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research-article  
Zhongran Chi, Haiqing Liu and Shusheng Zang
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4037131
This paper discusses the approach of cooling design optimization of a High Pressure Turbine (HPT) endwall with 3D Conjugate Heat Transfer (CHT) CFD applied. This study involved the optimization of the spacing of impingement jet array and the exit width of shaped holes, which were different for each cooling cavity. The optimization objectives were to reduce the wall temperature level and to increase the aerodynamic performance. The optimization methodology consisted of an in-house parametric design & CFD mesh generation tool, a CHT CFD solver, a database of CFD results, a metamodel, and an algorithm for multi-objective optimization. The CFD tool was validated against experimental data of an endwall at CHT conditions. The metamodel, which could efficiently estimate the optimization objectives of new individuals without CFD runs, was developed and coupled with Non-dominated Sorting Genetic Algorithm II to accelerate the optimization process. Through the optimization search, the Pareto front of the problem was found in each iteration. The accuracy of metamodel with more iterations was improved by enriching database. But optimal designs found by the last iteration are almost identical with those of the first iteration. Through analyzing extra CFD results, it was demonstrated that the design variables in the Pareto front successfully reached the optimal values. The optimal pitches of impingement arrays could be decided accommodating the local thermal load while avoiding jet lift-off of film coolant. It was also suggested that cylindrical film holes near throat should be beneficial to both aerodynamic and cooling performances.
TOPICS: Heat transfer, Cooling, High pressure (Physics), Computational fluid dynamics, Turbines, Pareto optimization, Optimization, Databases, Design, Algorithms, Stress, Coolants, Genetic algorithms, Mesh generation, Cavities, Wall temperature, Parametric design
research-article  
Yi-Hsuan Huang, Chiao-Hsin Chen and Yao-Hsien Liu
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4037132
Heat transfer of air/water mist flow in a single-side heated vertical duct was experimentally investigated. The mist flow was produced by introducing fine dispersed water droplets into the air stream and the water- air mass flow ratios were up to 15%. The Reynolds numbers of the air flow were 7900, 16000, and 24000. The rib spacing-to-height ratios were 10 and 20 in the current study. Mist flow cooling achieved higher heat transfer rates mainly because of the droplet deposition and liquid film formation on the heated surface. The heat transfer enhancement on the smooth surface by the mist flow was 4 to 6 times as high as the air flow. On the ribbed surface, a smaller rib spacing of 10 was preferred for air cooling since the heat transfer enhancement by the flow reattachment was better utilized. However, the rib induced intense secondary flow blew away the liquid films on the surface and the heat transfer enhancement was degraded near the reattachment region for the mist cooling. A larger rib spacing-to-height ratio of 20 thus achieved higher heat transfer because of the liquid film formation beyond the reattachment region. The heat transfer enhancement on the ribbed surface using mist flow was 2.5 to 3.5 times as high as the air flow. The friction factor of the mist flow was two times as high as the air flow in the ribbed duct.
TOPICS: Flow (Dynamics), Friction, Heat transfer, Boiling, Ducts, Water, Air flow, Liquid films, Cooling, Drops, Reynolds number
Guest Editorial  
Qingang Xiong, Jingchao Zhang and Giulio Lorenzini
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4037129
A special issue is launched to serve as a platform for researchers to report their recent activities on heat transfer studies related to processes of developing and applying renewable energies and novel materials. 15 research articles, ranging from nanoscale to macroscale and from theoretical to numerical, have been collected to discuss the fundamental mechanisms and practical applications of heat transfer in processes of developing and applying renewable energies and novel materials. The topics of published papers include computational fluid dynamics simulation of heat transfer in micro mixer and solar cavity receiver, experimental design and measurement of thermal properties for photovoltaic systems and two-dimensional materials, and theoretical analysis of heat transfer in novel nanofluids, etc.
