Polymer electrolyte fuel cells are regarded as one of the most promising alternatives to the depleting and high pollutant fossil fuel energy sources. High temperature Polymer electrolyte fuel cells are especially suitable for stationary power applications. However, the length scale of a PEM fuel cells main components range from the micro over the meso to the macro level, and the time scales of various transport processes range from milliseconds up to a few hours. This combination of various spatial and temporal scales makes it extremely challenging to conduct in-situ measurements or other observations through experimental means. Thus, numerical simulation becomes a very important tool to help understand the underlying electrochemical dynamics and transient transport phenomena within PEM fuel cells. In this thesis research a comprehensive, three- dimensional mathematical model is developed which accounts for the convective and diffusive gas flow in the gas channel, multi-component diffusion in the porous backing layer, electrochemical reactions in the catalyst layers, as well as flow of charge and heat through the solid media. The governing equations which mathematically describe these transport processes, are discretized and solved using the finite-volume based software, Ansys FLUENT, with its in-built CFD-solvers. To handle the significant non-linearity stemming from these transport phenomena, a set of numerical under-relaxation schemes are developed using the programming language C++. Good convergence is achieved with these schemes, though the model is based on a serpentine single-channel flow approach. The model results are validated against experimental results and good agreement is achieved. The result shows that the activation overpotential is the greatest cause of voltage loss in a high temperature PEM fuel cell. The degree of oxygen depletion in the catalyst layer, under the ribs, is identified and quantified for a given set of input parameters. This factor is followed by membrane resistance to protonic migration. The model can thus be suitable applied as a tool to predict cell performance. The results also show that performance is influenced by not just one, but a combination of inter-related factors, thus temperature increases, and flow rate changes will only be effective if simultaneously, the concentration of inlet oxygen, and the mobility of proton-ions in the membrane is increased. Not only does the model results verify these phenomena, but provide a quantitative output for any given set of input parameters. It can therefore be suitably applied as an optimisation tool in high temperature PEM fuel cell design.

Discusses types of mathematical errors that may occur in scientific work. / Typescript. / "Submitted to the Graduate Council of Florida State University in partial fulfillment of the requirements for the degree of Master of Arts." / Advisor: H. C. Griffith, Professor Directing Paper. / "August, 1958." / Includes bibliographical references (leaf 26).

Thesis: M.S., Massachusetts Institute of Technology, Department of Meteorology, 1977 / Bibliography : leaves 125-126. / M.S. / M.S. Massachusetts Institute of Technology, Department of Meteorology

Given the proper conditions, antennas applied in medicine can offer improved quality of life to patients. However the human body proves hostile to typical, analytical antenna design techniques as it is composed entirely of frequency- and temperature-dependent lossy media. By combining optimization techniques with numerical methods, many of these challenges may be overcome. Particle swarm optimization (PSO) models the solution process after the natural movement of groups such as swarms of bees as they search for food sources. This meta-heuristic procedure has proven adept at overcoming many challenging problems in the electromagnetics literature. Therefore, this dissertation explores PSO and some of its variants in the solution of two biomedical antenna problems. Recent advances in biosensor technology have led to miniaturized devices that are suitable for in vivo operation. While these sensors hold great promise for medical treatment, they demand a wireless installation for maximum patient benefit, which in turn demands quite specific antenna requirements. The antennas must be composed of biocompatible materials, and must be very small (no more than a few square centimeters) to minimize invasiveness. Here PSO is applied to design a 22.5 mm × 22.5 mm × 2.5 mm implantable serpentine planar inverted-F antenna for dual-band MedRadio and ISM operation. Measurements reveal the accuracy of the models. Hyperthermia is the process of elevating a patient’s temperature for therapeutic gain. Since the ancient Egyptians, physicians have employed hyperthermia in the destruction of cancerous tumors. Modern implementations typically apply electromagnetic radiation at radio and microwave frequencies to induce local or regional heating. In this dissertation PSO is used to evaluate candidate antennas for inclusion in an array of antennas with the aim of local adjuvant hyperthermia for breast cancer treatment. The nearield of the array is then optimized to induce a uniform specific absorption rate throughout the breast.

No description available.

No description available.

No description available.

No description available.

Polyhydroxyalkanoates (PHAs) are biodegradable plastic synthesized by microorganisms from renewable carbon resources and they are promising substitutes for conventional fossil-fuel-based plastics due to their similar physical properties. Pure cultures of particular microorganisms are commonly used for industrial PHA production but high production costs due to requirements of sterile conditions and refined substrates hinder the mass production of PHAs. Thus, model development for PHA production by microbes is essential to investigate the PHA formation and microbial metabolisms for enhanced productivity and PHA contents. In the present study, a comprehensive numerical model has been developed and calibrated for the non-growth associated PHA production process by Cupriavidus necator. The model parameters were calibrated with 8 selected experimental studies and the simulation results show good agreement with experimental data. Two methods were used to conduct sensitivity analysis: the simple method and the overall relative sensitivity analysis method. Maximum specific residual biomass growth rate was the most sensitive parameter. The calibrated model was used to investigate fed-batch feeding strategies that optimize PHA accumulation by limited nutrient feeding in the PHA production phase. The simulation results showed limited phosphorous feeding accumulated more PHA than limited nitrogen feeding. The optimal feeding strategy was determined to be limited phosphorous feeding at 5% of initial phosphorous during the PHB production phase, yielding simulated 226.0 g/L PHB at the end of the 168-hour operation. / Thesis / Master of Applied Science (MASc)

Carbon fiber reinforced polymers (CFRP) are widely used in advanced industry, like aerospace, modern sports, and automobile. Compared to traditional metals, CFRP laminates have a higher strength to weight ratio and better corrosion resistance. Because of the heterogeneous and anisotropic behavior of CFRP laminates, their damage mechanisms include fiber/matrix debonding, diffuse matrix damage, matrix cracking, fiber breakage, and delamination. These damage mechanisms develop in different length scales and are deeply coupled with each other, especially the intra/interlaminar damage coupling. Therefore, a well understanding of intra/interlaminar damage coupling is vital for predicting integrity of laminated structures. The dissipation during delamination process includes the intrinsic (depends on local material) and extrinsic (depends on non-local structural effect) parts. The intrinsic part could be straightly calibrated through standard test, while the non-local extrinsic part is usually not fully elaborated. In this work, we will devote to fill the gap, both in experiments and simulation, which will encounter the effect of intra/inter laminar damage coupling on the extrinsic dissipation during delamination process. The non-local extrinsic dissipation is usually triggered by the intra/inter laminar damage coupling, depending the loading conditions and curing process. In this thesis, we first design a two step test (tensile-DCB) on a cross ply to quantitatively study the influence of intralaminar damage on interlaminar performance. The intralaminar damage effect has proven to be two-fold on the interlaminar performance as the preset transverse cracks could lead to fiber bridging and also local delamination. Secondly, we proposed a hybrid cohesive element to encounter the intra/interlaminar coupling in a pragmatic local way. The hybrid cohesive element not only calculate the out-of-plane separation but also the in-plane strain of the two surfaces of the interface elements, which could be used to estimate the intralaminar damage of adjacent layers. Meanwhile, the coupling damage in multidirectional delamination is also investigated through a modified double cantilever beam (DCB) test. A general hybrid cohesive element is developed, in which the influence of delamination direction on the local apparent toughness is also considered. Last but not least, we implement an experimental campaign to study the curing process effect on fiber bridging development in unidirectional mode I fracture. Through these studies, the intra/interlaminar damage coupling mechanism is better understood and the hybrid cohesive element prove its potential on simulation efficiency and robustness.