Experimental observation of a confined bubble moving in shear-thinning fluids

The motion of a long gas bubble in confined capillary tube is ubiquitous wide range engineering and biological applications. While the understanding deposited thin viscous film near wall Newtonian fluids well developed, deposition dynamics commonly encountered non-Newtonian remains much less studied. Here, we investigate moving shear-thinning with systematic experiments, varying zero-shear-rate number $Ca_0$ $O(10^{-3}\unicode{x2013}10^2)$ considering viscosity. thickness liquid film, speed front/rear menisci are measured, which further rationalized recent theoretical studies based on appropriate rheological models. Compared fluids, decreases for both carboxymethyl cellulose Carbopol solutions when effect dominates. We show that follows scaling law from Aussillous & Quéré ( Phys. Fluids , vol. 12, no. 10, 2000, pp. 2367–2371) an effective $Ca_e$ characteristic shear rate as proposed by Picchi et al. J. Fluid Mech. 918, A7, 2021, 1–30). calculated Carreau power-law index Carreau–Yasuda model. also influences delays transition to parabolic region front rear menisci. In particular, high degree undulations surface results intricate viscosity distribution meniscus deviation between experiments theory may require investigation resolve axial velocity field. Our study advance fundamental understandings guidelines coating processes involving thin-film flows fluids.