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International audience; Electrical cable sheaths are the most abundant fire load in nuclear power plants, mainly in rooms that are kept in under slight pressure. This configuration leads fires to grow in under-ventilated and vitiated conditions. Assessing fire threat involves characterizing the heat released, responsible for fire growth, and the smoke evolved, which may interact with sensitive components in the area. For that purpose, a revisited controlled-atmosphere cone calorimeter has been designed, set up, and coupled to a Fourier transformed infrared spectrometer and an electrical low-pressure impactor to measure simultaneously the evolved gases and aerosols, respectively. This bench-scale apparatus has been first qualified with polymethylmethacrylate. It has second been used to characterize polyvinylchloride cable sheath representative material reaction to fire in under-ventilated and vitiated conditions. It appeared that vitiation in under-ventilated fires lowers the heat release rate and the fuel mass loss rate.

International audience; The purpose of this paper is to propose a time-step-robust cell-to-cell integration of particle trajectories in 3-D unstructured meshes in particle/mesh Lagrangian stochastic methods. The main idea is to dynamically update the mean fields used in the time integration by splitting, for each particle, the time step into sub-steps such that each of these sub-steps corresponds to particle cell residence times. This reduces the spatial discretization error. Given the stochastic nature of the models, a key aspect is to derive estimations of the residence times that do not anticipate the future of the Wiener process. To that effect, the new algorithm relies on a virtual particle, attached to each stochastic one, whose mean conditional behavior provides free-of-statistical-bias predictions of residence times. After consistency checks, this new algorithm is validated on two representative test cases: particle dispersion in a statistically uniform flow and particle dynamics in a non-uniform flow.; L’objectif de ce papier est de proposer un algorithme robuste en pas de temps permettant l’intégration face à face de la trajectoire de particules dans des maillage 3-D non-structurés pour des méthodes lagrangiennes stochastiques. L’idée principale est de mettre à jour de façon dynamique les champs moyens utilisés dans l’intégration temporelle. Pour ce faire, pour chaque particule, on subdivise le pas de temps en sous pas de temps, de façon à ce que chacun de ceux-ci correspondent au temps de résidence de la particule dans une cellule. Ce faisant on réduit l’erreur de discrétisation spatiale. Étant donnée la nature stochastique du modèle, un aspect prépondérant est de pouvoir dériver des estimations du temps de résidence des particules dans les cellules qui n’anticipent pas le futur des processus de Wiener. Dans ce but, le nouvel algorithme est basé sur une particule virtuelle attachée à chaque particule stochastique, dont le comportement conditionné moyen permet d’obtenir des temps de résidence qui ne sont entachés d’aucun biais statistique. Après une vérification de consistance, ce nouvel algorithme est validé sur deux cas de tests représentatifs : une dispersion de polluants dans un écoulement statistiquement uniforme et un écoulement non-uniforme dans lequel on traque la dynamique des particules.

International audience

We investigate artificial compressibility (AC) techniques for the time discretization of the incompressible Navier–Stokes equations. The space discretization is based on a lowest-order face-based scheme supporting polytopal meshes, namely discrete velocities are attached to the mesh faces and cells, whereas discrete pressures are attached to the mesh cells. This face-based scheme can be embedded into the framework of hybrid mixed mimetic schemes and gradient schemes, and has close links to the lowest-order version of hybrid high-order methods devised for the steady incompressible Navier–Stokes equations. The AC time-stepping uncouples at each time step the velocity update from the pressure update. The performances of this approach are compared against those of the more traditional monolithic approach which maintains the velocity-pressure coupling at each time step. We consider both first-order and second-order time schemes and either an implicit or an explicit treatment of the nonlinear convection term. We investigate numerically the CFL stability restriction resulting from an explicit treatment, both on Cartesian and polytopal meshes. Finally, numerical tests on large 3D polytopal meshes highlight the efficiency of the AC approach and the benefits of using second-order schemes whenever accurate discrete solutions are to be attained.

International audience; The present study is dedicated to the development of an original method f or the measurement of the individual amounts QASi of the acid sites ASi (acidity of Le wis and Brønsted) present on three TiO2 based solids of increasing composition compl exity: TiO2-P25, 6% WO3/TiO2-P25 and a sulfated 0.7% V2O5/9% WO3/TiO2 NH3-SCR catalyst. The method is based on quantitative characterizations of the NH3 adsor ption equilibrium (adsorption temperature Ta and pressure Pa) by the association of (a) the AEIR method providing the individual coverage qASi(Ta, Pa) of the adsorbed NH3 species on the ASi sites and (b) the total amount (in µmol/g) of the adsorbed NH3 spec ies: QTNH3(Ta, Pa) by using a mass spectrometer. For a solid having n types of ASi si tes, the QASi values are obtained from the numerical solution of linear equation system s (with at least n equation) obtained considering that QTNH3(Ta, Pa) is equal to the su m of the contribution of each adsorbed NH3 species: QASi qASi(Ta, Pa).This imposes the measurement of at least n QTNH3(Ta, Pa) in a Ta range preventing the contributio n of parallel surface processes (i.e NH3 oxidation). On TiO2-P25, n= 3 (two Lewis and one weak Brønsted acid sites) and the QASi amounts are ob tained from three QTNH3(Ta, Pa) values. The others solids having two Lewis (L1 and L 2) and two Brønsted (B1 and B2) acid sites impose a series of m measurements of QT NH3(Ta, Pa) with m>> n: the QASi are obtained by optimization between theoretical an d experimental QTNH3(Ta, Pa) curves such as 109, 202, 70 and 130 µmol/g for QL2, QL1, QB2 and QB1 respectively of 0.7% V2O5/9% WO3/TiO2. It is shown that these fo ur amounts of sites permit to conclude that the L2 Lewis acid site is the one forming the pivotal NH3ads-L2 species of the reaction by using nitrogen mass balances between the amounts of a dsorbed NH3 species and the N2 production in the presence of NO.

International audience; Large Eddy Simulation (LES) of the lab-scale methane fire plumes investigated experimentally by McCaffrey are performed using the steady laminar flamelet/presumed beta filtered density function model on grids of different resolution ranging from the Taylor length scale to about six times the Kolmogorov length scale. This work focuses on investigating existing subgrid (SGS) mixing models for mixture fraction variance prediction. Three different models based on the local equilibrium assumption, the variance transport equation (VTE) and the second moment transport equation (STE) are assessed. In the non-equilibrium modeling (VTE and STE), the scalar dissipation rate is modeled with an algebraic expression involving a SGS mixing timescale. The comparison of the solutions is based on the convergence properties of LES statistics for mixture fraction, temperature and axial velocity with respect to the filter width. The simulations show that the equilibrium algebraic model is not suitable for purely buoyant flows. On the other hand, simulations performed with the transport models show that grids coarser than 1 cm cannot resolved adequately the natural laminar instability near the edge of the plume that governs the formation of large scale vortex and, therefore, underestimate the mixing process, especially in the lower part of the continuous flame. For grid resolutions finer than 1 cm, the STE model is less sensitive to grid refinement than the VTE formulation and differences between the two models are reduced with grid refinement. The STE model predicts also a stronger mixing, resulting in a slightly larger lateral expansion of the fire plume. Predicted solutions by the two models are in quantitative agreement with the experimental data in terms of axial temperature, velocity and temperature fluctuations.

