Theses and Dissertations

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Open Access
A biomechanical analysis of venous tissue in its normal, post-phlebitic, and genetically altered conditions
(Colorado State University. Libraries, 2009) McGilvray, Kirk Cameron, author; Puttlitz, Christian M., advisor
The incidence of vein disease is very high, affecting more than 2% of the hospitalized patients in the United States; a number that is expected to increase. Post phlebitic veins, the result of chronic deep vein thrombosis, is considered to be one of the most important venous disease pathologies. Unfortunately, little information is currently available on the biomechanical effects of thrombus resolution in the deep veins. The aim of this research was to characterize the biomechanical response of both healthy and diseased venous tissue using a murine model. It was hypothesized that biomechanical response parameters derived from healthy and diseased tissue would give insight into the resultant clinical complications observed in patients following thrombus resolution. Biomechanical analysis revealed that statistically significant deleterious changes in vein wall compliance were observed following thrombus resolution. Data also revealed that matrix metallopeptidase 9 expression has a statistically significant effect on the biomechanical response of the tissue. These results indicate that clinical complications following deep venous thrombosis manifest from significant decreases in the compliance of the vein wall. Finite element analyses were also performed. Biomechanical data served as input material parameters for modeling. Finite element modeling was used to evaluate the response of the inferior vena cava under physiologic loads. The results indicate that peak stresses are generated in the circumferential direction of loading during luminal pressurization. Decreased dilatation was observed following thrombus resolution. The data indicates that deep venous thrombosis lead to increased vein wall stress in correlation with decreased luminal distensability.
Open Access
A calcium aluminate electride hollow cathode
(Colorado State University. Libraries, 2014) Rand, Lauren Paula, author; Williams, John, advisor; Reynolds, Melissa, committee member; Sampath, Walajabad, committee member; Yalin, Azer, committee member
The development and testing of a hollow cathode utilizing C12A7 (12CaO.Al2O3) electride as an insert are presented. Hollow cathodes are an integral part of electric propulsion thrusters on satellites and ground-based plasma sources for materials engineering. The power efficiency and durability of these components are critical, especially when used in flight applications. A low work function material internal to the cathode supplies the electrons needed to create the cathode plasma. Current state-of-the- art insert materials are either susceptible to poisoning or need to be heated to temperatures that result in a shortened cathode lifetime. C12A7 electride is a ceramic in which electrons contained in sub-nanometer sized lattice cages act as a conductive medium. Due to its unique atomic structure and large size, C12A7 electride has a predicted work function much lower than traditional insert materials. A novel, one-step fabrication process was developed that produced an amorphous form of C12A7 electride that had a measured work function 0.76 eV. A single electride hollow cathode was operated on xenon for over 60 hours over a two-month period that included 20 restarts and 11 chamber vent pump-down sequences with no sign of degradation, and on iodine for over 20 hours with no apparent reactivity issues. The operations of cathodes with three different orifice sizes were compared, and their effects on the interior cathode plasma modeled in a zero- dimensional phenomenological model.
Open Access
A computational and experimental study on combustion processes in natural gas/diesel dual fuel engines
(Colorado State University. Libraries, 2015) Hockett, Andrew, author; Marchese, Anthony J., advisor; Hampson, Greg, committee member; Olsen, Daniel B., committee member; Gao, Xinfeng, committee member; Young, Peter, committee member
Natural gas/diesel dual fuel engines offer a path towards meeting current and future emissions standards with lower fuel cost. However, numerous technical challenges remain that require a greater understanding of the in-cylinder combustion physics. For example, due to the high compression ratio of diesel engines, substitution of natural gas for diesel fuel at high load is often limited by engine knock and pre-ignition. Additionally, increasing the natural gas percentage in a dual fuel engine often results in decreasing maximum load. These problems limit the substitution percentage of natural gas in high compression ratio diesel engines and therefore reduce the fuel cost savings. Furthermore, when operating at part load dual fuel engines can suffer from excessive emissions of unburned natural gas. Computational fluid dynamics (CFD) is a multi-dimensional modeling tool that can provide new information about the in-cylinder combustion processes causing these issues. In this work a multi-dimensional CFD model has been developed for dual fuel natural gas/diesel combustion and validated across a wide range of engine loads, natural gas substitution percentages, and natural gas compositions. The model utilizes reduced chemical kinetics and a RANS based turbulence model. A new reduced chemical kinetic mechanism consisting of 141 species and 709 reactions was generated from multiple detailed mechanisms, and has been validated against ignition delay, laminar flame speed, diesel spray experiments, and dual fuel engine experiments using two different natural gas compositions. Engine experiments were conducted using a GM 1.9 liter turbocharged 4-cylinder common rail diesel engine, which was modified to accommodate port injection of natural gas and propane. A combination of experiments and simulations were used to explore the performance limitations of the light duty dual fuel engine including natural gas substitution percentage limits due to fast combustion or engine knock, pre-ignition, emissions, and maximum load. In particular, comparisons between detailed computations and experimental engine data resulted in an explanation of combustion phenomena leading to engine knock in dual fuel engines. In addition to conventional dual fuel operation, a low temperature combustion strategy known as reactivity controlled compression ignition (RCCI) was explored using experiments and computations. RCCI uses early diesel injection to create a reactivity gradient leading to staged auto-ignition from the highest reactivity region to the lowest. Natural gas/diesel RCCI has proven to yield high efficiency and low emissions at moderate load, but has not been realized at the high loads possible in conventional diesel engines. Previous attempts to model natural gas/diesel RCCI using a RANS based turbulence model and a single component diesel fuel surrogate have shown much larger combustion rates than seen in experimental heat release rate profiles, because the reactivity gradient of real diesel fuel is not well captured. To obtain better agreement with experiments, a reduced dual fuel mechanism was constructed using a two component diesel surrogate. A sensitivity study was then performed on various model parameters resulting in improved agreement with experimental pressure and heat release rate.
