Accepted Manuscripts

Aravindakshan Pillai, N Sreenivas, K Krishnaraj, Vinay Unnikrishnan and M Ajith
J. Heat Transfer   doi: 10.1115/1.4039584
In one of the launch vehicles of ISRO, there are two solid strap-ons attached to the core liquid engine. During the ascent phase, the external nozzle divergent of the strap-ons experiences heating due to radiation from the strap-ons and as well as convective heating from the impingement of plumes from the core engine. Hence the nozzle divergent of the strap-on beyond compliance ring is thermally protected by a coating of PC10 insulation applied over carbon/ epoxy structural backup. Though the system worked satisfactorily, application of PC10 had increased the inert weight of each nozzle by 165 kg. Building up entire thickness of PC10 (about 14 mm) was by brushing took almost 22 days of laborious operation for each nozzle. To reduce the inert weight as well as the time of application, precast phenolic based cork sheets (CkP) having lower density than PC10 was selected, as a replacement to PC10. As part of evaluating the thermal performance of the CkP material, specimen level tests with different configurations were carried out in 250 kW Plasma Jet Facility of VSSC wherein both the heat flux and shear stress as expected in flight were simulated simultaneously. At the end of the test program, CkP was found to be superior to PC10 for external TPS. This paper highlights details of the qualification tests carried out for clearing the cork phenolic system for use in the future launches.
TOPICS: Cork (Materials), Plasma jets, Performance evaluation, Nozzles, Heating, Engines, Weight (Mass), Coating processes, Coatings, Epoxy resins, Radiation (Physics), Density, Epoxy adhesives, Plumes (Fluid dynamics), Heat flux, Shear stress, Flight, Vehicles, Insulation, Carbon
Francisco Valentin, Narbeh Artoun, Masahiro Kawaji and Donald McEligot
J. Heat Transfer   doi: 10.1115/1.4039585
High pressure/high temperature forced and mixed convection experiments have been performed with helium and nitrogen at temperatures and pressures up to 893K and 64 bar, respectively. The test section had a 16.8-mm ID flow channel in a 108-mm OD graphite column. Flow regimes included turbulent, transitional and laminar flows with the inlet Reynolds numbers ranging from 1,500 to 15,000. Due to strong heating, the local Reynolds number decreased by up to 50% over the 2.7-m test section. In addition, heat transfer degradation and flow laminarization caused by intense heating led to Nusselt numbers 20~50% lower than the values given by the modified Dittus-Boelter and modified Gnielinski correlations. Flow laminarization criteria were considered based on a dimensionless acceleration parameter (Kv) and buoyancy parameter (Bo*). Upward turbulent flows displayed higher wall temperatures than downward flows, due to the impact of flow laminarization which is not expected to affect buoyancy-opposed flows. Laminar Reynolds number flows presented an opposite behavior due to the enhancement of heat transfer for buoyancy-aided flows. At low Reynolds numbers, downward flows displayed higher and lower wall temperatures in the upstream and downstream regions, respectively, than the upward flow cases. In the entrance region of downward flows, convection heat transfer was reduced due to buoyancy leading to higher wall temperatures, while in the downstream region, buoyancy-induced mixing caused higher convection heat transfer and lower wall temperatures.
TOPICS: Flow (Dynamics), High pressure (Physics), Graphite, High temperature, Buoyancy, Reynolds number, Wall temperature, Heating, Heat transfer, Turbulence, Convection, Mixed convection, Entrance region, Laminar flow, Temperature, Helium, Nitrogen
Technical Brief  
Debkumar Ghosh and Abhijit Lahiri
J. Heat Transfer   doi: 10.1115/1.4039554
A vector-matrix differential equation is formulated using normal mode analysis from the governing equations of a three dimensional anisotropic half space in presence of heat source and gravity. The corresponding solution is obtained with the help of eigenvalue approach. Numerical computations for displacement, thermal strain and stress component, temperature distribution are evaluated and presented graphically.
