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Precision of some forms of unified equation of state (on the basis of methane data)
Aleksandr Vasserman, Denis Fominsky

The precision of some well-known forms of unified equation of state for gas and liquid was investigated. The first form describes the compressibility factor, Z = pv/RT, the second the dimensionless Helmholtz energy, f = A/RT, as a function of reduced density, w = ρ/ρcr, and reduced temperature, t = T/Tcr (where p is pressure, v is specific volume, T is temperature, ρ is density, subscript cr refers to critical values, R is the gas constant, and A is the Helmholtz energy). Two versions of these equations were considered: simple polynomial and equations additionally containing exponents of density. The investigation was fulfilled with data on density and isochoric specific heat of methane covering the temperature range from the saturation line up to 620 K at pressures up to 1000 MPa. While compiling equations of state Maxwell’s rule was satisfied.

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