Applications and Perspectives of Ultrasonic Multi-Gas Analysis with Simultaneous Flowmetry

We have developed ultrasonic instrumentation for simultaneous flow and composition measurement in a variety of gas mixtures. Flow and composition are respectively derived from measurements of the difference and average of sound transit times in opposite directions in a flowing process gas. We have developed a sound velocity-based algorithm to compensate for the effects of additional gases, allowing the concentrations of a pair of gases of primary interest to be acoustically measured on top of a varying baseline from ‘third party’ gases whose concentrations in the multi-gas mixture are measured by other means. Several instruments are used in the CERN ATLAS experiment. Three monitor C$_3$F$_8$, (R218), and CO$_2$ coolant leaks into N$_2$-purged environmental envelopes. Precision in molar concentration of better than $2 \times 5^{-5}$ is routinely seen in mixtures of C$_3$F$_8$ in N$_2$ in the presence of varying known concentrations of CO$_2$. Further instruments monitor air ingress and C$_3$F$_8$ vapor flow (at high mass flows around 1.1 kg s$^{-1}$) in the 60 kW thermosiphon C$_3$F$_8$ evaporative cooling recirculator. This instrumentation and analysis technique, targeting binary pairs of gases of interest in multi-gas mixtures, is promising for mixtures of anesthetic gases, particularly in the developing area of xenon anesthesia.