Restriction orifice plate

[sbnz]

We have to design one (multiple?) restriction orifice plates in a DN150 (6"), 7 barg water line to reduce the pressure to 4 barg.

I do not have a copy of the BS/ISO standard readily available and am trying to look for other sources to calculate the orifice size. My initial questions are:
a) Is there a limitation of the pressure drop possible in single orifice plate? (I have a recollection of max dp = 0.75x upstream pressure - can't be sure if that was a rule of thumb or validated based on fluid mechanics)
b) struggling my way through to calculate flow coefficient (Cf) from 1st principle - suggestion/ web references will be much appreciated.
thanks,

 

[BigInch]

1) Try this,

http://www.engineeringtoolbox.com/orifice-nozzle-venturi-d_590.html

2) Search Eng-tips for this much (overly) discussed topic.
There are also tons of net references and a number of online calculators.

ISO 5167

http://www.pressure-drop.com/Online-Calculator/pda/0901.html

3) Come back if you still have a question.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[athomas236]

If you base your calculations on tapping positions of 2.5D upstream and 8D downstream then the pressure differential calculated by orifice formula approximates to the pressure drop across the orifice.

Regards,

athomas236

 

[katmar]

The basic strategy is to ensure that the pressure does not drop to below the vapor pressure of the liquid, and then recover to above the vapor pressure. If this happens, bubbles will form and then collapse making it a noisy process.

The problem was discussed in thread378-125921 where a link was provided to download an article by Tung and Mikasinovic which gives a detailed design procedure.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[sbnz]

Thanks BigInch and Katmar for very useful help.

Katmar - the link for the technical paper in the old discussion thread does not work any longer (expected, the thread dates back to 2005). By chance, would you have a copy of the paper or any other reference?

thanks all once again, I am getting the confidence towards a correct design approach.

 

[Latexman]

Scroll down in the old thread. References are provided with no link in one of the post so you can track down the articles.

Good luck,
Latexman