Choked Flow at Orifice For Water

[RJB32482]

Hello,
What is the determination of "choked" flow of an orifice in water applications? Is it where the velocity of the water reaches sonic velocity? Or is there another scenario about choked flow?

Is there a calculation to determine choked flow through an orifice for incompressible fluids?

Thanks.

 

[Latexman]

Technically, yes, liquid water will choke at it's sonic velocity. Practically, there will probably be some good reasons you don't want to flow water at a velocity near 1 mile/second, like the energy required/loss, noise, erosion, pressure transients, and maybe others.

Good luck,
Latexman

 

[sailoday28]

Consider the effect of temperature-flashing will probably choke the flow before sonic velocity is reached.

 

[mbeychok]

RJB32482:

Read this this Wikipedia article:

http://en.wikipedia.org/wiki/Choked_flow

Especially this paragraph:

If the fluid is a liquid, a different type of limiting condition (also known as choked flow) occurs when the Venturi effect acting on the liquid flow through the restriction decreases the liquid pressure to below that of the liquid vapor pressure at the prevailing liquid temperature. At that point, the liquid will partially "boil" into bubbles of vapor and the subsequent collapse of the bubbles causes cavitation. Cavitation is quite noisy and can be sufficiently violent to physically damage valves, pipes and associated equipment. In effect, the vapor bubble formation in the restriction limits the flow from increasing any further.

References:

http://www.fisherregulators.com/technical/sizingcalculations

Scroll to discussion of liquid flashing and cavitation

http://www.documentation.emersonprocess.com/groups/public/documents/book/cvh99.pdf

Search the PDF document for "Choked"


Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[CJKruger]

RJB32482, the explanation from mbeychok is correct. The only "catch" is that vaporization needs time. So, if you have a sharp edge orifice, then flashing will not choke it. For stable choke flow you need a nozzle length of 4 inches. Between 0 and 4 inches, what happens is anyone's guess.