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- Title
- CONTROLLER DESIGN AND DISTRIBUTED CONTROL WITHIN MULTI-AGENT SYSTEMS
- Creator
- Shao, Quan Min
- Date
- 2013, 2013-12
- Description
-
None
PH.D in Chemical and Biological Engineering, December 2013
- Title
- POLYMER ELECTROLYTE MEMBRANES FOR ELECTROCHEMICAL ENERGY CONVERSION AND STORAGE SYSTEMS: FUEL CELLS AND REDOX FLOW BATTERIES
- Creator
- Yun, Sukhwan
- Date
- 2014, 2014-12
- Description
-
Direct methanol fuel cells (DMFCs) and redox flow batteries (RFBs) are well-known electrochemical energy conversion/storage systems that...
Show moreDirect methanol fuel cells (DMFCs) and redox flow batteries (RFBs) are well-known electrochemical energy conversion/storage systems that utilize redox reactions to convert or store electricity. Ion exchange membranes (IEMs) are used in DMFCs and RFBs as electrolyte separators. The critical requirements for IEMs in these applications are high ionic conductivity, low electrolyte permeability, high stability, and low cost. Silsesquioxane (SQO)-based sulfonated poly(etheretherketone) composite membranes were synthesized. Morphological changes in the composite membranes resulting from the introduction of SQO were studied using small-angle x-ray scattering. A sharp decrease in proton conductivity with SQO loading (> 20 wt%) was attributed to morphological changes in the membrane, including agglomeration and inhomogeneous dispersion of SQO particles within the ionic domains. Anion exchange membranes (AEMs) based on quaternized cardo-poly(etherketone) (QPEK-C) were prepared and evaluated for all-vanadium RFB (VRFB) applications. The QPEK-C AEMs with different degrees of functionalization (0.9–1.6) exhibited sulfate ion conductivities ranging between 5.6 and 15.2 mS cm-1 at 30 oC. The AEM had a lower VO2+ permeability (2.8×10-8 cm2 s-), compared to that of Nafion® 212 (2.9±0.2 ×10-7 cm2 s-1), which was attributed to the Donnan exclusion effect. The mechanical strength of QPEK-C AEM degraded by 35% after exposure to a 1.5 M VO2+ solution for 1500 hours due to the oxidation of aromatic rings. A single-cell VRFB employing the AEM separator yielded current and energy efficiencies (at 30 mA cm-2) of 97-99% and 80-82 %, respectively. Enhanced sulfate ion conductivity (8.4 ± 0.2 mS cm-1) and decreased VO2+ permeability (0.53×10-9 cm2 s-1) were achieved by incorporating 20 wt% of n-(trimethoxysilylpropyl)-n,n,n-trimethylammonium additives into QPEK-C, (the pristine QPEK-C AEM yielded corresponding values of 4.5 ± 0.5 mS cm-1 and 1.09×10-9 cm2 s-1). About 99% coulombic efficiency was achieved with the VRFBs employing the composite AEM. However, a rapid reduction of the ionic conductivity down to the value of the pristine membrane was observed when the composite AEM was immersed in 1.5 M VO2+ solution for 3 days. Vanadium-cerium RFBs (V-Ce RFBs) evaluated with QPEK-C AEM separators yielded identical energy efficiency (84%) to corresponding RFBs evaluated with Nafion® 212. However, after over 20 charge-discharge cycles, the V-Ce RFB with the AEM separator yielded unchanged efficiency and capacity, while a 50% loss of capacity was observed with the Nafion® separator. This suggested that QPEK-C AEMs are promising candidates for RFB separators when different cations are used in the two electrolyte solutions, in that they act as efficient barriers that preclude the intermixing of the cations due to the Donnan exclusion effect.
Ph.D. in Chemical Engineering, December 2014
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- Title
- MATHEMATICAL MODELING OF POLY(ETHYLENE GLYCOL) DIACRYLATE HYDROGEL SYNTHESIS VIA VISIBLE LIGHT FREE-RADICAL PHOTOPOLYMERIZATION FOR TISSUE ENGINEERING APPLICATIONS
- Creator
- Lee, Chu-yi
- Date
- 2013, 2013-05
- Description
-
Crosslinked hydrogels of poly(ethylene glycol) diacrylate (PEGDA) have been extensively used as scaffolds for applications in tissue...
Show moreCrosslinked hydrogels of poly(ethylene glycol) diacrylate (PEGDA) have been extensively used as scaffolds for applications in tissue engineering. In this thesis, PEGDA hydrogels are synthesized using visible light free-radical photopolymeriza- tion (λ = 514 nm) in the presence of the visible light photosensitive dye, EosinY, the co-initiator, triethanolamine (TEA), a comonomer, N-vinyl pyrrolidone (NVP), a crosslinking agent, PEGDA, and an optional PEG monoacrylate monomer that contains the cell adhesive ligand YRGDS. The incorporation level of the YRGDS lig- and as well as the physical and mechanical properties of these hydrogels dictate cell behavior and tissue regeneration. These hydrogel properties may be tuned through variations in polymerization conditions. The goal of this thesis was to develop a math- ematical model for PEGDA hydrogel formation which predicts the incorporation level of YRGDS and the crosslink density of hydrogel as a variety of polymerization con- ditions. This model provides insight into the process of hydrogel crosslinking and in effectively guiding the experimental design of these scaffolds for tissue engineering applications. To accomplish this task two major components comprised the studies of this thesis. The first component involved an investigation of the visible light photo- initiation mechanism of EosinY and TEA, and the second component involved the develop of a hydrogel synthesis model and its validation. Experiments and modeling were used to determine an expression for the rate of initiation of the EosinY/TEA initiation system and to propose a photoinitiation mechanism. In Chapter 2, exper- imental data and parameter fitting were utilized to obtain an empirical expression for the rate of initiation. However, this empirical expression did not consider the ef- fect of inhomogeneous light distribution which is present in this experimental system. The dynamics of light absorption during polymerization were measured under differ- xiv ent conditions in order to gain insight into the kinetic photoinitiation mechanism as well as the rate of initiation. In Chapter 3, a mechanism for this photo-initiation was proposed. Using this mechanism the light absorption dynamics accounting for inhomogeneous light distribution were simulated which were found to be in an agree- ment with the light absorption measurements shown in Chapter 2. Further validation of this proposed mechanism was achieved from polyNVP conversion measurements. This photo-initiation mechanism was implemented in the hydrogel model. In Chapter 4, the hydrogel synthesis model was developed based on the kinetic approach of the method of moments combined with the Numerical Fractionation technique. The model was used to predict the dynamics of hydrogel properties such as gel fraction, crosslink density, and RGD incorporation under various polymerization conditions. Model predictions were compared with experimental data. Three sets of experiments were conducted. In the first set of experiments where hydrogels were formed in the absence of Acryl-PEG-RGD, the total double bond concentration was kept constant while varying the compositions of NVP and PEGDA. The model and the experiments showed a maximum crosslink density for an acrylate to double bond ratio of 0.5 to 0.6. This is related to the synergistic cross-propagation between NVP and PEGDA, which results in an increase in the rate of polymerization leading to higher crosslink density. In the second set of experiments, hydrogels were formed in the presence of Acryl-PEG-RGD to investigate its incorporation as well as the hydrogel crosslink density. The model showed reasonable agreement with the experimental data and in some cases the predicted RGD deviated from the experimental measurements due to changes in volume upon swelling. The effect of swelling was not considered by the model. The calculated crosslink densities were compared with the inverse swelling ratios from the experiments. The reduction of free volume due to the space occupied xv by the unreacted pendant double bonds was not considered by the model. This reduc- tion of free volume affected the apparent swelling ratio obtained from experiments thus resulting in the observed mismatch between the experimental trends and the predicted crosslink density by the model. In the third set of experiments, additional crosslink density measurements were conducted using a PEGDA macromer of lower molecular weight (MW = 575 Da.). The experiments were performed in the absence of Acryl-PEG-RGD. Few cases were not accurately predicted since the model did not consider the reduction in the concentration of available pendant double bonds when gelation occurs. Among the three set of experiments, the hydrogel synthesis model offers reasonable predictions for most of the experimental cases. This model can be used as a guide for experimen- tally designing PEGDA hydrogels with the desired properties for tissue engineering applications.
