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1
Srinivasan, Raghavan. "CFD Heat Transfer Simulation of the Human Upper Respiratory Tract for Oronasal Breathing Condition". Thesis, North Dakota State University, 2011. https://hdl.handle.net/10365/29310.
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In this thesis. a three dimensional heat transfer model of heated airflow through the upper human respiratory tract consisting of nasal, oral, trachea, and the first two generations of bronchi is developed using computational fluid dynamics simulation software. Various studies have been carried out in the literature investigating the heat and mass transfer characteristics in the upper human respiratory tract, and the study focuses on assessing the injury taking place in the upper human respiratory tract and identifying acute tissue damage based on level of exposure. The model considered is for the simultaneous oronasal breathing during the inspiration phase with high volumetric flow rate of 90/liters minute and a surrounding air temperature of 100 degrees centigrade. The study of the heat and mass transfer, aerosol deposition and flow characteristics in the upper human respiratory tract using computational fluid mechanics simulation requires access to a two dimensional or three dimensional model for the human respiratory tract. Depicting an exact model is a complex task since it involves the prolonged use of imaging devices on the human body. Hence a three dimensional geometric representation of the human upper respiratory tract is developed consisting of nasal cavity, oral cavity, nasopharynx, pharynx, oropharynx, trachea and first two generations of the bronchi. The respiratory tract is modeled circular in cross-section and varying diameter for various portions as identified in this study. The dimensions are referenced from the literature herein. Based on the dimensions, a simplified model representing the human upper respiratory tract is generated.This model will be useful in studying the flow characteristics and could assist in treatment of injuries to the human respiratory tract as well as help optimize drug delivery mechanism and dosages. Also a methodology is proposed to measure the characteristic dimension of the human nasal and oral cavity at the inlet/outlet points which are classified as internal measurements.
2
Shao, Ming. "Modelling simultaneous heat and mass transfer in wood". Thesis, Virginia Tech, 1994. http://hdl.handle.net/10919/42073.
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The fundamental and quantitative study of heat and mass transfer processes in wood plays an important role for understanding many important production processes, such as wood drying and hot-pressing. It will help us improve the existing products and production techniques and develop new manufacturing technology. The most difficult aspect of the study is the complicated interactions of heat and mass transfer mechanisms. Extensive characterization of these physical processes using a strictly experimental approach is extremely difficult because of the excessively large number of variables that must be considered. However, mathematical modeling and numerical techniques serve as a powerful tool to help us understand the complicated physical processes.
The goal of this research is to model the simultaneous heat and mass transfer in wood. The specific objectives of this research are:
1) develop a computer simulation program, implementing an existing one-dimensional mathematical drying model, using a finite difference approach, to numerically evaluate the mathematical model.
2) study sensitivity of the heat and mass transfer model to determine the effects of wood physical properties and environmental conditions on the drying processes.Master of Science
3
Baumgratz, Filipe Dias. "Estudo da distribuição da temperatura em encapsulamentos de dispositivos MOSFET utilizando simulação por métodos de elementos finitos". [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/259569.
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Orientador: Marco Antônio Robert AlvesDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Resumo: O transistor MOSFET teve uma evolução muito grande desde sua invenção até os dias de hoje. As dimensões foram reduzidas, a capacidade de integração de componentes e frequência de operação aumentaram, como consequência desta evolução houve um aumento da potência dissipada pelos circuitos integrados. Neste trabalho foi utilizada simulação por elementos finitos para estudar o comportamento térmico de um encapsulamento ao variar-se sua montagem interna, utilizando um MOSFET de potência como fonte de calor. A partir destas simulações foi possível identificar os pontos de maior e menor temperatura, bem como as regiões de melhor condução de calor. Ainda utilizando simulação por elementos finitos estudou-se o efeito da variação do tempo de chaveamento nas temperaturas observadas no interior do encapsulamento
Abstract: The transistor had a great evolution since its invention until today. The dimensions were reduced, the components integration and operating frequency increased, a result of these developments is higher power dissipation in integrated circuits. This work use finite element method simulation to study the thermal behavior of a package with different internal assembly, using a power MOSFET as heat source. From these simulations it is possible to identify the points of high and low temperature, and best thermal paths. Still using finite element method simulation was studied the effect of switching time in the thermal behavior of the package
Mestrado
Eletrônica, Microeletrônica e Optoeletrônica
Mestre em Engenharia Elétrica
4
Gempesaw, Daniel. "A multi-resolution discontinuous Galerkin method for rapid simulation of thermal systems". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42775.
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Efficient, accurate numerical simulation of coupled heat transfer and fluid dynamics systems continues to be a challenge. Direct numerical simulation (DNS) packages like FLU- ENT exist and are sufficient for design and predicting flow in a static system, but in larger systems where input parameters can change rapidly, the cost of DNS increases prohibitively. Major obstacles include handling the scales of the system accurately - some applications span multiple orders of magnitude in both the spatial and temporal dimensions, making an accurate simulation very costly. There is a need for a simulation method that returns accurate results of multi-scale systems in real time. To address these challenges, the Multi- Resolution Discontinuous Galerkin (MRDG) method has been shown to have advantages over other reduced order methods. Using multi-wavelets as the local approximation space provides an inherently efficient method of data compression, while the unique features of the Discontinuous Galerkin method make it well suited to composition with wavelet theory. This research further exhibits the viability of the MRDG as a new approach to efficient, accurate thermal system simulations. The development and execution of the algorithm will be detailed, and several examples of the utility of the MRDG will be included. Comparison between the MRDG and the "vanilla" DG method will also be featured as justification of the advantages of the MRDG method.
5
Li, Shuo. "A Numerical Study of Micro Synthetic Jet and Its Applications in Thermal Management". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7539.
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A numerical study of axisymmetric synthetic jet flow was conducted. The synthetic jet cavity was modeled as a rigid chamber with a piston-like moving diaphragm at its bottom. The Shear-Stress-Transportation (SST) k-omega and #61559; turbulence model was employed to simulate turbulence. Based on time-mean analysis, three flow regimes were identified for typical synthetic jet flows. Typical vortex dynamics and flow patterns were analyzed. The effects of changes of working frequency, cavity geometry (aspect ratio), and nozzle geometry were investigated. A control-volume model of synthetic jet cavity was proposed based on the numerical study, which consists of two first-order ODEs. With appropriately selected parameters, the model was able to predict the cavity pressure and average velocity through the nozzle within 10% errors compared with full simulations. The cavity model can be used to generate the boundary conditions for synthetic jet simulations and the agreement to the full simulation results was good. The saving of computational cost is significant. It was found that synthetic jet impingement heat transfer outperforms conventional jet impingement heat transfer with equivalent average jet velocity. Normal jet impingement heat transfer using synthetic jet was investigated numerically too. The effects of changes of design and working parameters on local heat transfer on the impingement plate were investigated. Key flow structures and heat transfer characteristics were identified. At last, a parametric study of an active heat sink employing synthetic jet technology was conducted using Large Eddy Simulation (LES). Optimal design parameters were recommended base on the parametric study.
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Mulcahey, Thomas Ian. "Convective instability of oscillatory flow in pulse tube cryocoolers due to asymmetric gravitational body force". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51808.
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Pulse tube cryocoolers (PTCs) are among the most attractive choices of refrigerators for applications requiring up to 1 kW of cooling in the temperature range of 4-123 K as a result of the high relative efficiency of the Stirling cycle, the reliability of linear compressors, and the lack of cryogenic moving parts resulting in long life and low vibration signature. Recently, PTCs have been successfully used in applications in the 150 K range, extending the useful range of the device beyond the traditional cryogenic regime. A carefully designed cylindrical cavity referred to as the pulse tube replaces the mechanical expander piston found in a Stirling machine. A network consisting of the pulse tube, inertance tube, and surge volume invoke out-of-phase pressure and mass flow oscillations while eliminating all moving parts in the cold region of the device, significantly improving reliability over Stirling cryocoolers. Terrestrial applications of PTCs expose a fundamental flaw. Many PTCs only function properly in a narrow range of orientations, with the cold end of the pulse tube pointed downward with respect to gravity. Unfavorable orientation of the cold head often leads to a catastrophic loss of cooling, rendering the entire cryocooler system inoperable. Previous research indicates that cooling loss is most likely attributed to secondary flow patterns in the pulse tube caused by free convection. Convective instability is initiated as a result of non-uniform density gradients within the pulse tube. The ensuing secondary flow mixes the cryogen and causes enhanced thermal transport between the warm and cold heat exchangers of the cryocooler.
This study investigates the nonlinear stabilizing effect of fluid oscillation on Rayleigh-Bénard instability in a cryogenic gas subject to misalignment between gravitational body force and the primary flow direction. The results are directly applicable to the flow conditions frequently experienced in PTCs. Research has shown that the convective component can be minimized by parametrically driven fluid oscillation as a result of sinusoidal pressure excitation; however, a reliable method of predicting the influence of operating parameters has not been reported. In this dissertation, the entire PTC domain is first fully simulated in three dimensions at various angles of inclination using a hybrid method of finite volume and finite element techniques in order to incorporate conjugate heat transfer between fluid domains and their solid containment structures. The results of this method identify the pulse tube as the sole contributor to convective instability, and also illustrate the importance of pulse tube design by incorporating a comparison between two pulse tubes with constant volume but varying aspect ratio. A reduced domain that isolates the pulse tube and its adjacent components is then developed and simulated to improve computational efficiency, facilitating the model’s use for parametric study of the driving variables. A parametric computational study is then carried out and analyzed for pulse tubes with cold end temperatures ranging from 4 K to 80 K, frequencies between 25-60 Hz, mass flow - pressure phase relationships of -30◦ and +30◦, and Stokes thickness-based Reynolds numbers in the range of 43-350, where the turbulent transition occurs at 500.
