Editing Distillation (section)

===Molecular distillation===
[[Molecular distillation]] is vacuum distillation below the pressure of 0.01 [[torr]]. 0.01 torr is one order of magnitude above [[Hard vacuum|high vacuum]], where fluids are in the [[free molecular flow]] regime, i.e., the [[mean free path]] of molecules is comparable to the size of the equipment. The gaseous phase no longer exerts significant pressure on the substance to be evaporated, and consequently, rate of evaporation no longer depends on pressure. That is, because the continuum assumptions of fluid dynamics no longer apply, mass transport is governed by molecular dynamics rather than fluid dynamics. Thus, a short path between the hot surface and the cold surface is necessary, typically by suspending a hot plate covered with a film of feed next to a cold plate with a line of sight in between. Molecular distillation is used industrially for purification of oils.