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Eric W Lemmon - One of the best experts on this subject based on the ideXlab platform.
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the precise measurement of vapor liquid equilibrium properties of the co _ isopentane binary mixture and fitted parameters for a Helmholtz Energy mixture model
International Journal of Thermophysics, 2017Co-Authors: H Miyamoto, Ryo Akasaka, Y. Shoji, Eric W LemmonAbstract:Natural working fluid mixtures, including combinations of CO\(_{2}\), hydrocarbons, water, and ammonia, are expected to have applications in Energy conversion processes such as heat pumps and organic Rankine cycles. However, the available literature data, much of which were published between 1975 and 1992, do not incorporate the recommendations of the Guide to the Expression of Uncertainty in Measurement. Therefore, new and more reliable thermodynamic property measurements obtained with state-of-the-art technology are required. The goal of the present study was to obtain accurate vapor–liquid equilibrium (VLE) properties for complex mixtures based on two different gases with significant variations in their boiling points. Precise VLE data were measured with a recirculation-type apparatus with a 380 cm\(^{3}\) equilibration cell and two windows allowing observation of the phase behavior. This cell was equipped with recirculating and expansion loops that were immersed in temperature-controlled liquid and air baths, respectively. Following equilibration, the composition of the sample in each loop was ascertained by gas chromatography. VLE data were acquired for CO\(_{2}\)/ethanol and CO\(_{2}\)/isopentane binary mixtures within the temperature range from 300 K to 330 K and at pressures up to 7 MPa. These data were used to fit interaction parameters in a Helmholtz Energy mixture model. Comparisons were made with the available literature data and values calculated by thermodynamic property models.
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The Precise Measurement of Vapor–Liquid Equilibrium Properties of the CO $$_{2}$$
International Journal of Thermophysics, 2017Co-Authors: H Miyamoto, Ryo Akasaka, Y. Shoji, Eric W LemmonAbstract:Natural working fluid mixtures, including combinations of CO $$_{2}$$ 2 , hydrocarbons, water, and ammonia, are expected to have applications in Energy conversion processes such as heat pumps and organic Rankine cycles. However, the available literature data, much of which were published between 1975 and 1992, do not incorporate the recommendations of the Guide to the Expression of Uncertainty in Measurement. Therefore, new and more reliable thermodynamic property measurements obtained with state-of-the-art technology are required. The goal of the present study was to obtain accurate vapor–liquid equilibrium (VLE) properties for complex mixtures based on two different gases with significant variations in their boiling points. Precise VLE data were measured with a recirculation-type apparatus with a 380 cm $$^{3}$$ 3 equilibration cell and two windows allowing observation of the phase behavior. This cell was equipped with recirculating and expansion loops that were immersed in temperature-controlled liquid and air baths, respectively. Following equilibration, the composition of the sample in each loop was ascertained by gas chromatography. VLE data were acquired for CO $$_{2}$$ 2 /ethanol and CO $$_{2}$$ 2 /isopentane binary mixtures within the temperature range from 300 K to 330 K and at pressures up to 7 MPa. These data were used to fit interaction parameters in a Helmholtz Energy mixture model. Comparisons were made with the available literature data and values calculated by thermodynamic property models.
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The Precise Measurement of Vapor–Liquid Equilibrium Properties of the CO$$_{}$$/Isopentane Binary Mixture, and Fitted Parameters for a Helmholtz Energy Mixture Model
International Journal of Thermophysics, 2017Co-Authors: H Miyamoto, Ryo Akasaka, Y. Shoji, Eric W LemmonAbstract:Natural working fluid mixtures, including combinations of CO\(_{2}\), hydrocarbons, water, and ammonia, are expected to have applications in Energy conversion processes such as heat pumps and organic Rankine cycles. However, the available literature data, much of which were published between 1975 and 1992, do not incorporate the recommendations of the Guide to the Expression of Uncertainty in Measurement. Therefore, new and more reliable thermodynamic property measurements obtained with state-of-the-art technology are required. The goal of the present study was to obtain accurate vapor–liquid equilibrium (VLE) properties for complex mixtures based on two different gases with significant variations in their boiling points. Precise VLE data were measured with a recirculation-type apparatus with a 380 cm\(^{3}\) equilibration cell and two windows allowing observation of the phase behavior. This cell was equipped with recirculating and expansion loops that were immersed in temperature-controlled liquid and air baths, respectively. Following equilibration, the composition of the sample in each loop was ascertained by gas chromatography. VLE data were acquired for CO\(_{2}\)/ethanol and CO\(_{2}\)/isopentane binary mixtures within the temperature range from 300 K to 330 K and at pressures up to 7 MPa. These data were used to fit interaction parameters in a Helmholtz Energy mixture model. Comparisons were made with the available literature data and values calculated by thermodynamic property models.
