Progress Towards a Gas-Flow Standard using Microwave and Acoustic Resonances.

Area of Science:

• Metrology
• Fluid Dynamics
• Acoustics

Background:

• Development of a novel gas flow standard is crucial for accurate flow measurements.
• Existing standards require precise knowledge of volume and gas density.
• Microwave and acoustic resonance techniques offer potential for high-accuracy measurements.

Purpose of the Study:

• To develop and validate a novel gas flow standard using microwave and acoustic resonances.
• To establish a primary standard for pressure, volume, speed of sound, and time (PVwt).
• To calibrate critical flow venturis (CFVs) using the developed gas flow standard.

Main Methods:

• Utilized microwave resonances to determine the pressure- and temperature-dependent volume (V_BBB) of a 1.85 m³ steel vessel.
• Employed acoustic resonances and a novel positive feedback system to measure the average gas density and "acoustic mass" (M_acst).
• Calibrated three NIST working standard critical flow venturis using the V_BBB, pressure, and acoustic resonance measurements.

Main Results:

• The V_BBB was determined with an expanded uncertainty of 0.022%.
• Acoustic mass measurements agreed with gravimetric measurements within 0.04%, even with temperature gradients.
• Independent calibrations of critical flow venturis agreed within 0.053%, demonstrating the standard's accuracy and reproducibility.

Conclusions:

• The novel gas flow standard, based on microwave and acoustic resonances, provides accurate measurements of volume and gas density.
• The developed PVwt primary standard successfully calibrated working standards, showing high agreement and reproducibility.
• The feasibility of dynamic tracking for flow measurements was demonstrated, indicating potential for real-time flow monitoring.