Equation of State of Fluid NH sub 3 from P-V-T and Ultrasound Measurements to 12 KBAR

摘要

A piston-cylinder apparatus was used to measure the pressure, volume, temperature, and ultrasonic velocity (P,V,T,u) of fluid NH sub 3 from 195 to 320 K at pressures up to 12 kbar. Over 1200 sets of P-V-T-u and P-V-T data were fitted to a Tait-type equation of state (EOS) by non-linear least-squares minimization. With quadratic terms in T for the two fitted parameters, the rms derivation is +-0.2% in V and +-0.9% in u, which is comparable to the experimental error. The simple Tait EOS is useful over the entire fluid range between the vaporization and melting curves up to T exceeding room temperature. Measurements of u and calculations of the constant-pressure heat capacity Cp show regular behavior, differing noticeably from values given by a 44-parameter EOS recently published by NBS. It is concluded that incorporating u or Cp in the formulation of an EOS improves its self consistency markedly. (ERA citation 08:045787)