Additional equation forms for alpha formulations

In addition to the set of alpha formulations from user-specified ALPHA data banks in AVEVA Thermodynamic Data Manager, you can use the Redlich-Kwong formulation or a generalized formulation[1,2] to calculate the alpha parameter (ai).

Because these alpha formulations are not available in AVEVA Thermodynamic Data Manager, you must override the alpha form coefficients to use them for your components. You override the alpha form coefficients on the <EOS>_Alpha tab in the Method Data section of the Fluid Editor, where <EOS> is the equation of state (EOS) that you are using in the Fluid Type. See Override the alpha form coefficients for the equations of state for more information.

If you set the Alpha Form value to 12 for a component, the software uses the Redlich-Kwong formulation to calculate alpha:

where

Tc is the critical temperature

If you set the Alpha Form value to 13 for a component, the software uses a generalized formulation that depends on the acentric factor (w) and the reduced temperature (Tr). You should use the generalized formulation only for petrocomponents.

If you use an EOS from the Soave-Redlich-Kwong (SRK) family, such as SRK or Soave-Redlich-Kwong Modified Panagiotopoulos-Reid (SRKM), the software uses the following formulation to calculate alpha:

where

w is the acentric factor

If you use an EOS from the Peng-Robinson (PR) family, such as PR or Peng-Robinson Modified Panagiotopoulos-Reid (PRM), the software uses the following formulation to calculate alpha:

Reference

1. Twu, C. H.; Coon, J. E.; Cunningham, J. R. A New Generalized Alpha Function for a Cubic Equation of State Part 1. Peng-Robinson equation; part 2: Redlich-Kwong equation. Fluid Phase Equil. 1995, 105 (1), 49–59. DOI: 10.1016/0378-3812(94)02601-V

2. Twu, C. H.; Coon, J. E.; Cunningham, J. R. A New Generalized Alpha Function for a Cubic Equation of State Part 2. Redlich-Kwong equation. Fluid Phase Equil. 1995, 105 (1), 61–69. DOI: 10.1016/0378-3812(94)02602-W