The velocity of sound with derived state properties in helium at −175 to 150 °C with pressure to 150 atm

Abstract

The velocity of sound was determined in helium on 14 equally spaced isotherms from −175 to 150 °C and at pressures from 10 to 150 atm. The results were correlated with an abbreviated perturbation equation of state which employs both the Lennard-Jones (n,6) and the exponential repulsion potentials. Six parameters in the equation of state were adjusted to fit the velocity data within the experimental precision of about 0.001%. The derived results reliably predict literature (P,V,T) values and other velocity-of-sound data for pressures as high as 7000 atm and for temperatures from −223 to 577 °C. A value of the gas constant was derived, R=8314.79±0.35 J K−1⋅kmol−1, which is statistically consistent with the accepted value. The results also support a recent gas thermometry result that indicates the 1968 temperature scale may be in error by 0.012 K at −183 °C.