A vinhaça da cana-de-açúcar constitui-se no principal resíduo líquido gerado pelo setor sucro-alcooleiro e, face aos enormes volumes produzidos , os problemas decorrentes de seu armazenamento e disposição o final passaram a constituir nos últimos tempos num grande desafio a técnicos envolvidos com essa questão. Este estudo tem por objetivo apresentar uma alternativa de aproveitamento desse resíduo, Aquelas tradicionalmente conhecidas no meio alcooleiro, por .intermédio do tratamento e transformação da vinhaça em biogás e sua utilização na geração de eletricidade. Para tanto, adotou-se a tecnologia de digestão anaeróbia de alta eficiência através de digestores de fluxo ascendente para a produção de biogás e, uma vez purificado, o aproveitamento desse gás em motores e turbinas adequadas a esse tipo de combustíve1, conforme a literatura consultada. No sentido de avaliar a viabilidade prática deste trabalho, optou-se pela elaboração de um estudo de caso, no qual foi dimensionada uma destilaria hipotética de \'cerca de 150.000 litros de álcool/dia, gerando um volume de cerca de 1.800.000 litros de vinhaça/dia. Por meio desta simulação, foram analisados os aspéctos técnicos e econômicos envolvidos, possibilitando assim, uma apreciação crítica e realista do estudo proposto. / The vinasse of sugar-cane represents the main liquid residue produced by the sugar-alcohol sector and, in view of the enormous volumes produced, the problems related to its storage and final disposal came to pose a great challenge to the technical people involved in this matter these last few years. This study aims to present an alternative for the exploitation of this residue, to these traditionally employed in the alcohol production industry, based on the treatment and transformation of vinasse to biogas, and its subsequent utilization in eletric generation. In this context the technology of high efficiency anaerobic digestion using up-flow anaerobic digestors for biogas production was adapted. Once purified, the biogas produced can be utilized in engines and turbines specially adapted for this fuel, as evinced in the literature consulted. With a view to evaluate the pratical feasibility of this work, the elaboration of a case study was selected, in which a hypothetical distillery with a capacity of about 150.000 litres of alcohol/day, would generate a volume of about 1.800.000 litres of vinasse/day. By means of this simulation, the technical and economic aspects involved were analyzed, thus making possible a critical and realistic appreciation of the study proposed.

Piezoelectric energy harvesting is the process of taking an external mechanical input and converting it directly into electrical energy via the piezoelectric effect. To determine the power created by a piezoelectric energy harvester, a specific application with defined input and design constraints must first be chosen. The following thesis established a concept design of a hydrokinetic energy harvesting system, the piezoelectric artificial kelp (PAK), which uses piezoelectric materials to harvest coastal ocean waves while having a beneficial impact on the surrounding environment. The harvester design mimics the configuration of sea-kelp, a naturally occurring plant that anchors to the ocean floor and extends into the water column. Underwater currents caused by wave-action result in periodic oscillations in the kelp. In order to determine the average power generated by this design concept, predictive tools were devised that allowed for the determination of the optimized average power produced by the piezoelectric energy harvester. For a stiff energy harvester, the linear differential equations were analytically solved to find an equation for the average power generated as a function of design parameters. These equations were used to compare the effect on power output of the design configuration and piezoelectric material choice between a piezopolymer (PVDF) and a piezoceramic (PZT). The homogeneous bimorph was found to have the optimal design configuration and it was shown that a harvester constructed using PVDF would produce approximately 1.6 times as much power as one using PZT. For a flexible energy harvester, an iterative nonlinear solution technique using an assumed polynomial solution for the local curvature of the energy harvester was used to verify and extend the analytic solutions to large deflections. An energy harvester was built using off-the-shelf piezoelectric elements and tested in a wave tank facility to validate experimentally the voltage and average power predicted by the analytical solution. The iterative code showed the PAK harvester to produce volumetric power on the order of other energy harvesting concepts (17.8 micro [mu]W/cm³). Also, a full-scale PAK harvester approximately ten meters long in typical wave conditions was found to produce approximately one watt of power.