The purpose of this review is to analyze the physics at play in particle resuspension in order to bring insights into the rich complexity of this common but challenging concern. Following the more-is-different vision, this is performed by starting from a range of practical observations and experimental data. We then work our way through the investigation of the key mechanisms which play a role in the overall process. In turn, these mechanisms reveal an array of fundamental interactions, such as particle-fluid, particle-particle and particle-surface, whose combined effects create the tapestry of current applications. At the core of this analysis are descriptions of these physical phenomena and the different ways through which they are intertwined to build up various models used to provide quantitative assessment of particle resuspension. The physics of particle resuspension implies to hold together processes occurring at extremely different space and time scales and models are key in providing a single vehicle to lead us through such multiscale journeys. This raises questions on what makes up a model and one objective of the present work is to clarify the essence of a modeling approach. In spite of its ubiquitous nature, particle resuspension is still at the early stages of developments. Many extensions need to be worked out and revisiting the art of modeling is not a moot point. The need to consider more complex objects than small and spherical particles and, moreover, to come up with unified descriptions of mono- and multilayer resuspension put the emphasis on solid model foundations if we are to go beyond current limits. This is very much modeling in the making and new ideas are proposed to stimulate interest into this everyday but challenging issue in physics., Comment: 123 pages, 65 figures, submitted to Physics Reports

International audience; A detailed computational study was performed for the case of a wall-bounded pin-fin-array in a staggered arrangement, representative of industrial configurations designed to enhance heat transfer. In order to evaluate the level of turbulence modelling necessary to accurately reproduce the flow physics at three (3) different Reynolds numbers (3, 000, 10, 000 and 30, 000), four models were selected: two eddy-viscosity URANS models (k-ω-SST and φ-model), an Elliptic Blending Reynolds-stress model (EB-RSM) and Large Eddy Simulation (LES). Global comparisons for the pressure loss coefficients and average Nusselt numbers were performed with available experimental data which are relevant for industrial applications. Further detailed comparisons of the velocity fields, turbulence quantities and local Nusselt numbers revealed that the correct prediction of the characteristics of the flow is closely related to the ability of the turbulence model to reproduce the large-scale unsteadiness in the wake of the pins, which is at the origin of the intense mixing of momentum and heat. Eddy-viscosity-based turbulence models have difficulties to develop such an unsteadiness, in particular around the first few rows of pins, which leads to a severe underestimation of the Nusselt number. In contrast, LES and EB-RSM are able to predict the unsteady motion of the flow and heat transfer in a satisfactory manner.

International audience; We focus here on a technique to compute compressible fluid flows in physical domains cluttered up with many small obstacles. This technique, referred to here as the integral formulation, consists in integrating the flow governing equations over the fluid part of control volumes including both fluid and solid zones; doing so, the integral of fluxes over solid boundaries may appear, for which expressions as a function of discrete variables must be provided. The integral formulation presents two essential advantages: first, we naturally recover the standard fluid approach when the mesh is refined; second, fluid/solid interactions may be, to some extent, modelled to recover the singular head losses at the interface between a free and a congested part of the computational domain. We apply here this approach to the Euler equations, using a collocated space discretization and a pressure correction algorithm, preserving the positivity of both the density and the internal energy. Verification test cases are performed, including a Riemann problem in a free domain and a shock wave reflection on a wall, using an equation of state whichis suitable for weakly compressible fluid flows. Finally, we address a two-dimensional situation, where a shock wave impacts a set of obstacles; we observe a very encouraging agreement between the integral approach results and a CFD reference solution obtained with a pure fluid approach on a fine mesh.

International audience; Background: Aggressiveness is a stigma frequently associated with schizophrenia. The role of insight as a risk factor of aggressiveness remains contradictory; mainly because single measures of these states mask their complexity and heterogeneity.Methods: This study was conducted on 666 patients aged 15 and above with a DSM-IV-TR diagnosis of schizophrenia spectrum disorder, drawn from the French national network of schizophrenia expert center database. Collected data comprised socio-demographics and standardized psychiatric assessments. Aggressiveness was evaluated using the Buss-Perry Aggression Questionnaire and insight using the Scale to assess Unawareness of Mental Disorder (SUMD) and Birchwood Insight Scale (BIS).Results: Hostility was the aggressiveness dimension the most strongly associated with SUMD insight dimensions. Patients aware of their illness were nearly twice as likely to show hostility than those seriously unaware (OR = 1.95, 95% CI.: 1.08-3.5), but not when further adjusting for depression. Similarly, those aware of the consequences of their illness and of their symptoms were more hostile. Patients moderately aware of illness consequences had a higher risk of both anger and physical aggressiveness than those unaware (OR = 2.63, 95% CI.: 1.42-4.86, OR = 2.47, 95% CI.: 1.33-4.60, respectively), even when adjusting for depression for anger.Conclusion: Our study confirms that a multi-dimensional approach to insight and aggressiveness is essential to understand the types of links between these clinical states. Insight may trigger the expression of an underlying hostile tendency, maybe via depression and self-stigmatisation. This should be taken into account in therapeutic approaches to improve insight.

International audience; Discontinuity of the dissipation rate associated with the temperature variance at the fluid-solid interface is analyzed in a turbulent channel flow at a Reynolds number, based on the friction velocity of 395 and a Prandtl number of 0.71. The analysis is performed with a wall-resolved Large Eddy Simulation and the results are used to derive a regression for the dissipation rate discontinuity, which depends only on the fluid-solid thermal diffusivity and conductivity ratios. Wall-resolved Large Eddy Simulations at a higher Reynolds number and a higher Prandtl number are used to investigate the validity of two correlations derived from the regression for the selected thermal properties ratios. The present results are obtained with the open-source Computational Fluid Dynamics solver Code Saturne, and use the fully conservative fluid-solid thermal coupling capability introduced by the authors in version 5.0.

In a global effort to decrease human sourced Greenhouse Gas (GHG emissions, the operation of GHG emitting plants is only justified if they offer a sufficient flexibility to satisfy a highly variable net electric demand in electric grids with a significant share of intermittent renewable power plants. The EU funded project sCO2 Flex aims at designing a highly flexible 25 MWe supercritical CO 2 cycle s uitable for such a complementarity with renewable energies, and testing its main components. However the performance of such a cycle should not be reached at the expense of its environmental impact. Therefore the present paper focuses on the analysis of the environmental impact of such a plant, following most of the guidelines of the Life Cycle Assessment (LCA) method, as described in the ISO 14040 14044 standards. The assessment described in this paper was conducted on the open source software OpenLCA usi ng the database Ecoinvent, both acknowledged by the LCA community. It encompasses four major steps: goal and scope definition of the project, inventory analysis of the data, impact analysis and interpretation. Data was picked directly from the Ecoinvent database, gathered from the project’s contributors, or extrapolated from hypotheses if data was to be missing in the inventory analysis. To compensate the uncertainties due to lack of data on equipment scaling and operation practices, an extensive sensitivity analysis has been carried out to bring additional robustness to the study. Considering the two impact categories selected in this paper (global warming potential at 100 years scope and abiotic resource depletion), the sCO2 Flex plant outperforms the reference water/steam plant for global warming potential thanks to its higher efficiency. This is however at the expense of a considerably higher abiotic resource depletion. Regarding the latter impact category, the most significant uncertainties arise from the amount of nickel based alloys used in the boiler., Conference Proceedings of the European sCO2 Conference4th European sCO2 Conference for Energy Systems: March 23-24, 2021, Online Conference, p. 194

Hybrid RANS–LES approaches have aroused interest for years since they provide unsteady information at a reduced numerical cost compared to LES. In the hybrid context, the use of temporal filtering, to control the energy partition between resolved and modeled scales, ensures a consistent bridging between RANS and LES models. In this regard, a new formulation of Hybrid Temporal Large Eddy Simulation (HTLES) is developed, aiming at improving the theoretical foundation of the model associated with an eddy-viscosity closure. The analytical development is performed, applying the Hybrid-Equivalence criterion, and the model is calibrated in decaying isotropic turbulence. In addition, an upgraded version of the approach is proposed to improve the behavior of the model in near-wall regions, introducing a two-fold shielding function and an internal consistency constraint to provide a suitable control of the RANS-to-LES transition. Applying HTLES to the k– $$\omega$$ SST model, the validation process is carried out on channel and periodic-hill flows, over a range of grids and Reynolds numbers. The predictive accuracy and the robustness to grid coarsening are assessed in these cases, ensuring that HTLES offers a cost-saving alternative to LES.

