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.

<p>Predmet istraživanja ove disertacije je monitoring i analiza ultraljubičastog zračenja, toplotnih indeksa i zagađujućih materija u vazduhu većih naselja na teritoriji Vojvodine. Cilj istraživanja je da se prostornom i vremenskom analizom posmatranih parametara dođe do &scaron;to optimalnijih saznanja o stanju kvaliteta životne sredine na području Vojvodine kao i stvaranje jedinstvene baze podataka koja će služiti za buduća istraživanja. U radu je ispitan odnos između sunčevog globalnog i UV zračenja, izvedena i verifikovana empirijska jednačina za procenu dnevnih suma UV-B zračenja u osam naselja za period 1981-2008, analizirane koncentracije pet zagađujućih materija u sedam naselja za period 2001-2008. godina i analizirani toplotni indeksi u sedam naselja u periodu od 1992. do 2008. Analiza pokazuje da rekonstruisane vrednosti dnevnih suma UV-B zračenja i srednji godi&scaron;nji toplotni indeksi u svim naseljima pokazuju tendenciju rasta i da dominantan uticaj na kvalitet vazduha u naseljima Vojvodine imaju čestice. Napravljena je jedinstvena baze podataka sa vrednostima koncentracija zagađivača vazduha, toplotnih indeksa, UV i globalnog zračenja.</p> / <p>This study analyzes UV radiation, heat indexes and air pollution in town in Vojvodina region. Objective of the thesis is to provide scientific facts about environmental quality in Vojvodina, as well as, to generate unique data base for the future research. The relationship between UV-B and global radiation has been studied and correlation equation for estimating UV-B from global radiation has been deduced. Equation was used for UV-B radiation calculation in eight towns in Vojvodina region during the period 1981-2008. This study also analyzes concentrations of five air pollutant in during the period 2001-2008, and heat index during the period 1992-2008. in seven towns in Vojvodina. The results from this study show growth UV-B radiation and heat index in all towns, and denote particulate maters as main air pollutants in Vojvodina towns.</p>

The surface area and radiative properties of an object influence the rate of radiative emission from the object's surface and the rate of radiative absorption into the surface. Control of these variables would allow for the radiative heat transfer behavior of the surface to be manipulated in real time. Origami tessellations, being a repeated pattern of linked, dynamic surfaces, provide a framework by which dynamic control of apparent radiative properties and surface area is possible. The panels within a tessellation form cavities whose aspect ratio varies as the device actuates. The cavity effect suggests that the apparent radiative properties of the cavity openings will vary as a function of aspect ratio. The apparent absorptivity of an accordion tessellation formed from folded shim stock is shown experimentally to increase by 10x as the tessellation actuates from fully extended to within 10\% of a completely-folded state. Analytical models and Monte Carlo ray tracing are used to quantify the apparent radiative properties of an infinite V-groove for a variety of conditions, including specular or diffuse reflection and diffuse or collimated incident irradiation. For a diffuse V-groove, apparent radiative properties increase with increasing V-groove aspect ratio but do not approach unity. Highly reflective surfaces exhibit the largest relative increase in apparent radiative properties with actuation. Closed-form correlations achieve an average relative error of 2.0\% or less. For a specular V-groove, apparent radiative properties approach unity as the V-groove collapses towards an infinite aspect ratio. The apparent absorptivity for a V-groove exposed to collimated irradiation shows significant variations over small actuation distances, increasing by 5x over a small actuation range. For certain conditions the apparent absorptivity of a V-groove subject to collimated irradiation decreases as the aspect ratio increases.For an isothermal accordion tessellation the net radiative heat exchange continuously decreases as the surface is collapsed for most conditions, indicating that the reduction in apparent surface area generally dominates the increase in apparent radiative properties. Net radiative heat transfer values decrease by 7x for collimated irradiation and specular reflection over small actuation distances. Specular V-grooves subject to collimated irradiation occasionally show an increase in net radiative heat transfer as the device collapses. A non-isothermal dynamic radiative fin achieves a 3x reduction in heat transfer as the fin collapses; this value can be increased with the use of highly conductive materials and by increasing the length of the fin. The fin efficiency of a collapsible fin increases as the fin collapses. An experimental prototype of a collapsible fin is developed and tested in a vacuum environment, achieving a 1.32x reduction in heat transfer for a limited actuation range, where a numerical model suggests this prototype may achieve a 2.23x reduction in heat transfer over the full actuation range.

