[SalvoCalvo]

Hi All,

i'm a new user of Comsol 3.5. In this moment i'm experiencing some problems of convergence to solve a steam flow in a pipe of 4.75 mm.

The flow is driven by a gradient pressure between the inlet and the outlet:
- inlet 500 kPa
- outlet 100 kPa (approx. atmospheric pressure)

I'm using the chemical engineering module>flow with variable density>non-isothermal flow>k-w turbulence model>steady state analysis because i'm interested on looking into also the temperature in the pipe as the steam's temperature at the inlet is 121°C.
I set as initial condition of temperature for the gas domain 298K. I used the material library of comsol to set the properties of the steam (there is exactly steam in it).

Boundary condition for the turbulent weakly compressible flow model are
-inlet: pressure> no viscous stress 500 kPa (default settings k0 turbulent kinetic energy 0.005 m^2/s^2 and w0 specific turbulent dissipation rate 10 1/s)
-outlet: pressure> no viscous stress 100kPa
-walls of the pipe: wall> logarithmic wall function (default setting deltaw=h/2)

Boundary condition for the convection and conduction model are:
-inlet: 394,15 K
-outlet: convective flux
-walls of the pipe: -1 W/m^2

The simulation does not converge. I've tried in different way...also with a lower pressure as 150 kPa doesn't converge! It converges only deactivating turbulence model and setting as inlet condition a low velocity inflow i.e. 0.1 m/s.

Does anybody know how to do? Maybe k0, w0, h/2 for the wall setting are wrong? To be honest I don't know how to set them.

Thanks in advance for anybody could support me!

Salvo