The Effect of Frosting on the Performance of Domestic Refrigerator-Freezer Finned Tube Evaporator Coils

Abstract

The effect of frost formation on the performance of a domestic refrigerator-freezer evaporator coil was investigated. A low temperature evaporator test facility was developed to closely simulate refrigerator-freezer conditions. The rate of frost deposition on the evaporator was determined to be constant with respect to time for a ten-hour testing period over a range of air inlet temperatures and relative humidities, refrigerant temperatures, and airflow rates. Higher humidities and air inlet temperatures and lower refrigerant temperatures were found to increase the frosting rate significantly. Varying the airflow rate was found to slightly affect the frosting rate. Increasing the airflow rate increased the frosting rate a small amount, while, decreasing the airflow rate decreased the frosting rate an equally small amount. However, it appears that the actual correlation between airflow rate and frosting rate is not this straight-forward, but is, instead, the result of the influences of the mass transfer coefficient, the evaporator surface temperature, and the air moisture capacity. How these factors balance one another determines the actual relationship between frost rate and airflow. rate. In addition to these findings, it was found that the UA-value of the evaporator increased as frost was-deposited on the coil while a constant airflow rate was maintained through the coil. The increase at the highest frosting rates was on the order of 40% but was accompanied by an exponentially increasing air side pressure drop.Air Conditioning and Refrigeration Center Project 0