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Abstract: This thesis focuses on the manufacturing of high carbide content wear-resistant parts by extrusion- based Additive Manufacturing (AM) based on the principles of Powder Metallurgy (PM). A new manufacturing technique, termed Fused Filament Fabrication of Cermets (FFFC) is presented. First, particle packing theory is applied to develop a methodology for maximizing packing density and carbide content in non-ideal binary powder mixtures. Based on this optimization, sinterable metal-ceramic polymer filaments suitable for Fused Filament Fabrication (FFF) are prepared and printed. It is shown that a traditional polymer 3D printer can be used to successfully deposit high- density polyethylene (HDPE) composite filaments containing up to 46 vol% Ni-TiC and Ni-WC fillers, to produce dense green parts for sintering. A characterization of the composite filaments and resultant printed parts is provided. An analysis of the random loose void fractions in dry fillers and the fraction of polymer in the composite after polymer is injected into the dry filler is presented. It is concluded that, the maximum void contraction (∆Θmax) is a function of the ratio of mean particles sizes (δ) in binary dry powder mixtures. As δ decreases and the particle sizes become more dissimilar, an increasing deviation from the ideal rule-of-mixtures law is observed. The critical δ is revealed to be 0.65. Furthermore, when dry filler is mixed with HDPE to form composite filaments for FFF, the particles are rearranged, and the polymer content of the filled composite is greater than the void fraction observed in dry filler packing. Fillers having lower dry void fractions, reported higher polymer contents in their composites. The important role of non- ideal particle packing in binary filler mixtures is emphasized, where the goal is to produce high carbide content cermet parts. Some remarks about process parameters that influence part quality and suggestions for future work are included.

The main goal of this research is to study the surface properties of liquid-vapor and liquid-liquid-vapor interfaces with high precision using the technique of surface light scattering spectroscopy (SLSS), which measures the power spectrum of light scattered from thermally generated capillary waves with an rms height ~1 nm. This power spectrum depends on both surface and bulk properties of the fluid, including surface tension and bulk viscosity, allowing the inference of the values of these and perhaps other parameters. In this dissertation, I focus on the surface tension and bulk viscosity associated with a liquid. Innovative optical design has increased signal and signal-to-noise ratio. This enhances measurement accuracy over the entire range of wave numbers, while enabling measurements at higher wave numbers above 1500/cm. After refining the apparatus and technique as much as possible, I apply it to a sequence of systems. (a) Simple Fluids: Standard materials including acetone, pentane, methanol and water serve to calibrate and validate the SLSS technique and experimental protocol. (b) Highly viscous fluids, relevant for capillary-driven fluid management to control propellant transfer in space flight. We explore the regime between the overdamped and underdamped cases, which have been difficult to characterize with SLSS, using well-characterized glycerol/water mixtures. (c) Mixtures: Measurements of pentane/2-methylpentane mixtures prepare for an upcoming NASA microgravity experiment to optimize the effectiveness of wickless heat pipes. (d) Thin organic films on water: coupling between upper and lower interfaces of a thin film allows the study of Casimir-Polder forces and measurement of the onset of wave mode transitions, for example, peristaltic suppression. (e) Molecularly thin films on water: thin films of a smectic liquid crystal on water have many applications, directly as biosensors, and indirectly, to develop a better understanding of alignment layers in LCD technology and a fundamental understanding of thin-film phase separation, which also applies to the biological sciences.

