Pulse-echo Technique for Speed of Sound Measurements in High-pressure Liquids

摘要

Measurements of the speed of sound in liquids at high pressures provide a simple and accurate method for obtaining fundamental thermodynamic information on the fluid under study. This work describes the design and construction of an ultrasonic cell intended to operate between 230 K and 400 K and up to 70 MPa. Owing to the high sensibility of speed of sound to temperature fluctuations, the apparatus is thermostated with a stability of +-3 mK over the working temperature range. The experimental technique is based on a pulse-echo method, adopted in reason of its high accuracy in time delays measurements, the overall accuracy being limited by the independent determination of the cell length. The experimental setup is currently under development. Preliminary results indicate an achievable accuracy in the speed of sound measurement in the order of +-0.05%.