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Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 127-136).

Thesis (Ph. D.)--Institute of Paper Science and Technology, Georgia Institute of Technology, 2004. / Includes bibliography.

Resumo: Quatro métodos de dimensionamento de dutos em sistemas de refrigeração, ventilação e ar condicionado são comparados em relação ao custo do ciclo de vida e à diferença de pressão que determinará a escolha do ventilador. Dois métodos comumente usados, denominados de método da velocidade e método da igual perda de carga e dois métodos otimizados, método T e método IPS são aplicados a dois sistemas, o primeiro mais simples, com coeficientes de perda de pressão pré-definidos e o segundo, um sistema mais complexo e que é indicado pela ASHRAE como padrão para estudos de métodos de dimensionamento de dutos. Neste caso os componentes têm seus coeficientes de perdas de pressão dependentes de parâmetros como vazão, dimensão e número de Reynolds. Os métodos foram estudados, aplicados e comparados e os métodos T e IPS apresentaram vantagens quanto ao custo de ciclo de vida e praticidade de aplicação, principalmente em sistemas mais complexos / Abstract: Four heating, ventilating and air-conditioning systems duct design methods are compared in relation to life-cycle cost and pressure differential that will determine the fan choice. Two methods commonly used, named velocity reduction method and equal friction method and two optimized methods, T-method and IPS method, were applied in two systems. The first one is a simple system, with fixed loss coefficients and the second, is a more complex system suggested by ASHRAE as standard system for duct sizing methods studies. In the second system, the fittings were considered to have dynamic loss coefficient dependents on parameters like flow, size and Reynolds number. The methods were studied, applied and compared and the optimized methods presented advantages about life-cycle cost in practicality of all the applications, especially in more complex systems / Orientador: Mauricio Araujo Zanardi / Coorientador: José Antonio Perrella Balestieri / Banca: Luiz Roberto Carroccci / Banca: José Rui Camargo / Mestre

Made available in DSpace on 2014-06-11T19:29:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-08-15Bitstream added on 2014-06-13T18:40:00Z : No. of bitstreams: 1 oliveira_rm_me_guara.pdf: 802847 bytes, checksum: 4df8785af5e9e77ed619a6b784735871 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Quatro métodos de dimensionamento de dutos em sistemas de refrigeração, ventilação e ar condicionado são comparados em relação ao custo do ciclo de vida e à diferença de pressão que determinará a escolha do ventilador. Dois métodos comumente usados, denominados de método da velocidade e método da igual perda de carga e dois métodos otimizados, método T e método IPS são aplicados a dois sistemas, o primeiro mais simples, com coeficientes de perda de pressão pré-definidos e o segundo, um sistema mais complexo e que é indicado pela ASHRAE como padrão para estudos de métodos de dimensionamento de dutos. Neste caso os componentes têm seus coeficientes de perdas de pressão dependentes de parâmetros como vazão, dimensão e número de Reynolds. Os métodos foram estudados, aplicados e comparados e os métodos T e IPS apresentaram vantagens quanto ao custo de ciclo de vida e praticidade de aplicação, principalmente em sistemas mais complexos / Four heating, ventilating and air-conditioning systems duct design methods are compared in relation to life-cycle cost and pressure differential that will determine the fan choice. Two methods commonly used, named velocity reduction method and equal friction method and two optimized methods, T-method and IPS method, were applied in two systems. The first one is a simple system, with fixed loss coefficients and the second, is a more complex system suggested by ASHRAE as standard system for duct sizing methods studies. In the second system, the fittings were considered to have dynamic loss coefficient dependents on parameters like flow, size and Reynolds number. The methods were studied, applied and compared and the optimized methods presented advantages about life-cycle cost in practicality of all the applications, especially in more complex systems

