Study On Cavitation Characteristics And Bubble Breakage Mechanism In Microbubble Generator

Due to their small size,micro-nano bubbles have the characteristics of large specific surface area,high adsorption efficiency,slow rise in water,etc.,making them more and more used in fields such as air flotation,water purification,water aeration,biopharmaceuticals,and enhanced chemical reactions.As a typical micro-bubble generator,the Venturi-type bubble generator has the advantages of simple structure,high foaming efficiency and uniform bubble size.This paper takes the Venturi-type bubble generator as the research object,through the method of combining numerical simulation and experiment,the characteristics of hydraulic cavitation and the mechanism of cavitation breaking bubbles were studied,and the following work was carried out:Firstly,the influence of wall roughness on cavitation flow characteristics in Venturi tube was investigated.The Reynolds time-mean N-S equation,the standard k-ε equation and the ZGB cavitation model were used to establish the numerical model.By analyzing the vapor phase distribution and the change of turbulent kinetic energy in the Venturi tube,the influence of roughness on the internal cavitation flow field was studied.The results show that the existence of roughness has two sides to cavitation,and the cavitation intensity can be enhanced only in a reasonable range.(2)Secondly,the ZGB cavitation model was modified considering the influence of non-condensable gas in water on the cavitation flow characteristics in the bubble generator.By analyzing the changes in the length of the cavitation cavity and the volume fraction of the vapor phase,the influence of non-condensable gas on hydraulic cavitation is studied.The results show that: non-condensable gas promotes the development of cavitation,the vapor phase volume fraction increases with the increase of non-condensable gas,but it does not affect the length of the cavitation cavity.(3)Thirdly,the influence of cavitation on the bubble breaking process in the bubble generator is studied.Based on the modified ZGB cavitation model and PBM,the effects of cavitation on bubble breakage were studied,and the accuracy of the modified model was verified by experiments.The cavitation intensity is controlled indirectly by controlling the content of non-condensable gas.It is found that with the increase of cavitation intensity,the average particle size of bubbles decreases,and the particle size distribution of bubbles becomes more concentrated.It is confirmed that cavitation is an important factor for the generation of micro and nano bubbles.(4)Finally,the bubble generator performance test equipment was designed and built.The structure of Venturi bubble generator was optimized by experiments,and the effects of different throat inner diameter and expanding Angle on the performance of bubble generator were studied.Based on the structure optimization of experimental research and the mechanism study of cavitation on bubble breakage,a micro-bubble generator with stepped throat and multiple flow channels is designed,which has the advantages of uniform bubble size distribution and large gas handling capacity.