Effect of dynamic contact angle behavior on droplet topological structure and film thickness evolutions in droplet mode

Abstract

The droplet mode falling film evaporation was an area of intense research due to its thin liquid film and large interfacial area. A two-dimensional mathematical model based on the dynamic contact angle (DCA) model was developed to quantitatively analyze the effect of DCA behavior on droplet topological structure and film thickness evolutions of droplet mode in falling-film evaporation. Due to the movement of the three-phase contact line (vc) considered in the DCA model, the fact that the calculated DCA was significantly greater than the static contact angle (SCA) resulted in the phenomena of the liquid ring and droplet pulsation captured by the DCA model. The observed fluctuations of the DCA and vc might be attributed to the break-up of the liquid neck. For the impact stage, the peaks of the transient film thickness calculated by the DCA model were thicker than those by the SCA model and their differences increased with the increasing circumferential angle. For the metastable stage, the average film thickness predicted by the DCA model was thicker than that by the SCA model due to the captured droplet pulsation and calculated shorter metastable state by the DCA model.