compressible flow
compressible flow
(OP)
I have compressible flow thru a 2" x 200ft pipeline,air inlet at 25 to 30 psig, outlet 2 psig.
In using the complete isothermal equation, with this DP ratio, I believe it is appropriate to use the average specific volume in the equation. (Using Crane TP410 Eq. 1-6)
Comments appreciated.
Thanks
YBM
In using the complete isothermal equation, with this DP ratio, I believe it is appropriate to use the average specific volume in the equation. (Using Crane TP410 Eq. 1-6)
Comments appreciated.
Thanks
YBM





RE: compressible flow
Good luck,
Latexman
RE: compressible flow
Appreciate the help.
YBM
RE: compressible flow
Regards
RE: compressible flow
Good luck,
Latexman
RE: compressible flow
"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics
http://virtualpipeline.spaces.msn.com
RE: compressible flow
http
Equation 10 corresponds to Crane equation 1-6. Equation 11 is pretty much the general pipe flow equation used today. Note that this book was published in 1922 and the Prandlt, von Karman and Colebrook equations for friction factor were not yet published. So for friction factor, use the more modern equations.
Also check out Engineering Thermodynamics by Charles Edward Lucke, page1111:
http:
RE: compressible flow
First I find the wording in Crane, "The velocity may be represented by the average velocity at a cross section." to be confusing, at least to me.
"...average velocity at a cross section" does not mean anything to me. What cross section? Average velocity? Reading the principles on page 1-9 does not seem to support this statement.
Next if we go back to page 1-6 where the Darcy equation is introduced in Eq. 1-4, it has the statement, "(For other forms of this equation see page 3-2)" and if you go there, and it will move you thru many forms, then to p. 3-3 where the same notes appear in relation to Darcy and it further takes you to Eq. 3-20, which has a simpler equation,also seen previously as Eq. 1-11 (last eq. on page 3-4). It also says (p. 3-3)to use this for DP>10% as well as >40%. This seems to say it is pretty much used for most situations.
Of course this has choking considered in the form of "Y".
Additional equations are in the Summary so I believe that this is not exact. I think I shall compare 3-7 to 3-20 substituting K for fL/D in 3-7 as I have entrance and exit losses, but they only increase the fL/D by about 10% and who knows how accurate f is anyway.
Does this make any sense?
RE: compressible flow
"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics
http://virtualpipeline.spaces.msn.com
RE: compressible flow
"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics
http://virtualpipeline.spaces.msn.com
RE: compressible flow
RE: compressible flow
I did compare eq. 3-7 to 3-20 and the results are significantly different. For 3-20 I get approx 18,000 vs 40,000 for 3-7. Note that 3-7 does not consider choking but even so Y=0.79 for my case and that will not account for the 40/18x larger. I found a British calculator online, and while I don't know what equations it uses, it calculated 24,000 for this case when factored by Y would agree with eq. 3-20.
YBM
RE: compressible flow
What are your flow units? 18,000 what?
Good luck,
Latexman
RE: compressible flow
"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics
http://virtualpipeline.spaces.msn.com
RE: compressible flow
RE: compressible flow
Good luck,
Latexman
RE: compressible flow
RE: compressible flow
The difference between isothermal (exit Mach = 0.45) and adiabatic (exit Mach = 0.38) was 0.6%, so it really doesn't matter in this case.
It took me longer to type this, than to get the answer out of my handy dandy spreadsheet.
Good luck,
Latexman
RE: compressible flow
Even so, it is not clear to me which is appropriate, but since this air has to be vented from a tank, I have little choice but to use the larger value, even though the vents may become larger, and possibly oversized.
I do appreciate your, and the others efforts on this.
YBM
RE: compressible flow
Good luck,
Latexman