Study On Interfacial Properties And Floating Characteristics Of The Contaminated Spherical Bubble

Bubbly flow exists widely in many industrial processes.However,due to the existence of impurities（or additives）,it is difficult to keep the absolute purity of liquid in industrial applications,resulting in the contamination of bubble interface and the change of bubbly flow structure.At present,the researches on the adsorption kinetic parameters of contamination is very limited,and surfactant is often used as the contamination medium to study the hydrodynamic characteristics of contaminated bubbles.In order to understand the hydrodynamic characteristics of contaminated spherical bubbles,surfactant was used as the contamination source.The hydrodynamic characteristics of single contaminated spherical bubble and multiple contaminated spherical bubbles were studied by numerical simulation and experiment.The improved stagnation cap model was used in the numerical study,and the high-speed camera was used in the experimental study analysis method.In order to study the interfacial parameter distribution and wake characteristics of multiple contaminated spherical bubbles at Reynolds number（Re）>1,based on the improved stagnation cap model,the hydrodynamic characteristics of a single contaminated spherical bubble at Re≤200 were calculated by fully considering the adsorption,desorption and transport of surfactant at the bubble interface.It is found that the bubble interfacial concentration is related to the average surfactant concentration（C₀）and Re in the liquid phase.The higher C₀and Re,the more uneven the bubble interfacial concentration distribution.When Re is given,the bubble clean interface range（θ）decreases with the increase of C₀.The larger Re is,the higher C₀is required to keepθconstant.The uneven distribution of surfactant molecules at the bubble interface leads to the generation of interfacial shear stress,and the peak value of interfacial shear stress appears at the abrupt change of bubble concentration.When Re≤20,no matter how contaminated the interface is,there will be no wake vortex.The larger the vorticity at the bubble interface,the easier the flow separation and the easier the wake vortex appears.Secondly,the hydrodynamic characteristics of a single contaminated spherical bubble when Re>200 are calculated.It is found that for a given Re,the smaller theθis,the smaller the bubble interfacial velocity is,and the more turbulent the wake is.For a givenθ,the larger Re is and the higher the bubble interfacial velocity is,the more disordered the bubble wake is.Moreover,the bubble interfacial concentration field and the surrounding local flow field interact with each other,which can achieve a dynamic equilibrium.When the bubble interfaceial concentration distribution is very uneven,the interfacial shear stress and interfacial velocity have multiple peaks.When Re>200 andθ<90°,the axisymmetric model is no longer valid.By identifying the adsorption domain of each bubble,each bubble interface can exchange mass with its adjacent basin.The distribution of interfacial parameters and wake characteristics of two contaminated spherical bubbles are studied.The results show that the interface parameters of the upstream bubble can not be changed by bubble spacing,but the interface parameters of the downstream bubble will be significantly changed.The effect of vortex on the downstream bubble is contrary to convection,which will drag surfactant flowing to the tail of bubble back to the upstream interface of bubble and lead to the change of hydrodynamic characteristics of the downstream bubble.In order to make up for the lack of numerical study,the buoyancy characteristics of single and multiple contaminated spherical bubbles are studied experimentally.It is found that for a single contaminated bubble,with the increase of surfactant concentration and the influence of convection,the concentration difference on the bubble surface increases.Due to the enhanced marangonin stress,the bubble rising velocity decreases.When bubble spacing（h/d_b）is greater than 8,there is no interaction between the two bubbles,and the bubble spacing tends to a fixed value;when h/d_bis reduced,the downstream bubbles will catch up with the upstream bubbles.It is also found that the bubble spacing has no significant effect on the upward motion of the upstream bubbles,but has a significant effect on the upward motion of the downstream bubbles,which is consistent with the numerical results.When the bubble spacing h/d_b≈2.8 and the average concentration of liquid phase C₀<5×10^-6mol/m³,for the two coaxial rising bubbles,the rising velocity of the downstream bubbles under the contaminated condition is close to that of the downstream bubbles under the clean condition.