On Spatial and Temporal Variations and Estimates of Energy Dissipation in Stirred Reactors

The flow in a standard configuration stirred vessel stirred by a Rushton turbine was studied with laser Doppler anemometry (LDA), particle image velocimetry (PIV) and computational fluid dynamics (CFD). The temporal and spatial variations of the viscous dissipation of the turbulent energy (ɛ) were quantified and its commonly-employed estimates were assessed. Values of ɛ were found to vary by 3 orders of magnitude from near the impeller to the bulk of the vessel. A significant variation of ɛ with blade angle by around two orders of magnitude and radial location was observed by means of angle-resolved measurements and numerical predictions. A comparison between direct measurements of ɛ and estimates obtained through dimensional analysis methods suggest that the latter may lead to an underestimation of ɛ by up to 50% in the vicinity of the impeller and to an overestimation at some locations in the bulk of the vessel.