Academic literature on the topic 'Limite à flux nul'
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Journal articles on the topic "Limite à flux nul"
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Anthore, Anne, Sébastien Jézouin, François Parmentier, Ulf Gennser, and Frédéric Pierre. "Limite quantique du flux de chaleur." Reflets de la physique, no. 42 (December 2014): 16–19. http://dx.doi.org/10.1051/refdp/201442016.
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Breuß, Michael, and Dominik Dietrich. "On the optimization of flux limiter schemes for hyperbolic conservation laws." Numerical Methods for Partial Differential Equations 29, no. 3 (July 20, 2012): 884–96. http://dx.doi.org/10.1002/num.21736.
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Kolev, Mikhail K., Miglena N. Koleva, and Lubin G. Vulkov. "Two positivity preserving flux limited, second-order numerical methods for a haptotaxis model." Numerical Methods for Partial Differential Equations 29, no. 4 (October 27, 2012): 1121–48. http://dx.doi.org/10.1002/num.21748.
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Aglietta, M., E. D. Alyea, P. Antonioli, G. Badino, G. Bari, M. Basile, V. S. Berezinsky, et al. "Upper limits to low energy $\bar\nu_\mathrm{e}$ flux from GRB 990705." Astronomy & Astrophysics 366, no. 2 (February 2001): 573–77. http://dx.doi.org/10.1051/0004-6361:20000233.
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Mohammed, Hussein, and Yasin Salman. "Laminar air flow free convective heat transfer inside a vertical circular pipe with different inlet configurations." Thermal Science 11, no. 1 (2007): 43–63. http://dx.doi.org/10.2298/tsci0701043m.
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Free convection heat transfer has been experimentally investigated for laminar air flow in a vertical circular pipe by using the boundary condition of constant wall heat flux in the ranges of local Rayleight number (RaL) from 1.1?109 to 4.7?109. The experimental setup was designed for determining the effect of different configurations placed at the inlet of a vertical heated pipe, on the surface temperature, the local and average heat transfer coefficients. The apparatus was made with an electrically heated aluminum pipe with length of 900 mm and inside diameter 30 mm. The inlet configurations included two circular pipes having the same diameter as the heated pipe but with lengths of 600 and 1200 mm, sharp-edge and bell-mouth. It was found that the surface temperature along the pipe surface for same heat flux would be higher values for inlet condition with length of 1200 mm and would be lower values for bell-mouth inlet condition. The results show that the local Nusselt number Nux and average Nusselt number (NuL) values would be higher for bell-mouth inlet condition and lower values for 1200 mm inlet condition. For all inlet configurations, the results reveal that the Nu increases as the heat flux increases. Empirical correlations have been proposed in a form of log NuL vs. log RaL for each case investigated and a general correlation for all cases has been obtained which reveals the effect of inlet conditions existence on the free convection heat transfer process in a vertical circular pipe. .
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KUMARAN, V. "Velocity distribution function for a dilute granular material in shear flow." Journal of Fluid Mechanics 340 (June 10, 1997): 319–41. http://dx.doi.org/10.1017/s0022112097005119.
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The velocity distribution function for the steady shear flow of disks (in two dimensions) and spheres (in three dimensions) in a channel is determined in the limit where the frequency of particle–wall collisions is large compared to particle–particle collisions. An asymptotic analysis is used in the small parameter ε, which is naL in two dimensions and n2L in three dimensions, where n is the number density of particles (per unit area in two dimensions and per unit volume in three dimensions), L is the separation of the walls of the channel and a is the particle diameter. The particle–wall collisions are inelastic, and are described by simple relations which involve coefficients of restitution et and en in the tangential and normal directions, and both elastic and inelastic binary collisions between particles are considered. In the absence of binary collisions between particles, it is found that the particle velocities converge to two constant values (ux, uy) =(±V, 0) after repeated collisions with the wall, where ux and uy are the velocities tangential and normal to the wall, V=(1−et) Vw/(1+et), and Vw and −Vw are the tangential velocities of the walls of the channel. The effect of binary collisions is included using a self-consistent calculation, and the distribution function is determined using the condition that the net collisional flux of particles at any point in velocity space is zero at steady state. Certain approximations are made regarding the velocities of particles undergoing binary collisions in order to obtain analytical results for the distribution function, and these approximations are justified analytically by showing that the error incurred decreases proportional to ε1/2 in the limit ε→0. A numerical calculation of the mean square of the difference between the exact flux and the approximate flux confirms that the error decreases proportional to ε1/2 in the limit ε→0. The moments of the velocity distribution function are evaluated, and it is found that 〈u2x〉→V2, 〈u2y〉 ∼V2ε and − 〈uxuy〉 ∼ V2εlog(ε−1) in the limit ε→0. It is found that the distribution function and the scaling laws for the velocity moments are similar for both two- and three-dimensional systems.
