A Computational Fluid Dynamics simulation of a multi-phase system. Done as part of summer project at Imperial College London, in 2014.
ABSTRACT
Under microfluidic confinement, the viscous forces and capillary forces dominate the flow patterns and bring about the drop formation and oscillating jets. Surfactant tends to be preferentially adsorbed at the interface and reduce the cohesiveness between solvent molecular, hence depress the interfacial tension and avoid the coalescence of droplets and jets. The convection-diffusion effect together with sorption kinetics causes the surfactant concentration gradient from bulk to interface and along in the interface, which in turn leads to spatial variation in local interfacial tension. This variation rules the stability or instability of produced jets and droplets. To take into account the influence of soluble surfactant on the behaviour of microfluidic jets, we present a computational fluid dynamics approach which takes the advantage of Volume-of-Fluid method capturing the interface topology accurately without mass loss. This approach employs the Langnuir isotherm law to associate the surfactant concentration at interface with the one adjacent to the interface. In addition, the convection term, diffusion term, dilution term and Marragoni stress term are considered for the interfacial source term. This method is incorporated into CFD code to study the dripping and jetting regimes of immiscible jets in a microchannel. The modelling results are validated against the experimental measurement.
Authors : J. Yang, G. Goel, O. K. Matar