PH.D in Chemical and Biological Engineering, May 2013
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- Title
- CORROSION-RESISTANT ELECTRO-CATALYSTS AND SUPPORTS FOR ELECTROCHEMICAL ENERGY CONVERSION
- Creator
- Wang, Guanxiong
- Date
- 2016, 2016-12
- Description
-
Polymer electrolyte fuel cells (PEFCs) convert chemical energy of fuels (eg. Hydrogen) directly to electrical energy with excellent power...
Show morePolymer electrolyte fuel cells (PEFCs) convert chemical energy of fuels (eg. Hydrogen) directly to electrical energy with excellent power density, high efficiency, and zero emissions. Several challenges have delayed the commercialization of fuel cells with one being the high cost and durability of the carbon-supported-platinum-based (Pt/C) electrocatalysts. The lifetime/durability issue is critical as insufficient durability/reliability of the catalysts affects the lifetime and economical viability of these devices. Carbon support corrosion is a major durability issue since the corrosion reaction is thermodynamically favorable but kinetically sluggish under normal operating conditions. The potential transients that occur during start and stop in automotive applications can lead to electrode potential excursions of up to 1.5 V and contribute to carbon corrosion. The best way to mitigate support corrosion in PEFCs is to replace the carbon supports with alternatives having high electronic conductivity, surface area and porosity. This dissertation investigates the following carbon alternatives: (i) tin doped indium oxide (ITO) and (ii) 1:1 mixed oxides of ruthenia and silica (RSO). Microstructure characterization and electrochemical evaluations, including accelerated stress tests (start-up/shut-down and load cycling protocols) were performed to evaluate ORR activity, fuel cell performance, and electrochemical stability under PEFC operating conditions. The ITO support and 40%Pt/ITO catalysts demonstrated exceptional electrochemical stability (and reasonable ORR activity) in rotating disk electrode (RDE) experiments under accelerated potential cycling that mimicked automotive drive cycles. However, Pt/ITO exhibited poor performance and stability during MEA evaluation in a PEFC. X-ray photoelectron spectroscopy (XPS) was employed to reveal the degradation modes of Pt/ITO during PEFC operation and it was found that the increase in the surface hydroxide concentration generates a passivating In(OH)3 layer that increases electrode resistance and undermines PEFC performance. The influence of the catalyst support on PEM degradation during PEFC operation was also studied. Rotating ring-disk electrode (RRDE) experiments were employed to estimate the fraction of H2O2 generated during the ORR on the supports (C and RSO) and catalysts (benchmark Pt/C and Pt/RSO). The percentage of H2O2 generated on C and Pt/C was 50% higher than that on RSO and Pt/RSO thus explaining the observed oxidative degradation resistance of the PEM with the latter supports/catalysts.
Ph.D. in Chemical Engineering, December 2016
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- Title
- OIL RECOVERY IN SINGLE CAPILLARIES AND POROUS MEDIA USING WETTING NANOFLUIDS
- Creator
- Zhang, Hua
- Date
- 2016, 2016-05
- Description
-
Recent experiments and modeling conducted in our laboratory have demonstrated that the spreading of nanofluids, liquid suspensions of...
Show moreRecent experiments and modeling conducted in our laboratory have demonstrated that the spreading of nanofluids, liquid suspensions of nanosized particles, on solids are enhanced due to self-structuring of nanoparticles in the confined three-phase oil-nanofluid-solid contact region. Nanofluids have recently been proposed as agents for enhanced oil recovery (EOR). Despite recently widely conducted research using nanofluids for EOR, the underlying operating mechanism is not well understood. In this thesis, we attempt to understand the mechanism of nanofluid based EOR and evaluate its performance from reservoir core samples and model systems (glass capillary and sintered bead-pack). To visualize how oil displacement in the rock pores by nanofluid, we conducted model study using hexadecane and single glass capillary and showed the oil film dynamics in air and nanofluid after oil was displaced in the capillary. Based on the understanding of the role of nanofluid on oil displacement in capillaries, we conducted imbibition tests using Berea sandstones and flooding experiments in sintered glass-beads. X-ray microtomography was used to visualize and analyze fluid distribution and to see the effect of nanofluid in EOR. We finally considered fractured media by fabricating such structures. The dynamics of a cylindrical hexadecane layer deposited inside glass capillaries after the oil/air displacement was studied experimentally and by modeling. The oil layer subject to surface perturbation becomes unstable forming uniform, regularly-spaced double concave menisci across the capillary that are bridged with dimples (collars). In order to reveal the phenomena of the film thinning and stability between the double concave meniscus and the dimple, we monitored an air bubble approaching a flat glass surface in hexadecane. We found that the oil film thinning in a cylindrical glass capillary and on a flat glass substrate were similar; We adapted the model proposed by Gauglitz and Radke for our system (oil-air displacement) and solved it numerically. The numerical result shows a stable film between the liquid bridge and the dimple, which is consistent with our experimental observations. We also estimated the meniscus-film-dimple thickness profile and found it was in fair agreement with the model prediction. The dynamics of cylindrical hexadecane film after displacement by a nanofluid in a glass capillary was studied. We found the thick hexadecane film is unstable, and over time it breaks and forms a thin film. Once the thick film ruptures, it retracts and forms an annular rim (liquid ridge) that collects liquid. As the volume of the annular rim increases over time, it forms a double concave meniscus across the capillary and dewetting stops. The thin film on the right side of the double concave meniscus then breaks and the contact angle increases. The process repeats until droplets build along the capillary wall. Finally, the droplets are displaced from the capillary wall by the nanofluid and spherical droplets appear inside the capillary. This is a novel phenomenon not observed during dewetting by a solution without nanoparticles. The theoretical model based on the lubrication approximation using the capillary pressure gradient was developed to estimate the annular rim dewetting velocity. The predicted dewetting velocity is found to be in fair agreement with the experimental value. We conducted imbibition tests using a reservoir crude oil and a reservoir brine solution with a high salinity and a suitable nanofluid that displaces crude oil from Berea sandstone and single glass capillaries. We present visual evidence of the underlying mechanism based on the structural disjoining pressure for the crude oil displacement using a polymeric nanofluid (our definition of such a fluid means a suspension of polymeric particles in an aqueous substrate) in high salinity brine. The polymeric nanofluid is specially formulated to survive in a high salinity environment and is found to result in an increased efficiency of 50% for Berea sandstone compared to 17% using the brine alone at a reservoir temperature of 55 oC. These results aid our understanding of the role of the nanofluid in displacing crude oil from the rock especially in a high salinity environment containing Ca++ and Mg++ ions. Results are also reported using Berea sandstone and a nanofluid containing silica nanoparticles. We conducted a series of flooding experiments at different capillary numbers to quantify the performance of a polymeric nanofluid compared to brine using the sintered glass-beads. A high resolution X-ray microtomography (microCT) was used to visualize oil and brine distribution in a sintered bead-pack before and after nanofluid flooding. The results of flooding experiments showed that an additional oil recovery of approximately 15% is possible with nanofluids compared to brine at low capillary numbers, and is as effective as high capillary number brine flooding. Nanofluid induced additional oil recovery decreases as we increase the capillary number and the total oil recovered shows a marginal decrease. At first glance, these results are opposite of what one expects in the conventional EOR, where oil recovery is known to increase progressively with increasing capillary number. These results cannot be explained based on mobilization theories due to the reduced capillarity. Our results however are consistent with the mechanism of wettability alteration caused by structural disjoining pressure leading to the formation of the wetting nanofluid film between oil and substrate.We presented experimental studies of nanofluid flooding in fractured porous media formed with sintered glass-beads. The nanofluid injection is conducted at a rate where structural disjoining pressure driven recovery is operational. We found an additional 23.8% oil can be displaced using nanofluid after brine injection with an overall displacement efficiency of 90.4% provided the matrix was in its native wettability state. In summary, nanofluids are excellent EOR agents and their economic viability needs to be examined.