Open Access
A computational examination of conjugate heat transfer during microchannel flow boiling using finite element analysis
(Colorado State University. Libraries, 2018) Burk, Bryan E., author; Bandhauer, Todd M., advisor; Windom, Bret C., committee member; Henry, Charles S., committee member
As technology advances, electronic components continue to produce more heat while at the same time growing smaller and being arranged in ever more compact packages. This has created the need for new thermal management systems able to both dissipate the large heat loads and meet the diminishing size requirements. Microchannel heat exchangers have become an integral part of such advanced cooling systems as they provide an exceedingly large surface area over which heat transfer can occur while maintaining a diminutive size. Current microchannel devices primarily use single-phase flow to dissipate the heat. As heat loads increase, so too must flow rates. Due to associated issues with extremely large pressure drops and high pumping power requirements, the practical capacity of single-phase microchannel coolers has largely been met. One particularly promising avenue forward is to utilize flow boiling with similar microchannel heat exchanger designs. The very high latent heat of vaporization associated with phase change for many fluids allows for a large amount of heat to be dissipated in flow boiling using a relatively low flow rate as compared to single-phase systems, drastically reducing the issues related to pressure drop. Additionally, two-phase heat transfer is associated with much higher heat transfer coefficients, allowing for smaller heat transfer surface areas (and thus smaller overall devices) and lower driving temperature differences for the same heat removal rates. Microchannel flow boiling studies to date have assumed 1D heat conduction through the heat exchanger material and have developed correlations to predict average heat transfer coefficients. Unfortunately, with the high heat fluxes expected in the near future, and with heat loads being applied at small, localized hotspots, the 1D assumption is no longer valid. Conjugate heat transfer must be considered, and local heat transfer coefficient correlations are necessary for the design of future thermal management systems. This thesis describes a first of its kind computational model that uses finite element analysis to analyze the conjugate heat transfer problem, complete with local heat transfer coefficients. This work serves as both proof of concept and an evaluation of the predictive capabilities of five published heat transfer correlations when applied locally to a high heat flux microchannel heat exchanger that has been previously tested. Modeling results show highly variable local heat flux profiles along the microchannel walls, confirming the need to consider conjugate heat transfer. Significant heat spreading resulted in peak local heat fluxes of roughly 0.5× that of the uniformly applied heat flux with 31.4% - 64.1% of total applied heat dissipated outside the region projected directly above the heater. As determined via local temperature comparisons, the correlation from Agostini and Bontemps provides the best overall agreement with average root mean square temperature differences of 2.6°C, though trends suggest that this difference may increase as heat flux increase further than those values tested here.
Open Access
A computational study of auto ignition, spark ignition and dual fuel droplet ignition in a rapid compression machine
(Colorado State University. Libraries, 2017) Bhoite, Siddhesh, author; Marchese, Anthony J., advisor; Olsen, Daniel B., committee member; Mahmoud, Hussam N., committee member
A series of computational modeling studies were performed using the CONVERGETM computational fluid dynamics (CFD) platform to gain in-depth understanding of the chemically reacting flow field, ignition and combustion phenomena in a various rapid compression machine (RCM) experiments conducted at CSU including homogeneous autoignition, laser ignition and droplet ignition experiments. A three-dimensional, transient computational modeling study was initially performed to examine premixed, homogeneous autoignition of isooctane/air and methane/air mixtures. A reduced chemical kinetic mechanism for isooctane comprising of 159 species and 805 reactions was developed using direct relation graph error propagation and sensitivity analysis (DRGEPSA) method. Computational results showed good agreement with experimental results capturing the negative temperature coefficient (NTC) behavior of isooctane. The premixed computations also revealed the importance of the piston crevice design for maintaining a homogenous flow field inside a RCM. The result showed that, as the volume of the piston crevices is increased, the roll up vortices are eliminated, which reduces the mixing of the lower temperature boundary layer gases with the higher temperature core gases, thereby maintaining the homogeneity of the flow field. Next, three-dimensional computational modeling laser-ignited premixed fuel/air mixtures at elevated temperatures and pressures in the RCM was performed with detailed chemical kinetics (86 species, 393 reactions). For methane/air mixtures, the computational results were compared against previously reported RCM experiments. Computations were also performed on laser-ignited n-heptane/isooctane/air mixtures under similar simulated conditions in the RCM. In the computations, a simulated spark modeled as a localized hotspot was