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1
Wang, Hengmao. "Inferring radiative fluxes from new generation of satellites model updates /." College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/7356.
Анотація:
Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Atmospheric and Oceanic Sciences. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
2
Sopkin, Kristin L. "Heat fluxes in Tampa Bay, Florida." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002398.
3
Tornow, Florian [Verfasser]. "Contributions to Estimating Top-of-Atmosphere Radiative Fluxes using EarthCARE’s Broadband Radiometer / Florian Tornow." Berlin : Freie Universität Berlin, 2018. http://d-nb.info/1176633597/34.
4
Guilbert, Simonne. "Comparaisons des flux ondes courtes POLDER / PARASOL et CERES / Aqua : amélioration des flux ondes courtes POLDER / PARASOL." Thesis, Université de Lille (2022-....), 2022. http://www.theses.fr/2022ULILR027.
Анотація:
Dans le contexte actuel du changement climatique, il est essentiel de bien caractériser et de pouvoir suivre dans le temps le bilan d'énergie radiative terrestre au sommet de l'atmosphère et à la surface. Du point de vue de la mesure, obtenir une estimation correcte du bilan radiatif passe par la détermination précise des flux radiatifs solaire et infra-rouge. L'objectif de cette thèse est d'étudier les flux radiatifs solaires obtenus à partir du radiomètre français POLDER embarqué sur le microsatellite PARASOL du CNES. Une première partie des travaux de thèse présentés consiste à comparer les produits opérationnels actuels de POLDER avec les flux de référence obtenus par les radiomètres à large bande spectrale CERES sur les plates-formes spatiales américaines Aqua et Terra. La comparaison est faite sur deux périodes, la première pour laquelle nous disposons de mesures coïncidentes (2005-2009), et la seconde qui correspond à une période de dérive du satellite PARASOL (2010-2013). Nous montrons que cette dérive a eu un impact direct sur les observations, avec des répercussions sur les flux calculés. En effet, sur la période de coïncidence des mesures les flux POLDER sont très proches des flux CERES pour deux des produits étudiés (SSF1deg, SYN1deg) avec des différences relatives inférieures à 2% jusqu'en décembre 2009. Après cette date, la différence relative augmente. Un effet de compensation terres/océans est par ailleurs mis en évidence. Les résultats obtenus suite à cette comparaison nous ont menés à étudier plus particulièrement la composante de l'algorithme qui permet d'obtenir les moyennes mensuelles des flux POLDER. Celle-ci concerne l'extrapolation diurne, utilisée pour obtenir des estimations de l'albédo à toutes les heures de la journée à partir d'une seule observation en utilisant des modèles qui dépendent de la scène observée. Les modèles utilisés actuellement sont issus de quatre mois d'observations POLDER-1 (1996-1997) et nous avons décidé de mettre à profit les données obtenues sur l'ensemble de la mission PARASOL pour améliorer ces modèles. Les flux solaires obtenus avec les nouveaux modèles présentent moins de dépendance à la dérive au-dessus des océans mais une tendance encore visible au-dessus des terres. Ces résultats nous ont amenés à proposer plusieurs pistes d'amélioration, principalement en augmentant le nombre de modèles POLDER. Ces travaux, basés sur les mesures de POLDER qui a cessé de fonctionner en décembre 2013 mais dont les données sont disponibles, seront en grande partie réutilisables pour le futur radiomètre multispectral, multi-angulaire et polarisé 3MI, développé par l'ESA et EUMETSAT et qui sera embarqué sur la prochaine mission spatiale opérationnelle EPS-SG d'EUMETSAT à partir de 2024 pour une durée d'environ 20 ansIn the context of climate change, it is essential to estimate precisely and be able to monitor over time the energy balance of the Earth at the top of the atmosphere and at the surface. In terms of measurement, obtaining a correct estimate of the radiative balance requires a precise determination of the shortwave (solar) and longwave (infrared) radiative fluxes. The objective of this thesis is to assess the solar radiative fluxes obtained from the French radiometer POLDER on board the PARASOL microsatellite supported by CNES. A first part of the thesis presents a comparison between the operational products computed from POLDER observations with the reference fluxes obtained through the broadband radiometers CERES on the NASA space platforms Aqua and Terra. The comparisons are made over two periods: first a period with coincident measurements (2005-2009), then a second period which corresponds to the drift of the PARASOL satellite (2010-2013). We show that this drift had an impact on the observations, with strong repercussions on the calculated fluxes. Over the period of coincidence of the measurements, POLDER fluxes are very close to the fluxes from CERES for two of the products studied (CERES SSF1deg and CERES SYN1deg) with relative differences under 2% until December 2009. After 2010, the relative difference increases with the drift. A land/ocean compensation effect is also revealed. The results obtained through these comparisons led us to study in detail the component of the algorithm used to obtain the monthly means of POLDER shortwave fluxes. This part of the algorithm is the diurnal extrapolation, used to estimate a value of albedo at all hours of the day from a single observation using models that are scene-dependent. The models used for the operational products were built using four months of POLDER-1 observations (1996-1997). We decided to take advantage of the data obtained throughout the entire PARASOL mission to improve these models. The shortwave fluxes obtained with the new models show less dependence on the drift over oceans but a drift is still present over lands. These results led to several propositions that could improve POLDER's shortwave fluxes, mainly by increasing the number of POLDER models. This work, based on measurements from POLDER-3, which was shut down in December 2013, but whose data is available, will be largely reusable for the future multispectral, multi-angular and polarized radiometer 3MI, developed by ESA and EUMETSAT and which will fly onboard the EPS-SG mission supported by EUMETSAT from 2024, for approximately 20 years
5
Moreira, Demerval S., Karla M. Longo, Saulo R. Freitas, Marcia A. Yamasoe, Lina M. Mercado, Nilton E. Rosário, Emauel Gloor, et al. "Modeling the radiative effects of biomass burning aerosols on carbon fluxes in the Amazon region." COPERNICUS GESELLSCHAFT MBH, 2017. http://hdl.handle.net/10150/626421.
Анотація:
Every year, a dense smoke haze covers a large portion of South America originating from fires in the Amazon Basin and central parts of Brazil during the dry biomass burning season between August and October. Over a large portion of South America, the average aerosol optical depth at 550 nm exceeds 1.0 during the fire season, while the background value during the rainy season is below 0.2. Biomass burning aerosol particles increase scattering and absorption of the incident solar radiation. The regional-scale aerosol layer reduces the amount of solar energy reaching the surface, cools the near-surface air, and increases the diffuse radiation fraction over a large disturbed area of the Amazon rainforest. These factors affect the energy and CO2 fluxes at the surface. In this work, we applied a fully integrated at-mospheric model to assess the impact of biomass burning aerosols in CO2 fluxes in the Amazon region during 2010. We address the effects of the attenuation of global solar radiation and the enhancement of the diffuse solar radiation flux inside the vegetation canopy. Our results indicate that biomass burning aerosols led to increases of about 27% in the gross primary productivity of Amazonia and 10% in plant respiration as well as a decline in soil respiration of 3%. Consequently, in our model Amazonia became a net carbon sink; net ecosystem exchange during September 2010 dropped from +101 to -104 TgC when the aerosol effects are considered, mainly due to the aerosol diffuse radiation effect. For the forest biome, our results point to a dominance of the diffuse radiation effect on CO2 fluxes, reaching a balance of 50-50% between the diffuse and direct aerosol effects for high aerosol loads. For C3 grasses and savanna (cerrado), as expected, the contribution of the diffuse radiation effect is much lower, tending to zero with the increase in aerosol load. Taking all biomes together, our model shows the Amazon during the dry season, in the presence of high biomass burning aerosol loads, changing from being a source to being a sink of CO2 to the atmosphere.
6
Wonsick, Margaret M. "High-resolution clouds and radiative fluxes from satellites transferability of methods and application to monsoon regions /." College Park, Md.: University of Maryland, 2009. http://hdl.handle.net/1903/9258.
Анотація:
Thesis (Ph. D.) -- University of Maryland, College Park, 2009.Thesis research directed by: Dept. of Atmospheric and Oceanic Sciences. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
7
Voogt, James Adrian. "Validation of an urban canyon radiation model for nocturnal long-wave radiative fluxes and the effect of surface geometry on cooling in urban canyons." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/27679.
Анотація:
The urban canyon radiation model of Arnfield (1976, 1982) is validated using measurements of long-wave fluxes taken within a scale urban canyon constructed from concrete building blocks. A custom-designed traversing system allowed miniature radiometers to be automatically moved around the perimeter of a canyon cross-section thereby providing for the validation of individual model grid-points.
Measured model input consists of surface temperatures obtained using fine wire themocouples, incident long-wave radiation at the canyon top, and emissivity of canyon materials. Tests were conducted to establish the expected accuracy and precision of the input data. Surface temperature data were filtered to remove a noise component. A probable error analysis of all measured model input and validation data is made.
Sensitivity tests of the model to variations in input data are presented. Surface temperature is the dominant control under the conditions tested. Model-calculated view-factors are shown to be in error for adjacent corner points and are replaced with view-factors calculated using equations derived from the Nusselt Unit Sphere method (Steyn, pers. comm.)
Validation results for a range of canyon height-to-width ratios, meteorological conditions and model parameters are presented. Excellent agreement between modelled and measured fluxes is obtained for points on the canyon floor and top. The agreement for fluxes at points on the canyon walls is generally good but is shown to suffer from errors in sensor orientation relative to the canyon walls. Use of the Unsworth and Monteith (1975) radiance distribution improves model performance statistics for incident and net long-wave radiation.
Four different estimates of surface temperature are used as model input in place of the measured values to investigate the differences in the model output. Surface temperature-based estimates are found to be superior to those based upon air temperature. The use of unmodified screen-level air temperatures measured at Vancouver Airport produces the poorest agreement.
The temporal and spatial variation of in-canyon temperatures and radiation are presented for three canyon height-to-width ratios. The canyon geometry is shown to significantly reduce the surface cooling on the canyon floor compared to an open site under ideal radiative cooling conditions. Results are compared to previous results from scale models (Oke, 1981) and field studies (Oke and Maxwell, 1975; Hogstrdm et al., 1978). . Atmospheric controls of incident long-wave radiation, wind speed and direction are also shown to affect the observed cooling.Arts, Faculty of
Geography, Department of
Graduate
8
Gruber, Simon [Verfasser]. "Contrails and Climate Engineering - Process Studies on Natural and Artificial High-Level Clouds and Their Impact on the Radiative Fluxes / Simon Gruber." Karlsruhe : KIT Scientific Publishing, 2019. http://d-nb.info/1186144742/34.
9
Gruber, Simon [Verfasser], and C. [Akademischer Betreuer] Kottmeier. "Contrails and Climate Engineering - Process Studies on Natural and Artificial High-Level Clouds and Their Impact on the Radiative Fluxes / Simon Gruber ; Betreuer: C. Kottmeier." Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/1177147173/34.
10
Zheng, Lu. "Examining the impact of wildfire smoke aerosol on clouds, precipitation, and radiative fluxes in Northern America and Russia using a fully coupled meso-scale model WRF-Chem-SMOKE and satellite data." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52338.
Анотація:
We developed a fully-coupled meso-scale model WRF-Chem-SMOKE by incorporating a selection of smoke emission models and improving the representations of aerosol-cloud interactions in the microphysics scheme. We find that the difference in smoke emissions between different datasets, even in one fire cluster, could lead to significant discrepancies in modeled AODs. The integrated smoke emission dataset improves the prediction of modeled AODs. We find that the modeled cloud properties and precipitation are extremely sensitive to the smoke loadings. Higher smoke loadings suppress precipitation initially, because of smoke-induced reduction of the collision-coalescence and riming processes, but ultimately cause an invigoration of precipitation.
