Experimental and numerical study on freezing process of water droplets under surfaces with different wettability

Abstract

• This paper conducts experimental and numerical study on droplets freezing process under different wettability conditions. • The effects of nucleation surface temperature, freezing image, volume factor, freezing time and freezing front on droplet freezing process are analyzed. • The maximum error between the theoretical and experimental values of droplet freezing time is only 9.05%. • The droplet freezing front with CA < 90° is concave, while the droplet freezing front with CA > 90° is convex at first and gradually becomes concave. Water droplet freezing experiment platform is designed, and the freezing process of droplet on different surfaces (hydrophilic surface and superhydrophobic surface) was studied in depth by experimental and simulation methods. The variation of water droplet freezing process (nucleation temperature, water droplet freezing image, volume factor, droplet freezing time and frozen front) is studied. The results show that the nucleation temperature range of the superhydrophobic surface is larger than that of the hydrophilic surface at the same cooling rate. And on the superhydrophobic surface, the number of bubbles in the water droplet increases with the increase of freezing rate. The volume factor of the water droplets on the hydrophilic surface increased significantly at the initial stage of freezing, while the volume factor of the water droplets on the superhydrophobic surface gradually increased with time. Compared with the hydrophilic surface, the droplet freezing time on the superhydrophobic surface decreases faster with the surface temperature. The error between the theoretical and experimental values of water droplet freezing time is small, and the maximum error is only 9.05%. Finally, in the process of water droplet freezing, the frozen front gradually grows from the bottom to the top and releases small bubbles. When the freeze is complete, spikes appear on top of the droplets. The temperatures at different positions during the freezing process of water droplets are different. The droplet frozen front with contact angle less than 90° is concave, while the droplet frozen front with contact angle greater than 90° is convex at first and gradually becomes concave.