Transfert de masse

Résumé

Dans le jargon automobile, le transfert de masse se rapporte à la redistribution du poids soutenu par chaque pneu pendant l'accélération (longitudinale et latérale). Cela inclut le freinage et la décélération (qui est une accélération négative). Le transfert de masse est un concept crucial en dynamique des véhicules. Le transfert de masse se produit lorsque le centre de gravité du véhicule se déplace pendant les manœuvres. L'accélération fait pivoter la masse suspendue autour d'un axe géométrique, ce qui a pour résultat la relocalisation du centre de masse. Le transfert de masse d'avant en arrière est proportionnel au rapport entre la hauteur du centre de gravité et l'empattement du véhicule, et le transfert de masse latéral (additionné à l'avant et à l'arrière) est proportionnel au rapport entre la hauteur du centre de gravité et la voie du véhicule. Automobile Modification du centre de gravité À titre d'exemple, quand une voiture accélère, on dit qu'un tran

Source officielle

https://fr.wikipedia.org/wiki/Transfert_de_masse

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Selective hydrogenation of an alkyne with Lindlar catalysts: mass transfer, kinetic study, and catalyst characterization

Andrea Brühwiler

EPFL2007

Chargement

Developing mathematical models for chemical reaction systems is essential for analysis, development, design, optimization and control of chemical, or biochemical industrial processes. Nowadays, more and more companies across the world have to deal with innovative concepts such as the Sustainable Chemistry (or "Green Chemistry"), which particularly require good knowledge of chemical reactions systems. Well-defined chemical operations involved in a process lead to its efficiency, energy saving and an improvement of the product quality. Furthermore, plants adopting this new philosophy minimize their byproduct production and pollutant formation. This master thesis works on developing a methodology for analysis and kinetic modeling of chemical reaction systems. In this present study, the case where chemical reactions take place in both phases of a heterogeneous biphasic fluid-fluid (F-F) reactor under isothermal conditions is considered. In order to model homogeneous or heterogeneous (F-F) chemical systems, a new approach called “Extent-based Incremental Identification” has recently been developed by the Laboratoire d’Automatique (EPFL). In contrast to the commonly used simultaneous approach, this extent-based incremental approach can compute parameters corresponding to reaction and mass transfer rates individually for each reaction and mass transfer laws, and also does not require prior postulation or knowledge of rate laws. This particular case is an extension of the dissertation done by Nirav Bhatt [1], which considers a heterogeneous chemical reaction system with reactions in one of the phases with steady state mass-transfer between the phases, and work done by Michael Amrhein [2], who developed a linear transformation that computed the extents of reaction from the numbers of moles in homogeneous reaction systems, with inlet and outlet streams. [1] Nirav Bhatt, EPFL Diss. n° 5028 (2011) [2] Amrhein et al., AIChE J. 56 (2010), 2873-2886

2013

Chargement

Incremental Model Identification of Gas-Liquid Reaction Systems with Unsteady-State Diffusion

Benoit Till Cretegny

Identification of kinetic models and estimation of reaction and mass-transfer parameters can be performed using the extent-based identification method, whereby each chemical/physical process is treated individually. This method is used here to analyze gas-liquid systems under unsteady-state mass transfer. Such a situation is common in the case of diffusion-controlled reactions and can be modeled by the film theory. In both the gas and liquid bulks, mass-balance relations describe the species dynamics as ordinary differential equations (ODE) and serve as boundary conditions for the film. On the other hand, the dynamic accumulation in the film is described by Fick's second lay. The resulting partial differential equation (PDE) system is solved by discretization and rearrangement into ODEs. Kinetic models are assessed and the corresponding parameters are estimated using extents of reaction. The estimation of diffusion coefficients follows a tow-steps procedure. First, the extents of mass transfer are computed from measurements in the two bulks. Diffusion coefficients are then estimated individually by fitting each extent of mass transfer to the extent obtained by solving the corresponding PDE. Comparison of the estimated diffusion coefficients with their literature values serves to validate the models identified in the two bulks. The estimation of both kinetic parameters and diffusion coefficients is investigated for gas-liquid reaction systems with unsteady-state diffusion. The approach is illustrated with simulated examples.

2013

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