Question

An electric motor with an output of 0.75 hp drives an air ventilating fan to produce a 24in diameter stream of air having a uniform speed of 40 ft/s. The air is at atmospheric pressure and 70^oF. The efficiency of the fan is?

Answer 1

Solution -

Given - Output of motor or input at Fan shaft = 0.75hp

P = 0.75 hp = 0.559 KW,

Diameter, D = 24 in =0.609 m

Area, A = 0.291 m²

Speed, V = 40 ft/s = 12.19 m/s

Presdure at Atmospheric = 0.101 mm Water column

Air density at atmospheric condition at 70^oF= 1.225 kg/m³

Calculation: -

The efiiciency of fan is-

={ discharge in m³/s x Pressure in mmWC/(102 x power in Kw)} x 100

={ x 0.101/(102 x0. 559)} x100

substituting all the values and we get-

= 76.97%

so we have the fan efficiency is 76.97%.

answered by: anonymous