US820398A - Centrifugal fan or pump. - Google Patents

Description

No. 820,398. PATEN'ITED MAY 15, 1906.

S. C. DAVIDSON.

CENTRIPUGAL FAN OR PUMP.

APPLICATION FILED 00125.1904.

4 SHEETSSHEET 1.

INVENTOR: Wl TNESSES: f By Azfameys,

No. 820,398. l PATENTED MAY 15, 1906. S. O. DAVIDSON.

GBNTRIFUGAL FAN OR PUMP.

APPLICATION FILED OGT.25. 1904.

4 SHEETSSHEET 2 FIG. 5. I

D INVENTOR': WITNESSES: M iwzzmm, 72? By Akzomeys,

No. 820,398. PATENTBD MAY 15, 1906.

' S. O. DAVIDSON.

OENTRIFUGAL PAN 0R PUMP.

APPLICATION FILED (C125, 1904.

4 SHEETS-SHEET 3 //vv/v70/ WITNESSES: I

dmamm b PATENTED MAY 15, 19.06.

S. U. DAVIDSON. OBNI'EIFUGAL FAN OR PUMP.

APPLICATION FILED 0GT.25. 1904.

4 SHEETSSHBET 4 T L L INVENTOR:

By A/zomeys, m.mm C;

wEssEs:

SAMUEL CLELAND DAVIDSON, OF BEL *ASEIRELAND;

CENTRIFUGAL FAN OR PUMP.

I Specification of Letters Patent.

Eatented May 15, 1906.

Application filed October 26,1904 s le No. 229,896.

T 0 all? whom it may concern:

Be it known that I, SAMUEL 'CLELAND DA- VIDSON, a subject of the King of Great Britain and Ireland, residing in Belfast, Ireland, have invented certainnew and useful Improvements in Centrifugal Fans or Pumps, of which the following is a specification.

This invention aims to improve the efficiency of rotary fans and pumps in which the fluid operated on enters the center of the said fans or pumps axially and. is discharged therefrom circumferentially againstra material degree of back pressure or suction resistance. Specifically my invention relates more particularly to the multibladed drum form of centrifugal ent No. 662,395, granted November 27; f9 O0, This fan has a high volumetric efficiency when the fluid operated on is under practi= cally no back pressure or suctionresistance; but its efficiency diminishes as the back pressure or resistance increases until a point is reached at which the type of fan shown in said patent possesses little advantage over other types of centrifugal fans which are desi ned for operating under or against a considerable pressure or resistance.

I have set forth in 'a pending application an invention for improving the efficiency of centrifugal fans by providing the fan-with an eye or inlet-opening .eccentrically located in relation to the axis of the fan whe'el or wherein the inlet-opening is formed of such shape that the boundary of the inlet area extends more to one side of the circle of the fan-blad es than the other, the said eyeor inlet-opening being preferably of D shape, such or any other shape of suitable contour or outline being included in the term eccentric, which is hereinafter employed for simplicity and clearness. ing application a preferred form of easing. Which is shown in another pending application.

In order that the present invention may be more clearly understood, I will repeat the experiments referred to in my said pending application, whereinI stated that I have ascertained by experiments that the operation of centrifugal fans generally, more definitely so in those of drum form, such as set forth in my aforesaid Patent No. 662,395, when inclosed in the usual form of spiral or snail shaped casing is materially altered from what takes place when same is operating with a fan set forth in my; Iat} I also described in my said pendeither a free intakeand free discharge for the fluid to and from the casing if the inlet or discharge to said casing be obstructed, so as to cause or a suction resistance to the fluid entering the-eye. In fans of the 'said drum form when uninca'sed the circumferential diseharge of fluid therefrom is uniform around the entire circumference of the fan in any given plane perpendicular to the axis of rotation, and when inclosed in a snail-casing having a free inlet and free discharge this action is only slightly modified, due to the tangentiallydischarged currents being collected by the casing delivered in one stream through the discharge-outlet. If, however, the discharge or suction be obstructed, an inequality of action around the circumference of the drum is caused, which inequality reaches its maximum when the discharge is nearly/ lair entirely closed, and under these circumstances instead of the air flowing outwardly through the ports or spaces between the blades around the entire circumference of the fan-wheel such outward flow mainly occurs von oneside of the drum, while on the opposite side there 1s a stream of fluid flowing 1nwardly through the ports and then partially across or around the interior space within the blades and finally passing outwardly again through the blades on the opposite sid co? the fan-wheel. These operative effects will be better understood by ref erenee to Figure 1 of accompanying drawings, which is a diagram corresponding to a section on the line 1 1 in Fig. 2 in my said other pending application. In this diagram, A designates the rotary fanwheel, which is shown of drum form of t: N type described in my former patent, No. 662,395, with its blades on a and with a snailc asing B, inclosing the fan-wheel. The eye or inlet-opening to the fan-wheel is indicated at C and is of approximately D-shaped form and'disposed eccentrically to the axis of rotation in accordance with the improvements 'set out in my'aforesaid pending application.

