Question

Which of the following meters has the lowest pressure drop for a given range of flow?

• A. Orifice meter
• B. Venturi meter
• C. Flow nozzle
• D. Rotameter

Hint:

Rotameters = low pressure loss + simplicity + direct reading → ideal for low-pressure systems.

Answer 1

The Correct Option is D

The correct answer to the question of which meter has the lowest pressure drop for a given range of flow is the Rotameter.

To explain the reasoning, let us consider the principle of operation and the characteristics of each type of flow meter involved:

• Orifice Meter: This flow meter uses a flat plate with a hole in it. As the fluid passes through the orifice, it causes a pressure drop due to the sudden constriction. This results in a significant pressure loss, making it suitable for applications where pressure drop is not a critical concern.
• Venturi Meter: This device consists of a gradually narrowing section (converging cone), a throat, and a gradually expanding section (diverging cone), which minimizes the pressure drop compared to orifice meters. Though it offers relatively lower pressure drop than an orifice meter, it is still greater than that of a rotameter.
• Flow Nozzle: Similar to the orifice meter but with a more streamlined design, the flow nozzle results in a smaller pressure drop than the orifice but does not outperform the rotameter in this regard.
• Rotameter: This is a variable area flow meter with a vertically oriented tube and a float inside that moves up and down based on flow rate. The cross-sectional area available for flow increases with the increase in flow rate, thus resulting in a very small pressure drop across the meter. It is particularly advantageous in systems where maintaining pressure is crucial.

In conclusion, the rotameter's design inherently provides a low-pressure drop through its variable area mechanism, making it the optimal choice when minimizing pressure loss is essential.