Dynamic changes in gas-liquid mass transfer during Taylor flow in long serpentine square microchannels

Abstract

The present work focuses on the hydrodynamics variation and mass transfer characteristics of Taylor flow along long serpentine microchannels with a square cross-section. The volumetric mass transfer coefficient (k L a) is regarded as the transient change value to characterize the gas-liquid mass transfer process of CO 2 in water. All experimental data of Taylor bubble are obtained from 1,000 continuously captured images. An online high-speed imaging method and the unit cell model are adopted in this study. The effects of gas and liquid flow rates, together with microchannel geometry are investigated on Taylor bubble characteristics in terms of length, velocity and the mass transfer performance. Taylor bubble length shrinks and subsequently plateaus out along the flow direction from the T-junction, resulting in the decrease in Taylor bubble velocity. k L a in a unit cell gradually decreases along the serpentine microchannel, and increases as the channel cross-sectional area decreases. As the gas flow rate increases under a given liquid flow rate, a critical point is found for the evolution of k L a and k L

The effect of liquid viscosity and modeling of mass transfer in gas–liquid slug flow in a rectangular microchannel

“…The film layer not only serves as a receptor of mass transfer from the lateral bubble body but also is a vital donor in feeding the bulk slug . Hence, the mass exchange between the film and the bulk slug is crucial for the overall k L . The results may be explained as follows: For solutions with low glycerol concentration, the film is thin and easily saturated, and its exchange with bulk liquid is slow.…”

“…32,33 Hence, the mass exchange between the film and the bulk slug is crucial for the overall k L . 18,26 The results may be explained as follows: • For solutions with low glycerol concentration, the film is thin and easily saturated, and its exchange with bulk liquid is slow. Hence, k L /D 0.5 is small.…”

“…Such phenomena are common for flow conditions with long bubbles and small flow rates. Whereas, for shorter bubbles or larger flow rates, both contributions from bubble caps and lateral film always play essential roles, leading to more complex dissolution behavior . For example, when increasing the gas flow rate, the competition between increased lateral film saturation and surface renewal rate can result in either an increase or decrease in the mass transfer coefficient ( k L ) …”

“…Whereas, for shorter bubbles or larger flow rates, both contributions from bubble caps and lateral film always play essential roles, leading to more complex dissolution behavior. 18,25,26 For example, when increasing the gas flow rate, the competition between increased lateral film saturation and surface renewal rate can result in either an increase or decrease in the mass transfer coefficient (k L ). 18 Furthermore, the insights of local transfer mechanism are investigated with CFD [27][28][29] and non-invasive technique with high spatial resolution.…”

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

“…The microreactor was made according to published procedures with minor adaptations. 24,25 Briey, the channel network was fabricated by precision milling on a polymethyl methacrylate (PMMA) sheet (thickness 5 mm), which was closed with a cover sheet (thickness 10 mm) by thermal bonding at a temperature of 50 C aer washing both in an ethanol bath at 70 C for 3 min. Before the experiments, all channels were ushed with n-hexadecane and then deionized water, followed by nitrogen drying.…”