Example 4.2 A pitot tube reads 1 in of mercury in a pipe. What is the velocity of air flowing in a pipe at 14.7 psi and 70 °F? Use the following information.
C = 0.98 - 1.00; diameter of pipe, d = 0.335 ft; density of mercury = 846.7 lb/ft3
Density of air = 0.075 lb/ft3; specific heat ratio k = 1.4, pressure drop (ΔP) = 70.55 lbf/ft2
Solution
Velocity of air, V
Velocity of the gas is greater than 200 ft/s,
Assume adiabatic flow.
Pressure at the wall, Po:
Inlet pressure P1 = 14.696 psi = 2116.2 lbf/ft2
Velocity of the air, V (Equation 4.3):