Speed of sound measurements in liquid methane (CH4) at cryogenic temperatures between (130 and 162) K and at pressures up to 10 MPa

This paper reports speed of sound experimental measurements in liquid methane (CH4) along five isotherms, in the temperature range of (130 and 162) K, and for pressures up to 10 MPa. A dedicated experimental apparatus, custom-designed for accurate speed of sound measurement at cryogenic temperatures and high pressures, has been developed and the double pulse-echo technique has been adopted. In order to characterize this new apparatus and its performance, experimental results have been compared with speed of sound values of liquid methane available in literature. A further comparison has been made between the experimental measurements and the speed of sound values obtained using the reference equation of state of methane of Setzmann and Wagner, as well as the GERG-2008 model. The ultrasonic path-length has been calibrated using pure water as a reference fluid, with a relative uncertainty of 0.026%. The temperature was measured with two platinum resistance thermometers with an absolute uncertainty of 0.02 K. Thermometers have been calibrated using the ITS-90 temperature scale between the triple point of argon and the triple point of water. Finally, the relative expanded uncertainty (k = 2) associated to the obtained results is of 0.4%, mainly influenced by the repeatability of the measurements.