TOPICS: Rotation, Gravity (Force), Heat, Space, Differential equations, Computation, Displacement, Eigenvalues, Temperature distribution, Stress, Anisotropy
James Grisham, Ashkan Akbariyeh, Weiya Jin, Dr. Brian H. Dennis and Bo P. Wang
J. Heat Transfer   doi: 10.1115/1.4039541
Sensitivity information is often of interest in engineering applications (e.g., gradient-based optimization). Heat transfer problems frequently involve complicated geometries for which exact solutions cannot be easily derived. As such, it is common to resort to numerical solution methods such as the finite element method. The semi-analytic complex variable method is an accurate and efficient approach to computing sensitivities within a finite element framework. The method is introduced and a derivation is provided along with a detailed description of the algorithm which requires very minor changes to the analysis code. Three benchmark problems in steady-state heat transfer are studied including a nonlinear problem, an inverse shape determination problem and a reliability analysis problem. It is shown that the semi-analytic complex variable method is superior to the other methods considered in terms of computation time and sensitivity to perturbation size.
TOPICS: Heat transfer, Event history analysis, Finite element methods, Algorithms, Engineering systems and industry applications, Finite element analysis, Optimization, Computation, Shapes, Steady state
Jinlin Song, Lu Lu, Dr. Qiang Cheng and Luo Zixue
J. Heat Transfer   doi: 10.1115/1.4039542
We investigate the near-field (NF) radiative heat transfer of the three-body system consisting of anisotropic magneto-dielectric hyperbolic metamaterials (AMDHMs), which can support coupled surface phonon polaritons and hyperbolic modes for both p and s polarizations. We numerically demonstrate that the NF heat transfer between two AMDHMs bodies can be further enhanced by inserting an AMDHMs slab. Due to the loss in AMDHMs, there exists an optimum thickness of the intermediate slab to maximize the NF heat flux flowing to the receiver for a fixed gap distance. Results obtained from this work will facilitate investigations of the NF heat transfer involving magnetic hyperbolic metamaterials.
TOPICS: Heat transfer, Anisotropy, Metamaterials, Slabs, Heat flux, Phonons, Polaritons, Radiative heat transfer
Özgür Ekici
J. Heat Transfer   doi: 10.1115/1.4039490
Mixed convection heat transfer of Al2O3 nanofluid in a lid-driven square cavity with differentially heated vertical walls is studied numerically with lattice Boltzmann method. In order to understand the reasons for the conflicting results on heat transfer enhancement in cavity problems; formulation of non-dimensional properties and modelling thermophysical properties, in accordance with the relative effects of natural and forced convection flows are examined. In addition to gain more insight into the physics, one of the goals of the study is to identify the reasons of existing contradictory findings, therefore a single phase formulation is adopted as has been the case in the majority of related literature to date. To isolate the effects of thermophysical properties on the results and to maintain the same natural and forced convection effects, all non-dimensional parameters are defined using the corresponding thermophysical properties of the fluid under examination. Two different effective thermal conductivity and viscosity models are tested for a range of Reynolds and Rayleigh numbers to investigate their effects on the nanofluid behavior. Depending on the effective viscosity model, an increase or decrease is obtained in the average Nusselt number. It is also illustrated that the relative magnitudes of effective thermal conductivity values for different models do not translate into the heat transfer enhancement due to convective effects. Moreover, it is shown that thermal behavior of nanofluid approaches to the one of base fluid's as the buoyancy driven flow gets stronger, which is independent of the employed effective property models.
