I am using the following formulae for orifice sizing to measure gas flows .
b = d/D ; d is orifice dia mm, D is pipe ID mm
use b to get sm
1/(b^4) = (0.6/sm)^2 + 1
after getting sm , use the following eqn to get dp
sm = Q / ( 0.1264 x D^2 x sqrt dp x sqrt de x sqrt z x f )
Q = flowrate in kg/hr
D = pipe id mm
dp = differential pressure in Kpa
de = density in kg/m3
z = compressibility factor
f = thermal expansion factor (usually taken as 1)
Thank you very much indeed! This is the simplest form I have seen to date. The one I had used tables to look up the gamma factor etc. Excellent and thank you!
Please tell me what is this thermal expansion factor.
This was my first post and I am glad you found it useful. However the formula is applicable only upto pipe size of 2 inch. This formula is actually used for sizing intergral orifice plate assembly to measure flowrate of gas using a dp transmitter. The formula is apllicable to liquids also with slight modification.
On thermal expansion factor , I will let you know soon.
Why is the formula restricted to 2" and what do u use after that? How is it modified for liquids? I have noticed that you seem to assume a Cd (discharge coefficient) of 0,6. Is this correct?
Marius, It's known as the "area factor for thermal expansion of orifice". It's takes into account the change in orifice area and geometry at high temps and low temps. If it's not used, the eq. will give false results.
Thermal expansion factor is used to account for the expansion for the orifice opening at the process temp. This is readily available in std texts. If you cant find i will send you a copy for the most common moc.
For liquids the modified formula is
1/(b^4) = (0.6/sm + 0.06)^2 + 1
I am trying to find why it is limited in usage upto 2 inch dia. Will let u know as i have an answer.
Thank you for your most gracious assistance. The way in which you have helped me is highly appreciated because it has provided me with a solution. I hope that I can (soon) reciprocate.
