US2393933A

US2393933A - Enclosing casing of propellers or impellers

Info

Publication number: US2393933A
Application number: US480062A
Authority: US
Inventors: Poole Ralph
Original assignee: Individual
Current assignee: Individual
Priority date: 1942-02-27
Filing date: 1943-03-22
Publication date: 1946-01-29
Anticipated expiration: 1963-01-29

Description

Jan. 29, 1946. R. POOLE -ENCLOSING CASING OF PROPELLER OR IMPELLER' Filed March 22; 1.945

Patented Jan. 29, 1946 ENCLOSING CASING OF PROPE'LLERS 0R1 IMPELLE-RSE i Ralph Poole, Bredbury, England? Application- March 22, 1943; Serial No; 480,062. InGreatBritain February-r27; 19142:

12..Claims. l (01. 2301-120).

This invention relates to the: enclosinga casing of apropelleror impeller and h'as for its-object to improve the general efficiency of *the-appara' tus which may I be employed for various purposes.-

Wherea propeller orimpeller'rotates in -a cas ing theclearance between the tip of each blade and the casin has a critical effect on-the per-r formance of the'apparatus; This isparticularly the case Where the rotating =member is" delivering a'-relative-ly" small volume of fluid'andtl'Ie lea-le age-back past the blade tips and between them and'the surrounding wallof the-casing is of great-- importance.

Where a propeller fan has -to operate-at high pressure it may be said to behave like a badl y fitting piston in a cylinderand'steps-have to be taken to reduce or controltheflow Which takes place along the wallof-the-cylinder or casing: In the case of an impeller whose bladesare -openended with' the tips free,- it 'is customary toreduce-the clearance at'the tips to a minimum-and it is known that an increase in'maximum pres sure can be obtained by joining the-ends ofthe blades with a shroudin'g ring. Since-the shroud itself presents an obstruction to the infl'owof-air at the ends of the blades it isusual 'to' arrange that the diameter of the casing-at the -inlet isreduced so as to correspond approximately-totlie inside diameter of'the shroudingring: The-edge of the inwardly projectingpart of the" casing is brought" as close as possible to the shroud of the impeller and the lace ofthis projecting part is hollowed out to-form a-groove. There is aldisadvantage in this arrangement, however, since the-shrouding ringgives rise toalosspf energy owine; to therotating surfacewhich it presents close to the stationary casing; To reduce this windage l'ossthe radialclearancebetween thea rotating shroud and the: casing: is maintained as largezas possible *providedi the gap in the; axial die motion can be kept: small;v In: this arrangement there is a disadvantage inxthatt ther-airgleahing back; past .theshroud has; a" substantial: radially inward r movement; and thus: tends to: reducer the effectiveadiameteri ofithe impeller; interfering with the main inflow of: air. Moreover, as-the gap in theaxial direction is made smalllthe velocity of the inwardly directed jets tends. to become high. In. the improved arrangement the use of. the shroudin'gring. is. dispensed. with andaby encouraging and controlling the.v circulation at .th'eQfree tips of the blades an. eflctivesealing can be -ef; fected.

According to this'invention the fixed'casing surrounding the propeller or impeller'has an'an;

nular thickening-J forming aflange; fillet or sim-g ilarpart-iwhich functions as aad'eflectorrfor fluid;

leaking back past thetips of the impeller blades;

this deflector member projectingrinwards from; the casing on'the ,low pressure;- side ofthe in peller adjacent/to. the leading. edges :of;the blades;

similar position in thecasing: adjacentwtogthe ed'ges of' the blades onathe downstream-r orhigh pressure side'of the impeller. of the deflector is conveniently though not; nee,

essarily equal toabout': twice the radialrdistancebetween v the. tips: of the blades: and; the; wall of; the casing surroundingthe. impeller: The face;

ofthe 'defl'ectorwhich is directed towardsstheimzpeller should be a: smooth surface of revolution-i This;v surface mayrbet about the impeller axis; fiat, but asmentionedzit ispreferably concave;

the curvature for-example beinglpartof';alparabe ola whos axis is parallel to the axis of thexima peller; The circulation of the fluid-:whichdeaks back over-thetips of the. blades of the-impeller may be assisted by placingp-in the hollow face of the deflector: an annular member which serves gto direct 'th'e desired fluid flow. The fluidqwilli tend to pass over and around this .guide ringwithin the hollow face of the deflector thus reversingrits direction of flow; V