TOPICS: Heat transfer, Simulation, Mixed convection, Cavities, Nanofluids, Lattice Boltzmann methods, Thermal conductivity, Viscosity, Flow (Dynamics), Buoyancy, Fluids, Physics, Rayleigh number, Modeling
Ignacio Mayo, Bogdan C. Cernat, Marco Virgilio, Alessio Pappa and Tony Arts
J. Heat Transfer   doi: 10.1115/1.4039419
The detailed flow field and heat transfer were experimentally investigated in a channel with a circular cross section and equipped with a helical rib of low blockage ratio. Stereoscopic Particle Image Velocimetry (S-PIV) was applied in order to measure the three components of the mean and turbulent velocities in the symmetry plane of the channel. Additionally, steady-state Liquid Crystal Thermography (LCT) and Infrared Thermography (IRT) were employed in order to study the convective heat transfer coefficient on the wall. Measurements were carried out more than six pitches downstream of the rib origin, presenting periodic velocity and heat transfer fields from this location on. The resulting velocity and heat transfer fields show similarities with those present in channels of plane walls, such as low momentum and heat transfer areas upstream and downstream of the obstacle, and high kinetic energy and heat transfer a few rib heights downstream of the obstacle. On the other hand, the shape of the rib induces a swirling motion with the same sense as the rib. The azimuthal mean velocity is negligible in the core of the pipe, but it increases considerably close to the wall.
TOPICS: Flow (Dynamics), Heat transfer, Cooling, Thermography, Convection, Pipes, Shapes, Steady state, Swirling flow, Liquid crystals, Particulate matter, Turbulence, Kinetic energy, Momentum
Ronen Haymes and Erez Gal
J. Heat Transfer   doi: 10.1115/1.4039420
This paper describes a thermal homogenization approach to the application of a multi-scale formulation for heat conduction with radiation problems in a porous material. The suggested formulation enables to evaluate the effective macroscopic thermal conductivity, based on the microscopic properties such as porosity, and can also provide the microscopic radiosity heat flux, based on the macroscopic temperature gradient field. This is done by scaling up and down between the microscopic and macroscopic models according to the suggested methodology. The proposed methodology involves a new iterative upscaling procedure, which uses heat conduction at macroscopic problem and heat transfer by conduction and radiation at microscopic problem. This reduces the required computational time, while maintaining the required level of accuracy. The suggested multi-scale formulation has been verified by comparing its results with reference finite element solutions of porous (filled with air) materials examples, the results shows excellent agreement (up to 5% discrepancy) with reference solutions. The efficiency of the suggested formulation was, demonstrated by solving a full scale engineering transient problem.
TOPICS: Porous materials, Radiation (Physics), Heat conduction, Transients (Dynamics), Thermal conductivity, Finite element analysis, Porosity, Heat flux, Temperature gradient, Heat transfer
Hyun Jin Kim, Leon Liebenberg and Anthony M Jacobi
J. Heat Transfer   doi: 10.1115/1.4039397
Heat transfer and pressure drop characteristics of R-134a boiling in a chevron-patterned brazed plate heat exchanger (BPHE) are studied experimentally. With corrugated BPHE channels having hydraulic diameter of 3.4 mm and low refrigerant mass flux, boiling near the micro-macroscale transition is speculated. Heat exchanger performance is characterized with varying mass flux, saturation pressure, heat flux, and vapor quality. The two-phase refrigerant heat transfer coefficient increases with heat flux as often observed during nucleate boiling. It also weakly increases with saturation pressure and the associated lower latent heat during convective boiling; heat transfer is improved by the decreased liquid film thickness surrounding confined bubbles inside the narrow BPHE channels, which is the main characteristic of microscale boiling. As often observed in macroscale boiling, the inertial forces of the liquid and vapor phases cause an unsteady annular film, leading to premature partial dryout. The onset of dryout is accelerated at the lower saturation pressure, due to increased surface tension, another microscale-like characteristic. Higher surface tension retains liquid in sharp corners of the corrugated channel, leaving lateral surface areas of the wall dry. Two-phase pressure drop increases with mass flux and vapor quality, but with decreasing saturation pressure. Dryout decreases the friction factor due to the much lower viscosity of the gas phase in contact with the wall. Several semi-empirical transition criteria and correlations buttress the current analyses that the thermal-fluidic characteristics peculiar to BPHEs might be due to macro-microscale transition in boiling.
