2005 SIAMUF Hamill - CFX-5.7 / ANSYS CFX 10.0 Eulerian & Lagrangian • Applications ......

$: 2005 SIAMUF Hamill - CFX-5.7 / ANSYS CFX 10.0 Eulerian & Lagrangian • Applications ... – large volume fraction loading ... – Time evolution of PSD and Sauter mean diameter$
ANSYS, Inc. Proprietary© 2004 ANSYS, Inc.

MULTIPHASE FLOWSMULTIPHASE FLOWSRecent Advances & Applications

Ian Hamill, ANSYS Europe Ltd., UK


Presentation Outline

• Recent Advances– CFX-5.7 / ANSYS CFX 10.0 Eulerian &

Lagrangian• Applications

– Fuel spray (droplet break-up)– Suspension polymerisation (chemistry & MUSIG)– Slug catcher (free surface flows)– TWISTER supersonic separator (ASM)– Boiling

• Questions & answers


New Features

• Eulerian multiphase– Non-drag Forces– Algebraic Slip Model– Boundary Conditions– Interphase Transfer– Numerics Improvements– Mass Transfer Improvements– MUSIG Model


New FeaturesEulerian Multiphase

• Non-drag Forces– Lift force– Wall lubrication force– Virtual mass force– Favre-averaged turbulence dispersion

force


Solids DistributionNew FeaturesEulerian Multiphase

– Validation from OPTIMUM project

– Experimental data of King’s College

– 600-710µm glass in water

– 800 rpm

Favre-averaged turbulent dispersion example


normalised particle volume fractions




0

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0.2

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0.7

0.8

0.9

0 0.5 1 1.5 2 2.5

C / Cav

z / H

r=0.25T - 710µm r=0.45T - 710µm

Validation



0

0.1

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0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

C / Cav

z / H


New Features




• Algebraic Slip Model– Drag force balance or slip velocity

specification– Turbulent dispersion via gradient diffusion

hypothesis– Energy drift flux is also included– Wall deposition

• Walls can be set as deposition walls• Deposition rate available for post-processing



• COPHIT project– Drug deposition in

upper airways– Bronchial tree

geometries:• constructed from

MRI data (Mainz)• resolved to 8th

generation

Algebraic Slip Model example



Lagrangian

50 µm

ASM

10 µm

Algebraic Slip Model example


New Features




• MUSIG– Multiple Size Group model– Accounts for coalescence and break-up in

polydispersed phases using population balance approach

– Status• Built-in solver model in CFX-5.7• GUI in ANSYS CFX 10.0


New Features

• Lagrangian particle tracking– Non-drag particle forces– Multi-component particles– Heat and mass transfer– Reacting particles– Particle/wall interaction and particle

absorption– Particle User Routines– Transient particle tracking– Secondary break-up


Transient ParticleTracking

New Features


New Features

• Transient particle tracking– Compatible with transient

grids (e.g. fuel sprays in I.C. engines)

– Example• Transient bubble plume


Secondary DropletBreak-up

Applications


New Features

• Secondary break-up models– Reitz & Diwakar– TAB– ETAB– CAB– Schmehl


Droplet Break-Up Mechanisms

• Bag break-up

• Multimode break-up

• Shear break-up– most important in cross-flow rig


Break-Up Regimes

Schmehl, Maier and Wittig,

ILASS 2000, Pasedena, CA


Spray rig and Nozzle Detail

Traversible back wall to allow adjustment of distance of nozzle from measurement area.

Traverse Motor

Rig mount location

Fuel Nozzle

Close up of back wall with nozzle detail

Fuel Nozzle

Air flow supplyPressure

[PSI]

Honeycomb section to act as flow straightener

30mm x 30mm cross section size

10mm gap to allow unobstructed optical access

Trough to avoid fuel splashing

Flow outlet

Plenum Chamber with wire gause to smooth flow


Effect of Droplet Break-up


Comparison of Spray Shape

Experiment LSICFD


D30 - 25mm Plane

Expt.

CFD

66 m/s 53 m/s 40 m/s


Volume Flux - 25mm Plane

Expt.

