US2489058A - Diffusion pump - Google Patents

Description

' 1949 G. R. STOLTENBERG 2,489,058

DIFFUSION PUMP Filed May 26, 1944 2 Sheets-Sheet 1 e Hy. 1 37 25 l7 1 O /6 /2 A9 f /5 l /a /4 6 owoooooywooocooooo 1 9 WITNESSES: lNVENTOR i fin ww 6/9/727/1? Kim/rem;

ATTORNEY Nov. 22, 1949 Filed May 26, 1944 G. R. STOLTENBERG DIFFUSION PUMP 2 Sheets-Sheet 2 Maw ATTORNEY Patented Nov. 22, 1949 UNITED .s TATES PATENT OFFICE GlennBJStoltenberg, New "York,"N. Y., assignor, by-mesne assignments, to' the United' states of America "as representeil by --the United States Atomic Encrgy-commission ApplicatiomMax-Zfi, 1944, Serial No. 537,461

-8 Claims. 1

This invention relates to new-and usefulimprovements in vacuum pumps, and'moreparticularly to vacuum pumps of the vapor ,difiusion type.

The usual vapor diffusion pump comprises a chamber connected between a backing pump and to an envelope or memberto be evacuatedah'd containing one or more nozzles or jets sofdirected that vapor ejected by the: jets entrains gasrnlecules entering the chamber 'fromllthe. envelop and expels them in the direction of;the outlet from the chamber to the'backing pump. ,The minimum pressureobta'inable at the inlettothe pump chamber is limited to'the vapor pressure of the most volatile constituent oftheliquidifrom which the entrainingvapor dischar ed fmm;the jets is generated, and such ,pumpsgenerally comprise, also, a boiler for generating thevaporan d one orrmore chimneys for conductinglthevapor to the jets or nozzles.

,In the past, certain oils have, been .emplqyedas the working .or pumping fluid, in.S11Ch pumpstand ithas been the practice generally tocQhStruut the jets of thepum so that ,theloil vaporsnexpand as rapidly, as possible andwith the resultant jet velocity parallel to the axis of lthe pumplin order to obtain the highest possible ,pumping speed. In prior diffusion; pumps, vJunvew.:r, the various designs ofJets or-nozzlesemployed, generally have been characterized :,by-a relatively large amount of oil migration ornimusion-hauk .into the envelope or member being -exhaust,e 1, and they have not afforded anyjsubstantiallditectional-v control. over the oil vapors. ,-In.,addition, the length of the jetsor nozzles=general ly has been such, as to require more powerto generate and discharge the vapors throughithepjets, and the vapor concentration in the workingparealof the jets ,usually is not vsufficient to produce Ia maximum exhaust pressure.

With the foregoing in mind, thepresent. inven tion contemplates the prcvisionuotavapor .diliu- .sion pump havin one or,.more jets ornozzles so constructed and arranged thatthe oilvaporsdis charged therefrom will expand 12in {a ,ldirection slightly toward the pump axis and thereforehave a velocity vectortowards'the. axis ,ofthe pump that must be overcome before the oil, molecules can migrate or'ldifiuse backinto the eny'elope or member being exhausted, "The invention also contemplates a jet, or nozzle construction thatis operable to maintain a=maximum density'and concentration of the vapor stream in orx'ierthat thepump may -operate effectively againsfihigh exhaust pressures, or in conjunction with abacking pump. Furthermore, the present invention contemplatesthe provisionfin a vapor difiusion pum of a jet or nozzle in which thei'lengthof the restriction in the jet opening, is comparatively shortin length so that the power requirements to generateand discharge the vapors may b ubstantially reduced, and, rat thesnme .tim will caus t m xpansion of the oil .vanorsto take place in the direction, of, or. toward, the eenteroraxisof thepump. Finally, in the case Qf multiple chimney. diffusion pmnnshit i desirabl that .the oil entering the boil er of the innenpr high vacuum jet stage be substantially freeof sediment and, therefore, the present v.,i;m/:Eht-ion contemplates the provision of suitabletmeansl lor de-entraining or removing -,-sediment ,and bother foreign particles from the ;oil prior to entrance thereof into the inner, orthigh vaouum:stage, of the pump- ;Accordingly,, it isan object of the: present in- :ventienzto provide a jet or-nozzle; for'vapor/rliif i- :sion pump "tha is; constructed and arran to rovideriadequate directionalcontrol-ov n theeDJ'l wapors discharged therethrough.