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Kunz, Martin, Jost V. Lavric, Rainer Gasche, Christoph Gerbig, Richard H. Grant, Frank-Thomas Koch, Marcus Schumacher, Benjamin Wolf, and Matthias Zeeman. "Surface flux estimates derived from UAS-based mole fraction measurements by means of a nocturnal boundary layer budget approach." Atmospheric Measurement Techniques 13, no. 4 (April 6, 2020): 1671–92. http://dx.doi.org/10.5194/amt-13-1671-2020.
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Abstract. The carbon exchange between ecosystems and the atmosphere has a large influence on the Earth system and specifically on the climate. This exchange is therefore being studied intensively, often using the eddy covariance (EC) technique. EC measurements provide reliable results under turbulent atmospheric conditions, but under calm and stable conditions – as they often occur at night – these measurements are known to misrepresent exchange fluxes. Nocturnal boundary layer (NBL) budgets can provide independent flux estimates under stable conditions, but their application so far has been limited by rather high cost and practical difficulties. Unmanned aircraft systems (UASs) equipped with trace gas analysers have the potential to make this method more accessible. We present the methodology and results of a proof-of-concept study carried out during the ScaleX 2016 campaign. Successive vertical profiles of carbon dioxide dry-air mole fraction in the NBL were taken with a compact analyser carried by a UAS. We estimate an average carbon dioxide flux of 12 µmolm-2s-1, which is plausible for nocturnal respiration in this region in summer. Transport modelling suggests that the NBL budgets represent an area on the order of 100 km2.
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Maroneze, Rafael, Otávio Costa Acevedo, and Felipe Denardin Costa. "RELAÇÃO ENTRE VELOCIDADE DO VENTO E ENERGIA CINÉTICA TURBULENTA EM MODELOS SIMPLIFICADOS DA CAMADA LIMITE NOTURNA." Ciência e Natura 38 (July 20, 2016): 75. http://dx.doi.org/10.5902/2179460x20091.
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The determination of the turbulent fluxes in very stable conditions is done, generally, through parameterizations. In this work the turbulent fluxes are estimated, by using a simplified model, through prognostic equations for the turbulent intensity, the sensible heat flux and the temperature variance. The results indicate that the model is able to reproduce both atmospheric coupling and the intermittent character of the turbulence in very stable conditions.
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Santana, Raoni Aquino Silva de, Cléo Quaresma Dias-Júnior, Julio Tóta, Rodrigo Da Silva, Roseilson Souza do Vale, Antônio Marcos Delfino de Andrade, Raphael Tapajós, Beatriz Freire Mota, Kewen Antônio Souza Vieira, and Luis Paulo Aquino Silva de Santana. "Estimando a altura da camada limite atmosférica sobre diferentes superfícies da região amazônica." Ciência e Natura 42 (August 28, 2020): e25. http://dx.doi.org/10.5902/2179460x46928.
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The Atmospheric Boundary Layer height (zi) is an important quantity used in many parameterizations in surface flux calculations. However, to obtain this height, it is necessary to use atmospheric radiosonde, which can be expensive or even logistically unfeasible in some places in the Amazon. The objective of this work is to estimate zi through the spectrum of the zonal wind component above multiple surfaces of the Amazon region, comparing with the results available in the literature. The zi daily cycle information was generally consistent with minimum values at night and maximum values during the day on all surfaces studied. On the other hand, results seem to run away from expectations, such as zi being larger for the lake than for the savana. It follows that the method has potential to be used in the zi calculation, but still needs further study to improve it.
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Assireu, Arcilan Trevenzoli, Felipe Mendonça Pimenta, and Ramon Morais de Freitas. "OBSERVAÇÕES E MODELAGEM DA CAMADA LIMITE INTERNA NO ENTORNO DE EXTENSOS SISTEMAS AQUÁTICOS." Ciência e Natura 38 (July 20, 2016): 305. http://dx.doi.org/10.5902/2179460x20238.
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The determination of the spatial extent of the internal boundary layer (IBL) across a step change in surface roughness and surface heat flux and temperature is an important environmental aspect to the operation of industries, fossil-fuel, nuclear and wind power plants. The IBL of the land-water transition zone, such as in coastal regions, lakes and reservoirs, is strongly influenced by surface properties, as the roughness and stability change considerably within this zone. An observational study was conducted to measure meteorological properties near a large tropical reservoir and investigate the IBL at the water-land transition. A 42 m height meteorological mast was instrumented with sonic wind anemometers, air temperature and relative humidity sensors at 3, 10, 20 and 40 m height. Comparisons of the log profile model with the Monin-Obukhov similarity theory (MOS) and the observed wind profiles, shown that the MOS estimated the wind profile more accurately, especially if winds were from water to land.
