Hydraulics And Fluid Mechanics MCQ Questions & Answers | Mechanical Engineering

In fluid mechanics, the center of pressure is the point where the total hydrostatic force on a submerged surface can be considered to act. This concept is crucial for understanding the distribution of pressure forces on submerged surfaces. When a body is submerged in a fluid, such as water, the fluid exerts pressure on the surface of the body. This pressure varies across the surface depending on factors like depth and orientation.

The center of pressure is the point through which the resultant of all these pressure forces can be assumed to act. It's important to note that the center of pressure may not necessarily coincide with the centroid or center of gravity of the submerged surface. Instead, it depends on the shape and orientation of the surface and the distribution of pressure on it.

Therefore, in the context of the question, the correct answer is Option B: "At center of pressure." This is because the resultant of all normal pressures in a fluid acts at the center of pressure, representing the combined effect of pressure forces on the submerged surface.

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.