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 under strong 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 is established that microexplosion occurrence is favored by the (partial) coalescence of water droplets before 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 basically consists of adding a fluorescent dye, fluorescein, which is soluble only in water, and exciting the emulsion drop by a laser sheet during its heating. The goal is to gain a better understanding of microexplosion by measuring the size evolution of dispersed droplets and targeting the water droplet that 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 average error, which happens to be < 10%. Results show that the size of this trigger droplet is not sufficient in order to determine whether an emulsion drop will undergo optimal atomization.