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Automatic Fitting of Binary Interaction Parameters for Multi-fluid Helmholtz-Energy-Explicit Mixture Models
Journal of Chemical & Engineering Data, 2016Co-Authors: Ian H. Bell, Eric W LemmonAbstract:In the highest-accuracy mixture models available today, these being the multi-fluid Helmholtz-Energy-explicit formulations, there are a number of binary interaction parameters that must be obtained through correlation or estimation schemes. These binary interaction parameters are used to shape the thermodynamic surface and yield higher-fidelity predictions of various thermodynamic properties including vapor-liquid equilibria and homogeneous p-v-T data, among others. In this work, we have used a novel and entirely automatic evolutionary optimization algorithm written in the python programming language to fit the two most important interaction parameters for more than 1100 binary mixtures. This fitting algorithm can be run on multiple processors in parallel, resulting in a reasonable total running time for this large set of binary mixtures. For more than 830 of the binary pairs, the median absolute relative error in bubble-point pressure is less than 5%. The source code for the fitter is provided as supplem...
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A Helmholtz Energy Equation of State for Sulfur Dioxide
Journal of Chemical & Engineering Data, 2016Co-Authors: Kehui Gao, Penggang Zhang, Eric W LemmonAbstract:A Helmholtz Energy equation of state with independent variables of temperature and density was developed for sulfur dioxide (SO2) based on thermodynamic property data from the literature. The equation of state is valid from the triple-point temperature of 197.7 to 525 K, with pressures up to 35 MPa and densities up to 25.4 mol·dm–3. The uncertainties in density of the equation of state are 0.1% in the liquid phase, 0.25% in the vapor phase, and 1% in the critical region. The uncertainty in vapor pressure is 0.2% and the uncertainty in saturated liquid density is 0.2% below 410 K. The uncertainty in isobaric heat capacity is 2% between 200 and 290 K. In the critical region, the uncertainties are higher for all properties except for vapor pressure. The behavior of the equation of state is correct not only within the region of validity, but also at high temperatures and pressures, and far below the triple-point temperature.
Ryo Akasaka - One of the best experts on this subject based on the ideXlab platform.
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the precise measurement of vapor liquid equilibrium properties of the co _ isopentane binary mixture and fitted parameters for a Helmholtz Energy mixture model
International Journal of Thermophysics, 2017Co-Authors: H Miyamoto, Ryo Akasaka, Y. Shoji, Eric W LemmonAbstract:Natural working fluid mixtures, including combinations of CO\(_{2}\), hydrocarbons, water, and ammonia, are expected to have applications in Energy conversion processes such as heat pumps and organic Rankine cycles. However, the available literature data, much of which were published between 1975 and 1992, do not incorporate the recommendations of the Guide to the Expression of Uncertainty in Measurement. Therefore, new and more reliable thermodynamic property measurements obtained with state-of-the-art technology are required. The goal of the present study was to obtain accurate vapor–liquid equilibrium (VLE) properties for complex mixtures based on two different gases with significant variations in their boiling points. Precise VLE data were measured with a recirculation-type apparatus with a 380 cm\(^{3}\) equilibration cell and two windows allowing observation of the phase behavior. This cell was equipped with recirculating and expansion loops that were immersed in temperature-controlled liquid and air baths, respectively. Following equilibration, the composition of the sample in each loop was ascertained by gas chromatography. VLE data were acquired for CO\(_{2}\)/ethanol and CO\(_{2}\)/isopentane binary mixtures within the temperature range from 300 K to 330 K and at pressures up to 7 MPa. These data were used to fit interaction parameters in a Helmholtz Energy mixture model. Comparisons were made with the available literature data and values calculated by thermodynamic property models.
