Showing papers in "Frontiers in Heat and Mass Transfer in 2013"
TL;DR: In this paper, the authors review the recent advances in near-field radiative energy transfer, particularly in its fundamentals and applications, covering from the essential physics to the most recent theoretical as well as experimental findings that will further promote the fundamental understanding.
Abstract: This article reviews the recent advances in near-field radiative energy transfer, particularly in its fundamentals and applications. When the geometrical features of radiating objects or their separating distances fall into the sub-wavelength range, near-field phenomena such as photon tunneling and surface polaritons begin to play a key role in energy transfer. The resulting heat transfer rate can greatly exceed the blackbody radiation limit by several orders magnitude. This astonishing feature cannot be conveyed by the conventional theory of thermal radiation, generating strong demands in fundamental research that can address thermal radiation in the near field. Important breakthroughs of near-field thermal radiation are presented here, covering from the essential physics that will help better understand the basics of near-field thermal radiation to the most recent theoretical as well as experimental findings that will further promote the fundamental understanding. Applications of near-field thermal radiation in various fields are also discussed, including the radiative property manipulation, near-field thermophotovoltaics, nanoinstrumentation and nanomanufacturing, and thermal rectification.
85 citations
TL;DR: In this article, the steady boundary layer stagnation-point flow of Casson fluid and heat transfer towards a shrinking/stretching sheet is studied and appropriate similarity transformations are employed to transform the governing partial differential equations into the self-similar ordinary differential equations and those are then solved numerically using very efficient shooting method.
Abstract: The steady boundary layer stagnation-point flow of Casson fluid and heat transfer towards a shrinking/stretching sheet is studied. Appropriate similarity transformations are employed to transform the governing partial differential equations into the self-similar ordinary differential equations and those are then solved numerically using very efficient shooting method. The numerical computations are carried out for several values of parameters involved (especially, velocity ratio parameter and Casson parameter) to know the possibility of similarity solution for the boundary layer stagnation-point flow. It is found that the range of velocity ratio parameter for which similarity solution exists is unaltered for any change in Casson parameter, though the skin friction changes with Casson parameter. Thus, the possibility of similarity solution for Casson fluid flow is same as that of Newtonian fluid flow.
59 citations
TL;DR: In this paper, an experimental thermal efficiency analysis for a novel flat plate solar air heater with several mass flow rates was presented, where the measurements were performed at different values of mass flow rate of air in flow channel duct.
Abstract: This paper presents an experimental thermal efficiency analysis for a novel flat plate solar air heater with several mass flow rates. The aims are to review of designed and analyzed a thermal efficiency of flat-plate solar air heaters. The measured parameters were the inlet and outlet temperatures, the absorbing plate temperatures, the ambient temperature, and the solar radiation. Further, the measurements were performed at different values of mass flow rate of air in flow channel duct. After the analysis of the results, the optimal value of efficiency is higher level of mass flow rate equal to 0.0202 kg/s in flow channel duct for all operating conditions and the single-flow collector supplied with maximum mass flow rate appears significantly better than that another flow rate. At the end of this study, the thermal efficiency relations are delivered for different mass flow rates. Maximum efficiency obtained for the single pass air heater between the air mass flow rates from 0.0108 to 0.0184 kg/s; were 39.72% and 50.47 % respectively, with tilt angle equal 45° in location Biskra city of Algeria. The thermal efficiency correspondently the mass flow rates were 28.63, 39.69, 46.98, 55.70 and 63.61 %, respectively.
25 citations
TL;DR: In this paper, the analysis of boundary layer flow and heat transfer of a nanofluid over a stretching circular cylinder in the presence of non-uniform heat source/sink is presented.
