Neste trabalho foi estudado o processo de moldagem por injeção em baixa pressão (LPIM do inglês: low-pressure injection molding) de pós cerâmicos submicrométricos para a produção de molas cerâmicas. O trabalho compreende a confecção de moldes e pequenas injetoras de laboratório, extração dos ligantes orgânicos utilizados durante a moldagem, a sinterização das peças e alguns ensaios preliminares para avaliar as propriedades mecânicas de molas cerâmicas. A LPIM apresenta muitas vantagens na produção de peças cerâmicas complexas, quando comparada à moldagem por injeção tradicional. Entretanto LPIM apresenta alguns problemas na remoção da mistura de ligantes que são maiores quando se confecciona peças cerâmicas preparadas com pós submicrométricos. Mas, por outro lado, a utilização destes pós permite a obtenção de corpos sinterizados com alta densidade e excelentes propriedades mecânicas. Os pós cerâmicos utilizados foram a alumina (Al2O3) e a zircônia (ZrO2), e o ligante principal utilizado foi a parafina. Moldes tubulares e moldes usinados multipartidos foram desenvolvidos para moldagem por injeção de molas de alumina e uma pequena injetora foi construída para injetar peças de zircônia. Os moldes tubulares mostraram-se pouco adequados. Por outro lado, a utilização do molde de latão multipartido, revestido com PTFE (politetrafluoretileno), melhorou o processo de fabricação de molas cerâmicas, possibilitando a confecção de quantidades maiores e com boa reprodutibilidade. No processo de sinterização das molas cerâmicas as distorções foram evitadas utilizando cilindros cerâmicos como suporte das molas. As molas de alumina e zircônia tiveram suas densidades e durezas medidas e estão de acordo com a literatura. Finalmente, foram feitos alguns ensaios preliminares de compressão com molas cerâmicas de alumina e zircônia para avaliar sua constante de mola e a carga máxima suportada antes da quebra. / In this work the low-pressure injection molding (LPIM) of submicrometer-sized ceramic powders was studied aiming to produce ceramic springs. The work comprised the production of molds and laboratory equipment for injection molding, the debinding of the organic vehicle used in the molding, the sintering of ceramic parts, and some preliminary experiments to evaluate the mechanical properties of the ceramics springs. The LPIM presents many advantages for complex ceramic parts production, in comparison with traditional high-pressure injection molding. However, LPIM has some difficulties associated to the debinding step, that are even greater for ceramic parts made with submicrometer-sized powders. But, on the other hand, the use of submicrometer-sized powders allows the production of sintered bodies with high density and better mechanical properties. The submicrometer-sized ceramic powders used in this work were alumina (Al2O3) and zirconia (ZrO2), and the main binder was the paraffin. Tubular molds and a multipart machined mold were developed for injection molding of alumina springs, and a little injection machine was build for injection molding of zirconia parts. The tubular molds had a limited performance. On the other hand, the multipart brass mold, coated with PTFE (polytetrafluorethylene), improved the ceramics spring molding process, making it possible to produce ceramic springs in greater quantities with good reproducibility. In the sintering process of the ceramic springs, major distortions of the parts were avoided using ceramic beams to support the springs. The alumina and zirconia ceramic springs had their measured density and hardness in good agreement with literature. Finally, some preliminary compression tests were performed with alumina and zirconia ceramic springs in order to evaluate their spring constant and maximum load before failure.

Increased electrical power demands are being experienced on the new generation of aircraft due to an increased reliance on electrical technology of systems such as air conditioning, de-icing systems and electrical flight control actuation. Distribution of power at higher AC and DC voltages is therefore now being seen in modern aircraft to avoid the penalties incurred due to high cable weights. Voltages have increased past the minimum of Paschen's law resulting in a risk that life limiting partial discharge (PD) damage can occur in the insulation systems. This thesis uses a theoretical analysis backed by PD experimental results to investigate the optimal operating voltage of a cabling system. In addition, it proposes a methodology for optimizing the operating voltage level based on an analysis of the power carrying capability of cabling within a fixed and a non-fixed volume system and the derivation of the cable weight as a function of voltage. Furthermore the power carrying capability of a certain round cable system is compared with an insulated flat conductor system as in a printed circuit board (PCB). An initial assessment has been carried out to determine whether more power can be delivered via insulated flat solid conductors as in a PCB, instead of using round cables. The reason why there is a need to investigate this aspect, is because using new PCB technology can offer several advantages over traditional cabling harnesses. The work done has shown that the optimal operating point (e.g. maximum power to weight ratio) for an aircraft power system, does not improve after certain voltage levels. A tradeoff between cable weight and power transfer is required and furthermore the use of DC systems can result in higher power transfers than conventional three phase/400Hz AC systems. The PCB maximum power transfer assessment has also shown that insulated flat conductor systems can offer higher power transfer efficiencies. In addition, experimental AC and DC PD tests on certain unscreened aerospace cables (laid out in different configurations), have shown that the theoretical analysis employed to determine cable safe operating voltages gives conservative results.

