This study presents the numerical analysis of steady laminar flow heat transfer in a horizontal rectangular duct with differential heating on the vertical walls. Three heating configurations: one uniform wall temperature (CS1) and two linearly varying wall temperature cases (CS2 and CS3) are analysed. The study considers the combined effects of natural convection, forced convection and radiation heat transfer on the overall heat transfer characteristics. Air, which is assumed to be a non-participating medium, is chosen as the working fluid. A computational fluid dynamics solver is used to solve a set of governing equations for a range of parameters.For chosen duct aspect ratios, the numerical model simulates the flow and heat transfer for two main effects: buoyancy and radiation heat transfer. Buoyancy effect is represented by Grashof number, which is varied from 2,000 to 1,000,000. The effect of radiation heat transfer is examined by choosing different wall surface emissivity values. The weak and strong radiation effect is represented by the emissivity values of 0.05 and 0.85 respectively. Three duct aspect ratios are considered - 0.5, 1 and 2. The heat transfer characteristics of all the above heating configurations - CS1, CS2, and CS3 are analysed and compared. The numerical results show that, for all heating configurations and duct aspect ratios, the overall heat transfer rate is enhanced when the buoyancy effect increases. Since buoyancy effect induces natural circulation, this circulation is therefore the main mechanism that enhances heat transfer. Radiation heat transfer is found to significantly influence convection heat transfer in high Grashof numbers.

An experimental activity was performed to observe and study the effects of graphite dispersion and deposition on thermal hydraulic phenomena in a Reactor Cavity Cooling System (RCCS). The small scale RCCS experimental facility (16.5cm x 16.5cm x 30.4cm) used for this activity represents half of the reactor cavity with an electrically heated vessel. Water flowing through five vertical pipes removes the heat produced in the vessel and releases it in the environment by mixing with cold water in a large tank. PIV technique was used to study the velocity field of the air inside the cavity. A set of 52 thermocouples was installed in the facility to monitor the temperature profiles of the vessel and pipes walls and air. 10g of a fine graphite powder (particle size average 2 [mu]m) were injected into the cavity through a spraying nozzle placed at the bottom of the vessel. Temperatures and air velocity field were recorded and compared with the measurements obtained before the graphite dispersion, showing a decrease of the temperature surfaces which was related to an increase in their emissivity. The results contribute to the understanding of the RCCS capability in case of an accident scenario.

Heat insulation is the process of blocking the transfer of thermal energy between objects at different temperatures. Heat transfer occurs due to conduction, convection, or radiation, as well as any combination of these three mechanisms. Fibrous insulations can completely suppress the convective mode of heat transfer for most applications, and also help to reduce the conductive and radiative modes to some extent. In this study, an attempt has been made to computationally predict the effects of microstructural parameters (e.g., fiber diameter, fiber orientation and porosity) on the insulation performance of fibrous materials. The flexible simulation method developed in this work can potentially be used to custom-design optimal multi-component fibrous insulation media for different applications. With regards to modeling conductive heat transfer, a computationally-feasible simulation method is developed that allows one to predict the effects of each microstructural parameter on the transfer of heat across a fibrous insulation. This was achieved by combining analytical calculations for conduction through interstitial fluid (e.g., air) with numerical simulations for conduction through fibrous structures. With regards to modeling radiative heat transfer, both Monte Carlo Ray Tracing and Electromagnetic Wave Theory were implemented for our simulations. The modeling methods developed in this work are flexible to allow simulating the performance of media made up of different combinations of fibers with different materials or dimensions at different operating temperatures. For example, our simulations demonstrate that fiber diameter plays an important role in blocking radiation heat transfer. In particular, it was shown that there exists an optimum fiber diameter for which maximum insulation against radiative transfer is achieved. The optimum fiber diameter is different for fibers made of different materials and also depends on the mean temperature of the media. The contributions of conduction and radiation heat transfer predicted using the above techniques are combined to define a total thermal resistance value for media with different microstructures. Such a capability can be of great interest for design and optimization of the overall performance of fibrous media for different applications.

