Experimental investigation of frost characteristics on vertical cold plate under forced convection influenced by surface temperature

Engineering equipment is mostly vertically installed to enhance its defrosting efficiency, while the detail early frosting under forced convection is not sufficiently investigated. To better understand the frosting mechanism, experiments on a vertical plate under forced convection, with the surface temperature varied at a range of −25 to −10 ℃, are carried out. A series of micro and dynamic frost characteristics, including frosting stage, frost thickness, dynamic frosting rate and frost layer surface roughness, are studied and discussed. Results show that three frosting stages, droplet condensation and coalescence, solidified liquid tip-growth and frost layer growth stages, end within 700 s with frost thickness less than 460 × 10⁻⁶ m. Compared with natural convection, promotion on the increase of frost thickness under forced convection is less obvious. At 1,200 s, the gap between the frost thickness under forced and natural convection has increased to 460.02 × 10⁻⁶ m. Lower surface temperature, less than −15 ℃, realizes large dynamic frosting rate when frosting begins and intensifies fluctuation of roughness, with the maximum fluctuation reaching 20.55 × 10⁻⁶ m. Higher surface temperature, around −15 to −10 ℃, leads to the formation of large droplets with the maximum diameter of 800.74 × 10⁻⁶ m, which influences the roughness value but has little influence on its variation. Results of this work are expected to provide references for optimization of anti-frosting and defrosting technologies in engineering applications.