界面传质中Rayleigh对流的定量分析

Quantitative analysis of Rayleigh convection in interfacial mass transfer process

通过纹影光路观察了特定气液传质装置中乙醇吸收CO2过程所引发的Rayleigh对流在垂直界面方向上的发展过程。随着溶质吸收的进行,液层的流体稳定性变弱,扰动加剧气液界面失稳并发生湍动,进而发展为羽状流并逐步向液相主体发展,在此过程中伴随着对流胞的融合与增长。液层的浓度分布可通过对相应液层纹影图像进行定量分析获得。液层浓度分布和瞬时传质系数变化表征了Rayleigh对流的引发与发展及其对传质过程的强化效果,界面浓度分布及临界Rayleigh数解释了非均匀传质对湍动的引发机理。羽状流将高浓度液体快速带入主体,加速了近界面液层与主体液层的混合,增强了气液传质。

Schlieren system was built to visualize the phenomenon of Rayleigh convection perpendicular to the gas-liquid interface during the absorption of carbon dioxide into pure ethanol in the special mass transfer device. As the absorption progressed, the stability of liquid layer weakened and disturbances aggravated the instability, which led to turbulence in the interfacial vicinity and went on to develop plume convection down to the bulk liquid with the growth and integration of convective cells. Quantitative method was applied to obtain the concentration contours of the liquid phase. Concentration distribution and variation of instantaneous mass transfer coefficient represented the onset and development of Rayleigh convection and its reinforcement effect on the mass transfer process. Interfacial concentration distribution and critical Rayleigh number explained the mechanism in which the nonuniform mass transfer contributed to the trigger of turbulence. The experimental results showed that the downward high concentration flows promoted the exchange of the liquid between interfacial vicinity and liquid bulk, showing that Rayleigh convection can enhance the mass transfer process.