introduced in the center of the combustion chamber resulting in an outwardly propagating flame, which, depending on the fuel reactivity, produced ignition in the end gas upstream of the flame. Methane/air computations were performed at equivalence ratio of 0.4 ≤ Ф ≤ 1.0 for direct comparisons with experimental measurements of instantaneous pressure, flame propagation rate, and lean limit. For compressed temperature of 782 K, a methane/air lean limit of Ф = 0.38 was predicted computationally (combustion efficiency, χ = 0.8), which was in good agreement with the experimental measurement of Ф = 0.43. For n-heptane/isooctane/air computations, auto-ignition of the end gas was predicted depending on the compressed temperature and Octane Number, which suggests the use of the laser ignition/RCM system as a means to quantify fuel reactivity for spark ignited engines. Lastly, RCM experiments in which single n-heptane droplets are suspended and ignited via compression-ignition in a quiescent, high-pressure, high-temperature, lean methane/air environments were simulated using the 86-species dual-fuel chemical kinetic mechanism developed previously. The simulations capture the ignition event in the vicinity of a spherical n-heptane droplet, which bifurcates into a propagating, premixed methane/air flame and stationary n-heptane/air diffusion flame. Comparisons against experimental measurements of droplet gasification rate, premixed flame propagation speed, and non-premixed flame position will be used to develop revised dual-fuel chemical kinetic mechanisms.
Open Access
A direct-reading particle sizer (DRPS) with elemental composition analysis
(Colorado State University. Libraries, 2023) Sipich, James Robert, author; Yalin, Azer P., advisor; Volckens, John, committee member; L'Orange, Christian, committee member; Carter, Ellison, committee member
There is a lack of aerosol measurement technology capable of quantifying, in real-time, the size, concentration, and composition of large inhalable particles with an aerodynamic diameter larger than 20 µm. Aerosols of this size penetrate the upper respiratory system upon inhalation and present surface contamination hazards upon settling. The ability to obtain information on the composition of airborne particles is necessary to identify and control risks from exposure to potentially toxic materials, especially in the workplace. The objective of this work was to validate the performance of a prototype Direct-Reading Particle Sizer (DRPS) that counts and sizes particles via time-of-flight light scattering and determines single-particle elemental composition via Laser-Induced Breakdown Spectroscopy (LIBS). Counting, sizing, and spectral measurement efficiency were evaluated using test aerosols of multiple materials with diameters between 25 and 125 µm. Particle sizing results showed good agreement with optical microscopy images. The relationship between the median aerodynamic diameters measured by the DRPS time-of-flight and optical microscopy was linear (Deming regression slope of 0.998) and strongly correlated (r2 > 0.999). The mean absolute difference between the median aerodynamic diameters measured by the instrument by time-of-flight and microscopy over all 8 test aerosol types was 0.9 µm with a mean difference in interquartile range of 1.9 µm. The prototype sensor uses an optical triggering system and pulsed Nd:YAG laser to generate a microplasma and ablate falling particles. Particle composition is determined based on collected emission spectra using a real-time material classification algorithm. The accuracy of the composition determinations was validated with a set of 1480 experimental spectra from four different aerosol test materials. We have studied the effects of varying detection thresholds and find operating conditions with good agreement to truth values (F1 score ≥ 0.9). Details of the analysis method, including subtracting the spectral contribution from the air plasma, are discussed. The time-of-flight aerodynamic diameter measurement and LIBS elemental analysis capabilities demonstrated by the DRPS provide a system capable of both counting, sizing, and identifying the composition of large inhalable particles.
Open Access
A dynamic engineering model of algal cultivation systems
(Colorado State University. Libraries, 2017) Compton, Samuel Lighthall, author; Quinn, Jason C., advisor; Marchese, Anthony, committee member; Peers, Graham, committee member
Proper assessment of the sustainability of algal products is constrained by the onerous process of pilot-scale experimental study. This study developed a bulk growth model that utilizes strain characterization, geospatial data, and cultivation platform geometry to predict productivity across different outdoor systems. The model interprets a minimum of measureable algal strain characteristics along with characteristics of the growth architecture to calculate a time-resolved algal concentration. Validation of the model illustrates an average accuracy of 7.33%+/5.65% for photobioreactors (PBR) and 6.7%+/5.33% for an open raceway pond (ORP) across five total species: Chlorella vulgaris, Desmodesmus intermedius, Galdieria sulphuraria, Galdieria sulphuraria Soos, and Nannochloropsis oceanica. The validated model assesses productivity at several locations in the United States with Chlorella vulgaris, grown in open raceway ponds and Galdieria sulphuraria grown in vertical flat panel photobioreactors. The model investigates seasonal variability through geospatially and temporally resolved extrapolation.
