×
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

Direct integration method API520, 2008

Direct integration method API520, 2008

Direct integration method API520, 2008

(OP)
Hi,

I want to follow Annex B eqn (B.2) and use a direct integration of the isentropic nozzle formula to work out the max flow through a bursting disc orifice.

I understand that the terms come from an isentropic flash at each 'pressure step' through the burst disc but what i dont get is how you know the condition at the throat (v_t , specific volume) somewhere inbetween upstream condition and vena contracta?.

some clarification on this and any advice would be appreciated. If i wanted to also model the process insethalpically the same equation applies? Ie: the properites for each step come from isenthalpic flash instead of isentropic.

Many thanks

RE: Direct integration method API520, 2008

You don't need to know the P and T at the throat. You simply do a series of isentropic flashes in small pressure steps ( I just do it from starting pressure to atmospheric) and then calculate the integral which is turn gives you a mass flux rate. The highest mass flux rate along with a Kd gives you the required area.

RE: Direct integration method API520, 2008

I would recommend this thread,

http://eng-tips.com/viewthread.cfm?qid=329093

it includes an Excel page which does the work,
as commented by TD2K the procedure described in API solves a series of isentropic or isenthalpic flash operations,
Prode has also a different method to solve the HEM model plus HNE , NHNE etc.

RE: Direct integration method API520, 2008

(OP)
Thanks for the replys, the API formula finds the maximum mass flux by dividing the integral by 'vt' the specific volume at the throat condition. My first problem was that i thought this was being integrated too... until i opened my eyes and read the formula correctly. I havent gone back to the problem yet but im still unsure following API's formula how you are supposed to find 'vt'

I am building a calc that uses several models to produce an envelope for discharge reaction force. So its still worthwhile understanding the API formula for me.

RE: Direct integration method API520, 2008

in the suggested thread you'll find the equation

Hin+Vin^2=Hout+Vout^2

with Hin, Vin, Hout, Vout fluid enthalpy and speed
which is the basis of the method,
I utilize the same procedure as that included in the Excel page (which does use Prode Properties for isentropic flash, enthalpy and volume)
the method takes in account the contribute of Vout (Vin is normally not included being very low compared to Vout)

RE: Direct integration method API520, 2008

I don't fully understand why a direct integration of the isentropic nozzle formula would be used to model a pipe with a rupture disk in it. I think the isothermal or adiabatic pipe flow model (with an appropriate, certified KRD) would be a better choice. Anyone else think this?

Good luck,
Latexman

RE: Direct integration method API520, 2008

Latexman, it was the original request,
API 520 annex B includes discussion of direct integration procedure which one can solve as shown.
There are several alternatives, for example one could estimate critical mass flow in a specified section (Prode has a rigorous method to calculate speed of sound in gas, liquid and two-phase fluids with HEM methodology) then introduce some correction.

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