Elmar Baumhögger

Apparatus for the measurement of the speed of sound of ammonia up to high temperatures and pressures

An apparatus for the measurement of the speed of sound based on the pulse-echo technique is presented. It operates up to a temperature of 480 K and a pressure of 125 MPa. After referencing and validating the apparatus with water, it is applied to liquid ammonia between 230 and 410 K up to a pressure of 124 MPa. Speed of sound data are presented with an uncertainty between 0.02% and 0.1%.

Burst design and signal processing for the speed of sound measurement of fluids with the pulse-echo technique

The pulse-echo technique determines the propagation time of acoustic wave bursts in a fluid over a known propagation distance. It is limited by the signal quality of the received echoes of the acoustic wave bursts, which degrades with decreasing density of the fluid due to acoustic impedance and attenuation effects. Signal sampling is significantly improved in this work by burst design and signal processing such that a wider range of thermodynamic states can be investigated. Applying a Fourier transformation based digital filter on acoustic wave signals increases their signal-to-noise ratio and enhances their time and amplitude resolutions, improving the overall measurement accuracy. In addition, burst design leads to technical advantages for determining the propagation time due to the associated conditioning of the echo. It is shown that the according operation procedure enlarges the measuring range of the pulse-echo technique for supercritical argon and nitrogen at 300 K down to 5 MPa, where it was limited to around 20 MPa before.