Sharif Digital Repository

Regularities shown by different fluids along the contour of the ideal compressibility factor Z= PV/(RT)=1 in the temperature density plane was used to test the accuracy of the equations of state and derive temperature dependencies of their parameters. The contour, also known as the Zeno line, was empirically observed to be nearly linear. The precision of the van der Waals equation in predicting the Zeno line was evaluated. It was shown that the equation could predict a linear relation between temperature and density on the Z=1 contour, qualitatively  

We present in this paper a simple method of obtaining various equations of state for hard sphere fluid in a simple unifying way. Using the first several virial coefficients of hard sphere fluid, we will guess equations of state by using the asymptotic expansion method. Among the equations of state obtained in this way are Percus-Yevick, Scaled Particle Theory, and Carnahan-Starling equations of state. Also by combining the Monte Carlo results on hard sphere fluid with the asymptotic expansion method many other equations of state for hard sphere fluid can be found where all of them give essentially similar results in the region of isotropic hard sphere liquid, i.e., up to η < 0.5, in which η... 

In this paper, the accuracy of Peng-Robinson equation of state for vapor-liquid equilibrium calculations has been studied for pure polar compounds and is compared with some other equations of state. This equation has then been modified using the volume-translation technique to improve saturated liquid-volume predictions in low to intermediate temperature and pressure ranges. Two different generalized forms of the translation parameter have been proposed in terms of critical compressibility factor and the reduced dipole moment multiplied by the acentric factor. The proposed generalized equations demonstrate more accurate results compared with the original Peng-Robinson and other selected... 

A viscosity model, based on Eyring's absolute rate theory combined with a cubic PR equation of state and Wong-Sandler mixing rule, has been proposed in order to correlate viscosities of aqueous solutions of alkanolamine mixtures at atmospheric pressure and different temperatures. In the proposed method, the energy and size parameters in studied Equation of State (EoS) have been obtained using the Wong - Sandler (WS) mixing rule combined with the NRTL and Wilson Gibbs equations. The NRTL and Wilson parameters for aqueous solutions of alkanolamine mixtures have been correlated using measured viscosity data at atmospheric pressure and different temperatures. The overall average deviation... 

In this work, we consider each normal alkane as a hypothetical mixture of methyl and methylene groups, in which the interaction potential of each pair is assumed to be the average effective pair potential. Then, the LIR equation of state (EOS) is extended for such a hypothetical mixture. Also, three basic compounds, namely, propane, n-butane and cyclohexane, are used to obtain the contribution of each carbonic group in the EOS parameters. Using the calculated EOS parameters along with the modified EOS, the density of n-alkanes and their mixtures at different pressures and temperatures are calculated. The average percentage error in density is found to be less than 1.5% for both the pure... 

The predictions of the pair radial distribution function (RDF) at contact value, compressibility factor, and chemical potentials for binary and ternary hard-sphere mixtures obtained with the Barrio-Solana, the Santos et al., and the generalized Lebowitz mixing rules are compared using the Carnahan-Starling, Kolafa, and Khoshkbarchi-Vera one-component hard-sphere EOS. An expression for the pair RDF at contact value for Barrio-Solana mixing rule and the expressions for the chemical potentials in multicomponent hard-sphere fluids are derived. As a general rule, the equations of state obtained based on the generalized Lebowitz mixing rule predict better the pair RDF at contact value simulated... 

Using the newly introduced asymptotic expansion method to obtain equations of state for hard sphere fluid, new simple equations of state for hard disks based on known virial coefficients are derived. Comparison of the obtained equations of state with computer simulation data shows that they are accurate in the whole fluid region. © 2007 Elsevier B.V. All rights reserved  

In this paper, the Heidaryan and Jarrahian equation of state (Heidaryan and Jarrahian, 2013) has been adapted as a first worldwide cubic EOS to calculate the density of dry natural gases, wet natural gases, and single-phase gas condensates "sweet and sour mixtures" (up to 73.85, 97.63 and 38.37 mol percent of H2S, CO2, and N2 respectively) even when the gas composition is unknown, through new gas specific gravity correlation equations. Correction terms of water content as high as 10 mol percent of H2O and hythane (natural gas + hydrogen) as high as 74.9 mol percent of H2 were obtained. The equation of state was validated with 8985 experimental compressibility factor data points from 308... 

Cubic plus association (CPA) equations of state (EoSs) have found great interest in describing thermodynamic properties of associating fluids. In CPA EoSs, the association contribution proposed by Wertheim is added to cubic EoSs such as Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR). In different developments of CPA EoSs, adjusting the pure component properties such as critical temperature and critical pressure in addition to the association parameters is proposed in some works in the literature. In this work, the PR EoS has been extended to water, phenol, and a number of alcohols (methanol up to dodecanol) by addition of the Wertheim association contribution. In contrast to other CPA... 

In the present work, the thermodynamic of dense fluids, both compressed liquids and dense supercritical fluids, has been modeled, solely, based on the contribution of attraction of effective pair potential. The intermolecular interaction is modeled by the hard-core Yukawa potential (HCY) as an effective pair potential (EPP) with temperature dependent hard-core diameter. Using this EPP in the exact thermodynamic relations, an equation of state (EoS) for the compressibility factor of dense fluid has been derived. This EoS shows that (Z - ZCS) as function of ρ1/3 must be linear for each isotherm of fluid where ZCS is the compressibility factor of the reference fluid (Carnahan-Starling (CS) EoS)... 