In order to validate the computational models reported and therefore justify their suitability to perform parametric exploration, the CFD codes are applied to a commercially developed single stage PTR design. The results of the CFD model are compared to laboratory-measured values of refrigeration power at temperatures ranging from 60 K to 120 K at inclination angles of 0◦ and 91◦. The modeled results are shown to agree with experimental values with less than 8.5% error for simulation times of approximately six days using high performance computing (HPC) resources through Georgia Tech’s Partnership for Advanced Computing (PACE) cluster resource, and 10 days on a common quad-core desktop computer. The results of the computational parametric study as well as the commercial cryocooler data sets are compiled in a common analysis of the body of data as a whole. The results are compared to the current leading pulse tube convective stability model to improve the reliability of the predictions and bracket the range of losses expected as a function of pulse tube convection number. Results can be used to bracket the normalized cooling loss as a function of the pulse tube convection number NPTC. Experimental data and simulated results indicate that a value of NPTC greater than 10 will yield a loss no greater than 10% of the net pulse tube energy flow at any angle. A value of NPTC greater than 40 is shown to yield a loss no greater than 1% of the net pulse tube energy flow at all angles investigated.
The computational and experimental study completed in this dissertation addresses static angles of inclination. Recent interest in the application of PTCs to mobile terrestrial platforms such as ships, aircraft, and military vehicles introduces a separate regime wherein the angle of inclination is dynamically varying. To address this research need, the development of a single axis rotating cryogenic vacuum facility is documented. A separate effects apparatus with interchangeable pulse tube components has also been built in a modular fashion to accommodate future research needs.
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Mioralli, Paulo Cesar. "Analise termica de um regenerador rotativo". [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263462.
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Orientador: Marcelo Moreira GanzarolliDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Este estudo concentra-se na análise térmica de um regenerador rotativo, no qual o processo de transferência de calor é investigado numericamente. As equações de transporte foram discretizadas utilizando o método de volumes finitos e um programa computacional em linguagem FORTRAN foi confeccionado para as simulações numéricas. Uma correlação para estimar o coeficiente médio de transferência de calor em um canal da matriz do regenerador foi obtida para o regime laminar de escoamento a partir da utilização do pacote numérico comercial PHOENICS 3.5. O valor de temperatura média de mistura na saída de cada escoamento foi obtido e comparado com o valor calculado por método existente em literatura. Os resultados foram analisados e também comparados com dados de campo e uma concordância relativamente boa foi observada. Através das simulações numéricas, foi possível obter a distribuição de temperatura ao longo de um canal do regenerador em diferentes posições angulares. Conhecendo essa distribuição de temperatura, é possível obter um dimensionamento adequado para o sistema de selagem acoplado na matriz do regenerador. Foi visto neste trabalho que o perfil de temperatura na direção axial é determinante no dimensionamento do sistema de selagem do regenerador
Abstract: This study focalizes on the thermal analysis of a rotary regenerator, in which the process of heat transfer is numerically investigated. The governing equations are solved using finite volume code. A computational code in FORTRAN programming language was made for the numerical simulations. A correlation for valuation the medium heat transfer coefficient in the duct, for flow in laminar regime, was obtained using a commercial code (PHOENICS 3.5). The value of mean temperature at the exit of each flow was obtained and compared with the value calculated by existent method in the literature. The results were analyzed and also compared with field data and a relatively good agreement was observed. Through the numerical simulations, it was possible to obtain the temperature distribution along a duct of the regenerator in different angular positions
Mestrado
Termica e Fluidos
Mestre em Engenharia Mecânica
8
Tomazeti, Cristina Autuori. "Analise numerica do desempenho termico de trocadores de calor de correntes cruzadas". [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264127.
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Orientador: Carlos Alberto Carrasco AltemaniTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Uma análise foi desenvolvida para avaliar o desempenho de trocadores de calor compactos de correntes cruzadas de placas aletadas com canais de seção transversal arbitrária. Os coeficientes convectivo e de atrito foram obtidos através de simulação numérica, tanto no regime de escoamento laminar quanto no turbulento, utilizando o pacote computacional PHOENICS. Estes resultados foram então usados junto com o método da efetividade para avaliar as características térmicas e de escoamento do trocador de calor. As simulações foram efetuadas inicialmente para o escoamento e a transferência de calor entre duas placas placa paralelas isotérmicas e bastante próximas, porque os resultados podiam ser comparados com aqueles disponíveis na literatura. Resultados numéricos adicionais foram obtidos, em seguida, para seis dutos de paredes isotérmicas com seções transversais distintas. Um deles era um duto retangular, e os outros cinco eram passagens típicas de placas aletadas utilizadas em trocadores de calor compactos. O fluido de trabalho era o ar e as simulações foram tridimensionais devido à presença das paredes das aletas. Perfis uniformes de velocidade e de temperatura sempre foram utilizados na entrada dos dutos, de forma que os resultados refletem os efeitos combinados de entrada hidrodinâmica e térmica. Os resultados para o duto retangular e o método da efetividade foram utilizados para prever o desempenho térmico de um trocador de calor de correntes cruzadas composto por um empilhamento de dutos retangulares idênticos. O desempenho deste trocador de calor foi avaliado também por uma simulação direta do escoamento cruzado e da transferência de calor através da parede de separação de dois dutos retangulares adjacentes do empilhamento. Os resultados obtidos foram bastante semelhantes, fornecendo confiança para a análise anterior. As simulações efetuadas para os cinco dutos típicos de placas aletadas de dimensões pequenas apresentaram resultados similares aos valores experimentais obtidos da literatura. Eles foram utilizados para avaliar o desempenho de trocadores de calor compactos de correntes cruzadas compostos por empilhamentos destas placas aletadas. Vários parâmetros como o volume total, o peso, a potência de bombeamento, a efetividade, a taxa de geração adimensional de entropia, e a eficiência exergética também foram avaliados para comparar os trocadores compactos de calor considerados
Abstract: An analysis was developed to evaluate the performance of cross flow compact heat exchangers with plate-fin passages of arbitrary cross section. The convective and the friction coefficients were obtained by numerical simulation, either in the laminar or the turbulent flow regimes, using the software PHOENICS. These results were then employed together with the effectiveness method to evaluate the heat exchanger thermal and flow characteristics. The simulations were performed initially for the flow and heat transfer between two closely spaced parallel isothermal plates, because the results could be compared with those available in the literature. Additional numerical results were obtained, next, for six isothermal wall ducts with distinct cross sections. One was a rectangular duct, and the other five were typical plate-fin passages employed in compact heat exchangers. The working fluid was air and the simulations were three dimensional due to the fins walls. Uniform velocity and temperature profiles were always assumed at the duct inlet, so that the results reflected the combined effects of hydrodynamic and thermal entrance. The results for the rectangular duct and the effectiveness method were employed to predict the thermal performance of a cross flow heat exchanger made from a stack of identical rectangular ducts. The performance of this heat exchanger was also evaluated by a direct simulation of the cross flow and the heat transfer through the separating wall of two adjacent rectangular ducts of the stack. The results compared favorably, lending confidence to the previous analysis. The simulations performed for the five typical plate-fin passages of small cross section presented results similar to the experimental values obtained from the literature. They were used to evaluate the performance of cross flow compact heat exchangers composed of stacks of these plate-fins. Several parameters like total volume, weight, pumping power, effectiveness, rate of dimensionless entropy generation, and exergetic efficiency were also evaluated to compare the distinct compact heat exchangers
Doutorado
Termica e Fluidos
Mestre em Engenharia Mecânica
9
Lavarda, Jairo Vinícius. "Convecção natural de fluidos de lei de potência e de Bingham em cavidade fechada preenchida com meio heterogêneo". Universidade Tecnológica Federal do Paraná, 2015. http://repositorio.utfpr.edu.br/jspui/handle/1/1306.
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CAPESVários estudos numéricos investigaram cavidades fechadas sob o efeito da convecção natural preenchidas com fluidos newtonianos generalizados (FNG) nos últimos anos pelas aplicações diretas em trocadores de calor compactos, no resfriamento de sistemas eletrônicos e na engenharia de polímeros. Neste trabalho é realizada a investigação numérica do processo de convecção natural de fluidos de lei de Potência e de Bingham em cavidades fechadas, aquecidas lateralmente e preenchidas com meios heterogêneos e bloco centrado. O meio heterogêneo é constituído de blocos sólidos, quadrados, desconectados e condutores de calor. Como parâmetros são utilizados a faixa de Rayleigh de 104 à 107, índice de potência n de 0, 6 à 1, 6, número de Bingham de 0, 5 até Bimax , sendo investigado da influência do número de Prandtl para cada modelo de fluido. Nas cavidades com meio heterogêneo são utilizadas as quantidades de blocos de 9, 16, 36 e 64, mantendo-se a razão entre a condutividade térmica do sólido e do fluido κ = 1. Para as cavidades com bloco centrado, são utilizados os tamanhos adimensionais de 0, 1 à 0, 9 com κ = 0, 1; 1 e 10. A modelagem matemática é realizada pelas equações de balanço de massa, de quantidade de movimento e de energia. As simulações são conduzidas no programa comercial ANSYS FLUENT R . Inicialmente são resolvidos problemas com fluidos newtonianos em cavidade limpa, seguida de cavidade preenchida com meio heterogêneo e posteriormente bloco centrado para validação da metodologia de solução. Na segunda etapa é realizada o estudo com os modelos de fluidos de lei de Potência e de Bingham seguindo a mesma sequência. Os resultados são apresentados na forma de linhas de corrente, isotermas e pelo número de Nusselt médio na parede quente. De maneira geral, a transferência de calor na cavidade é regida pelo número de Rayleigh, tamanho e condutividade térmica dos blocos, pelo índice de potência para o modelo de lei de Potência e do número de Bingham para o modelo de Bingham. O número de Prandtl tem grande influência nos dois modelos de fluidos. O meio heterogêneo reduz a transferência de calor na cavidade quando interfere na camada limite térmica para ambos os fluidos, sendo feita uma previsão analítica para o fluido de lei de Potência. Para bloco centrado, a interferência na camada limite com fluido de lei de Potência também foi prevista analiticamente. A transferência de calor aumentou com bloco de baixa condutividade térmica e pouca interferência e com bloco de alta condutividade térmica e grande interferência, para ambos os fluidos.