International audience; A new formulation of the model used in the near-wall region for the turbulent heat flux is developed, in order to extend the Elliptic Blending Differential Flux Model of Dehoux et al., Int. J. Heat Fluid Fl. (2017), to various boundary conditions for the temperature: imposed wall-temperature, imposed heat flux or Conjugate Heat Transfer (CHT). The new model is developed on a theoretical basis in order to satisfy the near-wall budget of the turbulent heat flux and, consequently, its asymptotic behavior in the vicinity of the wall, which is crucial for the correct prediction of heat transfer between the fluid and the wall. The models of the different terms are derived using Taylor series expansions and comparisons with recent direct numerical simulation data of channel flows with various boundary conditions. A priori tests show that this methodology makes it possible to drastically improve the physical representation of the wall/turbulence interaction. This new differential flux model relies on the thermal-to-mechanical timescale ratio which depends on the thermal boundary condition at the wall. The key element entering this ratio is ε θ , the dissipation rate of the temperature variance θ 2. Thus, a new near-wall model for this dissipation rate is proposed, in the framework of the second-moment closure based on the elliptic-blending strategy. The computations carried out in order to validate the new differential flux model demonstrate the very satisfactory prediction of heat transfer in the forced convection regime for all kinds of thermal boundary condition.

This article reports Large Eddy Simulation (LES) of 30 cm diameter methanol pool fires in order to investigate the effects of the burner boundary conditions on the pool dynamics. The numerical model involves state-of-the-art subgrid scale (SGS) sub-models for mixing, combustion and turbulence-radiation interaction with all the model constants computed dynamically. The non-adiabatic steady laminar flamelet (SLF)/presumed filtered density function (FDF) combustion model is used whereas the radiation model combines the Rank Correlated Full Spectrum k-distribution (RCFSK) for spectral radiation with the finite volume method (FVM) as radiative transfer equation (RTE) solver. The baseline case considers a burner located one-pool diameter above the floor and a fuel lip height of 1 cm as specified in the experiments used for model validation. Model predictions for puffing frequency, mean and rms temperature and velocity, mean molar fractions of major species, radiative loss to the surrounding and radiative and total heat feedback to the fuel surface are in good agreement with the available experimental data. Two other burner boundary conditions are designed. The first disregards the fuel lip height while keeping the burner located one-pool diameter above the floor. The second modifies the first configuration by assuming that the burner rim is floor flush. Model results show that the burner boundary conditions affect significantly the flow structure and the pool fire dynamics by altering the flame base instability near the edge of the pan. A non-zero fuel lip height produces significantly wider and shorter flames which affect the heat feedback toward the fuel surface whereas altering the air entrainment at the pool basis enhances substantially the puffing frequency. This shows that the experimental burner boundary conditions have to be reproduced scrupulously for relevant model validations.

International audience; This paper is devoted to the numerical analysis of a numerical scheme dedicated to the simulation of front advection (see https://hal.archives-ouvertes.fr/hal-02940407v1 for a preprint version presenting this scheme and some numerical results). The latter has been recently proposed and it is based on the ideas used for the Glimm's scheme. It relies on a two-step approach: a convection step is followed by a projection step which is based on a random choice. The main advantage of this scheme is that it applies to multi-dimensional problems. In the present paper a convergence result for this scheme is provided for a particular class of multi-dimensional problems. This work has been accepted for publication in IMA Journal of Numerical Analysis: https://doi.org/10.1093/imanum/drab053.

International audience; We discuss herein the suitability of some open boundary conditions while comparing approximate solutions of one-dimensional Riemann problems in a bounded sub-domain with the restriction in this sub-domain of the exact solution in the infinite domain, considering the Euler system of gas dynamics. Assuming that no information is known from outside of the domain, some basic open boundary condition specifications are given, and a measure of the L 1 norm of the error inside the computational domain enables to show consistency errors in situations involving outgoing shock waves, depending on the chosen boundary condition formulation. This investigation has been performed with Finite Volume methods, using approximate Riemann solvers in order to compute numerical fluxes for both inner and boundary interfaces.

International audience; We extend the Compatible Discrete Operator (CDO) schemes to the steady incompressible Stokes and Navier-Stokes equations. The main features of the CDO face-based schemes are recalled: a hybrid velocity discretization with degrees of freedom at faces and cells, a stabilized velocity gradient reconstruction defined on the face-based sub-cell pyramids, and a discrete pressure attached to the mesh cells. We introduce a discrete divergence operator that will account for the velocity-pressure coupling, and a hybrid discretization of the convection term. The results of several benchmark test cases validate the framework.

We develop face-based Compatible Discrete Operator (CDO-Fb) schemes for the unsteady, incompressible Stokes and Navier–Stokes equations. We introduce operators discretizing the gradient, the divergence, and the convection term. It is proved that the discrete divergence operator allows one to recover a discrete inf-sup condition. Moreover, the discrete convection operator is dissipative, a paramount property for the energy balance. The scheme is first tested in the steady case on general and deformed meshes in order to highlight the flexibility and the robustness of the CDO-Fb discretization. The focus is then moved onto the time-stepping techniques. In particular, we analyze the classical monolithic approach, consisting in solving saddle-point problems, and the Artificial Compressibility (AC) method, which allows one to avoid such saddle-point systems at the cost of relaxing the mass balance. Three classic techniques for the treatment of the convection term are investigated: Picard iterations, the linearized convection and the explicit convection. Numerical results stemming from first-order and then from second-order time-schemes show that the AC method is an accurate and efficient alternative to the classical monolithic approach., Nous développons des schémas dits face-based Compatible Discrete Operator (CDO-Fb) pour les équations de Stokes et Navier–Stokes incompressibles en régime instationnaire. Des opérateurs pour la reconstruction du gradient, de la divergence et un autre pour le terme de convection sont proposés. On montre que l’opérateur de divergence discret permet de satisfaire une condition inf-sup, tandis que l’opérateur de convection discret est dissipatif, propriété cruciale pour le bilan d’énergie. Le schéma de discrétisation est d’abord testé dans le cas stationnaire sur des maillages généraux mais aussi déformés, afin d’illustrer la flexibilité et la robustesse de la discrétisation CDO-Fb. Dans un deuxième temps, l’attention est placée sur les techniques de marche en temps. En particulier, nous étudions l’approche monolithique traditionnelle qui consiste à résoudre directement le système de point-selle, et la méthode de Compressibilité Artificielle (AC), qui permet de ne plus avoir un système de point-selle à résoudre au prix d’une relaxation du bilan de masse. Trois stratégies classiques pour le traitement du terme non linéaire dû à la convection sont examinées : l’algorithme de Picard, la linéarisation et l’explicitation. Des résultats numériques utilisant des schémas temporels du premier ordre d’abord, puis du deuxième ordre, montrent que la méthode AC constitue une alternative précise et efficace à l’approche monolithique traditionnelle.

International audience; We focus here on an integral approach to compute compressible or incompressible fluid flows in physical congested domains with discontinuous fluid sections. This approach is based on a multidimensional integral formulation of the fluid model equations and aims at unifying the porous approach used at component scale and CFD used at local scale. Its discretization uses a semi-implicit collocated finite volume scheme with an incremental pressure-correction algorithm, implemented in the open-source CFD software Code Saturne, version 6.0. Numerical tests are completed by simulating a plane steady-channel flow with a fluid section jump. The results are compared to the analytical solution and the computation obtained with a standard equivalent porous model.

