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Concept

Équilibre thermodynamique

Résumé

vignette|200px|Exemple d'équilibre thermodynamique de deux systèmes, en l'occurrence deux phases : l'équilibre liquide-vapeur du brome. En thermodynamique, un équilibre thermodynamique correspond à l'état d'un système ne subissant aucune évolution à l'échelle macroscopique. Les grandeurs intensives caractérisant ce système (notamment la pression, la température et les potentiels chimiques) sont alors homogènes dans l'espace et constantes dans le temps. Cet équilibre est stable s'il n'est pas susceptible d'évoluer sur une échelle de temps infinie, ou sous le coup d'une perturbation extérieure ou d'une fluctuation locale interne. Tout système évolue selon les premier et deuxième principes de la thermodynamique, qui définissent les fonctions d'état énergie interne et entropie. Un équilibre thermodynamique est stable lorsque le système ne peut plus évoluer, car cela impliquerait une diminution de l'entropie contraire au deuxième principe. L'équilibre thermodynamique d'un système isolé (q

Source officielle

https://fr.wikipedia.org/wiki/%C3%89quilibre_thermodynamique

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The student will acquire the basis for the analysis of static structures and deformation of simple structural elements. The focus is given to problem-solving skills in the context of engineering design.

This course covers the metallurgy, processing and properties of modern high-performance metals and alloys (e.g. advanced steels, Ni-base, Ti-base, High Entropy Alloys etc.). In addition, the principles of computational alloy design as well as approaches for a sustainable metallurgy will be addressed

L'étudiant acquiert les bases de l'analyse des contraintes et déformation des poutres élastiques linéaires soumises à la traction, cisaillement, torsion, flexion; les coefficients d'influence et la méthode de l'énergie pour analyser des systèmes isostatiques et hyperstatiques; critères de rupture.

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Séances de cours associées

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Thermodynamic and kinetic degradation reactions of organic substances in groundwater modelled with PHREEQC

Johann Jakob Holch

Aim of this diploma thesis is to approach to kinetic modelling of subsurface hydrochemistry with the program code phreeqc. The reaction considered is the degradation of organic mass and its concomitant reactions. Phreeqc is a program for thermodynamical based equilibrium calculations of geo- and hydrochemistry. Although the degradation of organic matter, and the associated reduction reactions due to the oxidation of organic matter, can be modelled with phreeqc, it does not account for kinetically controlled reactions, whose characteristic feature is the dependency of time. This study focuses on the state of the art of environmental modelling, the thermodynamical based calculation of the degradation of organic matter and on two mathematical approaches to model bacterial degradation of a contaminant, the Monod equation and the Michaelis-Menten approach. Sensitivity analyses of the respective models runs were done. As a result one can see, that the redox chemistry of a natural water depends strongly on the abundance of oxygen and nitrate and, as a matter of course, on the abundance of organic matter. Considering bacterial activity within the degradation process, two basic mathematical formulations have been stated. The Monod equation and the Michaelis-Menten formulation were implemented in a BASIC interpreter in PHREEQC. The sensitivity analyses show, that that a accurate determination of the parameters in laboratory or field is essential. The coupling of kinetically controlled reactions and thermodynamical based equilibrium calculations might lead to auspicious hydrochemical modelling capabilities.

2008

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Integrating rate based models into multi-objective optimisation of process designs using surrogate models

François Maréchal, Levent Sinan Teske

Multi-objective optimisation (MOO) of super-structured process designs are expensive in CPU- time because of the high number of potential configurations and operation conditions to be calculated. Thus single process units are generally represented by simple models like equilibrium based (chemical or phase equilibrium) or specific short cut models. In the development of new processes, kinetic effects or mass transport limitations in certain process units may play an important role, especially in multiphase chemical reactors. Therefore, it is desirable to represent such process unit by experimentally derived RBMs (rate based models) in the process flowsheet simulators used for the extensive MOO. This increases the trust engineers have in the results and allows enriching the process simulations with newest experimental findings. As most RBMs are iteratively solved, a direct incorporation would cause higher CPU-time that penalises the use of MOO. A global surrogate model (SUMO) of a RBM was successfully generated to allow its incorporation into a process design & optimisation (PDO) tool which makes use of an evolutionary MOO. The methodology was applied to a fluidised bed methanation reactor in the process chain from wood to Synthetic Natural Gas (SNG). Two types of surrogate model, an ordinary Kriging interpolation and an artificial neural network, were generated and compared to its underlying rate based model and the chemical equilibrium model. The analysis showed that kinetic limitations have significant influence on the result already for standard bulk gas chemical components. From experimental experience it can be stated that a significant amount of chemical compounds, which are near to complete conversion according the thermodynamic equilibrium, are measured in the gas phase after the reactor. Thus including RBMs in PDO improves the quality of results. This approach allows a significant improvement of information exchange between process design & optimisation workflow and experimental development of PUs in early stages of process development.

2013

Chargement

This thesis investigates the effects of aluminates, sulfates, and heterogeneous substrates on the nucleation and growth of synthetic calcium-silicate-hydrates (C-S-H) produced by dropwise precipitation. The use of synthetic C-S-H, separate from other cementitious phases, allows formation mechanisms and kinetics effects to be investigated in a simplified system. The addition of other ions and substrates then allows an approach to the more complicated, multi-phase system of cement and concrete. The first goal of this thesis was to reproducibly synthesize single-phase C-S-H with Ca:Si from 1 to 2. Guidelines were described for collection, drying, and handling of the precipitates to prevent the formation of Ca(OH)2 during synthesis and minimize carbonation. Interlayer spacing in precipitates was studied by transmission XRD to compare the effects of Ca:Si, relative humidity, and time, using the 14Å tobermorite structure as a baseline for synthetic C-S-H. The growth and nucleation kinetics of C-S-H were then investigated with the combined thermodynamic and population balance equation model (PBEM). The surface characteristics of C-S-H, C-A-S-H, and C-S-H +

were investigated by acoustophoresis to compare the effects of Ca:Si, washing, and dispersion media on zeta potential measurements. Results showed the necessity of full characterization of both solutions and precipitates in order to understand and compare acoustophoresis results. In the final section of the thesis C-S-H, C-A-S-H, and C-S-H +

were grown on the surface of heterogeneous substrates, quartz and calcite, to approach C-S-H growth in real systems. Overall, the results from this thesis provided helpful information on synthetic C-S-H, C-A-S-H, and C-S-H + $ at the full range of Ca:Si molar ratios, particularly ratios above 1.5, as observed in Portland cement. As we get closer to understanding and controlling C-S-H in real systems, this work will help provide insight as to how heterogenous substrates and aluminates introduced by SCMs, in addition to sulfates, commonly added to cement via gypsum, affect the early age strength and kinetics of C-S-H formation.

EPFL2022

Chargement

were investigated by acoustophoresis to compare the effects of Ca:Si, washing, and dispersion media on zeta potential measurements. Results showed the necessity of full characterization of both solutions and precipitates in order to understand and compare acoustophoresis results. In the final section of the thesis C-S-H, C-A-S-H, and C-S-H +

EPFL2022

Integrating rate based models into multi-objective optimisation of process designs using surrogate models

François Maréchal, Levent Sinan Teske

2013