US3059833A - Fans - Google Patents

Description

Oct- 23, 1962 R. A. BENolT 3,059,833

FANs

Filed oct. 1m 1958 z shees-sneet 1 16' FIM;

I N VEN TOR. few; a' A. 3800z R. A. BENOIT Oct. 23, 1962 FANS 2 Sheets-Sheet 2 Filed Oct. l'7 1956 IN V EN TOR. I wf A 36/701;

United States Patent O Filed Oct. 17, 1956, Ser. No. 616,458 6 Claims. (Cl. 230-119) The present invention relates to rotary fans, and has special reference to multi-blade fans or blowers.

Both centrifugal fans and axial fans, at present in general commercial use, have certain disadvantages.

Centrifugal fans take up considerable floor space and, consequently, their use is restricted. Also, in the case of centrifugal fans having a spiral housing, in order to make the assembly compact as well as to reduce costs, the housing must be made much wider than the wheel. In some instances, inasmuch as the air must distribute itself laterally as it enters the housing, the mechanical efliciency thereof is substantially reduced. Also, centrfugal fans cannot be used when straight line flow is desired.

Axial fans are designed for straight line flow but, when employed where substantial resistance is encountered, are very noisy and, hence, their use is restricted chiefly to industrial purposes, they being unsuitable for air-conditioning and general ventilating purposes where quietness is essential. Also, such fans are not usable over their entire pressure range, from wide open volume to no delivery. In some instances, volume selections can only be made over substantially one-third of the pressure range if stable operation is desired.

One of the objects of the present invention is to provide a fan or blower which overcomes the disadvantages above described of both centrifugal fans and axial fans, while retaining the advantages thereof.

Another of the objects of the invention is to provide a fan or blower of the Character indcated which is simple in construction and highly efficient in operation.

The several features of the invention, |whereby these and other objects 'may be attained, will be readily understood from the following description and accompanying drawings, in which:

FIGURE 1 is a longitudinal sectional view, partly in elevation, of a fan embodying features of my invention in their preferred form, the section being taken on line 1-1 of FIG. 2, and the driving means of the fan impeller being omitted;

HG. 2 is a transverse sectional view, taken on the line 2-2 of FIG. 1;

FIG. 3 is a schematic view of one of the vanes in the cylindrical housing of the fan, illustrating the preferred curvature of the vane with relation to the impeller;

FIGS. 4, 5, 6, 7, 8 and 9 respectively show quarter views of the front sides of impellers having their blades of different forms;

PIG. 10 is a view corresponding to FIG. 1 of a modified form, the fan being shown as belt driven;

TG. ll is a rear elevation of the same;

PIG. 12 is a view corresponding to FIGS. 1 and 10 of another modified form, the impeller being shown directly connected to the shaft of an electric motor;

FIG. 13 is a rear view of the same; and

FIG. 14 is a schematic view illustrating that the curvature of the vanes at their intersection with the surface of the fan housing, when projected by revolutions to a plane, is substantially the involute of a circle.

The fan illust-rated in FIGS. 1 and 2 of the drawings is provided with a centrifugal impeller 2 having a hub 4 which is adapted to be secured on the shaft of an electric motor or connected with other driving means (not shown).

The impeller has a backplate 6 secured on the rear ICC end of the hub 4, blades 8 which project radially from the hub, and a shroud 10. An inlet cone 12 forms a continuation of the shroud 10. The fan is further provided with a stationary dscharge thimble 14 which has its front edge arranged closely adjacent the rear edge of the backplate 6. The shroud 10 is preferably secured to the blades so as to be carried thereby. However, the shroud may be stationary, in which case it may be made integral with the inlet cone.

The fan is provided with a cylindrical housing 16 'which has annular angle irons 18 secured on the outer side of its front and rear ends, to which supporting means for the fan may be secured. The front end of the housing 16 has the front end of the inlet cone 12 secured thereto.

