Heating of a water droplet on inclined transparent polydimethylsiloxane (PDMS) surface

Abstract

Heat transfer from replicated hydrophobic and transparent PDMS surface to a water droplet is considered. The laser texturing of alumina surface is carried out to obtain hydrophobic surface and later the textured surface is replicated by polydimethylsiloxane (PDMS) via a solvent casting method. An experiment is carried out to assess the water droplet pinning on the replicated inclined PDMS surface while keeping the replicated surface at uniform temperature (308 K). The flow and temperature fields inside the inclined water droplet are simulated in line with the experimental conditions. The flow velocities inside the droplet are validated through the data obtained from the particle imaging velocimetry (PIV). It is found that the velocity predictions agree well with the PIV data. The droplet heating results in a circulation cell inside the droplet due to the Marangoni and the buoyancy currents. Increasing inclination angle of the PDMS replicated surface enhances the maximum velocity inside the droplet, which is more pronounced for the large size droplets. The Nusselt and the Bond numbers increase with the inclination angle of the PDMS surface.