Effect of face velocity during refrigeration on hot-gas coil-defrosting near-saturated conditions

Abstract

The heat input required to defrost coils within refrigerated spaces is partially removed with the melt, partially warms the coil and refrigerant and partially escapes to the refrigerated space as sensible heat by convection and radiation and as latent heat by evaporation and sublimation. The evaporated and sublimated portions return again both as a refrigeration load and as part of another defrosting cycle. A previous study by the authors showed that the evaporated and sublimated portions are much larger than originally thought relative to the melted portion. While the previous study considered only a coil-face velocity of 3.81 m/s (750ft/min), the focus of this study is to vary the coil-face velocity during the refrigeration portion of the refrigeration/defrost (R/D) cycle and examine their effect on the defrosting process. This study also examines the differences between the types of frost that form at different coil-face velocities during the operation of freezers near saturated or under supersaturated freezer air conditions. Some of the quantities analysed include the defrost efficiency and the fan defrost contribution.