Another. objectv of the invention is-tovprovide a novel dlifusionpump jet construction fiSLSEtIiQ -ith whereby expansion of the vaporsaften leaving-the pump takes place in a direction toward thesagris of the diffusion pump. I

Another object of the invention is to provide a novel jet for diffusion pumps that is constructed and operable to substantially minimize migration or back diffusion of the molecules of *the -dlscharged oil vapors.

-A'further'object of the invention is-to -provirle -aynoveljet construction having the attributesset =forth-wherein the length of the'restriction in the jet opening is comparativelys'hort inlen g-ththereby reducing the power required to generateand discharge the vapors therethrough'at the required velocity.

' "A still-further object oithe' invention; isito provide "a 1 multiple chimney vapor diffusion pump having suitable meansfonde-entraining and removing sediment'andother particlesifrqmthe oil D prior to entrance'thereof into,thej inner onhi h vacuum stage of the pump,

"These and other objects ofthe invention, and the various'featuresand details of'the construction-and operation thereof, are hereinafter f ully setforth and described with reference totheaccompanying drawings, in which:

Fig. 1 i sectional. viewztalsen vertioallyjhreu h "55 a multi-stage vapor diffusion pump embodyin a jet or nozzle construction according to the present invention.

Fig. 2 is an enlarged fragmentary view of the disclosure of Fig. 1 showing the details of construction and arrangement of the discharge jet of the first or primary stage of the pump, and

Fig. 3 is a view similar to Fig. 2 showing the details of construction and arrangement of the discharge jet of the second or high vacuum stage of the pump.

Referring now to the drawings, and more particularly to Fig. 1 thereof, the present invention is shown, for example, in conjunction with a vapor diffusion pump of generally conventional type comprising a cylindrical pump casin I, the lower end of which is closed by a base plate 2. The upper end of the casing I is provided with a flange 3 for connection to the system or structure (not shown) that is to be evacuated, and the upper end, therefore, represents the high vacuum or intake side of the pump, while the low vacuum, or exhaust, side of the pump is indicated by conduit 4 that leads from the casin I adjacent the bottom end thereof, and is connected, for example, to the usual backing pump (not shown) The cham ber enclosed by the casing I is cooled by circulating water within a tube or pipe 5 that is coiled externally of the casing I, and the conduit 4, near its outer end, is similarly cooled by passing thereabout a relatively small number of turns of the cooling water tube 5 as shown in the drawings. Water is circulated through the cooling tube 5, for example, in the direction indicated by tl e arrows.

Arranged vertically within the casing I, in spaced concentric coaxial relation with respect thereto and with respect to each other, is an outer chimney structure 6, and an inner chimney structure I, the latter being somewhat taller than the outer chimney 6 as shown. The chimneys 6 and I each have their bottom end portion flared outwardly as indicated at 8 and 9, respectively, and the bottom edges thereof are fixedly secured to the base plate 2, suitable openings I and II being provided adjacent the bottom of the chimneys 6 and "I, respectively, to permit flow of the vacuum pump oil radially inward to the bottom portions of said chimneys from the periphery of the easing I.

As more clearly shown in Fig. 2 of the drawings, there is secured to the upper end of the outer chimney 6 an annular ring member 12 of generally inverted U cross-section shape that has a portion I3 extending radially outward horizontally from the chimney 6 and terminates at its outer edge in an outwardly offset reversely directed flange portion I4 that extends angularly outward from said outer chimney at an acute angle with respect to the vertical wall surface of the pump casing I.

' Overlying the member I2 and surrounding the flange portion I4 thereof in outwardly spaced relation, is the depending outer peripheral edge portion I of an annular dome-shaped hood member I6 that has its inner peripheral edge portion fixedly secured to the exterior of the inner chimney as indicated at IT. The outer peripheral edge portion I5 of the hood I6 extends downwardly to a point a short distance below the edge of the flange portion I4 and is preferably disposed angularly with respect to the wall surface of the pump casing I at an acute angle that is slightly greater than the angular disposition of the flange portion I4 of the member I2.

