US2997228A - Vapour jet vacuum pumps - Google Patents

Description

Aug. 22, 1961 H. wYcLlFFE ET AL 2,997,228

vAPoUR JET VACUUM PUMPS Filed Nov. 20, 1958 3 Sheets-Sheeil 1 Aug. 22, 1961 H. wYcLlFFE ET AL 2,997,228

vAPoUR JET VACUUM PUMPS Filed Nov. 2o, 1958 s sheets-sheet 2 Aug. 22, 1961 H, wYcUl-FE E-l-AL 2,997,228

vAPoUR'y JET VACUUM PUMPS F/G. Z

lfiled Nov. 20, 1958, Ser. No. 775,283 Claims priority, application Great Britain Nov. 29, :1957 8 Claims. (Cl. 230-l01) This invention relates to vapour jet vacuum pumps and has particular reference to boilers which generate the operative vapour for such pumps.

The objects of the invention include provision of a boiler which will in a relatively short time start generating vapour at full capacity and thus bring the pumping action of the vapour jets quickly into operation and also in a relatively short time cease to generate vapour, when required to do so, and thus bring the pumping action of the vapour jets quickly out of operation. Another object of the invention is to provide a boiler which allows a. certain degree of boiler pressure control to be achieved by controuing the rate of vapour generation with little delay and thus provide some control of the pumping capacity of the vapour jets. A further object of the invention is to provide a boiler having an eiciencywhich will compare favourably with known vapour pump boilers.

According to the present invention, in a vapour vacuum pump the operative vapour is generated by one or more falling film ash boiler units. In this specification, the expression falling hlm flash boiler is meant to include a device or apparatus in which liquid to be evaporated is evenly distributed along or near the upper end of an inclined or vertical heat transfer surface, the liquid then being caused to flow in a substantially uniform manner through a significant distance while heat transfer from the surface to the liquid takes place, before bulk evaporation of the liquid begins.

Thus, further according to the invention, a vapour vacuum pump is provided with a dash boiler comprising an; inclined or vertical heated surface down which a film or thin layer of pump working liquid is caused to flow when vapour generation is required and the flow is discontinued when vapour generation is required to cease, the arrangement of the heated surface, the heat supply and the rate of pump working liquid delivery to it being such that most of the pump working liquid vapourises while the liquid is 'owing along the heated surface.

In a preferred form of pump having a boiler embodying the invention and which will be referred to as a flash boiler unit, the unit is mounted conveniently near the vapour nozzle or nozzles to be supplied by it and the operating uid liquid, contained in a reservoir, is supplied at a suitable rate by pumping means to distributing means situated at the top of a vertical cylindrical heated surface so that the liquid flows evenly down the surface and the vapour is generated to supply the jets connected to the flash boiler unit. VThe liquid condensate arising from the operating vapour after passage through the nozzles and condensation on cooled walls ofthe pump, together with any unevaporated liquid feed emerging from the bottom of the flash boiler unit, is directed back to the liquid reservoir or to the inlet to the liquid pumping means ready for recirculation through the flash boiler unit.

Other features of the invention will appear from the following description of alternative forms of flash boiler embodying the invention which will be described as examples with reference to the accompanying drawings in which:

FGURE l shows dlagrammatically a vapour jet vacutates Patent F j2,997,228 Patented Aug. 22,` 1961 ICE 21 um pump having such a boiler and including a working fluid circuit,1

FlGURE 2. shows diagrammatically in greater detail and to an enlarged scale, a flash boiler which can be used with advantage in the pump shown in FIGUREV l,

FIGURE 3 shows diagrammatically an alternative form. of ash boiler unit,

FIGURE 4 shows diagrammatically a further form of flash boiler unit constructed to supply high and low vacuum jets and in which` a fractioning effect is used,

FIGURES 5 and 6 show diagrammatically still further forms of flash boiler units constructed to supply high and low vacuum jets; and

FIGURE 7 shows diagrammatically three pumping stages connected. in series and utilising a f ractionatiug effect.

Referring to FIGURES l and, 2 of the drawings, the working fluid of a vapour jet pump, indicated generally at 1, is supplied. to the boiler 2 from a storage reservoir 3 by a circulation pump 4, through a delivery tube 5. The fluid, on entering the boiler, is delivered into a distribution ring or passageway 6 which opens through restrictive outlet means 6a to open distributing connection means 6b and. provides uniform circumferential feed of the working fluid to the generally cylindrical boiler sur-y face 7. Flowing along the surface 7, which is provided with grooves 8 designed to promoter controlled favourable duid flow and improved. heat transfer and which is heated by an electrical heater 9, the working fluid heats up and evaporates. The vapour thus generated flows through a vapour ducting 1l) to the pump nozzle l1 in which it expands and which it leaves in the form of ai jet that produces the pumping action.

