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Numerical Simulation of Multi-scale Transport Processes and Reactions in PEM Fuel Cells
Using Two-Phase Models
Munir Ahmed Khan
Division of Heat TransferDept. of Energy Sciences
LTH
Heat Transfer / Energy Sciences / LTH
Outline
• Introduction
• Brief History of Development
• Modeling Approach
• Numerical Modeling
• Results
• Conclusion
Heat Transfer / Energy Sciences / LTH
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)
Heat Transfer / Energy Sciences / LTH
Scientific Research Activities
Scientific Research
Experimental Approach Numerical Approach
Heat Transfer / Energy Sciences / LTH
Numerical Approach
PEMFCModels
Based on Thermal Analysis
Based on Flow domain
Single Phase
Multi Phase
Isothermal
Non-isothermal
Based on CatalystModels
Thin Interface
Discrete Volume
AgglomerateModel
Heat Transfer / Energy Sciences / LTH
Presented Modeling
• Interdigitated Flow Field
• Cathode Side Only
• 2-Phase– 2 Phase Flow
– 2 Phase Temperature
– 2 Phase Current
• Agglomerate Catalyst Modeling
Heat Transfer / Energy Sciences / LTH
Computational Domain
(Larminie J, 2003)
Component Dimension (mm)
Inlet 0.4
Outlet 0.4
Current Collector 0.8
PTL thickness 0.4
Catalyst layer thickness
0.1
Heat Transfer / Energy Sciences / LTH
Bridging Numerical and Experimental Modeling
NumericalModeling
ActualMachine
ExperimentalModeling
Heat Transfer / Energy Sciences / LTH
Idealized Catalyst Layer
ElectrolyteBulk
Gas Pores
AgglomerateNafion
Pt Particle
Carbon Particle
Heat Transfer / Energy Sciences / LTH
Transport Phenomena
• Multicomponent Diffusion• Oxygen Dissolution• Dissolved Oxygen Diffusion• Electron Transport• Proton Migration
H2O
H+ H+
H2O
e- e-e-O2
O2 O2
O2 O2
O2
Heat Transfer / Energy Sciences / LTH
Oxygen Reduction Reactions
• Reaction Steps
• Rate of Reaction
22 OMOM
HOMeHOM 22
MOHeHHOM 22 233
localOcO CkR
22 locallocalc Tfk ,
CurrentRO 2
surfaceOcrnetO CkER
22 ,
Heat Transfer / Energy Sciences / LTH
Boundary Conditions
1. Inlet
Gas Concentration
Fluid Temperature
Pressure
Water Saturation
1
2. Catalyst/Membrane InterfaceNominal Cathode Overpotential (NCO)
3. Current CollectorSolid Phase PotentialSolid Phase Temperature
2
3
Heat Transfer / Energy Sciences / LTH
Velocity and Pressure Fields
Velocity Distribution (m/s)
Pressure Field (N/m2)
Heat Transfer / Energy Sciences / LTH
Membrane Phase Conductivity
1.47
1.48
1.49
1.5
1.51
1.52
1.53
1.54
0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016
Lenght (m)
σm (
S/m
)
1.85
1.9
1.95
2
2.05
2.1
2.15
0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016
Length (m)
σm (
S/m
)
222.0cmAI 289.0
cmAI
Heat Transfer / Energy Sciences / LTH
Cathode Overpotential (V)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016
Length (m)
NC
O -
Lo
cal O
ver
Po
ten
tial
(V
)
0.89 A/cm2 0.57 A/cm2 0.22 A/cm2
Heat Transfer / Energy Sciences / LTH
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