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Hydrodynamics and reaction characteristics of gas-liquid flow in circular microchannels

Abstract : This dissertation mainly deals with the fundamental knowledge of hydrodynamics and reaction characteristics in gas-liquid microreactors. Extensive experimental investigations have been performed in horizontal circular microchannels with diameter from 302 µm to 916 µm. Gas-liquid two-phase flow patterns in the microchannel have been systematic experimental investigated, in which the influence of channel diameters, liquid viscosities and surface tension were considered. Flow pattern regime maps in the present microchannels were developed, and the comparison with existing regime maps and flow pattern transition models in literature implied that transitions in present work could not be well predicted. As a result, a new transition model taking the effects of channel size, liquid physical properties into account was proposed. The gas-liquid two-phase pressure drop characteristics in microchannels were studied. It has been found that the pressure drop was highly flow patterns dependent, and the main trend can be divided into three regions: surface tension-dominated region, transitional region and inertia-dominated region. The pressure drop characteristics in surface tension-dominated and inertia-dominated region were discussed respectively. A modified Lockhart-Martinelli separated flow model in which the effects of channel diameter and liquid properties on the C-value are taken into account was proposed, and it showed a good agreement with respect to our experimental data and others' reported in literature. Hydrodynamics characteristics of Taylor flow have been examined. It was shown that the formation of Taylor flow was dominated by squeezing mechanism, on which the effects of liquid viscosity and surface tension were dramatically. The two-phase pressure drop of Taylor flow could be well predicted with the Kreutzer's model modified by Walsh et al., when capillary number was relatively low. Oxidation of hydrogenated 2-ethyltetrahydroanthraquinone (THEAQH2) in a horizontal circular microchannel have been experimental investigated. Results of visualization study on oxygen-anthraquinone working solution two-phase flow in microchannel showed that the flow pattern transition model and pressure drop model for inertia-dominated region proposed in this dissertation had good predicting accuracy. It was indicated that the gas-liquid interfacial area and space-time yield of hydrogen peroxide in the microchannel are at least one to two orders of magnitude higher than those in the conventional gas-liquid reactors. Keywords: microchannel, two-phase flow pattern, pressure drop, gas-liquid reaction, Taylor flow..
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Tong Zhang. Hydrodynamics and reaction characteristics of gas-liquid flow in circular microchannels. Other. Université de Grenoble; Dalian Institute of Chemical Physics (Chine), 2012. English. ⟨NNT : 2012GRENA028⟩. ⟨tel-00804363⟩

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