Transport properties of dense fluid argon

We calculate using molecular dynamics simulations the transport properties of realistically modeled fluid argon at pressures up to $\simeq 50GPa$ and temperatures up to $3000K$. In this context we provide a critique of some newer theoretical predictions for the diffusion coefficients of liquids and a discussion of the Enskog theory relevance under two different adaptations: modified Enskog theory (MET) and effective diameter Enskog theory. We also analyze a number of experimental data for the thermal conductivity of monoatomic and small diatomic dense fluids.Comment: 8 pages, 6 figure

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 cP and cV 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 cP(T) thermal behaviour of these systems. In particular, they revisit empirical laws on the cP(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

Étude comparative entre les prévisions des théories du transport dans les fluides denses et les valeurs expérimentales de la conductivité thermique des gaz rares

In this paper one looks at the main assumptions used in the most recent formulations of transport theories in dense fluids. In these theories (Rice and Allnatt, Prigogine, Nicolis and Misguich, Allen and Cole) it is rather difficult to attach a precise physical meaning to the various assumptions introduced and, as a consequence, the quantitative importance they may have is unknown. Hence, the best test of the validity of these theories is to compare them to available experimental data. Such is the primary purpose of the present paper in the particular case of thermal conductivity. It is concluded that the theoretical expectations, although acceptable in certain circumstances, do not give a really satisfactory account of all the available experimental data and further theoretical refinment is needed.On rappelle les hypothèses fondamentales qui sont à la base des plus récentes théories du transport dans les fluides denses. Ces théories sont essentiellement celles de Rice et Allnatt (RA), de Prigogine, Nicolis et Misguich (PNM), et de Allen et Cole (AC). Dans ces développements théoriques, il apparaît cependant assez difficile de rattacher les hypothèses introduites à des considérations physiques précises, et le meilleur moyen de juger de la validité des théories reste encore la comparaison avec l'expérience. C'est le but principal du présent article dans le cas particulier de la conductivité thermique. Il apparaît que les prévisions théoriques, tout en étant assez satisfaisantes sur certains points, sont encore loin de représenter intégralement la réalité expérimentale, et que l'effort théorique doit être poursuivi

Pressure variation of the critical temperature in nitroethane-isooctane and nitroethane-3-methylpentane mixtures

The variation of the critical temperature as a function of pressure in nitroethane-isooctane (N-I) and nitroethane-3-methylpentane (N-3M) mixtures has been experimentally determined. Since both mixtures exhibit components having nearly the same refractive index, special care had to be taken to see the transition. The following values were found : and For N-3M, a comparison is made of the amplitude of the diverging part of the specific heat with the renormalization group prediction.La variation de la température critique Tc avec la pression p a été déterminée dans les mélanges de nitroéthane-isooctane et nitroéthane-3-méthylpentane. Pour ce dernier système, la valeur de (dTc/dp) permet de comparer l'amplitude de la partie divergente de la chaleur spécifique Cp1x0 avec les prédictions du groupe de renormalisation

Universal relations between critical amplitudes : the experimental determination of R+ξ

We have experimentally determined the universal constant R +ξ (for the class of fluids n = 1, d = 3) concerning the amplitude of the diverging part of the specific heat. For the first time a good accuracy is obtained, which allows the experimental values in 3 binary fluids (R+ξ = 0.29 ± 0.04; 0.280 ± 0.011 ; 0.255 ± 0.013) to be favourably compared to the renormalization group result (0.269 6 ± 0.000 8) and the high temperature series expansion value (0.253 ± 0.001), the renormalization group result giving a better agreement with the experimental results.Nous avons déterminé expérimentalement la constante universelle R +ξ (pour la classe des fluides n = 1, d = 3) concernant l'amplitude de la partie divergente de la chaleur spécifique. Pour la première fois une bonne précision est atteinte, permettant aux valeurs dans 3 fluides binaires (R+ξ = 0,29 ± 0,04 ; 0,280 ± 0,011; 0,255 ± 0,013) d'être comparées à celles du groupe de renormalisation (0,269 6 ± 0,000 8) et des séries haute temperature (0,253 ± 0,001), la première valeur étant en meilleur accord avec les résultats expérimentaux