An experimental investigation on the frosting and defrosting process of an outdoor heat exchanger in an air conditioning heat pump system for electric vehicles

Abstract

The heat pump air conditioning system is a promising solution for energy conservation and ensuring a good driving range can be maintained. Micro-channel heat exchangers are used as outdoor heat exchangers to improve the heat transfer efficiency. A heat pump system introduces frosting problems to the outdoor heat exchanger, especially in a low temperature and high humidity environment. This study conducted an experiment on the frosting and defrosting process of the outdoor heat exchanger of a heat pump air conditioning system for electric vehicles. The surface of the outside heat exchanger had an uneven distribution of the frost layer owing to the variation in the liquid-phase refrigeration occupation. Thermal parameters of the system were obtained. The suction pressure was sensitive to the frosting process, decreasing from (0.15–0.25) to (0.02–0.1) MPa, and it can be used as a frosting monitoring parameter. The frosting and defrosting behavior was also studied at a micrometer scale on the surface of the heat exchanger. The ice bridge phenomenon was observed in the frosting process. Hydrophilic and hydrophobic treatments of the heat exchanger surface were conducted for compassion and it was found that the hydrophilic treatment of the surface of the outdoor heat exchanger of the vehicle heat pump effectively slows frosting. Future experimental research should investigate the effects of superhydrophobic and superhydrophilic surface treatments, in addition to hydrophilic and hydrophobic surface treatments on the performance of the heat exchanger, to improve the performance of the overall heat pump system.