Frosting behavior of louvered-fin and tube heat exchanger after surface treatment: Experimental analysis

Abstract In heat pump systems, frost creates insulation, restricts airflow, and induces stress that can have serious negative effects on the heat exchanger. Hydrophobic surface treatment is a low-cost, efficient, passive defrosting method that has attracted widespread research attention. In this study, the hydrophobic-modification surfaces of louvered-fin heat exchanger (HEX) in heat pump systems were investigated at microscopic and macroscopic scales, respectively. Frosting and defrosting experiments were conducted on evaporators with hydrophobic surfaces on an automotive performance test bench to provide novel information regarding the hydrophobic louvered-fin HEX. The nucleation growth process of modified fins in the microscopic state was studied under classical nucleation theory and electron polarization theory. The experiments show that the refrigerant flow rate of the bare HEX is drastically reduced at 35 min, leading to a sharp decay in heat pump system performance. The air pressure drop in the HEX at this time is 140 Pa. The time taken to reach this air pressure drop for the coated HEX is 153 min, which indicates that the hydrophobic surface has excellent anti-frost performance. We also find that subcooling acts as an intrinsic driving force for nucleation. The nucleation work increases by 77.8% as the bare HEX moves from the surface temperature region of −20 °C to the −15 °C region. The nucleation work on the hydrophobic surface increases by 255% at −20 °C compared to the bare surface. The theoretical analyses of surface elemental composition, non-bonded electron polarization, and crystal perturbation are consistent with the experimental results.