Refrigeration – Low pressure cold trap process and apparatus
Patent
1989-08-16
1991-04-09
Caposselo, Ronald C.
Refrigeration
Low pressure cold trap process and apparatus
55269, 62268, 417901, B01D 800
Patent
active
050053639
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to vacuum engineering and, more specifically, to cryogenic sorption vacuum pump designs. The invention can be used to best advantage in vacuum equipment employed extensively in electronic, radio, and other industries, as well as for research studies, both as a preliminary means and as the principal facility for obtaining superclean and oil-free vacuum in working chambers of 1.multidot.10.sup.-3 to 1.multidot.10.sup.2 m.sup.3 volume and with a pressure range of 1.multidot.10.sup.5 to 1.multidot.10.sup.-2 or 1.multidot.10.sup.2 to 1.multidot.10.sup.-7 Pa or lower.
DESCRIPTION OF THE PRIOR ART
At the present time, improvements in cryogenic sorption pumps follow the route of optimizing their designs both by developing new arrangement versions and by providing new pump design elements. Both of these directions are aimed at improving the pumping (evacuation) and cryogenic characteristics of said pumps.
There is known a cryogenic sorption pump comprising a housing complete with a cover, a bottom, and an inlet nozzle provided on the cover, a vessel for cryogenic agent, arranged within the housing and provided with a gas-permeable screen, a heat bridge connecting the inlet nozzle with the cryogenic agent vessel, an adsorbent, and pipes to fill in cryogenic agent and remove cryogenic agent vapuors (N. P. Larin "Sverkhvysokovakuumny agregat s gelievym kriogennym nasosom". In: Pribory i tekhnika experimenta (Journal of the USSR Academy of Sciences), 1983, No. 6, pp. 128-132, p. 129).
One disadvantage of said pump is that, for completely oil-free high vacuum to be obtained by means of this pump in a working chamber, additional facilities have to be employed, such as a mechanical fore pump used in conjunction with a liquid nitrogen-cooled oil vapour trap. Currently used trap designs of this type are uneconomical, considering the high liquid nitrogen consumption rates and the short useful life for a single liquid nitrogen filling, up to 10-35 hours, necessitating a considerable amount of additional labour consumption for regeneration and washing of traps and connection piping, as well as unproductive liquid nitrogen consumption for subsequent trap cooling from room temperature to 77.4K.
Another known cryotenic sorption pump comprises a housing complete with a cover, a bottom, and an inlet nozzle arranged on the cover, a vessel for a cryogenic agent, accommodated within the housing and provided with a gas-permeable screen, a heat bridge connecting the inlet nozzle with the cryogenic agent vessel, an adsorbent, pipes to fill in cryogenic agent and remove cryogenic agent vapours, and a vacuum conductor arranged within the cryogenic agent vessel space and having one end taken out of the housing through its bottom (SU, A, 1333833).
The cryogenic agent vessel in said unit has the form of two coaxial--inner and outer--cylinders forming a space to be filled with the cryogenic agent. Arranged within the inner cylinder of the cryogenic agent vessel, coaxial therewith, is a gas-permeable screen forming a cavity to be filled with adsorbent. The cavity in the central part of the pump, enclosed by the closed gas-permeable screen, serves for the supply of evacuated gas to the adsorbent. The vacuum conductor is arranged inside the cryogenic agent vessel, with one end being taken out through the bottom, and the other, through the housing cover. The vacuum conductor is in the form of a half-turn of a helix, passing around the inner cylinder of the cryogenic agent vessel, with the dimensions of the vacuum conduit being defined by the following relationships: ##EQU1## where R is the radius of the half-turn of the helix, d is the diameter of the vacuum conductor, and h is the lead of the helix. The vacuum conductor is used at the preliminary stage of evacuation of the working chamber by the machanical fore pump, serving the function of a freeze-out trap, its walls condensing such gases and vapours that easily condense at the temperature of the cryogenic agent, thus oil vapours from the
REFERENCES:
patent: 3335550 (1967-08-01), Stearn
patent: 3344852 (1967-10-01), Bergson
patent: 3371499 (1968-03-01), Hagenbach et al.
patent: 3416326 (1968-12-01), Stuffer
patent: 3552485 (1971-01-01), LeJannou
patent: 3668881 (1972-06-01), Thibault et al.
patent: 3788096 (1974-01-01), Brilloit
patent: 4446702 (1984-05-01), Peterson et al.
Journal of the USSR Academy of Sciences, 1983 pp. 128-132.
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