In the electronics the quality, reliability, operational speed, device density and cost of circuits are fundamentally determined by carriers. If it is necessary to use better material than plastic carrier, it has to be made of ceramics or glass-ceramics. This study dealt with the ceramic based carrier production system. The types of the raw ceramics fired at low temperature (below 1000&deg / C) are called Low Temperature Co-Fired Ceramics (LTCC). In this study, a comprehensive thermal model is described for the high temperature oven which belongs to a Low Temperature Co-fired Ceramic (LTCC) substance production line. The model includes detailed energy balances with conduction, convection and radiation heat transfer mechanisms, view factor derivations for the radiative terms, thermocouple balances, heating filaments and cooling mechanisms for the system. Research was conducted mainly on process development and production conditions along with the system modeling of oven. Temperature control was made in high temperature co-firing oven. Radiation View Factors for substrate and thermocouples are determined. View factors between substrate and top-bottom-sides of the oven are calculated, and then inserted into the energy balances. The same arrangement was made for 3 thermocouples at the bottom of the oven. Combination of both expressions gave the final model. Modeling studies were held with energy balance simulations on MATLAB. Data analysis and DOE study were held with JMP Software.

A negative index material (NIM), which possesses simultaneously negative permittivity and permeability, is an emerging material that has caught many researchers attention after it was first demonstrated in 2001. It has been shown that electromagnetic waves propagating in NIMs have some remarkable properties such as negative phase velocities and negative refraction and hold enormous promise for applications in imaging and optical communications. This dissertation is centered on investigating the unique aspects of the radiative properties of NIMs. Photon tunneling, which relies on evanescent waves to transfer radiative energy, has important applications in thin-film structures, microscale thermophotovoltaic devices, and scanning thermal microscopes. With multilayer thin-film structures, photon tunneling is shown to be greatly enhanced using NIM layers. The enhancement is attributed to the excitation of surface or bulk polaritons, and depends on the thicknesses of the NIM layers according to the phase matching condition. A new coherent thermal emission source is proposed by pairing a negative permittivity (but positive permeability) layer with a negative permeability (but positive permittivity) layer. The merits of such a coherent thermal emission source are that coherent thermal emission occurs for both s- and p-polarizations, without use of grating structures. Zero power reflectance from an NIM for both polarizations indicates the existence of the Brewster angles for both polarizations under certain conditions. The criteria for the Brewster angle are determined analytically and presented in a regime map. The findings on the unique radiative properties of NIMs may help develop advanced energy conversion devices. Motivated by the recent advancement in scanning probe microscopy, the last part of this dissertation focuses on prediction of the radiation heat transfer between two closely spaced semi-infinite media. The objective is to investigate the dopant concentration of silicon on the near-field radiation heat transfer. It is found that the radiative energy flux can be significantly augmented by using heavily doped silicon for the two media separated at nanometric distances. Large enhancement of radiation heat transfer at the nanoscale may have an impact on the development of near-field thermal probing and nanomanufacturing techniques.

The development and advancement of microelectronics technology have been dramatically. The time and cost, for research and optimization of process and equipment, can be saved by using flow simulation. The governing equations of flow field, inside chemical vapor deposition (CVD) reactor, are constructed, dispersed, and solved by grid mesh and numerical method. At present, rapid thermal process (RTP) is becoming more important and popular for thin-film depositing technology. In this thesis, vertical type single wafer RTCVD reactor in poly-silicon thin-film depositing process is analyzed by numerical method. Several operating process parameters, such as: (a) the gap between shower head and wafer surface, (b) gas inlet velocity in shower head, and (c) operating pressure inside chamber of reactor, are considered for discussion and analysis of steady or unsteady phenomenon in three steps of thin-film depositing process, including (¢¹) heating for wafer, (¢º) deposition in steady state, (¢») cooling after deposition etc.. As shown in the results, each operating parameters performs different relations and phenomenon in these steady and unsteady steps: Operating pressure can affect the activity of chemical reaction strongly in unsteady or steady region. Larger gap between wafer and shower head causes less influence by flow effects or buoyancy. And also, radiation heat transfer, which is adopted by RTCVD process, can decrease the influence of some parameters on flow field.

