, Brian; Tong, Jonathan; Sambegoro, Poetro; Mavrokefalos, Anastassios; Chen, Gang
2012-02-01
The transition from heat conduction to radiation at extremely small gaps cannot be captured by current theories. Experimentally researchers are only slowly starting to learn how to approach this domain. To this end, the development of a measurement platform based on the picowatt sensitivity of optomechanical sensors will be presented. The bending of a custom designed bimorph cantilever accurately allows the absolute amount of transferred heat to be extracted and temperature to be determined based on the response from thermal inputs. The versatility of the platform permits thermal radiation and conduction measurements, as well as the characterization of material thermal conductivities and absorptivities in nearly identical configurations. Results of this measurement platform for fundamental heat transfer measurements will considerably improve the current understanding of nanoscale energy transport and conversion, as well as lead to advanced design guidelines for energy capture and conversion devices, in particular thermophotovoltaic cells, (solar) thermoelectric generators and waste heat recovery heat exchangers.
Heat transfer measurements and CFD simulations of an impinging jet
NASA Astrophysics Data System (ADS)
Petera, Karel; Dostál, Martin
2016-03-01
Heat transport in impinging jets makes a part of many experimental and numerical studies because some similarities can be identified between a pure impingement jet and industrial processes like, for example, the heat transfer at the bottom of an agitated vessel. In this paper, experimental results based on measuring the response to heat flux oscillations applied to the heat transfer surface are compared with CFD simulations. The computational cost of a LES-based approach is usually too high therefore a comparison with less computationally expensive RANS-based turbulence models is made in this paper and a possible improvement of implementing an anisotropic explicit algebraic model for the turbulent heat flux model is evaluated.
NASA Technical Reports Server (NTRS)
Morris, J. F. (Inventor)
1985-01-01
This invention is directed to transferring heat from an extremely high temperature source to an electrically isolated lower temperature receiver. The invention is particularly concerned with supplying thermal power to a thermionic converter from a nuclear reactor with electric isolation. Heat from a high temperature heat pipe is transferred through a vacuum or a gap filled with electrically nonconducting gas to a cooler heat pipe. If the receiver requires gratr thermal power density, geometries are used with larger heat pipe areas for transmitting and receiving energy than the area for conducting the heat to the thermionic converter. In this way the heat pipe capability for increasing thermal power densities compensates for the comparative low thermal power densities through the electrically nonconducting gap between the two heat pipes.
Electrohydrodynamic convective heat transfer in a square duct.
Grassi, Walter; Testi, Daniele
2009-04-01
Laminar to weakly turbulent forced convection in a square duct heated from the bottom is strengthened by ion injection from an array of high-voltage points opposite the heated strip. Both positive and negative ion injection are activated within the working liquid HFE-7100 (C(4)F(9)OCH(3)), with transiting electrical currents on the order of 0.1 mA. Local temperatures on the heated wall are measured by liquid crystal thermography. The tests are conducted in a Reynolds number range from 510 to 12,100. In any case, heat transfer is dramatically augmented, almost independently from the flow rate. The pressure drop increase caused by the electrohydrodynamically induced flow is also measured. A profitable implementation of the technique in the design of heat sinks and heat exchangers is foreseen; possible benefits are pumping power reduction, size reduction, and heat exchange capability augmentation. PMID:19426338
Heat-stop structure design with high cooling efficiency for large ground-based solar telescope.
Liu, Yangyi; Gu, Naiting; Rao, Changhui; Li, Cheng
2015-07-20
A heat-stop is one of the most important thermal control devices for a large ground-based solar telescope. For controlling the internal seeing effect, the temperature difference between the heat-stop and the ambient environment needs to be reduced, and a heat-stop with high cooling efficiency is required. In this paper, a novel design concept for the heat-stop, in which a multichannel loop cooling system is utilized to obtain higher cooling efficiency, is proposed. To validate the design, we analyze and compare the cooling efficiency for the multichannel and existing single-channel loop cooling system under the same conditions. Comparative results show that the new design obviously enhances the cooling efficiency of the heat-stop, and the novel design based on the multichannel loop cooling system is obviously better than the existing design by increasing the thermal transfer coefficient. PMID:26367826
Stagnation Region Heat Transfer Augmentation at Very High Turbulence Levels
Ames, Forrest; Kingery, Joseph E.
