Multiphase Interactions: Which, When, Why,...
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Multiphase Interactions: Which,
When, Why, How?Ravindra Aglave, Ph.D
Director, Chemical Process Industry
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Classification of Multiphase Flows
Examples: Free Surface Flow using Volume of Fluid
• Choice & Importance of Phase Interactions
• Mesh Size Influence
• Mesh Type Influence
Examples: Eulerian Multiphase
• Mesh and Turbulence
Examples: Lagrangian Models
Future advancements / Other models
Outline
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Multiphase Interactions
Liquid
Solids
Solid
Gas
Liquid
L-L
S-SG-L S-L
G-S
G-L-S
L-L-G
Suspended solids, erosion
Blast furnace
L-L Extractors,Hydro-cyclones
Separators
• Stirred vessel,• Bubble column
(EMP) • Offshore &
Marine (VOF)
• Coating (VOF)• Icing, SCR (fluid
film)• Windshield
(DMP)
Stirred vessel,Bubble Column,Pipeline flows
Cyclones,Fluidized bed
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Mixing of rubber in Banbury mixer
No Slip
Full Slip
Partial Slip
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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
S. Sikalo and E. Ganic , Phenomena of droplet-surface interactions, Experimental Thermal and Fluid Science, 2006
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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
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Drag! (D)
Buoyancy! (B)
Turbulent Dispersion!
Lift (LF)?
Wall Lubrication (WLF)?
Virtual Mass (VM)?
Influence of Phase Interaction
Buoyancy
Drag
VM
WLF
uf
LF
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Overview of the 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
Linearized Standard
• Constant
• Field Function
• Gidaspow (P)
• Syamlal O’Brien (P)
• Symmetric Drag
Coefficient (M)
• Constant
• Field Function
• Schiller-Naumann (S)
• Hamard and Rybczynski (S)
• Tomiyama (B)
• Bozzano-Dente (B)
• Wang Curve Fit (A)
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Bubble Regime Air / Water Bubble Size (d)
Non-dimensional Size Bubble Behaviors Suggested DragCorrection Method
Small spherical < 2.75 mm Eo < 1 Hindering Richardson Zaki
Small ellipsoidal ~ 5 mm Eo ~ 3.3 HinderingDeforming
Lockett Kirkpatrick
Intermediate size ~ 7-10 mm Eo ~ 6.6-13.4 Hindering:0-15% void fractionSwarming:15-30% void fraction
Simonnet
Large spherical-cap in churn-turbulent flow
~ 11-14 mm We(drift velocity) ~ 8 BreakupCoalescenceSwarming
Volume Fraction Exponent
Drag Correction Methods
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Flow Pattern – Water & Gas Holdup
No Aeration Aerated
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Results are almost mesh independent even with coarsest mesh (243k cells)
Mesh Independency (Polyhedral Mesh)
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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
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Polyhedral cells need more time
per iteration
Convergence is much faster
Influence of Cell Type on Simulation Time
0
50
100
150
200
250
300
Hex600k
Tet650k
Poly453k
Hex1.3M
Tet2.0M
t /
ite
rati
on
[s]
0
500
1000
1500
2000
Hex600k
Tet650k
Poly453k
Hex1.3M
Tet2.0M
Tota
l CP
U T
ime
[h
]BUT
Virtual mass, lift force & wall lubrication force of negligible importance in
stirred vessel simulations
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Drage Force: Tomiyama
Lift Force: Tomiyama
Turb. Disp. Force
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
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Air Buffer or Degassing?
With Large Scale Interface Capturing
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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-Oil:
1.5 m
flow-split(0.1)
min = 1.02 kg/s
1% VF oil
flow-split(0.9)
14M trimmed cells
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80 μmD = 40 μm 100 μm60 μm
oil volume-fraction
0
vf
0.0
5
pressure
0
p (
bar
) -1
.5
oil-water journey
oil
wa
ter
Fully-coupled transient Eulerian-Eulerian calculations for different droplet-sizes (D)
Eulerian – Eulerian Flow Field
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One-way steady-state Eulerian-Lagrangian calculations for different droplet-sizes (D)
oil-volume fraction 0 vf 0.05
D=40 μm 60 μm 80 μm
droplets distribution-1 z-vel (m/s) 1
100 μm
Lagrangian Approach
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Validation
Droplet diameter (µm)
Eff
icie
nc
y (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
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Elimnates the need of VOF with
extremely fine mesh to resolve
bubbles and droplets
Captures many different co-
existing flow regimes
– Stratified flow / free surfaces
– Dispersed sprays
– Dispersed bubbles
Eulerian Multiphase
Large Scale Interface (LSI) ModelD1863
Gas-Liquid Counter-Current flow in PWR
[Deendarlianto et al., NED, 39 (2012)]
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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
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Locally chooses the most suitable
model for the local flow regime
VOF - Fluid Film Interaction Model
D881
Jet
(VOF)
Thin Film
(Fluid Film)
Thick Film
(VOF)
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Edge stripping with fluid film
Wave stripping with fluid film
VOF film formationFluid film Multiple
particles
Trickle Bed reactors
– VOF-Fluid Film Interaction
– Packed bed modeling approach
Trickle Bed Reactors
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• Breadth + Flexibility + Best Practices = SUCCESS!
• Multiphase Training Tomorrow
Conclusions
Breadth & Flexibility
Mesh Size Influences
Mesh Type Influences
Phase Interaction Parameters
Degassing vs. Air Buffer
Expanding model
compatibilities
Solve wide range of
problems