Simplified Gas State Equations at Saturation and Isotherm

This paper further simplifies the gas state equation
(EOS) by introducing
a thermodynamic constant, Pc*, into the equation, a theoretical pressure
that all gas converts into liquid. In the gas–liquid saturation
system, linear regressions of ln P–ln x2 from M.P. to Tc give P = Pc*x2. It verifies Henry’s law of gas solubility. Meanwhile, Pc*s for most substances are found in the range of 15–16, i.e.,
3.269–8.886 MPa. Hence, EOS deforms into P=Pc*RT10−3Pc*VG+RT. Isotherm is a forced equilibrium system
sustained by an outer force. Isothermal EOS is derived by differentiating
heat over VG. P=(β+γ)Pc*RT10−3Pc*VG+(β+γ)RT, where γ=−[∂ln⁡P∂ln⁡VG]T or γ=−[∂ln⁡x2∂ln⁡VG]T. Empolying Ar as an example, EOS are demonstrated
over the whole pressure range, 0–1000 MPa, including the supercritical
state. Applausive results are obtained in the pressure range before
the gas–liquid transition and high temperatures (1000–2000
K), respectively. The supercritical state of intermediate temperatures
(160–800 K) is likely liquid-like. Hence, EOS is not fittable.