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Thème: Smoothed Particles Hydrodynamics (SPH); International audience; The Smoothed Particle Hydrodynamics method (SPH) is a meshfree Lagrangian simulation method widely applied for fluid simulations due to the advantages presented by this method for solving problems with free and deformable surfaces. In many scientific and engineering applications, surface tension forces play an important or even dominating role in the dynamics of the system. For instance, the breakage (instability) of a liquid jetor film is strongly affected by the strength of the surface tension at the liquid-air interface. Simulating deforming phase interfaces with strong topological changes is still today a challenging task. As a promising numerical method, here we use SPH to predict the interface instability at a water-air interface. With SPH, the main challenge in modelling surface tension at a free-surface is the accurate description of the interface (normal direction and curvature). When only the liquid phase is modelled (to decrease the computational cost), the standard SPH approximations to calculate the normal direction and curvature of the interface suffer from a lacking “full support”, i.e. the omitted and therefore missing gas particles. Various models for such free surface surface tension corrections were presented, see e.g. among others Sirotkin et al., Ordoubadi et al. or Ehigiamusoe et al. Many of these models follow the classical Continuum Surface Force (CSF) approach (Morris, Adami et al.) and incorporate different corrections/treatments at the surface. The objective of our ongoing study is to investigate the influence of different interface descriptions. We compare different free surface particle detection schemes, normal vector calculations and curvature estimations for the quality of the resulting surface-tension effect. In this work, we focus on two-dimensional problems and consider a static drop and oscillating drops as test cases.

National audience; La méthode de simulation numérique SPH (Smoothed Particle Hydrodynamics) est une méthode Lagrangienne largement utilisée dans diverses applications, allant de l’astrophysique à l’hydrodynamique naval [Monaghan, 2005]. L’objectif de ce projet de recherche est de coupler la méthode SPH avec le transfert thermique (conduction et changement de phase), les aspects de surface libre et la tension de surface. Dans ce travail, nous nous concentrons sur les équations SPH de transfert de chaleur, qui constituent la première brique de ce projet. Le principe de la méthode SPH est de modéliser un fluide continu en le discrétisant avec une série de particules ; chacune ayant une entité physique (dans ce cas, cette entité est la température) et la transfère aux particules voisines en passant par une fonction de lissage (Kernel/smoothing function) (Figure1). La nature sans maillage de la méthode SPH lui donne l’avantage d’être potentiellement applicable aux géométries complexes. Par contre la mise en oeuvre des conditions aux limites peut parfois être problématique. Nous présenterons des simulations 1D et 2D de problèmes de conduction et de changement de phase avec des comparaisons avec les solutions analytiques [Carslaw et Jaeger, 1959]. Cette approche pourrait être étendue pour simuler plusieurs processus notamment l’ablation au laser et la fabrication additive [Alshaer et al., 2017].

Sessions : Segregation and Mixing - Modeling, Simulations and Applications I; International audience; It is often desirable to produce spherical particles with a targeted size distribution. In this paper, we present an experimental setup able to generate droplets of a liquid that will further solidify into solid particles upon cooling. We show that a controlled mechanical vibration applied to a jet emanating from a circular orifice can lead to a monodisperse distribution with a mean size of the order of the orifice diameter (ranging between 50 and 250 µm in our experiments). By appropriately tuning the piezo-ceramic electrical stimulation, we show how to generate a controlled particle size distribution, with dmax/dmin of the order of 1.3. This size ratio is favorable to elaborate dense granular beds. The experiments are conducted with different materials.

Sessions : Segregation and Mixing - Modeling, Simulations and Applications I; International audience; The conical screw mixer was designed to ensure a high mixing efficiency thanks to the three dimensional flow pattern of particles. The mixing mechanism in the conical screw mixer is predominantly convective, insured by an axial transport by the screw and radial transport, where the screw orbits the conical vessel. However, the operating parameters and the granular properties can affect the quality of mixing. A limited works were devoted to study the mixing dynamics of powders in a conical screw mixer. A recent study of the conical screw mixer using DEM simulation demonstrated that the control of the rotating speed of the screw (axial and radial) leads to an improved mixing rate. In this work we aim to investigate the simulation parameters that influence the mixing criteria. The simulation of a conical screw mixer (5L) was carried out using one million of monodisperse particles (0.9 mm ± 5 % in diameter). Such a large number of particles leads to a high computational demand. In order to save the compuational time, the simulation parameters must be chosen carefully. We have investigated the impact of the Young’s modulus and density on the simulation time. We have observed that reducing the Young's modulus could be compensated by a choice of density so it has no impact on the macroscopic mixing dynamics. The simulation was next focused on the investigation of the flow pattern and the velocity profile of particles in a binary mixture with various particle size ratios (1, 1.2, 1.4 and 1.6). The induced size segregation in the mixer is yet to be studied.