Abstract: The present paper deals with the analysis of boundary layer flow and heat transfer of a nanofluid over a stretching circular cylinder in the presence of non-uniform heat source/sink. The governing system of partial differential equations is converted to ordinary differential equations by using similarity transformations, which are then solved numerically using the Runge–Kutta–Fehlberg method with shooting technique. The solutions for the temperature and nanoparticle concentration distributions depend on six parameters, Prandtl number Pr, Lewis number Le, the Brownian motion parameter Nb, the thermophoresis parameter Nt, and non-uniform heat generation/absorption parameters A*, B*. Numerical results are presented both in tabular and graphical forms for
16 citations
TL;DR: In this paper, the effects of tube orientation on flow boiling heat transfer coefficients were investigated for FC72 flowing in single mini-tubes with tube diameters of 0.13 and 0.51 mm to define boundaries on a dominant force regime map.
Abstract: Effects of tube orientation on flow boiling heat transfer coefficients were investigated for FC72 flowing in single mini-tubes with tube diameters of 0.13 and 0.51 mm to define boundaries on a dominant force regime map. For the tube diameter of 0.51 mm, when mass velocity and vapor quality was varied, heat transfer coefficients were influenced by tube orientation at Froude number Fr 4. The results indicated that the boundary between the body force dominated and the inertia dominated regimes was given by Fr 4. On the other hand, for tube diameter of 0.13 mm, almost no effect of tube orientation on heat transfer coefficients was observed for all combinations of mass velocity and vapor quality tested, where heat transfer coefficients were independent of mass velocity and vapor quality at Weber number We < 5, and vice versa. The results indicated that the boundary between the surface tension dominated and the inertia dominated regimes was represented by We 5. From the above results, the boundary between the surface tension dominated and the body force dominated regimes was existed between Bo = 0.51 and 0.033.
14 citations
TL;DR: In this paper, a model for the coefficient of thermal conductivity of binary mixtures of gases has been derived based on the assumption of random fluctuations between two possible extreme arrangements of a binary gas mixture.
Abstract: A model for the coefficient of thermal conductivity of binary mixtures of gases has been derived. The theory presented is based on the assumption of random fluctuations between two possible extreme arrangements of a binary gas mixture. The results obtained from the new model compared favorably with published experimental results. The proposed new model provides a simple approach without sacrificing much accuracy compared to previous models. It is applicable to any binary mixture of gases which includes monoatomic gas mixture, polyatomic gas mixtures and mixtures involving rare gases. The new model can be very useful in analysis like combustion where the main equations are already sophisticated.
13 citations
TL;DR: In this article, the authors derived an equation for thermal resistance of the disc for radial configuration of inserts based on the procedure used in constructal studies and implemented the optimized thermal resistances of elemental sectors.
Abstract: In the present study, conductive cooling of a disc is done by means of incomplete constant and variable cross-section highly conductive inserts embedded in radial and tributary configurations. Variational calculus is invoked to determine the optimum shape of the cross-sections of the inserts. Firstly, it is tried to derive an equation for thermal resistance of the disc for radial configuration of inserts based on the procedure used in constructal studies. This is done by implementing the optimized thermal resistances of elemental sectors. Then, the computed elemental sectors are put together so that they make branching configuration of inserts in the disc. Out of the comparison between the obtained thermal resistances of the disc with constant and variable cross-sections, it is concluded that using variable cross-sections reduces thermal resistance, but this effect differs in radial and tributary configurations, i.e., increasing the complexity of tributary patterns does not always reduce the thermal resistance more effectively in comparison with radial configurations.
10 citations
Journal Article•
TL;DR: In this article, a mathematical model is presented to analyse the steady boundary layer slip flow and mass transfer with n th order chemical reaction past a porous plate embedded in a Darcy porous medium.
Abstract: A mathematical model is presented to analyse the steady boundary layer slip flow and mass transfer with n th order chemical reaction past a porous plate embedded in a Darcy porous medium. Velocity as well as mass slips are considered at the boundary. The governing PDEs are transformed into self-similar nonlinear ODEs by similarity transformations. The reduced nonlinear equations are solved numerically. The momentum boundary layer thickness is reduced for increase of permeability and suction parameters, whereas it increases with blowing parameter. The increase of velocity slip parameter reduces the momentum boundary layer thickness and also enhances the mass transfer from the plate. Importantly, due to increase of mass slip the concentration and mass transfer decrease.
