Asymmetric Scaled Equation of State and Critical Behavior of Binary Mixtures

1988 ◽  
Vol 110 (4a) ◽  
pp. 986-991 ◽  
Author(s):  
M. A. Anisimov ◽  
S. B. Kiselev ◽  
I. G. Kostukova
Keyword(s):  
Heat Capacity ◽  
Free Energy ◽  
Equation Of State ◽  
Binary Mixtures ◽  
Critical Line ◽  
Universal Function ◽  
Wide Neighborhood ◽  
Critical Isochore ◽  
Experimental Heat ◽  
Capacity Data

An equation of state for binary mixtures, accounting for the asymmetry with respect to the critical isochore in the wide neighborhood of the liquid–gas critical line, has been obtained on the basis of the isomorphic scaled free energy of mixtures and the extended scaled equation of state for pure fluids. Universal behavior of critical binary mixtures is demonstrated. The universal function is used for the description of experimental heat capacity data for a number of binary mixtures.

scholarly journals Estimating a Stoichiometric Solid’s Gibbs Free Energy Model by Means of a Constrained Evolutionary Strategy

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 471
Author(s):  
Constantino Grau Turuelo ◽  
Sebastian Pinnau ◽  
Cornelia Breitkopf
Keyword(s):  
Heat Capacity ◽  
Free Energy ◽  
Evolutionary Strategy ◽  
Data Sets ◽  
Automatic Data ◽  
Physical Constraints ◽  
Stoichiometric Model ◽  
Covariance Matrix Adaptation ◽  
Dsc Measurements ◽  
Capacity Data

Modeling of thermodynamic properties, like heat capacities for stoichiometric solids, includes the treatment of different sources of data which may be inconsistent and diverse. In this work, an approach based on the covariance matrix adaptation evolution strategy (CMA-ES) is proposed and described as an alternative method for data treatment and fitting with the support of data source dependent weight factors and physical constraints. This is applied to a Gibb’s Free Energy stoichiometric model for different magnesium sulfate hydrates by means of the NASA9 polynomial. Its behavior is proved by: (i) The comparison of the model to other standard methods for different heat capacity data, yielding a more plausible curve at high temperature ranges; (ii) the comparison of the fitted heat capacity values of MgSO4·7H2O against DSC measurements, resulting in a mean relative error of a 0.7% and a normalized root mean square deviation of 1.1%; and (iii) comparing the Van’t Hoff and proposed Stoichiometric model vapor-solid equilibrium curves to different literature data for MgSO4·7H2O, MgSO4·6H2O, and MgSO4·1H2O, resulting in similar equilibrium values, especially for MgSO4·7H2O and MgSO4·6H2O. The results show good agreement with the employed data and confirm this method as a viable alternative for fitting complex physically constrained data sets, while being a potential approach for automatic data fitting of substance data.

scholarly journals High - temperature and high-pressure (p, ρ, T) measurements and derived thermodynamic properties of 1-octyl-3-methylimidazolium hexafluorophosphate

2020 ◽  
Vol 85 (2) ◽  
pp. 237-250
Author(s):  
Javid Safarov ◽  
Christoffer Bussemer ◽  
Abilgani Aliyev ◽  
Gorica Ivanis ◽  
Mirjana Kijevcanin ◽  
...  
Keyword(s):  
Heat Capacity ◽  
High Pressure ◽  
High Temperature ◽  
Equation Of State ◽  
Thermodynamic Properties ◽  
High Pressures ◽  
Type Equation ◽  
Isentropic Compressibility ◽  
Primary Data ◽  
Capacity Data

Densities of ionic liquid (IL) 1-octyl-3-methylimidazolium hexafluorophosphate [OMIM][PF6] at high temperatures and high pressures were measured. The measurements were made along 10 isotherms over a temperature range T = 278.15 to 413.15 K, at pressures up to 140 MPa by means of an Anton Paar DMA HPM vibration tube densimeter (VTD). The combined expanded relative uncertainties of the density, pressure and temperature measurements at the 95 % confidence level with a coverage factor of k = 2 are estimated to be 0.03 to 0.08 % (depending on temperature and pressure ranges), 0.1 %, and 0.015 K, respectively. We have critically assessed all of the reported high-pressure densities for [OMIM][PF6], together with the presented results, in order to carefully select primary data for development of a reference wide-ranging equation of state. Values of ??T isobars curvatures, (?2?/?T2)?, were estimated using the present high-pressure ?-T measurements and they were pretty low (0.78?10-7 to 1.50??10-7 m3 kg-1 K-1), indicating that the heat capacity of [OMIM][PF6] very weakly depends on pressure, since (?Cp/?P)T ?(?2?/?T2)?. Density data were fitted to the modified Tammann?Tait equation and the multiparametric polynomial-type equation of state (EOS) for the IL was developed using the measured high-pressure and high-temperature (p, ?, T) data. This EOS, together with our previous measured heat capacity data at atmospheric pressure, was used to calculate high-pressure and high-temperature derived thermodynamic properties, such as isothermal compressibility,isentropic compressibility, isobaric thermal expansion coefficient, heat capacities,etc.