On coming into Contact with the cooled pump wall l2 the vapour condenses and returns to the storage reservoir 3 from which,y in the liquid state, it is re-circulated back to the boiler. Working fluid that has not evaporatedin the boiler, returns through drain 13 and U-tube i4 to the circulating pump inlet l5 and together with fluid from the storagel reservoir isl supplied back to the boiler. A vacuum system to be exhausted is connected to conduit. coupling 16v and a' backing pump is connected to a conduit l'i.

When fluiddelivery is stopped and vapour generation is required to cease, the smooth finish of the relatively cool upper part. la of the boiler surface 7 ensures that it does not retain much working duid and the working huid-Which is adhering to the boiler walls is quickly evaporated because all parts of the boiler below the upper part are hot and some heat input continues after the supply of working iiuid is stopped. Vapour generation therefore: ceases in a short time. The liquid in the distribution ring 6- is withdrawn when vapour generation is required to cease and' this may be done in various ways, for example, byv reversing the direction of rotation of the circulatingv pump 4 or by a bellows arrangement l shown in broken lines, connected to the feed pipe S that expands on bringing the boiler to atmospheric pressure, and extracts the fluid contained in the distribution ring.

While vapour generation, is not required, the supply of the working fluid being cutoff, the temperature f the boiler is maintained at or `above its normal Working temperature so as to store heat energy in the boiler and obtain quick` vapour generation on start of delivery of the work-v ing fluid. Only a fraction of the normal operating heat input is required to maintain temperature during the idling'v period. A conventional thermally operated switch may bev provided to` guard against over-heating.

When the boiler is put into operation and during its operation, the timing of the heat input and the distribution of heat intensity along the boiler surface are arrangedv to'v ensure favourable heat transfer conditions and this is 3 lA l of the greatest importance for the correct functioning f the boiler.

The cylindrical boiler surface 7 along which the fluid is owing is surrounded by balle rings 19, the function of which is to catch and return back to the boiler surface working uid that may have been driven oif the hot surface during the initial stages of fluid supply, when the temperature difference between the boiler wall and Supplied luid may be large and not favourable for ecient evaporation, or due to gas liberation from the work-ing huid.

During the initial stages of working uid delivery when the normal evaporating conditions along the boiler wall have not been established and a considerable amount of working fluid remains unvapourised after traversing the vertical surface 7, a lower boiler cover 20serves as an additional vapour generating surface. The surface of the lower boiler cover 20 is slightly inclined so that the working fluid falling olf the cylindrical surface on the cover 2l) iiows radially inwards and partially evaporates. The remaining fluid drains through a drain 13 and returns via the U-tube 14 to the circulating pump inlet 15. The lower cover 20 of the boiler receives heat by radiation from the bottom of the boiler or it may also be provided with a heater 21. The cover 20 is designed 'to store heat energy whe the boiler is not generating vapour and this heat is effective during the initial working stages as explained above. The baille rings 19 can also be designed to accumulate or store heat energy when the boiler is idling and this heat would also be effective during starting.

FIGURE l includes a feature of the duid flow circuit designed to increase thermal etiiciency and thus to reduce the heater input required. The working fluid feed to the boiler is made to flow through some of the cooling coils formed by a portion of the pipe 5, or an alternative cooling jacket, the coils or jacket serving to cool the condensing surface l2 of the pump. Heat, which would otherwise have been carried away by cooling water if such were used, is exchanged between the vapour condensing lcnlthe pump wall and the working fluid feed to the The alternative form of boiler unit shown in FIGURE 3 may be used in the pump shown in FIGURE l and the heating surface is constituted by a shallow concave plate 23. Other parts corresponding with those of FIGURES l and 2, are identified by the reference numerals used in those figures.

The working fluid which does not evaporate in the boiler, and which ows through the drain 13 tends to comprise the less volatile components of the working fluid and can be supplied to a second boiler which may generate vapour for the jet yof a pumping stage capable of producing a better vacuum than can the stage supplied from the first boiler. If the two pumping stages are set to pump in series, that supplied by the rst boiler backing that supplied by the second, a fractionating pump results.

A method for achieving a similar fractionating effect with `a single boiler unit is shown in FIGURE 4 in which vapours generated along the upper part of the cylindrical boiler surface 24 are directed to the lower vacuum jets via vapour tube 25 and vapours generated along the lower part 26 of the boiler surface are directed to the high vacuum jets via vapour tube 27.

FIGURE shows the fractionation arrangement as applied to the shallow conical form of boiler in which vapours generated along the .surface 28 are directed to the lower vacuum jets via vapour tube 29 and those generated along surface 30 are directed to the high vacuum jets via vapour tube 31.

FIGURE 6 shows a double boiler fractonating arrangement as described in the specilication of British Patent No. 734,757, in which less volatile vapours generated on surface 32 are allowed to condense on a surface 3B and be carried, due to pressure difference, to a surface 34 where the vapours are re-evaporated and directed to supply the high vacuum jets via vapour tube 35.

4 low vacuum jets are supplied via vapour tube 36 from other vapours generated on the surface 32.

FIGURE 7 lillustrates diagrammatically an alternative or complementary form of fractionation depending on the differing readiness to condense of duid components of differing volatilities.