Em processos de combustão, uma determinação precisa dos parâmetros envolvendo transferência de calor influencia diretamente os demais fenômenos envolvidos. Dentre os mecanismos de transferência de calor presentes na combustão a radiação térmica é predominante, mas sua correta determinação impõe uma elevada complexidade, principalmente quando se trata da solução de meios participantes. O cálculo envolve propriedades de absorção que variam com a temperatura e o comprimento de onda, sendo então necessária a utilização de modelos espectrais para obter bons resultados com um baixo tempo computacional. Para o cálculo da transferência radiante, existem diversos modelos espectrais, desde modelos de simples implementação, como, por exemplo, o GG (gás cinza) e o WSGG (soma-ponderada-dos-gases-cinza), até modelos com um grau elevado de detalhamento, como o SLW (soma-ponderada-dos-gases-cinza baseado em linhas espectrais) e o CW (número de onda cumulativa). Como os modelos com maior grau de detalhamento são de complexa implementação, alguns autores preferem empregar modelos simplistas, como o GG (gás cinza), apenas por questões de conveniência, mesmo em detrimento da qualidade dos resultados. Uma forma de executar o cálculo da radiação térmica sem simplificações é levar em conta as absorções em cada comprimento de onda, sendo esses cálculos denominados integração linha-por-linha (LBL), por executar o cálculo da transferência radiante em cada linha de absorção, o que gera resultados benchmark, podendo ser utilizados para avaliar os diversos modelos existentes. Este trabalho tem por objetivo verificar e sintetizar a aplicação dos modelos espectrais, em configurações envolvendo concentração e temperatura não uniformes, onde são realizados cálculos em um meio contendo CO2, H2O e fuligem. São avaliados os modelos GG, WSGG, SLW e CW. Dentre os modelos avaliados, o que apresenta os melhores resultados para as condições apresentadas é o modelo WSGG. De forma a aprimorar o modelo WSGG, uma nova implementação para a solução de misturas é apresentada, a qual apresenta correlações para o H2O e para o CO2 geradas individualmente, possibilitando misturas com qualquer razão de concentração, mostrando que o modelo apresenta bons resultados em diversas situações e é uma boa opção para a solução de problemas de combustão. / In combustion processes a good determination of the heat transfer parameters are of great importance because of its direct influence in the computation of the chemical reactions rate in the process and, consequently, in the formation of the combustion products. Among the processes of heat transfer in combustion, thermal radiation is predominant, and their determination can be a very complex task, especially with participating medium. The analysis involves absorption properties that vary with the temperature and wavelength, and therefore it is necessary to use spectral models to ensure good results with low computational time. There are several spectral models developed along the years, since the simplistic models such as the GG (gray gas) and WSGG (weighted-sum-of-gray-gases), to more advanced methods such as the SLW (spectral line weighted-sum-of-gray-gases) and CW (cumulative wavenumber). Due advanced models are in general a hard task to implement, the option is to use simplified models, for example the GG, even working with considerably errors. In order to quantify these solutions, for temperature and concentration conditions of the absorbing species, it is necessary to implement the radiation heat transfer taking into account the absorption at each wavelength through line-by-line (LBL) integration, being this solution the exact one, or, the benchmark solution, which it is used to evaluate the spectral models. In this study, the LBL integration is carried out to evaluate some of the existing models in a non-isothermal and inhomogeneous medium containing CO2, H2O and soot. The work involves the GG, WSGG, SLW and CW spectral models. For the presented cases, the best results occur with WSGG model. In order to improve the WSGG model a new implementation for the mixture solution is presented, which solves the correlations for H2O and CO2 generated individually, enabling mixtures containing any concentration ratio, showing the good agreement of the spectral model at any condition, being the WSGG a good option to solve combustion problems.

