Thermodynamic Properties Of Mixtures Research Articles

Helmholtz energy and extended corresponding states model for the prediction of thermodynamic properties of mixtures of refrigerants

This work was concerned with developing an accurate model for the prediction of thermodynamic properties of mixtures of refrigerants. That model was the extension to mixtures of a recent work by the author about a Helmholtz and extended corresponding states model for refrigerants.In the proposed model the residual Helmholtz energy of the mixture was expressed as the contribution of three terms: one from an extended corresponding states model and the other two were corrections in terms of one-fluid mixing rules of functions of reduced temperature and density. The extended corresponding states model was based on the temperature- and density-dependent shape factors that the author has presented previously in the literature and the reference fluid was R-32 with properties calculated with the Tillner-Roth and Yokozeki reference equation of state.The fluids of interest were six binary systems and two ternary systems: (R-32+R-125), (R-32+R-134a), (R-125+R-134a), (R-125+R-143a), (R-134a+R-143a), (R-134a+R-152a), (R-32+R-125+R-134a) and (R-125+R-134a+R-143a). The following were the obtained percentage overall average absolute deviations: 0.347 in pρT data, 1.836 in isochoric heat capacities, 1.108 in isobaric heat capacities, 0.073 in speeds of sound, 0.467 in bubble-point saturation pressures and an overall average absolute difference of 3.367cm3mol−1 was obtained in second virial coefficients. These results compared satisfactorily with those from other models for mixtures of refrigerants.

An Improvement to COSMO-SAC for Predicting Thermodynamic Properties

A modified COSMO-SAC model is presented to calculate thermodynamic properties of pure fluids and mixtures using statistical thermodynamics and the surface charge density of each compound obtained from a quantum mechanics (QM) calculation. The main differences from the previous models are that the new model includes a dispersion contribution in the mixture interaction, and is reparametrized using measured pure and mixture thermodynamic data simultaneously. With a single set of universal parameters, the new model provides higher accuracy than our previous models for predicting mixture thermodynamic properties while maintaining the same accuracy for pure compound thermodynamic properties. The overall root-mean-square deviation (RMSD) in the logarithms of partition coefficients for 992 octanol–water partitioning systems and 829 other solvent–water partitioning systems with this new model is reduced by about 10% compared to the results from previous models. Also, the agreement between the predicted and measure...

Evaluation of the grand-canonical partition function using expanded Wang-Landau simulations. III. Impact of combining rules on mixtures properties

Combining rules, such as the Lorentz-Berthelot rules, are routinely used to calculate the thermodynamic properties of mixtures using molecular simulations. Here we extend the expanded Wang-Landau simulation approach to determine the impact of the combining rules on the value of the partition function of binary systems, and, in turn, on the phase coexistence and thermodynamics of these mixtures. We study various types of mixtures, ranging from systems of rare gases to biologically and technologically relevant mixtures, such as water-urea and water-carbon dioxide. Comparing the simulation results to the experimental data on mixtures of rare gases allows us to rank the performance of combining rules. We find that the widely used Lorentz-Berthelot rules exhibit the largest deviations from the experimental data, both for the bulk and at coexistence, while the Kong and Waldman-Hagler provide much better alternatives. In particular, in the case of aqueous solutions of urea, we show that the use of the Lorentz-Berthelot rules has a strong impact on the Gibbs free energy of the solute, overshooting the value predicted by the Waldman-Hagler rules by 7%. This result emphasizes the importance of the combining rule for the determination of hydration free energies using molecular simulations.

Thermodynamic properties of mixtures containing linear and cyclic ketones

Densities, ρ, speeds of sound, u and excess heat capacities, CPE (293.15, 298.15, 303.15, 308.15K) and excess molar enthalpies, HE (298.15K) for the binary acetone (i)+cyclopentanone or cyclohexanone or cycloheptanone (j) mixtures have been measured as a function of composition at atmospheric pressure. The measured ρ and u data have been employed to determine excess molar volumes, VE and excess isentropic compressibilities, κSE. The VE, κSE, HE, and CPE data of the investigated mixtures have been fitted to Redlich–Kister equation to obtain binary parameters and standard deviations. The analysis of thermodynamic data in terms of Graph theory suggests that VE, κSE, HE, and CPE values predicted by the Graph theory compare well with their experimental values.