TOPICS: Heat transfer, Simulation, Thermal properties, Computational fluid dynamics, Nanoscale phenomena, Solar energy, Cavities, Experimental design, Nanofluids, Photovoltaic power systems, Theoretical analysis
research-article  
Steven J. Young, D Janssen, Everett Wenzel, Brandon Shadakofsky and Francis Kulacki
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4037130
Onboard liquid cooling of electronic devices is demonstrated with liquid delivered externally to the point of heat removal through a conformal encapsulation. The encapsulation creates a flat microgap above the integrated circuit and is a CFD-enabled design that delivers a uniform inlet coolant flow over the device. The coolant is NovecTM 7200, and the electronics are simulated with a resistance heater on a 1:1 scale. Thermal performance is demonstrated at power densities of ~ 1 KW/cm3 in the microgap. Parameters investigated are pressure drop, average device temperature, heat transfer coefficient and coefficient of performance. Nusselt numbers for gap sizes of 0.25, 0.5 and 0.75 mm are reduced to a dimensionless correlation. With low coolant inlet subcooling, two-phase heat transfer is seen at all mass flows. Device temperatures reach 95 oC for power dissipation of 50 - 80 W (0.67 - 1.08 KW/cm3) depending on coolant flow for a gap of 0.5 mm. Coefficients of performance of ~100 - 70,000 are determined via measured pressure drop and demonstrate a low pumping penalty at the device level within the range of power and coolant flow considered. The encapsulation with microgap flow boiling provides a means for use of higher power CPU and GPU devices and thereby enables higher computing performance, for example, in embedded airborne computers.
TOPICS: Cooling, Coolants, Flow (Dynamics), Temperature, Pressure drop, Subcooling, Electronics, Heat transfer coefficients, Graphics processing units, Heat transfer, Heat, Energy dissipation, Boiling, Computational fluid dynamics, Design, Computers, Integrated circuits
research-article  
Javid Karbalaei Mehdi, Amir Nejat and Masoud M. Shariat Panahi
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036966
One important safety issue in automotive industry is the efficient cooling of brake system. This research work aims to introduce an optimized cooling vane geometry to enhance heat removal performance of ventilated brake disks. The novel idea of using airfoil vanes is followed as the basis of this investigation. In order to perform the optimization technique efficiently, an integrated shape optimization process is designed. According to the aerodynamic and heat transfer considerations, first an appropriate airfoil is selected as the base profile to be optimized. For the shape modification purpose, a curve parameterization method named Class Shape Transformation (CST) is utilized. The control parameters defined in CST method are then established as the geometrical design variables of an improved Territorial Particle Swarm Optimization (TPSO) algorithm. In order to overcome the potential bottleneck of high computational cost associated with the required CFD-based function evaluations, TPSO algorithm is coupled with a predictive Artificial Neural Networks (ANN), well-trained with an input dataset designed based on the Taguchi method. The obtained profile shows an evident convective heat dissipation improvement accomplished mainly via airflow acceleration over the vanes, avoiding early flow detachment and adjusting the flow separation region at the rear part of the suction sides. The results also reveal the approaches by which such a superior performance is achieved by means of the modified surface curvatures.
TOPICS: Heat transfer, Cooling, Algorithms, Disks, Artificial neural networks, Automotive brakes, Shape optimization, Airfoils, Brakes, Heat, Shapes, Taguchi methods, Flow (Dynamics), Flow separation, Geometry, Particle swarm optimization, Automotive industry, Computational fluid dynamics, Design, Optimization, Safety, Suction, Air flow, Energy dissipation
research-article  
Hossein Mohamad Ghasemi, Neda Gilani and Jafar Towfighi Daryan
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036801
A new arrangement of side-wall burners of an industrial furnace was studied by three dimensional-CFD simulation. This simulation was conducted on ten calculation domain. Finite rate/eddy dissipation model was used as a combustion model. Discrete Ordinate Model was considered as radiation model. Furthermore, weighted sum of gray gas model was used to calculate radiative gas properties. Tube skin temperature and heat flux profiles were obtained by solving mass, momentum and energy equations. Moreover, fuel rate variation was considered as an effective parameter. A base flow rate of fuel (m ?=0.0695 kg/s) was assigned and different ratios (0.25m ?, 0.5m ?, 2m ?, 4m ?) were assigned to investigate heat distribution over the furnace. Resulted temperature and heat profiles were obtained in non-uniform mode by proposed wall burner arrangement. According to the results, despite increased heat transfer coefficient about 34% for m ? to 4m ?, temperature profile for this rate is too high and is harmful for tube metallurgy. Also proper range for fuel rate variation was determined 0.5m ? to 2m ?. In this range, heat transfer coefficient and Nusselt number for m ? to 2m ? were increased by 21% and for m ? to 0.25m ? were decreased about 28%.
