Refrigeration – Low pressure cold trap process and apparatus
Patent
1989-11-14
1990-12-25
Capossela, Ronald C.
Refrigeration
Low pressure cold trap process and apparatus
55269, 62268, 417901, B01D 800
Patent
active
049793691
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to vacuum engineering, more specifically, to cryogenic sorption pumps, and can be used to produce superclean and oil-free vacuum within a pressure range of 10.sup.2 to 10.sup.-7 Pa while evacuating any gases excepting helium and including corrosive ones from chambers of various designations, measuring from 0.01 to several hundred cubic meters in volume.
2. Description of the Related
There is known a cryogenic sorption pump (SU,A,1333833) comprising a pumping element consisting of a circular vessel containing liquid nitrogen, a porous screen arranged coaxially with the vessel within a space encompassed by its inner side surface, and a sorbent located within the gap between the inner side surface of the vessel and the porous screen.
This pump is disadvantageous in that at the liquid nitrogen temperature the sorbent has a low sorption capacity at low equilibrium pressures (below 10.sup.-3 -10.sup.-4 Pa) of adsorbable gases. As a result, this type of pump fails to provide limiting pressures of below 10.sup.-3 Pa even after a shortterm gas load. To increase the sorption capacity of the pump, the sorbent may be cooled by means of solid nitrogen down to 55.degree.-50.degree. K., but the sorbent cannot be maintained at those temperature for a long time because of high natural heat input to the nitrogen-containing vessel, the nitrogen contents rapidly warming up after evacuation of nitrogen vapors is discontinued. The operation of this pump is hampered by the need for frequently charging the vessel with liquid nitrogen and repeatedly evacuating nitrogen vapors.
Another prior-art cryogenic sorption pump (M. P. Larin, Kondensatsionno-adsorbtsionnaya i sorbtsionnaya otkachka pri temperaturakh tverdogo azota, Zhurnal tekhnicheskoy fiziki, 1988, vol 58, No. 10, October, Nauka Publishers (Leningrad Branch), pp. 2026-2039) comprises a housing complete with a cover fitted with an inlet nozzle for connection of the space to be evacuated and, arranged in the housing, a pumping element and a radiation screen encompassing the pumping element. The pumping element has the form of a circular vessel designed to contain cryogenic agent, with a heat conductor disk welded to its bottom, and heat conductor and porous screen shells arranged coaxially with the vessel and attached to the heat conductor disk. The interspaces between the heat conductor shells and the porous screen shells adjacent thereto are filled with a sorbent material, while the interspaces between the adjacent porous screen shells communicate with the inlet nozzle of the pump.
The radiation screen contains a toroidal vessel adapted to contain cryogenic agent and installed under the pumping element vessel, a shell arranged coaxially with the pumping element, and a chevron screen installed between the pumping element and the inlet nozzle. The lower end of the radiation screen shell is attached in a pressure tight manner to the radiation screen vessel, with the upper end of the shell fitted with a cover connected with the inlet nozzle through a bellows-form heat bridge. The housing is provided with a nozzle for evacuation of the space between the housing and the radiation screen.
The pump also contains a thin-walled pipe installed within the space defined by the inner walls of the radiation screen vessel and having its upper end attached in a pressure tight manner to the cover of this vessel and its lower end attached to the housing bottom. Installed across the pipe in its upper section is a chevron screen having a thermal contact with the radiation screen vessel.
During pump operation the radiation screen vessel is filled with liquid nitrogen while the pumping element vessel is filled with solid nitrogen, i.e. with a cryogenic agent with a lower temperature. The presence of the radiation screen cooled by liquid nitrogen down to 77.4.degree. K. lowers considerably the heat input by radiation from the housing to the pumping element, making it possible for nitrogen to be maintained in a so
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Journal of Technical Physics, M. P. Larin, Kondensatsionno-absorbtionnaya i sorbtsionnaya otkashka pri temperaturakh tverdogo azota, Zhurnal tekhnicksskoy fiziki, 1988, vol. 58, No. 10, Oct., Nauka Publishers (Leningrad Branch, pp. 2026-2039).
Alexandrov Maxim L.
Larin Marxen P.
Nikolaev Valery I.
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