Experimental study of cyclic frosting and defrosting on microchannel heat exchangers with different coatings

This paper aims to further explore the frosting and defrosting performance of coatings applied to microchannel heat exchangers. A visualization cycle experiment of hydrophilic, desiccant and hydrophobic coated microchannel heat exchangers was performed, and compared with the uncoated sample, under frosting condition. The results show that the delayed frost formation of the hydrophilic coating and the desiccant coating is not obvious. Even worse, the average heat transfer of the hydrophilic coating sample is 19% lower than that of the uncoated coating. By contrast, in the first round, the hydrophobic coating has a significant anti-frost effect, with a 24% reduction in pressure drop and a 40% increase in heat transfer. But it attenuated the most after four cycles. Taken together, the application potential of hydrophobic coatings is the greatest, but the horizontal fins and crest and trough structures, making drainage difficult, are key factors that limit its superior performance. Additionally, when evaluating the frosting performance of the coating of the microchannel heat exchanger, it is not recommended to use the frosting amount alone or the index of thickness and pressure drop, but to comprehensively consider the heat exchange effect.