<p> Torrefaction is a thermal pre-treatment process used to enhance the properties of biomass, including calorific value, hydrophobicity, and grindability, which makes it economically viable as fuel. Bagasse has a strong potential as a fuel when torrefied and can be used in many commercial applications. This research primarily focuses on the evaluation of bagasse as a potential feedstock to produce solid fuel comparable to coal using torrefaction and investigation of torrefaction process parameters. </p><p> Bagasse was torrefied at five different temperatures, 250&deg;C, 270&deg;C, 290&deg;C, 310&deg;C, and 330&deg;C, for 1 hour to investigate the effect of temperature on degree of torrefaction. It was noticed that an increase in temperature improved the degree of torrefaction. This enhanced degree of torrefaction improved the properties of bagasse by reducing the hydrogen and oxygen contents, thereby increasing the percentage of carbon, which resulted in an increase of higher heating value. Decrease in moisture content was observed with temperature. The permanent gases obtained from the torrefaction mainly had carbon monoxide and carbon dioxide along with traces of hydrogen and methane. With temperature increase in the energy of permanent gases was noticed, and most of the energy was obtained from carbon monoxide. Condensable volatiles were also observed to increase with temperature. </p><p> The effect of residence time was studied by conducting the experiments with residence times 10, 30, and 60 minutes at 330&deg;C. Residence time had a similar effect as that of the temperature enhancing the degree of torrefaction, thereby the fuel properties of bagasse. </p><p> Influence of carrier gas on the torrefaction was studied with different gases at 290&deg;C with 1-hour residence time. The carrier gases used were nitrogen, carbon dioxide, and nitrogen in 80:20 ratio by volume, steam, synthesized syngas (46.978% N₂, 17.99% CO₂, 15.04% H₂, 14.99% CO, and 5.002% CH₄), and hydrogen and nitrogen in the ratios of 5:95 and 30:70. When carbon dioxide was used, bagasse had a better degree of torrefaction than that in the presence of nitrogen. It was noticed that steam, syngas, and hydrogen had a better influence on bagasse, enhancing its degree of torrefaction, than carbon dioxide and nitrogen.</p>

In order to fully understand a fluid flow (and the resulting implications, e.g. lift, drag, turbulence, etc.) accurate velocity measurements under experimental conditions are critical. Nonintrusive techniques are essential to accurate measurements whereas more common instrumentation affects the flow. Molecular Tagging Velocimetry (MTV) is a technique which utilizes a nonintrusive molecule as a tracer in a flow. An ideal molecular candidate for such work is NO because of its stable nature. Prior work has shown that NO can be produced through photo-ionization of N2 using a 193 nm Argon Fluoride (ArF) laser. Chemical kinetic simulations were performed to determine the effect of photo-ionization levels and pressure on the production of NO. The simulations predict that the NO production is nonlinearly dependent on the amount of N2 ionization and the NO production increases with increasing pressure. They further show a positive correlation with increasing pressure. An alternate photo-ionization scheme to the ArF laser was investigated utilizing a pulsed 10 ns 355 nm Nd:YAG laser. The alternate has benefits over the ArF in safety, versatility, prevalence, storage, etc. but has not been shown to be able to produce NO before. The investigation determined that NO can be produced by 355 nm light, however MTV work is precluded due to low NO production rate. Therefore, the ns Nd:YAG is found to be an unsuitable replacement to the ArF laser for NO tag formation.