Many studies have been carried out in square enclosures with generalized Newtonian fluids with natural convection in past few years for directly applications in compact heat exchangers, cooling of electronics systems and polymeric engineering. The natural convection in square enclosures with differently heated sidewalls, filled with power-law and Bingham fluids in addition with heterogeneous medium and centered block are analyzed in this study. The heterogeneous medium are solid, square, disconnected and conducting blocks. The parameters used are the Rayleigh number in the range 104 - 107 , power index n range of 0, 6 - 1, 6, Bingham number range of 0, 5 - Bimax , being the influence of Prandtl number investigated for each fluid model. The number of blocks for heterogeneous medium are 9, 16, 36 and 64, keeping constant solid to fluid conductive ratio, κ = 1. For enclosures with centered block are used the nondimensional block size from 0, 1 to 0, 9, with solid to fluid conductive ratio in range κ = 0, 1; 1 and 10. Mathematical modeling is done by mass, momentum and energy balance equations. The solution of equations have been numerically solved in ANSYS FLUENT R software. Firstly, numerical solutions for validation with Newtonian fluids in clean enclosures are conducted, followed by enclosures with heterogeneous medium and centered block. Subsequently, numerical solutions of power-law and Bingham fluids with same enclosures configurations are conducted. The results are reported in the form of streamlines, isotherms and average Nusselt number at hot wall. In general, the heat transfer process in enclosure is governed by Rayleigh number, size and thermal conductivity of the blocks, power index n for power-law fluid and Bingham number for Bingham fluid. Both fluid models are very sensitive with Prandtl number changes. Heterogeneous medium decrease heat transfer in enclosure when affects thermal boundary layer for both fluid models. One analytical prediction was made for power-law fluid. An increase in heat transfer occurs with low thermal conductivity block and few interference and with high thermal conductivity block and great interference, for both fluids.
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Spinelli, Jose Eduardo. "Simulação do lingotamento continuo de tiras finas de aços". [s.n.], 2000. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264701.
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Orientador: Amauri GarciaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Entende-se por modelagem de processo, o desenvolvimento de uma representação quantitativa ou qualitativa dos fenômenos físicos associados ao processo. Neste trabalho são realizadas simulações do processo twin roll de lingotamento contínuo de tiras de aços, utilizando como referência tecnológica o equipamento piloto instalado nas dependências do Instituto de Pesquisas Tecnológicas do Estado de São Paulo. São construídos dois simuladores para o processo: um simulador da solidificação unidirecional, com molde refrigerado de aço e paredes laterais de material refratário, utilizando-se o aço inoxidável 304 como material de simulação; e variando-se as temperaturas de vazamento; e outro simulador a frio, com componentes feitos de acrílico, água como fluido de simulação e permanganato de potássio como corante. Um modelo matemático previamente desenvolvido é utilizado para confrontar perfis térmicos teóricos com perfis experimentais, para a determinação do coeficiente de transferência de calor metal/molde. O levantamento de valores de espaçamento dendrítico secundário é realizado nas amostras, além da observação simultânea das estruturas de solidificação, o que comprovou a eficiência do simulador em caracterizar o processo de solidificação do equipamento piloto. O uso do modelo frio permitiu a caracterização do posicionamento de barreira a 15 cm ou a 20 cm da lateral esquerda do distribuidor como a melhor configuração
Abstract: It can be understood by process modeling the development of a quantitative or qualitative representation of the physical phenomena associated to the process. In this work, simulations concerning the twin roll continuous caster of steels process at IPT (Instituto de Pesquisas Tecnológicas do Estado de São Paulo) are performed. Two simulators were developed: (i) a simulator of unidirectional solidification with cooled steel mold and refractory lateral walls, by using a stainless steel as the reference metal (AISI 304), and varying superheat temperatures; (ii) a physical model, with components made of acrylic, water as the simulation fluid and potassium permanganate as a pigment. A previously developed mathematical model has been used to determine the metal/mold heat transfer coefficient by a method that compares experimenta1ltheoretical temperature curves. Measurement of secondary dendrite arm spacings is performed by microestructural examination of the samples, confirming the simulator efficiency in characterizing the solidification process in the pilot equipment. The use of the physical model has permitted to attain the best configuration for the tundish, by positioning the dam 15 cm or 20 cm from the left side of tundish
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica
11
Chen, Zong-Ping. "Three-dimensional hyperthermia cancer treatment simulation". Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184852.
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A simulation program to study the three dimensional temperature distributions produced by hyperthermia in anatomically realistic inhomogeneous tissue models has been developed. The anatomical data for the inhomogeneous tissues of the human body are entered on a digitizing tablet from serial CT scans. The program not only predicts temperature distributions in regions dominated by blood perfusion (with large number of small capillaries), but it can also predict the temperatures inside of and at the vicinity of large blood vessels. The program can be used for different power deposition patterns from various heating modalities, but they must be calculated independently. In this study, the author's attention has been focused on ferromagnetic implants. The program has been used to comparatively evaluate two and three dimensional simulations in a series of parametric calculations based on simple tissue models for both uniform power deposition and ferromagnetic implants. The conclusions drawn from these studies are that two dimensional simulations can lead to significant errors in many situations, and therefore three dimensional simulations will be necessary for accurate patient treatment planning. The conclusion from the geometrically simple model is substantiated by the results obtained using the full 3D model for actual patient anatomical simulations. The program has also been used for several parametric studies. The effect of the thermal conductivity used in the models on the temperature field has been studied, and the results show that its value in the range of 0.4 to 0.6 W/m/°C (valid for most soft tissues) has only a slight effect on the resultant temperature fields. The heating ability of the ferromagnetic implants has also been investigated for different blood perfusions. The effects of the Curie point of the ferromagnetic seeds, and seed spacing are also studied. Finally, the impact of large blood vessels on the resultant temperatures are studied, and the results show that the effect is dramatic and therefore it must be included in the simulations in order to predict accurate temperature fields. Finally, the program has been used to analyze a previously performed dog experiment, and a previously performed clinical treatment. A comparison between the predicted temperatures and the measured ones show that good agreement has been achieved for the clinical treatment, but not for the dog experiment. These results are studied in detail, and the conditions under which this program can be used as a hyperthermia patient treatment planning tool is discussed.
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Ben, Moussa Rim. "Contribution to thermal radiation to dust flame propagation : application to aluminium dust explosions". Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2401/document.
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Ces travaux de thèse sont consacrés à l’examen du rôle du rayonnement thermique dans le processus de propagation des flammes issues de la combustion des particules d’aluminium dans l’air. Le sujet étant complexe et d’un intérêt industriel, il nécessite de prendre en compte le couplage de nombreux phénomènes physico-chimiques afin de prédire finement les conséquences des explosions de poussières. Une analyse bibliographique approfondie est proposée, concernant les mécanismes d’inflammation et de combustion des particules d’aluminium et aussi concernant les connaissances relatives à la propagation des flammes de poussières. La question spécifique de la nature des échanges thermiques et de l’influence du rayonnement thermique est étudiée. La revue bibliographique souligne les approximations et les hypothèses simplificatrices utilisées dans la littérature permettant donc de définir les pistes d’améliorations. Compte tenu des limitations importantes concernant la physique de ces flammes, un outil de simulation de physique numérique nommé « RADIAN », proche de la simulation numérique directe, a été développé proposant un couplage fin entre les différents modes d’échanges thermiques et la combustion pour modéliser la propagation de la flamme dans un nuage de poussières. La méthode des éléments discrets (MED) est utilisée pour modéliser numériquement les échanges radiatifs entre les particules et les échanges conductifs entre gaz et particules. La méthode des différences finies est utilisée pour modéliser numériquement la conduction thermique dans la phase gazeuse et la combustion. Un modèle radiatif est proposé se basant sur la théorie de Mie sur les interactions rayonnement-particules. Les résultats des simulations sont comparés avec des solutions analytiques et des données expérimentales de la littérature. Mais en plus, une étude expérimentale est aussi conduite afin de mesurer la distribution du flux radiatif devant la flamme et la vitesse de combustion laminaire pour des flammes Méthane-Sic, Méthane-Alumine et Al-air. Un bon accord entre les simulations et les expériences est démontré. La loi de Beer-Lambert relative au transfert radiatif devant le front de flamme s’avère inapplicable et une nouvelle solution analytique est proposée. La présence de particules absorbantes du rayonnement promeut la propagation de la flamme. En particulier, il a été montré expérimentalement et confirmé numériquement que les mélanges riches d’AL-air sont susceptibles d’accélérer rapidementIn this thesis, the role of thermal radiation in aluminum-air flames propagation is studied. The subject being complex and of industrial interest, it requires the coupling of many physiochemical phenomena to accurately predict the consequences of dust explosions. A thorough literature review is proposed about the ignition and the combustion of aluminum particles and about the available theoretical models of dust flames propagation. The specific question of the nature of thermal exchanges and the influence of thermal radiation is studied. The bibliographic review underlines the simplifying assumptions and hypotheses used in the literature making possible the definition of improvement areas. Because of the limited amount of knowledge available to address these questions, a numerical tool “RADIAN” is developed enabling an accurate coupling between the different modes of heat exchange and combustion. The Discrete Element Method (DEM) is used to numerically model the radiative exchanges between particles and the gas-particle thermal conduction. The Finite Difference method is used to numerically model the thermal conduction through the gas phase and combustion. A radiative model based on Mie theory for radiation-particles interactions is incorporated. The results of the simulations are compared with available analytical solutions and experimental data. An original experimental study is also conducted to measure the distribution of irradiance ahead of the flame front and the laminar burning velocity for methane-air-Sic, methane-air-alumina and Al-air flames. A good agreement between numerical simulations and experiments is demonstrated. The Beer-Lambert’s law for radiative transfer in front of the flame front is found to be inapplicable and a new analytical solution is proposed. The presence of absorbing particles may promote the flame propagation. In particular, it is shown experimentally and confirmed theoretically/numerically that Al-air rich mixtures are likely to rapidly accelerate
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Janzen, Isaiah. "Modeling of Heat Treating Processes for Transmission Gears". Digital WPI, 2009. https://digitalcommons.wpi.edu/etd-theses/1123.