Em processos de combustão, uma determinação precisa dos parâmetros envolvendo transferência de calor influencia diretamente os demais fenômenos envolvidos. Dentre os mecanismos de transferência de calor presentes na combustão a radiação térmica é predominante, mas sua correta determinação impõe uma elevada complexidade, principalmente quando se trata da solução de meios participantes. O cálculo envolve propriedades de absorção que variam com a temperatura e o comprimento de onda, sendo então necessária a utilização de modelos espectrais para obter bons resultados com um baixo tempo computacional. Para o cálculo da transferência radiante, existem diversos modelos espectrais, desde modelos de simples implementação, como, por exemplo, o GG (gás cinza) e o WSGG (soma-ponderada-dos-gases-cinza), até modelos com um grau elevado de detalhamento, como o SLW (soma-ponderada-dos-gases-cinza baseado em linhas espectrais) e o CW (número de onda cumulativa). Como os modelos com maior grau de detalhamento são de complexa implementação, alguns autores preferem empregar modelos simplistas, como o GG (gás cinza), apenas por questões de conveniência, mesmo em detrimento da qualidade dos resultados. Uma forma de executar o cálculo da radiação térmica sem simplificações é levar em conta as absorções em cada comprimento de onda, sendo esses cálculos denominados integração linha-por-linha (LBL), por executar o cálculo da transferência radiante em cada linha de absorção, o que gera resultados benchmark, podendo ser utilizados para avaliar os diversos modelos existentes. Este trabalho tem por objetivo verificar e sintetizar a aplicação dos modelos espectrais, em configurações envolvendo concentração e temperatura não uniformes, onde são realizados cálculos em um meio contendo CO2, H2O e fuligem. São avaliados os modelos GG, WSGG, SLW e CW. Dentre os modelos avaliados, o que apresenta os melhores resultados para as condições apresentadas é o modelo WSGG. De forma a aprimorar o modelo WSGG, uma nova implementação para a solução de misturas é apresentada, a qual apresenta correlações para o H2O e para o CO2 geradas individualmente, possibilitando misturas com qualquer razão de concentração, mostrando que o modelo apresenta bons resultados em diversas situações e é uma boa opção para a solução de problemas de combustão. / In combustion processes a good determination of the heat transfer parameters are of great importance because of its direct influence in the computation of the chemical reactions rate in the process and, consequently, in the formation of the combustion products. Among the processes of heat transfer in combustion, thermal radiation is predominant, and their determination can be a very complex task, especially with participating medium. The analysis involves absorption properties that vary with the temperature and wavelength, and therefore it is necessary to use spectral models to ensure good results with low computational time. There are several spectral models developed along the years, since the simplistic models such as the GG (gray gas) and WSGG (weighted-sum-of-gray-gases), to more advanced methods such as the SLW (spectral line weighted-sum-of-gray-gases) and CW (cumulative wavenumber). Due advanced models are in general a hard task to implement, the option is to use simplified models, for example the GG, even working with considerably errors. In order to quantify these solutions, for temperature and concentration conditions of the absorbing species, it is necessary to implement the radiation heat transfer taking into account the absorption at each wavelength through line-by-line (LBL) integration, being this solution the exact one, or, the benchmark solution, which it is used to evaluate the spectral models. In this study, the LBL integration is carried out to evaluate some of the existing models in a non-isothermal and inhomogeneous medium containing CO2, H2O and soot. The work involves the GG, WSGG, SLW and CW spectral models. For the presented cases, the best results occur with WSGG model. In order to improve the WSGG model a new implementation for the mixture solution is presented, which solves the correlations for H2O and CO2 generated individually, enabling mixtures containing any concentration ratio, showing the good agreement of the spectral model at any condition, being the WSGG a good option to solve combustion problems.

Em processos de combustão, uma determinação precisa dos parâmetros envolvendo transferência de calor influencia diretamente os demais fenômenos envolvidos. Dentre os mecanismos de transferência de calor presentes na combustão a radiação térmica é predominante, mas sua correta determinação impõe uma elevada complexidade, principalmente quando se trata da solução de meios participantes. O cálculo envolve propriedades de absorção que variam com a temperatura e o comprimento de onda, sendo então necessária a utilização de modelos espectrais para obter bons resultados com um baixo tempo computacional. Para o cálculo da transferência radiante, existem diversos modelos espectrais, desde modelos de simples implementação, como, por exemplo, o GG (gás cinza) e o WSGG (soma-ponderada-dos-gases-cinza), até modelos com um grau elevado de detalhamento, como o SLW (soma-ponderada-dos-gases-cinza baseado em linhas espectrais) e o CW (número de onda cumulativa). Como os modelos com maior grau de detalhamento são de complexa implementação, alguns autores preferem empregar modelos simplistas, como o GG (gás cinza), apenas por questões de conveniência, mesmo em detrimento da qualidade dos resultados. Uma forma de executar o cálculo da radiação térmica sem simplificações é levar em conta as absorções em cada comprimento de onda, sendo esses cálculos denominados integração linha-por-linha (LBL), por executar o cálculo da transferência radiante em cada linha de absorção, o que gera resultados benchmark, podendo ser utilizados para avaliar os diversos modelos existentes. Este trabalho tem por objetivo verificar e sintetizar a aplicação dos modelos espectrais, em configurações envolvendo concentração e temperatura não uniformes, onde são realizados cálculos em um meio contendo CO2, H2O e fuligem. São avaliados os modelos GG, WSGG, SLW e CW. Dentre os modelos avaliados, o que apresenta os melhores resultados para as condições apresentadas é o modelo WSGG. De forma a aprimorar o modelo WSGG, uma nova implementação para a solução de misturas é apresentada, a qual apresenta correlações para o H2O e para o CO2 geradas individualmente, possibilitando misturas com qualquer razão de concentração, mostrando que o modelo apresenta bons resultados em diversas situações e é uma boa opção para a solução de problemas de combustão. / In combustion processes a good determination of the heat transfer parameters are of great importance because of its direct influence in the computation of the chemical reactions rate in the process and, consequently, in the formation of the combustion products. Among the processes of heat transfer in combustion, thermal radiation is predominant, and their determination can be a very complex task, especially with participating medium. The analysis involves absorption properties that vary with the temperature and wavelength, and therefore it is necessary to use spectral models to ensure good results with low computational time. There are several spectral models developed along the years, since the simplistic models such as the GG (gray gas) and WSGG (weighted-sum-of-gray-gases), to more advanced methods such as the SLW (spectral line weighted-sum-of-gray-gases) and CW (cumulative wavenumber). Due advanced models are in general a hard task to implement, the option is to use simplified models, for example the GG, even working with considerably errors. In order to quantify these solutions, for temperature and concentration conditions of the absorbing species, it is necessary to implement the radiation heat transfer taking into account the absorption at each wavelength through line-by-line (LBL) integration, being this solution the exact one, or, the benchmark solution, which it is used to evaluate the spectral models. In this study, the LBL integration is carried out to evaluate some of the existing models in a non-isothermal and inhomogeneous medium containing CO2, H2O and soot. The work involves the GG, WSGG, SLW and CW spectral models. For the presented cases, the best results occur with WSGG model. In order to improve the WSGG model a new implementation for the mixture solution is presented, which solves the correlations for H2O and CO2 generated individually, enabling mixtures containing any concentration ratio, showing the good agreement of the spectral model at any condition, being the WSGG a good option to solve combustion problems.

