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A Hybrid Numerical Methodology Based on CFD and Porous Medium for Thermal Performance Evaluation of Gas to Gas Micro Heat Exchanger

机译：基于CFD和多孔介质的气-气微型换热器热力性能混合数值方法。

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In micro heat exchangers, due to the presence of distributing and collecting manifolds as well as hundreds of parallel microchannels, a complete conjugate heat transfer analysis requires a large amount of computational power. Therefore in this study, a novel methodology is developed to model the microchannels as a porous medium where a compressible gas is used as a working fluid. With the help of such a reduced model, a detailed flow analysis through individual microchannels can be avoided by studying the device as a whole at a considerably less computational cost. A micro heat exchanger with 133 parallel microchannels (average hydraulic diameter of m) in both cocurrent and counterflow configurations is investigated in the current study. Hot and cold streams are separated by a stainless-steel partition foil having a thickness of m. Microchannels have a rectangular cross section of m m with a wall thickness of m in between. As a first step, a numerical study for conjugate heat transfer analysis of microchannels only, without distributing and collecting manifolds is performed. Mass flow inside hot and cold fluid domains is increased such that inlet Reynolds number for both domains remains within the laminar regime. Inertial and viscous coefficients extracted from this study are then utilized to model pressure and temperature trends within the porous medium model. To cater for the density dependence of inertial and viscous coefficients due to the compressible nature of gas flow in microchannels, a modified formulation of Darcy–Forschheimer law is adopted. A complete model of a double layer micro heat exchanger with collecting and distributing manifolds where microchannels are modeled as the porous medium is finally developed and used to estimate the overall heat exchanger effectiveness of the investigated micro heat exchanger. A comparison of computational results using proposed hybrid methodology with previously published experimental results of the same micro heat exchanger showed that adopted methodology can predict the heat exchanger effectiveness within the experimental uncertainty for both cocurrent and counterflow configurations.
机译：在微型热交换器中，由于存在分布和收集歧管以及数百个平行微通道，因此完整的共轭传热分析需要大量的计算能力。因此，在这项研究中，开发了一种新颖的方法来将微通道建模为多孔介质，其中可压缩气体用作工作流体。在这种简化的模型的帮助下，通过以相当少的计算成本研究整个设备，就可以避免通过各个微通道的详细流量分析。在当前研究中，研究了一种具有133个平行微通道（平均水力直径为m）并流和逆流配置的微型热交换器。冷热流由厚度为m的不锈钢分隔箔分隔开。微通道的矩形横截面为m m，壁厚介于m之间。第一步，仅进行微通道共轭传热分析的数值研究，而无需分配和收集歧管。增加了热流体域和冷流体域内的质量流量，使得两个域的入口雷诺数均保持在层流状态内。然后，将从这项研究中提取的惯性和粘性系数用于对多孔介质模型中的压力和温度趋势进行建模。为了适应由于微通道中气流的可压缩性而引起的惯性和粘性系数的密度依赖性，采用了达西-福施海默定律的修正公式。最终开发了具有收集和分配歧管的双层微型热交换器的完整模型，在该模型中，微通道被模拟为多孔介质，并被用来估算所研究的微型热交换器的整体热交换器效率。使用提议的混合方法与相同微型热交换器的先前发表的实验结果进行的计算结果比较表明，采用的方法可以在并流和逆流配置的实验不确定性范围内预测热交换器的有效性。

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