Mass transfer coefficient

Résumé

In engineering, the mass transfer coefficient is a diffusion rate constant that relates the mass transfer rate, mass transfer area, and concentration change as driving force: k_c = \frac{\dot{n}_A}{A \Delta c_A} Where: *k_c is the mass transfer coefficient [mol/(s·m2)/(mol/m3)], or m/s *\dot{n}_A is the mass transfer rate [mol/s] *A is the effective mass transfer area [m2] *\Delta c_A is the driving force concentration difference [mol/m3]. This can be used to quantify the mass transfer between phases, immiscible and partially miscible fluid mixtures (or between a fluid and a porous solid). Quantifying mass transfer allows for design and manufacture of separation process equipment that can meet specified requirements, estimate what will happen in real life situations (chemical spill), etc. Mass transfer coefficients can be estimated from many different theoretical equations, correlations, and analogies that are

Source officielle

https://en.wikipedia.org/wiki/Mass_transfer_coefficient

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Publications associées (62)

Numbering-up and mass transfer studies of liquid–liquid two-phase microstructured reactors

Akash Gupta, Madhvanand Namadeo Kashid, Lioubov Kiwi, Albert Renken

Microstructured reactors are known to provide high heat and mass transfer rates for liquid–liquid twophase systems when used as a single channel. For industrial scale production, scale-up of microstructured reactors is essential to achieve throughput in the required range which is done by numbering-up of a single channel. The important issues are uniform flow distribution and identical slug size in all channels. In the present work, a capillary microstructured reactor is numbered up for six capillaries and the mass transfer performance is investigated for various operating conditions. A cationic surfactant was used to study the effect of interfacial tension on the mass transfer performance. If compared to conventional contactors, the mass transfer coefficients were approximately one order of magnitude higher allowing the process intensification. The results obtained demonstrate the benefits of microstructured reactors and confirm that the throughput of conventional reactors can be achieved.

Elsevier2010

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

Andrea Brühwiler

EPFL2007

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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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The theoretical background and practical aspects of heterogeneous reactions including the basic knowledge of heterogeneous catalysis are introduced. The fundamentals are given to allow for the use of chemical reactors to study reaction kinetics and test various mechanistic assumptions.

This course covers fundamentals of heat transfer and applications to practical problems. Emphasis will be on developing a physical and analytical understanding of conductive, convective, and radiative heat transfer.

L'étudiant sera capable de :

Définir et décrire les principales OpUnit.
Elaborer l'analyse critique d'une OpUnit, optimiser son fonctionnement selon les contraintes.
Emettre des recommandations d'amélioration, en tenant compte de la technique de l'économie et du développement durable.

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