Debye Fluid State Equation

A new form of a fluid state equation, based on a conceptual extrapolation from the Debye equation for the specific heat of solid materials is described. The Debye characteristic temperature, , which is nominally a constant for solids, becomes a function of the fluid density ρ. Further assuming = c1ρ2/3(1+c2ρ+c3ρ2+· · ·) yields the conventional fluid virial equation in the high-T and low-ρ limits for a monatomic fluid. Additional terms must be added to describe (a) the compressibility of the dense subcooled fluid and (b) properties in the near-critical range. Discussion of the Gruneisen parameter and other factors is included. This Debye fluid theory was used as a state equation for 3He, continuous from 0.005K to above room temperature.