Browsing by Subject "Column"
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Item Examining supercritical CO₂ dissolution kinetics during carbon sequestration through column experiments(2011-08) Kent, Molly Elizabeth; Bennett, Philip C. (Philip Charles), 1959-; Romanak, Katherine; Cardenas, Meinhard B.Carbon sequestration is a method of capturing and storing excess anthropogenic CO₂ in the subsurface. When CO₂ is injected, the temperature and pressure at depth turn it into a supercritical (SC) fluid, where density is that of a liquid, but viscosity and compressibility resemble a gas. Ultimately the SC CO₂ is trapped at depth either by low permeability sealing layers, by reactions with minerals, or by dissolving into fluids. The injected CO₂ is buoyant and initially exists as a non-aqueous hydrophobic layer floating on top of the subsurface brine, up against the upper sealing formation, but over time it will dissolve into the brine and potentially react with minerals. The details of that initial dissolution reaction, however, are only poorly understood, and I address three basic questions for this research: What is the fundamental kinetics of SC CO₂ dissolution into water? How fast does dissolved CO₂ diffuse away from the source point? And what geochemical conditions influence the dissolution rate? To answer these questions I employed a high pressure flow-through approach using a column packed with coarse quartz sand. The system was both pressure and temperature controlled to have either liquid or SC CO₂ present, and was typically run at 100 Bar, 0.5 to 2.5 mls/min, and 28-60°C. After establishing the hydraulic parameters for the column using two conservative tracers (Br, As), injections (5 and 20 [mu]l) were made either as aqueous solutions equilibrated to high pressure CO₂, or as pure liquid or SC CO₂ into 0.1 mmol NaOH. For all experiments the pH of the system was monitored, and [CO₂] over time was calculated from those data. For injections of brine with dissolved CO₂, transport was conservative and was nearly identical to the conservative tracers. The CO₂ quickly mixes in the column and does not react with the quartz. The liquid and SC CO₂ injections, however, do not act conservatively, and have a very long tailing breakthrough curve that extends to tens of pore volumes. I hypothesize that the SC CO₂ is becoming trapped as a droplet or many droplets in the pore spaces, and the long breakthrough tail is related either to the rate of dissolution into the aqueous phase, the diffusion of dissolved CO₂ away from the phase boundary, or the reaction with the NaOH, limited to the narrow contact zones in the pore throats. Because of the speed at which acid-base reactions occur (nanosecond kinetics), I infer that the rate limiting step is either surface dissolution or diffusion. From plots of ln[CO₂] v. time I obtained values for k, the specific rate of the dissolution reaction R=-k[CO₂]. No trend for k was seen with respect to changes in temperature, but k did show a trend with respect to changing flow rate. k increased from an average value of 3.05x10⁻³ at 0.5 ml/min to an average value of 3.38x10⁻³ at 1.6 ml/min, and then held constant at the higher flow rates, up to 2.5 ml/min. I interpret these data to show that at low flow rates, the reaction is diffusion limited; the fluid nearest the contact zone becomes saturated with dissolved CO₂. At higher flow rates, the fluid is moving fast enough that saturation cannot occur, and the kinetics of the dissolution reaction dominate. Simple geometric models indicate that the CO₂/water interface is shaped like a spherical cap, indicating that the snapped-off CO₂ is forming a meniscus in the pore throat, limiting the surface area across which dissolution can occur.Item A re-evaluation of crinoid morphology and proposed relationship of crown groups, with insights from biogeography(2011-08) Womack, Kyle Richard; Sprinkle, James, 1943-; Molineux, Ann; Rowe, TimothyCrinoids are the most primitive living members of the Phylum Echinodermata. Though still present in reduced numbers today, crinoids were the dominant echinoderms from the Ordovician to the Permian. The crinoid body plan consists of three major regions, the column, the calyx, and the arms. Each region serves important functions in crinoids. The column raises the rest of the body into the water column for more efficient feeding. The calyx contains the visceral mass and mouth. Arms extend out from the top of the calyx to trap microorgansisms and suspended organic particles in the water column. A re-evaluation of these functional units is undertaken to understand the importance of various structures and to obtain discrete characters for use in a cladistic analysis. The relationship of crinoid crown groups has been an active area of research for the past couple of decades. With each proposed phylogenetic relationship, a new interpretation of thecal plate homology has been proposed. Here each study is re-examined in the light of new data. A review of functional morphology indicates a dual-reference system to be the most supported interpretation of plate homology. The two reference points in this system are the stem-cup and the cup-arm junctions, at the top and bottom of the calyx. The difference between a two-circlet and three-circlet crinoid is the presence or absence of the middle (basal) circlet. A new cladistic analysis is presented, with the topology of trees obtained giving support for the retention of Paleozoic crinoid stem and crown groups. Crinoids appear abruptly in the fossil record. Questions pertaining to origins and ancestral stock abound. A biogeography study is employed to look at the distribution of crinoids from the Early to Middle Ordovician. Locality information, combined with an understanding of the movement of major plates, paleoclimate data, an understanding of larval distribution, and a review of similar studies carried out on different taxa, gives insight into possible radiation and dispersal patterns of crinoids from the first half of the Ordovician.Item Seismic retrofit of RC columns with FRP composites and anchorage system(2015-05) Psaros Andriopoulos, Apostolos; Jirsa, J. O. (James Otis); Hrynyk, TrevorResearch on the use of composite materials in structural applications started more than 30 years ago but still remains active. The challenges that accompany those applications are diverse and seem to increase as the variety of applications grows. There are several fiber-reinforced polymer (FRP) systems that have been introduced through the years for strengthening reinforced concrete (RC) structures. Those systems focus on strengthening of slabs, beams and columns. The present study pertains to seismic retrofit of rectangular RC columns. The typical FRP materials used in structural applications are introduced, as well as, how FRP materials become an integral part of the force-resisting system. In addition, analysis work pertaining to a series of strengthened RC columns was conducted and the results were compared to the experimental data. Moreover, deficiencies of typical material models were highlighted. Design guidelines are discussed and recommendations about current design practices are provided. Finally, research gaps and future research recommendations are identified.Item Seismic retrofit of RC columns with FRP composites and anchorage system(2015-05) Psaros Andriopoulos, Apostolos; Jirsa, J. O. (James Otis); Hrynyk, TrevorResearch on the use of composite materials in structural applications started more than 30 years ago but still remains active. The challenges that accompany those applications are diverse and seem to increase as the variety of applications grows. There are several fiber-reinforced polymer (FRP) systems that have been introduced through the years for strengthening reinforced concrete (RC) structures. Those systems focus on strengthening of slabs, beams and columns. The present study pertains to seismic retrofit of rectangular RC columns. The typical FRP materials used in structural applications are introduced, as well as, how FRP materials become an integral part of the force-resisting system. In addition, analysis work pertaining to a series of strengthened RC columns was conducted and the results were compared to the experimental data. Moreover, deficiencies of typical material models were highlighted. Design guidelines are discussed and recommendations about current design practices are provided. Finally, research gaps and future research recommendations are identified.