Thermodynamic Properties Of Real Fluids Research Articles

Efficient Thermodynamic Properties Reconstruction Method with Adaptive Triangular Mesh

This paper presents an efficient procedure to reconstruct the thermodynamic properties of real fluids. An equation-of-state look-up table was constructed with adaptive triangular mesh, which not only provided user-specified accuracy over a selected thermodynamic plane with few grids, but also ensured reconstruction continuity. The triangle could be searched with either the tree data structure or the overlapping uniform index domain. Thermodynamic properties could be reconstructed with the , , or method, which provided different levels of function continuity and thermodynamic consistency. The overlapping uniform index domain increased the searching speed by a factor of 2 and the memory by less than 37% compared with the tree data structure. Property reconstruction on the adaptive triangular mesh was 8–27% slower than that on the uniform mesh and was 2 orders of magnitude faster than the complex equations of state.

Calculation of thermodynamic properties of simple fluids using a new derived pair correlation function

Based on a new derived radial distribution function (RDF) for potentials with a hard-core we have presented in this paper a method to apply the derived RDF for calculating thermodynamic properties of real fluids up to moderate densities. In order to use the derived RDF for real fluids, one of the potential parameters is chosen in such a way that the RDF behaves more like that for a real fluid. Hence we have been able to calculate all thermodynamic properties of a simple fluid analytically. We have then applied our procedure to a Lennard–Jones fluid and compared the results with simulation data. The agreement is good up to moderate densities, i.e. ρ* ≤ 0.6, which lies in the liquid range of Lennard–Jones fluid. We have also applied our method to a real fluid, i.e., argon. We supposed that argon is an example of a Lennard–Jones fluid. The calculated results are in good agreement with experimental data for gaseous state of argon. For the liquid state the agreement is not as good as that found for the gaseous fluid.

Statistical Approach to Calculate Thermodynamic Properties for Propane

The paper describes a mathematical model to compute equilibrium thermodynamic properties in the fluid phase of pure hydrocarbons with the aid of classical thermodynamics and statistical associating chain theories. In the present paper thermodynamic properties for propane, as an example of hydrocarbon substances, are calculated. To calculate the thermodynamic properties of real fluids, models based on the Lennard–Jones intermolecular potential were applied. To calculate the thermodynamic properties of real fluids with the aid of classical thermodynamics, Miyamoto–Watanabe (MW) equations, developed in terms of the Helmholtz energy were used. Analytical results obtained by statistical thermodynamics are compared with the MW model and show relatively good agreement.

A Novel Equation of State for the Prediction of Thermodynamic Properties of Fluids

This work proposes a new equation of state (EOS) based on molecular theory for the prediction of thermodynamic properties of real fluids. The new EOS uses a novel repulsive term, which gives the correct hard sphere close packed limit and yields accurate values for hard sphere and hard chain virial coefficients. The pressure obtained from this repulsive term is corrected by a combination of van der Waals and Dieterici potentials. No empirical temperature functionality of the parameters has been introduced at this stage. The novel EOS predicts the experimental volumetric data of different compounds and their mixtures better than the successful EOS of Peng and Robinson. The prediction of vapor pressures is only slightly less accurate than the results obtained with the Peng-Robinson equation that is designed for these purposes. The theoretically based parameters of the new EOS make its predictions more reliable than those obtained from purely empirical forms.

An application of statistical chain theories on thermodynamic properties of hydrocarbon refrigerants

The paper features the mathematical modeling to compute the equilibrium thermodynamic properties in the fluid phase of pure hydrocarbons with the aid of classical thermodynamics and statistical associating chain theories. In the present paper, we calculated thermodynamic properties for methane, ethane, n-butane and propane as the examples of hydocarbon substances. To calculate the thermodynamic properties of real fluid the models on the basis of Lennard–Jones intermolecular potential and statistical associating fluid theory were applied. We developed expressions for semi-theoretical Liu–Li–Lu model (LLL) and purely analytical Tang–Lu (TL) model obtained on the basis of salvation Orestein–Zernike EOS. To calculate the thermodynamic properties of real fluid with the aid of classical thermodynamics, we used Miyamoto–Watanabe (MW) equations developed in terms of Helmhotz energy. We developed the mathematical model for the calculation of all the thermodynamic functions of state for pure hydrocarbons. The analytical results obtained by statistical thermodynamics are compared with the MW model and show relatively good agreement.

