Knudsen Flow in a Straight Cylindrical Pore

In the Knudsen regime, the rate at which momentum is transferred to the pore walls surpasses the transfer of momentum between diffusing molecules. The rate at which molecules collide with a unit area of the pore wall is [2] 

The Physical Chemistry of Materials Energy and Environmental Applications 

FIGURE 5.29 Knudsen flow in a straight cylindrical pore of diameter dv = 2r. 

if the formerly discussed conditions for Knudsen diffusion are satisfied for a mesopore, that is, a pore of diameter in the range between 20-50nm, the diffusion coefficient for the Knudsen flow in a straight cylindrical mesopore is described by Equation 5.94. 

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