Modélisation de la ségrégation solutale et application à la purification du silicium photovoltaïque

La purification du silicium joue un rôle essentiel pour la production de cellules photovoltaïques. Dans le but de diminuer le coût et l'impact environnemental associés à cette étape, un procédé de purification alternatif est en développement à l'INES (Institut National de l'Energie Solaire). L'une des étapes de ce procédé consiste à éliminer les impuretés métalliques par ségrégation lors d'un processus de solidification dirigée. L'efficacité de ce procédé est directement liée au transport convectif des impuretés dans la phase liquide. Notre étude porte donc sur la modélisation du phénomène de ségrégation et sur l'optimisation du procédé par un système de brassage mécanique. Une étude numérique basée sur des simulations en régime transitoire a été réalisée. Dans un premier temps, des simulations de ségrégation en 2D ont permis de confirmer le domaine de validité d'un modèle analytique de ségrégation. Puis, dans un second temps, l'écoulement généré par le système de brassage a été caractérisé à l'aide de simulations numériques en 3D. Ces résultats numériques ont pu être comparés à des mesures de champ de vitesse réalisées par PIV sur un dispositif expérimental en eau

Added mass and damping of an hexagonal rod vibrating in highly confined viscous fluids

International audienceThis paper deals with fluid–structure interaction analysis of an hexagonal rod enclosed in a narrow viscous gap. A new analytical solution for a two-dimensional (2D) cylindrical case is derived and described. A numerical solution of 2D Navier–Stokes equations coupled with a harmonic structure model is applied to both cylindrical and prism geometries. The comparison between the numerical tool and the analytical solution is discussed and a method to apply the analytical solution to the hexagonal case is proposed. An original definition of the added mass and damping based on an energetic approach is provided avoiding the dependence from the geometry and the type of forcing (free or forced vibration). An experimental facility is provided accounting for an hexagonal prism vibrating within a 7 mm enclosure. Free vibration experiments in water allow assessing the added mass and added damping effect on the modal parameters. The fluid flow is affected by a three-dimensional (3D) effect—named down-strokes flow—at the top and the base of the assembly because of free surface and stocky geometry. This produces a higher frequency than the 2D theoretical value given both by the analytical solution and the numerical simulation. A geometry-based correction factor is suggested to taken into account in the 2D numerical simulation the 3D effect. Velocity measured within the gap provides further insight on this phenomenon and agrees well with the prediction of the transposed cylindrical analytical model

Etude de la stabilité et de l'interaction de cyclones intenses en fluide stratifié

L'influence de la stratification sur la stabilité et l'interaction des vortex à fait l'objet d'une étude expérimentale. En cuve fixe, une instabilité de courte d. longueur d'onde se développe au bord du vortex, là où la vitesse angulaire est proche de la ftéquence de stratification. Les résuItats suggérent que son mécanisme fait intervenir une résonance entre le mouvement horizontale et les oscillations gravitaires verticales. Au coeur du vortex, l'instabilité elliptique peut se développer avec des propriétés dépendantes du nombre de Froude basé sur la vitesse maximum et le rayon correspondant. La longueu d'onde augmente fortement pour des valeurs décroissantes et proches de la valeur critique d'inhibition. Pour des valeurs plus grandes, les propriétés de l'instabilité sont très proches de celle obtenues pour un fluide homogène. Ensuite, les différents régimes de stabilité et d'interaction de deux cyclones en fluide stratifié tournant on été étudiés en fonction de la distance de séparation initiale et du rapport d'aspect des vortex. Une instabilité de grande longueur d'onde conduit chaque cyclone à se couper en vortex de plus petit rapport d'aspect. Les résultats sont proches de ceux obtenus numériquement par Dritschel & la Torre Juarez (1996), en particulier, le critére sur le rapport NH/(fR) où N et f sont les ftéquences de stratification et de rotation. Cette instabilité intervient dans le mécanisme de coalescence pour NH/(fR"3 et cause une augmentation de la distance critique de coalescence. Ces résultats sont en accord avec de ressentent études numériques de Dritschel (2002).GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Experimental qualification of a PIV and two-dye LIF temperature field measurement system with the "filling box" experiment in liquid flow

