The Effect Of Bubble Size And Surfactant On Bubble Dynamics And Gas-liquid Mass Transfer In Bubble Column

The hydrodynamic and mass transfer behavior of bubble are very complicated in a bubble column.The bubble size and the presence of surfactants in liquid have an important influence on the transport phenomenon at the gas–liquid interface.In this paper,the gas–liquid two-phase flow and mass transfer behavior were systematically studied for bubbles with different size and multiple kinds of surfactants.Firstly,a gas–liquid co-current bubble column was built up.The absorption process of oxygen bubbles in tap water was studied.A high speed camera system was used to record the movement of the bubble swarm.Then every bubble in the image was identified.The size distribution,shape and other parameters of the bubble swarm were calculated by the software Image J.By using ceramic membrane modules(CMM)and plate gas distributors(PGD),two kinds of bubbles were generated: small bubbles(0.38mm–1.47 mm)and large bubbles(1.05 mm–4.88 mm).The hydrodynamics and mass transfer behaviors of the above two kinds of bubbles were investigated.The results shown that the liquid-phase mass transfer coefficient of the small bubbles was slightly lower than that of the large bubbles.However the volumetric mass transfer coefficient of small bubbles was obviously higher than that of large bubbles.In order to deeply delineate the hydrodynamics and mass transfer behavior of bubbles in bubble column,based on the above investigation of bubble swarm,the hydrodynamic and mass transfer behavior of single bubbles in tap water was studied.A virtual binocular stereo vision system(VBSVS)was established.VBSVS was used to record the movement of a single rising bubble in tap water.An image processing system for bubbles was developed based on the software Matlab.The velocity,rising trajectory,and liquid-phase mass transfer coefficient of a single bubble were obtained by utilizing the image processing system.It was found that the shape and terminal velocity of bubble were scattering,which presented poor repeatability in different experiments under the same operating conditions.In order to further clarify the reasons for the poor reproducibility,the hydrodynamic and mass transfer characteristics of single bubbles in ultrapure water,CTAB aqueous solution,SDS aqueous solution and Tween80 aqueous solution were studied.It was seen from experimental results that the shape and terminal velocity of bubble shown good repeatability under the same operating conditions in all the liquids except tap water.Besides,compared with ultrapure water,the velocity and mass transfer rate of bubbles in surfactant aqueous solution were significantly reduced.The variation of surfactant concentration had an obvious impact on hydrodynamic and mass transfer behavior of single bubbles.For the purpose of explaining this phenomenon,this paper introduced the adsorption model of surfactant on the bubble surface based on the stagnant cap model,and established a correlation for the bubble movement and mass transfer in the surfactant aqueous solution.The predicted results by the correlation were in good agreement with the experimental ones.