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The Precise Measurement of Vapor–Liquid Equilibrium Properties of the CO $$_{2}$$
International Journal of Thermophysics, 2017Co-Authors: H Miyamoto, Ryo Akasaka, Y. Shoji, Eric W LemmonAbstract:Natural working fluid mixtures, including combinations of CO $$_{2}$$ 2 , hydrocarbons, water, and ammonia, are expected to have applications in Energy conversion processes such as heat pumps and organic Rankine cycles. However, the available literature data, much of which were published between 1975 and 1992, do not incorporate the recommendations of the Guide to the Expression of Uncertainty in Measurement. Therefore, new and more reliable thermodynamic property measurements obtained with state-of-the-art technology are required. The goal of the present study was to obtain accurate vapor–liquid equilibrium (VLE) properties for complex mixtures based on two different gases with significant variations in their boiling points. Precise VLE data were measured with a recirculation-type apparatus with a 380 cm $$^{3}$$ 3 equilibration cell and two windows allowing observation of the phase behavior. This cell was equipped with recirculating and expansion loops that were immersed in temperature-controlled liquid and air baths, respectively. Following equilibration, the composition of the sample in each loop was ascertained by gas chromatography. VLE data were acquired for CO $$_{2}$$ 2 /ethanol and CO $$_{2}$$ 2 /isopentane binary mixtures within the temperature range from 300 K to 330 K and at pressures up to 7 MPa. These data were used to fit interaction parameters in a Helmholtz Energy mixture model. Comparisons were made with the available literature data and values calculated by thermodynamic property models.
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The Precise Measurement of Vapor–Liquid Equilibrium Properties of the CO$$_{}$$/Isopentane Binary Mixture, and Fitted Parameters for a Helmholtz Energy Mixture Model
International Journal of Thermophysics, 2017Co-Authors: H Miyamoto, Ryo Akasaka, Y. Shoji, Eric W LemmonAbstract:Natural working fluid mixtures, including combinations of CO\(_{2}\), hydrocarbons, water, and ammonia, are expected to have applications in Energy conversion processes such as heat pumps and organic Rankine cycles. However, the available literature data, much of which were published between 1975 and 1992, do not incorporate the recommendations of the Guide to the Expression of Uncertainty in Measurement. Therefore, new and more reliable thermodynamic property measurements obtained with state-of-the-art technology are required. The goal of the present study was to obtain accurate vapor–liquid equilibrium (VLE) properties for complex mixtures based on two different gases with significant variations in their boiling points. Precise VLE data were measured with a recirculation-type apparatus with a 380 cm\(^{3}\) equilibration cell and two windows allowing observation of the phase behavior. This cell was equipped with recirculating and expansion loops that were immersed in temperature-controlled liquid and air baths, respectively. Following equilibration, the composition of the sample in each loop was ascertained by gas chromatography. VLE data were acquired for CO\(_{2}\)/ethanol and CO\(_{2}\)/isopentane binary mixtures within the temperature range from 300 K to 330 K and at pressures up to 7 MPa. These data were used to fit interaction parameters in a Helmholtz Energy mixture model. Comparisons were made with the available literature data and values calculated by thermodynamic property models.
