US1822702A - Evacuating pump - Google Patents

Description

Patented Sept. 8, 1931 "UNITED STATES PATTETVOFFICE ERNST KOBEL, OF ENNETBADEN, SW'ITZERLAN'D, ASSIGNOR TO AKTIENGESELLSCHAFT BROWN BOVERI & GIE., OF BADEN, SWITZERLAND, A JOINT-STOCK COMPANY OF SWITZE ELAN D EVACUATITTG PUMP Application filed August 19, 1929, Serial No. 386,755, and in Germany August 27, 1928.

This invention relates to improvements in evacuating pumps and particularly to static pumps operating by diffusion of the fluids to be withdrawn from a chamber into a vapor created in the pump.

' A fluid may be withdrawn from a cham her by causing. the fluid tov mingle with a vaporized substance flowing away from an orifice in such chamber and by causing the mixture of fluid and vapor to flow into a space wherein the temperature relations are such that the vaporized substance will be condensed,thereby releasing the fluid mixed therewith and permitting such fluid to escape while the presently condensed and previously vaporized" substance is returned to its source. 1 a

The velocity of a molecule of vapor is greatest at that portion'of its path which is substantially in the direction of flow of the greater portion of the molecules which portion of the molecular path is nearest the point. of separation of the molecules from the mass. If, therefore, the gases to be u withdrawn from a chamber are drawn into an evacuating pump, operating on the diffusion principle, at that portion of the path which has the greatest molecular velocity, the amount of kinetic energy available w for producing mixture of the fluids and the vapor is at the maximum and the pump will operate at the highest efficiency. Metallic vapor pumps have been so constructed heretoforethat the fluids to be withdrawn from a chamber were discharged at some point in the path of flow of the vapor in the pump. Such constructions; however, do not fully 'utilizethe kinetic energy of the vapor so that the efficiency of the pumps and the de- 40 gree of evacuation attainable by the use of such pumps is limited by the degree of utilization of such kinetic energy.

It is, therefore, among the objects of the present invention to provide an evacuating Ipump operating on the diffusion principle -movement of the vapor is at its maximum.

space through which a cooling medium may in which the kinetic energy of the vapor within the pump is utilized as completely as possible.

Another object of the present invention is to provide a static evacuating pump in which the fluids to be withdrawn from a chamber to be evacuated are delivered into the pump below the surface of the substance forming the source of the evacuating vapor.

A further object of the invention is to provide a static evacuating pump in which the fluids to be evacuated from a chamber are delivered into the pump chamber at a point below that at which the molecular Objects and advantages, other than those above setforth, will be apparent from the following description and the drawing which shows, partially in cross section, an exemplary embodiment of the invention.

Referring more particularly to the drawing by characters of reference, reference numeral 1 indicates the side walls of a pump chamber which is formed with double walled portions 2 for the purpose of providing a be circulated. The operating chamber of the pump is closed by a top member, 3 hav ing a conduit 4;, connected therewith for attachment to a preliminary evacuating pump (not shown). A convex deflector 6 is attached in spaced relation to top 3 in front of the entrance into conduit 4: for a purpose which will appear hereinafter.

A false bottom 7, preferably integral with the side walls 1 of the pump, extends between the side walls in such position and in such manner that the side walls extend. downwardly to form. a space which is entirely inclosed by a true bottom 8. The false bottom 7 is pierced at a plurality of points and is provided with a plurality of nozzles 9 of such height as to ex tend to just beyond the upper surface of a layer 11 of vaporizable material such as punip chamber, with mercury. The nozzles may be uniformly or non-uniformly arranged with respect to the area of the false bottom as may appear desirable to secure the maximum utilization of the molecular energy.

