A catalytic cracking reactor is formed by a bed of spherical particles of 0.5 cm in diameter, whose cross section is 0.09 m? and whose height is 1.8 m. Determine the pressure drop that occurs when passing a gas stream at a velocity of 0.9 m/s. The density of the solid is 1600 kg/m3 and that of the bed 960 kg/m3. The density of the gas is 0.64 kg/m and its viscosity is 1.5105 kg/m.s