INSIGHT OF AWATER-IN-OIL EMULSION DROP UNDER LEIDENFROST HEATING USING LASER-INDUCED FLUORESCENCE OPTICAL DIAGNOSTICS

A water-in-oil emulsion droplet may undergo a phenomenon called microexplosion when understrong heating. A microexplosion can be defined as the atomization of the continuous phase (i.e., oil)by the dispersed droplets (i.e., water) phase change and the volume expansion that is induced. It isestablished that microexplosion occurrence is favored by the (partial) coalescence of water dropletsbefore phase change. This process has direct influence on the time evolution of water droplet size.For this purpose, an experimental method based on laser-induced fluorescence is set up. It basicallyconsists of adding a fluorescent dye, fluorescein, which is soluble only in water, and exciting theemulsion drop by a laser sheet during its heating. The goal is to gain a better understanding ofmicroexplosion by measuring the size evolution of dispersed droplets and targeting the water dropletthat triggers the atomization of the emulsion drop. The sizing procedure showed promising results.Manual and automatic measurements of the size were compared in order to quantify the averageerror, which happens to be < 10%. Results show that the size of this trigger droplet is not sufficientin order to determine whether an emulsion drop will undergo optimal atomization.