A connection 12 with the chamber to be evacuated (not shown) is provided with a double walled portion 13 through which a cooling medium may be circulated for the purpose of cooling and thereby condensing the fluids to be evacuated. The connection 12 discharges into the space between false bottom 7 and true bottom 8, hereinafter called the receiving space, through a conduit 14 which extends iii'to connection 12 for a short distance above the bottom 16 to form a trap for any condensed fluids entering the cooled connection 12. The connection 12 to the chamber to be evacuated is preferably also provided with a connection 17 discharging into the pump chamber below the surface of the layer of mercury therein in case the chamber to be evacuated contains vaporized mercury. Double walled portions 2 and 13 may beconnected as shown to provide for a continuous circulation of cooling medium, such as water, therethrough. Heating means such as code of tubing 18 arranged within the mercury layer 11 and provided with a circulatin heating medium, or a similarly arrange resistance for electrical heating, provide the heat necessary for vaporizing the mercury to obtain a rising molecular flow therefrom.

When a space is to be evacuated, the mercury layer 11 is heated so that a portion thereof is vaporized and the vapor rises fromthe upper surfaces of the mercury layer into the upper portion of the main chamber of the pump. 'The gases present in the receiving space between the true and false bottoms are withdrawn therefrom through the nozzles by a j etaction, and are diffused through the vapor rising in the reat speed and ease for the reason that the nozzles discharge into the main chamber of the pump at points at which thevelocity of the vaporized mercury is greatest. The temperature of gases flowing from the chamber to be evacuated is reduced by cooling in the connection 12,

by contact with the-cooled walls thereof, so that the gases are somewhat condensed and are allowed to flow into the receiving space at a relatively high vapor'density. As soon as the gases have been withdrawn from the space and diffused through the vapor arising from the layer of mercury, they are carried upwardlythrough the main operating chamber into contact with the cooled walls thereof whereupon 'the metallic vapor is condensed and allowed to return to the bottom and the gases released therefromare f withdrawn from the operating chamber by a preliminary evacuating pump connected to the discharge conduit.

Although but one embodiment of the invention has been illustrated and described,

surface-ofsa-id vaporizable material, and

means for heating said material to cause vaporization thereof.

2. In apump for evacuating gasesxfrom a vessel, an operating chamber, a receiving {chamber formed adjacent said operating chamber for connection with the vessel to'be operating chamber,'means for heating said material to cause vaporization thereof, and

evacuated, vaporizable material within said permitting :gases to flow therethrough, said nozzles discharging "into. said operating chamber at the p oint-of the greatest velocity of :the molecules freed by vaporization of said material therein.

3. .In a pump for; evacuating gases :1 from a vessel, an operating chamber, a :receiving chamber "for-med "adjacent .said' operating chamber 7 for connection with the vessel to :be

evacuated, vaporizable material within :said operating chamber, means for heating said material to cause vaporization thereof, and a plurality of nozzles for connecting said receiving and said operating chambers and permitting gases to flow therethrough, said nozzles discharging theggases t0 be-evacuated at the point within said operating chamber at which the vapor generated therein is; substantially free from gases.

4. In a vpump for evacuating-gases from.

asvessel, an operatingchamber, a receiving chamberbeneath said operating chamber for connection with the vessel to :be evacuated,

vaporizable material within ,saidoperating chamber, means for heating said-material to.

cause vaporization thereof, .andaplurality -0f nozzles extending upwardly fromwsaid receivingchainber into said operating chainber and extending through said vaporizable material in the latter, said nozzles discharg ing the gasesv to be evacuated directly above the surface of said vaporizablematerial in said operating chamber.

5. In a pump forevacuatinggasesfroma vessel, an operating chamber, a receivingchamber formed adjacent said operating chamber for connection with the vessel to be evacuated, vaporizable material Within said operating chamber, means for heating said material to cause vaporization thereof, and a plurality of nozzles connecting said receiving and said operating chambers, and permitting gases to flow therethrough, said nozzles being so arranged as to discharge the gases to be evacuated substantially uniformly into the bottom of said operating chamber directly above the surface of said vaporizable material.

In testimony whereof I have hereunto 5 subscribed my name this 2nd day of August,

ERNST KOBEL.

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