Internal fluid motion and particle transport in externally heated sessile droplets

Abstract

Experiments and numerical simulations were carried out for an evaporating sessile droplet. The droplet was confined in the narrow gap between two glass plates, making it a "Hele-Shaw" droplet and particle image velocimetry technique was used. In case of the evaporating droplet with pinned contact line and exposed to ambient condition, two symmetric but counterrotating convection cells were observed. After complete evaporation, the particles deposited on the substrate near the contact line. The direction of the flow was reversed for a droplet placed on uniformly heated substrate, and the final deposition pattern was a large spot at the center with a thin line at the periphery. For asymmetrically heated substrate a single convection cell appeared, and the final deposition was also asymmetric. When the liquid was subjected to localized heating, the contact line no longer remains pinned and a relatively uniform deposition was obtained after complete drying.

Comparing Internal Flow in Freezing and Evaporating Water Droplets Using PIV

“…The vortices caused by the impact to the surface were traced and the vortex strength was computed. The internal flow was also studied by Thokchom et al [20,21] using PIV in externally heated sessile droplets confined in a narrow gap between two glass plates. The benefit of using a "Hele-Shaw" droplet is in the optics since no image correction has to be done and the surface flow is seen.…”

Evaporation of a sessile water droplet subjected to forced convection in humid environment

“…[13][14][15] The effect of Marangoni flow in water droplets is, on the other hand, not as clearly manifested experimentally. Marangoni convection was observed in the experiments presented by Thokchom et al [16] and Wang and Zhao, [17] where heated water droplets were examined, but only a very weak contribution, if any, of Marangoni convection was observed by Savino et al [18] and Hu and Larson. [19] Small influence of Marangoni convection in water droplets is also in agreement with the findings by Xu et al, [10] where the effect of substrate size and conduction was further examined.…”

Marangoni convection in an evaporating droplet: Analytical and numerical descriptions

“…As a first step, we will test the heuristic extension of the lubrication approximation, substituting in Eqs. (8) and (9) the functionsh(r) and ∂h/∂r, which are obtained from (1), i.e., which correspond to the spherical cap profile of the sessile drop. The equations were written in the form of Eqs.…”

“…The equations were written in the form of Eqs. (8) and (9) in order to represent heuristic description for larger contact angles, where h(r) is substantially nonparabolic. This improves the accuracy for larger contact angles, without changing the solution for small contact angles.…”