Contribution to study of the thermodynamics properties of mixtures containing 2-methoxy-2-methylpropane, alkanol, alkane

Excess molar enthalpies for the ternary system {x1 2-methoxy-2-methylpropane (MTBE)+x2 1-pentanol+(1−x1−x2) hexane} and the involved binary mixture {x 1-pentanol+(1−x) hexane}, have been measured at T=298.15K and atmospheric pressure over the whole composition range. We are not aware of the existence of previous experimental measurement of the excess enthalpy for the ternary mixture under study in the literature currently available. Values of the excess molar enthalpies were measured using a Calvet microcalorimeter. The results were fitted by means of different variable degree polynomials. The ternary contribution to the excess enthalpy was correlated with the equation due to Verdes et al. (2004), and the equation proposed by Myers–Scott (1963) was used to fit the experimental binary mixture measured in this work. Smooth representations of the results are presented and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. The excess molar enthalpies for the binary and ternary system are positive over the whole range of composition. The binary mixture {x 1-pentanol+(1−x) hexane} is asymmetric, with its maximum displace toward a high mole fraction of decane. The ternary contribution is also positive with the exception of a range located around the rich compositions of 1-pentanol, and the representation is asymmetric.Additionally, the group contribution model of the UNIFAC model, in the versions of Larsen et al. (1987) [18] and Gmehling et al. (1993) [19] was used to estimate values of binary and ternary excess enthalpy. The experimental results were used to test the predictive capability of several empirical expressions for estimating ternary properties from binary results.

Accurate Thermodynamic-Property Models for CO2-Rich Mixtures

Carbon capture and storage (CCS) technologies result in demands on thermodynamic-property models that were previously unknown in energy technologies. This article summarises recent developments allowing for an accurate description of thermodynamic properties of mixtures that are typical for oxyfuel processes and for compression and transport of separated CO2. It addresses homogeneous fluid state as well as phase equilibria of fluid and solid phases. However, phase equilibria with scrubbing agents, as they are common for post combustion processes, are out of the scope of this article.

Experimental Determination of (p, ρ, T) Data for Three Mixtures of Carbon Dioxide with Methane for the Thermodynamic Characterization of Nonconventional Energy Gases

Experimental characterization of the thermodynamic behavior of gas binary mixtures containing components of fuel gases is of great importance due to the proved lack of reliable data of thermodynamic properties of mixtures. These data are essential not only for the improvement and test of the current reference equation of state for natural gases and related mixtures, GERG-2008, but also for the indirect determination of other properties. In this work density measurements of mixtures of carbon dioxide with methane are presented as a contribution to the research project EMRP ENG01 of the European Metrology Research Program, in the field of characterization of energy gases. Accurate density measurements for three binary mixtures of carbon dioxide with methane (xCO2 = 0.20, 0.40, and 0.60) were performed at temperatures between (250 and 400) K and pressures up to 20 MPa, using a single sinker densimeter with magnetic suspension coupling, which is one of the state of the art methods for density determination ov...

Generalization of SAFT + Cubic equation of state for predicting and correlating thermodynamic properties of heavy organic substances

The current study proposes a scheme for generalizing parameters of SAFT+Cubic EoS (GSAFT+Cubic) for predicting and correlating thermodynamic properties of heavy (18 and more carbon atoms) organic substances and of ionic liquids. The accuracy of the proposed approach might usually be compared with the multi-parameter empirical Tait equation. However, unlike the latter one, it has a predictive character. In the cases of the substances included in the databanks such as DIPPR, GSAFT+Cubic requires input of a single experimental density datum point. In the cases of complex fluids, such as the heavy oils, the ionic liquids or the ester lubricants, the proposed approach requires input of two experimental points of density and estimation of the ideal gas heat capacity for predicting various auxiliary properties in wide PVT range. A major advantage of GSAFT+Cubic over the empirical correlations is its applicability for estimating phase equilibria and other thermodynamic properties of mixtures while using the one-fluid approach. In particular, it has been demonstrated that GSAFT+Cubic yields accurate predictions of the available VLE and LLE data of mixtures of the heavy n-alkanes and the ionic liquids.

