Droplets Evaporation In Turbulent Flow: Statistical Study Based On Lagrangian Tracking And In Line Holography

Abstract

Turbulence has long been suspected to increase the evaporation rate of droplets via the convective effects it generates. The experimental data reported in this paper provides evidence of this increase and statistically quantify these effects. Measurements was performed following a Lagrangian approach, using Digital in-line holography based on a high speed camera and an inverse problem reconstruction algorithm. Ether droplets was released in a quasi isotropic and homogeneous turbulence generated by synthetic jets. Their Schmidt number is typically of the order of 2 and their Reynolds number is moderate (≤ 3). Results are based on a large number of droplets trajectories for various turbulence conditions. The Lagrangian statistics computed from these trajectories, totaling 1.3 million samples, show that the relative mean motion and turbulence seen by the droplets on average increases their evaporation rate. Within the parameter range investigated, this increase is not well predicted when estimating the convective effect in the Sherwood number with the norm of the instantaneous relative velocity seen by the droplets. In contrast, this increase is very well predicted when the Sherwood number is calculated using a Reynolds number based on the norm of the mean relative velocity plus its RMS fluctuation.