[Nishant_Sharma]

Hi all,

I am using a Species Transport model in simulating a fuel cell problem, and I am defining the diffusivities of all the species by using UDF, although the fluent is showing an error,
Warning: Mass_Diffusivity: invalid (zero) diffusivity.
Please check material properties.

Also, when I tried it on another PC, no such error is shown, but in my previous pc, it shows the error and the simulation won't run. Can anyone please tell how to remove this error.

Thank you

[rewol]

When i need to define mass diffusivities through UDF, i usually make all diffusivities of all species equal to 10e-12 at first even though mixture is composed of a single specie initially.(For instance, before combustion)

[Nishant_Sharma]

Thanks rewol for your reply, but I have defined the diffusivities of all the species already, still it is showing this error

[rewol]

Did you use mixture-averaged multicomponent diffusivities ?
The reason i am asking is because, when calculating D_i,m for example, in case of pure specie, D_i,m might still be zero.

[Nishant_Sharma]

Hi rewol,

Now I have figured out what was the problem, there are some extra species in my model, which cannot be removed, and since I have defined the diffusivities of species whaich I have created by myself, the diffusivities of other species are not defined, which is creating the problem.

[nmk539]

sir how to write udf for mixture mass diffusivity ie Dij diffusion of species i in j actually i am simulating pem fuel cell i found in paper authors are using binary mixture diffusion coefficient how to write udf
equation is as follow
P*Dij=a*(T/sqrt(TciTcj))^b*(PciPcj)^1/3*(TciTcj)^5/12*(1/Mi+1/Mj)^0.5
sir please share udf if you have made it already
thanks in advance