Before revision: The resulting flow-rate of air through the bed yields the specific surface by the Carman equationCarman P C, J.Soc.Chem.Ind., 57, p 225 (1938): where: S is specific surface, m2·kg-1 d is the cylinder diameter, m ρ is the sample particle density, kg·m-3 ε is the volume porosity of the bed (dimensionless) δP is the pressure drop across the bed, Pa l is the cylinder length, m η is the air dynamic viscosity, Pa·s Q is the flowrate, m3·s-1 It can be seen that the specific surface is proportional to the square root of the ratio of pressure to flow.
After revision: Kozeny–The resulting flow-rate of air through the bed yields the specific surface by the Carman equationCarman P C, J.Soc.Chem.Ind., 57, p 225 (1938): where: S is specific surface, m2·kg-1 d is the cylinder diameter, m ρ is the sample particle density, kg·m-3 ε is the volume porosity of the bed (dimensionless) δP is the pressure drop across the bed, Pa l is the cylinder length, m η is the air dynamic viscosity, Pa·s Q is the flowrate, m3·s-1 It can be seen that the specific surface is proportional to the square root of the ratio of pressure to flow.