The cylindrical housing 16 has volute-shaped vanes 24 secured to the inner cylindrical surface thereof. These vanes 24 extend generally longitudinally of the inner surface of the housing, and the inner corners of their leading ends make contact with the outer surface of the dscharge thimble 14, said corners being in proxirnity to the front edge of the thimble and, consequently, close to the inner corners of the trailing edges of the impeller blades. The thimble may be secured to the ends of the vanes so as to be supported thereby in fixed position.

The air enters the fan through the inlet cone 12 which directs the air to the intake of the impeller 2 along its blade-leading edges 26. Centrifugal force is imparted to the air as it passes between the impeller blades 8, and the air is discharged from the impeller through the area formed by the trailing edges 27 of the blades, the rear edge of the shroud 10 and the backplate 6. Thence, the air enters the confines of the cylindrical housing 16, thimble 14, and the vanes 24. The air passes from the vane leading edges 28 which are the points of cut-off of the air, to their trailing edges 30, the air leaving the fan through housing dscharge 32.

The impeller 2, shown in FIG. 1, is of the paddle wheel type with long radial blades 8. The outer ends of the blades are extended outwardly in =more or less of an inverted V-shaped form, the extended ends having their front edges 25 inclined outwardly and rearwardly, and their rear or trailing edges 27 inclined inwardly and rearwardly to the rear annular edge of the backplate 6.

These extensions of the blades 8, together with the shroud, provide effective means of directing the air in the general direction of ultimate dscharge with minimum turbulence or losses. Also, said extensions of the blades permit the use of a larger inlet, at the same time maintaining proper blade depth. Both increased inlet size and greater peripheral speed of the extended blades add materially to the pressure produced by the impeller.

The thimble 14, as shown in FIG. 1, is positioned with its front edge in running clearance with the rear annular edge of the backplate 6. The backplate may be extended to form the thimble 14, in which case the extension should have running clearance -with the front ends of the vanes 24. Higher pressures are produced when the eX- treme diameter of the backplate 6 exceeds the smallest inner diameter of shroud I10, this being due primarily to the radially diverging path the air is compelled to take when moving rearwardly from the region of the smallest inner diameter of shroud 10 and around backplate 6.

It is important that the corners of the leading edges 28 of vanes 24 be positioned within the width of the thimble C14, and preferably in close proximity to the front annular edge of the thimble. Also, the leading edges 28 of the vanes should be inclined outwardly and rearwardly as shown with relation to the thimble '14 and the trailin-g edges 27 of the blades. This arrangement eifectively eliminates turbulence and noise at the point of cut-off of the air stream leaving the inclined trailing edges 27 of the blades.

The vanes 24 should be so positioned in the cylindrical housing 116 that their surfaces are substantially orthogonal to the tangent at their point of contact with the inner cylindrical surface of the housing.

I have found that the straight and thin leading edges 28 of the vanes 24 at the points of cutoff, were more eicient than blunt edges, this apparently being due to the sharpness of the cutoif. I have also found that for quiet operation the best results are obtained, with the leading edges 28 cut in a manner as to be disposed diagonally to the trailing edges 27 of the impeller blades. The best performance, so 'far as quietness is concerned, with the impeller shown in PIG. 1, was obtained when a line parallel to the leading edges 28 of the vanes followed a direction toward the impeller inlet, while converging to- Ward the impeller axis as shown.

Actual tests of my new fan, with the diameter of backplate 6 equal to that of commercial centrifugal fan impellers in a spiral housing, gave higher efiiciency for the same Volume and pressure at equivalent rotative speeds.

With my new fan as shown in FIG. 1, a pressure curve was obtained where the pressure rises constantly without dips from wide open volume to no delivery. In other words, stability of volume discharge is obtained over the entire pressure range.

The total pressure or head produced by a centrifugal impeller may be utilized by converting various portions of kinetic energy into static pressure. The amount of this conversion depends on the design of the means employed for effecting it. It is desirable to convert part of the Velocity pressure of the air leaving the blades to static pressure. This static pressure is usable to overcome restrictions such as duct work, or to overcome the resistance of the system through which the air passes. It is desirable that the conversion of the state of the air be accomplished with minimum losses. The curvature of the vanes 24 in relation to impeller and housing is of great importance.

