Design and Uncertainty Analysis for a PVTt Gas Flow Standard

Area of Science:

• Metrology
• Fluid Dynamics
• Thermodynamics

Background:

• Accurate gas flow measurement is critical for various industrial and scientific applications.
• Existing primary gas flow standards have limitations in range and uncertainty.
• The National Institute of Standards and Technology (NIST) developed a new primary gas flow standard.

Purpose of the Study:

• To introduce and characterize a new pressure, volume, temperature, and time (PVTt) primary gas flow standard.
• To detail the novel features and uncertainty analysis of the standard.
• To validate the performance of the standard across a wide flow range.

Main Methods:

• Utilized two collection tanks and two diverter valve systems for gas flow measurement.
• Employed a thermostatted water bath for precise temperature control of collected gas.
• Determined tank and inventory volumes using gravimetric and volume expansion techniques.
• Analyzed uncertainty contributions from various sources, including pressure sensor drift and temperature variations.

Main Results:

• Achieved an expanded uncertainty (k = 2) between 0.02 % and 0.05 % for flow rates from 1 L/min to 2000 L/min.
• Demonstrated rapid thermal equilibrium of collected gas with an average temperature uncertainty of 7 mK.
• Showcased agreement between different collection systems (34 L and 677 L) within 150 × 10(-6) relative difference.
• Evaluated the 677 L system with double diversions, showing differences less than 75 × 10(-6).

Conclusions:

• The new PVTt primary gas flow standard offers significant improvements in accuracy and range.
• Novel design features, including a thermostatted water bath and advanced operating methods, contribute to low uncertainty.
• The standard provides a reliable and accurate method for gas flow metrology.