Hi All, I’m a bit new to this molflow+ software. I need to develop a model to calculate the conductance of pipes and connections leading to the pump from the cryostat. Cryostat top flange has a diameter around 400 mm. Cryostat is connected through a series of pipes with bends to the vacuum pump and KF25 (25 mm diameter) is used as the vacuum port on the cryostat. I am thinking of modelling only the pipe system and I need to figure out the sticking factor that needs to be used on the KF25 port placed on the cryostat. Is it reasonable to use a sticking factor of 1 at the cryostat end and pumping speed from the specifications at the vacuum pump end? (or do I need to use a different sticking factor?)
It’s correct to only model the pipes, not the cryostat or the pump.
The method depends on what you want to calculate.
If you want to get the conductance:
set both cryostat and pump flanges to sticking 1
release particles (outgassing) at any rate from the cryostat flange
make a formula that counts the ratio of particles making it to the pump flange: assuming the pump flange is facet 123, the formula is A123/SUMDES
That gives you the transmission probability, which you need to multiply by the inlet conductance (11.7l/s/cm2 * area_cryostat_flange_cm2) to get the conductance
The cryostat is the system you want to pump, so it will be outgassing. Set outgassing to 1mbar.l/s and sticking to 0, as you want the net flow towards the pump to be 1mbar.l/s (without particles going back to the cryostat, which would decrease that net flow).
Then set a realistic sticking on the pump flange, corresponding to the pump’s real pumping speed, as given by the manufacturer. Molflow converts between pumping speed and sticking.
Using p=Q/S, you can get S (effective pumping speed), since you know Q (1mbar.l/s), and molflow calculates P near the cryostat flange.