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Flow Behavior Description of Two-Phase Flow Based on Image Processing Techniques

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Tutor: DongFeng
School: Tianjin University
Course: Detection Technology and Automation
Keywords: Gas-liquid Two-phase flow,Bubble character,Bubble volume,High-speed video,Digita
CLC: TP391.41
Type: Master's thesis
Year:  2009
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Abstract:
The movement of bubble is a basic subject in two-phase flow research as bubble in water always plays an important role in solving problems of experiments and projects. The state and motion of bubble are closed with the operating conditions, the nature of liquid and the form of ventilation. If bubble state could be got by visualized method, that will inspirit the development of chemical industry and its relevant filed. A new two-phase flow experiment facility based on high-speed visualization was designed and set up. A mass of experimental images at different detect conditions were obtained by this facility to detect the characteristics of the rising bubble in the two-phase flow.Digital image processing algorithm fit for pre-processing the obtained image sequences was discussed in the paper: Shadow subtracting, wavelet and median filter were adopted to denoise image; The OTSU algorithm was selected to transform gray image into binary image; Two new algorithms for bubble filling named infective algorithm and modified infective algorithm were detailed; Bubble matching technique which apply to the low detachment frequency of bubble was developed; then ,the area, perimeter, diameter, distortion coefficient, center coordinate of the bubbles, bubble velocity, bubble acceleration and other parameter can be calculated conveniently. The experimental images were processed by Digital image processing method.Parameters of bubble were acquired and the track, velocity curve and acceleration curve were plotted. Analyze the experimental results, it was shown as follows. At the condition of lower gas flow, the diameter of air vent is main factor which decide the size of bubble. Bubble is rising with spirals and present form¡®S¡¯in 2-D image. Both of the velocity and acceleration of rising bubble, which related to the bubble detachment frequency microscopic, were microscopic oscillatory but macroscopic stabilized. Positive value alternates with negative value of vertical acceleration. The course of bubble rising is a gradual stable course.Two preliminary calculating methods for bubble volume were proposed. They are geometric method and force analysis method. For geometric method, ellipsoid similar to the size of bubble was constructed by bubble parameter calculation. Force analysis method was to get a volume formula by estibalishing a force balance function in the vertical direction. Bubble volumes were computed roughly. The volumes got by the two kinds of method were contrasted and the suitable stuation of the two methods was discussed.
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