Fundamental Behavior of PEM Fuel Cells
By
W. K. Lee, S. Shimpalee, J. Glandt
and J. W. Van Zee
Fuel Cell Research Laboratory
Department of Chemical Engineering
University of South Carolina
H. Naseri-Neshat
Department of Mechanical Engineering Technology
South Carolina State University
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
NUMERICAL STUDIES
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
OBJECTIVES
• To numerically simulate 3-D aspects of flow in
PEM fuel cells
• To predict the local current output from fuel cell
simulations.
• To include the thermal analysis to capture water
phase change effect on PEM fuel cell
performance.
• To include the transient analysis to capture the
effect of voltage change on the performance
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
PEM FUEL CELL
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
MODEL DEVELOPMENT
• 10 cm. straight channel fuel cell.
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
MODEL EQUATIONS
•
•
•
•
•
•
•
Conservation of mass.
Momentum transport.
Species transport.
Phase change model of water.
Energy equation.
Electrochemical equations of PEM fuel cells.
Steady state and time dependent
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
COMPUTATIONAL PROCEDURE
• Commercial CFD software (FLUENT)
• Modified subroutine for source terms of
continuity, species transport, heat and
electrochemical equations.
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
RESULTS
• Three-dimensional numerical simulation of straight
channel model.
– The effect of diffusion layer added in the model on the
performance.
– The effect of membrane thickness on the fuel cell
performance.
– These results are compared with previous numerical
works done by Fuller and Newman (1993) and Yi and
Nguyen (1998).
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
Effect of membrane thickness on the local –width current density
profile for cases 1 and 2 comparing to the result of Yi and Nguyen
2.4
Yi and Nguyen(1998)
Case1.0
Case1.1
Case1.2
Case2.0
Case2.1
Case2.2
I, Current density/ A cm
-2
2.0
1.6
1.2
0.8
0.4
0.0
0.00
0.02
0.04
0.06
0.08
0.10
x, Channel length/ m
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
Velocity vectors and mixture density contours at selected cross-flow
planes for operating condition of case 1 (similar to Yi and Nguyen)
2/3 of channel length
1/3 of the channel length
-1
reference vector(0.01m s )
0.004
0.0035
0.16
0.18
0.003
0.16
0.18
Channel height/ m
0.16
0.0025
0.15
0.15
0.17
0.17
0.002
0.58
0.74
0.75
0.0015
0.59
0.80
0.61
0.001
0.83
0.62
0.0005
0
0
0.0005 0.001 0.0015
0
Channel width/ m
FCR Laboratory
Dept. of Chemical Engineering
0.0005 0.001 0.0015
Channel width/ m
University of South Carolina
Velocity vectors and mixture density contours at selected cross-flow planes
for operating condition of case 3 (similar to Fuller and Newman)
1/3 of channel length
2/3 of channel length
reference vector(0.002m s-1)
0.0040
0.0035
0.28
0.26
Channel height/ m
0.0030
0.28
0.26
0.26
0.0025
0.28
0.28
0.26
0.0020
0.50
0.50
0.56
0.56
0.0015
0.57
0.0010
0.51
0.58
0.51
0.0005
0.0000
0
0.0005 0.001 0.0015
0
Channel width/ m
FCR Laboratory
Dept. of Chemical Engineering
0.0005 0.001 0.0015
Channel width/ m
University of South Carolina
Fuel Cell with twenty channel
serpentine flow path
n
Current collector
as
)i
2
(H
Gasket
)o
ut
ut
)o
Dept. of Chemical Engineering
Graphite flow-channel block
(A
ir
2
G
FCR Laboratory
Gasket
as
(H
MEA
G
G
as
a
Gas diffusion layer
G
ir
A
s(
University of South Carolina
End plate
)i
n
Fuel Cell model for twenty channel
serpentine flow path
z
x
Height (0.0026m)
y
Width (0.032 m)
Y
FLUENT
Grid File /* CONFIGURATION
= stagmodel3
*/
FCR Laboratory
Dept. of Chemical
Engineering
Feb 22 1999
University of South Carolina
RESULTS
• Three-dimensional numerical simulation of full-cell fuel
cell.
– The effect of diffusion layer properties (permeability)
on species transport inside PEM fuel cell
– The effect of inlet humidity on the fuel cell
performance
– Comparison of numerical results with available
experimental data.
