US2819011A - High vacuum diffusion pump - Google Patents

Description

Jan. 7, 1958 o.w1NKLER 2,819,011

HIGH VACUUM DIFFUSION PUMP F11ed June 13, 1951 2 sheets-sheet 1 sx v l u A 1 a m www1 Inventor:

' rfo h/f/vA/Ee l Maia/y Jan. 7, 1958 o. WINKLER 2,819,011

l HIGH VACUUM DIFFUSION PUMP Filed June 13, 1951 2 Sheets-Sheet 2 OTT@ MAM/L Le Arranca/y United States Patent 2,819,011 HIGH VACUUM DIFFUSION PUMI Otto Winkler, Balzers, Liechtenstein Application June 13, 1951, Serial No. 231,313 Claims priority, application Switzerland June 19, 195) 12 Claims. (Cl. 230-101) In the construction of high vacuum diffusion pumps with high suction it is necessary to have very large suction cross sections since the maximum rate of evacuation depends upon this ligure. ln diffusion pumps with suction above about 1000 litres/second, there are therefore, in the previously usual constructions, very large spaces between the edge of the discharge nozzle for the operating vapour and the condensation surfaces of the pump which are preferably cooled. This results in comparatively large heights, in order to ensure an undisturbed flow and suthcient condensation of the operating vapour. In order to obtain a high vacuum, such pumps must be formed as multi stage pumps-preferably three stage, so that diifusion pumps with a suction of for example 200G litres/ second are of a height of from 1-1.5 metres. This leads to considerable costs in construction and to erection difficulties.

A further disadvantage of the previously usual con struction of high vacuum diffusion pumps consists in that in the case of the resulting large width of clearances resulting between the discharge nozzle and the wall serving for the condensation of the operating vapour, the suction given by the geometric dimensions of this clearance can only be realised by low pressure, that is, high vacuum pres sures. The free length of path of the gas molecules is proportional to the pressure. As soon as the free length of path of the exhausted gas molecules is comparable in its order of size with the clearance width an increased back diffusion takes place into the high vacuum chamber, so that the suction of the pump becomes less. The upper limit at which the diffusion pump can still achieve its full suctions is thus improved the less is the width of the clearance.

A high vacuum diifusion pump of high suction must therefore on the one hand have a suction cross section as large as possible and on the other hand a width of clearance between the discharge nozzle and the condensation surface as small as possible. This could be achieved by mounting several, separate independent pumps of small suction parallel to each other. Space requirements, production costs, as well as work required for vaporising the driving substance would be too great in this arrangement to enable the problems arising to be solved by it.

There is therefore required a basic alteration of the previously usual process for the operation of such high vacuum pumps which, according to the invention, has been found in that at least two clouds of Working medium are produced and the clouds are condensed at condensation surfaces independent of each other and separated from each other. ln particular, outside of a first space, in which at least one cloud of working medium is produced and condensed, at least one further cloud of working medium of annular section is produced and condensed. The process makes it possible, above all, to produce and condense at least two further clouds of working medium of similar annular cross section diverging in radial directions opposite to one another, outside a rst space in which at least one cloud of working medium is produced and condensed. ln this connection it is advantageous to condense each of the clouds of working medium diverging in oppositely directed radial directions 'from one another from the same sources of annular cross section, on a c011- densing surface lying in its path. This process can if desired be repeated, so that outside the second space in wh1ch at least one further cloud of working medium of annular cross section is produced and condensed, additional clouds of working medium of annular section are produced and are condensed one in each of these spaces. If the vapour clouds are produced concentrically to each other and condensed in the same manner then there results a symmetrical construction of high vacuum diffusion pumps serving to carry out this process in particular if the vapour clouds are produced and condensed with annular cross sections, concentric to each other.

The high vacuum diifusion pump serving for carrying out this process is basically characterized in that it consists of at least two constituent pumps operating in parallel one of which surrounds the other. In so far as it applies to two constituent pumps it also is applicable to further constituent pumps.

lf between two adjacent pumps a cylindrical wall is provided whose inner surface is formed as the condensing surface for the pump which it surrounds and whose outer surface is formed as the condensing surface for the pump which surrounds it, there is a double utilisation of each condensing surface and thus a further simplification of the construction of such pumps.

Further details of the invention will be described with reference to a high vacuum pump formed according to the invention, with two constituent pumps concentric to each other, which are formed as three stage pumps.

in the drawings Figure l shows a vertical section through the diffusion` pump according to the invention,

Figure 2 a plan view of the open diifusion pump,

Figure 3 illustrates by way of example on alhigh vacuum diffusion pump of previous construction the physical conditions under consideration whilst Figure 4 illustrates the advantages obtained as to the physical conditions occurring with pumps constructed according to the invention.

