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
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Item ACTIVE AND PASSIVE MICROFLUIDICS FOR SAMPLE DISCRETIZATION, MANIPULATION AND MULTIPLEXING(2020) Padmanabhan, Supriya; DeVoe, Don L; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The use of microfluidic technology to compartmentalize an initial sample into discrete and isolated volumes is an important step for many biological and chemical applications, that allows molecules, cells, particles, reagents, and analytes to be spatially constrained, providing unique benefits for their characterization, sorting, and manipulation with low reagent consumption. Discretization can also increase the overall throughput and enable multiplexing. In this dissertation, two platforms are described to enable microfluidic sample discretization and manipulation. First, (2D) microwell arrays fabricated in thermoplastic cyclic olefin copolymer (COP) are explored as a new approach toward the development of high throughput, low-cost components in disposable diagnostics by utilizing a passive discretization technique. Performance of various 2D array designs is characterized numerically and experimentally to assess the impact of thermoplastic surface energy, fluid flow rate, and device geometry on sample filling and discretization. The design principles are used to successfully scale up the platform without affecting device performance. Loop-mediated isothermal amplification (LAMP) on chip is used to demonstrate the platform’s potential for discretized nucleic acid testing. Next, pin spotting in nanoliter-scale 2D arrays is demonstrated as technique for high resolution reagent integration to enable multiplexed testing in diagnostics. The potential for nucleic-acid diagnostics is evaluated by performing rolling circle amplification (RCA) on chip with integrated reagents. Finally, an innovative platform enabling complex discretization and manipulation of aqueous droplets is presented. The system uses simple membrane displacement trap elements as an active technique to perform multiple functions including droplet discretization, release, metering, capture, and merging. Multi-layer polydimethylsiloxane (PDMS) devices with membrane displacement trap (MDT) arrays are used to discretize sample into nanoliter scale droplet volumes, and reliably manipulate individual droplets within the arrays. Performance is characterized for varying capillary number flows, membrane actuation pressures, trap and membrane geometries, and trapped droplet volumes, with operational domains established for each platform function. The novel approach to sample digitization and droplet manipulation is demonstrated through discretization of a dilute bacteria sample, metering of individual traps to generate droplets containing single bacteria, and merging of the resulting droplets to pair the selected bacteria within a single droplet.Item Nanocomposite and Soluble Energetic Additives for Burning Enhancement of Hydrocarbon Fuels(2017) Guerieri, Philip Michael; Zachariah, Michael R; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Metallizing liquid fuels and propellants to improve performance of energy conversion and propulsion systems has been of interest for decades but past attempts to do so using micron-sized metal powders demonstrated inefficient combustion and low burning rates of modified hydrocarbons. “Nanofuels” composed of energetic nanoparticles like nanoaluminum suspended in liquid fuels have slowly emerged in scientific research over the last two decades with promising results. Increased burning rates, lower ignition delays, and high suspension stabilities compared to slurry fuels of micron-sized particles have been demonstrated; however, the effects of various energetic nanoparticles on the combustion of hydrocarbons remain poorly understood while particle agglomeration remains a performance-limiting problem. The research in this dissertation identifies strategies for inclusion of aluminum into hydrocarbons which promote combustion performance in a free-droplet burning experiment developed herein. Considering the low burning rates which plagued micron particle-based slurry fuels, specific attention is paid to characterizing and understanding effects on droplet burning rate constants. Classical characterization of this metric based on the D-squared-law for isolated droplet combustion is found to be unsuitable with heterogeneous energetic additives and thusly an original scheme for experimental approximation of burning rate constant is set forth. Several beneficial strategies for aluminum inclusion and burning rate enhancement are studied including co-addition of nanoaluminum with the gas generator nitrocellulose (NC), dissolution of Al-containing molecules including organometallic clusters into hydrocarbons, and burning rate enhancements realized with oxygen-carrying nanoparticle co-additives. Arguably the most impactful strategy identified however is the preassembly of active nanoparticles into NC-bound clusters or controlled agglomerates, termed “mesoparticles” (MPs), by electrospray