The equation is given as::formula_1where formula_2 is the pressure drop, formula_3 is the total height of the bed, formula_4 is the superficial or "empty-tower" velocity, formula_5 is the viscosity of the fluid, formula_6 is the porosity of the bed, formula_7 is the sphericity of the particles in the packed bed, and formula_8 is the diameter of the related spherical particle.