Dissertations / Theses on the topic "Limite à flux nul"
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Bally, Pascale. "Etude expérimentale des parties convective et à petits nombres d'onde des fluctuations de pression pariétale sous une couche limite turbulente en gradient de pression nul et positif." Aix-Marseille 2, 1989. http://www.theses.fr/1989AIX22073.
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Des mesures de densite spectrale des fluctuations de pression sont realisees a la paroi de maquettes de corps sonar presentant allongement limite et effet de gradient de pression statique nul ou positif evolutif. L'utilisation de techniques de decontamination acoustique et vibratoire ameliore l'information dans les basses frequences et l'utilisation de capteurs a trou d'aiguille permet de decrire l'essentiel des structures turbulentes. L'analyse statistique, caracterisant les proprietes convectives du champ de pression parietale, fait apparaitre l'epaisseur de la couche limite et la vitesse issue du taux de cisaillement maximal comme les echelles de longueur et de vitesse essentielles. Les resultats suggerent une proportionnalite du niveau d'energie spectral au facteur d'anisotropie d'echelle rapport de l'echelle integrale longitudinale a l'echelle integrale transversale des fluctuations normales de la vitesse. Un alignement de six microphones affleurants, constituant un filtre en nombre d'ondes, est utilise pour determiner le niveau des petits nombres d'ondes. Leur comportement frequentiel caracteristique apparait indubitable grace aux mesures en gradient positif, obtenues avec un meilleur rapport signal sur bruit qu'en gradient nul. Les echelles appropriees sont a nouveau l'echelle de couche limite et la vitesse de cisaillement maximale. Le modele de chase, applique a partir des resultats obtenus en soufflerie, montre une contamination convective moindre du niveau des petits nombres d'onde en gradient positif, ce qui explique que les experiences y soient plus correctes. A partir de ce modele, par extension des mesures, est proposee une evolution vecteur d'onde frequence du comportement spectral de la pression turbulente a la paroi de corps sous-marins
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Hrubý, Radomír. "Technologie odstranění oxidů síry (SOx) ze spalin pro velká spalovací zařízení." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-416651.
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In the specified large combustion plant, fuel with a large content of sulfur is burned. The current desulfurisation method is not able to meet the new emission limits, therefore it is necessary to design an adequate desulphurisation method. The theoretical part of this diploma thesis contains a description of the legislation related to emission limits for large combustion plants and an analysis of individual technological methods of desulphurization together with a description of the relevant sorbents. The practical part of the work contains a design of dry conditioned sorption with the using of a calcium-based sorbent. The basic technological and structural design is designed together with the spatial solution and dispositional solution of the whole technology.
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Poláková, Annamária. "Distribuce těžkých kovů na spalovně odpadů." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231703.
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The main scope of thesis is to describe the pollutant removal techniques with a focus on heavy metals. With that relate chapters describing the formation of pollutants and their effect on human health. The thesis focuses on a detailed description of flue gas cleaning technology and its evaluation. Evaluation is shown in tables comparing emission measurement on waste incineration plant SAKO Brno, a.s. with emission limits. The thesis also briefly describes other options for municipal waste management.
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Minář, Marek. "Snižování oxidů dusíku z proudu spalin na katalyzátorech při nestandardních podmínkách." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-442856.
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The objective of the presented diploma thesis is reduction of nitrogen oxides from the flue gas stream on catalyst under non-standart conditions. Emphasis is places on the description of selected pollutants in flue gas (especially nitrogen oxides), legislative requirements for air protection and technologies for removal of nitrogen oxides, expecially methods of selective catalytic and non-catalytic reduction. The practical part is devoted to the reduction of nitrogen oxides by selective catalytic reduction on a pilot plant INTEQ II in the laboratory NETME Center. The subject of interest is the determination of the NOx reduction efficiency depend on the temperature for selected catalyst. The end of the practical part pursues with comparison of measurement results and their evaluation.
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Brahic, N. "MECANISMES DE REMONTEE CAPILLAIRE EN NAPPE SUPERFICIELLE - Analyse des hypothèses du modèle de flux limite." Phd thesis, Institut national agronomique paris-grignon - INA P-G, 2002. http://tel.archives-ouvertes.fr/tel-00717750.
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La connaissance du flux d'eau que le sol peut transmettre entre une nappe peu profonde et la surface est d'importance pour la gestion de la ressource en eau et la pérennité des périmètres irrigués. En régime permanent, on estime classiquement ce flux en résolvant la loi de Darcy ; on admet donc que le processus de remontée capillaire s'effectue sous la forme d'un écoulement liquide isotherme. La solution de l'équation présente une asymptote : pour un sol et une profondeur de nappe donnés, il existe un flux limite indépendant des conditions à la surface du sol. A partir de mesures sur une colonne de sol et de calculs basés sur un modèle de transferts d'eau et de chaleur dans le sol et l'atmosphère, nous étudions l'effet de la diffusion vapeur et du couplage entre le sol et l'atmosphère sur le flux dans la zone non saturée. Nous montrons que la loi de Darcy est bien adaptée à l'estimation de ce flux d'autant que les variations climatiques diurnes sont sans conséquence sur le flux moyen.