The portions I4 and I5 of the members I2 and 4 I6, respectively, thus are cooperatively disposed with respect to one another and define therebetween an annular jet or orifice I8 for the discharge of the vapors generated in the outer chimney 6. Suitable spacers i9, of generally accurate configuration, are secured at intervals between the jet defining portions I4 and I5 of the members I2 and I6, respectively, to secure and maintain the said portions I4 and I5 in predetermined spaced relation with respect to each other, thereby positively fixing the radial dimension of the jet or orifice I8 through which the outer chimney vapors are discharged.

A generally similar discharge jet or orifice 20 is provided at the upper end of the inner chimney l for the vapors generated therein. To this end, there is secured to the upper end of the inner chimney I the lower end edge 2i of a funnelshaped member 22 having a side wall portion 23 that flares upwardly and outwardly and terminates at its upper end in a portion that curves outwardly and then downwardly, as shown, to provide an outwardly offset depending flange portion 24 that extends angularly outward from said inner chimney I and preferably at an acute angle with respect to the wall surface of the pump casing I.

overlying the funnel-shaped member 22, and supported or carried by one or more struts 25 secured to the casing I, is a dome-shaped hood member 23 that has its peripheral edge portion 21 surrounding the flange portion 24 of the member 22 in predetermined outwardly spaced relation with respect thereto. The peripheral edge portion 21 of the hood member 26 preferably extends a short distance below the edge of the flange 24 of member 22 and is disposed at an acute angle with respect to the wall of casing I greater than the angular disposition of the flange portion 24 of said member 22. The flange and edge portions 24 and 21 thus are cooperatively disposed with respect to one another and define therebetween an annular jet or orifice 26 for the discharge of vapors generated in the inner chimney I, suitable spacers 28, similar to spacers I9, being secured between the jet defining portions 24 and 27 to secure and maintain the same in predetermined spaced relation thereby fixing the radial dimension of the jet or orifice through which the vapors from the inner chimney are discharged.

The angular disposition and relationship of the flange and peripheral edge portions that define the several discharge jets is important, and, for example, in the particular embodiment of the diffusion pump illustrated, the flange portion I4 of the member I2 preferably is disposed at an acute angle of about 10 with respect to casing I, and .the surrounding peripheral edge portion I5 of the hood l6 preferably is disposed at an angle of about 16 with respect to said casing. In generally similar arrangement, the flange portion 24 of member 22 preferably is disposed at an angle of about 12 with respect to the casing I, and the surrounding peripheral edge portion 21 of hood 26 preferably is disposed at an angle of about 20 with respect thereto. Jets of the construction shown and described may be employed effectively on any size of diffusion pump with only slight modifications of the angular disposition and relationship of the respective jet defining elements to meet the requirements of the particular pump.

In addition to the angular disposition of the jet forming elements with respect to each other and the casing I, it will be observed that the vapor jets are spaced inwardly from the pump casing I,

a. relatively short distance,1for:example,- of "from about inchlto a maximum of about 1 inch, depending upon the size of'the particular pump.

In operation of the pump, the conduit 4 is connected to the intake of a suitable backing pump (not shown),'and the intakeend of the pump casing i is connectechbyits flange 3, to the system or vessel that=is to beevacuated. -A-quantity of a suitable volatile oil, for example, an .organic hydrogenated diphenyl compound sold under the trade name HBlO, is supplied to the bottom of the diiTusion pump at the inner periphery of the casing l, and this oil flows inwardly over the surface of the base platev 2, and successively through the openingslfl and H into the bottom of the outer and inner chimneys 6 and 1, respectively, where it is heated and vaporized by heat applied to the base plate 2, for example, by means of an electric or other type of heater 29.

