multiscale modeling and simulations of complex multiphase flows

8/12/2019 Multiscale Modeling and Simulations of Complex Multiphase Flows

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Multiscale Modeling and Simulations of

Complex Multiphase Flows

Vivek V. Buwa

Department of Chemical Engineering

Indian Institute of Technology-Delhi

New Delhi 110 016, India

email: [email protected]

CMERI Durgapur , 15 December 2012

11th Indo-German Winter Academy

11-17 December 2012


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One of seven (old) IITs, IIT-Delhi was

established in 1961 as an autonomous institutethrough the special act of parliament

13 Departments, 11 Centers & 2 Schools on the

campus of ~320 acres

~ 421 faculty and ~ 4931 students (2265 UG,

1601 PG, 978 Ph.D. & 114 M.B.A)

~1200 international publications per year

Vivek Buwa, Multiphase Flow Modeling

Indian Institute of Technology-Delhi


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Outline

Introduction

Multiphase flows/reactors

Process intensification/Micro-reactors

Large-scale (macroscopic) multiphase flows

Experimental characterization

Continuum (Euler/Euler) simulations Small-scale (microscopic) multiphase flows

Rise behavior of single/multiple bubbles

Dynamics of drop impact & spreading on solid surfaces

Gas-liquid flows through micro-channels

Closing remarks


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Introduction

Wide spread applications

Oil and gas, Chemical/Petrochemicals, Polymers/Plastics,Pharmaceuticals/Agro-chemicals , Food/Biotechnology, .

Touched upon many other fields .

Process equipments/Operations

Heat/Mass transfer equipments, reactors

Ways to achieve performance enhancement

Better synthesis (chemistry and catalysis)

Better design and operation

Better process control

Stirred vessels Bubble/slurry bubble columns Packed/Trickle beds

Fluidized beds


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Process Intensification: Vision of a Future Plant

Vision of a future plant using process

intensification

A conventional plant

(Source: DSM)


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Process Intensification: Miniaturized Reactors

Ways of process intensification: Micro-reactors/micro-

fluidic devices

Micro-structured reactor/heatexchanger (Rebrov et al., 2001)

Micro-heat exchanger

(IMM-Mainz)Falling film micro-reactor

(IMM-Mainz)

Typical micro-channelsMicro-reactor + heat exchanger

(Lowe & Erhfeld, 1999)


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Experimental Characterization of Laboratory-Scale

Multiphase Flows

Vg= 5 cm/s Vg= 10 cm/sVg= 20 cm/s Vg= 40 cm/s

Gas velocity

Dispersed gas-liquid flowsUg=4.8Umf

Ug=3.2Umf6.0 s 6.2 s 6.4 s 6.6 s 6.8 s 7.0 s

6.0 s 6.2 s 6.4 s 6.6 s 6.8 s 7.0 s

Dispersed gas-solid flows

0% Solids 5% Solids 10% Solids20% Solids

Dispersed gas-liquid-solid flows


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Characterization of Small-Scale Multiphase Flows

Microscopic bubbly flows

Single/Multiple bubbles rising in quiescent andsheared liquids (of different properties)

Investigations of drag and lift forces acting of single

isolated bubbles, homogeneous/heterogeneous

bubble swarms

Effect bubble size/shape and neighboring bubbles

(gas volume fraction) on the magnitude of drag and

lift forces

Liquid spreading on solid surface

Dynamics of drop impact & spreading on solid

surfaces (inclined, cylindrical, spherical)

Effect of surface wettability, drop size, impact

velocity, liquid properties on the spreading behavior

Microscopic gas-liquid flowsRabha & Buwa, ISCRE 21 (Philadelphia), 2010,

I&EC Research, 2010

Liquid spreading over solid surfaces

Bangonde, Nikure & Buwa, GLS-8 (Montreal) 2009

Varun Kumar & Buwa, GLS-10, Braga (Portugal), 2011


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Characterization of Small-Scale

Multiphase Flows

Local liquid distribution/wettingbehavior in trickle beds

Effect of packing size/shapes

Bed structures

Liquid distributors

Typical liquid distributions in pseudo 3D trickle bed packed

with glass beads of (a) 10 mm and (b) 5 mm [(i) non pre-

wetted, (ii) pre-wetted, single point injection, Bed I]

(a) (b)

(i) (ii)(i) (ii)

Anup Kundu (ongoing Ph.D. Thesis)


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Characterization of Microscopic Multiphase Flows

Multiphase flows in

microchannels/microreactors Gas-liquid/liquid-liquid/Gas-

liquid-liquid flows in micro-

channels

Controlled generation of

bubble/slugs in microchannels Effect of channel configuration,

distributor, flow rates, physical

properties on flow regimes,

bubble/slug formation

mechanisms, bubble/slug

size/shape

Gas-liquid-liquid flow regimes in a microchannel

(D=W=950 mm, working fluids: air, water & kerosene)

Multi-channel gas-liquid/liquid-liquid contactor

(fabricated at IIT-Delhi)

Rajesh & Buwa, Chem. Eng. J., 2012

Rajesh & Buwa, GLS-11, Korea, 2013 (accepted)


