Velocity of compressed air inside pipe
Velocity of compressed air inside pipe
(OP)
Can I use moody diagram for compressed air or there is some other mathematical simulation for this case?
I want to calculate basically friction loses inside compressed air pipeline.
Thanks in advance.
I want to calculate basically friction loses inside compressed air pipeline.
Thanks in advance.





RE: Velocity of compressed air inside pipe
RE: Velocity of compressed air inside pipe
The first step is therefore to calculate it from the Moody diagram as you would for a liquid and see what pressure drop you get. If it is high then redo it using a method that takes the compressibility into account.
RE: Velocity of compressed air inside pipe
If turbulence is controlling, that is a very high Nre, the friction factor is in basically independent of position along the pipe. If not,then a mean friction factor has to be determined over the length of the pipe, perhaps based on an inlet and outlet Nre.
Dependent upon the pressure and temperature, an estimate of compressibility factor, Z, should be made. If in the range of expected pressure and pressure drop, Z is approximately constant, then a perfect gas approach is satisfactory. Otherwise, an equation of state or use of a Mollier diagram for air should be incorporated is solving for the pressure drop/friction losses.
Heat transfer is another factor to be considered.
Does this answer the original question?
RE: Velocity of compressed air inside pipe
I will look for the mollier diagram
RE: Velocity of compressed air inside pipe
I would highly recommend getting a copy of Crane Technical Paper 410. An extremely valuable resource for pressure drop calculation work.
Deals with Liquid and Gas.
RE: Velocity of compressed air inside pipe
RE: Velocity of compressed air inside pipe
Notwithstanding the procedural advice:
Your pressure distribution and flow rates will be different with and without the "permeable material". You need some information concerning the flow characteristics of such material in order to calculate the changed flow path.
If shock waves are not involved in the flow, the discharge pressure of a "free jet" will always be atmospheric pressure (essentially by definition).
The previous post recommended Crane Technical Paper #410. You would also probably benefit from some of the information in TP-410.
RE: Velocity of compressed air inside pipe
The system is essentially being built to measure perm. rates of plastic films. I thought hitting a 6" diameter section of material with a known pressure would give me a distinction of which one would hold up best. To my knowledge, flow char. are unknown, hence this setup.
Regardless of the material, why would I be seeing an extremely high negative pressure at p2 (the 0.25" pipe)?
BTW, I'm neglecting shock waves out of simplicity.
I'll check out the T.P. as well.
RE: Velocity of compressed air inside pipe
RE: Velocity of compressed air inside pipe
Pressure drop is not given. SCFM is also dependent upon upstream pressure and upstream temperature which are not given.
If orifice flow diam is small compared to pipe size, then upstream flow velocity can be neglected for an approximation of the flow.