Flash Relief of subcooled liquid at valve inlet 1

[kmitra]

Hi everybody,

I've some queries regarding relief valve calculations for subcooled liquid at inlet. My process involves water in subcooled state (170bar, 320deg.C). The relevant equation for omega-s parameter as per API 520 is 9*((rholiq_at inlet/rho9)-1). My query

1. what is the origin/ justification for '(' used above & also the above equation in general

2. I've some confusion in estimating rho9. API says it is the density evaluated at 90% of Psat corresponding to inlet temperature. This means about 102bar for my case. IT also says about isentropic/ isenthalpic flash. Should I take enthalpy at inlet (i.e. subcooled conditions) & carry out the flash to 102bar? in that case i'll get superheated vapor condition (i understand that rho9 is the liquid density). Please help.

 

[apetri]

for (flashing) subcooled liquids HNE could be preferable over HEM,
see this discussion at eng-tips forum

"

http://www.eng-tips.com/viewthread.cfm?qid=332483"

you may compare results of HEM vs HNE ,
by the way Omega parameter gives a simplified solution of HEM method,
better to use the rigorous method (see Prode or similar tools).