Ph.D. in Chemical Engineering, May 2016
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- Title
- ECONOMIC BASED CONTROL SYSTEM DESIGN
- Creator
- Omell, Benjamin Peter
- Date
- 2013, 2013-12
- Description
-
EMPC differs from traditional MPC by directly utilizing a profit based function as the objective as opposed to a quadratic function that...
Show moreEMPC differs from traditional MPC by directly utilizing a profit based function as the objective as opposed to a quadratic function that minimizes the distance from a set point that is predetermined. However, implementation of EMPC can result in unexpected and at times pathological closed-loop behavior, including inventory creep, bang-bang actuation and instability. To address these issues, an infinite-horizon version of EMPC is developed and shown to avoid many of the performance issues observed in the finite-horizon version. First, modifications to the EMPC problem will be used for the conceptual development of the Economic Linear Optimal Controller (ELOC), which is a statistically constrained linear feedback controller. Then, pointwise- in-time constraints can be reintroduced using one of two methods; Constrained ELOC or Infinite-Horizon EMPC (IH-EMPC). We also investigate the impact of problem formulation modifications on the ELOC. The first issue is that of disturbance modeling and the second is the impact of controller sample-time. The third topic concerns incorporation of computational delay in the feedback-loop, using both full and partial state information structures. Finally an illustration of the impact of plant-model mismatch is presented. The Constrained ELOC formulation is further modified to allow for market responsive smart grid applications. In particular an Integrated Gasification Combined Cycle (IGCC) process with hydrogen storage will be used to demonstrate the Constrained ELOC for such applications. The ELOC will be used as a vehicle to exploit dispatch capabilities by pursuing directly the objective of maximizing revenue. The idea being that process modifications to enable dispatch capabilities will allow for a time-shift of power production away from periods of low energy value to periods of high value. An in depth discussion is provided on how energy value forecasts are incorporated into the design of the constrained ELOC. Finally, an extension of the ix ELOC to the controller embedded equipment design is provided. The work concludes with a discussion of the computational aspects of solving the ELOC problem. In particular, the impact of reverse-convex constraints inherent to the ELOC problem are discussed along with existing solution methods. The main contribution of this final chapter is a novel application of the Generalized Bender’s Decomposition (GBD) algorithm to the ELOC problem. This new approach is shown to retain global optimality, reduce computational effort (by orders of magnitude) and expand the class of problems one can solve.
PH.D in Chemical Engineering, December 2013
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- Title
- INVESTIGATION OF ANION EXCHANGE MEMBRANES FOR ELECTROCHEMICAL ENERGY CONVERSION AND STORAGE SYSTEMS
- Creator
- Wang, Lihui
- Date
- 2017, 2017-05
- Description
-
The alkaline stability of poly (arylene ether) backbones in anion exchange membranes (AEMs) derivatized with quaternary benzyl N, N-...
Show moreThe alkaline stability of poly (arylene ether) backbones in anion exchange membranes (AEMs) derivatized with quaternary benzyl N, N- dimethylhexylammmonium (DMH+) and trimethylammonium (TMA+) cation groups were investigated in poly (2,6- dimethyl 1,4-phenylene) oxide (PPO) and Udel® polysulfone (PSF) polymers. Previous studies have demonstrated that quaternary ammonium and phosphonium groups trigger backbone degradation in commercially available poly (arylene ether)-based AEMs, despite the base polymers’ resilience to alkaline solutions. Herein, I demonstrate that the electron withdrawing or donating character in the poly (arylene ether) backbone ultimately dictates whether the prepared AEMs will become brittle in alkaline media due to cation-triggered backbone degradation (Arges, Parrondo, Johnson, Nadhan, & Ramani, 2012a; Christopher G. Arges, Lihui Wang, Javier Parrondo, & Vijay Ramani, 2013). Mitigation of cation-triggered backbone degradation was only achieved when electron withdrawing substituents (not including the cation), such as sulfone or bromine, were eliminated from the polymer backbone (or, alternately, when electron donating groups were present). Hence, PPO AEMs prepared through chloromethylation, rather than free radical bromination, were resistant to backbone hydrolysis in alkaline media because each cation-functionalized repeat unit had two electron-donating methyl groups rather than a single methyl group. This study presents some design rules for preparing mechanically stable poly (arylene ether) AEMs from low cost, commercially available polymers for alkaline electrochemical devices.
Ph.D. in Chemical Engineering, May 2017
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- Title
- TOWARDS THE EXACT CALCULATIONS OF THE FREE ENERGY FOR ENTANGLED SEMIFLEXIBLE POLYMER CHAIN
- Creator
- Pilyugina, Ekaterina
- Date
- 2015, 2015-05
- Description
-
This work consists of two separate projects unified by the idea to extend the Discrete Slip-Link Model, which has been being successfully...
Show moreThis work consists of two separate projects unified by the idea to extend the Discrete Slip-Link Model, which has been being successfully developed in this group to predict rheological behavior of entangled flexible polymers, to new applications. The first project was dedicated to application of the Discrete Slip-Link Model to dielectric relaxation in order to simultaneously predict linear rheology and dielectric relaxation experiments of entangled polyisoprenes. Linear monodisperse, linear bidisperse and star-branched monodisperse systems were studied. It was found that all circumstances save one are well described. Namely, dilute long chains in a sea of short chains can be predicted rheologically, but dielectric relaxation data show a reduction in the relaxation time of long chains greater than that predicted by either the DSM or the expected Rouse motion. The second project was focused on the derivation of the exact free energy expression for semiflexible chains in the presence of entanglements in order to implement the DSM for semiflexible polymers. The special cases of chains with one, two and three strands are examined. An additional implementation of obtained results for one and two strands to buckling instability was performed. It is believed that in two dimensional case the critical buckling force is increased by thermal fluctuations in comparison to classical Euler buckling. However, how the critical buckling force is influenced by thermal fluctuations in three dimensions remains unclear. Some research groups calculate the critical buckling force approximately and conclude that, in opposite to 2D case, in 3D the force is decreased by thermal fluctuations. In this work the critical buckling force for semiflexible chain under compression was calculated exactly. It was shown that thermal fluctuations significantly increase the critical force over classical Euler buckling force in both two and three dimensions.
