Coil frosting and defrosting in industrial freezers operating near saturated conditions

Whenever moist air exists in the vicinity of a surface whose temperature is both below the dew-point temperature of water vapor in air and below the freezing point, frost will form. This frost contributes to coil heat-transfer performance degradation due to both the insulating effect of the frost layer and the resulting coil blockage. While the frosting problem has been extensively researched, no study has investigated the problem when the freezer is operating near saturated conditions. Field observations of industrial freezer operation indicate that this mode of operation is much more common than originally thought; and that the transition to supersaturated operation can easily occur if proper care is not exercised by either the refrigeration system designer or the freezer operator. Field observations also reveal that operating freezers in supersaturated conditions can significantly accelerate the occurrence of the negative aspects of frost formation vis-à-vis coil heat transfer performance. For this and other reasons, the study presented in this dissertation focused on that aspect of freezer operation with the hope of developing tools and protocols that may help guide refrigeration-system designers and freezer operators avoid the conditions that contribute to this mode of operation; and thus help improve the performance of freezer coils that are particularly prone to the frosting problem.