Bubble-train flow in capillaries of circular and square cross section

Optical sectioning for microfluidics: secondary flow and mixing in a meandering microchannel

“…The bubble velocity U b and, therefore, Ca can be estimated from the overall superficial velocity. 31 The Dean number and the capillary number were about 5.4 and 2.7 × 10 −4 , respectively, under the present experimental conditions. Since the flow has rapid, transient phenomena and the camera frame rate (1/T) is limited, it was impossible to acquire an instantaneous volume image.…”

“…5(b-d), the secondary flow caused by the curvature was also observed. The maximum primary liquid velocity around the center of the cross-section far from the bubbles is about 1.8 times higher 31,32 than the bubble velocity with a capillary number of 2.7 × 10 −4 . Therefore, a toroidal vortex per liquid slug was generated before and after the bubbles and made a longitudinal recirculation flow when this flow was seen in a coordinate system moving with the bubbles.…”

“…The hypothesis was that injecting air into two liquids enhances mixing. By injecting air, a bubble-train flow [30][31][32] was sustained in a quasi-steady-state. Through the third experiment, the velocity field, which governs a mixing phenomenon, was imaged.…”

Characteristics of slug flow with inertial effects in a rectangular microchannel

“…The figuration of slug flow contains regular sized gas bubbles that are longer than the channel diameter or width. The gas bubbles are surrounded by a thin liquid film with the bubble area occupying almost the entire channel cross-section (Fries et al, 2008;Thulasidas et al, 1995). Low axial mass transfer or back mixing occurs between two adjacent liquid slugs.…”

“…These merits make slug flow an ideal regime for improving the reaction performance. Wide attention has been paid to the bubble formation process (Fu et al, 2009;Garstecki et al, 2006;Pohorecki and Kula, 2008;van Steijn et al, 2007), the gas bubble and the liquid slug length (Garstecki et al, 2006;Leclerc et al, 2010;Qian and Lawal, 2006;Sobieszuk et al, 2010), the liquid film thickness around bubbles (Fries et al, 2008;Han and Shikazono, 2009a;Thulasidas et al, 1995), the phase distribution (Choi et al, 2011;Kawahara et al, 2005;Saisorn and Wongwises, 2010), the pressure drop (Kreutzer et al, 2005a(Kreutzer et al, , 2005bYue et al, 2009), and the mass transfer (Sobieszuk et al, 2011;van Baten and Krishna, 2004;Vandu et al, 2005), etc. However, a full understanding of slug slow for optimizing the design of microreactor remains pendent.…”