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Paddler
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Join Date: May 2007
Location: Sweet home Alabama
Posts: 144
Good Answers: 7

Gas Flow Forces

05/15/2009 3:43 PM

We are calculating forces around piping and have some problems with the initial flow development.

Does anyone have experience with the the flows and flow dynamics in a piping system with the initial surge of flow. Our situation is natural gas at 1440 PSIG venting through a two inch full port valve to a vent stack.

I understand what is happening after the flow is developed with a standing shock wave somewhere at end or change in diameter.

What happens during the time between no flow and fully developed flow? I understand that an expansion wave travels upstream to the source and a travelling shock wave travels downstream to the end.

Maybe the question is can we open a 2" valve fast enough to create a shock tube effect?

Is this a way to get supersonic flow for a short time without a converging diverging nozzle? How would it revert back to sonic flow?

Thank you,

Paddler
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nick name
Guru

Join Date: Mar 2007
Location: City of Light
Posts: 3943
Good Answers: 183
#1

Re: Gas Flow Forces

05/15/2009 6:41 PM

Most probably not, at least at 1st view. The opening time to generate a shock wave has to be very short. In shock wave generators the opening is obtained in some designs with the burst of a diaphragm. A valve will never have such a short opening time.
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Anonymous Poster
#2
In reply to #1

Re: Gas Flow Forces

05/15/2009 8:28 PM

Any idea how flow might develop? I suppose there might be a normal shock at the ball valve as it opened, but after it was opened, the shock would have to move to the end of the pipe. How does this happen?
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nick name
Guru

Join Date: Mar 2007
Location: City of Light
Posts: 3943
Good Answers: 183
#3
In reply to #2

Re: Gas Flow Forces

05/16/2009 6:58 PM

The dp/dt depends on the opening speed, the lower the da/dt (section/time) the lower the amplitude so that you cannot ant more consider it as a "shock wave" but only as a pressure wave. The wave amplitude and speed will depend on the pressure in the volume to which the gas flows.
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