Study on Heat Transfer Characteristics of Micro Channel Heat Exchangers

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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.