2015-06-17
A database for stagnation region heat transfer has been extended to include heat transfer measurements acquired downstream from a new high intensity turbulence generator. This work was motivated by gas turbine industry heat transfer designers who deal with heat transfer environments with increasing Reynolds numbers and very high turbulence levels. The new mock aero-combustor turbulence generator produces turbulence levels which average 17.4%, which is 37% higher than the older turbulence generator. The increased level of turbulence is caused by the reduced contraction ratio from the liner to the exit. Heat transfer measurements were acquired on two large cylindrical leading edge test surfaces having a four to one range in leading edge diameter (40.64 cm and 10.16 cm). Gandvarapu and Ames [1] previously acquired heat transfer measurements for six turbulence conditions including three grid conditions, two lower turbulence aero-combustor conditions, and a low turbulence condition. The data are documented and tabulated for an eight to one range in Reynolds numbers for each test surface with Reynolds numbers ranging from 62,500 to 500,000 for the large leading edge and 15,625 to 125,000 for the smaller leading edge. The data show augmentation levels of up to 136% in the stagnation region for the large leading edge. This heat transfer rate is an increase over the previous aero-combustor turbulence generator which had augmentation levels up to 110%. Note, the rate of increase in heat transfer augmentation decreases for the large cylindrical leading edge inferring only a limited level of turbulence intensification in the stagnation region. The smaller cylindrical leading edge shows more consistency with earlier stagnation region heat transfer results correlated on the TRL (Turbulence, Reynolds number, Length scale) parameter. The downstream regions of both test surfaces continue to accelerate the flow but at a much lower rate than the leading edge. Bypass transition occurs in these regions providing a useful set of data to ground the prediction of transition onset and length over a wide range of Reynolds numbers and turbulence intensity and scales.
NASA Astrophysics Data System (ADS)
Kuznetsov, V. V.; Kozulin, I. A.; Shamirzaev, A. S.
2012-11-01
Flow boiling in microchannel heat sinks is significantly influenced by capillary forces and by boundary constrains affecting the flow pattern and the heat transfer. In the present work, some characteristics of flow boiling heat transfer are explained using measurements of statistical parameters of gas-liquid two-phase flow in a rectangular microchannel. Such statistical characteristics of the flow as length distributions of elongated bubbles and liquid plugs, and also velocity distribution of the elongated bubbles are determined by dual laser scanning of the horizontal adiabatic nitrogen-water flow in a microchannel with the cross-section of 370×217 μm. Pressure gradients in gas-liquid flow are measured, and the results found well matching the predictions that account for capillary pressure on the gas-liquid interface. Heat transfer coefficients are measured for a horizontal copper microchannel heat sink with refrigerant R-21 as the working fluid. The heat sink contains 21 channels with cross section dimensions 930×335-μm. Distribution of local heat transfer coefficients along the length and the width of the microchannel plate is measured in the range of heat fluxes from 14 to 63 kW/m2; vapour quality was varied within 0.05-0.8, and pressure was about 1.6 bar. For flow boiling of R-21 refrigerant, contributions of nucleate boiling and forced convection are comparable. This allows us to examine the heat transfer mechanism for these complex conditions.
Effects of Freestream Turbulence on Turbine Blade Heat Transfer
NASA Technical Reports Server (NTRS)
Boyle, Robert J.; Giel, Paul W.; Ames, Forrest E.
