Experimental investigation on frosting performance of a microchannel heat exchanger in heat pump system for electric vehicles

Frosting of outdoor heat exchangers deteriorates the heat transfer performance of the electric vehicle (EV) heat pump system. This study conducted frost experiments on the outdoor heat exchanger of an EV heat pump air-conditioning system, considering different flow configurations, tube arrangements, and frontal air volume. The purpose of the study was to establish the optimal tube arrangements and flow configurations for minimizing frost formation and maximizing system performance. The results indicate that a three-flow configuration outperforms a two-flow setup under frosting conditions. Specifically, a flow sequence of 14-21-35 increases the heat capacity by 15.05 %–20.64 % compared to that of the reverse flow order of 35-21-14. The flow sequence a-b-c represents the number of flat tubes along the refrigerant flow process. Additionally, the coefficient of performance (COP) increases by 1.19 %–3.55 %. Higher airflow reduces frost formation. A significant correlation exists between the refrigerant distribution within the heat exchanger and the corresponding frost distribution on the surface of the microchannel heat exchanger. The frost formation rate was slower for the flat tube vertical arrangement. Furthermore, horizontal tube arrangements were more conductive than vertical ones, providing a more uniform temperature distribution and higher heat transfer rates (an increase of up to 2.7% in heat transfer and 3.4% in heat capacity). The COP of the vertical arrangement was consistently higher than that of the horizontal arrangement by 1.4 %–3 %.