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.