Taylor Bubble Generation Rules in Liquids with a Higher Viscosity in a T-Junction Microchannel

Abstract

Generation of bubbles in a T-junction microdevice is vital to microfluidic applications for its advantages of easy fabrication and scaling-up, but the bubble generation in liquids with a higher viscosity in the T-junction is rarely reported for the unstable dispersion behavior under the constant flow rate-driven condition. Accordingly, this work investigates the bubble generation rules in liquids with a higher viscosity (45.6−240.5 mPa•s) under the constant-pressure method. It shows that the bubble formation process in higher viscous liquids contains three stages, expansion, shrinking, and necking, which are obviously different from the filling and squeezing stages in the lower viscous liquid. Importantly, the generation of satellite bubbles as a new bubble generation performance could be observed for the first time in the gas−liquid microdispersion process. The new dispersion mechanism and some novel phenomena are revealed by the interface evolution rules. Finally, a novel mathematical model is developed to predict the bubble length.

Hydrodynamics and Scaling Laws of Gas–Liquid Taylor Flow in Viscous Liquids in a Microchannel

“…The physical properties (liquid density, viscosity, and surface tension) of the experimental materiel are listed in Table 1, which are consistent with our previous work. 20…”

“…To verify the reliability of this new model, we further used eq 11 to calculate the pressure drop data in the highly viscous system (240.5 mPa•s) obtained in our previous cross-flow squeezing work, 20 and Figure 13b demonstrates that this novel equation can also quantify the pressure drop well. In addition, we used eq 11 to calculate the pressure drop data obtained in a solution with smaller viscosity (8.9 mPa•s).…”

“…The depth ( H ) and width ( W ) of the T-junction microchannel were 400 μm, and the length of the downstream channel was 16 cm. The physical properties (liquid density, viscosity, and surface tension) of the experimental materiel are listed in Table , which are consistent with our previous work …”

“…30 Regarding the rectangular or square microchannel, the Taylor bubble has a nonuniformity liquid film thickness distribution due to the channel corner effect. Although the rectangular channel has been extensively used in the literature, 11,19,20,32 the prediction model to the δ f value in the rectangular or square microchannel is rarely reported because the liquid region distribution along the cross-area of the channel is complex. Importantly, the existing literature about the liquid film is usually carried out in the solutions with a lower viscosity of 1.0 mPa•s, and the effect of the liquid viscosity on liquid film distribution remains unclear.…”

“…Considering the contact model of the gas–liquid two phases in the T-junction microchannel, the bubble generation route could be classified into three types: cross-flow squeezing, vertical flow squeezing, and colliding flow squeezing . Regarding cross-flow squeezing and vertical flow squeezing, large numbers of the investigations about the Taylor bubble size have been systematically reported in terms of the influence of the aspect ratio of the microchannel, ,− the angle of T-junction intersection, ,− liquid viscosity, − liquid viscoelasticity, the gas injection method, pressure feedback, and so forth. Regarding colliding squeezing, Yao et al explored the effect of the outlet pressure on the bubble length, and they further tested the leakage flow in the colliding T-junction .…”