Species Transport Convergence

Emily

I am trying to eventually use Fluent's SOFC module and am having problems in the setup, namely the species transport model. I have a tubular SOFC geometry which has air flow through the tube at 873K and fuel, 89% H2 and 11% H2O, flowing on the outside at 1273K. The tube is made of a porous wall with a porosity of .3. When I run the fluid flow and heat transfer I have no problem but when I turn on the species transport model it causes the simulation to diverge. I get errors about temperature limits and reversed flow and then it diverges.

If I change the temperature of the flow it will diverge faster or slower depending on the numbers used but it does not make a big difference, I looked at temperature combinations between 800K and 1200K.

Can anyone offer me any suggestions about why this would happen? Or specific areas to look at?

Thanks Emily