A two-dimensional numerical study on the coalescence of viscous double emulsion droplets in a constricted capillary tube.

This article focuses on the numerical investigation of double-emulsion (DE) droplet dynamics in a two-dimensional constricted capillary tube, emphasizing the effects of interfacial tension, viscosity and density ratios, droplet sizes, pore throat size, and channel geometry on local extra pressure drop and droplet velocities. Using the finite element method coupled with the level set method for interface tracking, the study finds that higher interfacial tension leads to less deformable DE droplets that coalesce at constrictions, causing larger pressure drops and reduced fluid mobility, while lower interfacial tension allows easier deformation without coalescence. Increased oil-to-water viscosity ratios hinder droplet deformation and coalescence, elevating pressure drops, whereas density differences have negligible impact. Additionally, smaller inner water droplets maintain DE stability, but larger inner droplets destabilize it by escaping the oil phase; smaller pore sizes reduce droplet mobility due to coalescence, and rectangular constriction shapes cause greater resistance compared to circular or sinusoidal shapes. These findings contribute to understanding multiphase flow behavior relevant to enhanced oil recovery and porous media applications.