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.

Keywords:

• Air-source heat pump
• evaporator
• evaporation temperature
• heat and mass transfer
• condensation

Disclosure of interest statement

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work.

Additional information

Funding

This work was supported by the Research Foundation of Education Bureau of Hunan Province (Grant Number: 20A499) and the High-level Talent Gathering Project in Hunan Province (Grant Number: 2019RS1059)