EFFECT OF LIGUID-SOLID CONTACT-ANGLE ON DROPLET EVAPORATION

The effect of varying initial liquid-solid contact angle on the evapor ation of single droplets of water deposited on a stainless steel surfa ce is studied using both experiments and numerical modeling. Contact a ngle is controlled in experiments by adding varying amounts (100 and 1 000 ppm) of a surfactant to water. The evolution of contact angle and liquid-solid contact diameter is measured from a video record of dropl et evaporation. The computer model is validated by comparison with the experimental results. Reducing the contact angle increases the contac t area between the droplet and solid surface, and also reduces droplet thickness, enhancing heat conduction through the droplet. Both effect s increase the droplet evaporation rate. Decreasing the initial contac t angle front 90 to 20 degrees reduces droplet evaporation time by app roximately 50%. The computer model is used to calculate surface temper ature and heat flux variation during droplet evaporation: adding 1000 ppm of surfactant to the droplet is shown to enhance surface cooling b y up to 110%. (C) 1997 Elsevier Science Ltd.