Thermodynamic Properties Of Liquid Research Articles

Neural Network Corrections to Intermolecular Interaction Terms of a Molecular Force Field Capture Nuclear Quantum Effects in Calculations of Liquid Thermodynamic Properties.

We incorporate nuclear quantum effects (NQE) in condensed matter simulations by introducing short-range neural network (NN) corrections to the ab initio fitted molecular force field ARROW. Force field NN corrections are fitted to average interaction energies and forces of molecular dimers, which are simulated using the Path Integral Molecular Dynamics (PIMD) technique with restrained centroid positions. The NN-corrected force field allows reproduction of the NQE for computed liquid water and methane properties such as density, radial distribution function (RDF), heat of evaporation (HVAP), and solvation free energy. Accounting for NQE through molecular force field corrections circumvents the need for explicit computationally expensive PIMD simulations in accurate calculations of the properties of chemical and biological systems. The accuracy and locality of pairwise NN NQE corrections indicate that this approach could be applicable to complex heterogeneous systems, such as proteins.

A fresh look at the vibrational and thermodynamic properties of liquids within the soft potential model.

Contrary to the case of solids and gases, where Debye theory and kinetic theory offer a good description for most of the physical properties, a complete theoretical understanding of the vibrational and thermodynamic properties of liquids is still missing. Liquids exhibit a vibrational density of states (VDOS) which does not obey Debye law, and a heat capacity which decreases monotonically with temperature, rather than growing as in solids. Despite many attempts, a simple, complete and widely accepted theoretical framework able to formally derive the aforementioned properties has not been found yet. Here, we revisit one of the theoretical proposals, and in particular we re-analyze the properties of liquids within the soft-potential model, originally formulated for glasses. We confirm that, at least at a qualitative level, many characteristic properties of liquids can be rationalized within this model. We discuss the validity of several phenomenological expressions proposed in the literature for the density of unstable modes, and in particular for its temperature and frequency dependence. We discuss the role of negative curvature regions and unstable modes as fundamental ingredients to have a linear in frequency VDOS. Finally, we compute the heat capacity within the soft potential model for liquids and we show that it decreases with temperature, in agreement with experimental and simulation data.

A robust drift-flux model for two-phase CO2 pipe flow

CO2 transportation via pipelines and injection wells serves as the interface between carbon sources and storage sinks and thus plays a vital role in large-scale CCUS. CO2 is generally designed to be transported as dense-phase or supercritical fluids, but liquid-gas two-phase CO2 flow may occur during various scenarios such as pipeline start-up, shut-in, depressurization, capacity change, and subsurface injections. Despite the widespread existence of multiphase CO2 pipe flow during CO2 transportation, multiphase CO2 flow models are relatively scarce in the body of publicly available literature and existing models are only moderately accurate. In this work, we developed a robust drift-flux model capable of predicting the liquid holdup and pressure drop in two-phase pure CO2 pipe flow. The system of constitutive equations was solved by the marching method. The thermodynamic properties of liquid and vapor CO2 phases were determined by the highly accurate Helmholtz-type equation of state (EOS) developed by Span and Wagner. Supercritical CO2 friction correlation was employed to estimate the frictional pressure gradient of two-phase pure CO2 flow. A comprehensive verification against available two-phase CO2 flow loop test data shows that the model has superior performance over existing models in both horizontal and downward two-phase CO2 flow, with a maximum of 5% error in liquid holdup prediction and a maximum of 10% error in pressure drop prediction. This model may serve as a valuable tool for the design and optimization of CO2 pipelines in ongoing and future CCUS efforts worldwide.

Thermodynamic Behavior of (2-Propanol + 1,8-Cineole) Mixtures: Isothermal Vapor-Liquid Equilibria, Densities, Enthalpies of Mixing, and Modeling.

