Pitote Tube Flowmeter [Annubar Flow meter]

A Pitot tube measures fluid flow velocity by sensing the difference between stagnation pressure and static pressure. This pressure difference, related to the fluid’s velocity through Bernoulli’s principle, allows for accurate speed calculations. 

A. Static Pressure: Static pressure is the pressure of the fluid when it’s not disturbed by the Pitot tube’s presence. This pressure is measured using openings in the side of the tube or a separate static pressure port. 

B. Stagnation Pressure: A Pitot tube has an open end that faces directly into the oncoming fluid flow. When the fluid enters this opening, it is brought to a standstill, converting its kinetic energy into pressure energy. This pressure at the point where the fluid is brought to rest is called stagnation pressure or total pressure. 

C. Pressure Difference: The Pitot tube measures the difference between the stagnation pressure and the static pressure. This difference, known as the dynamic pressure, is directly proportional to the square of the fluid’s velocity. 

Velocity Calculation: By knowing the fluid’s density and the measured pressure difference, the velocity of the fluid can be calculated using a rearranged form of Bernoulli’s equation: V = √(2 * ΔP / ρ)

Where: 

• V is the velocity
•  ΔP is the difference between stagnation and static pressure (dynamic pressure)
• ρ is the density of the fluid