Speed-of-Sound Measurements in Liquid n-Pentane and Isopentane

Comprehensive and accurate measurements of the speed of sound in liquid n-pentane and isopentane were carried with a double-path-length pulse-echo instrument. The measurements cover the temperature ranges between 200 and 420 K for n-pentane and between 220 and 420 K for isopentane with pressures up to 100 MPa. The expanded uncertainties (at the 0.95 confidence level) are 2.1 mK for temperature, 0.005% for pressure, between 0.01% at low pressure and 0.008% at high pressure for the speed of sound in n-pentane, and between 0.014% at low pressure and 0.01% at high pressure for the speed of sound in isopentane. At high temperatures and low pressure, the uncertainty in the speed of sound in n-pentane increases up to 0.026% at 420 K, while for isopentane it reaches 0.04%. In isopentane, strong damping of the sound signals was observed at temperatures below 260 K, which indicated dispersion of the sound waves in the frequency range of our measurements near 8 MHz. Measured speeds of sound in this temperature range...