Thermal and Flow Behavior of a Droplet Fluid Wetted by Parallel Hydrophobic Walls

Abstract

Thermal analysis of a locally heated droplet located in two parallel plates with hydrophobic surfaces is considered. The spacing between the parallel plates is altered to modify the three-phase contact line of the droplet on both hydrophobic surfaces. The thermal state of the walls is altered via changing temperature difference between the parallel plates while initiating the droplet heat transfer. In this case, the bottom plate temperature is increased, while the top plate temperature is kept constant. The thermal field developed inside the droplet is obtained numerically incorporating the conditions used in the experiments. The influence of the droplet volume on the Nusselt and the Bond numbers is examined for the cases of droplets formed (i) on a hydrophobic plate and (ii) in between two parallel plates with hydrophobic wetting state. It is found that the droplet wetted by the parallelly located hydrophobic plates alters the circulation cell structure formed inside the droplet. Temperature field extends further inside the droplet as the wetted diameter is extended on the hydrophobic surfaces. The Nusselt number attains larger values for the two-plate case than the free droplet on a single plate case. The Bond number remains less than unity for the free and two-plate wetted droplets.