Since the conversion of kinetic energy of air to a required state of static pressure is in effect a conversion of high rvelocity to a lower Velocity, the differential in the respective Velocity heads is equal to the static pressure thus obtained. This state of conversion may be accomplished by gradual increase in area immediately after the air leaves the blades together with means of receiving the air at its initial high Velocity. Also, the conversion device should eliminate the spin of the air in the housing. I have found that with my improved fan having the vanes 24 curved and arranged as shown, it accomplishes all of these functions.

The air leaves the impeller blades in a path indicated by the Vectors in FIG. 3. It will be observed that each baffle vane.s convexed surface or front side immediately beyond its leading edge 28 diverts the air in its path of travel. This baffling effect produce'd by the vane causes the convexed surface to be air loaded while the bafile eliminates passage of air along the concave or back side of the vane. Due to the `gradual divergent curvature of the bafile vane, the air does not break away from the convex surface. However, the air Velocity diminishes progressively as the air travels towards the fan discharge. The reduction in air Velocity is due to the expanding area through which the air moves and the diverging path the air is compelled to take due to the curvature of the vane.

The baifiing effect of the vanes causes the air to be interceded by the leading surfaces of the convex side of the vanes at a Velocity close to that of the air leaving the impeller. This is accomplished with minimum losses. The air is released by the vanes at the fan discharge with greatly reduced Velocities. Thus, the initial kinetic energy of the air produced by the action of the impeller is converted to a useful form of pressure.

It was found Ithat the use of the concave side of the vane for converting the kinetic energy of the air to pressure was not efiicient. The reason for this is because the air leaves the impeller with considerable rotative direction in the housing. Thus, if the vane were so shaped as to load the concave side of the vane the successive bombardment of the air against the vane for the majority of its length would tend to maintain the Velocity of the air rather than reduce the Velocity. This, of course, makes an effective air straightening vane but does not efficiently convert the kinetic energy of the air to pressure. The baffie vanes employed with this new fan purposely not only eliminate the flow of air along the concave curvature but compel the air to cling and flow along the convex side of the vanes due to the bafling effect and the reasons stated above. This arrangement results in much higher conversion efficiencies. As the air moves along the conVeX vane 24 there is a Velocity pressure at this early point which corresponds very closely with the Velocity pressure measured at the impeller; whereas, progressively along this vane, toward its outer end, there is a constant drop in Velocity pressure.

The baflie vanes are so curved that their surface reaches or approaches an axial direction at the fan discharge. Since air tends to cling to a smooth and gradually curved surface, the air is drawn by the vane to also discharge in a substantially aXial direction. Additional vanes of the air straightening variety may be added at the fan discharge if desired to give tiuer axial flow.

The positioning of the inner Corners of the leading edges of the vanes in close proximity to the rotative path o-f the impeller blades is important in order to form definite points of cutoff, but a slight space as shown should be allowed to avoid turbulence and noise that might result. I have found that where two or three vanes as shown are employed, an efficient curvature of the vanes at their intersection with the surface of fan housing 16 when projected by revolution to a plane, FIGURE 3, is substantially the involute of a circle whose radius is about 21/2 times the extreme fan impeller diameter and where the ordinate perpendicular to the base line runs parallel to the axis of the impeller. The proper curvature of the vanes and the curvature of the cylindrical housing just beyond the point of cut oif of the vanes are important design features to successfully convert the kinetic energy of the air to static pressure. The curvature of the vanes regulates the spin Velocity of the air and the curvature of the cylindrical housing controls the passage of the air in a manner to cause the air to follow the dictates of the vanes.

