Convection in a droplet blown by gas flow

Abstract

The behavior of convection in a sessile and suspended water drops is considered. Evaporation of spray droplets can be divided into two stages: evaporation in a gas flow and that on the wall. Usually, in the calculation of heat transfer and evaporation, liquid convection is neglected, which can lead to a significant error in the calculation. Therefore, there is a need in simple evaluation formulas to describe of the convection. The ratio of several key factors: the velocity of the forced gas flow, the thickness of the wall boundary layer, the thermogravitation convection, and the influence of thermal and concentration factors, is considered. For the first time it is shown that the convection velocity in a sessile drop is 30–40% less than in a suspended drop. The ratio of the maximum convection velocity to the average velocity is three for both the suspended and the sessile droplet. For a sessile drop, the effect of the solutal Marangoni flow on convection is much stronger than in a suspended drop. The obtained results and dependences are important for evaluating the role of convection in droplets evaporation in the spray, as well as for sessile droplets on a hot wall.