Prode Properties allows to size / rate PSV and piping for critical or two-phase flows with 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.
NNHE MODEL
in NHNE (Non-Homogeneous, Non-Equilibrium Model) the vapor and liquid phases are not in thermodynamic equilibrium and traveling at different veleocities
This is the most flexible (but complex) model available in PRODE PROPERTIES
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
How to calculate mach number in Excel
With PRODE PROPERTIES you can calculate speed of sound for has,liquid and gas+liquid flows directly in Excel with the macro
=EStrMSS(1,t,p)
which returns the speed of sound for that fluid at specified t, p form that value
mach number = fluid velocity / speed of sound
Some details about models included in PRODE PROPERTIES
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.
Alternatives based on CONSTANT ENERGY FLASH
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.
Some Application examples in EXCEL
PRODE PROPERTIES includes a series of application examples in EXCEL (both Excel 32 bit and EXCEL 64 bit are supported) for solving
-PSV rate/design
-PSV compare HME (Homogeneous Equilibrium Model), HNE (Homogeneous Non Equilibrium Model), NHNE (NON Homogeneous Non Equilibrium Model)
-etc.
Attached Images
examples of Excel applications
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