This paper investigates oil-water two-phase flows in microchannels of 793 and 667 m hydraulic diameters made of quartz and glass, respectively. By injecting one fluid at a constant flow rate and the second at variable flow rate, different flow patterns were identified and mapped and the corresponding two-phase pressure drops were measured. Measurements of the pressure drops were interpreted using the homogeneous and Lockhart-Martinelli models developed for two-phase flows in pipes. The results show similarity to both liquid-liquid flow in pipes and to gas-liquid flow in microchannels. We find a strong dependence of pressure drop on flow rates, microchannel material, and the first fluid injected into the microchannel.Onétudie dans cet article lesécoulements diphasiques huile-eau dans des micro-canaux de 793 m et 667 m de diamètre hydraulique faits de quartz et de verre, respectivement. En injectant un fluideà un débit constant et le secondà un débit variable, différents schémas d'écoulements ontété observés et représentés en diagrammes, et les pertes de charge diphasiques correspondantes ontété mesurées. Les mesures de perte de charge ontété interprétéesà l'aide du modèle homogène et du modèle de Lockhart-Martinelli mis au point pour lesécoulements diphasiques dans les conduites. Les résultats montrent une similaritéà la fois avec l'écoulement liquide-liquide et l'écoulement liquide de gaz dans des microcanaux. On a trouvé une forte dépendance de la perte de charge aux débits, au matériau des micro-canaux et au premier fluide injecté dans le micro-canal.
The formation of solid calcium carbonate (CaCO 3 ) from aqueous solutions or slurries containing calcium and carbon dioxide (CO 2 ) is a complex process of considerable importance in the ecological, geochemical and biological areas. Moreover, the demand for powdered CaCO 3 has recently increased considerably in various fields of industry. The aim of this study was therefore to synthesize fine particles of calcite with controlled morphology by hydrothermal carbonation of calcium hydroxide at high CO 2 pressure ðinitial P CO 2 ¼ 55 barÞ and at moderate and high temperatures (30 and 90 1C). The morphology of precipitated particles was identified by transmission electron microscopy (TEM/EDS) and scanning electron microscopy (SEM/EDS). In addition, an X-ray diffraction analysis was performed to investigate the carbonation efficiency and purity of the solid product.Carbonation of dispersed calcium hydroxide (Ca(OH) 2(s) +CO 2(aq) -CaCO 3(s) +H 2 O) in the presence of supercritical (P T ¼ 90 bar, T ¼ 90 1C) or gaseous (P T ¼ 55 bar, T ¼ 30 1C) CO 2 led to the precipitation of sub-micrometric isolated particles (o1 mm) and micrometric agglomerates (o5 mm) of calcite. For this study, the carbonation efficiency (Ca(OH) 2 -CaCO 3 conversion) was not significantly affected by pressure-temperature (PT) conditions after 24 h of reaction. In contrast, the initial rate of calcium carbonate precipitation increased from 4.3 mol/h in the ''90 bar-90 1C'' system to 15.9 mol/h in the ''55 bar-30 1C'' system. The use of high CO 2 pressure may therefore be desirable for increasing the production rate of CaCO 3 , carbonation efficiency and purity, to approximately 48 kg/m 3 h, 95% and 96.3%, respectively, in this study. The dissipated heat for this exothermic reaction was estimated by calorimetry to be À32 kJ/mol in the ''90 bar-90 1C'' system and À42 kJ/mol in the ''55 bar-30 1C'' system. r 2007 Published by Elsevier B.V.
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