The breakup of a fluid thread surrounded by another Newtonian fluid in a coaxial tube in the absence of imposed flow is investigated using the Lattice Boltzmann (LB) model. We observe a confinement-induced transition between spherical droplets to plugs in the late-stage of capillary breakup when the tube radius Rtube becomes less than approximately twice the inital thread radius Rthread and metastable distorted droplets ('capsules') form at intermediate levels of confinement. The interaction of the liquid components with the tube boundary influences the rate of capillary breakup in confined threads and a strong slowing of instability growth ('kinetic stabilization') is generally found when the thread and tube have comparable dimensions. The thread breakup process for the confined threads is sensitive to the nature of the initial thread perturbation- discrete impulsive perturbations led to breakup through a bulging instability developing from near the tube wall followed by thread breakup through an in-pinch instability while random impulses along the thread led to a complex breakup process involving a competition between the capillary wave and end-pinch type breakup process. We also briefly consider the breakup of fluid threads between parallel plates and find similar phenomena to fluid threads confined to tubes.
Citation: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics)
Issue: No. 5
Pub Type: Journals
capillary breakup, instability, Lattice Bolzmann, surface tensions, Taylor-Tomotika