Pope JG, Schmidt JW, Gillis KA. Dynamic measurement of gas flow using acoustic resonance tracking.
THE REVIEW OF SCIENTIFIC INSTRUMENTS 2023;
94:034904. [PMID:
37012797 PMCID:
PMC10150644 DOI:
10.1063/5.0143819]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The National Institute of Standards and Technology measured gas flows exiting large, unthermostated, 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 known values of the gas's speed of sound w(p,T) to determine a mode-weighted average temperature ⟨T⟩φ of the gas remaining in a pressure vessel while the vessel acts as a calibrated source of gas flow. To track fN(t) while flow work rapidly changed the gas's temperature, we sustained the gas's oscillations using positive feedback. Feedback oscillations tracked ⟨T⟩φ with a response time of order 1/fN. In contrast, driving the gas's oscillations with an external frequency generator yielded much slower response times of order Q/fN. (For our pressure vessels, Q ∼ 103-104, where Q is the ratio of the energy stored to the energy lost in one cycle of oscillation.) 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 to 12.4 g/s to determine the mass flows with an uncertainty of 0.51 % (95 % confidence level). We discuss the challenges in tracking fN(t) and ways to reduce the uncertainties.
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