Droplet on oil impregnated surface: Temperature and velocity fields

Abstract

The water droplet dynamics on silicon oil impregnated polydimethylsiloxane (PDMS) replicated and inclined surface is considered and the droplet sliding velocity incorporating force and energy balance is formulated. Since silicon oil film is kept at 308 K and water droplet temperature is initially at 300 K, the droplet heat transfer due to temperature disturbance is examined during droplet sliding. Velocity and temperature fields are computed using the experimental conditions. The droplet sliding velocity resulted from the analytical formulation is compared with the high-speed camera data. In addition, the predictions of the droplet surface temperature are validated with the thermal camera data. The findings reveal that the droplet sliding velocity obtained from the analytical formulation is in agreement with the high-speed camera data. The predictions of droplet temperature also agree well with the thermal camera data. Droplet heat transfer results in two contour rotating circulating structures in the droplet, which contribute to convection heat transfer in the droplet fluid. Silicon oil cloaking on water droplet surface alters the heating rates and flow structure in the droplet. As the distance along the silicon oil surface increases, a unique circulation structure is developed inside the droplet, which enhances the Nusselt and the Bond numbers. Formation of a single circulation is attributed to increased silicon oil ridge height in the frontal region of the droplet.