The subject of this PhD thesis is the development of an efficient system that can simultaneously pump and separate a gas-liquid mixture, in particular an oil-air mixture. Two-phase flows are encountered in many applications (petroleum extraction, flow in nuclear power plant pumps, pulp and paper processing, etc.) but this study is mainly focused on lubrication systems of aircraft gas turbine engines.<p><p>The pump and separator system (PASS) for two-phase flows developed in this PhD thesis aims to perform three functions simultaneously:<p>• Send back the oil to the tank (oil pumping)<p>• Separate the air from the oil (de-aeration)<p>• Separate the oil from the air (de-oiling) and release the sealing air into the atmosphere (venting). <p>Particular care is given to the liquid flow rate lost at the gas outlet of the system.<p>Consequently, it could replace the scavenge pumps and oil-air separators existing in present lubrication systems. This modification provides several advantages: simplification of the lubrication circuit, reduction of oil consumption and of the size of the lubrication system.<p><p>This research is divided into three axes: the theoretical study of the important physical mechanisms taking place inside the two-phase flow pump and separator system, the experimental development, tests and optimization of different PASS prototypes, and also the numerical simulations of the two-phase flow inside these prototypes. Although the experiments were the central pillar of this research, the three axes were closely imbricated.<p><p>The PASS design includes three main components:<p>• An inlet chamber with one or several tangential inlets giving a natural centrifugation to the flow,<p>• An impeller (forced centrifugation) with an axial and a radial part followed by a volute chamber,<p>• A metallic foam that lets pass micron and sub-micron droplets and which is followed by an axial vent port.<p><p>The centrifugation causes the liquid (oil) to move radially outwards in an annular body (a liquid ring) generating pressure. The thickness of this liquid ring inside the impeller is mainly determined by the pressure coefficient (related to the back-pressure and the rotational speed). When the back-pressure increases, the thickness of the liquid ring increases too. An advantage of the PASS is that it does not impose any relation between the liquid head and the liquid flow rate, contrary to common centrifugal pump. It self-regulates the radial position of the gas-liquid interface to sustain the operating conditions.<p><p>The de-aeration efficiency mainly depends on the pressure coefficient (for a constant liquid viscosity or temperature) or on the thickness of the liquid ring. The pressure gradient which appears in the liquid rotating in an annular body acts like a dam for the gas phase. Indeed, the gas movement is mainly determined by the pressure field (buoyancy) while the liquid distribution is dominated by centrifugal and Coriolis forces. Buoyancy tends to accumulate the gas phase near low pressure areas (PASS hub, suction side of the blades, clearances between closed impeller and casing).<p><p>The first oil-air PASS prototype produces high viscous losses due to the high peripheral velocity and liquid viscosity. Therefore, the pumping efficiency is poor compared to common impeller pumps. However, the pumping is not the key function of the PASS and a power consumption below 5 kW is acceptable for the application considered in this work. For applications that require lower power consumptions, a reduction of the rotational speed must be considered.<p><p>Thus, the rotational speed and the impeller diameter are two major constraints for the PASS design which determine the de-aeration and pumping efficiencies. The impeller diameter also influences the size of passage sections for the air flow. The air velocity must be kept as low as possible because the entrainment of droplets increases when the air velocity rises (drag forces on droplets). Indeed, this large influence of the air flow rate on the oil consumption (de-oiling efficiency) was demonstrated by a theoretical analysis, the experiments and the CFD simulations. The production of droplets in the inlet pipes when the two-phase flow is annular is a key phenomenon regarding the oil consumption.<p><p>In addition to the air flow rate, other variables also influence the oil consumption:<p>• Air-oil temperature: when the temperature rises, the oil consumption increases because the surface tension and the oil density are reduced. Moreover, as the air density also decreases, the air velocity rises.<p>• Oil flow rate: the oil consumption rises more or less linearly with the oil flow rate. However, the influence of the oil flow rate on the inlet droplet size is uncertain.<p>• Rotational speed: the rotational speed has obviously a strong impact on the oil consumption without metallic foam. However, experiments showed that the metallic foam efficiency is almost independent on the rotational speed. Therefore, the oil consumption with the Retimet foam does not depend on the PASS rotational speed.<p>• Altitude or air density: the oil consumption decreases when the air density is reduced because the drag forces on droplets also decrease.<p>The gas density (altitude) is also supposed to influence the de-aeration efficiency but this could not be tested or simulated in this work (the de-aeration efficiency gets probably better when decreasing the gas density because the buoyancy forces increase).<p><p>Theory, experiments and numerical simulations also allowed the prediction of performance of the first oil-air prototype for real in-flight operating conditions. Two problems have been identified: the de-aeration efficiency at MTO and cruise ratings and the oil leak throughout the vent in cold start and windmilling. To solve them, some modifications of the lubrication system have been suggested. With these modifications, the oil-air PASS should become very efficient and attractive for engine manufacturers. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

No description available.