The operation of thedevicemay be ex'plainedas'follows. Th fiuidtleakingrback past the -tips of the blades is rotating at a considerable'speed about the axis of the impeller; This-is particularly' marked in the case ofa high pressure peller moving a: relatively small 7 quantity of fluid; where the axial velocity. of the, fluid ,remains: fair;- lysmall compared with the circumferential ve locityz- The thrust-of the'blades, on the fluidin the-axial direction decreases asthe rotationalgvelocity of the fluid increases; and the thrustyber comes zero when the fluid rotates at the same rate as the blades. The excess pressure of; the fluid on the high. pressure side of the; impeller always provides a "tendency for "backrleakage; but normallythe axial: thrust: will only, be overcome and leakage occur when the rotational; velocity of'the fluid hasincreased sufficiently'to'permit this. In the ordinary way 'fluid which has-leaked back past the impeller in'lthislway-issubsequently drawn through-i the-impeller again, but while: it

The radial width;

of movement reversed by the deflector being as sisted by the guide ring without appreciably re It is thus possible ducing its rotational velocity. to promote a circulation of the leakage fluid since substantially the same fluid after leakingback along the wall of the casing will have itsdirec xtion of flow reversed by and in the deflector and 7 thereby be caused to pass forwards again through 'the impeller at a small distance radially inwards from the wall of the casing,'this part of the fluid then again leaking backwards. 1 Although this may be described as a secondary circulation in a radial plane relatively tothe impeller axis, the

fluid is all the time rotating about that axis.

Thus the actual path of the fluid, which in effect provides an artificial seal, tends to be a complex I 'spiral or vortex havingas its core a circle-which ,is substantially coincident withthe path followed 'by the tips of the blades 'of'the impeller.-

This secondary circulation'may be increased if,

" as indicated, a similar deflector isarranged on This the high pressure side of the impeller. should have its face which is directed backwards towards the blades formed with a concave'surface of'revolution. Though thisqmay detract in some degree from the efliciency of the impeller when delivering large volumes of fluid at low pressure, on the other hand'it will improve .the

efficiency when delivering relatively small volumes at high pressure, and will substantially increasethe pressure obtainable when the delivery approaches zero. 1 T

The accompanying drawing illustrates by way of example two alternative arrangements embodying the present invention. In the drawing, Figure '1 is a longitudinal sectional elevation showing an impeller and the casing enclosing it as adapted for use for'example' with-air or other gas. i.

Figure 2 is a similar view of a screw'pump with the invention applied thereto. j

Referring to Figure 1, the impeller' there shown comprises'blades A mounted on a boss B ,to which rotation is imparted in some suitable manner. The casing C which immediately surrounds the This will, 7

' the fluid which has leaked back has its direction.

by a ring F which may be provided and is suit- I ably mounted by way of example, by means of spider or bracket elements F, in the annular space E intermediate between the wall of the casing C and the outer surface of the deflector D The air flow from the tips of the blades will thus 7 sisted or induced by providing on the downstream or high pressure side of the impeller A a thick... ening G-on the inner wall of the casing C as shown in dotted lines. This thickening or flllet "G is externally smoothly curved and its face which is directed towards the blades A is concave as'at.

' G The fluidlea-king-back past the blades can thus circulate around th ring F in the annular space E and being delivered forwardly will be returned by the hollow G in the face of the fillet G.

Turning now to the construction shown in Figure 2, this comprises an impeller formed to act surrounds the blades A and beyond this is a ring impeller in this case is cylindrical and has con-- 1 nected to it a flared member D constituting the suction entry to the impeller. This member has' an external flange D which is bolted up to a flange C onthe end of the casing C." The inner an annular space E. 'The external part of the ,member D which is adjacent to the flan e and faces the space E is hollowed as 'at- D so as to form a'smooth curve for the, wall ofthe annular space E which'will conduce to thereturn flow of the fluid which may leak back past the tips of the blades A. This circulatory flow a s s ed K formed internally to act as a deflector according to this invention. A spacing ring L is interposed between this ring K and the flared suction entry member M. All these parts are suitably bolted up together. The blades A of the impeller may be shaped as shown and they ar carried by a boss 13 on'a shaft B whichis driven in someconvenient manner. Internally the diameter of the deflector ring K is less than that of theadjacent part of the casing member J which surrounds the impeller blades and thus it has a part K which projects somewhat into the intake to the pump. On the side which faces the blades this part K -is hollowed out as at K and in this hollow is, preferably placed and suitably fixed a flat ring F I Fluid leaking back between the tips of the blades A and the interior of the surrounding casing J will enter the hollow K in the face of the deflector member KK? and with the assistance of the ring Fl'will be caused to reverse its direction of flow so that it will again be delivered by the impeller. On the suction side the interior of the flared member M isconveniently provided with a thickening or lining M which may be made of some suitable plastic material and moulded to the desired contour so as to give a smooth entry reducingthe diameter to that of the interior K of the deflector ring K. It is convenient to interpose the spacing ring L between the deflector ring K and the suction entry member M the ring L extending on the suction side the thickening effect within the casing of the deflector member KKK The'arrangement does not interfere with the normal flow of the fluid to the impeller while inducing or assisting a circulation at theblade tips which will tend to act as a seal. This construction is more especially designed to enable an existing pump structure to be modified and provided with the present invention by the interposition of the deass-a es fi'ector maybe-disposedadjacent to the blades A on thedownstreamsideoftheimpeller; I

