Development of a Light Absorption Technique for Mapping the Thickness of Falling Liquid Films

Abstract

The paper shows the development of a photometric technique for mapping the thickness of liquid films. The phenomenonof light absorption through a layer of dyed liquid is used to evaluate its thickness. The layer receives a back-illumination from the wetted wall and the transmitted intensity of light is measured by means of a digital camera. Non-uniformities in the original intensity field force us to build a calibration curve for each measurement point. The filtering and interpolation algorithm needed for transforming the intensity field into the thickness field is described in detail. In addition to being non-intrusive and inexpensive, the technique is capable of determining the local film thickness with an accuracy lower than 10% of its measuring range amplitude