Hydrodynamics and local mass transfer characterization under gas–liquid–liquid slug flow in a rectangular microchannel

Abstract

Gas-liquid-liquid three-phase slug flow was generated in a glass microreactor with rectangular microchannel, where aqueous slugs were distinguished by relative positions to air bubbles and organic droplets. Oxygen from bubbles reacted with resazurin in slugs, leading to prominent color changes, which was used to quantify mass transfer performance. The development of slug length indicated a film flow through the corner between bubbles and the channel wall, where the aqueous phase was saturated with oxygen transferred from bubble body. This film flow results in the highest equivalent oxygen concentration within the slug led by a bubble and followed by a droplet. The three-phase slug flow subregime with alternate bubble and droplet was found to benefit the overall mass transfer performance most. These results provide insights into a precise manipulation of gas-liquid-liquid slug flow in microreactors and the relevant mass transfer behavior thereof.

Manipulation of gas-liquid-liquid systems in continuous flow microreactors for efficient reaction processes

“…Understanding into transport characteristics within gasliquid-liquid flow in microreactors is of vital importance for the design, operation and optimization of such microreactor systems for their promising applications in the abovementioned fields. Compared with the extensive gas-liquid and liquid-liquid two-phase flow studies in microreactors [23,[45][46][47][48], limited research has been paid to the case of gas-liquid-liquid microflow [11,12,19,29]. A considerable fraction of the literature work in the latter case was focused on hydrodynamics therein [13,14,17,18,49,50], and few on the investigation of mass transfer property [12,14] and the preliminary exploration of the potential applications [21,29,30,38].…”

“…4b), which makes the whole mass transfer scenarios more complicated, especially for the gas transfer to the aqueous bulk (i.e., subsequently through the gas-oil interface, organic bulk, aqueous-oil interface and aqueous bulk). In a most recent work, Liu et al [12] revealed that the film flow through the gap between bubbles and the microchannel wall contributed significantly to the gas transferring into the continuous phase, and an alternating bubble/droplet sub-regime ( Fig. 1a (i)) is preferred towards mass transfer optimization.…”

“…However, the bubble/droplet collision configurations are subject to other factors as well, such as channel materials, flow ratios, bubble/droplet generation mechanisms and surfactant concentrations [70][71][72]. In fact, bubbledroplet clusters were also observed in many cases [12,52,70]. The draining of the continuous phase between bubbles and droplets often leads to flattened droplet caps (Fig.…”

“…1 mm, but this dimension could be extended reasonably to a few millimeters as long as the benefits due to miniaturization is kept [11]. Fluids delivered into the microreactor are commonly mixed and subsequently dispersed into the reaction microchannel via micromixers (e.g., based on a T- [12][13][14], Y- [15,16] or cross-junction [17][18][19], or flow-focusing geometry [16,20]) or membranes [21,22]. Due to the laminar flow nature and the dominance of interface…”

Dynamics and controllability of droplet fusion under gas–liquid–liquid three-phase flow in a microfluidic reactor

“…Liu et al 22 studied the characteristics of bubble splitting under three-phase ow in a double T-junction microchannel, revealing the critical breaking length and the size of the sub-bubble/slug. More recently, Liu et al 23 further investigated the effects of the threephase slug sub-regime ow on hydrodynamics and local mass transfer, conrming that the alternate bubble and droplet ow is in favor of mass transfer.…”