高黏体系中纳米颗粒稳定气泡的形变及破裂行为

Deformation and breakup behavior of nanoparticle-stabilized bubbles in high-viscosity systems

采用高速摄像机研究了微通道内高黏流体中纳米颗粒稳定的气泡在流动过程中的形态及其对下游对称Y型分岔口处气泡破裂的影响。在直通道内运动气泡呈现出弹状、哑铃状和手榴弹状3种形态,气泡的形态主要受分散相流率影响。Y型分岔口处气泡的破裂流型主要为部分阻塞破裂,吸附有纳米颗粒的气泡的破裂周期较常规气泡更大,其破裂周期之差ΔTb随毛细管数Ca变化呈现出3种不同的规律:当Ca>0.042时,ΔTb为正且与Ca呈正相关;当Ca<0.042时,存在ΔTb为正且与Ca呈负相关和ΔTb为负且与Ca呈正相关两种情况。此外,变形气泡在Y型分岔口处呈现非对称破裂行为,其破裂的非对称性与气泡的变形程度相关,当Ca大于临界毛细管数CaCr时气泡尾部直径减小的速度加快,从而加剧气泡的变形,气泡破裂的非对称性显著增大。研究表明,吸附纳米颗粒的气泡的CaCr值与无颗粒体系中气泡相同,但吸附有纳米颗粒的手榴弹状气泡的形变程度更大,破裂的非对称性也更明显。

A high-speed camera was used to study the morphology of nanoparticle-stabilized bubbles in the highly viscous fluid in the microchannel during the flow process and its impact on the bubble collapse at the downstream symmetrical Y-junction bifurcation.Three shapes of moving bubbles in the straight channel were observed:slug bubble,dumbbell bubble,and grenade bubble,and the bubble shape was mainly affected by the flow rate of the dispersed phase.The breakup flow pattern of the bubbles at the Y-junction is mainly breakup with partial blockage.The breakup period of bubbles adsorbing nanoparticles is larger than that of bubbles without nanoparticles,and the difference of their breakup periodΔTb shows three different rules.ΔTb is positive and positive correlation with Ca when Ca>0.042.There are two cases when Ca<0.042:ΔTb is positive and negative correlation with Ca;ΔTb is negative and positive correlation with Ca.In addition,the deformed bubbles show asymmetric rupture behavior at the Y-junction,and the asymmetry of their breakup is related to the degree of deformation of the bubbles.When Ca is larger than the critical capillary number CaCr,the reduction rate of diameter at the tail of the bubbles accelerates,which exacerbates the deformation of the bubbles and causes more significantly asymmetric breakups of the bubbles.The results show that the CaCr value of bubbles adsorbing nanoparticles is the same as that of bubbles in the particle-free system,but grenade bubbles adsorbing nanoparticles show a greater degree of deformation and more obvious breakup asymmetry.