The main objective of this work is to analyze the effects of gas radiative property models on the radiative outputs and flame structure in a 1 m diameter methanol pool fire. Large Eddy Simulation (LES) are run with the non-adiabatic steady laminar flamelet (SLF)/presumed filtered density function (FDF) model to close subgrid-scale (SGS) turbulence-chemistry and turbulence-radiation emission interactions. The radiative transfer equation (RTE) is solved using the Finite Volume Method (FVM) with different angular meshes, including uniform angular dicretizations comprising 16 (polar angle) × 24 (azimuthal angle) and 48 × 96 control angles and the FTn scheme with n up to 48. Four gas radiative property models, namely the Rank Correlated Full Spectrum k-distribution (RCFSK), the non-grey Weighted-Sum-of-Grey-Gases (WSGG), and two versions of the grey WSGG based on different evaluations of the mean path length are assessed. Model predictions with the RCFSK reproduce with fidelity the available experimental data in terms of flame structure and radiative loss to the surrounding. The radiative heat transfer within the flame, where radiation is isotropic, is adequately resolved with the FT12 angular resolution whereas finer angular meshes with at least 32 segments to discretize the polar angle are required to predict accurately the vertical distributions of radiative flux outside the flame. The grey models fail to reproduce the radiative structure of the flame, predicting an optically thin flame instead of an optically intermediate medium. In an opposite way, although the non-grey WSGG overestimates both emission and absorption, it provides predictions in overall reasonable agreement with the RCSFK.

This study reports the development of a LES-based numerical model dedicated to the simulation of well-ventilated and under-ventilated purely buoyant fire plumes. A new second-order low-Mach number variable-density flow solver was developed and verified in order to describe accurately the strong unsteady processes related to the purely buoyant nature of the flow. State-of-the art subgrid-scale turbulence, combustion and radiation models were specifically developed, including the non-adiabatic SLF (steady laminar flamelet) and FPV (flamelet/progress variable models). The RCFSK was considered as reference radiative property model whereas the performance of simpler models, including non-grey and grey versions of the weighted-sum-of-grey gases was assessed. The numerical model was exhaustively validated by simulating several well-documented non-reactive and reactive buoyant fire plumes. It was found capable to reproduce with high fidelity the dynamic and radiative structures of non-luminous fire plumes in both ventilated and under-ventilated configurations without adjusting any model parameters. In particular, the FPV allows addressing oxygen-diluted oxidizer conditions close to extinction. Several specific modelling issues were also investigated during the course of this work. The importance of resolving the laminar instabilities, which form periodically at the base of purely buoyant fire plumes and grow to generate energy containing structures that govern the mixing process, was demonstrated. The formation and growth of these instabilities are significantly affected by the burner geometry that has to be scrupulously consistent with the experiments to achieve an accurate description of the fire plume dynamics. The grey version of the weighted-sum-of-grey gases models have to be avoided whereas the non-grey versions can be a reasonable alternative for non-sooting pool fires. Finally, neglecting subgrid-scale turbulence-radiation interaction affects significantly the predictions of the fire plume structure and radiative heat flux even for lab-scale pool fires., Cette étude rapporte le développement d'un modèle numérique basé sur les simulations à grandes échelles en vue de simuler des panaches de feu bien-ventilés et sous-ventilés et entièrement contrôlés par les forces de flottabilité. Un nouvel algorithme de résolution pour les d'écoulements à densité variable à faible nombre de Mach, précis au second ordre en temps et espace, a été développé et vérifié afin de décrire avec précision les processus instationnaires forts liés à la nature purement contrôlée par les forces de flottabilité des écoulements. Des modèles de sous-maille à l’état de l’art pour la turbulence, la combustion et le rayonnement ont été développés, incluant les modèles non-adiabatiques SLF (steady laminar flamelet) et FPV (flamelet/progress variable). Le RCFSK a été considéré comme référence pour la modélisation des propriétés radiatives des gaz et la performance de modèles plus simples, tels que des versions non-grises et grises du modèle à somme pondérée des gaz gris, a été évaluée. Le modèle numérique a été intensivement validé en simulant plusieurs panaches de feu non-réactifs et réactifs. Le modèle s'est avéré capable de reproduire avec une grande fidélité les structures dynamiques et radiatives de ces panaches dans des configurations ventilées et sous-ventilées sans ajuster aucun des paramètres du modèle. En particulier, le modèle FPV permet de traiter des conditions d'oxydant dilué en oxygène proches de l'extinction. Plusieurs problèmes de modélisation spécifiques ont également été étudiés au cours de ce travail. L'importance de capturer directement les instabilités laminaires thermo-convectives, qui se forment périodiquement à la base des panaches de feux et croissent pour générer les larges tourbillons régissant le processus de mélange, a été démontrée. La formation et la croissance de ces instabilités sont significativement affectées par la géométrie du brûleur qui doit être scrupuleusement cohérente avec les expériences pour obtenir une description précise de la dynamique du panache de feu. Les versions grises des modèles à somme pondérée de gaz gris doivent être évitées tandis que les versions non-grises de ce modèle peuvent être une alternative raisonnable pour la simulation de feux de nappe sans suie. Finalement, les interactions rayonnement-turbulence de sous maille ont un effet non-négligeable sur la structure de flamme et les pertes radiatives et ce, même pour des feux de nappe à l’échelle du laboratoire.

CO2 capture and utilization (CCU) is a process that captures CO2 emissions from sources such as fossil fuel power plants and reuses them so that they will not enter the atmosphere. Among the various ways of recycling CO2, reduction reactions are extensively studied at lab-scale. However, CO2 reduction by standard methods is difficult. Sonochemistry may be used in CO2 gas mixtures bubbled through water subjected to ultrasound waves. Indeed, the sonochemical reduction of CO2 in water has been already investigated by some authors, showing that fuel species (CO and H2) are obtained in the final products. The aim of this work is to model, for a single bubble, the close coupling of the mechanisms of bubble dynamics with the kinetics of gas phase reactions in the bubble that can lead to CO2 reduction. An estimation of time-scales is used to define the controlling steps and consequently to solve a reduced model. The calculation of the concentration of free radicals and gases formed in the bubble is undertaken over many cycles to look at the effects of ultrasound frequency, pressure amplitude, initial bubble radius and bubble composition in CO2. The strong effect of bubble composition on the CO2 reduction rate is confirmed in accordance with experimental data from the literature. When the initial fraction of CO2 in the bubble is low, bubble growth and collapse are slightly modified with respect to simulation without CO2, and chemical reactions leading to CO2 reduction are promoted. However, the peak collapse temperature depends on the thermal properties of the CO2 and greatly decreases as the CO2 increases in the bubble. The model shows that initial bubble radius, ultrasound frequency and pressure amplitude play a critical role in CO2 reduction. Hence, in the case of a bubble with an initial radius of around 5 μm, CO2 reduction appears to be more favorable at a frequency around 300 kHz than at a low frequency of around 20 kHz. Finally, the industrial application of ultrasound to CO2 reduction in water would be largely dependent on sonochemical efficiency. Under the conditions tested, this process does not seem to be sufficiently efficient.

International audience; In the case of conjugate heat transfer, the dissipation rate associated with the temperature variance is discontinuous at the fluid-solid interface. The discon-tinuity satisfies a compatibility condition involving the fluid-solid thermal dif-fusivity and conductivity ratios and the relative contribution to the dissipation rate of its wall-normal part. The present analysis is supported by the Direct Numerical Simulations of an incompressible channel flow at a Reynolds number , based on the friction velocity, of 150, a Prandtl number of 0.71 and several values of fluid-solid thermal diffusivity and conductivity ratios.

