Calculating air velocity due to pressure in a tank

[pwilkins]

I have a tank of dry, compressed air at 72F and 200 psi and a 1/4" ID hose as the outlet (L=25 ft, but I am not worried about friction loss right now). Maybe I am just missing a really simple calculation, but I am having trouble calculating the velocity at the end of that hose. Can someone help me out?

 

[ivymike]

Figure out what your nozzle shape is, and have a look at a compressible flow table?

 

[TD2K]

You'll be choked at the outlet, the velocity will be the speed of sound in air.

 

[DLite30]

Depending on which flow equation you use, it'll be between 250 and 350 mph.

 

[pwilkins]

Thank you all for your responses. Which flow equation is the appropriate one?

 

[sailoday28]

Since the tank is of finite volume, the velocity a the pipe exit will be changing with time.

 

[dgallup]

Not as long as the pressure ratio is above critical and the flow is sonic.

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[sailoday28]

The outlet pressure may be sonic, but as long as the source changes pressure and temperature, the velocity will change.

 

[dgallup]

First of all "sonic" refers to a velocity, not a pressure. When you have a pressure ratio (in air) above 1.893 the flow will be sonic and the velocity through the orifice will be constant. The mass flow rate will be a function of the upstream density but the velocity will not.

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

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[sailoday28]

Sonic refers to Mach Number =1. It is the ratio of a velocity to the sound speed. For the simple case of isentropic flow from a finite tank, the tank temperature will drop. In that case, with choked flow the sound velocity will drop. Therefore at Mach 1, the choked velocity will drop.