Theoretical and Experimental Study on Drying Performance and Prediction Model of Heat Pump Clothes Dryer

The drying process of a heat pump clothes dryer (HPCD) has complex characteristics such as strong coupling (the thermal cycle of the refrigerant side is coupled with the drying cycle of the air side), time variation (the system operating parameters change with drying time), and integration (limited space integrating evaporator, condenser, fan, compressor, etc.), and such complexity makes theoretical analysis of the drying performance of HPCD difficult. Based on certain simplifications, this study analyzes the effects of different compressor capacities and fan airflows on the moisture extraction rate per unit time (MER) and moisture extraction rate per unit energy consumption (SMER) of the HPCD. Under the same airflow, the SMER increases first and then decreases with the condenser discharge air temperature and evaporator discharge air temperature, when the discharge air temperature of the condenser is between 20 ℃ to 80 ℃ and the discharge air temperature of the evaporator is between 10 ℃ to 50 ℃. For the HPCD analyzed in this paper, when drying a half load (5 kg) of clothes, theoretical calculations identified an optimal condenser discharge air temperature of 53 ℃ and an evaporator discharge air temperature of 27 ℃ that maximized the SMER. The optimal temperatures are related to the COP of the heat pump system and the mass and heat transfer capacity of air with clothes. Under the same evaporator discharge and condenser discharge temperatures, within the airflow range of 0.02~0.08 kg/s, the SMER first increases and then decreases with the airflow. There is an optimal working airflow of 0.047 kg/s that maximizes the SMER, which is related to the drum power and the airflow resistance characteristic of the clothes dryer. According to methods for measuring the performance of tumble dryers for household use, testing verified that the theoretical analysis results were consistent with experimental tests. This research method and its conclusions provide theoretical guidance for the design and optimization of HPCD.