A pore-to-core scale investigation of hysteresis for CO2 storage processes using a discrete-domain method

In this thesis we have studied a discrete-domain method that is implemented to demonstrate the immiscible, two-phase displacements of two fluids, namely CO2 and water (or brine) in an originally water-saturated reservoir (an aquifer). The method provides a model that is based on a free energy density function that gives a thermodynamic explanation of the dynamics of the interface between the fluids and describes the rugged energy landscape that represents the reversible and irreversibletransition states of the interface through metastable states and energy barriers. Furthermore, in this model a discretization of the reservoir into a number of compartments has been done and the model simulates the flow system in terms of the capillary pressure and the local water compartment saturations. This model works based on the theory that these compartments are weakly connected via an external drive, e.g., a fixed imposed capillary pressure or injection rate of CO2. The main purpose of this study is to investigate hysteresis in the drainage and imbibition processes both in the capillary pressure and local water saturation curves with regards to the global water saturation

Impact of humidity, temperature, and particulate fouling on membrane-based energy exchangers

Membrane-based energy recovery ventilators (ERVs) improve building energy efficiency by transporting heat and moisture between incoming and outgoing air streams. Although long-term studies are not available due to the recent implementation of this technology, there are preliminary indications that moisture transport might degrade with the extended operation, possibly as the result of exposure to air pollution or other environmental stresses. The scope of this dissertation is to quantify the influence of environmental factors on the permeation properties of current-generation composite membranes and the overall performance of ERV exchanger cores. First, the impact of particulate fouling was investigated via accelerated membrane- and core-level fouling experiments. The core-level experiments showed minimal impact on the effectiveness of ERV cores from coarse dust loadings. However, membrane-level examination with aerosol nanoparticles indicated that moisture transport through membranes was especially impaired when particles were hygroscopic or contained liquids. These results suggest that the optimal protection by filters and the orientation of the membrane would depend on the nature of the indoor and outdoor aerosols. Second, the effects of relative humidity and temperature on the transport of water vapor and CO₂ (as a surrogate for indoor air pollutants) was evaluated through a systematic study of some standard polymers suitable for ERV use. It was shown that the permeability and selectivity of membranes could vary up to an order of magnitude depending on the membrane material, the temperature and relative humidity on both feed and permeate sides of the membrane, as well as orientation in asymmetric composite membranes. A theoretical model for predicting permeability of composite membranes, based on a limited number of kinetic water vapor sorption tests of the selective coating polymer, was successfully developed and validated for a commercial membrane. This model was then coupled with a heat and mass transfer model of cross-flow ERV exchanger cores to interpret the membrane-level variations regarding ERV exchanger core performance. A study of the effects of outdoor air parameters showed that the effectiveness of ERV exchangers could increase or decrease significantly with outdoor air relative humidity, while outdoor air temperature had only a minimal influence on effectiveness parameters.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat

A pore-to-core scale investigation of hysteresis for CO2 storage processes using a discrete-domain method

In this thesis we have studied a discrete-domain method that is implemented to demonstrate the immiscible, two-phase displacements of two fluids, namely CO2 and water (or brine) in an originally water-saturated reservoir (an aquifer). The method provides a model that is based on a free energy density function that gives a thermodynamic explanation of the dynamics of the interface between the fluids and describes the rugged energy landscape that represents the reversible and irreversibletransition states of the interface through metastable states and energy barriers. Furthermore, in this model a discretization of the reservoir into a number of compartments has been done and the model simulates the flow system in terms of the capillary pressure and the local water compartment saturations. This model works based on the theory that these compartments are weakly connected via an external drive, e.g., a fixed imposed capillary pressure or injection rate of CO2. The main purpose of this study is to investigate hysteresis in the drainage and imbibition processes both in the capillary pressure and local water saturation curves with regards to the global water saturation

Characterization of Fouling with Hygroscopic and Non-hygroscopic Aerosols in Composite Polymer Membranes for Water Vapor Transport Applications

Composite membranes using a thin vapor-permeable polymer layer over a structural substrate are used in gas dehydration, food-packaging, and humidity control of indoor spaces. The impact of exposure to air pollution on the water vapor permeability and selectivity is investigated to develop an understating of potential air-side particulate fouling mechanisms and resulted performance degradation during membrane lifetime in the field. Samples of commercial membrane media were loaded with hygroscopic NaCl, and non-hygroscopic spark-generated graphite (SGG) aerosol particles. The effects of particle charge distribution and number concentration, air flowrate, temperature-gradient across membrane (Thermophoresis), and membrane surface on the rate of particle deposition were investigated using a Scanning Mobility Particle Sizer (SMPS). It was found that particle charge distribution and air flowrate had the largest impact on the rate of particle deposition. The results of permeability measurements showed that deposition of SGG and NaCl particles under a dry loading condition (RH70%) leading to surface condensation, the membrane permeability reduced by up to 30%. This is hypothesized to be caused by increased resistance of microporous membrane substrate due to a pore-narrowing process. Scanning electron microscopy (SEM) combined with EDX analysis was used to examine the morphology and chemical composition of the fouled membrane surface. Analysis of SEM images showed a significant reduction in the average pore diameter of degraded samples, proportional to the fouling degree. It was also found that cleaning of fouled samples can reverse their permeability back to nearly the initial value. The reversibility of the loaded membrane permeability along with the EDX analyses imply that re-crystallization of salt ions, entrained into the pores of membrane substrate in aqueous form, is a potential explanation for the changes observed.Applied Science, Faculty ofMechanical Engineering, Department ofUnreviewedGraduat

The effects of temperature and humidity on the permeation properties of membrane transport media used in energy recovery ventilators

We report on an experimental study of the effects of relative humidity and temperature on the transport of water vapor and CO² through a series of standard polymeric materials to determine their potential for use as membrane media in energy recovery ventilators (ERVs). Results are reported for four polymers of two major types (glassy and rubbery). The selectivity of water vapor over CO² is also evaluated from permeation experiments. Permeability results show that rubbery membrane samples, with glass transition temperatures well below the temperature range of experiments (30°C to 50°C), have a higher water vapor permeability and a much higher CO² permeability compared to glassy membrane samples. This is hypothesized to be mainly due to the higher diffusivity of water vapor and CO² in rubbery polymers with higher chain flexibility leading to a much lower selectivity for rubbery membrane samples. In all polymer samples, water vapor permeability increases with relative humidity (up to an order of magnitude) and decreases with temperature. This is attributed to the negative enthalpy of water vapor sorption dominating its activation energy of permeation, which is associated with a lower solubility at higher temperatures. In contrast, CO² permeability increases with temperature because of the positive activation energy of CO² permeation. CO² permeability decreases slightly with increasing relative humidity (up to 30%), which is hypothesized to be due to the competitive sorption between water vapor and CO² at higher humidity levels. Therefore, the selectivity of membrane samples for water vapor over CO² decreases with temperature and increases with relative humidity, and these trends are dominated by water vapor permeability variations. In general, the permeability results reported here suggest that ERV exchangers using polymer membranes can achieve high latent effectiveness (i.e. very high water vapor permeability) over a wide range of operating temperature and relative humidity while maintaining very low CO² permeability and crossover rates (<1%)Applied Science, Faculty ofMechanical Engineering, Department ofUnreviewedGraduat