TOPICS: Boiling, Heat exchangers, Pressure, Microscale devices, Vapors, Surface tension, Pressure drop, Refrigerants, Heat flux, Heat transfer, Heat transfer coefficients, Nucleate boiling, Friction, Viscosity, Bubbles, Corners (Structural elements), Latent heat, Liquid films
Andallib Tariq, Naveen Sharma and Manish Mishra
J. Heat Transfer   doi: 10.1115/1.4039398
The present work is an experimental study of detailed aerothermal characteristics inside a duct carrying array of solid, and permeable pentagonal ribs with a parallel and inclined slit, mounted on the bottom wall. The rib height-to-hydraulic diameter ratio, the rib pitch-to-height ratio, and the open area ratio fixed during experiments are 0.125, 12, and 25%, respectively. The heat transfer coefficient distribution is mapped by using transient Liquid Crystal Thermography (LCT), while detailed flow measurements were made by Particle Image Velocimetry (PIV). The primary focus of the study is towards assessing the influence of inter-rib region flow characteristics on the local heat transfer fields. The heat transfer and friction factor measurements were evaluated along with thermo-hydraulic performances at different Reynolds numbers, i.e. 26160, 42500, and 58850. Performance indexes show that the pentagonal ribs with inclined-slit are superior to other configurations from both perspective. Aerothermal features within inter-rib region were elucidated by analyzing the time-averaged streamlines, mean velocities, fluctuation statistics, vorticity, turbulent kinetic energy (TKE) budget terms, and local and spanwise-averaged Nusselt number as well as augmentation Nusselt numbers. Critical flow structures and coherent structures were identified, which illustrates about different flow dynamic processes. The flow emanating out of the inclined-slit pentagonal rib, significantly affects the magnitude of streamwise velocity, fluctuation statistics, vorticity, and TKE budget terms at the downstream corner; whereas the dissipation term of TKE budget exclusively correlates well with the surface heat transfer distribution.
TOPICS: Flow (Dynamics), Friction, Heat transfer, Liquid crystals, Particulate matter, Turbulence, Kinetic energy, Reynolds number, Thermography, Energy dissipation, Transients (Dynamics), Corners (Structural elements), Vorticity, Ducts, Flow measurement, Heat transfer coefficients, Statistics as topic
Sumanta Chaudhuri and P.K. Das
J. Heat Transfer   doi: 10.1115/1.4039352
Hydro-dynamically and thermally fully developed flow of a Sisko fluid through a cylindrical tube has been investigated considering the effect of viscous dissipation. The effect of the convective term in the energy equation has been taken into account which was neglected in the earlier studies for Sisko fluid flow. This convective term can significantly affect the temperature distribution if the radius of the tube is relatively large. The equations governing the flow and heat transfer are solved by the least square method (LSM) for both heating and cooling of the fluid. The results of the LSM solution are compared with that of the closed form analytical solution of the Newtonian fluid flow case and are found to match exactly. The results indicate that Nusselt number decreases with the increase in Brinkman number, and increases with the increase in the Sisko fluid parameter for the heating of the fluid. In case of cooling, Nusselt number increases with the increase in the Brinkman number asymptotically to a very large value, change its sign and then decreases with the increase in Brinkman number. With the increase in the non-Newtonian index, Nusselt number is observed to increase.
TOPICS: Fluids, Energy dissipation, Flow (Dynamics), Heat transfer, Cooling, Fluid dynamics, Heating and cooling, Temperature distribution, Heating
Patricio F. Mendez, Yi Lu and Ying Wang
J. Heat Transfer   doi: 10.1115/1.4039353
This paper presents a systematic scaling analysis of the point heat source in steady state on a semi-infinite solid. It is shown that all characteristic values related to an isotherm can be reduced to a dimensionless expression dependent only on the Rykalin number (Ry). The maximum width of an isotherm and its location are determined for the first time in explicit form for the whole range of Ry, with an error below 2% from the exact solution. The methodology employed involves normalization, dimensional analysis, asymptotic analysis, and blending techniques.The expressions developed can be calculated using a handheld calculator or a basic spreadsheet to estimate, for example, the width of a weld or the size of zone affected by the heat source in a number of processes. These expressions are also useful to verify numerical models.