CFD

66 m/s 53 m/s 40 m/s

N.B. Absolute level of volume flux in experiment not reliable


Batch SuspensionPolymerisation

Applications


Background

• Project OPTIMUM– Funded by the European Commission under

the ‘Competitive & Sustainable Growth’ Programme (1998-2002)

– Optimisation of Multiphase Mixing– G1RD-CT-2000-00263– Two processes studied:

• Suspension Polymerisation (Dow Benelux)• Particle Coating (Merck)


Background

• ANSYS Europe Ltd.– Christiane Montavon– Jane Pearson– Ian Hamill

• Dow Benelux BV– Gerrit Hommersom

• Dow Olefinverbund GmbH– Rolf-D. Klodt


Process Flowsheet:general process

Suspending agent

Water

Initiator

Reactor

Batchmixer

WasteWater

MaturationHopper

DewateringDrying

Screening

SiloHopper

PackingCar

Transport

MonomerAdditives

MaturationHopper

®


Batch Process Sequence

Temperature

Time

Tf

Tr

Ti

charging 1. h

eatin

g up

2. h

eat in

g up

1. polymerization step(Particle formation)

2. polymerization step(finishing - full

conversion)

3. c

ool in

g do

wn

Optimum focus

®


Reactor Process Characteristics

• Creation of oil-water suspension• Polymerisation of the dispersed oil phase

– polymer structure• Issues:

– control of the particle size (quality)• stabilization of phase interface• hydrodynamics

– control over particle growth (safety)• qualitative and local


• Physical features of process:– large volume fraction loading (~50:50)– order of magnitude range of droplet sizes– coalescence & break-up of droplets– range of disperse-phase viscosities– buoyant flow incl. evolution of density– reacting– turbulent– large range of timescales (O(s)-O(hrs))

Reactor Process Characteristics


• Chemical kinetics• Particle size distribution (population

balance model)

Model Implementation


Suspension Polymerisation –Chemical Kinetics


Reaction Scheme

i) Initiation

ii)

iii) Propagation

iv) Chain transfer to monomer

v) to polymer

vi) Termination combination

vii) disproportionation

*2II dk→

1* RMI ik→+

1RPMR nk

nf +→+

mnk

mn RPPR c +→+

mnk

mn PRR kt+→+ ,

mnk

mn PPRR dt +→+ ,

1+→+ nkp

n RMR

Process Simulation -Chemical Kinetics


• Low conversion rates

• High conversion rate during the Gel/Trommsdorff Effect

• Slowing down of conversion due to the Cage and Glass Effects

Three Stages of Conversion



Batch PolymerizationKinetic Phases


Six transport equations:• monomer, YM

• 2 initiators, YI ,YI2

• dead polymer, YP

• 0th & 2nd moments of dead polymer, µ0, µ2

Four algebraic equations:• 0th, 1st & 2nd moments of polymer radicals, λ0, λ1, λ2

• 1st moment of dead polymer, µ1



Verification Against Kinetic Model

• Isothermal.

• Zero-dimensional.

• Two sets of time-steps:1. Uniform 1 minute.2. Refinement to 1 second near Gel Point

followed by steps of 15 seconds.



0

0.1

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0.5

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0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

time

mon

omer

con

c

exptCFX variable time stepCFX 1 min time stepDow

Monomer Concentration

Model ValidationChemical Kinetics


Number-averaged molecular weight of dead polymer & polymer radicals

0

0.1

0.2

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

time

num

ber a

vera

ge m

olec

ular

wei

ght

exptCFX variable time stepsCFX 1 min time stepsDow

Model ValidationChemical Kinetics


Conclusions

• Good agreement with kinetic model and experimental results for consumption of monomer.

• Slight under-prediction of final average molecular weight compared with kinetic model. Both produce lower values than experimental measurements.

• Small sensitivity to size of time step.



Suspension Polymerisation –Population Balance Model


Why PopulationBalance Modelling?

Suspension polymerisation: suspended monomer droplets polymerise in time to solid polymer particles

Initial Final

polymerisation

How to model?

Population balance: particle identity followed in time

Here only one key parameter: particle volume(or diameter)


Population Balance Modelling

),,,(),,,(),,(),,(),,( tYrxDtYrxBtrxFvtrxFxttrxF

prx−=⋅∇+⋅∇+

∂∂ •

PBE in most general form*:

growth-rate convection birth death

Birth into volume x Death into volume x

* Ramkrishna, Rev. Chem. Eng. 1(3), 1985

x

Break-up

x

Coalescence

xBreak-up

xCoalescence


Population Balance

• Modification to implementation– Equations for size groups solved in a fully coupled

way– New type of discretisation– Lyon-Tobolski model for viscosity– One additional tuning constant to Maxwell

• Validation– Time evolution of PSD and Sauter mean diameter


Particle Size Evolution

• Samples from reactor, diluted and stabilized

0.25 batch time 0.5 batch time 0.75 batch time 0.875 batch time


CFD 3-D Model: Initial Condition

Velocity field Oil volume fraction


CFD 3-D model:Volume Fractions

Oil volume fraction: identity point Oil volume fraction: end


CFD 3-D model: Validation of Process Evolution


t/tgrowth=0.75

Model Validation –Population Balance

t/tgrowth=1.0

t/tgrowth=0.25 t/tgrowth=0.5


CFD Modelling Evaluation

• Kinetics implementation excellent• Model predicts correct trends for PSD• Runtime efficiency strongly dependent on model

size (grids/MUSIG groups) => improvement in CFX-5.7

• Some additional tuning required• Other process applications possible


Free Surface Flows


Free Surface Flows

• Compressive differencing in space & time• Surface tension effects (normal & Marangoni)• Homogeneous or multifluid treatment• Transient mesh adaption• Compatible with all physical models, e.g.

