Which of the following devices measures fluid flow rates?

The flowmeter is the device specifically designed to measure fluid flow rates. It operates by quantifying the amount of fluid passing through a given point in a specified period of time. Flowmeters can be used for various types of fluids, including liquids and gases, and come in various designs to suit different applications and accuracy requirements.

By accurately measuring the flow rate, flowmeters provide critical data that is essential for process control, monitoring, and optimizing operations in various industrial applications. This function highlights the importance of flowmeters in ensuring efficient resource management and system performance.

Other devices mentioned, while essential in their own capacities, do not measure fluid flow rates. For instance, pressure gauges are used to measure the pressure of a fluid, thermocouples measure temperature, and manometers measure pressure differences using columns of liquid. Each of these tools serves distinct purposes within instrumentation and process control but does not provide flow rate measurements.