Measurement of Liquid Film Thickness via Light Absorption and Laser Tomography

This paper presents film thickness measurement over a vertical falling liquid film, carried out with Light Absorption (LAbs) and a 2D laser tomography techniques known as Level Detection and Recording (LeDaR). The presented test cases are in the low Reynolds regime (Re = 1 − 8) and include undisturbed conditions, i.e. constant flow rate, and inlet-forced conditions, i.e. flow rate pulsing at frequencies in the range fp = 12−18Hz. The liquid used is Dipropilene Glycol (DPG), with Kapitza number Ka = 4.6. The results include average film thickness in the steady case, wave celerity and wave profile in the forced conditions. All the measurements are scaled using the Skhadov scaling, to facilitate the comparison with analytical low-dimensional models. Both LAbs and LeDaR techniques are presented in detail, including calibration, uncertainties and data processing aspects