El-Zehairy, A. A. (2020) 3D coupled pore-network modelling of flow and solute transport through porous media, from laminar to turbulent flow. PhD thesis, University of Warwick.

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Abstract

Subsurface hydrology including flow and solute transport modelling is essential for designing many engineering processes such as seepage, remediation of contaminated groundwater, improved oil recovery, etc. The processes involved in such activities are observed across a wide range of length and timescales; from nanometres to kilometres and from nanoseconds to years. The recent growth in imaging technologies has shown that the size of a single pore in a porous medium may range from 0.1 nm to a few centimetres (Marry & Rotenberg, 2015). Therefore, to perform reliable field-scale simulations, a deep understanding of the processes happening at the pore-scale level and their consequences at larger scales is needed (Mehmani, 2014). Most of the previous work that modelled flow and solute transport at the pore-scale assumed laminar flow and applied Darcy’s law. However, in some cases, such as the flow of gases through porous media, flow near wellbores, and flow through the hyporheic zone, non-Darcy flow can be observed. It is not clear how solute transport processes are affected by the flow behaviour in the non-Darcy (Forchheimer) and turbulent flow regimes. In this work, a pore-network model (PNM) capable of simulating flow and solute transport within the Darcy, Forchheimer and turbulent flow regimes was developed. One of the aims of this work is to determine the onset of non-Darcy flow and the onset of turbulence, after which Darcy’s law loses its validity. Using PNM, any porous medium can be simplified into large pores connected to each other’s by narrow pores, then analytical or semi-analytical equations can be implemented to model the flow and transport processes through the medium. The proposed model was verified against experimental data of a packed spheres sample and other data in the literature. X-ray Computed Tomography scans of the packed spheres, sandstone and carbonate samples were used to extract the equivalent pore-network. It was found that the onset of non-Darcy flow is highly dependent on the medium degree of heterogeneity, and in heterogeneous media, the onset velocity could be up to three orders of magnitude smaller compared to the homogenous media. In porous media with coarse particles, the assumption of fully developed flow in each pore is not valid and using the Hagen-Poiseuille equation does not predict the flow behaviour properly. After the onset of non-Darcy flow, if Darcy’s law is applied, this causes overestimation (up to ~10 times) of the Péclet number and the longitudinal dispersion coefficient (DL). In the turbulent flow regime, DL increased, due to the effect of turbulent diffusion, by a factor up to 1.6 compared to the DL value obtained under the Forchheimer flow conditions.

Item Type:	Thesis (PhD)
Subjects:	G Geography. Anthropology. Recreation > GB Physical geography Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Groundwater flow -- Computer simulation, Laminar flow, Pore water, Turbulence
Official Date:	January 2020
Dates:	Date Event January 2020 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Department of Engineering
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Nezhad, Mohaddesh Mousavi ; Guymer, I. (Ian)
Sponsors:	British Council ; Egypt. Wizārat al-Taʻlīm al-ʻĀlī wa-al-Dawlah lil-Buḥūth al-ʻIlmī
Format of File:	pdf
Extent:	297 leaves : illustrations (some colour)
Language:	eng

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