For gas flow in small characteristic dimensions (e.g., very fine sand, nanoporous structures etc.), the particle-wall interactions become more frequent, giving rise to additional wall friction (Knudsen friction). For a flow in this region, where both viscous and Knudsen friction are present, a new formulation needs to be used. Knudsen presented a semi-empirical model for flow in transition regime based on his experiments on small capillaries.
Great, I understand enough to be curious now on what the model was. My brain won’t shut off until I spend the next two hours in endless rabbit holes that will probably So far off the main search that I will scratch my head at the end as to how I got there. “I won’t search for it, I won’t search for it” You suck....
