Frost crystal growth characteristics on surface of frozen water droplets with collapse and reverse melting behaviors considered

Existing studies have demonstrated that frost layer consists of interlacing frost crystals that grow on the surfaces of numerous frozen droplets. To gain a deeper understanding of frosting mechanism, this study experimentally investigates the effects of droplet volume, relative humidity, and plate temperature on the growth characteristics of frost crystals on the surfaces of frozen droplets. The results show that the growth process of frost crystals on a frozen droplet can be categorized into three distinct stages based on the collapse and reverse melting behaviors of frost crystals. The frequency of frost crystal collapse along the contour of a frozen droplet increases from 0.21 Hz to 0.75 Hz as the droplet volume rises from 0.38 μL to 1.50 μL, and from 0.38 Hz to 0.76 Hz as the plate temperature decreases from −10 °C to −30 °C. In contrast, the minimum frequency of 0.54 Hz occurs at a moderate humidity level of 60 % among the tested humidity levels. Besides, the average reverse melting amplitudes of the topmost frost crystals range from 6.3 to 24.0 µm in the tested conditions. At 600 s, the topmost net height of frost crystals increases by 16.7 % when the droplet volume increases from 0.38 μL to 1.50 μL, by 50.6 % when the relative humidity increases from 45 % to 75 %, and by 94.2 % when the plate temperature decreases from −10 °C to −30 °C. These results can help reveal the law of frost crystal evolution and guide the development of accurate frosting models.