A Dual-Path Pulse-Echo Instrument for Liquid-Phase Speed of Sound and Measurements on p -Xylene and Four Halogenated-Olefin Refrigerants [R1234yf, R1234ze(E), R1233zd(E), and R1336mzz(Z)].

We describe an instrument to measure the speed of sound in liquids based on the dual-path, pulse-echo technique; it covers a temperature range of 228.15-423.15 K, with pressures of up to 93 MPa. It differs from similar instruments in the method of mounting the quartz-crystal transducer, a path-length ratio of 2.5:1, and automated data-collection protocols. The path-length difference was calibrated with measurements on high-purity propane. The performance of the instrument was verified by comparison with recent literature data on p -xylene. We present new liquid-phase measurements for the halogenated-olefin refrigerants 2,3,3,3-tetrafluoroprop-1-ene [R1234yf], trans -1,3,3,3-tetrafluoroprop-1-ene [R1234ze(E)], trans -1-chloro-3,3,3-trifluoroprop-1-ene [R1233zd(E)], and cis -1,1,1,4,4,4-hexafluorobut-2-ene [R1336mzz(Z)]. These measurements cover a combined temperature range of 230 to 420 K, with pressures of up to 50 MPa; these data are compared to literature data (where available) and multiproperty equations of state. The average relative expanded uncertainty in the speed of sound ranged from 0.035 to 0.088% for the different fluids.