3 replies to this topic

[aqassam]

Two common methods for calculating the relief load for a tube rupture with vapor on the high pressure side under critical flow:

 

1) Perry's (8th edition) Equation 10-31

 

wmax = CA (g * k * (P1/ V1) *  (2/(k+1))^ ((k+1)/(k-1)))^0.5

 

2) Wing-Wong Paper

 

wmax = CA (1-0.317 dP/ P1) * dP/P1) (dP/ rho)^0.5

 

where dP = P1 - P*, where P* is the greater of the relieving pressure or choking pressure 

 

I was under the impression that during choked flow, mass flow varies only with upstream pressure (P1), not with any sort of pressure differential. 

 

Why, then, does Wing Wong's equation seem to go against Perry's?

 

I tried to calculate using both equations and for the same fluid properties I get vastly different relief loads. Can someone help me navigate these equations, and point out what I might be missing? 

 

Thank you in advance, 

Edited by aqassam, 04 November 2014 - 01:21 PM.

[xavio]

aqassam,

 

I have used the Wing Wong's equation many times, but never knew there is one in Perry's Handbook.

So, I can't comment on Perry's equation right now.

 

For Wing Wong's, the equation is derived from orifice formula in Crane 410. I have checked myself that it is derived correctly.

I also feel that the logic behind the derivation is acceptable.

Of course there are lots of other equations pertaining to this subject, but I think Wing Wong's is sufficiently simple yet reliable (conservative maybe?).

However, if you're referring to their 1992 article, there is one very annoying typo error.

 

For gas, it is written as Wv = 1,891 Y d^2 C (dP/V)^0.5

You should be aware that V is specific volume, which is reciprocal of rho.

Therefore, after substituting some factors, the final equation should read Wv = ..... (dP . rho)^0.5, instead of (dP / rho)^0.5.

There are some calculation examples on the back of the article where the equation used is correct.

 

I don't know if after the correction you will have similar results between Wing Wong's and Perry's.

You should also check how Perry's equation is derived.

 

Good luck!

 

xavio

Edited by xavio, 04 November 2014 - 08:26 PM.

[Bhavinkumar]

Can anyone please share Wing-Wong Paper if it is not violating copy right issue.

[aqassam]

The paper is available on Scribd:

https://www.scribd.c...er-Tube-Rupture

 

Thank you for pointing out the error. I'll double check both calculations and report back the differences. 

Edited by aqassam, 05 November 2014 - 08:33 AM.