# thermo.acentric module¶

thermo.acentric.omega(CASRN, AvailableMethods=False, Method=None, IgnoreMethods=['LK', 'DEFINITION'])[source]

This function handles the retrieval of a chemical’s acentric factor, omega, or its calculation from correlations or directly through the definition of acentric factor if possible. Requires a known boiling point, critical temperature and pressure for use of the correlations. Requires accurate vapor pressure data for direct calculation.

Will automatically select a method to use if no Method is provided; returns None if the data is not available and cannot be calculated.

$\omega \equiv -\log_{10}\left[\lim_{T/T_c=0.7}(P^{sat}/P_c)\right]-1.0$
Parameters: Returns: CASRN : string CASRN [-] omega : float Acentric factor of compound methods : list, only returned if AvailableMethods == True List of methods which can be used to obtain omega with the given inputs Method : string, optional The method name to use. Accepted methods are ‘PSRK’, ‘PD’, ‘YAWS’, ‘LK’, and ‘DEFINITION’. All valid values are also held in the list omega_methods. AvailableMethods : bool, optional If True, function will determine which methods can be used to obtain omega for the desired chemical, and will return methods instead of omega IgnoreMethods : list, optional A list of methods to ignore in obtaining the full list of methods, useful for for performance reasons and ignoring inaccurate methods

Notes

A total of five sources are available for this function. They are:

• ‘PSRK’, a compillation of experimental and estimated data published in the Appendix of [15]_, the fourth revision of the PSRK model.
• ‘PD’, an older compillation of data published in (Passut & Danner, 1973) [16]_.
• ‘YAWS’, a large compillation of data from a variety of sources; no data points are sourced in the work of [17]_.
• ‘LK’, a estimation method for hydrocarbons.
• ‘DEFINITION’, based on the definition of omega as presented in [R1], using vapor pressure data.

References

 [R1] (1, 2) Pitzer, K. S., D. Z. Lippmann, R. F. Curl, C. M. Huggins, and D. E. Petersen: The Volumetric and Thermodynamic Properties of Fluids. II. Compressibility Factor, Vapor Pressure and Entropy of Vaporization. J. Am. Chem. Soc., 77: 3433 (1955).
 [R2] Horstmann, Sven, Anna Jabłoniec, Jörg Krafczyk, Kai Fischer, and Jürgen Gmehling. “PSRK Group Contribution Equation of State: Comprehensive Revision and Extension IV, Including Critical Constants and Α-Function Parameters for 1000 Components.” Fluid Phase Equilibria 227, no. 2 (January 25, 2005): 157-64. doi:10.1016/j.fluid.2004.11.002.
 [R3] Passut, Charles A., and Ronald P. Danner. “Acentric Factor. A Valuable Correlating Parameter for the Properties of Hydrocarbons.” Industrial & Engineering Chemistry Process Design and Development 12, no. 3 (July 1, 1973): 365-68. doi:10.1021/i260047a026.
 [R4] Yaws, Carl L. Thermophysical Properties of Chemicals and Hydrocarbons, Second Edition. Amsterdam Boston: Gulf Professional Publishing, 2014.

Examples

>>> omega(CASRN='64-17-5')
0.635

thermo.acentric.LK_omega(Tb, Tc, Pc)[source]

Estimates the acentric factor of a fluid using a correlation in [R5].

$\omega = \frac{\ln P_{br}^{sat} - 5.92714 + 6.09648/T_{br} + 1.28862 \ln T_{br} -0.169347T_{br}^6} {15.2518 - 15.6875/T_{br} - 13.4721 \ln T_{br} + 0.43577 T_{br}^6}$
Parameters: Tb : float Boiling temperature of the fluid [K] Tc : float Critical temperature of the fluid [K] Pc : float Critical pressure of the fluid [Pa] omega : float Acentric factor of the fluid [-]

Notes

Internal units are atmosphere and Kelvin. Example value from Reid (1987). Using ASPEN V8.4, LK method gives 0.325595.

