Eric Blond

Thermo-Chemo-Mechanical Modelling of Mixed Conductors in Transient Stages

This study deals with the modelling of the mechanical behaviour accounting for the expansion induced by the oxygen diffusion in MIECs membrane during semi-permeation transient stage. A dedicated model of chemical expansion and its numerical implementation is used to study the relationship between the mechanical stress and the oxygen flux. The impact of the ratio between oxygen bulk diffusion and surface exchange kinetics on mechanical stress in transient stage is discussed. At last, the need of a compromise between the oxygen flux performance and the mechanical reliability is underlined.

Experimental characterization and modeling of GF/PP commingled yarns tensile behavior

Three-dimensional (3D) fabrics of commingled yarns offer the possibility of a low-cost and fast manufacturing of complex-shaped composite parts. Textile-reinforcement behavior during the forming process is very important since the appearance of defects (for example wrinkles, yarn misalignment or breakage) can significantly affect the mechanical properties of the final part. Experimental characterization of the mechanical behavior of textile-reinforcements is expensive, time consuming, and a large scattering of results is often observed. To overcome this, meso-scale modeling is an interesting method to study and understand the textile behavior at the unit cell level. To perform realistic simulations, an accurate modeling and, therefore, knowledge of the yarn mechanical behavior are needed. In this paper, a simple protocol is proposed and validated in order to investigate the tensile behavior of commingled polypropylene/glass yarns. Influence of specimen length and strain rate are highlighted. A comparison of tensile behavior of yarns before and after weaving is carried out in order to evaluate the weaving damage effect. Finally, a model describing the commingled yarn behavior is proposed. The parameters of the model are defined. Their dependency to strain rate, specimen length, and weaving damage are highlighted.

Modeling of Coal Drying before Pyrolysis

The coking process is composed of two main stages: drying process and pyrolysis of coal. A heat and mass transfer model was developed to simulate the drying process of coal. The mechanisms of heat and mass transfer described in the model are: conduction through the coal cake; conduction and convection through the gas in pores; generation, flux and condensation of water vapor. The model has been implemented in finite element software. It requires basic data on the coke oven charge properties and oven dimensions as input. These input data were obtained by experiments or from the literature. The proposed model includes condensation and evaporation allowing us to reproduce the temperature plateau observed experimentally.

Modelling of the oxygen transport through MIEC membrane in transient stage

The transient stage is critical due to the stress induced by the chemical and thermal strain. In order to predict this strain, the oxygen activity field through the membrane needs to be known. Usually, the membrane is divided into three zones: the bulk where diffusion takes place and the two surfaces where exchanges between atmosphere and membrane take place. Oxygen bulk diffusion is well described by the Wagner theory. A consensus has not yet emerged regarding the surface exchange models proposed in the literature. Moreover, these models describe the permanent state, and cannot be extended to the transient stage. A new macroscopic surface exchange model which allows computing transient stage is proposed. This model assumed that the oxygen flux is governed by the association/dissociation of adsorbed oxygen and by the high energetic cost of oxygen reduction/oxidation. Then, the balance of transient specie only present on the surface is introduced to account for these two phenomena. The oxygen activity fields predicted by the proposed model are in agreement with the measures of chemical potential drop between the membrane and the atmosphere in permanent state. Transient stage measured during isothermal expansion test is partially reproduced.

Multiphysics Modelling Applied to Refractory Behaviour in Severe Environments

It is a common practice to design refractory linings with the help of thermal computations, thermochemistry analyses and strong workman know-how. Their mechanical design is often limited to simple thermo-elastic computations. Sometimes computations are refined considering non-linear mechanical behaviour, even if corrosion often induces additional chemical strain and strong change in service of the mechanical behaviour of the refractory. The aim of this presentation is to briefly recast the irreversible thermodynamic framework in order to underline the implications of some basic thermodynamic concepts in term of refractory behaviour modelling. Then, the use of these concepts to develop fully 3D finite element simulations accounting simultaneously for thermal, mechanical and chemistry phenomena will be illustrated on the particular case of SiC-based refractory. Comparison between long duration oxidation test at high temperature and model prediction allows the validation of the proposed approach. Then, an extension to the industrial case of refractory lining in Waste to Energy plant will be illustrated. The interest of taking into account the thermo-chemo-mechanical coupling effects is shown.

