Heating performance, exergy, and economic analysis of a heat pump drying system with an independent operating ability for drying shiitake mushrooms

In response to the problems of untimely drying in place of agricultural products after harvesting, low drying temperature of open heat pump drying system and low energy utilization of closed heat pump drying system. A novel heat pump drying system is proposed, which uses a gasoline generator as the power source and an open-closed combined heat pump system equipped with a box-type drying chamber. A prototype was constructed to investigate the feasibility and heating performance of this system, and experimental studies were carried out with wet towels and shiitake mushrooms as drying objects, and the system heating performance and specific moisture extraction rate (SMER) were analyzed. The results from the wet towels experiment revealed that the drying temperature decreased by 30%–74% when the system operation mode was the dehumidifying mode (open cycle) compared with the switching of the heating/dehumidifying mode. When the air speed was increased from 2.2 m/s to 4.3 m/s, the mass of water removed increased by 39.4%. The results of the shiitake mushrooms experiment showed that the SMER were 1.19 kg/kWh, 1.18 kg/kWh and 1.05 kg/kWh for gasoline generator drive and electric drive, respectively, which is an improvement of 42%∼61% comparing with the data of other researchers. This study provides guidance for heating performance and structural optimization of a new type of heat pump drying system driven by gasoline generator.