Thème 1: Le génie des procédés au service de la transition énergétique - Pyrolyse et gazéification; International audience; Parmi les solutions envisagées pour réaliser la transition énergétique, à l’échelle industrielle, la valorisation énergétique de la biomasse par voie thermochimique apparait comme une solution d’avenir. Cependant, ces procédés se heurtent aux mauvaises propriétés de cette dernière comme vecteur énergétique, ce qui freine le développement de ces filières. Dans ce contexte, la torréfaction apparait comme un prétraitement prometteur qui améliore les caractéristiques de ces matériaux, notamment sa densité énergétique, sa broyabilité, son hydrophobicité et sa résistance à la biodégradation. Ainsi, l’essor de la production et des flux de biomasse torréfiée à travers le monde est annoncé pour la décennie à venir. Néanmoins, il soulève la problématique de l’auto-échauffement. En effet, plus le système que l’on considère est volumineux, plus il est sujet à ce phénomène. L’auto-échauffement engendre une augmentation de la température et, dans le cas du bois torréfié en présence d’oxygène, il peut conduire à l’auto-combustion. L’objectif de ce travail est de modéliser la réaction exothermique qui a lieu pour mieux comprendre ces phénomènes et améliorer la sécurité du procédé

National audience; Nous développons une étude sur les écoulements en conduite 2D à section rectangulaire. Peu d’études expérimentales sont réalisées dans le cas de particules transportées par un liquide. Pourtant, ces écoulements partagent des similitudes avec des expériences dont la mise en mouvement des particules dépend uniquement de la force gravitaire (Zuriguel 2003). Cependant, le phénomène de blocage des suspensions n’est pas un phénomène systématique. Il faudra donc parvenir à caractériser les éléments responsables du blocage comme par exemple les interfaces fluides-particules, les écoulements denses, les forces hydrodynamiques. Nous présentons ici, un modèle en exponentielle qui décrit la répartition des blocages dans l’écoulement. Puis nous présenterons sous forme de graphique une probabilité de blocage en fonction de l’ouverture d’une restriction.

International audience; Torrefaction is a key step in the manufacturing process of fuel made from biomass pellets and has been studied widely in the literature [1] During and after the process, safety issues have to be managed, due to the risk of self-heating, thermal runaway and self-ignition. The physical origins of these phenomena involve heat transfer, thermochemistry and kinetics.Although these mechanisms have been studied recently [2], the impact of hydrodynamics has not been investigated so far. Actually, packing structure, anisotropy and pore size distribution can induce strong heterogeneities of gas flow velocity, temperature and composition. Thus, to get a better understanding of the impact of these heterogeneities, it is necessary to consider the local structure of the packing. The aim of this work is to propose a numerical simulation of gas flow on a few particles scale coupling thermal and reactive aspects with hydrodynamics. Simulations are run using a 2D CFD software which is being developed in our laboratory. It is based on a Lattice Boltzmann approach which is known to allow an easy implementation of coupled multiphysics models [3]. Fluid dynamics, thermal aspect and oxidation reaction have been implemented in the code. Our results show indeed that strong heterogeneities of gas flow velocity and temperature field appear according to the local structure. The influence of input gas velocity is enhanced by the fact that the industrial operating conditions can lead to different flow regimes. Thus, it appears that hydrodynamics aspects and packing structure have to be considered in the mean field approach which is commonly used to characterize the biomass chips behavior on the reactor scale.REFERENCES[1] Prins, Mark J., Krzysztof J. Ptasinski, and Frans JJG Janssen. "Torrefaction of wood: Part 1.Weight loss kinetics." Journal of Analytical and Applied Pyrolysis 77.1 (2006): 28 - 34.[2] Bates, Richard Burton. “ Modeling the coupled effects of heat transfer. thermochemistry, and kinetics during biomass torrefaction. ”Diss. Massachusetts Institute of Technology, 2012.[3] Dupuis, Alexandre. “From a lattice Boltzmann model to a parallel and reusable implementation of a virtual river”. Diss. Thèse soutenue à Genève en Suisse, 2002

Pour voir la présentation de cette communication cliquer sur "Voir les Fichiers annexes" / To see the presentation click on "Voir les Fichiers annexes"; International audience; Many industrial processes require the use of an hydraulic transport with macroscopic particles. Those methods are widely used in mining or food industries. However relatively few studies have been performed on the behavior on the transition between jamming and flowing states. Indeed, for that kind of flow, some intriguing effects are observable such as shear -thickenning or shear – thinning. It appears that fluid-particle interactions and hydrodynamic effects have an important impact on the suspension dynamic (especially for high packing volume fraction). For example, in oil industry, it is possible to observe interfaces problems for heavy oil extraction with sand or for hydrates crystals in off-shore pipe (in this case the hydrates are sedimenting leading to the jamming state).The jamming phenomenon is not systematic. This is why we have performed a lot of experiments in order to establish a statistical analysis. The experiments provided here intend to characterize the elements responsible for such a phenomenon (dense flow, fluid velocity, hydrodynamic forces…).We have performed a set of experiments with a rectangular pipe in 2D to investigate the jamming effect. We study the flow of non Brownian particles suspended in a liquid passing through a restriction. With image analysis we were able to count the total number of particles through the restriction between two jamming. We noticed that the total number of particles for different size (length) of restriction could be expressed as an exponential with only one fitting parameter.

We develop a study on the flow behavior in 2D rectangular section. Few experimental studies are carriedout in the case of particles carried by a fluid. However, these flows are sharing similarities withexperiences which the setting movement of particles depends solely on the gravitational force (Zuriguel2003). However, the suspensions of the jamming phenomenon is not a systematic phenomenon. It willtherefore be able to characterize the influence of parameters such as fluid-particle interfaces, dense flows,hydrodynamic forces. Here we present a model that describes the exponential distribution of blockages inthe flow. Then we present an interpolation representing the evolution law of avalanche size by the ratio R., Nous développons une étude sur les écoulements en conduite 2D à section rectangulaire. Peu d'études expérimentales sont réalisées dans le cas de particules transportées par un liquide. Pourtant, ces écoulements partagent des similitudes avec des expériences dont la mise en mouvement des particules dépend uniquement de la force gravitaire (Zuriguel 2003). Cependant, le phénomène de blocage des suspensions n'est pas un phénomène systématique. Il faudra donc parvenir à caractériser les éléments responsables du blocage comme par exemple les interfaces fluides-particules, les écoulements denses, les forces hydrodynamiques. Nous présentons ici, un modèle en exponentielle qui décrit la répartition des blocages dans l'écoulement. Puis nous présenterons sous forme de graphique une probabilité de blocage en fonction de l'ouverture d'une restriction.

