[sTARLIGHT4]

Hello!
This is my first time modelling condensation and my goal is to simulate steam (one of the initial conditions sets: at 5 bar, 153 C and 20 m/s) flowing and condensing in a long pipe with sides that are at 40 C. I'm using Fluid film model, Multiphase Gas and Liquid, Segregated flow and Implicit Unsteady model.
Step 1: I followed an official StarCCM tutorial with 50% steam and 50% air mixture flowing in a pipe (mixture is flowing at 1 m/s and is at 28 C, pipe is at - 30 C) and managed to recreate it without any problems.
Step 2: I changed the mass fraction of Air to 0 and steam to 1 - simulation diverged, I deleted Air from Multiphase gas and set Water mass fraction to 1 - again it diverged
Step 3: I set the mass fraction of Air to 0.01 and steam to 0.99 and changed initial conditions to the temperatures I want - simulations diverged
Step 4: I tried setting a small initial value (1e-4 mm) for Fluid film but simulations still diverged
Step 5: I tried initialising the simulation with the results of a simple Steady state sim with identical initial conditions but without condensation - this didn't help
I tried many other things, changing some settings, switching Segregated to Coupled solver...
Edit: I also tried switching to Antoine equation for saturation pressure and googled correct coefficients, but that didn't help either.
What am I doing wrong and what else can I try? Thanks!

[cwl]

Step 2: I changed the mass fraction of Air to 0 and steam to 1 - simulation diverged, I deleted Air from Multiphase gas and set Water mass fraction to 1 - again it diverged
Step 3: I set the mass fraction of Air to 0.01 and steam to 0.99 and changed initial conditions to the temperatures I want - simulations diverged

What are the relative humidity and expected/estimated condensation rate under these conditions?

[kdfluxit]

Dear sTARLIGHT4:
I am also interested in simulating condensing flow with Star ccm+.
I have installed Star ccm+ 2020, but I can not find the tutorial on condensing flow simulation in the official documents of this version.

Could you please (a) share the file about simulating the condensing flow, or (b) share me a link about the tutorial?