Which of the following accurately describes a rotameter?

A rotameter is accurately described as a variable-area flowmeter for closed tubes. This means that it measures the flow rate of a fluid by allowing the fluid to flow through a tapered tube. As the fluid flows, it lifts a float that rises and falls in the tube according to the flow rate. The position of the float indicates the flow rate, which is read against a calibrated scale on the tube.

The design of the rotameter allows it to provide a direct and continuous reading of flow rate, which is particularly useful in various applications within wastewater treatment and other fluid handling processes. The variable area refers to the changing cross-sectional area of the tube, which allows for more precise measurement as the flow increases or decreases.

Other devices mentioned, like those for measuring high pressures or contaminants, serve different purposes and are not related to the specific function of a rotameter. A manometer, on the other hand, is used for measuring pressure differences and is distinct from flow measurement. Understanding that the rotameter's primary function is to measure flow rate in a closed tube system helps clarify its importance and application in various industrial settings.