Orifice Flow/Pipe Entrance Loss Coefficient Question

[JoeChem]

Geetings,

Originally posted this on the Fluid Mechanics forum but no activity so I thought I would try here...

Was recently trying to calculate an accidental discharge of liquid from a tank (small hole) and was scratching my head about some things in Crane TP410 and was hoping to get some clarification. I was not sure if I should approach the leak rate calculation using an orifice equation or as a pipe entrance loss equation. This really boiled down to selecting a C for the orifice or a K for an entrance loss.

When considering a flow coefficient for an orifice, as the beta ratio decreases the approach Reynolds number decreases and C approaches 0.5 as shown on the graph on page A-20.

Struggled then with the formula given just below to calculate K for an orifice:

K = (1-beta^2)/(C^2 x beta^4)

K values begin to increase rapidly as beta decreases. The denominator is essentially 0 for low beta values, i.e., a small hole in a tank wall.

How do we make the leap to a pipe entrance loss K of 0.5? Wouldn't a hole in a tank wall be equivalent to an orifice with a beta ratio = 0?

Thanks in advance.

JoeChem

 

[Latexman]

This website may help you - Link

Good luck,
Latexman

Need help writing a question or understanding a reply? forum1529

 

[MortenA]

The rationale behind the 1 velocity height loss for sharp edged "exit" from tank to pipe (or a hole i guess) is that in the tank the liquid has no velocity.

But i think that the "beta method" is means for flow measurement orifices, where the D/Do ration is close to 1? So in general the beta method can not be used for holes or exits e.g. from tanks?

Best regards

Morten