US3239130A

US3239130A - Gas pumping methods and apparatus

Info

Publication number: US3239130A
Application number: US294078A
Authority: US
Inventors: Jr Charles H Naundorf
Original assignee: Consolidated Vacuum Corp
Current assignee: Consolidated Vacuum Corp
Priority date: 1963-07-10
Filing date: 1963-07-10
Publication date: 1966-03-08
Anticipated expiration: 1983-03-08

Description

M h 8, 1966 c. H. NAUNDORF, JR

GAS PUMPING METHODS AND APPARATUS Filed July 10, 1963 United States Patent 3,239,134 GAS PUMPING METHODS AND APPAEATUS Charles H. Naundorf, Era, Rochester, N.Y., assignor to Consolidated Vacuum Corporation, Rochester, NJiL, a corporation of New York Filed July it 1963, Ser. No. 294,078 7 Claims. (Cl. 2343-1) The present invention relates to gas pumping methods and apparatus and, more particularly, to methods and apparatus for moving or evacuating gas molecules from a space by means of an electric arc plasma.

The subject invention provides improved methods and apparatus for moving or evacuating gas molecules from a space without objectionable contamination of the space or the gas.

According to the invention a nozzle is prepared which has a tlu oat region and a divergent portion adjacent the throat region. The throat region is placed into communication with the space to be evacuated. An electric arc plasma is established in the throat region whereby gas molecules are drawn from the space to be evacuated through the throat region and are expelled through the divergent portion of the nozzle. The gas thus drawn from the space to be evacuated will be heated by the electric arc plasma as it passes through the throat region. In the divergent nozzle portion, this heated gas will expand and thus help to reduce the pressure at the nozzle throat. In this manner, the efiiciency of the pumping operation is greatly increased.

If desired, a negatively biased, apertured screen may be placed adjacent the open end of the divergent nozzle portion to accelerate the gas ions emerging from the arc plasma and thus further reduce the pressure at the nozzle throat and increase the efiiciency of the pumping operation.

A further increase in pumping efliciency is experienced if the nozzle is made to be of the convergent-divergent type, with the convergent nozzle portion being exposed to the space to be evacuated. A larger amount of gas molecules will then be advanced to the arc plasma during operation of the pump.

A large increase in pumping eificiency is also obtained by supplying the arc plasma with an ionizable gas, such as nitrogen, argon and the like, during the pumping operation. This gas is ionized and heated in the are plasma and leaves the nozzle through its divergent portion, thereby reducing the pressure at the nozzle throat.

The are plasma is preferably established by striking an electric arc in the throat region of the nozzle. To this end, the throat region may be made of electroconductive material and an electrode may be provided adjacent the throat region. The throat region is then preferably connected to the positive terminal of a direct-current source and the electrode to the negative terminal of this source. An arc is then struck between electrode and nozzle throat. The electrons traveling in this are from the cathode to the anode, that is from the electrode to the inner wall of the throat region, will entrain the gas molecules present in the region of the electric arc. In this manner, gas molecules are continuously removed from the space to be evacuated, inasmuch as the electrons in the arc travel at high velocity and occur in great number.

It will now be appreciated that the method of the invention has utility not only for evacuating spaces or vessels, but also for moving gasses in a predetermined direction. Thus, the expressions evacuated or space to be evacuated as used herein should be understood as referring not only to high vacuum evacuation processes, but also to gas pumping operations in general where the object is to move a gas in a predetermined direction.

The apparatus of the invention comprises a nozzle having a throat region adapted to communicate with the space to be evacuated and including a divergent portion communicating with the throat region. The apparatus of the invention includes means for establishing an electric arc plasma in the throat region to draw gas molecules from the space to be evacuated through the throat region and cause the gas molecules to be expelled through the divergent portion.

The throat region may comprise electroconductive material and the means for establishing the arc plasma may include an electrode located adjacent the throat region. Preferably, a direct-current source may be connected with its positive terminal to the throat region and with its negative terminal to the electrode. The direct-current source is dimensioned to maintain an electric are between the electrode and the throat region, with the electrode serving as a cathode and the throat region as an anode for the electric arc.

The electrode may have a hollow cylindrical configuration and an ionizable pumping gas may be supplied to the electric are through the hollow electrode. The ionizable pumping gas may, however, also be supplied to the electric are by means of nozzles arranged in the space between the electrode and the nozzle throat region.

The apparatus of the invention may include an apertured screen located adjacent the open end of the divergent nozzles portion. This screen may be negatively biased with respect to the nozzle, so that ionized gas molecules are accelerated from within the divergent nozzle portion towards the open end thereof. The gas molecules thus accelerated are substantially neutralized at the screen and leave the apparatus through the apertures in the screen.

