Edge-affected droplet dynamic and subsequent frost growth characteristics for horizontal cold plate under different humidity levels

Frosting widely exists in engineering applications and mostly has negative impacts. To better avoid or utilize frosting, more micro and systematic investigations into the frosting mechanisms are necessary. In this study, the combined effect of humidity and plate edge on droplet dynamic and the subsequent frost growth characteristics of a horizontal cold plate is experimentally investigated. The results show that the difference in the durations of droplet condensation stage between edge-affected and unaffected regions is little, and both decrease from around 480 to 43 s when relative humidity (RH) increases from 30% to 80%. In contrast, the difference in the durations of droplet freezing stage between edge-affected and unaffected regions is significant. The former is around 9 s at all humidity levels, while the latter decreases from around 100 s to 40 s when RH increases from 30% to 80%. Meanwhile, the average equivalent droplet diameters in the edge-affected region are 87.3 × 10⁻³–122.1 × 10⁻³ mm, which are 31.0 × 10⁻³–45.5 × 10⁻³ mm larger than in the unaffected region. The frost layer surface roughness at 80% RH is smaller than others due to the frost crystal reverse melting. This paper can help better understand the frosting mechanism from a microscopic scale and guide the accurate prediction of frost formation.