A Pitot tube is used to measure the local velocity of helium (and ideal gas) flo

Question

A Pitot tube is used to measure the local velocity of helium (and ideal gas) flowing in a duct at 60F and 30 psia. The tube points upstream into the flow, such that the pressure sensed by the tube is the stagnation pressure. The static pressure is measured at the same location in the flow by means of a wall pressure tap. Using a U-Tube manometer the difference between the stagnation and static pressure is measured as 2.0 in. Determine:

1) The helium density (slug/ft^3)

2) The helium velocity (ft/s)

Explanation / Answer

Hey! I made a mistake in calculation. Here's the new answer.

Stagnation Pressure = Static Pressure + 1/2 * rho * V^2

Thus

1/2 * rho * V^2 = 2 in = 1/6 ft of water = 2989 Pa

rho = M P / RT = (0.004 Kg * 206842 Pa) / (8.314 * 288 K) = 0.34553 Kg/m^3 = 66.5 x 10^-5 slug / ft^3

V = 131.53 m/s = 431.54 ft/s

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