An experimental study on the frosting characteristic and performance of a micro-channel evaporator in an air source heat pump unit

Frosting and refrigerant distribution uneven easily are two key problems restricting the wide application of micro-channel heat exchanger in the field of air source heat pump (ASHP). In this paper, frosting experiments were carried out on two kinds of micro-channel heat exchanger in three cases that with different refrigerant distribution characteristics. Frost and temperature distribution characteristics and their influence on the heat pump's COP and heating capacity was studied. The results show distribution of refrigerant in heat exchanger directly affects the frost and temperature distribution on the surface of micro-channel heat exchanger, and affects the heating capacity and COP of ASHP greatly. Vertical placement of flat tubes and horizontal placement of the headers can be beneficial to the refrigerant distribution compared with that with the headers vertically placed. Flow direction of refrigerant in the heat exchanger must be from bottom to top to avoid deteriorated heat transfer performance and instability of ASHP. Difference between the lowest temperature and largest temperature on heat exchanger surface can be used as an index to judge whether ASHP works in high performance state.