Meaning
Gas transport through extremely narrow pores occurs when the mean free path of the gas molecules is greater than the pore diameter. Under these conditions, Knudsen diffusion governs the rate of volatile contaminant removal from porous polymer matrices or during membrane separation. This transport mechanism differs from ordinary bulk diffusion.
Pore Dynamics
Polymer structures undergoing decontamination or foaming often contain microscopic voids that restrict gas molecule movement. When Knudsen diffusion is active, the molecules collide more frequently with the pore walls than with each other. This interaction creates a flow resistance that depends on the pore geometry and temperature.
Polymer Extraction
Deep vacuum decontamination of recycled resins relies on this specific transport behavior to extract organic impurities. As Knudsen diffusion takes place within the sub micron pores of the recycled material, the rate of volatile extraction becomes independent of the total system pressure once the vacuum falls below a specific threshold. This behavior requires precise temperature management to maintain high extraction rates.
Process Boundary
This diffusion mechanism ceases to be the dominant transport mode if the pores expand or if the pressure increases. When the pore size becomes significantly larger than the mean free path, bulk diffusion or viscous flow becomes the primary mechanism. Recognizing this boundary helps engineers design efficient vacuums for polymer processing.
