ICAE 2015

Frost formation and growth on heat exchanger surfaces in refrigeration, ventilation and air conditioning systems has posed a challenge to heat transfer engineers for decades. Frost buildup causes an increase in the airside pressure drop and thermal resistance, yielding a substantial decrease in operational efficiency. Freezing starts in surface defects owing to their geometric singularity and low free energy barrier for heterogeneous ice nucleation. This triggers the formation of a freezing weave, which eventually spreads over the entire surface. The development of a realistic laboratory test has proven to be crucial for the better understanding of the freezing process. Herein, we investigated various hydrophobic coatings and related their surface properties with the frost spreading behavior. While complete freeze-depression is expected to maintain unrealistic, we demonstrate that hydrophobic coatings with defined surface properties significantly reduce frost spreading. This phenomenon, which has most likely been interpreted as freeze-depression in many occasions, we believe it could be exploitable industrially to extend defrosting intervals.

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