orifice pressure loss 2

[kagadpencil]

I am looking for a formula for the pressure drop in an orifice. I know the flow rate through the duct in which orifice is fitted. My orifice is square edged. I was looking at CRANE Technical paper 410 - A-20 - But the geometry of orifice does not quite match with mine. I also looked at Handbook of Hydraulic Resistance by Dr. Idelchik. But the relations given are only for thick orifice.

Can someone please show me the reference where I can fine resistance coefficient for a thin square edged orifice?

For the time being, I am going along with the CRANE 410 relations hoping that they will not give me too different relations -- will they ?

 

[RWF7437]

Try King's Handbook of Hydraulics

 

[iainuts]

The discharge coefficient for a square edge orifice will vary slightly over the range of flow. For a gasseous medium, I've always used 0.81 when choked. If it's not choked, the discharge coefficient tends to drop slightly as flow drops, to about 0.7 for very low dP.

I don't know how that compares with liquids.

Crane 410 is the right source for pressure drop calculations.

 

[katmar]

Perhaps I am stating the obvious, but remember that there are two aspects to consider in looking at the pressure drop across an orifice.

Either you want the pressure drop in order to calculate the flowrate through the orifice, or you want the permanent pressure drop as part of an overall piping pressure drop calculation.

If you are calculating the flowrate then you need the correct equation for the geometry of the plate and the tappings, because you want to get it spot on.

However, if you are doing an overall piping calculation the Crane 410 method will be accurate within the uncertainty of the other elements, and as iainuts has said, its the way to go.