Effectiveness of Ultra-fine Structure Surface for Enhancement of Mist Cooling Heat Transfer : Evaporation Experiment of a Single Droplet

In order to pursue the effectiveness of an ultra-fine structure surface for the enhancement of mist cooling heat transfer, detailed experiments have been conducted on the evaporation of a droplet (distilled water and fluorocarbon KPF-72) formed on circular heated surfaces, which are ultra-fine structure surface and smooth surface. The ultra-fine structure surface was made from corroded the uni-directionally solidified alloy (Al-5.7 wt%Ni) with an alkaline solution. On the case of ultra-fine structure surface, it was observed that the deposited droplet instantly permeated into the structure layer and spreaded to radial direction. The reduction of the contact angle and an increase of the wetted area was also confirmed from an optical measurement. The evaporation time of droplet deposited on this surface was almost an order of magnitude lower than that on the smooth surface