Dynamic Characteristics Of Bubble In Air-Water System Based On3D Ellipsoid Model

The study of multiphase flow is often involved in the fields of chemicals, energy,environmental protection, oil and light industry. The Gas-Liquid two-phase flow is themost common pattern of multiphase flow and the study of bubbly flow is veryimportant in the flow mechanism study. Bubble volume, rising trajectory and velocitycan be predicted and tracked by studying the bubble characteristic parameters. In thispaper, rising bubbles are simulated as3D ellipsoid model according to the bubbleshape characteristics when rising in vertical pipe. And the flow mechanism is studiedbase on this space model. The main conclusions can be draw as follows:(1) Rising bubble image collection system is build up. Based on the experimentsin the vertical trough and the dual-camera image collection system, the high frequencyimages of disperse rising bubbles in static flow field can be taken from twoorthogonal directions at the same plane.(2) The methods of digital image processing for bubble images and2Dparameters extraction are proposed. For the bubble images, bubble edge can bedetected after image type conversion, image filtering, binarization, bubble hole fillingand edge detecting. And the bubble edge images lay a foundation for the2Dparameter detection. Hough transform and ellipse characteristic equation are used forthis detection work. Also the parameters of overlapped bubbles could be got accordingto the directional derivative information of ellipse edge points. The advantages anddisadvantages of these two methods are discussed. The ellipse characteristic equationmethod is used in the application and processing of real bubble images.(3) Rising bubbles are simulated as space ellipsoid model using the method ofellipsoid characteristic equation. Firstly, the two groups of2D parameters andcharacteristic points are matched together with space ellipsoid. Then we use theellipsoid characteristic equation to deduce the3D parameters. At last the bubble spaceellipsoid model can be achieved.(4) Using this ellipsoid model, the volume variation of rising bubbles is studied.After summarizing former study for bubble volume, we calculate the bubble volumewhen rising in vertical trough and discuss the effects of the hole diameter anddeparture frequency on the bubble volume. (5) Rising trajectory and velocity of single and dispersed bubbles are describedand analyzed using the bubble ellipsoid model. The Zigzag motion mode and CircularHelix mode of rising bubbles are discovered. We also discuss and analyze therelationship between hole diameter, departure frequency, bubble aspect ratio, bubblesteady-state volume and bubble rising trajectory and bubble rising instantaneousvelocity and terminated velocity.