Orientadores: Maria Angela de Almeida Meireles, Diego Tresinari dos Santos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-22T11:14:12Z (GMT). No. of bitstreams: 1 Vardanega_Renata_M.pdf: 2211548 bytes, checksum: 6075d57c9fcfd91ae66badca9ff3939a (MD5) Previous issue date: 2013 / Resumo: Espécies do gênero Pfaffia (Amaranthaceae) têm sido comercializadas como substitutas para Panax (ginseng, Araliaceae) e em função da morfologia similar de suas raízes são popularmente conhecidas como ginseng brasileiro. Dentre as espécies de Pfaffia conhecidas, a Pfaffia glomerata é a mais importante, uma vez que esta é a única que possui o composto ?-ecdisona, o qual representa a saponina de maior interesse desta planta, devido a seus efeitos terapêuticos. Atualmente, cápsulas contendo extratos de P. glomerata são comercializadas sob indicação de auxiliar da memória e tônico. Além destas indicações, as raízes desta planta apresentam teores expressivos de saponinas (10-17%), o que faz com que o extrato das raízes de P. glomerata apresente um grande potencial para aplicação como emulsificante/surfactante. Comercialmente, extratos de P. glomerata são obtidos por percolação em leito fixo, no entanto, com baixos rendimentos. O objetivo deste estudo foi obter um extrato de ginseng brasileiro (P. glomerata) rico em saponinas empregando o processo de extração por percolação a baixa pressão, o qual é um processo de extração já estabelecido comercialmente, sob a assistência do ultrassom, que vem se destacando como uma técnica emergente na melhoria de processos de extração. Deste modo, as variáveis resposta estudadas foram o rendimento global de extração (X0) e as propriedades emulsificantes/surfactantes dos extratos obtidos: Índice de emulsificação (E24) e redução da tensão superficial da água (RTSA); os parâmetros avaliados foram: método de extração (percolação, PE; percolação assistida por ultrassom durante toda extração, PEU; percolação assistida por ultrassom durante o início da extração, PEUI e percolação assistida por ultrassom com pulsos, PEUP), temperatura (40 e 60°C) e solventes (água; etanol:água [35:65, v/v]; etanol:água [70:30, v/v], isopropanol:água [35:65, v/v] e isopropanol:água [70:30, v/v]). As condições de extração que proporcionaram maiores valores de X0 (62,8%), E24 (54,4%) e RTSA (36,3%) foram água, 60°C, PEUP; isopropanol:água (70:30, v/v), 60°C, PEUP e isopropanol:água (70:30, v/v), 60°C, PEUI, respectivamente. Estas condições foram selecionadas para estudo cinético e obtenção de parâmetros cinéticos ajustados que mostraram que, quando água foi empregada como solvente de extração sob ultrassom, obteve-se a maior recuperação de extrato com menor tCER (período de taxa de extração constante). Portanto, a condição de extração com água, 60°C, PE, representa a condição ótima em termos de rendimento. Ainda, realizou-se a quantificação do teor de ?- ison nos xtr tos o ti os n s in ti s on o t v -s -14% (base seca) de ?-ecdisona nos extratos das raízes de P. glomerata. A condição de extração que proporcionou os extratos com maior teor de ?-ecdisona foi a isopropanol:água (70:30), 60°C, PEUI, comprovando a maior seletividade de extração da mistura de solventes isopropanol:água (70:30, v/v), já que este foi também o solvente que apresentou extratos com maiores propriedades surfactantes. Portanto, pode-se concluir que ao final deste estudo, ao empregar o método de percolação em leito fixo assistida por ultrassom no início da extração utilizando isopropanol:água (70:30) como solvente de extração a 60°C, obteve-se uma condição de extração otimizada que fornece extratos das raízes de P. glomerata com alta recuperação de compostos bioativos / Abstract: Species of the genus Pfaffia (Amaranthaceae) have been commercialized as substitute to Panax (ginseng, Araliaceae). Due to the similar morphology of its roots to those of ginseng, they are popularly known as Brazilian ginseng. Among the species of Pfaffia, the P. glomerata is the most important because it is the only one that contains ?- ecdysone; which is the most important saponin from this plant due their therapeutic effects. Nowadays, capsules containing P. glomerata roots extracts are commercialized under indication to of improving the memory and as a tonic. Besides these indications, the P. glomerata roots exhibit expressive saponins content (10-17%); therefore, its extract can potentially be used as an emulsifier/ surfactant. Commercially, P. glomerata roots extracts are obtained by low-pressure solvent extraction in fixed bed extractors, however, with low yields. The aim of this study was to obtain an extract from Brazilian ginseng roots (P. glomerata) rich in saponins applying the process of low-pressure solvent extraction, which is an extraction process commercially established, assisted by ultrasound ; ultrasound assisted extraction is an emerging technique used to improve extraction process. The effects of the following parameters were evaluated on the overall extraction yield (X0) and surfactant properties (Emulsification index, E24 and reduction of water surface tension, RTSA) of P. glomerata roots extracts: extraction method (percolation, PE; ultrasound assisted percolation during the entire process, PEU; ultrasound assisted percolation at the beginning of the process, PEUI and ultrasound assisted percolation with pulses, PEUP), temperature (40 and 60°C) and extracting solvents (water, ethanol:water [35:65], ethanol:water [70:30], isopropanol:water [35:65] and isopropanol:water [70:30]). The extraction conditions that provided higher values to X0 (water, 60°, PEUP), E24 (isopropanol:water [70:30], 60°C, PEUP) and RTSA (isopropanol:water [70:30], 60°C, PEUI) were selected for the kinetic study; the kinetic parameters were estimated fitting the experimental data to a linear spline with 3 straight lines. The kinetic parameters showed that when water was used as extracting solvent assisted by ultrasound, the higher extract recovery was obtained with the shortest tCER (constant extraction rate period). Therefore, the extraction condition with water, 60°C, PEUP is the optimum condition with respect to the X0. The content of ?-ecdysone was evaluated on the extracts obtained from kinetic study. The content of ?-ecdysone in the P. glomerata roots xtr ts w r -14% (dry base, d.b.). The extraction condition that provided the higher extraction of ?-ecdysone was that using isopropanol:water [70:30], 60°C, PEUI; the extracts with the best surfactant properties were obtained in this extracting condition . Therefore, it was concluded that applying ultrasound at the beginning of process using IsoC3OH:water (70:30) as extracting solvent at 60°C, was the optimized extraction condition to obtain extracts from P. glomerata roots / Mestrado / Engenharia de Alimentos / Mestra em Engenharia de Alimentos

