Question

16. (10p) Air in a heating system is distributed through a rectangular duct (0.2m x 0.3 m) made of commercial steel (average roughness height = 0.000045 m) at a rate of 0.5 m/s. Calculate the pressure drop and head loss in the 40 m length part of this duct and the needed pumping power to overcome the losses. Pair 1.169 kg/m3, Hair = 1.918x10-5kg/ms

Answer 1

Find out if the flow is laminar or turbulent. The flow is turbulent because Reynolds number is more than 4000. Then find out the friction factor by using the equation of turbulent flow with roughness pipe. Use the Darcy's equation to calculate the head loss. The pressure drop is the product of density, gravity and head loss. The needed power is the product of pressure loss and discharge rate.