What is "cold trap"

n. In vacuum applications, a device that condenses all vapours except the permanent gases into a liquid or solid, typically to prevent contamination of a vacuum pump.

In vacuum applications, a cold trap is a device that condenses all vapors except the permanent gases into a liquid or solid. 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 liquid nitrogen, 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.

In astronomy, a cold trap is a close to the surface layer of the atmosphere that is substantially colder than both the deeper and higher layers. It is called a trap because it keeps ascending gases with high melting points in by freezing them to a solid which then drops back to the planet surface. The most important gas to be kept in that way, on the Earth, is water vapor, which without the presence of a cold trap in the atmosphere (which for the earth resides at about 20 kilometers height) would gradually escape or dissociate into space, making life impossible. Some astronomers believe that the lack of a cold trap is why the planets Venus and Mars both lost most of their liquid water early in their histories.

Category:Atmosphere