Mechanisms of SiC Refractory High Temperature Corrosion by Molten Salts (Na,K,Ca,Cl,S) in Waste to Energy Facilities

Damage of SiC oxide bonded refractories in waste-to-energy facilities (WtE) has been characterized. Different phenomena were observed: wear by slag phases, volume expansion of tiles and fracture in different locations. These results are in agreement with laboratory experiments. The role of gas composition and tiles temperature profile on deposit composition, on condensation of gaseous alkali chloride and on formation of liquid phase inside the porosity of the refractories has been emphasized. Gaseous alkali species are involved, not only in the formation of liquid phases, but also as a precursor of cristoballite formation around the SiC grains as well as in the rich alumina-silica matrix. On the hot face of the refractories, oxo-reduction reactions produce the formation of wollastonite. Post-mortem analysis after several thousand hours of operation point to three main corrosion mechanisms:

Study of Reactive Impregnation and Phase Transformations during the Corrosion of High Alumina Refractories by Al2O3-CaO Slag

Corrosion of refractories results from reactive transport namely, transport of agents and chemical reactions of these agents with impregnated medium. On one hand, the transport involves either diffusion or impregnation depending on the state of the corrosive agents and the microstructure of the host media. On the other hand, chemical reactions may be very numerous and complex. This study focused on the reactive impregnation of Al2O3-CaO slag into porous high alumina refractory.Transport properties of the porous media have been assessed by performing wicking test. Chemical reactions between the solid high alumina skeleton and Al2O3-CaO slag involve successive dissolution/precipitation mechanisms forming aluminates of lime. Contrary to the thermodynamic properties of the binary system, the kinetics of these solid/liquid reactions is not well known. Corrosion tests associated with quenching method, XRD and high temperature XRD were performed for a better understanding of the kinetics.

Modelling of the Swelling of SiC-Based Refractory Lining Used in Waste-to-Energy Plants

This work provides a computational model of the chemo-mechanical behavior of based refractories used in waste to energy plant (WTE) linings. In this application, oxygen gas present in the atmosphere diffuses through the porosity and reacts with the refractory producing silica (SiO2). This new phase clogs gradually the pores and causes swelling of the refractory lining. The proposed thermo-chemo-mechanical model which simulates these phenomena is briefly summarized. The results obtained from the model implemented in a F.E code prove the ability of the model to reproduce qualitatively the swelling of post-mortem bricks taken from WTE linings.Copyright

A MACROSCOPIC MODEL OF THE THERMO-CHEMO-MECHANICAL BEHAVIOUR OF MIXED IONIC AND ELECTRONIC CONDUCTORS

This paper suggests a macroscopic model describing the thermo-chemo-mechanical behaviour of ceramic dense membrane for oxygen separation application. This work takes in account to oxygen permeation and strain induced by stoichiometry variation with working conditions. This model, developed within the traditional framework of phenomenological approach, is based on the assumption of strain partitions and requires only three state variables: oxygen activity, temperature and total strain. Oxygen bulk diffusion and surface exchanges are described thanks to the thermodynamic approach developed by Onsager. While many works focused on semi-permeation induced strain, the proposed model also includes the temperature effect on chemical expansion. Strains predicted by the proposed model are validated thanks to experimental test on La0.8Sr0.2Fe0.7Ga0.3O3-δ. Implemented in F.E.A code Abaqus, this model permits studying the design and the process management effects such as chemical shocks on the membrane reliability.

Electro-Magneto-Fluid-Structural Coupling Problem: The Vibrating Viscometer

This study presents a viscosity sensor that converts the vibration amplitude at the resonance frequency of a needle immersed in viscous fluid, into electric current. The goal of this work is to provide a dedicated numerical tool for the sensor design, that couples fluid, structure and magnetism.Copyright