Frosting characteristics of superhydrophobic surface under desublimation frosting conditions

Abstract

Frosting type of an air source heat pump under frosting conditions is divided into condensation frosting and desublimation frosting. Superhydrophobic surface has been proved to have good anti-frosting performance for air source heat pump under condensation frosting conditions. However, its frosting characteristics and anti-frosting performance are not clear under desublimation conditions. Therefore, a visual frosting experiment system was built to achieve frosting characteristics of superhydrophobic surface under desublimation conditions. The experimental results show that the frosting process of the superhydrophobic surface is similar to condensation frosting even under the desublimation conditions. The water vapor still forms condensate droplets and the frost crystals grow on the surface of the freezing droplets, while the frosting of the bare surface is very different from condensation frosting and the water vapor directly become solid frost crystals. The frost thickness of the bare surface is 1.27, 2.70 and 2.05 times than that of the superhydrophobic surface under various desublimation conditions, which indicates that the superhydrophobic surface can also inhibit frost layer growth under desublimation conditions. The reason for the preferential formation of condensation frosting on superhydrophobic surface under desublimation conditions was analyzed. The nucleation critical radius, nucleation barrier and nucleus surviving rate generate by desublimation and the supersaturation requires for desublimation on the cold surface with big contact angle are much larger than that of condensation. These are the main reasons why the superhydrophobic surface still preferentially chooses condensation frosting under desublimation conditions.