Vapor pressures and other thermodynamic properties of liquids, such as density and enthalpy of mixtures, are the key parameters in chemical engineering for designing new process units, and are also essential for understanding the physical chemistry, macroscopic and molecular behavior of fluid systems. In this work, vapor pressures between 278.15 and 323.15 K, densities and enthalpies of mixtures between 288.15 and 318.15 K for the binary mixture (2-propanol + 1,8-cineole) have been measured. From the vapor pressure data, activity coefficients and excess Gibbs energies were calculated via the Barker's method and the Wilson equation. Excess molar volumes and excess molar enthalpies were also obtained from the density and calorimetric measurements. Thermodynamic consistency test between excess molar Gibbs energies and excess molar enthalpies has been carried out using the Gibbs-Helmholtz equation. Robinson-Mathias, and Peng-Robinson-Stryjek-Vera together with volume translation of Peneloux equations of state (EoS) are considered, as well as the statistical associating fluid theory that offers a molecular vision quite suitable for systems having highly non-spherical or associated molecules. Of these three models, the first two fit the experimental vapor pressure results quite adequately; in contrast, only the last one approaches the volumetric behavior of the system. A brief comparison of the thermodynamic excess molar functions for binary mixtures of short-chain alcohol + 1,8-cineole (cyclic ether), or +di-n-propylether (lineal ether) is also included.

Prediction and Analysis of Sustained Annular Pressure of Gas Wells Considering the Influence of Production System and Liquid Thermodynamic Properties

Abstract Sustained annular pressure seriously affects the safety of wellbores. However, most models take the annulus liquid thermodynamic parameters and tubing pressure as constant values. Therefore, the prediction model of wellbore temperature and pressure field was first established based on the basic theory of heat transfer to provide basic parameters for the follow-up sustained annular pressure calculation. Second, based on fluid mechanics theory, a prediction model of sustained annular pressure was developed considering the influence of tubing pressure fluctuation and thermostatic coupling on the thermodynamic parameters of annulus fluid. Then, the iterative method was used to solve the annular pressure. Combined with the field monitoring data of a high-pressure gas well, the model’s accuracy was verified. Finally, a parameter sensitivity analysis was performed, and annular pressure regulation steps were determined. The obtained results revealed that the developed prediction model met engineering accuracy requirements. In a high-pressure gas well, after repeated cycles of shutting in and opening the well for 19 times, gas column height was equal to the leakage point position. Gas column height, leakage point depth, shut-in well annulus temperature, and liquid density were found to affect the change speed and stable value of the annular pressures of shut-in and open wells. The sensitivities of leakage point depth and shut-in annulus temperature to annular pressure regulation were the highest and lowest, respectively. Research results helped us reasonably and quickly manage and control sustained annular pressure gas wells.

Entropy of simple fluids with repulsive interactions near freezing

Among different thermodynamic properties of liquids, the entropy is one of the hardest quantities to estimate. Therefore, the development of models allowing accurate estimations of the entropy for different mechanisms of interatomic interactions represents an important problem. Here, we propose a method for estimating the excess entropy of simple liquids not too far from the liquid-solid phase transition. The method represents a variant of cell theory, which particularly emphasizes relations between liquid state thermodynamics and collective modes properties. The method is applied to calculate the excess entropy of inverse-power-law fluids with ∝r-n repulsive interactions. The covered range of potential softness is extremely wide, including the very soft Coulomb (n = 1) case, much steeper n = 6 and n = 12 cases, and the opposite hard-sphere interaction limit (n = ∞). An overall reasonably good agreement between the method's outcome and existing "exact" results is documented at sufficiently high fluid densities. Its applicability condition can be conveniently formulated in terms of the excess entropy itself. The method is also applied to the Lennard-Jones potential but demonstrates considerably lower accuracy in this case. Our results should be relevant to a broad range of liquid systems that can be described with isotropic repulsive interactions, including liquid metals, macromolecular systems, globular proteins, and colloidal suspensions.

Thermodynamic Assessment of the Co-Zr System

The assessment of the Co-Zr system was carried out in the frameworks of the CALPHAD-method. Composition dependence of the excess Gibbs energy of liquid alloys and solid solutions in the system was described using Redlich–Kister polynomials. Compound Energy Formalism was used to describe the thermodynamic properties of intermetallic compounds. The current assessment takes into account a complete set of experimental data on the thermodynamic properties of the phases and phase equilibria. The phase diagram, coordinates of invariant equilibria, and thermodynamic properties of liquid and solid phases are calculated.

Three-site and five-site fixed-charge water models compatible with AMOEBA force field.

