E-Thesis 261 views 47 downloads
Effect of Viscosity Contrast and Wetting on Frictional Flow Patterns / DAWANG ZHANG
Swansea University Author: DAWANG ZHANG
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PDF | E-Thesis – open access
Copyright: The author, Dawang Zhang, 2022. Released under the terms of a Creative Commons Attribution-Non-Commercial No–Derivatives (CC-BY-NC-ND) License. Third party content is excluded for use under the license terms.
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DOI (Published version): 10.23889/SUthesis.62298
Abstract
Multiphase flows involving two fluids and a granular material occur in such diverse sce-narios as mud and debris flows, methane venting from sediments, degassing of volatiles from magma, and the processing of granular and particulate systems in the food, pharmaceutical, and chemical industries. The...
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Swansea
2022
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| Institution: | Swansea University |
| Degree level: | Doctoral |
| Degree name: | Ph.D |
| Supervisor: | Sandnes, Bjørnar |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa62298 |
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| Abstract: |
Multiphase flows involving two fluids and a granular material occur in such diverse sce-narios as mud and debris flows, methane venting from sediments, degassing of volatiles from magma, and the processing of granular and particulate systems in the food, pharmaceutical, and chemical industries. The presence of the granular material introduces solid friction as a governing force in the dynamics, alongside viscosity and capillarity. This multitude of interacting elements and forces can give rise to instabilities and the emergence of patterns, making these multiphase frictional flows inherently difficult to predict or control. We refer to these granular-fluid-mixtures as frictional fluids.We explore here systematically the competition between frictional, viscous, and capillary forces in frictional fluid flows. Viscously stable (more viscous invading fluid) and unstable (more viscous defending fluid) scenarios are investigated, and we study wetting conditions from drainage (grains wetted by defending fluid), through mixed-wet, to imbibition (grains wetted by invading fluid). The emerging flow patterns are studied using both experiments and simulations. Firstly, the effect of viscous stabilization on frictional finger pattern formation is discovered. When the flow is viscously stable, increasing the viscous force leads to a striking transition from the growth of one solitary finger to the simultaneous growth of multiple, wandering fingers to the axisymmetric growth of a radial spoke pattern as the flow is increasingly viscously stabilised. When the flow is viscously unstable, in contrast, the invasion patterns transition from frictional fingering to classical viscous fingering as viscous force increases beyond a critical fluidisation threshold. Later, the effects of parameters such as plate spacing and its gradient along the cell, and the tilt angle of the cell, on the pattern formation is studied. Furthermore, viscously unstable fracturing in drainage is studied. A small change on the volume fraction of granular material which govern the friction stress in the system, can convert the invasion from bulldozing fractures to pore invasion. At high air pressure, the fractures form a radially symmetric pattern where the fractures also gradually widen over time. Finally, viscously stable displacement from imbibition through mixed-wet to drainage is explored. Here, three types of invasion dynamics happens simultaneously or sequentially: pore invasion, capillary bulldozing and erosion, and five regimes of invasion patterns are identified: (I) pure pore invasion, (II) pure capillary bulldozing, (III) capillary bulldozing followed by pore invasion, (IV) pore invasion followed by erosion and (V) capillary bulldozing followed by pore invasion and erosion. These are caused by the relative importance of capillarity, friction and viscous pressures determined by the experimentally controlled variables. |
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| Keywords: |
Frictional flow, patterns, viscosity contrast, wettability |
| College: |
Faculty of Science and Engineering |