Numerical investigation of viscous effect on Taylor bubble formation in co-flow microchannel

Abstract

In recent years, studies on two–phase flow in microchannels have attracted huge interest due to its wide range of application in lab–on–a–chip devices and microreactors. Regarding gas–liquid two–phase flow in microchannels, most of the previous research dealt with gas and Newtonian liquid phase. However, several fluids in practical application exhibit non–Newtonian behavior, as well. In this study, gas and non-Newtonian liquid phase flow in a circular co–flow microchannel has been numerically investigated. The developed CFD model is initially validated with the literature data, and thereafter the model is employed for non–Newtonian studies. Polyacrylamide (PAAm) aqueous solutions with different mass concentration, which exhibit shear thinning behavior are used as non–Newtonian liquid. The effects of PAAm concentration, gas and liquid inlet velocities, and surface tension on Taylor bubble have been systematically explored. The results show that Taylor bubble length decreases with increasing PAAm concentration. The bubble velocity is found to increase with increasing PAAm concentration due to increase in liquid film thickness around the bubble. The film around the Taylor bubble is precisely captured. It is observed that the rheological properties of continuous phase have significant effect on bubble shape and liquid film thickness. Squeezing break up mechanism is observed at higher liquid inlet velocity for lower concentration of PAAm. The bubble formation frequency is found to reach maximum with increasing liquid velocity and PAAm concentration. Different flow patterns are observed namely, Taylor bubble, and non–Taylor bubble, where the bubble length is smaller than the capillary diameter of the channel. Additionally, flow pattern maps are also reported based on inlet velocities. These understandings motivate for new predictive modeling approaches in design and applications demanding the use of non–Newtonian fluids.