Air flow through a 2" orifice

[Powerman81]

Hi,

I need to calculate the air flow through a 2” wall penetration between 2 rooms based on pressure difference of up to 1” of water. I am assuming that the penetration can be modeled as 2” round edge orifice. Crane Tech paper 410 provides the necessary equation for calculating the air flow for compressible and incompressible fluids.

My question is do I need to include the expansion factor Y and assume compressible flow or not.

Any help would be appreciated

Thanks

 

[hacksaw]

the expansion factor approaches unity for differential pressure << abs. pressure, so yes

 

[BigInch]

for 1" water differential (0.036 psi) air does not need to be assumed as compressible, unless one room's pressure is almost a complete vacuum.

If you had rooms with absolute pressures approximately atmospheric, expansion would only be (14.7 + 0.036)/14.7 that's only 1.002 x the volume in the lower pressure room.


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[quark]

The old equation for calculating leak rate across rooms is 2910xAxdP[sup]1/2[/sup], where A is area of opening in sq.ft and dP is differential pressure in inches WG. I still use this equation for design flow balancing in HVAC Systems.

You can use incompressible fluid flow equation, as suggested by BigInch. The best method to assess the leakage is Blower-Door Test.