An experimental investigation of frosting characteristics considering edge effect for aperture plate lower surface affected by relative humidity

There is a perforated fin that is widely used in air source heat pump units due to its outstanding heat transfer efficiency. An emerging low-cost method of frost suppression is to reduce relative humidity by placing a wire mesh. Perforated fin and wire mesh can be reduced to an aperture plate. To investigate the influence of relative humidity on the frosting characteristics of an aperture plate, a series of frosting experiments are conducted, with relative humidity varying at a range of 50.0% to 80.0%. The results show that, as the relative humidity rises, both the droplet condensation and growth and droplet solidification stages shorten, and the average frost layer thickness, frost layer surface roughness, and frost layer growth rate rise. At 1800 s, compared to the average frost layer thickness at 40.0%, 50.0% in the inside hole region rose by 46.81%, while 50.0%–80.0% in the edge-affected region rose by 50.27%, 109.26%, and 128.45%, respectively. Compared to the nonlinear variation in the inside hole region, the frequency of reverse melting in the edge-affected region decreases gradually with the increase of relative humidity. The results of this study contribute to the understanding of the frosting process of perforated fins or wire mesh.