Internal flow and heat transfer in a droplet located on a superhydrophobic surface

Flow and heat transfer inside a droplet located on a superhydrophobic surface are examined for various droplet contact angles. A polycarbonate wafer is immersed into a liquid acetone for 6 min to crystallize wafer surface generating a surface texture consisting of micro/nano pillars. To reduce the surface energy of textured polycarbonate wafer, octadecylichlorosilane coating is applied, which results in the superhydrophobic characteristics of the surface. A water droplet is formed on the superhydrophobic surface and it is heated from a constant heat source at the droplet bottom. The metallic powders consisting of Inconel 718 alloy with a nominal diameter of 30 mu m are sprayed at the superhydrophobic polycarbonate surface to establish foundations for a constant temperature heating of the droplet. It is found that the averaged Nusselt and the Bond numbers increase with increasing droplet contact angle. A new number, Ayse, is introduced to correlate the Bond number and the droplet contact angle, which is then used to develop the relation between the Nusselt number and the Ayse number. The Nusselt number increases with increasing Ayse number in the form of a power relation. (C) 2017 Elsevier Masson SAS. All rights reserved.