Mixtures of charged particles, where the components have different charge numbers (Z_A ), masses (m_A ) and densities (n_A ), with A = 1, 2 denoting the components, occur in Nature in a great variety. To be sure, even the simplest plasmas are necessarily multicomponent systems, consisting of negative and positive charges. This feature is, however, obscured within the centrally important and popular OCP (one component plasma) or jellium models, where the role of one of the components is reduced to providing a neutralizing background. When this background is inert, one is led to the Coulomb OCP model, while when the background is polarizable (such as an electron gas surrounding heavy particles), to a Yukawa OCP (YOCP), with a screened Yukawa potential replacing the Coulomb potential between the dynamically active particles. There are, however situations of physical importance, where the OCP description is inadequate and a genuine two component description of a plasma composed of two species is required. This Thesis focuses on the study of the dynamics of many-body systems consisting of two components of like charges (all the Z_A -s being of the same signature) in a neutralizing background. The methodology is based upon parallel attacks through theoretical analysis and Molecular Dynamics (MD) simulations, the latter yielding the capability of instant verification of the former. The investigation involves the study of the partial (i.e. species by species) structure functions S_AB (k, ω) and current-current correlation functions L_AB (k, ω). The Fluctuation–Dissipation Theorem (FDT) con- nects these quantities to the total and partial response functions χ_AB (k, ω) (matrices in species space), which are instrumental in the description of the collective mode excitations of the system. This analysis has revealed an entirely novel feature: both S_11 (k, ω) and S_22 (k, ω) exhibit very sharp and deep (several orders of magnitude) minima in the strongly coupled liquid phase at robust characteristic frequencies of the system, which are virtually coupling independent. The FDT then demands that these anti-resonances show up as well in the imaginary part of the partial density response function χ_AB (k, ω). Our theoretical analysis, based on the Quasi-Localized Charge Approximation (QLCA), has confirmed that this is indeed the case. These anti-resonant frequencies being related to the dissipative part of the response, require a physical description of the principal source of dissipation. This has been identified as the inter-species momentum transfer, governed by drag between the microscopic current fluctuations of the two species. The description of this effect was incorporatedv in the QLCA formalism, making it possible to derive a closed analytic representation of the fluctuation spectra in the frequency domain of interest and compare them with the results of the MD simulations. Other important novel concepts, such as the idea of coupling dependent effective mass, fast vs. slow sound, the mechanism of tran- sition from short-range to long-range interaction have been identified and analyzed. Furthermore, the investigation of the dynamics has led to the first comprehensive description of the mode structures of classical binary Coulomb and Yukawa mixtures at arbitrary coupling values, which has been a longstanding problem in statistical plasma physics. Focusing on the longitudinal excitations, we describe the transition from weak coupling (where one is acquainted with the RPA result yielding only the single plasmon mode in the Coulomb case or a single acoustic mode in the Yukawa case) to strong coupling, with a doublet of modes that arise from the complex rel- ative motion between the two components, as affected by the interaction with the background.

Two-phase spray cooling has been an emerging thermal management technique offering high heat transfer coefficients and critical heat flux levels, near-uniform surface temperatures, and efficient coolant usage that enables to design of compact and lightweight systems. Due to these capabilities, spray cooling is a promising approach for high heat flux applications in computing, power electronics, and optics. Two-phase spray cooling inherently depends on saturation temperature-pressure relationships of the working fluid to take advantage of high heat transfer rates associated with liquid-vapor phase change. When a certain application requires strict temperature and/or pressure conditions, thermo-physical properties of the working fluid play a critical role in attaining proper efficiency, reliability, or packaging structure. However, some of the commonly used single-component working fluids have relatively poor properties and heat transfer performance. For example, water is the best coolant in terms of properties, yet in certain applications where the system operates at low temperature ambient, it cannot be implemented due to freezing risk. The common solution for this problem is to use the antifreeze mixtures (binary mixtures of water and alcohol) to reduce the freezing point. In such cases, utilizing binary mixtures to tune working fluid properties becomes an alternative approach. This study has two main objectives; (1) to experimentally investigate the two-phase spray cooling performance of water/2-propanol binary mixture, and (2) to numerically investigate the performance of an advanced heat spreader featuring high and directional thermal conductivity materials for high heat flux focal sources. The first part of the study involves experimental characterization of heat transfer performance. Tests are conducted on a small-scale, closed loop spray cooling system featuring a pressure atomized spray nozzle. The test section, made of copper, measures 10 mm x 10 mm x 2 mm with a plain, smooth surface. A cylindrical copper block, with a matching size square protrusion attached onto the back side of the test section, generates heat using cartridge heaters and simulates high heat flux source. Embedded thermocouples are used to determine the spray surface temperature. The working fluid, water/alcohol mixture, has various concentration levels of 2-propanol by mass fraction 0.0 (pure water), 0.25, 0.50, 0.879 (azeotrope) and 1.0 (pure alcohol)), representing both non-azeotropic and azeotropic cases. Spray cooling tests are performed with a constant flow rate of 5.6 ml/cm².s at subcooled temperatures (~20oC) and atmospheric pressure. Experimental procedure involves controlling the heat flux in increasing steps, and recording the corresponding steady-state temperatures to obtain cooling curves in the form of surface superheat vs. heat flux. The second part of the study investigates an advanced heat spreader design for thermal management of a high heat flux focal source. The heat spreader comprises of three layers: a copper layer that interfaces with the heat source, a high and directional thermal conductivity material (such as CVD diamond and Pyrolytic graphite) layer, and another copper layer that is exposed to two-phase spray cooling. The analysis applies various heat fluxes on the heat source side and the experimentally obtained heat transfer coefficients on the spray side of the spreader design to determine the temperature and heat flux distributions, and examine the potential capabilities of this configuration.

