The penetration of a long bubble through a viscoelastic fluid in a tube

Abstract

The penetration of a long gas bubble through a tube filled with a viscoelastic fluid is studied. This problem has practical applications in gas-assisted injection molding, enhanced oil recovery, production of hollow fiber membranes, and coating of ceramic monoliths for the manufacture of catalytic converters. A hydrodynamic coating is formed on a capillary tube wall by injecting a single long gas bubble through the fluid. This problem has been studied extensively for Newtonian fluids, but little work has been done to understand how non-Newtonian fluids behave in this flow. The work presented in this paper is directed at identifying the effects of fluid elasticity on the hydrodynamic fractional coverage created by a long penetrating bubble. Experiments were performed with four test fluids including two Newtonian fluids and two highly elastic, constant shear viscosity fluids. Hydrodynamic fractional coverage, m was characterized in terms of the capillary number, Ca and Deborah number, De. For small Deborah number, De<1, both viscoelastic fluids exhibit a fractional coverage identical to that of a Newtonian fluid at an equivalent capillary number. The fractional coverage for both viscoelastic fluids begins to increase relative to the Newtonian result at De≈1. Fractional coverage continues to increase with Deborah number for all De≥1. At De≈5 fractional coverage is 30% greater than the Newtonian fluid result. A plot of fractional coverage versus capillary number is found to be independent of tube diameter for a Newtonian fluid. However, for a viscoelastic fluid, fractional coverage is found to be a strong function of tube diameter. The Deborah number is found to collapse fractional coverage data for experiments conducted with different tube diameters.