6 replies to this topic

[serra]

dear sirs,
I am modeling a discharge through a orifice plate with Prode Properties, generally I model this operation as adiabatic flash but I see that there is also a constant energy flash,
Prode includes several flash operations which support multiphase,
among others there are

HPF() for specified enthalpy and pressure
SPF() for specified entropy and pressure
EPF() which solves the constant energy flash operation

I know little of constant energy flash,
when should I use this operation ?

[PaoloPemi]

from Prode Properties operating manual
the EPF flash operation solves the constant energy flash where energy is calculated as sum of enthalpy and kinetic energy,
this method permits to model adiabatic expansions where the contribute of kinetic energy cannot be neglected,

you may consider for example the discharge from a stagnation point (vessel internal) to orifice and from orifice to atmosphere

[serra]

thank you,
what about to model a safety valve ?
Do you suggest HPF() adiabatic flash ?

[PaoloPemi]

Prode Properties returns rigorous properties as density, cp, cv etc. plus adiabatic and isentropic flash operations, it's easy to code the different methods, I have Excel pages for gas/vapors (see below), two-phase flow and flashing liquids (with Omega, see Leung "Easily size relief devices and piping for two phase flow" correlation)
for gas/ vapors in some cases I prefer a direct (numerical) integration of nozzle mass flux equation with multiple isentropic flashes, with Prode Properties working within Excel it's very simple with the macro =SPF() which solves the pressure-entropy flash specifications.
This kind of flexibility permits to solve even the most difficult cases...

[marchem]

for a RO the EPF() method should be ok,
energy balance gives

Hin*1/2*Vin^2 = Hout+1/2*Vout^2

the method EPF() takes in account the contribute of Vin and Vout

for a nozzle you should consider the method ISPF() which allows to solve a isentropic operation with HEM, HNE, HNE-DS and NHNE models

[serra]

thanks,

I have found that Prode Properties distribution includes a Excel page to design/rate pressure safety valves with critical or two-phase flow with

 

-HEM (Homogeneous Equilibrium Model)
-HNE (Homogeneous Non-Equilibrium) with boiling de...lay and gas-liquid split contributes
-HNE-DS (Homogeneous Non-Equilibrium)
-NHNE (Non-Homogeneous Non-Equilibrium)

so a whole range of models is available

[marchem]

yes, the main difference is that EPF() is a general purpose method solving a sopecific flash operation (constant energy flash) while ISPF() models a PSV (isentropic nozzle) of course the fields of application for these methods are different