Surface Tension of Binary Mixtures Including Polar Components Modeled by the Density Gradient Theory Combined with the PC-SAFT Equation of State (original) (raw)
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EPJ Web of Conferences, 2014
The density gradient theory (GT) combined with a SAFT-type (Statistical Associating Fluid Theory) equation of state has been used for modeling the surface tension of associating fluids represented by a series of six alkanols ranging from methanol to 1-pentanol. The effect of nonzero dipole moment of the selected alkanols on the predicted surface tension was investigated in this study. Results of the GT + non-polar Perturbed Chain (PC) SAFT equation of state were compared to predictions of GT combined with the PCpolar-SAFT, i.e. PCP-SAFT, equation. Both GT + PC-SAFT and GT + PCP-SAFT give reasonable prediction of the surface tension for pure alkanols. Results of both models are comparable as no significant difference in the modeled saturation properties and in the predicted surface tension using GT was found. Consideration of dipolar molecules of selected alkanols using PCP-SAFT had only minor effect on the predicted properties compared to the non-polar PC-SAFT model.
Gradient theory of nucleation in polar fluids
Atmospheric Research, 2006
Gradient theory (GT), a form of density functional theory (DFT), was applied to water, methanol, and ethanol using the cubic perturbed hard body (CPHB) equation of state (EOS). Compared to the standard form of classical nucleation theory (CNT), the GT results for water showed an improved temperature dependence, but the supersaturation dependence was slightly poorer. GT and several forms of CNT were also found to be in good agreement with a single high T molecular dynamics rate for TIP4P water. The rates predicted by GT for methanol and ethanol were improved by several orders of magnitude compared to CNT, but no improvement in the predicted temperature dependence of the rates was found.
EPJ Web of Conferences, 2013
In this work, we used the density gradient theory (DGT) combined with the cubic equation of state (EoS) by Peng and Robinson (PR) and the perturbed chain (PC) modification of the SAFT EoS developed by Gross and Sadowski [1]. The PR EoS is based on very simplified physical foundations, it has significant limitations in the accuracy of the predicted thermodynamic properties. On the other hand, the PC-SAFT EoS combines different intermolecular forces, e.g., hydrogen bonding, covalent bonding, Coulombic forces which makes it more accurate in predicting of the physical variables. We continued in our previous works [2,3] by solving the boundary value problem which arose by mathematical solution of the DGT formulation and including the boundary conditions. Achieving the numerical solution was rather tricky; this study describes some of the crucial developments that helped us to overcome the partial problems. The most troublesome were computations for low temperatures where we achieved great improvements compared to [3]. We applied the GT for the n-alkanes: nheptane, n-octane, n-nonane, and n-decane because of the availability of the experimental data. Comparing them with our numerical results, we observed great differences between the theories; the best results gave the combination of the GT and the PC-SAFT. However, a certain temperature drift was observed that is not satisfactorily explained by the present theories. 2 Nucleation Thermodynamic system consisting of the liquid and its vapor is in saturated state if it is in thermodynamic equilibrium stable to all fluctuations. In this state, temperature T ,
Nucleation of Polar Fluids from Gradient Theory
2004
Gradient theory (GT), a form of density functional theory (DFT), was applied to water methanol, and ethanol using the cubic perturbed hard body (CPHB) equation of state (EOS). Compared to the standard form of classical nucleation theory (CNT), the GT results for water showed an improved temperature dependence, but the supersaturation dependence was slightly poorer. GT and several forms of CNT were also found to be in good agreement with a single high T molecular dynamics rate for TIP4P water. The rates predicted by GT for methanol and ethanol were improved by several orders of magnitude compared to CNT.
HAL (Le Centre pour la Communication Scientifique Directe), 2005
The gradient theory of fluid interfaces is for the first time applied, without any lumping, to complex mixtures of more than three components, here made up of hydrocarbons and of a high proportion of carbon dioxide, nitrogen, or methane. It is combined with the volume-corrected Peng-Robinson equation of state. No adjustable parameters are used in the influence parameters mixing rule, which allows use of the gradient theory in a predictive manner. It gives very good estimates of the surface tension of the complex mixtures studied. In any case, it is found to be much superior to the traditional parachor method. The gradient theory is also used to compute the density profiles of the mixture components in the interface; it confirms that the low interfacial tensions of the systems studied are principally induced by a local accumulation of carbon dioxide, nitrogen, or methane in the interface.