The diploma thesis deals with the topic of the optimization calculation of the mass flow of injection from the condensing pumps of the second degree to the condensate of heating steam, flowing from the system of separation and reheating, with the main goal to achieve the maximum power of the block of the power plant. There is calculation of the secondary circuit of the nuclear power plant in Dukovany before and after the optimization. In the next part, there is calculated growth of electric power of the block, results are drawn in diagrams and technical solution is designed.

The subject of the thesis is the evaluation of the operation of the existing pressure sewer network in a selected location. The aim is to describe the problems with the operation of pressure sewerage and to evaluate the operation of this network based on design parameters.

This paper deals with production of the structures fabricated using low temperature co-fired ceramics. Focus is on the lamination of raw ceramic tapes. There are presented classical thermo-compressive methods and a new method using chemical solutions for tape bonding. Describes new lamination technology and their advantages are the absence of elevated temperatures and high pressures. This method reduces using of higher temperatures and high pressure during lamination. On the other hand, chemical process of tape bonding is not flawless. There are many problems including solvent deposition, extreme sensitivity to dust and other processing parameters. It also describes the fabrication of structures by chemical way. Specifically, analyzes the method Cold Chemical Lamination and provides examples of possible deposition solvents which are needed for etching the surface of the LTCC tape during the lamination.

