Residual Functions for the SRK and PR Equations of State

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In the gas phase, deviation from ideal behavior is taken into account by introducing residual functions, of the form . As pressure approaches zero, the gas behaves like an ideal gas, so that .


This Demonstration plots the gas-phase residual properties for the gas propylene versus temperature (in Kelvin) using either the Soave–Redlich–Kwong (SRK) or the Peng–Robinson (PR) equation of state (EoS) [1, 2]. Use the slider to set the value of the pressure (in bar) and choose among three thermodynamic properties: (enthalpy in J/mol), (entropy in J/mol.K) or (Gibbs free energy in J/mol). At , we get an excellent agreement between the results of our calculations (red curve for the SRK EoS, blue for PR EoS) and their counterparts obtained with the Aspen Plus process simulator [3] (green squares).


Contributed by: Housam Binous and Ahmed Bellagi (December 2016)
Open content licensed under CC BY-NC-SA




[1] J. M. Smith, H. C. Van Ness and M. M. Abbott, Introduction to Chemical Engineering Thermodynamics, 7th ed., Boston: McGraw-Hill, 2005.

[2] J. R. Elliott and C. T. Lira, Introductory Chemical Engineering Thermodynamics, 2nd ed., Englewood Cliffs, NJ: Prentice Hall International Editions, 2012.

[3] Aspentech. "Aspen Plus." (Dec 19, 2016)

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