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Question 5.11: Air flows through a duct, and the Pitot-static tube measurin...

Air flows through a duct, and the Pitot-static tube measuring the velocity is attached to a differential manometer containing water. If the deflection of the manometer is 100 mm, calculate the air velocity, assuming the density of air is constant and equals to 1.22 kg/m ^{3}, and that the coefficient of the tube is 0.98.

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From the differential manometer,

 

\frac{\Delta p}{\rho g}=\frac{(0.1) \times(9.81) \times 10^{3}}{1.22 \times 9.81}

 

= 81.97 m of air

 

where, \Delta p is the difference in stagnation and static pressures as measured by the differential manometer. Velocity of air is calculated using Eq. (5.72) as

 

V=C \sqrt{2 \Delta p / \rho} (5.72)

 

V=0.98 \sqrt{2 \times 9.81 \times(81.97)}

 

= 39.3 m/s

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