Browsing by Subject "Filtration"
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Item A new reservoir scale model for fracture propagation and stress reorientation in waterflooded reservoirs(2016-12) Bhardwaj, Prateek; Sharma, Mukul M.It is now well established that poro-thermo-elastic effects substantially change the magnitude and orientation of in-situ stresses. Fractures induced in injectors during water injection for waterflooding or produced water disposal have a profound impact on waterflood performance. These effects, coupled with injectivity decline due to plugging caused by injected particles, lead to permeability reduction, fracture initiation and propagation. Models are available for fracture propagation in single injection wells and single layered reservoirs that account for these effects. However, the impact of fluid injection and production on fracture growth in multiple wells and multi-layered reservoirs with competing fractures, has not been systematically modelled at a field scale. In this work, a three-dimensional, two-phase flow simulator with iteratively coupled geomechanics has been developed and applied to model the dynamic growth of injection-induced fractures. The model is based on a finite volume implementation of the cohesive zone model for arbitrary fracture propagation coupled with two-phase flow. A dynamic filtration model for permeability reduction is employed on the fracture faces to incorporate effects of internal damage and external filter cake build-up due to the injection of suspended solids and oil droplets. All physical phenomena are solved in a single framework designed for multi-well, field-scale simulation. The pressure distribution, saturation profile, thermal front, mechanical displacements and reservoir stresses are computed as fluids are injected and produced from the reservoir. Simulation results are discussed with single as well as multiple fractures propagating. Stress reorientation due to poroelastic, thermoelastic and mechanical effects is examined for the simulated cases. The orientation of the fractures is controlled primarily by the orientation of the stresses, which in turn depends on the pattern of wells and the rates of injection and production. The sweep efficiency of the waterflood is found to be impacted by the rate of growth of injection-induced fractures. Heterogeneities in multi-layered reservoirs strongly govern the expected vertical sweep and fluid distribution, which impacts the cumulative oil recovery. This is the first time a formulation of multiphase flow in the reservoir has been coupled with dynamic fracture propagation in multiple wells induced by solids plugging while including poro-thermo-elasticity at the reservoir scale. The model developed in this work can be used to simulate multiple water injection induced fractures, determine the reoriented stress state to optimize the location of infill wells and adjust injection well patterns to maximize reservoir sweep.Item Assessing sheep’s wool as a filtration material for the removal of formaldehyde in the indoor environment(2014-05) Wang, Jennifer, active 21st century; Corsi, Richard L.Formaldehyde is one of the most prevalent and toxic chemicals found indoors, where we spend ~90% of our lives. Chronic exposure to formaldehyde indoors, therefore, is of particular concern, especially for sensitive populations like children and infants. Unfortunately, no effective filtration control strategy exists for its removal. While research has shown that proteins in sheep's wool bind permanently to formaldehyde, the extent of wool's formaldehyde removal efficiency and effective removal capacity when applied in active filtration settings is unknown. In this research, wool capacity experiments were designed using a plug flow reactor and air cleaner unit to explore the capacity of wool to remove formaldehyde given different active filtration designs. Using the measured wool capacity, filter life and annual costs were modeled in a typical 50 m₃ room for a variety of theoretical filter operation lengths, air exchange rates, and source concentrations. For each case, annual filtration costs were compared to the monetary benefits derived from wool resale and from the reduction in cancer rates for different population types using the DALYs human exposure metric. Wool filtration was observed to drop formaldehyde concentrations between 60-80%, although the effective wool removal capacity was highly dependent on the fluid mechanics of the filtration unit. The air cleaner setup yielded approximately six times greater capacity than the small-scale PFR designed to mimic active filtration (670 [mu]g versus 110 [mu]g HCHO removed per g of wool, respectively). The outcomes of these experiments suggest that kinematic variations resulting from different wool packing densities, air flow rates, and degree of mixing in the units influence the filtration efficiency and effective capacity of wool. The results of the cost--benefit analysis show that for the higher wool capacity conditions, cost-effectiveness