Surface integrity is of great significance in grinding performance since grinding process is often used as a finishing step. For metallic materials, residual stresses play an important role in surface integrity for its strong effect on fatigue life, corrosion resistance, and part distortion. For ceramic materials, the surface damage induced by grinding process could greatly affect the mechanical strength and surface finish of the component. The functional behavior of machined components can be enhanced or impaired by the grinding process. Because of this, understanding the surface integrity imparted by grinding is very important. The use of fluid is common in grinding process, however, the high cost and environmental impact of the conventional flood cooling is very undesirable. The minimum quantity lubrication (MQL) have been introduced in industry for about two decades as a promising alternative to conventional flood cooling for economical and environmental advantages. A comprehensive understanding of the MQL effect on the process performances and surface integrity is of great value to the implementation of MQL technique in industrial situation. Grinding-induced residual stress prediction has been a topic of research since the 1970’s while the studies of MQL grinding is still on the early stage with experimental investigations. A comprehensive study and quantitative description of MQL effect on the residual stress generation in grinding is highly demanded. On the other hand, although there has been significant research in the area of surface damage in ceramic grinding, there are still opportunities for advancing predictive methods. Therefore, the objectives of the current research are set as follows: (1) develop a method of predicting residual stress based on an analytical description of the grinding process under MQL condition, (2) develop a method of predicting surface finish and damage in ceramic grinding, and (3) validate the model with experimental data. The research will first focus on predicting residual stresses in MQL grinding based on first principles. This includes predictive models of grinding forces, and grinding temperature stemmed from grinding kinematics and dynamics principles as part of the overall modeling effort. The effect of MQL on both lubrication and cooling aspects has been integrated into these models. The mechanical and thermal output parameters will serve as the basis for determining the loading history which generate residual stresses. The research will also aim at surface roughness modeling in ceramic grinding. A ductile-brittle mixed surface generation is predicted based on the nature of ceramic materials and grinding kinematics. The crack system developed from indentation fracture mechanics approach will be utilized in evaluating the brittle mode surface generation. The modeling techniques will be applied to a range of grinding conditions and materials. This research would aid in evaluating various surface integrities in grinding of metallic and ceramic materials with little experimental efforts. The output could be used to machine these materials effectively to order to improve the functionality of the component.

published_or_final_version / Dentistry / Master / Master of Dental Surgery

It has been reported that minimum quantity lubrication (MQL) provides better tool life compared to flood cooling under some drilling conditions. In this study, I evaluate the performance of uncoated HSS twist drill when machining AISI 1018 steel using a newly developed lubricant designed for MQL (EQO-Kut 718 by QualiChem Inc.). A randomized factorial design was used in the experiment. The results show that a tool life of 1110 holes with a corresponding flank wear of 0.058 mm was realized.