In order that the oil entering the inner chimney I may be substantially free from sediment and other'foreign particles, there is provided upon the base plate 2 an annular barrier or ring 30 that surrounds the base of the'inner chimney "l and functions as a dam to de-entrain and remove from the inwardly flowing oil substantially all particles of dirt and other material. The inflowing oil builds up and'fiows over the barrier or ring 30 in the course'of which the particles settle out and collect outwardly adjacent the barrier (it with the result that the'oil that flows over the barrier and enters'the'inner'chimney Tthrough its openings is substantially free from particles of dirt and other foreign particles.

Oil is-admitted to the proper depth in the lower ends of the chimneys'fi and'T'and the oil is heated and vaporized by the heater29. The oil vapors rise within the chimneys and discharge therefrom through the jets or-orifices I 9 and w respectively, in a generally downward direction with the result that'gas 'tmolecules entering the pump casing I through its intake end from the vessel or envelope to be exhausted, are entrained by the downwardly directedvapor jets and impelled therebyto or toward the exhaust'conduit 6. The discharged oil vapors-are condensed upon the interior wall surface of the casing l by the cooling pipe 5, thus releasing the gas molecules which are withdrawn from the casing 3' through the exhaust conduit 4 by the backing. gpump' (not shown) connected thereto, the'condensed vapors ultimately draining down the inner wall surface of the casing l to the periphery-of the base plate 2 over which they again flow inwardly through the openings iii and II into the bottoms of the inner and outer chimneys 6 and 1,. respectively, to be again vaporized. Preferably, the openings l8 and ii are of such size that'the'flow of oil therethrough to the chimney 6 andultimately to the chimney takes place substantiallyat'the rate at which vaporization'of the oil takes place in each chimney so'that the most volatile constituents of the oil have sufficient time to vaporize in the outer chimneyeand be'conducted away to the lower et IS-before'the constituentsof intermediate an'dlow volatility reach the inner chimney By virtue of the relatively close-spacing of'the vapor discharge jets with respect to the :casing l, and the angular disposition-thereof re'lati-vezto said casing, the vapors discharged .fromzsaidje'ts are caused to impinge against the inner wall of the casing almost-as soon as-they emerge from the jets with the result thatfnot only is amaximum density-and concentration of the vapor stream gprovided acrosszthe: gaprloetween :the jets and easing l that enables :the mump ito-toperate efiectively against high exhaust zpressures, but also causes the-dischargedMaporsltdexpand in a direction inwardly towardlthe pump axis thereby creating a velocity or force-vector inthat direction that must be overcomevby the-oil s molecules before they can migrate or difiuse upwardly past thejets and back into -the-ienvelope orvessel being exhausted.

Therefore, from the foregoing, :and in fulfillment of the several-objectsherein setiorth, it will be observed that the "present inventionprovides :anovel, jet construction :and arran ement for vapor difiusion pumps whereby the oil vapors are discharged .therefrom at a .-relatively small acute angle with respect-t the wall of the casing l'tvith the result thatexpansionofithe vapors occurs in a. directionrslightly :toward the pump axis andproducesawelocityrvector in that direction that-must be overcome by'theaoilmolecul-es before-they can migrate or diffuse upwardly-land back into the vessel- 02 system being: evacuated.

The invention also provides ajet construction and arrangement :that ,produces a maximum density and concentration ofvthe'vapor'stream so that the pump operates effectiyelyiagainst high exhaust pressure, .:or. in :conjunction witha a :backing pump. The invention also provides .a :jet construction .for 'difiusion -pumps wherein the length of the jet restriction istcomparatively-short in length with the result that less powerwis required to force the 'oil"vaporsitherethrough.

-While a particular-embodiment of the invention has been illustrated :andidescribediherein, it is not intended:fthatzitherinventionbeilimited to such disclosure butthatchangesand modifications may be madeaand incorporated therein without fidep arting from the spirit vof r the invention within thetscoperof' theifollowing' claims.