Figure 5 shows diagrammatically in section and Figure 6 in plan the space requirements of a three stage. high vacuum diffusion pump of previous construction whilst Figure 7 illustrates diagrtmmatically in section the reduction in height which occurs with high vacuum diffusion pumps constructed according to the invention, While according to Figure 8 the suction area will be seen to correspond nevertheless with that of Figure 6, so that for comparison of space requirements, the starting point of the same pumping capacity applies.

A high vacuum diffusion pump constructed according to the invention consists first in the usual manner of an outer housing l, which has at 2 a connection for the preliminary vacuum pump. The housing has a base 3 beneath which an electric heating device 4 is disposed. This serves for vaporising a liquid working medium 5 which is provided in a relatively thin layer on the base 3. The working medium consists normally of organic compounds with a rather low vapour pressure, preferably, suitable oils. Mercury can however also be used as working medium. The high vacuum diffusion pump has at 6 a central vaporisation space constructed in the usual Inanner, which is formed from a tube 7 open at the top. Above the mouth of the tube a nozzle cap 9 is provided which has a conical cover it), so that a ring nozzle 11 is formed which causes the production of a diverging cloud of operating vapour. This cloud contacts a cooled wall l2, which has a cooling medium inlet at 13 and outlet at 14. A second stage is provided in that. the tube 7 is surrounded by a tube 1S of larger diameter. This tube again has a nozzle cap 16' so that an annular evaporation space 17 results which serves to feed the annular nozzle 18. A third still larger tube 19 surrounds the tubes 7 l \ y 3 and 15. A nozzle cap serves to form the annular nozzle 21. High vacuum pumps of this kind are known per se.

The variations made according to the invention of the new construction of high vacuum diffusion pumps from the previous construction thereof consists in the following:

Outside the cooling jacket 12 a second pump is provided coupled in parallel to the first pump, by arranging a further annular evaporation space 22 by the mounting of two cylindrical tubes 23 and 24 concentrically to each other. The resulting upwardly open annular mouth section 25 is covered by an annular cap 56 which in combination with the tubes 23, 24 forms an inner annular nozzle 26 and an outer annular nozzle 27. The annular nozzle 26 lies opposite a condensing surface 28 which is formed by the outer surface of the previously mentioned cooling jacket 12, `such surface not being used for condensation purposes in the previous pump constructions. ln order to provide special condensing surfaces for the outer annular nozzle 27, the cooling jacket 29 is provided which is equipped with a separate cooling medium inlet 30 and a separate cooling medium outlet 31. Concentrically with the tubes 23, 24, further tubes of smaller height are arranged at 32 and 33, so that two additional vaporisation spaces 34' and 57 result which are covered by the annular covers 35 and S8. Thus two further nozzle sections 36, 37 result. Further annular tubes of still less height are shown at 38 and 39 so that two further vaporisation spaces 40 and 59 result which are covered by the annular covers 41 and 60. Th-us two further annular nozzles 42 and 43 result.

It will thus be apparent that the new construction of high vacuum diffusion pump serves for carrying out a process in which at least two clouds of operating medium are produced i. e. by the nozzle sections 11 and 26 or 27 and these clouds of operating medium produced are condensed on condensing surfaces 12 and 28 or 29 separated from each other and independent of each other, if only the first stage of each of the pumps is considered. What has been explained for the uppermost stage, also applies to the middle stages 18 and 36 or 37, and to the lowermost stages 21 and 42 or 43. Further it will be noticed that outside a first space 44 in which at least one cloud of working medium is produced and condensed, at least one further cloud of working medium of annular section is produced in the annular .space 45 and condensed. Moreover, as each of the annular covers 56, 35, 58, and 41 produce annular nozzles 26, 27; 36, 37; and 42, 43 outside the space 44 at least two further clouds of working medium diverging in opposed radial directions from each other are produced with the annular sections 25, 34, 40, 57 and S9 and are condensed on condensation surfaces 12, 28, and 29, 46 independent of one another and separated from one another. By the three stage construction of each of the constituent pumps, the same applies correspondingly for each of the three stages.

In a manner known per se the chamber to be highly evacuated is connected to the flange 47 of the housing 1. By the heating device 4 the liquid working medium covering the base 3 is heated and vaporising. In the vaporised spaces 6, 17 and 48, 59, 57, 22, 34 and 40 separate from each other the working medium vapour rises upwardly and is directed in inclined downwardly directed diverging clouds through the outlet nozzles 11, 18, 21, 26, 27, 36, 37 and 42, 43 against the condensation surfaces 12, 28 and 29 separated from each other and independent of each other. Thus the gas molecules present in the chamberto be evacuated diffuse into the interior of the pump and are drawn off therefrom by the preliminary vacuum pump. The working medium condensing on the surfaces 12, 28 and 29 is again conducted to the vaporising spaces in such a way that it passes each time through the outer vaporising spaces of each constituent pump gradually to the innermost vaporising space of the appropriate constituent pump. Thus the easily volatile constituents of '4 K the working medium are vaporised in the outer vaporising spaces 48 and 17 and 40 and 34 as well as 59 and 57 whilst the part of the working medium with the lowest vapour pressure enters the innermost vaporising spaces 6' and 22 and is used for supplying the nozzles 11 and 26, 27 lying nearest to the high vacuum chamber 49. This process known per se corresponds to a fractional distillation of the working medium and ensures a better high vacuum.