In the present work, several new thermodynamic linear isotherm regularities for the dense fluids have been derived for the first time. For this purpose, the thermodynamic perturbation theory (TPT) employing only the attractive effective pair potential (AEPP) as u(r) = - ϵeff (σeff / r)m was used, where σeff which is the effective hard core diameter, is temperature dependent and m > 0. Based on the derived regularities, the isotherm (Z - Z(0))v2 is a linear function of ρ2, ρ and 1/ρ, depends on the values of m = 12, 9 and 6, respectively where Z - Z(0) is the difference between the experimental compressibility factor of the real fluid (Z) and that of the reference fluid (Z(0)). Also, Z - Z(0)... 

Volumetric and equilibrium calculations for the natural gas and oil defined by a large number of components are not feasible in applications like compositional reservoir simulation. Therefore, the fluid mixture is grouped to reduce computational load and to make faster calculations. However, for several reasons, it is required to have the detailed fluid composition rather than the lumped one. In this work, an improved delumping method is presented to retrieve the phase composition of the detailed mixture based on the grouped mixture thermodynamic calculations. The method is based on previously proposed delumping techniques for non-cubic equation of state (Assareh et al. in Fluid Phase... 

Cubic plus association (CPA) equations of state (EoSs) have found great interest in describing thermodynamic properties of associating fluids. In CPA EoSs, the association contribution proposed by Wertheim is added to cubic EoSs such as Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR). In different developments of CPA EoSs, adjusting the pure component properties such as critical temperature and critical pressure in addition to the association parameters is proposed in some works in the literature. In this work, the PR EoS has been extended to water, phenol, and a number of alcohols (methanol up to dodecanol) by addition of the Wertheim association contribution. In contrast to other CPA... 

This paper concerns extending applicability of Dehaghani association equation of state (in short DA-EOS) to model non-ideality in phase behavior caused by hydrogen bonding. Advantageously, this equation only needs two and one parameters to treat self- and cross association, respectively, which were determined for methanol/water and ethanol/water mixture in this study. In this respect, DA was coupled with PR and SRK EOS to account for physical interaction between molecules. Notably, DA-PR persistently provides more accurate prediction than DA-SRK for both aqueous methanol and ethanol solutions  

A colorimeter equipped with a gas booster in conjunction with a PVT cell was used to measure the heat capacity of natural gas with different amounts of impurities. Based on new experimental and literature data, a general investigation of the isobaric specific heat capacity was carried out using the Jarrahian-Heidaryan equation of state (J-H-EOS). A model was obtained that is valid in wide ranges of pressures (0.1-40. MPa) and temperatures (250-414. K). The arithmetic average of the model's absolute error is acceptable in engineering calculations and has superiority over other methods in its class  

An algorithm has been developed to investigate the effect of asphaltene precipitation on calculation of minimum miscibility pressure (MMP), which is one of the key design parameters of any gas injection projects. In fact, this algorithm is the extension of procedure suggested by Jaubert et al. for prediction of MMP whatever the displacement mechanism. The vapor-liquid equilibrium calculation and then liquid-liquid equilibrium calculation are required to be taken account to estimate the amount of asphaltene precipitation. The association equation of state (AEOS) has been applied to determine the phase behavior of asphaltene. The algorithm has been used for the MMP prediction of Weyburn... 

Various models have been applied composed of the Peng-Robinson equation of state (PR-EoS) and the Soave-Redlich-Kwong equation of state (SRK-EoS) associated with three mixing rules including the following: Wong-Sandler (WS), van der Waals one (vdW1), and van der Waals two (vdW2) for phase behavior modeling of mixtures of supercritical CO2+different ionic liquids in vapor-liquid equilibrium (VLE) region. It has been found that the PR EoS implying the WS mixing rule can be used as a reliable thermodynamic model to perform a thermodynamic consistency test on the experimental data of phase behaviors of the supercritical CO2+ionic liquid systems (19 commonly-used ionic liquids have been studied).... 

Both the equation of state-excess Gibbs energy (EoS/GE) model and the cubic plus association (CPA) equation of state (EoS) are compared in this study with respect to their accuracy in the correlation of PVTx for systems such as water/methanol, water/ethanol, water/benzene, water/toluene, water/methane, water/n-butane, water/n-pentane, water/n-hexane, water/heptane, and water/octane, in supercritical conditions within temperature and pressure ranges of (573-698 K) and (7. 0-276. 0 MPa), respectively. In the proposed EoS/GE model, Peng-Robinson (PR) equation of state, linear combination Vidal-Michelsen (LCVM) and Wong-Sandler (WS) mixing rules in conjunction with UNIQUAC activity coefficient... 

In this paper the density and temperature dependencies of surface tension are investigated. Using the Lennard-Jones (12,6), as an effective pair interaction potential, a linear expression is derived for isotherms of γ /ρ 2 versus ρ 2 for some normal and ChloroFluoroCarbons (CFCs) fluids, where is surface tension and ρ = 1/v is molar density. The linearity behavior of the derived equation is well fitted onto the experimental data of surface tension for monatomic, diatomic, nonpolar, polar, hydrogen-bonded and chlorofluorocarbons. In addition, the temperature dependence of surface tension for 20 different fluids is examined, in which the contributions of both terms of the average effective... 

A large variety of modifications have been presented for the temperature dependent function (α) existing in the attractive term of cubic equations of state (CEOS). Most of α-functions attempted to modify the vapor pressure prediction of polar components while other modifications have focused on both polar and non-polar compounds and other relations have considered an expansion of polynomials in the acentric factor (ω) and reduced temperature (Tr) to predict vapor pressure more accurately. In most cases such as Soave and Peng-Robinson equations of state, the suggested α-functions do not show a limiting behavior when temperature increases infinitely. In addition, the incompetency of many...