Abstract: The heat pump system used in a dryer has the characteristics of miniaturization, closed-loop circulation, operation in high humidity environments, and transient performance. To address the shortcomings of current heat pump dryers, a systematic analysis of the R290 heat pump system used in dryers was conducted from both theoretical and experimental perspectives, focusing on the thermodynamic characteristics of the refrigerant side, the circulation characteristics and energy distribution of the humid air side, and the overall energy loss of the dryer. The theoretical analysis obtained the relationship between the heat entering the drum and the total heat released by the condenser in a closed-loop system. The experimental results showed that the R290 heat pump system had a high dryness at the inlet of the evaporator, which reduced the heat transfer efficiency of the evaporator and increased the resistance along the way. The heat released by the condenser could not all enter the drum. Effective means to increase the heat entering the drum include reducing the amount of re-evaporated water and increasing the relative humidity of the air leaving the drum. The entire dryer had a heat loss of approximately 20%, and an effective way to further improve energy efficiency would be to strengthen the seal of the drum to reduce leakage.

Key words: R290, Heat pump dryer, Closed-loop circulation, Moist air, Energy analysis