scholarly journals Method for constructing the fundamental equation of state that takes into account the peculiarities of the substance behaviour in a wide vicinity of the critical point

2021 ◽  
Vol 2057 (1) ◽  
pp. 012112
Author(s):  
S V Rykov ◽  
I V Kudryavtseva
Keyword(s):  
Heat Capacity ◽  
Free Energy ◽  
Equation Of State ◽  
Critical Point ◽  
Fundamental Equation ◽  
Virial Coefficients ◽  
Phenomenological Theory ◽  
Phase Region ◽  
Scale Functions ◽  
Fundamental Equation Of State

Abstract On the basis of the phenomenological theory of the critical point and the Benedek hypothesis, an expression for the Helmholtz free energy F with scale functions in the density-temperature variables has been developed. The proposed free energy equation has been tested on the example of constructing the fundamental equation of state of 2,3,3,3-tetrafluoropropene (R1234yf). By comparison with the known experimental data on the equilibrium properties of R1234yf – density and pressure on the phase equilibrium line, p-ρ-T-data in the single-phase region, the second and third virial coefficients, isochoric heat capacity, isobaric heat capacity and the sound velocity – the operating range of the equation of state of R1234yf has been established according to temperature from 220 K to 420 K and pressure up to 20 MPa.

Thermal Properties of Alcaline-Earth-Oxides / III. Analysis of Anharmonic Effects

1972 ◽  
Vol 27 (4) ◽  
pp. 605-612 ◽  
Author(s):  
E. Gmelin ◽  
S. Vieira
Keyword(s):  
Heat Capacity ◽  
Thermal Properties ◽  
High Temperature ◽  
Order Approximation ◽  
First Order ◽  
Anharmonic Effects ◽  
Experimental Heat ◽  
Theoretical Predictions ◽  
First Order Approximation ◽  
Capacity Data

Abstract Experimental heat capacity data for the alcaline-earth-oxides have been used to analyse by a new method the high temperature thermodynamic properties of these crystals in terms of quasi-harmonic and explicit anharmonic contributions. The explicit anharmonic contribution ΔC is consistent with theoretical predictions; ΔC is proportional to T in a first order approximation. The factor of anharmonicity A is negative for MgO, A = (-0.4 + 0.4) · 10-5 K-1 , for SrO A= (-2.8±1) · 10-5 K-1 and for BaO A=(-3.9±1) ·10-5 K-1 , but positive for CaO A = (2.3 ± 1.2) · 10-5 K-1. Comparison with the results of analysis of the anharmonic effects in the alcaline-halides shows that the alcaline-earth-oxides may be treated by the same models valuable for the alcaline-halides. The results suggest that the type of anharmonic forces is determined in the alcaline-halides as well as in the alcaline-earth-oxides primarily by the cation of the salt.

scholarly journals Saturated-liquid heat capacity calculation of alkanes

2005 ◽  
Vol 70 (12) ◽  
pp. 1545-1551 ◽  
Author(s):  
Jovan Jovanovic ◽  
Dusan Grozdanic
Keyword(s):  
Heat Capacity ◽  
Critical Point ◽  
Empirical Model ◽  
Heat Capacity Data ◽  
Saturated Liquid ◽  
New Model ◽  
Experimental Heat ◽  
Capacity Calculation ◽  
Liquid Heat ◽  
Capacity Data

An empirical model for the calculation of the heat capacity of alkanes is recommended. This model was tested and compared to known models (Luria-Benson and R?zicka-Domalski) using 68 sets with 1155 literature experimental heat capacity data of 39 alkanes. The obtained results indicate that the new model is slightly better of the existing models, especially near the critical point.

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