TOPICS: Fuels, Cracking (Materials), Computational fluid dynamics, Fracture (Process), Furnaces, Simulation, Heat transfer coefficients, Heat, Temperature, Combustion, Metallurgy, Radiation (Physics), Eddies (Fluid dynamics), Momentum, Flow (Dynamics), Industrial furnaces, Energy dissipation, Skin, Temperature profiles, Heat flux
research-article  
Mohsen Torabi, Alexander Elliott and N.K. Karimi
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036802
This paper presents a study of the thermal characteristics and entropy generation of a porous microchannel with thick walls featuring uneven thicknesses. The system accommodates a fully developed flow while the solid and fluid phases can include internal heat sources. Two sets of asymmetric boundary conditions are considered. The first includes constant temperatures at the surface of the outer walls, with the lower wall experiencing a higher temperature than the upper wall. The second case imposes a constant heat flux on the lower wall and a convection boundary condition on the upper wall. These set thermal models for micro-reactors featuring highly exothermic or endothermic reactions such as those encountered in fuel reforming processes. The porous system is considered to be under local thermal non-equilibrium (LTNE) condition. Analytical solutions are, primarily, developed for the temperature and local entropy fields and then are extended to the total entropy generation within the system. A parametric study is, subsequently, conducted. It is shown that the ratio of the solid to fluid effective thermal conductivity ratio and the internal heat sources are the most influential parameters in the thermal and entropic behaviours of the system. In particular, the results demonstrate that the internal heat sources can affect the entropy generation in a non-monotonic way and, that the variation of the total entropy with internal heat sources may include extremum points. It is, further, shown that the asymmetric nature of the problem has a pronounced effect on the local generation of entropy.
TOPICS: Thermodynamics, Microchannels, Entropy, Heat, Temperature, Fluids, Boundary-value problems, Flow (Dynamics), Heat flux, Fuels, Exterior walls, Equilibrium (Physics), Thermal conductivity, Convection
research-article  
Wang Lingling, Zhu Guihua, Wei Yu, Dahai Zhu, Yingchun Zhang, Liye Zhang and Huaqing Xie
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036800
Near-spherical gold nanoparticles were synthesized using a facile chemical reduction method. The optical properties, size and morphology of nanofluids were characterized using UV-Vis-NIR spectroscopy and TEM. All the gold nanofluids showed better photothermal conversion characteristics than H2O due to the strong localized surface plasmon resonance effect. The increase in gold nanoparticles diameters resulted in lower photothermal conversion properties, so appropriate reducing agents have great influence on the optical properties of gold nanofluids in our experimental system. Trisodium citrate is the optimum reducing agents compared with NaBH4 and ascorbic acid.
TOPICS: Surface plasmon resonance, Nanofluids, Nanoparticles, Water, Ultraviolet radiation, Spectroscopy
research-article  
Vikrant Khullar, Vishal Bhalla and Himanshu Tyagi
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036795
Nano-particle dispersions or more popularly 'nanofluids' have been extensively researched for their candidature as working fluid in direct-volumetric-absorption solar thermal systems. Flexibility in carving out desired thermo-physical and optical properties has lend the nanofluids to be engineered for solar thermal and photovoltaic applications. The key feature which delineates nanofluid based direct absorption volumetric systems from their surface absorption counterparts is that here the working fluid actively (directly) interacts with the solar irradiation and hence enhances the overall heat transfer of the system. In the present work, a host of nanoparticle materials have been evaluated for their solar weighted absorptivity and heat transfer enhancements relative to the basefluid. It has been found that solar weighted absorptivity is the key feature that makes nanoparticle dispersions suitable for solar thermal applications (maximum enhancement being for the case of amorphous carbon nanoparticles) . Furthermore, thermal conductivity enhancements reveal that an enhancement on the order of 1-5% could only be achieved through addition of nanoparticles into the basefluid. Finally, as a proof of concept experiment, a parabolic trough collector employing the amorphous carbon based nanofluid and distilled water has been tested under the sun. These experiments have been carried out at no flow condition so that appreciable temperatures could be reached in less time. It was found that for the same exposure time, increase in the temperature of amorphous carbon based nanofluid is approximately 3 times higher as compared to that in the case of distilled water.
