A wind tunnel made of circular duct consists of a contracting nozzle, a test section in which experiments are conducted, a system of piping to recirculate the flow, and a fan to drive the air (see figure). The throat of the tunnel is 10 ft. in diameter and the upstream diameter is 20 ft. Assume the nozzle velocity coefficient is 0.98, and that 20% of the velocity head in the throat is lost to friction in the remainder of the circuit.
a) What is the pressure drop (?P) across the nozzle in psi if the velocity in the test section is 235 ft/s?
b) If the fan efficiency is 85%, what horsepower is required to drive the fan in this tunnel?