×
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

Cp/Cv for PSV calculation

Cp/Cv for PSV calculation

Cp/Cv for PSV calculation

(OP)
Hi everybody. I'm sizing some PSVs and I have read the article "using the ideal gas Cp/Cv ratio for RV sizing" in which at the end the author concludes "In no case should the real gas specific heat ratio be used as an estimate of the isentropic expansion coefficient, as this can lead to significant under-prediction of the required discharge area for the RV". As it is said in the article I have verify that Hysys gives the real Cp/Cv, not the ideal one. Anyone know how can I calculate the ideal Cp/Cv to be used to size the RV? Changing the fluid conditions to Normal Conditions 0 atm and T = 0K? what are the "Ideal Conditions"?

RE: Cp/Cv for PSV calculation

MMII, instead of the ideal Cp/Cv, I have in the past used Cp/(Cp-R), where Cp was actual Cp from a simulator.  

RE: Cp/Cv for PSV calculation

by definition, Cv = Cp-R, it not something you use , it fact.

RE: Cp/Cv for PSV calculation

API 520 states in the definition of Coefficient "C" that "k" should be taken at "inlet relieving conditions".

 

RE: Cp/Cv for PSV calculation

dcasto, as far as I know, Cv=Cp-R is only true for an ideal gas.

lizking, good point. But to confuse us, they tell us to base the critical pres ratio on the ideal k value. Theoretically I do think the ideal k value is more correct, but given the other inaccuracies in our relief load calcs, it probably makes no difference.

 

RE: Cp/Cv for PSV calculation

thats why I use a empherical cubic equation form of Cp.  The constant R is truely a constant.

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