Editing Cold trap (section)

==Applications==
Pumps that use oil either as their working fluid ([[diffusion pump]]s), or as their lubricant (mechanical rotary pumps), are often the sources of contamination in vacuum systems. Placing a cold trap at the mouth of such a pump greatly lowers the risk that oil vapours will backstream into the cavity.

Cold traps can also be used for experiments involving vacuum lines such as small-scale very low temperature [[distillation]]s/[[condensation]]s.  This is accomplished through the use of a coolant such as [[liquid nitrogen]] or a [[freezing mixture]] of [[dry ice]] in [[acetone]] or a similar solvent with a low [[melting point]].  Liquid nitrogen is only used when dry ice or other cryogenic approaches will not condense the desired gasses since liquid nitrogen will also condense oxygen.  Any oxygen gas content in the vacuum line or any leak in the vacuum line will result in liquid oxygen mixed with the target vapors, often with explosive results.

When performed on a larger scale, this technique is called freeze-drying, and the cold trap is referred to as the condenser.

Cold traps are also used in [[cryopump]] systems to generate hard vacua by condensing the major constituents of the atmosphere ([[nitrogen]], [[oxygen]], [[carbon dioxide]] and [[water]]) into their liquid or solid forms.

An [[igloo]] or other snow bivouac may exploit the same principle – confinement of [[Density|denser]] cool air within an impermeable lower volume – to reduce cold air reaching the occupants through use of a sump or cill around a raised sleeping platform within.