Effect of defrost heat leakage on freezer temperature rise during periodical defrost cycles in a frost-free refrigerator-freezer with an electric defrost heater

摘要

Periodical defrost actions are essential for the frost-free refrigerator-freezer to remove frost on the evaporator and recover its heat transfer performance. However, defrost heat could leak into the freezer and raise its temperature during defrost cycles. In this article, the effect of defrost heat leakage on freezer temperature rise of a frost-free refrigerator-freezer using an electric defrost heater was experimentally investigated. The defrost cycle was subdivided into three stages: heating, melting, and draining. Results show that in the heating stage, little warm air leaked into the freezer due to the obstruction of the frosted evaporator, so freezer temperature hardly rose (by less than 0.1 degrees C/min). In the melting stage, flow area between adjacent fins gradually enlarged with frost melting from the bottom to the top of the evaporator; thus, warm air leaked into the freezer, raising its temperature by 0.6 degrees C/min in average. In the draining stage, the adjacent-fin flow area reached maximum as nearly all the frost had been removed throughout the evaporator; hence, large amount of warm air entered the freezer and raised its temperature by 1.0 degrees C/min. To the best of the author's knowledge, the stage-based acceleration in freezer temperature rise during defrost cycles was covered for the first time.