The Dynamic Characteristic Of Single Rising CO₂ Bubbles In Pine Resin Soltions

Bubble parameters such as size,shape,velocity,and trajectory are important features of gas-liquid two-phase flow.The study of characteristic parameters and dynamic characteristics of the bubble can provide important basis for the design and operation of gas-liquid mass transfer equipment,chemical reactors and effective control of related chemical reaction processes.In this paper,real-time high-speed imaging-MATLAB digital image processing technology is used to study the rising dynamics of single carbon dioxide bubbles in pine resin solutions.The main contents are as follows:In order to obtain a clear image sequence of rising bubbles,a set of visual two-phase flow field experiment system with constant pressure and temperature was independently designed,including a bubble generating device,a temperature and pressure control device,and an image acquisition system.The high-speed photographic technique was used to track the movement of a single CO2 bubble in a stationary turpentine solution at 25 ?.The video data was processed using MATLAB digital image processing.Based on the characteristics of bubble motion,the denoising,binarization,edge detection,filling and algorithm programming of bubble feature parameters are discussed.A suitable digital image processing algorithm is proposed to obtain the center of bubble,rising velocity,and bubble diameter,bubble aspect ratio and other motion parameters.The bubble shape characteristics and variation were discussed in detail.The results show that,when the bubble diameter d?1 mm,the bubbles can maintain a spherical shape.As the bubble diameter d>1 mm,the bubble gradually changes from the ellipsoid to the form of irregular spherical cap.In the solution with smaller viscosity,the surface of larger bubbles is accompanied with oscillation during the rising and the bubble aspect ratio showed fluctuation with increasing height.As the solution viscosity increased,the bubble aspect ratio was stable and the bubble shape was a regular ellipsoid.According to the deformation characteristics of a single C02 bubble in turpentine solution,it is related to the dimensionless parameters such as the Eotvos number(Eo),Weber number(We)and Reynolds number(Re),and the prediction model of bubble aspect ratio is proposed.The predicted value of the model agrees well with the experimental value.On the basis of digital image processing,the bubble center coordinates of the continuous motion bubble are tracked to obtain the rising trajectory and the rising velocity of the bubble.The results show that in the low concentration solution,when the diameter d?1 mm,the bubble rises along the straight path.When d>1 mm,the bubble rises in zigzag or spiral upward movement.As the concentration of the solution increases,the fluctuation amplitude of the left and right oscillations of the bubble trajectory gradually weakens.In the higher viscosity solution,the bubble always maintains a straight rise;the rising velocity of the bubble is related to the bubble size and the solution concentration.The bubble rising velocity increases with the increase of the bubble size.When the maximum velocity is reached,the bubble velocity slowly decreases with the further increase of the bubble size.By comparing the bubble velocity obtained from the experiment with the velocity prediction model in the literatures,it was found that the predicted velocity of the bubble by Tomiyama et al.is in agreement with the experimental result,and the maximum deviation is less than 7%.