Computational time to model radiative heat transfer in a cylindrical Pressurized Oxy-Coal (POC) combustor was reduced by incorporating the multi-dimensional characteristics of the combustion field. The Discrete Transfer Method (DTM) and the Discrete Ordinates Method (DOM) were modified to work with a computational mesh that transitions from 3D cells to axisymmetric and then 1D cells, also known as a dimensionally adaptive mesh. For the DTM, three methods were developed for selecting so-called transdimensional rays, the Single Unweighted Ray (SUR) technique, the Multiple Unweighted Ray (MUR) technique, and the Single Weighted Ray (SWR) technique. For the DOM, averaging methods for handling radiative intensity at dimensional boundaries were developed. Limitations of both solvers with adaptive meshes were identified by comparison with fully 3D results. For the DTM, the primary limit was numerical error associated with view factor calculations. For the DOM, treatment of dimensional boundaries led to step changes that created numerical oscillations, the severity of which was lessened by both increased angular resolution and increased optical thickness. Performance of dimensionally adaptive radiation calculations, uncoupled to any other physical calculation, was evaluated with a series of sensitivity studies including sensitivity to spatial and angular resolution, dimensional boundary placement, and reactor scaling. Runtime was most impacted by boundary layer placement. For the upstream case which had 3D cells over 40% of the reactor length, the speedup versus the fully 3D calculations were 743%, 18%, 220%, and 76% for the SUR, MUR, SWR, and DOM calculations, respectively. The downstream case which had 3D cells over the first 60% of the reactor length, had speedups of 209%, 3%, 109%, and 37%, respectively. For the DTM, accuracy was most sensitive to optical thickness, with the average percent difference in incident heat flux for SUR, MUR, and SWR calculations versus fully 3D calculations being 0.93%, 0.86%, and 1.18%, respectively, for a reactor half the size of the baseline case. The case with four times the reactor size had average percent differences of 0.28%, 0.41%, and 0.39% for the SUR, MUR, and SWR, respectively. Accuracy of the DOM was comparatively insensitive to the different changes studied. Performance of dimensionally adaptive radiation calculations coupled with thermochemistry was also investigated for both pilot and industrial scale systems. For pilot scale systems, flux and temperature differences from either solver were less than 5% and 6%, respectively, with speedups being between 200% - 600%. For industrial systems, temperature differences as high as 15% - 20% and flux differences as high as 50% - 75% were seen. In the case of the DTM, these differences between fully 3D and adaptive results come from a combination of high property gradients and comparatively few rays being drawn and could therefore be improved, at the cost of additional computation time, by using a more sophisticated ray selection method. For the DOM, these issues stem from poor performance of the 1D portion of the solver and could therefore be improved by using a more sophisticated equation to model the radiative transfer in the 1D region.