An up-to-date review of CO 2 capture technologies for coal-fired power plants is presented. This study is based on EDF experience on CO 2 capture build through collaborative projects and pilot plants operation follow up. This review focuses mostly on most mature technologies and provides insight on the interest of least developed technology with high potential. Technologies are compared and assessed based on energy performance, maturity and economic criteria. A specific method for assessing uncertainties in this process is proposed. Amine based post-combustion technology remains the best reference for short and medium terms with a tight competition with cryogenic oxy-combustion. Both share the highest maturity and similar energy performance in their most advanced embodiments. At the moment IGGC based capture looks less promising for power generation due to the high cost of the plant even without CO 2 capture. Regarding more innovative technology, promising candidates, such as inertial extraction, chemical looping combustion or oxy-fired CO 2 cycle, are highlighted but their effective development up to industrial ground is not guaranteed due to the constant improvement of reference technology and their difficulty to be retrofitted.

National audience; Nous presentons un ensemble d’algorithmes statistiques permettant d’effectuer le rendu d’une image thermique, en régime instationnaire, dans une scène quelconque. Simuler le signal reçu par chaque pixel de la camera consiste à propager les sources thermiques (conditions aux limites et initiales) par les phenomènes de conduction, convection et rayonnement. La technique ne nécessite pas un calcul préalable du champ de température en tout point de la scène et en tout temps. Un exemple en geométrie complexe est présenté, et qualitativement comparé à une prise de vue.

International audience; Objectives The present article is a synthesis of the first 10 years of follow-up of the FondaMental Academic Center of Expertise for Schizophrenia (FACE-SZ) cohort. Methods More than 700 community-dwelling stabilized subjects have been recruited and evaluated to date. The mean age was 32 years with 75 % males, the mean illness duration was 11 years, the mean age at illness onset was 21 years, the mean duration of untreated psychosis was 1.5 years and 55 % were current daily tobacco smokers. Results The major findings of the FACE-SZ cohort may be summarized as follows: the metabolic syndrome is twice more frequent in schizophrenia as compared to the general population and is not correctly assessed and treated; cognitive disturbances have been found in benzodiazepine consumers and in patients with chronic low-grade peripheral inflammation; major depressive disorder (MDD) is a common current comorbid condition in about 20% of the subjects at the evaluation. MDD is associated with impaired quality of life and with increased nicotine dependency in SZ daily tobacco smokers. Improving depression and negative symptoms may be the most effective strategies to improve quality of life in schizophrenia; the duration of untreated psychosis is much longer in cannabis smokers and in subjects with an age at illness onset < 19 years. Adherence to treatment is diminished in subjects who report a subjective negative feeling after treatment intake independent of objective side effects (extrapyramidal syndrome and weight gain). Akathisia has been found in 18% of the subjects and has been associated with antipsychotic polytherapy. Conclusions In the light of these results, some recommendations for clinical care may be suggested. The early detection of schizophrenia should be specifically increased in adolescents and/or cannabis smokers. All patients should be administered a comprehensive neuropsychological evaluation at the beginning of the illness and after stabilization under treatment. Improving metabolic parameters and lifestyle (diet and physical activity) should be reinforced. The benefit/risk ratio of benzodiazepine and antipsychotic polytherapy should be regularly reevaluated and withdrawn as soon as possible. If MDD remains underdiagnosed and undertreated, improving depression may strongly improve the quality of life of SZ subjects. In the end, Cognitive Remediation Therapy and anti-inflammatory strategies should be more frequently included in therapeutic strategies.; Objectifs Le présent article propose de faire un retour sur les 10 ans d’expérience du réseau national des 10 centres experts schizophrénie Français, à travers une revue des principales publications scientifiques qui en sont issues. Méthodes À ce jour, les données de plus de 700 patients ont pu être analysées. Globalement, cette population est composée de trois quarts d’hommes, est âgée en moyenne de 32 ans, la durée moyenne de maladie est d’environ 11 ans, l’âge moyen de début de maladie est de 21 ans, la durée de psychose non traitée est d’environ un an et demi. 55 % des sujets sont consommateurs de tabac au moment de l’évaluation. Enfin, un focus sera fait sur les projets de recherche multicentriques collaboratifs déployés au sein de ce réseau. Résultats Les principales données obtenues peuvent être résumées comme suit : le syndrome métabolique reste deux fois plus fréquent dans la schizophrénie qu’en population générale et n’est pas correctement pris en charge ; des troubles cognitifs spécifiques ont été identifiés chez les patients consommateurs de benzodiazépines et chez les patients présentant une inflammation périphérique. Des spécificités liées au sexe ont également été observées ; la dépression comorbide reste très fréquente, elle est associée à une diminution de la qualité de vie et à une augmentation de la dépendance nicotinique chez les fumeurs. Prendre en charge la dépression et les symptômes négatifs pourraient fortement améliorer la qualité de vie des patients ; le délai à l’instauration du traitement est plus long pour les schizophrénies se déclenchant avant 19 ans et chez les consommateurs de cannabis. L’adhésion au traitement est diminuée chez les patients rapportant un ressenti subjectif négatif du traitement, indépendamment de la prise de poids ou d’un syndrome extrapyramidal. Enfin, l’akathisie est très fréquente et fortement associée à la polythérapie antipsychotique. Conclusions Ces résultats conduisent à formuler plusieurs recommandations. Le dépistage du trouble et le traitement devraient être renforcés chez les adolescents et les consommateurs de cannabis. Tous les patients devraient bénéficier d’une évaluation neuropsychologique au début de leur trouble, après stabilisation sous traitement, puis de façon plus espacée au cours de leur suivi. La prise en charge des paramètres métaboliques, de l’alimentation et de l’activité physique devrait être renforcée. La balance bénéfice/risque de la prescription de benzodiazépines doit être réévaluée régulièrement au regard de son impact notamment sur la cognition. La monothérapie antipsychotique est recommandée autant que possible pour limiter les effets indésirables. La dépression reste sous-diagnostiquée et doit faire l’objet d’une évaluation systématique et d’un traitement spécifique. La remédiation cognitive doit également être plus largement proposée chez les patients présentant des troubles cognitifs.

The objective of this article is to investigate numerically the radiative structure of methane, ethylene and acetylene lab-scale jet flames ranging from the transitional to the momentum-driven regimes. The numerical model involves a hybrid flamelet/transported PDF method coupled to an acetylene-benzene soot production model and a Wide-Band Correleted-K gas radiation model. Model predictions in terms of mean and rms soot volume fraction and temperature, integrated soot volume fraction and radiant fraction are in reasonable agreement with the available experimental data. In particular, the model reproduces quantitatively the decrease in radiant fraction observed as the flow becomes momentum driven. This behavior results mainly from two mechanisms: (i) an increase in flame self-absorption due to an enhancement in flame volume and (ii) for the ethylene and acetylene flames a reduction in the soot emission per unit flame volume owing to a strong decrease in soot production. In addition, for a given fuel, gas emission per unit flame volume remains approximatively constant as the exit strain rate increases whereas the soot emission per unit flame volume and the characteristic soot volume fraction scale with the Kolmogorov time scale. It was also found that competitive mechanisms govern the effects of Turbulence-Radiation Interaction (TRI) on radiant fraction. Enhancement mechanisms are due to gas emission TRI and temperature self-correlation effects on soot emission whereas inhibiting mechanisms results from the negative correlation between soot volume fraction and temperature. Enhancement mechanisms dominate in weakly sooting methane flames and taking TRI into account increases the radiant fraction. On the other hand, inhibiting mechanisms become significant in moderately and highly sooting fuels, with their importance increasing with both the fuel sooting propensity and the Reynolds number. For flames dominated by soot radiation, the inhibiting mechanisms prevail and taking TRI into account reduces the radiant fraction.