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Recent trends in the development of Helmholtz Energy equations of state and their application to 3,3,3-trifluoroprop-1-ene (R-1243zf)
Science and Technology for the Built Environment, 2016Co-Authors: Ryo AkasakaAbstract:Recent trends in the development of Helmholtz Energy equations of state are briefly reviewed. Optimization procedures have been improved over the last two decades, and now nonlinear least-square fitting is effectively used in the optimization. This fitting technique makes it possible to develop a reliable equation of state for fluids with limited experimental data. The fitting is demonstrated for 3,3,3-trifluoroprop-1-ene (R-1243zf; CAS number 677-21-4). Experimental data for the critical parameters, vapor pressures, and liquid and vapor densities, including those at the saturation state, are available for this refrigerant. The fitting results in an equation with 17 terms. The equation of state is valid for temperatures from 234 to 376 K and for pressures up to 35 MPa. Comparisons to experimental data and verification of extrapolation behavior show that the equation of state has potential for most technical applications.
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A Thermodynamic Property Model for the R-134a/245fa Mixture
2014Co-Authors: Ryo Akasaka, Yukihiro HigashiAbstract:A thermodynamic property model explicit in the Helmholtz Energy is presented for the R-134a/245fa mixtures. A multi-fluid approximation based on pure-fluid Helmholtz Energy equations of state forms the basis of the property model. The Helmholtz Energy of the mixture is expressed as the sum of the ideal gas contribution, the compressibility contribution (real fluid contribution), and the contribution from mixing to represent the deviation from ideal mixtures. The independent variables are the temperature, molar volume, and composition. The model can be used to calculate all thermodynamic properties of the mixtures at various compositions. The estimated uncertainties in calculated properties from the model are ±0.2 % for the bubble and dew point pressures and ±0.24 % for the liquid and vapor densities. The critical parameters of the mixtures are properly represented with the model. The calculated critical temperatures correspond to experimental values within ±0. 5K .
Johann Fischer - One of the best experts on this subject based on the ideXlab platform.
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A mixing rule for the quadrupolar contribution to the Helmholtz Energy
Fluid Phase Equilibria, 2000Co-Authors: Ulrike Weingerl, Johann FischerAbstract:Abstract Recent investigations with BACKONE equations of state [S. Calero, Fluid Phase Equilib. 120 (1998) 1–22] revealed the importance of quadrupolar interactions for the thermodynamic behaviour of real fluids. In BACKONE an explicit expression for the quadrupolar contribution to the Helmholtz Energy FQ is used. In order to extend these equations to mixtures, a mixing rule for FQ is required. Here, an expression for a one-fluid quadrupole moment Qx is derived on the basis of perturbation theory using a spherical reference system. This mixing rule is tested first by comparing molecular simulation results for quadrupolar mixtures with those for the equivalent pure Qx-fluid for linear molecules of different elongations. Comparisons of pressures, internal energies, and quadrupole energies show in general good to excellent agreement. At high liquid densities, however, discrepancies start to occur at medium elongation which increase with molecular elongation. Excess free energies FE calculated from the BACKONE-FQ and the mixing rule show excellent agreement with values obtained from integrating simulation results even at high liquid densities. Finally, average quadrupole–quadrupole energies obtained from BACKONE-FQ using the mixing rule show again excellent agreement with simulation data.
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An equation of state for dipolar two-center Lennard–Jones molecules and its application to refrigerants
Fluid Phase Equilibria, 1998Co-Authors: Christian Kriebel, Jochen Winkelmann, Matthias Mecke, Jadran Vrabec, Johann FischerAbstract:Abstract For two-center Lennard–Jones molecules with embedded point dipole (2CLJD-molecules) a hybrid equation of state for the Helmholtz Energy F2CLJD is constructed as the sum of the Helmholtz Energy F2CLJ for nonpolar two-center Lennard–Jones molecules and the dipolar contribution to the Helmholtz Energy FD, F2CLJD=F2CLJ+FD. For pure fluids, predictions from this equation for the thermodynamic data of the homogeneous phase and for the vapour–liquid phase equilibria show good-to-excellent agreement with simulation data. To study deviations from the corresponding states theorem, acentric factors are calculated, and isoacentric curves are given as a function of the molecular elongation and the dipole strength. The equation is then used for a description of the real fluids R22 and R152a. Finally, it is shown that properties of model mixtures are also well predicted by using an appropriate mixing rule.