11
Sá, Pâmella Crisley Costa de. "Estimativa do saldo de radiação em cultivo irrigado de cana-de-açúcar utilizando dados de sensoriamento remoto orbital." Universidade Federal Rural do Semi-Árido, 2016. http://bdtd.ufersa.edu.br:80/tede/handle/tede/626.
Анотація:
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
In Brazil there is a great irregularity and no radiation data that has just committing several studies. Thus, the use of remote sensing techniques is presented as a promising field, with the advantage of determining the components of the radiation balance with high spatial coverage quickly and accurately, and together with surface data have been indispensable in the application models and algorithms to estimate the components of the energy balance at the surface and evapotranspiration at various scales of time and space, which is the main factor to be considered in estimating water needs of the crop. The aim of this research project was to determine the components of the radiation balance in sugarcane area from MODIS (MODIS) inserted in SEBAL model (Surface Energy Balance Algorithm for Land) and validate them with data to the surface in the production area of sugarcane irrigated belonging to the company Agribusiness of the São Francisco Valley SA - Agrovale in Juazeiro - BA. It was concluded that there was no unusual condition in the behavior of the terms of the radiation balance obtained on the surface, when considering the different growth stages although the absolute values of the terms were different. The terms of the Radiation Balance found through MODIS images by applying the model SEBAL had expected behavior for targets with consistent and similar values to those found on the surface except for the albedo that had errors 54.5%, 50%, 11.7% and 26% for phases I to IV, respectively. Finally, the evapotranspiration using Rn from the satellite imaging showed no significant difference we react to ETcBERB and ETcPM1. It follows, therefore, that remote sensing can be perfectly used in determining the water needs of the crop of sugarcane in the region under study
No Brasil há uma grande irregularidade ou inexistência de dados de radiação, que acaba comprometendo diversos estudos. Desta forma, o emprego de técnicas de sensoriamento remoto apresenta-se como um campo promissor, com a vantagem da determinação dos componentes do balanço de radiação com grande cobertura espacial de forma rápida e precisa e, juntamente com dados de superfície têm sido indispensáveis na aplicação de modelos e algoritmos destinados à estimativa dos componentes do balanço de energia à superfície e da evapotranspiração em várias escalas de tempo e espaço, sendo este o principal fator a ser considerado na estimativa das necessidades hídricas da cultura. O objetivo deste projeto de pesquisa foi determinar os componentes do balanço de radiação em área de cana-de-açúcar a partir de dados MODIS (Moderate Resolution Imaging Spectroradiometer) inseridos no modelo SEBAL (Surface Energy Balance Algorithm for Land) e validá-los com dados obtidos à superfície em área produtiva de cana-de-açúcar irrigada pertencente à empresa Agroindústrias do Vale do São Francisco S.A - Agrovale no município de Juazeiro - BA. Concluiu-se que não houve nenhuma condição atípica no comportamento dos termos do balanço de radiação obtidos à superfície, quando se consideraram os diferentes estádios de desenvolvimento da cultura embora os valores absolutos dos termos tenham sido diferentes. Os termos do Balanço de Radiação encontrados através de imagens MODIS aplicando o modelo SEBAL apresentaram comportamento esperado para os alvos, com valores consistentes e próximos aos encontrados à superfície, exceto para o albedo que apresentou erros de 54,5%, 50%, 11,7% e 26% para as fases de I a IV, respectivamente. Por fim, a evapotranspiração usando o Rn proveniente do processamento de imagens de satélite não apresentou diferença significativa em realação a ETcBERB e a ETcPM1. Conclui-se, portanto, que o sensoriamento remoto pode perfeitamente ser usado na determinação das necessidades hídricas da cultura da cana-de-açúcar na região em estudo
2016-11-14
12
Sauter, Esequia. "Modelos unidimensionais para fluxos condutivo-radiativos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/29971.
Анотація:
Fenômenos que envolvem transferência de calor em altas temperaturas exigem modelos condutivos-radiativos, como é o caso de modelos de resfriamento de vidro e de turbinas de gás. A formulação matemática resulta em um sistema de equações diferenciais parciais, sendo uma equação parabólica com condições de contorno não lineares acoplada a equação de transporte radiativo com condições de contorno semi-reflexiva. A teoria de existência para esse sistema já existe sob algumas condições restritivas. Neste trabalho tratamos essa teoria sem a necessidades de hipóteses não física no caso unidimensional. Também fizemos a teoria de existência para a equação do transporte não acoplada com espalhamento anisotrópico. Simulações numéricas para o transporte e para o problema acoplado foram feitas via discretização diretas dos operadores integrais oriundos da análise e diferenças nitas para a equação da temperatura. Comparamos resultados com os encontrados na literatura e calculamos o erro de truncamento do método usado na equação do transporte.Phenomena involving heat transfer in high temperature require conductive-radiative models, as is the case of models of glass annealing and gas turbines. The mathematical formulation results in a system of partial di erential equations, composed of a parabolic equation with nonlinear boundary conditions coupled the radiative transport equation with semi-re exive boundary conditions. The theory of existence for this system already exists for some restrictive sets of parameters. In this paper we consider the theory for the one-dimensional case without the need for non-physical hypotheses. Moreover, we establish the theory of existence for the neutron transport equation with general anisotropic scattering. Numerical simulations for the transport equation and the coupled problem were made by direct discretization of integral operators originating from the analysis and a nite di erence equation for the temperature. We compare results with those found in the literature and calculate the truncation error of the method used in the transport equation.
13
Lohmann, Ulrike, Leon Rotstayn, Trude Storelvmo, Andrew Jones, Surabi Menon, Johannes Quaas, Annica M. L. Ekman, Dorothy Koch, and Reto A. Ruedy. "Total aerosol effect: radiative forcing or radiative flux perturbation?" Copernicus Publications, 2010. https://ul.qucosa.de/id/qucosa%3A13832.
Анотація:
Uncertainties in aerosol radiative forcings, especially those associated with clouds, contribute to a large extent to uncertainties in the total anthropogenic forcing. The interaction of aerosols with clouds and radiation introduces feedbacks which can affect the rate of precipitation
formation. In former assessments of aerosol radiative forcings, these effects have not been quantified. Also, with global aerosol-climate models simulating interactively aerosols and cloud microphysical properties, a quantification of the aerosol forcings in the traditional way is difficult to
define properly. Here we argue that fast feedbacks should be included because they act quickly compared with the time scale of global warming. We show that for different forcing agents (aerosols and greenhouse gases) the radiative forcings as traditionally defined agree rather well with estimates from a method, here referred to as radiative flux perturbations
(RFP), that takes these fast feedbacks and interactions into account. Based on our results, we recommend RFP as a valid option to compare different forcing agents, and to compare the effects of particular forcing agents in different models.
14
Fernandes, Cássio Spohr. "Implementação de modelos atualizados de gás cinza no software FDS para predição do fluxo de calor radiativo em incêndios." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/184710.
Анотація:
Este trabalho tem como objetivo implementar e testar modelos de gás cinza atualizados na rotina de radiação térmica do software Fire Dynamics Simulator (FDS), além da utilização do próprio modelo de gás cinza disponível no software, para a predição do fluxo de calor radiativo. Os modelos de gás cinza estudados foram o modelo padrão do software FDS (aqui denominado como GC1), e os modelos de gás cinza mais atuais: o GC2, no qual o coeficiente de absorção do meio participante é dado por relações polinomiais, e o GC3, sendo este um modelo de gás cinza que baseia o cálculo do coeficiente de absorção no modelo WSGG. Os novos modelos de gás cinza foram implementados no código fonte do software FDS, o qual é um código aberto, e a verificação da implementação foi realizada através da solução numérica do equacionamento utilizando os valores reportados pelo software. Com os novos modelos de gás cinza já corretamente implementados, passou-se então para a simulação computacional dos casos previamente selecionados. Para todos os modelos de gás cinza, foram simulados incêndios em poças, para diferentes combustíveis (etanol, n-heptano e metanol) em diferentes cenários de incêndio, considerando ou não a presença de fuligem no sistema. Os cenários de incêndio eram: (i) totalmente fechado, (ii) totalmente aberto e (iii) com uma condição intermediária, fechado, porém com uma abertura para o meio externo. Um estudo de análise de malha e de diferentes parâmetros, como o estudo da quantidade necessária de ângulos sólidos discretos, foram realizados para correta padronização dos parâmetros. As simulações computacionais foram validadas para o modelo de gás cinza padrão do FDS através da comparação de resultados com aqueles reportados na literatura específica de cada caso. Com os modelos já validados simulou-se novamente cada cenário de incêndio com os diferentes modelos de gás cinza anteriormente implementados. A partir da análise dos resultados obtiveram-se boas concordâncias para os campos de temperatura, frações molares tanto de CO2 quanto de H2O e para as frações volumétricas de fuligem. Os fluxos de calor radiativos foram corretamente preditos para todos os modelos de gás cinza implementados. O modelo GC2 apresentou resultados com desvios médios na faixa de 15%, o modelo de gás cinza baseado no WSGG (GC3) apresentou os melhores resultados, com erros médios inferiores a 10%, enquanto que o modelo padrão do software, GC1, apresentou resultados intermediários.This work aims to implement and test updated gray gas models in the thermal radiation routine of the Fire Dynamics Simulator (FDS) software, as well as the use of the gray gas model available in the software to the prediction of radiative heat flux. The gray gas models studied were the default model of the FDS software (determined GC1), and the most current gray gas models: the GC2, in which the absorption coefficient of the participant medium is given by a polynomial relations, and the GC3, which is a gray gas model that was based on the calculation of the absorption coefficient in the WSGG model. The most recently gray gas models were implemented in the source code, which is an open source, and the verification of the implementation was performed by the numerical solution of the equations from the reported values of the software. With the new gray gas models already implemented, the next step was the computational simulation of the previously selected cases. For all the gray gas models, pool fires were simulated different scenarios of fire for different fuels (ethanol, nheptane and methanol), with and without considering soot presence in the system. The fire scenarios were: (i) fully closed, (ii) fully open and (iii) with an intermediate condition, closed but with an opening to the external environment. A study of a mesh analysis and different parameters, such as the study of the required amount of discrete solid angles, were performed to correct the standard parameters. The computational simulations were verified for the default gray gas model of the FDS by comparing the simulations results with those reported in the specific literature of each case. With the models already verified, each fire scenario was simulated with the different gray gas models previously implemented. From the analysis of the results, good agreements were obtained for the fields of temperature, molar fraction of CO2 and H2O and soot volume fraction. The radiative heat fluxes were correctly predicted for all gray gas models early implemented. The GC2 model present results with average deviation in the range of 15%, the gray gas model based on WSGG (GC3) presented the best results, with average deviation lower than 10%, while the default software model (GC1) presented intermediate results.
15
Waage, Magnus Heskestad. "Radiative corrections to van der Waals interaction in fluids." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18872.
Анотація:
The van der Waals interaction energy is derived for a homogenous fluid of polarizable particles. Low-temperature corrections to the van der Waals interaction energy are computed numerically for three cases: Dilute media with radiative interactions, arbitrarily dense media without radiative interactions, and arbitrarily dense media with radiative interactions. The validity of the model used to calculate the corrections at arbitrary densities is argued for, by comparison with the results for low densities.
