Experimental investigation on thermo‐driving heat transfer in porous medium in a centrifugal force field

Based on the research in turbine blade super cooling techniques, experiments were carried out to investigate the thermo‐driving heat transfer phenomenon in a new cooling configuration filled with porous medium in a centrifugal force field. Moreover, the heat transfer effectiveness of the configuration was compared to one with no porous medium. The results showed that the thermo‐driving heat transfer effectiveness of the configuration filled with porous medium could be enhanced by increasing the rotating speed, heat flux, and cooling air speed. Meanwhile, the heat transfer effectiveness of the configuration was strengthened with the installation of porous medium. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(6): 329– 338, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20219     

Forced Convective Heat Transfer in a Porous Plate Channel

INTRODUCTIONHeattransferenllancen1enttechniquesplayaveryimportantroleintllermalcontroltechnologies1lsedwithnlicroelectronicchips,powerfullasermirrors,aerospacecraft,thermalnuclearfusion,etc.Itiswidelyrecognizedthattl1eheattransfercanbein-creasedbyil1creasingthesurfaceareaincontactwiththecoolant.TuckermanandPease[1,2]pointedoutthatforlaminarflowinconfinedchannels,theheattransfercoefficientisinverselyproportionaltothewidthofthechannelsincethelimitingNusseltnum-berisconsta11t.Theybuiltawate…     

Natural convection and radiation heat transfer in a vertical porous layer with a hexagonal honeycomb core (Part 2: heat transfer experiment)

Combined natural convection and radiation heat transfer characteristics in a vertical porous layer with a hexagonal honeycomb core were investigated experimentally. The temperature distributions on the honeycomb core wall and the combined heat transfer rates through the porous layer were measured. The measurements of the heat transfer were accomplished using the guarded hot plate method. The honeycomb core wall was made of paper and large-mesh foamed resins were inserted into the honeycomb enclosures. The measurements were performed by varying the radiation parameters between 0.5 and 0.65, varying the temperature ratios between 0.01 and 0.1, and varying the Darcy-Rayleigh numbers between 5 and 80, and for a fixed aspect ratio H/L = 1. The experimental results for Nusselt numbers agreed well with our available numerical results. © 1999 Scripta Technica, Heat Trans Asian Res, 28(4): 295–306, 1999     

等温容器内多孔介质强化导热研究

等温容器是在充放气过程中容器内温度基本保持不变的一种特殊容器,在气动系统中有着广泛的应用.为强化放气过程中容器壁向内部的导热,以容器截面为研究对象,对内部铜丝的分布进行了探讨.在细铜丝填充密度一定的情况下,基于多孔介质模型,以容器截面导热热阻最小为目标,优化出两层和三层变密度填充下金属丝的分布.其热阻与均匀填充时相比,分别减少了37.63%和43.70%.研究结果表明,通过改变等温容器内细铜丝的分布可以强化容器壁向内部的导热.     

管内填充多孔介质强化换热的数值研究

管内填充多孔介质强化换热的基本原理是构造热边界层,增大壁面附近流体的温度梯度,并且流动阻力增幅不大。本文运用数值模拟的方法,模拟填充多孔介质管内的流场和温度场,探讨填充比例φ、渗透率Da以及空隙率ε对管内对流换热的影响规律。研究表明,提高填充比例φ和减小渗透率Da都能明显提高换热效果,但也增加了管内流动阻力。空隙率ε对强化换热作用不大,但高空隙率可以明显降低管内流动阻力,在实际中应选用空隙率较大的多孔介质。     

Numerical simulation of forced convective heat transfer of molten salt in tubes

熔融盐作为太阳能热发电中的重要的传热蓄热介质,其强制对流传热特性对如何强化对流传热和设计以熔融盐作为工质的换热器具有很重要的指导意义。建立了熔融盐-油套管式换热器内不同种类的熔融盐在不同工况下的强制对流传热模型,数值模拟并理论研究了管内熔融盐强制对流传热特性,提出数值模拟的熔融盐对流传热关联式;并将数值模拟结果与实验结果进行了对比。在此基础上分析了流速对管内熔融盐对流传热系数和热流密度的影响规律。结果表明在Re处于10000～60000的范围内数值模拟和实验结果具有较好的一致性。     

Natural convective heat transfer and fluid flow in a porous medium filled corrugated enclosure: Effect of discrete heat sources

