Experimental study on effect of drying air supply temperature on performance of a quasi-two-stage closed loop heat pump drying system for lentinus edodes

Abstract

A new closed loop quasi-two-stage enhanced vapor injection heat pump drying system with high drying air supply temperature and simple structure was proposed and built. Firstly, the system operation characteristics including parameters of both heat pump refrigerant and air cycle sides were analyzed. The effects of different drying air supply temperatures on heat pump system drying performance and drying quality for Lentinus edodes were investigated experimentally. The results showed that the maximum drying air supply temperature in the designed system could reach 70 °C. As the drying air supply temperature raised from 40 °C to 70 °C, the drying rate of L. edodes was significantly increased, the average coefficient of performance of the system (COPsys), average specific moisture extraction rate (SMER) and rehydration ratio first increased and then decreased. The average COPsys, average SMER, drying amount per unit energy consumption and rehydration ratio reached the maximum values when the drying air supply temperature was 55 °C, which were 4.19, 0.320 kg/(kW·h), 0.391 kg/(kW·h) and 3.6, respectively. Compared with hot-air drying of L. edodes, the heat pump drying system proposed in this paper also had a significant improvement in the quality (the rehydration ratio increased by more than 45%).