title: Viscoelastic Fluid Flow in Micro-porous Media
Creators: name: Ibezim, Victor
Publisher: name: University of Liverpool Repository
Year: 2023

description: The importance of the flow of viscoelastic fluids through porous media in the chemical, biological and oil industries has led to the topic receiving significant attention from researchers particularly over the past decade or so. Although good progress in understanding of such flows has been made in this time, the scarcity of comprehensive rheology data as well as the limitation of measurement techniques has restricted the majority of these studies to average macroscopically-measurable gross-flow quantities such as porosity, permeability, flow rate and pressure gradient. As a result, the subject remains incompletely understood. This is demonstrated in a detailed review of the literature in chapter 2. This thesis focusses on relating the bulk flow properties of the polymer solutions to the measurable rheological parameters as they flow through a distinctive micro-porous structure, by combining pressure-drop and micro-PIV (micro-particle image velocimetry) to measure the effects of pressure-gradient, velocity distribution, and velocity fluctuations within individual pores. The porous glass structure (with typical pore sizes of 500 microns) is formed using a sintering and dissolution process, which works by removing a pore-forming agent from slightly sintered glass beads (of size 50 microns). This is discussed in chapter 2. To investigate the effects of fluid elasticity at pore scale, aqueous solutions of a large molecular weight polyacrylamide (PAA) &amp; polyethylene oxide (PEO) in the concentration range of 50-200 ppm, which were characterised in detail in both shear and extensional flows using shear and capillary break-up extensional rheometers (CaBER) respectively, were used as working fluids. In order to quantify the importance of elasticity, a Weissenberg number (Wi) is calculated as a product of CaBER relaxation time and the nominal shear rate in the flows. This is detailed in chapter 3. The pressure-drop results are presented in chapter 5. As it shows, a critical Wi of roughly 0.01 where all working fluids reveal the onset of elastic dominance over viscous forces as pressure gradient is normalised with Newtonian data. Such a low critical value of Wi is due to the estimate of a nominal shear rate. Significant deviation from the universal behaviour is observed for high concentrations of the PAA, which is thought to be a result of shear thinning for these systems. Systematic degradation of the polymer caused an exponential decay in elasticity, which is reflected in the pressure-drop measurements. Chapter 7 presents the interstitial velocity field measurements. This includes the velocity magnitude and fluctuation intensity in several different pores within the porous material across a large Wi range of approximately 0.01 to 1 for each of the test fluids. The global averaged fluctuation intensity increase with Wi but the critical value, which indicates the onset of unsteadiness within the flow at pore scale gives a value of Wi~0.4, which is almost 40 times higher than that observed in the pressure-drop measurements for the data to rise above the Newtonian base line. This means that the enhanced pressure-drop behaviour of the bulk flow is not due to the local velocity fluctuations within the pores but due to mean flow effects, at least over a significant portion of the data (up to Wi~0.4).