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"The effects of heat treating process parameters on the microstructure, residual stress, and distortion of a vacuum carburized, quenched and cold treated ring gear made of Pyrowear 53 has been determined using Abaqus and DANTE software. The data from these finite element method simulations was compared to measured values from physical testing. It was found that the heat treating process of the ring gear could be simulated and provide similar results to the measured and specified values for hardness, carbon content, and distortion. The simulations and distortion in this paper provide a detailed view of the mass transfer, heat transfer, and stress that occur during heat treating. These simulations suggest nonuniform cooling of a ring gear leads to greater distortion than uniform cooling. Simulations compared the retained austenite and hardness in ring gears that were oil quenched and high pressure gas quenched."
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Yang, Xiaofei. "Inferring disease transmission networks". HKBU Institutional Repository, 2014. https://repository.hkbu.edu.hk/etd_oa/88.
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To investigate how an infectious disease spreads, it is desirable to use the observed surveillance data to discover the underlying (often hidden) disease transmission networks. Previous studies have provided methods for inferring information diffusion networks in which each node corresponds to an individual person within the diffusion network. However, in the case of disease transmission, to effectively propose and implement intervention strategies, it is more realistic and reasonable for policy makers to study the diffusion patterns at a metapopulation level, that is, to consider disease transmission networks in which nodes represent subpopulations, and links indicate their interrelationships. Such networks can be useful in several ways: (i) to investigate hidden impact factors that in.uence epidemic dynamics, (ii) to reveal possible sources of epidemic outbreaks, and (iii) to practically develop and/or improve strategies for controlling the spread of infectious diseases. Therefore, this thesis addresses the problem of inferring disease transmission networks at a metapopulation level. A network inference method called NetEpi (Network Epidemic) is developed and evaluated using both synthetic and real-world datasets. The experimental results show that NetEpi can recover most of the ground-truth disease transmission networks using only surveillance data.
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Roddier, Nicolas 1965. "Curvature sensing for Adaptive Optics: A computer simulation". Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/291948.
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This thesis describes computer simulations of a new wavefront sensing technique for Adaptive Optics based on local wavefront curvature measurements, along with edge slope measurements. The output signal from the curvature measurements, along with edge slope measurements. The output signal from the curvature sensor can be directly applied to the electrodes of a bimorph or membrane mirror. The mirror is used as an analog device to solve the Poisson Equation, providing a fast real time compensation for atmospheric disturbances. The open loop characteristics of the system are presented. The ideal response is analyzed, and side effects such as non-linearity, photon and diffraction noises are discussed. Closed loop simulations are presented thereafter. A seven actuator system showed a few unstable modes. A 13 actuator system with proper filtering corrects the atmospheric perturbations. To simulate atmospheric distorted wavefronts, an algorithm based on spectral decomposition of the Zernike covariance matrix was derived. This sensor can also be used to test large telescope mirrors using a modified program that solves the Poisson Equation with Neumann boundary conditions.
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Liao, Jen-Chyi. "Computer simulation of multiple coupled transmission lines in electronic packaging application". Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184659.
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A method for simulating the transient responses of networks containing lossless transmission lines and lumped parameter elements of circuits, both linear and nonlinear, has been developed and investigated. The method combines the technique of network analysis and that of modal decomposition of transmission lines. A prototype computer simulation program, called UANTL, based on the developed algorithm has been implemented. Several example networks have been simulated using this program. The results have been compared with those generated by the well known circuit simulator program called SPICE. UANTL has shown several advantages over SPICE in simulating the transient responses of networks containing transmission lines. A description of the prototype version of UANTL and a summary of the results of numerical experiments are included.
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Ahmad, Imtiaz 1962. "Simulation of turbulent flow and heat transfer under an impinging round jet discharging into a crossflow". Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66202.
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Bernier, Jessica A. (Jessica Ashley). "Numerical field simulation for parallel transmission in MRI at 7 tesla". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/66025.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 41-42).
Parallel transmission (pTx) is a promising improvement to coil design that has been demonstrated to mitigate B1* inhomogeneity, manifest as center brightening, for high-field magnetic resonance imaging (MRI). Parallel transmission achieves spatially-tailored pulses through multiple radiofrequency (RF) excitation coils that can be activated independently. In this work, simulations of magnetic fields in numerical phantoms using an FDTD solver are used to estimate the excitation profiles for an 8-channel RF head coil. Each channel is driven individually in the presence of a dielectric load, and the excitation profiles for all channels are combined post-processing into a B1+ profile of the birdcage (BC) mode. The B1 profile is calculated for a dielectric sphere phantom with material properties of white matter at main magnetic field strengths of 3T and 7T to demonstrate center brightening associated with head imaging at high magnetic field strengths. Measurements of a circular ROI centered in the image show more B1+ inhomogeneity at 7T than at 3T. The B1* profile is then simulated for a numerical head phantom with spatially segmented tissue compartments at 7T. Comparison of the simulated and in vivo B1* profiles at 7T shows agreement in the B1 inhomogeneity. The results provide confidence in numerical simulation as a means to estimate magnetic fields for human imaging. This work will allow further numerical simulations to model the propagation of electric fields within the body, ultimately to provide an estimate of heat deposition in tissue, quantified by the specific absorption rate (SAR), which is a limiting factor of the use of high-field MRI in the clinical setting.
by Jessica A. Bernier.
S.M.
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Kitchovitch, Stephan. "Computational modelling and analysis of seasonal influenza transmission and evolution". Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610402.
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Krempel, Louis A. "Experimental temperature measurements of microelectronic computer boards using an infrared camera". Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/16390.
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PLAISANT, ANDRE LUIZ DA ROSA. "DYNAMIC SIMULATION OF HIGH VOLTAGE DIRECT CURRENT TRANSMISSION SYSTEMS IN A PERSONAL COMPUTER". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1991. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8803@1.
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CENTRO DE PESQUISA DE ENERGIA ELÉTRICAEste trabalho trata do desenvolvimento e implementação de software destinado à simulação dinâmica de sistemas de transmissão 3m corrente contínua em microcomputador digital. A formulação matemática para a solução das equações diferenciais baseia-se nas vaiáveis de estado do sistema, e o método de integração numérica utilizado é o de Eüler Modificado. O modelo dinâmico de máquina síncrona é representado em suas grandezas de fase a, b, c. O programa digital conta, ainda, com telas gráficas para a visualização de resultados.
This work is concerned with the development and implementation of a sofyware for dynamic simulation fo high voltage direct current transmission systems in a personal computer. The mathematical formulation for the solution of the diferential equations is based on the system state variables and the Modified Eüler S numerical integration method is used. The dynamic model of the synchronous machines is represented through its phase variables a, b, c. the program makes use of a compactation scheme for dealing with the sparse nature of the primitive and incidence matrices. The program also provides CTR graphic interfaces to help in the analysis of simulation results.
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Rogers, Daniel J. "Molecular dynamics simulation of the carbon nanotube - substrate thermal interface resistance". Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31765.
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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010.Committee Chair: Dr. Jianmin Qu; Committee Member: Dr. CP Wong; Committee Member: Dr. Yogendra Joshi. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Smith, Brandon. "Simulation of Heat/Mass Transfer of a Three-Layer Impingement/Effusion Cooling System". Master's thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5509.
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Cooling techniques for high density electrical components and electronic devices have been studied heavily in recent years. The advancements in the electrical/electronic industry have required methods of high heat flux removal. Many of the current electrical components and electronic devices produce a range of heat fluxes from 20 W/cm2 – 100 W/cm2. While parallel flow cooling systems have been used in the past, jet impingement is now more desirable for its potential to have a heat transfer coefficient 3-5 times greater than that of parallel flow at the same flow rate. Problems do arise when the jet impingement is confined and a cross flow develops that interacts with impinging jets downstream leading to a decrease in heat transfer coefficient. For long heated surfaces, such as an aircraft generator rotor, span wise fluid management is important in keeping the temperature distribution uniform along the length of the surface. A detailed simulation of the heat/mass transfer on a three-layer impingement/effusion cooling system has been conducted. The impingement jet fluid enters from the top layer into the bottom layer to impinge on the heated surface. The spent fluid is removed from the effusion holes and exits through the middle layer. Three different effusion configurations were used with effusion diameters ranging from 0.5 mm to 2 mm. Temperature uniformity, heat transfer coefficients, and pressure drops were compared for each effusion diameter arrangement, jet to target spacing (H/d), and rib configuration. A Shear Stress Transport (SST) turbulence fluid model was used within ANSYS CFX to simulate all design models. Three-layer configurations were also set in series for long, rectangular heated surfaces and compared against traditional cooling methods such as parallel internal flow and traditional jet impingement models. The results show that the three-layer design compared to a traditional impingement cooling scheme over an elongated heated surface can increase the average heat transfer coefficient by 75% and reduce the temperature difference on the surface by 75%. It was shown that for a three layer design under the same impingement geometry, the average heat transfer coefficient increases when H/d is small. The inclusion of ribs always provided better heat transfer and centralized the cooling areas. The heat transfer was increased by as much as 25% when ribs were used. The effusion hole arrangement showed minimal correlation to heat transfer other than a large array provides better results. The effusion holes' greatest impact was found in the pressure drop of the cooling model. The pressure losses were minimal when the effective area of effusion holes was large. This minimizes the losses due to contraction and expansion.M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Thermofluids
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Bale, Siddalingaswamy. "Simulation of data link layer of communication protocols using Ada". Virtual Press, 1989. http://liblink.bsu.edu/uhtbin/catkey/722787.
