PEM Fuel Cell Modeling
with ANSYS-Fluent
Sandeep Sovani, Ph.D.
Director, Global Automotive Industry
April 8, 2014
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© 2011 ANSYS, Inc.
November 28,
2014
Contents
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•
Geometry Model
•
Physics Model
•
ANSYS-Fluent PEMFC Module
•
Model Validation with Experiments
•
Stack Simulation
© 2011 ANSYS, Inc.
November 28,
2014
Geometric Model
ANSYS-Fluent uses a Resolved Electrolyte Model
All of the following zones are resolved, i.e. have individual meshes
Coolant Channel
current collector
flow channel
anode
gas diffusion layer
Not to scale!
catalyst layer
membrane
catalyst layer
gas diffusion layer
flow channel
current collector
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© 2011 ANSYS, Inc.
electrolyte
November 28,
2014
cathode
Geometric Model
Also called “bipolar plate“ or “interconnect”.
Solid material, e.g. graphite. Used to conduct electrons
to/from the external circuit. Gives structural stability.
current collector
flow channel
Channel to provide fuel (anode) and oxidizer (cathode) and
to transport away the reaction products.
gas diffusion layer
Porous medium to allow diffusive flow of fuel (anode) and
oxidizer (cathode) and to permit transport of electrons.
Also called “electrode“. Porous medium to allow diffusive flow
of fuel (anode) and oxidizer (cathode) and to permit transport
of electrons. Partially filled with catalyst material, e.g. Platinum,
and membrane material.
catalyst layer
membrane
Proton conducting polymer material, e.g. Nafion.
Coolant Channel
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© 2011 ANSYS, Inc.
November 28,
2014
Coolant flow
Physics Model
• Fuel Cell Modeling requires to calculate
Standard ANSYS Fluent
– fluid flow with reacting species
– convective/conductive heat transfer (w/o radiation)
– mass transfer
– heterogeneous electrochemical reactions
– transport of electric current driven by electric potential
– multiphase flow (water condensation within the PEMFC)
ANSYS Fluent Fuel Cell Module
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© 2011 ANSYS, Inc.
November 28,
2014
Physics Model
A general purpose CFD solver is ideal for modeling
PEM fuel cells, however, some additional sub-models are needed
PEMFC multi-physics
– Laminar/Turbulent/Transitional Fluid Flow
– Heat Transfer
– Species Transport
General Purpose
CFD Code
– Chemical Reaction
– Multiphase Flow
– Electrochemistry
– Electric Potentials (current transport)
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© 2011 ANSYS, Inc.
November 28,
2014
Additional SubModels Needed
Physics Model
Additional submodels needed for complex PEMFC multiphysics
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•
Electrochemical submodel - model current density,
voltage, species sources/sinks at the MEA surfaces
•
Electrical submodel - model current and voltage
distribution in porous and solid conducting regions
•
MEA submodel - predict electrical losses and water
flow in MEA
•
Porous Media Multiphase Flow submodel -model
liquid water and oxidizer flow in porous cathode
diffusion layer
•
Thin Film Multiphase submodel - model flow of liquid
water in cathode gas flow passages
© 2011 ANSYS, Inc.
November 28,
2014
ANSYS-Fluent PEMFC Module
The PEMFC module is a separately licensed-managed
add-on module
−
−
−
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© 2011 ANSYS, Inc.
Included with FLUENT distribution
Fully supported and documented
Available for SERIAL and PARALLEL Fluent
November 28,
2014
ANSYS-Fluent PEMFC Module
Fluent’s PEMFC Module can be used for
– Single cell simulation
– Stack simulation
– Steady state simulation
– Transient simulation
– Computing current for fixed voltage
– Computing voltage for fixed current
One simulation per data point on the I-V curve
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© 2011 ANSYS, Inc.
November 28,
2014
ANSYS-Fluent PEMFC Module: Key Features
Detailed modeling of MEA with dual potential model from
Kulikovsky, Divisek and Kornyshev*
Compute current/voltage from specified voltage/current
Capabilities of modeling contact resistance and Joule heating,
cooling channels, etc.
Membrane water transport
Phase change and liquid water transport in porous media,
clogging to gas diffusion and reaction sites
Robust solution procedure and fast convergence
Fuel Cell Specific Graphical User Interface (GUI) set up
* Kulikovsky et al., J. Electrochem. Soc. 147 (3) (2000) 953-959
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© 2011 ANSYS, Inc.
November 28,
2014
ANSYS-Fluent PEMFC Module: Key Features
Parallelized computing
User-Modifiable properties, e.g. gas diffusitivity, electrolyte
conductivity etc. by using User Defined Functions (UDF)
written in C
Automated stack set-up
Multicomponent diffusion
Temperature dependent leakage current
Non-isotropic electrical and thermal conductivities in the gas
diffusion layer
Validated by experiments
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© 2011 ANSYS, Inc.