In a typical biomolecular simulation using Atomic Multipole Optimized Energetics for Biomolecular Applications (AMOEBA) force field, the vast majority molecules in the simulation box consist of water, and these water molecules consume the most CPU power due to the explicit mutual induction effect. To improve the computational efficiency, we here develop two new nonpolarizable water models (with flexible bonds and fixed charges) that are compatible with AMOEBA solute: the 3-site AW3C and 5-site AW5C. To derive the force-field parameters for AW3C and AW5C, we fit to six experimental liquid thermodynamic properties: liquid density, enthalpy of vaporization, dielectric constant, isobaric heat capacity, isothermal compressibility and thermal expansion coefficient, at a broad range of temperatures from 261.15 to 353.15 K under 1.0 atm pressure. We further validate our AW3C and AW5C water models by showing that they can well reproduce the radial distribution function g(r), self-diffusion constant D, and hydration free energy from the AMOEBA03 water model and the experimental observations. Furthermore, we show that our AW3C and AW5C water models can greatly accelerate (>5 times) the bulk water as well as biomolecular simulations when compared to AMOEBA water. Specifically, we demonstrate that the applications of AW3C and AW5C water models to simulate a DNA duplex lead to a threefold acceleration, and in the meanwhile well maintain the structural properties as the fully polarizable AMOEBA water. We expect that our AW3C and AW5C water models hold great promise to be widely applied to simulate complex bio-molecules using the AMOEBA force field.

Dynamics, thermodynamics and structure of liquids and supercritical fluids: crossover at the Frenkel line

We review recent work aimed at understanding dynamical and thermodynamic properties of liquids and supercritical fluids. The focus of our discussion is on solid-like transverse collective modes, whose evolution in the supercritical fluids enables one to discuss the main properties of the Frenkel line separating rigid liquid-like and non-rigid gas-like supercritical states. We subsequently present recent experimental evidence of the Frenkel line showing that structural and dynamical crossovers are seen at a pressure and temperature corresponding to the line as predicted by theory and modelling. Finally, we link dynamical and thermodynamic properties of liquids and supercritical fluids by the new calculation of liquid energy governed by the evolution of solid-like transverse modes. The disappearance of those modes at high temperature results in the observed decrease of heat capacity.

A SIMPLIFIED MATHEMATICAL MODEL OF THE EFFECT OF GAZ HYDRATES ON INTRA-TUBE CORROSION

Increasing domestic oil and gas production is one of the important stages in ensuring the country's energy security. In the short-term perspective, the main resource for increasing production is the development of low-yielding deposits. Natural gas contains from 60 to 98 % methane with impurities, such as water (H 2 O), carbon dioxide (CO 2 ), hydrogen sulfide (H 2 S) and oxygen (O 2 ). These impurities are capable of serious corrosion of the pipeline, and initiate the origin of gas hydrates. The formed hydrates can cause partial or complete closure of the inner part of the gas pipeline, and if not quickly removed, it will lead to increased pressure inside the pipe and to a possible extraordinary situation. In this paper, the prediction model of the corrosion rate of a gas pipeline under the influence of gas hydrates is considered. The model is based on the thermodynamic properties of liquid and gas, which are part of the formed gas hydrate under the influence of different operating conditions. The model shows that the rate of corrosion increases with the temperature, operating pressure of pumping and acidity. The sharp increase in the speed of corrosion negatively affects the operation of the pipeline, reducing the operational life of the pipeline. Increasing the working pressure raises the temperature of hydration, but at the same time leads to an increase in the rate of erosion corrosion. Research and forecasting of morphology of corrosion damage is extremely important for the achievement and preservation of the integrity of materials and structures, in particular gas pipelines. The proposed model enables prediction of corrosion processes on gas pipelines considering hydrate formation. The influence of pressure on the speed of corrosion processes is estimated and it is shown that under the most unfavorable conditions the rate of corrosion under the action of gas hydrates can reach 1,2 mm/yr (0,0033 mm/day. With such an indicator, the pipeline suffers significant damage in the absence of immediate repair measures. The sharp increase in the speed of corrosion negatively affects the operation of the pipeline, reducing the operational life of the pipeline. Increasing the working pressure raises the temperature of hydration, but at the same time leads to an increase in the rate of erosion corrosion. Also shown is the influence of the pH of the medium in which the gas hydrate is formed, according to the results of the prediction model, the rate of corrosion increases with the level of acidification of the medium.

Solubility Studies of Sodium Azide in Liquid Ammonia by In Situ Ultrasonic Velocity Measurement

AbstractUltrasonic velocity measurement data has been established as a simple and convenient tool to determine different thermodynamic properties of liquids and solutions. Such measurements were carried out in situ to determine the solubility of NaN3 in liquid ammonia within a defined temperature range. Different mixtures of NaN3 in ammonia were prepared and the ultrasonic velocities of these mixtures were measured within this temperature range in order to compile calibration curves. Further, these calibration curves were used to calculate the solubility in a saturated solution.

