Heating Analysis of a Water Droplet in Between Multi-Wall Hydrophobic Surfaces

Abstract

Droplet heat transfer in between parallelly located superhydrophobic plates is examined. The thermal field inside the droplet is predicted by adopting the experimental conditions. The influence of plates spacing (heights) on the thermal response of the droplet fluid is investigated. Particle injection velocimetry (PIV) is used to validate the velocity predictions. We demonstrated that predictions of flow velocity are in agreement with those of the PIV results. The heating of the droplet in the absence of the top plate gives four circulation cells in the droplet. Once the top superhydrophobic plate is introduced, the flow structure alters, and the number of the circulating structures reduces to two. Lowering the height of the plates increases the droplet Laplace pressure while modifying the fluid flow and thermal behavior. The Bond number is lower than one for all the cases considered; hence, demonstrating that the Marangoni force affects the formation of the circulation cells. The cells redistribute the heated fluid in the droplet interior, which is clearly apparent for the plates with small heights. Temperature enhancement in the droplet bottom section is attributed to the flow current formed due to heat diffusion. The Nusselt number corresponding to the bottom plate increases as the plate heights reduces; however, the opposite is true for that corresponding to the top plate.