chemistry, interphase mass transfer


Free Surface Flows

• Small-scale, incl. surface tension…


Free Surface Flows

• Large-scale, e.g. Hannibal Slug Catcher


Free Surface Flows

• Background– Gas pipeline from off-

shore field to land-based Hannibal terminal

– Slug catcher separates residual liquid from gas at end of pipeline

– Plan to increase pipeline capacity to supply new power station

– Question: Does capacity of slug catcher also have to be increased?

Inlet from pipeline

Gas outlet

Liquid outlets

Estimated cost of modifying slug catcher $25M


Free Surface Flows

• CFX Model– Inhomogeneous multiphase

free surface transient flow– Use centre plane symmetry -

only model half the system– Hex mesh with transient mesh

adaption– Every few days a sphere is

passed along the pipeline to remove residual liquid

– Analyse ‘worst case’ scenario when sphere has just arrived

• Inlet conditions from OLGA 1-D pipeline calculation

Initial coarse mesh


Free Surface Flows

Initial Mesh Adapted Mesh

• Transient mesh adaption in Inlet Header


Free Surface Flows

• Current operation– No liquid carry-over to gas outlet

• first separation finger (nearest symmetry plane) partially fillswith liquid

• other fingers receive less liquid


Free Surface Flows

Liquid carry-overFlow rates

Peak Level• High flow operation

– Can slug catcher cope with increase in capacity?

– Yes!– Liquid carry-over

only in form of fine aerosol


Free Surface Flows

• Test to overflow– Linear increase of liquid

flow rate until overflow occurs

– Liquid enters gas header first through third separation finger

– Large safety margin demonstrated for current and future operational conditions


TWISTER Supersonic Separator


TWISTER Supersonic Separator

• Founded May 2001– Shell owned– Independent company

• Delivers– Equipment – Services on

• process engineering• flow simulations


Typical mid Twister conditions:

30 bar, -45 degC

Schematic RepresentationSaturated Gas

Liquid / Gas Separation

Dry Gas

LiquidsTypical inlet conditions:

100 bar, 25 degC

Typical outlet conditions:

70 bar, 15 degC

Supersonic Wing (Mach 1-3)

Throat (Mach 1)

Acceleration to Mach 1 cools gasFurther cooling from acceleration to Mach > 1Cooling causes condensation

Axial velocityHigh

Low


CFX simulations

• High speed compressible flow up to Mach = 2• High pressure and low temperature (real gas properties)• Multi component

– hydrocarbons, water, etc. • Multiphase

– liquid droplets and film– coalescence and break-up (MUSIG)

• Non-equilibrium phase transitions– nucleation and condensation

• Strong swirl• Turbulent flow with flow separation


Nucleation and Droplet Growth

0.00E+00

1.00E-08

2.00E-08

3.00E-08

4.00E-08

5.00E-08

6.00E-08

-5.00E-02 0.00E+00 5.00E-02 1.00E-01 1.5

x (m)

Dro

plet

Rad

ius

(m)

2.20E+02

2.30E+02

2.40E+02

2.50E+02

2.60E+02

0.00E+00 5.00E-02 1.00E-01

x (m)

Tem

pera

ture

(K)

1-D model

T Rd

CFX CFX


Hunter experiment

Hunter simulation

Shock-Boundary Layer Interaction

Twister simulation


Radial Humidity Distribution

-0.02

-0.01

0.00

0.01

0.02

-0.02 -0.01 0.00 0.01 0.02z

y

Measured humidity distribution at VF=0

Particle distribution at VF=0 (CFX)

dry

wet

• Sample probe as Vortex Finder (at V.F. position = 0) • Measure RH, T and P of sample


Bulk Boiling


Bulk Boiling

• Example case– 2-D– 105Wm-2 heat flux at base– Adiabatic side walls– 3-fluid

• continuous water• disperse steam bubbles• continuous gas above surface

– Standard thermal phase change model– Constant bubble 1mm bubble size

• Continuing research & development in collaboration with FZ Rossendorf


Bulk Boiling

Temperature

[c]


Questions & Answers

2005 SIAMUF Hamill - CFX-5.7 / ANSYS CFX 10.0 Eulerian & Lagrangian • Applications ......

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