2004-01-01
Experiments have shown that moderate turbulence levels can nearly double turbine blade stagnation region heat transfer. Data have also shown that heat transfer is strongly affected by the scale of turbulence as well as its level. In addition to the stagnation region, turbulence is often seen to increase pressure surface heat transfer. This is especially evident at low to moderate Reynolds numbers. Vane and rotor stagnation region, and vane pressure surface heat transfer augmentation is often seen in a pre-transition environment. Accurate predictions of transition and relaminarization are critical to accurately predicting blade surface heat transfer. An approach is described which incorporates the effects of both turbulence level and scale into a CFD analysis. The model is derived from experimental data for cylindrical and elliptical leadng edges. Results using this model are compared to experimental data for both vane and rotor geometries. The comparisons are made to illustrate that using a model which includes the effects of turbulence length scale improves agreement with data, and to illustrate where improvements in the modeling are needed.
Gravity and Heater Size Effects on Pool Boiling Heat Transfer
NASA Technical Reports Server (NTRS)
Kim, Jungho; Raj, Rishi
2014-01-01
The current work is based on observations of boiling heat transfer over a continuous range of gravity levels between 0g to 1.8g and varying heater sizes with a fluorinert as the test liquid (FC-72/n-perfluorohexane). Variable gravity pool boiling heat transfer measurements over a wide range of gravity levels were made during parabolic flight campaigns as well as onboard the International Space Station. For large heaters and-or higher gravity conditions, buoyancy dominated boiling and heat transfer results were heater size independent. The power law coefficient for gravity in the heat transfer equation was found to be a function of wall temperature under these conditions. Under low gravity conditions and-or for smaller heaters, surface tension forces dominated and heat transfer results were heater size dependent. A pool boiling regime map differentiating buoyancy and surface tension dominated regimes was developed along with a unified framework that allowed for scaling of pool boiling over a wide range of gravity levels and heater sizes. The scaling laws developed in this study are expected to allow performance quantification of phase change based technologies under variable gravity environments eventually leading to their implementation in space based applications.
Heat transfer in rotating serpentine passages with smooth walls
NASA Technical Reports Server (NTRS)
Wagner, J. H.; Johnson, B. V.; Kopper, F. C.
1990-01-01
Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large scale, multi-pass, smooth-wall heat transfer model with both radially inward and outward flow. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages (coolant-to-wall temperature ratio, Rossby number, Reynolds number and radius-to-passage hydraulic diameter ratio). These four parameters were varied over ranges which are typical of advanced gas turbine engine operating conditions. It was found that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs and that the effect of rotation on the heat transfer coefficients was markedly different depending on the flow direction. Local heat transfer coefficients were found to decrease by as much as 60 percent and increase by 250 percent from no rotation levels. Comparisons with a pioneering stationary vertical tube buoyancy experiment showed reasonably good agreement. Correlation of the data is achieved employing dimensionless parameters derived from the governing flow equations.
Effectiveness and Fin Efficiency of Plate-fin and Tube Heat Exchangers
NASA Astrophysics Data System (ADS)
Seshimo, Yu
This paper presents a method for the determination of effectiveness on plate-fin and tube heat exchangers as a function of the parameters, viz. the thermal capacity ratio, the number of transfer unit and the flow arrangement. The analytical model of the heat exchanger which is adopted that of a multi-pass crossflow heat exchanger with one fluid mixed and another unmixed. For three kinds of flow arrangements of plate-fin and tube heat exchangers, equations on the effectiveness were obtained and the experimental verification of these equations was also performed. In addition, this paper is concerned with method which obtains the fin efficiency of the plate-fin and tube heat exchangers. It is usual practice to evaluate the fin efficiency by assuming that the uniform heat transfer and other suppositions. In this paper, a more realistic determination of fin efficiency is reported, which take into account the heat transfer distribution over the fin surface. It was confirmed that the results of fin efficiency by usual manner were almost equal to that of the realistic estimation in this study.
Heat-transfer and flow characteristics of perforated-plate heat exchangers with crosscut fins
Isogami, Hisashi; Saho, Norihide; Kunugi, Yoshifumi; Yokoi, Kazuaki; Yoshida, Chikashi
1995-12-31
A new type of perforated-plate heat exchanger with crosscut fins is proposed. The heat exchanger is made up of perforated plates separated by spacers. The perforated plates have crosscut fins that are oriented 90 degrees to the axis of flow, and the angle between the fins in consecutive perforated plates can be varied. Experiments were performed to investigate the heat transfer and the pressure loss in the proposed heat exchanger. The following results were obtained. (1) Calculated overall heat-transfer coefficients are almost the same as measured heat-transfer coefficients for Reynolds numbers above 60. (2) The coefficient of pressure loss is constant for Reynolds numbers above 60. (3) The spacer thickness and the orientation angle of alternate perforated plates don`t influence the coefficient of pressure loss.