I :claim:

'1. In a vapor diffusion; pump comprising: atubular casing having an outletzadjacent the lower end: thereof and an intakeispacedsabove saidroutlet; a vapor ichimn-ey: disposed :icoaxiall'y w said casing t and extending "train the lower end thereof' upwardly to :a .pointiintermediate said intake I and outletyisaidcchimney terminating .zat its upper'aend inr an outwardly offset reversely directed flangezportion extending:sangularlyaoutward from: said chimneyuat an acute angle'rwith respect to said 'casing,"an'd aihoddmember'positioned above said --chimney having .:-a -peripheral edge: portion surrounding said :flange portion-tin predetermined circumferentia'llyaspaced relation with respect thereto saidperipheral :edge portion of the hood-'being disposedat azgreateracute angle with respect to said casing than saidchimney flange portion-and "cooperating-with said chimney flange,t-portionetortormltherewith-a discharge jet for-vaporsrisingzrthrough said-chimney.

2. In :a vapor-diffusion vi pump comprising -a tubular casing having anioutlet adjacent the-lower end thereof and an. intake. spaced above said outlet, a vapor chimney dispesedcoaxia-lly' within said casing and extending from the lower end thereof upwardly to a ipointai-ntermediate said intake. and outlet-said :chimneyterminating at its upper end inaa reversely directed flange-portion extending -.angularly:outward iromsaidchimney, a hoodmember positioned aboversaid chimney having a-peripheral edge portion surrounding said flange; portion-in predetenminednircum- 75 ferentiallyspacedv relation with-respect. thereto,

said peripheral edge portion of the hood cooperating with said chimney flange portion to form therewith a discharge jet for vapors rising through said chimney,- and spacer members interposed between said hood edge and chimney flange portions operable to secure the same in predetermined spaced relation with respect to each other.

3. In a vapor diffusion pump comprising a tubular casing having an outlet adjacent the lower endthereof and an intake spaced above said outlet, a vapor chimney disposed coaxially within said casing and extending from the lower end thereof upwardly to a point intermediate said intake and outlet, said chimney terminating at its upper end in an outwardly offset reversely directed flange portion extending angularly outward from said chimney at an acute angle with respect to said casing, and a hood member positioned above said chimney having a peripheral edge portion surrounding said flange portion in predetermined circumferentially spaced relation with respect thereto, said peripheral edge portion of the hood being disposed at a greater acute angle with respect to said casing than said chimney flange portion and cooperating with said chimney'flange portion to form therewith a discharge jet for vapors rising through said chimney, and spacer member interposed between said hood edge and chimney flange portions operable to secure the same in predetermined spaced relation with respect to each other.

4. In a vapor diflusion pump comprising a tubular casing having an outlet adjacent the lower end thereof and an intake spaced above said outlet, a vapor chimney disposed coaxially within said casing and extendingfrom the lower end thereof upwardly to a point intermediate said intake and outlet, said chimney terminating at its upper end in an outwardly offset reversely directed flange portion extending angularly outward from said chimney at an acute angle with respect to said casing, and a hood member positioned above said chimney having a peripheral edge portion surrounding said flange portion in predetermined clrcumferentially spaced relation with respect'thereto and extending a short distance below the edge of said flange portion, said peripheral edge portion of the hood being disposed at a greater acute angle with respect to said casing than said chimney flange portion and cooperating with said chimney flange portion to form therewith a discharge jet for vapors rising through said chimney, and spacer members interposed between said hood edge and chimney flange portions operable to secure the same in predetermined spaced relation with respect to each other.

5. In a vapor diffusion pump comprising a tubular casing having an outlet adjacent the lower end thereof and an intake spaced above said outlet, an outer and an inner chimney extending in spaced concentric relation coaxially within the casing from the lower end thereof upwardly to points spaced axially of said casing between said intake and outlet thereof, said outer and inner chimneys respectively terminating at their upper ends in reversely directed flange portions extending angularly outward therefrom, a first hood member surrounding said inner chimney and overlying the upper end of said outer chimney having a peripheral edge portion surrounding the flange portion of said outer chimney in predetermined circumferentially spaced relation with respectthereto and extending a short distance-below the edge of said flange portion, said peripheral edge portion of said hood member cooperating with said outer chimney flange portion to form therewith a vapor discharge jet for vapors rising through said outer chimney, and a second hood member positioned above said inner chimney having its peripheral edge portion surrounding the flange portion of said inner chimney in circumferentially spaced relation with respect thereto and extending a short distance below the edge of said flange portion, said peripheral edge portion of the second hood member cooperating with said inner chimney flange portion to form therewith a discharge jet for vapor rising through said inner chimney.