Open Access
A fine resolution CDF simulation approach for biomass cook stove development
(Colorado State University. Libraries, 2011) Miller-Lionberg, Daniel David, author; Willson, Bryan, advisor; DeFoort, Morgan, committee member; Sakurai, Hiroshi, committee member; Volckens, John, committee member
More than half of the world's population meets cooking and heating needs through small-scale biomass combustion. Emissions from these combustion processes are a major health hazard and air pollution concern. Simple improvements over traditional cooking fires have been shown to increase combustion and heat transfer efficiency while reducing physically harmful gaseous and particulate matter (PM) emissions. Over approximately 30 years of modern stove development history, designs have largely been based on empirical guidelines, and attempts at improvements have been made through an iterative, trial-and-error approach. Feedback in this design process is typically attained through bulk measurements made during experimental testing of prototypes. While important for assessing the performance of a stove, such testing offers no information on the fine spatial or temporal scales of phenomena within the stove, leaving it a "black box" in the view of the designer. Without higher resolution information, the rate and ultimate level of design improvement may be limited. In response, a computational fluid dynamic (CFD) simulation of a common, production cook stove is conducted using ANSYS FLUENT 13.0 software. Aspects critical to achieving high spatial and temporal resolution flow and temperature field results are included, enabled by necessary simplifications to less important elements. A model for the steady, time-averaged drying and pyrolysis of wood stick fuel is used in conjunction with a consideration for the simultaneous oxidation of the resulting char, to generate gas-phase fuel boundary conditions for the simulation. Fine spatial and temporal resolution are simultaneously possible in an unsteady formulation with the use of the simplified fuel condition, reduced-mass solid boundaries, and abbreviated runtimes. Employment of a large eddy simulation (LES) turbulence model is proposed as necessary to realistically consider the larger scales of gas mixing. Combustion heat release is approximated by reactions dictated by a mixture fraction formulation, assuming equilibrium conditions in a non-adiabatic system, affected by turbulent fluctuations through a probability density function (PDF). Sensitivity studies are conducted on grid parameters, boundary condition assumptions, and the duration of simulation runtime necessary to achieve result significance. A model for particulate emission formation is secondarily explored. A thermocouple-instrumented stove is used in an experiment to generate internal gas temperature profiles for the validation of the CFD simulation through comparable results. Likewise, a heat-exchanger integrated into a cooking pot is employed with the instrumented stove to measure short time-scale heat transfer values that are compared to the CFD simulation results, as well as to benchmark test data from the production stove. Recommendations for future efforts in stove simulation are made.
Open Access
A fourth-order finite volume algorithm with adaptive mesh refinement in space and time for multi-fluid plasma modeling
(Colorado State University. Libraries, 2022) Polak, Scott E., author; Gao, Xinfeng, advisor; Guzik, Stephen, committee member; Tomasel, Fernando, committee member; Ghosh, Debojyoti, committee member; Bangerth, Wolfgang, committee member
Improving our fundamental understanding of plasma physics using numerical methods is pivotal to the advancement of science and the continual development of cutting-edge technologies such as nuclear fusion reactions for energy production or the manufacturing of microelectronic devices. An elaborate and accurate approach to modeling plasmas using computational fluid dynamics (CFD) is the multi-fluid method, where the full set of fluid mechanics equations are solved for each species in the plasma simultaneously with Maxwell's equations in a coupled fashion. Nevertheless, multi-fluid plasma modeling is inherently multiscale and multiphysics, presenting significant numerical and mathematical stiffness. This research aims to develop an efficient and accurate multi-fluid plasma model using higher-order, finite-volume, solution-adaptive numerical methods. The algorithm developed herein is verified to be fourth-order accurate for electromagnetic simulations as well as those involving fully-coupled, multi-fluid plasma physics. The solutions to common plasma test problems obtained by the algorithm are validated against exact solutions and results from literature. The algorithm is shown to be robust and stable in the presence of complex solution topology and discontinuities, such as shocks and steep gradients. The optimizations in spatial discretization provided by the fourth-order algorithm and adaptive mesh refinement are demonstrated to improve the solution time by a factor of 10 compared to lower-order methods on fixed-grid meshes. This research produces an advanced, multi-fluid plasma modeling framework which allows for studying complex, realistic plasmas involving collisions and practical geometries.
