09-28-2021-2028 - Cold Trap

In vacuum applications, a cold trap is a device that condenses all vapors except the permanent gases into a liquid or solid.^[2] The most common objective is to prevent vapors being evacuated from an experiment from entering a vacuum pump where they would condense and contaminate it. Particularly large cold traps are necessary when removing large amounts of liquid as in freeze drying.

Cold traps also refer to the application of cooled surfaces or baffles to prevent oil vapours from flowing from a pump and into a chamber. In such a case, a baffle or a section of pipe containing a number of cooled vanes, will be attached to the inlet of an existing pumping system. By cooling the baffle, either with a cryogen such as a dry ice mixture, or by use of an electrically driven Peltier element, oil vapour molecules that strike the baffle vanes will condense and thus be removed from the pumped cavity.

Cold trap immersed in cold medium in Dewar flask. Some workers prefer the opposite arrangement, where vapors flow down the wall of the trap, and are sucked up the inner tube; this reduces blockage.^[1]

https://en.wikipedia.org/wiki/Cold_trap