Digital holographic measurement of the Lagrangian evaporation rate of droplets dispersing in a homogeneous isotropic turbulence

Abstract

The evaporation rate of diethyl ether droplets dispersing in a homogeneous , nearly isotropic turbulence is measured by following droplets along their trajectory. Measurements are performed at ambient temperature and pressure by using in-line digital holography. The holograms of droplets are recorded with a single high-speed camera (3kHz) and droplets trajectories are reconstructed with an Inverse problem approach algorithm (IPA) previously used in Chareyron et al (2012); Marie et al (2014). The thermal-vapor concentration wakes developing around the droplets are visible behind each hologram. A standard reconstruction process is applied, showing that these wakes are aligned with the relative La-grangian velocity seen by droplets at each instant. This relative velocity is that obtained from the dynamic equation of droplets motion and the positions and diameter of the droplets measured by holography and the IPA reconstruction. Sequences of time evolution of droplets 3D positions, diameter, and 3D relative velocity are presented. In a number of cases, the evaporation rate of droplets changes along the trajectory and deviates from the value estimated with a standard film model of evaporation. This shows that turbulence may significantly influence the phase change process.