US2083996A - Centrifugal fan - Google Patents

Description

Patented June 15,1937

s UNITED STATES PATENT oel-"TCE 2,083,996 cENTmUGAL FAN Tage G. donn, Chicago, Ill., assigner to Breuer Electric Mfg. Co., Chicago, lll., a corppration of Illinois Application February 2, 1935, serial No. 4,616

6 claims.' (cl. 23o-121) My invention relates to improvements in centrifugal fans and particularly to theshape of their blades or varies; and the objects of my improvement are: rst, to reduce the power required for operating a centrifugal fan; second, to increase the pressure of the fluid it delivers; and, third; to diminish the noise, characteristic oi' high speed fans.

I have attained these objects by inventing a 10 new and novel type of blades, the prime feature of which is the introduction of the principle of streamlining, which I have `applied to the rear of said blades and whereby the suction or drag, always created by rapidly moving bodies, is greatly reduced. l v

When in addition, the pressure sides-as distinguished from the rear sides-of the fan blades are so shaped that the outer, or peripheral, parts of them take the form of cams, and as such act against the compressed air expelled from the fanV and surrounding said. fan within the fan chamber, a most considerable increase can be obtained in the pressure of the air delivered by said fan.

Further, a centrifugal fan the blades of which are properly streamlined will operate more quietly than if said blades were not streamlined, because of the smoother flow of the air through such a fan, but the major source of noise in a high speed fan of this type, is created when the blades pass'4 the cutoff point; that is, lthe point at which the air is directed from the fan chamber and into the outlet from the same. Now, all sounds are due to vibrations and if all thej blades in the fan are of exactly the same shape they' will g5 cause'. the same kind of vibrations when passing said 4cutoff point.y This constant repetition of the same kind of vibrations will have a cumulative effect and the resultant noise will be of great enough volume to be offensive.` However, if the 40 blades differ in shape (and the dierence does not'need to be great) .the vibrations they cause when passing the cutoff, will also diier and' there will bev produced a steady stream of varied Figure 3 represents la similar cross section of another fan, slightly different in. construction, but embodying my invention.

Figure 4 shows another applicationY of my in- A vention to a fan of the same general type as 5 illustrated in Figure 1. y

Figure 5 shows still additional modifications of fan blades, slightly different in contour but all in accordance with the-presentdnvention.

Figure 6 illustrates threeei'zamples of my inl0 vention as applied in multiblade fans.

.Figure 7 is a section on line 1--1 in Figure 6, showing-however, only one 'of theblades.

Figure 8 shows two kinds -of blades, heretofore conventionally used in the type ofI fans illusl5 trated in Figures 1 to 5 and without the appli- -cation of my present inventionrbutV the illustration is included for explanatory purposes.'

'v As this invention is 'adaptable 'to all types of l centrifugal fans andasI such fans are'designed 20 for many purposes, itisnotpossible to show one embodiment thereof that would be preferable in al1 cases, but Figure 1 clearly illustrates its principal features. 'The fan show n here consists of a. central hub i suitable for mounting ona V'25 drive shaft 2 and a plurality of blades or'vanes 3 held together by a disc or web 4. The direction of the rotation of thefan is indicated by an arrow and the fan is positioned in a common type of casing 5, provided with an .outlet s. so

' In operation the air is drawn into-Aa fan of this type at its center and discharged at its periphery into the surrounding space of a casing, commonly called fan chamber, from which it is exhausted through an outlet; and it isobvious that: the 35 action of the blades against the air will cause .said air to be compressed onthe pressure or forward sides of said blades, whilel behind the g 'blades there, willpbe areas of rareied air, causing suction, eddies, and drag, provided means 40 are not incorporated into the'design of the blades to avoid this undesirable condition which is found wherever there isa moving body, but

i. which is magnified in a fan as heretofore` constructed because fof the fact that the space be. 45

tween the blades in such a fan becomes greater the further they extend from the center, while A at the same time the air between them, as it .travels from the center and toward the periphery, becomes more and more compressed on the pressure sides -of said blades and more and' more rareed at their rear sides. (See Figure 8, illustrating two types of heretofore commonly used fan blades, 3a and 3b.); This 'rarefactlon of the air, creating a partial vacuum behind re- 10 tionable.

