Air speed in a pipe 1

[Aptx4869]

Hi all,

We have the below parameters taken from our control system, and using below data I calculated the air speed and got around 66.4 m/s which is quit high

Data:

Air Temp: 605 F
Air Pressure: 121.6 psig
Calculated mass flow rate (calculated by control system): 25.6 lbm/s
Valve opening: 100%
Pipe size: 8 inch

Am I missing something in my calculation ? I got a speed of 66.4 m/s

I used the below table for air density

https://www.engineeringtoolbox.com/air-temperature-pressure-density-d_771.html

 

[btrueblood]

Looks about right.

I'd look into how the mass flow rate is measured/predicted/calculated.

 

[EdStainless]

I agree, maybe an issue with units?
8 is large pipe, but 26 lb/s is an awful lot of air.
What volumetric flow did you use? And what flow in ft/sec?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[LittleInch]

How is the control system calculating the mass flow.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[pierreick]

Hi,
Sounds reasonable to me
Pierre


P abs 136.3 PSIA 939755 Pa
T 605 F 591.483 K
Mw 29 g/mol
Ro 5.541921322 kg/m3
d 8 inches 203.2 mm
S 0.032429279 m2
Qm 25.6 lb/s 11.612 kg/s
Qv 2.095302211 m3/s
V 64.61143441 m/s

 

[Aptx4869]

not sure how the control system calculates the flow. I will have a look at it

 

[katmar]

A velocity of 66.4 m/s is towards the upper end of the normal range for high pressure gases but is by no means absurd. There are different reasons for wanting to limit the velocity of fluids and you should consider what reason there is to limit the velocity in this particular case. The most likely reasons for a clean gas are to limit the noise or to limit the compression costs.

Also, remember that this velocity is at the upstream end of the pipe. If your pipe is 400 meters long the velocity at the downstream end will be double that at the beginning.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[Snickster]

The velocity you calculate looks correct. Normally velocity in compressible gas flow is limited to 60 ft per second to limit noisy piping. In relief systems velocity is allowed to reach higher levels up to sonic velocity at pipe exist as long as back pressure does not limit relief valve flow.

 

[hacksaw]

The velocity is a worse case estimate, with valve full open.
The normal flow will typically be far less from start to normal operation.