Transport and reaction in microscale segmented gas–liquid flow

Abstract

We use micro particle image velocimetry (microPIV) and fluorescence microscopy techniques to characterize microscale segmented gas-liquid flow at low superficial velocities relevant for chemical reactions with residence times of up to several minutes. Different gas-liquid microfluidic channel networks of rectangular cross section are fabricated in poly(dimethylsiloxane) (PDMS) using soft lithography techniques. The recirculation motion in the liquid segments associated with gas-liquid flows as well as the symmetry characteristics of the recirculations are quantified for straight and meandering channel networks. Even minor surface roughness effects and the compressibility of the gas phase induce loss of symmetry and enhance mixing across the centerline in straight channels. Mixing is further accelerated in meandering channels by the periodic switching of recirculation patterns across the channel center. We demonstrate a new, piezoelectrically activated flow injection technique for determining residence time distributions (RTDs) of fluid elements in multiphase microfluidic systems. The results confirm a narrowed liquid phase RTD in segmented flows in comparison to their single-phase counterparts. The enhanced mixing and narrow RTD characteristics of segmented gas-liquid flows are applied to liquid mixing and in sol-gel synthesis of colloidal nanoparticles.

Characteristics of slug flow with inertial effects in a rectangular microchannel

“…Low axial mass transfer or back mixing occurs between two adjacent liquid slugs. Moreover, both radial mass and heat transfer can be intensified by internal circulation in the single slugs (Günther et al, 2004;Thulasidas et al, 1997). These merits make slug flow an ideal regime for improving the reaction performance.…”

Improved Temporal Resolution for in Vivo Microdialysis by Using Segmented Flow

“…Segmented flow can eliminate Taylor dispersion by localizing samples as aqueous droplets or plugs formed in a stream of water-immiscible carrier fluid. [22][23][24][25] A surge of recent research into segmented flows has shown the potential of this approach for chemical measurement. Droplets or plugs from femtoliter to microliter volume can be reproducibly created using a variety of microfluidic geometries including tee junctions, 26 Yjunctions, 23 The goal of this study was to combine in vivo microdialysis sampling with a segmented flow microfluidic device to conserve temporal resolution while sample plugs were transported from the probe to a downstream detection system.…”

Using Three-Phase Flow of Immiscible Liquids To Prevent Coalescence of Droplets in Microfluidic Channels: Criteria To Identify the Third Liquid and Validation with Protein Crystallization

“…23,24 Gas bubbles were used in liquid-gas twophase segmented flow as well. 25,26 For applications involving long arrays of plugs, two drawbacks may need to be overcome in using gas bubbles as spacers: (1) compressible gas bubbles could cause flow fluctuation and a lag in response to the change of flow rates in pressure-driven flow, and (2) gas bubbles may dissolve in the fluorinated carrier fluid under high pressure. 27 Solving these problems would be especially useful when performing screens using cartridges 28 preloaded with reagent plugs.…”