Measurement of thin liquid film thickness in pipes based on optical interferometry

Abstract

Accurate measurement of the thin liquid film thickness in pipes is the foundation for studying the characteristics of the film. In this paper, an interferometry-based measurement of liquid film thickness in transparent pipes is developed, which can greatly improve the accuracy, extend the lower limit of measurement and provide a new technical approach for the calibration and traceability. The light intensity distribution is established based on the optical path analysis and a mathematical model. A new algorithm to solve the direction ambiguity is developed to reconstruct the phase distribution. Besides, the effect of the pipe wall is taken into account, which can be suppressed by image subtraction and enhancement technology. The proposed method is of high accuracy and robustness, whose reconstruction errors are 0.064% and 0.25% for the smooth and slight fluctuating liquid films, respectively.