The connection member 2 is connected with the annular space 5) which is bounded on the outside by the outer jacket 1 of the high vacuum pump, and inwardly by the cooling jacket 29, 46. The cooling jacket 29, 46 is however interrupted at 51 to connect the annular space 45, and the space 53 via the tubular connection 52 and the space 44 through the connection 54, with the suction connecting member 2.

ln Figures 3 and 4 the different effects of known pumps and those constructed according to the invention are explained diagrammatically.

In Figure 3 references are made with the same indications as in Figures 1 and 2, to 7 as the central vaporising tube, 9 the nozzle cap therefor and 12 the associated condensing surface. Accordingly a vapour cloud 61 results, which on account of the nozzle 11 and through the internal molecular pressure diverges in the direction of ilow. At the condensing surface 12 the internal pressure of the vapour cloud is at a minimum. This vapour pressure is indicated by an arrow au perpendicular to a unit of the surface. As the unit of surface approaches the nozzle 11 the surface pressure increases continuously. The lowest surface pressure am during the pumping operation is in equilibrium with the counter pressure of the gas pumped, which is indicated at each unit of surface by b. At each other surface position of the diffusion cloud, the surface pressure a is greater than the surface pressure b. The pump is accordingly enabled, by compression of the gas volume sucked up to deliver just so much gas that b is equal to the minimum pressure (112 at the condensing surface 12. The same considerations apply for the two other stages of the diffusion pump, that is, for the nozzle sections 18 and 21.

Figure 4 on the other hand reproduces the conditions for a pump constructed according to the invention, wherein the scales correspond to the conditions of Figures 5 toA 8 to be further described. From the nozzle 11v as also from the annular nozzles 26, 27 gas clouds again emerge which according to the nozzle shape and the internal molecular pressure show divergence. The path, which a molecule now has to take to the condensing surfaces 12, or 2S and 29 is far less than in Figure 3. At the same angle of divergence the vapour clouds have, in the vicinity of the condensing surfaces 12, 28 and 29 a considerably higher internal pressure which corresponds about to the internal pressure of the unit of surface of Fig. 3, which lies geometrically centrally between the edge of the nozzle 11 and the condensing surface 12. This pressure is a multiple of the internal pressure of the vapour cloud in the vicinity of the condensing surface 12 of Figure 3.

If the internal pressure of the vapour cloud according to Fig. 4, per unit of the area is indicated C, then the counter pressure d which the compressed gas can reach is as great as C in the vicinity of the condensing surfaces in Fig. 4, i. e. as great as C29, C28 or C12. Accordingly the pump according to Fig. 4 is in a position to maintain a gas pressure in the condensing chamber the equivalent of many times higher than is the case in the condensing chamber of the pump according to Figure 3. These considerations also apply for the further stages of the pump according to Figure l.

The technical advantages thus achieved is shown by reference to Figures 5-7. By similar sections of Figures 6 and 8 indicated by shading the advantages obtained with reference to the reduction of size of construction is expressed directly by comparison of Figs. 5 and 7.

The size of the pump described with a suction of, for example, 2,000 litres/sec. is herein not greater than the size of a previously usual diffusion pump with a suction of only 100 litres/ sec. The characteristic of the suction curve in dependence on pressure is similar to the characteristic of curves occurring with smaller diffusion pumps, i. e. the slope of the suction curve for increasing pressure is considerably slower than in a diffusion pump of the same suction of the previous construction.

Therefore the interposition of a steam ejector between the diffusion pump and the preliminary vacuum pump can be avoided. Such steam ejector stages were previously necessary, to bridge the range in which a diffusion pump possesses a poor efficiency and the preliminary vacuum pump has not yet reached the suction which is necessary. In spite of the short length the cross sectional area requirement is not greater than is expressed by the com` parison of Figs. 6 and 8. Space requirements, production costs and work required for the vaporising of the working medium are considerably smaller than in the case of parallel connections of individual pumps of the same rating. The reliability is higher since an equivalent dividing of the working medium into the vaporising chambers occurs. Furthermore simplcations occur by the common feeding of the gases pumped into the conduit leading to the preliminary vacuum pump.

