Dispersion model

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The dispersion model is a model for describing the residence time of substances in chemical reactors . In addition to the cascade model, it is a dwell time model that is used in process and bioreactor technology.

However, the term dispersion model is also used in other dispersion processes, e.g. B. in electromagnetic waves or in geology .

The dispersion model is suitable for describing the residence time in reactors such as stirred tanks and flow tubes , in which there is approximately a piston flow . In systems in which there is strong mixing , however, the model can only poorly serve to determine the residence time.

The dispersion model refers to the unitless parameter of the Bodenstein number :

  • with a high Bodenstein number there is almost a piston flow and therefore no axial backmixing takes place.
  • a small Bodenstein number, on the other hand, indicates a strongly (axially) backmixed system.

When adjusting a stirred tank reactor, the lowest possible Bodenstein number should be achieved in order to achieve optimal proportions of the mixture. It is then an ideally back-mixed reactor.


  • M. Steiner: The dispersion model. In: heat and mass transfer. 10, 1977, pp. 245-253, doi : 10.1007 / BF00998726 .
  • D. Wiemann, D. Mewes: Are dispersion models still useful? In: Chemical Engineer Technology. 76, 2004, pp. 1301-1302, doi : 10.1002 / cite.200490219 .
  • Michael Ulrich: The unsteady dispersion model for reactions with any number of reactants. In: Chemical Engineer Technology. 44, 1972, p. 904, doi : 10.1002 / cite.330441407 .

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