International audiencePredicting the evolution of reactor core thermo-hydraulic systems in accidental conditions is a major topic in the industry, aimed at ensuring the safety of nuclear plants. The behavior of these systems is studied by solving the volume, momentum, and energy equations of fluid mechanics. Given the size of the hydraulic circuit, various averaging methods are applied to achieve an acceptable computational cost. One such method is the macro-porous double filtering method, suggested by Drouin [1] and others. This method exposes instantaneous and local diffusion and dispersion terms in the energy balance equation, requiring physical models and experimental calibrations. This study aims to establish and qualify an instantaneous measurement system for the temperature and velocity field, combining PIV (Particle Image Velocimetry) and LIF (Laser-Induced Fluorescence). This combined system, which has not been set up, could calibrate the diffusion and dispersion terms. The qualification is conducted in the 'filing box' experiment, characterized by a physical model, connecting the velocity and temperature fields of buoyancy-driven flow. This experiment will serve as our case study. Subsequently, this system be adapted to METERO-V loop, an experimental thermal-hydraulic facility, dedicated for the modeling of 3D flows in nuclear reactor cores, generating velocity and thermal mixing layers in rod bundles, encountered in loss-of-coolant accidents

Uniform and non-uniform flows through a PWR-type rod bundle with mixing grids at Reynolds number ranging from 800 up to 70000: pressure loss measurements

International audienceWe present two sets of experiments performed on the METERO-V set-up. METERO-V is a closed loop, equipped with a test section made of two halves of PWR-type rod bundles (8x34 rods) at full scale. The set up allows injection of different flow rates and temperatures at the inlet of each half of rod bundles. METERO-V experimental program focuses on IBLOCA (Intermediate Break Loss of Coolant Accident), SBLOCA (Small Break) and SLB (Steam Line Break) situations where significant 3D effects may occur in the core, with the aim to develop models and to validate them in a separated-effect way for CFD to system thermal-hydraulic scales. We present preliminary results for a homogeneous inflow, varying the Reynolds number from laminar regime to fully turbulent regime. We measure pressure loss along the flow, across the grids and for the bare bundle. For non-symmetrical inlet velocity, we measure also transverse pressure across the test section at different elevations. For the homogeneous injections, the axial pressure drop is successfully compared with available literature models and experimental data. Principle of tests in non-symmetrical configuration is presented

Infrared Absorption Measurements of the Velocity of a Premixed Hydrogen/Air Flame Propagating in an Obstacle-Laden Tube

International audienceFlame acceleration and explosion of hydrogen/air mixtures remain a key problem for severe accident management in nuclear power plants. Empirical criteria have been developed in the early 2000s by Dorofeev et al. (2001) providing effective tool to discern possible flame acceleration (FA) or deflagration-to-detonation transition (DDT) scenarios. A large experimental database, composed mainly by middle-scale experiments in smooth tubes and obstacle-laden ducts, has been used to validate these criteria. In these devices the position of the reaction front is usually detected by photo-diodes or photomultiplier tubes uniformly distributed along the tube axis. As a result, only a coarse representation of the velocity profile can be achieved. In this paper we develop a new technique to track the flame position along the tube at any time. This method consists in performing time-resolved IR absorption measurements by doping the fresh mixture with an alkane. The velocity profile is then derived by measuring the variation of the extension in depth of the unburnt gas along the tube axis. Correction factors are eventually drawn from the comparison between longitudinal (IR absorption measurements) and cross-sectional (photomultiplier tubes) flame velocity diagnosis techniques. Finally, experimental results are compared to numerical simulations and analytical models proposed by V. Bychkov group

Simultaneous Temperature and Velocity measurements by LIF and PIV in a complex geometry

