Heat transfer and internal fluidity a droplet located in between parallel hydrophobic surfaces with varying spacing.

Highlights • Flow and temperature fields inside droplet are significantly influenced by hydrophobic plates spacing. • Almost stagnation region is developed in central region of droplet when plates spacing is reduced. • Nusselt number remains almost same for further reduction of the plates spacing. • Maximum Bond number remains less than unity in droplet indicating importance of Marangoni current. Abstract Heat transfer and fluid flow inside the droplet located in between two parallel hydrophobic surfaces are considered. The functionalized silica nano-particles are deposited on the glass plates to create hydrophobic wetting state. The influence of hydrophobic glass plate spacing (plate heights) on the heat transfer characteristics and internal fluidity of droplet is examined. Temperature disturbance is introduced across the droplet via altering temperature settings on the top and the bottom plates. An experiment is carried out to monitor the droplet geometric features via high speed camera during squeezing action of the plates. The flow and temperature fields in the droplet fluid are simulated incorporating the experimental conditions. The direction of heat transfer from the plate surface to the droplet fluid is changed and the effect of heat transfer direction on internal fluidity of the droplet is investigated. The velocity predictions are validated with the Particle image velocimetry (PIV) data. It is found that velocity predictions agree well with the PIV data. The flow and temperature fields are influenced significantly by changing the plates height. In this case, reducing the plates height alters the size and orientation of the circulation cells inside the droplet fluid. Varying the plates temperature changes the Nusselt number; in which case, droplet heating from the bottom plate results in higher values of the Nusselt number than that of the top plate heating. The Bond number remains less than unity while indicating the importance of the Marangoni current on the flow field and heat transfer. [ABSTRACT FROM AUTHOR]