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