Artificial neural networks (ANNs) have been widely used in many engineering applications. This dissertation applies ANNs in the field of radiation heat transfer and applied optics. The topics of interest in this dissertation include both forward and inverse problems. Forward problems involve applications in which numerical simulation is expensive in terms of time consummation and resource utilization. Artificial neural networks can be applied in these problems for speeding up the process and reducing the required resources. The Monte Carlo ray-trace (MCRT) method is the state-of-the-art approach for modeling radiation heat transfer. It has the disadvantage of being a complex and computationally expensive process. In this dissertation, after first identifying the uncertainties associated with the MCRT method, artificial neural networks are proposed as an alternative whose computational cost is greatly reduced compared to traditional MCRT method. Inverse problems are concerned with situations in which the effects of a phenomenon are known but the cause is unknown. In such problems, available data in conjunction with ANNs provide an effective tool to derive an inverse model for recovering the cause of the phenomenon. Two problems are studied in this context. The first is concerned with an imager for which the readout power distribution is available and the viewed scene is of interest. Absorbed power distributions on a microbolometer array making up the imager is produced by discretized scenes using a high-fidelity Monte Carlo ray-trace model. The resulting readout array/scene pairs are then used to train an inverse ANN. It is demonstrated that a properly trained ANN can be utilized to convert the readout power distribution into an accurate image of the corresponding discretized scene. The recovered scene of the imager is helpful for monitoring the Earth's radiant energy budget. In the second problem, the collection of scattered radiation by a sun-photometer, or aureolemeter, is simulated using the MCRT method. The angular distribution of this radiation is summarized using the probability density function (PDF) of the incident angles on a detector. Atmospheric water cloud droplets are known to play an important role in determining the Earth's radiant energy budget and, by extension, the evolution of its climate. An extensive dataset is produced using an improved atmospheric scattering model. This dataset is then used to train and test an inverse ANN capable of recovering water cloud droplets properties from solar aureole observations. / Doctor of Philosophy / This dissertation is intended to extend the research in the field of theoretical and experimental radiation heat transfer and applied optics. It is specifically focused on efforts for more precisely implementing the radiation heat transfer, predicting the temperature evolution of the Earth's ocean-atmosphere system and identifying the atmospheric properties of the water clouds using the tools of Machine learning and artificial neural networks (ANNs). The results of this dissertation can be applied to the conception of advanced radiation and optical modeling tools capable of significantly reducing the computer resources required to model global-scale atmospheric radiation problems. The materials of this thesis are organized for solving the following three problems using ANNs: 1: Application of artificial neural networks into radiation heat transfer: The application of artificial neural networks), which is the basis of AI methodologies, to a variety of real-world problems is an on-going active research area. Artificial intelligence, or machine learning, is a state-of-the-art technology that is ripe for applications in the field of remote sensing and applied optics. Here a deep-learning algorithm is developed for predicting the radiation heat transfer behavior as a function of the input parameters such as surface models and temperature of the enclosures of interest. ANN-based algorithms are very fast, so developing ANN-based algorithms to replace ray trace calculations, whose execution currently dominates the run-time of MCRT algorithms, is useful for speeding up the computational process. 2. Numerical focusing of a wide-field-angle Earth radiation budget imager using an Artificial Neural Network: Traditional Earth radiation budget (ERB) instruments consist of downward-looking telescopes in low earth orbit (LOE) which scan back and forth across the orbital path. While proven effective, such systems incur significant weight and power penalties and may be susceptible to eventual mechanical failure. This dissertation intends to support a novel approach using ANNs in which a wide-field-angle imager is placed in LOE and the resulting astigmatism is corrected algorithmically. The application of this technology is promising to improve the performance of freeform optical systems proposed by NASA for Earth radiation budget monitoring. 3: Recovering water cloud droplets properties from solar aureole photometry using an ANNs: Atmospheric aerosols are known to play an important role in determining the Earth's radiant energy budget and, by extension, the evolution of its climate. Data obtained during aerosol field studies have already been used in the vicarious calibration of space-based sensors, and they could also prove useful in refining the angular distribution models (ADMs) used to interpret the contribution of reflected solar radiation to the planetary energy budget. Atmospheric aerosol loading contributes to the variation in radiance with zenith angle in the circumsolar region of the sky. Measurements obtained using a sun-photometer have been interpreted in terms of the aerosol single-scattering phase function, droplet size distribution, and aerosol index of refraction, all of which are of fundamental importance in understanding the planetary weather and climate. While aerosol properties may also be recovered using lidar, this dissertation proposes to explore a novel approach for recovering them via sun-photometry. The atmospheric scattering model developed here can be used to produce the extensive dataset required to compose, train, and test an artificial neural network capable of recovering water cloud droplet properties from solar aureole observations.

