表面活性物质影响下单个自由上升微气泡传质过程的直接数值模拟

Direct numerical simulation of mass transfer process of single free rising microbubbles under the influence of surface active materials

2017年,国际标准化组织将直径介于1~100μm之间的气泡定义为微气泡,本研究参照上述定义,针对微气泡容易受到表面活性物质影响的特点,通过直接数值模拟对不同尺寸单个自由上升微气泡在表面活性物质影响下的传质速率进行研究。通过与模拟结果对比发现,微气泡的运动速度及传质速率均可用Clift等总结的爬流范围内的理论进行较为准确的预测。表面活性物质在微气泡表面的吸附会降低气泡的液相传质系数,但对于受表面活性物质影响程度较大的微气泡,其液相传质系数随气泡尺寸减小呈持续增加趋势,而与洁净微气泡先减小后增加的趋势有所不同。因此在无法排除表面活性物质影响的应用场合,进一步缩小微气泡的初始尺寸,不仅可以增加气相的比表面积,微气泡的液相传质系数也会进一步增加,其传质能力将得到进一步加强。

The international organization for standardization(ISO)has defined bubbles with the diameter between 1~100μm as microbubbles in 2017.According to the above definition and the fact that microbubbles are easily affected by surface active materials,the mass transfer rate of single free rising microbubbles with various diameters under the influence of surface active materials was studied by direct numerical simulation.It was found that the velocity and mass transfer rate of the microbubbles were in good agreement with the theoretical results of creeping flow recommended by Clift et al.The adsorption of surface active materials on the surface of microbubble reduced the liquid-side mass transfer coefficient.However,for microbubbles that were greatly affected by surface active materials,the liquid-side mass transfer coefficient increased with the decrease of bubble size,which was different from the trend of clean microbubbles that decreased first and then increased.Therefore,in the application where the effect of surface active materials cannot be excluded,further reduction of the initial size of microbubbles can not only increase the specific surface area of the gas phase but also further increase the liquid-side mass transfer coefficient of the bubble,and the mass transfer capacity can be further enhanced.