In the sub joined claims the term partial pump will be employed to designate each of the pump sections operating in parallel and so arranged that one of them is disposed within and surrounded by the others. Thus. in the embodiment illustrated in Fig. l, the innermost partial pump is composed of the parts 7, 9, 15, 16, 19, 20 and 12; the next outer partial pump includes the parts 24, 56, 26, 35, 32, 39, 60 and 28; while the outermost partial pump is comprised of the parts 23, 56, 27, 33, 58, 38, 41 and 29.

What l claim is:

l. A high vacuum diffusion pump comprising, in combination, a pump housing providing at the bottom thereof a container for a supply of working medium, means for evaporating the working medium, tubular separating walls in said housing arranged to divide the pump housing space into partial housings, one of the tubular separating walls being arranged within and surrounded by the other tubular walls, conduits for the vaporized working medium in each of said partial housings, discharge nozzles for the vaporized working medium at the discharge ends of said conduits, said conduits and nozzles forming partial pumps in said partial housings, each of the opposite surfaces of each of said separating walls bounding the two partial pumps separated by each such wall being arranged in the path of the working medium vapor clouds formed by the nozzles of said partial pumps, means for cooling said separating wall surfaces .to cause condensation and precipitation of the vapor clouds in the partial pumps, said pump housing providing a common space with which all of the partial pumps communicate separately and independently of each other, so that said partial pumps operate in parallel.

2. A diffusion pump as defined in claim l, wherein the component partial pumps are disposed concentrically to each other.

3. A diffusion pump as defined in claim 1, wherein the walls are in the form of annular jackets each surrounding a component partial pump.

4. A diffusion pump as defined in claim 1, wherein the component partial pumps are disposed concentrically to each other, the said walls being in the form of annular jackets concentric to each other and each surrounding a partial pump space.

5. A diffusion pump as defined in claim 1, wherein each partial pump is provided with a plurality of nozzles spaced longitudinally of the axis of such partial pump and adapted to discharge vaporized diffusion medium at different levels in each partial pump.

6. A diffusion pump as defined in claim 1, wherein the housing is spaced from the outermost separating wall, and wherein the said walls are provided with an opening for connecting the vapor spaces of the compo-nent partial pumps, a connection between said partial pumps and the space between the common housing and the outermost of said walls, and means for connecting said housing to a preliminary vacuum pump.

7. A diffusion pump as defined in claim l, wherein the vapor medium container is common to all of the component partial pumps.

8. A high vacuum diffusion pump comprising, in combination, a container for the diffusion medium, means for vaporizing the diffusion medium, two component partial pumps arranged one within the other and each having a plurality of conduits for the vaporized diffusion medium leading from the container, the conduits of the outer partial pump being all of annular form and being concentric with respect to the center of the inner partial pump, the conduits of each partial pump decreasing in height from the central to the outermost conduit, discharge nozzles for said diffusion medium at the discharge ends of said conduits, the central conduits of the partial pumps being of approximately the same height and terminating within a common space which is adapted to communicate with a chamber to be evacuated, a substantially cylindrical wall arranged between and separating the partial pumps and adapted to be impinged by streams of vapor discharged by nozzles of both partial pumps, means for cooling the said wall, and a common housing surrounding the outer partial pump.

9. A diffusion pump as defined in claim 8, wherein the container for the diffusion medium is common to both partial pumps, there being a connection between the two partial pumps at a point below the lowermost nozzles thereof.

l0. A high vacuum diffusion pump comprising, in combination, a container for the diffusion medium, means for vaporizing the diffusion medium, a plurality of component partial pumps each having a plurality of conduits for the vaporized diffusion medium leading from the container, said partial pumps including discharge nozzles for said diffusion medium at the discharge end of said conduits, annular walls disposed in the path of the discharging streams of vapor and separating radially adjoining partial pumps, means for cooling said Walls to effect condensation and precipitation of said vapor, and a common housing surrounding and enclosing all of the component partial pumps, one of said component partial pumps being arranged in the central axis of the housing and being disposed within and surrounded by the other partial pumps, and the vapor conduits of an outer partial pump being of annular form and concentric with and surrounding said one component partial pump, one of said walls separating such two partial pumps and disposed to be impinged on its opposite surfaces by the streams of vapor discharged by the nozzles of said two partial pumps, said housing providing a common vacuum space with which all of said partial pumps communicate, whereby said partial pumps operate in parallel.

11. A diffusion pump as defined in claim 10, wherein the nozzles of said outer partial pump are of annular form, there being an annular nozzle inwardly and also an annular nozzle outwardly of the annular vapor conduits of such outer partial pump.

l2. A diffusion pump as defined in claim l0, wherein the separating walls are in the form of annular jackets,

each surrounding a component partial pump..

References Cited in the file of this patent UNITED STATES PATENTS 192,042 Worthen June l2, 1877 FOREIGN PATENTS 407,503 Great Britain Mar. 22, 1934

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