Study of Thermal Energy Production by Combustion of Lard and Diesel Mixtures

This work presents the experimental results of lard combustion with diesel for heating. The work is divided into two parts, the first of which deals with the identification of lard as fuels and characterization of diesel, as well as determining the chemical and thermodynamic properties of mixtures of both components. The second part studies the optimum combustion point of lard and oil mixtures in a conventional plant, varying the percentage of lard in mixing, air flow, and injection pressure.

Rapid determination of entropy and free energy of mixtures from molecular dynamics simulations with the two-phase thermodynamic model

The two-phase thermodynamic (2PT) model is generalized to determine the thermodynamic properties of mixtures. In this method, the vibrational density of states (DoS), obtained from the Fourier transform of the velocity autocorrelation function, and quantum statistics are combined to determine the entropy and free energy from the trajectory of a molecular dynamics simulation. In particular, the calculated DoS is decomposed into a solid-like and a gas-like component through the fluidicity parameter, allowing for treatments for the anharmonic effects in fluids. The 2PT method has been shown to provide reliable thermodynamic properties of pure substances over the whole phase diagram with only about a 20 ps MD trajectory. Here we show how the 2PT method can be used for mixtures with the same degree of accuracy and efficiency. We have examined the 2PT determined excess Gibbs free energies of Lennard-Jones (LJ) mixtures over a wide range of conditions (1 ≤ T* ≤ 3, 0.5 ≤ P* ≤ 2.5, 1 ≤ σ(BB)/σ(AA) ≤ 2, and 1 ≤ ε(BB)/ε(AA) ≤ 2), including the change of the off-diagonal LJ interactions. The 2PT determined values are in good agreement with those from Widom insertion or thermodynamic integration (TI). Our results suggest that the 2PT method can be a powerful method for understanding thermodynamic properties in more complicated multicomponent systems.

Heat transfer enhancement in a small pipe by spinodal decomposition of a low viscosity, liquid?liquid, strongly non-regular mixture

Abstract We report experimental evidence of a 20–40 % enhancement of the effective heat transfer coefficient for laminar flow of a partially miscible binary liquid–liquid mixture in a small diameter horizontal tube that obtains when phase separation occurs in the tube. A mixture of acetone–hexadecane is quenched into the two-phase region so as to induce spinodal decomposition. The heat transfer rate is enhanced by self-induced convective effects sustained by the free energy liberated during phase separation. The experimental heat transfer coefficients obtained when separation occurs are compared to the corresponding values predicted for flow of a hypothetic mixture with identical properties but undergoing separation. For such comparison, the energy balance equation must carefully take into account both the sensible heat and the excess enthalpy difference between the inlet and the outlet streams because our liquid–liquid binary mixture is a very asymmetric system with large excess enthalpies. The non-ideal mixture thermodynamic properties needed for the energy balance are obtained by an empirical procedure from the experimental data available in the literature for our mixture. The experimental setup and calculation procedure is tested by experiments performed using single-phase water flow and single-phase mixture flow (above the critical point). The convective heat transfer augmentation that results in the presence of liquid–liquid phase separation may be exploited in the cooling or heating of small scale systems where turbulent convection cannot be achieved.

Thermodynamic modeling based on a generalized cubic equation of state for kerosene/LOx rocket combustion

Based on a generalized cubic equation of state proposed by Cismondi and Mollerup [Fluid Phase Equilib. 232 (2005) 74–89], this study derived formulations for the thermodynamic properties of mixtures that are needed for combustion simulations of liquid rocket engines. The present model was validated thoroughly against reference data provided by NIST in order to assess its validity over a wide range of critical compressibility factors, pressures, and temperatures. The numerical results clearly indicate that the present model is superior in its handling of fluid mixtures with quite different critical compressibility factors, while maintaining the advantages of the cubic equation of state compared to those of the Soave–Redlich–Kwong and Peng–Robinson equations of state. In addition, steady flamelet analysis has been performed to investigate the effects of detailed chemical kinetics, real fluid behavior, and increased pressure on the local flame structures of the kerosene surrogate and liquid oxygen relevant to liquid rocket engines.