TOPICS: Heat, Steady state, Computer simulation, Dimensional analysis, Errors
Xing Huang, Hong Qi, Xiao-luo Zhang, Yatao Ren, LiMing Ruan and He-Ping Tan
J. Heat Transfer   doi: 10.1115/1.4039305
Combined with the light-field imaging technique, the Landweber method is applied to the reconstruction of three-dimensional temperature distribution in absorbing media theoretically and experimentally. In the theoretical research, simulated exit radiation intensities on the boundary of absorbing media according to the computing model of light field are employed as inputs for inverse analysis. Compared with the commonly used iterative methods, i.e., the least-square QR decomposition method and algebraic reconstruction technique, the Landweber method can produce reconstruction results with better quality and less computational time. Based on the numerical study, an experimental investigation is conducted to validate the suitability of the proposed method. The temperature distribution of the ethylene diffusion flame is reconstructed by using the Landweber method from the flame image captured by a light-field camera. Good agreement was found between the reconstructed temperature distribution and the measured temperature data obtained by a thermocouple. All the experimental results demonstrate that the temperature distribution of ethylene flame can be reconstructed reasonably by using the Landweber method combined with the light-field imaging technique, which is proven to have potential for use in non-contract measurement of temperature distribution in practical engineering applications.
TOPICS: Temperature, Imaging, Temperature distribution, Flames, Iterative methods, Thermocouples, Temperature measurement, Radiation (Physics), Engineering systems and industry applications, Diffusion flames, Algebra
A.M. Rashad, Dr. Ali J. Chamkha, Muneer Ismael and Taha Salah
J. Heat Transfer   doi: 10.1115/1.4039213
This study investigates the convective heat transfer of a hybrid nanofluid filled in a triangular cavity subjected to a constant magnetic field and heated by a constant heat flux element from below. The inclined side of the cavity is cooled isothermally while the remaining sides are thermally-insulated. The finite difference method with the stream function-vorticity formulation of the governing equations has been utilized in the numerical solution. The problem is governed by several pertinent parameters namely, the size and position of the heater element, B = 0.2 — 0.8 and D = 0.3 — 0.7, respectively, the Rayleigh number, Ra = 102 — 106, the Hartmann number, Ha = 0 — 100, the volume fraction of the suspended nanoparticles, ? = 0 — 0.2, and the heat generation parameter Q = 0 — 6. The results show that the effect of increasing the volume fraction of the hybrid nanofluid becomes significant in the situations where the natural convection is very small. Moreover, the hybrid nanofluid composed of equal quantities of Cu and Al2O3 nanoparticles dispersed in water base fluid has no significant enhancement on the mean Nusselt number compared with the regular nanofluid.
