By W. K. Lee, S. Shimpalee, J. Glandt and J. W. Van Zee F uel C ell R esearch Laboratory

1. 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

2. NUMERICAL STUDIES

3. 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 OBJECTIVES

4. PEM FUEL CELL

5. 10 cm. straight channel fuel cell. MODEL DEVELOPMENT

6. 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 MODEL EQUATIONS

7. Commercial CFD software (FLUENT) Modified subroutine for source terms of continuity, species transport, heat and electrochemical equations. COMPUTATIONAL PROCEDURE

8. 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). RESULTS

9. Effect of membrane thickness on the local –width current density profile for cases 1 and 2 comparing to the result of Yi and Nguyen

10. Velocity vectors and mixture density contours at selected cross-flow planes for operating condition of case 1 (similar to Yi and Nguyen)

11. Velocity vectors and mixture density contours at selected cross-flow planes for operating condition of case 3 (similar to Fuller and Newman)

12. Fuel Cell with twenty channel serpentine flow path

13. Length(0.032m) Height (0.0026m) Fuel Cell model for twenty channel serpentine flow path

14. 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. RESULTS

15. FUEL CELL MODEL FOR TWENTY CHANNELS SERPENTINE FLOW PATH

16. The velocity vectors of secondary flow and pressure of the mixture at center cross-flow plane for high humidity with low permeability

17. The velocity vectors of secondary flow and pressure of the mixture at center cross-flow plane for high humidity with high permeability

18. EXPERIMENT RESULTS Current Density

19. Prediction of local current density contours for very low inlet humidity

20. Prediction of local current density contours for very high inlet humidity

21. Comparison of experiment current density data with the numerical predictions(average in x and y) for each inlet humidity.

22. Prediction of contours of water vapor activity at the membrane interface on the anode side for the very high inlet humidity.

23. Comparison of experiment current density data with the numerical predictions(average in x and y) for each inlet humidity.

24. `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 CONCLUSIONS

25. Temperature and water phase change effects on the performance

26. Experiment results

27. Temperature (K) contours on anode membrane surface for high inlet humidity

28. Temperature distribution (K) at selected cross flow plane Channel height (mm) Channel height (mm) Channel width (mm)

29. liquid water presented (mass fraction) at cathode membrane surface inlet outlet

30. Local current density contours on the membrane surface for selected operating condition Isothermal and single phase With water phase change effects

31. Local current density along the flow path

32. Local current density (A/m2) contours on the membrane surface For high inlet humidity (Ta/c = 85/75 oC) Avg current density Numerical ~ 0.67 A/cm2 Exp.~ 0.64 A/cm2

33. 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 CONCLUSIONS

34. Our PEM model can be applied to any flow-field configuration: CONCLUSIONS Single pass with 4 serpentine channels Triple passes with 11 serpentine channels