COSI 2015

Hydrophobic coatings were applied to decelerate the spreading of frost origination from ice nucleation spots. The application of these coatings to extend defrosting intervals for devices that are periodically defrosted, for example specific heat exchangers used for heating and ventilation, was evaluated with a novel ice test chamber. The probability of ice nucleation at low subzero temperatures, for example -4°C, is considerably low. However, in case of freezing, a bare aluminum surfaces freeze at once and completely. On hydrophobic coatings, the ice nucleation spot is isolated and growth slowly. At -4°C surface temperature in a +12°C/90% rel. humidity environment, on a surface providing advancing and receding water contact angles of 106° and 96°, a rate for the growth of the average radius of the frozen area of 4 µm/s was observed. Submitting the surface to an air flow of 1 m/s leads to faster frost spreading in flow direction.

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