Study on Heat Transfer Characteristics of Micro Channel Heat Exchangers

对于分散的能源系统和化工厂，由于换热器占据了很大的空间，因此需要减小气体-气体换热器的尺寸。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。对文献的仔细搜索未能揭示任何关于气体-气体微型热交换器的换热性能的先前研究。这促使了本研究对气体-气体微型换热器的换热性能进行研究。本研究的目的是得到：1.薄隔墙换热器；2.厚隔墙换热器的换热特性。对隔壁无厚度的两通道换热器进行了数值计算。数值结果表明，在某些情况下，由于能量转换，热通道的平均温度比冷通道的平均温度低。给出了发生温度反转的Re数和Ma数的范围。数值结果还表明，如果由一面墙在均匀温度下、另一面墙保温的平行管道的换热系数求出总的换热系数K，则可以用所谓的NTU-ε方法来估算换热系数。所使用的微型换热器由10块厚度为500μm的不锈钢板组成。每块板上刻蚀了34个高度为200μm、宽度为300μm的通道。工质为空气，流动方式为逆流。揭示了雷诺数对换热性能的影响。并提出了壁面温度恒定的原始换热模型来估算换热系数。该模型可以用来估算厚隔墙微通道换热器的换热系数。

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.