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Communication and networking are vast areas which are developing rapidly. It is very important to know in detail how the system works, how it can be enhanced to meet today's requirement, how to implement the appropriate techniques to obtain desired results etc. To explain all of the above, simulation techniques were adopted. Simulation plays an important role in developming new designs and modifying existing systems to make them more feasible and efficient.Protocols are the back bones of the communication systems and play a major role in data transfer. The review of literature provides an explanation of ISO/OSI models, layered approach and concepts of simulation. The simulation was carried out to explain the concepts of error detection, error correction and flow control in Data Link layer. Ada was used to develop the software, because of its concurrent processing tools called tasks. Also state-of-the-art utilities like Vax/Vms Screen Management System, File Definition Language, and Debugger were us ed in the program development.Department of Computer Science
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Schwentker, Robert Andrew. "Advances to a computer model used in the simulation and optimization of heat exchangers". College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2997.
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Thesis (M.S.) -- University of Maryland, College Park, 2005.Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Salazar, Santiago. "Conjugate heat transfer on a gas turbine blade". Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4546.
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Clearances between gas turbine casings and rotating blades is of quite importance on turbo machines since a significant loss of efficiency can occur if the clearances are not predicted accordingly. The radial thermal growths of the blade may be over or under predicted if poor assumptions are made on calculating the metal temperatures of the surfaces exposed to the fluid. The external surface of the blade is exposed to hot gas temperatures and it is internally cooled with air coming from the compressor. This cold air enters the radial channels at the root of the blade and then exists at the tip. To obtain close to realistic metal temperatures on the blade, the Conjugate Heat Transfer (CHT) approach would be utilized in this research. The radial thermal growth of the blade would be then compared to the initial guess. This work focuses on the interaction between the external boundary conditions obtained from the commercial Computational Fluid Dynamics software package CFX, the internal boundary conditions along the channels from a 1D flow solver proprietary to Siemens Energy, and the 3D metal temperatures and deformation of the blade predicted using the commercial Solid Mechanics software package ANSYS. An iterative technique to solve CHT problems is demonstrated and discussed. The results of this work help to highlight the importance of CHT in predicting metal temperatures and the implications it has in other aspect of the gas turbine design such as the tip clearances.ID: 029049805; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.M.S.E.)--University of Central Florida, 2010.; Includes bibliographical references (p. 44-46).
M.S.M.S.E.
Masters
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
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Ghasemi, Hamid-Reza M. R. "Computer simulation of carburization corrosion of nickel-base superalloys". Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/76035.
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A computer model for diffusion-controlled internal precipitation was used to simulate the corrosion behavior of Ni-based superalloys in carburizing atmospheres. The model is based on Crank-Nicholson finite difference solution of the diffusion equation. The code also includes the ternary cross diffusion effect due to substitutional alloying elements that are preferentially oxidized. The model can treat two sets of boundary conditions corresponding to the presence or absence of a protective oxide scale. It accounts for internal precipitation of corrosion products whenever thermodynamic solubility limits are exceeded. Up to four different carbides can be treated simultaneously. The solubility product is computed for each reaction and the amount of carbon that reacts is removed from the diffusion process. Under non-protective conditions, the predictions of model were compared to carburization profiles obtained experimentally in H₂-CH₄ environment tests. Results are presented for the formation of Cr, Mo, Ti, W, and Nb carbides in Ni-based superalloys. The predicted corrosion profiles are in qualitative agreement with experimental data.Master of Science
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Robinson, Robert Allen. "An Electroacoustic Analysis of Transmission Line Loudspeakers". Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14579.
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The concept of mounting a loudspeaker on one end of a sound-absorbing tube has existed since at least 1936. Surprisingly, a detailed mathematical analysis of the configuration has not been performed, nor has a design method been established. This configuration, known as a transmission line loudspeaker, has received little consideration in the reviewed literature. Instead, it has become frequently featured in magazines for audio hobbyists, where it is experimentally designed with rules seemingly derived from hearsay and described with terms of high praise. In this dissertation, an electro-acoustical model of a fiberglass-filled transmission line is presented. This model represents the transmission line as two separate lines -- a mechanical line that models the mechanical motion of the fiberglass and an acoustical line that models the motion of the air. The lines are linked by the flow resistance of the fiberglass. From the model, solutions for the acoustic pressure, acoustical volume velocity of the air, mechanical velocity of the fiberglass fibers, and mechanical force on the fiberglass in the line are obtained. The fiberglass is characterized and empirical formulas that describe its characteristics are found. It is shown that the modeled input impedance to the transmission line is a good fit to measured data. The performance of the system is assessed by comparing it with the performances of typical loudspeaker mountings, i.e., the infinite baffle, the closed box, and the vented box. Finally, an example is shown of how the equations derived from the model can be used to evaluate the design of a transmission line loudspeaker system.
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Padgett, James D. "Effectiveness of Additive Correction Multigrid in numerical heat transfer analysis when implemented on an Intel IPSC2". PDXScholar, 1992. https://pdxscholar.library.pdx.edu/open_access_etds/4429.
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The effectiveness of the Additive Correction Multigrid (ACM) algorithm, a line-byline Tri-diagonal Matrix Algorithm (TDMA), and simple Gauss-Seidel (GS) iteration in numerical heat transfer analysis is investigated on a conventional single processor computer and on a distributed memory parallel computer. The performance of these methods is studied by solving a two-dimensional, steady heat conduction problem. The execution time of ACM on a single processor is proportional to the number of unknowns to the 1.5 power. This is in contrast to the execution time of the TDMA for which the execution time is proportional to the number of unknowns to the 2.0 power. The GS , TDMA and ACM algorithms are adapted to a model IPSC2 Intel hypercube which has a 32 processing nodes each with 8 MBytes oflocal memory. Because GS is a local method, it has almost perfect speed up, but it also converges more slowly than TDMA, The TDMA, on the other hand, is affected by domain decomposition to a greater extent than GS. As the number of processors used to solve the problem is increased, the execution times for GS and TDMA are essentially equal. Solving the model problem with 32 processors on a 192x192 grid resulted in parallel efficiencies of 95%, 80% and 78% for the GS, TDMA, and ACM algorithms, respectively. Though the parallel efficiency of ACM was the lowest of the three, the parallel ACM algorithm required an order of magnitude less time to solve the model than either parallel GS or parallel TDMA without multigrid.
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Uzelac, Lawrence Stevan. "A Multiple Coupled Microstrip Transmission Line Model for High-Speed VLSI Interconnect Simulation". PDXScholar, 1991. https://pdxscholar.library.pdx.edu/open_access_etds/4526.
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A model is presented which incorporates the advantages of a mixed mode simulation to characterize transmission line behavior in multiple coupled Transmission line systems. The model is intended for use by digital circuit designers who wish to be able to obtain accurate transmission line behavior for complex digital systems for which continuous time simulation tools such as SPICE would time prohibitive. The model uses a transverse electromagnetic wave approximation to obtain solutions to the basic transmission line equations. A modal analysis technique is used to solve for the attenuation and propagation constants for the transmission lines. Modal analysis done in the frequency domain after a Fast Fourier Transform of the time-domain input signals. Boundary conditions are obtained from the Thevinized transmission line input equivalent circuit and the transmission line output load impedance. The model uses a unique solution queue system that allows n-line coupled transmission lines to be solved without resorting to large order matrix methods or the need to diagonals larger matrices using linear transformations. This solution queue system is based on the method of solution superposition. As a result, the CPU time required for the model is primarily a function of the number of transitions and not the number of lines modeled. Incorporation of the model into event driven circuit simulators such as Network C is discussed. It will be shown that the solution queue methods used in this model make it ideally suited for incorporation into a event-driven simulation network. The model presented in this thesis can be scaled to incorporate direct electromagnetic coupling between first, second, or third lines adjacent to the line transitioning. It is shown that modeling strictly adjacent line coupling is adequate for typical digital technologies. It is shown that the model accurately reproduces the transmission line behavior of systems modeled by previous authors. Example transitions on a 8-line system are reviewed. Finally, future model improvements are discussed.
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Zhao, Ruijie. "Analysis, simulation and optimization of ventilation of aluminum smelting cells and potrooms for waste heat recovery". Doctoral thesis, Université Laval, 2015. http://hdl.handle.net/20.500.11794/25771.