Ph.D. in Chemical Engineering, May 2015
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- Title
- CO2 CAPTURE AND HYDROGEN PRODUCTION IN SORBENT ENHANCED WATER-GAS SHIFT (SEWGS) PROCESS WITH REGENERABLE SOLID SORBENT
- Creator
- Zarghami Khanehsar, Shahin
- Date
- 2015, 2015-07
- Description
-
Carbon dioxide emission from fossil fuel combustion and its impact on global warming is one of the most critical environmental issues nowadays...
Show moreCarbon dioxide emission from fossil fuel combustion and its impact on global warming is one of the most critical environmental issues nowadays. Coal as a main source of produce energy is the most CO2-intensive fossil fuel. Advanced power generation processes that use gasification technology, such as Integrated Gasification Combined Cycle (IGCC), which offer higher efficiency, are among the leading contenders for power generation in the 21st century. In an IGCC process, because of high pressure, carbon dioxide in the fuel gas is at higher concentration, which can be captured and sequestered at lower costs. Utilization of regenerable MgO-based sorbents has been shown to be an effective method for capturing CO2 from gasification-based processes at elevated temperatures and pressures (i.e. p > 20 atm and 330° < T < 450°C). Low cost MgO based sorbent can be prepared through modification of natural dolomite. The reactivity of the sorbent in carbonation/regeneration cycles has a significant impact on the economics of the proposed regenerable process. Although the sorbent can be regenerated in successive cycles, the sorbent reactivity and capacity gradually decline during the cyclic process. Therefore, it is crucial to develop a better understanding on the role of the key parameters affecting the reactivity of the sorbent going through the cyclic carbonation/regeneration process. In this work, a systematic study on the sorbent preparation parameters (i.e., calcination temperature, calcination duration, calcination temperature ramp, potassium concentration, impregnation duration, drying temperature, re-calcination temperature, and re-calcination duration) was conducted to understand the effect of each parameter on the overall capacity and reactivity of the sorbent. The concentration of potassium additive (as carbonation reaction promoter) has the most significant effect on the reactivity of the sorbent and the optimum K/Mg molar ratio appears to be in the range of 0.1-0.16. The reactivity of the sorbent toward carbon dioxide at various operating conditions (i.e. temperature, CO2 concentration and steam concentration) was experimentally evaluated. The presence of steam significantly improves the reactivity of the sorbent which is attributed to formation of more favorable pore structure as well as the existence of a parallel carbonation reaction pathway involving the formation of a transient MgO.H2O* compound. The optimum carbonation reaction temperature in the presence of steam is around 380˚C. The effect of cycling on CO2 capture capacity of MgO-based sorbent was also experimentally investigated in this work. Series of carbonation/regeneration cycles (up to 25) have been carried out in a dispersed bed reactor to determine the effect of various variables on long term durability of the sorbent. The gradual loss of CO2 sorption capacity appears to be mainly due to loss potassium (a carbonation reaction promoter) in the cyclic process. Durability of the sorbents improves in the presence of steam, which is likely due to the favorable changes in the pore structure of the sorbents. A kinetic model was developed to fit the reactivity curves obtained from the dispersed bed tests at different operating conditions which was needed to predict the sorbent/catalyst performance in the regenerative process. Model parameters were defined and discussed for each of the operating conditions, as well as dispersed bed cyclic tests. Furthermore, the thermal behavior and the kinetics of partial decomposition of dolomite were studied in a dispersed-bed reactor to improve the reactivity of the sorbent. The microstructure and the nature of the solid products were found to be strongly dependent on the CO2 partial pressure near the reacting interface and on the decomposition temperature. A significant increase in the rate of the dolomite decomposition reaction was found in the presence of steam. Steam improves the kinetics of decomposition, modifies the radial distribution of the pores; and improves the connectivity of the pores inside the dolomite particles, which decreases the diffusion resistance of produced carbon dioxide inside the particle. A shrinking core model with variable product layer diffusivity was used to fit the experimental data and determine the kinetic parameters of the dolomite decomposition reaction. The results indicate that transport of CO2 across the reacting interface in the porous particle was the main limiting factor in the decomposition reaction at the experimental conditions investigated. A lab-scaled high-pressure/high-temperature packed-bed reactor was utilized to evaluate the performance of the sorbent in simultaneous water-gas shift reaction and sorbent carbonation environment. It was shown that the CO2 in the coal gas can be removed by regenerable MgO-based sorbents at temperatures around 350°C, and the CO2 removal can shift WGS reaction to enhance hydrogen production. Therefore, Sorbent Enhanced Water-Gas-Shift (SEWGS) can result in much higher hydrogen production without lowering the temperature, leading to higher overall process efficiency.
Ph.D. in Chemical Engineering, July 2015
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- Title
- PEGYLATION OF FIBRONECTIN AND ITS FUNCTIONAL DOMAINS: EFFECT ON STABILITY AND BIOLOGICAL ACTIVITY
- Creator
- Zhang, Chen
- Date
- 2013, 2013-07
- Description
-
Delayed wound healing in many chronic wounds has been linked to the lack of extracellular matrix (ECM) support and the degradation of...
