Study on the Three-dimensional Measurement of Bubble Characteristic Parameters in Gas-Liquid Two Phase Flow
|Course||Detection Technology and Automation|
|Keywords||gas-liquid two phase flow bubble characteristics three-dimensional measurement virtual stereo vision sensor digital image processing|
With the developments of science and technology, gas-liquid two-phase flow has been widely used in many fields such as: electrical, chemical, nuclear, petroleum, metallurgy and environmental areas etc. The performances of its applications depend largely on the bubble movement patterns and the interactions between discrete phase and continuous phase. In order to investigate the principle of gas-liquid two-phase flow and describe the movement characteristics of the dispersed phase accurately and thus guiding the manufacture as well as practical applications, achieving bubble’s 3D characteristics and velocity field are of great significance.After reviewing the development of the measurement of gas-liquid two-phase flow parameters, digital image processing technique, and the application of high-speed photography in parameter detection of two-phase flow, this paper investigated and analyzed three-dimensional measurement of the sparse bubble characteristics.Two-dimensional characteristic parameters of sparse bubble are extracted based on the digital image processing technique. The improved Otsu method with dynamic threshold compression is presented for image binarization after image pre-processing. Scan line seed filling algorithm and morphological image processing are combined to implement holes filling, and the automatic identification of bubble regions is achieved based on the edge-area features and then the disturbance is filtered out. Finally, the shape feature parameters of bubble such as perimeter, area, circularity, mass center coordinate can be extracted effectively, and the bubble motion velocity is also achieved.The basic principles of three-dimensional measurement for bubble characteristic parameters in gas-liquid two-phase flow are investigated in this thesis. After the analysis of different camera calibration methods, main work is done on the Tsai two steps calibration algorithm and providing the main steps.Virtual stereo vision sensor was designed in this thesis. After the analysis of measuring principle and the establishment of mathematical models, three aspects-such as the size of actual field of view, the sensor structure and the error-were taken into account to determine the structural parameters of the sensor and the simulation results were also provided. Then, the general principles and steps are summarized and this thesis also finished designing the base platform according to the size of the actual field of view. Therefore, a complete set of virtual stereo vision imaging system was accomplished and tested in the experimental device. The results show the distance error is better than 2.67mm and the relative error is better than 6%.The three dimen- -sional reconstruction of bubble motion is primarily realized.