Measurement of 3-D Characteristics of Falling Liquid Film Based on SLIF

Falling liquid film is widely practiced in industrial applications, and its flow characteristics can be investigated more deeply by 3-D measurement. However, few research can perform high-accuracy 3-D measurements due to the lack of access to interface velocity. Based on the scanning laser-induced fluorescence (SLIF) and similar image retrieval methods, an advanced velocity measurement method named transcendence encounter is introduced. Combined with the contour interpolation algorithm based on inverse distance transformation, dynamic image interpolation is proposed to accomplish slice image interpolation with different interpolation numbers. Moreover, the marching cubes method is utilized for the 3-D liquid film reconstruction. Coupled with the slice volume summation based on integration principle and the velocity difference between the scanning laser and the falling liquid film, an advanced flow rate measurement method is proposed, which is verified with the mean absolute percentage error (MAPE) of 2.89%. Subsequently, the morphological characteristics and radial distribution of falling liquid film under the different flow conditions are analyzed, and the essence of flow regime transition is revealed quantitatively. The results show that the generation of 3-D waves and the increase of their size and frequency promote the transition from turbulent flow regime to fluctuating turbulent flow regime. In addition, the instantaneous flow rate is investigated, and the positive correlation to interface velocity is determined by investigating the joint distributions of these two parameters. Finally, according to the average liquid film thickness measured by the 3-D measurement method with high accuracy, the existing prediction models are evaluated and a new prediction model is established. The validation results are within ±6% and the MAPE is 2.10%, which demonstrates the better performance of the new prediction model. These 3-D measurement methods and research findings provide new solutions for further understanding the flow characteristics.