I check the equation given in the manual of MOLFLOW+:
P=4QMChits/DesAV, where P is the pascal unit.
My questions are:
How and where does the relation come from? What is the relation between MC hits and out-gassing rate with Desorption?
We all know desorption and out-gassing particles are the same for the UHV system then why does MOLFLOW+ show in a different form?
What are virtual particles and how does it calculate the total number of particles in MOLFLOW+?
What is the equation meaning given in below:
Kreal/virtual=sum of dNreal\dt/Nvirtual
and thanks for using Molflow+ and coming to this forum.
The equations that you are questioning come from the kinetic theory of gases, after some renormalization to the units used in Molflow+ (i,e. centimeters for the lengths, cm2 for the areas and liters for volumes, while SI units would need to have m and m2, and m3 for volumes).
Molflow+ can’t simulate the REAL number of molecules in a vacuum system, simply because there are too many even at extremely low pressures. These formulae allow a sampling of this large number, attributing to each VIRTUAL particle in Molflow+ a weight which converts it into a fraction of the REAL number of molecules in the system. This weight (a conversion factor) clearly changes as the simulation progresses, because the initial virtual molecule in the simulation corresponds to the total number of real molecules, while after the program has generated 1 million virtual molecules the weight is reduced by 1/1million. It’s a straightforward calculation which is done automatically in Molflow+ for the user, you do not have to worry about it. Plus, it has been tested and retested since late 80s when I first wrote the code under DOS in TurboPascal and FORTRAN. In addition to that, Molflow+ has been validated against experimental data and analytical formulae when they exist, and cross-checked with the results of many papers in the gas dynamic literature.
Thank You for the clearance.
But my question is why desorption and out-gassing rate (terms gas-flux in MOLFLOW) are differently shown in molflow and why both the parameters take part in the calculation if both are the same?
Kindly clear this on, please.
Could you help understand the question? What or which part of Molflow do you refer to as outgassing (facet physical parameter?) and what as desorption (hit count?)?
If I calculated the value of density and pressure of an addition facet numerically, the value matched with the MOLFLOW+ tools calculated value, but when I calculated in the pumping area using the same formula the results of pressure and density can not be matched with the value given by MOLFLOW+ tools.
I send a drawing to you where a chamber is connected with a pump. I used the simple equation PV=NRT for calculating density in molecules/cubic meter and for pressure in Pa.
and thanks for using our code and for inquiring on this forum.
Be careful when you compare pressure and density via the PV=nRT, because in front of surfaces where gas is desorbed or there is a “strong” pumping (i.e. sticking coefficient) there is no “conversion” possibly between the two via the said equation. The reason is that density is just a number, while pressure in molecular flow is NOT a scalar value, it is a vector depending on the orientation of the facet.
Unfortunately the data you give are not enough for me to examine your model and tell you exactly what’s going on… if you can somehow send the zip file then I’ll look at it, promised.
Also, please update the version of Molflow+ you’re using!