November 28,
2014
ANSYS-Fluent PEMFC Module
PEMFC: Domains modeled
e-
e-
current collector
coolant
channel
flow channel
coolant
channel
anode
gas diffusion layer
Membrane
Electrode
Assembly
MEA
2 H 2 → 4 H + + 4e −
H+
catalyst layer
membrane
H+
O2 + 4 H + + 4e − → 2 H 2O catalyst layer
gas diffusion layer
coolant
channel
e12
flow channel
current collector
e-
© 2011 ANSYS, Inc.
November 28,
2014
cathode
coolant
channel
ANSYS-Fluent PEMFC Module
Equations Solved
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© 2011 ANSYS, Inc.
November 28,
2014
ANSYS-Fluent PEMFC Module
Electric Sub-Model
Two electric potentials are computed
•
Solid phase potential (e- transport in conducting solid)
•
Membrane phase potential (H+ transport in MEA)
Advantages
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•
Account for current transport in all regions
•
Facilitate modeling of contact resistance at material interfaces
© 2011 ANSYS, Inc.
November 28,
2014
ANSYS-Fluent PEMFC Module
Electrochemical Sub-Model
Ran and Rcat are calculated using the Butler-Volmer function
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© 2011 ANSYS, Inc.
November 28,
2014
ANSYS-Fluent PEMFC Module
Liquid Water Transport
Inside the membrane
• water content
• diffusion model with consideration of the osmotic drag
• MEM-CAT interface: Springer et al. (1991) and Eaton (2001, account for
phase change )
Outside the membrane
• water saturation in GDL
• fine mist in flow channel (vw = vgas)
• condensation/vaporization
• capillary diffusion and surface tension in porous zones
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© 2011 ANSYS, Inc.
November 28,
2014
ANSYS-Fluent PEMFC Module
PEMFC: Solution Procedure
Specify solid phase potential BCs at cathode current collectors:
Cell voltage Vcell or average current density Iave
Specify inlet temperature boundary conditions
Solve the system of equations for u, v, w, p, yi, T, φs, φm, s, λ
For prescribed Vcell:
For prescribed Iave:
Get polarization curve (Iave, Vcell)
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© 2011 ANSYS, Inc.
November 28,
2014
I ave
R
∫
=
a
dVa
Amem
Vcell = φs |cathode external contact
ANSYS-Fluent PEMFC Module
Post-Processing
ANSYSs-Fluent’s standard post-processing features are all available with
the PEMFC module, e.g. Contour plots, vectors, iso-surfaces, graphs,
etc.
Variables available for post-processing
Standard quantities
•
– Pressure, X,Y,Z Velocities, Temperature,
– Species mass (or mole) fractions
PEMFC specific scalars
•
–
–
–
–
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UDS-0 Solid Phase Potential (Volts)
UDS-1 Membrane Potential (Volts)
UDS-2 Liquid Saturation (Liquid Water Volume Fraction)
UDS-3 Water Content
© 2011 ANSYS, Inc.
November 28,
2014
ANSYS-Fluent PEMFC Module
Post-Processing
More PEMFC specific scalars available for post-processing
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© 2011 ANSYS, Inc.
November 28,
2014
Model Validation vs. Experiments
50 cm2 MEA
1.0
Inlet
Channel depth: 3.18; width: 2.16
Data: 1.50 equiv.
0.9
Fluent: 1.50 equiv.
Data: 2.25 equiv.
Fluent: 2.25 equiv.
0.8
V (V)
0.7
0.6
71.12
0.5
0.4
Outlet
0.3
2.54
0.2
0.0
70.99
Schematic diagram of the test cell of Mench et al [1]: all
numbers in mm
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© 2011 ANSYS, Inc.
November 28,
2014
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
I (A/cm2)
Computed (lines) and measured (symbols) global
polarization curves for cathode stoichiometry of 1.5
and 2.25 equiv.
Model Validation vs. Experiments
1.2
1.0
Exp. 0.85 V
Exp. 0.80 V
Exp. 0.70 V
Exp. 0.65 V
Exp. 0.85 V
Exp. 0.80 V
Exp. 0.70 V
Exp. 0.65 V
Cal. 0.85 V
Exp. 0.55 V
Cal. 0.80 V
Exp. 0.45 V
Cal. 0.70 V
Exp. 0.40 V
Cal. 0.65 V
Exp. 0.35 V
Cal. 0.85 V
Exp. 0.55 V
Cal. 0.80 V
Exp. 0.45 V
Cal. 0.70 V
Exp. 0.40 V
Cal. 0.65 V
Exp. 0.35 V
Cal. 0.55 V
Cal. 0.45 V
Cal. 0.40 V
Cal. 0.35 V
Cal. 0.55 V
Cal. 0.45 V
Cal. 0.40 V
Cal. 0.35 V
1.0
0.8
0.6
2
I (A/cm )
2
I (A/cm )
0.8
0.6
0.4
0.4
0.2
0.2
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
x/L
Computed (lines) and measured (symbols) local
current density distributions for cathode
stoichiometry of 1.5 equiv.