The implementation of the “priority preliminary rulings on the issue of constitutionality” definitely installs the constitutional justice in the political system of the Fifth Republic. The new mechanism induces a renewal of the relationship between Parliament and the Constitutional Council. It causes an institutional imbalance inherent in the judicial function of the Council. This change reinforces the functional balance between the two institutions. The process raises questions about the place given to the judges in a democratic regime., L'instauration de la question prioritaire de constitutionnalité permet d'ancrer définitivement la justice constitutionnelle au sein du régime politique de la Cinquième République. En déconnectant le contrôle de la loi de la procédure législative, le nouveau mécanisme induit un renouvellement de la relation unissant le Parlement au Conseil constitutionnel. Il acte un déséquilibre institutionnel inhérent à la fonction juridictionnelle du Conseil. Seule cette évolution était susceptible de renforcer l'équilibre fonctionnel entre les deux institutions. Le processus conduit à s'interroger sur la place accordée aux juges au sein d'un régime démocratique.

The implementation of the “priority preliminary rulings on the issue of constitutionality” definitely installs the constitutional justice in the political system of the Fifth Republic. The new mechanism induces a renewal of the relationship between Parliament and the Constitutional Council. It causes an institutional imbalance inherent in the judicial function of the Council. This change reinforces the functional balance between the two institutions. The process raises questions about the place given to the judges in a democratic regime., L'instauration de la question prioritaire de constitutionnalité permet d'ancrer définitivement la justice constitutionnelle au sein du régime politique de la Cinquième République. En déconnectant le contrôle de la loi de la procédure législative, le nouveau mécanisme induit un renouvellement de la relation unissant le Parlement au Conseil constitutionnel. Il acte un déséquilibre institutionnel inhérent à la fonction juridictionnelle du Conseil. Seule cette évolution était susceptible de renforcer l'équilibre fonctionnel entre les deux institutions. Le processus conduit à s'interroger sur la place accordée aux juges au sein d'un régime démocratique.

National audience; La tomographie est une technique non destructive qui consiste à reconstruire un objet à trois dimensions à partir d’un ensemble d’images obtenues selon différentes orientations de l’échantillon par rapport au faisceau de rayons X. Cette technique est utilisée dans le domaine médical et celui de la science des matériaux. Dans notre laboratoire spécialiste des poudres cette technique d’analyse est un atout notamment pour les études de mise en forme des poudres. En effet, nous pouvons suivre les textures tout au long de la mise en forme. Pour les poudres initiales nous pouvons avoir la structure des agglomérats. Ensuite, nous pouvons déterminer les caractéristiques des empilements granulaires avec les structures des pores en trois dimensions ainsi que les évolutions des caractéristiques (densités, compacités, coordinances) tout au long de l’empilement. Pour finir, les caractéristiques texturales (porosités, répartitions des pores) ainsi que les densités locales peuvent être calculées pour les comprimés, mais aussi des analyses d’homogénéité de composition et de répartition spatiale dans le cas de comprimés obtenus avec des mélanges.

7th World Congress on Particle Technology: New Paradigm of Particle Science and Technology - Procedia Engineering Volume 102 - Editeur: Elsevier Procedia - ISBN: 978-1-5108-0304-6; International audience; Synthesizing fuels from biomass sounds a promising path to reduce the overall green house gases emissions and replace the oil-based fuels. Among the main conversion routes, i.e. biological and thermochemical, the latter presents the advantage of being in the continuation of traditional process engineering, thus more inclined to be rapidly industrialized. Here, we investigate two key points of the process consisting in the transformation of solid wood into suitably sized particles, their transport and injection into an entrained flow gasifier and the Fischer-Tropsch conversion of the resulting syngas in liquid fuel. Because of the very large elasticity of ligno-cellulosic materials, the size reduction by grinding requires too much energy to be economically competitive. In order to increase the wood fragility, and thus decrease the energy consumption, the biomass is preliminarily torrefied (i.e. heated up to 300°C under inert atmosphere). In this section, we present new results correlating the required specific energy, the size of the grid holes used in the knife-mill, the torrefaction intensity and the resulting particle size. For two types of wood (beech for hard wood and spruce for softwood), it is evidenced that the grinding energy decreases exponentially when the particle size increases. Both the prefactor and the characteristic length linearly decrease when the torrefaction becomes more severe. The anisotropic microstructure of ligno-cellulosic materials is the cause of the elongated particles morphology. The poor flowability associated with this particle shape makes the pneumatic transport and injection problematic, which is clearly an obstacle to the industrialization of the process. Indeed, to avoid jamming, larger flow rates of inert gas must be used to convey the particles, with an increasing cost of gas separation at later stages. Here, we present new experimental results showing how flowability is modified by the particles size and shape, which in turn depend on the wood species and the torrefaction intensity. Due to its complex nature, the flowability is characterized in three configurations. The jammed-unjammed threshold is evaluated by shear tests performed on a packed bed. The dense quasistatic flowability is evaluated using a powder rheometer that measures the energy required by a rotating blade to circulate through the bed. The fluidization ability is evaluated at two different scales: in the powder rheometer in presence of an upwards air flow and in a standard fluidization column. Results show that the flowability of torrefied wood particles is very poor and very dependent on the wood species (hardwood or softwood). Due to particles interlocking, the bed is highly porous. This is evidenced by the pressure drop which is about 4 times smaller than expected by the Wu & Yen correlation for compact particles of same size. Also, this interlocking is the cause of an apparent cohesivity, which manifests itself by a channeling tendency and a minimum fluidization velocity about 5 to 10 times larger than expected by the Wu & Yen correlation. The significant difference between spruce and beech flowability is attributed to the particles morphology.