Open Access
A fourth-order solution-adaptive finite-volume algorithm for compressible reacting flows on mapped domains
(Colorado State University. Libraries, 2019) Owen, Landon, author; Gao, Xinfeng, advisor; Guzik, Stephen, committee member; Marchese, Anthony, committee member; Estep, Donald, committee member
Accurate computational modeling of reacting flows is necessary to improve the design combustion efficiency and emission reduction in combustion devices, such as gas turbine engines. Combusting flows consists of a variety of phenomena including fluid mixing, chemical kinetics, turbulence-chemistry interacting dynamics, and heat and mass transfer. The scales associated with these range from atomic scales up to continuum scales at device level. Therefore, combusting flows are strongly nonlinear and require multiphysics and multiscale modeling. This research employs a fourth-order finite-volume method and leverages increasing gains in modern computing power to achieve high-fidelity modeling of flow characteristics and combustion dynamics. However, it is challenging to ensure that computational models are accurate, stable, and efficient due to the multiscale and multiphysics nature of combusting flows. Therefore, the goal of this research is to create a robust, high-order finite-volume algorithm on mapped domains with adaptive mesh refinement to solve compressible combustion problems in relatively complex geometries on parallel computing architecture. There are five main efforts in this research. The first effort is to extend the existing algorithm to solve the compressible Navier-Stokes equations on mapped domains by implementing the fourth-order accurate viscous discretization operators. The second effort is to incorporate the species transport equations and chemical kinetics into the solver to enable combustion modeling. The third effort is to ensure stability of the algorithm for combustion simulations over a wide range of speeds. The fourth effort is to ensure all new functionality utilizes the parallel adaptive mesh refinement infrastructure to achieve efficient computations on high-performance computers. The final goal is to utilize the algorithm to simulate a range of flow problems, including a multispecies flow with Mach reflection, multispecies mixing flow through a planar burner, and oblique detonation waves over a wedge. This research produces a verified and validated, fourth-order finite-volume algorithm for solving thermally perfect, compressible, chemically reacting flows on mapped domains that are adaptively refined and represent moderately complex geometries. In the future, the framework established in this research will be extended to model reactive flows in gas turbine combustors.
Open Access
A high-speed mass spectrometer for characterizing flash desorbed species in pulsed power applications
(Colorado State University. Libraries, 2022) Ossareh, Susan J., author; Williams, John D., advisor; Yalin, Azer P., committee member; Roberts, Jacob L., committee member
Sandia National Laboratories operates the largest pulsed power facility in the world that hosts the Z machine that is utilized for research in fusion, energy, and national security. It can simulate extreme environments in these research areas in a single "shot" or "pulse of power," where large capacitor banks are rapidly discharged simultaneously, sending power to the center of the machine where a load is compressed into a z-pinch. A shot on the Z machine occurs in 150ns with peak currents on the order of 26 mega-amperes. However, there is a power flow obstacle that limits its ability to reach these extreme conditions. Approximately 1-3 MA of current is lost per shot. This could be partially attributed to chemisorbed contaminants on the cathode and anode stack in the center section of the machine being liberated in a flash desorption process, forming a conductive plasma between the anode and cathode electrodes that causes current to bypass the load and limits the power flow into the load. This project is focused on the design and development of a high-speed mass spectrometer to make measurements of the gasses evolved from the electrodes that are heated to 1000°C in 100 nanoseconds. The measurements from this diagnostic would allow for more accurate predictive modeling of current loss for Next Generation Pulsed Power Drivers, such as the Z machine. Since a probe does not exist commercially, the project requires the development of new mass spectrometry technology, however a pre-existing probe was used to begin the design process. This probe is known as the Energy and Velocity Analyzer for Distributions of Electric Rockets (EVADER) probe, which combines an electrostatic analyzer and a Wien velocity filter. Within this study, two different plasma sources were used separately to simulate the plasma generated in the Z machine, and steady state measurements were made of the ions produced while working towards taking transient measurements. The design and development efforts described in this thesis were guided by: (1) using the EVADER to collect steady state data in its original configuration as a basis of comparison, (2) then replacing an ammeter in the experimental system with a transimpedance amplifier (TIA) circuit to speed up the data sampling rate over that of the ammeter, (3) incorporate a micro-channel plate within the probe to amplify the current feed to the TIA and enable even faster data sampling rates, and (4) design a high speed electric shutter to quickly turn "on" and "off" ion flow to the probe to enable measurement of the temporal response of the probe with the transimpedance amplifier and micro-channel plate elements. The end goal of the project is to improve transient performance of a probe from 10s of seconds to 10s of micro-seconds in a stepwise manner to support pulsed power research.
Open Access
A low-cost monitor for simultaneous measurement of fine particulate matter and aerosol optical depth
(Colorado State University. Libraries, 2018) Wendt, Eric, author; Volckens, John, advisor; Jathar, Shantanu, committee member; Yalin, Azer, committee member; Pierce, Jeffrey, committee member
Exposure to airborne particulate matter with diameters less than 2.5 µm (PM2.5) is a leading cause of death and disease globally. In addition to affecting health, PM2.5 affects climate and atmospheric visibility. NASA currently uses satellite imaging technology to measure particulate matter air pollution across the world. Satellite image data are used to derive aerosol optical depth (AOD), which is the extinction of light in the atmospheric column. Although AOD data are often used to estimate surface PM2.5 concentration, there is considerable uncertainty associated with the relationship between satellite-derived AOD and ground-level PM2.5. Instruments known as Sun photometers can measure AOD from the Earth's surface and are often used for validation and calibration of satellite data. Reference-grade Sun photometers generally do not have co-located PM2.5 measurements and are too expensive to deploy in large numbers. The objective of this work was to develop an inexpensive and compact integrated PM2.5 mass and AOD sampler known as the Solar-Powered Aerosol Reference Calibrator (SPARC). PM2.5 is sampled using an ultrasonic pumping system, a size-selective cyclone separator, and a filter. Filter measurements can be used to correct the output from a low-cost direct-reading PM2.5 sensor housed within the SPARC. AOD is measured using optically filtered photodiodes at four discrete wavelengths. A suite of integrated sensors enable time-resolved measurement of key metadata including location, altitude, temperature, barometric pressure, relative humidity, solar incidence angle and spatial orientation. The AOD sensors were calibrated relative to a reference monitor in the Aerosol Robotics Network (AERONET). Field validation studies revealed close agreement for AOD values measured between co-located SPARC and AERONET monitors and for PM2.5 mass measured between co-located SPARC and EPA Federal Reference Method (FRM) monitors. These field validation results for this novel monitor demonstrate that AOD and PM2.5 can be accurately measured for the evaluation of AOD:PM2.5 ratios.
