Phase Change Characteristics of Alternative Refrigerants in Double-tube Heat Exchanger

本研究对替代工质和非共沸混合工质的冷凝和蒸发过程进行了实验研究，获得了开发以环境可接受工质为工质的热泵/制冷系统所需的基础数据。工质为纯HCFC22、CFC114、CFC12和HFC134a以及非共沸混合工质(NARMS)。试验冷凝器和蒸发器采用双管式换热器。结果表明：(1)纯制冷剂的冷凝换热系数与Nozu等人的半经验方程有很好的关联性。(2)对于NARMS的冷凝，在一定的假设条件下，得到了一个关联式。并提出了一种预测双管冷凝器内换热特性的新方法。(3)纯制冷剂在环状流区的蒸发换热系数与发展陈的方程得到的关联式很好。(4)通过对纯制冷剂方程的修正，得到了NARMS的蒸发换热系数关联式。(5)得到了双管换热器内HCFC22的蒸发换热和压降的暂态特性，发现其瞬时换热系数比定常流下的低。

In this research project condensation and evaporation of alternative refrigerants and nonazeotropic refrigerant mixtures have been investigated experimentally to obtain the basic data which are necessary to develop heat pump/refrigeration systems using environmentally acceptable refrigerants as working fluids. Pure refrigerants of HCFC22, CFC114, CFC12 and HFC134a and nonazeotropic refrigerant mixtures (NARMs) of HCFC22 and CFC114 were used as working fluids. The double-tube heat exchangers were used as test condenser and evaporator. The results are as follows :(1) The condensation heat transfer coefficient of pure refrigerants is correlated well with the equation obtained by modifying a semi-empirical equation of Nozu et al.(2) For condensation of NARMs, a correlation equation of vapor mass transfer is obtained under some assumptions, and a new method to predict the heat transfer characteristics in a double-tube condenser is proposed.(3) The evaporation heat transfer coefficient of pure refrigerants in the annular flow regime is correlated well with the equation obtained by developing Chen's idea.(4) A correlation equation for evaporation heat transfer coefficient of NARMs is also obtained by modifying the equation of pure refrigerants.(5) Transient characteristics of evaporation heat transfer and pressure drop of HCFC 22 in a double-tube heat exchanger are obtained and it is found that the transient heat transfer coefficient is lower than that for steady flow.