Shao, N.; (2010) Gas-liquid two-phase flow and reaction in microstructured reactors. Doctoral thesis , UCL (University College London).

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Abstract

The thesis presents investigations on two-phase gas-liquid microstructured reactors operating in Taylor flow and the dependence of reactor performance on design parameters. Literature review revealed that flow patterns in microchannels are affected not only by channel dimension, fluids flowrates and surface tension, but also by wall wettability and gas inlet size. A universal flow regime map does not seem to exist. The hydrodynamic parameters of Taylor flow were investigated both by Computational Fluid Dynamics simulations and experiments in microstructures with sizes 0.3mm – 1mm and various inlet configurations such as T- and Y- junctions fabricated in-house. The same parameters that influence flow patterns and their transitions were also found to affect Taylor bubble sizes. To account for the effect of inlet conditions, correlations were developed for predicting bubble/slug size in the T- and Y- inlet geometries that were used subsequently. Mass transfer with and without chemical reaction was investigated numerically in Taylor flow microreactors using CO2 physical absorption into water or chemical absorption into NaOH aqueous solution. Chemical absorption was enhanced by a factor of 3-18 over physical absorption. With reaction present, the reactor performance depended mainly on the gas-liquid interfacial area, while mixing within the phases was only important in physical absorption. This agreed with the experimental results of a similar reaction system, which showed that bifurcating main channels, where new interfaces are generated, significantly improved reaction conversion while meandering channels that enhance liquid mixing had little impact. Finally, the performance of a Taylor flow microreactor was evaluated for an industrial fast gas-liquid reaction of CO2 absorption from fuel gas into amine solutions. The Taylor flow microreactor offered the largest specific area and the smallest reactor volume compared to other microreactor types. However, in order to meet absorption specifications for the case considered multistage absorption would have been necessary.

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