Knudsen flow straight cylindrical pore

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

Relative importance of molecular (continuum), Knudsen diffusion and Poiseuille flow for air at 20°C in a straight cylindrical pore (after Karger and Rutven [3])... 

Then, 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. 

As the membrane pore widths dimmish, or the mean free path of the molecules rise, the permeating particles tend to collide more with the pore walls than among themselves [60,64], In this case, the Knudsen flow regime is established therefore, the molar gas flow, J, for the Knudsen flow, in a straight cylindrical mesopore of length, /, and trans-pore pressure, AP = Px - P2, is given by [64]... 

---