Browsing by Subject "Absorption"
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Item Absorption of chlorine and mercury in sulfite solutions(2002-08) Roy, Sharmistha; Rochelle, Gary T.Item Carbon dioxide absorption, desorption, and diffusion in aqueous piperazine and monoethanolamine(2009-12) Dugas, Ross Edward; Rochelle, Gary T.This work includes wetted wall column experiments that measure the CO₂ equilibrium partial pressure and liquid film mass transfer coefficient (kg') in 7, 9, 11, and 13 m MEA and 2, 5, 8, and 12 m PZ solutions. A 7 m MEA/2 m PZ blend was also examined. Absorption and desorption experiments were performed at 40, 60, 80, and 100°C over a range of CO₂ loading. Diaphragm diffusion cell experiments were performed with CO₂ loaded MEA and PZ solutions to characterize diffusion behavior. All experimental results have been compared to available literature data and match well. MEA and PZ spreadsheet models were created to explain observed rate behavior using the wetted wall column rate data and available literature data. The resulting liquid film mass transfer coefficient expressions use termolecular (base catalysis) kinetics and activity-based rate expressions. The kg' expressions accurately represent rate behavior over the very wide range of experimental conditions. The models fully explain rate effects with changes in amine concentration, temperature, and CO₂ loading. These models allow for rate behavior to be predicted at any set of conditions as long as the parameters in the kg' expressions can be accurately estimated. An Aspen Plus® RateSep™ model for MEA was created to model CO₂ flux in the wetted wall column. The model accurately calculated CO₂ flux over the wide range of experimental conditions but included a systematic error with MEA concentration. The systematic error resulted from an inability to represent the activity coefficient of MEA properly. Due to this limitation, the RateSep™ model will be most accurate when finetuned to one specific amine concentration. This Aspen Plus® RateSep™ model allows for scale up to industrial conditions to examine absorber or stripper performance.Item Carbon dioxide solubility and mass transfer in aqueous amines for carbon capture(2015-08) Li, Ph. D., Le; Rochelle, Gary T.; Freeman, Benny D; Sanchez, Isaac C; Svendsen, Hallvard F; Dugas, Ross EAmine scrubbing is the state of the art technology for CO2 capture, and solvent selection can significantly reduce the capital and energy cost of the process. This work presents rigorous CO2 mass transfer and solubility data at expected process conditions for more than 20 aqueous amines and amino acid salts. Amino acid salts are generally not competitive with aqueous amines as solvents for CO2 capture, particularly from coal fired power plants. The capacity of amino acid salts is intrinsically low (0.2 – 0.35 mol/mol alkalinity). Piperazine (PZ) blends have good overall performance. 3.5 m PZ/3.5 m 2-amino-2-hydroxymethyl-propane-1,3-diol (Tris) shows good absorption rates, good capacity, and low solvent viscosity. 6 m PZ/2 m hexamethylenediamine (HMDA) has moderate absorption rates, capacity, and a high viscosity. High solvent viscosity has been shown to reduce CO2 absorption rate and increase sensible heat cost. A simplified speciation model (SSM) was developed in MATLAB to represent CO2 VLE in a mono-amine solvent using only four adjustable parameters. The model can also predict liquid phase speciation. Primary and secondary amines were shown to have different CO2 VLE dependence on amine pKa. At pKa higher than 8, secondary amines have lower carbamate stability than primary amines. A correlation was developed to predict the SSM parameters based on the amine type and amine pKa. The third order overall reaction kinetic expression better explains the mass transfer data at process conditions than the more widely applied second order overall expression. A new Bronsted correlation was developed to represent the third order concentration based kinetic constant at 40 °C for primary and secondary amines: 〖log〗_10 (〖k_(c-3)〗^* )=-11.728+1.113∙p〖K_a〗_amine. This work shows the absorption rate of CO2 at process conditions do not always increase with amine pKa. As the reaction rate constant increases with amine pKa, the free amine available for CO2 absorption decreases. As the result, for primary and secondary mono-amines, the optimum amine pKa for the best mass transfer performance is around 8.7 (at 40 °C).Item The experience of absorption : comparison of the mental processes of meditation between emic yogic and etic neuroscientific perspectives on Ishvara Pranidhana meditation(2010-05) Holte, Amy Jo 1972-; Neff, KristinModernity has seen the exchange of ideas about cognition between western science and eastern meditation