Question

The gasflow with respect to molecular mean free pathlength, could be divided into 4 regions. What are these and describe them briefly?

Answer 1

According to molecular mean free pathlenth (λ) the 4 regions will be,
1) Continuous flow which flows viscously in low vaccum and λ is very much less than the actual
diameter of the gas channel.
2) Knudsen flow : If the knudsen number is in between 0.01 and 0.5 then that type
   of gas flow is said to influenced by medium vaccum knudsen flow. This is a transition
between continuous and molecular flow regions.
   K = λ / D = ranging between 0.01 to 0.5
3) Molecular flow with high vaccum : It has K greater than or exceeding 0.5, here λ
   is very high
4) Molecular flow with Ultra-high vaccum : same explanation as above
[ i.e) for Molecular flow with high vaccum]