Pour évaluer l'impact d’un rejet accidentel ou chronique de polluants dans les écosystèmes, il est important d’étudier le dépôt sec des aérosols en milieu rural. Le manque de données expérimentales en milieu rural sur la vitesse de dépôt sec des particules ayant une taille inférieure à 1 μm conduit à des incertitudes au vu des modèles et de leurs différences, qui vont jusqu’à dépasser un ordre de grandeur. Le but de cette étude est de développer une mesure directe de la vitesse de dépôt sec des aérosols (Vd), notamment en utilisant un impacteur à basse pression (Electrical Low Pressure Impactor, ELPI, DEKATI), à travers des mesures expérimentales in situ. L’originalité de la méthode est le calcul des flux de dépôt par corrélation turbulente. Les vitesses de dépôt sec ont été obtenues pour des aérosols atmosphériques de tailles comprises entre 7 nm et 2 μm, sur un terrain plat dans le sud-ouest de la France, sous différentes conditions atmosphériques, ainsi que sur différents couverts (maïs, herbe, sol nu). Vd est analysée en fonction du diamètre des particules et l’impact des conditions micro météorologiques est étudié. / To evaluate the impact of accidental or chronic pollutant releases on ecosystems, we must study the dry deposition of aerosols in rural areas. The lack of experimental data on the dry deposition velocity of particle sizes below 1 μm over rural environments leads to uncertainties regarding models and differences between them, which exceed one order of magnitude. The aim of thisstudy is to develop a method, especially using an Electrical Low Pressure Impactor (Outdoor ELPI, DEKATI) to determine aerosol dry deposition velocities (Vd) over rural areas through experimental measurements. This method is based on eddy covariance flux calculation and spectral analysis correction. Dry deposition velocities were obtained for atmospheric aerosols sizing from 7 nm to2 μm, in the South-West of France on a flat terrain under varied meteorological conditions andvaried substrates (maize, grass and earth). Vd was analysed as a function of the particle diameters, and the impact of micrometeorological parameters was studied.

Chaque année, une quantité de 107tonnes de suie est produite à l'échelle mondiale. Le carbone-suie dans l'atmosphère a des effets graves sur le changement climatique et la santé humaine. Les impacts dépendent de nombreux facteurs comme les composés organiques adsorbés, le vieillissement et les processus de mélange. Par conséquent, afin de réduire la quantité de suie émise, outre l'examen des facteurs mentionnés, les études de la cinétique de formation, de la structure et des propriétés optiques des suies sont également essentielles. Il existe plusieurs méthodes optiques dans les études sur la suie. La spectroscopie Raman occupe un rôle particulier puisqu'elle est un outil puissant pour l'étude structurale des matériaux carbonés grâce à sa sensibilité aux structures à l’échelle moléculaire. Dans ce travail, des sections Raman différentielles de suies et quelques autres particules carbonées ont été mesurées pour progresser vers la spectroscopie Raman quantitative de ces particules. Les suies produites par des flammes d'éthylène pré-mélangées à basse pression ont été étudiées par mesure Raman ex-situ sur des films déposés et des mesures Raman in-situ (enligne) dans la phase gazeuse. La combinaison de la spectroscopie Raman de suies échantillonnées sur substrat avec les spectroscopies infrarouge et optique et la microscopie électronique en transmission a permis de progresser sur l'interprétation des spectres Raman de suie. Les mesures en phase gazeuse, obtenues pour la première fois, fournissent de nouvelles informations sur la naissance des suies et leurs structures dans les flammes à basse pression avec, par exemple, la détection d'une grande quantité d'atomes de carbones hybridés sp lors de la formation et de la croissance des premières suies. Ces étude s’ouvrent la voie à la détection et à l'analyse des suies directement en phase gazeuse et à leur détection quantitative dans l’atmosphère au travers de leurs spectres Raman. / Every year, an amount of 107 tons of soot is produced on the world scale. Soot, as part of atmospheric black carbon, has serious impacts on climate change and human health. The impacts depend on many factors including adsorbed compounds, aging and mixing processes. Therefore in order to reduce the soot amount, besides considering these mentioned factors, the study of formation kinetics, structure and optical properties is also essential. There are several methods applied in soot investigations. Raman spectroscopy plays a particular role as it is a powerful tool for structural investigation of the carbon-based materials because it is sensitive to molecular structures. In this work, differential Raman cross sections of soot and some other carbonaceous particles were measured to progress toward quantitative Raman spectroscopy. Soot particles produced by premixed ethylene flames at a low pressure were investigated by ex-situ Raman measurement on deposited films and in-situ(online) Raman measurement in the gas phase. Combination of the Raman spectroscopy of soot sampled on substrates with infrared and optical spectroscopy and transmission electron microscopy allowed progressing on the interpretation of soot Raman spectra. The online gas phase measurements provided a novel view on soot birth and structures in low pressure flames with, for instance, the detection of a large amount of sp hybrized carbon atoms during nascent soot growth. These studies pave the way to soot detection and analysis directly and quantitatively in the atmosphere.

