The mechanism of Defrost Heaters

- Mar 21, 2020-

Electric defrost methods make use of electrical heating elements which are mounted adjacent to the evaporator coil or integrated into the evaporator coil. During a defrost cycle, the refrigerant flow to the evaporator is interrupted and the heating elements are energized. The evaporator fans then blow hot air over the evaporator surface. Radiation, conduction and/or convection heat transfer between the heating elements, air and the evaporator cause the frost to melt. Electric heating defrosting usually involves electrically heating up the surface of an outdoor coil to melt off frost. Since heat is being added externally to the evaporator, only a portion of the heat generated is used to melt the frost. The remaining portion of the heat is transferred to the surroundings. Approximately 1% or more of the heat generated by the electric defrost heaters goes into melting the frost while the remaining excess heat is transferred to the air and food products within the display case. This excess heat must then be removed when the refrigeration system resumes operation after the defrost cycle. Compared to off-cycle defrosting, the electric defrost method is relatively quick. In addition, electric defrost has low first cost but high operating cost.  Experimental study was carried out to investigate feasibility and efficiency of the defrost method with air bypass circulation and electric heater for cold storage. Five defrost cases with different defrost heaters and defrost air circulation modes were comparatively studied.