The first part is a bibliographic study. We study the conditions for thermodynamic equilibrium of the hydrates as a bulk medium and the composition of the liquid and solid phases. We then describe the basics of fluid dynamics in a porous medium. Eventually, we merge the two approaches and study the influence of the porous medium on the hydrate stability. An off-shore hydrate field (Blake Ridge) and an on-shore field (Mallik) are precisely described. The latter will be used as a reference case for subsequent numerical simulations. The second part is devoted to the experiments. Their goal is to measure the permeability of a sediment containing crystals. To get closer to natural geologic conditions, crystals are synthesized in absence of free gas. It turns out that hydrates form in a very heterogeneous way in the porous medium, which makes the measurements non representative. We believe that this result has a general character and that, at the laboratory time-scale, it is difficult, to say the least to achieve a uniform distribution of gas hydrates grown from dissolved gas. To circumvene this difficulty, we show, with a theoretical approach, that ice crystals behave much the same way as the hydrate crystals, concerning the Van der Waals forces that govern the agglomeration. This allows us to calculate the Hamaker constant of the hydrates. The second serie of experiments focuses on the permeability of a non consolidated porous medium under mechanical stress, where the pores are filled with ice crystals. Two silica beads populations are used to form a porous medium : 3 mm and 0.2 mm. With the large grains, results show two thresholds : for saturations below the lower threshold, the presence of crystals does not modify the permeability. For saturations above the upper threshold, the permeability vanishes almost completely (percolation phenomenon). Between these two limits, the permeability decreases exponentially with the saturation. With the fine grains, the permeability decreases with the same rate. The last part concerns the numerical study of the Mallik field. We write the equations describing the heat and mass transfers as a function of space and time. Then, we study a one-dimensional limiting case. This allows us to evaluate the influence of the experimentally obtained 'Permeability = f(saturation)' curve on the amount of produced gas. The proposed code gives a way to assess different production scenario, as the pressure reduction enhanced by ice formation., La première partie est une étude bibiographique. Nous étudions les conditions thermodynamiques de stabilité des hydrates dans un milieu bulk et la composition des phases solide et liquide. Nous décrivons ensuite les écoulements dans les milieux poreux. Enfin, nous fusionnons les deux approches en étudiant l'influence du confinement sur la stabilité des hydrates. Un champ offshore (Blake Ridge) et un champ on-shore (Mallik) sont décrits dans le détail. Ce dernier servira de base aux simulations numériques ultérieures. La deuxième partie est consacrée aux expériences. Leur but est de mesurer la perméabilité d'un sédiment contenant des cristaux. Pour nous rapprocher des conditions géologiques naturelles, les cristaux sont réalisés en l'absence de phase gazeuse. Il s'avère que les hydrates se forment de manière très hétérogène dans le milieu poreux et ceci rend les mesures non représentatives. Nous pensons que ce résultat est général et qu'à l'échelle de temps du laboratoire, la formation d'hydrates de gaz répartis uniformément dans un milieu poreux est très difficile. Pour contourner cette difficulté, nous montrons de manière théorique que les cristaux de glace ont un comportement analogue aux cristaux d'hydrate (du point de vue des forces de Van der Waals qui gouvernent l'agglomération). Ceci nous permet de calculer la constante de Hamaker des hydrates. La deuxième série d'expériences s'intéresse donc à la perméabilité d'un milieu poreux non consolidé et sous contrainte dont les pores sont occupés par des cristaux de glace. Deux populations de grains de silice sont utilisées pour former le milieu poreux : 3 mm et 200 microns. Avec les gros grains, les résultats font apparaître deux seuils : pour des saturations plus faibles que le seuil inférieur, la présence des cristaux n'affecte pas la perméabilité. Pour des saturations plus grandes que le seul supérieur, la perméabilité est quasiment nulle (phénomène de percolation). Entre les deux, la perméabilité décroît exponentiellement en fonction de la saturation. Avec les grains fins, la perméabilité décroît avec la même vitesse. La dernière partie est une étude numérique sur le champ Mallik. Après avoir posé les équations décrivant les transferts massiques et de chaleur dans l'espace et au cours du temps, nous étudions un cas limite unidimensionnel. Ceci nous permet de voir l'influence de la courbe 'Perméabilité = f(saturation)' obtenue expérimentalement sur la quantité de gaz produite. Le code proposé permet également d'évaluer différents scénarios de production, dont la dépressurisation assistée par formation de glace.