Show moreDelayed wound healing in many chronic wounds has been linked to the lack of extracellular matrix (ECM) support and the degradation of fibronectin (FN) by an abnormally high protease level. The ECM is important in wound healing because it provides physical and chemical cues that direct tissue growth and development. FN is a key ECM protein that attracts and binds different molecules and cells and thereby supports biological responses associated with wound healing. The goal of my study is two fold: (1) To create an ECM analogue based on a composite of polyethylene glycol (PEG) hydrogels and FN binding domains and (2) To stabilize FN against proteolytic degradation by conjugating it to PEG. To address the first goal, I used Michael addition chemistry to covalently link the cell-binding domain of FN, III9−10, to PEG diacrylate and cross-linked the conjugate to PEG hydrogels. The conjugation of PEG to III9−10 was through cysteines in the affinity tag Glutathione S Transferase (GST). The conjugate of GST-III9−10 and PEG was characterized by: (i) Circular dichroism studies to determine secondary structure, (ii) Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) to determine molecular weight, and (iii) Ellmans reagent to determine the efficiency of PEG conjugation to GST-III9−10. The conjugate of PEG and GST-III9−10 had comparable secondary structure to GST-III9−10. SDS-PAGE studies showed that up to three PEG molecules were attached to one GST-III9−10 molecule. The efficiency of PEG conjugation was greater than 90% and occurred within 30 minutes after PEG diacrylate addition. Adhesion assays were used as a metric of biological activity. These assays demonstrated that on a molar basis cell adhesion and spreading were significantly higher on PEG hydrogels with GST-III9−10 than those with the commonly used arginine-glycine-aspartic acid (RGD) peptide. Scaffold rigidity is an important biological cues that influence xi cell responses. However, a comparative study of rigidity on GST-III9−10 and RGD functionalized PEG hydrogels demonstrated that differences in rigidity could not account for differences in cell adhesion and spreading between RGD and GST-III9−10 functionalized PEG hydrogels. Thus as ECM analogues, GST-III9−10 functionalized hydrogels provide more robust biochemical cues than RGD functionalized hydrogels. Studies of PEG hydrogel composites with mixtures of III9−10 and a fibronectin binding domain demonstrated that biological responses of adhesion and spreading and extracellular matrix assembly could be controlled by varying the ratio of these two domains and the rigidity of the PEG hydrogels. FN was stabilized against proteolytic degradation by covalent attaching it to PEG or by PEGylating it. FN was first isolated from human plasma by gelatin affinity chromatography and then PEGylated using two methods. The first method is to PEGylate human plasma fibronectin (HPFN) at cysteine residues with 3.4 kDa PEG diacrylate. The second method is to PEGylate HPFN at lysine residues on the surface with 2-10 kDa PEG Succinimidyl carboxy methyl esters. Cysteine PEGylation of HPFN was first carried out because cysteines are concentrated in the amino- terminus of HPFN which leaves two-thirds of the molecule, including the cell-binding domain, unperturbed. PEGylation of HPFN on cysteines resulted in a molecule that supported cell adhesion, spreading, focal adhesion formation and cell migration in a comparable manner to native HPFN. Moreover, PEGylated HPFN was incorporated into the ECM in a similar manner to native HPFN when present in the culture media but not when coated on a surface indicating that PEGylation on cysteines modified some biological activity of HPFN. Additionally, HPFN PEGylated by this manner could not bind denatured collagen or gelatin. The gelatin-binding domain is at the site of cysteine PEGylation. The second approach for PEGylation of HPFN was through lysine residues xii on the surface of the protein. This approach was used because it targeted different amino acid residues in FN. The length of PEG and extent of PEGylation have been reported to influence biological activity of proteins. In the second approach, both PEG length and extent were varied. HPFN completely PEGylated on lysines residues was significantly more proteolytically stable than native HPFN but had reduced cell attachment and spreading. Furthermore, cell spreading and attachment on surfaces conjugated with this lysine PEGylated HPFN decreased with increasing PEG length. Partially PEGylated HPFN was synthesized by masking the cell and gelatin binding domains during PEGylation. The partially PEGylated HPFN supported cell adhesion and spreading in a similar manner to native HPFN and was more proteolytically stable. For the partially PEGylated HPFN, the size of PEG poly had no significant influence on the attachment and spreading of cells. These studies are the first attempt by any laboratory to stabilize FN against proteolytic degradation while retaining activity and show the feasibility of this approach as a potential therapeutic approach. The work presented here shows a two-prong approach by which the problem of ECM degradation and deficiency chronic wound healing can be addressed. The first approach for addressing ECM deficiency is through a scaffold design methodology. The novelty of the scaffold approach is that it uses the cell-binding domains of FN instead of the often-used RGD peptide. I demonstrate that a PEG hydrogel with the cell-binding domain produces a more robust biological response in cells than a PEG hydrogel with the RGD peptide. I also demonstrate that varying different functional domains of fibronectin can be used to controllably stimulate multiple biological responses. The second approach demonstrates a method by which FN, a key ECM protein, is stabilized against proteolytic degradation without perturbing its activity. These studies of creating PEG-FN conjugates are the first of their kind. Collectively, the data that I present in this thesis will lead to novel therapeutic methods for treating chronic wounds.
PH.D in Chemical Engineering, December 2012
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- Title
- A METHODOLOGY FOR UTILIZATION OF DEGRADED WATER IN THERMOELECTRIC POWER PLANT COOLING SYSTEMS
- Creator
- Safari, Iman
- Date
- 2013, 2013-12
- Description
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The overall objective of this study was to develop a comprehensive methodology to identify viable treatment strategies for utilization of...
Show moreThe overall objective of this study was to develop a comprehensive methodology to identify viable treatment strategies for utilization of degraded waters for cooling in thermoelectric power systems. To achieve this objective a process simulation model was developed using Aspen Plus® with the OLI (OLI System, Inc.) water chemistry model to predict water quality and the rate of fouling in the recirculating cooling loop utilizing secondary-treated municipal wastewater (MWW) and tertiary-treated municipal wastewater as the sources of makeup water. This process simulation model includes sub- models for pre-treatment units; the cooling tower with water, CO2, and NH3 evaporation; as well as the recirculating cooling system and condenser with salt precipitation and fouling. The input parameters of the model, including CO2 mass transfer coefficients in the cooling tower and kinetics of salts precipitation reactions, were determined by developing mathematical models and calibrating the models with the experimental data obtained from literature. The process simulation module was used to predict the water quality in the recirculating cooling loop and the results were compared with pilot-scale experimental data from literature on makeup water alkalinity, loop pH and ammonia evaporation. The effects of various parameters including makeup water quality, salt formation, NH3 and CO2 evaporation mass transfer coefficients, heat load and operating temperatures were investigated. The results indicate that stripping of CO2 and NH3 in the cooling tower can significantly affect the cooling loop pH. x viii The model was also used to determine the rate of fouling in the condenser. The results indicate that the fouling rate of MWW as makeup water is significantly higher than that expected with fresh water, and tertiary treatment of MWW such as nitrification and/or softening can significantly reduce the fouling potential. Finally, the rate of fouling obtained from this study was integrated into the existing cost model developed earlier (at Illinois Institute of Technology) to perform the overall economic analysis. The results show that the use of municipal wastewater (MWW) to replace freshwater as makeup for the recirculating cooling loops of thermoelectric power plants is economically viable when tertiary treatments such as nitrification or softening are applied. Among various treatment strategies studied, nitrification of MWW has the lowest cost of 0.29 $/m3 for utilization in a 550 MW power plant. Furthermore, it was concluded that utilization of secondary treated municipal wastewater (MWW) without tertiary treatments such as nitrification or softening is not economically viable due to its significant fouling costs.
PH.D in Chemical Engineering, December 2013
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- Title
- RHEOLOGY OF ENTANGLED POLYMER LIQUIDS IN EQUIBIAXIAL ELONGATIONAL FLOWS
- Creator
- Mick, Rebecca M.
- Date
- 2015, 2015-05
- Description
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Equibiaxial deformation is an important flow in industrial processes such as film blowing and blow molding. Unfortunately, it is very...
Show moreEquibiaxial deformation is an important flow in industrial processes such as film blowing and blow molding. Unfortunately, it is very difficult to implement experimentally which has led to empirical design of these processes. A technique called continuous lubricated squeezing flow (CLSF) has been developed to perform equibiaxial deformation on systems such as polymer melts. This technique is used in this study to measure the behavior of entangled polymer melts in equibiaxial elongation to further the understanding of these materials in industrially relevant flows. The results of CLSF experiments on three linear chain polymer systems show strain softening for strain rates resulting in Weissenberg numbers, Wi = ε˙Bτd > 1. Higher rates lead to greater softening. The deviation from the linear viscoelastic (LVE) prediction occurs at about a strain of one for all the materials. Equibiaxial and shear behavior were compared for two monodisperse linear systems. When normalized by LVE behavior, the two flows yield similar behavior such that the equibiaxial rheology could be inferred from shear rheology. Unfortunately, polydisperse linear and branched systems did not show the same behavior. The two monodispere systems were compared to the GLaMM and Discrete Slip-Link molecular theories. Neither model could successfully predict the equibiaxial behavior; both predicted excessive strain softening and a premature deviation from LVE. Recent literature has suggested that based on uniaxial measurements, dilution changes the behavior of an entangled polymer system. This is contrary to theories of polymer dynamics. A pure melt and diluted melt with the same entanglement density were compared in shear and equibiaxial flows after adjusting for changes in friction. The results were consistent with universality principles of entangled polymers; the uniaxial results require further investigation.
