A numerical study of liquid compound filament contraction

Abstract

Droplets resulting from liquid filament contraction have been widely used in industrial processes. However, detailed investigations of liquid compound filament contraction processes are lacking in the literature. Therefore, this study provides a numerical investigation of the contraction of a two-layered compound filament. The simulations are based on an axisymmetric front-tracking method. It is found that because of the interfacial tension force, the initially long cylindrical filament contracts to a compound droplet without any breakup or breaks up into smaller droplets during contraction. Unlike simple filaments, the presence of the inner filament inside the compound filament results in a more complicated compound filament breakup process with various droplet types, e.g., simple droplets, single-core compound droplets, and multi-core compound droplets. We find that the inner filament breaks up into droplets, while the outer does not induce breakup. Such a breakup mode produces a multi-core compound droplet after contraction. In some cases, while the inner filament only contracts to a single droplet, its enclosing filament breaks up to produce simple droplets at each end. We also find a breakup mode that combines these two modes, where both the inner and outer filaments perform breakup. In addition, the breakup of the compound filament occurs via one of two mechanisms: end-pinching and necking. These breakup modes and mechanisms are affected by various parameters such as the inner and outer aspect ratios, the Ohnesorge number, the interfacial tension ratio, and the viscosity ratios. Based on these parameters, various regime diagrams of breakup and non-breakup are proposed.