Open Access
A model of the effects of automatic generation control signal characteristics on energy storage system reliability
(Colorado State University. Libraries, 2012) Campbell, Timothy M., author; Bradley, Thomas H., advisor; Zimmerle, Daniel, committee member; Young, Peter M., committee member
No electrochemical batteries constructed to date have the storage capacities necessary for integration into conventional energy markets; aggregation will be required to meet industry-standard metrics for reliability and availability. This aggregation of individual energy storage devices into a distributed energy storage (DES) system will be useful not only to allow standard connection to the grid, but to provide higher-quality fast-response grid services with low-cost technologies. These smaller installations will have lower capital costs than traditional energy storage facilities. Ancillary services, and more specifically frequency regulation services, are understood to be the most technically viable and economically valuable market available to DES. Accordingly, this study is based on the properties of the frequency regulation market. This study presents a simplified model of a DES resource, its frequency regulation actuation signal, and its mode of market participation. The inputs to the model are scaling parameters of the DES system and of the actuation signal. The outputs from the model are the individual and aggregated reliability of the DES system. An analytical calculation of reliability is performed and analytical results are compared to numerical simulation solutions. Results show that the reliability of the energy storage device can be characterized using a set of non-dimensional parameters. These device-level reliability results are then translated into system-level reliability through several different models of ancillary services contracting and dispatch. Previous studies of DES systems have assumed that the energy storage system has no energy storage limitations and that the actuation signal has no net or instantaneous energy content. This model includes these conditions so as to capture the interaction between the energy content of the Automatic Generation Control (AGC) signal and the device-level and system-level reliability of DES systems. These results are novel in that they can guide the independent system operator/balancing authority in constructing an AGC signal specific to the needs of DES system resources.
Open Access
A modeling tool for household biogas burner flame port design
(Colorado State University. Libraries, 2017) Decker, Thomas J., author; Bradley, Thomas, advisor; Prapas, Jason, committee member; Sharvelle, Sybil, committee member
Anaerobic digestion is a well-known and potentially beneficial process for rural communities in emerging markets, providing the opportunity to generate usable gaseous fuel from agricultural waste. With recent developments in low-cost digestion technology, communities across the world are gaining affordable access to the benefits of anaerobic digestion derived biogas. For example, biogas can displace conventional cooking fuels such as biomass (wood, charcoal, dung) and Liquefied Petroleum Gas (LPG), effectively reducing harmful emissions and fuel cost respectively. To support the ongoing scaling effort of biogas in rural communities, this study has developed and tested a design tool aimed at optimizing flame port geometry for household biogas-fired burners. The tool consists of a multi-component simulation that incorporates three-dimensional CAD designs with simulated chemical kinetics and computational fluid dynamics. An array of circular and rectangular port designs was developed for a widely available biogas stove (called the Lotus) as part of this study. These port designs were created through guidance from previous studies found in the literature. The three highest performing designs identified by the tool were manufactured and tested experimentally to validate tool output and to compare against the original port geometry. The experimental results aligned with the tool's prediction for the three chosen designs. Each design demonstrated improved thermal efficiency relative to the original, with one configuration of circular ports exhibiting superior performance. The results of the study indicated that designing for a targeted range of port hydraulic diameter, velocity and mixture density in the tool is a relevant way to improve the thermal efficiency of a biogas burner. Conversely, the emissions predictions made by the tool were found to be unreliable and incongruent with laboratory experiments.
