En fonction de la configuration avion, de son altitude du vol, du type de carburant, différents phénomènes physiques modifient les caractéristiques de l'alimentation du moteur en carburant. En effet, il se produit principalement un phénomène de dégazage qui pourrai être couplé à de la cavitation. Les écoulements diphasiques ainsi obtenus contiennent des microbulles, des bulles ou des poches de gaz qui risquent d'induire des dysfonctionnements du moteur. Ces dysfonctionnements se traduisent par des fluctuations de poussée pouvant conduire à une perte de contrôle de l’appareil. De cette problématique industrielle découlent de nombreux verrous scientifiques encore mal connus. Dans le cadre de cette thèse des travaux sur la modélisation numérique et la caractérisation expérimentale du couplage entre la cavitation et le dégazage. Pour cela deux bancs d’essai et un code propre capable d'étudier la problématique scientifique retenue ont été développés et exploités. Trois régimes de cavitation pure et trois autres de cavitation aérée sur une géométrie de venturi 8° symétrique ont été étudiés." / Depending on the configuration of the plane, its flight altitude, the type of fuel, different physical phenomena significantly change the characteristics of the fuel supply to the engine. Indeed, it primarily occurs a fuel degassing phenomenon that could be coupled to the cavitation phenomenon. As a result, the thus obtained multiphase flows contain micro bubbles, larger bubbles or vapor pockets which might induce engines malfunctions. The latter result in thrust fluctuations which can lead to a loss of power. The scientific context of the industrial problem lies in the development of a numerical and experimental representation of the cavitation and degassing phenomena on a smaller scale. As a result, it is of primary importance for one to understand the mechanisms of occurrence of gas and cavitation in the given industrial configuration. In order to deal with those issues, two test benches have been developed, as well as an in-house numerical code capable of simulating aerated cavitation phenomenon. Therefore, three different pure cavitation regimes and three other aerated cavitation are shown, as a result of the experimental work. The multiphase flow observations are based on a statistical post-processing of images taken by a high-speed camera. Moreover, two 2D aerated cavitation numerical simulations, as well as the first 3D pure cavitation simulation have been shown.

Dala Vatten AB has been operating two municipal wastewater treatment plant namely Gagnef wastewater treatment plant and Tällberg wastewater treatment plant since 1970’s and 1950’s respectively in Dalarna, middle of Sweden. These both traditional treatment plants have been updated with continuous and intermittent aerated biological treatment facilities: Moving bed biofilm reactor (MBBR) in 2012 and 2007 respectively. Recently, more detailed process performance and evaluation of both plants is required focusing on energy consumption. The objective of this master thesis is thus to investigate the opportunities in reducing energy consumption from both plants to save operation cost, identify the opportunities for chemical saving, if possible reduce the excess sludge so produced from the plant and potential optimization of the process for its plant’s sustainability. The laboratory study was made in May and August, 2015 with grab sampling and flow proportional sampling method. The analysation was carried out with several wastewater parameters: BOD7, COD, TOC, TP, NH4-N and TN with Hach Lange analysing method. Results showed that both continue and intermittent aerated plants have higher process performance with lower effluent organic (BOD7, COD) and TP loading to the recipient. Gagnef WWTP with continuous aeration has demonstrated an excessive use of chemical, sludge production and high-energy consumption by the blower serving MBBR during the studied period. By contrast, Tällberg WWTP with intermittent aeration has proved to be successful in terms of lower energy consumption by the blower serving the MBBR but failed to show improved specific energy efficiency for each pollutant load during the studied period. The recommendation in improvising energy saving and saving operation cost at both treatment plants was put forward.

No description available.

Over the last two decades, implementation of membrane bioreactors (MBRs) has increased due to their superior effluent quality and low plant footprint. However, they are still viewed as a high-cost option, both with regards to capital and operating expenditure (capex and opex). The present thesis extends the understanding of the impact of design and operational parameters of membrane bioreactors on energy demand, and ultimately whole life cost. A simple heuristic aeration model based on a general algorithm for flux vs. aeration shows the benefits of adjusting the membrane aeration intensity to the hydraulic load. It is experimentally demonstrated that a lower aeration demand is required for sustainable operation when comparing 10:30 to continuous aeration, with associated energy savings of up to 75%, without being penalised in terms of the fouling rate. The applicability of activated sludge modelling (ASM) to MBRs is verified on a community-scale MBR, resulting in accurate predictions of the dynamic nutrient profile. Lastly, a methodology is proposed to optimise the energy consumption by linking the biological model with empirical correlations for energy demand, taking into account of the impact of high MLSS concentrations on oxygen transfer. The determining factors for costing of MBRs differ significantly depending on the size of the plant. Operational cost reduction in small MBRs relies on process robustness with minimal manual intervention to suppress labour costs, while energy consumption, mainly for aeration, is the major contributor to opex for a large MBR. A cost sensitivity analysis shows that other main factors influencing the cost of a large MBR, both in terms of capex and opex, are membrane costs and replacement interval, future trends in energy prices, sustainable flux, and the average plant utilisation which depends on the amount of contingency built in to cope with changes in the feed flow.

