×
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

Cv Calcs & Choked Pressure

Cv Calcs & Choked Pressure

Cv Calcs & Choked Pressure

(OP)
Hi all,

I'm developing software to be able to size our ball valves properly for compressible & incompressible flow. I've been searching for easy methods to calculate choked pressure drop (to compare it to actual pressure drop & determine if flow is choked) and I haven't had too much luck.

I have searched through these forums and have found a link: Link
which seems useful, but we do not have cavitation index the formula calls for.

I'm currently using this equation: FL^2 (P1 - FF * PV) FL - some kind of shape factor ~0.55-0.60 for ball valves (not sure where this came from), P1 - inlet pressure, FF in ISA S75.01-1985 Annex G as 0.96-0.28(vapor pressure/critical pressure)^1/2, PV - vapor pressure.

I need to know if this is OK by ISA standards. My company has been using this equation, but in order to use it in the software I need to prove that it is valid by some credible reference. I'm not entirely sure where the equation came from, but we have been using it for a while.

Is this equation OK or is there something else I should be using? Please assume I have little to no empirical data about our valves and am unable to attain data.

Thanks in advance,
K

RE: Cv Calcs & Choked Pressure

(OP)
EDIT: the above equation I described is supposed to be equal to choked pressure drop (ie deltaP_choked = FL^2...)

RE: Cv Calcs & Choked Pressure

Try the method defined in the "ISA handbook for control valves". That method implies you will need to characterize your ball valves for Cv and Xt, and the individual cases for choked flow will also vary according to the flowing gase's Cp/Cv ratio.

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