traditions. In particular, western ways of thinking about the natural world have infiltrated Indian theories of yoga. This intersection of ideas in the twentieth-century has resulted in a problematic trend to theorize yogic phenomena, including meditation, in scientific terms. These translations converge on explicating yogic processes within a context of advancing knowledge about the brain. This translational approach to bringing etic and emic perspectives together in the same framework results in interpretations of meditation that succumb to problems cognitive science faces at a broader level in theorizing cognition and mind-body interrelations. In this study, I take a different approach to bringing emic and etic perspectives together by placing a phenomenologically interpreted emic account of absorption (the meditative shift in consciousness) into dialogue with current scientific understandings of three central mental processes of meditation. Specifically, I analyze ways of conceptualizing attention, memory, and emotion, and their underlying mechanisms as posited in yoga and science, focusing on the problem of how each system interprets the reality of absorption. This comparison suggests a basic similarity between the two systems: theorizing cognition and meditative absorption in terms of embodiment. This finding emphasizes the dual nature of embodiment as both experiential and physical. Finally, I consider this dialogue from an embodied mind perspective, an emerging way of thinking about and theorizing the mind-body in cognitive science, because this perspective challenges longstanding theoretical problems in western understandings of how the mind works. This analysis suggests that theorizing meditation in these dual terms of embodiment potentially solves the reductive challenges of dualistic and materialist philosophy that have plagued both religious and naturalistic attempts to explain absorption. This interdisciplinary dialogue provides a framework with which to think more critically about translational and cross-disciplinary efforts that have previously confused the goals of yoga and science and their respective foci on practice and mechanisms. I conclude that bridging ideas in this dialogical way reveals a complementary perspective between phenomenological and biological ways of understanding the mind that both hinge on embodied cognition.Item A fundamental investigation of non-Fickian and Case II penetrant transport in glassy ploymers(2010-08) Ekenseair, Adam Keith; Peppas, Nicholas A., 1948-; Paul, Donald R.; Freeman, Benny D.; Lloyd, Douglas A.; Ketcham, Richard A.The relative rates of the diffusional and relaxational processes during the absorption of penetrant molecules in glassy polymers determine the nature of the transport process and lead to Fickian, Case II, and anomalous absorption behavior. While previous models account for anomalous behavior, there is still a disconnect between theory and experiment, as data must be fit to the model with previously determined independent parameters. With trends leading to smaller device scales and increasingly complex polymer structures, there is a need for a quantitative understanding of the manner in which a polymer’s network structure alters both the rate and the mode of penetrant transport. To this end, samples of glassy poly(methyl methacrylate), poly(2-hydroxyethyl methacrylate), and poly(vinyl alcohol) were synthesized primarily by an iniferter-mediated, thermally-initiated free radical polymerization procedure. The thermal and mechanical properties of these polymers, as well as the polymer network structure, were varied through crosslinking and confirmed by detailed characterization. The dynamics of small molecule penetrant transport were examined in each polymer, with an emphasis on the occurrence of non-Fickian and Case II transport. The degree of crosslinking and choice of crosslinking molecule were shown to be powerful tools in tuning the observed penetrant transport process. For instance, the transport dynamics were altered from Fickian to Case II by increasing the degree of crosslinking and from Case II to Fickian by increasing the crosslinking interchain bridge length. Within the purely Case II regime, the rate of penetrant transport, or the Case II front velocity, was shown to scale with the square root of the degree of crosslinking in all systems investigated. A novel procedure for the in situ examination of penetrant transport in glassy polymers was developed utilizing high-resolution X-ray computed tomography. This completely nondestructive technique was used to visualize features in the interior of opaque solid objects and obtain digital information on their 3-D structure and properties. In this manner, the time-dependent penetrant concentration profiles