AND T.J. NAPIER-MUNN

Large Eddy simulations coupled with the mixture model and lagrangian particle tracking has been applied to the study of medium segregation and coal particle partitioning in a dense medium cyclone using Fluent. The mixture model was modified with corrections for wall lift forces, hindered settling, slurry rheology and particle interactions. Predicted velocity profiles are in agreement with the experimental data of Fanglu and Wenzhen (1987), measured by laser doppler anemometry. Predicted density profiles are close to gamma ray tomography data, showing a density drop near the wall. The turbulence analysis showed that the change in the body shape from cylindrical to the conical section is one of the sources for the turbulence inside the cyclone. Once correct medium segregation was predicted, the performance characteristics of the DMC on coal were modelled using Lagrangian particle tracking for particles ranging in size from 0.5 to 4 mm. The predicted Ep values are very close to the experimental values although a slight deviation in the cut-point predictions was observed. NOMENCLATURE Greek symbols α volume fraction ρ density kg.m-3 εijk permutation tensor τij stress tensor kg.m-1.s-2 ωij rotation or vorticity vector µ viscosity kg.m-1.s-1 Other symbols Cd drag coefficient Clp lift coefficient d particle or phase diameter- m Dc cyclone diameter – m Ep cyclone efficiency parameter frep drag correction Flpi lift force on particle- N gi gravity- m.s-2 kd fluid particle exchange coefficient Pg Granular pressure- pa Re Reynolds number t time- s xi co-ordinate i- m ui velocity- m.s-1 Subscripts c continuous phase d discrete (coal) phase m mixture p particulate (medium) phas