Air flow in vacuum vessel 2

[Braagaard]

Hi there

I need some help calculating the pressure in a vacuum system.
I have a vessel to witch a vacuum pump is attaced. The pump provides a
flow of 400 m3/h at 20"HG. If the vessel i a closed vessel it is easy to calculate the vacuum and the time to create it. But if I make some holes in the vessel, how do I calculate the highest possible vacuum?

The holes can be from 6 mm up to 20mm in diameter and there can be from 4 to 7 holes i the vessel.. As I see it, it must be the different between the possible flow trough the hole depended on the air velocity and the flow that the pump provides. If the hole is under app.8mm the air velocity will be the speed of sound witch is possible for me to calculate.
How do I calculate this?

Thanks in advance.

Anders Braagaard

 

[pipehead]

I'd graph or set up the sonic equation for the holes. to solve for volume that will enter through the holes based on the differential pressure from atmosphere to vacuum. Then you need the capacity of the vacuum pump as a function of suction pressure (I do not know of any vacumm compressor that moves the same volume at atmospheric pressure and 19 inHg). Then when then itererate or used ecxcel goal seek to solve for the vacuum that staisfies both equtions or graph.