16
Liu, Xianglei. "Tailoring thermal radiative properties and enhancing near-field radiative heat flux with electromagnetic metamaterials." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54960.
Анотація:
All substances above zero kelvin temperature emit fluctuating electromagnetic waves due to the random motions of charge carriers. Controlling the spectral and directional radiative properties of surfaces has wide applications in energy harvesting and thermal management. Artificial metamaterials have attracted much attention in the last decade due to their unprecedented optical and thermal properties beyond those existing in nature. This dissertation aims at tailoring radiative properties at infrared regime and enhancing the near-field radiative heat transfer by employing metamaterials. A comprehensive study is performed to investigate the extraordinary transmission, negative refraction, and tunable perfect absorption of infrared light. A polarizer is designed with an extremely high extinction ratio based on the extraordinary transmission through perforated metallic films. The extraordinary transmission of metallic gratings can be enhanced and tuned if a single layer of graphene is covered on top. Metallic metamaterials are not the unique candidate supporting exotic optical properties. Thin films of doped silicon nanowires can support negative refraction of infrared light due to the presence of hyperbolic dispersion. Long doped-silicon nanowires are found to exhibit broadband tunable perfect absorption. Besides the unique far-field properties, near-field radiative heat transfer can be mediated by metamaterials. Bringing objects with different temperatures close can enhance the radiative heat flux by orders of magnitude beyond the limit set by the Stefan-Boltzmann law. Metamaterials provide ways to make the energy transport more efficient. Very high radiative heat fluxes are shown based on carbon nanotubes, nanowires, and nanoholes using effective medium theory (EMT). The quantitative application condition of EMT is presented for metallodielectric metamaterials. Exact formulations including the scattering theory and Green’s function method are employed to investigate one- and two-dimensional gratings as well as metasurfaces when the period is not sufficiently small. New routes for enhancing near-field radiative energy transport are opened based on proposed hybridization of graphene plasmons with hyperbolic modes, hybridization of graphene plasmons with surface phonon modes, or hyperbolic graphene plasmons with open surface plasmon dispersion relation. Noncontact solid-state refrigeration is theoretically demonstrated to be feasible based on near-field thermal radiation. In addition, the investigation of near-field momentum exchange (Casimir force) between metamaterials is also conducted. Simultaneous enhancement of the near-field energy transport and suppress of the momentum exchange is theoretically achieved. A design based on repulsive Casimir force is proposed to achieve tunable stable levitation. The dissertation helps to understand the fundamental radiative energy transport and momentum exchange of metamaterials, and has significant impacts on practical applications such as design of nanoscale thermal and optical devices, local thermal management, thermal imaging beyond the diffraction limit, and thermophotovoltaic energy harvesting.
17
Kubota, Yuko. "Study on Variation of Radiation Belt Electron Fluxes Through Nonlinear Wave-Particle Interactions." Kyoto University, 2018. http://hdl.handle.net/2433/232003.
18
Riedinger, Xavier. "Instabilité radiative d'un tourbillon dans un fluide stratifié." Aix-Marseille 1, 2009. http://www.theses.fr/2009AIX11053.
Анотація:
Les tourbillons dans les ecoulements geophysiques sont souvent nombreux et presents a plusieurs echelles. Ils interviennent aussi bien dans la dynamique des ecoulements que dans leurs proprietes statistiques. Afin d'identifier precisement le r^ole des tourbillons dans les proprietes globales d'un ecoulement geophysique, il est important de conna^itre aussi finement que possible leur dynamique individuelle. Avec cet objectif, nous etudions dans cette these par des moyens theoriques, numeriques et experimentaux, les proprietes de stabilite de tourbillons stratifies modeles : le tourbillon de Lamb-Oseen et une famille d'ecoulements en rotation de Taylor-Couette et de Kepler. Nous montrons notamment que ces ecoulements, stables en milieu homogµene, peuvent devenir instables en presence d'une stratification stable le long de leur axe de rotation. Les trois types d'ecoulements sont soumis a une m^eme forme de destabilisation, l'instabilite radiative dont nous decrivons le mecanisme. Pour le tourbillon de Lamb-Oseen, une etude numerique exhaustive des proprietes de stabilite est realisee en fonction des nombres de Reynolds et de Froude, caracterisant les forces visqueuses et de flottabilite du fluide. Pour de faibles nombres de Reynolds, nous montrons que le mode le plus instable conduit µa une ondulation du vortex que l'on reussit a retrouver experimentalement. Pour l'ecoulement de Taylor-Couette genere par un cylindre en rotation, le mode le plus instable est egalement helicoïdal mais il conduit a une structure rayonnante plus marquee. Nous reussissons egalement a identifier ce mode dans les experiences. En utilisant l'ombroscopie et la technique du "synthetic schlieren", nous montrons aussi que la frequence et la longueur du mode observe sont en tres bon accord avec les predictions numeriques. D'autres resultats numeriques sont presentes qui montrent notamment que l'instabilite radiative n'est que partiellement reduite par la rotation planetaire et qu'elle pourrait etre presente dans un ecoulement keplerienVortices are widely present in geophysical flows at all scales. They are involved in the dynamics of flows as well as in their statistical properties. In order to identify precisely their role in the global properties of the flow it is important to know their individual dynamics as finely as possible. With this purpose, we study in this thesis through theoretical, numerical and experimental means, the stability properties of models of stratified vortices : The Lamb-Oseen vortex and a family of Taylor-Couette and Keplerian rotative °ows. We show, in particular, that these flows, stable in a homogeneous fluid, can become unstable in the presence of a stable stratification along their rotation axis. The three kinds of flows are subject to the same form of destabilisation, the radiative instability of which we describe the mechanism. For the Lamb-Oseen vortex, a comprehensive numerical study is performed by varying the Reynolds number and the Froude number which characterize the viscosity and the buoyancy of the fluid. For low Reynolds numbers, we show that the most unstable mode leads to an undulation of the vortex that we have obtained successfully in the experiments. For the Taylor-Couette flow generated by the rotation of a cylinder, the most unstable mode is also helical but it exhibits a more pronounced radiative structure. We also succeeded in obtaining this mode experimentally. The frequency and wavelength of the mode have been measured using shadowgraphy and the synthetic schlieren technique, and a very good agreement with the numerics has been demonstrated. Other numerical results are presented which show, in particular, that the radiative instability is only partially reduced by planetary rotation and that it could be present in Keplerian flows
19
Baud, Germain. "Conception de récepteurs solaires à lit fluidisé sous flux radiatif concentré." Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0106/document.
Анотація:
L'objectif de ce travail est d’évaluer le positionnement et le potentiel des récepteurs à lit fluidisé à changement de section par rapport aux autres méthodes de chauffage de gaz à haute température par voie solaire. A cette fin, une connaissance approfondie des phénomènes thermiques et hydrodynamiques du récepteur est nécessaire. Pour acquérir cette connaissance, nous avons modélisé les transferts thermiques dans le récepteur en portant une attention particulière sur les transferts radiatifs en prenant en compte les diffusions multiples de la lumière dans le milieu particulaire, les effets de parois sur les transferts radiatifs et la directionnalité du rayonnement solaire concentré. La détermination précise de la distribution de particules dans le ciel du lit fluidisé s'est avérée un paramètre critique pour le calcul des transferts thermiques. Ces modèles, plus tard affinés par une confrontation avec des références expérimentales, nous ont permis d'explorer l'effet de la géométrie sur les transferts thermiques dans le récepteur. Il ont permis entre autres de mettre en évidence l'intérêt d'utiliser une colonne de fluidisation à changement de section et l'importance de l'optimisation du couple concentrateur solaire / récepteur afin d'éviter d'éventuelles surchauffes au niveau des parois du récepteur. De même, il semble que l'homogénéisation de la température dans le lit fluidisé contenu dans le récepteur soit favorable à son rendementThe aim of this work is to evaluate the position and the potential of solar fluidized bed receivers compared to other methods for the solar heating of gases at high temperature. To this end, a thorough knowledge of the heat transfer and hydrodynamic of the receiver is necessary. To acquire this knowledge, we modeled the heat transfer in the receiver with a focus on the radiative transfer by taking into account the multiple scattering of light in the particle medium, the effect of walls on radiative heat transfer and the directionality of the concentrated solar radiation. The accurate determination of the distribution of particles within the fluidized bed has been a critical parameter for the calculation of heat transfer. With these models, later refined by a confrontation with experimental references, we have studied the effect of geometry on heat transfer in the receiver. This study highlighted the necessity to use a switching section fluidization column and the importance to optimize the pair : solar concentrator / receiver to avoid any overheating at the walls of the receiver. Moreover, it appears that the homogenization of the temperature in the fluidized bed of the receiver increase its performance
20
Kabbaj, Narjisse. "Etude du transfert radiatif d'un plasma thermique d'air : influence des propriétés radiatives dans la modélisation d'un arc libre." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30024.
Анотація:
Dans la simulation des arcs électriques, une estimation de la contribution radiative est indispensable pour fournir une description satisfaisante du comportement thermique du plasma. La prédiction précise de la divergence du flux radiatif (DFR) est essentielle pour déterminer l'évolution de la température de l'arc. Afin de décrire avec précision les effets radiatifs, la résolution de l'équation de transfert radiatif (ETR) est nécessaire moyennant la connaissance du coefficient d'absorption du milieu. Malheureusement, ce coefficient étant dépendant de la température et de la longueur d'onde, cette équation s'avère complexe à résoudre et coûteuse en temps de calcul. De nombreuses méthodes approximatives sont ainsi développées pour simplifier le calcul des propriétés radiatives. Dans ce travail, nous décrivons finement le spectre d'un plasma d'air avec près de 7.106 points en fréquence (ou longueur d'onde). A partir de ce découpage, nous calculons la DFR, soit à partir de la méthode approchée du coefficient d'émission nette (CEN) basée sur une simplification géométrique du plasma, soit à partir de coefficients moyens d'absorption (CMA) obtenus après découpage du spectre en 6 intervalles spectraux utilisant différentes moyennes (Classique, Planck, Planck modifiée et Rosseland), soit à partir d'un calcul " exact " correspondant à la résolution directe de l'ETR. Les calculs sont réalisés pour 9 configurations simples en 1D simulant un plasma cylindrique dont la température ne varie qu'en fonction du rayon. Les différentes étapes de calcul y sont présentées mettant en évidence l'influence de certains paramètres comme la largeur et la température maximale du profil de température, la pression, les vapeurs de cuivre .... Une grande partie de ce travail porte sur la comparaison des résultats obtenus par le calcul " exact " avec ceux déduits des différentes méthodes approchées dans le but de valider leur utilisation ainsi que leur précision. Cette comparaison nous a permis de développer une méthodologie d'optimisation apportant des améliorations au calcul des méthodes approchées (CEN et CMA) permettant ainsi une meilleure description du rayonnement. Enfin, ce travail présente le développement d'un modèle d'arc libre 2D axisymétrique résolvant les équations de Navier-Stockes et de Maxwell par la méthode des volumes finis. Celui-ci permet une comparaison entre la méthode du CEN et la méthode P1 qui tient compte de l'absorption du rayonnement des zones froidesIn the simulation of electrical arc, the representation of radiative contribution is essential to provide a satisfactory description of the thermal behavior of the plasma. The accurate prediction of the radiative emission is essential to determine the evolution of the arc temperature. For a precise description of radiative effect, a resolution of the Radiative Transfer Equation (RTE) , is necessary necessary with knowledge of the absorption coefficient. Unfortunatly, the complexity of this coefficient - dependent on temperature and wavelenghth- makes this equation impossible to solve in term of computational cost. This is why many approximative methods are developed to simplify the calculation of the radiative properties. In this work, we have carried out a detailed description of the spectrum of an air plasma with about 7.106 points on frequency. From this description, we have calculated the divergence of the radiative flux either from the net emission coefficient (NEC) based on a geometric simplification of the plasma, or from the mean absorption coefficients (MAC) calculated after a division of the spectrum into 6 intervals in which we have used different mean functions (Classic, Planck, Planck Modified and Rosseland), or from an exact calculation corresponding to a direct solution of the RTE. This is why many approximative methods were developed to reduce numerical demands . The calculations have been done for 9 simplified configurations in 1D assuming a cylindrical plasma for which the temperature profile varies only with the radius. The different steps of the work are presented and highlight the influence of several parameters such as the temperature profile, the pressure, the copper vapors.... A great part of this work deals with the comparison between the results obtained from the exact resolution with the results deduced from the other approaches in order to validate the use and the accuracy of the different methods. This comparison allowed us to develop an optimization methodology providing improvements to the calculation of the approximate methods (NEC and MAC) allowing a better description of the radiative properties. Finally, this work presents the development of an axisymmetric 2D free-burning arc model solving the Navier-Stockes and Maxwell equations by the finite volume method. This model allows a comparison between the NEC method and the P1 method which takes into account the absorption of radiation in the cold areas
21
Colomer, Rey Guillem. "Numerical methods for radiative heat transfer." Doctoral thesis, Universitat Politècnica de Catalunya, 2006. http://hdl.handle.net/10803/6691.
