Advances in Cyclonic Flow Regimes. Dr. Dimitrios Papoulias, Thomas Eppinger

Transcription

1 Advances in Cyclonic Flow Regimes Dr. Dimitrios Papoulias, Thomas Eppinger

2 Agenda Introduction Cyclones & Hydrocyclones Modeling Approaches in STAR-CCM+ Turbulence Modeling Case 1: Air-Air Cyclone Case 2: Oil-Water Hydrocyclone with LMP & EMP Case 3: Gas-Solid Cyclone Summary

3 Cyclones Separation of particulates from a continuous stream (air/liquid) without filter medium Separation based on rotational effects/centrifugal forces and gravity (density difference!) Advantages Low capital cost High temperature Disadvantages High operating cost (pressure drop) Low efficiency for small particles Low maintenance cost (no moving parts) Low space requirement

4 Modeling Approaches Two-Phase Modeling techniques: Eulerian-Lagrangian model (LMP): dispersed phase is realized as discrete populations of droplets droplet trajectories are tracked by Newton's 2 nd law of motion integrated forces included drag, lift, pressure-grad. & added-mass turbulent dispersion effects (random-walk model) Eulerian-Eulerian model (EMP): two-fluid method based on the interpenetrating continua assumption; each flowphase is treated by its own set of N-S the continuous & dispersed phases are coupled by incorporating source-terms for the acting forces i.e. drag, lift, virtual mass & turbulent dispersion

5 Case 1: EMP-RSM Model Verification Verification of the applicability of EMP-RSM for cyclone simulation. Overcome Lagrangian limitations: Low volume fraction of the dispersed phase Including disperse phase interaction Performance Testing RSM on ERCOFTAC singlephase cyclone Model predictions are compared against LDV measurements

6 Case 1: EMP-RSM Model Verification 700k trimmed cells (polys also tested) Single-phase: Air. EMP with two identical phases (Air) and VF ratios of: Velocity inlet (20m/s) and pressure outlet. RSM (k-epsilon also tested) Transient (dt = 0.005s) Drag and TDF included.

7 Case 1: EMP-RSM Model Verification Mean-axial velocity (m/s) position Y (m) RSM can successfully replicate the experimental measurements for single phase flow as well as for EMP.

8 Case 1: EMP-RSM Model Verification RSM RLZ STD Trim-Hex (0.7M) Polyhedral (0.8M) Trim-Hex (0.2M) Trim-Hex (0.7M) BASELINE BASELINE Uaxial/Uin z=0.77 x/d 0 uz (m/s) 25 RLZ: Realizable k-e STD: Standard

9 Case 2: Geometry Description Property Value Chamber Diameter D 60 mm Outlet D_o 3.6 mm Dn / D 0.5 α 20 β 1.5 Lc / D 1 Lo / D 15 Total height 1200 mm Hydrocyclones for oil/water separation, Int. Confer. Hydrocyclones, Colman et al.

10 Turbulence and Mesh Resolution The RSM turbulence model is used in order to capture vortical twophase dynamics i.e. pressure-drop, flow mixing & separation) Two-phase flow interactions and separation occurs at length-scale equivalent to the size of the dispersed droplets i.e. in order of a few µm Resolution of vortex separation regimes requires fine spatial discretization (14M trimmed cells (hexahedrons). top-view mid-section

11 Case 2: Simulation Setup CAD model generated in STAR-CCM+ 2 inlets m WWWWW = 1.02 kg/s, m OOO = kg/s Flow split outlet Top(oil) = 0.1, bottom(water) = 0.9 Density Water = 997 kg/m^3; Oil = 840 kg/m^3 Phase interaction Drag (Schiller-Naumann) Turbulent Dispersion Virtual Mass Shear Lift (Sommerfeld) Pressure gradient Particel Size Distribution (log-normal, [ µm]) Rebound at wall. Lagrangian: One-way coupling, steady (C=0.01) EMP: Fully coupled, transient (dt = 0.001s) Out_top in in Out_bottom

12 Case 2: Results LMP & EMP Pressure drop (inlet/oil_outlet) of 4bar agrees well with exp. Data. Separation efficiency well predicted. p efficiency (η) Droplet diam. (µm)

13 Case 3: Gas-Solid Cyclone Two-phase air & solid-particles cyclone case Eulerian-Lagrangian validation calculations in Stairmand s cyclone geometry. Single-phase simulations for different flow-rates & Multiphase cases for different particle diameters pressure-drop tangential vel p ΔP (Pa) U inlet (m/s)

14 Case 3: LMP Results mean tangential-velocity Z=0.58 d=10 µm d=0.1 µm U tang. /U in Z=0.18 diam. [μm] exp. % x/d cfd %

15 Summary STAR-CCM+ predicts for cyclones and hydrocyclones pressure drop, Flow profile and Separation efficiency. Both approaches (EMP and LMP) shows very good agreement with experimental data. Turbulence modeling and mesh resolution are key parameters for an accurate result.

16 Thank you!