Screw compressors intermediate pressure estimation

[jimbio]

Hello,

I'm trying to create an excel sheet where I can simulate screw compressor but I can't understand how to estimate intermediate pressure.

I've tried using pi=(p1*p2)^.5 with no results.

I've also tried using intermediate Vi without success.
pi=p1*Vi^k

The situation gets worse if I try with partial load where intermediate pressure is close to suction pressure (because of slide valve opening).

Is there any equation???

Thanks in advance

 

[crjones]

You might look through some of te work by Stosic at City University of London

 

[jimbio]

Thanks for the suggestion.

Those books are too expensive... and I only want the equation...

Using compressor manufacturer' software I drawn two diagram:
- suction pressure (x) vs intermediate
- discharge pressure (x) vs intermediate

and in both of them I found that intermediate pressure is linearly dependent on them...

I think that the equation could be

pi = a*p1 + b*p2 +c

The drawing shows that a>>b,
but I have no idea on their values,
and I have no interpretation of real mechanism...

Bye