Study on Heat Transfer Characteristics of Micro Channel Heat Exchangers

对于分散能量系统和化工厂，需要减小气-气热交换器的尺寸，因为热交换器在这样的系统中占据许多空间。然而，对微型换热器换热性能的研究仅限于以水为工质的微型换热器。仔细搜索的文献未能披露任何先前的研究，气-气微型换热器的热交换性能。因此，本研究的动机，以获得气-气微型换热器的换热性能。为了获得1.薄隔墙换热器和2.厚隔墙换热器的换热特性，对无隔墙的双通道换热器进行了数值计算。数值结果表明，在某些情况下，由于能量的转换，热通道的平均温度会低于冷通道的平均温度。揭示了发生温度反转的Re数和Ma数范围。数值计算结果表明，如果总传热系数K由一壁恒温、另一壁绝热的平行通道的传热系数求得，则可以用Ntu-ε法估算换热量。微型换热器由10块500 μm厚的不锈钢板组成。在每个板上蚀刻34个200 μm高和300 μm宽的通道。工作流体为空气，流动方式为逆流。揭示了Re数对换热性能的影响。并提出了一种以壁温为常数的原始换热模型来估算换热速率。该模型可用于估算具有厚隔壁的微通道换热器的换热量。

It is required to reduce the size of a gas-gas heat exchanger for a dispersed energy system and a chemical plant, since heat exchangers occupy many space in such a system. However, investigations on the heat exchange performance of micro heat exchangers were limited to one with water as working fluid. A careful search of the literature failed to disclose any prior study for the heat exchange performance of gas-gas micro heat exchangers. This has motivated the present study to obtain the heat exchange performance of a gas-gas micro heat exchanger. Objectives of the present study are to obtain the heat exchange characteristics of ; 1.heat exchangers with thin partition walls.2.heat exchangers with thick partition walls.Numerical computations were conducted for two-passages type heat exchangers whose partition wall has no-thickness. Numerical results show that in some cases the averaged temperature of the hot passage becomes lower than that of the cold passage due to the energy conversion. The ranges of Re and Ma numbers where the temperature inverse occurs, are revealed. Also, numerical results show that the heat exchange rate can be estimated by using the so called Ntu-ε method if the overall heat transfer coefficient, K, is obtained from the heat transfer coefficients for a parallel duct with one wall at a uniform temperature and the other wall insulated.Experiments were conducted for thick partition wall case. The micro-heat exchanger used is consist of 10 stainless plates of 500 μm thick. 34 channels of 200 μm height and 300 μm width are etched on each plate. Working fluid is air anf the flow type is counter flow. The effects of Re numbers on heat exchange performance are revealed. And also a primitive heat exchange model whose wall temperature is constant to estimate the heat exchange rate is proposed. The proposed model can estimate the heat exchange rate of a micro-channel heat exchanger with thick partition wall.