Hi I am modeling a fuel cell in fluent. There are two mixtures (one air and the next H2 and H2O(vapor) at a temperature of 100 degrees centigrade). My problem is that I need the absolute pressures occurring at the interface of the mixtures and the solid separating region. The thing is that I will be able to set the reference pressures only at one flow domain. The pressures there are quite alright. In the other domain the pressures are negative. Will patching help? cavitation is not a problem as the fluid is gas. Will refining my mesh help? The size is 14.6x500 mm. So how much can I refine my mesh?

Another problem is that I need to provide multi-component diffusivity, but I can only give one mixture in fluent (not 2 as the physics say to me). So there are some diffusivities that i just have to give in my model that I don't have to give if I am writing my own code. Is there any problem with this????

The temperature is 1000 degrees centigrades. Please post a reply guys.

Pasted from previous reply,

Check the physics of the model. Check if there is any phase change. If you do not model this you may get the negative pressure. e.g. cavitation in case of liquid fluids. If the fluid is gaseous, switch on compressibility.

Secondly wait to get the full convergence. It may vanish after some time.

Hope this helps