Thermodynamic properties of gas mixtures 4

[mfqd13]

Hi,

I can't find anything to calculate the thermodynamic propertis of gas mixtures, like:
Butane, propane, pentane, ethylene, methane, hydrogen, etc.

Is there any website where i can do this? Can anyone help me?

 

[MortenA]

Maybe if you are not a process engineer or experienced with thermodynamics, then this is the time to seek assistance beyond this fine site? Maybe a consultant if you cant find somebody in house?

I can recommend several software packages but they are all expensive - but worthless if you dont understand thermodynamics.

Best regards

Morten

 

[mfqd13]

Dear MortenA,

You are suposing i don't understand thermodynamics....maybe not so good as yours.
That's why i use forums...to ask for stupid ans basic questions...

I don't use any HYSYS software or something like that because i'm not a process engineer or chemical...i'm a mechanical that often needs to solve problems that i usually don't need and thats why i come to ENG-TIPS...otherwise i wouldn't.

Thanks anyway.

 

[Latexman]

marcosdias,

Let you look here: NIST

I believe it is exactly what you seek.

Good luck,
Latexman

 

[mfqd13]

Hi,

I know NIST and i am using it now, but what about mixed components?
Can i integrate them through molar basis (say %) and obtain an average value of a mixture?

 

[MortenA]

I didnt think your question were stupid - i just dont htink they are easy to aswer in this type of fora. I have contributed here for more than 11 years and my answer to some degree is influenced with what i have seen before. But i will maintain that the same way that i wouldnt do stress calculations you should perhaps accept that the work a chemical engineer does is more complicated that entering data into a form in a web site? I will of course stop bothering you altogether from now on.

Best regards

Morten

 

[mfqd13]

Dear MortenA,

My answer was not intended to be ofensive.
What i was trying to say was that the explanation for my problem is only thermodynamics, you can post it because i will understand. Of course if it is chemical i may not understand it... (or maybe yes). You can't assume that i will not understand it because that is a "non post". If you think that it will be complex, give for example a site or book to consult and to see how complex it may be.

Thanks anyway.

 

[prex]

Perry's Chemical Engineers' Handbook has a quite extensive chapter on predicting thermodynamic properties of substances, including gas mixtures.
And of course this task is generally not that simple as using the weight or molar composition. Specific density and heat capacity are easily obtained that way, but other properties like viscosity, critical properties, etc., require special treatment.
By being more specific on which properties you need you could get more help.

prex
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[ione]

If you're looking for a reasonable priced tool (200 $) you can try Refprop from NIST

http://www.nist.gov/srd/nist23.cfm

 

[mfqd13]

The most important for me it would be Cp (heat capacity) and K (thermal conductivity).
Thanks!

 

[prex]

For low pressure gas mixtures the heat capacity may be weighted by weight composition; for thermal conductivity a suggested relationship is:
k=[Σ]y_ik_iM_i^1/3/[Σ]y_iM_i^1/3
where y is a mole fraction and M a molecular weight.

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[mfqd13]

Thank you very much for the replies!
I will try!

 

[apetri]

I would recommend Prode Properties,
there is a free copy for personal use, see

http://www.prode.com,

features are comparable to those of simulators.

 

[zdas04]

I use REFPROP from NIST. As I recall it cost $150 USD or so and I find myself opening it a couple of times a week. You can build whatever mixture of gases you want in it and then either just use that mixture to get the properties you need or save it for later use. I'm not a ChemE either, but I do know a bit of Thermo and have actually contributed to process discussions with the "experts". Maybe all ME's are not ham fisted dolts. When HySys and REFPROP have disagreed on a parameter every single time so far it either was because I had an error in my gas analysis input or the HySys guy had an error in his input. Transient behavior is much more robust in HySys, but REFPROP costs $150 instead of $20k/year

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[chemlite]

I have Prode,
differently from Nist it works with a database with properties of many pure fluids (which you can edit) and thermodynamic packages which you select for the different calc's (phase equilibria, enthalpy, entropy, volume),
In my opinion Nist or GERG models (available in products as Refprop and Prode) are probably the best for properties of pure fluids (since thay include many specific parameters tuned on each fluid) ,
for mixtures things are more complex,
GERG is accurate but it includes only a limited number of fluids (about 20),
for enthalpy, entropy (and related properties as cp) the std. approach is based on evaluation of departures with a EOS, the advantage being that properties are available for all the fluids in database (Prode has about 1700 components).
Finally there is phase equilibria,
in this field Prode has features comparable to much more expensive simulators.
For my usual applications, separations, fluid properties, compression etc. Prode works just fine and I can easily recommend it.

 

[mfqd13]

Thank you all!

I've downloaded PRODE and i'm starting to use it.

chemlite,
You've said that prode has 1700 componentes, but i've opened it in excel and i only can see 30 or 40...can you help me?

I know that there are some formulas to calculate some properties like Cp, enthalpy, thermal cond., etc, and they are mentioned in PRODE. They are function of some fixed values: a,b,c,etc.
Can anyone refer some book where i can find this parameters, so i can calculate the properties on my own?

Thanks to all!

 

[chemlite]

I am afraid to have not mentioned that,
the free version of Prode Properties includes about 60 components (1700 components are available in commercial versions)
however you can add components (I did that for the purpose of testing before to purchase a license).
As said the database includes for each component the parameters (up to 5) for temperature dependent correlations for the different properties as enthalpy, viscosity etc. , for enthalpy, entropy, cp the software calculates departures according selected EOS (there are several available).
I would recommend "The properties of gases & liquids" by Reid, Prausnitz, Poling as a good reference to these matters.
If you wish to calculate directly the properties (not with Prode) then the book includes a limited database for more than 200 chemicals, also there is a Excel compilation available.
Note that you need a good knowledge of thermodynamics to define the models and validate the results, in many cases one prefers to have something tested to utilize (which is the main reason why so many engineers have simulators)

 

[mfqd13]

Dear chemlite,

Thank you very much for the anwer. It was great! I will look deep in this and try to take a look to that book.

Thanks!

 

[nft999]

Check with the Naritonal Renewable Energy Laboratory (NREL.gov)