(189bt) CFD Simulations for Gas Solubility Measurements with Gas-Liquid Segmented Flows

Gas absorption in liquid solutions involves a multiphase mass transfer mechanism. The resistance present at phase boundaries controls the mass transfer rates and hampers the measurement of thermodynamic properties such as gas solubility and reaction rates. Gas-liquid systems in microfluidic scale overcome the limitation in the mass transfer rate by increasing the specific interfacial contact area across phases and reducing the mass transfer resistance [1]. Recirculation flows present in liquid slugs further improve mass transfer [2]. Mass transfer rate is faster in microfluidic scale which significantly reduces the timescale of measurement [3]. We study the solubility of CO₂ gas in water and in aqueous NaCl solution (at 298K) using Computational Fluid Dynamics simulations. CFD simulations allow accurate examination of pressure profile, velocity, and concentration fields in the system. We design a unit cell geometry in CFD which depicts a single unit of a bubble and slug train. Periodic conditions across the unit cell geometry are used which makes unit cell design a good approximation and significantly reduces computation time. The level set method coupled with momentum balance and continuity equation are used in CFD to capture fluid flow profiles. To address mass transfer in CFD, we use the convection-diffusion transport equation to capture the concentration profile. CFD simulation results show pressure profile, velocity profile, and concentration field which can be used to calculate the solubility. We show that CFD simulations coupled with gas dissolution experiments in gas-liquid segmented flows can identify the solubility of CO₂ in different solutions and reduce the experimental effort.

References

[1] Günther, A. and Jensen, K.F. “Multiphase microfluidics: from flow characteristics to chemical and materials synthesis.” Lab on a Chip, 6(12), 1487-1503, 2006.

[2] Taylor, G.I. “Deposition of a viscous fluid on the wall of a tube.” Journal of Fluid Mechanics, 10(2), 161-165, 1961.

[3] Yang, L. Nieves-Remacha, M.J. and Jensen, K.F. “Simulations and analysis of multiphase transport and reaction in segmented flow microreactors.” Chemical Engineering Science, 169, 106-116, 2017.