Since the vanes curve gradually toward an axial direction, the air emerges from the discharge of the housing substantially in an axial direction, the rotative spin imparted by the impeller being substantially eliminated. It was found that the area between each vane 24 and dotted line 34 (iFIG. 3) shown on the concave side of the vane held air in a static state. This is due to the direction of the spin Velocity of the air leaving the impeller which bypasses the concave side of the vane due to the flatness of the vane along its leading surface. The back or concave side of the bafile vanes may be filled in or a partition may be added so as to isolate the area where air motion does not exist, if desired, without departing from the spirit of the invention.

The preferred amount of turn or wrap of the vanes inside the |fan housing may be expressed in degrees of the fan housing circumference. For instance, if the vanes make one complete turn inside the housing, the vanes would terminate 360 degrees from their point of origin. It will be obvious therefore, that the fan housing must have sutficient length to provide the required degree of turn of the vanes as well as the proper curvature of the vanes to effect the desired amount of conversion of the total pressure produced by the impeller to static pressure. I have found that vanes extending from 20 to circumferential degrees could be used depending on the number of vanes and the amount of conversion desired.

A convenient method of obtaining the convolute shape of thevanes from their point of origin to their termination aoeassa is to establish the angle formed by lines tangent to both the inner surface of the fan housing and the points along the surface of the vanes where the vanes meet the fan housing with a plane orthogonal to the impeller axis, as shown schematically in FIG. 14.

I have found that a tangent line, as described above, to the point of origin of the vanes may form an angle with the plane varying between to 30 degrees. The angle between the limits of 5 to 30 degrees being selected depending on the number of vanes and the amount of pressure Conversion desired. Where three vanes are employed it has been found that a generally suitable angle for a tan-gent line at the point of origin of the vanes is about 20 degrees.

The curvature of the vanes 24, FIG. 14, may also be determined mathematically by obtaining the values of (X) and (Y) for various angles 0 or the angles formed by the sweep of the radius arm (E) as follows:

Where K=1.5 to 5 D=Extreme irnpeller diameter WKDH S 180 For large fans with wheel diameters exceeding 24 inchcs, six or more vanes may be used to reduce the length of the fan housing. In the case where six vanes are used the vanes may extend about 60 circumferential degrees, or as little as 20 circumferential degrees depending on the number of vanes.

Impellers with blades curved as shown in FIGURES 4, 5, 6, 7, 8 and 9 were found to perform satisfactorily in my new fan. The impellers shown in FIGS. 4, 5, 6, and 7 are all backward curved types, while FIGS. 8 and 9 show forward curved blading. The impeller shown in FIG. 5 requires a higher rotative speed than radial blade impeller of FIG. 1 to produce the same quantity of air and pressure, while impellers shown in FIGS. 8 and 9, have lower rotative speeds. The impeller shown in FIG. 5 has non-overloa'ding power characteristics which is advantageous where such features are desired. Slight modifications of the curvature of the vanes 24 is desirable for efiicient operation when using impellers of different blading such as backward or forward curved. The reason for this is because each type of blading directs the air leaving the impeller at a slightly different angle in relation to the vanes and the housing.

In FIG. 10 the impeller shaft 36 is shown driven th-rough a pulley 38 thereon, and a V-belt 40, the shaft being mounted in bearings 42.

In this figure the thimble 14 of FIG. 1 is replaced with a long, receding, conical shaped air dilfuser 44. The three vanes 24 extend from the housing 16 to the cone as shown in FIGURE 11.

This diffuser cone permits the air to leave the fan discharge at slightly lower velocities without losses due to turbulence and, consequently, a greater amount of conversion of the kinetic energy of the air to static pressure.

In FIGURE 12 the impeller is shown mounted directly on the shaft of a motor 46. The discharge thimble 48 is shown slightly tapered which has been found tends to reduce noise, even where a narrow thimble is employed. In the case where the diameter of the motor housing is approximately equal to the diameter of the thimble, the motor casing can serve to do the work of the thimble.

It also has been found that the performance of my new fan can be varied within limits, by varying the degree of curvature of the vanes. For instance, by reducing angle "A" (FIG. 3) formed between a tangent line B to a point along the curvature of projection of the vane with the rotative parts of the blades, the pressure developed by the fan tends to increase while the volume decreases. If such angle A is increased, the pressure developed by the fan tends to decrease while the volume tends to increase.

