pressure loss

[BlueGlow]

I am designing a test loop that will have water flow (~30 gal/min) through a 4 cm pipe with an orifice of about .75 cm. I cannot find any information about approximate pressure drop accross an orifice with such a small diameter ratio. Does anyone have a back of the envelope equation I could approximate this loss (+- 10 psi)? Thanks

 

[smckennz]

Hi Bluegow

try:

((V2^2-V1^2)^0.5 = (alpha)(2 X g X Htap)^0.5

Permanent Pressure Loss (PPL) = (1- d^2/D^2)

V2 is velocity through orifice in m/s
V1 is velocity down pipe m/s
alpha is the discharge coefficient normally about 0.61 (better values in fluids books)
g is gravitational acceleration 9.8 m/s^2
Htap is the head difference immediately across the orifice in metres of fluid
d is orifice diameter.
D is downstream pipe diameter (infinite for open end so PPL=1 in open end case. Units consistent with d.

So the head loss caused by an orifice in a pipeline is
PPL X Htap

As d/D approaches 1 the results become less accurate.

Cheers

Steve

 

[m777182]

The ISO 5167-1(1995)gives calculations for a dP through an orifice but there is a limitation: d(orifice)>=12,5mm and d/D(pipe)>0,2....0,75. So your rates are slightly out of the range and the estimations will be less precise.
M777182

 

[FredGarvin]

ASME does have a standard for flow through small orifices.

American Society of Mechanical Engineers (ASME). 2001. Measurement of fluid flow using small bore precision orifice meters. ASME MFC-14M-2001.

You may also try this:

http://www.lmnoeng.com/Flow/SmallOrificeLiq.htm

 

[mohtogh]

There is an old method for estimating shut off head of pump (means maximum attainable head in zero flowrate).
Follow this link:

http://www.mcnallyinstitute.com/13-html/13-07.htm

 

[mohtogh]

sorry wrong place.

 

[sailoday28]

Velocity thru orifice seems to be pretty high. Dependent upon upstream pressure, you might check for cavitation at orifice.
Also, I expect a large delta p. Will thickness of orifice be adequate to take the force created by the pressure drop?