Research on drying Lentinus edodes in a direct expansion heat pump assisted solar drying system and performance of different operating modes.

In this study, a direct expansion heat pump assisted solar drying system was proposed and applied for drying Lentinus edodes. The operation modes of this system were divided into three types according to the purpose of reducing drying energy consumption. Under different environment conditions, the operation performance of direct expansion heat pump assisted solar drying system was investigated. In addition, the system was compared with open solar drying to analyze the drying characteristics of Lentinus edodes. The results showed that the direct expansion heat pump assisted solar drying system under solar collector drying operation mode could increase the outdoor air temperature by 9.8 °C, and the air temperature of the drying chamber could be maintained above 40 °C. The average performance coefficient of the direct expansion heat pump continuous drying was 2.56, and the duration of the drying chamber temperature above 40 °C was 63.8% of the total drying time. The average performance coefficient of the direct expansion heat pump assisted solar energy intermittent drying can reach a maximum value of 6.01. High compressor operating frequency and solar radiation intensity are the main factors affecting the coefficient of performance improvement of the direct expansion heat pump assisted solar drying system. Furthermore, the moisture content of Lentinus edodes under open sun drying was 0.274 g water/g dry matter higher than that under direct expansion heat pump assisted solar drying system. The Page model with R 2 value of 0.996 and RMSE value of 0.0211 was considered the best drying kinetics model for direct expansion heat pump assisted solar drying for Lentinus edodes. [ABSTRACT FROM AUTHOR]