National audience; Les procédés de compaction par vibrations sont largement utilisés dans l'industrie (génie civil par exemple pour densifier les soubassements de routes). Plus récemment, dans le domaine des fusibles, les vibrations horizontales ont permis d'améliorer le remplissage de sable dans les récipients contenant les éléments fusibles. L'objectif scientifique est de développer la compréhension des mécanismes mis en jeu dans un milieu granulaire vibré horizontalement permettant d'optimiser le procédé industriel. Deux approches ont été utilisées en parallèle, l'une expérimentale, l'autre par simulation numérique. L'approche expérimentale a été réalisée sur des grains de silice de diamètre moyen 500 mm. Un récipient de dimensions allant de 1.5 centimètre à 80 cm est soumis à un mouvement sinusoïdal de fréquence comprise entre 20 et 200 Hz, avec des accélérations allant jusqu'à 10 g. Le dispositif instrumenté permet la mesure instantanée de la force, de l'accélération, de la vitesse des grains aux parois (PIV) et de la densité globale du milieu. L'approche numérique est basée sur la méthode des éléments discrets (DEM). Nous avons développé des méthodes spécifiques d'analyse des résultats pour assurer la comparaison avec l'expérience. Elles permettent d'obtenir des informations qui ne sont pas accessibles expérimentalement comme les densités, vitesses et contraintes locales dans l'ensemble de l'empilement. Dans le cas d'un récipient ouvert, la simulation permet de retrouver les résultats expérimentaux : rouleaux de convections, seuils de comportement, influence de l'accélération... Des résultats originaux ont été établis dans les expériences et les simulations comme une croissance de la vitesse des grains avec la longueur du récipient. La simulation a aussi permis d'obtenir des résultats comme l'influence du coefficient de friction sur le sens des rouleaux et la caractérisation des contraintes au sein de l'empilement. Le comportement du sable dans un récipient fermé (milieu confiné) a été étudié expérimentalement au cours d'un remplissage progressif. De nettes différences par rapport au milieu ouvert ont été constatées lorsque le taux de remplissage devient élevé. Des mesures d'accélération et de force sur l'ensemble du dispositif ont permis de définir et mesurer une masse apparente et l'énergie dissipée par le dispositif. This work on the densification of a granular medium under horizontal vibrations was realised in the context of an industrial study on sand in fuses. The scientific purpose is the understanding of the mechanisms involved in horizontally vibrated granular media, either in open box as in closed systems. Both experiments and computer simulations were used to follow the behaviour of the sand packing. Experiments were conducted with 500 μm silica grains. Sinusoidal accelerations up to 10 g were applied to a container of a few centimetres using frequencies between 20 and 200 Hz. The experimental device enables instantaneous force, acceleration, grain velocity on the walls (PIV) and mean bulk density to be measured. Discrete element method (DEM) was used for the computer simulations. Specific techniques were developed to analyse the results and compare them with experiments. Computer simulations provided data which are not experimentally available such as local values of density, velocities and stress inside the particle packing. In the case of an open container, simulation results are in good agreement with experimental ones (convection rolls, thresholds, effect of acceleration...). Original results are obtained in both experiments and simulations, such as the grain velocity increasing with the container length. Simulation provided specific results such as the effect of friction coefficients on the direction of rotation of convection rolls and the haracterization of stress inside the particle packing. The behaviour of sand in a closed container (confined medium) was studied during a progressive filling. Significant differences were observed when the filling rate becomes high. The dissipated energy and the apparent mass of the vibrated device were defined and measured using acceleration and force measurements. The highest densities were reached for very high relative acceleration.

International audience; The development of highly dispersible silica micropearls by Rhodia led to the introduction of silica as a reinforcing filler in Green tyres in 1992 by Michelin. However new environmental constraints imply to further improve the silica dispersion process.The objective of the present work was to investigate the role of silica intrinsic parameters on its dispersibility in order to determine key parameters to improve the silica dispersion. The behaviour of different silica grades was thus investigated: two classical silica micropearl grades for tyre applications different in their specific area (silica Z1165MP with a high specific area and silica Z1115MP with a lower specific area), the same grades chemically modified with a covering agent (silane), and pilot grades (same specific area, same aggregate structure as Z1165MP) synthesized by Rhodia where the physico-chemistry of the silica surface was modified during the silica process. The dispersion behaviour was characterized in model conditions: in air (impact on wall) and under shear in a SBR matrix (rheo-optical device).The direct observation of dispersion mechanism in a SBR matrix under shear showed that the Z1115MP dispersed via an efficient mechanism of disintegration with the sudden breakage of the micropearl into micron size fragments above a low critical stress whereas the Z1165MP ruptured into a few large fragments at a higher stress. The post-chemical modification of the silica surface using silane had no effect on the silica dispersion compared to raw materials. However the modification of the physico-chemistry of the silica surface during the silica process implied changes in the internal organisation of the micropearl and allowed to modify the dispersion mechanism.This work was performed in the framework of DURAMAT project, programme of AXELERA for innovative, durable and environmental friendly materials. The authors thank the other partners of the project (LRMP-IMP, LTDS/ECL in Lyon) for their collaboration.

International audience; Precipitated silica is traditionally used as reinforcing filler in rubber applications. In pneumatic manufacture, it offers several advantages compared to carbon black. Indeed, in tyre treads, precipitated silica can yield a lower rolling resistance and better wet grip at equal wear resistance than carbon black.Filler dispersion can be characterized using different methods (. In the present work we use three different approaches to compare the dispersability of two grades of amorphous precipitated silica in the shape of micropearls, characterized by different specific areas. The three approaches are: the first approach is based on the analysis of the behaviour of silica micropearls under mechanical stress in air (fluidized bed and impact on wall) and in water (ultrasounds), dispersion kinetics of silica measured into air or water with the development of specific descriptors to follow dispersion kinetics, the second method is based on the characterization of dispersion mechanisms of silica micropearls into the elastomer matrix in the diluted regime via the use of a transparent counter-rotating plate-and-plate shear cell coupled with an optical microscope. In this case, the micropearl is subjected to hydrodynamic stresses due to the shear of the elastomer matrix, the last method is based on the analysis of dispersion during the mixing operation of silica and the elastomer in an internal mixer coupling information from rheology, bound rubber and SEM to follow the dispersion.We will show that the different approaches bring complementary information on the dispersion mechanisms but also on the intrinsic properties of silica.

