A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item A VALIDATED MODELING FRAMEWORK FOR PERFORMANCE ANALYSES OF EXPERIMENTAL AND PROVEN DESALINATION TECHNOLOGIES(2022) Romo, Sebastian Antionio; Srebric, Jelena; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There is a wide array of desalination methods available for treating water at different salinities and production rates, but there are no systemic approaches on how to directly compare performance of different desalination systems. Existing comparison efforts focus solely on isolated performance metrics for a single desalination system, resulting in segregated case studies and/or incomparable systems. Numerical models for desalination systems can bridge this gap as they can take account of specific deployment needs. However, models in the literature are not mutually compatible, and they seldom disclose all the parameters or equations necessary for development and validation. This dissertation conceives a cross-comparison enabling simulation framework for the most relevant desalination processes. To achieve this, modeling approaches and thermophysical property correlations are curated from volumes of literature and used to create metamodels for six relevant desalination methods. The models are integrated into a simulation framework based on parameter hierarchies imposed in the model structures. The simulation suite is validated with data from the literature and actual operational data from desalination facilities in the field. The results show that the cross-comparison across equal parameter hierarchies is possible for all desalination technologies. A comparative analysis between the dominant technologies in the thermal and molecular transport families, Multi-Effect Distillation (MED) and Reverse Osmosis (RO), respectively, shows that energy intensity in MED is an order of magnitude greater for equivalent operational conditions, but actual operational costs are comparable. The models are further refined to reflect conditions from actual systems in the field and an iterative sampling algorithm is developed to find plausible operation scenarios given the scarce data from the field. This method achieves excellent agreement with data from four desalination plants with percent differences ranging between 2.5% and 9.3%. Furthermore, the results identify two plants performing 20% below their theoretically achievable recovery. Apart from evaluating existing deployments, the simulation suite helps identify a niche in the operational map of existing desalination methods characterized by high recovery rates and high feed salinities that is generally unfulfilled by conventional desalination.Item QUANTIFYING THE ADDED VALUE OF AGILE VIEWING RELATIVE TO NON-AGILE VIEWING TO INCREASE THE INFORMATION CONTENT OF SYNTHETIC SATELLITE RETRIEVALS(2022) McLaughlin, Colin; Forman, Barton A; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Satellite sensors typically employ a “non-agile” viewing strategy in which the boresight angle between the sensor and the observed portion of Earth’s surface remains static throughout operation. With a non-agile viewing strategy, it is relatively straightforward to predict where observations will be collected in the future. However, non-agile viewing is limited because the sensor is unable to vary its boresight angle as a function of time. To mitigate this limitation, this project develops an algorithm to model agile viewing strategies to explore how adding agile pointing into a sensor platform can increase desired information content of satellite retrievals. The synthetic retrievals developed in this project are ultimately used in an observing system simulation experiment (OSSE) to determine how agile pointing has the potential to improve the characterization of global freshwater resources.Item Development of Hybrid Air-Water Rotor Transition Thrust Prediction and Control(2020) Semenov, Ilya Yevgeniyevich; Chopra, Inderjit; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hybrid vehicles are able to function in some combination of aerial, underwater, and terrestrial environments, which greatly expands the scope of missions a vehicle can perform. Hybrid aerial-water (HAW) vehicles are a promising subcategory that are designed to operate in two vastly different fluid mediums. Multirotor HAW vehicles configurations have advantages in maneuverability, but pose a challenge in the water entry or water exit transitions. The interaction of a powered rotor with the air-water interface and its performance in a mixed air-water medium are poorly understood. Previous HAW vehicle strategies avoid a powered rotor with additional propulsion and buoyancy systems, constraining the design space. A custom test stand was constructed to better understand rotor performance during the air-water transition. By recording powered rotor performance during controlled water entries and exits in a large tank, several novel observations were made. Previously unrecorded phenomenon such as the gradual height and RPM dependent transition and the underwater ceiling effect are determined. These observations inform the development of the Transition Index TI, a novel metric that indicates the transition state of the rotor, without the need for specialized sensors or computationally intensive modeling. TI is applied to experimental data to make further observations, and is also used in a novel thrust prediction formulation. The first known low-order prediction of thrust through the transition is validated against experimental data, and allows for the development of a TI based controller. A preliminary controller implementation shows promising results in maintaining constant thrust through the air-water transition. Finally, a HAW vehicle to apply this controller is built. Careful consideration to the waterproofing and motor choice is shown and preliminary flight tests are demonstrated. Future expansion on the application of the novel TI and thrust prediction has great potential to advance the capabilities of hybrid