surface characteristics, liquid behaviors, contact angle hysteresis, condensation, frost melt water retention
Liquid behaviors, including droplet condensation and frost melt water retention, of fins during frosting and defrosting processes on three aluminum fins with different surface characteristics under winter operating conditions of an air source heat pump were investigated. The effects of the surface characteristics, including the contact angle and the contact angle hysteresis, were analyzed. Droplets were observed firstly on a bare fin and on a super hydrophobic fin last, and exhibited different sizes and shapes under the effects of the surface characteristics. The droplet distribution was sparser on the super hydrophobic fin than on the other two fins because of the consolidation, rolling and departure of droplets. There was an obvious difference on frost melt water retention between the three fins. Residual water formed a thin water film on a hydrophilic fin, while only a few spherical droplets of small sizes stayed on the super hydrophobic fin. The effects of the surface characteristics were found to be significant on the mass of residual water, which decreased by 79.82% on the super hydrophobic fin compared with that on the hydrophilic fin. Finally, the effects of the contact angle and the contact angle hysteresis on frost melt water retention were quantitatively analyzed. Results indicate that the super hydrophobic fin can restrain the droplet condensation and frost melt water retention.