Study On Mechanism Of Bubble-driven Janus Particle Based On Pseudo-potential Lattice Boltzmann Method

The interaction between bubbles and interfaces is a research hotspot in bubble dynamics and multiphase flow.In the case of close to the gas-liquid interface,typical Pt-SiO₂ Janus self-driving particles will cause bubbles to precipitate and drive particle motion.The mechanism of bubble-driven microparticle motion is complex,involving micro-scale flow,gas-liquid-solid three-phase Coupling,heat and mass transfer between phases,fluid compressibility,etc.In this paper,a micro-scale multiphase flow model was established based on the improved pseudo-potential lattice Boltzmann method to study the flow field changes of bubble coalescence and bubble collapse,as well as the interaction between bubble motion and micro-particles of the same scale.First,in order to meet and restore the real physical state,the original pseudo-potential model and a class of improved pseudo-potential model were investigated and verified,and a multi-phase flow model that can simulate the real density ratio flow field was established based on the result.It was found that the improved pseudo-potential multiphase model can achieve a larger density ratio than the original pseudo-potential model,while maintaining a smaller pseudo-velocity,which expands the application range of the pseudo-potential model in the field of micro-flow.In addition,the correctness of the improved pseudo-potential model in multiphase flow was verified.The morphological evolution of bubble coalescence and collapse under different conditions was studied,the interaction between the bubble phase interface motion and the surrounding flow field was analyzed.The bubble coalescence process changes the peripheral flow field by the phase interface deformation.The collapse process is both under the pressure difference between the inside and outside of the bubble and the asymmetric effect of the pressure of the flow field around the bubble,the flow field flow causes the bubble phase interface to deform and collapse.The effects of fluid physical parameters and bubble size on bubble coalescence and collapse were compared.The results showed that the characteristic time and state of bubble coalescence are greatly affected by the bubble size.The deformation during the bubble collapse,the generation of high-speed jets and pressure waves,and the state of the flow field after the bubble collapse were all related to the obstruction of the wall.The interaction between the solid wall and the movement of the bubble nearby is the direct cause of the asymmetric evolution of the bubble and the flow field.The process of bubble coalescence and bubble collapse near solid walls with different curvatures was studied,and it was found that the curvature of the solid wall can affect the location of bubble coalescence and the location of bubble collapse,thereby affecting the movement state of the coalesced bubbles and the intensity of the collapsing jet.The flow field characteristics of the bubble and the curved surface after coalescence and the flow characteristics of the jet on the curved surface after collapsing were analyzed.Finally,based on the results of the numerical simulation and the comparison with the experiment,the mechanism of the two driving modes of bubble coalescence and bubble collapse was explained.The numerical simulation results showed that the driving was qualitatively consistent with the experimental results.Analysis showed that optimizing the ratio of the radius of bubbles to microparticles can improve the efficiency of advancing microparticles by influencing the locations of bubble coalescence and bubble collapse points.By controlling the bubble motion state of the Janus particle reaction surface,the movement mode of the bubble-driven Janus particle was changed,and it provided a reference for improving the driving effect of the bubble-driven Janus particle.