Анотація:
L'objectiu principal d'aquesta tesi es l'estudi de la transferència d'energia per radiació. Per aquest motiu, s'ha estudiat la fenomenologia bàsica de la transferencia de calor per radiació. Tenint en compte el tipus d'equació que descriu aquesta transferència d'energia, aquesta tesi esta encarada als metodes numèrics que ens permetran incorporar la radiació en els nostres càlculs. Donat que aquest és el primer treball d'aquestes característiques en el grup de recerca CTTC ("Centre Tecnològic de Transferència de Calor"), està limitat a geometries senzilles, cartesianes i cilíndriques. En el capítol 1 s'exposa una breu introducció a la transferència d'energia per radiació, i una explicació de les equacions que la governen. Es tracta de l'equació del transport radiatiu, formulada en termes dels coeficients d'absorció i de dispersió, i l'equació de l'energia. També s'indica quan cal tenir en compte aquest fenòmen, i a més a més, es defineixen totes les magnituds i conceptes que s'han utilitzat en aquesta tesi. També es dóna una breu descripció d'algunes simplificacions que es poden fer a les equacions governants.
El mètode de les radiositats s'explica en el capítol 2. També s'hi descriu un procediment numèric que permet calcular els factors de vista en geometries amb simetria cilíndrica, i es presenten resultats obtinguts amb el mètode descrit. Tot i que aquest capítol està una mica deslligat de la resta de la tesi, l'algoritme ideat per tractar geometries tridimensionals amb un temps computacional molt proper al de geometries bidimensionals, sense un increment de memòria apreciable, dóna uns resultats prou bons com per formar part de la tesi.
El mètode de les ordenades discretes (DOM) es detalla en el capítol 3. L'aspecte més important d'aquest mètode es l'elecció del conjunt d'ordenades per integrar l'equació del transport radiatiu. S'enumeren quines propietats han d'acomplir aquests conjunts. S'hi explica amb detall la discretització de la equació del transport radiatiu, tant en coordenades cartesianes com en cilíndriques. Es presenten també alguns resultats ilustratius obtinguts amb aquest mètode.
En el moment en que es vol resoldre un problema real, cal tenir present que el coeficients d'absorció pot dependre bruscament de la longitud d'ona de la radiació. En aquesta tesi s'ha considerat aquesta dependència amb especial interés, en el capítol 4. Aquest interès ha motivat una recerca bibliogràfica sobre la modelització aquesta forta dependència espectral del coeficient d'absorció. Aquesta recerca s'ha dirigit també a l'estudi dels diferents models numèrics existents capaços d'abordar-la, i de resoldre la equació del transport radiatiu en aquestes condicions. Es descriuen diversos mètodes, i, d'aquests, se n'han implementat dos: el mètode de la suma ponderada de gasos grisos (WSGG), i el mètode de la suma de gasos grisos ponderada per línies espectrals (SLW). S'hi presenten també resultats ilustratius.
S'han realitzat multitud de proves en el codi numèric resultant de l'elaboració d'aquesta tesi. Tenint en compte els resultats obtinguts, es pot dir que els objectius proposats a l'inici de la tesi s'han acomplert. Com a demostració de la utilitat del codi resultant, aquest ha estat integrat en un codi de proposit general (DPC), resultat del treball de molts investigadors en els darrers anys.
Aquesta esmentada integració permet la resolució de problemes combinats de transferència de calor, analitzats en els capítols 5 i 6, on la radiació s'acobla amb la transferència de calor per convecció. La influència de la radiació en la transferència total de calor s'estudia en el capítol 5, publicat a la International Journal of Heat and Mass Transfer, volum 47 (núm. 2), pàg. 257-269, 2004. En el capítol 6, s'analitza l'efecte d'alguns paràmetres del mètode SLW en un problema combinat de transferència de calor. Aquest capítol s'ha enviat a la revista Journal of Quantitative Spectroscopy and Radiative Transfer, per què en consideri la publicació.
The main objective of the present thesis is to study the energy transfer by means of radiation. Therefore, the basic phenomenology of radiative heat transfer has been studied. However, considering the nature of the equation that describes such energy transfer, this work is focussed on the numerical methods which will allow us to take radiation into account, for both transparent and participating media. Being this the first effort within the CTTC ("Centre Tecnològic de Transferència de Calor") research group on this subject, it is limited to simple cartesian and cylindrical geometries.
For this purpose, chapter 1 contains an introduction to radiative energy transfer and the basic equations that govern radiative transfer are discussed. These are the radiative transfer equation, formulated in terms of the absorption and scattering coefficients, and the energy equation. It is also given a discussion on when this mode of energy transfer should be considered. In this chapter are also defined all of the magnitudes and concepts used throughout this work. It ends with a brief description of some approximate methods to take radiation into account.
The Radiosity Irradiosity Method is introduced in chapter 2. In this chapter it is also described a numerical method to calculate the view factors for axial symmetric geometries. The main results obtained in such geometries are also presented. Although a little disconnected from the rest of the present thesis, the algorithm used to handle "de facto"' three dimensional geometries with computation time just a little longer than two dimensional cases, with no additional memory consumption, is considered worthy enough to be included in this work.
In chapter 3, the Discrete Ordinates Method (DOM) is detailed. The fundamental aspect of this method is the choice of an ordinate set to integrate the radiative transfer equation. The characterization of such valuable ordinate sets is laid out properly. The discretization of the radiative transfer equation is explained in etail. The direct solution procedure is also outlined. Finally, illustrative results obtained with the DOM under several conditions are presented.
In the moment we wish to solve real problems, we face the fact that the absorption and scattering coefficients depend strongly on radiation wavelength. In the present thesis, special emphasis has been placed on studying the radiative properties of real gases in chapter 4. This interest resulted on a bibliographical research on how the wavenumber dependence of the absorption coefficient is modeled and estimated. Furthermore, this bibliographical research was focussed also on numerical models able to handle such wavenumber dependence. Several methods are discussed, and two of them, namely the Weighted Sum of Gray Gases (WSGG) and the Spectral Line Weighted sum of gray gases (SLW), have been implemented to perform non gray calculations. Some significant results are shown.
Plenty of tests have been performed to the numerical code that resulted from the elaboration of this thesis. According to the results obtained, the objectives proposed in this thesis have been satisfied. As a demonstration of the usefulness of the implemented code, it has been succesfully integrated to a general purpose computational fluid dynamics code (DPC), fruit of the effort of many researchers during many years.
Results of the above integration lead to the resolution of combined heat transfer problems, that are analyzed in chapters 5 and 6, where radiative heat transfer is coupled to convection heat transfer. The effect of radiation on the total heat transfer is studied in chapter 5, which has been published as International Journal of Heat and Mass Transfer, volume 47 (issue 2), pages 257--269, year 2004. In chapter 6, the impact of some parameters of the SLW model on a combined heat transfer problem is analyzed. This chapter has been submitted for publication at the Journal of Quantitative Spectroscopy and Radiative Transfer.
22
Issenmann, B. "Déformations d'interfaces fluides par la pression de radiation acoustique." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2007. http://tel.archives-ouvertes.fr/tel-00283449.
Анотація:
Nous avons étudié expérimentalement la statique et la dynamique des déformations d'interfaces fluides induites par la pression de radiation acoustique d'un faisceau focalisé. Deux situations expérimentales ont été plus particulièrement étudiées : – nous avons réalisé un travail de métrologie pour tester pour la première fois la validité de l'expression de la pression de radiation acoustique sur des interfaces acoustiquement transparentes. Ce test a nécessité de mettre au point une technique de mesure de tension interfaciale in situ et sans contact utilisant la pression de radiation acoustique et de modéliser précisément la dynamique de la déformation d'interface. – lorsque l'interface liquide est parfaitement réfléchissante, une cavité acoustique se forme entre l'interface et l'émetteur, qui induit un fort couplage entre la propagation des ondes ultrasonores et la déformation de l'interface. Nous avons montré que ce couplage donne lieu à des phénomènes d'hystérésis, d'atténuation d'ondes capillaires par rétroaction passive, et d'oscillations spontanées de l'interface liquide.
23
Issenmann, Bruno. "Déformations d'interfaces fluides par la pression de radiation acoustique." Bordeaux 1, 2007. http://www.theses.fr/2007BOR13505.
Анотація:
Nous avons étudié expérimentalement la statique et la dynamique des déformations d'interfaces fluides par la pression de radiation acoustique d'un faisceau focalisé. Deux situations expérimentales ont été plus particulièrement étudiées : - Nous avons réalisé un travail de métrologie pour tester pour la première fois la validité de l'expression de la pression de radiation acoustique sur des interfaces acoustiquement transparentes. Ce test a nécessité de mettre au point une technique de mesure de tension interfaciale in situ et sans contact utilisant la pression de radiation acoustique et de modéliser précisément la dynamique de la déformation d'interface. -Lorsque l'interface liquide est parfaitement réfléchissante, une cavité acoustique se forme entre l'interface et l'émetteur, qui induit un fort couplage entre la propagation des ondes ultrasonores et la déformation de l'interface.
24
Semlitsch, Bernhard. "Advanced Ray Tracing Techniques for Simulation of Thermal Radiation in Fluids." Thesis, KTH, Mekanik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-150111.