Ph.D. in Chemical Engineering, May 2015
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- Title
- THE EFFECT OF NANOPARTICLE SELF-STRUCTURING ON WETTING AND SPREADING OF NANOFLUIDS ON SOLID SURFACES
- Creator
- Kondiparty, Kirtiprakash
- Date
- 2011-11, 2011-12
- Description
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Nanofluids are suspensions of nanometer-sized particles in liquids. The nanoparticles self-structure at the three-phase contact region...
Show moreNanofluids are suspensions of nanometer-sized particles in liquids. The nanoparticles self-structure at the three-phase contact region resulting in the structural disjoining pressure gradient which causes enhanced the spreading of nanofluids compared to simple fluids without nanoparticles. In this thesis, we attempt to understand the effect of the structural disjoining pressure on the spreading dynamics of nanofluids on solid surfaces. We observed nanoparticle self-structuring phenomena during film thinning on a smooth hydrophilic glass surface using a silica-nanoparticle aqueous suspension and reflected light interferometry. Our experiments revealed that film formed from small drop is thicker and contains more particle layers than a film formed from large drop. The data for the film-meniscus contact angle verses film thickness were obtained and used to calculate the structural energy isotherm of an asymmetric film. We studied the effect of structural disjoining pressure on the wedge meniscus profile formed by an oil drop on solid surface surrounded by nanofluid using Laplace Equation augmented with the structural disjoining pressure. Our analyses indicate that a suitable combination of the nanoparticle concentration, nanoparticle size, contact angle, and capillary pressure can result not only in the displacement of the three-phase contact line, but also in the spontaneous spreading of the nanofluid as a film on solid surface. We validated our theoretical predictions using experiments where we observed spreading of nanofluid on glass surface displacing a sessile drop of canola oil. The dynamic spreading of the nanofluid on a solid surface between a sessile oil drop on solid surface was experimentally measured using reflected light microscopy. We xiv obtained the rate of nanofluid spreading by plotting the position of the inner contact line with time. The nanofluid film was found to spread at a constant velocity. We modeled the spreading dynamics of the nanofluid film using the lubrication approximation of the Navier-Stokes Equation, taking into consideration the structural disjoining pressure in the over-all pressure balance. The model was evaluated by estimating the rate of nanofluid spreading for the 10v% nanofluid. The rate of spreading thus predicted by the dynamics model for 10v% nanofluid was in good agreement with the experimental observations.
Ph.D. in Chemical Engineering, December 2011
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- Title
- STABILITY OF AQUEOUS FOAMS: FOAM FILM STRATIFICATION PHENOMENON AND THE EFFECTS OF DISPERSED VERSUS SOLUBILIZED OIL
- Creator
- Lee, Jongju
- Date
- 2016, 2016-05
- Description
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A foam is a system consisting of a concentrated dispersion of gas bubbles in a liquid. Foams are encountered in many industries such as food,...
Show moreA foam is a system consisting of a concentrated dispersion of gas bubbles in a liquid. Foams are encountered in many industries such as food, agriculture, chemicals, petroleum, and paper manufacturing. Aqueous foams are formed by using surfactants or nano-colloidal particles. Thin liquid films containing surfactant micelles or other nano-colloidal particles are considered to be the key structural elements of foams containing gas and liquid. We thus probed the effects of the micellar concentration and the film size (area) on the stability of a dry bulk foam by studying the stability of a single foam lamella containing micelles; this is so we can establish the importance of the micellar structuring phenomenon and the foam film size (area) affecting the bulk foam stability. The film stratification phenomenon (stepwise film thinning) was experimentally observed by the reflected light microinterferometry. The stepwise layer-by-layer decrease of film thickness is due to the appearance and growth of dark spot (of one layer less film thickness) in the film. We used the two-dimensional diffusion model to model the dynamics of dark spot expansion considering the apparent diffusion coefficient and the film size. Based on this model, we carried out a parametric study depicting the effects of film thickness (or the number of micellar layers) and film area on the rate of dark spot expansion. Many practical applications involving three-phase foams (aqueous foams containing oil) commonly employ surfactants at several times their critical micelle concentration (CMC). We investigated the influence of both the dispersed and solubilized oils, and the surfactant concentration (above CMC) on the stability of an aqueous foaming system. In foam stability, the relative importance of the dispersed oil versus oil solubilized within the micelles depends on the stability of the aqueous asymmetric (i.e., pseudoemulsion) film between the oil and the air-water interface and the second virial coefficient. Also, the micellar structuring phenomenon tests using the single foam lamella revealed that the multi-layering structure was well pronounced in the absence of the solubilized oil; as a consequence, the foam lamellae thinned slowly layer-by-layer and the oil solubilized in micelles weakened the micellar structure formation. The foam lamellae thinned faster, making the foam less stable.
Ph.D. in Chemical Engineering, May 2016
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- Title
- MODELING AND COMPUTATIONAL FLUID DYNAMICS SIMULATION OF A BUBBLING FLUIDIZED BED PROCESS AT DIFFERENT SCALES
- Creator
- Jang, Jungkee
- Date
- 2012-11-14, 2012-12
- Description
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In recent years there has been increased research activity in the experimental and numerical study of gas-solid flow system in the bubbling...
