1,354,419 research outputs found
Development of an Equivalent Porous Medium Model for a Tubular Receiver Equipped With Raschig Rings
No full textThe porous insert has become one of the promising methods for heat transfer enhancement in many industrial applications ranging from small electronic devices to nuclear reactors, and large solar fields. For the assessment of such systems, the CFD numerical studies are usually employed by scientists to investigate the heat and mass transfer inside the region in micro or macro scales. Although micro studies are accurate and provide a detailed analysis of the process, they cannot be used for every study due to complex and costly computational resource they may demand for the case under study. Therefore, sometimes macro-scale simulations become more favorable thanks to the reduction in time and cost as well as the simplification over the morphology of the porous medium they offer. For these reasons, this study aims at developing a macro model for a novel porous disc made of Raschig Rings, to be applied to the tubular solar absorber for future simulations. The methodology devised in this study was to exploit detailed micro-scale simulations, achieving the macro properties and then developing a new equivalent macro model of a porous medium, based on the obtained properties. Numerical data indicated that when the developed macro model is compared to the micro simulations, the thermo-hydraulic results are in good agreement. Applying the macro model to a solar absorber working under linear Fresnel heating showed that the proposed porous disc could reduce the temperature rise on the tube wall by 40%
Optimization of the flow distribution in a gyrotron cavity using evolutionary CFD simulations driven by a genetic algorithm
No full textThe steadily increasing performance requested to gyrotrons, to comply with their function of heating and current drive in fusion reactors, put a progressively increasing burden on the heat removal from the interaction cavity, where the heat flux can easily reach 20 MW/m2 on its inner surface. The cavity is actively cooled by subcooled water in forced flow in an annular region, and the water flow typically enters and exits through a single inlet and outlet. The high-speed flow entering from the inlet potentially drives an inhomogeneous flow azimuthally in the cavity region, but helps in locally bursting the heat removal due to the impinging effect of the cold-water flow. Here a new design of the water inlet in the cavity region is performed through a simplified genetic algorithm, in such a way that the flow homogeneity in the gyrotron cavity is maximized, without reducing the beneficial cooling due to the impact of the water jet on the cavity wall. The presence of multiple holes feeding the cavity, with their azimuthal location driven by the genetic algorithm, is analyzed through Computational Fluid Dynamics (CFD) simulations. Once the multi-inlet location is optimized, the dimension of the inlet holes is tuned to burst the heat transfer effect, reaching a high level of temperature and flow homogeneity in the cavity
Allio à distance de Brecht
No full textAllio et le brechtisme… Non, Allio ou le brechtisme… J’hésite ! La formule n’est-elle pas trop limitative et, par-là, trop définitive ? Sur le rapport de René Allio à Brecht, ou du moins à ce qu’il a laissé : la distanciation en tête, je n’ai aucune certitude, aucun a priori. Peut-être, toutefois, aurais-je envie de quelques nuances sur la mise en place de ce syntagme figé, un peu trop vite décrété, un peu rapidement arrêté… Pourquoi ? Parce que – un ..
First Numerical Evaluation of the Thermal Performance of a Tubular Receiver Equipped With Raschig Rings for CSP Applications
No full textPorous media are typically capable to enhance heat transfer, at the cost of an increase of the pressure drop, mainly in view of the huge increase in the surface wetted by the fluid. In this work, a tubular receiver for CSP applications, partly filled with a porous medium constituted by a packed bed of copper Raschig Rings is investigated for the first time. The analysis, carried out numerically, aims at studying in detail the mechanisms of the heat transfer from the wall to the gaseous heat transfer fluid (air) through the porous metal matrix in symmetric and asymmetric heating conditions. The computed results are compared to what occurs in a smooth tube subjected to the same heating, to check the increase in the heat transfer. The investigation carried out in this work represents the first step in the optimization of the porous medium structure inside the tubular receiver
Les Histoires de René Allio
