Which device is commonly used to measure flow?

The Venturimeter is a device specifically designed to measure the flow rate of fluids in a pipe. It operates on the principle of the Bernoulli equation, which relates the pressure and velocity of a fluid. A Venturimeter has a converging section, a throat, and a diverging section. As fluid flows through the narrowing section, its velocity increases, leading to a decrease in pressure. By measuring the pressure difference between the wider and narrower sections of the pipe, the flow rate can be calculated with high accuracy.

In contrast, the other devices listed serve different purposes. A thermometer measures temperature, a pressure gauge measures pressure at a specific point in a system, and a manometer is used to measure the pressure of fluids relative to the atmospheric pressure. Therefore, none of these alternatives are suited for measuring flow rates in the same direct and effective manner as a Venturimeter.