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
Z
FUEL CELL MODEL FOR TWENTY CHANNELS
SERPENTINE FLOW PATHz
x
y
Width (0.032 m)
FLUENT Grid File /* CONFIGURATION = stagmodel3 */
Y
X
Grid ( 33 X 199 X 27 )
FCR Laboratory
Dept. of Chemical Engineering
Feb 22 1999
Fluent 4.48
University of South Carolina
Fluent Inc.
Channel height(m)
Channel height(m)
The velocity vectors of secondary flow and pressure of the mixture at
center cross-flow plane for high humidity with low permeability
reference vector(0.005m/s)
0.003
0.0025
0.002
0.013
0.014
0.013
0.014
0.015
0.016
Channel width(m)
reference vector(0.005m/s)
0.017
0.0015
0.001
0.0005
FCR Laboratory
0.015
0.016
Channel width(m)
Dept. of Chemical Engineering
0.017
University of South Carolina
Channel height(m)
Channel height(m)
The velocity vectors of secondary flow and pressure of the mixture at
center cross-flow plane for high humidity with high permeability
reference vector(0.5m/s)
0.003
0.0025
0.002
0.013
0.014
0.015
0.016
0.017
reference vector(2.0m/s)
0.0015
0.001
0.0005
0.013
FCR Laboratory
0.014
0.015
0.016
Channel width(m)
Dept. of Chemical Engineering
0.017
University of South Carolina
EXPERIMENT RESULTS
Current Density
12
10
T A /C = 85/75 o C
C urrent (A )
8
T A /C = 75/65 o C
o
T A /C = 65/55 C
6
T A /C = 95/85 o C
4
2
0
0
10
20
30
40
50
60
T im e (hour)
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
Prediction of local current density contours for very low inlet humidity
2
Current (A/m ): 2418.95
2460.01
2563.49
2679.3
2795.11
2910.92
3026.73
3142.55
3258.36
3374.17
outlet
inlet
0.03
Channel length (m)
0.025
0.02
0.015
0.01
0.005
0.01
0.02
Channel width (m)
FCR Laboratory
Dept. of Chemical Engineering
0.03
University of South Carolina
Prediction of local current density contours for very high inlet humidity
Current (A/m2): 6172.99
6441.01
6606.69
6698.42
6797.66
7185.27
8881.4
10976.4
outlet
inlet
0.03
Channel length (m)
0.025
0.02
0.015
0.01
0.005
0.01
0.02
Channel width (m)
FCR Laboratory
Dept. of Chemical Engineering
0.03
University of South Carolina
Comparison of experiment current density data with the numerical
predictions(average in x and y) for each inlet humidity.
Current density/ A cm-2
1.4
exp. avg
num. max
num. min
num avg
1.2
1.0
0.8
0.6
0.4
0.2
0.0
very low humidity
1.9<<2.5
FCR Laboratory
low humidity
2.90<<4.12
Dept. of Chemical Engineering
high humidity
5.0<<7.0
very high humidity
5.3<<10.3
University of South Carolina
Prediction of contours of water vapor activity at the membrane
interface on the anode side for the very high inlet humidity.
aa: 0.929 0.932 0.937 0.942 0.946 0.953 0.963 0.972 0.980 0.986 1.086 1.108 1.129 1.142
inlet
outlet
0.03
Channel length (m)
0.025
0.02
0.015
0.01
0.005
0.01
0.02
Channel width (m)
FCR Laboratory
Dept. of Chemical Engineering
0.03
University of South Carolina
Comparison of experiment current density data with the numerical
predictions(average in x and y) for each inlet humidity.
Current density/ A cm-2
1.4
exp. avg
num. max
num. min
num avg
1.2
1.0
0.8
0.6
0.4
0.2
0.0
very low humidity
1.9<<2.5
FCR Laboratory
low humidity
2.90<<4.12
Dept. of Chemical Engineering
high humidity
5.0<<7.0
very high humidity
5.3<<10.3
University of South Carolina
CONCLUSIONS
• `The effects of inlet humidity
– The fuel cell performance changes with inlet humidity condition.
• The condition where insufficient water lowers the membrane
conductivity and low currents
• The condition where excess water leads to flooding of the electrode
and low currents due to decreased reaction area.
• The effect of diffusion layers added into the model
– Create larger reaction area.
– The current density is lower but uniform.