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Tesař, Jan. "Snížení emisí SO2 ve spalinách z fluidního kotle." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-241676.
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Aim of this thesis is to design a technology of a flue gas desulphurization of fluidized bed boiler. Currently, the state of technology is not able to provide flue gas desulphurisation to required level. For this reason it is necessary to build additional device for the desulphurisation. Theoretical part of the thesis deals with the emission limits of sulphur dioxide, available methods of desulphurization and sorbents suitable for the desulfurization. In practical part conditioned dry sorption method is chosen for the specified source, technological and structural design for suggested desulphurization technology including design of all device is proposed. The thesis also includes a technology design and a 3D model.
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Said, Frédérique. "Etude expérimentale de la couche limite marine structure turbulente et flux de surface (expérience Toscane-T) /." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb376183904.
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Maroneze, Rafael. "Modelo simplificado para turbulência na camada limite noturna." Universidade Federal de Santa Maria, 2016. http://repositorio.ufsm.br/handle/1/9256.
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Conselho Nacional de Desenvolvimento Científico e TecnológicoThe appropriate estimation of turbulent fluxes in very stable conditions is a great challenge for numerical models that simulate the average behavior of the stable boundary layer. Although many features of the flow are usually reproduced, the intermittent variation turbulence is not simulated by most atmospheric models that use K theory for the determination of turbulent fluxes in the stable boundary layer. Moreover, the transition between the very stable and weakly stable regimes of the stable boundary layer is not well understood and described by numerical models. Therefore, in this work a one-and-a-half order numerical model is proposed to represent the average behavior of the nocturnal boundary layer. The model is based in the one proposed by Costa et al. (2011). In the presently proposed scheme, both the sensible heat flux and temperature variance are solved by prognostic equations in order to add degrees of freedom and physical detail to the model. Throughout the work, comparisons are made among the solutions varying different parameters. Results are also compared to the solutions obtained using the model proposed by Costa et al. (2011). The results show that the present model is able to reproduce the transition between the coupled and decoupled stable boundary layer regimes, in a manner similar to what is observed in nature. It also reproduces the occurrence of intermittent non periodical events and the formation of shallow mixing in weak wind conditions. The inclusion of prognostic equations for the sensible heat flux and for the temperature variance provides transitions between regimes at larger winds than those obtained when these quantities are parameterized, and closer to the observed values. The model provides a dependence of the potential temperature scale, θ∗ and of the sensible heat flux on the wind speed that is similar to observations. It also reproduces abrupt transitions between the stable boundary layer regimes, something not observed in the model proposed by Costa et al. (2011). The turbulent kinetic energy balance obtained by the model is closer to the observed by Acevedo et al. (2016) than was obtained by Costa et al. (2011). Dissipation is the dominat mechanism of turbulence destruction in very stable conditions, a role played by buoyant destruction in the model by Costa et al. (2011). The results sustain the hypothesis proposed by Van Weil et al. (2012), that the very stable regime happens when turbulence is not capable of sustaining turbulent heat fluxes large enough to accompany the long wave radiative loss.
A estimativa adequada dos fluxos turbulentos em condições muito estáveis ainda é um grande desafio para os modelos numéricos que descrevem o comportamento médio da CLE. Embora, muitas características do escoamento sejam simuladas, a variação intermitente da turbulência não é reproduzida por grande parte dos modelos atmosféricos que utilizam teoria K na estimativa dos fluxos turbulentos na CLE. Além disso, a transição entre os regimes muito estável e fracamente estável da CLE, ainda, não é bem compreendida e descrita pelos modelos numéricos. No presente trabalho é proposto um modelo numérico, de uma ordem e meia, para descrever o comportamento médio de uma camada limite noturna. O modelo é baseado no que foi proposto por COSTA et al. (2011). O modelo aqui proposto tanto o fluxo de energia na forma de calor sensível como a variância de temperatura são estimados através de equações prognósticas, afim de acrescentar graus de liberdade ao sistema e de modo a acrescentar detalhamento físico à solução. Ao longo do trabalho, foram realizadas comparações entre as soluções obtidas no modelo variando diferentes parâmetros. As soluções também são comparadas com as obtidas utilizando o modelo proposto por Costa et al. (2011). Os resultados mostram que o presente modelo é capaz de reproduzir as transições entre os estados acoplado e desacoplado da camada limite estável, de forma semlhante à observada na natureza. São simulados eventos intermitentes não periódicos que se assemelham aos observados na camada limite. O modelo também reproduz a ocorrência de mistura rasa em condições de vento fraco. A inclusão de equações prognósticas para o fluxo de energia na forma de calor sensível e para a variância de temperatura proporciona transições entre os estados e em condições de vento mais intensas que as obtidas quando essas quantidades são parametrizadas, e mais próximo dos valores observados. Ao observar a dependêndia das quantidades turbulentas, tais como a escala de temperatura potencial, θ∗, e o fluxo de energia na forma de calor sensível em função da velocidade do vento, o presente modelo modelo apresentou os resultados mais semelhante aos observados, se mostrando capaz de reproduzir as transições entre os estados de forma abrupta, diferente do que ocorre no modelo proposto por Costa et al. (2011). O balanço de ECT obtido pelo presente modelo, se aproxima mais do observado por Acevedo et al. (2016) que o obtido por Costa et al. (2011). A dissipação é o mecanismo dominante de destruição de turbulência no estado desacoplado, papel que era ocupado pela destruição térmica no modelo de Costa et al. (2011). Os resultados coroboram a hipótese de Van de Weil et al. (2012), de que o regime muito estável ocorre quando a turbulência não é capaz de produzir fluxos de energia na forma de calor sensível capazes de acompanhar a perda de energia por radiação.