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Simulation studies on mixtures of dipolar with nonpolar linear molecules. II. A mixing rule for the dipolar contribution to the Helmholtz Energy
Fluid Phase Equilibria, 1996Co-Authors: Andreas Müller, Jochen Winkelmann, Johann FischerAbstract:Abstract In recent equations of state an explicit expression for the dipolar contribution to the Helmholtz Energy F D is used. If such equations are applied to mixtures the problem of mixing rules for F D arises. As a solution, a “one-fluid dipole moment μ x ” is introduced which is based on perturbation theory. The accuracy of the approach is tested by simulation results for mixtures of dipolar with nonpolar linear molecules. In addition to the simulation runs from Part I (Muller et al. (1994)), results from 97 new NVT simulations are presented. Comparisons of pressures, internal energies, dipole energies and excess free energies from simulations with those obtained from the equation for F D in combination with the one-fluid dipole moment μ x shows good to excellent agreement.
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A hybrid equation of state for Stockmayer pure fluids and mixtures
Fluid Phase Equilibria, 1996Co-Authors: Christian Kriebel, Jochen Winkelmann, Andreas Müller, Johann FischerAbstract:A hybrid equation of state for the Helmholtz Energy F of Stockmayer fluids is constructed as the sum of the Helmholtz Energy FLJ for the Lennard-Jones fluid and the dipolar contribution to the Helmholtz Energy FD, F = FLJ + FD. Predictions from this equation for the thermodynamic properties of the homogeneous phases and for the vapour-liquid phase equilibria show good to excellent agreement with simulation data. Moreover, the properties of mixtures of Stockmayer with Lennard-Jones molecules are shown to be well predicted by using an appropriate mixing rule. For these mixtures, also liquid-liquid phase separations and vapour-liquid phase equilibria are calculated.
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Construction and application of physically based equations of state: Part II. The dipolar and quadrupolar contributions to the Helmholtz Energy
Fluid Phase Equilibria, 1992Co-Authors: Berthold Saager, Johann FischerAbstract:Abstract Saager B. and Fischer J., 1992. Construction and application of physically based equations of state. Part II. The dipolar and quadrupolar contributions to the Helmholtz Energy. Fluid Phase Equilibria , 72: 67-88. In this and a previous paper a class of equations of state with four or five parameters is constructed on the assumption that the Helmholtz Energy can be written as F = F H + F A + F pol , where F H denotes the hard body contribution, F A the contribution due to the attractive dispersion forces and F pol the contribution of polar interactions. In the present paper the contributions F D of dipolar and F D of quadrupolar interactions as relevant specifications of F pol are derived via the lambda coupling technique on the basis of extensive molecular dynamics simulations on a Cyber 205. Explicit expressions for F D and F Q as functions of temperature, density and multipele moment are given in which all their partial derivatives are thermodynamically consistent with simulated data and represent the second virial coefficients properly. F D is a sum of 28 terms and F Q of 17 terms which were obtained by a simple two-step search technique. Whilst the sophisticated technical details and the results of the dipolar simulations have already been published (B. Saager, J. Fischer and M. Neumann, 1991. Mol. Simul., 6: 27-49), the present paper also contains results from 168 simulation runs for two-center Lennard-Jones molecules with point quadrupoles.
J.f. Estela-uribe - One of the best experts on this subject based on the ideXlab platform.
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Helmholtz Energy and extended corresponding states model for the prediction of thermodynamic properties of mixtures of refrigerants
Fluid Phase Equilibria, 2014Co-Authors: J.f. Estela-uribeAbstract:Abstract 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 3.367 cm 3 mol −1 was obtained in second virial coefficients. These results compared satisfactorily with those from other models for mixtures of refrigerants.
