For a liquid flowing through a packed bed, the pressure drop per unit length of the bed ΔP / L is Where: V̅₀ is the superficial liquid velocity
ε is the bed porosity
d_p is average particle size
ϕ_s is particle sphericity
ρ_f is liquid density
μ_f is liquid viscosity
On further increasing ‾V₀ incipient fluidisation is achieved. Assuming that the porosity of the bed remains unaltered, the pressure drop per unit length (in Pa/m) under incipient fluidisation condition is