Cyclone SeparatorSTAR-CCM+ v6.02 Introduction • • • • • Cyclones are employed for removal of particulate contaminants from polluted air streams in a wide variety of engineering applications Nature of flow-particle dynamics in the cyclone lends itself as an excellent example for demonstrating the Lagrangian Particle Transport (LPT) approach In this tutorial, we have outlined the methodology to set-up a simulation to characterize the performance of a cyclone; Incidentally, results of the current effort also serve to validate the applicability of STAR-CCM+ for similar applications (strong swirling flows) Further, additional information elucidating the fluid and particle behaviour inside the cyclone are presented Simulation of Cyclone Separators with STAR-CCM+ Geometry and Operating Conditions De D = 0. 4. 2003 Simulation of Cyclone Separators with STAR-CCM+ velocity.25 b H Air a h S PRESSURE OUTLET (1 bar) velocity. m/s 20 density. m/s density. Wang et al. kg/m3 D 20 1. . Australia. Third International Conference on CFD in the Mineral and Process Industries.2 m a/D b/D De/D S/D h/D H/D B/D .25 . mm 5x10-3 . kg/m3 3320 volume fraction 3% size.205 VELOCITY INLET Solid Particles Air + Solid particles Reference: Numerical Study of Gas-Solid Flow in a Cyclone Seperator. CSIRO.5 .625 2.. PP 371-376.5 . Models & Reference Conditions • The following models were involved in the problem setup: • Three-dimensional. Reynolds-Averaged Navier-Stokes Reynolds Stress Turbulence Two-layer All Y+ Wall Treatment Linear Pressure Strain Two-layer Segregated Flow Segregated Fluid Isothermal Reference Conditions – – – Pressure: Atmospheric Temperature: 300 K Turbulent Intensity and Viscosity Ratio: 1 % & 10 . Gravity Constant Density Gas (Air) Implicit Unsteady Turbulent. Modeling Information • • • • • • CAD model of the geometry was created in star-design® based on data provided in the reference Geometry imported into STAR-CCM+ Surface and Volume meshing performed using the Surface Remesher and Polyhedral Volume Mesher Prism layer option was activated at the volume meshing stage to generate prism layers on all wall boundaries Final computational mesh comprised polyhedral cells and two prismatic cells (of total thickness 5 mm) at all wall boundaries Mesh count (trimmer + 2 prism layers on the walls) – 35732 . Polyhedral Mesh 2 prism layers Number of cells: 35732 Simulation of Cyclone Separators with STAR-CCM+ . a plot of mass-flow averaged inlet pressure value was also monitored to judge convergence For validation purposes.01 sec Continued till the residuals attained a steady value @ which time a four-order reduction in the residuals was observed Further. simulations were repeated at six more inlet velocity values (ranging from 5 to 35 m/s) to generate the pressure drop curve as a function of velocity Simulation of Cyclone Separators with STAR-CCM+ .Boundary Conditions • • • • • • • Velocity inlet (with base case value of 20 m/s) Pressure outlet (with atmospheric pressure) Rest all boundaries treated as no-slip walls Simulations performed in the implicit unsteady fashion with a time step 0. Velocity and Static Pressure Contours(@ 20 m/s) Simulation of Cyclone Separators with STAR-CCM+ . Velocity and Static Pressure Contours(@ 20 m/s) Simulation of Cyclone Separators with STAR-CCM+ . Velocity Vectors and Streamlines Simulation of Cyclone Separators with STAR-CCM+ . Axial and Tangential Velocity @ Line Probe Location Simulation of Cyclone Separators with STAR-CCM+ . Comparison @ Different Inlet Velocities (35. 20 and 5 m/s) Simulation of Cyclone Separators with STAR-CCM+ . Validation (Expt & FLUENT data from reference) Simulation of Cyclone Separators with STAR-CCM+ . Performance Characterization • • • • Performance of a Cyclone is normally characterized by its ability to classify particles of different sizes For a particular geometrical configuration. a unique curve expressing the classification (particle collection efficiency in the outflow stream) as a function of particle size is obtained for a particular flow rate The detailed procedure to generate the classification curve for the base case (20 m/s) is outlined in the next few slides Further salient features with respect to particle tracking are illustrated using . Virtual Mass and turbulence dispersion forces were considered to act on the particles Particles (parcels) impacting on the wall surfaces were assumed to be rebounding except the bottom one where they were assumed to escape Particles were released on the presentation grid and tracked till they exited either the bottom wall (or) the top outlet .Particle Tracking • • • • • • One-way coupling (from gas to particle) was assumed between the gas and particle phases Particle tracking performed under the steady flow mode Spherical particles (parcels) with client supplied density were tracked on the converged flow field Drag (Schiller-Neumann). a presentation grid (as shown in the illustration below) was defined and located just downstream of the inlet patch •Injection points were uniformally distributed in a grid 8 x 16 = 128 total points Simulation of Cyclone Separators with STAR-CCM+ .Injection Definition • Particle injection into the domain can be achieved by different mechanisms • In the present case. we have estimated the separation efficiency based on the fraction collected at both the bottom as well as the top outlet .Methodology • • • • Specified number of mono-disperse particles (parcels) of different sizes (ranging from a minimum to a maximum value) are seeded at the inlet boundary and tracked in succession through the frozen flow field A no-slip condition is assumed for the parcels seeded at the inlet boundary Efficiency of separation for each particle (parcel) size is estimated by calculating the fraction of the total number of parcels seeded at the inlet boundary that reach the either boundary (top/bottom outlet) In the present case. Classification Characteristics [@ 20 m/s] Simulation of Cyclone Separators with STAR-CCM+ . 5 mm and above is ~ 95% and above. that for 0.75 mm and below is ~ 5 % and below Classification curve seen to be pretty steep with a sharpness of cut (D95%/D5%) of ~2 Simulation of Cyclone Separators with STAR-CCM+. whereas. CD-adapco Torino Office .Observations • • • Results of the LPT indicate that the cut point diameter (particle size corresponding to 50% separation) is of the order of 1.2 mm Separation performance for particle sizes 1. 1.25 mm.Tracks for 1 mm. 1.5 mm Particles Simulation of Cyclone Separators with STAR-CCM+ . 0 mm Simulation of Cyclone Separators with STAR-CCM+ .Velocity/Residence Time for 0.5 mm & 2. Animation Depicting 25 Tracks (1.25 mm) (individual tracks) Simulation of Cyclone Separators with STAR-CCM+ . 25 mm) (gradual progress as a group) Simulation of Cyclone Separators with STAR-CCM+ .Animation Depicting Transport of 25 Tracks (1. Summary • • • • Detailed step-wide procedure involved in setting up a LPT routine to simulate fluid-particle flow in a cyclone separator was demonstrated Predicted pressure drop curve @ various flow rates generated from simulation results seen to be in very good comparison to experimental results Methodology to generate the particle classification curve for the cyclone was elucidated Classification curve generated for the base flow rate value seen to be pretty steep (value ~2) . cut point diameter seems to be ~ 1.2 mm Simulation of Cyclone Separators with STAR-CCM+ .
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