Generator-absorber-heat exchange heat transfer apparatus and method and use thereof in a heat pump
Phillips, B.A.; Zawacki, T.S.
1998-07-21
Numerous embodiments and related methods for generator-absorber heat exchange (GAX) are disclosed, particularly for absorption heat pump systems. Such embodiments and related methods use, as the heat transfer medium, the working fluid of the absorption system taken from the generator at a location where the working fluid has a rich liquor concentration. 5 figs.
Generator-absorber-heat exchange heat transfer apparatus and method and use thereof in a heat pump
Phillips, Benjamin A.; Zawacki, Thomas S.
1998-07-21
Numerous embodiments and related methods for generator-absorber heat exchange (GAX) are disclosed, particularly for absorption heat pump systems. Such embodiments and related methods use, as the heat transfer medium, the working fluid of the absorption system taken from the generator at a location where the working fluid has a rich liquor concentration.
Numerical Analysis of Heat Transfer in Fire-Protective Coatings Deformable upon Heating
NASA Astrophysics Data System (ADS)
Rudzinsky, V. P.; Garashchenko, A. N.
2016-02-01
Numerical studies of heat transfer in fire-protective coatings deformable (intumescent) upon heating have been conducted. The optimum combination of the computation-scheme parameters providing stability, convergence and satisfactory accuracy of solutions has been determined. An effect of basic characteristics of materials in real range of their change that made it possible to estimate the degree of influence of properties on the fire-protective efficiency of coatings and the level of warm-up (flame resistance) of structures to be protected with them has been studied. The possibility of using developed models and techniques to estimate and provide the required level of fire safety of polymer-based materials (in particular, elastomers and structures and products on their basis) is considered. The results of estimating the mass rate of evolving gaseous thermal-decomposition products that determine, in a considerable extent, the material combustibility have been presented. The numerical analysis results have demonstrated the potentiality of reducing the combustibility of such materials and increasing limits of their fire resistance at the expense of organizing the intumescence of a material upon heating by means of modification of their initial formulations as well as with the aid of an additional layer made of the intumescent coating compatible with an elastomer.
Heat Transfer Study for HTS Power Transfer Cables
NASA Technical Reports Server (NTRS)
Augustynowicz, S.; Fesmire, J.
2002-01-01
Thermal losses are a key factor in the successful application of high temperature superconducting (HTS) power cables. Existing concepts and prototypes rely on the use of multilayer insulation (MLI) systems that are subject to large variations in actual performance. The small space available for the thermal insulation materials makes the application even more difficult because of bending considerations, mechanical loading, and the arrangement between the inner and outer piping. Each of these mechanical variables affects the heat leak rate. These factors of bending and spacing are examined in this study. Furthermore, a maintenance-free insulation system (high vacuum level for 20 years or longer) is a practical requirement. A thermal insulation system simulating a section of a flexible FITS power cable was constructed for test and evaluation on a research cryostat. This paper gives experimental data for the comparison of ideal MLI, MLI on rigid piping, and MLI between flexible piping. A section of insulated flexible piping was tested under cryogenic vacuum conditions including simulated bending and spacers.
Study of the average heat transfer coefficient at different distances between wind tunnel models
NASA Astrophysics Data System (ADS)
Gnyrya, A.; Korobkov, S.; Mokshin, D.; Koshin, A.
