×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

sonic flow in nozzle

sonic flow in nozzle

sonic flow in nozzle

(OP)
Hi,

I am a new engineer working on a derivation for maximum flow of a gas in a nozzle.  

API RP 520, Pt. I, Para. 4.3.2.1 gives the equation for max flow to be  

W=C*A*P*sqrt(T/M)

I've left out the correction factors for back pressure, non-ideal flow, and compressibility of a non-ideal gas.
Now I've been able to start with a tank of initial pressure and temperature, Po and To, and get to the following equation on my own.

W=Po*A*[(M/Ru/To)(k(2/(k+1))^((k+1)/(k-1))]^1/2

M being molecular weight, and Ru the universal gas constant.
Now the term C in the first equation is given as

C=520*[(k(2/(k+1))^((k+1)/(k-1))]^1/2

which makes the first equation almost match up with mine except for the 520 term, and the universal gas constant in my equation.

My question is this.  Where did this C term come from and what are its units?

 After putting in 1545.35 ft*lbf/lbmol/R for Ru and converting all the units to make sure W came out in lbm/s  my term for C instead of being 520 would be 0.1443

A big thank you for any help on this.

RE: sonic flow in nozzle

If the API derivation was for lb/hr their constant would be 0.1443 * 3600 = 519.48 !!

RE: sonic flow in nozzle

The fastest flow velocity you can have in a converging nozzle is sonic (Mach 1).  Once the flow becomes sonic, the mass flow rate scales linearly with pressure, according to Fliegner's formula (which is only good for Mach 1 flow).  If you can't find Fliegner's formula in your fluids references, let me know, and I'll type it out.

If you have a converging-diverging nozzle, flow will become supersonic under sufficient stagnation pressure and the Mach number can be calculated according to the area ratio of the nozzle.  Flow will still be sonic at the throat, however, and therefore mass flowrate can still be calculated using Fliegner's formula (using properties at the throat).

Haf

  

RE: sonic flow in nozzle

(OP)
Argh!  Of course.  I was doing lbm/s instead of the lbm/hr I should have been converting to.  I think that I'd been staring at it too long, and I fried my brain.

Thanks a bunch for getting me back on track.

RE: sonic flow in nozzle


A link to "Fliegner's formula" is:

http://www.ijee.dit.ie/articles/999982/experime.htm

You might also want to refer to Thread# 378-31540; it is specifically concerned with transient flow, but deals with the same subject, broadly speaking.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources