9. Icing and defrosting

The frost that forms and the snow that settles on the cold parts of a refrigeration appliance come from the humidity of the ambient air introduced through the opening, and in some cases result from the loss of water from unpackaged foodstuffs.

This moisture transforms into ice, with a density ranging from 0.2 (light snow) to 0.9 (pure ice), on contact with surfaces at temperatures below 0°C. This frost settles preferentially on the evaporator, which is the coldest part of the unit, in the supply and return air ducts, reducing the evaporator's cooling capacity.

This decline is due to the interaction of several factors:

• increase in the pressure drop across the air flow (known as pressure drop) caused by the reduction in the free cross-sectional area of the air flow between the frost-covered fins;...