conductance of Conical Shape cone

General discussion
1

Hello I would like to pump out the gas from the connected cylinder and conical cone as in attached file. 

I know the pumping speed at the outlet.

I would like to caculate conductance at the entrance.

Could anyone help me please?

Thank you very much in advance.

/sites/molflow.web.cern.ch/files/u366/conductance.zip

 

2

Hello:  

  I have downloaded the file and looked at it.  

  There are 2 desorbing facets... so it is difficult for me to tell what conductance you want to calculate... from where to where.  

  Usually one should have ONE desorbing facet and ONE exit, and both facets should have sticking =1 , so that the transmission probability P_tr can be calculated.  

  Once P_tr is known, the conductace C_tr is obtained by multiplying P_tr times the area of the desorbing surface (in cm2) times a kinetic factor.  

 I also see that facet #2, at the transition between the cylindrical part and the conical one, is SOLID, i.e. it has opacity=1... I guess you wanted that to be transparent, i.e. opacity=0.  

  If I change it to opacity=0 and desorb from facet 1, I get the conductance C_tr to facet #3 of ~1953 l/s (for mass 28 and 293.15K = 20C).  

  I have reversed the inlet-outlet in the copy of your geometry (see attached file), where facet 1 become facet 84 and facet 3 becomes facet 86.  

  I have also defined 4 formulae (press Alt-F to see them).  

  I include the new file I made, and two screenshots showing the textures from two different directions.   Notice that in order to get the correct pressure calculations for the textures on the facets with sticking 1 and (eventually) desorbing, you need to check the boxes "Count reflection", "Count desorption", and "Count absorption", in the "Advanced facet parameters" menu.  If you don't do that you do not get the correct pressures!  

  In the two screenshots I have "hidden" the two transparent facets at the edge of the cylinder to cone, by selecting them and un-checking the boxes "Draw volume" and "Draw Texture" and pressing the "Change draw" in the same "Advanced facet parameters" menu... that's a way of hiding facets which you do not want to be visible.

  Hope it helps, if not write back... no problem. :-)  

  Cheers,    Roberto

 

3

Me again... the two screenshot and linked file did not appear... don't know why... sorry about it.

conductance_and_reversed.jpg
conductance_and_reversed.jpg1919×1079
conductance_and_reversed_2.jpg
conductance_and_reversed_2.jpg1919×1079
/sites/molflow.web.cern.ch/files/pictures/conductance_and_reversed.zip

4

Dear Roberto,

Thank you very much for your detail reply.

It helps a lot. 

1. I would like to pump out gas from face 3 to face 1. (Inlet =face 3 and outlet=face 1)

And I would like to know Conductance of face 3. 

I tried as in attached file, but my conductance is far away from that of other program.

2. I would like to know how to get individual conductance for cylinder part and conical shaped parts.

Thank you very much again.

/sites/molflow.web.cern.ch/files/u366/conductance%20rev.zip

With best regards,

Nang Htwe

5

Glad to be of help, Nang.

Tell me one thing... what is "the other program", and what value does it give you for the conductance 3-->1?

 Let me know, please.

  Anyway, I just noticed that in your new file you generate molecules on facet 1, so you're calculating the conductance to 1-->3. Also, your formula is not correct, it reads...

  A3/D1*11.77*AR3

  ... while it should be A3/D1*11.77*AR1 ... the area is the area of the desorbing facet, in your case no.1.

  For the 3-->1 conductance case, as per your description above, the formula should be changed to 

  A1/D3*11.77*AR3 

  ... after you remove desorption from facet 1 and set it to facet 3.

  Cordially,

   R.

6

Dear Roberto,

Thank you very much for your help.

It works.

The program is just inhouse one.

Now I follow your example and my results become perfect.

With best regards,

Nang