The objective of this work is to develop a film thickness and velocity measurement technique using laser intensity measurement in liquid film flow. This technique was developed for annular flow studies, but it has been scarcely used due to the equipment's complexity, as compared with other techniques. The laser technique uses the reflection of the laser beam in water interface and the attenuation of its intensity to determine the interface position. Thus, the relation between intensity and thickness must be obtained by calibration. A theoretical model was proposed for the optical phenomena present in the film thickness measurement and its results were compared with experimental results using a planar mirror. A controlled experiment was conducted using one-dimensional waves in a short channel where the wave frequencies were varied by changing the vibrator's frequency and the film thickness was modified by changing the liquid volume. The reference film thickness was obtained by the analysis of photographic data taken through the transparent channel walls, allowing the comparison to the results from the laser technique. The experimental results for the film thickness presented a good agreement with the reference thickness from photographic data. The interface wave propagation velocities were measured with good accuracy, showing good agreement with the theoretical data.
Film thickness; laser intensity; wave velocity; optical method
