Heating performance of a novel two-stage evaporator air-source heat-pump for drying applications

Abstract

In this study, a novel air-source heat-pump drying-system, with a two-stage evaporator is designed and studied. The two evaporators of the heat-pump are connected in series with respect to the airflow direction, and the low-humidity air, which is dehumidified by the two evaporators, can be used for drying. Furthermore, a heat and mass transfer model of the two-stage evaporator is established. The performance and characteristics of the evaporator with different operating-parameters are studied. The second evaporator can recover the heat after the air has been dehumidified by the first evaporator. There is evidence for a sudden-change zone in the evaporator’s heat-absorption capacity, when the evaporation temperature is near the air dew-point temperature. The heat absorption capacity of the evaporator, at per unit heat-transfer temperature-difference, increased with decreasing ambient air-temperature and increasing evaporation-temperature. To enable different drying conditions, an air-velocity control method for the two-stage evaporator is presented. Highlights A two-stage evaporator air-source heat pump for drying was designed. There was a sudden heat change zone of evaporator along the evaporation temperature. Evaporation temperature could effect the heat gain under 1 °C temperature difference. The control strategy of air velocity of the two-stage evaporator was given.