10 citations
TL;DR: In this paper, a computational model was presented that extends prior work on unsteady natural convection in a tall rectangular cavity with aspect ratio 10 and applies Proper Orthogonal Decomposition to the results.
Abstract: A computational model is presented that extends prior work on unsteady natural convection in a tall rectangular cavity with aspect ratio 10 and applies Proper Orthogonal Decomposition to the results. The solution to the weakly compressible Navier-Stokes equation is computed for a range of Rayleigh numbers between 2 10 7 and 2:2 10 8 with Prandtl number 0.71. A detailed spectral analysis shows dynamic system behavior beyond the Hopf bifurcation that was not previously observed. The wider Rayleigh range reveals new dynamic system behavior for the rectangular geometry, specifically a return to a stable oscillatory behavior that was not predicted in prior work. Proper Orthogonal Decomposition (POD) has been used to analyze the computational results. Five eigenvalue modes were required to capture correctly the basic flow structure. The POD failed to capture subtle aspects of the flow structure at high Rayleigh numbers for the model, indicating that a POD and Galerkin projection for several Rayleigh numbers will be needed to reproduce the complex behavior of the system.
8 citations
Journal Article•
TL;DR: In this article, the fluid flow and heat transfer in an evaporating extended meniscus are numerically studied and the numerical results strongly depend on the choice of the accommodation coefficient and Hamaker constant as well as initial perturbations.
Abstract: The fluid flow and heat transfer in an evaporating extended meniscus are numerically studied Continuity, momentum, energy equations and the Kelvin-Clapeyron model are used to develop a third order, non-linear ordinary differential equation which governs the evaporating thin film It is shown that the numerical results strongly depend on the choice of the accommodation coefficient and Hamaker constant as well as the initial perturbations Therefore, in the absence of experimentally verified values, the numerical solutions should be considered as qualitative at best It is found that the numerical results produce negative liquid pressures under certain specific conditions This result may suggest that the thin film can be in an unstable state of tension; however, this finding remains speculative without experimental validation Although similar thin-film models proved to be very useful in gaining qualitative insight into the characteristics of evaporating thin films, the results shown in this study indicate that careful experimental investigations are needed to verify the mathematical models
7 citations
TL;DR: In this paper, the diffusion process of deep seawater drawn up by a vertical pipe deployed in the ocean is investigated, based on numerical simulations of seawater upwelling from the pipe.
Abstract: The diffusion process of deep seawater drawn up by a vertical pipe deployed in the ocean is investigated. This vertical pipe is based on the principal of perpetual salt fountain. Numerical simulations of seawater upwelling from the pipe are performed based on experiments conducted in the Mariana trench region. Two turbulence modeling approaches were examined: k-e model and Large Eddy Simulations (LES). The results in both models show that diffusion of the deep seawater diffusion after ejection from the pipe. The LES results show a 50% lower vertical penetration compared to the k-e model as well as well as predicting that the horizontal diffusion is stronger than the vertical one.
TL;DR: In this article, a numerical analysis of laminar natural convection in a quadrantal cavity filled with water having variable length heaters attached on the adjacent walls has been made to examine heat and fluid flow.
Abstract: A numerical analysis of laminar natural convection in a quadrantal cavity filled with water having variable length heaters attached on the adjacent walls have been made to examine heat and fluid flow. Numerical solutions are obtained using a commercial computational fluid dynamics package, FLUENT, using the finite volume method. Effects of the Rayleigh number, Ra, on the Nusselt number, Nu, as well as velocity and temperature fields are investigated for the range of Ra from 10 to 10. Computations were carried out for the non-dimensional heater lengths on the vertical wall (m=0.2, 0.4 and 0.6) and horizontal wall (n=0.2, 0.4 and 0.6). It is observed that heat transfer increases with increase in Rayleigh number and the flow strength increases with increase in size of heater on the vertical wall compared to the bottom wall and temperature fields are also affected. In contrast, with increase in size of heater on both side of adjacent walls flow strength does not changes significantly.