O presente trabalho aborda a modelagem unidimensional do regime misto de lubrificação para problemas caracterizados por condições genéricas de carga, velocidade e geometria. Tal modelagem foi desenvolvida a partir de modelos clássicos, tais como a equação de Reynolds relacionada com os fenômenos hidrodinâmicos, e as formulações de Greenwood & Williamson e Greenwood & Tripp utilizadas na descrição do contato de asperezas entre superfícies rugosas. A cavitação do fluido lubrificante foi considerada através dos modelos tradicionais de half-Sommerfeld e Swift-Steiber (Reynolds). Com relação à reologia do lubrificante, as possíveis variações de viscosidade devidas ao próprio campo de pressões hidrodinâmicas e às altas taxas de cisalhamento do fluido (\"shear-thinning\") foram também contempladas na modelagem proposta. Adicionalmente, quatro filtros não convencionais de rugosidade foram propostos e implementados com o objetivo de eliminar as distorções verificadas na definição do plano (ou linha) médio(a) de referência em topografias caracterizadas pela presença de vales profundos, tais como as obtidas após a aplicação da técnica de texturização a laser (LST). A definição adequada desse plano (ou linha) médio(a) de referência é imprescindível para a correta determinação dos parâmetros necessários para a utilização dos modelos de contato de Greenwood a partir das metodologias consideradas neste trabalho. Toda a modelagem unidimensional foi implementada em um programa computacional denominado VTL (\"Virtual Tribology Laboratory\"), cujo código fonte está disponível para qualquer usuário interessado em realizar simulações envolvendo sistemas lubrificados caracterizados por perfis com geometrias genéricas. A validação da modelagem unidimensional proposta foi verificada utilizando os resultados experimentais de um teste de atrito com movimento alternado (\"reciprocating test\") publicado na literatura. Como resultado, a correlação experimental dos resultados calculados com o programa VTL foi excelente. O programa VTL foi também utilizado para verificar a possibilidade da redução de atrito em sistemas lubrificados envolvendo superfícies planas texturizadas, como as obtidas utilizando a técnica de texturização a laser (LST). Devido à limitação unidimensional da modelagem proposta, as fileiras ortogonais de 7 micro-cavidades foram aproximadas como sendo ranhuras (\"grooves\") de dimensões fixas. Para tais situações, apesar da limitação comentada acima, a modelagem unidimensional proposta pode ser utilizada para analisar qualitativamente o mecanismo de micro-mancais responsável pela geração de pressão hidrodinâmica entre superfícies paralelas caracterizadas por esse tipo de micro-texturas. / This dissertation focuses on one dimensional modelling of the mixed lubrication regime for problems with general conditions of load, velocity and geometry. Such modelling was based on classical models, such as the Reynolds equation related to the hydrodynamic phenomena, and the Greenwood & Williamson and Greenwood & Tripp formulations for the description of the asperity contact between rough surfaces. Cavitation of the lubricant was considered adopting the well-known half-Sommerfeld and Swift-Steiber (Reynolds) models. As for the lubricant rheology, the viscosity-pressure dependence and viscosity-shear-thinning effects were considered. Furthermore, four non-conventional roughness filters were conceived and implemented in order to eliminate the distortions observed on the definition of the reference mean plane (or line) of topographies (or profiles) with deep valleys, such as those obtained with the laser surface texturing (LST) technique. The proper definition of the reference plane (or line) is indispensable for the calculation of the Greenwood\'s contact parameters according to the methodologies used in this work. The complete one dimensional modelling proposed was implemented as a computational program named Virtual Tribology Laboratory (VTL), an open source code available for any user interested in performing simulations of lubricated systems with generic profiles. In order to validate the one dimensional model, experimental results of a frictional reciprocating test published in the literature were considered for comparison. The correlations between the experimental and simulated results calculated with VTL were excellent. Simulations using the VTL program were also performed in order to evaluate the friction reduction potentialities of textured surfaces (LST). Due to the one dimensional model limitations, grooves were considered instead of micro-cavities (dimples). In such scenery, regardless the above mentioned limitations, the one dimensional modelling proposed yielded good qualitative descriptions of the micro-bearing mechanism that generates hydrodynamic load carrying capacity between parallel textured surfaces.

Neste trabalho foram conduzidos experimentos de laboratório no intuito de avaliar o efeito da textura superficial no desempenho de óleos lubrificantes aditivados e não aditivados. Os materiais envolvidos nos ensaios são referentes a materiais de anel e camisa de motores de combustão interna e as condições de superfície envolveram processamentos de lixamento e retífica, bem como texturização de microcavidades a laser. Os ensaios foram do tipo alternado, com regime limítrofe de lubrificação. Inicialmente foram feitas análises sobre a metodologia utilizada para o cálculo do coeficiente de atrito em ensaios alternados, mostrando que os valores fornecidos diretamente pelo equipamento (aqui chamados de coeficiente de atrito pico a pico) não foram efetivos para este estudo, pois apresentam alta dispersão entre as réplicas dos ensaios e não é representativo em termos de eficiência do tribossistema. Foram geradas microcavidades nas superfícies de alguns blocos de ferro-fundido mediante texturização a laser. Esta texturização gerou rebarbas que foram retiradas por um processo de lixamento. Com isso, uma parte dos resultados avaliou o efeito do lixamento nos parâmetros de rugosidade, no entanto que o processo acaba por aumentar os valores de raio de aspereza e reduzir a altura média dos picos. Por fim, ensaios com óleo sem aditivo tiveram formação de óxido em todas as condições de superfície, com pouca variação do coeficiente de atrito. Já nos ensaios com óleo aditivado, os resultados mostraram pouca influência das microcavidades e maior contribuição das características de picos (raio e altura) na formação de tribofilmes redutores de atrito (neste caso MoS2). / This work was conducted by experimental tests in order to evaluate the effect of surface texture on fully formulated oil and base-oil performance. In these tests, the materials were related to the piston ring and cylinder, in which surfaces were sanded, grounded and textured by laser. In addition, the tests were carried out by reciprocating movement and boundary conditions. A coefficient of friction study in reciprocating tests was performed, showing that peak-to-peak methodology does not represent properly the tribosystem efficiency. Burr was generated around the dimples (made by laser surface texturing), in which were removed by sanded process. The results showed that sanded process increased the peak radius and decreased the peak height. The results considering the base oil showed oxide formation on the surface in all the cases, occurring low variation of friction coefficient in the system. On the other hand, in the fully formulated oil results, the dimples had no influence on MoS2 formation; however, it was possible to see a strong relation with the radius and average height of the asperities.