TOPICS: Heat transfer, Fluids, Absorption, Solar energy, Thermal systems, Nanofluids, Nanoparticles, Carbon, Water, Disperse systems, Temperature, Flow (Dynamics), Thermal conductivity, Irradiation (Radiation exposure), Parabolic troughs
research-article  
Dahai Zhu, Yu Qi, Wei Yu, Lifei Chen, Mingzhu Wang and Huaqing Xie
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036796
Graphene nanoplatelets (GNPs) have excellent thermal conductivity. It can significantly improve the heat-conducting property of epoxy resin (EP) matrix. In this paper, the GNPs/EP composites were successfully prepared by using ultrasonication and the cast molding method. The prepared GNPs/EP composites were systematically characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermal conductivity analyzer. Some factors affecting the thermal transfer performance of the composites were discussed. The defoamation has great influence on the thermal conductivity of composite. There is a nearly linear relationship between the mass fraction and the thermal conductivity of composite when the mass fraction of GNPs is below 4.3%. The results show that when the mass fraction of GNPs is 4.3% with crushing time of 2s, the thermal conductivity of GNPs/EP composite is up to 0.99 W/m?K. The thermal conductivity is increased by 9.0% compared with that without pulverization treatment. When it is ground three times, the thermal conductivity of composite reaches the maximum (1.06W/m?K) and it is increased by 307.7% compared with that of epoxy resin matrix.
TOPICS: Composite materials, Epoxy resins, Thermal conductivity, Graphene, Heat, Scanning electron microscopy, X-ray diffraction, Molding
research-article  
Yingchun Zhang, Wei Yu, Liye Zhang, Junshan Yin, Jingkang Wang and Huaqing Xie
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036797
A simple approach is developed to obtain a multiscale network of heat conducting by filling spherical alumina (S-Al2O3) and graphene nanoplatelets (GnPs) into silicon rubber. This unique structure effectively minimizes the thermal contact resistance between fillers and interface. The physical properties of the composites are characterized by thermal conductivity, density and tensile strength. A high thermal conductivity of 3.37Wm-1K-1 has been achieved, which is 47.1% higher than the single filler at the same loading. A strong and obvious synergistic effect has been observed as S-Al2O3 and GnPs filled into silicon rubber matrix. It is interesting that the composites with GnPs have the lower density (2.62g/cm3, reduced by 6%) and the superior tensile performance, compared to silicone rubber composite with neat S-Al2O3. The composites have the potential applications in heat dissipation of light-emitting diode.
TOPICS: Density, Mechanical properties, Thermal conductivity, Graphene, Silicone rubber, Composite materials, Rubber, Fillers (Materials), Heat, Silicon, Tensile strength, Light-emitting diodes, Contact resistance, Energy dissipation
research-article  
Hua Dong, Ranran Chen, Yongqiang Mu, Shouting Liu, Jingkui Zhang and Huan Lin
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036798
The thermal transport in metallic thin films can be reduced by the electron scattering and there are very little available knowledge can be used to explain the mechanism. In this work, we characterized the thermal and electron transport of 3.2 nm thin gold films coated on alginate fiber by the transient electro-thermal (TET) technique. The results reveal that the thermal conductivity and electrical conductivity are reduced significantly from the respective values of bulk material by 75.9% and 93%. At the same time, the Lorenz number is calculated as 8.64 ×10-8 W O K-2 and it is three times increased from that value of bulk material. The intrinsic thermal diffusivity of alginate fiber is 3.25×10-7 m2 s-1 and the thermal conductivity is 0.51 W m-1 K-1.
TOPICS: Fibers, Electrical properties, Thermal conductivity, Bulk solids, Thermal diffusivity, Transients (Dynamics), Electron scattering, Electrical conductivity, Electron transport, Metallic thin films
research-article  
Hussein M. Maghrabie, M. Attalla, Hany Fawaz and Mohamed Khalil
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036788
Numerical study of the effect of jet position on cooling process of an array of heated obstacles simulating electronic components has been investigated based on Realizable k-e model. Jet positions have been changed to impinge each row of obstacles consecutively. The experiments have been achieved at three different values of jet-to-channel Reynolds number ratios, Rej/Rec=1, 2, and 4. In the present study, a comparison between two different cooling processes; cross flow only (CF) and jet impingement with cross flow (JICF) has been achieved. The flow structure, heat transfer characteristics over all array obstacles, and the pumping power have been investigated for different jet positions. The results show that the jet position affects significantly the flow structure, as well as the heat transfer characteristics. Ac-cording to the results of average heat transfer coefficient and the pumping power, the more effective jet position for all values of jet-to-channel Reynolds number ratios (1, 2, and 4) is achieved when the jets impinge the third row of obstacles (JP3).
