Thermodynamic properties of water from SAFT and CPA equations of state: A comprehensive assessment

The performance of eight versions of the representative and most commonly used Statistical-AssociationFluid-Theory (SAFT) equations of state for water along with the Cubic-Plus-Association (CPA) equation are examined in detail both throughout the entire liquid phase region and at supercritical conditions. In addition to the temperature-pressure dependence of density, the fundamental response functions, namely, isothermal compressibility, isobaric expansivity, and isobaric heat capacity, have been evaluated and compared with experimental data along five isobars from P = 0:1 MPa up to 1000 MPa, and along four isotherms within the range from 300 K to 750 K. It turns out that to draw a general conclusion on the quality and accuracy of these equations (for pure water) is practically impossible with different equations reproducing reasonably well different properties and at different thermodynamic conditions but failing in other instances. In general, the equations seem to be able to capture simple pressure dependence at isothermal conditions but fail primarily in estimating isobaric properties. All the equations (i) tend to perform reasonably well at pressures above the critical one where the excluded volume begins to predominate and the effect of hydrogen bonding becomes insignificant, (ii) but fail again at very high pressures, and (iii) have the most serious problems with predicting the residual isobaric heat capacity. The most successful results are obtained from the recently developed Association Dependent PC-SAFT equation, which can be mainly attributed to its fitting using a broader set of experimental data compared to other equations; nonetheless, its performance still cannot be considered as overall reliable.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

The performance of eight versions of SAFT equations and CPA equation for water is examined in different thermodynamic conditions. It is found that these equations have inconsistent results for different properties of water, making it practically impossible to draw a general conclusion. The equations can reasonably reproduce pressure dependence at isothermal conditions but fail in estimating isobaric properties. The Association Dependent PC-SAFT equation shows the most successful performance due to its fitting using a broader set of experimental data.