Numerical and Experimental Analysis of Heat and Mass Transfer Processes on Water Trays in Household Refrigerators

Frost formation on the cold evaporator surface is a typical problem in household refrigerators. It happens due to humidity present in the ambient air associated with frequent door openings. In addition, mass transfer from stored goods to dry internal cabinet air and moisture infiltration through door gaskets also contribute to frost formation on the evaporator surface. To prevent this, the evaporator has to be defrosted manually or automatically (as in modern refrigerators). To do so, an electrical heater is switched on at a preset time and frequency and defrosts the evaporator. During this time, defrosted water is drained through a pipe into a water tray which is usually placed at the vicinity of the compressor. There the water evaporates mainly due to heat transfer from hot compressor shell. This system of defrosting and evaporation works well in areas with low relative humidity, where the amount of defrosted water is small and the evaporation rate is higher when compared to places with high relative humidity. Moreover, the compressor shell temperatures of high efficient compressors are not usually high enough to provide the minimum evaporation rate to balance the defrosted water flow rate and thus avoid water overflow. The aim of this work is to get a better understanding of the defrosted water evaporation process and to come up with low cost, practical and more efficient designs of water trays. To this end a test facility was designed and constructed to reproduce the compressor operating conditions and the defrosted water flow rate and temperature. The test rig was placed within a climate-controlled room with a strict control of air temperature and relative humidity. A mathematical model was also developed to predict the water evaporation rate based on the fundamental conservation equations of mass and energy. Several tests were carried out under different operating conditions and with different water trays designs. The model predictions were compared to the experimental data base with most of the points falling within an error band of ?10%