Flow of water in a pipe about 3 meters in diameter can be measured by

Option A: Orifice Plate

An orifice plate measures flow by creating a pressure drop across a sharp-edged plate with a hole in it. The flow rate is calculated from this pressure difference.

Limitations: Although simple and inexpensive, it causes significant head loss and is less efficient for very large diameter pipes like 3 m. Over time, wear and tear can affect accuracy.

Option B: Venturimeter

A Venturimeter works on Bernoulli’s theorem, where the fluid passes through a converging section, a throat, and then a diverging section. The difference in pressure between the inlet and throat is used to calculate the flow rate.

Advantages: It produces low head loss, can handle large flow volumes, and gives accurate results even in very large diameter pipes. Its design makes it highly suitable for permanent installation in high-capacity systems like a 3 m water pipe.

Option C: Rotameter

A Rotameter is a variable area flowmeter where a float moves up and down inside a tapered vertical tube depending on the flow rate.

Limitations: It is mainly used for small to medium flow rates and works only in vertical orientation. It is impractical for huge diameters such as 3 m, both due to size limitations and mechanical constraints.

Option D: Pitot Tube

A Pitot tube measures the velocity of the fluid at a single point by comparing stagnation and static pressure.

Limitations: To determine total flow in a large pipe, multiple velocity measurements at various points are required, along with integration of the velocity profile. This is cumbersome and less accurate compared to using a Venturimeter for a 3 m diameter pipe.

Conclusion: Among the given options, the Venturimeter is the most suitable for measuring flow in a large diameter (about 3 m) water pipe because it is accurate, causes minimal head loss, and is practical for large-scale applications.