Temperature and moisture effects on the failure mode of highly shrinkable raw catalyst supports

International audienceShrinkage implies generally the development of mechanical stresses and then, the formation of cracks. In this work, four formulations of alumina based hydrogels underwent a standard experimental procedure involving drying and mechanical characterizations. The thermo-hydro-mechanical behaviour of such highly shrinkable hydrogels is analysed by determining their specific surface area, calculated from the desorption isotherms. Brazilian test allowed identifying the cracking stress of the four hydrogel formulations, and the ultimate tensile strength as a function of the water content was obtained for each of them. During the drying experiments inside a convective dryer, two formulations of hydrogels displayed a capacity for self-healing. The results showed a real improvement of the strength property due to the self-repair phenomenon when it occured, proving the importance of taking into account the roles of residual water and of applied temperature conditions in the drying process of the catalyst support production line

Estimation sur des bases orthogonales des propriétés thermiques de matériaux hétérogènes à propriétés constantes par morceaux

Ce travail se propose de caractériser thermiquement des composites à microstructures complexes. Il s agit de développer des méthodes d estimation permettant d identifier les propriétés thermiques des différentes phases en présence, ainsi que celles associées à leurs interfaces, à partir de mesures issues de la thermographie infrarouge. Cette estimation paramétrique nécessite la connaissance au préalable de la structure géométrique de l échantillon. Le premier objectif concerne donc l identification de la structure de l échantillon testé par la discrimination des différentes phases et interfaces. Une fois la structure de l échantillon connue, le second objectif est l identification des paramètres thermiques des différents constituants ainsi que ceux de leurs interfaces. On se propose d exploiter deux tests spécifiques utilisant le même dispositif expérimental. Deux méthodes mathématiques différentes ont été développées et utilisées pour exploiter les mesures de champ issues du premier test et permettre de retrouver la microstructure de l échantillon. La première est fondée sur la décomposition en valeurs singulières des données de températures recueillies. Il est montré que cette méthode permet d obtenir des représentations de la microstructure de très bonne qualité à partir de mesures même fortement bruitées. La seconde méthode permet de raffiner les résultats obtenus à l aide de la méthode précédente. Elle repose sur la résolution d un problème d optimisation sous contraintes en exploitant la technique dite Level-Set pour identifier les frontières des différents constituants de l échantillon. L étape d identification des propriétés thermiques des constituants et des interfaces exploite les mesures de champs issues du second test expérimental. La méthode développée, la SVD-FT combine des techniques de décompositions en valeurs singulières avec desfonctions tests particulières pour dériver des estimateurs linéaires des propriétés recherchées.Cette méthode permet de limiter les effets du bruit de mesure sur la qualité de l estimation et de s affranchir des opérations de filtrage des données.This work reports on the thermal characterization of composites with a complex microstructure. It aims at developping mathematical methods to identify the thermal properties of the constituants and thoses associate at their interfaces. The first step consistsin discriminating the microstructure of the sample to be tested. Then, when the sample structure is known, the second step consists in estimating the thermal parameters of the different phases and those at their interfaces. One experimental device has been set up to realize those two steps. Two mathematical methods have been developped and used to discriminate the microstructure based on the images of the sample recorded bu an infrared camera. The first method is based on the singular value decomposition of the temperature data. It has been shown that this method gives a very good representation of the microstructure even with very noisy data. The second method allows to refine the results obtained by the first one. This method is based on the resolution of an optimization problem under constraints and use a Level-Set technic to identify the boundary of each phase. To estimate the thermal properties of each phase and its interface, the infrared images of the second experiment have been used. The SVD-FT method developed in this work combines the singular values decomposition technic with particular tests functions to derive linear estimat or for the thermal properties. As a result, a significant amplification of the signal/noise ratios is reached.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Option pricing under regime-switching models: Novel approaches removing path-dependence

A well-known approach for the pricing of options under regime-switching models is to use the regime-switching Esscher transform (also called regime-switching mean-correcting martingale measure) to obtain risk-neutrality. One way to handle regime unobservability consists in using regime probabilities that are filtered under this risk-neutral measure to compute risk-neutral expected payoffs. The current paper shows that this natural approach creates path-dependence issues within option price dynamics. Indeed, since the underlying asset price can be embedded in a Markov process under the physical measure even when regimes are unobservable, such path-dependence behavior of vanilla option prices is puzzling and may entail non-trivial theoretical features (e.g., time non-separable preferences) in a way that is difficult to characterize. This work develops novel and intuitive risk-neutral measures that can incorporate regime risk-aversion in a simple fashion and which do not lead to such path-dependence side effects. Numerical schemes either based on dynamic programming or Monte-Carlo simulations to compute option prices under the novel risk-neutral dynamics are presented