International audience; Biomass flowability is a major issue in the processes dedicated to the thermochemical conversion of biomass based on technologies such as downward-moving bed reactor, dense fluidized bed reactor and entrained flow gasifier. Torrefaction is an example of process influencing powder mechanical property: researchers [1] recently proved torrefaction changes the physical and chemical properties of the material. In particular, it improves the feedstocks homogenization and makes the grinding easier. In the field of this biomass pretreatment for biofuel production, IFP Energies nouvelles and Ecole des Mines de Saint-Etienne study the effects of the combined torrefaction and grinding processes. An experimental protocol then was developed to observe (i) the major particle behavior: anhydrous weight loss (AWL), grindability, particle size and shape, surface state, (ii) and the major powder behavior: bulk density, flowability, compressibility, aerability. One parameter is studied there, the torrefaction temperature. To perform the particles and powders characterization, several techniques were used: optical microscopy, scanning electron microscopy, Flodex® methodology and powder rheometer. Samples of spruce are first torrefied at different temperatures (S240, S300) then ground with a sieving grid of 0.5 mm. From 200 to 300°C, the AWL increases from 1 to 26%. The rheological study of the biomass powders shows that flowability is significantly improved in the only case of a high torrefaction (S300). Compressibility and aerability are also increased with the level of torrefaction temperature. These results are correlated to particles morphological characterization: the powder rheological behavior is only influenced by a characteristic size parameter, such as Sauter mean diameter.

The thermochemical processes for biomass conversion such as downward-moving bed reactor, dense fluidized bed reactor and entrained flow gasifier need a good knowledge of biomass flowability. By its study, transfers (mass, momentum, heat) and reactions (drying, torrefaction, gasification) could be optimized into reactors. Moreover, its control depicts a technology challenge for efficient handling, transportation and injection in order to prevent the process from caking, bridging or other dysfunctions. Torrefaction is a thermal pretreatment of lignocellulosic biomass before gasification. This mild form of pyrolysis, carried out at temperatures between 200 and 300 °C, changes the physical and chemical properties of the material. In particular, it improves the feedstocks homogenisation, enhances the aeration ability and makes the grinding easier (Repellin et al.). Researchers usually devote some techniques to evidencing a posteriori the effects of parameters such as particle size distribution, moisture content of the biomass, humidity of the surrounding atmosphere and temperature (Ganesan et al.). However, a priori explanation of what makes biomass powders flowable requires a complete experimental procedure that combines the simultaneous characterization of the powders and their particles. IFP Energies nouvelles and Ecole des Mines de Saint Etienne have co-developped experimental procedures and related tools for the characterization of wood biomass flowability. The effects of the combined torrefaction and grinding processes are studied on (i) the major particle behavior: grindability, surface state, particle size, shape distribution (ii) and the major powder behavior: bulk density, compressibility, aerability. In this article, the only studied parameter we chose to present is the torrefaction temperature.

National audience; Torrefaction is a thermal pretreatment of lignocellulosic biomass before gasification. This mild form of pyrolysis, carried out at temperatures between 200 and 300 °C, changes the physical and chemical properties of the material. In particular, it improves the feedstocks homogenisation, enhances the aeration ability and makes the grinding easier. Our project deals with the study of the effects of the combined torrefaction and grinding processes on (i) the major particle behaviour: grindability, surface state, particle size, shape distribution (ii) and the major powder behaviour: bulk density, compressibility, aerability. In this article, the studied parameter is the torrefaction temperature. The characterisation of the particles and powders is performed using the following techniques: optical microscopy, Flodex® methodology and powder rheometry. The rheological behaviours of spruce torrefied at different temperatures then ground in the same apparatus (a knife mill with a sieving grid of 500 µm) are compared. It is shown that spruce torrefied at 240 °C (S240) has similar rheological properties compared to natural spruce (NS) after being ground, while the one torrefied at 300 °C exhibits a different rheological behaviour. The results are correlated to reproduce the coupled effect of the torrefaction and grinding conditions on the powder rheological behaviour.

International audience; Precipitated silica is traditionally used as reinforcing filler in rubber applications. In pneumatic manufacture, it offers several advantages compared to carbon black. Indeed, in tyres treads, precipitated silica can yield a lower rolling resistance and better wet grip at equal wear resistance than carbon black. The development of a new method to study the fragmentation mechanism of precipitated silica is investigated. Usually, the dispersion of granules is done in high viscous media (elastomer or oils). In this paper, the study is carried out in a friendlier medium (air or water).

Torrefaction is a thermal pretreatment of lignocellulosic biomass before gazification. This mild form of pyrolysis, carried out at temperatures between 200 and 300 °C, changes the physical and chemical properties of the material. In particular, it improves the feedstocks homogenization, enhances the fluidization ability and makes the grinding easier. Our project deals with the study of the effects of the combined torrefaction and grinding processes on (i) the main particle behavior: anhydrous weight loss (AWL), grindability, particle size distribution (ii) and the main powder behavior: bulk densities, flowability and compressibility. The studied parameters are (i) the species of the biomass (spruce and beech) (ii) the torrefaction temperature (iii) and the sieving grid size of the used knife mill (0.12 and 0.5 mm). The characterization of the particles and powders is performed using the following techniques: optical microscope and powder rheometer. The rheological behaviours of spruce torrefied at different temperatures and ground at different grid sizes are compared. It is shown that spruce torrefied at 240 °C and ground at 0.5 mm (S240/0.5) has rheological properties not as good as S240/0.12 and S300/0.5 that seem to have similar characteristics. Finally, further experiments are necessary to obtain a better morphological and rheological particle characterization., Proceedings of the 19th European Biomass Conference and Exhibition, 6-10 June 2011, Berlin, Germany, pp. 1902-1904

