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Why Hysys Isn't Providing Proper Steam Properties

hysys steam

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#1 IonCube

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Posted 18 October 2017 - 10:23 AM

The image says it all. One can observe enthalpy values kJ/kg of HYSYS are a total mismatch when compared with two of my trusted JAVA calculators 

 

In the screenshot a portion of propeties (HYSYS) is shown where I have used (as Inputs) Vapour Fraction, Molar flowrate, Pressure & lastly the composition which is only H2O

 

HYSYS do calculate Saturated Temperature correctly, have also checked specific volume but why not enthalpy or am I missing something? 

 

2642rmb.jpg



#2 latexman

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Posted 18 October 2017 - 10:38 AM

Attachment did not open for me.



#3 IonCube

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Posted 18 October 2017 - 12:38 PM

I am sorry I had hotlinked the image ...now its added as attachment

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Edited by IonCube, 18 October 2017 - 12:39 PM.


#4 Bobby Strain

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Posted 18 October 2017 - 12:54 PM

Have you checked HYSYS values using the HYSYS ASME properties for your model? And, we don't know anything about your favorite JAVA calculators. You should reference one of the widely accepted standards for steam/water properties

 

Bobby



#5 Pilesar

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Posted 18 October 2017 - 01:04 PM

It is not the absolute value of enthalpy that matters. It is the change in enthalpy from one process condition to the other. Not all enthalpy scales use the same reference basis.



#6 latexman

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Posted 18 October 2017 - 01:12 PM

That does look strange.  Is it a reference difference between the different methods?  Can you make HYSYS condense the stream and see what it says for the latent heat of vaporization?  That will subtract out the reference within that thermo model.

 

The HYSYS value appears to be almost exactly a factor of 5 higher than the other two.  Does that mean anything to you?



#7 IonCube

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Posted 18 October 2017 - 04:27 PM

Have you checked HYSYS values using the HYSYS ASME properties for your model? And, we don't know anything about your favorite JAVA calculators. You should reference one of the widely accepted standards for steam/water properties

 

Bobby

In a short sentence they are trusted ..values of specific vol. ,temps ...match with what HYSYS calculate  secondly as a redundancy I have used two calculators!

 

It is not the absolute value of enthalpy that matters. It is the change in enthalpy from one process condition to the other. Not all enthalpy scales use the same reference basis.

 

I haven't attached this stream to anything, out of intuition I have just added single Material Stream. This is from HYSYS xml

 

Component Lists


Property Name Property Value Status or Type 
ComponentListName Component List - 1 Specified 
ElectrolyteList 1 Specified 
ComponentName H2O Specified 
ComponentType PureCompObject Specified 




Reaction Package


Property Name Property Value Status or Type 
NumberOfReactions 0 Specified 
NumberOfReactionSets 1 Specified 
ReactionSetName Global Rxn Set Specified 
SetType Unknown Specified 
SetSolver FEMPTY Specified 
NumberOfActiveRxns 0 Specified 
NumberOfInactiveRxns 0 Specified 
VolumeContinuation False Specified 
InitialVolumeFraction 1e-006 Specified 
NumberOfSteps 10 Specified 
TraceLevel 0 Specified 
PreviousSolutionAsEstimates True Specified 
UsePreviousTempAsAdiaEst True Specified 
IEGDampingFactor 1 Specified 
IEGTolerance 0.001 Specified 
SolverMaximumIterations 200 Specified 
SolverTolerance 1e-005 Specified 




Fluid Packages


Property Name Property Value Status or Type 
FluidPackageName Basis-1 Specified 
FluidPackageType PengRobObject Specified 
ComponentList Component List - 1 Specified 
IsComThermo False Specified 
PropPackage Peng-Robinson Specified 
EOSEnthalpyMethodSpecs EOS Specified 
Component H2O Specified 
TreatmentofInteractionCoefficients False Specified 
UseEOSLiquidDensity False Specified 
SmoothLiquidDensity True Specified 
EstimationMethod UNIFAC VLE Specified 
TryIOFlashFirst False Specified 
UseMultiPhaseFlash False Specified 
Deleted True Specified 
AverageOfExisting False Specified 
IdealGas False Specified 
WilsonsEquation True Specified 
MaximumStagesAllowed 3 Specified 
StabilityTestMethod Low Level Specified 
PhaseSortMethod Use Phase Type and Density Specified 
 

 

 

That does look strange.  Is it a reference difference between the different methods?  Can you make HYSYS condense the stream and see what it says for the latent heat of vaporization?  That will subtract out the reference within that thermo model.

 

The HYSYS value appears to be almost exactly a factor of 5 higher than the other two.  Does that mean anything to you?

 

please refer to the XML above. Heat of vaporization (2325 versus ~2305 ) does match ...also the specific volume (HYSYS gives 58.66m^3/kgmol then divide by 18.02 its the same as my calculators) see the attachment 

Attached Files


Edited by IonCube, 18 October 2017 - 04:28 PM.


#8 Saml

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Posted 18 October 2017 - 06:11 PM   Best Answer

As far as I know the enthalphy in Aspen and Hysys is referred to the pure components at reference T and P (so it would be the reference to Oxygen and Hydrogen). It is done this way to account for heat of reaction where there are reactions.

 

Your Steam table use liquid water 0°C as the zero so the value of 2645 kJ/kg

 

Hysys use the enthalphy with the zero set  to oxygen and hydrogen in reference condition.

 

So Heat of Formation of Water at 25 °C (Liquid)

-285 kJ/mol = -15833 kJ/kg

Delta H to go from 25°C and bar to your condition = 2540 kJ/Kg

Net = 13293, very close to the 13270 that Hysys is reporting

 

The heat evolved in any transition should be correct.

 

By the way, IAPWS or Steam Tables are better methods than Peng Robinson or UNIFAC when you have only water .



#9 pavanayi

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Posted 19 October 2017 - 02:30 AM

Echo ing what has been said above,

PR is not a good option in your case. If it is only H2O, then I would go for NBS Steam. 

Also, absolute enthalpy values vs. delta enthalpy values have been been discussed a few times in the past in these forums.

Just to add, if you are interested, you can check the reference basis for enthalpy calculations in Hysys on their support centre (search article ID 000042545). If I am not mistaken, it is also covered in the simulation basis reference.



#10 serra

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Posted 19 October 2017 - 03:20 AM

yes, there are many discussions at cheresources, see for example :

https://www.cheresou...ation-packages/

some software allow to redefine base values but starting from heat of formation is useful for solving reactions, see a example about how this works and how different base values can affect results (it's for prode, but the same for aspen),

https://www.cheresou...ences-in-prode/






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