Cavitation effects in round edged orifice entrance 1

[sykhan88]

I have been looking at pressure profiles and cavitational effects through sharp-edged orifice plates. How do these profiles, effects and the mathematical formulas change for round edged orifices? Are there any specific correction factors?

 

[ione]

The coefficient of discharge enters in the formula which relates flow rate and pressure drop through an orifice. Since cavitation occurs when liquid pressure drops below its vapour pressure, you can understand the way edge shape affects this issue.

As far as I know the coefficient of discharge is assumed to be 0.6 for sharp-edge and 0.98 for round edge orifice.

The only equation I am aware of for the coefficient of discharge is from ISO 5167 (Stoltz equation) that you can find at the link below.

http://www.lmnoeng.com/orifice.htm#equations

Hope it could help

 

[Mech85]

Hi Sykhan88,

Please refer to attached figure for "Correction Factors for Edge Radii" for orifice plates from Internal Flow Systems by Miller.

Hope this helps

 

[sykhan88]

How are these correction factors implemented in a formula?
Also, for the first graph, are the x-axis values ratios between orifice length and orifice cross section, or orifice cross section and pipe cross section?

 

[Mech85]

Hi Sykhan88,

Please refer to additional page for orifice plates from Internal Flow Systems by Miller. The X -axis on the first graph is the ratio of the CSA of the orifice divided by the upstream pipe CSA.

The Ko value for a sharp edged is simply multiplied by the correction factor Crad for rounded orifice edges as the pressure loss is less for these types of orifice plates.

Regards