International audience; Numerical and experimental studies have been undertaken to analyze three parameters controlling the compaction of granular media submitted to sinusoidal horizontal vibrations. We have characterized the influence of the dimensionless acceleration "Gamma", the geometry of the container and the friction coefficients on the grain velocities and on the packing densities. Above a critical acceleration "Gamma" critiq, the velocities increases with "Gamma". For low values of "Gamma", the surface layers are compacted, whereas the bottom layers remain at their initial density. For high values of "Gamma", the bottom layers get compacted, the surface layers are fluidized so that the bulk dynamic and relaxed densities decreased. In the same way, the effect of the dimensions of the container and of the friction coefficients on the packing properties has been studied for given heights of sand, acceleration and frequency. It has been shown that the influence of the two last parameters is similar to that of acceleration. The numerical results given by the Discrete Element Method appear to be in good agreement with experimental results.

National audience; Numerical and experimental studies have been undertaken to analyze the compaction of a granular media submitted to sinusoidal horizontal vibrations. We characterize especially the influence of the dimensionless acceleration Γ of the vibrations and of the size of the box. For low value of Γ, the surface layers are compacted and the bottom layers remain at their initial density. The jamming effect of the bottom layers is explained by the influence of the pressure in these layers, which constraints the grains in their displacements. For high values of Γ, the bottom layers get compacted, the surface layers are fluidized and the density is decreased. We have also noticed that the compaction intensity depends on the size of the box: when the size of the box is lowered, the compaction becomes smaller.

International audience; We report experimental observations of a horizontally vibrated granular medium made out of sand grains. For large enough acceleration, two counter-rotating convection rolls appear in the upper part of the granular packing, whereas the bed remains unperturbed in the lower part. For increasing acceleration, the free surface exhibits different shapes: slight dome, two ridges and single roof. A quantitative characterization is performed by mean of PIV and image analysis. It shows that both relaxed and dynamic densities present a maximum at =3.8 and that the measured thickness of the fluidized region scales with a square root law (as a function of the dimensionless acceleration). In the discussion, a convection mechanism is proposed, as well as an analogy with classical Newtonian fluids.

International audience; Sinusoidal horizontal vibrations have been applied to a parallelepiped containing rounded sand grains. To model the granular medium behavior, a commercial software based on Molecular Dynamics has been used. The influence on the rheologic behavior of many process parameters, such as the dimensionless acceleration and the frequency has been studied. The velocity, density, pressure and mass flow fields have been computed, both in dynamic and static modes and compared with experimental results. The correlation between these different parameters has been also examined.

International audience; One industrial process used by Nexter Munitions to manufacture pyrotechnical materials consists in preparing an emulsion of wax in TNT (2,4,6-trinitrotoluene) and adding Aluminium and ONTA (3-nitro-1,2,4-triazole-5-one) particles. When the suspension is homogeneous, it is allowed to flow by gravity through a pipe located at the bottom of the tank and to fill up a shell body. The suspension is characterized by a solid volume fraction of 53.4%, which leads to high viscosities. In some circumstances, the emptying time is prohibitively long and the economic profitability is reduced. This study has been performed to make the emptying time lower with the constraint of unchanged volume fractions and grains mean diameter. So, we investigated the influence of the grain size distribution on the suspension viscosity. Different samples of Aluminium and ONTA have been used, with rather small differences in grain size distributions. The suspensions have been prepared in the industrial tank and the flow cast times measured. It has been observed that they differ by one order of magnitude. To avoid situations with too high emptying times, a procedure has been implemented to make prior characterization of the suspension rheology. Because of particles sedimentation and emulsion destabilisation, the classical Couette rheometer is not adapted. So, we designed and built a small size tank (113 cm3), where the suspension is continuously stirred and kept homogeneous. The measurement of the torque and rotational speed together with the use of the Couette analogy allowed us to observe an Ostwald fluid behaviour (flow consistency index k, flow behaviour index n). To gain in prediction, we established a correlation between the measured (k, n) values and the grain size distributions. We characterized each suspension by the ratio of to , where is the solid volume fraction (imposed by the commercial specifications) and is the maximum packing fraction. Because of the strong analogy between concrete and energetic paste, we chose the widely used De Larrard model to compute . A linear dependance between the ratio and the indices k and n was observed. The second step was to provide an analytical expression for the flow cast time of a power-law suspension from a tank with a given geometry. Considering the large difference between the industrial inner tank diameter and the evacuation pipe diameter, we assumed that all the pressure drop was located in the evacuation pipe. Then, extending the Hagen-Poiseuille equation to Ostwald fluid, we were able to predict the emptying time with the knowledge of k and n. Experimental and predicted emptying time are in very good agreement. This work helped the industrial manufacturer to divide the emptying time by a factor 12.