What-I claim as myinv ention and'desire tb=secureby-LettersPatentis:' 1-. A rotary-pump" or fan of the a-xial new typecomprising; in combination an impeller having open ended blades with their tips free; acasing enclosing the-impeller and having 'a suction-en-.

impellerserving to deflect-first inwards: and then:

again towards the impeller the: flow 10f fluidfleakjingback pastthe tips ofthe blades-fromthe high pressure to; the low pressure side of the impeller; the annulus on: the side; remote from the impeller sloping away t'o'the part of the wall'of-th e-suce tion entry of, the casing which has a; larger diameter;

2 A rotarypump or-fan ofthe axial flow 'type comprising in combination an impeller having open ended blades with their'tips'free; a casing enclosing the impeller; a thickening-of the wall of said casing which projects-inwardlyas-an-an= nulus adjacent to the tips-of theimpeller-bl'a-des on the low "pressuresid'e of the: impeller; this pro: j ectingannulus having a face which is concave and is directed towards theimpeller; anda ring member mounted in the annular concavity in the said faceof-"the s aid projecting annulus; this ringmember lying betweema-nd being spacedradially' from the opposed sides of the concavity whereby fluid leaking back past; the tips of the blades from'thehigh pressureto the low pressure side ofthe impeller-isdefl'ectedand passing-in the concavity round the said ring member is again directed'towards the impeller.

3. A rotary-pump or fan of t'he axial fiow'type comprising in combination an impeller having open ended blades with their tips-free, a casing 4 enclosing the impeller-and'havinga s-ucti'on'entry partoh the wall of which isof" largerdiameter than the remainder and constituted by a part which immediately surrounds the impeller'adjacent to the tips of' theblades; a fiaredpart which is on the low pressure side of the impeller and serving as the suction entryand. apart on the high pressure side of the impeller through which the'fiuid is delivered by the impeller; anannulus which projects into the said' suction entry from the wall of the casing of which it constitutes a thickening; this projecting; annulus =having aface which is concave andis directed towards the im peller, and a ring member mounted in the-annular concavity in the said face ofthe said proj ecting annulus this ringmemberlying between and being spaced radially from the opposed" sides of the concavity whereby-fluid leaking back past the tipsof the blades from thehigh-pressureto the low'pressure-side of the impeller -is deflected and passing in the concavity roundthesaid ring member is again directed towards theimpeller; the said projectingannuIuspn-thesuction sicle thereof sloping away; to the wall of larger diameterof' the said suction entry partof-thecasing.

4. A rotary pump or fanof theaxial flow type comprising in combination an impeller having open ended bladeswiththeir-tips free,- a casing enclosing the impeller, a thickeningofthewallof said casing which projects inwardlyas an annuliis adiiacent -to the tips of the impeller; blades on: the=lowpressure side 1 of-ithe impeller; projecti'ng annulus-having a': face which: is concave and is directed towards the impeller; a ring mem ber mounted in the annular concavity in the said face of the said-projectingannulus this ring memberlyingbetween and being spaced radially from. the opposed sides 1 of the-= concavity whereby fluid; leakingba'ck past thetips-of" the' blades :from the high pressure to the low' pressure side' of the -im-- peller isdefiected and" passing in 1 the. concavity round thesaid ring memberds again directed to-- wards the impeller; and a second thickening of the wall of the casing which proj ectsginwardly as an annulus adjacent t0-- the tips of the impeller blades: on-th high pressure side of' the impeller, this-second projecting; annulus: having" a face which is concave andbeing directedz' towards: the impeller-- tendstodeflect and assist-in the circurlation of fluid which leakspast' the tipsof? the blades to theilow pressure side of the impeller and istherecaused by thesaid: projecting annulus on the low: pressure side of the impellerto return towards-the high pressure side. A