Rapid surface ablation by a turbulent flow creates complex flow and surface phenomena arising from the evolving boundary topography and its interaction with a turbulent flow that transports the ablative agent onto the surface. The dynamic nature of ablative flow boundaries generate unsteady flow dynamics and thermodynamics occurring over a wide range of scales. The non-equilibrium nature of these phenomena pose a major challenge to the current fundamental understanding of turbulence, which is mostly derived from equilibrium flows, and to Computational Fluid Dynamics (CFD). The simulation of moving boundaries is a necessary tradeoff between computational speed and accuracy. The most accurate methods use surface-conforming grids, forcing the grid to move and deform in time at a high computational cost. The technique used in this study, immersed boundary methods, removes the need for a surface-conforming grid, typically at the expense of numerical accuracy. The objectives of the present study are (i) to develop an Energy Immersed Boundary Method (EIBM) to simulate conjugate heat transfer and phase change with a spatial order of accuracy larger than one, and (ii) use the EIBM to study the dynamics of ablative flows. A generalized finite volume (FV) flow solver with second-order accuracy in time and space and energy conserving schemes is the basis of the EIBM algorithm development. The EIBM com- bines level-set method for the definition and transport of the fluid/solid interface with an immersed boundary method, i.e. a modification of the transport equation to enforce the proper boundary conditions at the solid surface. The proposed algorithm is shown to be second order accurate in space in the simulation of conjugate heat transfer flows. The validation also included comparison with phase-change (melting) experiments where it was shown to correlate very well to previous ex- periments of a rectangular slab of gallium melted from one side. As well as showing second order convergence for the mass loss and the ablated shape of a cylinder in a melting cross flow. The EIBM is applied to an investigation of the interactions between turbulence and an erodible surface. The study first focuses on the response of a turbulent flow over a receding wall, with constant recession velocity. It is found that wall recession velocities, near the small scale, the Kolmorgorov microscale, velocity of the buffer layer, produce minute shear free layers near the wall which both enhanced and stretched out the low and high velocity streaks near the wall. The larger streak area produced larger turbulent intensities on the dynamic boundary side of the channel, and far more semi-streamwise vortices. In the Second study the EIBM is applied to the ablation of a generic slab in a turbulent channel heated from one side in the absence of gravity. The study focuses on the characterization of the surface topography in relation to the evolution of coherent structures in the flow as ablation proceeds. The produced surface topology is linked to the flow topology and the turbulent generating and dissipating forces inside the turbulent flow. It is shown that the streaks for stefan numbers producing average ablation velocities slightly smaller than the Kolmorgorov microscale create groves in which the high speed buffer layer streaks sit, and their sinus motion in the spanwise direction is reduced.

<p> Transport of momentum and heat in non-equilibrium wall-bounded flows is studied analytically and experimentally to better understand the underlying physics, transition dynamics, and appropriate flow scaling in non-equilibrium flows. Non-equilibrium flows, in which the mean flow time scales are comparable to turbulent flow time scales, do not exhibit universal behaviors and cannot be characterized only in terms of local parameters. Pressure gradients, fast transients and complex geometries are among the sources that can perturb a flow from an equilibrium state to a non-equilibrium state. Since all or some of these perturbation sources are present in many engineering application relevant flow systems and geophysical flows, understanding and predicting the non-equilibrium flow dynamics is essential to reliably analyze and control such flows. </p><p> Reynolds-averaged Navier-Stokes (RANS) simulations are extensively used to model and predict fluid transport across a wide range of disciplines. The shortcoming is that most turbulence models used in RANS simulations use almost exclusively wall-models based on equilibrium boundary layer behaviors, despite the fact that many basic assumptions required of equilibrium boundary layers are not satisfied in the majority of the flow systems in which RANS simulations are used. In particular, pressure gradients, dynamic walls, roughness, and large-scale flow obstacles produce boundary layers that are strongly non-equilibrium in nature. Often the prediction of RANS simulations in complex engineering systems (with perturbations that induce non-equilibrium flow behaviors) fail spectacularly primarily owing to the fact that the turbulence models do not incorporate the correct physics to accurately capture the transport behaviors in non-equilibrium boundary layers. These failures result in over-engineered and hence, less efficient designs. This lack of efficiency manifests in higher economic and environmental costs. The broad objective of this dissertation work is to develop analytical and experimental tools needed to better understand the underlying transport physics in non-equilibrium boundary layers. </p><p> The key scaling parameter in wall-bounded flows is the wall flux of momentum and heat. It follows that an accurate determination of the wall fluxes is essential to study the dynamics of non-equilibrium wall-bounded flows. As part of this dissertation research, an integral method to evaluate wall heat flux suitable for experimental data is developed. The method is exact and does not require any streamwise gradient measurements. The integral method is validated using simulation and experimental data. Complications owing to experimental limitations and measurement error in determining wall heat flux from the method are presented, and mitigating strategies are described. In addition to the ability to evaluate the wall heat flux, the method provides a means to connect transport properties at the wall to the mean flow dynamics. </p><p> The integral method is further developed to formulate a novel and robust validation technique of Reynolds-averaged Navier-Stokes (RANS) turbulence models. Validation of the turbulence models employed in RANS simulations is a critical part of model development and application. The integral based validation technique is used to evaluate the performance of two low-Reynolds-number and two high-Reynolds number RANS turbulence models of reciprocating channel flow, and results are compared to the so-called standard validation technique. While the standard validation technique indicates that the low-Reynolds-number models predict the wall heat flux well, the integral validation technique shows that the models do not accurately capture the correct physics of thermal transport in reciprocating channel flow. Moreover, it shows that the correct prediction of the wall heat flux by the models is owed to the serendipitous cancellation of model errors. </p><p> One of the identified failures of the RANS simulations of reciprocating channel flow is the inability to accurately predict the flow dynamics during the laminar-turbulence transition. The development of improved RANS turbulence models, therefore requires an improved understanding of the underlying laminar-turbulent transition mechanisms. As part of this dissertation work, the balance of the leading order terms in the phase-averaged mean momentum equation are used to study the transition mechanism in a reciprocating channel flow. It is concluded that the emergence of an internal layer in the late acceleration phase of the cycle triggers the flow to transition from a self-sustaining transitional regime to an intermittently turbulent regime. In the absence of this internal layer, the flow remains transitional throughout the cycle. </p><p> Lastly, since experimental studies of heat transfer in non-equilibrium wall-bounded flows are very limited, a unique experimental facility was developed to study non-equilibrium boundary layers with heat transfer. The facility consists of boundary layer wind tunnel that nominally measures 303&times;135<i> mm</i> cross-section and 2.7<i>m</i> in length. A freestream heater and a thermal wall-plate are used to maintain the desired outer and inner thermal boundary conditions, respectively. A rotor-stator assembly is fabricated to generate a periodic pressure gradient used to produce pulsatile boundary layer flow. (Abstract shortened by ProQuest.)</p>