Thermal radiative and thermodynamic properties of solid and liquid uranium and plutonium carbides in the visible–near-infrared range

The knowledge of thermal radiative and thermodynamic properties of uranium and plutonium carbides under extreme conditions is essential for designing a new metallic fuel materials for next generation of a nuclear reactor. The present work is devoted to the study of the thermal radiative and thermodynamic properties of liquid and solid uranium and plutonium carbides at their melting/freezing temperatures. The Stefan-Boltzmann law, total energy density, number density of photons, Helmholtz free energy density, internal energy density, enthalpy density, entropy density, heat capacity at constant volume, pressure, and normal total emissivity are calculated using experimental data for the frequency dependence of the normal spectral emissivity of liquid and solid uranium and plutonium carbides in the visible-near infrared range. It is shown that the thermal radiative and thermodynamic functions of uranium carbide have a slight difference during liquid-to-solid transition. Unlike UC, such a difference between these functions have not been established for plutonium carbide. The calculated values for the normal total emissivity of uranium and plutonium carbides at their melting temperatures is in good agreement with experimental data. The obtained results allow to calculate the thermal radiative and thermodynamic properties of liquid and solid uranium and plutonium carbides for any size of samples. Based on the model of Hagen-Rubens and the Wiedemann-Franz law, a new method to determine the thermal conductivity of metals and carbides at the melting points is proposed.

United polarizable multipole water model for molecular mechanics simulation.

We report the development of a united AMOEBA (uAMOEBA) polarizable water model, which is computationally 3-5 times more efficient than the three-site AMOEBA03 model in molecular dynamics simulations while providing comparable accuracy for gas-phase and liquid properties. In this coarse-grained polarizable water model, both electrostatic (permanent and induced) and van der Waals representations have been reduced to a single site located at the oxygen atom. The permanent charge distribution is described via the molecular dipole and quadrupole moments and the many-body polarization via an isotropic molecular polarizability, all located at the oxygen center. Similarly, a single van der Waals interaction site is used for each water molecule. Hydrogen atoms are retained only for the purpose of defining local frames for the molecular multipole moments and intramolecular vibrational modes. The parameters have been derived based on a combination of ab initio quantum mechanical and experimental data set containing gas-phase cluster structures and energies, and liquid thermodynamic properties. For validation, additional properties including dimer interaction energy, liquid structures, self-diffusion coefficient, and shear viscosity have been evaluated. The results demonstrate good transferability from the gas to the liquid phase over a wide range of temperatures, and from nonpolar to polar environments, due to the presence of molecular polarizability. The water coordination, hydrogen-bonding structure, and dynamic properties given by uAMOEBA are similar to those derived from the all-atom AMOEBA03 model and experiments. Thus, the current model is an accurate and efficient alternative for modeling water.

Applications of statistical mechanical theories for estimating thermodynamic properties of ternary and binary solutions using ultrasonic velocity and density data

Thermodynamic properties of liquids and liquid mixtures play very important role in understanding the nature of molecular interactions occurring in the system. In the present work density (ρ) and ultrasonic velocity (u) of the ternary system benzene+carbon tetrachloride+cyclohexane and its three constituent binaries namely, benzene+cyclohexane, carbon tetrachloride+cyclohexane and benzene+carbon tetrachloride have been measured at 298.15K. Different thermodynamic properties of ternary and binary solutions have also been computed with the help of Flory's statistical theory (FST), hard sphere equation of state (HSE) and hole theory (HT) simultaneously. The calculated values are compared with the experimental findings and quite satisfactory results are obtained.

Thermodynamic properties of liquid (antimony + tin) and (gold + antimony + tin) alloys determined from e.m.f. measurements

The thermodynamic properties of liquid (Sb+Sn) and (Au+Sb+Sn) alloys were determined using solid oxide galvanic cells with zirconia electrolyte:(I)Re+kanthal,Sbx-Sn(1-x),SnO2//ZrO2+(Y2O3)//NiO,Ni,Pt,(II)Re+kanthal,Aux-Sby-Sn(1-x-y),SnO2//ZrO2+(Y2O3)//NiO,Ni,Pt,over the temperature range from (973 to 1273)K. Using the Gibbs free energy of formation of pure solid tin oxide SnO2, at first the activities of tin were determined in the binary (Sb+Sn) system. Next, measurements were conducted in the ternary (Au+Sb+Sn) system along two cross-sections specified by the ratio of mole fractions xAu/xSb=1:2 and 2:1. Thermodynamic properties of the liquid phase were described by the Redlich–Kister–Muggianu formula. In this procedure, the heat of mixing determined in our previous paper was included. The results of the calculations were compared with the experimental values obtained for this system.

