Interfacial Convection Measurement And Effect On Gas-liquid Mass Transfer

In the gas-liquid and liquid-liquid mass transfer process, surface tension gradientand density gradient caused by the concentration gradient can generate interfacialinstability and ultimately induce interfacial convection, which has important effect onthe interfacial mass transfer. The interfacial convection induced by surface tensiongradient is referred to as Marangoni effect and that induced by density gradient isreferred to as Rayleigh-Bénard effect.In this work, a simulator of horizontal gas-liquid interfacial mass transfer processis firstly established. By making use of Particle Image Velocimetry (PIV), a series ofquantitative measurement of the velocity distributions are made for the interfacialconvections generated in the gas-liquid mass transfer of the binary systems ofethanol-water, methane acid-water, acetone-ethyl acetate and carbonbisulfide-acetone. Velocity vectors measured in a cross section of liquid phaseperpendicular to the interface and their statistics indicate that Marangoni convectionhas effect mainly on the vicinity region of the interface where an obvious velocitygradient is developed, while Rayleigh-Bénard convection has effect not only in thevicinity of the interface but also on the bulk liquid where eddies are generated.Liquid-side mass transfer coefficient is measured for the systems, the effects ofthe interfacial convections on the mass transfer are examed trough Sherwood numberSh for the systems. It is shown that the interfacial convection can increase obviouslythe Sh value, and then enhance the mass transfer process. By fitting experimental data,a new correlation of mass transfer coefficient is proposed, in which the dimensionlessSherwood number, ShL, is correlated with the dimensionless Marangoni number Maand Rayleigh number Ra. The proposed correlation is shown to be in good agreementwith the experimental results.