2015-01-01
The paper presents investigations of physical and climatic factors with regard to design and process variables having effect on heat transfer in the building model system at different distances between them in the airflow direction. The aim of this work is to improve energy efficiency of exterior walls of buildings. A method of physical simulation was used in experiments. Experimental results on the average values of the heat transfer coefficient in the building model system are presented herein. A series of experiments was carried out on a specific aerodynamic test bench including a subsonic wind tunnel, heat models and devices for giving thermal boundary conditions, transducers, and the record system equipment. The paper contains diagrams of the average heat transfer distribution at fixed Reynolds number and the airflow angle of attack; the average values of the heat transfer coefficient for each face and wind tunnel models as a whole at maximum, medium, and large distances between them. Intensification of the average heat transfer was observed on the downstream model faces depending on the distance between models.
Effects of Nonequilibrium at Edge of Boundary Layer on Convective Heat Transfer to a Blunt Body
NASA Technical Reports Server (NTRS)
Goekcen, Tahir; Edwards, Thomas A. (Technical Monitor)
1996-01-01
This investigation is a continuation of a previous study on nonequilibrium convective heat transfer to a blunt body. In the previous study, for relatively high Reynolds number flows, it was found that: nonequilibrium convective heat transfer to a blunt body is not strongly dependent on freestream parameters, provided that the thermochemical equilibrium is reached at the edge of boundary layer; and successful testing of convective heat transfer in an arc-jet environment is possible by duplicating the surface pressure and total enthalpy. The nonequilibrium convective heat transfer computations are validated against the results of Fay and Riddell/Goulard theory. Present work investigates low Reynolds number conditions which are typical in an actual arc-jet flow environment. One expects that there will be departures from the Fay and Riddell/Goulard result since certain assumptions of the classical theory are not satisfied. These departures are of interest because the Fay and Riddell/Goulard formulas are extensively used in arc-jet testing (e.g., to determine the enthalpy of the flow and the catalytic efficiency of heat shield materials). For practical sizes of test materials, density of the test flow (and Reynolds number) in an arc-jet is such that thermochemical equilibrium may not be reached at the edge of boundary layer. For blunt body flows of nitrogen and air, computations will be presented to show the effects of thermochemical nonequilibrium at the boundary layer edge on nonequilibrium heat transfer.
Heat transfer enhancement by fins in the microscale regime
Chou, F.C.; Lukes, J.R.; Tien, C.L.
1999-11-01
The current literature contains many studies of microchannel and micro-pin-fin heat exchangers, but none of them consider the size effect on the thermal conductivity of channel and fin walls. The present study analyzes the effect of size (i.e., the microscale effect) on the microfin performance, particularly in the cryogenic regime where the microscale effect is often appreciable. The size effect reduces the thermal conductivity of microchannel and microfin walls and thus reduces the heat transfer rate. For this reason, heat transfer enhancement by microfins becomes even more important than for macroscale fins. The need for better understanding of heat transfer enhancement by microfins motivates the current study, which resolves three basic issues. First, it is found that the heat flow choking can occur even in the case of simple plate fins or pin fins in the microscale regime, although choking is usually caused by the accommodation of a cluster of fins at the fin tip. Second, this paper shows that the use of micro-plate-fin arrays yields a higher heat transfer enhancement ratio than the use of the micro-pin-fin arrays due to the stronger reduction of thermal conductivity in micro-pin-fins. The third issue is how the size effect influences the fin thickness optimization. For convenience in design applications, an equation for the optimum fin thickness is established which generalizes the case without the size effect as first reported by Tuckerman and Pease.
On heat transfer at microscale with implications for microactuator design
NASA Astrophysics Data System (ADS)
Ozsun, Ozgur; Alaca, B. Erdem; Yalcinkaya, Arda D.; Yilmaz, Mehmet; Zervas, Michalis; Leblebici, Yusuf
2009-04-01
The dominance of conduction and the negligible effect of gravity, and hence free convection, are verified in the case of microscale heat sources surrounded by air at atmospheric pressure. A list of temperature-dependent heat transfer coefficients is provided. In contrast to previous approaches based on free convection, supplied coefficients converge with increasing temperature. Instead of creating a new external function for the definition of boundary conditions via conductive heat transfer, convective thin film coefficients already embedded in commercial finite element software are utilized under a constant heat flux condition. This facilitates direct implementation of coefficients, i.e. the list supplied in this work can directly be plugged into commercial software. Finally, the following four-step methodology is proposed for modeling: (i) determination of the thermal time constant of a specific microactuator, (ii) determination of the boundary layer size corresponding to this time constant, (iii) extraction of the appropriate heat transfer coefficients from a list provided and (iv) application of these coefficients as boundary conditions in thermomechanical finite element simulations. An experimental procedure is established for the determination of the thermal time constant, the first step of the proposed methodology. Based on conduction, the proposed method provides a physically sound solution to heat transfer issues encountered in the modeling of thermal microactuators.