TL;DR: In this paper, the thermoelectric performance of an integrated thermal device (iTED) with rectangular, round end slots and circular flow channel designs applied to waste heat recovery for several hot stream flow rates has been investigated using numerical methods.
Abstract: In this study, the thermoelectric performance of an integrated thermoelectric device (iTED) with rectangular, round end slots, and circular flow channel designs applied to waste heat recovery for several hot stream flow rates has been investigated using numerical methods. An iTED is constructed with p- and n-type semiconductor materials bonded to the surfaces of an interconnector with flow channels drilled through it. This interconnector acts as an internal heat exchanger directing waste heat from the hot stream to thermoelectric elements. The quantity of heat extracted from the waste heat source and the subsequent amount of electrical power generated P0 from the iTED is increased significantly for the circular flow channels, followed by round end slots and rectangular flow channels, respectively. At Re = 100, the round end slots and the circular flow channels showed nearly 2.6 and 2.9 times increment in P0, and 1.5 and 1.65 times in when compared to the rectangular flow channels values. Conversely, when Re is increased from 100 to 500, the iTED with rectangular flow channels showed 2.67- and 1.6-fold improvement in P0 and , respectively. However, the circular configurations showed 2.27- and 1.41-fold increases in P0 and values, respectively. Within theRe range studied, the inclusion of flow channels’ pumping power in calculations showed negligible effect. For an iTED with circular flow channels, an increase in a cold side convective heat transfer coefficienthc resulted in an enhancement inP0 and values. Besides a hc effect, the heat loss to the ambient via convective and radiation heat transfer exhibited an increase inP0 and decrease in .
TL;DR: In this paper, a novel nano-thermal interface material has been developed, which is composed of tin (Sn) solder and graphite nanoplatlets, which can be adjusted to match well with the substrate materials.
Abstract: Carbon-based materials draw more and more attention from both academia and industry: its allotropes, including graphene nanoplatlets, graphite nanoplatlets and carbon nanotubes, can readily enhance thermal conductivity of thermal interface products when served as fillers. Structuraloptimization in micro/nano-scale has been investigated and expected to finely tune the coefficient of thermal expansion (CTE) of thermal interface materials (TIMs). The capability of adjusting CTE of materials greatly benefits the design of interface materials as CTE mismatch between materials may result in serious fatigue at the interface region that goes through thermal cycles. Recently, a novel nano-thermal-interface material has been developed, which is composed of tin (Sn) solder and graphite nanoplatlets. CTE of such sort of TIMs can be adjusted to match well with the substrate materials. A customized, optical CTE measuring system was built to measure CTEs of these thin and flexible samples. The averaged CTEs of samples made by this new approach range from -0.267×10 -6 /°C to 5×10 -6 /°C between 25°C and 137°C, which matches CTEs of typical semiconductor materials (the CTE of silicon is ~3×10 -6 /°C in the same temperature range). This unique CTE-matching feature of a bonding material
TL;DR: In this paper, the authors examined the thermophysical properties of the AS4/3501-6 composite using the xenon flash method to measure the thermal diffusivity in accordance with ASTM E1461 and differential scanning calorimetry to calculate the thermal conductivity.
Abstract: Thermal diffusivity, specific heat, and thermal conductivity are important thermophysical properties of composite materials. These properties play a significant role in the engineering design process of space systems, aerospace vehicles, transportation, energy storage devices, and power generation including fuel cells. This paper examines these thermophysical properties of the AS4/3501-6 composite using the xenon flash method to measure the thermal diffusivity in accordance with ASTM E1461 and differential scanning calorimetry to measure the specific heat in accordance with ASTM E1269. The thermal conductivity was then calculated using a proportional relationship between the density, specific heat, and thermal diffusivity.