<p> Various environmental and economic factors have lead to increased global investment in alternative energy technologies such as solar and wind power. Although methodologies for synchronous generator control are well researched, wind turbines present control systems challenges not presented by traditional generation. The varying nature of wind makes achieving synchronism with the existing electrical power grid a greater challenge. Departing from early use of induction machines, permanent magnet synchronous generators have become the focus of power systems and control systems research into wind energy systems. This is due to their self excited nature, along with their high power density. The problem of grid synchronism is alleviated through the use of high performance power electronic converters. In achievement of the optimal levels of efficiency, advanced control systems techniques oer promise over more traditional approaches. Research into sliding mode control, and linear matrix inequalities with nite time boundedness and H&infin; performance criteria, when applied to the dynamical models of the system, demonstrate the potential of these control methodologies as future avenues for achieving higher levels of performance and eciency in wind energy.</p>

<p> Wind turbines typically rely on feedback controllers to maximize power capture in below-rated conditions and regulate rotor speed during above-rated operation. However, measurements of the approaching wind provided by Light Detection and Ranging (lidar) can be used as part of a preview-based, or feedforward, control system in order to improve rotor speed regulation and reduce structural loads. But the effectiveness of preview-based control depends on how accurately lidar can measure the wind that will interact with the turbine. </p><p> In this thesis, lidar measurement error is determined using a statistical frequency-domain wind field model including wind evolution, or the change in turbulent wind speeds between the time they are measured and when they reach the turbine. Parameters of the National Renewable Energy Laboratory (NREL) 5-MW reference turbine model are used to determine measurement error for a hub-mounted circularly-scanning lidar scenario, based on commercially-available technology, designed to estimate rotor effective uniform and shear wind speed components. By combining the wind field model, lidar model, and turbine parameters, the optimal lidar scan radius and preview distance that yield the minimum mean square measurement error, as well as the resulting minimum achievable error, are found for a variety of wind conditions. With optimized scan scenarios, it is found that relatively low measurement error can be achieved, but the attainable measurement error largely depends on the wind conditions. In addition, the impact of the induction zone, the region upstream of the turbine where the approaching wind speeds are reduced, as well as turbine yaw error on measurement quality is analyzed.</p><p> In order to minimize the mean square measurement error, an optimal measurement prefilter is employed, which depends on statistics of the correlation between the preview measurements and the wind that interacts with the turbine. However, because the wind speeds encountered by the turbine are unknown, a Kalman filter-based wind speed estimator is developed that relies on turbine sensor outputs. Using simulated lidar measurements in conjunction with wind speed estimator outputs based on aeroelastic simulations of the NREL 5-MW turbine model, it is shown how the optimal prefilter can adapt to varying degrees of measurement quality. </p>

<p> In this study, the effect of a passive trapped-vortex cell on lift to drag (L/D) ratio of an FFA-W3-301 airfoil is studied. The upper surface of the airfoil was modified to incorporate a cavity defined by seven parameters. The L/D ratio of the airfoil is modeled using a radial basis function metamodel. This model is used to find the optimal design parameter values that give the highest L/D. The numerical results indicate that the L/D ratio is most sensitive to the position on an airfoil&rsquo;s upper surface at which the cavity starts, the position of the end point of the cavity, and the vertical distance of the cavity end point relative to the airfoil surface. The L/D ratio can be improved by locating the cavity start point at the point of separation for a particular angle of attack. The optimal cavity shape (o19_aXX) is also tested for a NACA0024 airfoil.</p>

