Research progress on preparation of microbubbles by ejectors
Ejectors are employed for efficient mixing of gases and liquids,as well as for producing a substantial number of microbubbles.They are characterized by low equipment costs,high energy efficiency,and suitability for large-scale industrial applications.However,the current ejector techniques for microbubble production suffer from a wide distribution in bubble sizes.Moreover,the structural parameters and operational conditions of ejectors exert significant influence over microbubble size.The following patterns in microbubble size variation have been identified based on the factors mentioned above.It has been demonstrated that reducing the length and diameter of the mixing section,and increasing the angle and cross-sectional ratio of the diffusion section effectively decrease bubble size.However,the angle of the contraction section has a minor impact on bubble size.The narrowing of the range of gas bubble sizes can be achieved by a reduction in the gas flow rate and an increase in the liquid flow rate,with the bubble size exhibiting a linear relationship to the gas volume ratio.Utilizing computational fluid dynamics(CFD)simulations and particle image velocimetry(PIV)technology to investigate gas-liquid transfer mechanisms within the ejector,it is evident that efficient gas-liquid shear at the nozzle outlet of the suction chamber and within the mixing section is critical for microbubble formation,while the diffuser section is the site for bubble breakage and refinement.Furthermore,the application scenarios of microbubble production using ejectors are discussed,and future research directions are proposed.
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