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An improved Helmholtz Energy model for non-polar fluids and their mixtures. Part 1: Application to non-polar pure fluids
Fluid Phase Equilibria, 2013Co-Authors: J.f. Estela-uribeAbstract:Abstract This is the first part of a series of two communications in which a Helmholtz Energy model is developed and applied to the prediction of thermodynamic properties of non-polar fluids and their mixtures. In this first part, the application is concerned only with pure non-polar fluids. The Helmholtz Energy model is based on previous work by the author and co-workers in which the Helmholtz Energy of the fluid is represented as a contribution of two terms: one is an extended corresponding states model and the other is a correction term. In the case of single components, this correcting term is a function of temperature and density. In this study 18 fluids were considered, namely: the normal alkanes from ethane to octane, isobutane, ethylene, cyclohexane, benzene, toluene, nitrogen, carbon dioxide, carbon monoxide, oxygen and argon. Percentage absolute average deviations (AADs) were calculated with the following results: 0.175 for pρT data; 0.279 for saturation pressures; 0.168 and 0.324 for saturated-liquid and saturated-vapour densities, respectively; 1.364 and 1.563 for isochoric and isobaric heat capacities, respectively, and 0.638 for speeds of sound. This performance is, by and large, quite comparable with the demanded accuracy of modern technical Helmholtz Energy models for fluids of industrial interest and practical applications in process design and simulation.
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An improved Helmholtz Energy model for non-polar fluids and their mixtures. Part 2: Application to mixtures of non-polar fluids
Fluid Phase Equilibria, 2013Co-Authors: J.f. Estela-uribeAbstract:Abstract This is the second part of a series of two communications in which a Helmholtz Energy model is developed and applied to the prediction of thermodynamic properties of non-polar fluids and their mixtures. In this second part, the application is concerned only with mixtures of non-polar fluids. The Helmholtz Energy model is based on previous work by the author and colleagues in which the Helmholtz Energy of the fluid is represented as a contribution of two terms: one is an extended corresponding states model and the other is correction term. In the case of mixtures, this correcting term is mixing rule, in terms of local compositions, of a temperature- and density-dependent function. Local compositions are calculated with a coordination number model for square-well fluids. The mixtures that were considered were eight “primary” systems and 29 “secondary” systems of methane, ethane, propane, isobutane, n -butane, nitrogen, carbon dioxide, carbon monoxide, hydrogen and argon and a few ternary and quaternary systems. Percentage absolute average deviations (AADs) were calculated with the following results: 0.114 and 0.255 for pρT data of primary and secondary mixtures, respectively; 0.094 and 0.052 for pρT data of ternary and quaternary systems, respectively; 1.153 and 0.108 for isobaric heat capacities and speeds of sound of primary mixtures, respectively; 1.210 and 1.280 for bubble-point vapour pressures of primary and secondary mixtures, respectively; and absolute average deviations of 0.744 cm 3 /mol and 288 cm 6 /mol 2 for second and third virial coefficients, respectively. This performance was found to be very satisfactory when compared with the expected accuracy of mixture Helmholtz Energy models, i.e. that by Lemmon and Jacobsen, which is cited further ahead.
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An improved Helmholtz Energy model for non-polar fluids and their mixtures. Part 3: Application to natural gases and related systems
Fluid Phase Equilibria, 2013Co-Authors: J.f. Estela-uribeAbstract:Abstract In this work a Helmholtz Energy mixture model that had been previously published by the author was applied to natural gases and the related multicomponent systems. The Helmholtz Energy of the mixture is the sum of two terms: one is an extended corresponding states model and the other is a correction term that is mixing rule, in terms of local compositions, of a temperature- and density-dependent function. Local compositions are calculated with a coordination number model for square-well fluids. The systems of interest were ternary, quaternary, multicomponent systems and natural gases. Deviations were calculated for pρT data, speeds of sound, isobaric heat capacities, isobaric and isenthalpic enthalpy differences, saturated-liquid densities of liquefied natural gases and vapour pressures of ternary systems. Representative percentage average absolute deviations were: 0.060 in pρT data of pipeline-quality natural gases; 0.099 in pρT data of unusual-composition natural gases; 0.249 in pρT data of rich natural gases; 0.220 in speeds of sound; 1.150 in isobaric heat capacities; 0.146 in saturated-liquid densities of liquefied natural gases and 1.267 in vapour pressures of ternary systems. Those results met the international standards of accuracy in the prediction of natural gas thermodynamic properties and were also comparable with those obtained with the GERG-2004 equation of state.