which drastically improves droplet burning rate increases and nanofuel suspension stabilities observed compared to nanofuels of unassembled nanoparticles. Mechanisms of the various additives studied are probed with a variety of diagnostic techniques and burning rate enhancements are linked to physical effects of droplet disruptions on the diffusion-limited burning droplet system. The MP architecture causes a feedback loop between physical disruptions by gas liberation from droplets, transport of active additives into the flame where they react, and promotion of further gas evolution repeating and accelerating this process.Item The Effect Of Surfactants On The Breakup Of An Axisymmetric Laminar Liquid Jet(2012) Walker, Justin Robert; Calabrese, Richard V; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The contacting of multiple liquid phases is a complex process, and one that is difficult to study experimentally. Liquid dispersion studies in stirred tanks and high shear mixers frequently involve the use of surfactants without a strong physical understanding of how the surfactants affect the mechanics of droplet production and breakup. In this study, experiments are performed using the axisymmetric laminar jet system. The breakup of a laminar axisymmetric jet is a well-studied fluid dynamics phenomenon. Despite the extensive literature on jet breakup, the impact of surface active agents on jet breakup has received limited attention. An extensive series of experiments with water-air and oil-water jet systems with and without surfactants has been performed, varying fluid flow rate, jet diameter, jet bulk viscosity, surfactant type, and surfactant concentration. Surfactants were found to significantly affect the breakup of laminar liquid jets. Significant effects on both the length of jets and the size of resulting droplets are reported. In general, the effect of surfactants is to reduce the interfacial tension of the system in question, which results in longer jet breakup lengths and larger diameter droplets. However, the interfacial tension alone is insufficient to explain the physics of the jet breakup phenomena. Several breakup mechanisms were identified, and the regimes in which each operates vary not only due to jet geometry and velocity, but on the interfacial properties as well. The effect of surfactants on the breakup phenomena differs in each of these distinct breakup regimes. A mechanistic model for the prediction of breakup length for surfactant laden jets is presented. This model results in good agreement between predicted and experimentally observed values over a wide variety of surfactant concentrations and jet conditions and was shown to be useful for both the oil-water and water-air systems, within the axisymmetric jetting regime.Item Electrostatic Gas-Liquid Separation from High Speed Streams--Application to Advanced On-Line/On- Demand Separation Techniques(2009) Alshehhi, Mohamed Saeed; Ohadi, Michael M; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The separation of suspended droplets from gases has been one of the basic scientific and technical problems of the industrial era and this interest continues. Various industrial applications, such as refrigeration and HVAC systems, require control of fine droplets concentrations in moving gaseous mediums to maintain system functionality and efficiency. Separating of such fine droplets can be achieved using electrostatic charging as implemented in electrostatic precipitators (ESPs). They use electrostatic force to charge and collect solid particles. The objective of the present work was to study the feasibility of using wiretube electrostatic separator on the removal of fine water and oil droplets from air stream based on corona discharge ionization process. A parametric study was conducted to find key parameters affecting the separation process. This goal was approached by simulating the charging and separation phenomena numerically, and then verifying the modeling findings through experiments. The numerical methodology simulated the highly complex interaction between droplets suspended in the flow and electrical field. Two test rigs were constructed, one for air-water separation and the other for air-oil separation. A wiretube electrostatic separator was used as the test section for both test rigs. The separation performance was evaluated under different electric field and flow conditions. Finally, based on the results, a novel air-water separator prototype was designed, fabricated and tested. The numerical modeling results qualitatively showed acceptable agreement with the experimental data in terms of the trend of grade efficiency based on droplets size. Both numerical modeling results and experimental data showed that with a proper separator design, high separation efficiency is achievable for water and oil droplets. Based on the experimental data, at flow velocity of 5 m/s and applied voltage of 7.0 kV, the maximum separation efficiency for water and oil was 99.999 % and 96.267 %, respectively. The pressure drop was as low as 100 Pa and maximum power consumption was 12.0 W.