In this work, we investigate the two-dimensional unsteady natural convective fluid flow problem in a porous-corrugated enclosure with a fixed sinusoidal heated upper wall. The corrugations of the enclosure are discretely heated while vertical walls are maintained isothermally cold. Subject to where the heat sources are located, five different cases are taken into consideration. The vorticity–streamfunction equations are discretized using a transformation-free higher order compact approach, and the hybrid BiCGSTAB technique is used to solve the system of algebraic equations that derives from the numerical discretization. To validate our findings, we first compare them to previously published numerical and experimental data. The numerically simulated outcomes are then examined over a variety of essential parameters, such as the Darcy (10⁻⁵ ≤ Da ≤ 10⁻¹), Rayleigh (10³ ≤ Ra ≤ 10⁶), and Prandtl (0.1 ≤ Pr ≤ 10) numbers. Symmetric and asymmetric fluid flow phenomena are observed. Asymmetric flow phenomenon can be caused by miscible or non-miscible movements of lighter fluids by heavier fluids, or almost exclusively by nonuniform buoyancy-driven forces caused by density variations that have arisen because of variations in fluid temperature. The averaged Nusselt value for Case 1 and Case 5 exhibits the highest percentage ratio. The thermal boundary layer is strongly affected by compression, dispersion, suppression, the zone of stratification, and the outweighing of isotherms. The simulated results are visualized by stream functions, isotherms, local and averaged Nusselt number plots.     

三维填充床内换热及热回流机理研究

利用计算流体力学（CFD）对顺序排列多孔介质小球的三维填充床进行数值模拟。研究填充床内位置及空气流速变化对温度分布、努塞尔数影响,并对多孔介质小球的热回流特性进行分析,揭示填充床内传热机理。结果表明：相比于气-固两相交替存在处,与小球相切处的热的非平衡性更强。最高温度上游的换热强度与下游相比更强烈;当流速增加时,上游的对流换热作用增强,下游变化不大。在热回流过程中,在入口区域对流换热占主导地位,导热和辐射换热作用较弱;在主流场区域,导热占主导地位,其次是辐射换热,对流换热作用最弱。     

Effect of variable viscosity and thermal conductivity on heat transfer in a circular porous passage with axial conduction

In this study, heat transfer in a circular porous passage with axial conduction and variable viscosity and thermal conductivity numerically has been investigated. Heat transfer for the different values of Da and Pe is investigated. The results found show that Nusselt distribution with variable viscosity does not significantly differ from that with constant viscosity in both thermally developing and fully developed regions. However, in the developing region there is a significant difference between Nusselt distribution with variable thermal conductivity and Nusselt distribution with constant thermal conductivity. In the fully developed region Nusselt distribution with variable and constant thermal conductivities does not drastically differ. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21028     

Natural convection and radiation heat transfer in a vertical porous layer with a hexagonal honeycomb core (Part 1: numerical analysis)

Combined heat transfer characteristics were obtained numerically for three-dimensional natural convection and thermal radiation in a long and wide vertical porous layer with a hexagonal honeycomb core. We assumed that the porous layer was both homogeneous and isotropic. The pure Darcy law for fluid flow and Rosseland's approximation for radiation were used. The numerical methodology was based on an algebraic coordinate transformation technique and the transformed governing equations were solved using the SIMPLE algorithm. The effect of radiation on the heat transfer characteristics was investigated over a wide range of radiation numbers and temperature ratios for two Darcy-Rayleigh number values (Ra^* = 100 and 1000) and for a fixed aspect ratio of H/L = 1. The results are presented in the form of combined radiation and convection heat transfer coefficients and are compared with the corresponding values for pure natural convection. © 1999 Scripta Technica, Heat Trans Asian Res, 28(4): 278–294, 1999     

Investigation of Boiling Heat Transfer of Binary Mixture from Vertical Tube Embedded in Porous Media

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多孔介质对冷热流体横向射流混合过程热波动的影响

运用流固耦合方法建模,应用FLUENT计算软件平台对填充有多孔介质的T型连接方形管道内冷热流体横向射流混合过程的流动和热传递进行大涡模拟,采用了Smagorinsky-Lilly亚格子模型,获得了瞬时速度和温度分布.结果表明,填充多孔介质能够有效减少T型连接管道中冷热流体横向射流混合的温度和速度波动.固体骨架的导热率较...     

热质渗透壁面饱和多孔介质通道流动与热质传递的数值模拟

利用数值模拟方法研究了多孔介质中存在温度梯度、浓度梯度并具有热质渗透壁面时的受迫对流对传热传质的影响。采用有限容积法在同位网格上离散控制多孔介质内流体流动与热质传递方程守恒方程(即N-S)，对流项采用二阶精度的QUICK格式，扩散项采用中心差分格式。利用SIMPLE算法求解压力和速度耦合问题。利用所发展的程序研究了在不同孔隙率，不同的温度、浓度边界条件下，流场、温度场和浓度场以及Nu和Sh的变化规律。     

Heat transfer performance of a flexible looped heat pipe using R134a as a working fluid: Proposal for a method to predict the maximum heat transfer rate of FLHP

