Experimental Study On The Interfacial Turbulence Phenomena

During the mass transfer process,the concentration gradient induced by the mass diffusion usually can produce the surface tension gradient and the density gradient. These may cause the interfacial turbulence.In general,the interfacial turbulence is attributed to the Rayleigh-B(?)nard effect and the Marangoni effect.In the volatilization process of the binary systems,the convection structures of the interfacial turbulence vertical and horizontal to the interface were visualized by the shadowgraph and Schlieren optical observation methods.The results show that the convection structures induced by the Rayleigh-B(?)nard effect and the Marangoni effect are obviously different.The main characteristic of the Rayleigh-B(?)nard convection is plume,and the interfacial fluid move slowly and develop downward the deep liquid.The major sign of the convection structure created by the Marangoni effect is vortex that exists only in the vicinity of the liquid interface,and the fluid motion induced by the Marangoni effect is quite fast.For both Rayleigh-B(?)nard and Marangoni simultaneously unstable system,the convection structures are influenced by the experimental operating conditions,shapes and sizes of text boxes and thickness of the liquid layer.With respect to the different conditions,either the Rayleigh-B(?)nard effect or the Marangoni effect may be dominant,and the dominative one will strongly influence the interfacial phenomenon and decide the shape of the convection structure.By utilizing water,methanol and ethanol as adsorbents and different types of theθcircle and the triangle helix circle as the porous packing medium,the mass transfer influenced by the Rayleigh-B(?)nard convection was studied by the static-state carbon dioxide absorption experiment.The results show that the absorption rate of CO₂ using the different packings is enhanced significantly by the Rayleigh-B(?)nard convection, and the sequence of the absorption rate is 3mm×3mmθDixon ring＞2mm×2mmθDixon ring＞3mm×3mm triangle spring.The porosity of the packings influence the development of the Rayleigh-B(?)nard convection and the mass transfer efficiency.With and without the presence of the Marangoni effect,the absorption of CO₂ by water was investigated,and the Marangoni effect were induced artificially by depositing the low surface tension liquid at the gas-liquid interface.The results show that the absorption rate of CO₂ in the presence of the induced Marangoni convection is larger than that in the absence of the Marangoni convection.The liquid surface velocity distribution was measured by the photographing,and the results indicate that the presence of the Marangoni convection increase the movement speed of the interfacial liquid.The increased liquid surface speed facilitates the surface renewal and intensifies the mass transfer rate.