×
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 and mass flow rate

Cv and mass flow rate

Cv and mass flow rate

(OP)
Hello everyone.

I fill the data sheet for a choke valve. I know the fluid (gas) and the pressures of inlet and outlet. I have to give CV values required and the mass flow rate.
For example:
p1 = 234 barg,
p2 = 1 barg,
temperature = 20 ° C,
Density @ T1, p1 = 202 kg/m3,
molecular weight = 23KJ/Kmol,
Cp / Cv = 2.31
compressibility = 0.59

How should I proceed?


Thanks

RE: Cv and mass flow rate


....well, you could of course use a sensible link, as the one below:

http://www.engineeringtoolbox.com/flow-coefficients-d_277.html

... but then you would find you lack the most essential of necessary information: the required mass flow per time unit.

This can not be calculated, but has to be determined from other facts.

The pressure drop you give is so large that it is possible you have to use more than one valve in series - I have not looked into this.

If this is a pressure relief valve/situation a single step is possible, perhaps by rupture disc as an alternative.

 

RE: Cv and mass flow rate

(OP)
Grazie for reply gerhardl
therefore without knowing the mass flow not I continue? not I do assumptions and then verify? For example, I think, take the exit Mach numbers less than a certain value.

RE: Cv and mass flow rate


Trying again: this is a practical case. The throtteling is for some real purpose. Ask the user or pipe engineer: what is the real output needed at this throtteling point: maximum, minimum and average over time.  

RE: Cv and mass flow rate

You can calculate the Cv if you know the mass flow rate, or you can calculate the mass flow rate if you know the Cv.  One depends upon the other.  

The most fundamental Cv equation: Cv=Q Sqrt(SG/Delta-P)
Q would be flowrate
SG=specific gravity (water=1)
Delta-P= inlet pressure - outlet pressure, PSI.  

This equation does not apply to your choke, but it still gives you the idea.   

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