The present study focuses on the physical and chemical mechanisms of lubricant removal during the first step of the sintering process during powder metallurgy (P/M) processing of ferrous systems. Previous works on the kinetics of delubrication made it possible to develop an empirical model which accounts for the typical weight loss profile observed upon heating of green compacts. It has been established that the rate at which the parts are heated dictates the overall process kinetics, and fitting curve methods yield two parameters which contain the corresponding information: (i) TMAX is the temperature of 50% lubricant removal, and (ii) b is representative of the slope of the curve during weight loss stage. Phase I of this study aims at determining the dependencies of these two parameters with respect to a series of physical variables: green density of the compacts; presence of an alloying element potentially catalytic for the reaction of lubricant pyrolysis; and procedure of compaction and geometry of the compacts. Also, it is suggested that the two parameters obtained from the fitting curve methods can be related to the main two mechanisms of delubrication: evaporation of the lubricant and conversion of the lubricant molecules into smaller hydrocarbons, assuming that these two mechanisms are the kinetically limiting mechanisms. Furthermore, recent studies of the delubrication process have been opening the way to the potential development of gas sensors, which could eventually allow the direct monitoring of the emissions of gaseous species. Several key features have been reported in the literature, including a peak emission of hydrocarbons at the delubrication temperature, as well as strong emissions of CO and CO2 at temperatures above 700°C. The scope of Phase II of this project was thus to verify that these features were retained under various processing conditions, so that the development of a sensor suitable for various sintering environments is viable. Variations in the emission profiles of gaseous species were observed as the processing conditions were changed, and when possible, potential justifications for these changes have been proposed.

O presente trabalho aborda a modelagem unidimensional do regime misto de lubrificação para problemas caracterizados por condições genéricas de carga, velocidade e geometria. Tal modelagem foi desenvolvida a partir de modelos clássicos, tais como a equação de Reynolds relacionada com os fenômenos hidrodinâmicos, e as formulações de Greenwood & Williamson e Greenwood & Tripp utilizadas na descrição do contato de asperezas entre superfícies rugosas. A cavitação do fluido lubrificante foi considerada através dos modelos tradicionais de half-Sommerfeld e Swift-Steiber (Reynolds). Com relação à reologia do lubrificante, as possíveis variações de viscosidade devidas ao próprio campo de pressões hidrodinâmicas e às altas taxas de cisalhamento do fluido (\"shear-thinning\") foram também contempladas na modelagem proposta. Adicionalmente, quatro filtros não convencionais de rugosidade foram propostos e implementados com o objetivo de eliminar as distorções verificadas na definição do plano (ou linha) médio(a) de referência em topografias caracterizadas pela presença de vales profundos, tais como as obtidas após a aplicação da técnica de texturização a laser (LST). A definição adequada desse plano (ou linha) médio(a) de referência é imprescindível para a correta determinação dos parâmetros necessários para a utilização dos modelos de contato de Greenwood a partir das metodologias consideradas neste trabalho. Toda a modelagem unidimensional foi implementada em um programa computacional denominado VTL (\"Virtual Tribology Laboratory\"), cujo código fonte está disponível para qualquer usuário interessado em realizar simulações envolvendo sistemas lubrificados caracterizados por perfis com geometrias genéricas. A validação da modelagem unidimensional proposta foi verificada utilizando os resultados experimentais de um teste de atrito com movimento alternado (\"reciprocating test\") publicado na literatura. Como resultado, a correlação experimental dos resultados calculados com o programa VTL foi excelente. O programa VTL foi também utilizado para verificar a possibilidade da redução de atrito em sistemas lubrificados envolvendo superfícies planas texturizadas, como as obtidas utilizando a técnica de texturização a laser (LST). Devido à limitação unidimensional da modelagem proposta, as fileiras ortogonais de 7 micro-cavidades foram aproximadas como sendo ranhuras (\"grooves\") de dimensões fixas. Para tais situações, apesar da limitação comentada acima, a modelagem unidimensional proposta pode ser utilizada para analisar qualitativamente o mecanismo de micro-mancais responsável pela geração de pressão hidrodinâmica entre superfícies paralelas caracterizadas por esse tipo de micro-texturas. / This dissertation focuses on one dimensional modelling of the mixed lubrication regime for problems with general conditions of load, velocity and geometry. Such modelling was based on classical models, such as the Reynolds equation related to the hydrodynamic phenomena, and the Greenwood & Williamson and Greenwood & Tripp formulations for the description of the asperity contact between rough surfaces. Cavitation of the lubricant was considered adopting the well-known half-Sommerfeld and Swift-Steiber (Reynolds) models. As for the lubricant rheology, the viscosity-pressure dependence and viscosity-shear-thinning effects were considered. Furthermore, four non-conventional roughness filters were conceived and implemented in order to eliminate the distortions observed on the definition of the reference mean plane (or line) of topographies (or profiles) with deep valleys, such as those obtained with the laser surface texturing (LST) technique. The proper definition of the reference plane (or line) is indispensable for the calculation of the Greenwood\'s contact parameters according to the methodologies used in this work. The complete one dimensional modelling proposed was implemented as a computational program named Virtual Tribology Laboratory (VTL), an open source code available for any user interested in performing simulations of lubricated systems with generic profiles. In order to validate the one dimensional model, experimental results of a frictional reciprocating test published in the literature were considered for comparison. The correlations between the experimental and simulated results calculated with VTL were excellent. Simulations using the VTL program were also performed in order to evaluate the friction reduction potentialities of textured surfaces (LST). Due to the one dimensional model limitations, grooves were considered instead of micro-cavities (dimples). In such scenery, regardless the above mentioned limitations, the one dimensional modelling proposed yielded good qualitative descriptions of the micro-bearing mechanism that generates hydrodynamic load carrying capacity between parallel textured surfaces.