The invention and its operation and utility will become more readily apparent from the following detailed description of preferred embodiments thereof, illustrated by way of example in the accompanying drawings, in which:

FIG. 1 shows diagrammatically and partially in section a vacuum pump according to the invention;

FIG. 2 shows a first modification of the apparatus illustrated in FIG. 1; and

FIG. 3 shows a detail, partially in section, of a second modification of the apparatus of FIG. 1 or a modification of the apparatus of FIG. 2.

The object of the vacuum pump 10 illustrated in FIG. 1 is to pump gas or gas molecules from a region 14 to a region 15. A wall 16 has been schematically illustrated between

regions

14 and 15 to indicate that these two regions are separated and isolated from each other. In practice, the region 14 may be the inside of a vessel to be evacuated, or of a chamber connected to a vessel to be evacuated, and the region 15 may be a chamber that is pre-evacuated by any suitable conventional means, such as mechanical, oil difiusion or mercury pumps (not shown).

The vacuum pump 10 comprises a nozzle 18 having a throat region 19 and a divergent portion 20. The divergent portion 20 communicates with the throat region 19 and has a discharge opening 21. The nozzle 13 also has a convergent portion 22 which, in the instant embodiment, is integral with the throat region 19. In brief, the nozzle 2% is of the convergent-divergent type. In addition, the nozzle 28* has a symmetrical configuration about longitudinal axis 25.

An electrode 26 is located on axis 25 and in the vicinity of the throat region 19. Nozzle 20 is of electroconductive material and has the positive terminal of a directcurrent source 27 connected thereto. The negative terminal of source 27 is connected to electrode '26. While source 27 has been illustrated in the general area of electrode 26 and convergent portion 22, it will of course be J! understood that the source 27, in practice, will be located outside region 14, as well as region 15.

Source 27 is constructed and dimensioned to strike and maintain an are 30 between electrode 26 and nozzle region 19. To this effect, the source 27 may include a high voltage source for striking an arc and a low voltage source (not shown in detail) for maintaining the are 30. This low voltage source, which is connected to electrode 26 and nozzle 18 as long as the are 30 is to be maintained, may, for example, h ve a voltage of some 50 to 500 volts and a nominal current rating of some 100 to 300 amperes. During the existence of are 30, electrons will it w from electrode or cathode 25 to throat region or anode 19 and part of convergent portion 22, as has been schematically indicated in the drawings by means of arrows 32.

Electrode 26 is of the non-consumable type to prevent undue contamination of the regions 14 and and of the gas being pumped. For example, electrode may be a tungsten electrode or may be of another one of the conventional high-temperature and consumption resistant electrode materials. The nozzle 18 may, for example, be of stainless steel or other suitable consumption resistant material. The apparatus 1% includes a cooling jacket which encompasses the throat region 19. The cooling jacket 35 has an inlet 36 and an outlet 37 for admission and withdrawal of a suitable cooling medium 33, such as water, to and from the cooling jacket 35. This cooling jacket 25 serves to maintain the nozzle 13 at throat region 19 at reasonable temperatures. If desired, heat-conducting elements (not shown) may be provided between nozzle 18 and jacket 35 or the jacket 35 may be disposed in close proximity to or in contact with nozzle 18 to accomplish a desired cooling effect.

The electrons in the are 34 will flow in great numbers and at great velocity fronrelectt'ode 26 to the wall of nozzle throat region 19 and will thus entrain gas molecules present in throat region 19. These molecules will be ionized as schematically indicated at 4d, and will thus be driven through convergent nozzle portion 26, as indicated at 4-1, and the opening 21 thereof. In this manner, gas molecules will be drawn from region 14 and moved to region 15. The electrons traveling within throat region 19 form a dense sheath which prevents backfiow or migration of pumped gas molecules into t e region 14.

It will now be appreciated that FIG. 1 shows an apparatus for evacuating a space in an efiicient and advantageous manner. If desired, this apparatus could also be employed for moving or transferring gasses in a circulation or pumping system.

FIGS. 2 and 3 shows apparatus similar to that of FIG. 1, so that like reference numerals have been employed for like elements.

In the apparatus of FIG. 2, a hollow cylindrical electrode 26' with a longitudinal bore is employed in the place of electrode 26 shown in FIG. 1. During operation of the apparatus an ionizable gas 51, such as nitrogen, argon or the like, is supplied through bore 58 to the arc plasma or are 3t To this effect, a gas transfer chamber 53 is connected to the electrode 26 so as to be in communication with bore 59. Gas is supplied to transfer chamber 53 by a conduit 55 which is connected to a suitable supply of pressurized gas 55, such as a steel bottle located outside

regions

14 and 15. In this manner, the ionizable gas 14 will be supplied to the are 36' without entering the low-pressure region 14. This gas will be entrained and ionized by the electrons in are 39 along with the gas molecules pumped from region 14. Subsequently, this gas will also pass through and expand in divergent portion 20 and will thus significantly increase the aspiration of gas molecules from region 14. If desired, a pump (not shown) may be associated with gas supply as for recovery of ionizable gas from region 15 and re-use thereof in are 30.