is achieved by the majority of room cases when sensitive populations like children and infants are present. However, for the average population scenarios, filtration was rarely worthwhile, showing that adults benefit less from reductions in chronic formaldehyde exposure. These results suggest that implementation of active filtration would be the most beneficial and cost-effective in settings like schools, nurseries, and hospitals that have a high percentage of sensitive populations.Item Grain-scale mechanisms of particle retention in saturated and unsaturated granular materials(2010-12) Rodriguez-Pin, Elena; Bryant, Steven L.; Balhoff, Matthew; DiCarlo, David; Huh, Chun; Lloyd, Douglas R.The phenomenon of particle retention in granular materials has a wide range of implications. For agricultural operations, these particles can be contaminants transported through the ground that can eventually reach to aquifers, consequently contaminating the water. In oil reservoirs, these particles can be clays that get detached from the rock and migrate with the flow after a change of pressure, plugging the reservoir with the consequent reduction in permeability. These particles can also be traceable nanoparticles, introduced in the reservoir with the purpose of identifying bypassed oil. For all these reasons it is important to understand the mechanisms that contribute to the transport and retention of these particles. In this dissertation the retention of micro and nano size particles was investigated. In saturated model sediments (sphere packs), we analyzed the retention of particles by the mechanism of straining (size exclusion). The analysis focused on experiments reported in the literature in which particles smaller than the smallest pore throats were retained in the sediment. The analysis yields a mechanistic explanation of these observations, by indentifying the retention sites as gaps between pairs of sediment grains. A predictive model was developed that yields a relationship between the straining rate constant and particle size in agreement with the experimental observations. In unsaturated granular materials, the relative contributions of grain surfaces, interfacial areas and contact lines between phases to the retention of colloidal size particles were investigated. An important part of this analysis was the identification and calculation of the length of the contact lines between phases. This estimation of contact line lengths in porous media is the first of its kind. The algorithm developed to compute contact line length yielded values consistent with observations from beads pack and real rocks, which were obtained independently from analysis of high resolution images. Additionally, the predictions of interfacial areas in granular materials were consistent with an established thermodynamic theory of multiphase flow in porous media. Since there is a close relationship between interfacial areas and contact lines this supports the accuracy of the contact line length estimations. Predictions of contact line length and interfacial area in model sediments, combined with experimental values of retention of colloidal size particles in columns of glass beads suggested that it is plausible for interfacial area and contact line to contribute in the same proportion to the retention of particles. The mechanism of retention of surface treated nanoparticles in sedimentary rocks was also investigated, where it was found that retention is reversible and dominated by attractive van der Waals forces between the particles and the rock’s grain surfaces. The intricate combination of factors that affect retention makes the clear identification of the mechanism responsible for trapping a complex task. The work presented in this dissertation provides significant insight into the retention mechanisms in relevant scenarios.Item HVAC filters as a sampling mechanism for indoor contaminants(2010-05) Noris, Federico; Kinney, Kerry A.; Siegel, Jeffrey A.; Corsi, Richard L; Kirisits, Mary J; Szaniszlo, Paul jIndoor air quality investigations often focus on air and settled dust samples to assess chemical and biological contamination. Although the information provided by these techniques is useful, HVAC filters represent a new option for investigating contaminants in the indoor environment. This dissertation explores the potential use of HVAC filters as long-term, passive samplers by investigating the contaminants found in HVAC dust and other indoor locations and by evaluating the likelihood that HVAC filters will capture indoor particles. A field investigation of heavy metal and culturable microbial contaminants found in air, settled dust and HVAC filter dust corroborated the hypothesis that HVAC filters hold promise as a sampling mechanism in residences. However, several factors including filter efficiency, HVAC cycling and particle size seemed to influence the results. Also, it was unclear how the composition of the microbial communities varied with sampling location. Subsequently, the bacterial and fungal communities present