Dissolved oxygen refers to the mass of oxygen that is contained in water. The concentration of dissolved oxygen is an important indicator of the environments water quality. The presence of oxygen in water is desirable therefore it is a positive sign; whereas the absence of oxygen is a sign of severe pollution. An adequate supply of dissolved oxygen is important for waste water treatment processes. Many naturally occurring biological and chemical processes use oxygen, thereby diminishing the dissolved oxygen concentration in the water. The physical process of oxygen transfer or oxygen absorption from the atmosphere acts to replenish the used oxygen. This process has been termed aeration. Aeration is the primary requirement of the biological treatment of water and wastewater treatment. As reported in the literature, the aeration process consumes as much as 60-80% of total power requirements in wastewater treatment plants. Therefore, it is necessary that the design and operation of aeration process should be economized in terms of their energy efficiency. The performance of surface aeration systems is rated in terms of their oxygen transfer rate; hence the choice of a particular surface aeration system depends on its performance and efficiency of oxygen transfer rates. Oxygen transfer rate and the corresponding power requirement to rotate the rotor are very vital parameters for the design and scale-up of surface aerators. Basically two types of operation are in use for surface aeration systems – batch operation and continuous operation. Batch operation involves a single vessel which is filled, aerated then completely emptied. Continuous operation method of operating a biological treatment plant is characterized by a steady input stream (in terms of chemical and biological composition and flow rate, when flow and concentration equalization is practiced), steady process conditions during the treatment steps and by a fairly consistent flow of treated material with only little variation in its composition. The work presented in this thesis consists of two parts. The first one deals with the experimental investigations on the three types of batch surface aeration tanks. A comprehensive design analysis has been worked out and presented on these types of surface aeration systems. In the second category, experimental investigations have been carried out extensively on continuous flow surface aeration systems of different sizes. Analysis has led to the formulation of optimal geometric dimension and the simulation criteria for the design purposes. As far as the first category of investigations is concerned, a substantial work has been reported on batch surface aerators on various issues, during the past several years. Still, a general methodology to scale up or scale down the process phenomena is lacking. In the present work, experiments were done on different shaped batch surface aeration system for generalizing or devising the scale up and scale down criteria for oxygen transfer coefficient and power consumption. Present work through experimental observations established that unbaffled circular tanks are more energy efficient than baffled when used as surface aerator. Power consumption in surface aeration systems is characterized by a fundamental non-dimensional parameter named power number. This number relates drag force to the inertial force in fluid flow system. Power number scaling up of unbaffled surface aerators of square, circular and rectangular shaped tanks is one of the most important contributions of the present work. Design charts have been developed for all the three shape of tanks for the installation as the batch surface aeration systems. Based on the experimental analyses in the present work, it was found that circular shape is the most efficient than any other shape and it is also established that generally a number of smaller sized tanks were more economic and efficient than using a single big tank while aerating the same volume of water. Based on the energy economy analysis, present work suggests the optimal speed range of batch systems of different shaped surface aeration tanks. Different sized rectangular aeration tanks with different aspect ratios (that is length to width ratio) were tested along with a series of square and circular tanks for comparing their relative performances. Present work by doing experiments answered this fact and found that square tank (aspect ratio =1) was more efficient than any other aspect ratio rectangular tanks. Vortexes are inherently present in any type of unbaffled tanks. Present work analyzed the vortex behavior of unbaffled surface aeration systems to determine the critical impeller speed in unbaffled batch surface aeration systems at which oxygen transfer rates are more. The second part of the present work establishes the optimal geometrical parameters of a continuous flow surface aeration systems. These types of operations were found to be least reported in the available literature and there appears to be of no report in the literature on optimal geometrical parameters. Extensive experimental work is reported in the present thesis on the establishment of the optimal geometrical parameters of continuous flow surface aeration systems. From there, simulation criteria are established by maintaining optimal geometrical similarity in different sized continuous flow surface aeration tanks; so that the scale up or scale down criteria can be applied to predict oxygen transfer rates and power number.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

LD2668 .T4 1954 O74 / Master of Science

In this work, an automated statistical approach for the condition monitoring of a fluid power system based on a process sensor network is presented. In a multistep process, raw sensor data are processed by feature extraction, selection and dimensional reduction and finally mapped to discriminant functions which allow the detection and quantification of fault conditions. Experimentally obtained training data are used to evaluate the impact of temperature and different aeration levels of the hydraulic fluid on the detection of pump leakage and a degraded directional valve switching behavior. Furthermore, a robust detection of the loading state of the installed filter element and an estimation of the particle contamination level is proposed based on the same analysis concept.

