Bismuth-Strontium-Calcium-Copper-Oxide (BSCCO) compounds are an important family of compounds that have one of the highest transition temperatures among all high-temperature superconductors. The compound is known to exist in three distinct phases, commonly referred to as the 2201, 2212 and 2223 phases. Of these three phases, the 2212 and 2223 phases are the most important, as their transition temperature is higher than the boiling point of liquid nitrogen. It is desirable to produce the compound in thin film form, as the bulk samples are normally polycrystalline. This thesis compares thin films produced by two techniques for depositing BSCCO in order to understand the effect of various processing parameters on the final quality of the thin films. Thin films were grown by flash evaporation at Texas A&M University, and by pulsed laser deposition (PLD) at the University of Wollongong, Australia. The latter of these techniques is widely used for growing thin films of various compounds. Single-phase 2212 films were grown on a MgO substrate using the pulsed laser deposition technique from commercially available 2212 powder. The effect of annealing on the thin films was also studied.

The development and evaluation of a fuel cell test stand incorporating various methods for controlling the temperature and humidity of fuel cell reactants is described. The test stand is capable of accurately metering gas flows, controlling the temperature and humidity of the gases, and delivering the gases to the fuel cell in a safe manner. Additionally, the test stand can measure the voltage and current produced by the fuel cell during operation. Two test stands were constructed and evaluated, one using steam injection for fuel cell stacks and the other using flash evaporation for individual fuel cells. Both test stands were shown to provide adequate control at the upper end of the design range. The flash evaporation test apparatus was used to investigate the effect of inlet gas humidity on fuel cell performance. The results from this investigation showed that, for a fuel cell and reactant temperature of 75°C, the best performance was achieved with a high relative humidity (90%RH) for the hydrogen and a comparatively low relative humidity (60%) for the air. / Master of Science

Dans la littérature, que ce soit pour un explosif secondaire ou un matériau composite, une balance en oxygène (BO) proche de 0% est assimilée à de bonnes performances énergétiques (vitesse de détonation, chaleur de décomposition, etc…). L’objectif majeur de cette thèse est d’améliorer les performances énergétiques d’explosifs secondaires courants (RDX, HMX, CL-20) par l’ajout d’un oxydant (DNA) afin d’obtenir un matériau composite avec une BO de -1%. Le mélange intime de ces deux composés est permis par un procédé d’évaporation flash de spray, utilisé habituellement pour réduire la taille de particules des explosifs. Les matériaux composites ont été cristallisés dans les trois cas avec succès, avec la présence d’explosif submicrométrique et de DNA nanostructuré. Un tel résultat a été permis grâce à une meilleure compréhension du procédé, et en conséquence l’ajustement des conditions expérimentales. L’étude de la réactivité de ces matériaux composites montre dans certains cas une désensibilisation, une diminution de la distance de la déflagration à la détonation, ou encore une augmentation de la vitesse de détonation, comparée aux explosifs correspondants. / In literature, for secondary explosive or composite material, an oxygen balance (OB) close to 0% is often linked to good energetic performances (detonation velocity, heat of decomposition, etc.). The main objective of this thesis is to enhance energetic performances of current secondary explosives (RDX, HMX, CL-20) by adding oxidizer (ADN) to obtain a composite material with an OB of -1%. The spray flash evaporation process, usually used for particle size reduction of explosives, enables to obtain an intimate mixture of these two compounds. Composite materials were successfully crystallized in three cases, resulting of submicrometric explosives and nanostructured ADN particles. These results were obtained thanks to a preliminary study for better process understanding and the optimization of experimental conditions. Reactivity studies show some desensitization, shorter distance from deflagration to detonation, and/or higher detonation velocity, compared to corresponding explosives.

Polyvinyl alcohol (PVA) desize effluent is a high COD contributor to towel manufacturing plant's Primary Oxygenation Treatment of Water operation, and being non-biodegradable, is a threat to the environment. When all-PVA/wax size is used in weaving, significant incentives exist to recover the synthetic polymer material from the desize wash water stream and reuse it. A new technology that would eliminate the disadvantages of the current Reverse Osmosis Ultrafiltration (UF) PVA recovery process is Vacuum Flash Evaporation (VFE). This research adapts the VFE process to the recovery and reuse of all-PVA size emanating from towel manufacturing, and compares the economics of its implementation in a model plant to current plant systems that use PVA/starch blend sizes with no materials/water recovery. After bench scale research optimized the VFE PVA recovery process from the desize effluent and determined the mass of virgin PVA that was required to be added to the final, recycled PVA size formulations. The physical changes in the recycled size film and yarn composite properties from those of the initial (conventional) slashing were determined using a number of characterization techniques, including DSC, TGA, SEM, tensile testing, viscometry, number of abrasion cycles to first yarn breaks, microscopy and contact angle measurements. Cotton chemical impurities extracted from the yarns during desizing played an important role in the recovered PVA film physical properties. The recovered PVA improved the slashed yarn weave ability. Along with recovered PVA, pure hot water was recovered from the VFE. Virgin wax adds to the final, recycled size formulations were determined to be unnecessary, as the impurities extracted into the desize effluent stream performed the same functions in the size as the wax. Using the bench results, the overall VFE process was optimized and demonstrated to be technically viable through six cycles, proof-of-concept trials conducted on a Webtex Continuous Pilot Slasher. Based on the pilot scale trials, comparative economics were developed. Incorporation of the VFE technology for PVA size recovery and recycling resulted in ~$3.2M/year in savings over the conventional PVA/starch/wax process, yielding a raw ROI of less than one year based on a $3M turnkey capital investment.

