A Laser Multi-Reflection Technique Applied for Liquid Film Flow Measurements

This work is devoted to a non-intrusive experimental approach, based on Laser Multi-reflection technique, in the investigation of thickness distribution variations and wave's dynamics of a liquid film flowing over an inclined plane. This investigation was first founded on the needs of quantifying the liquid film thickness and on minimizing, as much as possible, some drawbacks pointed out, in the literature, throughout the experimental techniques available. Moreover, the technique could be applied to transparent, opaque as well as particle laden liquid films. The technique is validated and evaluated using two approaches according to the flow case: stable or instable. In case of stable flow, the comparison was made using Spectroscopic Ellipsometry and theoretical prediction established by the Nusselt model. For a wavy interface a setup, especially devoted to that purpose, was used to validate the accuracy of the measurements. In both cases the uncertainties were within 5%. The experiments are discussed hereafter including the accuracy of the results. Some experimental data, for plane inclination ranging from 1 degrees to 10 degrees, are reported. The data takes into account the film thickness at various positions. The instability threshold is also reported.