Recent Blogs Posts

for additional information see this thread
'http://www.egpet.net/vb/threads/27092-Excel-library-for-process-calc-s-including-distillation'

Prode Properties allows to size / rate a PSV for critical or two-phase flows with different models including HEM (Homogeneous Equilibrium Model)
The HEM model for the nozzle applied in Prode Properties solves

hin+1/2*vin^2 = ho+1/2*vo^2

(in = inlet, o = orifice)
where vo (for a critical flow) is the speed of sound
ho, vo calculated at vena contracta conditions

this model works well for critical and two-phase flows,
it is also applicable for subcritical flows within certain limits.
For subcritical flows Prode calculates the area solving a constant energy operation but since usually for a nozzle we do not specify the internal area of pipe (which is required for calculating vin in above formula the procedure estimates the value, this may generate errors when the rate vo/vin is low.
For such cases it is suggested to use as alternative to ISPF() the method EPF

double t = EPF(integer stream, double p, double E, double aout, double et)

this method allows to specify both inlet and outlet condition thus modeling a adiabatic, irreversible expansions when the contribute of kinetic energy cannot be neglected.

Tags: hem, nozzle, psv, safety, sizing

Categories

Uncategorized

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 alows 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

PIPE
this method allows to simulate single phase, two-phases, multiphase flow on circular pipes,
for multiphase flow different models are available including HEM (Homogeneous Equilibrium)

Speed of Sound
the methods StrMSS(), EStrMSS() in Prode Properties allow to calculate the speed of sound for gas, liquid and gas+liquid (mixed phases) with

HEM model

A TEST CASE
Prode Properties allows to compare HEM (Homogeneous Equilibrium Model) against different models as HNE (Homogeneous Non-Equilibrium Model)

and NHNE (Non-Homogeneous Non-Equilibrium Model),
this allows to select the most suitable pressure relief valve for a specific application

...

Tags: equilibrium, hem, hne, homogeneous, model

Categories

Oil And Gas Process

Attached Thumbnails

 

Attached Files

• HEMvsHNE.txt (1.8 KB, 56 views)

I have found several papers discussing this topic, one is "Improved control valve sizing for multiphase flow" from Hydrocarbon Processing March 200, the authors say "HNE-DS method basically assumes that the flow pattern in the control valve is homogeneous but gas and liquid are not in equilibrium – a non-equilibrium factor N represents the boiling delay"
your comment agrees with this statement.
By the way I found also an interesting thread comparing API PSV formulation for gas flow here

'http://www.cheresources.com/invision/topic/16104-psv-discharging-temperature'

the author has provided a Excel page to compare different procedures

Discharging temperature (PSV outlet)
1) calculated with isentropic + adiabatic flash (the default in nozzle.xls)
2) calculated with adiabatic flash
3) calculated with isentropic flash

Calculated Area
1) rigorous numerical solution of isentropic nozzle
2) API formulation for gas and vapors, ideal cp/cv
3) API formulation for gas and vapors, real cp/cv
4) API formulation for gas and vapors, real cp/cv, Zv = 1

all the required properties are calculated by Prode library , for personal/academic use you can download a free -with limited number of components- copy from 'www.prode.com'

I recommend to read this thread to everyone interested in PSV sizing.
psvcompare1.xls

Tags: flow, gas, hem, liquid, psv

Categories

Uncategorized

cbadia wrote
for a two phase discharge I am sizing a relief valve with the isentropic Nozzle unit available in Prode Properties,
the procedure allows to specificy the HEM (Homogeneous Equilibrium Model) and NHNE (Non-Homogeneous Non-Equilibrium Model) for isentropic flow.
While the HEM model gives results consistent with those calculated by Excel page nozzle.xls distributed with the program the NHNE model requires specific settings and may give results quite different.
Which is the best option (HEM or NHNE) for modeling a PSV discahrge ?

I think it depends from several factors as for example the size of the valve and the physical properties of the fluid,
my version of Prode Properties has three models
HEM (Homogeneous Equilibrium Model)
HNE-DS (Homogeneous Non Equilibrium, simplified model)
NHNE Non Homogeneous Non Equilibrium)
the last two require a specific parameter which for HNE-DS is available in several papers while for NHNE you have to estimate the value, generally I select HEM and I do a test with HNE-DS

Tags: hem, hne-ds, psv, two-phase

Categories

Uncategorized