Effect of liquid-solid contact angle on droplet evaporation

Abstract

The effect of varying initial liquid-solid contact angle on the evaporation of single droplets of water deposited on a stainless steel surface is studied using both experiments and numerical modeling. Contact angle is controlled in experiments by adding varying amounts] (100 and 1000 ppm) of a surfactant to water. The evolution of contact angle and liquid-solid contact diameter is measured from a video record of droplet evaporation. The computer model is validated by comparison with the experimental results. Reducing the contact angle increases the contact area between the droplet and solid surface, and also reduces droplet thickness, enhancing heat conduction through the droplet. Both effects increase the droplet evaporation rate. Decreasing the initial contact angle from 90 to 20° reduces droplet evaporation time by approximately 50%. The computer model is used to calculate surface temperature and heat flux variation during droplet evaporation: adding 1000 ppm of surfactant to the droplet is shown to enhance surface cooling by up to 110%.