TL;DR: In this article, the thermal properties through the thickness of Carbon-Carbon and the impact of graphitization are examined, and the effect of Graphitization on specific heat, thermal diffusivity, and thermal conductivity is explored.
Abstract: Thermal characterization is essential to the proper assignment of composites to specific applications. Specific heat, thermal diffusivity, and thermal conductivity are critical in the engineering design process and in the analysis of aerospace vehicles, space systems, power generation, transportation systems, and energy storage devices including fuel cells. This paper examines the thermal properties through the thickness of Carbon-Carbon and the impact of Graphitization is explored. Following ASTM standards, the Flash Method and Differential Scanning Calorimetry measured thermal diffusivity and specific heat respectively. These measurements and density data allowed for the computation of thermal conductivity.
TL;DR: In this article, the effects of varying the heat flux at the chip's 1 and 4 mm 2 CHS and the impedance of thermal interface material (TIM) between the Cu substrate and underlying chip were investigated.
Abstract: Advanced spreaders for cooling a 10 x 10 mm underlying computer chip with a central hot spot (CHS) could remove > 85 W of dissipated thermal power at junctions’ temperature < 100 o C. The spreaders comprise a 1.6 - 3.2 mm thick Cu substrate and an 80-μm thick micro-porous copper (MPC) surface cooled by saturation nucleate boiling of PF-5060 dielectric liquid. Investigated are the effects of varying the heat flux at the chip’s 1 and 4 mm 2 CHS and the impedance of thermal interface material (TIM) between the Cu substrate and underlying chip. Results confirmed the effectiveness of the MPC spreaders for cooling the chip and mitigating the effect of CHSs. With a TIM impedance of 0.19 o C-cm 2 /W, the MPC spreader with a 3.2 mm-thick Cu substrate removes 90.1 W and 87.85 W for the chip with 1 and 4 mm 2 CHS when the heat flux ratio (HFR) at CHSs = 6. The chip maximum surface temperatures at the CHSs are 90.16 o C and 96.6 o C and the spreader’s footprint areas are 25.5 and 25.25 cm 2 , respectively. Decreasing the TIM impedance to 0.02 o C-cm 2 /W decreases the chip’s maximum surface temperatures to 73.4 and 76.1 o C, but slightly changes the removed thermal powers from the MPC surface to 90.3 W and 86.24W, respectively.
TL;DR: In this article, the effect of radiation parameters and chemical reaction parameter and power law index on convection heat and mass transfer along a vertical plate embedded in non-Newtonian Power-law fluid saturated porous medium in the presence of first order chemical reaction and radiation is studied.
Abstract: The natural convection heat and mass transfer along a vertical plate embedded in non-Newtonian Power-law fluid saturated porous medium in the presence of first order chemical reaction and radiation is studied. The governing partial differential equations are transformed into ordinary differential equations using similarity transformations. The resulting equations are solved numerically using Shooting method. The effect of radiation parameters and chemical reaction parameter and power law index on non-dimensional velocity, temperature and concentration fields are discussed. The variation of different parameters on heat and mass transfer rates is presented in tabular form.
TL;DR: In this paper, a 3D human body has been designed by unstructured grids and the aim is to obtain convection coefficient of human body by applying finite volume method for each grid and extracted by the weighted area method.
Abstract: In this paper, the aim is obtaining convection coefficient of human body. At first a 3D human body has been designed by unstructured grids. Feet and hands are stretched completely in considered sample. Two segments (standing and supine) are considered for body. Soles and the back of entire body are considered in contact with the ground respectively in these segments. Other parts of human body are exposed to surrounding air. The heat transfer and the body temperature are assumed steady and constant. The results are obtained by applying finite volume method for each grid and extracted by the weighted area method. Then the attained results are validated with the recent experimental results. Good agreement is observed between the obtained results and the previous experimental results. Finally two formulas are derived for natural convection coefficient of human body.
