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

This work reviews the available data on thermodynamic properties of argon a nd presents a new equation of state in the form of a fundamental equation e xplicit in the Helmholtz energy. The functional form of the residual part o f the Helmholtz energy was developed by using state-of-the-art linear optim ization strategies and a new nonlinear regression analysis. The new equatio n of state contains 41 coefficients, which were fitted to selected data of the following properties: (a) thermal properties of the single phase (p rho T) and (b) of the liquid-vapor saturation curve (p(s), rho', rho ") includ ing the Maxwell criterion, (c) speed of sound w, isochoric heat capacity c( v), second and third thermal virial coefficients B and C and second acousti c virial coefficient beta(a). For the density, the estimated uncertainty of the new equation of state is less than +/- 0.02% for pressures up to 12 MP a and temperatures up to 340 K with the exception of the critical region an d less than +/- 0.03% for pressures up to 30 MPa and temperatures between 2 35 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 calc ulated speeds of sound is in general less than +/- 0.02%, The new formulati on shows reasonable extrapolation behavior up to very high pressures and te mperatures. Independent equations for the vapor pressure, for the pressure on the sublimation and melting curve and for the saturated liquid and satur ated vapor densities are also included. Tables for the thermodynamic proper ties of argon from 84 to 700 K for pressures up to 1000 MPa are given. (C) 1999 American Institute of Physics and American Chemical Society. [S0047-26 89(99)00203-2].