Experimental investigation of the effects of hydrophobic coating on air-side pressure drop, condensate retention, and frost layer growth in wavy fin-and-tube heat exchanger

This work presents an experimental study on wavy fin-and-tube heat exchangers with uncoated and hydrophobically coated surfaces, evaluated under frosting and dehumidifying conditions. The objective was to examine how surface treatment influences phase-change behavior, condensate retention, and overall air-side performance. The coating did not postpone frost initiation but altered its growth pattern, yielding a more homogeneous distribution and a lower-density structure than that observed on uncoated coil. For equivalent frost mass, coated surfaces produce frost layers up to 89% thicker while maintaining lower pressure drop. The possible reasons for this seemingly counterintuitive behavior will be discussed in this work. When comparing coated surfaces to uncoated ones, thermal conductance improved by as much as 7.8% during frosting. Hydrophobic treatment also reduces water retention significantly, with at least 40% less condensate retention compared with the bare surface. To facilitate prediction and design, empirical models were formulated for the mass of retained condensate and relative air-side pressure drop on coated coils, all achieving satisfactory agreement. The findings demonstrate that surface modification can alleviate maldistribution of frost, suppress condensate accumulation, and enhance heat exchanger performance. These insights, supported by validated correlations, offer practical tools for advancing the design of energy-efficient heat exchangers for air conditioning, heat pump, and refrigeration systems operating in humid or subfreezing environments.