1. Boundary Layer Analysis of Flow through a Single Channel PEM Fuel Cell
Viscous Flows
Dr. Kirk
By Chris Jojola

2. Introduction

3. How They Work

4. Uses Small voltage for each cell.
They must be stacked in series for automotive purposes.

5. My Research The effect of channel path on PEM fuel cell performance.
Several different configurations, including square, serpentine, and spiral.
For this project the serpentine configuration was chosen.

6. My Research cont.

7. Sample Results
~ 2 million cells

8. Problem
The goal of this project was to resolve the boundary layer along the inside of the channels to improve the accuracy of computations.
Once accomplished, the next goal was to determine if the improved accuracy was worth the extra computational time and power.

9. Splitting the Problem in Two
The cell has nearly 2 million cells.
Adding more points and using Fluent’s PEM module could take an entire day per case.
Instead I performed two different tests for three cases (6 total)

10. Part One
For the first test, I reduced the cell to a single channel and ran hot air through it.

11. Part One – Cont.
The goal was to observe the change in velocity, temperature, and pressure profiles.
The overall pressure drop was also taken into consideration.

12. Part Two
The second part was to reduce the cell to a single sweep and run using the full PEM module.
The velocity, pressure, etc. were also observed, but the main goal was to see how the change affected electrical parameters such as cell voltage and current density.

13. Part Two – Cont.
Course
Original
Fine

14. Conditions Parameter Value Unit Inlet Temp 353 K Mass flow rate, H2
8 x 10-7
kg/m3
Mass flow rate, O2
8 x 10-6
Channel Dim.
3.125 x 3.125 mm
Cell Voltage
0.65 V
Viscosity
2.09 x 10-5
kg/(ms) Re
120 1

15. Results
The results for both tests showed that the grid change did very little to improve the accuracy of the test.

16. Results – Part One
Grid refinement had an almost negligible change on the pressure drop over the entire channel.
However, the time needed for convergence increased dramatically (close to 50%)

17. Results – Part One Cont. Pressure Velocity Velocity (Zoom) Course
Original
Fine

18. Results – Part 1 Cont. Case ∆p % Difference Course 18.3 Pa 2.7%
Original
18.8 Pa 0%
Fine
19.0 Pa
1.1%

19. Results – Part Two
The grid refinement on the small section of the cell running the full PEMFC software led to less than 1% change in pressure and current density.
Since two channels had a significant number of cells added, the computational time increased dramatically for the refined grid.

20. Results – Part Two Cont. Case Current Density % Diff Time/ Iteration
Course
.0814 A/cm3
0.47%
2.3 s
2/3
Original
.0818 A/cm3 0%
3.6 s 1
Fine
.0820 A/cm3
0.27%
32.4 s 9

21. Results – Part Two Cont.
Course
Original
Fine

22. Conclusions
The boundary layer within the anode and cathode channels is sufficiently large to be captured by the current grid.
Increasing the cell count would add considerable computing with a minimal effect on the results.

23. Questions ?