Air at 20 °C is drawn through a 0.5 m diameter duct by a fan. If the volume flow rate is 4.5 m3 s−1 and the duct is 12 m long, with a friction factor of 0.005, determine the fan shaft power necessary,...

Air at 20 °C is drawn through a 0.5 m diameter duct by a fan. If the volume flow rate is 4.5 m3 s−1 and the duct is 12 m long, with a friction factor of 0.005, determine the fan shaft power necessary, assuming 80 per cent mechanical efficiency. Take air density as 1.2 kg m−3 and viscosity as 1.8 × 10−5 N s m−2.