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Said, Frédérique. "Etude expérimentale de la couche limite marine : structure turbulente et flux de la surface (expérience TOXANE-T)." Toulouse 3, 1988. http://www.theses.fr/1988TOU30022.
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Le travail presente est une etude experimentale des transferts turbulents de chaleur, humidite et quantite de mouvement dans la couche limite marine. La phase experimentale (experience toscane-t) s'est deroulee en mars 1985, au large de la baie d'audierne (finistere). Le principal vecteur utilise pour le travail presente est un avion instrumente pour la physique de l'atmosphere. Ce moyen a permis de determiner une topographie des caracteristiques turbulentes, sur une echelle horizontale de l'ordre de 50km sur 50km, et de calculer les flux par la methode des correlations. Les conditions experimentales rencontrees correspondent a des vents compris enre 3 et 12 metres par seconde et a des conditions d'instabilite caracterisees par des longueurs de monin obukhov negatives comprises entre 50 et 300 metres. La structure turbulente de la couche limite marine est presentee dans le cadre de la theorie de similitude. Les resultats obtenus sont en accord avec les donnees acquises en couche limite dynamique, marine ou continentale. Ils sont egalement compares aux caracteristiques turbulentes des couches limites convectives. La finalisation de cette etude est resumee au moyen d'une parametrisation des flux de surface. Celle-ci est utilisable dans les modeles de grande echelle et consiste a calculer les coefficients aerodynamiques. Dans les conditions experimentales de l'etude les valeurs obtenues sont les suivantes: 1. 8 10**(-3) pour la quantite de mouvement (cd::(10)); 1. 5 10**(-3) pour la chaleur sensible (ct::(10)); et 1. 5 10**(-3) pour la chaleur latente (cq::(10)); ces coefficients sont independants de l'echelle d'integration spatiale a laquelle ils ont ete determines (de 5 km sur 5 km a 50 km sur 50 km).
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Phordoy, Jacques. "Influence d'une transpiration sur un écoulement turbulent en canal, mesure des flux de chaleur." Toulouse, INPT, 1992. http://www.theses.fr/1992INPT108H.
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Les ecoulements de geofluides se caracterisent souvent par la presence de gradients de densite. Ces derniers jouent un role tres important car ils conditionnent les echanges turbulents de masse, de quantite de mouvement et d'energie entre la couche melangee de surface et le fond de l'ecoulement. La connaissance de ces processus necessite une investigation experimentale qui repose, entre autres, sur la mesure et l'analyse des flux turbulents de chaleur. C'est cette question qui fait l'objet du travail presente: l'etude a ete menee sur un ecoulement d'eau en canal ou les flux de chaleur ont ete produits par injection parietale, au travers d'une paroi poreuse en bronze fritte, l'eau injectee etant a temperature plus faible que celle de l'ecoulement principal. Dans un premier temps, la velocimetrie laser a ete validee en etudiant l'ecoulement etabli en canal sans transpiration. Dans un deuxieme temps, l'ecoulement en canal a ete perturbe par une injection parietale d'eau en regime isotherme. Cette etude de reference a permis de retrouver l'essentiel des resultats de la litterature et de montrer l'influence de la transpiration, aussi bien que les quantites moyennes que sur les caracteristiques turbulentes. Dans un troisieme temps, l'ecoulement principal a ete perturbe par une injection parietale avec flux de chaleur. Les flux turbulents ont ete mesures par l'association d'un anemometre a laser et d'un thermocouple. On observe une forte correlation fluctuations de vitesse longitudinale fluctuations de temperature. Enfin, des resultats numeriques sont presentes
Book chapters on the topic "Limite à flux nul"
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LEBEDEV, Eugene, and Hanna LIVINSKA. "Limites de diffusion et gaussiennes pour les réseaux de files d’attente multicanaux." In Théorie des files d’attente 1, 207–46. ISTE Group, 2021. http://dx.doi.org/10.51926/iste.9001.ch7.