Calculation of thermodynamic properties for refrigerants

For the Lennard-Jones fluid, a mathematical model for computing thermodynamic functions of state in the liquid and gas domain with the help of statistical thermodynamics is developed. To calculate the thermodynamic properties of real fluid, the Johnson-Zollweg-Gubbins model based on the modified Benedict-Webb-Rubin equation of state, Chunxi-Yigui-Jiufang (revisited Cotterman) equation of state based on simple perturbation theory, and complex Tang-Tong-Lu model based on the solution of the Ornstein-Zernike equation with the help of perturbation theory, were applied. The analytical results are compared with the experimental and thermodynamic data and models obtained by classical thermodynamics, and show relatively good agreement.

Generalised hydrogen-bonding lattice-fluid theory for thermodynamics of complex systems

A generalised hydrogen-bonding molecular theory of associated systems is proposed based on the nonrandom-lattice-fluid theory and Veytsman statistics. By the two-fluid approximation, configurational Helmholtz free energy was derived from the lattice of the Guggenheim combinatory. The approximate nature of the model makes it possible to unify the classical lattice theory with hydrogen bonding. The model requires only two molecular parameters for a pure fluid. For a binary mixture an additional interaction parameter is needed. Results demonstrated that the model correlates quantitatively the first-order and second-order thermodynamic properties of real fluids. The model is especially relevant to (multi)phase equilibria of systems containing molecularly complex species such as electron donor- acceptors and macromolecules. The model is quantitatively applied to vapour and liquid densities and vapour pressures of pure systems, various vapour-liquid equilibria, and vapour--solid equilibria of associated mixtures with temperature-independent interaction parameters. Also, the model even characterised liquid-- liquid equilibria employing temperature-dependent binary interaction parameters well.

The Calculation of Velocity of Sound near the Liquid‐Gas Transition

AbstractThe paper features the mathematical model of thermodynamic functions of state in gas‐liquid region for pure refrigerants with the help of classical thermodynamics and statistical thermodynamics. To calculate the thermodynamic properties of real fluid we used models on the base of Lennard‐Jones intermolecular potential.

A sequential-analytic method for determining the radial distribution function and predicting the thermodynamic properties of real fluids

A new concept of differential phase has been proposed. The flux of molecules between two phases, rather than the fugacity, is used to formulate the phase equilibrium. A double-resistance physical model is presented for modelling the flow of molecules through the interface of two phases. By equating the equilibrium between differential phase and bulk phase, a generalized sequential-analytic method for determining the radial distribution function (RDF) is developed. The proposed method is capable of giving RDF values close to those obtained by molecular simulation. It has been shown that when coupled with the Lennard-Jones potential model, the pressure-volume-temperature (PVT) relation of pure fluids with molecular size up to n-hexane can be predicted satisfactorily in wide ranges of temperature and pressure.

The Lennard-Jones fluid revisited: new thermodynamic data and new equation of state

Abstract The Lennard-Jones fluid appeared as a natural benchmark during the work on the project aimed at utilizing the rigorous statistical mechanical results for practical equation of state calculations for real fluids. As already reported, however, the so far available molecular simulation data and analytical equations of state were found unsatisfactory for the purpose. Hence a new highly accurate set of data on pressure (-volume-temperature) and internal energy by the Monte-Carlo and molecular dynamics methods and on the chemical potential by Monte Carlo with the new version of the insertion particle method was generated. The data has been used to develop and test a new accurate perturbed hard body equation of state for the Lennard-Jones fluid. The performance of the equation of state on pseudoexperimental data is documented and possible applications of the equation of state for calculating the thermodynamic properties of real fluids are discussed.