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Non-nulling Protocols for Fast, Accurate, 3-D Velocity Measurements in Stacks



Iosif Isaakovich Shinder, Aaron Johnson, James Filla, Vladimir B. Khromchenko, Michael R. Moldover, Joey Boyd, John D. Wright, John R. Stoup


We present protocols for making fast, accurate, 3-D velocity measurements in the stacks of coal-fired power plants. The measurements are traceable to internationally-recognized standards; therefore, they provide a rigorous basis for measuring and/or regulating the emissions from stacks. We used novel, five-hole, hemispherical, differential-pressure probes optimized for non-nulling (no-probe rotation) measurements. The probes resist plugging from ash and water droplets. Integrating the differential pressures for only 5 seconds determined the axial velocity Va with an expanded relative uncertainty Ur(Va) ≤ 2 % of the axial velocity at the probe's location, the flow's pitch and yaw angles with expanded uncertainties U(yaw) = U(pitch) = 1 degree, and the static pressure ps with Ur(ps) = 0.1 % of the static pressure. This accuracy was achieved 1) by calibrating each probe in a wind tunnel at 130, strategically-chosen values of (Va, yaw, pitch) spanning the conditions found in the majority of stacks (|Pitch| ≤ 20 degrees; |Yaw| ≤ 40 degrees; 4.5 m/s ≤ Va ≤ 27 m/s), and 2) by using a long forgotten definition of the pseudo-dynamic pressure that scales with the dynamic pressure. The resulting calibration functions span the probe-diameter Reynolds number range from 7,600 to 45,000.
Journal of Air and Waste Management Association


Airspeed vector, 5-hole hemispherical probe, flow, stack flow measurements, multi-hole pitot probe, velocity profiling, non-nulling 3 D velocity measurements, stack flow measurements, pseudo-dynamic pressure, Relative accuracy test audit (RATA).


Shinder, I. , Johnson, A. , Filla, J. , Khromchenko, V. , Moldover, M. , Boyd, J. , Wright, J. and Stoup, J. (2023), Non-nulling Protocols for Fast, Accurate, 3-D Velocity Measurements in Stacks, Journal of Air and Waste Management Association, [online],, (Accessed May 20, 2024)


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Created July 28, 2023, Updated October 6, 2023