<p> Piezoelectric materials have a unique characterization which can absorb energy from the environment and convert it to electrical energy. In this conducted research energy harvesting of the THin layer UNimorph DrivER (THUNDER) were investigated. THUNDER is a curved PZT which bring considerable benefits in compare of flat PZT such as better vibration absorption capacity and higher energy recovery efficiency. Also one of the most important characteristics of THUNDER is its low resonance frequency. Because the maximum power a harvester can achieve is at its resonance frequency. So it has application in low resonance frequency situations. In this work, general constitutive law for piezoelectric materials is reduced because it is assumed THUNDER is thin and modeled as a Euler-Bernoulli beam. To obtain mechanical-electrical coupling equations, Hamilton principle is used. Hamilton principle is using kinetic and potential energy and work due to the external force as its input. As a result, modals and natural frequency of THUNDER are obtained. Then based on boundary condition, natural frequency can be achieved. By using Rayleigh-Ritz approach and in-extensional assumption and assuming excitation is sinusoidal, discretize mechanical-electrical coupling equations can be written. For the experiment part, two modes energy harvesting circuit is used, the first one is full bridge rectifier in low-level excitation and steps down converter in high-level excitation. Also, resistor and battery are used as an external load. Because rectified voltage is equal battery voltage, so the model needs to be adjusted by putting a step-down converter in the circuit to adjust Voltage and get the maximum power from the model. In the case of the resistor as an external load, the maximum power will achieve near resonance frequency and also by increasing the amplitude of resistors, more power can be achieved by the circuit. Also, step down converter is used in two modes, continuous conduction mode(CCM) and Discontinuous conduction mode(DCM). Power harvesting in this two mode also compared.</p>

Axial turbomachines have inherently unstable flow fields due to the interaction between rotating and nonrotating blade rows. In addition, combustor instabilities add considerable stress on the blading via the introduction of localized radial and/or circumferential temperature discontinuities known as hot streaks. To alleviate the losses due to nonconformities within the turbine a computational effort has been undertaken investigating the effects of clocking an imbedded stage in a multi- stage axial turbine and a separate study considering the effects of an imposed temporally oscillating hot streak within a 1 1/2 stage turbine. Time-dependent hot streak results show little relation of rotor surface heating to hot streak frequency (non-dimensional) for hot streak frequencies less than unity. The general trend for stator 2 is observed to be as hot streak frequency increases stator 2 observes a decreasing trend in surface heating for frequencies less than unity. At unity rotor surface heating is minimized and stator 2 surface heating is maximized, if the rotor is properly phased (180°) with the hot streak. When the hot streak is in phase with the rotor a rotor maximum surface temperature is observed and the stator 2 is at a minimum. Multi-stage clocking shows a periodic effect on loss and efficiency for the clocked airfoils and the rotor between. Loss and effeciency in the current study are observed to vary inversely to one another with high vane loss corresponding to higher efficiency in the vane rows, while high loss in the vane corresponds to low losses of greater magnitude in the rotor row.