TOPICS: Magnetohydrodynamics, Heat, Natural convection, Cavities, Nanofluids, Water, Heating, Nanoparticles, Vorticity, Convection, Finite difference methods, Fluids, Magnetic fields, Rayleigh number, Heat flux
Vikrant Khullar, Himanshu Tyagi, Todd Otanicar, Yasitha Hewakuruppu and Robert Taylor
J. Heat Transfer   doi: 10.1115/1.4039214
Given the largely untapped solar energy resource, there has been an ongoing international effort to engineer improved solar-harvesting technologies. Towards this, the possibility of engineering a solar selective volumetric receiver (SSVR) has been explored in the present study. Common heat transfer liquids (HTLs) typically have high transmissivity in the visible-near infrared (NIR) region and high emission in the mid-infrared region, due to the presence of intra-molecular vibration bands. This precludes them from being solar absorbers. In fact, they have nearly the opposite properties from selective surfaces such as cermet, TiNOx, and black chrome. However, liquid receivers which approach the radiative properties of selective surfaces, can be realized through a combination of anisotropic geometries of metal nanoparticles and transparent heat mirrors. In this paper, the 'effective' solar absorption to infrared emission ratio has been evaluated for a representative SSVR employing copper nanospheroids and Sn-In2O3 based heat mirrors. It has been found that a solar selectivity comparable to (or even higher than) cermet-based Schott receiver is achievable through control of the cut-off solar selective wavelength. Theoretical calculations show that the thermal efficiency of Sn-In2O3 based SSVR is 6 to 7% higher than the cermet-based Schott receiver. Furthermore, stagnation temperature experiments have been conducted on a lab-scale SSVR to validate the theoretical results. It has been found that higher stagnation temperatures (and hence higher thermal efficiencies) compared to conventional surface absorption-based collectors are achievable through proper control of nanoparticle concentration.
TOPICS: Solar energy, Solar thermal power, Cermets, Absorption, Nanoparticles, Heat, Temperature, Tin, Borosilicate glasses, Mirrors, Emissions, Thermal efficiency, Transparency, Vibration, Heat transfer, Wavelength, Metals, Copper, Engineers, Anisotropy
Farrokh Mobadersani, Goodarz Tulabi, Samad Jafarmadar, Javid Nasiri and Amin Habibzadeh
J. Heat Transfer   doi: 10.1115/1.4039215
The aim of the study is the analysis of a uniform magnetic field applying effect on flow and heat performance and entropy generation through the operation of a pulsating heat pipe. Furthermore, the impacts of different evaporator temperatures and pipe diameters have been scrutinized.For each case study, Bejan number has been derived to find the heat transfer share in entropy generation. According to the results, the performance of the oscillating heat pipe decreased by applying uniform magnetic fluid intensity increasing. Moreover,the latent and sensible heat into the pulsating heat pipe enhance because of increasing the pipe diameter, so that, the liquid slugs oscillate in high amplitudes. In addition, the entropy generation value increases with an augmentation in the value of the pipe diameter. The evaluated Bejan numbers indicate that the viscous impacts in entropy generation decreases as the pipe diameter increases. Furthermore, the results depict that the heat removing performance of pulsating heat pipe improves by increasing temperature difference between evaporator and condenser sections. The obtained results illustrate enhancement in total entropy generation. With an enhance in the value of the evaporator temperature, the Bejan number will increase, so that, this phenomenon reveals the inconsiderable role of viscous impacts in high evaporator temperatures.In order to validate the calculations, the calculated results have been compared to the previous studies which show good agreement.
TOPICS: Entropy, Heat pipes, Flow (Dynamics), Magnetohydrodynamics, Pipes, Temperature, Heat, Heat transfer, Magnetic fields, Magnetic fluids, Condensers (steam plant), Slug flows
Marina Astanina, Dr. Eiyad Abu-Nada and Mikhail A. Sheremet
J. Heat Transfer   doi: 10.1115/1.4039217
Numerical investigtion of natural convection in a differentially heated square cavity filled with a CuO-water nanofluid having variable properties is investigated. Governing partial differential equations formulated in non-dimensional stream function, vorticity, temperature and nanoparticles volume fraction are solved by a second order accurate finite difference method and taking into account the Brownian diffusion and thermophoresis. The effects of Rayleigh number (Ra = 1e+04-1e+06), initial nanoparticles volume fraction (C0 = 0-0.09), location of the heater (? = 0.0-0.9), dimensionless time (tau = 0-300) on flow patterns, isotherms and concentration fields, and average Nusselt number at the heater surface are investigated. The isoconcentrations reveal that for most of the cavity domain the nanoparticle concentration is around the initial average concentration of nanoparticles except for a very limited variation in a region next to the cavity walls that experience minor deviation from the initial concentration. It was found that the flow strength within the cavity is inversely proportional to the heater location ? and is directly proportional to the Rayleigh number. Also, it was found that the best location of the heater, from a heat transfer perspective, is placing it entirely at the left wall of the cavity where a maximum average Nusselt number is registered. Study revealed that for all heater locations there is always an adverse impact of nanoparticles on the heat transfer and the worst case is registered for the ? =0 and the least deterioration is noticed for ? = 0.9.
