Numerical Study On Taylor Flow And Gas-liquid Two-phase Flow Regimes In Microchannel

This dissertation is devoted to numerical investigation of fluid dynamiccharacteristics of Taylor flow and gas-liquid two-phase flow regimes in microchannel,adopting appropriate mesh resolution to simulate fluid dynamic characteristics,investigating the influence of physical properties on flow regimes.A Gradient mesh approach used in numerical simulation for capturing liquid filmof gas-liquid Taylor flow in T-junction microchannel was proposed. Two-dimensionalmodeling was performed with CFD software FLUENT and the volume of fluid (VOF)model. The gas-liquid two-phase flow in a microfluidic T-junction with differentcross sectional widths (0.1-1mm) and gas-liquid superficial velocities wereinvestigated numerically. The gradient mesh was shown to be able to capture theliquid film accurately and enhance the computing efficiency simultaneously. Thehydrodynamic characteristics were shown to be in good agreement with existingcorrelations and experimental data as well as rules of gradient mesh to capture theliquid film were suggested. The application method of gradient mesh could besummarized for capturing the liquid film accurately and steadily. Because of theexistence of liquid film in simulation, new correlations of slug length were proposed.Comparison of the slug length from experimental data and correlations was carriedout and demonstrated the validity of the slug length correlations.To simulate the gas-liquid two-phase flow patterns in T-junction microchannel, asuitable grid size used in the numerical solution was selected by comparing thesimulation results. According to the simulated results in different gas and liquidsuperficial velocity, the flow regime was formed to compare with the publishedexperimental data. The simulated results agreed well with the published flow patternsand flow regime. Therefore, the established model could be known as reliable forsolving the gas-liquid two-phase flow regimes in microchannel. The different physicalproperties were used to investigate the influence of viscosity and surface tension onthe flow regimes in the simulation. The comparison between simulated results andexperimental data was carried out. It was found that, when liquid viscosity increases,the transitions remained almost unvaried, and the smaller surface tension was, the smaller area of Taylor flow would be. These indicated a great impact of the surfacetension on the form of Taylor flow in microchannel.