Abstract
This work investigates the change of the flow topology of Taylor flow and qualitatively relates it to the excess velocity. Ensemble-averaged 3D2C-upmu PIV measurements simultaneously resolve the flow field inside and outside the droplets of a liquid–liquid Taylor flow that moves through a rectangular horizontal microchannel. While maintaining a constant Capillary number Ca = 0.005, the Reynolds number (0.52 le {text{Re}} le 2.14), the viscosity ratio (0.24 le lambda le 2.67) and surfactant concentrations of sodium dodecyl sulfate (0–3 CMC) are varied. We experimentally identified the product of the Reynolds number Re and the viscosity ratio lambda to indicate the momentum transport from the continuous phase (slugs) into the droplets (plugs). The position and size of the droplet’s main vortex core as well as the flow topology in the cross section of this vortex core changed with increased momentum transfer. Further, we found that the relative velocity of the Taylor droplet correlates negatively with the evoked topology change. A correlation is proposed to describe the effect quantitatively.Graphical abstract
Highlights
The versatile possibilities of microfluidic applications have been recognized in the beginning millennium (Ehrfeld et al 2004; Seeberger and Blume 2007; Angeli and Gavriilidis 2008; Dietrich 2009; Huebner et al 2008)
We discuss the relation between the change of the flow topology and the net flow through the gutter
We found no obvious relation between the momentum coupling Re ⋅ -related flow topology change and the net volume flow that bypasses the Taylor droplets through the gutter (Fig. 14a)
Summary
The versatile possibilities of microfluidic applications have been recognized in the beginning millennium (Ehrfeld et al 2004; Seeberger and Blume 2007; Angeli and Gavriilidis 2008; Dietrich 2009; Huebner et al 2008). Examples range from general chemical reactions (Song et al 2006) to chemically catalyzed processes transferred from macro- to microscale like fluorination (Chambers et al 2003; Lang et al 2012), heterogeneous or multiphase catalysis (Kobayashi et al 2006; Tanimu et al 2017; Rossetti 2018), photo-catalysis (Yusuf et al 2018), syngas production (Chen et al 2018), extraction (Kralj et al 2007), to mixing tasks (Wong et al 2004) or the usage of reactions in monolith reactors (Kreutzer et al 2005). The great interest in downscaled liquid–liquid multiphase flows has persisted in recent years (Zhao and Middelberg 2011; Chou et al 2015; Shi et al 2019): The process driving forces such as pressure, temperature and concentration gradients and their resulting heat and mass transfer rates can be precisely adjusted (Haase et al 2016; Sattari-Najafabadi et al 2018). This could mean fewer hazards and higher selectivity (Sun et al 2016) or sustainable operation modes close to the optimal working point (Magnaudet and Eames 2000; Ern et al 2012)
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