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Calibration of gas flow meters using choked flow and an evacuated vessel.
Meas. Sci. Technol. 32:105105 (2021)
The measurement of gas flow rates is of great importance in a wide range of modern technologies. This paper introduces a simple, yet accurate technique for in-house calibration of gas FMs (mass and volumetric) even under harsh environmental conditions such as encountered during field measurement campaigns. The method requires only readily available, low cost components: a vessel of known volume, an air pump, a pressure sensor and a metal plate orifice or a needle valve to act as a CO. The unique property of choked flow in the CO is used here for flow calibration. In the method presented here a vessel is evacuated to below the critical pressure (<0.53 of upstream pressure) and then allowed to refill with ambient air (or some other process gas) under so-called choked flow conditions through the CO. The method presented here leverages that the flow rate upstream of the CO is not only constant but readily determined from (a) the known V (VESS), (b) the measured time rate of change of the absolute pressure in the vessel and (c) the ideal gas law. This calculated flow rate can be used for calibration of FMs. The accuracy of the method depends only on the accuracy of the pressure measurement, the timer and the value of the V (VESS). The flow rate computed in this way is found to be in excellent agreement (typically 1% difference) with the flow rate measured by a soap film FM (Gilibrator). As expected from theory this method is found to work for all kinds of CFRs (here: various types of metal plate orifices and needle valves were tested), gas types (here: air, Argon, and CO2) and upstream pressures (here: between 650 hPa and 1400 hPa). The accuracy of this technique (similar to 1%) is as good as that of standard volume displacement methods (e.g. soap film FMs) (typically 1% difference), the standard of laboratory-based flow calibrators, but less expensive and more suitable for harsh environments.
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Publication type
Article: Journal article
Document type
Scientific Article
Keywords
Calibration ; Gas Flow Meters ; Choked Flow ; Aerosols; Auxiliary Power Unit; Alternative Fuels; Pm Emissions; Aircraft; Aviation; Engine
ISSN (print) / ISBN
0957-0233
e-ISSN
1361-6501
Quellenangaben
Volume: 32,
Issue: 10,
Article Number: 105105
Publisher
Institute of Physics Publishing (IOP)
Publishing Place
Temple Circus, Temple Way, Bristol Bs1 6be, England
Non-patent literature
Publications
Reviewing status
Peer reviewed
Institute(s)
Institute of Lung Health and Immunity (LHI)
Grants
U.S. Federal Aviation Administration Office of Environment and Energy through ASCENT
FAA Center of Excellence for Alternative Jet Fuels
Environment, project 02 through FAA
FAA Center of Excellence for Alternative Jet Fuels
Environment, project 02 through FAA