La compression de poudre céramique nécessite l'incorporation de molécules organiques assurant la cohésion des grains entre eux. Comprimer des poudres céramiques formulées revient à leur fournir une certaine énergie. En fonction de la formulation de la poudre, on peut mesurer l'énergie stockée par unité de masse, caractéristique de la poudre. Récemment, une technique employée dans la métallurgie des poudres, la Compaction Grande Vitesse (CGV), a été utilisée pour la mise en forme d'objets céramiques. Cette méthode apporte des particularités au niveau des propriétés physiques des comprimés, notamment en terme d'homogénéité par rapport au pressage uniaxial dit conventionnel. Des comprimés issus des deux méthodes de mise en forme, et élaborés à partir de poudres formulées différemment, seront comparés en terme de comportement à la compression et via l'utilisation d'un modèle mathématique. - The compression of ceramic powders requires the addition of organic materials to insure tablet cohesion. For the compaction of formulated ceramic powders it is necessary to supply them energy. As a function of the formulation of ceramic powders, one can measure the specific energy acquired during the tablet compression. Recently, a technique used in powder metallurgy, High Velocity Compaction (HVC), has been studied to form ceramic compacts. This method brings special physical properties to tablets in terms of homogeneity compared to conventional uniaxial pressing. The properties of tablets prepared by the two processes are compared and discussed through a phenomenological model.

L'arrivée des nanomatériaux parmi les objets du quotidien semble porteuse de fonctions d'usage innovantes, mais pose de nombreux problèmes de mise en œuvre lors de l'intégration de particules nanométriques dans des procédés de fabrication standardisés. Il semble donc impératif d'adapter les procédés de transformation habituels.

National audience; Cette étude expérimentale d'un milieu granulaire 3D soumis à des vibrations horizontales montre que ce milieu subit une transition vers la fluidisation pour une valeur critique de l'accélération c1 croissante avec la fréquence. Deux rouleaux de convection contrarotatifs ont été observés. Des mouvements ascensionnels de grains sur les parois perpendiculaires aux vibrations sont observés pour fortes valeurs de . Partant d'un état initial peu dense Ci~0,6, les vibrations horizontales ont tendance à le densifier. Le taux de densification augmente presque linéairement avec l'accélération. Il décroît ensuite pour se stabiliser finalement pour les fortes accélérations.

Colloque avec actes et comité de lecture. Internationale.; International audience; L'objectif de ces travaux est de proposer un modèle prédictif des temps d'écoulement des suspensions concentrées en matériaux énergétiques dans une configuration similaire au procédé de mise en oeuvre développé en production. Les résultats expérimentaux sont comparés à trois modèles de fluide biphasique (Quémada, Krieger-Dougherty, Mooney) représentant la viscosité dynamique comme étant fonction de la fraction volumique solide , de l'empilement compact maximal et de la viscosité du fluide interstitiel . Le modèle de De Larrard est utilisé pour le calcul de . Les hypothèses d'un fluide parfait et incompressible, pour le calcul du temps de coulée du fluide interstitiel , aboutissent à la relation de Bernoulli et satisfont à l'expérience. Nous montrons que le modèle de Quémada conduit à des valeurs théoriques du temps de coulée de la suspension en bon accord avec les valeurs expérimentales.

6 pages; L'arrivée de nanomatériaux parmi les différents matériaux utilisés en pyrotechnie pose de nombreux problèmes de mise en œuvre. En effet, leurs propriétés texturales particulières ne permettent pas de les utiliser comme des matériaux classiques. Il est impératif d'adapter les procédés de mise en œuvre habituels. Pour obtenir l'adéquation de ces nouveaux matériaux et de nos procédés, des études spécifiques du comportement des nanomatériaux au cours des procédés de mise en œuvre par coulée ont été réalisés. L'observation des écarts de comportement des nanomatériaux par rapport aux "micro-matériaux" pour une même nature chimique et des conditions identiques de mise en œuvre permet d'établir des lois de comportement spécifiques, fonction de la taille des particules manipulées. Les mentalités, comme les procédés, doivent évoluer et prendre en compte l'élévation de surface spécifique qu'offre le passage à l'échelle nanométrique. Ainsi un chargement moindre en nanomatériaux ne sera pas forcement synonyme de lacunes sur les caractéristiques du produit fini (propriétés mécaniques ou pyrotechniques). Deux questions peuvent alors se poser : faut-il adapter les formulations aux procédés, en prenant en compte les caractéristiques des matières premières ou bien adapter des procédés devant supporter des taux de chargement élevés en nanomatériaux ? Le manque de connaissance et le recul sur le comportement des nanomatériaux sont un frein à leur intégration dans des composés pyrotechniques mais les propriétés exhibées laissent présagées d'un grand intérêt en vue de l'optimisation des propriétés des composés fabriqués.

5 pages; The ForDiMHyS project is a program devoted to experimental studies and the model development of the kinetics of FORmation and Dissociation of Methane Hydrates in Sediments. The first part of the project that is presented hereafter is designed to obtain experimental data on hydrate formation & dissociation under in-situ temperature and pressure conditions of methane hydrate in well constrained porous materials. The second part presented in another paper (Jeannin et al., 2002) consists in modelling the flows inside the core; a specific numerical model has been developed to simulate the experimental set-up described in part one. The numerical model is 3D three phases and simulates the kinetics of hydrate dissociation and formation, taking into account the solubility of methane in water and the heat of phase transitions.

5 pages; The ForDiMHyS project is a program devoted to experimental studies and the model development of the kinetics of FORmation and Dissociation of Methane Hydrates in Sediments. The first part of the project which is presented in another paper (Bonnefoy and Herri, 2002) is designed to obtain experimental data on hydrate formation & dissociation under in-situ temperature and pressure conditions of methane hydrate in well constrained porous materials. The second part presented hereafter consists in modelling the flows inside the core; a specific numerical model has been developed to simulate the experimental set-up described in part one. The numerical model is 3D three phases and simulates the kinetics of hydrate dissociation and formation, taking into account the solubility of methane in water and the heat of phase transitions.