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Ce chapitre donne des résultats de base sur la diffusion et l’approximation gaussienne des réseaux de files d’attente multicanaux dans des conditions de trafic dense. L’approche locale est utilisée pour l’approximation de diffusion du processus de service dans le cas d’une structure clairement définie des flux d’entrée. Pour les flux d’entrée plus complexes, le processus limite est décrit comme un processus gaussien multidimensionnel. Les caractéristiques des processus limites dans les deux cas sont spécifiées via les paramètres du réseau. Ce chapitre donne des résultats de base sur la diffusion et l’approximation gaussienne des réseaux de files d’attente multicanaux dans des conditions de trafic dense. L’approche locale est utilisée pour l’approximation de diffusion du processus de service dans le cas d’une structure clairement définie des flux d’entrée. Pour les flux d’entrée plus complexes, le processus limite est décrit comme un processus gaussien multidimensionnel. Les caractéristiques des processus limites dans les deux cas sont spécifiées via les paramètres du réseau.
Conference papers on the topic "Limite à flux nul"
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Bhowmik, H., and K. W. Tou. "Air Cooling Study of Transient Natural Convection Heat Transfer From Simulated Electronic Chips." In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-59503.
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Experiments are performed to study the heat transfer characteristics during the power-on transient period from an array of 4 × 1 discrete heat sources in a vertical rectangular channel using air as the working fluid. The heat flux ranges from 1000 W/m2 to 5000 W/m2. For 2 mm protrusion of the heater, the effect of heat fluxes and chip numbers are investigated and observed that the transient Nul strongly depends on the number of chips. Correlations are presented for individual chips as well as for overall data in the transient regime.
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Bhowmik, H., K. W. Tou, and C. P. Tso. "Experimental Thermal Behavior of Electronic Chips in a Channel During Pump-On Transient Period." In ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56287.
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Experiments are performed to study the heat transfer characteristics during the pump-on transient period from an array of 4 × 1 flush mounted discrete heat sources in a vertical rectangular channel using water as the working fluid. The experimental data covers the flow regime with Reynolds number based on heat source length ranging from 1050 to 2625. The applied uniform heat fluxes to the chips are 1, 3, 5 and 7 W/cm2. The effects of heat flux, flow rates and chip numbers are investigated and empirical correlations are developed for investigated and empirical correlations are developed for individual chips as well as for overall data in the transient regime. The transient correlation recommended is Nul/(Pel)1/3 = 3.5(Fo)1/4.
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Mohammed, H., T. Yusaf, and Y. Salman. "Experimental Investigation of Free Convection Heat Transfer With Entrance Restriction Placed at Top of a Vertical Circular Tube." In ASME 8th Biennial Conference on Engineering Systems Design and Analysis. ASMEDC, 2006. http://dx.doi.org/10.1115/esda2006-95229.
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A free convection from the inside surface of vertical circular tube with a uniformly heated surface (constant wall heat flux) was investigated experimentally for laminar air flow in the ranges of RaL from 6.9 × 108 to 5 × 109. The effect of restriction lengths placed at top position of the heated tube on the surface temperature distribution and the local and average heat transfer coefficient were studied. The experimental apparatus consists of aluminum tube with 900mm length and 30mm inside diameter. The entry restrictions were included a circular tube of same diameter as the heated tube but with different lengths of 60cm, 90cm, 120cm, 150cm, and 180cm. It was found that the surface temperature along the tube surface higher values for restriction with length of 180cm and smaller values for the restriction with length of 120cm. The results showed that the local Nux and average Nusselt number Nu were higher values for the restriction with length of 120cm and smaller values for the restriction with length of 180cm. The results obtained are correlated by dimensionless groups as Log NuL against Log RaL for each case and proposed a general correlation for all cases.
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Lee, Kok-Meng, Hungsun Son, and Jong-Kweon Park. "Design Analysis of a Spherical Magnetic Bearing for Multi-DOF Rotational Stage Applications." In ASME 2007 International Manufacturing Science and Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/msec2007-31189.
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This paper presents an analytical method to facilitate design of a spherical magnetic bearing (SMB) for a multi-DOF rotational stage. Both passive and active regulations of the SMB are considered. We formulate the SMB dynamic model along with the method of computing the magnetic force and torque required to null any deviation of the rotor, which requires solving the magnetic field. For this, we introduce and validate a general method, referred to here as distributed-multi-pole (DMP) modeling method which requires only a limited set of known (numerical or experimental) field solutions, to derive closed-form solutions for precise calculation of the magnetic field around a permanent magnet (PM). The DMP method has been validated by comparing its modeled potential field and flux density against analytical solutions, as well as the computed force (using DMP modeled field) against published experimental data; both show excellent agreement. Finally, we demonstrate the concept feasibility of the spherical magnetic bearing, and analyze its dynamics and control performance using the DMP modeled field and computed force/torque.
