Which instrument measures flow by utilizing the Doppler effect?

The ultrasonic flow meter is the instrument that measures flow using the Doppler effect. This technique relies on the principle that when sound waves are transmitted through a fluid, their frequency changes based on the movement of particles within the fluid. When the fluid flows, the frequency of the sound waves reflects the velocity of the flow, allowing for accurate measurement of the flow rate.

This method is particularly advantageous because it provides non-invasive measurement capabilities. Ultrasonic flow meters can be used in a variety of applications and are versatile enough to handle different types of fluids, including clean water and more viscous substances. The Doppler effect principle used in these meters enables them to measure the flow rate without the need for moving parts or direct contact with the fluid, thus minimizing wear and maintenance.

Other options serve different purposes; for instance, rotameters measure flow based on the position of a float in a tapered tube, while Venturi tubes rely on pressure changes to calculate flow rates. Coriolis flow meters measure the mass flow and density of fluids using vibration and are based on different principles entirely.