Heat recovery scheme design and thermodynamic analysis of closed-cycle heat pump drying system

In order to improve the specific moisture extraction rate (SMER) of the closed-cycle heat pump drying (CHPD) system applied to paddy drying, three types (Heating evaporator outlet moist air with drying chamber outlet moist air, heating evaporator outlet refrigerant with condenser outlet refrigerant, heating evaporator outlet moist air with condenser outlet refrigerant) of heat recovery schemes are designed based on the CHPD system. Thermodynamic models of various CHPD systems are established, and their thermodynamic characteristics are calculated through sensitivity analysis and exergy analysis. The results indicate that using drying chamber outlet moist air and condenser outlet refrigerant to heat evaporator outlet moist air can improve the SMER of the CHPD system, with the improvements of 0.46 kg/kWh and 0.50 kg/kWh, respectively. And these two can achieve a benign combination to form an optimal heat recovery scheme, resulting in a 35.59% improvement in the SMER of the CHPD system from 2.61 kg/kWh to 3.54 kg/kWh. Moreover, the exergy loss of the CHPD system with the optimal heat recovery scheme is mainly in the auxiliary condenser, compressor, drying chamber, and evaporator, accounting for 32.38%, 17.62%, 15.28% and 13.33%, respectively.