<p>Lignocellulosic biomass is a renewable, sustainable resource that can replace or supplement fossil fuels use for liquid fuels and chemicals. However, its recalcitrant structure including interwoven cellulose, hemicelluloses, and lignin biomacromolecules is challenging to deconstruct. Pretreating biomass so that it can be converted to useful liquids dominates process economics. Many pretreatment methods exist, but most require hazardous chemicals or processing conditions. Many ionic liquids (ILs), salts molten below 100&deg;C, can be used to deconstruct lignocellulosic biomass and are less hazardous than the volatile organic compounds typically used. </p><p> While effective, relatively safe, and recyclable, ILs are expensive. To reduce costs, dilution with other safe compounds is desirable, if there is no impact on deconstruction efficiency. Glycerol, a food additive, is inexpensive and becoming even more so since it is a by-product of the burgeoning biodiesel industry. Use of glycerol as an additive or diluent for ILs is extensively evaluated in this work. </p><p> Rice hulls are an abundant biomass, with over 100 million tons produced per year, but with little practical use. The IL 1-ethyl-3-methylimidazolium formate ([C2mim][O2CH] or EMIM Form) when mixed with an equal amount of glycerol has been shown to be effective in pretreating rice hulls. Ambient pressure, a pretreatment temperature of 110&deg;C, and a reaction time of three hours produced rice hulls that could be enzymatically hydrolyzed to give reasonably good glucose and xylose yields considering the recalcitrance of this silica-armored biomass. </p><p> The IL [C2mim][O2CH] was also effective when mixed with an equal amount of glycerol to pretreat loblolly pine, a fast-growing softwood. Loblolly pine was pretreated at 140&deg;C for three hours to produce a solid rich in cellulose and hemicelluloses, while a lignin-rich product could be precipitated from the IL. Similar products were obtained from pretreatment with a mixture of 75% 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc] or EMIM Ac) and 25% glycerol. Enzymatic hydrolysis of the pretreated solids gave glucose, mannose, and xylose yields up to 18 times that of the raw pine. </p><p> Viscosity measurements of pure glycerol, [C2mim][O2CH], [C2mim][OAc], and IL-glycerol mixtures were very different at ambient temperature, but were similar at typical biomass pretreatment temperatures. Biomass pretreated by mixtures with higher viscosity tended to give better carbohydrate yields after enzymatic hydrolysis. Higher excess molar volumes, <i>V_m^E</i>, tended to align with better carbohydrate yields after enzymatic hydrolysis. This phenomenon may relate to more energy put into shearing flow of the IL-glycerol-biomass system resulting in biomass particle shearing or stretching that allowed better solvent access into the biomass. </p>

<p> The development of better energy conversion and storage devices, such as fuel cells and batteries, is crucial for reduction of our global carbon footprint and improving the quality of the air we breathe. However, both of these technologies face important challenges. The development of lower cost and better electrode materials, which are more durable and allow more control over the electrochemical reactions occurring at the electrode/electrolyte interface, is perhaps most important for meeting these challenges. Hence, full characterization of the electrochemical processes that occur at the electrodes is vital for intelligent design of more energy efficient electrodes. </p><p> X-ray absorption spectroscopy (XAS) is a short-range order, element specific technique that can be utilized to probe the processes occurring at operating electrode surfaces, as well for studying the amorphous materials and nano-particles making up the electrodes. It has been increasingly used in recent years to study fuel cell catalysts through application of the &Delta;&mgr; XANES technique, in combination with the more traditional X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) techniques. The &Delta;&mgr; XANES data analysis technique, previously developed and applied to heterogeneous catalysts and fuel cell electrocatalysts by the GWU group, was extended in this work to provide for the first time space resolved adsorbate coverages on both electrodes of a direct methanol fuel cell. Even more importantly, the &Delta;&mgr; technique was applied for the first time to battery relevant materials, where bulk properties such as the oxidation state and local geometry of a cathode are followed.</p>