With my improved fan, the vanes or baffles 24 complete to a desired degree the conversion of kinetic energy to static pressure, at a point close to the discharge of the cylindrical casing, at which point the maximum pressure is obtained. This point of maximum pressure is remotely positioned from the leading edges of the vanes or points of cutof. Therefore, the amount of leakage back through the wheel is greatly reduced and is substantially negligible.

By increasing the number of vanes 24 from two to four `and consequent increase in the number of points of cutoif, the pressure and volume tend to increase, which is a decided advantage. Apart from the increased pressure produced by the addition of one or more vanes, the amount of wheel exposure may be substantially reduced or entirely eliminated. This reduces the loss due to wheel exposure at the discharge which occurs with centrifugal fans in a spiral housing, the latter having considerable exposure of the wheel when viewed from the discharge of the housing.

Since the area of the point of air discharge from the impeller is substantially 'the same as the area between the thimble and the housing, there is no lateral expansion as in the case of centrifugal fans with spiral housings, and thus distribution losses are negligible. This represents an appreciable increase in efficiency.

My improved fan occupies much less space than the present centrifugal fan. It may be mounted in any desired direction of flow and as part of a straight line flow from inlet duet to discharge duct. The fan can be installed in out of way places, and saves floor space which today is at such a high premium. Manufacturing costs as well as installation costs are lower than with the present day blowers.

The fan does not occupy any greater space than vane axial fans in commercial use at the present time. However, it out-performs the vane axial fan. Also, my fan operates at much lower speeds than the vane axial fan for the same working conditions, which is one of the reasons it is much quieter. The vane axial fan when employed for use where considerable resistance is encountered, has been found to be very noisy. Consequently its use is being restricted chiefiy to industrial purposes. On the other hand my new fan can be used for air-conditioning and general ventilating purposes where quietness is essential regardless of the resistance encountered with such systems.

The scope of use of my fan is wide and varied, can be used in any fan application where centrifugal blowers or vane axial fans are employed today with important advantages over both, but without the disadvantages above pointed out.

What I claim is:

1. In a fan of the class described, a housing having a cylindrical inner bore surface., a rotary impeller positioned concentrically within the housing bore surface and comprising a hub, a backplate carried by the hub, and a plurality of blades on the front side of the backplate, said blades having end extensions projecting beyond the periphery of the backplate, an inlet cone in front of said impeller, a substantially cylindrical discharge thimble having its front edge arranged closely adjacent the rear edge of said backplate, and a plurality of vanes of convolute form projecting inwardly from the inner bore surface of said housing and substantially orthogonal thereto and extending generally longitudinally thereof with their forward ends extending over the cylindrical surface of the thimble to points in proximity to the front end edge of said thimble, said vanes being sufficiently spaced apart so that the air flow is not confined between two adjacent vanes and being gradually curved in the general direction of rotation of said impeller, each of said vanes presenting a convex surface to the air delivered by said impeller and defining with the rotative path of the outer edges of the impeller blades a constantly increasing space, substantially all of the air from said impeller being delivered to said convex surfaces of the vanes and directed and guided therealong through said constantly increasing spaces, whereby the kinetic energy of the air is converted to static pressure as the air travels to the dscharge end of said housing.

2. In a fan of the class described, a housing having a cylindrical inner bore surface, a rotary impeller positioned concentrically within the housing bore surface and comprising a hub, a backplate carried by the hub, and a plurality of blades on the front side of the backplate, Said blades having end extensions projecting beyond the periphery of the backplate, an inlet cone in front of said impeller, a shroud for the blades having a leading edge substantially contiguous with the trailing edge of said inlet cone, a substantially cylindrical discharge thimble having its front edge arranged closely adjacent the rear edge of said backplate, and a plurality of vanes of convolute form projecting inwardly from the inner bore surface of said housing and substantially orthogonal thereto and extending generally longitudinally thereof with their forward ends extending over the cylindrical surface of the thimble to points in proximity to the front end edge of said thimble,' said vanes being sufficiently spaced apart so that the air flow is not confined between two adjacent vanes and being gradually curved in the general direction of rotation of said impeller, each of said vanes presenting a conveX surface to the air delivered by said impeller and defining with the rotative path of the outer edges of the impeller blades a constantly increasing space, substantially all of the air from said impeller being delivered to said convex surfaces of the vanes and directed and guided therealong through 'said constantly increasing spaces, whereby the kinetic energy of the air is converted to static pressure as the air travels t'o the discharge end of said housing.