Applicability of Infrared Thermography for the Detection of Phase Transitions in Metal Alloys

This work aims at assessing the applicability of a screening-oriented device dedicated to the establishment of increasingly complex phase diagrams of phase change materials. A thermography-based method has recently been proven to allow the detection of phase transitions of organic materials for multiple samples at a time. The phase transition detection capability of the infrared thermography method is here evaluated for metal systems based on well-referenced materials commonly employed in DSC calibration (pure sample of Gallium and a mixture of Gallium and Indium). The detected transitions are compared to literature data and DSC measurements. All transitions documented in the literature could be retrieved by thermography, and liquidus transitions are validated with DSC measurements. The encouraging nature of the results is discussed, and avenues for improving the method are considered

On the Use of Infrared Thermography for the Estimation of Melting Enthalpy

A calorimetry method based on infrared thermography is showing promise for material screening, allowing the simultaneous detection of phase transitions of multiple samples at a time, hence enabling the establishment of phase diagrams in a record time. The working principle of this method is similar to the one of Differential Thermal Analysis. Therefore, this work aims at identifying if the melting enthalpy of materials could be estimated on the same basis using infrared thermography. In this work, the melting of six eutectic mixtures of fatty acids is estimated under three considerations. The results are compared to Differential Scanning Calorimetry measurements and literature data. The accuracy of the method is discussed and improvements are proposed

Characterization of Fatty Acids as Biobased Organic Materials for Latent Heat Storage

This work aims to characterize phase change materials (PCM) for thermal energy storage in buildings (thermal comfort). Fatty acids, biobased organic PCM, are attractive candidates for integration into active or passive storage systems for targeted application. Three pure fatty acids (capric, myristic and palmitic acids) and two eutectic mixtures (capric-myristic and capric-palmitic acids) are studied in this paper. Although the main storage properties of pure fatty acids have already been investigated and reported in the literature, the information available on the eutectic mixtures is very limited (only melting temperature and enthalpy). This paper presents a complete experimental characterization of these pure and mixed fatty acids, including measurements of their main thermophysical properties (melting temperature and enthalpy, specific heats and densities in solid and liquid states, thermal conductivity, thermal diffusivity as well as viscosity) and the properties of interest regarding the system integrating the PCM (energy density, volume expansion). The storage performances of the studied mixtures are also compared to those of most commonly used PCM (salt hydrates and paraffins).This research work was developed in the framework of SUDOKET project (Interreg Sudoe SOE2/P1/E0677). The authors are grateful to the European Regional Development Fund (ERDF) to co-fund the project through the Interreg Sudoe Programme and the Region Nouvelle Aquitaine for subsidizing BioMCP project (Project-2017-1R10209-13023). The authors would also like to extend their thanks to CNRS for promoting the I2M Bordeaux-CICenergiGUNE exchanges in the framework of the IEA PHASE-IR project

Review on the Integration of Phase Change Materials in Building Envelopes for Passive Latent Heat Storage

Latent heat thermal energy storage systems incorporate phase change materials (PCMs) as storage materials. The high energy density of PCMs, their ability to store at nearly constant temperature, and the diversity of available materials make latent heat storage systems particularly competitive technologies for reducing energy consumption in buildings. This work reviews recent experimental and numerical studies on the integration of PCMs in building envelopes for passive energy storage. The results of the different studies show that the use of PCMs can reduce the peak temperature and smooth the thermal load. The integration of PCMs can be done on the entire building envelope (walls, roofs, windows). Despite many advances, some aspects remain to be studied, notably the long-term stability of buildings incorporating PCMs, the issues of moisture and mass transfer, and the consideration of the actual use of the building. Based on this review, we have identified possible contributions to improve the efficiency of passive systems incorporating PCMs. Thus, fatty acids and their eutectic mixtures, combined with natural insulators, such as vegetable fibers, were chosen to make shape-stabilized PCMs composites. These composites can be integrated in buildings as a passive thermal energy storage material