Ergun equation
The Ergun equation, derived by the Turkish chemical engineer Sabri Ergun in 1952, expresses the friction factor in a packed column as a function of the modified Reynolds number. == Equation == f p = 150 G r p + 1.75 {\displaystyle f_{p}={\frac {150}{Gr_{p}}}+1.75} where: f p = Δ p L D p ρ v s 2 ( ϵ 3 1 − ϵ ) , {\displaystyle f_{p}={\frac {\Delta p}{L}}{\frac {D_{p}}{\rho v_{s}^{2}}}\left({\frac {\epsilon ^{3}}{1-\epsilon }}\right),} G r p = ρ v s D p ( 1 − ϵ ) μ = R e ( 1 − ϵ ) , {\displaystyle Gr_{p}={\frac {\rho v_{s}D_{p}}{(1-\epsilon )\mu }}={\frac {Re}{(1-\epsilon )}},} G r p {\displaystyle Gr_{p}} is the modified Reynolds number, f p {\displaystyle f_{p}} is the packed bed friction factor, Δ p {\displaystyle \Delta p} is the pressure drop across the bed, L {\displaystyle L} is the length of the bed (not the column), D p {\displaystyle D_{p}} is the equivalent spherical diameter of the packing, ρ {\displaystyle \rho } is the density of fluid, μ {\displaystyle \mu } is the dynamic viscosity of the fluid, v s {\displaystyle v_{s}} is the superficial velocity (i.e.