Expressions for chemical potentials in Cantera Matlab

[Davide Masiello]

Hi,

I apologize if this subject has already been covered somewhere, I don't seem able to find anything about it.

I am using Cantera with Matlab to calculate the properties of a mixture of gases using the class GRI30('Mix').

Is there any way for me to understand what equations are used to compute the chemical potentials of the various components of the mixture?

Thanks in advance,

Davide

[Steven DeCaluwe]

Hi Davide,

The ideal gas equation of state (which GRI30 utilizes) assumes that all species activity coefficients are unity, so the chemical potential of a species mu_k is:

mu_k = mu^o_k + RT ln(C_k / C^o_k)

where mu^o_k is the chemical potential at the standard / reference state, which is determined from inputs in the cti file (via NASA polynomials, for GRI30, but other options exist).  

C_k is the species molar concentration (or molar density, in Cantera’s parlance), C_k = X_k*P/R/T (where X_k is mole fraction, P is pressure, R the universal gas constant and T the temperature).

C^o_k is the molar concentration of species k at the reference state, which is at the reference pressure P^o, the current temperature, and assumes a mole fraction of 100%.  i.e. C^o_k = P^o/R/T.

Putting it all together, the chemical potential is:

mu_k = mu^o_k + RTln(P*X_k/P^o)

IMHO, this should be spelled out in the science section of Cantera's website, but we just haven’t gotten there, yet.

Thanks - hope this helps,

Steven

——————————————————————————————————

Steven DeCaluwe, PhD | Associate Professor of Mechanical Engineering

COLORADOSCHOOLOFMINES

Brown Building W410B

Golden, CO 80401

email: deca...@mines.edu

phone: (303) 273-3666

Twitter: @CORESresearch
http://people.mines.edu/decaluwe/

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