PEM fuel cell numerical 061101

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PEM fuel cell numerical 061101 Powered By Docstoc
					     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
                                       2.0
                                                                                              Case1.1
                                                                                              Case1.2
                                                                                              Case2.0
           -2



                                                                                              Case2.1
            I, Current density/ A cm



                                       1.6
                                                                                              Case2.2


                                       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
                                                                                                      reference vector(0.01m s-1)
                                  0.004


                                 0.0035
                                                        0.18                           0.16

                                  0.003                0.18                            0.16
                                                                                      0.16

                                 0.0025
             Channel height/ m




                                                      0.17                            0.15
                                                      0.17                           0.15
                                  0.002
                                                         0.74                         0.58
                                                         0.75                         0.59
                                 0.0015
                                                       0.80                           0.61
                                  0.001
                                                       0.83
                                                                                       0.62

                                 0.0005


                                     0
                                          0     0.0005 0.001 0.0015       0    0.0005 0.001 0.0015
                                                   Channel width/ m              Channel width/ 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 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
                                0.0030                0.28
                                                                                       0.26


                                0.0025                                               0.26
            Channel height/ m




                                                      0.28
                                                      0.28                         0.26
                                0.0020
                                                      0.56                          0.50
                                                      0.56                             0.50
                                0.0015
                                                     0.57
                                                                                       0.51
                                0.0010
                                                     0.58                              0.51

                                0.0005


                                0.0000
                                         0     0.0005 0.001 0.0015       0     0.0005 0.001 0.0015
                                                 Channel width/ m                Channel width/ m




FCR Laboratory                               Dept. of Chemical Engineering         University of South Carolina
                 Fuel Cell with twenty channel
                     serpentine flow path



                                                                                                                                                                 n
                                                                                       )i
                                                                                         n                                                                     )i
                                                   Current collector                  2                                                                   ir
                                                                                   (H                                                                   (A
                                                                              as                      Gas diffusion layer                            as
                                                                             G                                                                   G




                                                                                             Gasket            MEA          Gasket
                                                                                                                                              End plate
                                                    ut




                                                                                                                                          t
                                               )o




                                                                                                                                        ou
                                                                                                                                       r)
                                               2
                                          (H




                                                                                                                                     Ai
                                     as                                Graphite flow-channel block




                                                                                                                                   (
                                                                                                                                as
                                    G




                                                                                                                               G
FCR Laboratory   Dept. of Chemical Engineering                              University of South Carolina
                                Fuel Cell model for twenty channel
                                       serpentine flow path
                                                                                      z
                                                                                             x
                                                                              y
    Height (0.0026m)




                                       Width (0.032 m)




Y            FLUENT Grid File /* CONFIGURATION = stagmodel3 */
             FCR Laboratory          Dept. of Chemical Engineering                          Feb 22
                                                                     University of South Carolina 1999
                                   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
                     FUEL CELL MODEL FOR TWENTY CHANNELS
                             SERPENTINE FLOW PATHz x
                                                                             y




                                      Width (0.032 m)




    Y       FLUENT Grid File /* CONFIGURATION = stagmodel3 */                             Feb 22 1999
        X   Grid ( 33 X 199 X 27 )                                                        Fluent 4.48
Z
            FCR Laboratory           Dept. of Chemical Engineering   University of South Carolina
                                                                                           Fluent Inc.
                                     The velocity vectors of secondary flow and pressure of the mixture at
                                       center cross-flow plane for high humidity with low permeability
                Channel height(m)
                                                                                                   reference vector(0.005m/s)
                                     0.003



                                    0.0025



                                     0.002

                                                                                                  reference vector(0.005m/s)
Channel height(m)




                                             0.013       0.014            0.015         0.016             0.017
                                                                  Channel width(m)
                                    0.0015



                                    0.001



                                    0.0005

                                             0.013        0.014            0.015         0.016              0.017
                                                                  Channel width(m)


   FCR Laboratory                                    Dept. of Chemical Engineering   University of South Carolina
                           The velocity vectors of secondary flow and pressure of the mixture at
                            center cross-flow plane for high humidity with high permeability
Channel height(m)

                                                                                      reference vector(0.5m/s)
                           0.003



                          0.0025



                           0.002

                                   0.013    0.014             0.015          0.016              0.017
      Channel height(m)




                                                                                         reference vector(2.0m/s)


                          0.0015



                           0.001



                          0.0005

                                   0.013    0.014            0.015          0.016             0.017
                                                     Channel width(m)


                          FCR Laboratory   Dept. of Chemical Engineering   University of South Carolina
                                                EXPERIMENT RESULTS
                                                            Current Density
                        12




                        10




                                                                             T A /C = 85/75 o C
                         8
                                                     T A /C = 75/65 o C
        C urrent (A )




                                          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

                                    inlet                                                                                                    outlet


