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Calculating Air Flow

by Cheesefry
Tags: flow
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Jun16-10, 04:07 PM
P: 2
The following is the only information that is given at this point in time:
Air flow through SS SCH40 1" pipe (ID 1.048"). Pressure required is 80 psi at the discharge point. Assume supply pressure is 100 psi and unlimited in quantity at a constant pressure, supplied from a tank. The pipe will discharge to atmospheric pressure.

I can't seem to remember how to determine how to calculate flow rate or velocity of the air based only on these values. I feel that I need more information to be able to calculate equivalent length at the very least, but even assuming a arbitrary length, I am having problems on figuring out how to approach this problem.

Any help here will be appreciated. (switching gears from chemical reactions to this stuff at 4pm is killing me)

I'll try to check back and answer any other questions so that I can get a quick answer.

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Jun16-10, 07:18 PM
P: 22,234
Welcome to PF.

80 psi is above the pressure for choked (supersonic) flow, so that is the maximum you could get air to flow through the pipe at pressure.

Also, these two sentences:
pressure required is 80 psi at the discharge point...

...The pipe will discharge to atmospheric pressure.
...contradict each other. The pressure at the discharge point is always atmospheric pressure and unless there is an orifice or some other obstruction at the discharge point, the pressure right before it will also be atmospheric.

So could you explain in some more detail what you are trying to do?
Jun17-10, 07:33 AM
P: 2
Sorry I didn't proof read what I wrote.

Anyways -
I'm trying to size an accumulator. It's for a cleaning cycle on a filter that requires a constant flow of 80 psi air for 5 minutes. The length of pipe is in question right now, but it would be safe to assume an equivalent length of 150 ft. Supply air temperature would be around 80 F. The compressor supplying the air to the accumulator supplies air at 100 psi.

Sorry for the confusion - I'll check back here throughout the day.

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