Gases may be measured by the use of a Venturi Tube or Orifice.

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

Answer: (D)

Measuring gas flow relies on how a restriction converts some of the flow’s kinetic energy into a pressure difference. A Venturi tube does this with a smooth, gradual constriction, which speeds up the gas and lowers its static pressure at the throat. The pressure difference between the upstream section and the throat is then related to the volume flow rate, allowing accurate determination of how much gas is moving through. For gases, this smooth geometry minimizes energy losses and handles compressibility better, giving stable, reliable readings.

An orifice plate also creates a pressure drop to infer flow, but its sharp edge causes greater energy loss and can be more sensitive to upstream conditions, making it less ideal for precise gas flow measurement. Barometers and manometers measure pressure, not flow, so they don’t provide flow rates.

So, the Venturi tube is the better choice for measuring gas flow.