• The effect of membrane thickness
– Increasing membrane thickness: the current density is decreased
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
Temperature and water phase change effects
on the performance
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
Experiment results
12
10
T A /C = 85/75 o C
C urrent (A )
8
T A /C = 75/65 o C
o
T A /C = 65/55 C
6
T A /C = 95/85 o C
4
2
0
0
10
20
30
40
50
60
T im e (hour)
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
Temperature (K) contours on anode membrane surface for high inlet humidity
inlet
outlet
0.03
Channel length (m)
0.025
TEMP (K)
352.13
351.39
350.86
348.54
347.18
345.37
344.94
344.26
344.01
343.84
343.53
343.42
0.02
0.015
0.01
0.005
0.01
0.02
0.03
Channel width (m)
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
(mm)
height(mm)
Channel
Channel
height
Temperature distribution (K) at selected cross flow plane
temp (K): 343.18 343.36 343.54 343.89 344.25 344.79 345.32 345.68
3
2.5
Anode
2
15
16
17
18
19
(mm)
height (m)
Channel height
Channel
Channel width(mm)
temp (K): 343.19 343.38 343.57 343.94 344.51 345.07 345.45 345.83
1.5
Cathode
1
15
FCR Laboratory
16
17
Channel
Channelwidth
width(mm)
(m)
Dept. of Chemical Engineering
18
19
University of South Carolina
liquid water presented (mass fraction) at cathode membrane surface
5.3 7E-0 2
5.19 E-0 2
5.0 1E-0 2
4 .8 3 E-0 2
4 .6 5E-0 2
4 .4 7E-0 2
4 .2 9 E-0 2
4 .11E-0 2
3 .9 4 E-0 2
3 .76 E-0 2
3 .58 E-0 2
3 .4 0 E-0 2
3 .2 2 E-0 2
3 .0 4 E-0 2
2 .8 6 E-0 2
2 .6 8 E-0 2
2 .50 E-0 2
2 .3 3 E-0 2
2 .15E-0 2
1.9 7E-0 2
1.79 E-0 2
1.6 1E-0 2
1.4 3 E-0 2
1.2 5E-0 2
1.0 7E-0 2
8 .9 4 E-0 3
7.15E-0 3
5.3 7E-0 3
3 .58 E-0 3
1.79 E-0 3
3 .0 5E-0 7
inlet
outlet
FLUENT Grid File /* CONFIGURATION = stagmodel3 */
Y
X
Cw Mole Fraction
FCR Laboratory
Dept. of Chemical Engineering
Sep 07 2000
University of South Carolina
Fluent 4.48
Local current density contours on the
membrane surface for selected operating condition
Frame 001  31 Oct 2000  curren density membrane surface without heat transfer
Frame 001  31 Oct 2000  CURRENT AND TEMP ON MEMBRANE SURFACE
inlet
outlet
inlet
0.03
0.03
Channel length (m)
0.025
Channel length (m)
outlet
0.02
0.015
0.01
0.005
0.025
I (A/m2)
8371.46
0.02
7669.51
6967.56
6265.61
5563.66
4861.71
4159.75
0.015
3457.80
2755.85
2053.90
0.01
1351.95
966.20
650.00
0.005
0.01
0.02
0.03
Channel width (m)
Isothermal and single phase
FCR Laboratory
Dept. of Chemical Engineering
0.01
0.02
Channel width (m)
With water phase change effects
University of South Carolina
0.03
Local current density along the flow path
10000
with water phase change and temperature effects
without water phase change and temperature effects
Current density (A/m2)
8000
6000
4000
2000
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Flow distance (m)
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
Local current density (A/m2) contours on the membrane surface
For high inlet humidity (Ta/c = 85/75 oC)
inlet
outlet
2
current (A/m )
8704.33
8492.76
8281.2
8069.63
7858.07
7646.5
7434.94
7223.37
7011.81
6800.25
6588.68
6377.12
6165.55
5953.99
5742.42
0.03
Channel length (m)
0.025
0.02
0.015
Avg current density
Numerical ~ 0.67 A/cm2
Exp.~ 0.64 A/cm2
0.01
0.005
0.01
0.02
0.03
Channel width (m)
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
CONCLUSIONS
• Energy generation = temperature rise in 3-D =Water evaporation
= dehydrates the membrane
= decreases its performance.
• Non-isothermal model predicts
– Temperature changes between inlet and outlet
– Large current density differences for fixed operating condition
– Anode and cathode flooding for high humidity condition
– Good agreement with experimental I-V data and water balance
closure (±10%) for an independently measured, fixed set of
parameters
FCR Laboratory
Dept. of Chemical Engineering
University of South Carolina
CONCLUSIONS
• Our PEM model can be applied to any flow-field
configuration:
Single pass with 4 serpentine channels
FCR Laboratory
Dept. of Chemical Engineering
Triple passes with 11 serpentine channels
University of South Carolina