Study On Bubble Generation And Dispersion In Liquid-gas Two-phase System Under Electric Field

Liquid-gas two-phase system is widely used in industrial productions.The dispersed phase is always injected to the continuous phase in forms of particles,droplets or bubbles to increase the interfacial area.Generally,the smaller the dispersed phase is,the larger the interfacial area is,then the better the heat and mass transfer efficiency will be.Traditional methods to mixture bubbles into liquid and produce micro bubbles are mechanical agitation with various types of impellers and fluid pulsation through perforated plates.Even if these methods provide relatively smaller bubbles,they cause much energy consumption on liquid agitation instead of the increase of the interfacial area.An efficient method to generate small bubbles and increase liquid-gas interfacial area is electrostatic dispersion.The applied electric field changes the charge distribution around the liquid-gas interface,leading to negative charge accumulation.The surface tension is weakened due to the effect of coulomb repulsion of negative charge near the gas-liquid interface.When the applied voltage increases to a certain value,the coulomb repulsion will increase to a value larger than the surface tension.As a result,the liquid-gas interface ruptures,providing a large number of micro bubbles.The electrostatic dispersion has the advantages of high efficiency and low energy consumption.Scholars at home and abroad have made a large number of studies on electrostatic dispersion process,focusing on the electrostatic dispersion of liquid in gas named electrostatic atomization.Different dispersion modes have been observed and the transition conditions have been studied to provide a mature theoretical model of liquid dispersion in gas.However,there is little research on the dispersion process of gas in liquid.The mechanism of gas dispersing in liquid has not been fully revealed and the theoretical model is not yet perfect.Therefore,the dispersion of gas in liquid under electric field has been studied by visual measurement method in this paper.The main contents are as follows:Firstly,the dispersion state of gas under the action of electric field was studied.The gas electrostatic dispersion experimental setup was designed and established.With the help of high-speed microscopic camera technology,bubbles' micro appearance characteristics and growing states were accurately captured and different dispersion modes were observed.The relationship among bubble size,applied voltage and the air flow rate was obtained.Secondly,the gas dispersion process under different electric fields was studied.The control of bubble growth direction was realized through the original "U" electrode,the bubble growth direction changed from vertical to horizontal.At the same time,the bubbles of horizontal growth direction caused disturbance to the liquid in the experimental area and accelerated the convection of the liquid,so that the bubbles could disperse evenly to the whole experimental area.The variation of bubble size,bubble injection angle and gas rate with the system parameters of applied voltage and air flow rate were obtained.Finally,the model of bubble dispersion under electric field is established.Through dimensionless analysis,the bubble size and influence parameters were dimensionless,and the relationship between dimensionless bubble size,Reynolds number and electrical Weber number was established.