Hello, I am simulating a tube with 2 curves through which water-vapor is sent. Fluent has problems to solve this when I set a heat flux profile (udf) as a boundary condition. I am using ideal gas law for the density of water-vapor. With under-relaxation factor 1 for energy the solution shows divergence and gives error: temperature limited, turbulent viscosity limited. With lower under-relaxation factor the simulation convergence goes too slow. I already tried to solve flow and energy separately. Does someone know what to do about it? Thank you.

Hello Kaatje,

can you please give some more info. A double bended tube can have strange physics, so maybe the physics cause problems.

Is your model converging without the UDF? What flow inlet velocity do you have? Is it mass flow in - pressure out?

cheers, Laika, still orbiting

There are some simulations without the udf but with constant heat flux or constant temperature as boundary condition that converge. But with increasing heat flux they show divergence. I also managed to do one simulation (operating pressure=4.025 bar) with the udf that converges but when I try to do the same simulation with a different operating pressure (4.035 bar) the simulation isn't converging anymore. The inlet velocity with the ideal gas law is about 30 m/s (mass flow inlet=0.29 kg/s). I use mass flow in and pressure out. Kaatje

Hi Kaatje,

how does your mesh look like?

Does it diverge rigth from the start, or after a while?

cheers, Laika, still orbiting