Open Access
A multi-functional electrolyte for lithium-ion batteries
(Colorado State University. Libraries, 2016) Westhoff, Kevin A., author; Bandhauer, Todd M., advisor; Bradley, Thomas H., committee member; Prieto, Amy L., committee member
Thermal management of lithium-ion batteries (LIBs) is paramount for multi-cell packs, such as those found in electric vehicles, to ensure safe and sustainable operation. Thermal management systems (TMSs) maintain cell temperatures well below those associated with capacity fade and thermal runaway to ensure safe operation and prolong the useful life of the pack. Current TMSs employ single-phase liquid cooling to the exterior surfaces of every cell, decreasing the volumetric and gravimetric energy density of the pack. In the present study, a novel, internal TMS that utilizes a multi-functional electrolyte (MFE) is investigated, which contains a volatile co-solvent that boils upon heat absorption in small channels in the positive electrode of the cell. The inert fluid HFE-7000 is investigated as the volatile co-solvent in the MFE (1 M LiTFSI in 1:1 HFE-7000/ethyl methyl carbonate by volume) for the proposed TMS. In the first phase of the study, the baseline electrochemical performance of the MFE is determined by conductivity, electrochemical stability window, half and full cell cycling with lithium iron phosphate (LiFePO4), lithium titanate oxide (Li4Ti5O12), and copper antimonide (Cu2Sb), and impedance spectroscopy measurements. The results show that the MFE containing HFE-7000 has comparable stability and cycling performance to a conventional lithium-ion electrolyte (1 M LiPF6 in 3:7 ethylene carbonate/diethyl carbonate by weight). The MFE-containing cells had higher impedance than carbonate-only cells, indicating reduced passivation capability on the electrodes. Additional investigation is warranted to refine the binary MFE mixture by the addition of solid electrolyte interphase (SEI) stabilizing additives. To validate the thermal and electrochemical performance of the MFE, Cu2Sb and LiFePO4 are used in a full cell architecture with the MFE in a custom electrolyte boiling facility. The facility enables direct viewing of the vapor generation within the channel in the positive electrode and characterizes the galvanostatic electrochemical performance. Test results show that the LiFePO4/Cu2Sb cell is capable of operation even when a portion of the more volatile HFE-7000 is continuously evaporated under an extreme heat flux, proving the concept of a MFE. The conclusions presented in this work inform the future development of the proposed internal TMS.
Open Access
A non-invasive Hall current distribution measurement system for Hall effect thrusters
(Colorado State University. Libraries, 2015) Mullins, Carl Raymond, author; Williams, John, advisor; Shipman, Patrick, committee member; Yalin, Azer, committee member
A direct, accurate method to measure thrust produced by a Hall Effect thruster on orbit does not currently exist. The ability to calculate produced thrust will enable timely and precise maneuvering of spacecraft—a capability particularly important to satellite formation flying. The means to determine thrust directly is achievable by remotely measuring the magnetic field of the thruster and solving the inverse magnetostatic problem for the Hall current density distribution. For this thesis, the magnetic field was measured by employing an array of eight tunneling magnetoresistive (TMR) sensors capable of milligauss sensitivity when placed in a high background field. The array was positioned outside the channel of a 1.5 kW Colorado State University Hall thruster equipped with a center-mounted electride cathode. In this location, the static magnetic field is approximately 30 Gauss, which is within the linear operating range of the TMR sensors. Furthermore, the induced field at this distance is greater than tens of milligauss, which is within the sensitivity range of the TMR sensors. Due to the nature of the inverse problem, the induced-field measurements do not provide the Hall current density by a simple inversion; however, a Tikhonov regularization of the induced field along with a non-negativity constraint and a zero boundary condition provides current density distributions. Our system measures the sensor outputs at 2 MHz allowing the determination of the Hall current density distribution as a function of time. These data are shown in contour plots in sequential frames. The measured ratios between the average Hall current and the discharge current ranged from 0.1 to 10 over a range of operating conditions from 1.3 kW to 2.2 kW. The temporal inverse solution at 2.0 kW exhibited a breathing mode of 37 kHz, which was in agreement with temporal measurements of the discharge current.
Open Access
A novel design methodology for osseointegrated implants and the effects of heat-treatment on shape setting nitinol foil
(Colorado State University. Libraries, 2020) Morrone, Adam, author; Simske, Steven, advisor; Popat, Ketul, committee member; Kawcak, Christopher, committee member
Nitinol, approximately equiatomic nickel and titanium and a popular shape memory alloy, has been used extensively in modern, implantable medical devices due to its natural biocompatibility, remarkable shape memory properties, and superelasticity. Much of the current literature on processing and handling this material focuses on thin wires, as this is what has historically been of most interest (e.g. for orthopedics, orthodontia, and orthognathics); however, as this technology advances, there are emerging applications of nitinol that require other form factors such as films and foils. In addition, although many manufacturers can produce three-dimensional nitinol structures, much of the information on shaping techniques is still proprietary. In an effort to fill these gaps in the literature and add to the knowledge of nitinol shaping techniques, this study compares the effects of various heat-treatments on the shape-setting of nitinol foil. Foils of two different NiTi compositions (50.2 and 50.8 percent Ni by atomic mole fraction) were rigidly fixed into a cylindrical shape and heat-treated at five different temperatures (400, 450, 500, 550, and 600 degrees C) and for five different durations (5, 10, 15, 20, and 25 minutes). The morphological rebound of these samples was evaluated, and a model was developed to described this shape setting behavior. In addition, the Austenite finishing temperature (Aƒ), and fatigue effects of all samples were evaluated to further quantify the effects of heat-treatment. The results from this materials study were then used in part to develop a novel design methodology for osseointegrated implants. Devices using this methodology have anchors that deploy from the main body to lock the implant in place. The contact points act as "active sacrificial zones" which can experience bone resorption without losing rigidity, while the remainder of the implant body undergoes normal loading conditions. This methodology aims to improve the quality and speed of bone ingrowth.
