Thermodynamic properties of propane and n-butane 2. Speeds of sound in the liquid up to 60 MPa

Measurements of the Speed of Sound in Liquid n-Butane

“…In a previous work, we measured the speed of sound in liquid and supercritical propane between 240 and 420 K at pressures up to 100 MPa with an expanded uncertainty of 0.02% (at the 95% confidence level). Niepmann also published speed-of-sound data for liquid propane in refs and . In ref , we observed that Niepmann’s propane data deviate from our data by up to 1%.…”

“…A total of 384 speed-of-sound data in n -butane were measured during the course of this work. The distribution of our measurements and the two literature data sets of Ewing et al and Niepmann , is depicted in the pressure–temperature plane in Figure . Our data cover the liquid region between 200 and 420 K with pressures up to 100 MPa and were carried out on 12 isotherms in steps of 20 K. Moreover, additional measurements at 430 K were conducted up to 20 MPa in order to provide a few data on a supercritical isotherm.…”

“…The gray area denotes the region of our measurements. The critical point is at (425.13 K, 3.796 MPa): × , this work; + , ref ; ○, ref ; –, vapor pressure; ············, critical temperature and pressure.…”

“…Fractional deviations Δ c = c (expt) – c (calc) of our experimental speeds of sound c (expt) in n -butane, Niepmann’s data at nearby temperatures, and three Helmholtz energy formulations from values c (calc) calculated with the formulation of Bücker and Wagner as a function of pressure at 200, 220, 240, and 260 K. Experimental data: × , this work; ○, ref . Helmholtz energy formulations: - - - -, ref ; , ref ; ············, ref .…”

“…Unfortunately, M’Hirsi reported the results only in graphical form, from which they cannot be extracted with high accuracy. Niepmann , measured the speed of sound in the saturated liquid and the homogeneous liquid region with a pulse-echo technique. His data cover the temperature range from 200 to 375 K with pressures up to 60 MPa.…”