5.1a; rotary pumporrfan of the axial flow type comprisin in combination: an: impellerhaving open ended blades with their tips free; acasing enclosing the impeller and'constituted bya part which immediately surrounds theimpeller adj a cent-tothe'tips of 'the blades, apartflared which is onthe low pressure side of the impeller and serves as: the suctionentry and a part on; the high pressure side of' the impeller through which the fluid is delivered by' the: impeller; an annulus which: projects into the said suction entry from the-wall of the casingof which it" constitutes-iathickening; this projecting annulus having aztf'ace which is concave and is I directed towards:thezime peller, a ring member mount'ed in the annular concavity in the said" face of thesaid projecting annulus this ring member lying between and being spaced radially from'the opposed sides of the concavity whereby fluid" leaking back pastthe tips oftheblades from the high pressure to the low pressure side of the impeller is deflected and passing in theconcavity round the said ring member is again directed towards the impeller,

the said projecting annulus on the-suction side thereof'sloping awayito-the wall ofl'arger diameter-of the said suction entry part of the: casing;

and a secondannulus: which projects as athi'ck-s ening-of thewall int'othe said part of the casing on-the delivery and high pressure "side of the impeller this-annulus lying: adjacent to the tips: of the-impeller bladesand having a face which is concaveand being directed towards the impeller tends todeflect and assistin a circulation of the fluid'which leaks'back past th tipspf'the blades to thel'ow' pressure sideofthe impellerand is there caused bythesaid projecting: annulus: on

the low: pressure side-of" the impeller to return which' projects'into the'said suction;entry from.

the wall of the said separateinsertedcasing section of, which wall the annulus constitutes a thickening, the'projecting annulus having aface,

which is concave and is directed towards the'im- V peller, and a ring member mounted in the annular'concavity in the said face of the said pro- 7 jecting annulus this ring member lying between and'beingspaced radially from the opposed sides of the concavity whereby fluid leaking back past the tips of the blades from the high pressure to the low pressure side-of the impeller is deflected and passing inthe concavity round the said ring member is again directed towards the impeller.

7. A rotary pump or 'fan of the'axial flow type comprising in combination an impeller comprising'a single blade set having open ended blades with their tips free, a single concave face system including a casing enclosing the impeller and constituted by a part which immediately surrounds the impeller adjacent to thetips of the blades, a

flared part which is on the low pressure side of e the impeller and serves as the suction entry and of the impeller is concave and serves to direct first inwards-and thenagain towards the impeller the flow of fluid leaking back past the tips of the blades, and the face directed towards thefimpeller of the said second annulus which projects on the high pressure side of the impeller is also concave and tends to deflect and assist in the circulation of fluid which leaks past the tips of the blades to the low pressure side of the impeller, I

V 10. A rotary pump or fan of the axial flow type comprising in combination an impeller comprising a single blade set having open ended blades with their tips free, a single concave face system including a casing enclosing the impeller and constituted by apart which immediately surrounds the impeller-adjacent to the tips of. the

' blades, a flared part which is on the low pressure sideof the impeller and serves as the suctionentry and a part on the high pressure side of s the impeller through whichthe fluid isdelivered a part on the high pressure side of the impeller through which the fluid is delivered by the impeller, and an annulus which projects into the said suction entry from the wallof the casing of which it constitutes a thickening, this annulus having a face directed towards the tips of the-impeller blades to which it is adjacent,