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An improved Helmholtz Energy model for air and the related systems
Fluid Phase Equilibria, 2010Co-Authors: J.f. Estela-uribeAbstract:In this work a Helmholtz Energy model is applied to the prediction of thermodynamic properties of air, the related binary mixtures and the intervening pure components. The Helmholtz Energy of the mixture is represented as two contributions: one from a proven accurate extended corresponding states model and the other is a correction term. The corresponding states model relies on pure-component shape factors relative to nitrogen and extension to mixtures with the van der Waals one-fluid mixture model with ordinary combining rules. The correction term is temperature-, density- and composition-dependent with the use of a theoretically consistent local composition model with a coordination number model derived from lattice gas theory. For air the obtained average absolute deviations in densities were 0.090 per cent, 0.15 per cent in speeds of sound, 0.28 per cent in bubble-point pressures and 0.30 per cent for dew-point pressures. For the three associated binary mixtures, the absolute average deviations in densities were within 0.14 per cent and 0.63 per cent for bubble-point pressures. For oxygen and argon, the absolute average deviations were within 0.07 per cent in densities, 0.45 per cent in VLE properties and 0.012 per cent in speeds of sound.
Joachim Gross - One of the best experts on this subject based on the ideXlab platform.
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An equation of state for Stockmayer fluids based on a perturbation theory for dipolar hard spheres.
The Journal of chemical physics, 2019Co-Authors: Marc Theiss, Thijs Van Westen, Joachim GrossAbstract:We develop a perturbation theory for the difference between the Helmholtz Energy of a Stockmayer fluid, i.e., a fluid interacting by a Lennard-Jones plus point-dipole potential, and a Lennard-Jones fluid. We show that the difference can be approximated by the perturbational Helmholtz Energy contribution of a dipolar hard-sphere fluid with a suitably chosen effective hard-sphere diameter, relative to a hard-sphere fluid with the same effective diameter. We analyze both a third and fourth order perturbation theory, both written as Pade approximations. Several recipes for calculating the hard-sphere diameter are investigated; we find that the Weeks-Chandler-Andersen diameter is most suitable. Results of the perturbation theory are shown to be in good agreement with reference data for the Helmholtz Energy, internal Energy, and isochoric heat capacity as obtained from molecular simulations performed in this work and to vapor-liquid equilibrium data from the literature. Theoretical predictions of the proposed model are compared to results from the perturbation theory of Gubbins and Twu [Chem. Eng. Sci. 33, 863 (1978)], which is a theory based on a Lennard-Jones reference fluid. We find the theories are in good agreement. Our approach can easily be applied to van der Waals potentials, other than Lennard-Jones potentials. If a dipolar Mie fluid is considered, the approach merely requires calculation of the effective hard-sphere diameter for a Mie potential. We further note that the approach has a reduction in the variable space of the underlying correlation integrals, i.e., the correlation functions of a hard-sphere fluid depend on density only, whereas the Lennard-Jones reference correlation functions depend on density and temperature.
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Dipolar Hard Spheres: Comprehensive Data from Monte Carlo Simulations
Journal of Chemical & Engineering Data, 2019Co-Authors: Marc Theiss, Joachim GrossAbstract:In this work, we report comprehensive molecular simulation data for the Helmholtz Energy, the internal Energy, the constant-volume heat capacity, and the relative permittivity of pure nonpolarizable dipolar hard spheres. The dimensionless density (ρ*) thereby covers a range from 0.05 to 1.0, and dimensionless squared dipole moments (μ*2) range from 0.04 to 7.0. An empirical polynomial correlation of the Helmholtz Energy is parametrized, which can be used to substitute molecular simulations within this range of density and dipole moment. The correlation and its derivatives may facilitate the development of new theories and equation-of-state models of dipolar fluids. The simulation results further confirm noteworthy chain and ring structures of the dipolar hard-sphere particles at lower densities and at high dipole moments, which are known to have an impact on the thermodynamic properties of a system.
