Frosting and defrosting characteristics of surface-treated louvered-fin heat exchangers: Effects of fin pitch and experimental conditions

Frosting experiments were conducted on surface-treated (hydrophilic, hydrophobic, and dual) louvered-fin heat exchangers with varying fin pitches, and the frosting behavior of the rows was investigated in terms of the experimental conditions. In the early stage of experiments, three of these surface-treated heat exchangers exhibited the highest heat transfer rate at 16 FPI (fins per inch), in particular, the hydrophobic unit had the smallest reduction in the heat transfer rate during the latter stage due to the frost-retardation effect. Hence, the hydrophobic unit had the largest overall heat transfer rate. For the hydrophilic and dual-treated heat exchangers, the first row (front side) showed more active frost growth than the second row (rear side), and thus the leading-edge effect was demonstrated in these two heat exchangers. By contrast, with the hydrophobic heat exchanger, the leading-edge effect was not observed when the refrigerant temperature was higher than −10 °C, or the airflow rate was higher. The ratio of remained water after defrosting was the highest for the hydrophobic unit, but this unit still showed the highest overall heat transfer rate during the repeated frosting and defrosting experiments cycle, due to frost retardation.