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En raison des quantités d’énergie requises par la production primaire d’aluminium et le rendement relativement faible, les rejets thermiques de cette industrie sont énormes. Ils sont par contre difficiles à utiliser à cause de leur faible température. De plus, tout changement apporté pour augmenter la température des rejets peut avoir un impact important sur la production. La compréhension du transfert thermique et de l’écoulement d’air dans une cuve peut aider à maintenir les conditions de la cuve lorsque des modifications y sont apportées. Le présent travail vise à développer cette compréhension et à apporter des solutions pour faciliter la capture des rejets thermiques. Premièrement, un circuit thermique est développé pour étudier les pertes thermiques par le dessus de la cuve. En associant des résistances thermiques aux paramètres physiques et d’opération, une analyse de sensibilité par rapport aux paramètres d’intérêt est réalisée pour déterminer les variables qui ont le plus d’influence sur la qualité thermique des rejets de chaleur dans les effluents gazeux. Il a été montré que la réduction du taux de ventilation des cuves était la solution la plus efficace. Ensuite, un modèle CFD a été développé. Un bon accord a été trouvé entre les deux modèles. Deuxièmement, une analyse systématique de la réduction de la ventilation des cuves a été réalisée par la simulation CFD. Trois problèmes qui peuvent survenir suite à une réduction du taux de ventilation sont étudiés et des modifications sont proposées et vérifiées par des simulations CFD. Le premier problème, maintenir les pertes thermiques via le dessus de la cuve, peut être résolu en exposant davantage les rondins à l’air pour augmenter les pertes radiatives. Le second problème soulevé par la réduction de ventilation concerne les conditions thermiques dans la salle des cuves et une influence limitée de la ventilation est observée par les simulations. Finalement, l’étanchéité des cuves est augmentée par une réduction des ouvertures de la cuve de manière à limiter les émissions fugitives sous des conditions de ventilation réduite. Les résultats ont révélé qu’une réduction de 50% du taux de ventilation est techniquement réalisable et que la température des effluents d’une cuve peut être augmentée de 50 à 60˚C.Due to the high energy requirement and ~50% efficiency of energy conversion in aluminum reduction technology, the waste heat is enormous but hard to be recovered. The main reason lay in its relatively low temperature. Moreover, any changes may affect other aspects of the production process, positively or negatively. A complete understanding of the heat transfer and fluid flow in aluminum smelting cells can help to achieve a good trade-off between modifications and maintenance of cell conditions. The present work aims at a systematic understanding of the heat transfer in aluminum smelting cell and to propose the most feasible way to collect the waste heat in the cell. First, a thermal circuit network is developed to study the heat loss from the top of a smelting cell. By associating the main thermal resistances with material or operating parameters, a sensitivity analysis with respect to the parameters of interest is performed to determine the variables that have the most potential to maximize the thermal quality of the waste heat in the pot exhaust gas. It is found that the reduction of pot draft condition is the most efficient solution. Then, a more detailed Computational Fluid Dynamics (CFD) model is developed. A good agreement between the two models is achieved. Second, a systematic analysis of the reduction of draft condition is performed based on CFD simulations. Three issues that may be adversely affected by the draft reduction are studied and corresponding modifications are proposed and verified in CFD simulations. The first issue, maintaining total top heat loss, is achieved by exposing more anode stubs to the air and enhancing the radiative heat transfer. The second one is to verify the influence of the draft reduction on the heat stress in potroom and limited influence is observed in the simulations. Finally, the pot tightness is enhanced by reducing pot openings in order to constrain the level of fugitive emissions under reduced pot draft condition. The results have revealed that 50% reduction in the normal draft level is technically realisable and that the temperature of pot exhaust gas can be increased by 50-60 ˚C.
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Miller, Mark W. "Heat transfer in a coupled impingement-effusion cooling system". Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4807.
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The efficiency of air-breathing gas turbine engines improves as the combustion temperature increases. Therefore, modern gas turbines operate at temperatures greater than the melting temperature of hot-gas-path components, and cooling must be introduced in order to maintain mechanical integrity of those components. Two highly effective techniques used in modern designs for this purpose are impingement cooling and use of coolant film on hot-gas-path surface introduced through discrete film or effusion holes. In this study, these two mechanisms are coupled into a single prototype cooling system. The heat transfer capability of this system is experimentally determined for a variety of different geometries and coolant flow rates. This study utilizes Temperature Sensitive Paint (TSP) in order to measure temperature distribution over a surface, which allowed for local impingement Nusselt number, film cooling effectiveness, and film cooling heat transfer enhancement profiles to be obtained. In addition to providing quantitative heat transfer data, this method allowed for qualitative investigation of the flow behavior near the test surface. Impinging jet-to-target-plate spacing was varied over a large range, including several tall impingement scenarios outside the published limits. Additionally, both in-line and staggered effusion arrangements were studied, and results for normal injection were compared to full coverage film cooling with inclined- and compound-angle injection. Effects of impingement and effusion cooling were combined to determine the overall cooling effectiveness of the system. It is shown that low impingement heights produce the highest Nusselt number, and that large jet-to-jet spacing reduces coolant flow rate while maintaining moderate to high heat transfer rates. Staggered effusion configurations exhibit superior performance to in-line configurations, as jet interference is reduced and surface area coverage is improved. Coolant to mainstream flow mass flux ratios greater than unity result in jet blow-off and reduced effectiveness. The convective heat transfer coefficient on the film cooled surface is higher than a similar surface without coolant injection due to the generation of turbulence associated with jet-cross flow interaction.ID: 030646180; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; .; Thesis (M.S.M.E.)--University of Central Florida, 2011.; Includes bibliographical references (p. 171-176).
M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Thermo-Fluids Track
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Amini, Manesh Navid. "Heat transfer in multi-layer energetic nanofilm on composites substrate". Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4587.
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Numerical model was also used to estimate three major variables for a range of 30-60 m/s. In fact, the maximum combustion flame temperature that corresponds to flame speed along with the length of the flame, density of the product behind the flame, and maximum penetration depth in steady reaction, were calculated. These studies will aid in the design of nEM multilayer thin film. As further numerical and experimental results are obtained for different nEM thicknesses, a unified model involving various parameters can be developed.; The main purpose of this work is to find a physical and numerical description related to the reaction of the multilayer nano energetic material (nEM) in dense film. Energy density of nEM is much higher than the conventional energetic material; therefore, nEM finds more applications in propulsions, thermal batteries, material synthesis, nano igniters, waste disposals, and power generations. The reaction model of a multilayer nEM in a dense film of aluminum and copper oxide deposits on a composite substrate of silica/silicon is studied and solved in different stages. The two main interests in this study are propagation speed and maximum temperature of the reaction. In order to relate speed of reaction and maximum flame temperature a number of other variables such as heat loss, the product porosity, and the reaction length should be estimated. The main aim of this study is to introduce a numerical model which estimates and relates these values in multilayer nEM in a dense film. The following is a summary of the execution steps to achieve this goal. In Part I of this thesis, flame front speed and the reaction heat loss were the main targets. The time-of-flight technique has been developed to measure the speed of flame front with an accuracy of 0.1 m/s. This measurement technique was used to measure the speed of propagation on multilayer nEM over different substrate material up to 65 m/s. A controllable environment (composite silicon\silica) was created for a multilayer standard thin film of aluminum and copper oxide to control the reaction heat loss through the substrate. A number of experimental results show that as the thickness of silica decreases, the reaction is completely quenched. Reaction is not in self-sustaining mode if the silica thickness is less than 200 nm. It is also observed that by increasing silica's thickness in substrate, the quenching effect is progressively diminished.; The speed of reaction seems to be constant at slightly more than 40 m/s for a silica layer with thickness greater than 500 nm. This would be the maximum heat penetration depth within the silica substrate, so the flame length was calculated based on the measured speed. In Part II, a numerical analysis of the thermal transport of the reacting film deposited on the substrate was combined with a hybrid approach in which a traditional two-dimensional black box theory was used, in conjunction with the sandwich model, to estimate the maximum flame temperature. The appropriate heat flux of the heat sources is responsible for the heat loss to the surroundings. A procedure to estimate this heat flux using stoichiometric calculations is based on the previous author's work. This work highlights two important findings. One, there is very little difference in the temperature profiles between a single substrate of silica and a composite substrate of silicon\silica. Secondly, by increasing the substrate thickness, the quenching effect is progressively diminished at given speed. These results also show that the average speed and quenching of flames depend on the thickness of the silica substrate and can be controlled by a careful choice of the substrate. In Part III, a numerical model was developed based on the moving heat source for multilayer thin film of aluminum and copper oxide over composite substrate of silicon\silica. The maximum combustion flame temperature corresponding to the speed of flame front is the main target of this model. Composite substrate was used as a mechanism to control the heat loss during the reaction. Thickness of the substrate, the length of flame front, and the density of the product were utilized for the standard multilayer thin film with 43 m/s flame front speed. The calculated heat penetration depth in this case was compared to the experimental result for the same flame front speed.ID: 030422800; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 140-149).
Ph.D.
Doctorate
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
34
Hardy, Matthew. "Heat Flux Modeling of Asymmetrically Heated and Cooled Thermal Stimuli". Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6654.
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Thermal sensation is one of the most dynamic stimulus-response systems in the human body. It is relied upon for safety, comfort and general equilibrium of the human body. Thermal sensation is dependent upon many variables such as area of effected skin, rate of temperature change and location of stimulation. It has been shown that certain rates of change can intensify the sensation of heating or cooling. Conversely, sufficiently low rates of change can go undetected by the skin. As such, the thermal response system can be manipulated by the proper combination of applied hot and cold stimuli. Previous research has shown that through precise application of an asymmetrically heated and cooled thermal display, a sensation of constant cooling can be perceived. This thesis seeks to (1) explore the heat flux characteristics of the thermal display through the use of computer simulations, (2) test a hypothesis about the relationship between thermal sensation and heat flux and (3) examine modifications of the thermal display patterns with the intention of producing more intense thermal sensations.
To characterize the heat flux patterns produced by the thermal display, finite element simulations, performed using commercially available software ANSYS©. Simulations are conducted on individual heating and cooling rates to examine the expected values of heat flux as temperatures approach and diverge from skin temperature. Evaluated in the cylindrical coordinate system (axial, angular and radial), the simulations showed a slight nonlinear heat flux generation at the beginning of heating and cooling, but after the initial transient period, this gave way to a strong linear generation of increasing or decreasing heat flux.
Simulations were performed that represent the physical experiments implemented in pre- vious research. These simulations were done in two parts: the first examines a small subregion with finer detail on the area between heating and cooling stimuli, the second is a larger scale examination of the heat flux profile of the thermal display. Initially it was observed that directly under the thermal stimulus, in the radial direction, the heat flux was almost perfectly in-phase with the oscillation of temperature whereas between the stimuli, it was nearly 180 degrees out of phase. The heat flux in the axial and angular directions under the thermal stimulus were negligible. Additionally, between stimuli, the values were nearly 180 degrees out of phase with temperature. Additionally, it was observed that the heat flux profiles for all patterns used in the thermal display were approximately identical.
