Flow visualisation and velocity measurements in a vertical spindle coal mill static classifier☆

The aerodynamics within a reduced scale model of a vertical spindle coal mill static classifier are investigated to provide data for improving classifier particle separation predictions and the validation of computational simulations. Quantitative data for these purposes was obtained by measuring velocities using three-dimensional Laser Doppler Anemometry. Flow visualisation was also used to provide qualitative understanding. The results demonstrate that the flow in the main classifier volume closely resembles that reported in the literature for cyclones. However, the flow in the upper section of the classifier is highly three-dimensional. The effect of varying the inlet vane angle, within the range of industrially useful vane angles, is shown to principally only affect the tangential velocity magnitude.