Multiphase Interactions: Which, When, Why, How? Ravindra Aglave, - - PowerPoint PPT Presentation
Multiphase Interactions: Which, When, Why, How? Ravindra Aglave, Ph.D Director, Chemical Process Industry Outline Classification of Multiphase Flows Examples: Free Surface Flow using Volume of Fluid Examples: Eulerian Multiphase Choice
Multiphase Interactions: Which, When, Why, How?
Ravindra Aglave, Ph.D Director, Chemical Process Industry
Classification of Multiphase Flows Examples: Free Surface Flow using Volume of Fluid
Examples: Eulerian Multiphase
Examples: Lagrangian Models Future advancements / Other models
Outline
Multiphase Interactions
Liquid Solids Solid Gas Liquid
L-L S-S G-L S-L G-S G-L-S L-L-G
Suspended solids, erosion Blast furnace L-L Extractors, Hydro-cyclones Separators
(EMP)
Marine (VOF)
film)
(DMP) Stirred vessel, Bubble Column, Pipeline flows Cyclones, Fluidized bed
Mixing of rubber in Banbury mixer
No Slip Full Slip Partial Slip
d = 2.7 mm v= 4.551 m/s. Surface: waxed Contact angle advancing = 105° Contact angle receding = 95° σ = 0.073 N/m We = ρu2D/σ = 263 (convective/surface) At wall: 6 µm Time step: 0.2 µs
Coating
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 Cb 1.12m Impeller distance Ci 1.45m Impeller diameter 0.7m Liquid level H 6.55m Liquid volume 22m3 Tank diameter T 2.09m Baffles 4
Vrabel, P. et al. (2000), Chem. Eng. Sci. 55
Drag! (D) Buoyancy! (B) Turbulent Dispersion! Lift (LF)? Wall Lubrication (WLF)? Virtual Mass (VM)?
Influence of Phase Interaction
Buoy
ancy Drag ag VM VM WLF uf LF LF
Integrated models for the interphase drag or friction force. Specifying complete models for particle drag that already include multi-particle effects
Composed together from a Standard Drag Coefficient for a single particle Drag Correction factor to account for multi-particle and other effects Describes how concentration modifies the single-particle Drag Coefficient model in a multi-particle system
Drag Force Models
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
Overview of the Drag Force Models
Linearized Standard
Coefficient (M)
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 Lockett Kirkpatrick Intermediate size ~ 7-10 mm Eo ~ 6.6-13.4 Hindering: 0-15% void fraction Swarming: 15-30% void fraction Simonnet Large spherical-cap in churn-turbulent flow ~ 11-14 mm We(drift velocity) ~ 8 Breakup Coalescence Swarming Volume Fraction Exponent
Drag Correction Methods
Flow Pattern – Water & Gas Holdup
No Aeration Aerated
Results are almost mesh independent even with coarsest mesh (243k cells)
Mesh Independency (Polyhedral Mesh)
Monodisperse bubble size (1, 2 and 3mm) 450k polyhedral cells S-gamma model incl. coalescence &breakup (log.-normal distribution: 1e-4mm < BS < 10mm)
Influence of Bubble Size
Polyhedral cells need more time per iteration Convergence is much faster
Influence of Cell Type on Simulation Time
50 100 150 200 250 300 Hex 600k Tet 650k Poly 453k Hex 1.3M Tet 2.0M
t / iteration [s]
500 1000 1500 2000 Hex 600k Tet 650k Poly 453k Hex 1.3M Tet 2.0M
Total CPU Time [h]
BUT Vir Virtual ual mass ass, lift lift forc rce e & w & wall ll lu lubricat cation ion forc rce e of n neglig gligible ible im importanc
e in in stirr irred ed vessel ssel sim imula ulati tions
Drage Force: Tomiyama Lift Force: Tomiyama
Bubble Induced Turbulence (Troshko&Hassan) Virtual Mass Force
Bubble Column
Diaz et al. (2008), Chem. Eng. J. 139, 363-379 Ziegenhein (2013), CIT, accepted manuscript
Air Buffer or Degassing?
With Large Scale Interface Capturing
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
Liquid-Liquid: Water Oil Separation
Water er-Oil Oil:
1.5 m
flow-split (0.1) min = 1.02 kg/s 1% VF oil flow-split (0.9)
14M trimmed cells
80 μm D = 40 μm 100 μm 60 μm
0 vf 0.05
pressure 0 p (bar)
journey
water water
Fully-coupled transient Eulerian-Eulerian calculations for different droplet-sizes (D)
Eulerian – Eulerian Flow Field
One-way steady-state Eulerian-Lagrangian calculations for different droplet- sizes (D)
Lagrangian Approach
0 vf 0.05
D=40 0 μm 60 μm 80 μm droplets distribution
100 μm
Validation
Droplet diameter (µm) Efficiency (η) η=100*(1-mout/min)
mout: is the oil mass exiting from the clean outlet (top) min: is the total oil mass imported in the hydrocyclone
Elimnates the need of VOF with extremely fine mesh to resolve bubbles and droplets Captures many different co- existing flow regimes
– Wave formation due to interfacial shear – Spray generation – Droplet carry-over by the gas flow – Bubble entrainment into liquid – Slug flow – Stratified flow / free surfaces – Dispersed sprays – Dispersed bubbles
Eulerian Multiphase Large Scale Interface (LSI) Model
Gas-Liqui iquid d Counter ter-Cur urrent rent flow in PWR [Deendar ndarli liant anto et al., NED, 39 (2012)] )]
LSI: A simple flow topology detection method
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.5 1
Variation of Blending Function with Volume Fraction of reference Dispersed Phase
Dispersion Inversion Free Surface
Volume Fraction of reference Dispersed Phase Blending Function
, d threshold
, i threshold
Bubbly Droplet Transition (free surface)
Air-Water Stratified flow experiment of Fabre et al. (1987)
12m long horizontal channel. Approx. Re=40,000. Cross-section : 10 cm high x 20 cm deep. 2D grid (12m x 0.1m) : 400 x 54
LSI – Interface Turbulence Damping
For r Inter ernal nal Use e Only ly
Pressure Drop (Pa/m) Experimental 2.1 LSI – No interface damping 19.68 LSI – with interface damping 2.63
Air (3.66 m/s) Water (0.395 m/s)
LMP->VOF Impingement, new feature in STAR-CCM+ v10.02 VOF->LMP Stripping, currently under development, targeting STAR-CCM+ v10.04/10.06
LMP-VOF
Locally chooses the most suitable model for the local flow regime
VOF - Fluid Film Interaction Model
D881
Jet (VOF OF) Thin Film (Fluid uid Film) m)
Thick Film (VOF)
Edge stripping with fluid film Wave stripping with fluid film VOF film formation Fluid film Multiple particles
Trickle Bed reactors
– VOF-Fluid Film Interaction – Packed bed modeling approach
Trickle Bed Reactors
Conclusions Breadth & Flexibility
Mesh Size Influences Mesh Type Influences Phase Interaction Parameters Degassing vs. Air Buffer Expanding model compatibilitie s Solve wide range of problems