Multi-criteria Optimization for Parameterization of SAFT-type Equations of State for Water

Finding appropriate parameter sets for a given equation of state (EoS) to describe different properties of a certain substance is an optimization problem with conflicting objectives. Such problem is commonly addressed by single-criteria optimization in which the different objectives are lumped into a single goal function. We show how multi-criteria optimization (MCO) can be beneficially used for parameterizing equations of state. The Pareto set, which comprises a set of optimal solutions of the MCO problem, is determined. As an example, the perturbed-chain statistical associating fluid theory (PC-SAFT) EoS is used and applied to the description of the thermodynamic properties of water, focusing on saturated liquid density and vapor pressure. Different options to describe the molecular nature of water by the PC-SAFT EoS are studied and for all variants, the Pareto sets are determined, enabling a comprehensive assessment. When compared to literature models, Pareto optimization yields improved models.

A New Four-Parameter Cubic Equation of State for Predicting Fluid Phase Behavior

<p>A new four-parameter cubic equation of state (EoS) is generated by incorporating the critical compressibility factor (Z_c) apart from the critical pressure (P_c) and temperature (T_c). One free parameter in the denominator of the attractive term and two parameters in the alpha function are adjusted using the experimental data of saturated liquid density, vapor pressure, and isobaric liquid heat capacity of 48 components including hydrocarbons and non-hydrocarbons. Applying this equation of state, saturated liquid density, saturated vapor density, and vapor pressure of pure components are accurately reproduced compared with experimental values. Furthermore, the predicted properties including derivatives of alpha function, such as enthalpy of vaporization, entropy of vaporization and isobaric heat capacity of liquid, also have decent accuracy. The global average absolute relative deviation (AAD) of saturated liquid density, saturated vapor density, saturated vapor pressure, enthalpy of vaporization, entropy of vaporization, and isobaric heat capacity of liquid in a wide reduced temperature (Tr) range of subcritical region reproduced by this work are 4.33%, 4.18%, 3.19%, 2.26%, 2.27%, and 5.82%, respectively. Substantial improvement has been achieved for the isobaric liquid heat capacity calculation.</p>

A New Four-Parameter Cubic Equation of State for Predicting Fluid Phase Behavior

<p>A new four-parameter cubic equation of state (EoS) is generated by incorporating the critical compressibility factor (Z_c) apart from the critical pressure (P_c) and temperature (T_c). One free parameter in the denominator of the attractive term and two parameters in the alpha function are adjusted using the experimental data of saturated liquid density, vapor pressure, and isobaric liquid heat capacity of 48 components including hydrocarbons and non-hydrocarbons. Applying this equation of state, saturated liquid density, saturated vapor density, and vapor pressure of pure components are accurately reproduced compared with experimental values. Furthermore, the predicted properties including derivatives of alpha function, such as enthalpy of vaporization, entropy of vaporization and isobaric heat capacity of liquid, also have decent accuracy. The global average absolute relative deviation (AAD) of saturated liquid density, saturated vapor density, saturated vapor pressure, enthalpy of vaporization, entropy of vaporization, and isobaric heat capacity of liquid in a wide reduced temperature (Tr) range of subcritical region reproduced by this work are 4.33%, 4.18%, 3.19%, 2.26%, 2.27%, and 5.82%, respectively. Substantial improvement has been achieved for the isobaric liquid heat capacity calculation.</p>

BACKONE equation of state for Cis-1, 3, 3, 3-tetrafluoropropene (R1234ze(Z))

This paper presents the study on the determination of the thermodynamic properties of Cis-1,3,3,3-tetrafluoropropene (R1234ze(Z)) with the BACKONE equation of state. The BACKONE's characteristic temperature T0, characteristic density ρ0, anisotropy factor α, and reduce quarupole moment Q*2 were found by fitting the BACKONE EOS to experimental data of vapor pressure and saturated liquid density. All thermodynamic properties such as vapor pressure, pressure in gaseous phase, saturated liquid density, and liquid density can be determined easily from the found molecular characteristic properties. Thermodynamic properties of the R1234ze(Z) were evaluated with available experimental data. Average absolute deviations between calculated vapor pressure data and experimental data were 0.43%. Average absolute deviations between calculated saturated liquid density data and experimental data were 0.43%. In the prediction of the thermodynamic properties, average absolute deviations between calculated liquid density data and experimental data were 0.68% and average absolute deviations between calculated gas density data and experimental data were 1.6%.