<p> The existence and morphology, as well as the dynamics of micro-scale gas-liquid interfaces is investigated numerically and experimentally. These studies can be used to assess liquid management issues in microsystems such as PEMFC gas flow channels, and are meant to open new research perspectives in two-phase flow, particularly in film deposition on non-wetting surfaces. For example the critical plug volume data can be used to deliver desired length plugs, or to determine the plug formation frequency. The dynamics of gas-liquid interfaces, of interest for applications involving small passages (e.g. heat exchangers, phase separators and filtration systems), was investigated using high-speed microscopy - a method that also proved useful for the study of film deposition processes. </p><p> The existence limit for a liquid plug forming in a mixed wetting channel is determined by numerical simulations using Surface Evolver. The plug model simulate actual conditions in the gas flow channels of PEM fuel cells, the wetting of the gas diffusion layer (GDL) side of the channel being different from the wetting of the bipolar plate walls. The minimum plug volume, denoted as critical volume is computed for a series of GDL and bipolar plate wetting properties. Critical volume data is meant to assist in the water management of PEMFC, when corroborated with experimental data. The effect of cross section geometry is assessed by computing the critical volume in square and trapezoidal channels. Droplet simulations show that water can be passively removed from the GDL surface towards the bipolar plate if we take advantage on differing wetting properties between the two surfaces, to possibly avoid the gas transport blockage through the GDL. </p><p> High speed microscopy was employed in two-phase and film deposition experiments with water in round and square capillary tubes. Periodic interface destabilization was observed and the existence of compression waves in the gas phase is discussed by taking into consideration a naturally occurring convergent-divergent nozzle formed by the flowing liquid phase. The effect of channel geometry and wetting properties was investigated through two-phase water-air flow in square and round microchannels, having three static contact angles of 20, 80 and 105 degrees. Four different flow regimes are observed for a fixed flow rate, this being thought to be caused by the wetting behavior of liquid flowing in the corners as well as the liquid film stability. Film deposition experiments in wetting and non-wetting round microchannels show that a thicker film is deposited for wetting conditions departing from the ideal 0 degrees contact angle. A film thickness dependence with the contact angle theta as well as the Capillary number, in the form <i>h_R &ap; Ca(^2/3)/cos(&thetas;)</i> is inferred from scaling arguments, for contact angles smaller than 36 degrees. Non-wetting film deposition experiments reveal that a film significantly thicker than the wetting Bretherton film is deposited. A hydraulic jump occurs if critical conditions are met, as given by a proposed nondimensional parameter similar to the Froude number. Film thickness correlations are also found by matching the measured and the proposed velocity derived in the shock theory. The surface wetting as well as the presence of the shock cause morphological changes in the Taylor bubble flow.</p>

<p> This thesis estimates the impacts of rooftop photovoltaic (PV) capacity on electricity generation and CO2 emissions in America's Pacific Northwest. The region's demand for electricity is increasing at the same time that it is attempting to reduce its greenhouse gas emissions. The electricity generated by rooftop PV capacity is expected to displace electricity from fossil fueled electricity generators and reduce CO2 emissions, but when and how much? And how can this region maximize and focus the impacts of additional rooftop PV capacity on CO2 emissions? To answer these questions, an hourly urban rooftop PV generation profile for 2009 was created from estimates of regional rooftop PV capacity and solar resource data. That profile was compared with the region's hourly fossil fuel generation profile for 2009 to determine how much urban rooftop PV generation reduced annual fossil fuel electricity generation and CO2 emissions. Those reductions were then projected for a range of additional multiples of rooftop PV capacity. The conclusions indicate that additional rooftop PV capacity in the region primarily displaces electricity from natural gas generators, and shows that the timing of rooftop PV generation corresponds with the use of fossil fuel generators. Each additional Wp/ capita of rooftop PV capacity reduces CO2 emissions by 9,600 to 7,300 tons/ year. The final discussion proposes some methods to maximize and focus rooftop PV impacts on CO2 emissions, and also suggests some questions for further research.</p>

<p> Proton exchange membrane fuel cells are a promising technology for the automotive industry. However, it is necessary to develop effective diagnostic tools to improve system reliability and operational life to be competitive in the automotive market. Early detection and diagnosis of fuel cell faults may lead to increased system reliability and performance. An efficient on-line diagnosis system may prevent irreparable damage due to poor control and system fatigue. Current attempts to monitor fuel cell stack health are limited to specialized tests that require numerous parameters. An increased effort exists to minimize parameter input and maximize diagnostic robustness. Most methods use complex models or black-box methods to determine a singular fault mode. Limited research exists with pre-processing or statistical methods. This research examines the effectiveness of a Na&iuml;ve Bayes classifier on determining multiple states of health; such as healthy, dry, degraded catalyst, and inert gas build-up. Independent component analysis and principal component analysis are investigated for preprocessing. An automotive style fuel cell model is developed to generate data for these purposes. Since automotive applications have limited computational power, a system that minimizes the number of inputs and computational complexity is preferred.</p>