munir ahmed khan division of heat transfer dept. of energy sciences lth

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


PEMFC Schematic

(Jacobson, 2004)


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)


Scientific Research Activities

Scientific Research

Experimental Approach Numerical Approach


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


Presented Modeling

• Interdigitated Flow Field

• Cathode Side Only

• 2-Phase– 2 Phase Flow

– 2 Phase Temperature

– 2 Phase Current

• Agglomerate Catalyst Modeling


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


Flow Fields

(www.me.udel.edu)


Bridging Numerical and Experimental Modeling

NumericalModeling

ActualMachine

ExperimentalModeling


Idealized Catalyst Layer

ElectrolyteBulk

Gas Pores

AgglomerateNafion

Pt Particle

Carbon Particle


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


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 ,


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


Velocity and Pressure Fields

Velocity Distribution (m/s)

Pressure Field (N/m2)


Oxygen Mass Fraction

222.0cmAI

257.0cmAI

289.0cmAI


Water Saturation

222.0cmAI

257.0cmAI

289.0cmAI


Fluid Temperature (K)

222.0cmAI

257.0cmAI

289.0cmAI


Solid Temperature (K)

222.0cmAI

257.0cmAI

289.0cmAI


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


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


Model Verification & Comparison


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


THANKS TO ALL

Jinliang Yuan Bengt Sundén

HEC Pakistan Swedish Research Council

& Special Thanks to

munir ahmed khan division of heat transfer dept. of energy sciences lth

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