aerial-water vehicles.Item EVALUATION AND IMPROVEMENT OF MECHANICAL AND CHEMICAL RESILIENCE OF INTERMEDIATE-TEMPERATURE SOLID OXIDE FUEL CELL ANODES(2017) Hays, Thomas; Wachsman, Eric D; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Solid oxide fuel cells are in the process of reaching maturity as an energy generation technology, but a number of technical challenges exist, namely mechanical and chemical resilience, that hinder the realization of their full potential and widespread deployment. As more research and development work has been performed on intermediate temperature SOFCs based on gadolinium doped ceria, there persists a number of gaps in the understanding of the behavior of these devices. The mechanical properties of component material and SOFC structures in non-ambient conditions, the nature and degree of damage caused by sulfurized hydrocarbon fuels, and the potential for leveraging produced thermal energy are not satisfactorily characterized for GDC-based SOFCs. Mechanical testing of porous GDC and anode supported SOFC coupons from room temperature to 650°C was performed in air and reducing conditions using a test system designed and built for this application. Spherical porosity was determined to result in the higher strength compared to other pore geometries and a positive linear dependence between temperature and strength was determined for SOFC coupons. Additionally, placing the electrolyte layer in compressive stress resulted in higher strengths. Standard SOFCs were operated while exposed to hydrogen and methane containing ppm level hydrogen sulfide concentration. An infiltration technique was used to deposit a fine layer of GDC on the inner surfaces of some cell anodes, and the results of sulfur expose was compared between infiltrated and unmodified cells. GDC infiltration allowed cells to operate stably for hundreds of hours on sulfurized fuel while unmodified cells were fatally damaged in less than two days. A primary and a resulting secondary degradation mechanism were identified and associated with sulfur and carbon respectively through surface analysis. A novel technique for measuring thermal power output of small-scale SOFCs operating on a variety of fuels was developed and used to evaluate electrical and thermal outputs while operating on simulated anaerobic digester biogas. These findings were used to propose a multi-utility generation system centered on a nominal 10 kW SOFC unit fed by anaerobic digesters and capable of producing clean water and electricity for 50 individuals through direct contact membrane distillation driven by captured waste heat from the SOFC.Item Silane Cross-Linked Graphene Oxide Membrane Demonstrating Unique Transport Phenomena in Aqueous Phase Separation(2015) Zheng, Sunxiang; Mi, Baoxia; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Graphene oxide (GO) membranes are considered promising for water purification applications. We synthesized a novel GO membrane using inorganic silane as a cross linker. Briefly, a pH 3 GO solution was filtrated through polyethersulfone (PES) membrane supports by vacuum filtration. The GO layers deposited on the PES supports were subsequently soaked in a saturated sodium metasilicate solution for crosslinking and stabilization. As a final step, the readily stabilized GO membranes were transferred into a 10% H2SO4 solution for further stabilization. The GO membrane exhibits unique rejection properties to uncharged organic species (~ 85%) and ionic species (~6%). A high water flux of 39 L/m2/h and a reasonable back solute flux of 0.011 mol/m2/h were observed with 0.25M trisodium citrate dehydrate (TSC) as draw solution in forward osmosis (FO). The GO membrane also demonstrates some interesting Janus effects and enables directional water gating (by blocking the permeation in one direction while allowing the permeation in the other direction).Item GRAPHENE OXIDE MEMBRANES FOR WATER PURIFICATION(2015) Hu, Meng; Mi, Baoxia; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Graphene oxide (GO) is a two-dimensional material with a single layer carbon lattice, which is decorated with oxygenated functional groups on the basal plane as well as on the edges. Due to its unique properties, GO has attracted many applications including electronics, energy, sensors, optics, etc. Recently, it has been demonstrated that the graphene surface of GO presents long slip lengths of water, thus allowing for an unimpeded water flow. It was anticipated that the ultrafast water transport would be translated into membrane separations, in order to address one of the major challenges for membrane technology—low performance. It was also expected that GO might provide solutions to other obstacles facing membrane technology, such as membrane fouling. These two overarching themes, the technical limitations for membrane technology and the potential of GO to overcome those restrictions, inspired the current study. The main objective of this dissertation was to develop highly efficient membranes for water purification based on GO. Also investigated were the transport mechanisms for the designed GO membranes, the potential of GO to mitigate membrane fouling, and the feasibility of GO membrane regeneration. Major achievements of the study include: (1) the development of high performance GO membranes for nanofiltration and forward osmosis by two facile and sustainable methods, (2) the elucidation of transport mechanisms to guide better GO membrane design, (3) the application of GO for fouling mitigation in pressure retarded osmosis processes, and (4) the validation for regenerable GO membranes. Collectively, not only do the findings provide the first experimental verification for the ultrafast water transport in GO membranes, they also suggest that the GO membrane could be a promising prototype of next generation membranes with high performance, low fouling propensity, and full regenerability. The work has already begun to show its profound impact in the membrane field, as seen in the publications it has prompted.