back pressure against the discharge Assuming the outlet of the casing to be closed and the fan-wheel rotated, the air-currents will be somewhat as indicated by the arrows; but the precise direction, as well as the velocity ofthcse currents, varies with different back pressures, speeds of the fanwheel, and other conditions; Consequently only an approximate illustration can be given ofsame. Taking, however, the exmate.

ample indicated, it will. be seen that from a point indicated approximately at X around (in the direction of rotation) to another point (approximately indicated at Y) the air is discharged outwardly and tangentiall from the blades, while beyond Y (in the direction of rotation) to a point adjacent to the nearest point Z of the casing there is an inflow of air through the ports between the blades, .as indicated by the broken arro'ws, and thence a current or stream 0 0 within the fan-Wheel, which stream passes outwardly again through the ports between the blades from about the point X. onward- (in the direction of rotation) toward Y. This current or stream 0 c is found to be flowing at a high velocity, similar to that pertaining on the outer side of the blades at Y, and the direction of the current can be conclusively shown by means of a thread attached on the end of a Wire, and a line may be plotted indicating what I may call the inner margin of this current and is shown by the dotted line (i d d. As the position of said line d d d varies with diflerent degrees of back pressure or suction resistance, it 1s to be understood that the location indicated by said dotted line is onl approxi- This line maybe taken as the inner limit of the reflow of this inwardly-regurgitated or return stream of fluid, which stream is marked by letters 0 c. In accordance with the improvements in my aforesaid pending application an outblow of air through the eye of the fan on the side coincident with the stream 0 c is revented by disposing the eye eccentric wit the axis of rotation, its position being more nearly concentric to the outline of the casing than formerly, and by preference the eye 1s, as stated, of non-circular shape, conforming on its side which is adja cent to the internal current or stream to the form taken by such stream, and on the opposite or suction side of the fan-wheel its circumference preferably coincides, or nearly so, in outline with the inner margin of the path of the fanblades.- Thus the eye assumes a shape roughly approximating to an ellipse somewhat flattened on the side, which axially confines the return or internal current 0 c and takes the D shape referred to. In the operation of a fan of this general type the air is found to leave the blades between the points X and Y with a whirling motion, which tends to cause it to return inwardly throu h the blades into the interior of the fan. T is action, however, is so far modified by the tangential or rotary movement imparted to the air that the latter moves a considerable distance circumferentially of the fan before flowinginwardly. The greater part of the air hence does not show anymarked tend- In a fan in which the blades extend fully across the casing nearly all of the air whic thus seeks to reenter the fan-chamber between the points Y and Z is compelled to the fan-blades themselves, the latter oppose the'ingress of the air, with the effect of materially checking the velocity of the latter and reducing the output of the fan.

According to the resentinvention I shorten the blades of t e fan so as to leave between the intake end of the fan-wheel and the opposite side of the casing a space 0, (see Fig. 2,) which may be approximately equal to the length of the blades. By this construction the air which is seeking to reenter the fan-chamber instead of having to force its way back through the ports between the blades is enabled in large part to pass into said chamber around the ends of the blades,

as indicated by the continuous arrows in Figs. 1 to 3. The latter course offers much current, and a considerable gain in the efficiency of the fan is thus roduced.