As energy demand steadily increases, sulfur battery chemistries gain more and more attention for their promise to enable long-duration portable energy (Li-S system) and extremely low cost stationary storage for incorporation of renewables (Na-S system). The Li-S battery, which converts metallic lithium and elemental sulfur to lithium sulfide (Li2S) reversibly at the cathode, promises 6X the energy storage of the conventional Li-ion battery. This dissertation enables high performance Li-S cathodes by mitigating poor electrical conductivity and solubility of active materials with careful nanomaterial design. Further, this work champions dramatically improved sulfur composite processing technique using low temperature (175°C), isothermal vapor, which facilitates optimal performance of the nanomaterial electrode designs. This process also boasts enhanced scalability over the conventional melt infiltration with 60X throughput at the same low temperature. By pushing the limits of the isothermal vapor infiltration technique, this work demonstrates one of the first highly stable, low-cost room temperature Na-S cathodes. This electrode, developed from table sugar, provides significant hope for, grid storage, competitive in price with burning natural gas, to allow penetration of renewable resources into the grid by load leveling weather related intermittencies.

<p> The goal of this work is to investigate the effect of electric and magnetic field on the optical resonances of electrostrictive and magnetorheological optical resonators. The optical resonances, also known as whispering gallery modes (WGM) or morphology dependent resonances (MDR) experience a shift in the transmission spectrum whenever the resonator changes its size and/or index of refraction. Their small size, the elimination of electrical cabling, and the high optical quality factor, Q, make them attractive for a large number of applications. In these studies, we investigate the magnetostrictive and the electrostrictive effect of fiber coupled photonic spherical resonators. The electrostrictive and the magnetostrictive effect are the elastic deformation of a solid when subject to an electric or magnetic field respectively. In these studies, three different configurations were investigated to tune the optical modes of the spherical optical resonator. In the first configuration, the resonator was fabricated by embedding magnetic micro particles in a polymeric matrix of PVC plastisol (commercial name super soft plastic, SSP). For these configurations we studied the WGM shift that was induced when the sphere was immersed in a static and a harmonic magnetic field. These results lead to the development of a magnetic flied sensor and a non-contact transduction mechanism for displacement measurements. The sphere showed a sensitivity to the magnetic field of 0.285 pm/mT and to the displacement of 0.402 pm/?m. These values lead to a resolution of 350 ?T and 248 nm respectively. The second configuration was a microsphere that was made of pure super soft plastic and was subject to a static and harmonic electric field. The results lead to the development of a non-contact displacement sensor whose sensitivity is 0.642 pm/?m and the resolution is 155 nm. Both studies also indicate for the first time that it is possible to couple light into a PVC compound and achieve high optical quality factor of the order of 106. The third configuration was a metglas film that was mechanically coupled to a PDMS microsphere. The results of these studies lead to the development of a magnetic field sensor with sensitivity and resolution of 0.6 pm/?T and 166 nT respectively. In conclusion, these studies lead to a fundamental understanding of the dynamical behavior of electrostrictive and magnetorheological optical resonators and its potential for sensing applications. In addition, these devices could be embedded into polymeric matrix for the development of materials with actuation and sensing capabilities.</p><p>

<p> A computational fluid dynamics (CFD) model is developed for pulsatile flows and particle transport to evaluate the possible thrombus trajectory in the feline aorta for Hypertrophic Cardiomyopathy (HCM) heart conditions. An iterative target mass flow rate boundary condition is developed, and turbulent simulations with Lagrangian particle transport model are performed using up to 11M grids. The model is validated for human abdominal aorta flow, for which the results agree within 11.6% of the experimental data. The model is applied for flow predictions in a generalized feline aorta for healthy and HCM heart conditions. Results show that in the HCM case, the flow through the iliac arteries decreases by 50%, due to the large recirculation regions in the abdominal aorta compared to the healthy heart case. The flow recirculation also result in stronger vortices with slower decay, causing entrapment of particles in the thoracic aorta and trifurcation regions.</p>

<p> The increasing power density of high-performance electronics has created a need for advanced thermal management strategies. Vapor compression cycles (VCC) offer large heat transfer coefficients via low coolant temperatures and boiling heat transfer, and thus are attractive for electronics cooling. However, the high heat flux imposed by electronics requires new modeling and control techniques for VCC implementation. Challenges include transient heat loads, critical heat flux (CHF), refrigerant charge management, and multi-evaporator management. This dissertation presents research to improve the fundamental understanding of systems-level design, modeling and control of multiple evaporator VCC for high heat flux removal. An experimental testbed is presented, with the option of switching between a heated accumulator and a recuperator to maintain cycle active charge. Static component, heat transfer, and dryout models are identified, and low-order lumped dynamic system models are developed and validated for both accumulator and recuperator operation. The static and dynamic models are used to develop robust, decoupled dryout avoidance controls to provide stability, reject large thermal disturbances and improve cycle energy efficiency. Finally, experimental and simulation results are presented for control validation.</p>