Evaluating Cubic Equations of State with Various α Functions for Viscosity Predictions of 124 Industrial Important Fluids Based on Residual Entropy Scaling

Accurate prediction of viscosity remains a challenge
in industry
due to the lack of reliable simple universal models. This work investigates
the accuracy of four cubic equations of state (EOS) with different
α functions for pure fluid viscosity predictions based on the
residual entropy scaling (RES). The cubic EOS are Peng–Robinson
(PR), Soave–Redlich–Kwong (SRK), Patel-Teja-Valderrama
(PTV), and Yang-Frotscher-Richter (YFR), and the α functions
are those proposed by Twu et al., Coquelet et al., Mahmoodi and Sedigh,
and Heyen et al. The investigation utilizes the approximately 54,000
experimental viscosity data of 124 pure fluids at pressures below
60 MPa, mainly obtained from the NIST TDE (ThermoData Engine) database.
Compared to a previous study (ACS Omega 2025, 10, 6124), which focused on the Soave α function,
the adoption of modified α functions led to improved viscosity
predictions for 39 out of the 124 studied substances. Notable enhancements
are observed for R1234ze(E) and SO2 with PTV-Heyen and
for CO2 with PR-Twu. The absolute average deviation (AAD)
between experimental values and model predictions is 3.1% (PR, SRK,
and YFR), 3.0% (PTV), 3.4% (PR-Twu and SRK-Coquelet), 3.2% (PTV-Heyen
and SRK-MS), 3.5% (PR-Coquelet), and 3.3% (PR-MS). As a reference,
the AAD of the various reference models implemented in REFPROP 10.0
is 2.7%. This work demonstrates the potential of integrating optimized
α functions to improve the predictive capabilities for viscosity
within the cubic EOS + RES framework for certain specific pure fluids.
Additionally, a recommended combination of cubic EOS and α function
is provided for each fluid studied.