Equations forms for alpha formulations
- Last UpdatedJul 08, 2025
- 4 minute read
When you configure a Fluid Type that uses an equation of state (EOS) as the thermodynamic method, you can choose whether the Fluid Type uses the standard acentric factor formulation to calculate the alpha parameter (ai) or uses the set of alpha formulations from user-specified ALPHA data banks. If you select Alpha Databanks in the Alpha Selection list in the Fluid Editor, the software uses different alpha formulations for each component depending on the alpha data in the data banks that you add to the Alpha Data Banks box.
If there is any alpha data missing from the selected ALPHA data banks, the software calculates the alpha value based on the acentric factor formulation.
Warning: If you use a custom ALPHA data bank, you should also use a binary interaction data bank that contains adjusted binary interaction parameters that correspond to the alpha data in your custom ALPHA data bank.
The following table lists the available alpha formulations. The number in the Form column in this table corresponds to the number that you enter in the FORM column in AVEVA Thermodynamic Data Manager when you specify the alpha data.
|
Form |
Equation |
Reference |
|---|---|---|
|
01 |
|
Soave (1972) |
|
02 |
|
Peng-Robinson (1980) |
|
03 |
|
Soave (1979) |
|
04 |
|
Boston-Mathias (1980) |
|
05 |
|
Twu (1988) |
|
06 |
|
Twu-Bluck-Cunningham-Coon (1991) (Recommended by SimSci) |
|
07 |
|
Alternative for form (04) |
|
08 |
|
Alternative for form (06) |
|
09 |
|
Mathias-Copeman (1983) |
|
10 |
|
Mathias (1983) |
|
11 |
|
Melhem-Saini-Goodwin (1989) |
For all alpha formulations:
where
C1, C2, and C3 are constants from the ALPHA data bank
Tc is the critical temperature
References
-
Soave, G., "Equilibrium Constants from a Modified Redlich-Kwong Equation of State", Chem. Eng. Sci., 1972, 27(6), 1197–1203.
-
Peng, D. -Y. and Robinson, D. B., "Two- and Three-Phase Equilibrium Calculations for Coal Gasification and Related Processes", Thermodynamics of Aqueous Systems with Industrial Applications, 1980, 393–414.
-
Soave, G, "Application of a Cubic Equation of State to Vapor-Liquid Equilibria of Systems Containing Polar Components", Inst. Chem. Eng. Symp. Ser., 1979, 56(1), 1.2/1–1.2/1.6.
-
Boston, J. F. and Mathias, P. M., "Phase Equilibria in a Third Generation Process Simulation", Proc. of the 2nd Inter. Conf. on Phase Equil. & Fluid Properties in the Chemical Process Industries, Berlin (West), 1980, March 17–21.
-
Twu, C. H, "A Modified Redlich-Kwong Equation of State for Highly Polar, Super-critical Systems", Inter. Symp. on Thermodynamics in Chemical Engineering and Industry, 1988, May 30–June 2.
-
Twu, C. H., Bluck, D., Cunningham, J. R., and Coon, J. E., "A Cubic Equation of State with a New Alpha Function and New Mixing Rule", Fluid Phase Equil., 1991, 69, 33–50.
-
Mathias, P. M. and Copeman, T. W., "Extension of the Peng-Robinson Equation of State to Complex Mixtures", Fluid Phase Equil., 1983, 13, 91–108.
-
Mathias, P. M., "A Versatile Phase Equilibrium Equation of State", Ind. Eng. Chem. Proc. Des. Dev., 1983, 22, 358–391.
-
Melhem, G. A., Saini, R., and Goodwin, B. M., "A Modified Peng-Robinson Equation of State", Fluid Phase Equil., 1989, 47, 189–237.