Bodenstein number
Physical key figure  

Surname  Bodenstein number  
Formula symbol  
dimension  dimensionless  
definition  


Named after  Max Bodenstein  
scope of application  Chemical reaction engineering 
The Bodenstein number (after Max Bodenstein ), Bo for short , is a dimensionless number from reaction engineering that describes the ratio of the moles supplied by convection to those supplied by diffusion . The Bodenstein number thus characterizes the backmixing within a system (the larger the Bodenstein number, the lower the backmixing) and enables statements to be made about whether and how much volume elements or substances mix within a reactor due to the prevailing currents.
The Bodenstein number is defined as the ratio of the convection flow to the dispersion flow. It is part of the dispersion model and is therefore also referred to as the dimensionless dispersion coefficient.
Mathematically, two idealized borderline cases are obtained for the Bodenstein number, which, however, cannot be fully achieved in practice:
 if the Bodenstein number were zero, the state of total backmixing would have been achieved, which is ideally desired in a continuously operated stirred tank reactor .
 If the Bodenstein number were infinitely large, there would be no backmixing, but only a continuous flow that prevails in an ideal flow pipe.
By regulating the flow rate within a reactor, the Bodenstein number can be set to a previously calculated, desired value. In this way, the backmixing of the substance components desired within the respective reactor can be achieved.
determination
The Bodenstein number is calculated through
With
 the flow velocity
 the length of the reactor
 the axial dispersion coefficient in m² / s.
The Bodenstein number can be obtained experimentally from the residence time distribution. Assuming an open system, the following applies:
With
 the dimensionless variance
 the variance around the mean residence time
 the hydrodynamic residence time .
Individual evidence
 ↑ Matthias Bohnet (Ed.): Mechanical process engineering. WileyVCH, Weinheim 2004, ISBN 3527310991 , pp. 213229.