Experimental measurements of the surface coating and water retention effects on frosting performance of microchannel heat exchangers for heat pump systems

Frost formation on louvered fin microchannel heat exchangers was experimentally investigated in this paper with the aim of studying the effect of hydrophilic and hydrophobic surface coatings and of water retention on their frosting performance and on their frost growth rates. Frost mass and thickness growth rates, corresponding coil heat transfer rates, capacity degradation, and air-side pressure drop for five microchannel coils with different surface coatings were measured and discussed. The experimental data showed that the hydrophilic and hydrophobic surface coated coils considered in the present work accumulated frost on the heat transfer surfaces with visible difference in the type, appearance, and patterns of the frost. The duration of the frosting cycle, the heat transfer rate, and air-side pressure drop were similar to the ones of a louvered aluminum fin microchannel heat exchanger with uncoated surfaces. For the operating conditions tested in this work, hydrophobic and hydrophilic coatings on microchannel coils affected the heat transfer capacity in frosting conditions by up to 15%.

► Frost formation on microchannel coil was experimentally investigated.
► Effect of four different coating was assessed on water retention behavior.
► Fin temperature is the primary influential parameter.
► Different coatings and water retention had a minor impact on the frosting performance.