Experimental Study on the Effect of Loading Density on the Performance of a Closed Drying System Using Quasi-Two-Stage Heat Pump for Lentinus edodes

Drying of Lentinus edodes is an effective method to prevent problems such as rotting and browning. During the drying process, the loading density has a significant impact on system performance and drying quality. Based on a newly designed quasi-two-stage enhanced vapor injection heat pump closed drying system, the effects of different loading densities of Lentinus edodes on moisture ratio, drying rate, coefficient of performance of the system (COP_sys), specific moisture extraction rate (SMER), drying capacity per unit energy consumption, and rehydration ratio were experimentally investigated. The results showed that when the drying air supply temperature was 55 ℃ and the circulating air volume was 580 m³/h, the drying rate of Lentinus edodes decreased gradually with the loading density in the drying chamber, from 1.5 kg/m² to 3.0 kg/m². Meanwhile, the average COP_sys, average SMER, drying capacity per unit energy consumption, and rehydration ratio increased first and then decreased. When the loading density was 2.4 kg/m², the average SMER, drying capacity per unit energy consumption, and rehydration ratio reached the maximum values of 0.320 kg/ (kW·h), 0.391 kg/ (kW·h), and 3.6, respectively. When the loading density was 2.4 kg/m², the average COP_sys reached its maximum of 4.22.