(310e) Effect of Critical Geometric and Physical Parameters on the Coalescence Dynamics of Droplet Pairs in Confined Shear Flows

Geometric and physical parameters are essential factors in determining the hydrodynamic nature of droplet coalescence that is encountered in many practical multiphase flow applications. Computational analysis has been performed to investigate such parametric influence on the coalescence of a pair of initially spherical droplets subjected to a confined shear flow. Free-energy based lattice Boltzmann method has been adopted to carry out the simulations with a Reynolds number of 1.0 and Capillary number of 0.08. We explore the characteristics of droplet morphology, course trajectory, and the eventual collision state as a function of density ratio (60 to 800), viscosity ratio (24 to 60), initial offset, and confinement. Variation in initial offset leads to three different outcomes of collision (reverse-back, coalescence, and pass-over), separating them by two critical initial offset values. In addition to the initial offset of droplets, geometrical confinement plays a critical role in the coalescence enhancement. Though the change in density ratio and viscosity ratio slightly impacts governing collision mode, their interaction dominates in controlling droplet’s deformation, course trajectory, and behavior throughout the evolution. Some unusual motion and undulation have been observed at high density and viscosity ratios, particularly near the critical initial offset, which we have addressed and explained based on the underlying physics of interactions among different forces acting on them. Taken together, the reported results are expected to provide new insight into the combined effect of geometric and physical parameters on the intrinsic nature and the condition of coalescence.