Freezing of sessile water droplet for various contact angles

• Numerical and experimental studies of sessile droplet freezing.
• Use the Young-Laplace equation to determine the profile of sessile droplets.
• Agreement between the predicted and observed moving water–ice interface.
• The freezing time exponentially increases with contact angle.

We present both modeling and experimental study of the freezing of a sessile water droplet on a cold surface with different contact angles. The numerical model consists of two parts. One is to determine the geometric profile of sessile droplets by the Young-Laplace equation, and the other is to solve the two-dimensional Stefan problem via the equivalent heat capacity method. An experimental setup is built to observe the freezing process, and the moving water–ice interface is recorded by a CCD camera. A good agreement is found between the experimental observations and the numerical simulations of the moving water–ice interface in a sessile droplet deposited on both hydrophilic and hydrophobic cold surfaces, suggesting that the present model can well describe the freezing process of sessile droplets. Based on the modeling and simulations, it is shown that for a given droplet the freezing time exponentially increases with increasing contact angle. Results of our study are helpful to better understand the anti-ice/-frost mechanism of the superhydrophobic surfaces.