From the data gathered by the simulations in conjunction with the thermal sensation data from previous research, a linear relationship is hypothesized that relates these two quantities. This relationship was then used to determine the theoretical thermal sensations of newly developed thermal display patterns in order to determine which are best suited for future physical experimentation.
35
Koh, Jin Hou. "Simulation modeling and analysis of device-aware network architectures". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Dec%5FKoh.pdf.
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Priedeman, Douglas Kelly. "Testing of a residential GAX absorption heat pump and chiller and verification of a computer cycle simulation /". The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487948440827071.
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Beller, Douglas K. "Alternate Computer Models of Fire Convection Phenomena for the Harvard Computer Fire Code". Digital WPI, 2000. https://digitalcommons.wpi.edu/etd-theses/892.
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"Alternate models for extended ceiling convection heat transfer and ceiling vent mass flow for use in the Harvard Computer fire Code are developed. These models differ from current subroutines in that they explicitly consider the ceiling jet resulting from the fire plume of a burning object. The Harvard Computer fire Code (CFC) was used to compare the alternate models against the models currently used in CFC at Worcester Polytechnic Institute and with other available data. The results indicate that convection heat transfer to the ceiling of the enclosure containing the fire may have been previously underestimated at times early in the fire. Also, the results of the ceiling vent model provide new insight into ceiling vent phenomena and how ceiling vents can be modeled given sufficient experimental data. this effort serves as a qualitative verification of the models as implemented; complete quantitative verification requires further experimentation. Recommendations are also included so that these alternate models may be enhanced further. "
38
Johnson, Wesley Louis. "Thermal performance of cryogenic multilayer insulation at various layer spacings". Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4681.
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Multilayer insulation (MLI) has been shown to be the best performing cryogenic insulation system at high vacuum (less than 10[super]-3 torr), and is widely used on spaceflight vehicles. Over the past 50 years, many numerous investigations of MLI have yielded a general understanding of the many variables associated with MLI. MLI has been shown to be a function of variables such as warm boundary temperature, the number of reflector layers, and the spacer material in between reflectors, the interstitial gas pressure and the interstitial gas. Because conduction between reflectors increases with the thickness of the spacer material, and yet the radiation heat transfer is inversely proportional to the number of layers, it stands to reason that the thermal performance of MLI is a function of the number of layers per thickness, or layer density. Empirical equations that were derived based on some of the early tests showed that the conduction term was proportional to the layer density to a poweID: 029050581; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.A.E.)--University of Central Florida, 2010.; Includes bibliographical references (p. 79-85).
M.S.A.E.
Masters
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Aerospace Engineering
39
French, Ian Dept of Computer Science Australian Defence Force Academy UNSW. "Visualisation techniques for the computer simulation of bushfires in two dimensions". Awarded by:University of New South Wales - Australian Defence Force Academy. Dept. of Computer Science, 1992. http://handle.unsw.edu.au/1959.4/38721.
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This thesis examines techniques that provide a method of computer visualisation of bushfire spread. Existing techniques studied include, Kourtz & O???Regan, Green???s Contact, Heat Accumulation, Percolation modelling and Huygens??? Principle by Anderson et.al., French, Roberts, Richards. Many of these techniques are extended as part of a comprehensive study into how they perform in a two dimensional reference frame (ie over flat terrain only). New techniques are defined for Percolation Modelling and Huygens??? Principle. Each technique is examined in a series of test cases which include computer simulations with no wind, constant wind, variable wind, variable vegetation (including patchy fuel and two fuels) and where fuel burns out. These test cases provide: (a) an incremental approach to understanding the operation of each technique; (b) a basis for comparison; and (c) verification of correctness of the technique in two dimensions. Several of the techniques are shown, by these test cases, to be equivalent. For instance, the Kourtz & O???Regan technique using a square template is equivalent to the Contact Technique, Site percolation is similar to the Heat Accumulation technique and Template percolation is similar to the Contact Technique. Overall the Huygens??? Principle techniques provide the most accurate simulations of bushfire spread.
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Assanis, Dennis N. "A computer simulation of the turbocharged turocompounded diesel engine system for studies of low heat rejection engine performance". Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/15089.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.
Bibliography: leaves 135-140.
by Dionissios Nikolaou Assanis.
Ph.D.
41
Shojae, Ghias Masoumeh. "Numerical simulations of coupled groundwater flow and heat transport incorporating freeze/thaw cycles and phase change in a continuous permafrost environment". Doctoral thesis, Université Laval, 2017. http://hdl.handle.net/20.500.11794/27693.
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Dans les régions nordiques, l’une des conséquences du réchauffement climatique est le dégel du pergélisol. En plus de favoriser la libération de quantités importantes de méthane et de dioxyde de carbone dans l’atmosphère, le dégel du pergélisol entraînera une modification des conditions hydrologiques locales et régionales, affectant ainsi les écosystèmes. Ce dégel pourra aussi conduire à un affaissement des sols et endommager ainsi les infrastructures routières. Dans le cadre de cette étude, des simulations numériques couplant l’écoulement des eaux souterraines et le transport de chaleur ont été réalisées dans le but de mieux appréhender les interactions entre l’écoulement des eaux souterraines et la dynamique thermique relative au dégel du pergélisol sur les pistes de l’Aéroport d’Iqaluit, Nunavut, Canada. Un modèle conceptuel du site est d’abord développé et le modèle numérique bidimensionnel correspondant est calé à partir des températures observées du sol. Les impacts futurs du réchauffement climatique sur le régime thermique et le système d’écoulement, aussi que le tassement dû au dégel, sont ensuite simulés sur la base des scénarios climatiques proposés par le Groupe Intergouvernemental sur l’Évolution du Climat (GIEC). Dans le cadre d’un réchauffement climatique, la couverture neigeuse de surface est identifiée comme le facteur principal affectant la dégradation du pergélisol, y compris par son rôle dans l’accroissement de la sensibilité de la dégradation du pergélisol aux changements de divers facteurs hydrogéologiques. Dans ce cas, le transfert de chaleur par advection joue un rôle relativement mineur, quoique non négligeable, vis-à-vis du transfert de chaleur par conduction, du fait de l’extension importante d’un sol de faible perméabilité à proximité de la surface. Le transfert de chaleur par convection, qui est fortement influencé par la couche de neige superficielle, contrôle la libération de l’eau non gelée et la profondeur de la couche active aussi bien que l’amplitude du tassement et du soulèvement par le dégel. L'effet de la zone non saturée sur le dégel du pergélisol est plus important dans les sols fins, recouverts de neige en surface. De plus, l’ampleur du tassement dû au dégel augmente considérablement en présence d’une couverture neigeuse. Enfin, les simulations ont montré que, le long de routes, les zones les plus vulnérables au tassement sont les accotements recouverts de neige ainsi que les zones de transition adjacentes au bloc de pergélisol. Les simulations numériques ont également montré l’importance d’utiliser les fonctions de gel appropriées pour les types de sols impliqués. En effet, la position du front de gel (couche active) varie en fonction des caractéristiques du sol. Les résultats des simulations ont également mis en évidence les effets d'une distribution stochastique de la conductivité hydraulique sur l’advection thermique. Les taux de dégel du pergélisol sont relativement plus élevés dans des zones de haute perméabilité, trouvées dans la structure du sol d'un système hétérogène, que dans le cas d’un sol homogène. Paradoxalement, les résultats ont montré que dans les zones de décharge, le transport de chaleur par advection a pour conséquence d'augmenter le plafond du pergélisol. En effet, l'eau froide s'écoulant dans ce secteur annule le gain de chaleur résultant du processus de conduction.At high northern latitudes, climate warming will induce permafrost degradation that will modify local and regional hydrogeological systems and ecosystem functionality, as well as increase the release of carbon and methane to the environment. Northern infrastructure, in particular roads and embankments, will also experience significant degradation. In this study, numerical simulations of coupled groundwater flow and heat transport have been developed to assess the effects of realistic combinations of hydrogeological parameters and surface conditions on the temporal and spatial evolution of permafrost degradation in a cold-region paved terrain, at the Iqaluit airport, Nunavut. A conceptual model is first developed for the site and a corresponding 2D numerical model is calibrated to the observed groundwater flow and thermal regime. Future climate warming impacts on the thermal regime and flow system, as well as thaw settlements are then simulated based on climate scenarios proposed by the IPCC (Intergovernmental Panel on Climate Change). Under climate warming, the surface snow cover is identified as the leading factor affecting permafrost degradation, and significantly contributes to positive feedback between the hydrogeological flow system and the frozen ground. In this case, advective heat transport plays a relatively minor, but non-negligible role compared to conductive heat transport, due to the significant extent of low-permeability soil close to surface. Conductive heat transport, which is strongly affected by the surface snow layer, controls the release of unfrozen water and the depth of the active layer as well as the magnitude of thaw settlement and frost heave. The effect of the unsaturated zone on permafrost thaw was most important in finer soil where overlain by snow. The magnitude of thaw settlement also significantly increases with a snow cover. The most vulnerable areas to permafrost thaw settlement along a road or taxiway embankment would be the snow-covered shoulders, as well as the transition zones at the adjacent margins of the permafrost block. The simulation results also showed the importance of selecting the appropriate freezing function based on the type of soil, when frequent freezing and thawing cycles occur in a permafrost setting. The thaw front simulated with a smooth (low slope) freezing function, was deeper compared to that for a steeper freezing function. The simulation results also highlighted the contributing effects of a stochastic hydraulic conductivity distribution on thermal advection. Permafrost thaw rates in high permeability zones, found in the soil structure of a heterogeneous system, are larger than rates for a homogeneous soil. Advective heat transport can paradoxically also increase the permafrost table in downgradient areas where the flowing cold water negates heat gain from conduction alone.
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Taskin, Ertan M. "CFD simulation of transport and reaction in cylindrical catalyst particles". Link to electronic thesis, 2007. http://www.wpi.edu/Pubs/ETD/Available/etd-081507-135028/.
