3. The formula for flow through a randomly packed bed of spheres is given by Ergun's equation 150(1 - )?,, 1.75 (1- )? H zP Where : Ap is the pressure drop across the bed, H is the length of the bed d is the equivalent spherical diameter of the packing, pis the density of fluid, u is the dynamic viscosity of the fluid, lo is the superficial velocity e is the void fraction of the bed Using dimensional analysis (MLT), show that this equation is either valid or invalid in any system of units. Explain.