TOPICS: Brownian motion, Natural convection, Cavities, Nanofluids, Nanoparticles, Rayleigh number, Flow (Dynamics), Heat transfer, Partial differential equations, Water, Temperature, Diffusion (Physics), Cavity walls, Vorticity, Finite difference methods
Sheng-Yen Hsu
J. Heat Transfer   doi: 10.1115/1.4039220
In this study, the heat-blocking performance of intumescent coating under various combinations of external radiative and convective heat fluxes is investigated numerically. The results show that the temperature distribution and heat fluxes near the coating surface are significantly affected by the heat-source combination, and consequently, the thermal responses of coating are different. For the same magnitude of convective heat source, the higher flame temperature (lower heat convection coefficient) has larger thermal effect on coating response. For the same magnitude of heat source, the radiative heat source generates more thermal response of coating than the convective one. Moreover, if the external heat flux is not intense enough to cause large expansion ratio (2 < xL / L < 11) in 3600 sec, the combination of heat source can significantly affect the substrate temperature and the total heat flux at the coating surface. However, if the expansion ratio is sufficiently large (xL / L > 11) at the quasi-steady state (3600 sec), the substrate temperature and the total heat flux are independent of the combination of heat source, which only affects the temperature and the radiative and convective heat fluxes near the coating surface (~3 mm in this study).
TOPICS: Coating processes, Coatings, Flux (Metallurgy), Heat, Temperature, Heat flux, Temperature effects, Convection, Flames, Temperature distribution
Liang-Ying Zhong, Qi-Mei Zhao, Tong-Biao Wang, Tian-Bao Yu, Qing-Hua Liao and Nian-Hua Liu
J. Heat Transfer   doi: 10.1115/1.4039221
A hyperbolic metamaterial (HMM) alternately stacked by graphene and silicon carbide (SiC) is proposed to theoretically study near-field radiative heat transfer. Heat transfer coefficients (HTCs) are calculated using the effective medium theory (EMT). We observe that HMMs can exhibit better heat transfer characteristic than graphene-covered SiC bulks when appropriate SiC thickness and chemical potentials of graphene are selected. Transfer matrix method is also employed to calculate HTC between HMMs with thicker SiC given the invalidity of EMT in this case. We deduce that with increasing SiC thickness, HTC first increases rapidly and then decreases slowly when it reaches maximum value. HTC is high for graphene with small chemical potential. Results may benefit applications of thermophotovoltaic devices.
TOPICS: Graphene, Radiative heat transfer, Chemical potential, Heat transfer, Metamaterials, Silicon, Heat transfer coefficients
Technical Brief  
Sichao Hou and Ming Su
J. Heat Transfer   doi: 10.1115/1.4039219
This study establishes an image based approach to determine the thermal conductivity of a metal material as a function of temperature using isotherm movement. The thermal conductivity within a range of temperature can be derived from a combined experimental and theoretical study based on Wiedemann-Franz law. A cubic relation between heating time and distance from heat source has been observed, proved, and used to determine the thermal conductivity at different temperature. The temporal and spatial information provided by infrared imaging allow continuous temperature dependence of thermal conductivity to be derived with high accuracy. This method has the potential to determine thermal conductivities of multiple samples at high throughput, and to derive thermal conductivity along different crystal orientation in a thermally anisotropic system.
TOPICS: Temperature, Thermal conductivity, Wiedemann-Franz law, Infrared imaging, Heating, Crystal structure, Metals, Anisotropy, Temperature effects, Heat

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