Abstract: Fluidized beds offer efficient solutions for segregation of clay and bitumen pellets in the oil production industry. However, the hydrodynamics of these systems is not well-known and they are mostly operated as ``black box''. The removal of clay pellets in the mechanical separation of oil sands method, requires an efficient method of separation of the pellets. By using computational fluid dynamics (CFD), the hydrodynamics of these equipments can be studied and the affecting parameters on the flow behavior be identified. In this thesis challenges in preparation of a validated CFD model are addressed and the effects of design and operating parameters on the efficiency of the method are studied. The Eulerian-Lagrangian approach is used in the CFD simulations of a slice of the bed and results are compared to a 3D full size bed and to results from literature for validation. The first study is dedicated to the analysis of the fluidization process in a fluidized bed formed with mono-dispersed sand particles. Results of the simulations are compared against experimental data and empirical solutions. A validated and grid-converged numerical model which can present the hydrodynamics of the fluidized bed is the outcome of this study. Later, bitumen pellets are added to the fluidized bed simulations, as the third phase, to study the segregation process. Results of simulations are compared to the published experimental and analytical works. To study the effect of design and operating parameters of the fluidized bed on the segregation of particles, the density ratio of the particles is decreased to increase the sensitivity of the problem. The results of the simulations showed that the carrier phase properties, as well as the width and the height of the bed, are not affecting the final degree of the mixture. However, the rate of segregation of particles is increased by reducing the static height of the bed. Also, the model showed that there should be an optimum inlet velocity at which the rate of segregation of particles is fastest and which produces the best level of segregation of particles, as expected. Among the tested values in the current study the inlet velocity of 1.25 times the minimum fluidization velocity of the jetsam was the fastest rate of segregation and most segregated state of the mixture.

Hydrothermal liquefaction (HTL) refers to the process of converting biomass to bio-oil by contacting the biomass with water at high temperatures (> 200 °C) and sufficient pressures to maintain water in the liquid state. HTL of algae producing bio-oil has the advantage of energy efficiency and capability of dealing with wet biomass. Very little is known about the mechanism and chemistry of biomacromolecules reactions in high temperature water (HTW). In this project, we overcome the existing gap by studying ethyl oleate, phenylalanine, phytol, and DOPC as representative model compounds for triglycerides, proteins, chlorophyll and phospholipid, respectively, in HTW. We examined the behavior of model compounds from 175 – 350 °C. Hydrolysis of ethyl oleate (to oleic acid) was autocatalytic. A phenomenological and mechanistic kinetics model was developed that was consistent with the experimental data. We suggest that hydrolysis of ester is catalyzed by both H+ and fatty acid. Phenylalanine primarily formed phenylethylamine, while minor products included styrene and phenylethanol isomers. Major products from phytol included neophytadiene, isophytol, and phytone, while pristene, phytene, phytane, and dihydrophytol were the minor products. Phenylalanine and phytol disappearance followed first order kinetics. DOPC hydrolyzed to form 1-acyl and 2-acyl lyso-phosphatidylcholine (LPC) along with oleic acid as primary products. LPC subsequently formed other phosphorus-containing intermediates, which finally led to phosphoric acid as the ultimate P-containing product. Hydrolysis of DOPC was catalyzed by oleic and phosphoric acids. A kinetics model based on proposed pathways was consistent with experimental data for the model compound. Lastly, we studied the effects of inorganic (salts and boric acid) and organic (ethyl oleate) additives on phenylalanine conversion and product distribution at 250 °C and 350 °C, respectively. Inorganic additives increased phenylalanine conversion favoring formation of high molecular weight compounds. Higher concentration of ethyl oleate lead to an increase in the rates of deamination of phenylethylamine and hydration of styrene. Amides are also formed due to the interaction of fatty acid/ethyl oleate and amines/ammonia. Taken collectively, the results from this study provide new insights into the reactions of algae during its HTL to produce crude bio-oil.

