Theory of gas–gas phase transition in rare‐gas binary mixtures

Thermostatic properties of nitrate molten salts and their solar and eutectic mixtures

Nitrate molten salts are extensively used for sensible heat storage in Concentrated Solar Power (CSP) plants and thermal energy storage (TES) systems. They are the most promising materials for latent heat storage applications. By combining classical molecular dynamics and differential scanning calorimetry experiments, we present a systematic study of all thermostatic, high temperature properties of pure KNO₃ and NaNO₃ salts and their eutectic and "solar salt" mixtures, technologically relevant. We first study, in solid and liquid regimes, their mass densities, enthalpies, thermal expansion coefficients and isothermal compressibilities. We then analyze the c_P and c_V specific heats of the pure salts and of the liquid phase of the mixtures. Our theoretical results allow to resolve a long-standing experimental uncertainty about the c_P(T) thermal behaviour of these systems. In particular, they revisit empirical laws on the c_P(T) behaviour, extensively used at industrial level in the design of TES components employing the "solar salt" as main storage material. Our findings, numerically precise and internally consistent, can be used as a reference for the development of innovative nanomaterials based on nitrate molten salts, crucial in technologies as CSP, waste heat recovery, and advanced adiabatic compressed air energy storage.

Temperature and composition dependence of the Soret coefficient in Lennard-Jones mixtures presenting evaporation/condensation phase transition

The thermodiffusive behavior of a Lennard-Jones binary mixture has been studied by using nonequilibrium molecular dynamics. In particular, the dependence of the Soret coefficient, S(T), on the temperature and composition has been investigated, exploring a wide range of temperatures from 1000 K to the condensation temperature of the mixture. In a previous paper the dependence of S(T) on the temperature and the composition was studied for Lennard-Jones binary mixtures presenting mixing/demixing (consolute) phase transition, and the results allowed the formulation of a very simple expression with the computed values of S(T) in the one phase region outside the critical region closely fitted by the function [T - T(c)(x(1))](-1), with T(c)(x(1)) the demixing temperature of the mixture under study. The results of the present work show that the same expression of S(T) can be found for the one phase region outside the evaporation/condensation region but now with T(c) representing the condensation temperature of the mixture under study.

Temperature and composition dependence of the Soret coefficient in Lennard-Jones mixtures presenting consolute critical phenomena

Nonequilibrium molecular dynamics calculations have been carried out o Lennard-Jones binary mixtures with the aim to investigate the dependence of the Soret coefficient on the temperature and on the composition for systems presenting phase transitions. By an appropriate choice of the cross interaction parameter, epsilon(12) (0 < epsilon(12) < min{epsilon(11),epsilon(22)}), these systems show a mixing/demixing (consolute) phase transition. The other parameters are those of a binary mixture of Argon and Krypton. This system has been considered over a wide range of temperatures (up to approximately or equal to 1000 K), of compositions (0.1 < or = x(1) < or = 0.9), and of cross interaction parameter (0 < epsilon(12) < min{epsilon(11),epsilon(22)}). The study allows the formulation of a very simple expression for the Soret coefficient, S(T), as a function of temperature and composition. Indeed the computed values of S(T) in the one phase region outside the critical region are closely fitted by the function [T-T(c)(x(1))](-1) where T(c)(x(1)) is the demixing temperature of the mixture under study. This result indicates for this type of systems a dependence of S(T), as a function of the temperature, on a unique characteristic property of the fluid mixture, the demixing temperature T(c), which, in turn, is a function of the binary mixture composition x(1).

A generating equation for mixing rules and two new mixing rules for interatomic potential energy parameters

A generating equation for the mixing rules of interatomic potential energy parameters is proposed. It is demonstrated that this equation can, indeed, reproduce many popular mixing rules. A weighting matrix is used with the generating equation. This weighting matrix approach is superior to the present status of mixing rule development. A systematic framework is given for devising new mixing rules and/or comparing them. Two new mixing rules, which are more accurate than the available rules in the literature, are proposed. These rules are capable of reproducing the collision diameter and well-depth parameters for the binary values of noble gases to within their experimental uncertainties.