Dynamics of Taylor bubbles in non-Newtonian shear thinning continuous phase

Droplet-based microfluidics has emerged as an efficient platform in a number of lab-on-chip devices for chemical or biomedical analysis. In most of such applications, a non-Newtonian complex liquid constitutes the continuous phase. In the present study, a two-phase gas-non-Newtonian liquid flow has been studied in a horizontal rectangular microchannel with a built-in T-junction. Aqueous solutions of carboxy-methyl cellulose (CMC) of different mass concentrations (0.4%-4%) have been taken as the liquid phase which behaves like a shear-thinning (non-Newtonian) liquid. The air has been used as the gaseous phase. Effects of non-Newtonian continuous phase on the shape, size, and hydrodynamics of the Taylor bubbles inside a microchannel were investigated to understand the influence of viscous stress and surface tension force under various flow conditions. Effects of contact angle (nature of confining walls), gas-liquid superficial velocity ratio, channel dimension etc. were studied at different Capillary numbers (Ca) and viscosity ratios. The rheological properties of CMC solutions are found to affect the formation characteristics and dynamics of the Taylor bubbles significantly. The present work covers a wide range of viscosity ratios and shows the effect of concentration variation of CMC of the non-Newtonian liquid on the bubble dynamics inside the microchannel.