In this study, the techno-economic feasibility of converting an existing process steam plant into a combined heat and power plant, using an external solar thermal field as the additional heat source was studied. Technical feasibility entailed designing a suitable heat exchanger, which uses hot oil from the solar field to raise the steam conditions from dry saturated to superheated. The solar field was sized to heat a selected heat transfer fluid to its maximum attainable temperature. A suitable turbine-alternator was chosen which can meet the required plant power demand. For this to be a success, the processes which require process steam were analysed and a MathCAD model was created to design the heat exchanger and check turbine output using the equations adapted from various thermodynamics and power plant engineering texts, together with the Standards for the Tubular Exchanger Manufacturer's Association. The U.S. National Renewable Energy Laboratory system advisor model was used to size the suitable solar field. A financial model was developed in Excel to check the economic feasibility of the project, using discounted payback period as the economic indicator. It was found out that amongst loan interest rates, variation of system output and the electricity output, the profitability of the project was largely influenced by the electricity tariff. An optimum size for the heat exchanger of 30ft was established from the sensitivity analysis and it was concluded that the project is currently not economically viable on an independent investor financing model, unless either the electricity tariff improves or the solar thermal energy and turbine technology costs decrease.

Buffer sizing is an important network configuration parameter that impacts the quality of data traffic. Falling memory cost and the fallacy that ‘more is better’ lead to over provisioning network devices with large buffers. Over-buffering or the so called ‘bufferbloat’ phenomenon creates excessive end-to-end delay in today’s networks. On the other hand, under-buffering results in frequent packet loss and subsequent under-utilization of network resources. The buffer sizing problem has been studied extensively for wired networks. However, there is little work addressing the unique challenges of wireless environment. In this dissertation, we discuss buffer sizing challenges in wireless networks, classify the state-of-the-art solutions, and propose two novel buffer sizing schemes. The first scheme targets buffer sizing in wireless multi-hop networks where the radio spectral resource is shared among a set of con- tending nodes. Hence, it sizes the buffer collectively and distributes it over a set of interfering devices. The second buffer sizing scheme is designed to cope up with recent Wi-Fi enhancements. It adapts the buffer size based on measured link characteristics and network load. Also, it enforces limits on the buffer size to maximize frame aggregation benefits. Both mechanisms are evaluated using simulation as well as testbed implementation over half-duplex and full-duplex wireless networks. Experimental evaluation shows that our proposal reduces latency by an order of magnitude.

Inventory control problems constitute one of the most important research problems due to their connection with real life applications. Naturally, real life is full of uncertainty so are the most of the inventory problems. Unfortunately, it is a very challenging task to manage inventories effectively especially under uncertainty. This dissertation mainly deals with single-item, periodic review, and stochastic dynamic inventory control problems particularly on replenishment cycle control rule known as the (R, S) policy. Contribution of this thesis is multiold. In each chapter a particular research question is investigated. At the end of the day, we will be showing that non-stationary (R, S) policies are indispensable not only for its cost efficiency but its effectiveness and practicality. More specifically, the non-stationary (R, S) policy provides a convenient, efficient, effective, and modular solution for non-stationary stochastic inventory control problems.

Master of Science / Particulate ingestion has been an ongoing issue in the aviation industry as aircraft are required to operate in hostile environments. Ingesting particulates such as sand or dust can erode and damage engine components. This damage will affect the life cycle of parts and compromise the safety of the aircraft. This issue is very costly and dangerous. In order to combat these issues, a particle sensor with the ability to monitor in-stream particulate size, shape, and mass flow rate is necessary. Our team with the Advanced Propulsion and Power Laboratory developed a non-intrusive optical sensor that is able to characterize non-spherical particles. This sensor has been used in various applications through the years; however, most recently, the sensor has been demonstrated at the Virginia Tech M250 engine inlet. This was the first time that the sensor was directly attached to an engine's inlet and subjected to engine conditions. For this validation, highly erosive, coarse quartz was used. Utilizing laser and cameras, the sensor is able to deduce the particles' average shape and size distributions. From those measurements, the mass flow rate of the particle can be calculated. The works provided in the thesis show that particle ingestion rates can be measured to an acceptably high accuracy. In contrast, refinement of the processing techniques can provide spatially resolved measurements of particle characteristics as well.

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