Three pumping stages P1, P2 and P3 are shown connected in series and supplied from three individual flash boiler units each with its own fluid reservoir and supply pump, these items being designated by reference numerals used in FIGURES l and 2. The condensing walls of the first and second pumping stages, and the walls of the interstage connecting ducts 37 between rst and second and third stages are cooled to an extent and in a manner inadequate to ensure complete condensation within each of the rst two stages of all the pumping fluid vapour supplied from their nozzles. Thus the more volatile constituents of the vapour feed to the rst stage nozzle tend to pass out of the iirst stage uncondensed and to condense in the second or third stage and the more volatile oonstituents of the vapour feed to the second stage nozzle tend to pass out of the second stage uncondensed and to condense lin the third stage.

The effect is to concentrate the more volatile components of the operating Huid in the liuid reservoirs feeding the third 4and to a lesser extent the second stage, and to retain only the least volatile components in the reservoir feeding the first stage-with consequent advantage to the vacuum it can produce.

If the reservoirs supplying the third and second stages tend to become overfull of fluid, then the excess duid runs along overow pipes 3S which feed from the third stage reservoir to the inlet of the liquid pump supplying the second stage and from the second stage reservoir into the inlet of the liquid pump supplying the first-stage so that appropriate liquid levels are maintained.

A pump operated by a flash boiler or boilers embodying the features of the invention as described has the following main advantages:

(l) The initial warming up period on putting into service, which may be the order of one hour for a large vapour pump employing a conventional boiler, is greatly reduced.

(2) Subsequently, the boiler can be put into operation, producing vapour from a hot falling film of operating fluid, land put out of operation, so that no hot operating fluid is present inside the pump, so rapidly that atmospheric air can be admitted to the pump with but little delay whenever desired, without danger of damage to hot operating fluid. Thus, when the pump is operating on a production cycle such that the pumped process chamber must be periodically brought up to atmospheric pressure, there is no need to isolate the pump under vacuum during the periods when the chamber is at atmospheric pressure and the large and expensive isolation valve and the by-pass system conventionally employed can be eliminated.

(3) Because the main heater input to the boiler is switched off during the periods when the process chamber is at atmospheric pressure, a considerable saving of power consumption over the conventional pump is achieved.

We claim:

l. A vapour vacuum pump comprising a main pump body, a ash boiler unit having an annular passageway formed at the radi-ally outer, marginal and upper portion thereof, a heat transfer surface in said boiler unit connected to and extending down from the annular passageway, pump uid circulating means connected to said annular passageway for supplying pump working fluid to said annular passageway and thence to said surface down which a thin layer of pump working fluid is caused to ow when vapour generation is required, said flow being discontinued when vapour generation is required to cease,

controlled heating means for heating said surface, nozzle The means providing vapour communication between said boiler unit and the main pump body, an open annular connection connecting said surface with said yannular passageway and serving to distribute said pump working fluid over said surface in a uniform manner, baffle means surrounding the surface to catch and return back to the surface the working Huid that may have been driven oit the surface, said pump -uid circulating means being constructed and arranged to provide the ow of iluid at such a rate that substantially the entire thin layer of pump working fluid is ashed off as vapour during `a single pass of the uid over said surface.

2. The vapour vacuurn pump according to claim 1 in which said surface comprises a cylinder, said heating means being an electrical heating element.

3. The vapour vacuum pump according to claim 1 in which at least a portion of said surface is formed with grooves to facilitate controlled flow of the working fluid and to improve the heat transfer to working fluid.

4. The vapour vacuum pump according to claim 2 in which the upper portion of the outer surface of said cylinder is smooth.

5. The Vapour vacuum pump `according to claim 2 in which the bottom of the ash boiler unit for housing said cylinder is inclined so that any pump working fluid reaching the bottom of said boiler unit ows radially inwards, an outlet connected from the Hash boiler unit to iluid circulating means for discharging and recycling said Working fluid reaching said bottom.

6. A vapour Vacuum pump comprising a main pump body and including a nozzle, a Hash boiler unit including a distributing passageway and having a heat transfer surface down which -a thin layer of pump working uid is ca-used to flow when vapour generation is required, said iiow being discontinued when vapour generation is required to cease, controlled heating means for said surface,1 means providing vapour communication between said unit and said nozzle in the main pump body, a restricted outlet from said distributing passageway for controlling the flow of said pump working fluid, open distributing connection means connecting said surface with said distributing passageway by way of said restricted outlet and serving to distribute said pump working fluid over said surface in a uniform manner, said controlled iiow of fluid being at such a rate that substantially the entire thin layer of pump working fluid is flashed olf as vapour during a single pass thereof over said surface.

7. A vapour vacuum pump according to claim 6 in which said surface is constituted by a shallow concave plate.

8. A vapour vacuum pump according to claim 7 in which the face of said concave plate over which the pump fluid ows is provided with uid guiding grooves.

References Cited in the file of this patent UNITED STATES PATENTS

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