Multiphase Interactions: Which, When, Why,...
Transcript of Multiphase Interactions: Which, When, Why,...
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
• 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
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
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
S. Sikalo and E. Ganic , Phenomena of droplet-surface interactions, Experimental Thermal and Fluid Science, 2006
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
Buoyancy
Drag
VM
WLF
uf
LF
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)
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
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
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
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
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-Oil:
1.5 m
flow-split(0.1)
min = 1.02 kg/s
1% VF oil
flow-split(0.9)
14M trimmed cells
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
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
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
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)]
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)
Thin Film
(Fluid Film)
Thick Film
(VOF)
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
• 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