TOPICS: Cooling, Reynolds number, Flow (Dynamics), Heat transfer, Cross-flow, Jets, Electronic components, Heat transfer coefficients
research-article  
Zhaoxiang Zhang, Huiqing Liu, Xiaohu Dong and Huanli Jiang
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036789
Steam assisted gravity drainage (SAGD) process has been an optimized method to explore heavy oil reservoirs in the world. The oil viscosity reduction and gravity force near the interface of steam chamber are the main development mechanisms. In classical models, conductive heat transfer plays the only or dominant role in the heat transmission from high-temperature steam to low-temperature oil sands. Although some mathematical studies have paid attention to the convective heat transfer, the role of heat transfer by flowable oil normal to the steam chamber interface has been given little attention. In SAGD, the viscosity of bitumen can be reduced by several orders of magnitude by the release of latent heat from injected steam. In this study, an analytical model is developed for the heat transfer process induced by flowable oil. Also, in order to accurately simulate the oil viscosity characteristics in steam chamber, a correlation between oil viscosity and pressure is proposed. Results indicate that the oil mobility plays an important role on the flow normal to interface when the distance is smaller than 6 m. Even under the most extreme circumstances (µw = 0.1127 cp), the flowing of oil normal to steam chamber interface also cannot be ignored. Comparing to Irani and Ghannadi model, it can be easy to draw the conclusion that new model consists with the UTF field data much better. This new analytical model will benefit to understanding the convective heat transfer mechanism in SAGD process.
TOPICS: Gravity (Force), Drainage, Convection, Steam, Heat transfer, Viscosity, Asphalt, Oil sands, Pitch (Bituminous material), Pressure, Flow (Dynamics), High temperature steam, Hydrocarbon reservoirs, Mechanical admittance, Low temperature, Latent heat, Bituminous materials
research-article  
Alok Ghanekar, Mingdi Sun, Zongqin Zhang and Yi Zheng
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036790
We theoretically and numerically demonstrate optimal design of wavelength selective thermal emitter using one dimensional (1-D) and two dimensional (2-D) metal-dielectric gratings for thermophotovoltaic (TPV) applications. Proposed design consists of tungsten (W) and silicon dioxide (SiO2) gratings which can withstand high temperatures. Radiative properties of 1-D grating were calculated using a numerical method, while effective medium approximation was used for 2-D gratings. Optimal designs were obtained such that output power is maximum for GaSb photovoltaic cell at emitter temperature of 1500 K and radiated energy for longer wavelengths is limited to a low value. A constrained optimization was performed using Genetic Algorithm (GA) to arrive at optimal design.
TOPICS: Design, Wavelength, Diffraction gratings, Temperature, Metals, Numerical analysis, Optimization, Approximation, Genetic algorithms, Photovoltaic cells, Quartz, Silicon, Tungsten, High temperature
research-article  
Hao-Chun Zhang, Yan-Qiang Wei, Cheng-Shuai Su, Gong-Nan Xie and Giulio Lorenzini
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036791
With the rapid development of the supersonic aircraft technology, the aircraft Mach number continues increasing, but on the other hand, the working condition becomes progressively poor. The photonic crystals (PCs) material could reflect the energy of the thermal radiation effectively and prevent heat transferring into the substrate due to its low thermal conductivity. Consequently, the PCs material could be applied to thermal protection for the supersonic aircraft. In this paper, the aircraft state of Mach 5 is set as the target operating condition, and the PC thermal protection ability is simulated by the method of computational fluid dynamics. Based on the theory of the electromagnetics, the characteristics of the photonic band gaps for three dimensional PCs are calculated and the effects of PCs medium radius, refractive index and lattice constant are fully taken into account. For the three-dimensional diamond PCs structure, two major categories and totally five optimized design schemes are proposed, through combining the condition of supersonic aircraft aerodynamic heating. Results show that the temperature is reduced by 948.431K when the heat passes through thermal protection layer and reduced by 930.4K when the heat passes through PC layer. By the method of “Coupled Optimization Strategy (COS)”, the energy density which enters into substrate material would decrease by 7.99%. In conclusion, the thermal protection capacity for supersonic aircraft could be effectively improved by using the PCs.
