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REFPROP 10 vs REFPROP 8 GUIs for Ammonia-Water mix #60

Closed GaneshDoiphode closed 5 years ago

GaneshDoiphode commented 5 years ago

I defined Ammonia-Water mix (43/57) in REFPROP 10 GUI and obtained Enthalpies and Entropies for the inputs of Temp and Pressure for two state points that can be found in the screenshot below. These values obtained do not match with the results obtained in the reference paper I have been replicating. refprop 10

However, for the same mixture when used REFPROP 8 GUI, yields different Enthalpies and Entropies that can be seen in the screenshot below. These values obtained MATCH with the results obtained in the reference paper I have been replicating.

refprop 8

So, my question is how to get REFPROP 8 GUI values (second screenshot) using REFPROP 10 GUI (or more importantly REFPROP MATLAB wrapper for version 10)? My intent is to use REFPROP 10 in calculations and not the previous version.

GaneshDoiphode commented 5 years ago

Any solution over this issue? I would really appreciate.

ianhbell commented 5 years ago

The short answer is that entropy and enthalpy are relative properties and you should never count on them having any fixed value in particular. You can decide on the value by selecting the reference state.

The longer answer is that in the case of ammonia + water, there is actually a standard value for the reference state that I believe REFPROP 10 no longer agrees with. If so, that is a bug. What value are you comparing with?

GaneshDoiphode commented 5 years ago

Hello @ianhbell, you are true about relativity! Actually, I am not comparing with any value. I want REFPROP 10 to give me results obtained by REFPROP 8. What reference state should I put in REFPROP 10 so that I will get the same results as that of in version 8? and how do I do it in Matlab?

EricLemmon commented 5 years ago

What you are seeing is simply the effect of the new pure fluid equation of state for ammonia and the new mixture model for ammonia/water that came with version 10 of Refprop. The ammonia equation of state in Version 8 had a 6 percent error in the speed of sound in the liquid, and that error propagated into other things such as enthalpy. It also did not correctly account for the association of the molecules in the vapor phase. The new equation fixed both of those, and then a new mixture model had to be developed because the old one was no longer compatible with the new pure fluid equation of state for ammonia. The differences are shown in the picture below. The blue line is Refprop 10 and the red line is Refprop 8. Both are calculated at 4.7 bar and the points are the first ones in each of your tables.

So, this is not just a matter of reference states, it is an advance in the thermophysical properties of the fluids. The are many new equations in Refprop 10, including updated thermodynamic equations of state, updated transport equations, and new mixture models or updated mixture interaction parameters. We continue year after year to keep updating these equations or making new ones as new measurements are made or technology changes so that we can make better equations.

image

EricLemmon commented 5 years ago

If this answers your question, could you please close this issue?

GaneshDoiphode commented 5 years ago

I just closed the issue, thank you.

On Sun, Nov 25, 2018 at 5:49 PM Eric Lemmon notifications@github.com wrote:

If this answers your question, could you please close this issue?

— You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub https://github.com/usnistgov/REFPROP-issues/issues/60#issuecomment-441481075, or mute the thread https://github.com/notifications/unsubscribe-auth/Apka4ITlU8dy3fTyBoUtAd91EMhHzA3mks5uyx5fgaJpZM4XzFPX .

-- Regards,

Ganesh D.

MS in Mechanical Engg, Florida Institute of Technology, Melbourne FL

Contact: +1 321 317 5523 Email: gdoiphode2016@my.fit.edu