Study On The Performance Of Quasi Two-stage Compression Heat Pump Drying System

Drying is a process with high energy consumption,accounting for 12% of the total energy consumption in society.In this context,heat pump-drying technology has received an increasing amount of attention due to its wide application range,energy saving and better maintenance of the drying quality of materials.To further reduce the drying energy consumption,this paper proposes a quasi-two-stage compression heat pump drying system based on the traditional heat pump-drying system.The characteristic of the system is that a two-stage compressor is used to achieve two-stage compression.The refrigerant outlet of the airway high temperature evaporator and the airway low temperature evaporator is connected to the high pressure suction port of the compressor,respectively.This article first compares the performance of the quasi-two compression heat pump drying system and the traditional heat pump-drying system.The results show that under the same air state point parameters(drying box inlet temperature 60℃,outlet temperature 53℃),quasi-two compression heat pump drying the COP of the system is 6.954,and the COP of the traditional heat pump drying system is5.177,which confirms the energy-saving characteristics of the quasi-two-stage compression heat pump-drying system.In view of the characteristics of high-temperature evaporator and low-temperature evaporator that process hot and humid air in stages,three air treatment processes are proposed,and a prediction model for the performance of the quasi-two-stage compression heat pump drying system is established.Using EES software to compile the program,COP and dehumidification energy consumption ratio(SMER)under the three air treatment processes according to the calculation results,and analyze the air condition of the inlet and outlet of the drying box and the outlet air of the high temperature evaporator.The influence of parameters,air volume,evaporating temperature and condensing temperature on system performance(COP,SMER,etc.),the final determination is that the inlet temperature of the drying oven is 55°C,and the outlet temperature is 48°C.In this state,the COP is 6.035 and the SMER is 0.9kg/kW· h.Then,the exergy analysis model of the quasi-two-stage compression heat pump drying system was established,and the exergy loss rate of each link of the quasi-two-stage compression heat pump drying system and the exergy efficiency of the system was obtained.The exergy efficiency of this system is73.4% in the preheating stage and 39.6% in the stable drying stage.Among the main components,in the preheating stage,the condenser accounts for the largest exergy loss rate of 63.1%;in the stable stage,the compressor has the largest exergy loss rate,accounting for 68.7%.Based on the optimal parameters obtained by theoretical analysis,various components of the secondary compression heat pump drying system were selected,and a set of quasi-secondary compression heat pump drying experimental devices and test systems were developed.The experimental device can achieve single-stage compression of the preheating stage,or two-stage compression of the temperature-made drying stage,which can meet the drying process requirements of different materials.Finally,the drying characteristics of white radishes were conducted using this experiment.The results showed that compared with constant temperature drying,the finished product with variable temperature drying had better color and less obvious wrinkle.Therefore,the variable temperature drying was of more research significance.