Pitot Tube

A pitot tube is a small transparent open tube bent at right angle. The basic purpose is to measure the flow i.e. Velocity of the fluid. The point where the velocity of the fluid is zero is known as stagnation point. The pressure at that point is known as stagnation pressure.

p + 1/2 ρ v² + γ h = constant along a streamline         (1)

where

p = static pressure (relative to the moving fluid) (Pa)

ρ = density (kg/m³)

v = flow velocity (m/s)

γ = ρ g =  specific weight (N/m³)

g = acceleration of gravity (m/s²)

h = elevation height (m)

Each term of this equation has the dimension force per unit area - N/m² or in imperial units psi, lb/ft².

If pitot tube is used in a close conduit, then pressure can be measured with the help of piezometer.

Equation for ideal velocity is

V_o= (2gh)^½

^{For local velocity the equation becomes}

V_o= C(2gh)^½

Where C is pitot tube co efficient  which is less than unity.

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