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 Tj 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 Tj 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.
, Gillis, K.
and Schmidt, J.
Dynamic Measurement of Gas Flow using Acoustic Resonance Tracking, Review of Scientific Instruments, [online], https://doi.org/10.1063/5.0143819, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=935707
(Accessed May 29, 2023)