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Dynamic Measurement of Gas Flow using Acoustic Resonance Tracking



Jodie Gail Pope, Keith A. Gillis, James W. Schmidt


We measured gas flows exiting large, un-thermostated, gas-filled, pressure vessels by tracking the time-dependent pressure P(t) and resonance frequency fN(t) of an acoustic mode N of the gas remaining in each vessel. This is a proof-of-principle demonstration of a gas-flow standard that uses P(t), fN(t), and literature values of the speed-of-sound to determine a mode-weighted average temperature Tj of the gas remaining in a pressure vessel. Therefore, the vessel is a calibrated source of gas flow. To track fN(t) while flow work rapidly changes the gas's temperature, we sustained the gas's oscillations using positive feedback. Feedback oscillations track Tj with a response time of order 1/fN. In contrast, driving the gas's oscillations with externally-determined frequencies yields much slower response times of order Q/fN. (For our pressure vessels, Q 104.) We tracked fN(t) of radial modes in a spherical vessel (1.85 m3) and of longitudinal modes of a cylindrical vessel (0.3 m3) during gas flows ranging from 0.24 g/s to 12.4 g/s to determine the mass flows with a standard uncertainty of 0.51 %. We discuss the challenges in tracking of fN(t) and plans to reduce the uncertainties.
Review of Scientific Instruments


Flow, acoustic, Self-oscillation, standard


Pope, J. , Gillis, K. and Schmidt, J. (2023), Dynamic Measurement of Gas Flow using Acoustic Resonance Tracking, Review of Scientific Instruments, [online],, (Accessed April 18, 2024)
Created March 21, 2023, Updated April 3, 2023