Анотація:
For modeling thermal heat transfer, not only the effects of convection and conduction are relevant, but also thermal and visible radiation. Radiation is especially important for setups with large temperature differences, as well as for interaction with external light sources.Common computational fluid dynamic models usually treat radiation transport as a minor effect, that can be handled by simplified algorithms. All these normal models, e.g. surface to surface model, discrete transfer model, P_N method, discrete ordinates model, exhibit disadvantages in the computing performance and the physical modeling. Hence, there are many technical applications, where the fluid simulation are limited both in accuracy and calculation time by the available radiation model. As exemplary cases combustion chambers, smoke and soot creation, solar power generation, UV water disinfection, condensation in car headlights, fusion and fission reactor chambers, electric arc movement, as well as low-emissivity glass windows can be named. In the fields investigating radiation as main effect, e.g. cinematic 3d animation or illumination simulation for lamps and workspaces, the mentioned methods are not in use anymore as ray tracing is the first choice. In this work, the existing methods for ray tracing were adapted and implemented with the goal to interact with fluid flow simulations and replace existing radiation modeling. This can be regarded as innovative, interdisciplinary method for the interaction of fluids and solids with radiation, incorporating physical effects that could not be included in previous simulations. While in usual light calculations, the geometry exists solely in the form of surfaces and their triangulation, fluid flow requires volumetric calculation grids. Hence, methods are implemented that actually use the volumetric grid, and incorporate volumetric effects with little additional effort. Spectral volumetric path tracing with Monte Carlo integrated, importance sampled emission was hence the method of choice for this work. The implemented ray tracer is able to emit radiation from point sources, geometric surfaces, as well as from volumetric sources. Spectral dependence of material values is treated using radiation bands with hardly no increase of calculation time, whereas in all other models, the calculation time scales linearly with the amount of bands. Direct, diffuse and mixed surface reflection is modeled. The volumetric refraction index is implemented, so refraction is modeled, even including partial and total reflexion. The focusing of lenses or mirror systems can hence be simulated satisfactory, which cannot be treated sufficiently by any other radiation model. Surface and volumetric absorption are implemented, as well as surface and volumetric scattering effects. The radiation emission can be caused by a temperature field at surfaces and volumes. These fields are imported from software calculating the fluid and the thermal system. Ray tracing results in volumetric and surface heat sources that can be returned to the original code, and their effect further calculations. This coupling was implemented and tested with the commercial computational fluid dynamics code Fluent, using its plug-in interface. As most of Fluent's radiation models are only performed after a fixed number of implicit flow and turbulence iterations, no further disadvantages or limitations occur, that are not as well existing for the existing radiation simulations. A fully implicit treatment of radiation is unlikely to be performed, as stability is already sufficient for most applications. Of course, systems containing only heat sources caused by light and no secondary heat radiation can be treated by the implemented ray tracer with high performance. The implemented ray tracer is validated with analytically solved systems, and compared to quantitative simulation results of other simulation methods. Also, the scattering effects are validated against experimental and simulation results from literature. The observed calculation performance is similar or faster then for standard models with geometries of approximately 150000 volume elements, while the modeling is done more accurately. For larger models, even larger advantages can be expected.
25
Yang, Chenxing. "Simulation studies of liquids, supercritical fluids and radiation damage effects." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/24858.
Анотація:
The work in this thesis aims to gain fundamental understanding of several important types of disordered systems, including liquids, supercritical fluids and amorphous solids on the basis of extensive molecular dynamics simulations. I begin with studying the diffusion in amorphous zirconolite, a potential waste form to encapsulate highly radioactive nuclear waste. I find that amorphization has a dramatic effect for diffusion. Interestingly and differently from previous understanding, diffusion increases as a result of amorphization at constant density. Another interesting insight is related to different response of diffusion of different atomic species to structural disorder. I calculate activation energies and diffusion pre-factors which can be used to predict long-term diffusion properties in this system. This improves our understanding of how waste forms operate and provides a quantitative tool to predict their performance. I subsequently study the effects of phase coexistence and phase decomposition in Y-stabilized zirconia, the system of interest in many industrial applications including in encapsulating nuclear waste due to its exceptional resistance to radiation damage. For the first time I show how the microstructure emerges and evolves in this system and demonstrate its importance for self-diffusion and other properties. This has not been observed before and is important for better understanding of existing experiments and planning the new ones. I subsequently address dynamical properties of subcritical liquids and supercritical fluids. I start with developing a new empirical potential for CO2 with improved performance. Using this and other potentials, I simulate the properties of supercritical H2O, CO2 and CH4 and map their Frenkel lines in the supercritical region of the phase diagram. I observe that the Frenkel line for CO2 coincides with experimentally found maxima of solubility and explain this finding by noting that the Frenkel line corresponds to the optimal combination of density and temperature where the density is maximal and the diffusion is still in the fast gas-like regime. This can serve as a guide in future applications of supercritical fluids and will result in their more efficient use in dissolving and extracting applications. I extend my study to collective modes in liquids. Here, my simulations provide first direct evidence that a gap emerges and evolves in the reciprocal space in transverse spectra of liquids. I show that the gap increases with temperature and is inversely proportional to liquid relaxation time. Interestingly, the gap emerges and evolves not only in subcritical liquids but also in supercritical fluids as long as they are below the Frenkel line. Given the importance of phonons in condensed matter physics and other areas of physics, I propose that the discovery of the gap represents a paradigm change. There is an active interest in the dynamics of liquids and supercritical fluids, and I therefore hope that my results will quickly stimulate high-temperature and high-pressure experiments aimed at detecting and studying the gap in several important systems.
26
Roberts, Sarah Marie. "Three-dimensional radiation flux source areas in urban areas." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/28541.
Анотація:
Outdoor physical scale modeling is a potentially powerful compromise between the more common numerical and observational techniques to understand urban climates, because it incorporates the experimental control of physical and numerical modeling but is subject to the real complexities associated with natural environmental forcing. An outdoor physical model of simple concrete “buildings” was constructed to simulate an “urban” array in three different configurations. Observations of both facet surface temperatures and of radiation fluxes within and above the urban canopy layer investigate the impact of surface-sensor-sun relations on measured radiation flux source areas. Field measurements from the scale model were complemented by analyses using two numerical models. The combined results guide development of a protocol to guide the optimal siting of radiation sensors in measurement projects of the urban surface energy balance. The siting protocol considers both the influence of surface structure and orientation on radiation source areas and on the streamwise dimensions of the equivalent turbulent flux source area ‘seen’ by turbulence sensors. Observed thermal patterns from the scale model compare well with those at similar full-scale urban sites. Measurements of the spatial variation in radiation fluxes reveal that measurement heights above approximately 2.5 times the mean building height generate uniform flux density patterns. An agreement index used to quantify the strength of correspondence between what a sensor ‘sees’ of an urban surface and the actual surface morphology demonstrates that measurement locations near a street intersection give results closest to those sought to represent the local scale. Relations derived to describe the measurement height at which the radiation flux source area of a radiation sensor encompasses the source area of a turbulent flux sensor, reveal the common practice of co-locating tower-based radiation and turbulence flux sensors is often not sufficient to ensure their overlap. To match radiation flux source areas to the streamwise extent of turbulence flux source areas, it is recommended that radiation flux sensors be sited so as to contain the location of the maximum turbulent flux source weight. This suggests that radiation sensor(s) should be about two- to three times higher in elevation than the turbulence sensor(s).
27
Otter, Stephen. "Simulation of the radiative flux at the Martian surface between 180 and 1100 nm." Thesis, Open University, 2010. http://oro.open.ac.uk/54218/.
Анотація:
A multi-layer radiative transfer model of the atmosphere of Mars, the UVIS simulation, has been created to simulate the non-ionising radiative flux at the surface of Mars. The simulation operates over the range 180 - 1100 nm and determines the diffuse component of the surface flux using the delta-Eddington approximation. Latitude, l, and areocentric longitude, Ls, dependent abundance models of the dust and ice cloud aerosols and of the gaseous species ozone and water vapour are incorporated. Alternative aerosol distributions are also used corresponding to observations made by the Thermal Emission Spectrometer onboard Mars Global Surveyor. Studies of the variation in surface flux in response to increasing dust optical depth predict reduced surface intensities at UV wavelengths (180 - 400 nm) but at longer wavelengths the surface flux exhibits a local increase relative to the initial incident flux at optical depths < 2.5 for VIS wavelengths (401 - 750 nm) and < 6.0 for NIR wavelengths (751 - 1100 nm). This is explained in terms of the influence of aerosol scattering parameters. Enhancement of the total surface flux by -20% or greater is shown to occur at latitude and Ls values corresponding to the presence of the aphelion cloud belt and during the annual dust maximum. The potential of a surface based spectrometer to be utilised as a means of detecting the trace gases, ozone, hydrogen peroxide and methane in the atmosphere is assessed. Ozone proves the only suitable candidate and the spatial and seasonal distribution of ozone is discussed in the context of potential instrument deployment sites. The effects of varying aerosol scattering parameters on the surface flux is characterised and changes in aerosol scattering parameter 'values of < 5% are shown to be theoretically detectable by a spectrometer of sensitivity 1.0x10-2 Wm-2nm-1.
28
Machado, Antonio Jaschke. "Distribuição espacial do fluxo radiativo em ondas longas na Região Metropolitana de São Paulo." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/8/8135/tde-04122009-163851/.
Анотація:
Muitas vezes, é necessária uma melhor compreensão a respeito da distribuição espacial do fluxo radiativo em ondas longas. Este fluxo é em geral representado pelos estudos em climatologia urbana. Alternativamente, é representado como um estudo interdisciplinar. Novos procedimentos são considerados, porque a superfície urbana é composta de uma variedade muito ampla de elementos. Incluindo um conjunto amostral baseado em observações de transetos móveis automáticos através de várias travessias na Região Metropolitana de São Paulo, além de estimativas paramétricas e considerações de análise escalar. Olhando os objetivos da tese, é fornecida uma contribuição ao desenvolvimento metodológico nos trabalhos de campo, em particular aos climatologistas e planejadores urbanos. Os resultados obtidos implementam a discussão a respeito dos ambientes modificados pelo homem. É apresentada a natureza do fenômeno estudado e o método aplicado é focalizado. São analisados os aspectos essenciais que contribuem para a distribuição do fluxo radiativo nos canyons urbanos. Como a expressão do balanço de energia é uma importante ferramenta para a compreensão do clima urbano, estimativas dos fluxos turbulentos também são considerados.Many times, it is necessary a better comprehension about the spatial distribution of the longwave radiative flux. This flux is represented just as much by the studies on urban climatology. Alternatively, it is represented as an interdisciplinary study. New procedures are considered, because the urban surface is made up of widely varying elements. Including a sampled dataset based on automatic mobile transects observations through several traverses in the Metropolitan Area of São Paulo, besides parametric estimates and scalar analysis considerations. Regarding the thesis objectives, it is given a contribution to the method development in the fieldworks, in particular to the urban climatologists and urban planners. The obtained results improve the discussion on the manmodified environments. It is explained the nature of the studied phenomena and the applied method it is focused. It is analyzed the essential aspects that contibute to the radiative flux distribution in the urban canyons. As the energy balance expresion is an important framework to the comprehension of the urban climate, estimates of the turbulent fluxes are also considered.
29
Nasri, Nacer. "Étude thermique du comportement en régime transitoire d'une matrice poreuse soumise à un flux radiatif : application a la conversion thermique de l'énergie solaire." Nancy 1, 1994. http://www.theses.fr/1994NAN10134.
