What is the main purpose of a rotameter?

The main purpose of a rotameter is to meter the flow of fluids, which can include various gases and liquids. Rotameters operate on the principle of variable area flow measurement, which allows for a visual indication of flow rate through a tapered tube. This device is particularly effective for measuring the flow rates of gases due to the characteristics of gas flows, such as lower density and viscosity compared to liquids.

While the flow of chlorine gas is indeed one of the applications of rotameters due to the need for precise monitoring of chemicals in water treatment processes, it's important to understand that rotameters can also measure the flow of water and other liquids. Therefore, the broader defining purpose of a rotameter encompasses the measurement of any fluid flow, not exclusively chlorine gas.

The other options—measuring temperature and measuring pressure—are functions attributed to different types of devices. Temperature measurement is typically performed using thermometers or temperature sensors, and pressure measurement is conducted using pressure gauges or transducers. Thus, while rotameters are versatile, their primary function is related to flow measurement of fluids, making the focus on chlorine gas somewhat limiting compared to the broader application.