Which device is used to measure gas flow in pipes according to the material?

• A. Venturi Tube
• B. Orifice
• C. Barometer
• D. Thermometer

Answer: (A)

Measuring gas flow in piping uses a device that turns a pressure change into a flow rate. The Venturi tube does this by shaping the flow: gas speeds up as it passes through a narrow throat, so the static pressure drops in that region while the upstream pressure remains higher. By comparing the pressure before the throat to the pressure at the throat, you obtain a differential pressure that, with the appropriate equations (and compressibility corrections for gas), relates directly to the flow rate. The smooth, gradual constriction minimizes energy losses and gives a stable, accurate signal over a wide range of flow rates, which is ideal for gases in pipes.

Other options either measure something else or are less suitable for gas flow in pipes. An instrument that simply measures atmospheric pressure or temperature isn’t measuring flow at all. An orifice plate also creates a differential pressure to infer flow, but its abrupt restriction causes larger pressure losses and can be less accurate for gases, especially at high speeds or varying densities.