this face serving'to deflect inwards the flow of fluid leaking back past the tips of the blades from the high pressure to the low' pressure side ofthe impeller, the annulus on the suction side thereof sloping away to the partof the Wall of the said'suction entry of the casing which has a larger diameter, th face of the said annulus which is directed towards the impeller is concave 'and'serves-to'deflect first inwards and then again 7 comprising in combination an impeller comprising a single blade set having open ended blades with their tips free, a single concave face system including a casing enclosing the impeller, a thickem'ng of the wall of this casing which projects inwardly as an annulus adjacent to the tips 01; the'impeller blades on the low pressure side of the impeller, this projecting annulus having a face which being directed towards the impeller serves to deflect inwards the flow 'of fluid leaking back past the tips of the blades from the high pressure to the low pressure side of the impeller, and a second thickening of the wall of the casing which projects inwardly as an annulus adjacent to the tips of the impeller blades on the high pressure side of the impeller, this second projecting annulus having a face which is directed towards the impeller and tends to deflect and assist in a circulation of the fluid which having leaked back past the tips of the blades has been deflected by the said projecting annulus on the on the low pressure side adjacent to the blades by the impeller, an annulus which projectsinto the said suction entry from the wall of the casing of which it constitutes a thickening, this annulus having a face directed towards the tips of the impeller blades to which it is adjacent, this face serving to. deflect inwardsthe-flow of fluid leaking back past the tips of the blades'from the high pressure to the low pressure side of, the impeller, the annulus on the suction side thereof sloping away tolthe part of the wall of the'said suction entry of thecasin-g which has a larger diameter, and a second annulus which projects as a thickening of the wall into the said part of the casing on-the deliveryand high pressure side of the impeller, this annulus lying adjacent to the tips of the impeller blades and having a face which is directed towards the impeller and tends to deflect and assist in a circulation of the fluid which having leaked back past the tips of the blades has been deflected by the saidprojecting annulus on the 'low pressure side of the impeller and caused to be returned towards the high pressure. side by the action of the blades, theface directed towards, the impeller of the said annulus which projects on the low pressure side of the impeller adjacent to the. blades is concave and serves to direct first inwards'and then again towards the impeller the flow of fluid leaking back past the tips of the blades, and the fac directed towards the impeller of the said second annulus which projects on the high pressure side of the impeller is also concave and tends to deflect and assist in the circulation of fluid which leaks past the tips of the blades to the low pressure side of the impeller.

cluding a casing enclosing the impeller and 'constituted by. a part which immediately surrounds the impeller adjacent to the tips of the blades, a flared part which is on the low pressure side of the impeller and serves as the suction entry and a part on the high pressurev side of the imi peller through whichthe fluid is delivered b the impeller, an annulus which projects into the said suction entry from the wall of the casing of which it constitutes a thickening, this annulus having a face directed towards the tips of the impeller blades to which it is adjacent, this face serving to deflect inwards the flowof fluid leaking back past the tips of the blades from the high pressure to the .low pressure side of the impeller, the annulus on the suction side thereof sloping away to the part of the wall of the said suction entry of the casing which has a larger diameter, and a second annulus which projects as a thickening of'the wall into the said part of the casing on the delivery and high pressure side of the impeller, this annulus lying adjacent to the tips of the impeller blades and having a face which is directed towards. the impeller and tends to deflect and assist in a circulation of the fluid which having leaked back past the tips of the blades has been deflected by the said projecting annulus on the low pressure side of the impeller and caused to be returned towards the high pressure side by the action of the blades, the side of the said second annulus remote from the impeller slopes away to the wall of larger diameter of the said part of the casing through which the fluid is delivered by the impeller.

12. A' rotary pump or fan of the axial flow type comprising in combination an impeller comprising a single blade set having open ended blades with their tips free, a single concave face system including a casing enclosing the impeller, a part of which casing immediately surrounds the impeller adjacent to the tips of the blades, a flared part which is on the low pressure side of the impeller and serves as the suction entry and a part on the high pressure side of the impeller through which the fluid is delivered by the impeller, an annulus which projects into the said suction entry from the wall of the casing of which it constitutes a thickening, this annulus having a face directed towards the tips of the impeller blades to which it is adjacent, this face serving to deflect inwards the flow of fluid leaking back past the tips of the blades from the high pressure to the low pressure side of the impeller, the annulus on the suction side thereof sloping away to the part of the wall of the said suction entry of the casing which has a larger diameter, and a second annulus which projects as a thickening of the wall into the said part of the casing on the delivery and high pressure side of the impeller, this annulus lying adjacent to the tips of the impeller blades and having a face which is directed towards the impeller and tends to deflect and assist in a circulation of the fluid which having leaked back past the tips of the blades has been deflected by the said projecting annulus on the low pressure side of the impeller and caused to be returned towards the high pressure side'by the action of the blades, the wall of that part of the casing which lies on the high pressure side of the impeller is thickened forming a second inwardly projecting annulus adjacent to the tips of the impeller blades, this second projecting annulus having a face which is directed towards the impeller and tends to deflect and assist in a circulation of the fluid which having leaked back past the tips of the blades has been deflected by the said projecting annulus on the low pressure side of the impeller and caused to be returned towards the high pressure side by the action of the blades.

RALPH POOLE.