Theses and Dissertations from UMD

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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    ENERGY CONVERSION IN NANOCHANNELS GRAFTED WITH POLYELECTROLYTE AND POLYZWITTERION BRUSHES
    (2018) Patwary, Jahin; Das, Siddhartha; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A continuous mission in the sciences is the never-ending search for more energy and fuel. As time brings the reality of how limited natural resources are, we seek toexpand to more synthetic methods of preserving and converting energy. Prevalent applications of renewable energy include solar energy, wind power, tidal power, and hydropower to list a few. It is no surprise that several of these applications stem from the involvement of fluid flow and the fluid pressure. This thesis explores a specific method of energy conversion in charged nanochannel flows of electrolytic solution, a subject that has gained great attention in recent years. This particular method of nanofluidic energy conversion inside a charged nanochannel is an example of Electrokinetic Energy generation in pressure-driven liquid transport. A charged nanochannel in contact with an electrolyte solution develops an Electric Double Layer (EDL) of charge where the number of counterions (ions of charge opposite in sign to that of the nanochannel wall) is much larger than the number of coions (ions of charge identical in sign to that of the nanochannel wall) in order to screen the wall charge. In presence of a pressure-driven flow, the ions within the EDL are advected downstream. The counterions number density being much larger than the coions, such a downstream migration would imply the accumulation of a net charge in the downstream direction, thereby triggering an axial electric field. This electric field when multiplied with the current generated due to the streaming of the ions would lead to an energy generation this energy generation is effectively an example of Electrochemomechanical Energy conversion, where the mechanical energy of the pressure-driven flow and the chemical energy of the EDL gets converted into an electrical energy. The purpose of this thesis is to explore the such Electrokinetic Energy Conversion in nanochannels grafted with pH-responsive charged polyelectrolyte (PE) brushes. Grafting of nanochannels with polyelectrolyte (PE) brushes, invariably attribute a smartness to the nanochannels that have been used for a plethora of applications ranging for ion and biosensing, gating of ion transport, current rectification, fabrication of nanofluidic diodes and nano-actuators, etc. All these applications strictly depend on the modification of the ionic current by the presence of the PE brushes. On the contrary, the energy generation/conversion that we study here is a rare example where we utilize the Electrohydrodynamic (EHD) transport in brush-functionalized nanochannels. In this thesis, we experiment with parameters that would provide significant electrochemomechanical energy conversion in the presence of a pressure-driven back ground transport. Weve gathered the optimal parameters to result in a 4-5% energy conversion efficiency. This is possible when the PE brushes exhibit a pH-dependent charge density. Further, we extend our research by determining the possible electrochemomechanical energy conversion in a nanochannel grafted with polyzwitterionic (PZI) brushes. PZI brushes are capable of inducing a significantly high charge on both acidic and basic solutions. This allows electrokinetic induced power to be accessible over a wide range of pH values, as opposed to being confined to a narrow pH range compared to other EDL channels. This thesis therefore sheds light on the smartness of nanochannels and their capabilities to generate power. We anticipate that our results will be able to provide a way for energy to be induced and produced in nanochannel-related applications, and maybe even find means to be a measure for developing more sustainable energy in larger scale applications.
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    A SUNLIGHT TO MICROWAVE POWER TRANSMISSION MODULE PROTOTYPE FOR SPACE SOLAR POWER
    (2013) Jaffe, Paul; Granatstein, Victor L; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The prospect of effectively limitless, continuous electricity from orbiting satellites for use on earth has captured many people's interest for decades. The proposed approach typically entails collection of solar energy, its conversion to microwave energy, and the wireless transmission of the microwaves to the earth. This offers the benefit of providing baseload power while avoiding diurnal cycle and atmospheric losses associated with terrestrial solar power. Proponents have contended that the implementation of such systems would offer energy security, environmental, and broad technological advantages to those who would undertake their development, while critics have pointed out economic, political, and logistical barriers. Niche applications, such as provision of power to remote military bases, might better tolerate the higher energy costs associated with early operational systems. Among recent implementations commonly proposed for solar power satellites, highly modular concepts have received considerable attention. Each employs an array of modules for performing conversion of sunlight into microwaves for transmission to earth. This work details results achieved in the design, development, integration, and testing of photovoltaic arrays, power electronics, microwave conversion electronics, and antennas for 2.45 GHz microwave-based "sandwich" module prototypes. Prototypes were fabricated and subjected to the challenging conditions inherent in the space environment, including solar concentration levels in which an array of modules might be required to operate. This testing of sandwich modules for solar power satellites in vacuum represents the first such effort. The effort culminated with two new sandwich module designs, "tile" and "step", each having respectively area-specific masses of 21.9 kg/m2 and 36.5 kg/m2, and mass-specific power figures of 4.5 W/kg at minimum one sun and 5.8 W/kg at minimum 2.2 suns (AM0) simulated solar illumination. The total combined sunlight to microwave efficiency of the modules was shown to be on the order of 8% and 7% for vacuum operation in the 10-6 torr regime. These represent the highest reported combined sandwich module efficiencies under either ambient or vacuum conditions, nearly quadrupling the previous efficiency record. The novel "step" concept was created to address thermal concerns and resulted in a patent publication. Results from module characterization are presented in context and compared with figures of merit, and practical thresholds are formulated and applied. The results and discussion presented provide an empirical basis for assessment of solar power satellite economic models, and point to several opportunities for improvements in area-specific mass, mass-specific power, and combined conversion efficiency of future prototypes.