Bryant, R.
and Chernovsky, A.
(2025),
The NIST 20 MW Calorimetry Measurement System – Exhaust Flow Characterization and Calibration, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.TN.2325, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958781
(Accessed January 14, 2025)
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The NIST 20 MW Calorimetry Measurement System – Exhaust Flow Characterization and Calibration
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Abstract
Accurate flow measurements at the exhaust systems of large fire test facilities are critical for achieving accurate measurements of heat release rate. A detailed characterization of exhaust flow for the National Fire Research Laboratory (NFRL) has been conducted to verify the accuracy of its routine flow monitoring devices. Following the procedures of standard test methods for determining average flow in exhaust ducts and stacks, experiments were conducted using S type pitot probes to measure the flow distribution on two orthogonal chords of the exhaust ducts. The results characterize the distribution of near-axial velocity, flow angle, and gas temperature at each of the exhaust ducts, and provide data to evaluate the impact of the fire and off-axis flow on the flow distribution. Routine flow monitoring during large fire experiments in the NFRL is provided by averaging pitot probes installed in the exhaust ducts. Average velocity computed from the flow distributions served as a reference measurement and was used to determine flow calibration constants with estimated expanded uncertainty ranging from 4 % to 6 %. Agreement with calibration constants determined previously using tracer gas dilution was confirmed, completing the goal of conducting in-line calibrations of NFRL's averaging pitot probes using independent reference measurements to verify measurement accuracy. This effort has established a benchmark for the accuracy of NFRL's exhaust flow measurement. It has also provided additional evidence that in-situ calibration of the flow monitoring devices used for large fire calorimetry is best practice. Procedures for the flow calibration exist as consensus standards and can be applied for similar large fire test facilities.Citation
Technical Note (NIST TN) - 2325
Report Number
2325
NIST Pub Series
Pub Type
NIST Pubs
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Keywords
Flow Characterization, Flow Calibration, S-Probe, S-type Pitot, Large Fire Calorimetry, Emissions, Exhaust Flow Monitoring
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Created January 8, 2025