Getting/Computing Acentric Factor in Cantera?

[Chris N]

I found that critical properties for species can be queried from Cantera.  I couldn't find any documentation on the acentric factor. It is a parameter that(to me at least) seems like it could be computed.   omega = -1.000 - log10(P_sigma / P_c) where, P_c is the critical pressure(check), and P_sigma is the vapor pressure at the temperature where T/T_c = 0.7 (reduced temperature = 0.7), and T_c is the critical temperature(check).  So that leaves the P_sigma, and being able to find the value for it at the point where the reduced temperature is 0.7.  Has anyone else used the acentric factor when using Cantera?  What did you do?

Thanks,

Chris

[Steven DeCaluwe]

Hi Chris,

We currently have it enabled such that you can provide the acentric factor with the transport properties, as `acentric_factor`.

See lines 956--988 of `ctml_writer.py`.  We store it as w_ac.

As far as I’m aware, it is currently only used in `transport::HighPressuureGasTransport`  as you say, this has to do with the theory of corresponding states, which we use here to calculate transport properties for high-pressure gases.

In our case, it is explicitly input by the user.  Your equations below would appear to be another method by which to calculate it, but if I understand correctly, it requires the user to instead provide the vapor pressure where T_r = 0.7.  So we’d be trading one input parameter for another.  Is that correct?

Thanks,

Steven

——————————————————————————————————

Steven DeCaluwe, PhD

Assistant Professor of Mechanical Engineering

Colorado School of Mines

Brown Building W410B

Golden, CO 80401

email: deca...@mines.edu

phone: (303) 273-3666

Twitter: @DeCaluweGroup

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[Chris N]

I believe you are correct that one way or another, some empirical value must be provided. I think keeping an explicit acentric factor specification is the best option.  I'm using it for a Peng-Robinson evaluation(where I need critical properties & the acentric factor), so I was hoping to use Cantera to get the critical properties & the acentric factor. But I think I'll grab the critical properties from Cantera & parse a database of common species acentric factors separately.

I have very little experience with the CTI input file, but would it be possible to read in a mechanism using Cantera, then provide values for the acentric factors for some subset of species that are both present in the mechanism & present in my acentric factor database?  Or would the acentric factor need to be provided by manually writing it to the input file?

On Tuesday, April 24, 2018 at 2:26:52 PM UTC-4, S. DeCaluwe wrote:

Hi Chris,

We currently have it enabled such that you can provide the acentric factor with the transport properties, as `acentric_factor`.

See lines 956--988 of `ctml_writer.py`.  We store it as w_ac.

As far as I’m aware, it is currently only used in `transport::HighPressuureGasTransport`  as you say, this has to do with the theory of corresponding states, which we use here to calculate transport properties for high-pressure gases.

In our case, it is explicitly input by the user.  Your equations below would appear to be another method by which to calculate it, but if I understand correctly, it requires the user to instead provide the vapor pressure where T_r = 0.7.  So we’d be trading one input parameter for another.  Is that correct?

Thanks,

Steven

——————————————————————————————————

Steven DeCaluwe, PhD

Assistant Professor of Mechanical Engineering

Colorado School of Mines

Brown Building W410B

Golden, CO 80401

email: ...@mines.edu

phone: (303) 273-3666

Twitter: @DeCaluweGroup