Multiphase Interactions: Which, When, Why, How? Ravindra Aglave, Ph.D Director, Chemical Process Industry

Transcription

1 Multiphase Interactions: Which, When, Why, How? Ravindra Aglave, Ph.D Director, Chemical Process Industry

2 Outline Classification of Multiphase Flows Examples: Free Surface Flow using Volume of Fluid Examples: Eulerian Multiphase Choice & Importance of Phase Interactions Mesh Size Influence Mesh Type Influence Examples: Lagrangian Models Mesh and Turbulence Future advancements / Other models

3 Multiphase Interactions L-L Extractors, Hydro-cyclones Separators Liquid Suspended solids, erosion Blast furnace Stirred vessel, Bubble column (EMP) Offshore & Marine (VOF) Coating (VOF) Icing, SCR (fluid film) Windshield (DMP) L-L Gas Liquid L-L-G G-L G-L-S G-S S-L S-S Solid Stirred vessel, Bubble Column, Pipeline flows Solids Cyclones, Fluidized bed

4 Mixing of rubber in Banbury mixer No Slip Full Slip Partial Slip

5 Coating d = 2.7 mm v= m/s. Surface: waxed Contact angle advancing = 105 Contact angle receding = 95 σ = N/m We = ρu2d/σ = 263 (convective/surface) At wall: 6 µm Time step: 0.2 µs S. Sikalo and E. Ganic, Phenomena of droplet-surface interactions, Experimental Thermal and Fluid Science, 2006

6 Gas Liquid Dispersed Flow in Stirred Vessel: Geometric Setup Property Value Rushton impellers 4 Blades per impeller 6 Blade height 0.14m Blade length 0.17m Bottom clearance C b 1.12m Impeller distance C i 1.45m Impeller diameter 0.7m Liquid level H 6.55m Liquid volume 22m 3 Tank diameter T 2.09m Baffles 4 Vrabel, P. et al. (2000), Chem. Eng. Sci. 55

7 Influence of Phase Interaction Drag! (D) Buoyancy! (B) Buoyancy Turbulent Dispersion! Lift (LF)? WLF LF Drag VM Wall Lubrication (WLF)? u f Virtual Mass (VM)?

8 Overview of the Drag Force Models Linearized Constant Field Function Gidaspow (P) Syamlal O Brien (P) Symmetric Drag Coefficient (M) Standard Constant Field Function Schiller-Naumann (S) Hamard and Rybczynski (S) Tomiyama (B) Bozzano-Dente (B) Wang Curve Fit (A) The options are qualified by the main application areas: (A) air bubbles in water systems only. (B) bubbles (M) fluid-fluid mixtures in separation applications. (P) solid particles at high concentration. (S) spherical particles at moderate concentration - including small droplets or bubbles

9 Drag Correction Methods Bubble Regime Air / Water Bubble Size (d) Non-dimensional Size Bubble Behaviors Suggested Drag Correction Method Small spherical < 2.75 mm Eo < 1 Hindering Richardson Zaki Small ellipsoidal ~ 5 mm Eo ~ 3.3 Hindering Deforming Intermediate size ~ 7-10 mm Eo ~ Hindering: 0-15% void fraction Swarming: 15-30% void fraction Large spherical-cap in churn-turbulent flow ~ mm We(drift velocity) ~ 8 Breakup Coalescence Swarming Lockett Kirkpatrick Simonnet Volume Fraction Exponent

10 Flow Pattern Water & Gas Holdup No Aeration Aerated

11 Mesh Independency (Polyhedral Mesh) Results are almost mesh independent even with coarsest mesh (243k cells)

12 Influence of Bubble Size Monodisperse bubble size (1, 2 and 3mm) 450k polyhedral cells S-gamma model incl. coalescence &breakup (log.-normal distribution: 1e-4mm < BS < 10mm)

13 t / iteration [s] Total CPU Time [h] Influence of Cell Type on Simulation Time Hex 600k Tet 650k Poly 453k Hex 1.3M Tet 2.0M 0 Hex 600k Tet 650k Poly 453k Hex 1.3M Tet 2.0M Polyhedral cells need more time per iteration BUT Convergence is much faster Virtual mass, lift force & wall lubrication force of negligible importance in stirred vessel simulations

14 Bubble Column Drage Force: Tomiyama Lift Force: Tomiyama Turb. Disp. Force Bubble Induced Turbulence (Troshko&Hassan) Virtual Mass Force Diaz et al. (2008), Chem. Eng. J. 139, Ziegenhein (2013), CIT, accepted manuscript

15 Air Buffer or Degassing? With Large Scale Interface Capturing

16 Liquid-Liquid: Water Oil Separation Water-Oil: flow-split (0.1) min = 1.02 kg/s 1% VF oil Acting flow-forces Pressure-gradient Drag & lift, Added & virtual mass Turbulent dispersion Gravity Algebraic Reynolds stress model Linear/quadratic eddy-viscosity models LES/DES filtering flow-split (0.9) 1.5 m 14M trimmed cells

17 0 p (bar) -1.5 water 0 vf 0.05 oil Eulerian Eulerian Flow Field Fully-coupled transient Eulerian-Eulerian calculations for different droplet-sizes (D) pressure oil-water journey oil volume-fraction D = 40 μm 60 μm 80 μm 100 μm

18 Lagrangian Approach One-way steady-state Eulerian-Lagrangian calculations for different dropletsizes (D) -1 z-vel (m/s) 1 droplets distribution oil-volume fraction 0 vf 0.05 D=40 μm 60 μm 80 μm 100 μm

19 Efficiency (η) Validation Droplet diameter (µm) η=100*(1-m out /m in ) m out : is the oil mass exiting from the clean outlet (top) m in : is the total oil mass imported in the hydrocyclone

20 D1863 Eulerian Multiphase Large Scale Interface (LSI) Model Elimnates the need of VOF with extremely fine mesh to resolve bubbles and droplets Captures many different coexisting flow regimes Stratified flow / free surfaces Dispersed sprays Dispersed bubbles Gas-Liquid Counter-Current flow in PWR [Deendarlianto et al., NED, 39 (2012)]

21 LMP-VOF LMP->VOF Impingement, new feature in STAR-CCM+ v10.02 VOF->LMP Stripping, currently under development, targeting STAR-CCM+ v10.04/10.06

22 VOF - Fluid Film Interaction Model D881 Locally chooses the most suitable model for the local flow regime Jet (VOF) Thin Film (Fluid Film) Thick Film (VOF)

23 Trickle Bed Reactors Trickle Bed reactors VOF-Fluid Film Interaction Packed bed modeling approach Edge stripping with fluid film Wave stripping with fluid film VOF film formation Fluid film Multiple particles

24 Conclusions Breadth & Flexibility Breadth + Flexibility + Best Practices = SUCCESS! Mesh Size Influences Mesh Type Influences Phase Interaction Parameters Degassing vs. Air Buffer Expanding model compatibilitie s Solve wide range of problems Multiphase Training Tomorrow