A modeling study of different kinds of sessile droplets on the horizontal surface with surface wettability and gravity effects considered

Droplet phase change is important for energy storage and saving technology. The initial profile of the droplet is extremely important for its vaporization or solidification on a horizontal surface. To understand the effect of liquid physical properties on droplet profile, a theoretical model was developed in this study, based on the Young-Laplace equation with gravity effect specially considered. After the model was experimentally validated by comparing the geometric shape of water droplets, it was further used for predicting droplet shapes of other materials, and thus analyzing the influence of different physical properties, such as temperature, pressure, surface wettability, etc. Results show that the results of this model agree well with the experimental data. The maximum and average deviations are less than 4.5% and 1.5%, respectively. For all kinds of droplets on the fixed surfaces, when the temperature increases, the droplet contact radius increases and height decreases. The droplets of nitrogen and carbon dioxide are more sensitive to temperature than ethanol and ethylene glycol droplets. For 20 μL droplets on the surface of contact angle 150°, when the temperature changes from 273.15 K to 293.15 K, the droplet contact radiuses increase by 30.6% for carbon dioxide, 1.2% for ethanol and 0.67% for ethylene glycol, and the droplet heights decrease by 42.9%, 2.5%, 1.1%, respectively. Results of this study are meaningful for predicting the phase change process of droplets on the horizontal surface by controlling their initial profiles.