TOPICS: Structural optimization, Aircraft, Crystals, Dynamic light scattering, Heat, Temperature, Electromagnetism, Density, Mach number, Thermal radiation, Electromagnetic force, Thermal conductivity, Computational fluid dynamics, Design, Optimization, Refractive index, Diamonds, Energy gap, Heating
research-article  
Jiabin Fang, Nan Tu, Jinjia Wei, Tao Fang and Xuancheng Du
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036792
The effects of tube layout on the heat losses of solar cavity receiver were numerically investigated. Two typical tube layouts were analyzed. For the first tube layout, only the active surfaces of cavity were covered with tubes. For the second tube layout, both the active cavity walls and the passive cavity walls were covered with tubes. Besides, the effects of water-steam circulation mode on the heat losses were further studied for the second tube layout. The absorber tubes on passive surfaces were considered as the boiling section for one water-steam circulation mode, and as the preheating section for the other one, respectively. The thermal performance of the cavity receiver with each tube layout was evaluated according to the previous calculation model. The results show that the passive surfaces appear to have much lower heat flux than the active ones. However, the temperature of those surfaces can reach a quite high value of about 520 ? in the first tube layout, which causes a large amount of radiative and convective heat losses. By contrast, the temperature of passive surfaces decreases by about 200-300? in the second tube layout, which leads to a 38.2-70.3% drop in convective heat loss and a 67.7-87.7% drop in radiative heat loss of the passive surfaces. The thermal efficiency of the receiver can be raised from 82.9% to 87.7% in the present work.
TOPICS: Solar energy, Cavities, Heat losses, Steam, Water, Temperature, Cavity walls, Boiling, Heat flux, Thermal efficiency
research-article  
Ayoub Gounni and Mustapha El Alami
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036794
In order to really assess the thermal performance of a wall incorporating Phase Change Material (PCM), a reduced scale cavity has been monitored during two heating cycles. For each cycle, the heat source inside the test cell is switched "on" for 5 hours and its setpoint is 38°C then switched off for 4 hours. The outdoor air temperature is kept constant at a low temperature of 20°C. Two walls are equipped with a PCM layer at different depths in order to study the optimal PCM location. The other walls are wooden and glass to model a real building. The comparison between the four walls is made based on the absorbed heat fluxes and outside surface temperatures. The results show that the location of the PCM close to the heat source reaches its melting temperature and then reduces the surface temperatures. At this location, the PCM layer stores the major part of the inlet heat flux. It takes 10 hours to release the absorbed heat flux. However, the PCM layer, practically, does not have effect on the surface temperatures and absorbed heat fluxes, when it is placed far from the heat source.
TOPICS: Heat transfer, Cavities, Heat, Temperature, Flux (Metallurgy), Cycles, Heat flux, Heating, Melting, Phase change materials, Low temperature, Glass
research-article  
Han Shen, Xueting Liu, Hongbin Yan, Gongnan Xie and Bengt Sunden
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036767
Internal Y-shaped bifurcation has been proved to be an advantageous way on improving thermal performance of microchannel heat sinks according to the previous research. Metal foams are known due to their predominate performance such as low-density, large surface area and high thermal conductivity. In this paper, different parameters of metal foams in Y-shaped bifurcation microchannel heat sinks are designed and investigated numerically. The effects of Reynolds number, porosity of metal foam, and the pore density (PPI) of the metal foam on the microchannel heat sinks are analyzed in detail. It is found that the internal Y-shaped bifurcation microchannel heat sinks with metal foam exhibit better heat transfer enhancement and overall thermal performance. This research provides broad application prospects for heat sinks with metal foam in the thermal management of high power density electronic devices.
TOPICS: Bifurcation, Heat sinks, Metal foams, Microchannels, Density, Heat transfer, Reynolds number, Thermal conductivity, Porosity, Thermal management, Power density
research-article  
Tasawar Hayat, Muhammad Ijaz Khan, Maria Imtiaz and Ahmed Alsaedi
J. Thermal Sci. Eng. Appl   doi: 10.1115/1.4036768
A simple model of homogeneous-heterogeneous process for Maxwell fluid flow in the stagnation region over a stretched surface is constructed. It is assumed that the homogeneous process in the ambient fluid are governing by first order kinetics and the heterogeneous process on the wall surface are given by isothermal cubic autocatalator kinetics. Flow is caused by stretched surface with homogeneous-heterogeneous process. Present problem is reduced to ordinary differential equations through appropriate transformation. Resulting problems are solved for the convergent solutions. Intervals of convergence for the obtained series solutions are explicitly determined. Behavior of important variables on the physical quantities of interest are analyzed in detail. It is observed that velocity profile decreases for larger values of Deborah number.
TOPICS: Heat, Mass transfer, Fluids, Chemical reactions, Fluid dynamics, Flow (Dynamics), Differential equations

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