La cristallisation en continu de nanoparticules énergétiques est un défi de longue date. Le Spray Flash Evaporation (SFE) est une technique majeure développée et brevetée en interne, pour la production en continu de matériaux énergétiques submicroniques ou nanométriques ; la technologie se base sur la surchauffe d’un solvant pulvérisé dans le vide et s’évaporant de manière flash. Ce présent travail de recherche a pour but de comprendre et contrôler la cristallisation au sein du procédé SFE. Le RDX et le cocristal CL-20:HMX 2:1 sont étudiés. La sursaturation, concernant le SFE, est une fonction du temps et de l’espace liée aux tailles et vitesses de gouttes : elle fut variée par un anti-solvant et par l’amélioration du SFE avec un système double buse. Ensuite, PVP 40K et PEG 400 ont été utilisés afin de contrôler la nucléation et la croissance. Les particules ont pu être ajustées d’une taille de 160 nm à 5 µm, avec des morphologies facettées ou sphériques et avec des sensibilités moindres. / The continuous formation of nanosized energetic material is a long-standing challenge. Spray Flash Evaporation (SFE) is a major technique, internally developed and patented, for continuously producing energetic materials at submicron or nano scale; it relies on the superheating of a solvent sprayed into vacuum and thus flashing. This present research project aims to understand and control the crystallisation occurring in the SFE process. RDX and the cocrystal CL-20:HMX 2:1 was studied overcome the limited in situ characterizations also. The supersaturation is a function of time and space in SFE, linked to the size distribution and velocity of droplets. Supersaturation was raised with an anti-solvent and by the enhancement of the SFE with a dual nozzle system. Then PVP 40K and PEG 400 were successfully used to alter the nucleation and the growth. The particles were subsequently tuned from 160 nm spheres to 5 µm grains and were less sensitive, especially toward electrostatic discharge.

This dissertation thesis deals with the development of technology which could tackle two major issues related to biogas plants. These issues concern the insufficient use of waste heat from biogas combustion and its subsequent processing. It also concerns the use of the fermentation residues which are formed in large quantities and whose use is restricted by law. Based on a literary search of separation methods, a vacuum evaporator was selected as the most suitable technology. Its advantages include its simple construction, operational reliability and robustness, low costs of thickening medium pre-treatment, potential for a quick commercial application and, especially, the chance to use a low-potential waste heat. A primary purpose of this technological unit is the reduction in the volume of fermentation residues. Other benefits include the efficient use of waste heat from a biogas plant, which would otherwise be wasted. Evaporators with a low consumption of electrical energy (which is a main product of a biogas plant) seem to be the best option for applications in the biogas plants. Three of these technologies were subjected to a more thorough analysis, which included the development of computational models and their quantification for conditions in a sample biogas plant. A one-stage evaporator with a forced circulation (680 – 712 kWhth/m3, 25.9 – 30.5 kWhel/m3) was evaluated as the least suitable option in terms of energy demands. The energy intensity of a three-stage evaporator with a falling film (241 – 319 kWhth/m3, 12.0 – 23.6 kWhel/m3) and a nine-stage flash evaporator (236 – 268 kWhth/m3, 13.6 – 18.4 kWhel/m3) is significantly lower. A multi-stage flash evaporator (MSF) was then chosen for development and will form the central focus of this thesis. The reasons for the choice are as follows: the low requirements on the heat transfer surface, good operational experience in the field of desalination, its simple construction, modularity and evaporation outside the heat transfer surface. A thorough technical-economic evaluation was also performed on the integration of the evaporator into the biogas plant. The main part of the work included the experimental development of a MSF evaporator prototype. The main objective of this development was to achieve a stable flow rate of the thickening liquid digestate fraction and the continuous formation of the distillate. This was not an easy objective to achieve, especially due to the properties of the liquid digestate, which has a non-newtonian characteristic and increased density and viscosity compared to water. The tendency of the liquid digestate to form foam was also the subject of analysis. The development of the evaporator and first successful operational test are described in the thesis in detail. This required the use of an anti-foaming product. A fully-developed prototype of the MSF evaporator allowed us to achieve continuous operation with a distillate production, reaching from 5 to 10 kg/h at a liquid digestate flow rate of 0.4–0.5 m3/h. The main drawback of this technology is the pollution of the distillate with ammonia nitrogen, and it is for this reason that the basic procedures of its subsequent elimination was selected for further analysis.