The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Calculation of Multicomponent Mass Transfer Between Dispersed and Continuous Phases

Ville Alopaeus

Dissertation for the degree of Doctor of Technology to be presented with due permission for public examination and debate in Auditorium Komppa at Helsinki University of Technology (Espoo, Finland) on the 15th of June, 2001, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-5704-1)   [1881 KB]
Dissertation is also available in print (ISBN 951-666-574-8)

Abstract

In many industrially important unit operations, mass transfer between dispersed and continuous phases takes place. The accurate and fast solution of the mass transfer model equations is essential in order to design these unit operations accurately.

The mass transfer rate between phases is calculated in two parts. The first part is to solve the interphasial mass transfer fluxes. With multicomponent systems, this is best done with the Maxwell-Stefan diffusion model along with a mass transfer model. The other part is to calculate the mass transfer area between the phases. This can be done with population balance models, preferably with a flow model that discriminates various regions of the modeled system. The flow model is needed if the phenomena affecting the development of the mass transfer area are not homogeneous in separate parts of the considered region. The mass transfer rate needed in the material balances is then a product of the mass transfer fluxes and the mass transfer area.

The mass transfer calculations with the Maxwell-Stefan model leads to complicated matrix function calculations. This is very time consuming because these models need to be solved many times during the solution of a unit operation or reactor model. Two simplifications to these complicated functions are presented in this work. The first is a method to calculate general matrix functions related to the multicomponent mass transfer models approximately. It is based on the fact that the diffusion coefficient matrices have larger diagonal than off-diagonal elements. The other approximation is a linearization of the high flux correction. The applicability of these two approximations, along with other modeling aspects, is considered with a distillation tray model. An approximation was also presented in this work for calculating diffusion, and further the mass transfer coefficients, within spherical particles.

A population balance approach is used with a stirred tank flow model to calculate drop size distributions in liquid-liquid dispersions. In order to test the applicability of the flow model with population balances, drop size distributions are measured and the drop breakage and coalescence function parameter values are estimated. The inhomogeneous character of the dispersion in a stirred tank can be used in the parameter estimation process.

This thesis consists of an overview and of the following 6 publications:

  1. Alopaeus, V., Aittamaa, J., Nordén, H. V., Approximate High Flux Corrections for Multicomponent Mass Transfer Models and Some Explicit Methods, Chem. Eng. Sci. Vol. 54 (1999) pp. 4267-4271. © 1999 Elsevier Science. By permission.
  2. Alopaeus, V., Nordén, H. V., A Calculation Method for Multicomponent Mass Transfer Coefficient Correlations, Computers & Chem. Eng. Vol. 23 (1999), pp. 1177-1182. © 1999 Elsevier Science. By permission.
  3. Alopaeus, V., Koskinen, J., Keskinen, K. I., Simulation of the Population Balances for Liquid-Liquid Systems in a Nonideal Stirred Tank, Part 1 Description and Qualitative Validation of the Model, Chem. Eng. Sci. Vol. 54 (1999), pp. 5887-5899. © 1999 Elsevier Science. By permission.
  4. Alopaeus, V., Aittamaa, J., Appropriate simplifications in calculation of mass transfer in a multicomponent rate-based distillation tray model, Ind. Eng. Chem. Res. Vol. 39 (2000), pp. 4336-4345. © 2000 American Chemical Society. By permission.
  5. Alopaeus, V., Mass Transfer Calculation Methods for Transient Diffusion Within Particles, AIChE J. 46 (2000) pp. 2369-2372. © 2000 AIChE. By permission.
  6. Alopaeus, V., Keskinen, K. I., Koskinen, J., Utilization of Population Balances in Simulation of Liquid-Liquid Systems in Mixed Tanks, Presentation at AIChE Annual meeting 2000, Los Angeles, USA. © 2000 by authors.

Errata of publication 5

Keywords: multicomponent mass transfer, Maxwell-Stefan theory, matrix approximations, mass transfer models, population balances, liquid-liquid dispersions, stirred tank inhomogeneity, simulation

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© 2001 Helsinki University of Technology

Last update 2011-05-26