Boundary Condition Heat Exchanger counter-corrent
 

Hi, I'm studying this Heat Exchanger:

http://img593.imageshack.us/img593/2238/scamb.jpg

I've used these boundary conditions, with ideal-gas model: 2 mass flow inlet (for the inlet of the two gases) and two pressure outlet, fixing for all of them pressure and temperature.
When I try to iterate I've this problem:
"Error: divergence detected in AMG solver: temperature"


I don't know what is the problem because if I use Incompressible ideal gas or Costant Density I have a solution. But With normail Ideal Gas Model I've that error. Can someone help me?

Thanks!