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Yoon, K. K., and J. B. Hall. "Alternative RTNDT for Linde 80 Weld Materials." In ASME 2002 Pressure Vessels and Piping Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/pvp2002-1362.
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The ASME Boiler and Pressure Vessel Code provides fracture toughness curves of ferritic pressure vessel steels that are indexed by a reference temperature for nil ductility transition (RTNDT). The ASME Code also prescribes how to determine RTNDT. The B&W Owners Group has reactor pressure vessels that were fabricated by Babcock & Wilcox using Linde 80 flux. These vessels have welds called Linde 80 welds. The RTNDT values of the Linde 80 welds are of great interest to the B&W Owners Group. These RTNDT values are used in compliance of the NRC regulations regarding the PTS screening criteria and plant pressure-temperature limits for operation of nuclear power plants. A generic RTNDT value for the Linde 80 welds as a group was established by the NRC, using an average of more than 70 RTNDT values. Emergence of the Master Curve method enabled the industry to revisit the validity issue surrounding RTNDT determination methods. T0 indicates that the dropweight test based TNDT is a better index than Charpy transition temperature based index, at least for the RTNDT of unirradiated Linde 80 welds. An alternative generic RTNDT is presented in this paper using the T0 data obtained by fracture toughness tests in the brittle-to-ductile transition temperature range, in accordance with the ASTM E1921 standard.
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Guo, Y., D. E. Bullock, I. L. Pioro, and J. Martin. "Measurements of Sheath Temperature Profiles in Bruce LVRF Bundles Under Post-Dryout Heat Transfer Conditions in Freon." In 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/icone14-89621.
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An experimental program has been completed to study the behaviour of sheath wall temperatures in the Bruce Power Station Low Void Reactivity Fuel (shortened hereafter to Bruce LVRF) bundles under post-dryout (PDO) heat-transfer conditions. The experiment was conducted with an electrically heated simulator of a string of nine Bruce LVRF bundles, installed in the MR-3 Freon heat transfer loop at the Chalk River Laboratories (CRL), Atomic Energy of Canada Limited (AECL). The loop used Freon R-134a as a coolant to simulate typical flow conditions in CANDU® nuclear power stations. The simulator had an axially uniform heat flux profile. Two radial heat flux profiles were tested: a fresh Bruce LVRF profile and a fresh natural uranium (NU) profile. For a given set of flow conditions, the channel power was set above the critical power to achieve dryout, while heater-element wall temperatures were recorded at various overpower levels using sliding thermocouples. The maximum experimental overpower achieved was 64%. For the conditions tested, the results showed that initial dryout occurred at an inner-ring element at low flows and an outer-ring element facing internal subchannels at high flows. Dry-patches (regions of dryout) spread with increasing channel power; maximum wall temperatures were observed at the downstream end of the simulator, and immediately upstream of the mid-bundle spacer plane. In general, maximum wall temperatures were observed at the outer-ring elements facing the internal subchannels. The maximum water-equivalent temperature obtained in the test, at an overpower level of 64%, was significantly below the acceptable maximum temperature, indicating that the integrity of the Bruce LVRF will be maintained at PDO conditions. Therefore, the Bruce LVRF exhibits good PDO heat transfer performance.
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Alrbee, K., Y. S. Muzychka, and X. Duan. "Heat Transfer Enhancement in Laminar Graetz and Taylor Flows Using Nanofluids." In ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icnmm2018-7756.
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This paper focuses on heat transfer in mini scale tubes under laminar developing flow conditions for a constant wall temperature boundary condition. An experimental study was preformed using Aluminum Oxide nanoparticles (< 50nm) for continuous and segmented fluid streams. A two step method was employed to prepare several samples of aluminum oxide nanofluid with different concentrations 0.25, 0.5 and 1% by volume. Heat transfer enhancement in mini scale tubes (∼1 mm) was assessed using the dimensionless Graetz parameter L*, dimensionless mean wall heat flux q*, and Nusselt number Nu. In this study we investigate the effect of nanofluid concentration on laminar heat transfer enhancement in mini-scale circular tube under continuous and segmented flow using gas as a segmenting medium. The initial results show a maximum of 10–65% enhancement of Nusselt number as compared with pure water under the same conditions as a function of L*. For the upper limit of concentration of 1% Al2O3 nanofluid, the friction factor was found to be less than 5% greater, which means a small sacrifice on pumping power is to be expected. This study provides new insights on the thermal behaviour of nanofluids under laminar developing flow and segmented flow conditions in straight tubes.