Interest in non-traditional fuel sources, carbon dioxide sequestration, and cleaner combustion has brought attention on gasification to supplement fossil fueled energy, particularly by a fluidized bed. Developing tools and methods to predict operation and performance of gasifiers will lead to more efficient gasifier designs. This research investigates bed fluidization and particle decomposition for fluidized materials. Experimental methods were developed to model gravimetric and energetic response of thermally decomposing materials. Gravimetric, heat flow, and specific heat data were obtained from a simultaneous thermogravimetric analyzer (DSC/TGA). A method was developed to combine data in an energy balance and determine an optimized heat of decomposition value. This method was effective for modeling simple reactions but not for complex decomposition. Advanced method was developed to model mass loss using kinetic reactions. Kinetic models were expanded to multiple reactions, and an approach was developed to identify suitable multiple reaction mechanisms. A refinement method for improving the fit of kinetic parameters was developed. Multiple reactions were combined with the energy balance, and heats of decomposition determined for each reaction. From this research, this methodology can be extended to describe more complex thermal decomposition. Effects of particle density and diameter on the minimum fluidization velocity were investigated, and results compared to empirical models. Effects of bed mass on pressure drop through fluidized beds were studied. A method was developed to predict hydrodynamic response of binary beds from the response of each particle type and mass. Resulting pressure drops of binary mixtures resembled behavior superposition for individual particles.

Liquid crystals are a group of unique functional materials showing stimuli responses. This dissertation focused on two general directions—synthesis and characterizations of liquid crystal and liquid crystal polymers. The synthesis includes the preparation of (1) side chain liquid crystal polysiloxane of various molecular weights, with cyano phenyl benzoate as mesogens, for miscibility, electrorheology and neutron scattering study; (2) deuterated 4-pentyl-4’-cyano biphenyl(d-5CB), used as the solvent for neutron scattering study; (3) hyperbranched liquid crystals based on dendritic polyols, with cyano biphenyl as the mesogens, for electrorheological study. In the miscibility study with binary mixtures of liquid crystal polysiloxane/low molar mass liquid crystals, the induced smectic phase was observed within certain composition ranges, when 4-pentyloxyl-4’-cyano biphenyl was used; while no new phase was present with the study on another series of mixtures with 4-pentyl-4’-cyano biphenyl, although exactly the same polymers were used. The induced new phase with 5OCB was confirmed with DSC thermal analysis, POM textures, X-ray study and finally, computer simulation. In neutron scattering part, d-5CB with high substitution ratio was used as the solvent with liquid crystal polysiloxane as the solute. The substitution ratio was high enough to yield enough contrast, which in return indicates the successful deuteration reactions (80% overall yield; 20% from literature). The chain confirmation measured by neutron scattering qualitatively matched that from electrorheological experiments. Electrorheological study was carried out with the dilute solutions of hyperbranched liquid crystals in 5CB, which gave the conformational anisotropy around 1.5. The modified Brochard theory (by our group) predicts no tumbling behavior with this system, which was confirmed in stress transient experiments.