Experimental investigation of forced convection on evaporation of continuously-fed sessile droplets

Abstract

Experiments using an open-loop wind tunnel and computer-vision-based control system were conducted to determine the influence of forced convection on the evaporation rate of continuously-fed sessile droplets. This work was motivated by biomimicry of the human perspiration system, and the possibility of using continuously-fed evaporating sessile droplets for thermal management (heat removal), with an aim to develop an understanding of the potential for enhancing evaporation rates through the use of an external air flow. Experiments revealed gains of approximately 50% to 60% when air flow was initially introduced. These gains ceased to increase at higher air velocities once the evaporation rate of the droplet became limited by energy transport as opposed to the earlier limitation due to the vapour removal rate. A higher temperature of the flowing air was found to result in a lower evaporation rate at lower velocities, but approximately equal evaporation rates at higher velocities. Boundary layer formation caused by a surrounding flat surface inhibited benefits from the forced convection, indicating that thermal management systems will require droplets on raised pedestals or curved surfaces to benefit from forced convection, similar to the curved surfaces of the human body.