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Measurement of thickness of annular liquid films based on distortion correction of laser-induced fluorescence imaging.

Liquid film flow is widely used in a variety of modern industrial applications. The liquid film thickness is a key characteristic in both annular flow and falling film. In this paper, based on planar laser induced fluorescence imaging, an optical distortion correction and measurement method of film thickness is proposed. The optical path distortion is analyzed, and a mathematical model to correct the distortion is established. The instantaneous images of liquid film under different Reynolds numbers are captured, and then the binary image of liquid film is processed to extract the average thickness. The flow fluctuation of the liquid film under different Reynolds numbers is investigated, and then a prediction model of average film thickness is presented. With the proposed method, refractive index matching is not needed to eliminate the distortion due to curvature of the tube containing the annular flow. Compared with the classical prediction model of average film thickness, the experimental results show that the proposed method can achieve non-invasive measurement of the liquid film accurately, and the new prediction model is effective and with high precision.