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Pirbastami, Sogol, and Samir Moujaes. "Effect of Groove Dimension on Thermal Performance of Turbulent Fluid Flow in Internally Grooved Tube." In ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-66236.
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A Computational Fluid Dynamics (CFD) study of heat enhancement in helically grooved tubes was carried out by using a 3-dimensional simulation with the STARCCM+ simulation package software. The k-ε model selected for turbulent flow simulation and the governing equations were solved by using the finite volume method. Geometric models of the current study include 3 rectangular grooved tubes with different groove width (w) and depth (e) which varies from 0.2 mm to 0.6 mm for the same tube length of 2.0m and diameter of 7.1 mm. The simulations were performed in the Reynolds number (Re) range of 4000–10000 with a uniform wall heat flux of 3150 w/m2 applied as a boundary condition on the surface of each tube. The purpose of this research is to investigate the effect of different groove dimensions on the thermal performance and pressure drop of water inside the grooved tubes and clarify the structural nature of the flow in regards to flow swirl and turbulent kinetic energy distributions. It was found that the highest performance belongs to the groove with these dimensions (w = 0.2 mm and e = 0.2 mm) which was considered for further study. Then, for these same groove dimensions four pitch size to tube diameter (p/D) ratios ranging from 1 to 18 were simulated for the same 2.0 m length tube. The results for Nusselt number (Nu) and friction factor (f) showed that by increasing the (p/D) ratio both the Nu numbers and the friction factors (f) values decrease. With a smaller pitch length (p) the turbulence intensity generated by the internal groove was also found to increase. The physical behavior of the turbulent flow and heat transfer characteristics were observed by contour plots which showed an increasing swirl flow and turbulent kinetic energy as p/D decreases. With an increase of the Nu number for smaller p/D ratio, a penalty of a higher pressure drop was obtained. The results were validated with a previous experimental work and the average error between the experimental and CFD Nu numbers and f were 13% and 8% respectively. A higher level of turbulent kinetic energy is observed near the grooves, as compared to the smooth areas of the pipe surface away from the grooves, which are expected to lead to higher levels of heat transfer. The effect of pitch length (p) on the flow pattern were plotted by streamlines along the tubes, by decreasing the pitch size (p/D ratio) an increase in the swirl is noticed as evidenced by the plots of the path lines. Finally, empirical correlations for Nusselt number and friction factor were provided as a function of p/D and Re number. This study indicates that the incorporation of the internal groove, of particular dimensions, can lead to an improvement of performance in heat exchanger devices. A limited variation of the groove dimensions was conducted and it was found that the values of Nu and f do not improve with an increase of (w) nor with that of (e) from 0.2–0.6 mm.
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Collins, Matthew, Kam Chana, and Thomas Povey. "Improved Methodologies for Time Resolved Heat Transfer Measurements, Demonstrated on an Unshrouded Transonic Turbine Casing." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-43346.
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The HP rotor tip and over-tip casing are often life-limiting features in the turbine stages of current gas turbine engines. This is due to the high thermal load, and high temperature cycling both at low and high frequency. In the last few years there have been numerous studies of turbine tip heat transfer. Comparatively fewer studies have considered the over-tip casing heat transfer. This is in part, no doubt, due to the more onerous test facility requirements to validate computational simulations. Because the casing potential field is dominated by the passing rotor, to perform representative over-tip measurements a rotating experiment is an essential requirement. In this paper we describe improved methodologies for time resolved heat transfer measurements. Specifically we show that: 1. Changes in driving temperature (within limits) can be accounted for in both time-resolved and steady heat transfer measurement processing. This allows useful data to be extracted even under varying inlet temperature. 2. Superposition of several runs with different starting wall temperatures can be used to improve the accuracy of time resolved regressions by extending the wall temperature range over which the unsteady regressions are conducted. 3. A new time-resolved data processing technique that can be applied to data sets involving changes in wall temperature has been developed and is applied to experimental measurements to compute time resolved TAW and Nu. These improvements are demonstrated using unsteady heat transfer measurements conducted on the stationary casing above an unshrouded transonic turbine. The measurements were taken in the Oxford Turbine Research Facility (OTRF), an engine-scale rotating turbine facility which replicates engine-representative conditions of Mach number, Reynolds number, and gas-to-wall temperature ratio. High density arrays of miniature thin-film heat-flux gauges were used with a spatial resolution of 0.8 mm and temporal resolution of ∼120 kHz. The small size of the gauges, the high frequency response, and the improved processing methods allowed very detailed measurements of the heat transfer in this region. Time-resolved measurements of TAW and Nu are presented for the casing region (−30 % to +125% CAX) and compared to other results in the literature. The results provide an almost unique data set for calibrating CFD tools for heat transfer prediction in this highly unsteady environment dominated by the rotor over-tip flow.