in several sampling locations within residences and in an unoccupied test house were investigated. In residences, the microbial communities encountered in HVAC filter dust were not different from those in high surface dust. High efficiency HVAC filters also seem to be a viable alternative to long-term air sampling. Occupants influence the composition of the microbial communities in residences and are viii associated with Actinobacteria and Firmicutes, while Proteobacteria dominate the air samples and might have an outdoor air origin. A fate analysis to assess the magnitude of the different particle removal mechanisms revealed that small and large particles are likely to deposit on surfaces, while intermediate sized particles stay suspended in air longer. HVAC filters can collect particulate matter over a broad size range and may be effective overall samplers of particle-bound contaminants. Nevertheless, filter efficiency and air recirculation rate are important parameters that influence the likelihood that filters will capture particles, while air exchange rate has little effect. The results from this study indicate that HVAC filters can be used as an alternative to traditional indoor sampling mechanisms for contaminants associated with particles.Item Pollutant control strategies for acceptable indoor air quality and energy efficiency in retail buildings(2013-12) Zaatari, Marwa; Novoselac, Atila; Siegel, Jeffrey A.Indoor air is associated with substantial health risks and is estimated to be responsible for the loss of over 4.7 million healthy life years (years lost due to morbidity and mortality) annually in the U.S. The highest indoor air-related health benefits can be expected from policies and strategies that efficiently target pollutants having the greatest contribution to the burden of disease. This burden is caused by indoor sources as well as by outdoor pollutants transported to the indoors. The diversity of pollutants, pollutant sources, and the resulting health effects challenge the comparison of the impacts of different control strategies on energy consumption and indoor air quality. To address this challenge, this work presents a quantitative framework for reaching the optimal energy cost for the maximum achieved exposure benefits, specifically for retail buildings and their understudied energy, economic, and health risk influence. The main objectives of this dissertation are to 1) determine pollutants of concern in retail buildings that contribute the greatest to the burden of disease, and 2) determine energy-efficient, exposure-based control strategies for different retail types and locations. The research in this dissertation is divided into four specific aims that fulfill these two objectives. The first specific aim (Specific aim 1.a) addresses Objective 1 by applying available disease impact models on pollutant concentrations taken from 15 literature studies (150 stores, a total of 34 pollutants). Of those pollutants, there was little data reported on particulate matter (PM) concentrations and none on emission rates for PM, limiting our understanding of exposure to this pollutant. The second specific aim (Specific aim 1.b) also addresses Objective 1 by characterizing particulate matter (PM) concentrations, emission rates, and fate of ambient and indoor-generated particles in retail buildings. The tasks of this specific aim consisted of particulate matter and ventilation measurements in 14 retail buildings. Among the findings of Objective 1, PM2.5 and acrolein are the main contaminants of concern for which control methods should be prioritized, contributing to 160 disability-adjusted life years (DALYs; years lost due to premature mortality and disability) per 100,000 persons annually. Employees in grocery stores mainly drove this burden. An efficient indoor exposure reduction strategy should take into account all mechanisms that influence pollutant concentrations: indoor and outdoor sources (highlighting the importance of retail type and location), infiltration, ventilation, and filtration. The remaining specific aims address Objective 2 by investigating the energy and air quality impact of two commonly used exposure control scenarios, ventilation (Specific aim 2.a) and filtration (Specific aim 2.b). The tasks of Specific aim 2.a consisted of modeling the impact of multiple ventilation strategies on contaminants of concern for six major U.S. cities and two retail types. The tasks for Specific aim 2.b consisted of conducting field measurements on 15 rooftop units to determine the fan energy impacts of filter pressure drop. These results are used in combination with a large dataset of 75 filters commonly installed in commercial buildings to estimate the energy consequences of filtration. Results for Objective 2 are presented from the quantitative comparison of the impact on energy usage and DALYs lost of three main approaches: (1) adjusting ventilation only; (2) adjusting filtration only; and (3) adjusting ventilation and filtration together. All approaches were able to provide