A aeração artificial em meio líquido visa suprir a baixa concentração de oxigênio dissolvido em ambientes deficientes deste, sendo um processo comumente aplicado na área de tratamento de efluentes por processos aeróbios. Uma forma de produzir aeração artificial é através de difusores submersos no fundo de um tanque com formação de bolhas, que ascendem e transferem seu oxigênio ao longo da coluna dágua. Para simular e melhor entender este processo e sua fluidodinâmica, um modelo inicial simplificado foi proposto, baseado em conceitos teóricos e equações que representem o fenômeno, como a de dispersão de bolhas, velocidades médias e concentração de oxigênio dissolvido. Foi considerado para realização dos cálculos um tanque retangular, com entrada de água a esquerda e saída de água a direita, com superfície sólida ao fundo e superfície livre acima, em contato com o ar. As equações de transporte de massa foram discretizadas no tempo, utilizando a técnica de Crank-Nicolson e no espaço segundo metodologia de diferenças centrais, solucionadas posteriormente por meio de técnicas iterativas do tipo Gauss-Seidel. As equações de transporte de quantidade de movimento foram resolvidas com o método MAC, explícito nas velocidades do fluido e implícito na pressão, para fornecer o campo de velocidade e pressão. A equação de que fornece o perfil de espalhamento das bolhas foi tomada como uma Equação Gaussiana de dispersão bidimensional. A implementação computacional necessária para aplicação das abordagens foi no ambiente de programação MATLAB. O método MAC e a técnica Crank-Nicolson apresentaram resultados satisfatórios para simulações rápidas e noção do comportamento do fluido e da concentração de oxigênio dissolvido. / The artificial aeration in aqueous mean aims to supply low concentration of dissolved oxygen in deficient atmospheres of it. This process is commonly applied in the field of wastewater treatment by aerobic processes. One way to produce artificial aeration is through diffusers submerged at the bottom of a tank with the formation of bubbles, which ascend and transfer its oxygen throughout the water column. To simulate and better understand this process and its fluid dynamics, a simplified initial model was proposed based on theoretical concepts and equations that represent the phenomenon, as the dispersion of bubbles, average speeds and dissolved oxygen concentration. It was considered for the calculations one rectangular tank with the water inlet and water outlet from left to right, with solid surface to the bottom and free surface at the top in contact with air. The mass transport equations were discretized in time, using the Crank-Nicolson technique and in space according to the methodology of central differences, subsequently resolved by Gauss-Seidel technique iterative. The transport equations of momentum were solved with the MAC method, explicit on the velocities of the fluid and implicit on pressure, to afford the velocity field and pressure. The equation which provides the spreading profiles of bubbles was taken as a two-dimensional Gaussian dispersion equation. The computational implementation necessary for application of the approaches was the programming environment MATLAB. The MAC method and Crank- Nicolson technique showed satisfactory results for quick simulations and notion of the behavior of the fluid and the concentration of dissolved oxygen.

Esta dissertação trata da aeração induzida em vertedores com objetivo de mitigar os efeitos da cavitação sobre os mesmos. A análise bibliográfica do tema está calcada na introdução ao mecanismo da cavitação e no levantamento do estado da arte a partir dos trabalhos pioneiros, nos clássicos e nos recentes. Com base nos princípios da física: Conservação de Massa e Primeira Lei da Termodinâmica, foi desenvolvido um modelo matemático para aeração induzida em vertedores. O modelo proposto, após ser analisado do ponto de vista de sua consistência, foi avaliado em comparações com resultados fornecidos por outros pesquisadores, obtidos através de modelos físicos reduzidos. Os resultados obtidos pelo modelo matemático proposto correspondem a boas estimativas das grandezas envolvidas na aeração induzida em vertedores, o que credencia o modelo proposto como uma ferramenta apropriada para projetos de engenharia hidráulica e futuros desenvolvimentos científicos. / This study adress prompt aeration in spillways reaching to reduce the cavitation effects on them. References were based on introduction to cavitation machanism and, state of art survey, to leave on not only earlier studies, but also on classical and most recent ones. Based on principles of Physics, such as Mass Conservation and the First Law of Thermodynamics, a mathematical model has been developed as an example of prompt aeration in spillways. After extensive consistency analyses the proposed model has been validated by comparing different results furnished by studies on physical reduced models by other researchers. Results obtained from the mathematical model proposed here correspond to good estimates of greatnesses involved in prompt aeration is spillways and that turns the proposed model into an adequate tool for Hydraulic Engineering projects and for future scientifics stydies.