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Multiscale Modeling Strategy for Computations of

Multiphase Flows

Continuum (Two-

fluid) Model

Discrete Particle/

Bubble Model

Flow around geometrically resolved

bubbles (or particles)

(or DNS of particulate/bubbly flows)

Computational Effort

Modeling efforts/empiricism

21

3

1 & 2: A two-fluid

(Euler-Euler) and poly-

dipsersed Euler-

Lagrange simulation ofga-liquid flow in a flat

bubble column (Parul

Tyagi, 2011)

3: Free surface flow

simulations of multiple

bubbles rising in a

sheared liquid

(Swapna Rabha, 2009)


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CFD Simulations of Laboratory-Scale Gas-Liquid Flows

Euler-Euler simulations of dispersed gas-liquid flows in

bubble columns: Simulated gas hold-up and liquid

velocity (Rampure et al., 2003)Euler-Lagrange simulations of mono-dispersed (figures on left) and

poly-dispersed (figures on right) gas-liquid flow in a flat bubble

column (Tyagi & Buwa, 2012)


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Limitations of Continuum (Two-Fluid) Approach:

Simulations of Turbulent Dispersed Gas-Liquid Flows

Superficial

GasVelocity

m/s

Grid

(Totalcells)

Drag Correction Simulated

Overall GasHoldup

Experiment

al OverallGas Holdup

0.4 51k 0 0.8227

0.3680.4 51k 2 0.487

0.4 51k 4 0.367

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 0.1 0.2 0.3 0.4 0.5

Superficial Gas Velocity, m/s

Overallgashold-up,-

Rampure et. al.,2007

51k (radially node-10)

Experiment rampure et. al., 2007

UG=40 cm/s

Effect of the drag correctionfactor (Unpublished work,

Kaushik & Buwa, 2009)

pGDOD CC 1


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Limitations of Continuum (Two-Fluid) Approach:

Simulations of Turbulent Dispersed Gas-Liquid Flows

On the role of lift force


Instantaneous gas hold-up distribution [10 uniform contours 0 (blue) to 0.05 and above (red)] and

Instantaneous liquid velocity field (maximum velocity corresponds to 0.6 m/s)

Role of lift force on the dynamics of meandering bubble plume (H/W = 4.5)Buwa & Ranade (CES, 2002; CJChE, 2003; AIChEJ, 2004), Buwa et al. (IJMF, 2006)

0.73 cm/s0.30 cm/s 0.30 cm/s 0.73 cm/s(CL = 0.2)(CL = 0.5)


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CFD Simulations of Laboratory-Scale Slurry Flows/Reactors


Simulated axial distribution

of solids at different solid

loadings

Gas-liquid-Solid flow in a slurry bubble column(Rampure, Buwa, Ranade, CJChE, 2003)

Simulated radial

distribution of gas and solid


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CFD Simulations of Laboratory-Scale Gas-Solid Flows


Time-evolution of gas volume fraction distribution in pseudo-3D fluidized bed (UG=10Umf,

dp=257 mm) (Monga and Buwa, APT 2009)

t=6 s 6.2s 6.4s 6.6s 6.8s 7s


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Limitations of Continuum Models

Present status of the predictive capabilities of thecontinuum models

In most of the simulations, only the drag force is used to account forthe inter-phase momentum exchange

Effect of swarm of bubbles/cluster of particles is included byapplying empirically adjusted corrections factors

Very often, the standard k-emodel is used

In most cases, the reported agreement between the predicted andmeasured macroscopic flow behavior is based on the empiricallyadjusted model parameters.

Local wetting in trickle beds/structured reactors?

Detailed simulations of microscopic flow aroundsingle/multiple bubbles/particles

Understanding effects of bubble/particle size/shape on themagnitude of inter-phase coupling (drag & lift) forces

Effect of presence of neighboring bubbles /particles (or gas volumefraction)

Understanding the dispersed phase induced turbulence using DNS?

Free Surface Flow Simulations


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Experimental Investigations of Microscopic Bubbly Flows

Single/multiple bubbles rising in

(initially) quiescent liquids

0

0.2

0.4

0.6

0.8

1

0 0.05 0.1 0.15 0.2

CD

/CD0,-

G,-

d = 4.75 mm

d = 3.3 mm

d = 1.5 mmTypical experimental images of mono-dispersed bubbly

flow in air-watersystem (a) dB~ 1.5 mm; (G= 0.03), (b)dB~ 3.3 mm (G= 0.09) & (c) dB~ 4.75 mm (G= 0.16)

Typical experimental images of mono-dispersed bubbly flow

in air-glycerolsystem (a) dB = 3.63 mm (G= 0.11), (b) dB=

5.41 (G= 0.054) & (c) dB= 11.2 mm (G= 0.067)

Rabha & Buwa, ISCRE 21 (Philadelphia), 2010

Rabha & Buwa, I&EC Research, 2010


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Experimental Investigations of Microscopic Bubbly Flows

Single/multiple bubbles rising in sheared liquids

Lift force acting on bubbles rising in multiple

chains in water (dB=3.8 0.2 mm ,G=0.07,L=

0.001 kg.m-1.s-1; = 6.2 s-1).

