Electric defrosting analysis of a finned-tube evaporator coil using the enthalpy method

Abstract

When moist air comes into contact with a surface maintained at a subfreezing temperature, which is also below the dew-point temperature of water vapour in air, frost will form. Although this frost formation process is associated with a temporary increase in the heat transfer rate in the initial stages of deposition, the overall thermal performance over an extended period of time is degraded due to the insulating effect of the frost and also due to blockage of the coil and the accompanying reduction in air flow. One method of defrosting employs electric heat to melt the frost of the coil. This paper describes how the enthalpy method can be used to calculate the defrosting time and the temperature distribution in the frost layer during the defrosting process of a finned-tube evaporator coil. While the analysis presented applies mainly to electric defrosting, the method can be easily modified to handle different defrosting methods and processes.