Discrete models for describing photophysical and thermodynamic properties of polar liquids

A number of properties of liquids with polar molecules are considered using water and ammonia as examples in the discrete approach, i.e., placing the centers of molecules on nodes of a particular lattice while assuming different orientations of the molecules. Different experimental properties are explained by different assumptions concerning the average values of pair orientations of adjacent molecules. Rather than using a uniform thermodynamic distribution over orientations to study fast processes related to the formation and migration of solvated electrons, a quasi-chemical approximation of the lattice gas model is used to calculate the thermodynamic properties of a liquid.

Thermodynamic properties of alloys of the Ni-Sc and Ni-Y systems

Partial and integral enthalpies of mixing for Ni-Y melts at 1775 K (0 < xY < 0.34), 1850 K (0.72 < xY < 1) and Ni-Sc at 1880 K (0 < xSc < 0.35, 0.51 < xSc < 1) are determined by means of calorimetry. Thermodynamic properties of liquid and solid alloys and phase diagrams of Ni-Sc(Y) systems in wide ranges of concentration and temperature are modeled using the ideal associated solution theory. It is found that the activities of components exhibit strong negative deviations from the Raoult’s law.

Thermodynamic properties of alloys of the Al-Co and Al-Co-Sc systems

Enthalpies of mixing for melts of the binary Al-Co system at 1870 K in the range 0 < x Co < 0.25, and at 1620 K, 0 < x Co < 0.12, are investigated by means of isoperibolic calorimetry. Enthalpies of mixing for melts of the ternary Al-Co-Sc system are investigated at 1870 K for sections Al0.75(1 − x)Co0.25(1 − x)Sc x , 0 < x < 0.024, and Al0.88(1 − x)Co0.12(1 − x)Sc x , 0 < x < 0.044. Using the literature data on the enthalpies of mixing for liquid and solid alloys, the activities of melt components, and the phase diagram of the Al-Co system, the thermodynamic properties of liquid and solid alloys of the Al-Co system over a wide range of temperatures and compositions are calculated using a software package of our own design, based on the model of ideal associated solutions (IAS). The enthalpies of mixing and the liquidus surface of the phase diagram of the ternary Al-Co-Sc system over the interval of concentrations are estimated by modeling with data on binary boundary subsystems. All of the components of both the binary Al-Co and ternary Al-Co-Sc systems tend to interact with one another quite strongly: ΔH min(Al-Co) = −32.5 kJ/mol at x Co = 0.44; ΔH min(Al-Co-Sc) = −46 kJ/mol for Al0.4Co0.3Sc0.3 (estimated).

Developing models for correlating ionic liquids density: Part 2 – Density at high pressures

In this paper, two models for calculation of ionic liquids density above 0.1MPa are presented. The range of pressure was from 0.1MPa to 200MPa. The volume at 0.1MPa (v0) in both models was calculated by our recent proposed correlation which was a modification of Rackett equation. In order to consider effect of pressure on v0, two methods were applied. The first method was based on Taylor's series expansion of ionic liquid volume and the second model was in the form of Padé’s approximation of volume as a function of pressure. The models involved adjustable parameters in terms of ionic liquid's thermodynamic properties which were obtained by correlating experimental data. The models results were compared to experimental data and these correlations were accurate enough to calculate ionic liquid density above 0.1MPa where average absolute percent deviation for 32 ionic liquids was 1.09 and 1.12 for two models, respectively. To evaluate the accuracy of the correlations, Aalto and Keskinen model which is a reliable correlation for compressed liquid density calculation and Gardas and Coutinho equation were applied and more agreement between presented correlations and experimental data was observed.

Off-centered impact of water droplets on a thin horizontal wire

The current work focuses on the initial basic stage of filtering droplets. We study the factors that have an effect upon the amount of liquid trapped on a dry smooth horizontal wire. These factors include the impact velocity, impact eccentricity, initial drop size, wire thickness, and liquid thermodynamic properties. Based on elementary analysis of some simple experiments, we propose a non-dimensional criterion for the critical eccentricity for which the maximum amount of liquid is trapped by the wire.