Modeling of gas-liquid and liquid-liquid Taylor flow in mini- and microchannels

Etminan, Amin (2022) Modeling of gas-liquid and liquid-liquid Taylor flow in mini- and microchannels. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

An experimental and numerical study of viscous Taylor flow through capillaries is performed to investigate the effects of viscosity, superficial phase velocity ratio, channel diameter, channel diameter expansion, and gas holdup on the hydrodynamic and heat transfer. Through millimetric and microfluidic devices, two-phase Taylor flows have been a significant drive in almost all energy-related industrial applications to reduce the size and enhance heat and mass transport phenomena. A topical and comprehensive review of the hydrodynamic of Taylor flow and liquid film surrounding the slugs is conducted to shed more light on gas-liquid, and liquid-liquid Taylor flows better. An in-detailed step-by-step numerical method solves such flows in a two-dimensional axisymmetric plan of a circular tube which can be extended to mass transfer applications. The validity of the experimental setup is greatly appreciated by benchmarking of single-phase theory and the empirical/analytical correlations reported in the literature. The numerical study differentiates flow characteristics of slug flow under two flow conditions: developing and fully developed. The slug profile, slug length, liquid film thickness, and pressure drop are compared to show the influence of slug breakup on these flow parameters as the slug moves downstream. The effects of the dynamic viscosity ratio of phases of gas-liquid and liquid-liquid Taylor flows are studied to display a five-stage slug formation process: introducing, expanding, contracting, necking, and breakup. A new linear logarithmic correlation is proposed to compute the gas holdup in terms of the superficial phase velocity ratio. Another correlation is also developed to predict the liquid film thickness using liquid and gas Weber numbers and gas holdup for such Taylor flows in tubes with only a 1.42% discrepancy. In the experiments, the hydrodynamic and thermal analyses of Taylor flow are examined by the flow visualization, pressure drop, and heat transfer measurements which are accompanied by CFD results. The impact of interfacial pressure drop on the total pressure loss and isothermal bath temperature on the thermal performance is investigated over a wide range of volumetric flow rate ratios. The flow patterns inside and outside Taylor slugs are visualized, indicating a significant change in recirculation regions as the volumetric flow rate ratio increases. It is found, in good agreement with the literature, that the pressure drop generated by the interface increases the total pressure loss up to 200% compared to the single-phase flow. The influence of interfacial pressure drop decreased as the dimensionless length of the channel approached beyond 0.1, resulting in concise water slugs and long oil plugs.

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