STUDY ON THE CONDENSATION HEAT TRANSFER AND FLOW MECHANISM OF ALTERNATIVE REFRIGERANTS IN MICRO CHANNELS

点击翻译按钮获取中文摘要

In this study, it is aim to contribute to develop the very small and high performance condensers by clarifying the characteristics of local heat transfer and pressure drop in parallel channels with small diameter experimentally. The results are summarized as follows.(1) The Chischolm-Laird type correlation is proposed. In this correlation, the coefficient of second term changed from 21 to 4.81 and using X_<11> instead of X from the experimental results of total pressure drop with changing the outlet quality and mass velocity as a parameter. As a result, by using the correlation, predicted values are within ±30% error for most of all data of total pressure drop.(2) It is confirmed that the predicted values of the present correlation agree with the data of pressure distribution along the flow direction within ±30% error.(3) Compared the pressure drop data with the correlation of Mishima-Hibiki, the data agree with the correlation within ±30% by using X_<11>. The data also compared with t … More he correlation of Haraguchi et al. The data, however, don't agree with the correlation. In this study, hydraulic diameters of the tubes are 0.7 to 0.9, Mishima and Hibiki proposed the correlation based on the data of the tube with 1 to 4mm in diameter, but Haraguchi et al. proposed the correlation based on the tube with 8.5mm in diameter, therefore, the data agree with the correlation of Mishima-Hibiki, however, the data don't agree with the correlation of Haraguchi et al.(4) Compared the heat transfer data with the correlation of Moser et al., the data agree with the correlation within ±30% error in the case of the mass velocity above 300kg/m^2s, but disagree with the correlation in the case of the mass velocity below 200kg/m^2s. This reason is that Moser et al. didn't take account of the influence of the natural convective condensation heat transfer, and so, in the case of low mass velocity, when the influence of natural convection isn't small, it is hard to present the phenomena by using this correlation.(5) The data also disagree with the correlation of Haraguchi et al., which is based on the data of the tube of 8.5mm in diameter. However, using the correlation of Mishima-Hibiki for the pressure drop multiplier factor instead of the correlation of Haraguchi et al. for the pressure drop in their heat transfer correlation, most of all the data agree with this modified heat transfer correlation within ±50%. This reason is that Haraguchi et al. take account of both of the forced convective and natural convective condensation heat transfer, and so predicting accuracy becomes higher when the influence of tube diameter is took account of.(6) From the results (4) and (5), there is the influence of gravity even in the case of small diameter tubes when the mass velocity is low. Less