Effect of drying air supply temperature and internal heat exchanger on performance of a novel closed-loop transcritical CO2 air source heat pump drying system

Abstract

A novel closed-loop transcritical CO2 air-source heat pump drying (HPD) system with a relatively simple structure, higher drying temperature, and internal heat exchanger (IHX) for the drying of medical equipment was proposed and built. With or without the IHX in the system, the effects of different drying air supply temperatures on the performance of transcritical CO2 HPD system were studied experimentally. The results showed that the maximum drying air supply temperature (DAST) in the designed system could reach 72.9 °C. As the DAST raised, whether with or without the IHX in the system, the coefficient of heating performance (COPh), coefficient of system performance (COPsys), and specific moisture extraction rate (SMER) decreased gradually and moisture extraction rate (MER) increased continuously. When the DAST was 70 °C, COPh, COPsys, MER and SMER were respectively 3.68, 6.07, 3.27 kg/h and 1.68 kg/(kW·h) in the HPD system without the IHX, and were respectively 4.00, 6.89, 3.67 kg/h and 1.97 kg/(kW·h) in the HPD system with the IHX. In contrast, the compressor discharge pressure decreased 4.26 %–5.99 %, COPh increased 1.39 %–8.65 %, COPsys increased 1.89 %–13.57 %, MER increased 4.68 %–14.01 %, SMER increased 6.93 %–17.18 % in the HPD system with the IHX.