This article investigates the effects of increasing pressure on radiative heat transfer in sooting methane and ethylene momentum-driven turbulent jet flames by using state-of-the-art chemical mechanism, combustion, soot production and radiation models. A transported PDF method is used to close properly the emission TRI term and a Narrow-Band CK (NBCK) model is considered. The absorption TRI is modelled by considering the Optically-Thin Fluctuation Approximation (OTFA). In accordance with a previous study dealing with non-sooting hydrogen flames (Nmira et al., JQSRT 220 (2018) 172-179), the 4-atm flames are designed from the atmospheric ones by using a Froude modeling that allows to preserve the flame geometry and the global residence time as the pressure is scaled-up. The radiant fraction evolves with increasing the pressure as a result of two competitive mechanisms: i) an increase in soot production that reduces significantly the emission characteristic time scale leading to an increase in radiant fraction and ii) a reduction in flame transparency that tends to reduce the radiant fraction. This differs from non-sooting flames where only the second mechanism is present. These two mechanisms are balanced in the methane flames whereas the first mechanism prevails in the ethylene flames. It is also found that the increase in net radiative loss owing to TRI is reduced as the pressure is scaled up. This is due to an enhancement of the contribution of soot emission which is less sensitive to TRI than gas emission. This behavior differs also from non-sooting flames where TRI effects were found to be enhanced by pressure rise., 9th International Symposium on Radiative Transfer, RAD-19, June 3-7, 2019, Athens, Greece

This article aims to determine the most relevant engineering global method for gas radiative property modeling to be applied in the simulations of combustion problems. Two versions of the full-spectrum correlated k (FSCK) model, the Rank-Correlated full-spectrum k-distribution/ Spectral-Line-Weighted-sum-of-gray-gases (RC-FSK/RC-SLW) and a new version of the Weighted-Sum-of-Grey-Gases (WSGG) model are compared with the Narrow-Band CK (NBCK) model in four turbulent axisymmetric jet diffusion flames fueled either by hydrogen or methane at atmospheric and higher pressures. These comparisons are performed in decoupled radiative heat transfer calculations with the thermal fields being prescribed. The databases and coefficients associated to these different models are determined from a unique Line-By-Line database in order to allow a relevant comparison. Model results suggest that the SLW/FSCK methods coupled to the so-called improved scheme proposed by Cai and Modest or the Rank-Correlated SLW/FSK model, along with k-g distributions generated from accurate high-resolution high-temperature databases are the most mature gas radiative property models to be implemented in CFD codes dealing with combustion problems involving gas-soot mixtures.

Introduction This study aimed was to investigate the relationship between different types of childhood trauma and the level of insight (i.e., awareness of having a psychiatric disorder) in subjects suffering from schizophrenia, as well as the putative role of clinical mediators. Methods 294 community-dwelling subjects with stable schizophrenia were included into FACE-SZ, a multicentre cross-sectional study. All patients were assessed by specialized multidisciplinary teams. The level of insight was assessed by the Scale to assess Unawareness of Mental Disorder (SUMD), and childhood trauma by the Childhood Trauma Questionnaire (CTQ). Path analyses from the five CTQ subscales (physical abuse and neglect, emotional abuse and neglect, and sexual abuse) and the SUMD, with current symptomatology (i.e., positive, negative, global psychopathology and depression) as mediator, was performed. Results Physical neglect (β = 0.14) and abuse (β = 0.13) were significantly associated with poor insight. Negative symptoms were a clinical mediator of the relationship between physical neglect and poor insight. Moreover, positive (β = 0.21) and negative (β = 0.30) symptoms were associated with poor insight, whereas depression (β = −0.14) was associated with higher levels of insight. Discussion For the first time, this study shows a significant relationship between childhood trauma, specifically physical neglect and abuse, and poor insight. The level of insight was linked to different clinical dimensions. Among subjects with schizophrenia, these results provide support for a role of childhood trauma in poorer management outcomes, and the need to provide treatment, including psycho-education that better targets the consequences of childhood trauma.

For reasons of efficiency and accuracy, water wave propagation is often simulated with potential or inviscid models rather than Navier-Stokes solvers, but for wave-induced flows, such as wave-structure interaction, viscous effects are important under certain conditions. Alternatively, general purpose Navier-Stokes (CFD) models can have limitations when applied to such free-surface problems when dealing with large amplitude waves, run-up, or propagation over long distances. Here we present an Arbitrary Lagrangian-Eulerian (ALE) algorithm with special care to the time-stepping and boundary conditions used for the free-surfaces, integrated into Code_Saturne, and we test its capabilities for modeling a variety of water wave generation and propagation benchmarks, and finally consider interaction with a vertical cylinder. Two variants of the mesh displacement computation are proposed and tested against the discrete Geometric Conservation Law (GCL). The more robust variant, for highly curved or sawtoothed free-surfaces, uses a Compatible Discrete Operator scheme on the dual mesh for solving the mesh displacement, which makes the algorithm valid for any polyhedral mesh. Results for standard wave propagation benchmarks for both variants show that, when care is taken to avoid grids with excessive numerical dissipation, this approach is effective at reproducing wave profiles as well as forces on bodies.

This work analyzes the performance potential of solar-only powered combined cycles, comparing the impact of two different solar receiver technologies (opaque-heat-exchanger-type vs. volumetric). Due to material and receiver performance constraints, as well as the absence of internal combustion, the gas turbine inlet temperature (TIT) is limited to considerably lower values than observed in current fossil-fired state-of-the-art combined cycle plants. Therefore, the analysis includes the evaluation of a reheated topping Brayton cycle, aiming for a higher mean temperature of the heat input, thereby allowing fair conversion efficiencies despite moderate TITs. An extensive parametric optimization analysis compares different solar combined cycle configurations and benchmarks them against conventional CSP single-cycle plants. High thermal losses in the receiver tend to offset the gain allowed by the power cycle. The innovative coupling of an open volumetric air receiver with a regenerative heat exchange system that works in alternating operating modes (non-pressurized heating period, pressurized cooling period) could be a promising solution to efficiently drive a solar powered combined cycle. Furthermore, the optimum solar combined cycle performance for typical mean concentration ratios (C≈500) is fully compatible with high temperature TES, providing the promising possibility of fully dispatchable operation at highest thermal-to-electric conversion efficiency.

International audience; The nuclear industry is interested in better understanding the behavior of turbulent boiling flowsand in using modern computational tools for the design and analysis of advanced fuels and reactorsand for simulation and study of mitigation strategies in accident scenarios. Such interests serve asdrivers for the advancement of the 3-dimensional multiphase Computational Fluid Dynamicsapproach. A pair of parallel efforts have been underway in Europe and in the United States, theNEPTUNE and CASL programs respectively, that aim at delivering advanced simulation tools thatwill enable improved safety and economy of operations of the reactor fleet. Results from acollaboration between these two efforts, aimed at advancing the understanding of multiphaseclosures for pressurized water reactor (PWR) application, are presented. Particular attention is paidto the assessment and analysis of the different physical models implemented in NEPTUNE_CFDand STAR-CCM+ codes used in the NEPTUNE and the CASL programs respectively, forapplication to turbulent two-phase bubbly flows. The experiments conducted by Liu and Bankoff(Liu, 1989; Liu and Bankoff 1993a and b) are selected for benchmarking, and predictions from thetwo codes are presented for a broad range of flow conditions and with void fractions varyingbetween 0 and 50percent. Comparison of the CFD simulations and experimental measurements revealsthat a similar level of accuracy is achieved in the two codes. The differences in both sets of closuremodels are analyzed, and their capability to capture the main features of the flow over a wide rangeof experimental conditions are discussed. This analysis paves the way for future improvements ofexisting two-fluid models. The benchmarks are further leveraged for a systematic study of thepropagation of model uncertainties. This provides insights into mechanisms that lead to complexinteractions between individual closures (of the different phenomena) in the multiphase CFDapproach. As such, it is seen that the multi-CFD-code approach and the principled uncertaintyquantification approach are both of great value in assessing the limitations and the level of maturityof multiphase hydrodynamic closures.