Show moreIn recent years there has been increased research activity in the experimental and numerical study of gas-solid flow system in the bubbling fluidized bed process. The bubbling fluidized bed process have numerous applications in the energy, pharmaceuticals, and chemicals process industries since it has provides a number of advantages such as large heat capacity inside a bed, and rapid heat and mass transfer rate. A reliable design and scale-up approach for a bubbling fluidized bed process requires a very detailed model based on the fundamentals of multiphase transport phenomena. The present works address the simulation and scale-up of rather complex gas-solid flow behavior in bubbling beds using Computational Fluid Dynamics (CFD) approach. The CFD model developed in this study which is based on two fluid model was used to optimize the performance and utilized as a scale-up tool for an isothermal and a non-isothermal bubbling fluidized bed process. For isothermal case, 2-Dimensional and 3-Dimensional simulations of bubbling beds for both PSRI laboratory and large scales fluidized beds using a kinetic theory approach were performed. The FLUENT code was used to conduct the simulations. Our simulation results were validated and refined by comparing them with the laboratory-scale experimental data of PSRI. Then, our modified 2-D and 3-D CFD models were used to predict the large-scale PSRI bubbling fluidized bed performance at different operating conditions. In our 3-D simulations, we used exactly the same bed dimensions and inlet configurations (such as air distributor) as the experimental one to predict the characteristics of gas-solid flow patterns in the PSRI large-scale bubbling fluidized bed. The numerical simulation results compared well with both PSRI large scale experimental xx data on pressure drop and time-averaged void fraction near the wall, which could be a very good proof for demonstrating the capability of CFD as a tool to be used in the design and scale-up of bubbling fluidized bed systems. For non-isothermal case, the set of equations necessary to describe the flow patterns and heat/mass transfer phenomena of bubbling beds at three different scales were developed. CFD simulations were performed to investigate the characteristics of pharmaceutical particle drying process in bubbling fluidized beds at three different scales (e.g., lab, kilo, and 10-kilo scales). The results of CFD simulation were compared with the experimental data obtained at laboratory-scale (Duquesne University experiments), to validate and refine our CFD model. The modified model was used to simulate the drying of the same material in Abbott laboratory kilo and 10-kilo scale units. Our simulation results for solid particles drying as a function of dimensionless time showed that our CFD model along with similar dimensionless group similarity approach can be used as a tool to scale-up the drying process from experimental scale to both kilo-scale and 10-kilo scale fluidized bed dryer. Moreover, to determine the optimum particle mixing, numerical simulations were performed at different particle diameters, bed heights, inlet velocities and inlet velocity distributions, respectively. The numerical simulation results compared well with the experimental data (performed by Duquesne University and Abbott laboratory) on moisture removal rate and outlet gas temperature. This also could be a very good proof for demonstrating the capability of CFD as a tool to be used in the design and scale-up of non-isothermal bubbling fluidized bed processes.
PH.D in Chemical Engineering, December 2012
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- Title
- INVESTIGATION OF PERFORMANCE AND DURABILITY OF POLYMER ELECTROLYTES FOR ELECTROCHEMICAL ENERGY STORAGE AND CONVERSION TECHNOLOGIES
- Creator
- Jung, Min-suk
- Date
- 2016, 2016-07
- Description
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Polymeric ion exchange membranes are integral components of electrochemical conversion/storage devices such as fuel cells, water electrolyzers...
Show morePolymeric ion exchange membranes are integral components of electrochemical conversion/storage devices such as fuel cells, water electrolyzers, and redox flow batteries. There has been dramatic progress in the research and development of cation exchange membranes (CEM). Nafion® (perfluorosulfonic acid membranes) is one example of a state-of-the-art CEM and has been successfully demonstrated in various electrochemical energy devices. Unlike CEMs, anion exchange membranes (AEMs) have been of limited utility to date due to their drawbacks, including poor chemical/mechanical stability and low ionic conductivity. However, alkaline environments result in better activity for electrochemical reactions and afford the possibility of using non-platinum group metal (PGM) electrocatalysts. AEMs, therefore, are still being studied in order to resolve existing challenges in terms of conductivity and stability in alkaline media and in strongly oxidizing solutions. In this work, AEMs derived from different types of polymer backbones were prepared, and their chemical stability and electrochemical property were investigated. Polysulfone (PSF) AEMs were prepared by first chloromethylating polysulfone, then by functionalizing chloromethylated polysulfone (CMPSF) with different base reagents. PSF-trimethylamine (TMA) AEMs showed a 40-fold reduction in vanadium (IV) ion (VO2+) permeability when compared to a Nafion® membrane and exceptional oxidative stability after exposure to a 1.5 M vanadium (V) ion (VO2 +) solution for 90 days. PSF-TMA AEMs were successfully demonstrated in the all-vanadium redox flow battery. Excellent energy efficiencies (>75 %) were attained and sustained over 75 chargedischarge cycles for a vanadium redox flow battery prepared using the PSF-TMA separator. Crosslinking of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) AEMs using diamine was tried with intentions to improve the mechanical stability and electrochemical property of PPO AEM. Crosslinked PPO AEMs (30 ± 4 % at 25 oC) showed less liquid water uptake than non-crosslinked PPO AEMs (46 ± 5% at 25 oC) while maintaining comparable ionic conductivities (hydroxide ion conductivity of 45 mS/cm at 60 oC). Crosslinked PPO AEMs maintained mechanical integrity and still showed some mechanical stability (ultimate tensile strength of 3~4 MPa and elongation at break of 13~17 %) after exposure to 1 M KOH at 60 oC for 14 days, while noncrosslinked PPO AEMs completely lost their mechanical durability. Finally, this dissertation presents research related to perfluorinated AEMs prepared using a Grignard reagent. These membranes exhibited 0.7 mmol/g of Cl- ion exchange capacity (IEC), 20 mS/cm of hydroxide ion conductivity at 20 oC, and 10 % of water uptake at room temperature. The membranes also maintained 90 % of their initial conductivity after an exposure to 1.5 M VO2+ in 3 M H2SO4 solution for seven days.
Ph.D. in Chemical Engineering, July 2016
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- Title
- Thermoelectric Power Systems and the Energy-Water Nexus
- Creator
- Walker, Michael Edward
- Date
- 2012-04-26, 2012-05
- Description
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The goal of this Thesis is the development of a comprehensive methodology to evaluate the total cost of water use in the recirculating cooling...
Show moreThe goal of this Thesis is the development of a comprehensive methodology to evaluate the total cost of water use in the recirculating cooling loops of thermoelectric power plants. This methodology expands upon the work presented in the literature to improve estimations of the economic impact of condenser fouling. The methods developed in this Thesis are incorporated into a user friendly Combined Cost Model (CCM) interface that will allow future researchers, students and plant personnel to perform the same comparative analyses presented herein. The objective of this Thesis is the application of the CCM to determine the economic viability of treated municipal wastewater (MWW) use to replace freshwater for cooling in power plants with recirculating cooling systems. To accomplish this objective, a set of case study evaluations are included to (1) evaluate the sensitivity of the economic impact of fouling to condenser design and operation, (2) determine the cost of treated MWW use in pulverized coal power plants, and (3) compare the relative cost of degraded water use in advanced power systems such as IGCC and oxy-combustion. The results of these evaluations show that current freshwater prices do not provide an economic incentive to switch to the use of treated MWW water. However, results indicate that the breakeven differential price of freshwater, at which the total costs of using freshwater and treated MWW are equal, is only 0.52 $/1000Gal. (USD 2009). In addition, the use of treated MWW for cooling is shown to be a better economic alternative to dry air cooling technology (DACT) for the conservation of freshwater resources. Cost-to-conservation estimates of treated MWW use are 1.1 $/1000 Gal., in contrast to 5.6 $/1000 Gal. for DACT. This Thesis also presents a novel, hybrid coal conversion concept, the dry gasification oxy-combustion (DGOC) power cycle. This process is similar to oxycombustion, in that it maintains a concentrated CO2 flue stream and does not utilize a complex separation step. However, coal conversion and sulfur removal are performed within a gasification unit. It is estimated to achieve CCS goals with a higher efficiency than the leading alternative strategies.
Ph.D. in Chemical Engineering, May 2012
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- Title
- ANISOTROPIC MICROSRHEOLOGY OF SELF-ASSEMBLING COLLAGEN NETWORKS
- Creator
- Dutov, Pavel
- Date
- 2015, 2015-05
- Description
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Collagen is the main component of human connective tissue and extracellular matrix. Here we report multiple novel methods for utilizing...