substantial reductions in the health risks (19-26% decrease in DALYs lost); the magnitude of the reductions depended on the ventilation/filtration scenario, the retail type, and the city. The magnitude of energy cost to achieve the maximum health benefits depended on the city and the retail type (for example for a 10,000 m2 grocery store, the energy cost ranged from $1,100 for the annual cost of filtration energy in Los Angeles to $24,000 for the annual cost of ventilation in Austin). The uncertainties of the estimates driving these findings are discussed throughout the results section. The finding that emerges from this analysis is the pollutant exposure control ventilation (PECV) strategy. This strategy is superior to the ventilation rate procedure (VRP; ASHRAE Standard 62.1-2010) and the indoor air quality procedure (IAQP; ASHRAE Standard 62.1-2010) as it decides on a range of ventilation rates by weighing the exposures of contaminants of concern found in retail buildings. Then, among the range of ventilation rates identified, the PECV recommends the optimal ventilation rate that leads to energy usage savings in the climate considered. Overall, the work presented here prioritizes specific contaminants of concern in retail buildings and proposes an exposure-based, energy-efficient control strategy for different retail types and locations. Policy makers, engineers, and building owners can use these results to decide amongst appropriate control strategies that will lead to minimum energy consumption and, at the same time, will not compromise occupant health. This work can be repeated for different types of buildings, notably for residences, schools, and offices where abundant information is available on both pollutant concentrations and ventilation rates, but where information is lacking on how to optimize the control strategies for better indoor air quality.Item Pressure Drop and Filtration through Fibrous Porous Media on the Sump Strainer of Light Water Reactors(2014-12-15) Lee, SayaFibrous porous media has been found in a variety of industrial applications including filters and insulation materials. In nuclear power plants, fibrous media are found as insulation materials to prevent heat loss and protect the containment structures and other components from thermal effects. However, in spite of efficient thermal insulation, fibrous media have been focused on as a hazard in the Emergency Core Cooling Systems (ECCSs). Fibrous debris generated from fiberglass insulation materials during a Loss of Coolant Accident (LOCA) might accumulate on the containment sump strainer causing loss of Net Positive Suction Head (NPSH), called the upstream effect, or it might penetrate through the strainer becoming a source of clogging for flow channels in the core (downstream effect). In the present work, head loss through fibrous porous media made of the same fiberglass insulation material used in pressurized water reactors (PWRs) were experimentally investigated to study upstream effects. Porosity of fibrous porous media was also considered by measuring build-up of debris beds. In order to study downstream effects, quantity of debris bypass was examined by changing the type of water, concentration of debris, fluid approach velocity, and temperature. As results, a head loss model, a compression model, and a debris bypass model were proposed for the given conditions in this study. Additionally, a microscope system was developed to characterize size distribution of irregular-shaped fibrous debris. The methodology was applied to three samples and the maximum fraction of debris bypass was found in the size range of 10 to 250 ?m.Item Size-Dependent Filtration of Non-Loaded Particulate Traps(2014-12-12) White, JessicaThis work investigates the filtration efficiency of uncoated, commercial Diesel Particulate Filter (DPF) substrates of three porosities (55.8%, 61.1%, 65.0%) for particulate sizes representative of Gasoline Direct Injection (GDI) exhaust, and also refines a model suitable for predicting filtration efficiency for these non-loaded particulate traps. GDI produces lower concentrations of smaller particulates as compared to diesel combustion, which results in the absence of a soot-cake and yields changes in filtration behavior compared to diesel particulate. To produce a model that simulates the filtration efficiency of non-loaded particulate traps, an existing flow field model of DPF filtration was modified to better capture the fundamental physics of deep-bed filtration. The improved model includes additional sedimentation and thermophoretic modes of filtration and the soot-cake related filtration approximations were removed. Size-dependent particulate concentrations were measured using a Scanning Mobility Particle Sizer (SMPS), both upstream and downstream of the filters. By comparing upstream and downstream particle number concentrations, the particle size-dependent filtration efficiency of filter samples was determined. Experimental results were compared to model predictions, and showed excellent agreement.