The Journal of chemical physics, 2017
Homogeneous droplet nucleation has been studied for almost a century but has not yet been fully understood. In this work, we used the density gradient theory (DGT) and considered the influence of capillary waves (CWs) on the predicted size-dependent surface tensions and nucleation rates for selected n-alkanes. The DGT model was completed by an equation of state (EoS) based on the perturbed-chain statistical associating fluid theory and compared to the classical nucleation theory and the Peng-Robinson EoS. It was found that the critical clusters are practically free of CWs because they are so small that even the smallest wavelengths of CWs do not fit into their finite dimensions. The CWs contribute to the entropy of the system and thus decrease the surface tension. A correction for the effect of CWs on the surface tension is presented. The effect of the different EoSs is relatively small because by a fortuitous coincidence their predictions are similar in the relevant range of critic...
Nucleation Rates of Water Using Statistical Association Fluid Theory
Bulletin of the American Physical Society, 2018
The SAFT-0 is an equation of state (EOS) that considers the effects of molecular association based on the statistical association fluid theory (SAFT). This EOS recently showed relatively successful calculations of the phase-equilibrium properties and the classical and nonclassical nucleation rates of methanol. Motivated by methanol results, we use the SAFT-0 EOS for water, in particular within the temperature range of anomalous density behavior below Tmax = 277.15K. To do so, the effective temperature-dependent hard sphere diameter was adjusted for the SAFT-0 EOS in an away that it reproduces the water vapor-liquid equilibria and the vapor pressures in such temperature range. The Gibbsian form of classical nucleation theory (CNT) (known as the P-form) and nonclassical gradient theory (GT) calculations were carried out using the SAFT-0 EOS with and without including this adjusted diameter. Calculated rates were compared to the experimental values of Wölk and Strey [J. Phys. Chem. B 2001, 105, 11683-11701]. In addition to the phase-equilibrium properties, this adjustment improved the nucleation rates from both GT and CNT by factors of 500 and 100, respectively. To explore this further, the GT and experimental rates were analyzed using Hale's scaled model [J. Chem. Phys., 2005, 122, 204509]. This analysis shows that the predictions of GT scale relatively well with those of the experimental data.
Surface tension of water droplets upon homogeneous droplet nucleation in water vapor
Colloid Journal, 2017
A method has been proposed for determining interfacial free energy from the data of molecular dynamics simulation. The method is based on the thermodynamic integration procedure and is distinguished by applicability to both planar interfaces and those characterized by a high curvature. The workability of the method has been demonstrated by the example of determining the surface tension for critical nuclei of water droplets upon condensation of water vapor. The calculation has been performed at temperatures of 273-373 K and a pressure of 1 atm, thus making it possible to determine the temperature dependence of the surface tension for water droplets and compare the results obtained with experimental data and the simulation results for a "planar" vapor-liquid interface.
Fluid Phase Equilibria, 2017
The perturbed-chain polar statistical associating fluid theory (PCP-SAFT) and density gradient theory are used to calculate interfacial properties of multicomponent systems. The constant influence parameters are adjusted to experimental surface tension data of pure fluids and the cross-influence parameters are determined from a geometric combining rule. The influence parameters of simple branched alkanes, in the absence of experimental surface tension data, can be estimated from a correlation for n-alkanes. Results for surface tension of hydrocarbon mixtures of up to twenty components as well as systems including polar and supercritical species are in good agreement with experiments as long as bulk densities are reproduced accurately and molecular interactions between the components are symmetric or only weakly asymmetric.
A New Correlative Model for Surface Tension of Mixtures : Hydrocarbon Mixtures
2014
This article presents a new correlative model for surface tension of mixtures. This model is an extension of a predictive model recently proposed by our group. Other correlative models were evaluated and compared to the proposed model. Hydrocarbons mixtures exhibiting chemical nature or shape and chain size asymmetries were chosen as the standard to test the performance of the chosen models at several temperatures. A total of 1433 experimental data was used. All of the correlative models studied showed very good results. However, an F-test study pointed out that there are still opportunities in modeling for describing the studied data within the experimental uncertainties.