Effect of compressor speeds on performance of a closed loop heat pump drying system

Abstract

• A novel heat pump drying prototype with relatively high air temperature is proposed. • The effects of compressor speed on the performance of the system is studied. • The maximum drying temperature that the system can achieve is greater than 70 °C. • The drying system has high energy efficiency and excellent drying effect. In view of the current situation about environmental pollution and high energy consumption in industrial metal parts drying methods, a closed loop heat pump drying (CLHPD) system with a relatively high circulating air temperature was proposed and established. The compressor speed is a vital parameter that affects the performance of the CLHPD system. The effect of compressor speeds on circulating air temperature, coefficient of performance (COP), moisture extraction rate ( MER · ) and specific moisture extraction rate ( SMER · ) of the system were experimentally studied in this work. The results showed that, with the raise of compressor speed within 3000 to 4200 r/min, the drying air temperature and the MER · of the system increased, the COP and SMER · of the system decreased. The drying air temperature reached a maximum of 75 °C and the MER · obtained a maximum of 3.90 kg/h at the compressor speed of 4200 r/min. The COP reached a maximum of 6.4 and the SMER · obtained a maximum of 1.62 kg/(kW·h) at the compressor speed of 3000 r/min. In an actual industrial production, the compressor speed should be adjusted according to the specific demand to balance the relationship between MER · and SMER · . These can provide references for further research and application of heat pump drying technology in the metal parts drying and even other industrial drying fields.