Research On Heating Performance Of A Heat Pump Drying System Driven By Gasoline Generator

Agricultural products are widely distributed and far away from the heat pump drying room,which seriously affects the application of heat pump drying system in the post-harvest drying.The application of heat pump drying is restricted due to the unequal distribution of agricultural products and electricity in rural areas.The open and close heat pump drying systems have the problems of low drying temperature,low energy utilization rate,respectively.A heat pump drying system driven by a gasoline generator with an independent operating ability was proposed to solve this problem.The system had two operating modules,namely,heating and dehumidifying modes.The waste heat of air discharged from the drying chamber and gasoline generator was utilized.The main research contents are as follows:(1)The main components of heat pump drying system were designed and calculated.The type and quality of agricultural special products,the input energy in drying room and dehumidification load were determined.The heat pump units,gasoline generators,exhaust gas heat exchanger,air-air heat exchanger,chamber drying chambers and fans were designed and calculated.According to calculation results,a prototype of the HPDs driven by a gasoline generator was built.(2)The heating performance and economics of the system were studied using by drying wet towel.Results showed that the inlet air temperature of the drying chamber reached a maximum of 80°C in heating mode.Meanwhile,the inlet air relative humidity of the drying chamber rapidly reduced to less than 20% in dehumidifying mode.When the drying wind speed increased,the heating capacity of the system increased and the water removal rate increased.Therefore,the maximum drying wind speed is determined as 4.3m/s in the subsequent tests.When the ambient temperature decreases,the heating capacity of condenser and exhaust gas heat exchanger reduced,but the heating duration increases.(3)The heating performance and economics of the system were studied using by drying shiitake mushroom.Results showed that when driven by gasoline generator,the inlet air temperature reached a maximum value of 80°C.The heating capacity of condenser,air-air heat exchanger and exhaust heat exchanger were 2.78 k W?1.84 k W and 0.49 k W.The drying cost was 3.77 yuan/kg.When driven by electricity,the maximum inlet air temperature was65°C.The heating capacity of condenser and air-air heat exchanger were 2.36 k W and 1.37 k W.The drying cost was 0.40 yuan/kg.(4)The exergy analysis were performed to investigate the optimization direction of the system.The exergy analysis of the system for drying shiitake mushroom found that the evaporator,condenser,exhaust gas heat exchanger,air regenerator,and gasoline generator had larger avoidable exergy destruction,indicating that these components possessed higher improvement priority.Accordingly,55% of exergy destruction can be reduced when these components are optimized.(5)The simulation study was carried out with mushroom as agricultural specialty products in low temperature.The results showed that when the ambient temperature decreases,the drying temperature,heating capacity,water removal and primary energy utilization rate decrease,and the drying cost increases;If the insulation is strengthened,the heat loss of the system is reduced,the drying temperature is increased,and the heating capacity of the system is increased.