Thermophysical properties from the speed of sound
The speed of sound in various gases between 250 and 350 K has been obtained from measurements of the frequencies of the radial modes of spherical acoustic resonators; two resonators were used and both apparatus are described. The radius of each resonator was obtained from the speed of sound in argon. Measurements with the 60 mm radius resonator were made below 115 kPa on the six substances: n-butane; methyipropane; n-pentane; methylbutane; dimethylpropane; and, methanol. Perfect gas heat capacities and second and third acoustic virial coefficients for these substances have been calculated from the results, and estimates are given for the second and third (p,Vm,T) virial coefficients. A sealed resonator of radius 40 mm was used to obtain acoustic results below 7 MPa on argon and the industrially important gases methane, a natural gas, and air. Measurements with argon provided an opportunity to study the model used to account for acoustic energy losses in the resonator. The speed of sound, for the industrially important gases, was compared with estimates obtained from several equations of state.