Regulation Of Bubble Motion Behavior And Gas-liquid Flow Characteristics In Venturi Bubble Generators

Compared with conventional bubbles,microbubbles have the advantages of smaller diameter,longer residence time in the liquid,more stable phase interface,larger specific surface area and better mass transfer effect.Venturi bubble generator as a kind of equipment to generate tiny bubbles,has the advantages of simple structure,high efficiency,power consumption is low,reliability and so on.It has a wide perspective in the industrial,industrial chemical and environmentally protection and other fields.This paper investigates the bubble deformation and breakage behaviour in the three-dimensional flow field by the Volume of Fluid(VOF)multi-phase flow model in the CFD software ANSYS Fluent,and reveals the variation of velocity and flow field distribution in the Venturi channel,especially in the divergent section,and uses the particle image velocimetry(PIV)system to study the motion pattern and bubble breakage process between multiple bubbles.The velocity and shape of the bubbles were analyzed in combination with image processing to describe the motion pattern between multiple bubbles,and then the gas-liquid flow velocity analysis,turbulent kinetic energy distribution and flow field changes were used to reveal the bubble fragmentation mechanism in depth.In revealing the bubble fragmentation mechanism,the following conclusions are obtained: both shear stress and turbulent collision play a role in inducing bubble fragmentation.The velocity has a large velocity gradient in the low velocity region near the wall of the evanescent section,which hinders the advance of the bubble,and the shear stress caused by the velocity gradient near the wall of the evanescent section contributes greatly to the bubble deformation.Multiple mechanisms lead to the deformation and rupture of the bubbles.It is found that the bubble behavior changes more obviously with the increase of the flow rate,and the bubble movement is hindered by the external flow field and pressure,etc.,and a significant deceleration occurs.The reason of bubble fragmentation and the deceleration process of the bubble have a great relationship,and the bubble deceleration causes the bubble to deform violently,and at the same time strengthens the interaction between the bubble and the flow field,which finally induces the bubble to fragment violently at the location.In the process of the study,it is found that the bubbles will be aggregated and broken at different liquid flow velocities in the Venturi channel,and the larger the velocity,the more obvious the aggregation phenomenon.In response to the aggregation phenomenon,the original device was improved,and we proposed a new porous Venturi structure,optimized the air inlet and water inlet of the Venturi device,respectively,and evaluated the bubble generation performance and mass transfer capacity of the device.For the optimization of Venturi equipment inlets.In this study,we analyzed the changes of bubble motion behavior and flow field under different number of inlet tube conditions and found that different gas distributions affect the flow field.It was found that for the double-tube inlet:(1)the gas content rate distribution was more uniform;(2)the residence time of the gas in the Venturi was longer;and(3)the mass transfer effect was better.For the optimization of the Venturi equipment inlet.It is mainly aimed at the convergence phenomenon of Venturi equipment under high flow.The novel Venturi bubble generator combines the bubble breaking mechanism to break the coalescence bubble again,and the results are found: the novel Venturi bubble generator produces smaller sub-bubble size.Under the same experimental conditions,the mass transfer capacity of the novel self-priming Venturi bubble generator is about 1.26 times higher than that of the ordinary Venturi;the radial,axial,pore size and number variations of the second inlet of the novel Venturi bubble generator are analyzed with the help of CFD numerical simulations on the influence of bubble behavior.In conclusion,the bubble flow characteristics in self-priming Venturi bubble generators are studied through this paper.The mechanism of bubble crushing is revealed;and the new porous Venturi structure is proposed through the regulation of bubble motion behavior,which provides a design reference for the design of Venturitype bubble generator;it plays a certain reference significance for the structure optimization of Venturi equipment,and also provides a new idea for strengthening bubble crushing.