Air - Orifice coefficient 1

[ddsancho]

Hello,

In my machine, atmosphere air goes into my vacuum system through some holes.

Trying to apply the following formula, I would like to know where I can find the K coefficient.

h = K * Q2

h: pressure drop
Q: flow
K: Constant flow

The orice is 2 mm diameter, in a 3 mm thikness wall.

Thanks,

 

[Eltron]

There is an abundance of information about gas flow through a orfice at the O'Keefe Controls web page:

http://www.okcc.com/default.htm

Check in the catalogs for specific flow calculations and empirical charts.

Hope that helps.

 

[ddsancho]

Thanks Eltron,

The information you gave me is good but I am looking for hole flow coefficients at low vacuum pressure:
0 - 0.3 psig
0 - 1 inchH2O
0 - 200 mmH2O

 

[Eltron]

For subcritical flow through an orifice you can use the equation : Cv = (Q / 962) x SQRT((SGx x T) / (P12 -P22))

Where:

Cv = Coefficient of flow
Q = Gas flow rate / ft3 / hr
SGx = Specific gravity of gas x
T = Temperature / ?R
P1 = Inlet pressure / psia
P2 = Outlet pressure / psia
SQRT = Square root

I know vacuum calculations seem a little weird, especially first thing in the morning. Just look at it as being 0-200inH2O below whatever your atmospheric pressure is, and the numbers should work out fine.