Measurement of the Speed of Sound in Near-Critical and Supercritical n-Heptane at Temperatures from (513.40 to 650.90) K and Pressures from (2.5 to 10.0) MPa

The speed of sound in n-heptane was measured by the Brillouin light scattering (BLS) method. The examined region is T = (513.40 to 650.90) K along seven isobaric lines at p = (2.5, 3.0, 4.0, 5.0, 6.0, 8.0, and 10.0) MPa, which was near the critical point of n-heptane. The relative expanded uncertainty (k = 2) of BLS experimental system is estimated to be <0.013 for the speed of sound measurement. The variation tendencies of the speed of sound with increasing temperature and pressure were illustrated. Moreover, the calculated results from the multiparameter equation of state (EOS) proposed by Span and Wagner were employed to assess the experimental data in this paper. The absolute average of the deviations (AAD) between the experimental data and the calculated results is 1.22% in the whole investigated p–T region.