Анотація:
Le transfert de chaleur entre un fluide et un milieu poreux revêt un intérêt important dans de nombreux processus industriels tels que les régénérateurs, les réacteurs catalytiques et nucléaires et plus récemment les collecteurs solaires. Les travaux présentés constituent une contribution à l'étude des transferts couples de chaleur au sein d'un milieu poreux soumis à un flux radiatif et traversé par un fluide gazeux. Une fois exposées, les approches classiques, on détermine, à partir d'une analyse théorique, les champs de température du milieu solide et du fluide au cours de leurs phases d'évolution dynamique. Par la suite, dans le cadre d'une représentation concrète, l'étude détaillée d'un capteur à absorbeur poreux conduit à la formulation mathématique de trois modèles d'évolution spécifiques au régime transitoire. Pour confirmer la validité de l'analyse, des expériences sont conduites dans les conditions correspondant au modèle. Par ailleurs, une importance particulière est donnée au coefficient d'échange volumique interne au milieu poreux. On examine ainsi à travers des développements simples quelques méthodes conduisant à sa détermination en admettant qu'elles représentent une approche immédiate dans un cadre de conditions aux limites très restrictives. Les équations d'énergie couplées pour le gaz et le milieu poreux sont linearisées pour être résolues analytiquement par leur formulation intégrale, plus numériquement sur une base plus complète
30
Bebeau, Robert R. "Simulation of Radiation Flux from Thermal Fluid in Origami Tubes." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7666.
Анотація:
Spacecraft in orbit experience temperature swings close to 240 K as the craft passes from the shadow of the Earth into direct sunlight. To regulate the craft’s internal energy, large radiators eject unwanted energy into space using radiation transfer. The amount of radiation emitted is directly related to the topology of the radiator design. Deformable structures such as those made with origami tessellation patterns offer a mechanism to control the quantity of energy being emitted by varying the radiator shape. Three such patterns, the Waterbomb, Huffman Waterbomb, and Huffman Stars-Triangles, can be folded into tubes. Origami tubes offer greater control and simplicity of design than flat radiators. Using FLUENT, Origami Simulator, and Solidworks to first simulate and then analyze the flow of a thermal fluid through the patterns and the radiation emitted from the created bodies, it was determined that the Waterbomb pattern achieved a 17.6 percent difference in emitted radiation, over a 2 percent change in fold. The Huffman Waterbomb pattern displayed a 42.7 percent difference in emitted radiation over a 20 percent change of fold. The simulations demonstrated both the feasibility and benefits of the origami designed tubes.
31
Gagnier, Damien. "Dynamique des étoiles massives proches de la rotation critique." Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30159.
Анотація:
La rotation joue un rôle majeur sur la dynamique, la structure et l'évolution séculaire des étoiles massives, souvent rotateurs rapides. Elle implique le mélange des éléments chimiques synthétisés dans leur cœur convectif, et la redistribution du moment cinétique dans leur enveloppe radiative. La rotation influence également le vent radiatif présent à leur surface, et modifie ainsi les pertes de masse et de moment cinétique associées. L'objectif de ce travail de thèse est multiple : nous cherchons à déterminer le rôle de la rotation sur les pertes de masse et de moment cinétique associées aux vents radiatifs des étoiles massives, comprendre le rôle de ces vents radiatifs sur leur évolution rotationnelle séculaire, et déterminer les implications d'une perte de moment cinétique sur la dynamique de l'enveloppe radiative de ces étoiles. Nous montrons que deux régimes de vent peuvent exister, l'un d'eux résulte en un fort flux de masse équatorial, donc en une forte perte de moment cinétique. Cette perte accrue de moment cinétique peut empêcher les étoiles massives d'atteindre une rotation critique avant la fin de la séquence principale. Enfin, l'étude du couplage entre les vents radiatifs et la dynamique de l'enveloppe radiative des étoiles massives en rotation montre que la couche de Stewartson est une caractéristique clé de l'écoulement pour le transport des éléments chimiques entre le cœur convectif et la surface des étoiles massivesRotation plays a major role in the dynamics, structure and secular evolution of, often rapidly rotating, massive stars. It leads to the mixing of chemical elements synthesised in their convective core, and to the transport of angular momentum in their radiative envelope. Rotation also influences the radiation-driven wind on their surface, and thus modifies the associated losses of mass and angular momentum. The objective of this thesis is multifold: we seek to determine the role of rotation on the mass and angular momentum losses associated with massive stars radiation-driven winds, to understand the role of such radiation-driven winds on their secular rotational evolution, and to determine the implications of a loss of angular momentum on the dynamics of the radiative envelope of these stars. We show that two different wind regimes can exist, one of them results in a strong equatorial mass flux, and thus in a high angular momentum loss rate. Such increased angular momentum loss may prevent massive stars from reaching critical rotation before the end of the main sequence. Regarding the coupling between radiative winds and the dynamics of the radiative envelope of massive rotating stars, we show that the Stewartson layer is a key component for the transport of chemical elements between the convective core and the surface of massive stars
32
Sun, Xue-Zhong. "Fast infrared spectroscopy in supercritical fluids." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311743.
33
Itjoko, Serge. "Optimisation des propriétés radiatives de revêtements alumine/luminophores pour lampes fluorescentes." Paris 6, 2008. http://www.theses.fr/2008PA066316.
Анотація:
Ce travail a pour objectif l’optimisation de l’émission lumineuse des revêtements fluorescents de tubes à décharge. Premièrement, nous avons construit un modèle permettant de rendre compte de l’émission visible dans un système hétérogène dont la géométrie se rapproche de celle des revêtements fluorescents. Ce modèle, basé sur la théorie du Transfert Radiatif, permet de calculer les coefficients de réflexion (R), de transmission (T), et le flux émis par la couche. Les simulations de ce dernier montrent qu’on peut l’optimiser par différents paramètres morphologiques de la couche. Dans un deuxième temps, nous avons caractérisé des revêtements existants afin de déterminer leurs paramètres morphologiques et leurs propriétés d’émission, données indispensables à notre modèle. Les simulations de R et T sont en accord quantitatif et qualitatif avec les mesures. Après validation par des mesures d’émission, ce modèle devrait permettre de simuler la lumière émise par divers revêtements fluorescents.
34
Mathis, Stéphane. "Effet du mélange interne sur l'évolution des étoiles : processus de transport dans les zones radiatives." Paris 11, 2005. http://www.theses.fr/2005PA112118.
Анотація:
Cette thèse présente une étude détaillée du mélange rotationnel, c'est à dire des processus de transport et de mélange dûs à la rotation différentielle dans les zones radiatives des étoiles. Tout d'abord, nous examinons le mélange rotationnel de type I: le moment cinétique et les éléments chimiques y sont transportés par la circulation méridienne induite par le déséquilibre thermique engendré par la rotation et par la turbulence dûe aux instabilités de cisaillement. Nous généralisons sa modélisation actuelle en traitant simultanément le coeur des régions radiatives et leur(s) interface(s) avec les régions convectives, les tachoclines. Puis, nous dérivons une nouvelle prescription pour le transport turbulent horizontal en utilisant les résultats des expériences de laboratoire de type Couette-Taylor qui permettent d'étudier la turbulence engendrée par la rotation différentielle. Cependant, la prise en compte de ces deux mécanismes dans les modèles conduisent à des résultats en désaccord avec les observations pour les étoiles de type solaire. Ces dernières ont en effet été ralenties au cours de leur évolution et les processus de transport dûs à la rotation y sont donc moins efficaces. Nous étudions alors le mélange rotationnel de type II où les composés chimiques sont toujours transportés par la circulation méridienne et par la turbulence, mais où le transport du moment cinétique est assuré par un agent de transport plus efficace, le champ magnétique ou les ondes internes que nous introduisons de manière consistante. Les applications astrophysiques sont présentées à la fin de chaque chapitreThis thesis presents a detailed study of transport and mixing processes due to differential rotation in stellar radiation zones, which are called rotational mixing. First, we study the rotational mixing of type I where angular momentum and chemical species are transported by the meridional circulation due to the thermal imbalance caused by rotation and by the turbulence due to shear instabilities. We generalize its present modelling to treat simultaneously the bulk of radiation zones and their interfaces with convective zones, the tachoclines. Then, we present a new prescription for the horizontal turbulent transport which is derived from Couette-Taylor laboratory experiments that allow to study turbulence induced by differential rotation. However, the introduction of those two mechanisms in stellar models leads to results which do not agree with observations of solar type stars, because these have been slowed down by the wind during their evolution and hence the rotational processes are less efficient. Therefore, we consider the rotational mixing of type II where chemicals are still transported by meridional circulation and turbulence, but where angular momentum is carried by another process, the magnetic field or the internal waves which are introduced in a consistent way. The astrophysical applications are presented at the end of each chapter
35
Burnett, Benjamin F. "Exploratory Eddy Covariance Measurements of Surface Heat and CO2 Fluxes in the Roughness Sublayer of an Urban Environment." PDXScholar, 2010. https://pdxscholar.library.pdx.edu/open_access_etds/401.
Анотація:
In this study eddy covariance was used to measure sensible heat, latent heat, and carbon dioxide fluxes for the months of August, September, and October of 2009 within the roughness sublayer (RSL) of the urban center of Portland, OR. Vehicle traffic and solar radiation were also measured for the month of October. Flux measurements were compared with measurements from other urban areas as a test of reasonableness. CO₂ fluxes were nearly always positive and were strongly correlated with the weekday diurnal traffic cycle. CO₂ fluxes averaged 6.6 μmol/m^²s, which is less than other published measurements in urban areas. Sensible and latent heat fluxes followed the expected diurnal profile associated with solar radiation. Average sensible heat flux decreased as the season changed from summer to fall, moving from an average of 39 W/m^² in August to 12 W/m^² in October. A corresponding increase in latent heat flux was observed during this period, changing from an average of 10 W/m^² in August to 17 W/m^² in October. Heat flux behavior and amplitude was consistent with other urban measurements, though amplitude varies considerably from city to city. Stationarity was shown to positively influence measured CO₂ fluxes, but to have little effect on measured heat fluxes. Preliminary comparisons of October sensible heat and CO₂ fluxes to an inventory-based estimate of vehicle emissions indicate that eddy covariance measurements underestimate the true fluxes by 50%.
36
MUNIZ, RAFAEL O. R. "Desenvolvimento de um simulador antropomorfico para simulacao e medidas de dose e fluxo de neutrons na instalacao para estudos em BNCT." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9559.
Анотація:
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
37
FELIPPE, MONICA T. S. D. "Estudo de fluxo de oxido nitroso (Nsub(2)O) regional na bacia amazonica." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9547.
Анотація:
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
38
De, Almeida Jose Sergio. "Measurement of radiation in complex geometries and comparison with calculational techniques." Thesis, Loughborough University, 2000. https://dspace.lboro.ac.uk/2134/36072.
Анотація:
During the development of flight tests of a spacecraft, heat exchange occurs among the many physically separated subsystem surfaces through the phenomenon of thermal radiation. Considering the increasing complexity of the geometrical forms and shapes in the design of such systems, the monitoring and control of the radiative heat fluxes taking place in the multi-reflecting, absorbing and emitting heat transfer environment are very critical. Because the analytical solution of thermal radiation in such geometrically complex three-dimensional systems is not practical, extensive numerical modelling techniques are widely used to predict radiative heat fluxes on the many thermally active surfaces. From experience, it is found that this can be very difficult and not at all commensurate with fast feedback unless the analysis is from a simple system layout. Considering that a relatively new approach dedicated to the basic analysis of radiative heat flux has been developed by the heat transfer community as a numerical approximation called the Discrete Ordinates Method (DOM), a first question did arise in terms of how well an enhanced and more comprehensive formulation based on this concept would fulfil the task of achieving faster results whilst still accurately predicting radiative heat transfer in three-dimensional, more complex geometries.