6. In a vapor diffusion pump comprising a tubular casing having an outlet adjacent the lower end thereof and an intake spaced above said outlet, an outer and an inner chimney extending in spaced concentric relation coaxially within the casing from the lower end thereof upwardly to points spaced axially of said casing between said intake and outlet thereof, said outer and inner chimneys respectively terminating at their upper ends in outwardly oflset reversely directed flange portions extending angularly outward therefrom at an acute angle with respect to said casing, a first hood member surrounding said inner chimney and overlying the upper end of said outer chimney having a peripheral edge portion surrounding the flange portion of said outer chimney in predetermined circumferentially spaced relation with respect thereto at an acute angle with respect to said casing greater than the angle of said outer chimney flange portion, said peripheral edge portion of said hood member cooperatin with said outer chimney flange portion to form therewith a vapor discharge jet for vapors rising through said outer chimney, and a second hood member positioned above said inner chimney having its peripheral edge portion surrounding the flange portion of said inner chimney in circumferentially spaced relation with respect thereto at an acute angle with respect to said casing greater than the angle of said inner chimney flange portion, said peripheral edge portion of the second hood member cooperating with said inner chimney flange portion to form therewith a discharge jet for vapor rising through said inner chimney.

7. In a vapor difiusion pump comprising a tubular casing having an outlet adjacent the lower end thereof and an intake spaced above said outlet, an outer and an inner chimney extending in spaced concentric relation coaxially within the casing from the lower end thereof upwardly to points spaced axially of said casing between said intake and outlet thereof, said outer and inner chimneys respectively terminating at their upper end in reversely directed flange portions extending angularly outward therefrom, a first hood member surrounding said inner chimney and overlying the upper end of said outer chimney having a peripheral edge portion surrounding the flange portion of said outer chimney in predetermined circumferentially spaced relation with respect thereto, said peripheral edge portion of said hood member cooperatin with said outer chimney flange portion to form therewith a vapor discharge jet for vapors rising through said outer chimney, and a second hood member positioned above said inner chimney having its peripheral edge portion surrounding the flange portion of said inner chimney in circumferentially spaced relation with respect thereto, said peripheral edge portion of the second hood member cooperating with said inner chimney flange portion to form therewith a discharge jet for vapor rising through said inner chimney, and spacer members interposed between said hood edge and chimney flange portions operable to secure the same in predetermined spaced relation with respect to each other.

8. In a vapor diffusion pump comprising a tubular casing having an outlet adjacent the lower end thereof and an intake spaced above said outlet, an outer and an inner chimney extendin in spaced concentric relation coaxially within the casing from the lower end thereof upwardly to points spaced axially of said casing between said intake and outlet thereof, said outer and inner chimneys respectively terminating at their upper ends in outwardly offset reversely directed flange portions extending angularly outward therefrom at an acute angle with respect to said casing, a first hood member surrounding said inner chimney and overlying the upper end of said outer chimney having a peripheral edge portion surrounding the flange portion of said outer chimney in predetermined circumferentially spaced relation with respect thereto at an acute angle with respect to said casing greater than the angle of said outer chimney flange portion, said peripheral edge portion of said hood member cooperating with said outer chimney flange portion to form therewith a vapor discharge jet for vapors rising through said outer. chimney, and a second hood member positioned above said inner chimney having its peripheral edge portion surrounding the flange portion of said inner chimney in circumferentially' spaced relation with respect thereto at an acute angle with respect to said casing greater than 'the angle of said inner chimney flange por: tion, said peripheral edge portion of the second hood member cooperating with said inner chim ney flange portion to form therewith a discharge jet forvapor risin through said inner chimney, and spacer members interposed between said hood edge and chimney flange portions operable to seoure'the same in predetermined spaced relation-with respect to each other.

' GLENN R. STOLTENBERG.

REFERENCES CITED The following references are of record in the file of this patent:

, UNITED STATES PATENTS I Date

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