When using a bellow in a vacuum system they have all the same dimensions but are differently bent. My goal is to simulate different conductance losses of pipes that have the same length and diameter but are differently bent.
Does this make sense at all, as the simulation/calculation is based on straight pipes?
Also in my experiments I adjusted a constant pressure on the downstream side of the pipe, as well as the pumping speed of the pumps was on the same side (see figure below).
And now I’m not sure how to simulate this in Molflow.
Maybe a high desorption on the downstream side of the pipe attached to another pipe that has a facet with a pumping speed? Then increasing the desorption of the facet as long as it reaches my desired pressure?
As molflow simulates molecular flow this simulation makes only sense for pressures below 1E-3 mbar as above will start the Knudsen flow right?
Your help is very much appreciated as I’m not sure if all the time that I already spent on this was worth and is still worth it.
It is listed in our web site’s Articles List, 2019.
2.Yes, I think you should do that. Set sticking=1 on a facet (or other value) and then changing the desorption from the same facet until it reaches the pressure you want it to stabilize to.
Correct: in the transition regime, when the inter-molecular collisions are rare/not too frequent you can get a result which is not far from the one obtained using more sophisticated codes (like Boltzmann equation or DSMC), I’ve checked that many times with papers in literature. Once the mean free path becomes too short for your geometry, then you can’t use Molflow+ anymore, you must use some other viscous flow simulator (our colleagues here at CERN working on high-pressure components often use LTspice and the Electric Circuit Analogy method… where you can use the time-dependent simulation with pressure-dependent pumping speeds (as per factory’s data).