39
Thiagarajah, Jay Ram. "Structure and function relationships in the colon : the role of the pericryptal sheath." Thesis, King's College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368218.
40
Coleman, Peter John. "Plasma protein flux across arterial walls in vivo, with relation to atherosclerosis." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307647.
41
Iles, Roger Henry Anthony. "A study of relativistic electron flux enhancements in the earth's outer radiation belt." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270953.
42
Vidhi, Rachana. "Organic Fluids and Passive Cooling in a Supercritical Rankine Cycle for Power Generation from Low Grade Heat Sources." Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5322.
Анотація:
Low grade heat sources have a large amount of thermal energy content. Due to low temperature, the conventional power generation technologies result in lower efficiency and hence cannot be used. In order to efficiently generate power, alternate methods need to be used. In this study, a supercritical organic Rankine cycle was used for heat source temperatures varying from 125°C to 200°C. Organic refrigerants with zero ozone depletion potential and their mixtures were selected as working fluid for this study while the cooling water temperature was changed from 10-25°C. Operating pressure of the cycle has been optimized for each fluid at every heat source temperature to obtain the highest thermal efficiency. Energy and exergy efficiencies of the thermodynamic cycle have been obtained as a function of heat source temperature.
Efficiency of a thermodynamic cycle depends significantly on the sink temperature. At areas where water cooling is not available and ambient air temperature is high, efficient power generation from low grade heat sources may be a challenge. Use of passive cooling systems coupled with the condenser was studied, so that lower sink temperatures could be obtained. Underground tunnels, buried at a depth of few meters, were used as earth-air-heat-exchanger (EAHE) through which hot ambient air was passed. It was observed that the air temperature could be lowered by 5-10°C in the EAHE. Vertical pipes were used to lower the temperature of water by 5°C by passing it underground. Nocturnal cooling of stored water has been studied that can be used to cool the working fluid in the thermodynamic cycle. It was observed that the water temperature can be lowered by 10-20°C during the night when it is allowed to cool. The amount of water lost was calculated and was found to be approximately 0.1% over 10 days.
The different passive cooling systems were studied separately and their effects on the efficiency of the thermodynamic cycle were investigated. They were then combined into a novel condenser design that uses passive cooling technology to cool the working fluid that was selected in the first part of the study. It was observed that the efficiency of the cycle improved by 2-2.5% when passive cooling system was used.
43
George, Tyrel Daniel Frank. "Design and testing of long-lifetime active sensor arrays for in-core multi-dimensional flux measurements." Thesis, Kansas State University, 2016. http://hdl.handle.net/2097/35229.
Анотація:
Master of ScienceDepartment of Mechanical and Nuclear Engineering
Douglas S. McGregor
Fission chambers are a common type of detector used to determine the neutron flux and power of a nuclear reactor. Due to the limited space and high neutron flux in a reactor core, it is difficult to perform real-time flux measurements with present-day in-core instrumentation. Micro-pocket fission detectors, or MPFDs, are relatively small in size and have low neutron sensitivity while retaining a large neutron to gamma ray discrimination ratio, thereby, allowing them to be used as active neutron flux monitors inside a nuclear reactor core. The micro-pocket fission chamber allows for multiple detectors to be inserted into a flux port or other available openings within the nuclear reactor core. Any material used to construct the MPFD must be rugged and capable of sustaining radiation damage for long periods of time. Each calibrated MPFD provides measurements of the flux for a discrete location. The size of these detectors allows for a spatial map of the flux to be developed, enabling real-time analysis of core burnup, power peaking, and rod shadowing. Small diameter thermocouples can be included with the array to also measure the temperature at each location. The following document details the research and development of MPFDs for long term use in nuclear power reactors. Previous MPFD designs were improved, miniaturized, and optimized for long term operations in reactor test ports designed for passive measurements of fluence using iron wires. Detector chambers with dimensions of 0.08 in x 0.06 in x 0.04 in were attached to a common cathode and individual anodes to construct an array of the MPFDs. Each array was tested at the Kansas State University TRIGA Mark II nuclear reactor to demonstrate functionality. The linear response in reactor power was measured. These arrays have also demonstrated reactor power tracking by following reactivity changes in steady state operations and reactor pulsing events. Stability testing showed consistent operation at 100 kW for several hours. The MPFDs have been demonstrated to be a viable technology for in-core measurements.
44
Leray, Cedric. "Etude du comportement thermique et thermomécanique des récepteurs solaires sous haut flux radiatif." Thesis, Perpignan, 2017. http://www.theses.fr/2017PERP0003/document.
Анотація:
Dans le contexte énergétique qui se profile, la production d’électricité par voie solaire thermodynamique s’avère une solution prometteuse, que ce soit pour des considérations économiques, d’échelle de production ou environnementales. Une voie d’amélioration du rendement des centrales solaires à tour consiste à utiliser des cycles thermodynamiques à haut rendement type cycles combinés. Cela nécessite de pouvoir fournir un fluide de travail pressurisé à très haute température (10bar et 1000°C minimum). Ce manuscrit présente les travaux menés afin de développer et de viabiliser un concept d’absorbeur solaire surfacique modulaire en céramique (carbure de silicium) capable de répondre à ces exigences. Le choix du carbure de silicium s’est imposé pour sa résistance aux hautes températures et aux problèmes d’oxydation. Cependant, l’utilisation d’une céramique comme matériau implique un risque de casse des modules. Les céramiques sont en effet fragiles lorsqu’elles sont soumises à des contraintes de traction. C’est la connaissance et la maitrise de ce risque qui fait l’objet de cette étude. L’approche adoptée combine le développement d’outils numériques et d’études expérimentales réalisées sur le site de la centrale solaire Thémis (Targassonne, 66, France). La méthodologie desimulation développée permet de prédire le comportement thermique et le comportement mécanique de l’absorbeur. Ceci permet de réduire les risques encourus par l’absorbeur et d’en connaitre les performances. Cette méthodologie a été éprouvée à l’aide des résultats expérimentauxFor the future, using thermodynamical solar power plant seems to be a good solution to ensure electrical production. Solar tower plants are able to produce electricity in significant amount, are environmentally friendly and economically competitive. One way to increase the yield of these plants is using high efficiency thermodynamical cycles, like combined cycle. That requires to providing a working fluid at high temperature and high pressure (10bar and 1000°C at least). This PHD thesis presents the works performed to develop and enhance a concept of modular plate solar ceramic absorber that can ensure the required air production. We chose the silicon carbide as material due to its resistance to high temperatures and oxidation problems. The drawback is ceramic modules are weak to traction stresses. The study focuses on the knowledge and the control of this phenomenon. This work combines the developments of numerical tools and experimental studies performed at Thémis power plant (Targassonne, 66, FRANCE). The numerical method permits simulations to predict the thermal behavior and the mechanical behavior of a solar module absorber. It allows the reduction of the mechanical stresses undergone by solar receiver and the prediction of its performances. This methodology was tested using experimental results
45
Singo, Thifhelimbilu Daphney. "Development of a high flux neutron radiation detection system for in-core temperature monitoring." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/19999.
Анотація:
Thesis (PhD)--Stellenbosch University, 2012.ENGLISH ABSTRACT: The objective of this research was to develop a neutron detection system that incorporates a mass spectrometer to measure high neutron flux in a nuclear reactor environment. This system consists of slow and fast neutron detector elements for measuring fluxes in those energy regions respectively. The detector should further be capable of withstanding the harsh conditions associated with a high temperature reactor. This novel detector which was initially intended for use in the PBMR reactor has possible applications as an in-core neutron and indirect temperature-monitoring device in any of the HTGR. Simulations of a generic HTGR core model were performed in order to obtain the neutron energy spectrum with emphasis on the behavior of three energy regions, slow, intermediate and fast neutrons within the core at different temperatures. The slow neutron flux which has the characteristic of a Maxwell- Boltzmann distribution were found to shift to larger values of neutron flux at higher energies as the fuel temperature increased, while fast neutron flux spectra remained relatively constant. In addition, the results of the fit of the slow neutron flux with a modified Maxwell-Boltzmann equation confirmed that in the presence of the neutron source, leakage and absorption, the effective neutron temperatures is above the medium temperatures. From these results, it was clear that the detection system will need to monitor both slow and fast neutron flux. Placing neutron detectors inside the reactor core, that are sensitive to a particular energy range of slow and fast neutrons, would thus provide information about the change of temperature in the fuel and hence act as an in-core temperature monitor. A detection mechanism was developed that employs the neutron-induced break-up reaction of 6Li and 12C into α-particles. These materials make excellent neutron converters without interference due to γ-rays, as the contributions from 6Li(γ,np)4He and 12C(γ,3α) reactions are negligible. The mass spectrometer measures the 4He partial pressure as a function of time under high vacuum with the help of pressure gradient provided by a high-vacuum turbomolecular pump and a positive-displacement fore-vacuum pump connected in series. A cryogenic trap, which contains a molecular sieve made of pellets 1.6 mm in diameter, was also designed and manufactured to remove impurities which cause a background in the lighter mass region of the spectrum. The development and testing of the high flux neutron detection system were performed at the iThemba Laboratory for Accelerator Based Sciences (LABS), South Africa. These tests were carried out with a high energy proton beam at the D-line neutron facility, and with a fast neutron beam at the neutron radiation therapy facility. To test the principle and capability of the detection system in measuring high fluxes, a high intensity 66 MeV proton beam was used to produce a large yield of α-particles. This was done because the proton inelastic scattering cross-section with 12C nuclei is similar to that of neutrons, with a threshold energy of about 8 MeV for both reactions. Secondly, the secondary fast neutrons produced from the 9Be(p,n)9B reaction were also measured with the fast neutron detector. The response of this detection system during irradiation was found to be relatively fast, with a rise time of a few seconds. This is seen as a sharp increase in the partial pressure of 4He gas as the proton or neutron beam bombards the 12C material. It was found that the production of 4He with the proton beam was directly proportional to the beam intensity. The number of 4He atoms produced per second was deduced from the partial pressure observed during the irradiation period. With a neutron beam of 1010 s−1 irradiating the detector, the deduced number of 4He atoms was 109 s−1. When irradiation stops, the partial pressure drops exponentially. This response is attributed to a small quantity of 4He trapped in the present design. Overall, the measurements of 4He partial pressure produced during the tests with proton and fast neutron beams were successful and demonstrated proof of principle of the new detection technique. It was also found that this system has no upper neutron flux detection limit; it can be even higher than 1014 n·cm−2·s−1. The lifetime of this detection system in nuclear reactor environment is practically unlimited, as determined by the known ability of stainless steel to keeps its integrity under the high radiation levels. Hence, it is concluded that this high flux neutron detection system is excellent for neutron detection in the presence of high γ-radiation level and provides real-time flux measurements.
