A gravity filter for water treatment is made from a bed of granular particles comprising two layers with 0.75m height of 1.0 mm diameter particles above another bed of 0.5 mm diameter particles of height 0.5 m. The porosity throughout the bed is 0.43. If the bed is 3 m in diameter, at what rate will water flow through the bed at the beginning of the operation if there is a constant head of 1.0 m of water above the bed. Data: Density of water - 1000 kg m-? Viscosity of water - 8 x 10-4 kg mg-1 Acceleration due to gravity - 9.81 m 5-2 It may be assumed that the particles are roughly spherical. Ergun equation for pressure drop AP across a packed bed : 1- *2 . 1.75 (1 - 2) = 150 2