The Knudsen Number (Kn) is a dimensionless quantity used to characterize the flow regime. It is defined as the ratio of the mean free path of the gas molecules to a characteristic dimension of the system (such as pore diameter). Mathematically, it can be expressed as: Kn = λ / L where λ is the mean free path and L is the characteristic length. Knudsen flow typically occurs when 0.01