References

 [R5] (1, 2) Lee, Byung Ik, and Michael G. Kesler. “A Generalized Thermodynamic Correlation Based on Three-Parameter Corresponding States.” AIChE Journal 21, no. 3 (1975): 510-527. doi:10.1002/aic.690210313.

Examples

Isopropylbenzene

>>> LK_omega(425.6, 631.1, 32.1E5)
0.32544249926397856

thermo.acentric.omega_mixture(omegas, zs, CASRNs=None, Method=None, AvailableMethods=False)[source]

This function handles the calculation of a mixture’s acentric factor. Calculation is based on the omegas provided for each pure component. Will automatically select a method to use if no Method is provided; returns None if insufficient data is available.

Parameters: Returns: omegas : array-like acentric factors of each component, [-] zs : array-like mole fractions of each component, [-] CASRNs: list of strings CASRNs, not currently used [-] omega : float acentric factor of the mixture, [-] methods : list, only returned if AvailableMethods == True List of methods which can be used to obtain omega with the given inputs Method : string, optional The method name to use. Only ‘SIMPLE’ is accepted so far. All valid values are also held in the list omega_mixture_methods. AvailableMethods : bool, optional If True, function will determine which methods can be used to obtain omega for the desired chemical, and will return methods instead of omega

Notes

The only data used in the methods implemented to date are mole fractions and pure-component omegas. An alternate definition could be based on the dew point or bubble point of a multicomponent mixture, but this has not been done to date.

References

 [R6] Poling, Bruce E. The Properties of Gases and Liquids. 5th edition. New York: McGraw-Hill Professional, 2000.

Examples

>>> omega_mixture([0.025, 0.12], [0.3, 0.7])
0.0915

thermo.acentric.StielPolar(Tc=None, Pc=None, omega=None, CASRN='', Method=None, AvailableMethods=False)[source]

This function handles the calculation of a chemical’s Stiel Polar factor, directly through the definition of Stiel-polar factor if possible. Requires Tc, Pc, acentric factor, and a vapor pressure datum at Tr=0.6.

Will automatically select a method to use if no Method is provided; returns None if the data is not available and cannot be calculated.

$x = \log P_r|_{T_r=0.6} + 1.70 \omega + 1.552$
Parameters: Returns: Tc : float Critical temperature of fluid [K] Pc : float Critical pressure of fluid [Pa] omega : float Acentric factor of the fluid [-] CASRN : string CASRN [-] factor : float Stiel polar factor of compound methods : list, only returned if AvailableMethods == True List of methods which can be used to obtain Stiel polar factor with the given inputs Method : string, optional The method name to use. Only ‘DEFINITION’ is accepted so far. All valid values are also held in the list Stiel_polar_methods. AvailableMethods : bool, optional If True, function will determine which methods can be used to obtain Stiel-polar factor for the desired chemical, and will return methods instead of stiel-polar factor

Notes

Only one source is available for this function. It is:

• ‘DEFINITION’, based on the definition of Stiel Polar Factor presented in [R7], using vapor pressure data.

A few points have also been published in [R8], which may be used for comparison. Currently this is only used for a surface tension correlation.

References

 [R7] (1, 2) Halm, Roland L., and Leonard I. Stiel. “A Fourth Parameter for the Vapor Pressure and Entropy of Vaporization of Polar Fluids.” AIChE Journal 13, no. 2 (1967): 351-355. doi:10.1002/aic.690130228.
 [R8] (1, 2) D, Kukoljac Miloš, and Grozdanić Dušan K. “New Values of the Polarity Factor.” Journal of the Serbian Chemical Society 65, no. 12 (January 1, 2000). http://www.shd.org.rs/JSCS/Vol65/No12-Pdf/JSCS12-07.pdf

Examples

>>> StielPolar(647.3, 22048321.0, 0.344, CASRN='7732-18-5')
0.024581140348734376