Calculation of droplet coalescence in binary liquid-liquid systems: An incompressible cahn-hilliard/navier-stokes approach using the non-random two-liquid model

Due to their lower costs regarding money and time compared to performing experiments, computer simulations grow in importance when developing industrial separation processes. On plant scales, process simulators are widely applied, and on particular scales, computational fluid dynamics (CFD) calculations can support design. In this work, the incompressible Cahn-Hilliard/Navier-Stokes equations and the non-random two-liquid (NRTL) model were applied to perform numerical simulations in order to investigate droplet interactions of extraction systems. In contrast to other CFD approaches, no assumptions regarding the evolution of drop size distributions are required. The impact of the influence parameter and mobility coefficient within this framework was studied for the first time. While the mobility coefficients show a low impact on the flow field, different values of the influence parameter can lead to completely different behavior, with low influence parameters causing small morphologies and requiring larger grid resolutions in the simulation. A method is proposed to incorporate various thermodynamic data like phase equilibrium, interfacial tension, and diffusion coefficients into CFD simulation. Especially, the interfacial tension is not a direct parameter but rather determines the density gradient theory (DGT) influence parameter and therefore enables us to consider the variation of interfacial tensions in a system with different temperatures or compositions.