Study on the effect of circulating air volume on the performance of closed loop heat pump drying system

Abstract

• 1. A closed heat pump drying system for high temperature industrial drying is proposed. • 2. The effect of circulating air volume on the system drying performance is studied. • 3. The maximum drying temperature of 71.1℃ can be obtained for drying metal parts. • 4. The system has high energy efficiency and excellent dehumidification performance. Considering the fact that high energy consumption and low drying temperature of current drying system was not appropriate for the high temperature industrial drying, a closed loop heat pump drying system with high drying temperature was designed, established and explored. As a key operation parameter, the circulating air volume was closely related to the drying temperature and could affect the system performance. The effect of circulating air volume on the circulating air temperature, coefficient of performance (COP), moisture extraction rate (MER) and specific moisture extraction rate (SMER) were all experimentally investigated in this study. The results showed that with the increase of circulating air volume, the circulating air temperature was gradually decreased, while the system COP was oppositely increased. And both the system MER and SMER firstly increased and then decreased with increasing air volume. The drying temperature could exceed 70 °C when the circulating air volume was below 539.8 m 3 /h, and reach its maximum value 71.11 °C when the circulating air volume was 388.5 m 3 /h, meeting the high drying temperature requirement. At the same time, both the system MER and SMER could reach their maximums (i.e., 3.27 kg/h and 1.40 kg/(kW·h)), showing the excellent dehumidification performance of this system. Besides, when the circulating air volume was 736.1 m 3 /h, the system COP could reach its maximum 6.56, indicating high energy efficiency. These results can provide guidance for the popularization and application of heat pump drying technology in the industrial drying field.