| Abstract: | Modelling multiphase flow in reactors. This paper is intended to enhance the knowledge of two phase reactors. Their performance depends not only on reaction kinetics but essentially on fluid-dynamically fixed quantities such as volume fractions, dispersion coefficients in the fluid and in the gas phase, as well as the volumetric mass transfer coefficient. These are basically dependent on the slip velocity of the phases and on the internal circulation speed of the fluid. The circulation either results from the fluid passing through the vessel (as in a bubble column) or it has to be effected separately in order to avoid separation. Suspension of solids or aeration of liquids in loop and stirred reactors can serve as examples. Dimensionless groups that characterize the main material and geometric properties can be derived using the slip velocity of the largest stable bubble and a certain circulation parameter. The power of this method will be shown by the characterization of bubble columns and gas-liquid mixers. Simple laws comparable with those applying to bubble columns emerge when approaching the flooding point of a disc turbine in a tank. Power numbers, gas volume fractions, and volumetric mass transfer coefficients can be bundled over the whole spectrum of the non-flooded states, when their characteristic quantities are divided by the quantities relating to the flooding point. |