AFRIKAANSE OPSOMMING: Die doel van hierdie navorsing was om ’n neutrondetektorstelsel te ontwikkel wat hoë neutronvloed binne in ’n kernreaktor kan meet. Die stelsel bevat twee aparte detektorelemente sodat die termiese sowel as snelneutronvloed gemeet kan word. Die detektor moet verder in staat wees om die strawwe toestande, kenmerkend aan ’n hoë temperatuur reaktor, te kan weerstaan. Die innoverende detektorstelsel, oorspronklik geoormerk vir gebruik in die PBMR reaktor, het toepassingsmoontlikhede as in-kern neutron- sowel as indirekte temperatuurmonitor. Simulasies van ’n generiese model van ’n HTGR reaktorkern is uitgevoer ten einde die neutronenergiespektrum in die kern by verskillende temperature te bekom met klem op die gedrag van neutrone in drie energiegroepe: stadig (termies), intermediêr en snel (vinnig). Daar is bevind dat die stadige neutrone, wat ’n Maxwell-Boltzman verdeling toon, in intensiteit toeneem en dat die piek na hoër energie verskuif met toename in temperatuur, terwyl die vinnige neutronspektrum relatief onveranderd bly. ’n Passing van die stadige spektrum op ’n gemodifiseerde Maxwell-Boltzmann verdeling het bevestig dat die effektiewe neutrontemperatuur weens die teenwoordigheid van bronterme, verliese en absorpsie, hoër as die temperatuur van die medium is. Hierdie resultate maak dit duidelik dat die detektorstelsel beide die stadige sowel as die vinnige neutronvloed moet kan waarneem. Deur detektorelemente wat sensitief is vir die onderskeie spekrale gebiede in die reaktorhart te plaas, kan informasie bekom word wat tot in-kern temperatuur herleibaar is sodat die stelsel inderdaad as indirekte temperatuurmonitor kan dien. Die feit dat alfa-deeltjies geproduseer word in neutron-geïnduseerde opbreekreaksies van 6Li en 12C is as die basis van die nuwe opsporingsmeganisme aangewend. Hierdie materiale funksioneer uitstekend as neutron-selektiewe omsetters in die teenwoordigheid van gamma-strale aangesien laasgenoemde se bydraes tot helium produksie via die 6Li(γ,np)4He en 12C(γ,3α) reaksies, weglaatbaar is. Die massaspektrometer meet die tydgedrag van die 4He parsiële druk binne ’n hoogvakuum wat met behulp van ’n seriegeskakelde kombinasie van ’n turbomolekulêre en positiewe-verplasingsvoorpomp verkry word. ’n Koueval met ’n molekulêre sif, bestaande uit 1.6 mm diameter korrels, is ontwerp en vervaardig om onsuiwerhede te verwyder wat andersins as agtergrond by die ligter gedeelte van die massaspektrum sou wys. Die ontwikkeling en toetsing van die hoëvloed detektorstelsel is te iThembaLABS (iThemba Laboratories for Accelerator Based Sciences) gedoen. Dit is uitgevoer deur gebruik te maak van die hoë energie protonbundel van die D-lyn neutronfasiliteit asook van die bundel vinnige neutrone by die neutronterapiefasiliteit. Om die beginsel en vermoë te toets om by ’n hoë neutronvloed te kan meet, is van die intense 66 MeV protonbudel gebruik gemaak om ’n hoë opbrengs alfa-deeltjies te verkry. Dit is gedoen omdat die reaksiedeursnit vir onelastiese verstrooiing van protone vanaf 12C kerne soortgelyk is aan die van neutrone, met ’n drumpelenergie van 8 MeV vir beide reaksies. Tweedens is die sekondêre vinnige neutrone afkomstig van die 9Be(p,n)9B reaksie ook met die neutrondetektor gemeet. Daar is bevind dat die reaksietyd van die deteksiestelsel tydens bestraling relatief vinnig is, soos gekenmerk deur ’n stygtyd van etlike sekondes. Laasgenoemde manifesteer as ’n toename in die parsiële druk van die 4He sodra die proton- of neutronbundel op die 12C teiken inval. Daar is verder bevind dat die 4He produksie direk eweredig aan die bundelintensiteit is. Vir ’n neutronbundel van nagenoeg 1010 s−1, invallend op die neutrondetektor, is vanaf die gemete parsiële druk afgelei dat die produksie van 4He atome sowat 109 s−1 beloop. In die geheel beoordeel, was die meting van die 4He parsiële druk tydens die toetse met vinnige protone en neutrone suksesvol en het dit die nuwe meetbeginsel bevestig. Dit is verder bevind dat die meetstelsel nie ’n beperking op die boonste neutronvloed plaas nie, maar dat dit vloede van selfs hoër as 1014 s−1 kan hanteer. Die leeftyd van die detektorstelsel in die reaktor is prakties onbeperk en onderhewig aan die bevestigde integriteit van vlekvrystaal onder hoë bestraling. Die gevolgtrekking is dus dat die nuwe detektorstelsel uitstekend geskik is vir die in-tyd meting van ’n baie hoë vloed van neutrone ook in die teenwoordigheid van intense gammabestraling.
46
Wang, Aiguo. "Dépôts de ZrB2 par L. P. C. V. D : comportement sous flux radiatifs intenses." Montpellier 2, 1991. http://www.theses.fr/1991MON20157.
Анотація:
Le systeme chimique heterogene zrcl#4-bcl#3-h#2 a ete etudie aussi bien du point de vue theorique qu'experimental. Il a ete aborde par une etude thermodynamique previsionnelle et des diagrammes theoriques de depot de la phase solide ont ete etablis. L'etude experimentale realisee par c. V. D. Sous pression reduite, assortie des caracterisations necessaires des solides deposes, a permis d'etablir un diagramme de depot qui concorde bien avec le diagramme theorique. Cette etude met principalement en evidence l'influence des parametres operatoires sur la cinetique globale du systeme ainsi que sur la microstructure des couches. Elle montre en particulier: -l'action preponderante de la reduction du chlorure de bore par l'hydrogene sur le processus d'ensemble du depot; -l'identification du diborure de zirconium(zrb#2) comme seul compose present dans les solides deposes; -l'existence de differentes orientations preferentielles. Des essais de comportement thermique des depots de diborure de zirconium soumis a des flux radiatifs intenses a l'aide d'un concentrateur solaire montre, comparativement a des couches de nitrure de silicium (si#3n#4), une bonne tenue au choc thermique, un niveau superieur d'adherence sur le substrat, mais une moins bonne resistance a l'oxydation
47
Fleury, Rob. "Evaluation of Thermal Radiation Models for Fire Spread Between Objects." Thesis, University of Canterbury. Civil and Natural Resources Engineering, 2010. http://hdl.handle.net/10092/4959.
Анотація:
Fire spread between objects within a compartment is primarily due to the impingement of thermal radiation from the fire source. In order to estimate if or when a remote object from the fire will ignite, one must be able to quantify the radiative heat flux being received by the target. There are a variety of methods presented in the literature that attempt to calculate the thermal radiation to a target; each one based on assumptions about the fire.
The performance of six of these methods, of varying complexity, is investigated in this research. This includes the common point source model, three different cylindrical models, a basic correlation and a planar model. In order to determine the performance of each method, the predictions made by the models were compared with actual measurements of radiant heat flux. This involved taking heat flux readings at numerous locations surrounding a propane gas burner. Different fire scenarios were represented by varying the burner geometry and heat release rate. Video recordings of the experiments were used to determine the mean flame heights using video image analysis software.
After comparing the measured data with predictions made by the theoretical radiation methods, the point source model was found to be the best performing method on average. This was unexpected given the relative simplicity of the model in comparison to some of its counterparts. Additionally, the point source model proved to be the most robust of the six methods investigated, being least affected by the experimental variables. The Dayan and Tien method, one of the cylindrical models, was the second most accurate over the range of conditions tested in this work.
Based on these findings, recommendations are made as to the most appropriate method for use in a radiation sub-model within an existing zone model software. The accuracy shown by the point source model, coupled with its ease of implementation, means that it should be suitable for such a use.
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BITELLI, ULYSSES D. "Medida e calculo da distribuicao espacial e energetica de neutrons no nucleo do reator IEA-R1." reponame:Repositório Institucional do IPEN, 1988. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9883.
Анотація:
Made available in DSpace on 2014-10-09T12:32:26Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:10:14Z (GMT). No. of bitstreams: 1 03179.pdf: 2430358 bytes, checksum: 41a2d3d65c5815ac7b2215aa1300d72a (MD5)
Dissertacao(Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Ishak, Muhammad Izzuddin Syakir. "A Reconnaissance Study of Water and Carbon Fluxes in Tropical Watersheds of Peninsular Malaysia: Stable Isotope Constraints." Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/30564.
Анотація:
Evapotranspiration is a nexus for planetary energy and carbon cycles, as yet poorly constrained. Here I use stable isotopes of oxygen and hydrogen to partition flux of water due to plant transpiration from the direct evaporative flux from soils, water bodies and plant. The study areas, Langat and Kelantan watersheds represent examples of domains dominated by the respective Southwest and Northeast monsoons on the two sides of the main orographic barrier (Titiwangsa mountain range). Mean annual rainfall for the Langat watershed, obtained from 30 years of hydrological data, is 2145 ± 237 mm. Tentatively, 48% of this precipitation returns to the atmosphere via transpiration (T), with 33% partitioned into discharge (Q), 8% into interception (In), and 11% into evaporation (Ed). In the Kelantan watershed, the mean annual rainfall, also based on the 30 year hydrological data, is 2383 ± 120 mm. Similar to Langat, the T accounts for 43% of precipitation (P), 45% is discharged into South China Sea (Q), 12% partitioned into interception (In) and tentatively 0% for evaporation (Ed). Ed for the Langat watershed represents only a small proportion in terms of volumetric significance, up to almost ~11% with strong effect on the isotopic fingerprints of waters associated with the summer Southwest Monsoon (SWM). Note, however, that insignificant Ed for the Kelantan watershed may be an artefact of rain and river water sampling at only coastal downstream portion of the watershed. High humidity (80%) also was recorded for the Malaysian Peninsula watershed.
T appropriates about half of all solar energy absorbed by the continents, here ~1000*103 g H2O m-2 yr-1 similar to other tropical regions at 900-1200*103 g H2O m-2 yr-1. The associated carbon fluxes are ~ 1300 g C m-2yr-1, independent of P. Vegetation responses to solar irradiance, via T and photosynthesis reflects the importance of stomatal regulation of the water and carbon fluxes. In order to maintain high transpiration in the tropical region, “constant” water supply is required for continuous pumping of water that delivers nutrients to the plant, suggesting that water and carbon cycle are co-driven by the energy of the sun. The existence of the water conveyor belt may be precondition for nutrient delivery, hence operation of the carbon cycle. Potentially, this may change our perspective on the role that biology plays in the water cycle. In such perspective, the global water cycle is the medium that redistributes the incoming solar energy across the planet, and the anatomical structures of plants then help to optimize the loop of energy transfer via evaporation and precipitation in the hydrologic cycle.
The main features of aquatic geochemistry of the Langat and Kelantan rivers inferred from the Principal Component Analysis are controlled by three components that explain 80% and 82% of total variances. These components are reflecting of the geogenic factor with superimposed pollution, the latter particularly pronounced in urbanized sections of the Langat river and dominant in downstream of the Kelantan river. There is no correlation between seasonal variations in major ion chemistry and environmental variables such as precipitation, discharge, temperature or solar activity.
50
Hocini, Smaïn. "Influence des correlations sur les proprietes radiatives d'un plasma de protons et d'electrons." Paris 6, 1987. http://www.theses.fr/1987PA066432.
Анотація:
Etude theorique du rayonnement de plasmas composes de protons et d'electrons et qui sont le siege d'effets quantiques. Le parametre de born mesure l'importance des effets quantiques: inferieur a 1 pour les temperatures elevees , superieur a 1 pour les basses temperatures. Lorsque les effets quantiques interviennent en tant que correction, la methode des sommes de slater permet d'obtenir un potentiel effectif. On calcule le rayonnement classiquement a l'aide de ce potentiel effectif. Cette situation est valable lorsque la temperature est elevee