Which device is most effective for measuring gas flow?

The rotameter is a device designed specifically for measuring the flow rate of gases and liquids in a closed tube. It operates on the principle of variable area flow measurement, where the flow passes through a tapered tube and raises a float to a level corresponding to the flow rate. This design makes it highly effective for determining gas flow, as it provides a direct visual indication of the flow rate.

Rotameters are particularly advantageous because they can be used for a wide range of flows, they operate with minimal pressure drop, and they can be calibrated for specific fluids and conditions. They are also generally easy to read, making them suitable for various applications in wastewater treatment and other industries.

The other devices listed serve different purposes. Flow meters may refer to general devices used to measure the flow of liquids or gases, but they can vary widely in design and application. Pressure gauges measure the pressure of gases or liquids, which does not directly indicate flow rate. Barometers are used to measure atmospheric pressure, providing no information about flow whatsoever. Thus, the unique design and functionality of a rotameter make it the most effective choice for measuring gas flow.