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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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Vivek Buwa, Multiphase Flow Modeling
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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Vivek Buwa, Multiphase Flow Modeling
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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Vivek Buwa, Multiphase Flow Modeling
Process Intensification: Vision of a Future Plant
Vision of a future plant using process
intensification
A conventional plant
(Source: DSM)
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Vivek Buwa, Multiphase Flow Modeling
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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Vivek Buwa, Multiphase Flow Modeling
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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Vivek Buwa, Multiphase Flow Modeling
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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Vivek Buwa, Multiphase Flow Modeling
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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Vivek Buwa, Multiphase Flow Modeling
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
Vivek Buwa, Multiphase Flow Modeling
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
Vivek Buwa, Multiphase Flow Modeling
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
Vivek Buwa, Multiphase Flow Modeling
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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Vivek Buwa, Multiphase Flow Modeling
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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Vivek Buwa, Multiphase Flow Modeling
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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Vivek Buwa, Multiphase Flow Modeling
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
Vivek Buwa, Multiphase Flow Modeling
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
Vivek Buwa, Multiphase Flow Modeling
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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Vivek Buwa, Multiphase Flow Modeling
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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Vivek Buwa, Multiphase Flow Modeling
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
Vivek Buwa, Multiphase Flow Modeling
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
Vivek Buwa, Multiphase Flow Modeling