No full textInternational audienceRené Allio, né à Marseille en 1924, choisit d'abord la voie de la peinture. Décorateur et scénographe, il fut aux côtés de Roger Planchon, l'homme de la décentralisation théâtrale, introduisant l'art dramatique en région comme en banlieue. Mais c'est avec le cinéma qu'il trouva son plein accomplissement. Après le succès de La Vieille Dame indigne (1964), René Allio poursuit son parcours de réalisateur. Attentif aux voix du passé, il alterna des films dont le sujet s'enracinait dans l'histoire - Les Camisards (1970), Moi, Pierre Rivière, ayant égorgé ma mère, ma sœur et mon frère (1974) - et des films hybrides, insaisissables, à la confluence des mémoires individuelles et collectives dont témoigne subtilement L'Heure exquise (1981). René Allio, qui avait fondé en 1979 un éphémère Centre Méditerranéen de Création Cinématographique, sut donner corps à ses utopies dans une œuvre protéiforme, foisonnante, engagée.Pour la première fois, un livre retrace toutes les histoires de René Allio. Des documents largement inédits sont présentés par des chercheurs de divers horizons. Des photographies, affiches, tableaux se mêlent aux textes de l'artiste, aux notices sur ses réalisations et aux témoignages de ses partenaires et proches collaborateurs. À travers les multiples facettes du créateur, l'ouvrage dévoile un itinéraire esthétique, politique et intellectuel d'une grande exigence.Contributions de Paul Allio, Paul Chemetov, Gérard Desarthe, Gérard-Denis Farcy, Arlette Farge, Fabienne Galangau-Quérart, Jean A. Gili, Pascale Goetschel, Robert Guédiguian, Annette Guillaumin, Jean Jourdheuil, Chrtine Laurent, Sylvie Lindeperg, Gérard Mordillat, Priska Morrissey, Bernard Papin, Nicolas Philibert, Roland Rappaport, Malka Ribowska, Christiane Rorato, Serge Toubiana, Myriam Tsikounas, Marguerite Vappereau, Dimitri Vezyroglou et Annette Wieviorka
Two-fluid modelling for poly-disperse bubbly flows in vertical pipes: Analysis of the impact of geometrical parameters and heat transfer
No full textThe bubbly flow of air or steam in subcooled water are investigated here in several test cases, characterized by different pipe sizes, bubble dimensions and flow rates, by means of CFD using a Eulerian-Eulerian approach. The performance of models that differ for the turbulence closure in the continuous phase, as well as for the description of the lift force on the dispersed phase, are compared in detail. When air is considered, the space of the experimental parameters leading to a reasonable performance for the selected models are identified and discussed, while the issues left in the modelling of the concurrent condensation are highlighted for the cases where steam is used
René Allio, Les Carnets I 1958-1975
No full textRené Allio, décédé en 1995, était à la fois ou successivement peintre, metteur en scène de théâtre et réalisateur de films. Le vingtième anniversaire de sa mort a été l’occasion de le sortir de l’oubli relatif dans lequel on le tenait (voir 1895 no 74 et 75). Après l’édition de deux coffrets DVD, le travail de réhabilitation se poursuit avec cette grosse entreprise éditoriale qui fait apparaître un Allio écrivain et théoricien de sa pratique, aspect de sa personnalité que n’ignoraient pas ceu..
René Allio, Les Carnets I 1958-1975
No full textRené Allio, décédé en 1995, était à la fois ou successivement peintre, metteur en scène de théâtre et réalisateur de films. Le vingtième anniversaire de sa mort a été l’occasion de le sortir de l’oubli relatif dans lequel on le tenait (voir 1895 no 74 et 75). Après l’édition de deux coffrets DVD, le travail de réhabilitation se poursuit avec cette grosse entreprise éditoriale qui fait apparaître un Allio écrivain et théoricien de sa pratique, aspect de sa personnalité que n’ignoraient pas ceu..
Biogeography-Based Optimization of the Resonator Cooling in a MW-Class Gyrotron for Fusion Applications
No full textThe performance of MW-class gyrotrons, candidate technology for the plasma external heating in magnetic-confined fusion machines, crucially depends on the heat sink capability and thermomechanical stability of the resonator cavity. Because of the high and nonlinear heat flux and consequent high temperature reached on the cavity inner surface, high thermomechanical stresses are typically observed, and large displacements jeopardize the operation. An efficient cooling, typically with subcooled water in forced flow, beside reducing the displacement and stress of the cavity, allows to select operative modes with high beam/wave interaction efficiency. An optimized solution for the cavity cooling is addressed here, which should minimize the frequency shift of the radio frequency wave by controlling the displacements on the inner wall of the cavity while respecting the yield strength limit. The optimization study is based on a biogeography-based optimization (BBO) algorithm, which targets the optimal profile of the heat transfer coefficient (HTC) to the coolant, capable to guarantee that the maximum stress in the resonator is lower than its yield strength while minimizing the inner wall displacements. The optimum analytical HTC is translated into an engineering design and its thermal-hydraulic as well as mechanical performance (hot spot temperature, pressure drop, and displacements/stresses) is compared to the current existing cooling solution, showing potential advantages
René Allio, cinéaste de la lumière
No full textC’est donc ça que je n’ai pas supporté. Cet abandon du plaisir de peindre…René Allio Allio lui-même, dans les entretiens qu’il accordait à la presse, parlait plus de Chardin que de Brecht.Guy Gauthier La mutation ultime À l’origine, il y a la lumière. Celle d’abord que le cinéaste imprime aux choses en peintre qu’il a été puis qu’il a cessé d’être pour devenir cinéaste précisément. Cette lumière enfouie – au même..
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