Inviscid flow Inviscid flow Inviscid flow is the flow of an inviscid fluid, in which the viscosity of the fluid is equal to zero. Though there are limited examples of inviscid fluids, known as superfluids, inviscid flow has many applications in fluid dynamics. The Reynolds number of inviscid flow approaches infinity as the viscosity approaches zero. When viscous forces are neglected, such as the case of inviscid flow, the Navier-Stokes equation can be simplified to a form known as the Euler equation. This simplified equation is applicable to inviscid flow as well as flow with low viscosity and a Reynolds number much
Knudsen flow Knudsen flow Knudsen flow describes the movement of fluids with a high Knudsen number, that is, where the characteristic length in the flow space is of the same or smaller order of magnitude as the mean free path. For a gas passing through small holes in a thin wall in the Knudsen-flow regime, the number of molecules that pass through a hole is proportional to the pressure of the gas and inversely proportional to its molecular mass. It is therefore possible to effect a partial separation of a mixture of gases if the components have different molecular masses. The technique