Turbines encounter blade failures due to fatigue and creep. It has been shown in the literature that the primary cause of steam turbine blade failures worldwide can be ascribed to fatigue in low pressure (LP) turbine blades. The failure and damage to these blades can lead to catastrophic consequences. Some utilities use empirical methods to determine the forces experienced by turbine blades but desire more accurate methods. The inaccurate prediction of high-cycle fatigue (HCF), thermal durability and stage performance is introduced when one does not consider blade row interaction. Blade row interactions can, however, be accounted for by means of computational fluid dynamics (CFD). Furthermore, modern high- fidelity CFD tools would be able to contribute greatly in predicting the forces experienced by turbine blades. Numerical tools such as CFD and nite element analysis (FEA) can greatly contribute to the estimation of the remaining useful life (RUL) of turbine blades. However, in this estimation process, there are various uncertainties and aspects that affect the estimated RUL. Understanding the sensitivity of the estimated RUL to these various uncertainties and aspects is of great importance if RUL is to be estimated as accurately as possible. In this dissertation, a sensitivity analysis is performed with the purpose of establishing the sensitivity of the estimated RUL of the last stage rotor of an LP steam turbine, to the number of harmonics used in a nonlinear harmonic (NLH) CFD simulation. The sensitivity of the estimated RUL is evaluated in the HCF regime, where the cyclic stresses occur below the yield strength of the turbine blade. A CFD model, FE model, and fatigue model were therefore developed in such a manner that would suffice, regarding the purpose of the sensitivity analysis. The CFD model is validated by comparing the predicted CFD power to that of actual generated power of a dual 100MW LP steam turbine. The sensitivity analysis is performed for 3 operation conditions, and for each operational condition the aerodynamic forces were computed using 1, 2, and 3 harmonics in an NLH simulation. The estimation process considers a weak coupling between the CFD model and FE model. NLH simulations are firstly performed to calculate the unsteady static surface pressure distributions on the last stage rotor. This is followed by the mapping thereof to the FE model, for which a transient structural analysis is performed. Finally, the RUL is estimated by performing a fatigue analysis on the stress history obtained from the transient structural analysis. Based on the results of the sensitivity analysis, the following recommendations were made, from a conservative point of view. Firstly, in general, if the RUL is to be estimated with reasonable accuracy, just using 1 harmonic in an NLH simulation will not be sufficient and 2 harmonics should be used. Secondly, if the RUL has to be estimated with high accuracy, 3 harmonics should be used. / Dissertation (MEng)--University of Pretoria, 2018. / National Research Foundation (NRF) / Mechanical and Aeronautical Engineering / MEng / Unrestricted

Plastic waste is accumulated in landfills and the environment at an exponentially increasing rate. Currently, about 350 million tons of plastic waste is generated annually while only 9% is recycled. Plastic waste and its degradation products, microplastics, pose a severe threat to the ecosystem and eventually human health. Polyolefin (Polyethylene (PE) and Polypropylene (PP)) waste is 63% of the total plastic waste. Converting polyolefin waste into useful products including clean gasoline, diesel, wax, and monomers, via hydrothermal processing (HTP) can help reduce the plastic waste accumulation. In this study, sorted PE waste was converted via supercritical water liquefaction (SWL) into gasoline blendstock, No.1 ultra-low-sulfur diesel, and clean waxes with high yields and high purities. Comprehensive reaction pathways for PE conversion were proposed based on detailed GC×GC analyses. Furthermore, a new low-pressure (~2 MPa) hydrothermal processing (LP-HTP) method was developed to convert mixed polyolefin waste. This new LP-HTP method can save 90% of the capital cost and energy compared to SWL. The oil products were distilled into clean gasoline and No.1 ultra-low-sulfur diesel. The reaction pathways of PE and PP were independent while the synergistic effects improved the fuel qualities. With this LP-HTP method, polyolefin waste can be converted into up to 190 million tons of fuels globally, while 92% of the energy and 71% of the GHG emissions can be saved compared to conventional methods for producing fuels. Overall, this method is robust, flexible, energy-efficient, and environmental-friendly. It has a great potential for reducing the polyolefin waste accumulation in the environment and associated risks to human health.<br>