Question

For measurement of velocity of fluid flowing through a pipe, the device used would be

• A. Venturimeter
• B. Orifice meter
• C. Rotameter
• D. Pitot tube

Hint:

Flow Devices Functions:
Fluid Point VELOCITY Measurement = PITOT TUBE ($v = \sqrt{2gh}$).
Volumetric DISCHARGE ($Q$) = Venturimeter, Orifice meter, Rotameter.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Flow measurement instrumentation: Pitot tubes (and Pitot-static tubes) measure local point flow velocity ($v = \sqrt{2g \Delta h}$) by converting kinetic energy at the stagnation point into impact pressure head, whereas Venturimeters, Orifice meters, and Rotameters measure volumetric flow rate ($Q$).
Key Formula or Approach:
\[ \text{Stagnation Pressure Equation: } P_{\text{stagnation}} = P_{\text{static}} + \frac{1}{2} \rho v^2 \implies \mathbf{Point \text{ } Velocity \text{ } (v)} = \sqrt{\mathbf{2 g \cdot \Delta h}} \]

Step 2: Detailed Explanation:
In fluid instrumentation and dairy pipeline metering devices:
1. Pitot Tube (Henri Pitot, 1732) (D): An L-shaped open-ended tube aligned facing directly into the oncoming fluid stream. It converts the local fluid velocity head into a stagnation pressure head. By measuring the difference between stagnation and static pressure, it directly measures Point Velocity of fluid flowing through a pipe ($v = C \sqrt{2g \Delta h}$).
2. Venturimeter Orifice Meter (A, B): Obstruction meters designed to measure total Volumetric Flow Rate Discharge ($Q$, in $\text{m}^3/\text{s}$ or L/h).
3. Rotameter (C): A variable-area meter measuring total Flow Rate ($Q$).

Step 3: Final Answer:
Therefore, the device used for velocity measurement is Pitot tube, corresponding to option (D).