International audienceAdvanced Sodium Technological Reactor for Industrial Demonstration ASTRID is a project of construction of a 4th generation reactor cooled by sodium. There are thermal-hydraulic issues of upper plenum of ASTRID which can’t be studied from past reactors feedback and numerical simulations since the calculation codes do not allow to model these problems with sufficient confidence .Thus in order to validate thenumerical approaches and systems concept of ASTRID, it is important to measure temperature and velocity simultaneously using optical measurement techniques. For these reasons, a prototype is developed to study the thermal hydraulic behavior of ASTRID. Sodium experiments are very complicated to perform since sodium is opaque and reacts violently with water. Thus it is more practical to perform measurements on a water model since both have similar physical properties concerning viscosity and density. From what preceded, the MICAS mockup was designed . It is a water model of the ASTRID, made up of PMMA foroptical measurements since laser methods will be implemented to measure both temperature and velocity. The challenge in implementing non-intrusive optical techniques to simultaneously measure temperature and velocity on the MICAS mock up resides in designing the experiments so that they are carried out under ambient optical conditions with accuracy and precision attained as much as possible during the execution. Laser Induced Fluorescence LIF and Particle Image Velocimetry PIV are used to measure temperature and velocity respectively. In the LIF technique, a dye absorbs a portion of the excitation energy and spon-taneously reemits a portion of the absorbed energy as fluorescence. Calibration experiments using onecolor LIF were carried out to choose the right dyes. The fluorescence response of three dyes: FL27, RhWTand Rh6G was studied as function of three parameters: dye concentration, laser power and temperature variation from 20°C till 60°C. After that, two color LIF technique will be carried out using two dyes, one temperature dependent and the other insensitive using a pulsed 532 nm Nd:YAG laser .The temperature isdetermined from the ratio of the signal of two dyes, which have highly different temperature sensitivities. When pulsed lasers are used for the excitation of the fluorescence, their irradiance usually exceeds thesaturation intensity of common fluorescent dyes. Therefore, the fluorescence signal loses its linear depen-dence on the laser irradiance. Studies have shown that this loss of linearity is not necessarily an importan tsource of error for the ratio metric methods. Experiments are followed by coupling between PIV and LIF ona simple aquarium and then on the complex geometry MICAS. The same optical approach will be appliedon another experiment which is in progress of preparation. It is a representative prototype and a dimen-sional analysis of the thermal hydraulics of the core in the MICAS mock up. The mixture of the two jets of different temperatures must be studied. The first jet is being hot and the second cold. The prototype aimsto study the interaction between two jets at different temperature

METERO-V experimental set-up: presentation and first results. Uniform flows through a 8x34 PWR-type rod bundle with mixing grids at Reynolds number ranging from 800 to 70000: pressure loss measurements

International audienceWe present the METERO-V set-up and preliminary results from the first set of experiments performed. METERO-V is a closed loop, equipped with a test section made of two halves of PWR-type rod bundles (8x34 rods) at full scale. The set up allows independent injection of different flow rates and temperatures at the inlet of each half of rod bundles. METERO-V experimental program focuses on IBLOCA (Intermediate Break Loss of Coolant Accident), SBLOCA (Small Break) and SLB (Steam Line Break) situations where significant 3D effects may occur in the core, with the aim to develop models and to validate them in a separated-effect way for CFD to system thermal-hydraulic scales. We present the preliminary results for a homogeneous inflow, varying the Reynolds number from laminar regime to fully turbulent regime. We measure pressure loss along the flow, across the grids and for the bare bundle. The axial pressure drop is successfully compared with available literature models and experimental data. Reproducibility and accuracy of the measurements is also very good. Future work will consist in non-symmetrical injections: velocities and/or temperatures

METERO-V and PRIUS experimental programs: complementary separate effects tests for core mixing validation

International audienceThe analysis of Large Break-Loss of Coolant Accidents (LB-LOCAs) required specific experimental programs to investigate large-scale 3D effects, particularly during downcomer refill and core reflooding. SB-LOCAs (Small Break) and IB-LOCAs (Intermediate Break) also encounter significant 3D effects in core due to the radial power profile, with crossflows and diffusion-dispersion. Other transients such as steam line break are sensitive to all mixing phenomena in the core. Then a need exists for a more precise validation of each of the mixing processes, including turbulent terms, 3D interfacial friction and wall friction.In order to provide experimental data to validate thermal hydraulic codes for PWR core in transient situations, two experimental programs are being carried out at CEA and KAERI. At CEA, METERO-V experimental program mainly focuses on LOCAs, and SLB (Steam Line Break) accidents are also considered. These situations, where significant 3D effects may occur in the core, are reproduced in an 834 rod-bundle test section with the aim to develop models and to validate them in a separated-effect way for CFD to system thermal-hydraulic scales. At KAERI, a test facility called PRIUS-II (in-PWR Rod-bundle Investigation of Undeveloped mixing flow across Sub-channel) is devoted to generate an experimental database for a multi-dimensional flow distribution using the MIR technique in a 612 rod-bundle geometry, in LOCAs situations. It is useful for component scale analysis codes and CFD codes in open medium validation.METERO-V and PRIUS-II experiments are complementary in terms of geometry and range of Reynolds numbers, and the data allows separate-effect validation of all codes which may be used for core thermal hydraulic simulations including system codes, sub-channel codes, and CFD codes. New data could be generated in additional single-phase conditions (METERO-V, PRIUS) or two-phase conditions (METERO-V) and could be provided to participants of an international project

Impact of a gaseous jet on the capillary free surface of a liquid: experimental and numerical study

Abstract # V&V2012-6072International audienc