Collective dissolution of bubbles in pore networks: modelling and experimental studies
File(s)
Author(s)
Joewondo, Nerine
Type
Thesis
Abstract
The dissolution of bubbles confined in porous media is relevant to subsurface engineering applications, such as soil remediation, carbon sequestration, and hydrogen storage. Controlling these processes require the understanding of the collective evolution of bubbles (e.g., entrapment, mobilisation, dissolution, growth) in partially saturated porous media.
In the simplest case, a bubble grows or dissolves due to mass transfer across its interface. This process is driven by the gradient between a concentration proportional to the bubble's Laplace pressure and the concentration of the dissolved solute in the liquid. When considering a cluster of bubbles, the interdependence between solute transport and bubble dissolution processes becomes substantially more complex to predict. One of the main reasons for this is that the dissipation rate of dissolved solute is affected by the development of a local concentration field around each bubble. In this regard, the presence of a porous medium introduces unique challenges. The tortuosity of the pore space effectively reduces the diffusive solute transport rate relative to diffusion in bulk liquid, while the local connectivity of pores affects the mixing of solute.
This thesis presents the development and implementation of a pore-network model (PNM) and microfluidic experiments to investigate the diffusion-driven collective evolution of bubble clusters in porous media, focusing on the relationship between solute transport and dissolution processes. The predictions of the PNM demonstrate that a wide variety of collective dissolution behaviors can be obtained depending on the initial solute concentration, the size distribution of bubbles, and the connectivity of the pore network. The latter controls the intensity of the collective effects with respect to that observed in bulk liquid. The experimental results presented in this work provide direct evidence of these effects. For instance, a bubble that undergoes periods of growth and dissolution alternately in a small bubble cluster is the manifestation of the interplay between differing diffusion fluxes (across the gas-liquid interface and between neighboring pore bodies). In interpreting the experiments, the PNM can be further exploited to predict the solute concentration field in the medium, which is otherwise very challenging to obtain experimentally. The findings of this work establish the pore network's critical role in modulating the relationship between solute transport and the growth/dissolution of bubbles in porous media. The application of the PNM to estimate statistical measures that describe the collective behavior of bubbles, such as the average dissolution rate and an effective diffusion coefficient, may prove very useful in the context of applications dominated by the presence of a so-called residual gas phase consisting of disconnected bubbles that are immobilized by capillary forces.
In the simplest case, a bubble grows or dissolves due to mass transfer across its interface. This process is driven by the gradient between a concentration proportional to the bubble's Laplace pressure and the concentration of the dissolved solute in the liquid. When considering a cluster of bubbles, the interdependence between solute transport and bubble dissolution processes becomes substantially more complex to predict. One of the main reasons for this is that the dissipation rate of dissolved solute is affected by the development of a local concentration field around each bubble. In this regard, the presence of a porous medium introduces unique challenges. The tortuosity of the pore space effectively reduces the diffusive solute transport rate relative to diffusion in bulk liquid, while the local connectivity of pores affects the mixing of solute.
This thesis presents the development and implementation of a pore-network model (PNM) and microfluidic experiments to investigate the diffusion-driven collective evolution of bubble clusters in porous media, focusing on the relationship between solute transport and dissolution processes. The predictions of the PNM demonstrate that a wide variety of collective dissolution behaviors can be obtained depending on the initial solute concentration, the size distribution of bubbles, and the connectivity of the pore network. The latter controls the intensity of the collective effects with respect to that observed in bulk liquid. The experimental results presented in this work provide direct evidence of these effects. For instance, a bubble that undergoes periods of growth and dissolution alternately in a small bubble cluster is the manifestation of the interplay between differing diffusion fluxes (across the gas-liquid interface and between neighboring pore bodies). In interpreting the experiments, the PNM can be further exploited to predict the solute concentration field in the medium, which is otherwise very challenging to obtain experimentally. The findings of this work establish the pore network's critical role in modulating the relationship between solute transport and the growth/dissolution of bubbles in porous media. The application of the PNM to estimate statistical measures that describe the collective behavior of bubbles, such as the average dissolution rate and an effective diffusion coefficient, may prove very useful in the context of applications dominated by the presence of a so-called residual gas phase consisting of disconnected bubbles that are immobilized by capillary forces.
Version
Open Access
Date Issued
2023-03
Date Awarded
2023-07
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Pini, Ronny
Garbin, Valeria
Sponsor
Department of Chemical Engineering
Publisher Department
Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)