API 520 sizing for 2-phase 1

[MortenA]

Why is it that API 520 section C.2.1.1.3 states that sucessive _isentropic_ flashes at lower pressure with the fixed entrphy equal to stagnation conditions shall be used for these calculations? I would have though that a valve is isenthalpic? Where does the "work" go when you keep the entrophy constant? Is it because its "worst case" (with regards to low temperature) or what?

Best regards

Morten

 

[CJKruger]

MortenA, theoretically we need to do the following flashes:

- From inlet to nozzle thoat: Isentropic flash as work goes into accelerating the fluid (mostly).

- From inlet to outlet: Isenthalpic flash as most of the velocity is destroyed. This is the flash calc we are used to.

 

[MortenA]

hmm - okay i think i can buy into this.

Thank you Kruger

Best regards

Morten