Simulation investigation on a novel open-loop air cycle heat pump drying system

Different from conventional drying technology, the novel technology of an air cycle heat pump drying (ACHPD) system, using air as its working medium, is proposed to solve the problems of low energy efficiency, HCFC refrigerant use, and so on. A mathematical simulation model is constructed to evaluate system performance under various working conditions, and its verification via experimental results from a constructed test bench produced errors of temperature within +/- 1.6%, of drying rate within +/- 0.01%, and of system power within +/- 7%. Compared with a conventional electric heater drying (EHD) system, the energy-saving rate of the ACHPD system reaches about 15-27% when the mass evaporation rate increases from 0.75 kg h-1 to 3.45 kg h-1. Under set working conditions, an increase of inlet air flow rate (150-400 kg h-1) improved the dehumidification energy efficiency ratio (MER) by about 1%. However, the increase of inlet air temperature (10-40 degrees C) and relative humidity (30-80%) reduced MER by about 7% and 21% respectively. The efficiency improvements of heat exchanger (0.3-0.8) can improve the energy efficiency of system by 20%; however, the efficiency improvements of expander (0.55-0.8) and compressor (0.4-0.9) can deteriorate the energy efficiency of system by 17% and 36% respectively. These results would provide new technical references for the application of heat pump technology in drying field from a different perspective.