Power Plant Β· Flow
Ultrasonic Transit-Time Flow
Flow from the upstream and downstream transit times of a clamp-on or spool-piece ultrasonic meter: path velocity, measured speed of sound, and an IAPWS-IF97 sound-speed plausibility check for water.
Standard method β stated scope limits apply
Meter data
Ratio of area-mean to path velocity; Reynolds dependent. Take from the meter maker (single-path ~0.90β0.96 turbulent).
Enter the inputs and press Calculate.
About This Calculation
A transit-time ultrasonic meter sends pulses upstream and downstream along an angled path. The flowing fluid shortens the downstream and lengthens the upstream time; their difference gives the path velocity and their mean gives the speed of sound, which is a useful sanity check of the measurement.
Frequently Asked Questions
Why is the measured speed of sound useful?
It should match the known value for the fluid at its temperature; a deviation points to a wrong path length, temperature or timing offset.
What is the profile factor k?
The ratio between area-mean velocity and the velocity along the acoustic path; it depends on Reynolds number and path layout and is normally supplied by the meter maker.
What is the difference between clamp-on and spool-piece meters?
A spool-piece meter has transducers built into the pipe and a known path, giving lower uncertainty. A clamp-on meter attaches outside the pipe, so its accuracy also depends on how well the pipe wall thickness, material and diameter are known.
Why does the meter need both upstream and downstream transit times?
The difference between them gives the flow velocity, while their average gives the speed of sound. Using both cancels the effect of temperature on the sound speed, so the velocity measurement does not depend on knowing the fluid temperature.