In the apparatus of FIG. 3, a screen 60 with apertures 61 is located in front of opening 21 of divergent nozzle portion 28. The remaining structure of the apparatus of FIG. 3 may be the same as that shown in FIG. 1 or in FiG. 2, so that only the larger end of divergent nozzle portion 26, a high-voltage source 62, and the screen 69 with apertures 61 have been illustrated in FIG. 3. The screen may be a metal sheet with a largenumber of apertures or may also consist of wire mesh. The apertured or perforated screen 60 is baised negatively with respect to nozzle 13 by means of the high-voltage source 62 which is connected to screen and nozzle 18 as shown and which, in ractice, is preferably located outside region 15. Screen 6% is effective to accelerate the gas molecules within divergent portion 28 towards the opening 21. At screen 69, the gas molecules are neutralized and pass through the apertures 5-9. In this manner, the aspiration of gas molecules from region 16 is further increased. if desired, the gas supply structure of FIG. 2 may be combined with the screen structure of FIG. 3 to realize maximum pumping efficiency.

While an arcing electrode structure has been shown in the drawings, convention or other types ofi plasmaproducing means could be employed in its place. Various other modifications will be apparent to those skilled in the art.

I claim:

1. Apparatus for evaluating gas molecules from a chamber, comprising a nozzle having a throat region connected to said chamber, and including a divergent electrically conductive nozzle portion connected to the throat region, and means for establishing a continuous electric arc plasma in the throat region to draw gas molecules from said chamber through the throat region and expel the gas molecules through the divergent portion.

2. Apparatus for evacuating gas molecules from a chamber, comprising a nozzle having an electroconductive throat region connected to said chamber, and including a divergent electrically conductive nozzle portion communicating with the throat region, an electrode located at the throat region, and means for establishing a continuous electric are between the electrode and the throat reg-ion and maintaining a flow of electrons from the electrode to the throat region.

3. Apparatus for evacuating gas molecules from a space, comprising a convergent-divergent nozzle having a symmetrical configuration with respect to a longitudinal axis through the nozzle and being connected to said chamber, an electrode located on said axis and projecting into the convergent portion of the nozzle, and means for establishing a continuous electric are between the electrode and the nozzle and maintaining a flow of electrons in said are from the electrode to the nozzle.

4. Apparatus for evacuating gas molecules from a chamber, comprising a nozzle having an electroconductive throat region connected to said chamber, and including a divergent portion connected to the throat region, an electrode located at the throat region, means for establishing a continuous electric are between the electrode and the throat region and maintaining a flow of electrons from the electrode to the throat region, and means for introducing ionizable gas into the electric arc.

5. Apparatus for evacuating gas molecules from a chamber, comprising a convergent-divergent nozzle having a symmetrical configuration with respect to a longitudinal axis through the nozzle and being connected to said chamber, a hollow cylindrical electrode located on said axis adjacent the convergent portion of the nozzle, means for establishing a continuous electric are between the electrode and the nozzle, and means for supplying ionizable gas through the hollow cylindrical electrode and into said arc.

6. Apparatus for evacuating gas molecules from a chamber, comprising a nozzle having a throat region connected to said chamber, and including an electrically conductive divergent nozzle portion connected to the throat region, means for establishing an electric arc plasma in the throat region to draw gas molecules from said chamber through the throat region and expel the gas molecules through the divergent portion, an apertured screen adjacent said divergent nozzle portion, and means for electrically biasing said screen with respect to said divergent nozzle portion to accelerate gas molecules from said divergent nozzle portion to said screen and through the apertures thereof.

7. Apparatus for evacuating gas molecules from a chamber, comprising a nozzle having an electrically conductive throat region connected to said chamber, and including an electrically conductive divergent portion connected to the throat region, an electrode located at the throat region, means for establishing an electric are between the electrode and the throat region and maintaining a flow of electrons from the elect-rode to the throat region, means for introducing ionizable gas into the electric are, an apertured screen adjacent said divergent portion, and means for electrically biasing said screen with respect to said divergent nozzle portion to accelerate gas molecules from said divergent portion to said screen and through the apertures thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,279,586 4/ 1942 Bennett 23069 2,327,588 8/1943 Bennett 23069 2,182,751 12/ 1939 Reitherman 23069 2,765,975 10/ 1956 Lindenblad 23069 2,798,181 7/1957 Foster 23069 2,809,314 10/1957 Herb 1031 2,862,099 11/1958 Gage.

3,041,824- 7/ 1962 Berhman -35.5 3,077,108 2/1963 Gage et al 1031 3,081,020 3/1963 Rostas 230-60 3,091,079 5/1963 Kunen 60-355 FOREIGN PATENTS 1,246,669 10/ 1960 France.

OTHER REFERENCES Discovery, page 16 (FIG. 2), July 1963.

LAURENCE V. EFNER, Primary Examiner.