Air entrainment within water is a common feature of flows over hydraulic works – spill over a dam, wave breaking on a dike, etc. – and its accurate modeling is a key to better design such structures. The Smoothed Particle Hydrodynamics (SPH) method appears as a natural way to model such highly distorted flows. To avoid computationally prohibitive costs related to the full discretization of bubbles or drops, a mixture model for high density ratio flows relying on a volume-based formulation with relative velocity between phases has first been developed and validated in Fonty et al. (Proceedings of 13th international SPHERIC workshop. Galway, Ireland, 2018; Int J Multiph Flow 111:158–174, 2019. https://doi.org/10.1016/j.ijmultiphaseflow.2018.11.007 ). Instead of having a once and for all assigned phase as in multifluid SPH, each particle now carries both phases through their respective volume fractions. In the present work, in order to handle practical air entrainment application cases, the open boundary formulation described in Ferrand et al. (Comput Phys Commun 210:29–44, 2017. https://doi.org/10.1016/j.cpc.2016.09.009 ) is adapted to this mixture model. Then, after introducing turbulence through a $$k{-}\epsilon$$ model, a specific closure on the air bubbles relative velocity is proposed including a Stokesian drag term and turbulent diffusion. This model is then applied to two cases of air entrainment: a stepped spillway for interfacial aeration and a plunging jet for local aeration. Finally a 3D industrial test case of discharge-control structure at the La Coche power plant (France) is considered. While valuable insights are obtained for the volume fraction field, further investigations are required to improve the modeling of the flow dynamics.

International audience; Conjugate heat transfer represents the actual thermal coupling between a fluid and a solid part. It is of prime importance in nuclear industrial applications where fluctuating thermal stresses are a concern, e.g. in case of a severe emergency cooling (Pressurized Thermal Shock) or long-term ageing of materials such as thermal striping occurring in T-junctions. The present paper aims at contributing to the improvement of refined RANS approaches for conjugate heat transfer. Using wall-resolved LES of a turbulent channel flow at Re τ = 395 and P r = 0.71, a correlation for the discontinuity of ε θ at the fluid-solid interface is proposed, based on 49 different combination of fluid-solid thermal properties ratios.

International audience; This work considers the shape optimization of a crossflow plate heat exchanger air/water. The two objectives are to maximize the effectiveness while minimizing the total pressure drop. The shape variation concerns a trapezoidal rib mounted on the hot channels plates. A multiscale approach is presented, coupling CFD simulations and a NTU method. The optimization method is based on a genetic algorithm and kriging metamodels with adaptive sampling. Infill criteria are the maximum mean square error (MMSE) and multipoints expected improvement (q-EI). A clustering of the Pareto front individuals highlights a finite number of optimal shapes.

International audience; In this note, basic turbulent statistics in a pipe flow are computed accurately by large-eddy simulation using a mesh resolution coarser than the viscous sublayer. These results are obtained when a regular Cartesian mesh is used for the spatial discretization of the circular pipe thanks to an immersed boundary method combined with high-order schemes. In this particular computational configuration, the near-wall features of mean velocity and Reynolds stress profiles are found to be correctly captured at a scale significantly smaller than the mesh size. Comparisons between channel and pipe flow configurations suggest that an irregular mesh distribution in terms of wall distance may be a favourable condition to explicitly compute by large-eddy simulation reliable wall turbulence without any extra-modelling in the near-wall region.

This article addresses the one-dimensional modeling of a charring polymer decomposition in the cone calorimeter used to reproduce at bench scale the radiative heating from a fire. The rate-controlling phenomena are first discussed in a preliminary analysis of dimensionless numbers. Then, the role of three critical assumptions is highlighted by simulations: (1) transport of the gaseous products within the material or instantaneous release of gaseous products, (2) volume variation or constant volume, and (3) absorption of applied heat flux at the exposed face or through the thickness. Their influence in thermally thick regime is shown in particular on mass loss rate and time to extinction. Under the conditions tested, the influence of internal transport by convection on mass loss rate and time to extinction is minor. The assumption of constant volume appears to have a moderate influence on the mass loss rate and time to extinction. Variations of optical properties affect the numerical results by an increase of the maximum peak of mass loss rate and a decrease of time to extinction. Finally, the effects of applied heat flux and initial material thickness on the mass loss rate and time to extinction are important. With a higher heat flux or a smaller thickness, the decomposition is earlier, faster, and more intense.

International audience; Ce travail porte sur l’optimisation de l’efficacité et de la perte de charge totale d’un échangeur à plaques par variation de la forme d’une ailette. Une approche multiéchelle est proposée, liant une modélisation numérique de l’ailette à une méthode NUT. La méthode d’optimisation repose sur un algorithme génétique (NSGA-II) et un métamodèle (krigeage). Le métamodèle est construit itérativement à partir des maxima de variance et d’amélioration attendue. Une agrégation des résultats obtenus le long du front de Pareto met en évidence un nombre fini de formes optimales.

The Next-CSP project aims at improving the performances of central receiver Solar Thermal Electric (STE) plants through the development and integration of a new technology based on high temperature (800°C) particles used as both heat transfer fluid and storage medium. The objective of the present paper is to define the best combined cycle configuration by exploring various design options where Turbine Exhaust Temperature (TET) and compressor outlet temperature vary. Regarding the Dense Particle Suspension Heat eXchanger (DPS-HX) train that provides the heat input to the gas turbine’s working air, a particular attention is paid to the particle-side layout. A decent net cycle efficiency can be achieved by a two-reheat topping cycle with a TET of 600°C, with equal expansion ratios and a 3 pressure-reheat Rankine cycle at 160-20-3 bars / 585 / 575°C. Further increasing the low pressure (LP) turbine expansion ratio would result in a less bulky and cheaper LP DPS-HX, at the expense of cycle efficiency. Adjusting the HP and IP pressure ratios can simplify the particle-side layout of the DPS-HX train, again at the expense of efficiency (at least 0.5% pt). With a two-reheat topping cycle, the particles cannot be expected to enter the receiver at a temperature far below 600°C. The impact of that high receiver inlet temperature and of the resulting moderate storage density on the plant’s efficiency and economics should be discussed further. Similarly, a detailed techno-economic optimization of the DPS-HX train should be performed in order to define the optimal pressure drops and temperature differences.

International audience; The Large Eddy Simulation (LES) of two-phase flows with resolved scale interfaces is investigated through the a priori filtering of Direct Numerical Simulations (DNS) of one-fluid and multifield models. A phase inversion benchmark [ 1 –4] is considered highlighting many coalescence and interface rupture events in a kind of atomization process. The order of magnitude of specific two-phase subgrid LES terms is first considered with the two modeling approaches. Then, different existing models such as Smagorinsky [5], Wall-Adapting Local Eddy-viscosity (WALE) model [6], Bardina [7], Mixed [8] and Approximate Deconvo-lution Model (ADM) [9] are used to account for two-phase subgrid effects. These models are compared to filtered DNS results. The main conclusion concerning a priori LES filtering is that the inertia term is not predominant in two-phase flows with fragmentation and rupture of interface. This conclusion is different from that of the studies of [3, 10–13]. Concerning LES models, functional modeling do not correlate to filtered DNS results whereas structural approaches do. Bardina and ADM are clearly the good LES framework to consider for two-phase flows with resolved scale interfaces. ADM is clearly better than Bardina in our study.