throughout a swelling polymer were determined and analyzed.Item Inversion-based petrophysical interpretation of multi-detector logging-while-drilling sigma measurements(2014-05) Ortega, Edwin Yamid; Torres-Verdín, CarlosPulsed-neutron borehole measurements involve a physical process in which a source emits energetic neutrons that lose energy upon collisions with formation nuclei, and are eventually captured by a nucleus to form a heavier, excited state. The excited nucleus decays to its ground state by the emission of gamma rays. Both thermal-neutron and gamma-ray populations decay with time at a rate defined by Sigma, which is a nuclear property that quantifies a material’s ability to capture thermal neutrons. The large contrast in Sigma between hydrocarbon and salty connate water enables calculations of water saturation directly from pulsed-neutron measurements. Sigma logs have proven useful in the assessment of thinly bedded formations because they exhibit a small volume of investigation, and have been deemed superior to resistivity logs in the petrophysical evaluation of carbonate formations. The recognized potential of Sigma logs in formation evaluation initiated the development of multi-detector Logging-While-Drilling (LWD) Sigma measurements. These measurements are acquired using one thermal-neutron and two gamma-ray detectors at different spacings from the source. Such a design is aimed at providing distinct radial depths of investigation to detect filtrate invasion in the near-wellbore zone. Despite their formation-evaluation potential, multi-detector time-decay measurements commonly remain affected by invasion, shoulder-bed, and well-deviation effects. The purpose of this dissertation is to develop a fast-forward simulation method to reproduce multi-detector time decays and combine the method with inversion techniques to improve the petrophysical interpretation of LWD Sigma measurements. First-order perturbation theory and a library of pre-calculated Monte Carlo detector-specific sensitivity functions and time decays are used to numerically simulate borehole Sigma measurements in realistic logging environments. The new simulation method is one hundred thousand times faster than rigorous Monte Carlo calculations and remains within two capture units of disparity. Next, the fast-forward simulation method is embedded within inversion algorithms to estimate layer-by-layer radial length of invasion and formation Sigma corrected for shallow invasion, shoulder-bed, and well-deviation effects. Both fast-forward and inverse modeling algorithms are benchmarked against laboratory and synthetic time decays. The improvement of formation Sigma obtained with inversion-based interpretation leads to an improvement in the estimation of Sigma-derived water saturation. Likewise, the estimated radial length of invasion is combined with neutron and density measurements to correct the latter for invasion effects. Results indicate that the inversion-based interpretation method is well suited for the evaluation of high-porosity formations invaded by salty mud filtrate. Inversion-based interpretation of field LWD time decays enables the estimation of lower values of water saturation when compared to conventional Sigma interpretation or resistivity methods. Estimated values of water saturation are as much as fifty percent lower than predicted by conventional interpretation of Sigma logs in the case of measurements affected by shoulder-bed effects, and as much as one hundred percent lower than predicted by the conventional interpretation method for measurements additionally affected by salty filtrate invasion. The key attributes of the combined petrophysical interpretation of multi-detector Sigma, neutron, and density measurements developed in this dissertation are that it explicitly enforces the physics of all nuclear measurements, honors the pressure and temperature dependency of reservoir fluid nuclear properties, and takes into account a-priori information such as mud-filtrate salinity, connate-water salinity, and bed-boundary locations.Item Mass transfer area of structured packing(2010-05) Tsai, Robert Edison; Eldridge, R Bruce; Rochelle, Gary T.; Bonnecaze, Roger T.; McGlamery, Gerald G.; Seibert, A Frank; Truskett, Thomas M.The mass transfer area of nine structured packings was measured as a function of liquid load, surface tension, liquid viscosity, and gas rate in a 0.427 m (16.8 in) ID column via absorption of CO₂ from air into 0.1 mol/L NaOH. Surface tension was decreased from 72 to 30 mN/m via the addition of a surfactant (TERGITOL[trademark] NP-7). Viscosity was varied from 1 to 15 mPa·s using poly(ethylene oxide) (POLYOX[trademark] WSR N750). A wetted-wall column was used to verify the kinetics of these systems. Literature