Effects of Marangoni Convection on Transient Droplet Evaporation

Results from a computational model of transient droplet vaporization are presented. In this model, axisymmetric flows around translating single component droplets are assumed. The governing equations are expressed in finite volume form and solved numerically for transient velocity, species and temperature profiles. Fully variable properties in the gas and liquid phases are allowed (except for liquid densities, which are held constant), and pressures of 1 and 10 atm are considered. A unique feature of the calculations is the inclusion of surface-tension gradients resulting from droplet surface temperature variations. Results show that surface-tension gradients significantly affect droplet internal temperature and velocity fields even when initial droplet Reynolds numbers, based on droplet diameters and free-stream conditions, are as large as 50. When surface-tension gradients are allowed at high initial Reynolds numbers (SO), droplet internal circulation rates are found to be initially increased for a short period of time and then significantly reduced, causing bulk liquid temperatures and droplet vaporization rates to increase at smaller rates than when surface-tension gradients are neglected.