Calculate the pressure drop of air flowing at 20C and 1 atm pressure through a bed of 1.25 cm diameter spheres, at a rate of 50 kg/min. The bed is 150 cm diameter and 250 cm height. The porosity of the bed is 0.4. The viscosity of air is 0.0182 centi-poise and the density is 0.001156 gm/cc.