Most of the rolling element bearings are lubricated with Grease lubricant. Generally, the grease is expected to serve for life. The major causes of the bearing failure are due to the failure of the lubrication. The grease will experience creeping, oil permeation, oil separation etc. The separated oil will be lost permanently from the bearing. The widely used grease for general application is the lithium grease. The thickener of the grease consists covalent bond. When the grease is sheared, the breakage of the covalent bond will be permanent, resulting in the permanent loss of the rheological properties. The gels have unique properties such as thermal reversibility, viscoelasticity and thixotropy. They become mobile under shear stress and solidify again when the shear stress is removed. This property can be harnessed to avoid the base oil creeping, oil permeation, leakage in gears and bearings. Due to the presence of the polar group in the gels, they form a good tribo film and prevent the wear.  Under the shear stress, weak supramolecular interactions will be distorted, and this leads to the release of the oil and they re-form the structure after a certain period of rest. When the gel is in the solid-state, it will avoid creeping and evaporation. Many classes of gels are either derived from natural sources or from environmentally friendly materials. Thus, the lubricant formed out of gel would effectively solve both environmental as well as lubrication problems. In this work, supramolecular gel lubricants were prepared out of fully green, cellulose derivatives and starch hydrolysates. The non-ionic hydroxyethyl cellulose (HEC) and anionic sodium carboxymethyl cellulose (NaCMC) were chosen to understand the effect of ionic and non-ionic gelators on the rheological and the tribological parameters. Traditionally fat was used as a lubricant, now, in food industry various fat replacers are being used. To study whether the fat replacers can act as a thickener, Dextrin and maltodextrins were chosen.  Dextrin and maltodextrin with the different DE values were selected to understand the influence of molecular weight on gelation and tribological performance.  Inspired by the recent developments and advantages of aqueous lubrication, mixer of water and poly(ethylene glycol) 200 (PEG 200) is chosen as the base fluid. It was found that a very small amount of gelator can increase the viscosity of the PEG/water to several orders. The thermal stability of the gels was studied using thermogravimetric analysis (TGA) and found that gels can increase the thermal stability of the base fluid. FTIR results showed the formation of a non-covalent bond between the PEG molecules and water. It is shown that anionic gelator will result in producing low friction and wear in comparison to non-ionic gelator. The possible tribo-film formation due to the negative charge in the NaCMC molecules is attributed to these results. The very low friction and low wear was exhibited by the dextrin and maltodextrin gels. It is proposed that this could be due to the microspherical particles of gels which can act as nano bearings. It was found that choosing the optimum concentration of the gelator is important to reduce friction and wear. The higher gelator concentration will form the hard gel, which cannot flow and replenish the sliding contact, resulting in the starved lubrication. This will cause high wear and friction. These gel lubricants can be used in food, pharmaceutical and biomedical industries.