# Acoustic Flowmeter

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

This type of flowmeter (ultrasonic) can give a continuous measurement of the flow rates of both open channel or pipe. It is nonintrusive, nonmechanical and can give a reading in either flow direction.

There are two types used:

• Ultrasonic Doppler Meter
• Ultrasonic Transit-time Meter

## Acoustic Flowmeter FORMULA

$$\large{ v_a = \frac {l} {2 \; \cos \; \theta} \left( \frac {1} {t_d} - \frac {1} {t_u} \right) }$$
Symbol English Metric
$$\large{ v_a }$$ = average axial velocity of water flow $$\large{ \frac{ft}{sec} }$$ $$\large{ \frac{m}{s} }$$
$$\large{ l }$$ = acoustic path length between transducer faces $$\large{ ft }$$ $$\large{ m }$$
$$\large{ t_d }$$ = acoustic signal downstream travel time $$\large{ sec }$$ $$\large{ s }$$
$$\large{ t_u }$$ = acoustic signal upstream travel time $$\large{ sec }$$ $$\large{ s }$$
$$\large{ \theta }$$ = angle between acoustic path and the pipe's longitudinal axis $$\large{ deg }$$  $$\large{ rad }$$