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

在这个研究项目中，实验研究了替代制冷剂和非共沸制冷剂混合物的冷凝和蒸发，以获得开发使用环境可接受的制冷剂作为工作流体的热泵/制冷系统所必需的基本数据。采用纯制冷剂HCFC22、CFC114、CFC12和HFC134a以及HCFC22和CFC114的非共沸制冷剂混合物（NARMs）作为工质。采用双管换热器作为试验冷凝器和蒸发器。结果表明：(1)纯制冷剂的冷凝换热系数与Nozu等人修正半经验方程得到的方程具有较好的相关性。(2)对于narm的冷凝，在一定的假设条件下，得到了蒸汽传质的相关方程，并提出了一种预测双管冷凝器传热特性的新方法。(3)纯制冷剂在环空流态的蒸发换热系数与发展Chen思想得到的方程具有较好的相关性。(4)通过对纯制冷剂方程的修正，得到了narm蒸发换热系数的相关方程。(5)获得了HCFC - 22在双管换热器中的瞬态蒸发换热特性和压降，发现其瞬态换热系数低于定常流。

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.