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. Field observations suggest that the nature of the frost forming on the surface is dependent on a host of variables, including the existence of haze and fog in the air during the frost formation process. These observations suggest that formations taking place when the air is supersaturated produce a more dense snowlike frost with an associated larger defrost energy penalty and a poorer coil heat transfer performance. An experimental investigation has been conducted to determine the relationship between formations of the type described above (which happen in the supersaturated zone of the psychrometric chart) and the psychrometric theory of moist air. One of the objectives of the experimental program upon which this paper partly reports is to search for a demarcation line between snowlike formations and the more traditional formations and to correlate the findings with those predicted using psychrometric theory. One benefit is to eventually develop a protocol that guides refrigerating system design engineers in their quest for a better refrigeration system design and more efficient operation. This paper reports on the findings of this experimental investigation and supports the results with visual observations and images taken inside the laboratory freezer under study.

Units: I-P