Transcript Numerical Simulation of Multi-scale Transport Processes and Reactions in PEM Fuel Cells Using Two-Phase Models Munir Ahmed Khan Division of Heat Transfer Dept.

Numerical Simulation of Multi-scale Transport
Processes and Reactions in PEM Fuel Cells
Using Two-Phase Models
Munir Ahmed Khan
Division of Heat Transfer
Dept. of Energy Sciences
LTH
Outline
• Introduction
• Brief History of Development
• Modeling Approach
• Numerical Modeling
• Results
• Conclusion
Heat Transfer / Energy Sciences / LTH
PEMFC Schematic
(Jacobson, 2004)
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History of PEMFC Development
•
•
•
•
•
•
1839 (Fuel Cell Principle)
1965 (NASA)
1968 (Nafion)
1969 (Biosatellite Missions)
1970 – 1989 (Abeyance)
1990 – Present (Ballard Power and Los Alamos Labs)
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Scientific Research Activities
Scientific Research
Experimental Approach
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Numerical Approach
Numerical Approach
PEMFC
Models
Based on Thermal
Analysis
Based on Flow domain
Based on Catalyst
Models
Isothermal
Single Phase
Thin Interface
Non-isothermal
Multi Phase
Discrete Volume
Agglomerate
Model
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Presented Modeling
• Interdigitated Flow Field
• Cathode Side Only
• 2-Phase
– 2 Phase Flow
– 2 Phase Temperature
– 2 Phase Current
• Agglomerate Catalyst Modeling
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Computational Domain
Component
(Larminie J, 2003)
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Dimension (mm)
Inlet
0.4
Outlet
0.4
Current Collector
0.8
PTL thickness
0.4
Catalyst layer thickness
0.1
Flow Fields
(www.me.udel.edu)
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Bridging Numerical and Experimental Modeling
Experimental
Modeling
Actual
Machine
Numerical
Modeling
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Idealized Catalyst Layer
Pt
Particle
Gas Pores
Carbon
Particle
Electrolyte
Bulk
Nafion
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Agglomerate
Transport Phenomena
H+
H+
•
•
•
•
•
Multicomponent Diffusion
Oxygen Dissolution
Dissolved Oxygen Diffusion
Electron Transport
Proton Migration
H2O
H2O
O2
O2
O2 O2
O2
e-
e-
e-
O2
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Oxygen Reduction Reactions
• Reaction Steps
M  O2  M  O2
M O2  H   e   M O2 H
M O2 H  3H   3e   2H 2 O  M
• Rate of Reaction
k c  f Tlocal , local 
RO2  k c COlocal
2
RO2  Current
RO2 ,net  E r k c COsurface
2
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Boundary Conditions
1.
Inlet
Gas Concentration
Fluid Temperature
Pressure
Water Saturation
2.
Catalyst/Membrane Interface
Nominal Cathode Overpotential (NCO)
3.
Current Collector
Solid Phase Potential
Solid Phase Temperature
2
1
3
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Velocity and Pressure Fields
Velocity Distribution (m/s)
Pressure Field (N/m2)
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Oxygen Mass Fraction
I  0.22
A
I  0.57
A
cm 2
I  0.89 A
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cm 2
cm 2
Water Saturation
I  0.22
A
I  0.57
A
cm 2
I  0.89 A
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cm 2
cm 2
Fluid Temperature (K)
I  0.22
A
I  0.57
A
cm 2
I  0.89 A
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cm 2
cm 2
Solid Temperature (K)
I  0.22
A
I  0.57
A
cm 2
I  0.89 A
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cm 2
cm 2
Membrane Phase Conductivity
2.15
1.54
1.53
2.1
1.52
1.51
σm (S/m)
σm (S/m)
2.05
1.5
2
1.95
1.49
1.9
1.48
1.47
0
0.0002
0.0004
0.0006
0.0008
0.001
Lenght (m)
I  0.22
A
cm 2
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0.0012
0.0014
0.0016
1.85
0
0.0002
0.0004
0.0006
0.0008
Length (m)
I  0.89 A
cm 2
0.001
0.0012
0.0014
0.0016
Cathode Overpotential (V)
0.4
NCO - Local Over Potential (V)
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0
0.0002
0.0004
0.0006
0.0008
0.001
Length (m)
0.89 A/cm2
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0.57 A/cm2
0.22 A/cm2
0.0012
0.0014
0.0016
Model Verification & Comparison
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Conclusion
• Effect of Liquid Water
– More prominent at higher current density
• Membrane Phase Conductivity
– Highly dependant on water activity
• Losses
– Higher losses are observed at higher current density
• Mass Limitation Effects
– Adequately captured by agglomerate model
• Power
– Maximum power is observed at 0.55 V
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THANKS TO ALL
& Special Thanks to
Jinliang Yuan
Bengt Sundén
HEC Pakistan
Swedish Research Council
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