This paper presents the heat transfer performance of a Flexible Looped Heat Pipe (FLHP) using R134a as a working fluid. In our evaluation system, an evaporator and a condenser are connected by long flexible tubes with a diameter of 3 mm, and the total piping length of this looped heat pipe system is approximately 7500 mm. We selected porous Teflon with an effective pore diameter of 2r_cw = 1.2 µm to overcome high gravitational heads. Elevation of the evaporator above the condenser ΔH = H_e ? H_c) was changed in three conditions [ Top heat mode (ΔH = +1 m), Horizontal mode (ΔH = 0), Bottom heat mode (ΔH = ?1 m)] considering the terrestrial application and the influence of gravity on the FLHP performance was investigated. FLHP provided high thermal transport capacities over long distances through small cross‐sectional flexible tubes compared with conventional heat pipes. We also proposed an analysis method to predict the maximum heat transfer rate of FLHP. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(4): 306–318, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10093     

基于格子Boltzmann方法的饱和土壤渗流与传热数值模拟

本文利用随机多孔介质生成算法重构了与真实土壤外貌相近的多孔介质几何结构。通过引入不可压耦合双分布格子Boltzmann模型（lattice Boltzmann model ,LBM）对孔隙尺度下单相饱和土壤渗流和传热进行了模拟。着重讨论了不同渗流压差、孔隙率、土壤固体颗粒尺寸分布对流动与传热的影响。结果表明：土壤渗流速度与渗流压差呈线性单调递增关系,平均温度随渗流压差增加而增大,但温升速率逐渐减缓;当孔隙率增大时,渗流速度增加,且当孔隙率大于0.58时,对流换热作用迅速增强,土壤温升速率显著加快;对于相同孔隙率,当土壤固相颗粒尺寸较大时,流动出现典型优先流效应;随着土壤固相颗粒尺寸减小,土壤温度变化逐渐趋于平缓,平均温度降低。     

Magnetohydrodynamics boundary layer flow and heat transfer in porous medium past an exponentially stretching sheet under the influence of radiation

Buoyancy forces result from the cooling or heating of a continuous stretching sheet, which causes a change in the resulting flow and thermal fields, and hence the heat transfer behavior in the manufacturing process. The study of the thermal buoyancy induced in boundary layer flow is important due to its recent advances in the areas of nuclear energy, electronics, and space technology. In this perspective, the aim of the present study is to investigate the effect of the buoyancy parameter on the magnetohydrodynamics boundary layer flow over an exponentially stretched sheet in the presence of nonlinear thermal radiation and porous media. Using similarity transformation, the flow model of partial differential equations is transformed into a set of coupled nonlinear ordinary differential equations. The efficient fourth‐order Runge‐Kutta scheme with the shooting method is used to solve the reduced equations. The impact of various associated parameters on velocity and temperature profiles were analyzed and computed through graphs. The major outcome of the present study shows the enhancement in the velocity distribution with the increase in the buoyancy parameter. Also, the increase in thermal buoyancy and thermal radiation leads to an increase in fluid temperature. Moreover, it is worth to note that the fluid velocity declines with the augmentation of the magnetic parameter.     

Heat Transfer and hydrodynamics in Annular Chromatography：CFD—Simulation and Experiments

IntrotctiouAImular chrDmatography Provides the POssibility ofseparating multicomponent fixtures continuously inone single unit. The rotating annulus of thechromatotw can be filled with arbitw stationalsPhases depending on the existing separation Problem.The feed is introduced at a fixed and stationary sechonat the top of the unit, while the eluent is distributedeverywhere else around the upper circumference. At thebottom the separated Products can be collected atcendn stationals exit angle…     

含内热源可燃性多孔介质中的传热研究

煤粉、弹药等含内热源的可燃性多孔介质传热过程在自然界和工程中广泛存在。文中分析了可燃多孔介质的热传递机理，建立了相应的导热计算模型，给出了典型物种在内热源作用下的内部温度场。     

Forced convective heat transfer for fluid flowing through a porous medium with internal heat generation

Forced convection in channels filled with packed beads with internal heat source was numerically analyzed by using the extended Darcy model for the flow and energy conservation equations with nonthermal equilibrium (NTE). The temperature difference between the matrix and fluid phases was discussed with three dimensionless parameters (Re_p, H/d_p, and k_s/k_f). It is concluded that the thermal equilibrium assumption may be adopted for the situation when the solid conduction dominated over the convection or when the heat transfer coefficient between the two phases is large at large Re_p. The Nusselt number at the wall with the variation of Re_p for different k_s/k_f was also investigated. © 2001 Scripta Technica, Heat Trans Asian Res, 30(3): 213–221, 2001