Thermodynamics and transport properties of citral

In this work, transport and thermodynamic properties of mixtures of n-hexane with the aldehydes citral, citronellal and dihydrocitronellal, important to the fine chemicals industry, were determined experimentally and compared to theoretical predictions. Liquid binary diffusion coefficients were measured using the Taylor dispersion technique at various temperatures. The Wilke-Chang correlation gave precise approximations. The second part of this work is concerned with the gas-liquid phase equilibrium of citral/n-hexane. The mixture is slightly nonideal and may be sufficiently described by applying the modified UNIFAC (Dortmund) group contribution method. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2557–2562, 2012

Application to mixtures of non-polar fluids of a three-parameter three-fluid corresponding states model based on reference equations of state

In this work a three-parameter three-fluid corresponding states model is applied to the prediction of thermodynamic properties of mixtures of non-polar fluids. Residual thermodynamic properties were calculated by quadratic interpolation between those of three reference fluids, i.e. methane, ethane and carbon dioxide. The properties of these three fluids were obtained from the corresponding multiparameter reference equations of state: the Setzmann and Wagner equation for methane, the Bücker and Wagner equation for ethane and the Span and Wagner equation for carbon dioxide. By this device, the accuracy of the model was quite satisfactory as is demonstrated in this work by comparison with a recent generalised corresponding states model by Sun & Ely. Also, the proposed model showed to be more accurate than the Peng−Ronbison equation of state with volume translation. The percentage average absolute deviations for binary systems were: 0.194 in pρT data, 1.696 in isobaric heat capacities, 0.174 in speeds of sound and 1.322 in bubble-point vapour pressures. Percentage average absolute deviations in pρT data of ternary systems were 0.134 and 0.094 for quaternary systems.

Excess Thermodynamic Properties of Mixtures Involving Xenon and Light Alkanes: A Study of Their Temperature Dependence by Computer Simulation

As a natural extension of a previous work, excess molar enthalpies and excess molar volumes as a function of composition in a wide range of temperatures have been obtained for binary mixtures of xenon with ethane, propane, and n-butane by Monte Carlo computer simulation. Xenon was modeled by a simple spherical Lennard-Jones potential, and the TraPPE-UA force field was used to describe the n-alkanes. One of the main goals of this study is to investigate the temperature dependence of the excess properties for mixtures of xenon and n-alkanes and, if possible, to supplement the lack of experimental data. For all three systems, the simulation results predicted excess volumes in good agreement with the experimental data. As for the excess enthalpies, in the case of (xenon + ethane), the simulation results confirm the negative experimental result and the weak temperature dependence. In the case of (xenon + propane) and (xenon + n-butane), however, the simulation predicts negative excess enthalpies, but those estimated from experimental data are positive. Both excess volumes and enthalpies display a complex dependence on temperature that in some aspects resembles that found for mixtures of n-alkanes.The structure of the liquid mixtures was also investigated by calculating radial distribution functions [g(αβ)(r)] between each pair of interaction groups for all the binary systems at all temperatures. It is found that the mean distance between xenon and CH(2) groups is systematically higher than the distance between xenon and CH(3). In addition, the number of groups around xenon in the first coordination sphere was calculated and seems to be proportionally more populated by methyl groups than by methylene groups. The results seem to reflect a preferential and stronger interaction between xenon and CH(3), in agreement with previous findings.

A COSMO‐RS based QSPR model for the lubricity of biodiesel and petrodiesel components

ABSTRACTThe development of a new, optimised fuel is a process in which various necessary fuel properties have to be taken into account. For an inclusion of candidates not synthesised yet into the design process, a fully predictive model relying on nothing but the molecular structure is mandatory for each relevant property. One of the most important aspects for the design of a fuel is its lubricity. In this study, the predictive method conductor‐like screening model for realistic solvation (COSMO‐RS) for the calculation of thermodynamic mixture properties is adopted for deriving a quantitative structure–property relationship for the lubricity of fuel components. COSMO‐RS calculates molecular descriptors (sigma moments) based on quantum chemical calculations. These descriptors are adapted to describe the underlying phenomena causing the film formation ability and lubricity of the fuel. The lubricity is assessed via high‐frequency reciprocating rig measurements taken from literature. The molecular descriptors and experimental data are evaluated via statistical methods in order to find the most influential molecular descriptors. Copyright © 2011 John Wiley & Sons, Ltd.