I 135 rrr-mn` what -peint volving blades 'such as 8a and Ib, not only causes power consuming suction and drag, butit has the elIect of permitting some of the air that is r being 'expelled from the pressure sides of the 5 blades to re-enter the fan in the areas of rarefaction atv the rears of the blades.. 'Ihis backlash "creates noise, causes some of .the air to be re- 'handled by the Ian, preagents a smooth and even ilow-of theair streams, rand is altogetherpblec- VBy'now obs rving the blades I (Figure l) which are designed according to my present invention, it

readily will be seeuthitt` all .f theabove inentlone'd objectionable features have been, eliminated. The front or pressure sides of the blades may be shaped Iin many'desired forms according to the use for which a fan is intended. as wlllbe i discussed later, but their rear,:sides are turned backward and away from the. front sides of the blades so as to eliminate the spaces that otherwise would be the areas of rareiiedair; th'e actual shape of said rear sides may be curves, straight lines or a combination ofthe two-l-and these bacia` sides, however thusshaped, will hereinafter be referred to as being curved. A The frontsides of the blades are also turned backward 'sro that said front and rear sides'join in edges il pointing.

v backward in relation tothe fans,rotation. Thus the two streamsof air'emerging from each side v of such'a blade will unite without creating suction, eddles, or backlash.. Shortly expressed, I

have streamlined the rear of the fan blades and obtained the known beneilts accruing to streamlined bodies.

the r'ear sides of the blades should start curving backwardand away from the front sides and how far this' curvature should reach will depend ontwo main factors; i.e., the speed of the ian. andits intendeduse. As general .'speed ofthe fan blades the morefpronounced should bethevst'reamlining; second, if a high pressure is of greater importance than the volume of the expelled air,` then the best result is ob tained by extending the rear sides ofthe blades so far backward and toward the front sides of the following blades that the openings between said. blades are comparatively small at* the peripheryof the fan; while, third, if thevolurne of be as large asrpossible, having in mind, however.,

that the streamlining always shouldbe suilicient' te prevent areas of rareiled air-Lbehind the blades.

'55 A high pressure of the discharged air is'oirvtained by restricting o uuet s. frias, however, wiu

cause the fan tooperate againsta` backpressurer' with the greatest load on the blades o f said fariv at Y theirouter ends, wherethe density of .the air is the greatest, thus4 vany load will require the greatest amount of power for rotating the fan,-

wheresaid blades move the fastest. With these points in mind, Il have, in one embodiment of the present invention,'(designed a fan blade which in '65 -addition to thec'entrifugal forcealso utilizes the principleeof 'the cam-.for developing a high pres# sure.l The poweroi' afcamis'too well known'to Vagainst a liquid, gas, or air and under conditions I as herein discussed-its power of compressing said substances has practicalv limitations. However.

-the principle 'is the same and. a fanV` blade so .'75 formed merits. pressure .sideterniinetesin the rules it may be stated: tlrst, that the greater thethe exhausted air is of 4prime importance', the'n' the spaces between the tips of the blades should.

1ro ded corner. And bl shape of a cam Il, at its outer end, one form of which is shown in Figure l (blade I) will coun-v v press the air to amuch higher degree than any other type of blade vwith which I am familiar or with which I have experimented. l

Having nowdescribed the cardinal featuresv of this invention, Iwill briefly [explain those o! its.

many possible applications which are illustrated 1 in the drawingr Y f The fan shown in Figures l andi! has already been described, but asimilar ian will have greater eiiiciency if provided'with a front plate or ring l A. (see Figure 3). Such aplateis used in manyv y -types o f fans and 'it isftherefore not claimed u a part of my`preeent inventiombutit is illustrated l5 as another type of fan to which this invention isl adaptable. The same plate may also be used in the -fans shown in Figures' 4 and 5i! the intended use of said fans makesit advisable.

y Ihe blades Ic illustrated in Figure 4 are suitable in fans intended primarily for suction, where there is such a minor resistance at theexhaust as would bexcaused, for example-by the dustbag o! 'a household vacuum cleaner. 'I'he front side of eeen ef seid biedes is convex and turned slightly 2s backward', but not enough to give said side the characteristics of a cam as in Figure 1.l The rear side with a concaved surface is also -turnedbackward and said front and rear sides are united at their outer ends by a third side which prevents 30 air already expelled into the fan chamber from re-entering the fan. The rear end ,of thispe- `ripheral side 8 joins the curved back side of the blade, streamlining said 4sides into an edge Il. thus permitting the outflowing stream of air from between theblades to meet and mingle with the air already in the fan chamber, without creating disturbing currents and eddies.