Show moreCollagen is the main component of human connective tissue and extracellular matrix. Here we report multiple novel methods for utilizing optical tweezers to measure mechanical properties of different hierarchical levels of collagenous materials. First, we introduce a method for optical trap calibration that is suitable for viscoelastic material. The method is designed for use on experimental setups with two optical tweezers and is based on pulling a trapped particle with one trap while holding it with the other. The method combines advantages of commonly known PSD-fitting and fast-sweeping methods, allowing calibration of a completely fixed trap in a fluid of unknown viscosity/viscoelasticity without additional expensive equipment. Then we report an approach to measure the longitudinal component of the elastic moduli of biological fibers under conditions close to those found in vivo and apply it to type I collagen from rat tail tendon. This approach combines optical tweezers, atomic force microscopy, and exploits Euler-Bernoulli elasticity theory for data analysis. The approach also avoids the traditional drying-soaking cycle, since samples are freshly extracted. Importantly, strains are kept below 0.5%, which appear consistent with the linear elastic regime. We find, surprisingly, that the longitudinal elastic modulus of type I collagen cannot be represented by a single quantity but rather is a distribution that is broader than the uncertainty of our experimental technique. Lastly, we report a new method for characterizing anisotropic viscoelastic response of collagenous matrices. Anisotropic collagenous extracellular matrices are used in biomedicine to enhance the wound healing process by directing fibroblast proliferation. We utilize an optical trap to monitor the thermal fluctuations of microspheres embedded into collagenous network to extract a viscoelastic response function of the network along the principal axes of anisotropy.
Ph.D. in Chemical Engineering, May 2015
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- Title
- DRUG UPTAKE AND RELEASE BY STIMULI RESPONSIVE CYLINDRICAL AND SPHERICAL GELS
- Creator
- Ninawe, Pravin Ramkrishna
- Date
- 2011-08, 2011-07
- Description
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ABSTRACT Polymeric gels that undergo deformation upon appropriate changes in pH or temperature have considerable promise as drug delivery...
Show moreABSTRACT Polymeric gels that undergo deformation upon appropriate changes in pH or temperature have considerable promise as drug delivery vehicles. Uptake of drug macromolecules into swelling and non-swelling cylindrical and spherical gels and release of drug macromolecules from deswelling and non-deforming gels into a target fluid are investigated here. A mathematical model for gel-solution composite, a composite of a distributed parameter system (gel spheres or cylinders) and a lumped parameter system (surrounding solution), is developed. The polymer network displacement in swelling/deswelling gels is described by a stress diffusion coupling model. The analytical solution for network displacement is used to predict solvent intake by swelling gels, solvent efflux from deswelling gels, and changes in pressure, porosity and effective drug diffusivity resulting from network displacement. These in turn influence drug uptake during and after gel swelling and drug release from gel during and after gel deswelling. Numerical results illustrate benefits of gel swelling for drug loading and merits of different modes of drug release. Also, the attempt is made to analyze he effect of gel mesh size on the loading and release of large molecular weight drugs. Comparisons are made, as concerns drug uptake and drug release, with gels not subject to deformation. As a special case of application of the above developed model, we tried to simulate drug delivery to the human eye. Since, the therapeutic modalities for posterioreye diseases involve mostly interventions through the anterior eye, which are difficult for physicians and patients alike, sustained drug delivery to the posterior eye is gaining importance. A study for sustained delivery of an anti-VEGF agent (IgG) to the posterior eye from an implant, made of poly(N-isopropylacrylamide) (NIPAM) and placed episclerally, is presented. The model developed in the study is used to simulate the phase transition of the implant made of a thermo-sensitive polymer. The study xvii utilizes compartments for various eye tissues, with individual compartments considered to be completely mixed and drug transport between compartments occurring by one-dimensional diffusion. Further implementation of this model to predict drug concentrations in the eye tissues to arrive at optimum drug loading conditions is also presented here.
Ph.D. in Chemical Engineering, July 2011
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- Title
- INVESTIGATION OF OXIDATIVE DEGRADATION AND DEGRADATION MITIGATION IN POLYMER ELECTROLYTE FUEL CELLS USING IN-SITU FLUORESCENCE SPECTROSCOPY
- Creator
- Prabhakaran, Venkateshkumar
- Date
- 2014, 2014-05
- Description
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Hydrogen/air polymer electrolyte fuel cells (PEFCs) possess high efficiency and modularity. However, significant technical advances are...
Show moreHydrogen/air polymer electrolyte fuel cells (PEFCs) possess high efficiency and modularity. However, significant technical advances are required to facilitate their commercialization in targeted applications. A key issue is component durability under an array of adverse operating conditions. The polymer electrolyte membrane (PEM) in a PEFC is one of the components whose long-term durability is of concern since it undergoes mechanical, thermal, and chemical degradation during fuel cell operation. The chemical (oxidative) degradation processes that take place in a PEM are attributed to reactive oxygen species (ROS) that are generated in-situ during PEFC operation. It is essential to quantify the rate of ROS generation within the PEM during PEFC operation prior to proposing an effective degradation mitigation strategy. This is a daunting challenge, given the high reactivity and very short lifetime of these species. The rate of generation of ROS within the PEM of an operating PEFC was accurately measured, for the very first time, using in-situ fluorescence spectroscopy. The influence of fuel cell operating parameters (temperature, relative humidity, and electrode potential/current density) on the rate of ROS generation was studied. The ROS generation reaction rate constant (estimated from the in-situ fluorescence experiments) correlated perfectly with the macroscopic rate of PEM degradation (estimated from the ex-situ fluoride emission rate) across all conditions, demonstrating unequivocally for the first time that a direct correlation existed between in-situ ROS generation and PEM macroscopic degradation. The utility of using regenerative free radical scavengers (FRS) such as CeO2 nanoparticles to mitigate ROS induced PEM degradation was also demonstrated using xxii xxii in-situ fluorescence spectroscopy. Though CeO2 was shown to scavenge the generated ROS, its scavenging efficacy declined with time and hence it was not truly a regenerative scavenger. The FRS efficacy was found to scale with the number of surface oxygen vacancies in its non-stoichiometric lattice. The regenerative FRS activity of CeO2 nanoparticles was improved by tuning its lattice via nitrogen doping (N-doping). It was demonstrated that N-doping increased both the number of Ce3+ active clusters in the lattice and the Ce-O bond distance; these structural attributes enhanced the regenerative ROS scavenging activity of CeO2. In addition, the influence of catalyst support on PEM degradation during PEFC operation was studied. A novel and highly corrosion-resistant non-carbon catalyst support (RuO2-SiO2; RSO) developed by our group was compared against a benchmark carbonbased catalyst support (Vulcan XC 72; C). It was found that the ROS generation rate, and hence the macroscopic PEM degradation rate, was lower when RSO was used as the electrocatalyst support in place of C. In conjunction with its remarkable corrosionresistance, this finding further illustrated the viability of RSO as an outstanding PEFC electrocatalyst support. Apart from PEM degradation, the applications of fluorescence spectroscopy in the context of other electrochemical devices was also discussed. Proofof- concept studies to study the Pt dissolution rate (in PEFC electrodes) and vanadium crossover rate (in vanadium redox flow batteries) were successfully undertaken; these areas, along with probing degradation processes secondary batteries, would be rich grounds for future study.
PH.D in Chemical Engineering, May 2014
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