                                 0.03


           Channel length (m)   0.025



                                 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
Prediction of local current density contours for very high inlet humidity
                                                      2
                                           Current (A/m ): 6172.99   6441.01   6606.69   6698.42   6797.66   7185.27   8881.4   10976.4

                                   inlet                                                                                                  outlet


                                0.03



                           0.025
           Channel length (m)



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


                                 1.4
                                         exp. avg
                                         num. max
                                 1.2     num. min
       Current density/ A cm-2


                                         num avg

                                 1.0


                                 0.8


                                 0.6


                                 0.4


                                 0.2


                      0.0
                   very low humidity            low humidity           high humidity       very high humidity
                     1.9<<2.5                   2.90<<4.12             5.0<<7.0             5.3<<10.3




FCR Laboratory                         Dept. of Chemical Engineering       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



                                 0.025
                 Channel length (m)



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



                                  1.4
                                           exp. avg
                                           num. max
                                  1.2      num. min
        Current density/ A cm-2


                                           num avg

                                  1.0


                                  0.8


                                  0.6


                                  0.4


                                  0.2


                       0.0
                    very low humidity             low humidity          high humidity       very high humidity
                      1.9<<2.5                    2.90<<4.12            5.0<<7.0             5.3<<10.3




FCR Laboratory                          Dept. of Chemical Engineering      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
                       8
                                                   T A /C = 75/65 o C
      C urrent (A )




                                        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



                               0.025                                                                              TEMP (K)
                                                                                                                   352.13
          Channel length (m)

                                                                                                                   351.39
                                                                                                                   350.86
                                0.02                                                                               348.54
                                                                                                                   347.18
                                                                                                                   345.37
                                                                                                                   344.94
                               0.015                                                                               344.26
                                                                                                                   344.01
                                                                                                                   343.84
                                                                                                                   343.53
                                0.01                                                                               343.42



                               0.005



                                                         0.01                  0.02                  0.03
                                                           Channel width (m)


    FCR Laboratory                             Dept. of Chemical Engineering          University of South Carolina
             Temperature distribution (K) at selected cross flow plane


         Channel height (mm)
        Channel height (mm)
                                     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
                                                          Channel width(mm)
  Channel height (mm)




                                     temp (K): 343.19 343.38 343.57 343.94 344.51 345.07 345.45 345.83
  Channel height (m)




                               1.5

                                                                                                              Cathode
                                1



                                           15            16              17            18             19
                                                          Channel width (mm)
                                                           Channel width (m)




FCR Laboratory                               Dept. of Chemical Engineering     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 */                                           Sep 07 2000

   Y      X       Cw Mole Fraction                                                                            Fluent 4.48
  FCR Laboratory              Dept. of Chemical Engineering           University of South Carolina
                  Lmax = 5.366E-02   Lmin = 3.049E-07                                                         Fluent Inc.
                                                                  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                                                    outlet

                        0.03                                                                                                         0.03

                                                                                                                                                                                                                    2
                                                                                                                                                                                                              I (A/m )
                       0.025                                                                                                        0.025                                                                     8371.46
                                                                                                                                                                                                              7669.51
  Channel length (m)




                                                                                                               Channel length (m)
                                                                                                                                                                                                              6967.56
                        0.02                                                                                                         0.02                                                                     6265.61
                                                                                                                                                                                                              5563.66
                                                                                                                                                                                                              4861.71
                                                                                                                                                                                                              4159.75
                       0.015                                                                                                        0.015
                                                                                                                                                                                                              3457.80
                                                                                                                                                                                                              2755.85
                                                                                                                                                                                                              2053.90
                        0.01                                                                                                         0.01                                                                     1351.95
                                                                                                                                                                                                               966.20
                                                                                                                                                                                                               650.00
                       0.005                                                                                                        0.005



                                                                        0.01            0.02        0.03                                                             0.01               0.02      0.03
                                                                            Channel width (m)                                                                               Channel width (m)

                                                                Isothermal and single phase                                                                     With water phase change effects




                                FCR Laboratory                                         Dept. of Chemical Engineering                                         University of South Carolina
                                            Local current density along the flow path

                              10000

                                                                     with water phase change and temperature effects
                                                                     without water phase change and temperature effects
                              8000
     Current density (A/m2)




                              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
                         0.03                                                        current (A/m )
                                                                                        8704.33
                                                                                        8492.76
                                                                                        8281.2
                                                                                        8069.63
                                                                                        7858.07
                        0.025                                                           7646.5
                                                                                        7434.94
                                                                                        7223.37
   Channel length (m)




                                                                                        7011.81
                                                                                        6800.25
                         0.02                                                           6588.68
                                                                                        6377.12
                                                                                        6165.55
                                                                                        5953.99
                                                                                        5742.42
                        0.015



                         0.01                                                       Avg current density
                                                                                    Numerical ~ 0.67 A/cm2
                                                                                    Exp.~ 0.64 A/cm2
                        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                    Triple passes with 11 serpentine channels




 FCR Laboratory           Dept. of Chemical Engineering      University of South Carolina

				
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