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Prediction of Contact Angles and Density Profiles of Sessile Droplets Using Classical Density Functional Theory Based on the PCP-SAFT Equation of State.
Langmuir : the ACS journal of surfaces and colloids, 2018Co-Authors: Elmar Sauer, Marc Theiss, Alexandros Terzis, Bernhard Weigand, Joachim GrossAbstract:This study demonstrates the capability of the density functional theory (DFT) formalism to predict contact angles and density profiles of model fluids and of real substances in good quantitative agreement with molecular simulations and experimental data. The DFT problem is written in cylindrical coordinates, and the solid–fluid interactions are defined as external potentials toward the fluid phase. Monte Carlo (MC) molecular simulations are conducted in order to assess the density profiles resulting from the Helmholtz Energy functional used in the DFT formalism. Good quantitative agreement between DFT predictions and MC results for Lennard-Jones and ethane nanodroplets is observed, both for density profiles and for contact angles. That comparison suggests, first, that the Helmholtz Energy functional proposed in a previous study [Sauer, E.; Gross, J. Ind. Eng. Chem. Res. 56, 2017, 4119−4135] is suitable for three-phase contact lines and, second, that Lagrange multipliers can be used to constrain the number...
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A critical evaluation of perturbation theories by Monte Carlo simulation of the first four perturbation terms in a Helmholtz Energy expansion for the Lennard-Jones fluid
The Journal of chemical physics, 2017Co-Authors: Thijs Van Westen, Joachim GrossAbstract:The Helmholtz Energy of a fluid interacting by a Lennard-Jones pair potential is expanded in a perturbation series. Both the methods of Barker-Henderson (BH) and of Weeks-Chandler-Andersen (WCA) are evaluated for the division of the intermolecular potential into reference and perturbation parts. The first four perturbation terms are evaluated for various densities and temperatures (in the ranges ρ*=0-1.5 and T*=0.5-12) using Monte Carlo simulations in the canonical ensemble. The simulation results are used to test several approximate theoretical methods for describing perturbation terms or for developing an approximate infinite order perturbation series. Additionally, the simulations serve as a basis for developing fully analytical third order BH and WCA perturbation theories. The development of analytical theories allows (1) a careful comparison between the BH and WCA formalisms, and (2) a systematic examination of the effect of higher-order perturbation terms on calculated thermodynamic properties of fluids. Properties included in the comparison are supercritical thermodynamic properties (pressure, internal Energy, and chemical potential), vapor-liquid phase equilibria, second virial coefficients, and heat capacities. For all properties studied, we find a systematically improved description upon using a higher-order perturbation theory. A result of particular relevance is that a third order perturbation theory is capable of providing a quantitative description of second virial coefficients to temperatures as low as the triple-point of the Lennard-Jones fluid. We find no reason to prefer the WCA formalism over the BH formalism.
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Classical Density Functional Theory for Liquid–Fluid Interfaces and Confined Systems: A Functional for the Perturbed-Chain Polar Statistical Associating Fluid Theory Equation of State
Industrial & Engineering Chemistry Research, 2017Co-Authors: Elmar Sauer, Joachim GrossAbstract:A Helmholtz Energy functional based on the Perturbed-Chain Polar Statistical Associating Fluid Theory Equation of State is proposed. A weighted density approximation is used to develop two variants of dispersion functionals. We conduct molecular simulations (Monte Carlo) in order to assess both models. The structure of thin liquid adsorbed layers of a few molecular diameters thickness are shown to be particularly meaningful to detect deficiencies of Helmholtz Energy functionals and thus discriminate between models. We further compare the model to experimental data of interfacial tensions for pure components and for binary mixtures exhibiting vapor–liquid equilibria and liquid–liquid equilibria. The proposed Helmholtz Energy functional is in good agreement with experimental data of pure (organic) substances and mixtures and compares well with molecular simulation data of fluids adsorbing at solid interfaces.