model predictions matched the wetted-wall column data within 10%. These models were applied in the interpretation of the packing results. The packing mass transfer area was most strongly dictated by geometric area (125 to 500 m²/m³) and liquid load (2.5 to 75 m³/m²·h or 1 to 30 gpm/ft²). A reduction in surface tension enhanced the effective area. The difference was more pronounced for the finer (higher surface area) packings (15 to 20%) than for the coarser ones (10%). Gas velocity (0.6 to 2.3 m/s), liquid viscosity, and channel configuration (45° vs. 60° or smoothed element interfaces) had no appreciable impact on the area. Surface texture (embossing) increased the area by 10% at most. The ratio of effective area to specific area (a[subscript e]/a[subscript p]) was correlated within limits of ±13% for the experimental database: [mathematical formula]. This area model is believed to offer better predictive accuracy than the alternatives in the literature, particularly under aqueous conditions. Supplementary hydraulic measurements were obtained. The channel configuration significantly impacted the pressure drop. For a 45°-to-60° inclination change, pressure drop decreased by more than a factor of two and capacity expanded by 20%. Upwards of a two-fold increase in hold-up was observed from 1 to 15 mPa·s. Liquid load strongly affected both pressure drop and hold-up, increasing them by several-fold over the operational range. An economic analysis of an absorber in a CO₂ capture process was performed. Mellapak[trademark] 250X yielded the most favorable economics of the investigated packings. The minimum cost for a 7 m MEA system was around $5-7/tonne CO₂ removed for capacities in the 100 to 800 MW range.Item Near infrared laser propagation and absorption analysis in tissues using forward and inverse Monte Carlo methods(2014-05) Nasouri, Babak; Berberoglu, HalilFor understanding the mechanisms of low level laser/light therapy (LLLT), accurate knowledge of light interaction with tissue is necessary. In order to have a successful therapy, laser energy needs to be delivered effectively to the target location which depending on the application can be within various layers of skin or deeper. The energy deposition is controlled by input parameters such as wavelength, beam profile and laser power, which should be selected appropriately. This thesis reports a numerical study that investigates the laser penetration through the human skin and also provides a scale for selection of wavelength, beam profile and laser power for therapeutic applications. First, human skin is modeled as a three-layer participating medium, namely epidermis, dermis, and subcutaneous, where its geometrical and optical properties were obtained from the literature. Both refraction and reflection are taken into account at the boundaries according to Snell’s law and Fresnel relations. Then, a three dimensional multi-layer reduced-variance Monte Carlo tool was implemented to simulate the laser penetration and absorption through the skin. Local profiles of light penetration and volumetric absorption densities were simulated for uniform as well as Gaussian profile beams with different spreads at 155 mW average power over the spectral range from 1000 nm to 1900 nm. The results showed that lasers within this wavelength range could be used to effectively and safely deliver energy to specific skin layers as well as to achieve large penetration depths for treating deep tissues, without causing any skin damage. In addition, by changing the beam profile from uniform to Gaussian, the local volumetric dosage could be increased as much as three times for otherwise similar lasers. In the second part of this thesis, a three-dimensional single-layer reduced-variance inverse Monte Carlo method was developed to find the optical properties of the skin using the experimental values of transmittance and reflectance. The results showed that both transmittance and reflectance scale well with transport optical thickness. Moreover, it was also shown that penetration depth is highly sensitive to the laser wavelength and varied within the range from 1.7 mm to 4.5 mm.Item Optical absorption of pure water in the blue and ultraviolet(Texas A&M University, 2007-09-17) Lu, ZhengThe key feature of the Integrating Cavity Absorption Meter (ICAM) is that it produces an isotropic illumination of the liquid sample and thereby dramatically minimizes scattering effects. The ICAM can produce an effective optical path length up to several meters. As a consequence, it is capable of measuring absorption coefficients as low as 0.001 m-1. The early version of the ICAM was used previously to measure the absorption spectrum of pure water over the 380-700 nm range. To extend its range into the ultraviolet, several