# Acoustic Flowmeter

on . Posted in Fluid Dynamics

Acoustic flowmeter is a type of device used to measure the flow rate of a fluid, typically a liquid or gas, by utilizing sound waves or acoustic signals.  These flowmeters operate on the principle that the speed of sound in a fluid is influenced by the flow velocity of the fluid itself.  By measuring the time it takes for an acoustic signal to travel against and with the flow direction, an acoustic flowmeter can calculate the fluid's velocity and, consequently, its flow rate.  There are several types of acoustic flowmeters, each with its own method of generating and measuring acoustic signals.

### two primary types coustic flowmeter

• Doppler Flowmeter  -  Doppler flowmeters use the Doppler effect to measure flow velocity. They emit high-frequency sound waves, which bounce off particles or bubbles in the flowing fluid.  The change in frequency of the reflected sound waves is used to determine the velocity of the fluid.
• Transit-Time Flowmeters  -  Transit-time flowmeters work by measuring the time it takes for an acoustic signal to travel both upstream and downstream through the fluid.  The difference in travel times is directly related to the flow velocity of the fluid.

Acoustic flowmeters are often used in various industrial applications, including monitoring the flow of liquids in pipelines, measuring the flow of gases in HVAC systems, and even in medical equipment for measuring blood flow.  They are preferred in situations where other flow measurement methods may be impractical or less accurate. The choice of which type of acoustic flowmeter to use depends on the specific application, fluid properties, and the level of accuracy required.

## 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 $$\large{ deg }$$  $$\large{ rad }$$