Two-phase flow distribution in parallel flow mini/micro-channel heat exchangers for refrigeration and heat pump systems: A comprehensive review

Heat pump and refrigeration systems consume a large amount of energy annually around the world. Heat exchanger is an important component of heat pump and refrigeration systems, and its heat transfer performance has a significant influence on their overall efficiency. With the high heat transfer rate and compact structure, mini/micro-channel heat exchangers (MCHXs) have a great potential to improve the cooling and heating capacity of heat pump and refrigeration systems. However, the two-phase flow in parallel channels is prone to maldistribution due to phase separation, which significantly affects the heat transfer rate of MCHXs. This review paper focuses on the research progress of two-phase flow distribution in MCHXs over the last two decades. Experimental studies on the geometry and operating conditions of heat exchanger as well as the fluid properties affecting the distribution of two-phase flow in a mini/micro-channel evaporator are first summarized and analyzed. Then, the addition of insert devices and atomization devices to improve the distribution uniformity of two-phase flow is discussed. Moreover, empirical correlations and simulation models developed to predict the two-phase flow distribution are analyzed. The distribution characteristics of two-phase flow in mini/microchannel condensers are also reviewed, and two typical methods to achieve phase separation are comprehensively summarized. The major conclusions on the inherent mechanisms of two-phase flow distribution are summarized based on reviewed literature. Finally, the outlook for future research in this field is presented. This review aims to serve as a reference guide for further experimental and simulation studies on two-phase flow distribution in MCHXs.