I prefer to provide a t 'roat, which extends across the space 0 upon the side of the regurgitated current, to confine such current to a definite path and to separate it at this point from the incoming current passing through the eye. Such a threat is, however, not strictly necessary, as it is found in practice that the regurgitated current tends of itself to follow a sufiiciently-restricte d course to avoid any material loss of efficiency on this account. The effective opening of such throat'should be eccentric to the axis of rota tion of the fan-wheel, so that there is left a free passage for the regurgitated current into the lnterior of such wheel. If the throat is constructed asshown in Figs. 1 to 3,'such o ening will assume the form of a meniscuss a ed space 2 2, located principally at the disc iarge side of the fan, as shown in Fig. 1.

I have also found in practice that a fanwheel of the type shown when rotated at an appropriate speed is capable of delivering substantially the theqlre tg' cally-correct quantity of air required to supply" the discharge-opening if the blades of su' 'ch-fan-wheel approximate one-half the depth-ef the casing. As such a fan-wheel can ,-"be driven at a given speed with a muchless expenditure of power than- Referring to the drawings, which illustrate less resistance to the'inward passage of the several forms of my invention, Figs. 1', 2,. and r 3, as before stated, are diagramsillustratfan with free intake and dischar e. Figs.

and 5 are horizontal sections s owing two- Fig. 6 is a side eleforms ol my invention. ration of Fig. 5. A Fig. 7 is a horizontal section showing a further modification, and Fig. 8 is aside elevation thereof.

modification. Fig. 10 is a side elevation thereof, and Fig. 11 a view illustrating the application of my'invention to the paddle-wheel type off'an. Y

in the drawings, A designates the fanreason of the shorteningof the blades to the point m, or thereabout, is free to flow inwardly without being obstructed by the blades. The air passing'into the fan is indicated by the arrows at the eye, and this in- 0w of air will, owing to its being restricted or determined by the eccentricity 'oi the eye, keep the higlnpressure flow 0 c to substantially its own path, even though no throat is used.

Where a fan such as shown in Fig. 3 is required for use as a volumetric fan working against little or no pressure, the shortening of the blades combined with the eccentric eye will be equally suitable, because although under such conditions there occurs no regurgitation. of the fluid back irorn the dischargeoutlet toward the center of the fans nevertheless the strongestsu ction from the eye to the blades occurs through that half of thefanwheel which in its rotation leads up to the slight induction which discharge-outlet, and as the curved side of the D-shaped eye is coincident, or nearly so, with this part of the fan-wheel-the admission thereto of the iresh infiowing fluid is as free as it can be, while there is but little tendency on the part of the opposite half of the fan- Wheel to draw fluid into it. Hence its being sheltered by the plate on the flat side of the D-shaped eye constitutes no detrimental obstruction, and, further, the unobstructed discharge or" the fluid from the blades through the discharge-outlet from the casing creates a 7 draws afurther volume of air outward through the space 0, where same is in line with the discharge-outlet. This action, which is illustrated in Fig. 4, only takes place when working against a free discharge, and the action referred to in Fig. 3 always takes place when the discharge is obstructed and the fan is working against back pressure or suction resistance.

Fig. 9 is a-- horizontal section showing a still further flattened side D it v I have discovered that the eiiiciency of the fan may be further increased by extending I the eccentric eye inward over the space 0 and up to the plane of the intake ends of the blades,

and, further, that the side of the eye which latera'lly confines the return current a c' and guides it into'thecenter of the fan-wheel may be projected into the interior of the fan-wheel to, within a short clearance-space from the fan-wheel disk and that such extension beneficially affects the pressure e'iiiciency and still more so the suction ei'liciency.

Figs. 5 5 and 6 show in section vation, respectively, 'ection of the eye, which is of D-shaped outlineup to the intake ends of the blades.

and ele- Figs. 7 and 8 similarly show the same projection of the eye as in Figs. Band 6, but. with that part of said projection which is adjacent to the return-current c 0 carried into the space within the path of the blades.