3. In a fan of the class described, a housing having a cylindrical inner bore surface, a centrifugal rotary impeller positioned concentrically within the housing bore surface and comprising a hub, a substantially fiat backplate having va rounded peripheral edge carried by the hub, and a plurality of blades on the front side of the backplate, said blades having end extensions projecting beyond the periphery of the backplate, an inlet cone in front of said impeller, an angular shroud for the blades having a leading edge -substantially continguous with the trailing edge of said inlet cone, a substantially cylindrical discharge thimble having its front edge arranged closely adjacent the rear edge of said backplate, and a plurality of vanes of convolute form projecting inwardly from the innner bore surface of said housing and substantially orthogonal thereto and eXtending generally longitudinally thereof with their 'forward ends exitending over the cylindrical surface of the thimble lto points in proximity to the front end edge of said thimble, said vanes being sufiiciently spaced apart so that the air flow is not confined between two adjacent vanes and being gradually curved in the general direction of rotation of said impeller, each of said vanes presenting a convex surface to the air delivered by said impeller and defining with the rotative path of the outer edges of the impeller blades a constantly increasing space, substantially all of the air from said impeller being delivered to said convex surfaces of the vanes and directed and guided therealong through said constantly increasing spaces, whereby the kinetic energy of the air is converted to static pressure as the air travels to the discharge end of said housing.

4. Apparatus as defined in claim 3, wherein the trailing edges of said blades are inclined inwardly and rearwardly in relationship to the leading edges of said vanes and wherein said leading edges are inclined outwardly and rearwardly.

5. Apparatus as defined in claim 3, wherein the curvature of each vane is such that a tangent line common to both the surface of the vane and the surface of the housing bore at t.e leading edge of the vane forms an angle with a plane orthogonal with said longitudinal aXis of between to 30, and each subsequent tangent line advancing unit degrees eircumferentially along said housing bore surface from the leading edge thereof and common to the aforesaid vane and bore -surfaces forms progressively increasing angles with said plane and wherein said vanes extending circumferentially from their respective leading edges to their trailing ends thereof through an are at least 10 and no greater than 160 of said housing surface.

6. In a fan of the class described, a housing having a cylindrical inner bore surface, a rotary centrifugal impeller positioned concentrically within the housing bore surface and comprising a hub, a backplate carried by the hub, and a plurality of blades on the front side of the backplate, said blades having end extensions projecting beyond the periphery of the backplate, an inlet cone in front of said impeller, a substantially cylindrical discharge thiinble having its front edge arranged closely 'adjacent the rear edge of said backplate, and a plurality of vanes of convolute form projecting inwardly from the inner bore surface of said housing and substantially orthogonal thereto and extending generally longitudinally thereof with their forward ends extending over the cylindrical surface of the thiinble to points in proXimity to the front end edge of said thimble, said vanes being sufliciently spaced apart so that the air flow is not confined between two adjacent vanes and being gradually curved in the general direction of rotation of said impeller, each of said vanes adjacent said thirnble presenting a substantially fiat surface portion to intercept the air from said centrifugal impeller and a progressively conveX surface therealong and defining with the rotative path of the outer edges of the impeller blades a constantly increasing space, substantially all of the air from said impeller being delivered to 'said convex surfaces of the vanes and directed and guided therealong through said constantly increasing spaces, whereby the kinetic energy of the air is converted to static pressure as the air travels to the discharge end of said housing.

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