Heating Enhancement of a Droplet on a Superhydrophobic Surface

Enhancement of heating of a droplet on a hydrophobic surface is investigated. A vertical metal (column) pin is introduced in the droplet and the fluid heating, due to the column pin, is examined. The droplet heating is initiated at the hydrophobic surface and the column pin located in the droplet. The effect of the flow currents on the thermal fields inside the droplet fluid is assessed. An experiment is conducted to assure the velocity simulation results while using the particle image velocimetry (PIV). We demonstrated that the velocity simulations are in good agreement with the data obtained from PIV measurements. Two circulating structures are observed inside the droplet, which are related to the buoyancy and the Marangoni currents. The presence of the column pin changes the number of circulations cells to four inside the droplet. Heated fluid in region of the droplet-solid interface is transferred by the buoyancy current towards the droplet sides and heat diffusion increases temperature rise in the droplet central region. The Nusselt number attains larger values for the droplet with column pin configuration than that of the free droplet, which becomes apparent for the large droplet volumes. The Bond number improves with the presence of the column pin in the droplet; but, the Bond number values become smaller than unity for all the droplets with and without column pin configurations considered.