The pyrolysis of two woody biomasses (Douglas and oak) was investigated on both micro-fluidized bed reactor (MFBR) and fixed bed reactor (FBR) combined with a single photoionization (SPI) mass spectrometer. The soft ionization capability of SPI technique allows real-time and on-line analysis of the labile primary tars from biomass pyrolysis. The slow pyrolysis of wood powders is achieved in the FBR at 5 °C/min up to 500 °C. Final mass yields of permanent gases and major primary tars are measured by GC analysis, whereas the SPI allows monitoring the evolution of some primary tars as a function of time. The same on-line analysis is achieved for fast pyrolysis of biomass particles introduced in the MFBR maintained at 400 or 500 °C. In that case, the wood particles have different size and shape: powder, thin lamella or cylinder. These experimental results are presented and compared with predictions of a pyrolysis model that combines external and internal heat transfer in biomass particles and recently published detailed kinetics. The comparison indicates that the experimental and simulation results are mostly in agreement, but more detailed kinetic mechanisms still need to be developed to capture the complex biomass pyrolysis.

Work presented at the 13th International Conference on Greenhouse Gas Control Technologies, GHGT-13, 14-18 November 2016, Lausanne, Switzerland, The paper gives a high level overview of the work performed in the EU-FP7 funded project SUCCESS (Scale-up of oxygen carrier for chemical looping combustion using environmentally sustainable materials). The project is the most recent one in a series of successful EU-funded research projects on the chemical looping combustion (CLC) technology. Its main objective is to perform the necessary research in order to demonstrate the CLC technology in the range of 10 MW fuel power input. The main focus is on scale-up of production of two different oxygen carrier materials using large scale equipment and industrially available raw materials. This will guarantee availability of oxygen carrier material at tonne scale. The scale-up of the two materials, a Cu and a Mn based, was successful and first tests with the Cu material have already been performed in four different pilot units up to 150 kW where the material showed excellent performance regarding fuel conversion. In addition to technology scale-up, extensive end-user evaluation is performed. This evaluation includes investigations on health, security and environmental impacts (HSE), a life cycle analysis and a techno-economic analysis to compare the CLC technology for steam generation against the current state-of-the-art technologies., The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 608571. Financial support is gratefully acknowledged.

International audience; Several modifications are introduced to the Elliptic Blending Differential Flux Model proposed by Shin et al. (2008) to account for the influence of wall blockage on the turbulent heat flux. These modifications are introduced in order to reproduce, in association with the most recent version of the EB-RSM, the full range of regimes, from forced to natural convection, without any case-specific modification. The interest of the new model is demonstrated using analytical arguments, a priori tests and computations in channel flows in the different convection regimes, as well as in a differentially heated cavity.

We propose in this work an original finite volume scheme for the system of gas dynamics in a nozzle. Our numerical method is based on a piecewise constant discretization of the cross-section and on an approximate Riemann solver in the sense of Harten, Lax and van Leer. The solver is obtained by the use of a relaxation approximation that leads to a positive and entropy satisfying numerical scheme for all variation of section, even discontinuous sections with arbitrary large jumps. To do so, we introduce, in the first step of the relaxation solver, a singular dissipation measure superposed on the standing wave, which enables us to control the approximate speeds of sound and thus the time step, even for extreme initial data.

12th International Conference on Greenhouse Gas Control Technologies (GHGT), Austin, TX, OCT 05-09, 2014; International audience; CO2 capture is recognized as necessary to achieve significant greenhouse gas emission reduction before 2050. Regarding these technologies, the main issue is the high cost of avoided CO2 related to capture (approximate to 40 (sic)/t). In conventional amine-based CO2 capture process, the four main key parameters driving the cost of avoided CO2 are the regeneration duty, the compression works, the compressor cost and the solvent make-up cost. On the one hand, the use of hollow fibre membrane contactor (HFMC) for CO2 capture is foreseen to be an efficient technology for absorber intensification; but regarding the impact of the absorber cost on the cost of avoided CO2, the use of HFMC for process intensification does not seem relevant. On the other hand, ammonia as solvent for CO2 capture is a cheap solvent with no degradation problem. Moreover, it allows a high pressure regeneration reducing the compression works. The key idea of this work is to find a membrane with high CO2/NH3 selectivity and high permeability in order to use aqueous ammonia as a solvent in a HFMC in order to reduce significantly the ammonia slip in flue gases while maintaining high absorption rate. The work has been divided in three main steps: the screening of available material for the membrane, the laboratory test of the membrane and the modelling of the system for process assessment. For this absorption device a total equivalent work of 240 kWh/ t(CO2) has been calculated for CO2 capture on a coal-fired power plant.

The flow over a flat plate at a Reynolds number of 750 is numerically investigated via fine large-eddy simulation (LES), first at normal ($90\textdegree $) and then at oblique ($45\textdegree $) incidence flow direction with a uniform steady inlet. The results are in complete agreement with the direct numerical simulation (DNS) and experimental data, thereby serving as a validation for the present simulations. For the normal ($90\textdegree $) uniform inflow case, coherent vortices are alternately shed from both leading edges of the plate, whereas for the oblique ($45\textdegree $) uniform inflow case the vortices shed from the two sides of the plate interact strongly resulting in a quasi-periodic force response. The normal flat plate is then analysed with an incident gust signal with varying amplitude and time period. For these incident coherent gust cases, a reference test case with variable coherent inlet is first studied and the results are compared to a steady inlet simulation, with a detailed analysis of the flow behaviour and the wake response under the incident gust. Finally, the flat plate response to 16 different gust profiles is studied. A transient drag reconstruction for these incident coherent gust cases is then presented based on a frequency-dependent transfer function and phase spectrum analysis.

ISBN 978-961-6207-39-3; International audience; Conjugate heat transfer describes the thermal coupling between a fluid and a solid. It is of prime importance in industrial applications where fluctuating thermal stresses are a concern, e.g. in case of a severe emergency cooling (Pressurized Thermal Shock) or long-term ageing of materials (T junctions). For such complex applications, investigations often rely on experiments, high Reynolds RANS (Reynolds-Averaged Navier-Stokes) or wall-modelled LES (Large Eddy Simulation). However , experimental data on conjugate heat transfer are scarce as walls in lab rigs are often made of plexiglas and the transported scalar studied is often a dye. The development of RANS models for conjugate heat transfer is relatively recent, see Craft et al. [1]. In this paper, we establish that the dissipation rate associated with the temperature variance is discontinuous at the fluid-solid interface, in case of conjugate heat transfer. This discontinuity is verified using some DNS (Direct Numerical Simulation) of the turbulent channel flow with conjugate heat transfer. There is currently no RANS model for conjugate heat transfer that takes into account this discontinuity.

International audience; Understanding wood segregation in bubbling fluidized beds is of importance for the global analysis, comprehensive modeling, and scale-up of bubbling fluidized bed biomass gasifiers. This study presents measurements of voidage and segregation taken during experiments in fluidized beds containing inert materials mixed with biomass particles. The features of the wood particles affect the bed axial homogeneity; a small particle size or a high density increase homogeneity. When gas fluidization velocity is low, the biomass particles are more segregated from olivine compared to the results achieved with larger velocities. In all experiments, a significant portion of the wood remains within the bed (50–80%), while the rest of the biomass floats at the bed surface. The experimental modeling accurately represents the voidage of the bed, with the exception of the upper part of the bed and the floating portion of the biomass particles. The results of the present study are in agreement with recent publications.