CFD study on Taylor bubble characteristics in Carreau-Yasuda shear thinning liquids

Abstract

In the present study, Taylor bubble formation in two-phase gas-non-Newtonian Carreau liquid flowing through a confined co-flow microchannel is investigated. Systematic analysis are carried out to explore the influences of rheological properties, inlet velocities, and surface tension on Taylor bubble length, shape, velocity and liquid film thickness. Aqueous solutions of carboxymethyl cellulose (CMC) with different mass concentrations are considered as the non-Newtonian liquids to understand the fundamentals of flow behaviour. With increasing solution viscosity and liquid phase inlet velocity, Taylor bubble formation frequency and velocity increased, however, the bubble length was found to decrease. Velocity profiles inside the Taylor bubble and liquid slug were analyzed, and distinct velocity distributions were found for different CMC concentrations. Flow pattern maps are constructed based on inlet velocities for Carreau liquids in co-flow microchannel. This study essentially provides useful guidelines in designing non-Newtonian microfluidic system for precise control and manipulation of Taylor bubbles.

Figures (10)

• Figure 1: (a) 3D schematic of the Taylor bubble formation in circular co– flow microchannel, (b) 2D representation of the computational domain with imposed boundary conditions, (c) interface tracking comparison between two different mesh element sizes (5 $\mu m$ vs. 6 $\mu m$), highlighting elongated thread in coarse mesh (6 $\mu m$) and, (d) grid independence study of the bubble length for air– CMC–1.0% system for $U_G=0.5~m/s$, $U_L=0.5~m/s$.
• Figure 2: (a) Comparison of Taylor bubble length for different injection length ($L_{in}$) for $\eta_w$= 1.003$\times10^{-3}$ kg/m.s, $Q_{G}= 0.47$$\mu L/s$, and $Q_{L}= 2.01$$\mu L/s$ with the results of Wang wangg-2015, and (b) comparison of Taylor bubble shape with Gupta et al. gupta-2009 for air– water system with $U_G=0.5~m/s$, $U_L=0.5~m/s$.
• Figure 3: Effect of CMC concentration on (a) non– dimensional bubble length and formation frequency, (b) surrounding liquid film thickness, (c) velocity profile in the middle of a Taylor bubble, and (d) velocity profile in the middle of a liquid slug at $U_{L}$ = 0.5 m/s and $U_{G}$ = 0.5 m/s.
• Figure 4: Effect of CMC concentration on velocity distribution (upper halves are volume fraction and lower halves are velocity field) for (a) CMC– 0.1 %, (b)CMC– 0.4 %, (c) CMC– 0.6 %, and (d) CMC– 1.0 % at $U_{L}$ = 0.5 m/s and $U_{G}$ = 0.5 m/s.
• Figure 5: Effect of CMC concentration on non-homogeneous viscosity distribution (upper halves are volume fraction and lower halves are viscosity distribution) for (a) CMC– 0.1 %, (b)CMC– 0.4 %, (c) CMC– 0.6 %, and (d) CMC– 1.0 % at $U_{L}$ = 0.5 m/s and $U_{G}$ = 0.5 m/s.