Relationship between irregular shape and stardard oriifice size.

[Abiodun1]

Hi,

I need information on how to generate the relationship between irregular shape to standard orifice size. I want to use in calculating the flow of fluid through the orifice.

I would appreciate urgent responce.

Thanks

 

[dcasto]

We use a circular area in orifice because it is repeatable and simple. Then we used emperical results to generate the equations for metering. If you read Miller and Spinks along with AGA3, there was some work done on putting a "weep hole" at the bottom of the orifice to allow liquids to drain from time to time. The resulting data inducated that if the area of the weep hole is added to the area of the orifice and a new pseudo diameter is entered into the equations you can get resonable results. I don't recall error analysis results but +/-3% from base isn't bad.

NOW, could this idea be expanded to say a square hole, I believe it will get a resonable result. It might make for an interesting comparison.

 

[zdas04]

A significant portion of the AGA-3 arithmetic is empirical. A key feature of empirical equations is that they are rarely very scaleable. This particular equation is very sensitive to plate thickness for example. I would guess that any non-circular hole in a plate of random thickness would give you numbers that don't relate in any predictable way to measurement.

It all depends on what you are trying to do. If you are replacing a +/-50% guess on a vent flow, you'll probably get better numbers. If you are doing custody-transfer measurement, you'll probably get sued. I don't think that I'd rely on an irregular orifice for a plant material balance, but then I've spent too much time on that sort of exercise where a +/-10% device generally results in too much uncertainty.

David