# PEMFC Simulation Problem!

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 September 15, 2004, 05:53 PEMFC Simulation Problem! #1 circle2000 Guest   Posts: n/a Hello everyone I am now using Fluent to model PEMFC performance, but the H2 can always flow to the cathode side and O2,N2 to the Anode. I have tried to set a large H2 diffusivity in the cathode and membrane by UDF, but it doesn't work, there's still much H2 in the cathode. I have also tried to fix the H2 fraction to 0 in cathode side and membrane in the BC pannel, this time the H2 only exists in anode but it's really hard to convergent, and even it can get to the convergence the result is unreasonable. So can someone help me solve this problem or give me some suggestion?

 September 15, 2004, 10:48 Re: PEMFC Simulation Problem! #2 Ari Guest   Posts: n/a Hi!!! There are many messagges on this argument, try to looking for them; according to many of them diffusivity's values must be very small(about 10-9) for solve your problem...I hope this could be help. Ari

 September 15, 2004, 21:49 Re: PEMFC Simulation Problem! #3 circle2000 Guest   Posts: n/a Thanks for your reply. I have searched massages posted on this forum and tried to set a even smaller value, but it doesn't work. I don't know the reason. DEFINE_DIFFUSIVITY(my_diff,c,t,i) { Thread *thread; real diffu; Domain *domain=Get_Domain(1); if(thread==Lookup_Thread(domain,MEA_ID)) diffu=1e-10; else diffu=2.88e-5; return diffu; } I use this code to define diffusivity of the mixture, when in the membrane, it is e-10, in other zones, it is 2.88e-5. But I think I cann't see the effect.Can u help me out?

 September 16, 2004, 06:51 Re: PEMFC Simulation Problem! #4 Ari Guest   Posts: n/a Hi!!! Try to define a diffusivity's value for every specie, I hope this could solve your problem. I've a question for you:since there is the argument t in the DEFINE_DIFFUSIVITY MACRO, why is it necessary the line Thread *thread; ??? Ari

 September 16, 2004, 21:34 Re: PEMFC Simulation Problem! #5 circle2000 Guest   Posts: n/a Thank u very much, I think your suggestion is very helpful for me. I deleted the Thread *thread, and it works. Thank u again.

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