The front sides of the blades shown in Figure 6 are concave. otherwise-with reference to 'the present 'invention-they are much like those shown in Figure 4. However, blades thus shaped will create more noise when v.passing the cutoff l (Figure 1) than' blades curved as shown in Figures if and 4. I have therefore selected this type to illustrate that feature' of this invention by vwhich a slight change in the blades contour will vmaterially reducethe noise of the fans operation.- Blade 3d has a sharpdfor'ward edge where the front side lJoins the peripheral side at It. At re tivelythe same point in blade 3e there is a e 3f is shown with a similarly sharp edge 'as in blade 3d, but it is 'disposed slightly inside the periphery of the fan I whereby the outer side of the blade becomes s 'canf I la. Any 'number ofvariations or con'ibina-V tion-of variations oi.' such or similar nature may be introduced in designing the blades of a fan for the purpose ofU decreasing `the noise of operation of said fan,I as has already been explained. 00

f In additionto the fans already discussed. there are also centrifugal multiblade i'a'nsof which simple type is illustrated somewhat dit 'ically in Figures 6 and 7. It -is shown with a drive shaft n en wines-two side putterv lz are mounted. es'

so also-finv these fans tlievane's may ave several shapes. of which'areillust tedinFlgureajBladeIahasaboncaveps-es- 1I aosaeae sure side, a streamlined rear side. and a periph-4 eral side that connectsthe other two. AIn blade 3h thepressure side is straight, the peripheral'side is formed into a cam Mb, and the rear is streamlined. 'Blade 3i is very similar to 3g,except that the pressure side is convex.

While I have shown and described several ap-*f plications of my invention, other modifications may be made without departing from its spirit or the scope of the appended claims.

. What I claim is: 1. A centrifugal fan with a plurality of blades 'radiating fromv the hub toward the fans periphery; the forward surface.. which is presented to the air, of each of said blades being curvedback v wardly relative .to the fans rotation and so formed that said surface will have the shape and function of a cam; said cam reaching7the fans periphery at a point so`close to the forward surface of the following blade that the peripheral opening lbetween the blades is restricted relatively -to the distance between said blades. at a point s'ome distance inside of the fans periphery.

2. In .fa centrifugal fan, a plurality. Aof blades radiating from the hub of said fan toward the.

fans periphery, each of said blades comprising a .forward side which curves backward relatively to the direction of -the fans rotation, a rearside also curving backward but at a shallowercurvature than said -forward side, said forward and rear sides joining in a trailing edge at a point on the fans periphery so close. to the forward side of a following blade that the peripheral opening. between the 'blades is restricted relatively to the distance between said blades at a point closer to the hub of said fan.v

3. In a centrifugal fan, a plurality of blades each comprising a forward side, arear side and a' peripheral. side connecting said forward side to said rear side; the junction point of said pe- I of blades beingat a different position relative to the fans peripherythanthe corresponding points in another group of blades.

5. In a centrifugal fan, a plurality of blades` -each comprising a forward side, a rear side, and

aperipheral side connecting said forward side to lsaid rear side; the junction point of said peripheral side with saidforward side on each of A said blades having 4a different shape than the corresponding point on eachof the other blades. 6. In a .centrifugal fan, a plurality of blades each comprising a forward side, a rar side, and

a peripheral sideconnecting said forward side to said rear side; the junction point of said peripheral side with said forward side on each of said blades having a different shape than the corresponding point on each of the other blades and each of said points beingat a different position on each of said blades relative to the .fans periphery.- l

' TAGE G. JONN.

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