Figs. 9 and 10 show a similar projection of 'the'eye to that shown in Figs. 7 and 8 with, in addition, the extreme end of the portion which ro'ects into the interior of the fanwheel itself slightly curved inward toward the center of the fan, which curvature promotes the union of the fluid entering the eye with the return-current crossing the center of the fan-wheel, as indicated by the ar-- rows, without concussive noise, both currents being guided by this curvature into the same direction of flow beforemeeting.

Referring now to 5 to 10, r is the inward extension of the eye d over the space 0 and up to the intake ends of the blades. "1" is the further extension of the eye on the side adjacent to the return-current c 0, so as to more fully divide same from the fluid entering axially through the eye, and r is the curved end of 1 Although I have described these improvements in their applicability more particularly to drum-shaped fans, such as described in my said prior patent, the said improve,- ments are equally applicable to fans of ordinary type, and for an example I have shown in Fig. 11 in a sectional plan corresponding to Fig. 9 the a plication of the invention to a paddle-wheel type of fan of the hitherto ordinary construction, in which, however, the blades extend too far inwardly to ive best results, and while in herein-descri )cd invention can be employe with same, nevertheless as this amount of inward extension tends to break up and confuse the flow of the return-current c c it is distinctly preferable to have the blades of a less radial'depth, and accordingly I have only shown the ordinary inward extension of same in dotted lines and their preferable radial depth in solid lines. The letters used to indicate the various parts in this figure are the same as emplo ed for similar parts in the previouslydescri ed figures.

the above-described pro- What I claim, and desire to secure by Letters Patent, is

1. A centrifugal fan or pump comprising a snail-casing, and a fan-wheel mounted eccentrically therein, said fan-wheel being formed of blades of a length materially less than the depth of the casing, and arranged to .form a space between the blades and easing throughtrieally therein, said fan-wheel being-formed chamber, and having tlon extending across said space into sai of blades of a length materially less than the depth of the casing, and arranged to form a s ace between the blades and the casing tlirough which fluid may fiow past the ends of the blades, said fan having an eye dis osed eccentrically to the axis of the fan-whee and said eye being formed as a throat having a portion extending across said space to the plane of the end of the fan-wheel.

3. A centrifugal fan or pump, comprising a snail-casing, and a fan-wheel mounted eccen trically therein, said fan-wheel being formed of blades of a length materially less than the depth of the casing, and arranged to form a space between the blades and the casing through which fluid may flow past the ends of the blades, saidtfan having an intaketrically to the axis 0 the fan-wheel, and said eye being formed as a throat having a per- (v intakechamber.

4. A-centrifugal fan or pump, comprising a snail-casing, and a fan-wheel mounted eccentrically therein, said fan-wheel being formed of blades of a length materially less than the depth of the casing, and arranged to form a space between the blades and the casing t i rough which fiuid may flow past the ends an eye disposed eccen of the blades, said fan having an'intakechamber, and havin an eye disposed eccentrically to the axis of eye being formed as a throat having a ortion extending across'said space into sai intake-chamber, such portion at its mner end 's ace'between the-blades and the casing t rough which fluid may flow past the ends of the blades, said fan having an eye disposed the fan-wheel, and said eccentrically to the axis of the fan-wheel, and

said eye being formed as a throat having a portion extending across said space, said throat being of less depth on the side most remote-from fan-wheel axis.

6, Ina centrifugal fan or pump, a fanwheel having a practically unobstructed intake-chamber, and an eye disposed eccentricallyto the axis of said fan-Wheel, and formed as a threat extending into said intakechamber. g

7. In a centrifugal fan or ump, a snailcasing, a fanheel mounte eccentrically therein adjacent to one side thereof, said fan wheel having a practically unobstructed intake-chamber, and an e e disposed eccentrically to the axis of said tn-wheel, and adapted to deliver a larger ro ortion offluid to that side of the fan-w ee which is farthest from the casing, said eye formed as athroat extending into said intake-chamber.

In witness whereof I have hereunto si ned my name in the presence of two subscri ing witnesses.

, SAMUEL CLELANI) DAVIDSON.

Witnesses:

JOHN MOORE,

THOMAS DIXON.

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