Black coatings essentially absorb incident light at all wavelengths from all directions. They are used when minimal reflection or maximum absorption is desired and therefore are effective in applications that require control of stray light. Our motivation stems from the use of black coating Lord Aeroglaze® Z302 in aerospace and remote sensing applications and the desire to support the development of bidirectional spectral models that can be used successfully to predict the performance of optical instruments such as telescopes. The bidirectional reflectance distribution function (BRDF) is an indispensable parameter in the optical characterization of such coatings. The current effort involves investigation of the BRDF of the commercial black coating Aeroglaze® Z302. An automated goniometer reflectometer has been designed, fabricated and successfully used for performing the BRDF measurements of Z302 at visible and ultraviolet wavelengths and at both polarizations. The current contribution involves study of Z302 samples prepared at different thicknesses and by different methods, which provides insight about influence of surface roughness on BRDF of Z302. / Master of Science / When light falls on different materials it undergoes various phenomenon such as reflection, refraction, absorption and scattering. The amount of each phenomenon varies with the optical nature of a material as well as the wavelength and direction of the light. Therefore, understanding the optical properties of materials at various wavelengths of light is necessary for effectively using those materialsin specific applications which require light to be efficiently reflected or absorbed. This research studies an optical property known as Bidirectional Reflectance Distribution Function (BRDF) of a black coating called Lord Aeroglaze Z302. Black coatings are materials that ideally absorb almost all light that falls on them irrespective of the light’s direction and wavelength. They are used in applications where maximum absorption of light is required. One such application which relates to the motivation for this research is absorbing unwanted light in instruments used in space such as telescopes and radiometers. Z302 is used in the Clouds and the Earth’s Radiant Energy System (CERES) instruments developed by NASA. BRDF is an important parameter which gives information about all other optical properties of a surface and can be used to know optical performance of that surface. The current work describes the experiments and an automated device developed, called reflectometer, to measure the BRDF of Z302 at different angles and wavelengths of light. The results are reported for different thickness samples of Z302 coating, and two different wavelengths of light that belong to the visible and ultraviolet spectrum of light.

The thesis describes a completely new biofuel system to generate particle-free heat from combustion of ash-containing biofuel particles at high temperatures. The suggested system gives opportunities to introduce biofuels in new areas. Main components in the suggested system is a heat radiating combustion chamber intended for pulverized wood, combined with regenerators to extract heat from flue gases and simultaneously preheating the combustion air. The thesis contains a description of the suggested system, theoretical considerations, calculations regarding the combustion, and includes results from tests performed. The results from calculations and tests performed concludes that the system is workable and possible to apply. / Uppsatsen beskriver ett helt nytt system för att åstadkomma partikelfri värme och höga temperaturer från biobränslen. Det föreslagna systemet ger goda möjligheter att använda biobränslen inom helt nya områden. Systemet består huvudsakligen av en brännkammare för träpulver, utförd som en hålrumsstrålare, samt regenerativa värmeväxlare mellan avgående rökgas och inkommande förbränningsluft. Uppsatsen innehåller en beskrivning av det föreslagna systemet, teoretiska överväganden, beräkningar rörande förbränningen, samt redovisar resultat från gjorda försök. Resultat från beräkningar och genomförda försök visar att det föreslagna systemet fungerar och är praktiskt möjligt att tillämpa.

Thermo-mechanical failure of components in planar-type solid oxide fuel cells (SOFCs) is a major obstacle on the path to bringing this technology to commercial viability. The probability of material degradation and failure in SOFCs depends strongly on the local temperature gradients at the interfaces of different materials. Therefore, it is of paramount importance to accurately predict and manage the temperature fields within the stack, especially near the interfaces. In this work we consider three effects in detail. First, we analyze radiative heat transfer effects within the semi-transparent solid electrolyte and compared them to thermal conduction. We also, present the modeling approach for calculation of surface-to-surface exchange within the flow channels and from the stack to the environment. The simplifying assumptions are identified and their carefully justified range of applicability to the problem at hand is established. This allows thermal radiation effects to be properly included in overall thermal modeling efforts with the minimum computational expense requirement. Second, we developed a series of reduced-order models for the transient heating and cooling of a cell, leading to a framework for optimization of these processes. The optimal design is one that minimizes heating time while maintaining thermal gradients below an allowable threshold. To this end, we formulated reduced order models (validated by rigorous CFD simulations) that yield simple algebraic design rules for predicting maximum thermal gradients and heating time requirements. Several governing dimensionless parameters and time scales were identified that shed light on the essential physics of the process. Finally, an analysis was performed to assess the degree of local thermal non-equilibrium (LTNE) within porous SOFC electrodes, and through a simple scaling analysis we discovered the parameter that gives an estimate of the magnitude of LTNE effects. We conclude that because of efficient heat transfer between the solid and gas in the microscale pores of the electrodes, the temperature difference between gas and solid is often negligible. However, if local variations in current density are significant, the LTNE effects may become significant and should be considered.