Research On Particle Entrainment Behavior And Mechanism By Bubble Wake In Bubbling Washing

Bubbling washing is one of the commonly used wet gas treatment methods in chemical process.Particle entrainment is a common phenomenon in bubbling washing process,which is caused by the wake of rising bubble.The entrained particles rise to the surface of the liquid layer with the bubbles.When the bubbles burst,the particles escape from the washing tower with the mist,causing the washing efficiency to decrease.Therefore,the research of the particle entrainment behavior is of great significance for understanding the entrainment mechanism and improving the washing efficiency.Bubbles and particles are the main body of bubbling washing system,and the interaction between them is very important to understand the entrainment behavior of particles.In this thesis,the movement characteristics of bubble wake and the entrainment behavior of fine particles during a single bubble ascent in a static liquid-solid suspension system are studied by the combining numerical simulation and experimental research.The main research contents and conclusions were as follows:The particle entrainment behavior caused by single bubble rising in liquid-solid suspension system under low liquid layer was studied by numerical simulation.The accuracy of the model was verified by the experimental comparison.The wake generation and vortex shedding process of single bubble with different sizes and the movement characteristics of entrained particles were deeply analyzed.The results showed that the number of entrained particles depended on the jet entrainment beneath the initial bubble base and the vortex shedding after the bubble entered the pure liquid region.When only the total entrained particles were considered,the entrainment capacity of the bubble wake increased with the bubble diameter.The wake region beneath the bubble can be divided into the stable bubble wake region,the fluctuating bubble wake region and the vortex tail region.The entrained particle number depended on the particle concentration of stable bubble wake region.Vortex shedding tended to cause particles in vortex tail region to converge to the fluctuating bubble wake region,resulting in a zigzag distribution of axial particle concentration.The stable bubble wake region was not affected by vortex shedding,so the total particle concentration in the region remained at a stable value.Compared with the particle density,particle diameter had a more significant effect on entrainment by bubble wake,and the entrainment rate of mixed particle sizes was significantly lower than that of single particle size.Based on the research of single bubble wake structure and entrainment particle movement characteristics,the wake movement and particle entrainment behavior in different initial states of bubbles were analyzed,and the key influence of binary bubble breaking behavior on entrainment by bubble wake was found.The feasibility of placing a periodic open cellular structure(POCS)to control the binary bubble breaking behavior was investigated,and the influence of wettability and placement height of POCS on bubble breaking behavior was analyzed.The results showed when the wetting angle was unchanged,the stage of the shape oscillation dominated whether the breaking behavior occurred or not,as the bubble passed through the internal component.If the shape oscillation of bubble was in the expansion process,the breaking behavior occurred.When the dimensionless height of POCS was 0.4 and the wetting angle was 60°,the 8 mm bubble can achieve the best entrainment reduction effect,and the entrainment ratio of particles was less than 0.005.In summary,the addition of POCS will inevitably lead to the decrease of entrainment rate.