Standard for two phase relief valve sizing

[fucheng]

Hi everybody,

Other than HEM in API, is there any international standard on two phase relief valve sizing?

thanks.

[carlo.stenali]

the Omega method discussed in API std. adopts a simplified model for HEM , the limits of the model are discussed in API
for a discussion of HEM model you may consider other sources as DIERS,

PRODE PROPERTIES (see prode.com) includes a rigorous (not simplified) solution of HEM as well as HNE and NHNE models,

herebelow the basis for the different models

HEM MODEL
HEM (Homogeneous Equilibrium Model) is based on two assumptions (Homogeneous flow)
1) velocity of gas an liquid phases are equal
2) vapor and liquid phase are in thermodynamic equilibrium
this is a general purpose model which gives good results for a broad range of problems

HNE MODEL
in HNE model (Homogeneous Non-Equilibrium Model) the vapor and liquid phases are not in thermodynamic equilibrium,
HNE has found (Fauske, Schmidt ...) to describe well the behaviour of subcooled fluids which reach two-phase equilibria in a nozzle, pipe

etc. for example the fluid residence time could be too short for a significant vaporisation.

SOME APPLICATIONS WITH PRODE PROPERTIES

Isentropic Nozzle model
this method allows to design/rate safety/relief devices as PSV etc. for critical and two-phase flow.
The Isentropic Nozzle model allows to define
1) HEM Homogeneous Equilibrium (Solution of Mass Flux integral)
2) HNE Homogeneous Non-equilibrium (HEM with Boling Delay and Gas-Liquid Slip Contributes)
3) HNE-DS , Homogeneous Non-equilibrium
4) NHNE Non-homogeneous Non-equilibrium

see these posts for additional information on these topics

'http://www.egpet.net/vb/entries/82303-PSV-sizing-with-HEM-%28Homogeneous-Equilibrium-Model%29-limits-of-application'

'http://www.egpet.net/vb/entries/82302-Comparison-of-Homogeneous-equilibrium-%28HEM%29-VS-NON-equilibrium-%28HNE%29-models'

[asanter]

in addition to HEM standard (see the description given by Carlo.Stenali) you should be able to find HNE-DS as ISO std.
all these are included in PRODE PROPERTIES which we utilize for PSV sizing / rating.