Supersonic flow across Restriction Orifice?

[DoraeS]

Hi,

I would like to ask if it is possible to generate supersonic flow across a restriction orifice?
I know that supersonic flow can be generated by passing subsonic flow through a converging and then diverging nozzle, but I am not sure if the same will happen for an orifice.

Thanks.

 

[Latexman]

No.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[EdStainless]

An orifice should just generate choked flow. The shock waves will prevent further acceleration.


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P.E. Metallurgy, Plymouth Tube

 

[zdas04]

I like Latexman's answer, but I can't help myself from elaborating. In a diverging nozzle, choked flow (limited by the shock waves as EdStainless said) sees an expanding shock wave area and can pass Mach 1.0. Without that expanding shock wave the velocity is limited to Mach 1.0.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[Latexman]

I was in a hurry this morning, and didn't want to create a monster compressible flow thread like we've had in the past. Like mentioning thin-plate orifices, which don't really choke, and thick-plate orifices, that do choke.



Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[DoraeS]

With the answers collected here, I would expect the piping segment downstream of the orifice will not experience supersonic flow. Is this correct?
More specifically, downstream of a blowdown (or depressuring) orifice used in offshore gas processing or onshore gas plant, it is not possible to have supersonic flow?

Thank you.

 

[georgeverghese]

Yes, it is not possible to generate velocities approaching Mach 1 at a thick plate depressuring orifice. Engineering practices usually limit the velocity to Mach 0.5 at the piping segment downstream of blowdown orifices, coincident with the max built up backpressure.
Expressions for the max permissible compressible gas flow in piping segements can be found in Perry Chem Engg Handbook for either isothermal or adiabatic flow modes.
The max possible flow through a thick plate RO, for a given fixed upstream pressure, is high limited when the RO downstream pressure is at or below that corresponding to the critical pressure ratio. This ratio is a function of gas Cp/Cv ratio (at the upstream pressure) and the RO beta ratio.