A Kirkwood–Buff force field for the aromatic amino acids

In a continuation of our efforts to develop a united atom non-polarizable protein force field based upon the solution theory of Kirkwood and Buff i.e., the Kirkwood-Buff Force Field (KBFF) approach, we present KBFF models for the side chains of phenylalanine, tyrosine, tryptophan, and histidine, including both tautomers of neutral histidine and doubly-protonated histidine. The force fields were specifically designed to reproduce the thermodynamic properties of mixtures over the full composition range in an attempt to provide an improved description of intermolecular interactions. The models were developed by careful parameterization of the solution phase partial charges to reproduce the experimental Kirkwood-Buff integrals for mixtures of solutes representative of the amino acid sidechains in solution. The KBFF parameters and simulated thermodynamic and structural properties are presented for the following eleven binary mixtures: benzene + methanol, benzene + toluene, toluene + methanol, toluene + phenol, toluene + p-cresol, pyrrole + methanol, indole + methanol, pyridine + methanol, pyridine + water, histidine + water, and histidine hydrochloride + water. It is argued that the present approach and models provide a reasonable description of intermolecular interactions which ensures that the required balance between solute-solute, solute-solvent, and solvent-solvent distributions is obtained.

Enthalpies of mixing predicted using molecular dynamics simulations and OPLS force field

Enthalpy of mixing (EOM) is one of the most basic thermodynamic properties of mixtures. To assess feasibility of predicting EOM using force field simulation methods, fifteen (15) representative binary mixtures were investigated using MD simulations based on OPLS and TIP4P force fields. The simulation conditions and errors were carefully examined. The precision level of 0.04 kJ/mol was obtained for calculated EOM data. However, the predictions, measured by deviations from experimental data, were only qualitatively correct. Among various factors influencing the accuracy of predictions, force field quality representing interactions among different molecules plays the most significant role. Using methanol/benzene and ethanol/benzene as examples, we demonstrated that non-additive interaction terms between polarizable atoms can be used to significantly improve the quality of predictions. In addition, it appears that charge-dependent LJ parameters are required in order to represent the polarization effects accurately.

The effect of the size and packing of molecules on the thermodynamic properties of mixtures

The suggested approach explains the concentration dependence of density and of bulk-and-elastic properties of thermodynamically ideal mixture from the structural standpoint. It is demonstrated that the deviations of the concentration dependence of volumetric density and of the coefficient of isothermal compressibility from the mole-additive rule are caused by the difference between the structure parameters of pure liquids contained in the mixture (molecular volume, packing factors, and molecular densities). The contribution made by each one of the structure parameters to the deviation of the behavior of density of thermodynamically ideal mixture from the mole-additive rule is identified and estimated within suggested simulation for mixtures of different types.

The Soave, Twu and Boston–Mathias alpha functions in cubic equations of state. Part II. Modeling of thermodynamic properties of pure compounds

Cubic equations of state (EoS) are commonly used for industrial applications, due to their simplicity in predicting pure compound and mixture thermodynamic properties in vapor and liquid phases. The accuracy of their predictions mainly depends on the choice of the attractive term a( T) and numerous models were developed in literature for this purpose. Among them, the Soave and the Twu models have acquired a wide popularity, as well as the Boston–Mathias model commonly used for supercritical applications. However, most of the works concerned with the comparison of literature attractive terms only focuses on the representation of pure component saturation properties. In particular, the analysis of the respective influence of the EoS and the first and second derivatives of the alpha function on the modeling of enthalpies and heat capacities with respect to temperature and pressure, especially in the supercritical range, was never reported in literature. This is precisely the purpose of the present study.