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Tansakul, Ampawan. "A 3-Dimensional Computer Simulation Model for Temperature Distribution Prediction in a Seafood Shipping Container". Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-06062008-144840/.
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Osborne, William F. "Influence of Heater Orientation on Fluctuations in Steady-state Nucleate Boiling". PDXScholar, 1995. https://pdxscholar.library.pdx.edu/open_access_etds/4958.
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In observations of steady-state nucleate boiling, fluctuations in the temperature and heat flux might initially appear to be completely random. However, it was shown that, for a vertically mounted platinum wire in liquid nitrogen, the fluctuations about the steady-state exhibit an average counterclockwise circulation when the heat flux is plotted versus the superheat temperature. An area associated with the average circulation was proposed as a numerical measure of stability for steady-state nucleate boiling. The mechanisms for the generation of these fluctuations are thought to be the feedback of the bubbles rising past the wire and the differential heating and cooling that this engenders. Data similar to the data on the vertical wire have been obtained using the same wire mounted horizontally. Although the counterclockwise circulation mentioned above is still seen, the measure of stability as proposed earlier, is less useful for prediction of the transition to film boiling. This reduced sensitivity can be attributed to the fact that the possibility of feedback through the rising bubbles has been eliminated.
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Vazquez, Diane Marie. "Experimental studies of the heat transfer characteristics of silica nanoparticle water-based dispersion in pool boiling using nichrome flat ribbons and wires". Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4575.
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This work deals with a study of enhanced critical heat flux (CHF) and burnout heat flux (BHF) in pool boiling of water with suspended silica nanoparticles using ribbon-type and wire heaters. Previously our group and other researchers have reported three-digit percentage increase in critical heat flux in silica nanofluids. This study investigates the effect of various heater surface dimensions and cross-sectional shapes on pool boiling heat transfer characteristics of water and water-based nanofluids. CHF and BHF were analyzed for circular and rectangular cross-section nichrome wires and ribbons of increasing sizes in the range of 0.32mm to 2.38mm width, approaching a flat-plate scenario. Experimental trends showed that the CHF and BHF in water pool boiling decrease as heater surface area increases, and for similar surface area, the wire had a 25% higher CHF than that of the ribbon. For concentrations from 0.1vol% to 2vol%, various properties such as viscosity, pH, and surface tension as well as silica deposition on surface and glowing length of ribbon were measured in order to study the possible factors in the heat transfer behavior of nanofluids. The deposition of the particles on the wire allows high heat transfer through inter-agglomerate pores, resulting in a nearly 3-fold increase in burnout heat flux at very low concentrations. Results have shown a maximum of up to 340% CHF enhancement for ribbon-type heaters, and the relationship of CHF with respect to nanoparticle concentration has been found to be non-monotonic with a peak around 0.2vol% to 0.4vol%. Visualization of boiling experiments aided with determination of relative bubble sizes, nucleation, and flow regimes. The surface morphology of the heater was investigated using SEM and EDS analyses, and it was inferred that the 2vol% concentration deposition coating had higher porosity and rate of deposition compared with 0.2vol% case.ID: 028916806; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.M.E.)--University of Central Florida, 2010.; Includes bibliographical references (p. 79-83).
M.S.M.E.
Masters
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering
46
Wirnsberger, Peter. "Computer simulation and theoretical prediction of thermally induced polarisation". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/282988.
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In this thesis, we study the phenomenon of thermally induced polarisation using a combination of theory and computer simulation. Molecules of sufficiently low symmetry exhibit thermo-molecular orientation when subjected to a temperature gradient, leading to considerable electrostatic fields in polar liquids. Here, we first use non-equilibrium molecular dynamics simulations to study this interesting effect numerically. To this end, we propose an integration algorithm to impose a constant heat flux in simulations and show that it greatly improves energy conservation compared to a previous algorithm. We next investigate the thermal polarisation of water and find that truncation of electrostatic interactions can lead to severe artefacts, such as the wrong sign of polarisation and an overestimation of the electric field. We further show that the quadrupole-moment contribution to the electric field is significant and responsible for an inversion of its sign. To facilitate the theoretical description of electrostatic interactions, we propose a new dipolar model fluid as a perturbation of a Stockmayer fluid. Using this modified Stockmayer model, we provide numerical evidence for the recently proposed phenomenon of thermally induced monopoles. We show that the electrostatic field generated by a pair of heated/cooled colloidal particles immersed in such a solvent can be trivially described by two Coulomb charges. Finally, we propose a mean-field theory to predict the thermo-polarisation effect exhibited by our model fluid theoretically, and demonstrate near quantitative agreement with simulation results.
47
Lee, Chun-kwong y 李振光. "Computer modelling and simulation of geothermal heat pump and ground-coupled liquid desiccant air conditioning systems in sub-tropicalregions". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B41290768.
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Chen, Cuiren 1962. "Application of computer simulation and artificial intelligence technologies for modeling and optimization of food thermal processing". Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37877.
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The major objective of this project was to evaluate the feasibility of artificial neural networks (ANNs) and genetic algorithms (GAs) for modeling and optimization of food thermal processing. The specific objectives were: (1) to develop a comprehensive computer simulation program for thermal processing, (2) to apply ANNs and GAs for modeling and optimization of constant retort temperature (CRT) thermal processing and variable retort temperature (VRT) thermal processing, (3) to develop dynamic models for thermal processing using ANNs, and (4) to explore ANN-model-based analysis of critical control points for deviant thermal processes.As a preliminary research, neural network models were successfully developed for modeling of residence time distribution (RTD) under aseptic processing conditions. The main configuration parameters of neural networks such as the number of hidden layers and their neurons, learning runs, choice of transfer functions and learning rules were optimized.
In order to provide experimental data needed for developing and testing of ANN models and GA optimization, a comprehensive finite difference computer simulation program for thermal processing was first developed in MS Visual Basic language, which could be used for simulating different thermal processes such as constant retort temperature (CRT) and variable retort temperature (VRT) thermal processing.
The second objective was focused on developing modeling and optimization methods for CRT thermal processing using ANNs and GAs. The ANN models were developed for predicting process time, average quality retention, surface cook value, final temperature difference, lethality ratio, and equivalent energy consumption. Using this optimization program, the effects of process variables on the optimal retort temperature and the maximum average quality retention were investigated.
The final part of the thesis research was focused on applying ANN methods for the analysis of critical control points (CCPs) for deviant thermal processes, one of the important steps required for developing hazard analysis of critical control points (HACCP) program. The results indicated that ANN models could be efficiently used for the analysis of CCPs of thermal processing. Such a concept can be expanded for developing an ANN based HACCP expert system for thermal processing. (Abstract shortened by UMI.)
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Lützow, Joel y Cecilia Mikiver. "Simulation of airborne transmission of infection in a confined space using an agent-based model". Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-280336.
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As the world observes a new pandemic with COVID-19, it is clear that pathogens can spread rapidly and without recognition of borders. Outbreaks will continue to occur, and so the diseases’ transmission method must be thoroughly understood in order to minimize their impact. Some infections, such as influenza, tuberculosis and measles are known to be spread through droplets in the air. In a confined space the concentration can grow as more droplets are released. This study examined a simulated confined space modelled as a hospital waiting area, where people who could have underlying conditions congregate and mix with potentially infectious individuals. It further investigated the impact of the volume of the waiting area, the number of people in the room, the placement of them as well as their weight. The simulation is an agent-based model (ABM), a computational model with the purpose of analysing a system through the actions and cumulative consequences of autonomous agents. The presented ABM features embodied agents with differing body weights that can move, breathe and cough in a ventilated room. An investigation into current epidemiological models lead to the hypothesis that one may be implemented as a corresponding ABM, where it could possibly also be improved upon. In this paper, it is shown that all parameters of the Gammaitoni and Nucci model can be taken into account in an ABM via the MASON library. In addition, proof is produced to suggest that some flaws of the epidemiological model can be mended in the ABM. It is demonstrated that the constructed model can account for proximity between susceptible people and infectors, an expressed limitation of the original model.När världen observerar en ny pandemi, COVID-19, är det tydligt att patogener kan spridas fort och utan hänsyn till landsgränser. Utbrott kommer att fortsätta ske och därför måste sjukdomarnas överföringsmetod förstås, så att deras påverkan kan minimeras. Det är känt att vissa infektioner, såsom influensa, tuberkulos och mässling kan spridas via droppkärnor i luften. I ett begränsat utrymme kan koncentrationen växa när fler droppar tillförs. Denna studie utvärderar ett simulerat begränsat utrymme modellerat som ett väntrum på ett sjukhus, där människor som kan ha underliggande sjukdomar samlas och beblandar sig med potentiellt smittsamma individer. Inverkan av volymen av väntrummet, antalet personer i rummet, var de var placerade i rummet samt deras vikt undersöktes också. Simuleringen är en agent-baserad modell (ABM), en beräkningsmodell med syftet att analysera ett system genom handlingarna och kumulativa konsekvenserna av självstyrande agenter. Personer med olika kroppsvikt som kan röra sig, andas och hosta i ett ventilerat rum simuleras i denna ABM. Efterforskning av aktuella epidemiologiska modeller leder till hypotesen att en sådan skulle kunna implementeras som en motsvarande ABM, där den möjligtvis också kan förbättras. I denna rapport kommer det att uppvisas att alla parametrar av Gammaitonioch Nucci-modellen kan tas hänsyn till i en ABM via MASON biblioteket. Därtill produceras bevis som pekar på att vissa brister i den epidemiologiska modellen kan hämmas i denna ABM. Det demonstreras att den konstruerade modellen kan beakta distansen mellan mottagliga personer och smittsamma, vilket är en känd begränsning i originalmodellen.
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Lee, Chun-kwong. "Computer modelling and simulation of geothermal heat pump and ground-coupled liquid desiccant air conditioning systems in sub-tropical regions". Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B41290768.
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