Open Access
A novel smoother-based data assimilation method for complex CFD
(Colorado State University. Libraries, 2024) Hurst, Christopher L., author; Gao, Xinfeng, advisor; Guzik, Stephen, advisor; Troxell, Wade, committee member; van Leeuwen, Peter Jan, committee member
Accurate computational fluid dynamics (CFD) modeling of turbulent flows is necessary for improving fluid-driven engineering designs. Traditional CFD often falls short of providing truly accurate solutions due to inherent uncertainties stemming from modeling assumptions and the chaotic nature of fluid flow. To overcome these limitations, we propose the integration of data assimilation (DA) techniques into CFD simulations. DA, which incorporates observational data into numerical models, offers a promising avenue to enhance predictability by reducing uncertainties associated with initial conditions and model parameters. This research aims to advance our understanding and application of DA for CFD modeling of highly chaotic dynamical systems. This dissertation makes several novel contributions in DA and CFD: i) A novel DA algorithm, the maximum likelihood ensemble smoother (MLES), has been developed and implemented to provide better model parameter estimation and assimilate time-integrated observations while addressing nonlinearity, ii) Multigrid-in-time techniques are applied to enhance the computational efficiency of the MLES by improving the optimization processes, and iii) The MLES+CFD framework has been validated by classical test problems such as the Lorenz 96 model and the Kuramoto-Sivashinsky equation. The effectiveness of the MLES has been demonstrated through a few test problems featuring chaos, discontinuity, or high dimensionality.
Open Access
A numerical model for the determination of biomass ignition from a hotspot
(Colorado State University. Libraries, 2015) McArdle, Patrick, author; Williams, John, advisor; Gao, Xinfeng, committee member; Shipman, Patrick, committee member
The determination of biomass ignition from an inert spherical hotspot using a fourth-order finite-volume method is presented. The transient ignition-combustion system is modeled by two coupled reaction-diffusion equations. One equation governs the heating characteristics of the biomass while the other governs the mass loss of the biomass. The combustion assumes a one-step, 1st-order Arrhenius reaction. This work is motivated and funded by the Department of Defense Legacy Program to create a munition specific fire danger rating system. Improving fire danger rating systems on military lands would minimize the economic and environmental impact of soldiers training on protected habitats. A better understanding of these ignition characteristics would also improve current fire spread models. Our result shows that given the ignition criteria derived from a simplified non-dimensional model and specifying critical values found by Gol'dshleger et al., an ignition probability can be established by varying the biomass properties based on moisture content. Following the procedure developed in this thesis, the computed ignition probabilities correlate well with experimental ignition data that was obtained at the Center for Environmental Management of Military Lands. Moreover, numerically solving the coupled reaction-diffusion system provides additional insight into more realistic ignition criteria involving mass loss. The numerical solution suggests more sources of heat loss, in addition to convection, must be considered for a more realistic ignition model.
Open Access
A personal thermophoretic sampler for airborne nanoparticles
(Colorado State University. Libraries, 2010) Thayer, Daniel Lee, author; Marchese, Anthony, advisor; Volckens, John, advisor; Popat, Ketul, committee member; Prieto, Amy, committee member
Engineered nanoparticles are materials with at least one dimension measuring less than 100 nm that are designed on the molecular scale to produce unique or enhanced properties that differ from the bulk material. However, the same properties that make engineered nanoparticles attractive to industry also may present potential health risks to the workers who manufacture them. Very little human exposure data exist for these particles, although they are known enter the body through a number of routes (e.g., respiration, dermal penetrations, and ingestion). Nanoparticles that enter the body can also translocate from one organ to another by virtue of their small size. A cost-effective personal sampler is necessary to evaluate levels of worker exposure to these materials to determine the relative levels of individual risk. Such a sampler must be capable of collecting nanoparticles with high efficiency for subsequent analysis of size, surface chemistry, morphology, and other properties. In addition, the sampler must be able to differentiate between incidental nanoparticles, which are nanoparticles that are naturally present in the environment, and engineered nanoparticles. As detailed in this thesis, a small thermal precipitator was designed to measure breathing-zone concentrations of airborne nanoparticles. The thermal precipitator samples aerosol by producing a 1000 °C cm ' temperature gradient between two aluminum plates (0.1 cm separation distance) using a resistive heater, a thermoelectric cooler, a temperature controller, and two thermistor sensors. The collection efficiency was evaluated for 15, 51, 100, and 240 nm particles at flow rates of 5 and 20 mL/min. Tests were also performed with a zero temperature gradient to determine losses in the device for measurement correction. The homogeneity of particle collection across the collection surface was evaluated using electron microscopy and imaging software. The results indicate that thermal precipitation is a feasible approach for personal monitoring of airborne nanoparticle concentrations in the workplace.