Short Answer:

A pitot tube is a simple device used to measure the velocity of a fluid flowing through a pipe or open channel. It works on the principle of measuring the difference between static pressure and total (stagnation) pressure. This pressure difference is then used to calculate the fluid’s velocity.

It consists of a small tube pointing directly into the flow. Pitot tubes are widely used in fluid mechanics, aerodynamics, water flow studies, and industrial pipe systems due to their simplicity, low cost, and effectiveness in measuring flow speed.

Detailed Explanation:

Pitot tube 

A pitot tube is an instrument used to determine the velocity of a moving fluid, such as water or air. It was invented by Henri Pitot in the 18th century and is still used in both civil and mechanical engineering. The basic function of a pitot tube is to convert the kinetic energy of the flowing fluid into pressure energy and use this pressure difference to calculate velocity.

Pitot tubes are commonly used in water distribution networks, aircraft airspeed measurement, and hydraulic laboratories. They are favored for their non-intrusive nature, meaning they do not disturb the flow much while measuring.

How a Pitot Tube Works

1. Construction
   A basic pitot tube has two main openings:
   • Impact opening (facing the fluid flow): measures total pressure (also called stagnation pressure)
   • Side openings (parallel to the flow): measure static pressure
2. Working Principle
   When fluid enters the front opening, it comes to rest (stagnates) and creates total pressure. The side openings sense the fluid’s static pressure (the pressure if the fluid were not moving). The difference between total and static pressure is called dynamic pressure.
3. Velocity Calculation
   Using Bernoulli’s equation, the velocity (V) of the fluid is calculated as:

V=2(Pt−Ps)ρV = \sqrt{\frac{2(P_t – P_s)}{\rho}}V=ρ2(Pt​−Ps​)​​

Where:

1. • VVV = fluid velocity
   • PtP_tPt​ = total pressure
   • PsP_sPs​ = static pressure
   • ρ\rhoρ = density of the fluid

This formula gives the point velocity at the location of the pitot tube tip.

Applications of Pitot Tubes

• Water pipelines and ducts: To check fluid speed for flow monitoring
• Aircraft and wind tunnels: To measure airspeed
• Hydraulic labs: For velocity profiling in channels
• HVAC systems: For airflow measurement
• Open channels: With slight modifications, can measure velocity in water canals

Advantages of Pitot Tubes

• Simple design and easy to use
• Low cost and low maintenance
• Can be used in high-velocity flow
• No moving parts → longer life
• Suitable for both gas and liquid flows

Limitations of Pitot Tubes

• Measures velocity only at a single point
• Accuracy depends on proper alignment with the flow
• Not ideal for low-speed or very turbulent flows
• Needs fluid density information for velocity calculation

Conclusion:

A pitot tube is a useful device for measuring fluid velocity by comparing the total and static pressures in the flow. Based on Bernoulli’s principle, it provides an easy and accurate way to determine the speed of a fluid, especially in pipelines and open flows. Its simplicity, reliability, and affordability make it widely used in both field and lab conditions.