Air at 30 °c (rho = 1.18 kg/m3 , μ = 1.85 × 10 – 5 kg/m∙s) flows through 450 m of 30 cm × 90 cm galvanized steel duct at a rate of 0.25 m 3 /sec. • find the pressure drop. roughness e = 0.046 mm.