(177f) Experimental Study and Numerical Simulation of the Marangoni Effect On Hydrodynamics of Single Drop In the Liquid–Liquid System

The Marangoni effect is a frequently observed phenomenon which enhances interphase mass transfer in liquid-liquid systems, originating from the hydrodynamic instability induced by interface tension sensitivity to interface concentration of transferred solute. Problems of instability onset and development are studied intensively already for many decades because of their fundamental and technological importance. The accompanying deformation of free interface and drop oscillation makes the interphase mass transfer more complicated and particularly difficult to quantitatively understand the mass transfer mechanism. In the present work, the deformation of droplet is experimentally studied using a computer-controlled optical contact angle measuring instrument with a digital camera recording the time evolution of the droplet. Deformable and oscillating single droplets in the sec-butyl acetate/acetic acid/water system are presented which shows strong interfacial instabilities. Acetic acid is the solute, water the dispersed phase and sec-butyl acetate the continuous phase. Parameters varied are the initial solute concentration and the mass transfer direction. The experimental results are in good agreement with the classic theoretical analysis. Moreover, a level set method is applied for simulating the moving process of single drop in an immiscible liquid, calculating the drop deformation in two-dimensional and three-dimensional space. The level set application mode finds the fluid interface by tracing the isolines of the level set function φ. The level set or isocontour φ=0.5 determines the position of the interface. The level set function is a smooth step function. From continuous phase to disperse phase,φ goes smoothly from zero to one. To resolve the Marangoni effect underlain by local interfacial hydrodynamic disturbance, the continuity equation and incompressible Navier-Stokes equation including surface tension are solved in an axisymmetrical coordinate system. Acetic acid is the solute, evolution of the Marangoni convection in the both cases of water is the disperse phase and the continuous phase is performed for different initial solute concentrations. The numerical calculation results are consistent with the experimental results, both of them reveal that the Marangoni effect occurs only when the surface tension sensitivity to the solute concentration variation is above certain critical level and become more striking along with the increase of the solute concentration. The results would promote better understanding of such complex dynamic phenomena in solvent extraction systems.