Optical Analysis and Correction for Circumferential Liquid Film Measurement Based on Planar Laser-induced Fluorescence Method

Due to its advantages of non-invasion and high temporal-spatial resolution, Planar Laser-induced Fluorescence (PLIF) is widely applied to measure the liquid film which is significant for heat and mass transfer. In the circumferential liquid film measurement, the image distortion is led by the refractive index difference between the air, water and the circular pipe wall. Traditionally this issue is eased by installing an extra refractive index matching box outside the pipe or corrected by a calibration target. In this paper, an optical path analysis is carried out to calibrate the distortion which needs not any extra equipment. The analysis is conducted on different planes. And the non-distortion images are reconstructed by means of image processing. To verify the method, the average film thickness is extracted and compared with the classical prediction models. The result is in good agreements with the predictions which indicates this method is capable for the image distortion correction and measurements of circumferential liquid film.