Author Topic: MoleculeDefinition--critical constants  (Read 309 times)

Junran Lu

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MoleculeDefinition--critical constants
« on: April 12, 2018, 07:28:27 AM »
Hi, David Professor:

In the molecules/TraPPE dictionary, the "critical constants: Temperature [T], Pressure [Pa], and Acentric factor [-]" of some molecules were set to "0.0, 0.0, 0.0", such as 3mC9, 4mC9 and BDC. The numbers of "0.0, 0.0, 0.0" means unknown ? Besides, if I don't know of the "critical constants" of a specific molecules, could use the "0.0, 0.0, 0.0" to represent the "critical constants" values?

Thanks very much!
Looking forward to your reply!
Best Wishes!

David Dubbeldam

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Re: MoleculeDefinition--critical constants
« Reply #1 on: April 12, 2018, 03:10:29 PM »
Yes, but you can look them up somewhere if you need them. These are used to convert pressure to fugacity using an equations of state.
Alternatively, if you use fugacity in your simulations (instead of pressure) then these number are not used.

Junran Lu

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Re: MoleculeDefinition--critical constants
« Reply #2 on: April 13, 2018, 04:37:20 AM »
Hi, David Professor:

Thanks for your reply. One more question: if I use the "0.0, 0.0, 0.0" to represent the "critical constants" values´╝î is that to say the fugacity is equal to 1?
Thank you very much!

Best wishes!

David Dubbeldam

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Re: MoleculeDefinition--critical constants
« Reply #3 on: April 13, 2018, 08:14:46 AM »
No, you do that by setting for the component:
FugacityCoefficient 1.0
Then you compute vs fugacity (see the manual).