Experimental study on the motion of a confined bubble in a non-Newtonian fluid

When a confined long gas bubble translates in a capillary tube, a thin film of liquid separates the bubble surface and the tube inner wall, with its thickness determined by the interplay of viscous, inertial and capillary effects. Although the dynamics of a confined bubble in a Newtonian liquid has been the subject of quite a few studies since the pioneering works of Taylor and Bretherton, the case where the fluid exhibits a non-Newtonian behavior is much less understood, while in applications, such as enhanced oil recovery and drug delivery, the fluids are likely to exhibit non-Newtonian properties. Here we consider the classical Bretherton problem with a non-Newtonian fluid. We provide quantitative measurements of the thickness of deposited liquid film for carboxymethyl cellulose solutions with different concentrations in the range of small Capillary numbers. Depending on the concentration of CMC, the thickness of the liquid film shows distinguished behaviors compared with that of Newtonian case. We further compare our observations with the scaling law considering the effective viscosity to extend the classical Bretherton's correlations to non-Newtonian fluids. Our results may enrich the fundamental understanding of multi-phase flows involving a non-Newtonian fluid.