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© 2011 ANSYS, Inc.
November 28,
2014
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
x/L
Computed (lines) and measured (symbols) local
current density distributions for cathode
stoichiometry of 2.25 equiv.
0.9
Model Validation vs. Experiments
25 cm2 MEA of Liu et al (2005)

Outlet


48.36
0.8
Inlet
50.0
Unit: mm
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© 2011 ANSYS, Inc.
November 28,
2014
0.84

3-channel serpentine gas
flow channel for both
anode and cathode sides
Anode and Cathode outlet
pressure = 1 atm
Air and fuel stoichiometric
ratio = 2
Cell temperature = 353 K
Model Validation vs. Experiments
Global IV polarization for fully humidified fuel (H2)
Potential (V)
1
0.9
0.8
Experiments
Simulation
0.7
0.6
0.5
0.4
0.3
Air humidity = 100 %
0.2
0.1
0
0
0.2
Potential (V)
1
0.9
0.8
0.6
0.8
Experiments
Simulation
0.7
0.6
0.5
0.4
0.3
Air humidity = 50 %
0.2
0.1
0
0
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0.4
I (A/cm2)
0.2
© 2011 ANSYS, Inc.
0.4
I (A/cm2)
November 28,
2014
0.6
0.8
ANSYS
FC Module
Liu et al
(2005)
Model Validation vs. Experiments
Global IV polarization for partially humidified fuel (H2)
Potential (V)
1
0.9
0.8
Experiments
Simulation
0.7
0.6
0.5
0.4
0.3
Air humidity = 100 %
0.2
0.1
0
0
0.2
Potential (V)
1
0.9
0.8
0.6
0.8
Experiments
Simulation
0.7
0.6
0.5
0.4
0.3
Air humidity = 30 %
0.2
0.1
0
0
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0.4
I (A/cm2)
0.1
0.2
© 2011 ANSYS, Inc.
0.3
0.4
I (A/cm2)
November 28,
2014
0.5
0.6
0.7
ANSYS
FC Module
Liu et al
(2005)
Stack simulation
415,000 FV per FC
MEA area 50 cm2
Anode Inlet Conditions
• mass flow rate
• YH2
• YH2O
1e-5 kg/s
0.2
0.8
Cathode Inlet Conditions
• mass flow rate
1e-5 kg/s
• YO2
0.22
• YH2O
0.22
Wall Temperature fixed at 80°C
Potentiostatic BCs:
• 0.7V per cell : i ≈ 0.5 A/cm2
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© 2011 ANSYS, Inc.
November 28,
2014
Stack Simulation
Channels
Air
Fuel
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November 28,
2014
Stack Simulation
Oxygen Consumption
Cathode Catalyst
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November 28,
2014
Stack Simulation
Temperature
Membrane
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© 2011 ANSYS, Inc.
November 28,
2014
Stack Simulation
Robustness and rapid solution convergence (Residuals)
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© 2011 ANSYS, Inc.
November 28,
2014
Stack Simulation
Performance: Computing Time
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2nd
Solution
Cluster of PCs with
Computing Time
(h)
#CPUs
Single PEMFC
1
2:45
2.8 GHz
4-PEMFC Stack
4
4:10
8 GB Memory
4-PEMFC Stack
8
2:11
Fast Interconnect
4-PEMFC Stack
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1:21
8-PEMFC Stack
8
4:29
8-PEMFC Stack
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© 2011 ANSYS, Inc.
November 28,
2014
2:26
2 Dual Core CPUs
Note:
increase in
• problem size :
8 times
• computing time:
< 2 times
Stack Simulation – Example 2
• 5 PEMFC stack with end plates (omitted in this picture).
• Close to 9.3 Mio mesh cells.
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© 2011 ANSYS, Inc.
November 28,
2014
Stack Simulation – Example 2
Temperature °C on outer walls
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© 2011 ANSYS, Inc.
Y
November
H2 28,
2014
Temperature °C in an anode
YO2
Summary
Strengths of ANSYS-Fluent PEMFC Solution
•
Detailed, accurate model
• All zones resolved
• Detailed physics sub-models
•
Highly customizable
• Most aspects of the module are user customizable
• Detailed customization documentation
•
Services
• ANSYS has extensive experience in consulting and
funded development services for PEM Fuel Cells
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© 2011 ANSYS, Inc.
November 28,
2014