[Golnaz]

Hi everyone,

i am tring to model a PEM fuel cell using fluent
i have gone through the related tutorial and the fuel cell manual.
I have a nonisotropic electrical conductivity.
we also i have specofic values for in plane and through plane electrical conductivity in unit on S/m.
what i understood, from the tutrial and the manual i would need to used UDS to be able to input the two values for electrical conductivity.

but, my problem is that when i try using UDS diffusivity with the orthogonal option the values that i can put in are in kg/ms!!! but the values that i have are in S/m(unit of electrical conductivity) !!!
I really dont understand how can i do that, it seems like am missing something, or misunderstanding some part.

whats more, i dont understand how the UDS diffusivity can be defined as the electrical conductiviy..

Any Input is much appreciated..

Many Thanks

[MASOUD]

Golnaz,

UDS is a general concept which can be employed to solve various problems. Fluent can not understand what variable we intend to model through UDS. That's why you find the unit of diffusivity as m/s.

You just enter your value in S/m and go ahead with that.

Hope this helps.

[Golnaz]

thank you Masoud for your reply...
i will try that..
but how dose fluent realise that this input value in the uds diffussivity is the electrical conductivity...?!
especially that its showing the unit as kg/s..
many thanks

[MASOUD]

Well, Fluent doesn't have to recognize what that is.

The UDS equation you probably are going to define is :

D[-(Electrical Conductivity) x D(Potential)]=(0 or Volumetric Current Density)

These terms just have to be consistent. If you define the first term in S/m and specify the electronic potential boundary condition in Volt and the source term in A/m3 you will be all set.