A New Equation of State for Argon Covering the Fluid Region for Temperatures From the Melting Line to 700 K at Pressures up to 1000 MPa

Abstract

This work reviews the available data on thermodynamic properties of argon and presents a new equation of state in the form of a fundamental equation explicit in the Helmholtz energy. The functional form of the residual part of the Helmholtz energy was developed by using state-of-the-art linear optimization strategies and a new nonlinear regression analysis. The new equation of state contains 41 coefficients, which were fitted to selected data of the following properties: ͑a͒ thermal properties of the single phase (pT) and ͑b͒ of the liquid-vapor saturation curve ͑p s , Ј, Љ͒ including the Maxwell criterion, ͑c͒ speed of sound w, isochoric heat capacity c v , second and third thermal virial coefficients B and C and second acoustic virial coefficient ␤ a. For the density, the estimated uncertainty of the new equation of state is less than Ϯ0.02% for pressures up to 12 MPa and temperatures up to 340 K with the exception of the critical region and less than Ϯ0.03% for pressures up to 30 MPa and temperatures between 235 and 520 K. In the region with densities up to half the critical density and for temperatures between 90 and 450 K the estimated uncertainty of calculated speeds of sound is in general less than Ϯ0.02%. The new formulation shows reasonable extrapolation behavior up to very high pressures and temperatures. Independent equations for the vapor pressure, for the pressure on the sublimation and melting curve and for the saturated liquid and saturated vapor densities are also included. Tables for the thermodynamic properties of argon from 84 to 700 K for pressures up to 1000 MPa are given.

Molecular dynamics study on evaporation and reflection of monatomic molecules to construct kinetic boundary condition in vapor–liquid equilibria

“…To obtain the precise values of the macroscopic variables and the velocity distribution function, the simulation continued until 200 ns. The densities of vapor and liquid obtained from the present simulation are 5.0 kg/m 3 and 1390 kg/m 3 , which agree with the experimental ones [24]. As shown in Fig.…”

Thermodynamic R-diagrams reveal solid-like fluid states

“…Phenomenological equations of state have been fit to experimental data for a number of fluids, with various critical temperatures T c , and compiled by NIST [17]. Such fits allow for the ready computation of R. Particularly good fits are those for argon (T c = 150.69 K) [18], hydrogen (T c = 33.15 K) [19], carbon dioxide (T c = 304.13 K) [20], and water (T c = 647.10 K) [21], with corresponding contour plots of R shown in Figure 2. The fit accuracy for quantities involving second derivatives of f (T, ρ) is typically about 1%, not too near the critical point.…”

Nonequilibrium thermodynamics of interfaces using classical density functional theory

“…Note that these values are different from the values of the LJ parameters given for the Xu and Ge cases in Table I. The LJ parameters in Table I are the values which give best fit between the phase diagram obtained with molecular dynamics ͑MD͒ and Monte Carlo ͑MC͒ simulations and the experimental phase diagram of argon, see Tegeler et al 41 for experimental data for argon. Vrabec et al 28 also used this approach to find and ⑀ / k B .…”