Heat transfer in rocket engine combustion chambers and nozzles
NASA Technical Reports Server (NTRS)
Anderson, P. G.; Chen, Y. S.; Farmer, R. C.
1992-01-01
The complexities of liquid rocket engine heat transfer which involve the injector faceplate and regeneratively and film cooled walls are being investigated by computational analysis. A conjugate heat transfer analysis will be used to describe localized heating phenomena associated with particular injector configurations and coolant channels and film coolant dumps. These components are being analyzed, and the analysis verified with appropriate test data. Finally, the component analysis will be synthesized into an overall flowfield/heat transfer model. The FDNS code is being used to make the component analyses. Particular attention is being given to the representation of the thermodynamic properties of the fluid streams and to the method of combining the detailed models to represent overall heating. Unit flow models of specific coaxial injector elements have been developed and will be described. Film cooling simulations of film coolant flows typical of the subscale Space Transportation Main Engine (STME) being experimentally studied by Pratt and Whitney have been made, and these results will be presented. Other film coolant experiments have also been simulated to verify the CFD heat transfer model being developed. The status of the study and its relevance as a new design tool are covered. Information is given in viewgraph form.
Simulation of a High Efficiency Multi-bed Adsorption Heat Pump
TeGrotenhuis, Ward E.; Humble, Paul H.; Sweeney, J. B.
2012-05-01
Attaining high energy efficiency with adsorption heat pumps is challenging due to thermodynamic losses that occur when the sorbent beds are thermally cycled without effective heat recuperation. The multi-bed concept described here effectively transfers heat from beds being cooled to beds being heated, which enables high efficiency in thermally driven heat pumps. A simplified lumped-parameter model and detailed finite element analysis are used to simulate the performance of an ammonia-carbon sorption compressor, which is used to project the overall heat pump coefficient of performance. The effects of bed geometry and number of beds on system performance are explored, and the majority of the performance benefit is obtained with four beds. Results indicate that a COP of 1.24 based on heat input is feasible at AHRI standard test conditions for residential HVAC equipment. When compared on a basis of primary energy input, performance equivalent to SEER 13 or 14 are theoretically attainable with this system.
Implant Fixture Heat Transfer During Abutment Preparation.
Aleisa, Khalil; Alkeraidis, Abdullah; Al-Dwairi, Ziad Nawaf; Altahawi, Hamdi; Lynch, Edward
2015-06-01
The purpose of the study was to evaluate the effect of water flow rate on the heat transmission in implants during abutment preparation using a diamond bur in a high-speed dental turbine. Titanium-alloy abutments (n = 32) were connected to a titanium-alloy implant embedded in an acrylic resin within a water bath at a controlled temperature of 37°C. The specimens were equally distributed into 2 groups (16 each) according to the water flow rate used during the preparation phase. Group 1 had a water flow rate of 24 mL/min, and group 2 had a water flow rate of 40 mL/min. Each abutment was prepared in the axial plane for 1 minute and in the occlusal plane for 1 minute with a coarse tapered diamond bur using a high-speed dental handpiece. Thermocouples embedded at the cervix of the implant surface were used to record the temperature of heat transmission from the abutment preparation. Heat generation was measured at 3 distinct times (immediately and 30 seconds and 60 seconds after the end of preparation). Statistical analyses were carried out using 2-way analysis of variance and the Student t test. Water flow rates (24 mL vs 40 mL) and time interval had no statistically significant effect on the implant's temperature change during the abutment preparation stage (P = .431 and P = .064, respectively). Increasing the water flow rate from 24 to 40 mL/min had no influence on the temperature of the implant fixture recorded during preparation of the abutment. PMID:23713452
Heat transfer and core neutronics considerations of the heat pipe cooled thermionic reactor
NASA Technical Reports Server (NTRS)
Determan, W. R.; Lewis, Brian
1991-01-01