Lift force acting on bubbles rising in multiple

chains in water+glycerol (dB=4.07 0.2 mm ,G

=0.11,L= 0.018 kg.m-1.s-1; = 6.2 s-1).

Rabha & Buwa, GLS-10(Braga, Portugal), 2011, to be submitted for publication


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Numerical Simulations of Rise Behavior of

Single/Multiple Bubbles in Sheared Liquids

Volume-of-fluid simulations


Vorticity

(dVy/dx) s-1 t= 0.01 s t= 0.1 s

Instantaneous bubbles shape and vorticity

distributions for six mono-dispersed bubbles

(dB=8 mm) in water + glycerol system.

Time averaged CLof the individual bubble

for dB= 8mm was found to be within -0.2 to

-0.8 as compared to CLof -2.4 for single

bubble riseRabha & Buwa, GLS-9, Montreal, 2009

l l f h f


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Numerical Simulations of Rise Behavior of

Single/Multiple Bubbles in Sheared Liquids

1.35 dB11.35 dB11.35 dB1 1.35 dB1

1.2 dB21.2 dB2

dB3

1.2 dB2

dB3

1.8dB2

2.1dB2

B6

B1

B4 B5

B2 B31.35 dB11.35 dB11.35 dB1 1.35 dB1

1.2 dB21.2 dB2

dB3

1.2 dB2

dB3

1.8dB2

2.1dB2

B6

B1

B4 B5

B2 B31.35 dB11.35 dB11.35 dB1 1.35 dB1

1.2 dB21.2 dB2

dB3

1.2 dB2

dB3

1.8dB2

2.1dB2

B6

B1

B4 B5

B2 B3


Vorticity

(dVy/dx) s-1

t = 0.11s t = 0.18 s

t = 0. 20s t = 0.23s t = 0.25 s

t = 0.15s

Initial configuration of six poly

dispersed air bubble (dB= 3.52 mm,5.54mm, 10mm) in water+ glycerol

Instantaneous bubbles shape and vorticity distributions

for six mono-dispersed bubbles in water + glycerol

system

Wake induced by the central

bubble influence the lateral

migration of trailing bubbles


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Dynamics of impact and spreading of a water

drop on the glass sphere

Comparison of experimental and predicted drop shapes for a water drop impacting and

spreading on the glass sphere (a) predictions with o= 40o, (b) experiments, (c) predictions

with Aavg= 116oand R

avg= 12o (d = 5.25 mm, D = 12.2 mm, U = 0.37 m/s)

A

30 ms 36 ms0 ms 12 ms 18 ms06 ms

B

0 ms 06 ms 12 ms 18 ms 30 ms 36 ms

C

Bangonde, Nikure, Buwa, GLS-8 (Montreal) 2009

f d d f


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Dynamics of impact and spreading of a water

drop on the wax-coated glass sphere

Comparison of experimental and predicted drop shapes for a water drop impacting and spreading

on the wax-coated glass sphere (a) experiments, (b) predictions with o= 100o(c) predictions with

Aavg= 122oand R

avg= 85o (d = 5.1 mm, D = 12.2 mm, U = 0.145 m/s)

0 ms 12 ms 24 ms 36 ms 48 ms 60 ms

0 ms 12 ms 24 ms 36 ms 48 ms 60 ms

60 ms48 ms36 ms24 ms12 ms0 ms

(a)

(b)

(c)


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Segmented Gas-Liquid Flow in Micro-systems

Experimental & predicted (using OpenFOAM) flow regimes in a Tjunction micro

channel (Channel & gas inlet cross-section: 1x1 mm2, air-water system)

(i) bubbly flow (UG=0.085326 m/s, UL= 0.44308 m/s)

(ii) slug flow (UG=0.085326 m/s, UL= 0.18895 m/s)

(iii) slug flow (UG=0.085326 m/s, UL= 0.09365 m/s)

(iv) long-slug flow (UG=0.085326 m/s, UL= 0.030116 m/s)


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Predicted Slug Lengths

Comparison of predicted and measured (van

Steijn et al.) slug lengths for flow of air and

ethanol in a T-junction micro-channel (AGI = 0.8 x

0.8 mm2, ACh= 0.8 x 0.8 mm2)

Comparison of predicted and measured slug

lengths for flow of air and water in a T-junctionmicro-channel (AGI = 1 x 1 mm

2, ACh= 1 x 1 mm2)


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Closing Remarks

Development of toolkit for characterization of dispersed

multiphase flows

Wall pressure sensors

Pressure fluctuations

Voidage probes

Local/instantaneous gas hold-up, bubble rise velocities, bubble sizedistribution

Optic fiber probes

Local/instantaneous solid hold-up


PIV/m-PIV (images from commercial supplier)


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Closing Remarks

Large-scale/industrial multiphase flows

Improved closure for the continuum models

Multi-fluid models with population balances to account for

bubble coalescence/break-up, particle agglomeration/

fragmentation

Rigorous experimental validation

Microscopic flow simulations Applications to product/process engineering


multiscale modeling and simulations of complex multiphase flows

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