TL;DR: In this paper, a mathematical model is presented to analyse the steady boundary layer slip flow and mass transfer with n th order chemical reaction past a porous plate embedded in a Darcy porous medium.
Abstract: A mathematical model is presented to analyse the steady boundary layer slip flow and mass transfer with n th order chemical reaction past a porous plate embedded in a Darcy porous medium. Velocity as well as mass slips are considered at the boundary. The governing PDEs are transformed into self-similar nonlinear ODEs by similarity transformations. The reduced nonlinear equations are solved numerically. The momentum boundary layer thickness is reduced for increase of permeability and suction parameters, whereas it increases with blowing parameter. The increase of velocity slip parameter reduces the momentum boundary layer thickness and also enhances the mass transfer from the plate. Importantly, due to increase of mass slip the concentration and mass transfer decrease.
TL;DR: In this article, a 3D Computational Fluid Dynamics methodology is adopted by injecting fuel at specified temperatures of 313 K, 353 K and 393 K to overcome the tedious experimental task, and the validation is accomplished after the optimal spatial and temporal steps of discretization are found out.
Abstract: In this work, fuel spray parameters are studied by varying the fuel temperature. To overcome the tedious experimental task, a 3-D Computational Fluid Dynamics methodology is adopted by injecting fuel at specified temperatures of 313 K, 353 K and 393 K. The validation is accomplished after the optimal spatial and temporal steps of discretization are found out. At a fuel temperature of 313 K, advancing the injection timing from 6 deg bTDC to 20 deg bTDC increases cylinder peak pressure from 79.8 bar to 90.9 bar. Relation between the emission characteristics and spray SMD and temperature is studied.
TL;DR: Cyclic and continuous radio frequency heating was applied to implanted chitosan and alginate scaffolds at 4 applied voltages, 3 frequencies, and 2 thermally conditioning environments to simulate the RF treatment.
Abstract: Heat can be potentially used for accelerating biodegradation of implanted tissue engineered scaffolds. Cyclic and continuous radio frequency (RF) heating was applied to implanted chitosan and alginate scaffolds at 4 applied voltages, 3 frequencies, and 2 thermally conditioning environments. A 3D finite element model was developed to simulate the RF treatment. A uniform RF heating was achieved at the scaffold top. For alginate, voltage was the only significant RF heating factor while both frequency and voltage significantly affected RF heating of chitosan. Less temperature gradient across the scaffold was achieved at a conditioning environment at <30 °C. Surrounding tissue was insignificantly affected by RF heating of scaffolds.
TL;DR: In this paper, an experimental study has been made to determine the effect of geometrical (length of vortex tube) and thermo-physical (pressure) parameters on vortex tube performance and air also used as a working fluid.
Abstract: Vortex tube is a simple device which separate an inlet gas with a proper pressure into hot and cold flows .This device is well-suited for generating cooling load gas because it provides the cold gas without using any refrigerants . Many research works has been carried out in order to identify the factors which contribute to Vortex tube performance. Here, an experimental study has been made to determine the effect of geometrical (length of vortex tube) and thermo-physical (pressure) parameters on vortex tube performance and air also used as a working fluid.
TL;DR: In this article, the authors discussed exhaust gas temperature and pollutant emissions characteristics of the combustion of rich natural gas-air mixtures in Pd metal based honeycomb monoliths burner during the period of start-up process.
Abstract: This article discussed exhaust gas temperature and pollutant emissions characteristics of the combustion of rich natural gas-air mixtures in Pd metal based honeycomb monoliths burner during the period of start-up process. The burner needs to be ignited by gas phase combustion with the excessive air coefficient (a) at 1.3. The chemistry at work in the monoliths was then investigated using the stagnation point flow reactor or SPFR. The experimental results in catalytic monolith can be explained from SPFR. The exhaust gas temperature and pollutant emissions were measured by thermocouple K of diameter 0.5 and the analyser every 1 minute, respectively. Meanwhile combustion efficiency were calculated. Catalytic combustion of natural gas plays an important role for low carbon energy in industrial applications.