Simulations of density driven convection in porous media
File(s)
Author(s)
Cen, Jiajun
Type
Thesis or dissertation
Abstract
The focus of this thesis is on Density Driven Convection (DDC) in porous media. In the context of CO$_2$ storage in saline aquifers, DDC can enhance solubility trapping of CO$_2$ into formation brine. To better comprehend this, analogue fluid experiments are being performed. However, validated one-to-one simulations thereof that are easy to amend are lacking. Having such a numerical model available would help advance research and cut the associated costs.
A numerical model of DDC in a porous medium has been developed using a commercially available software: COMSOL Multi-physics. This model is validated by comparing one-to-one simulation results of analogue fluid experiments performed in a bowl filled with beads. The bowl geometry is divided into a top- and bottom domain, which are initially filled with, respectively, a mixture of methanol \& ethylene glycol (MEG) and water. Over time MEG dissolves in water and increases the fluid density at the interface. Eventually, it initiates DDC which speeds up the mixing process.
This work furthermore details a predictive study where the bead diameter is varied (which in its turn changes the porous medium's permeability and hence also the Rayleigh number of the experiments). I found a linear relationship between the Sherwood number ($Sh$) and the Rayleigh number ($Ra$) i.e. $Sh = 0.125Ra$, however, this result is strongly dependent and sensitive to the choice of the constant flux regime at a given $Ra$. When the peak values of the flux $J/J_{\mathrm{dif}}$ are considered, I find another linear relationship with $Ra$ i.e. $J/J_{\mathrm{dif}}\mathrm{(peak)} = 0.139Ra$.
In this dissertation, I included a comparison between 2D and 3D simulations as well as different geometries (i.e. bowl, block and cylinder). Moreover, I discuss the effect of the orientation of layering in the aquifer, or experiment, relative to the gravity direction at an angle $\theta$. Finally, I show the effect of various viscosity transition curves and mobility ratios have on DDC in a porous medium.
A numerical model of DDC in a porous medium has been developed using a commercially available software: COMSOL Multi-physics. This model is validated by comparing one-to-one simulation results of analogue fluid experiments performed in a bowl filled with beads. The bowl geometry is divided into a top- and bottom domain, which are initially filled with, respectively, a mixture of methanol \& ethylene glycol (MEG) and water. Over time MEG dissolves in water and increases the fluid density at the interface. Eventually, it initiates DDC which speeds up the mixing process.
This work furthermore details a predictive study where the bead diameter is varied (which in its turn changes the porous medium's permeability and hence also the Rayleigh number of the experiments). I found a linear relationship between the Sherwood number ($Sh$) and the Rayleigh number ($Ra$) i.e. $Sh = 0.125Ra$, however, this result is strongly dependent and sensitive to the choice of the constant flux regime at a given $Ra$. When the peak values of the flux $J/J_{\mathrm{dif}}$ are considered, I find another linear relationship with $Ra$ i.e. $J/J_{\mathrm{dif}}\mathrm{(peak)} = 0.139Ra$.
In this dissertation, I included a comparison between 2D and 3D simulations as well as different geometries (i.e. bowl, block and cylinder). Moreover, I discuss the effect of the orientation of layering in the aquifer, or experiment, relative to the gravity direction at an angle $\theta$. Finally, I show the effect of various viscosity transition curves and mobility ratios have on DDC in a porous medium.
Version
Open Access
Date Issued
2019-03
Date Awarded
2020-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
Advisor
Crawshaw, John
Xu, Yun
Sponsor
Natural Environment Research Council
Publisher Department
Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)