PSV - Flashing

[Chem2020]

What it means flashing for Psv sizing? How to know fluid would flash?

 

[Latexman]

If the fluid from the PSV outlet has a larger vapor fraction than the fluid from the PSV inlet, there is flasking.

Flashing = vaporizing.

Flashing = boiling.

Good luck,
Latexman

 

[rense]

as Latexman suggested it means there is a change of phase liquid->vapor,
you may need to consider HEM or HNE models which are more complex than usual API methods,
you may find a thread discussing these applications with Prode software,
there is an Excel page to do the calc's.

 

[itdepends]

If the PSV discharges to a location where the pressure is less than the vapour pressure of the fluid- it will flash.

e.g. If you're storing a liquid above it's atmospheric boiling point and your PSV discharges to an atmospheric tank- it will flash across the PSV.

As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"

 

[cosh]

for a PSV flashing you may consider two different models, HEM and HNE,
you will find a detailed discussion of HEM model in API,
these models will predict the amount of vapor and liquid at PSV outlet,
the main difference is that HNE do not condider a homogeneous equilibrium (as HEM) but only a partial change of phase (where the final result depends from inlet conditions),
if you wish to compare HEM and HNE models (plus different variants as HNE-DS etc.) there is a Excel page distributed with Prode Properties Software.