Study On Interface Pinch-off Dynamics And Motion Behavior Of Particle-loaded Bubble

The motion behavior of particle-loaded bubble in gas-liquid-solid multiphase flow systems is widely found in energy and chemical engineering,biopharmaceutical,environmental protection,food processing and other engineering fields.The gas-liquidsolid three-phase characteristics determine the motion behavior,residence time and relative motion of particle and bubble in the system,which has an important influence on the heat transfer,mass transfer and reaction performance of the whole system.Indepth study of the pinch-off and rising behavior of particle-loaded bubble in fluid is helpful to understand the formation and movement mechanism of particle-loaded bubble,and provide theoretical guidance and technical support for the design and optimization of gas-liquid-solid multiphase flow reactor and the strengthening of gasliquid-solid multiphase flow separation process.Firstly,the high-speed camera technology was used to experimentally study the particle-loaded bubble interface pinch-off in different solutions.The internal relationship between the minimum neck width of the gas-liquid interface and the fluid properties and particle properties after the bubble was loaded with particles was explored,and the bubble formation behavior of the particles was analyzed from the perspective of the temporal and spatial evolution of the neck.The experimental results show that the process of particle-loaded bubble pinch-off can be divided into three types:particle adhesion above the bubble neck region(PLB-u),particle adhesion in the bubble neck region(PLB-n),and particle adhesion below the bubble neck region(PLB-b).For the PLB-n pinch-off type,the particle-loaded bubble has a slower pinch-off speed than the pure bubble,resulting in an increase in the power-law index,and only the gas-liquid interface on the side of the unattached particle moves to the center.This was due to the outward hydrophobic effect of the particle adhering to the neck of the bubble on the surrounding fluid,resulting in a smaller squeezing effect of the fluid on the neck.In the two pinch-off types of PLB-u and PLB-b,the particle adhered to the upper(lower)side of the bubble neck produce an inward hydrophobic effect on the fluid around the neck,resulting in an enhanced squeezing effect of the fluid on the bubble neck,which accelerates the pinch-off speed of the bubble,resulting in a power-law index of PLB-u and PLB-b smaller than that of pure bubbles.In addition,the particle-loaded bubble pinch-off dynamics was also related to fluid rheology and surface tension.Secondly,the high-speed camera technology was used to study the bubble rising and rising motion of particle in different fluids.The effects of different fluids(surface tension,viscosity and rheology)and different particle(size,density and type)on the bubble rising and rising behavior of particle were investigated.It was found that:(1)The existence of particle in deionized water will lead to the change of bubble rising shape from irregular ellipsoid to sphere,and the range of bubble aspect ratio decreases by 71.4%.And the particle will slip repeatedly at the gas-liquid interface,resulting in the change of the centroid distance between the particle and the bubble between 1.41 ～1.91 mm,the dynamic change of the angle between the particle and the bubble between0° ～ 90°,and the rising speed of the bubble after loading the particle decreased from0.22 m/s to 0.198 m/s.(2)In the low surface tension fluid,the surfactant molecules adsorbed on the gas-liquid interface will hinder the particle sliding motion,resulting in the increase of the oscillation frequency of the particle-loaded bubble trajectory,the decrease of the angle between the particles and the bubble,and the decrease of the rising velocity with the decrease of the surface tension.(3)For Newtonian fluid,with the increase of fluid viscosity,the viscous force increases,and the particle cannot slip at the gas-liquid interface due to the viscous force.The rising trajectory of the particle becomes straight and the rising speed decreases.(4)For non-Newtonian fluids,the motion behavior of particle-loaded bubble was related to the viscosity of the fluid at a constant shear rate: In non-Newtonian fluids with low viscosity,the trajectory of particle-loaded bubble becomes curved and the particle has obvious slip in the later stage of rising.The range of the angle between particle and bubble gradually increases with the rising height.When the viscosity of non-Newtonian fluid increases,the particle hardly slip at the gas-liquid interface,and the rising velocity decreases with the increase of fluid viscosity.When the viscosity of the non-Newtonian fluid further increases,the fluid viscous force dominates,and the aspect ratio and centroid distance of the particleloaded bubble increase.In an elastic non-Newtonian fluid,the bubble was elongated vertically and show teardrop shape.(5)The bubble aspect ratio,particle-bubble centroid distance and particle-loaded bubble velocity increase with the increase of bubble size.And the increase of the size and density of the loaded particle will significantly reduce the rising velocity of the particle.Finally,based on the classical drag coefficient correlation and the final velocity prediction correlation,combined with the parameters such as particle size,particle density,fluid viscosity,fluid rheology,fluid surface tension and gas-liquid-solid threephase density,the drag coefficient correlation and the final velocity prediction correlation of the particle-loaded bubble are obtained by dimensionless analysis.Compared with the classical prediction model,the model was more consistent with the experimental values.