The authors summarize the results of detailed neutronic and thermal-hydraulic evaluations of the heat pipe cooled thermionic (HPTI) reactor design, identify its key design attributes, and quantify its performance characteristics. The HPTI core uses modular, liquid-metal core heat transfer assemblies to replace the liquid-metal heat transport loop employed by in-core thermionic reactor designs of the past. The nuclear fuel, power conversion, heat transport, and heat rejection functions are all combined into a single modular unit. The reactor/converter assembly uses UN fuel pins to obtain a critical core configuration with in-core safety rods and reflector controls added to complete the subassembly. By thermally bonding the core heat transfer assemblies during the reactor core is coupled neutronically, thermally, and electrically into a modular assembly of individual power sources with cross-tied architecture. A forward-facing heat pipe radiator assembly extends from the reactor head in the shape of a frustum of a cone on the opposite side of the power system from the payload. Important virtues of the concept are the absence of any single-point failures and the ability of the core to effectively transfer the TFE waste heat load laterally to other in-core heat transfer assemblies in the event of multiple failures in either in-core and radiator heat pipes.
Constructal tree networks for heat transfer
NASA Astrophysics Data System (ADS)
Ledezma, G. A.; Bejan, A.; Errera, M. R.
1997-07-01
This paper addresses the fundamental problem of how to connect a heat generating volume to a point heat sink by using a finite amount of high-conductivity material that can be distributed through the volume. The problem is one of optimizing the access (or minimizing the thermal resistance) between a finite-size volume and one point. The solution is constructed by covering the volume with a sequence of building blocks, which proceeds toward larger sizes (assemblies), hence, the "constructal" name for this approach. Optimized numerically at each stage are geometric features such as the overall shape of the building block, its number of constituents, and the internal distribution of high-conductivity inserts. It is shown that in the optimal design, the high-conductivity material has a distribution with the shape of a tree. Every aspect of the tree architecture is deterministic: the shapes of the largest assembly and all its constituents, the number of branches at each level of assembly, the relative position of building blocks in each assembly, and the relative thicknesses of successive branches. The finer, innermost details of the tree architecture (e.g., the branching angle) have a negligible effect on the overall thermal resistance. The main conclusion is that the structure, working mechanism, and minimal resistance of the tree network can be obtained deterministically, and that the constrained optimization of access routes accounts for the macroscopic structure in nature.
Constructal tree networks for heat transfer
Ledezma, G.A.; Bejan, A.; Errera, M.R.
1997-07-01
This paper addresses the fundamental problem of how to connect a heat generating volume to a point heat sink by using a finite amount of high-conductivity material that can be distributed through the volume. The problem is one of optimizing the access (or minimizing the thermal resistance) between a finite-size volume and one point. The solution is constructed by covering the volume with a sequence of building blocks, which proceeds toward larger sizes (assemblies), hence, the {open_quotes}constructal{close_quotes} name for this approach. Optimized numerically at each stage are geometric features such as the overall shape of the building block, its number of constituents, and the internal distribution of high-conductivity inserts. It is shown that in the optimal design, the high-conductivity material has a distribution with the shape of a tree. Every aspect of the tree architecture is deterministic: the shapes of the largest assembly and all its constituents, the number of branches at each level of assembly, the relative position of building blocks in each assembly, and the relative thicknesses of successive branches. The finer, innermost details of the tree architecture (e.g., the branching angle) have a negligible effect on the overall thermal resistance. The main conclusion is that the structure, working mechanism, and minimal resistance of the tree network can be obtained deterministically, and that the constrained optimization of access routes accounts for the macroscopic structure in nature. {copyright} {ital 1997 American Institute of Physics.}