Edge-affected frosting characteristics on a horizontal cold plate at different surface temperatures considering the initial sessile droplet

Frosting phenomenon widely occurs in engineering applications and causes significant damage. Following defrosting, sessile droplets would remain on the equipment surfaces, adversely affecting the subsequent frosting stage. To quantitatively investigate the effect of the sessile droplet on the frosting process, the edge-affected frosting experiments considering the initial sessile droplet at different surface temperatures are conducted. The results show that the freezing moment would not be advanced in the presence of the sessile droplet in this study. The presence of the sessile droplet suppresses condensation in the inner region to a certain degree, as evidenced by the average values of the equivalent contact diameter, which decreases by 25.1 %, 21.7 %, and 27.2 % from Cases 1(b) to 3(b), respectively. Furthermore, the frost layer thickness catch-up mechanism between the edge and inner regions can also be revealed through a comparison analysis of crystal behaviors observed on the sessile droplet (Region A) and those on condensate droplets (Region B). In general, the height difference of frost layers between the two regions increases first and then decreases, and the process is significantly impacted by crystal collapse. At the surface temperature of −12 °C, the maximum height difference observed before the notable collapse of the crystal is 0.362 mm, which subsequently decreases by 17.1 % following the collapse of the crystal. Besides, the surface roughness goes through three stages of increasing, fluctuating, and decreasing, corresponding to the frost crystal behaviors of growth, collapse, and reverse melting. This study contributes to enhancing the comprehension of the frosting with residual sessile droplets, further providing theoretical support for the defrosting strategy.