The effect of frost on the UA-value and the air-side pressure drop of a domestic refrigerator-freezer evaporator with interference fit fins was evaluated. Over a ten-hour test period, during which the air flow was maintained at a constant rate, the UA-value was found to steadily increase as frost was deposited on the coil. This UA-value increase was accompanied by a substantial increase in the air-side pressure drop. In an effort to determine the reasons behind the increase in the UA-value, a section of the evaporator was instrumented with thermocouples. It was determined that the increase was due to an increased air-side heat transfer coefficient and an increase in the surface of the evaporator due to the surface roughness of the frost. The decrease in the contact resistance due to the filling of the gaps between the evaporator tube and mechanically joined fins was determined to be negligible.

KEYWORDS: frost, performance, domestic, refrigerators, freezers, pressure drop, coils, evaporators, finned tubes, thermocouples, heat transfer coefficient, surface area