EXPERIMENTAL STUDY OF INTERACTION BETWEEN FROST GROWTH ON EVAPORATOR AND DYNAMIC CHARACTERISTICSOF AN AIR SOURCE HEAT PUMP

摘要

The frosting process on the surface of the fin-and-tube evaporator and the dynamic performance of an air source heat pump (ASHP) adopting R410A refrigerant were investigated experimentally. The frost thickness was measured by using micro-photograph, and the frost accumulation mass was estimated in terms of the difference in measured humidity before and after the test evaporator. The experimental results indicate that the frost layer thickness increases in a manner of the stepwise pattern as quickly increasing, slowly increasing (or no increasing) and rapidly increasing during the frost formation process. Corresponding to the rapid increasing of the frost thickness, the performance of the ASHP unit degrades in the third stage. It is suggested that the vicious spiral formed by the interaction between the frost growth and the drops in the wall temperature and the air flow rate mainly causes the rapid performance degradation in the third stage. At the meantime, it is found that the performance of the ASHP system, the frost growth rate and the duration of frost-growth cycle are strongly affected by outdoor air relative humidity under frosting conditions.