modifications have been completed. The preliminary tests showed that the modified ICAM was able to measure the absorption of pure water for the wavelength down to 300 nm. After extensive experimental investigation and analysis, we found that the absorption of Spectralon® (the highly diffusive and reflective material used to build the ICAM) has a higher impact on measurements of absorption in the UV range than we had expected. Observations of high values for pure water absorption in the UV, specifically between 300 and 360 nm, are a consequence of absorption by the Spectralon®. These results indicated that even more serious modifications were required (e.g. Spectralon® can not be used for a cavity in the UV). Consequently, we developed a new diffuse reflecting material and used fused silica powder (sub-micron level) sealed inside a quartz cell to replace the inner Spectralon® cavity of the ICAM. The new data is in excellent agreement with the Pope and Fry data (380-600 nm) and fills the gap between the 320 nm data of Quickenden and Irvin and 380 nm data of Pope and Fry. We present definitive results for the absorption spectrum of pure water between 300 and 600 nm.Item Picosecond pump-probe spectroscopic study of electronic energy relaxation in H-aggregates of 1,1'-diethyl-2,2'-dicarbocyanine (DDC) on colloidal silica(Texas Tech University, 1988-12) Chen, Sun-yungPolarized transient bleaching measurements of H-aggregates of l, l'-Diethyl-2.2'-Dicarbocyanine (DDC) on colloidal silica were performed using picosecond time-resolved pump-probe spectroscopy. The aggregates were nonfluorescent but exhibited a broad absorption band, between 550 and 600 nm, which was blue-shifted from the monomer band at 711 nm. These spectral properties are consistent with the simple theory for one-dimensional excitons. The transient bleaching signals can be filled well by a stretched exponential function. The nonexponential signals are attributed to a distribution of aggregates with different lifetimes, with the most probable lifetime being equal to 120-130 ps. The absorption anisotropy was constant and equal to 0.30 ± 0.04. The anisotropy is discussed in terms of the coherence properties of excitons.Item Sorption of selected endocrine disrupters by synthetic membrane vesicles and effects of natural organic matter(2002-05) Yamamoto, Hiroshi, 1973-; Liljestrand, Howard M. (Howard Michael)In this study, synthetic membrane vesicles (liposomes) were prepared from phospholipids and cholesterol as a model biological phase, and the bioavailability of four estrogens and five estrogenic compounds were evaluated by determining the sorption coefficients (Klipw values) into liposomes. Since natural organic matter (NOM) is likely to bind hydrophobic organics such as endocrine disrupters and influence their bioavailability and the fate in the environment, the effects of a wide variety of model NOM compounds, including humic substances, polysaccharides, and tannic acid, on the liposome-water system were investigated by determining the sorption coefficients onto NOM (Koc values). Reasonably reproducible preparations of liposome suspensions were characterized by quasi-elastic laser light scattering (QELS) analysis and transmission electron microscopy (TEM). Reproducible measurements of Klipw values were obtained by the equilibrium dialysis technique. The Klipw values determined strongly depend on the lipid components of the liposome. Liposome with shorter acyl-chain or increased number of double bonds had higher values of Klipw, while those including cholesterol had significantly lower Klipw values than those without. Moreover, log Klipw values of the selected endocrine disrupters did not show a strong linear correlation with their log Kow. Thus, the use of linear free energy relationships (LFER) to estimate Klipw values is limited for these compounds with a wide variety of chemical structures. Koc values for the selected NOM compounds were determined by the fluorescence quenching technique. The Koc values for the selected compounds had a good linear correlation with the absorptivity at 272 nm and the concentration of phenolic groups of each NOM. However, log Koc showed no correlation with log Kow for the selected endocrine disrupters. Nominal sorption coefficients into liposome ( ) slightly decreased with an increase of NOM concentration, but the decrease was not significant at the highest NOM concentration. Simple models developed in this study showed satisfactory agreement of the estimated K values with those measured for two humic acids. Other linear sorption models were developed for activated sludge treatment and found to agree with literature results. Simple models were also developed to estimate the relative health-related risks of endocrine disrupters.