US2439933A - Centrifugal blower - Google Patents

Description

Ap 1943- c. F. JENKINS CENTRIFUGAL BLOWER Filed July 28, 1943 INVENTOR (/mr/es Jenkins.

ATTORNEY WITNESSES:

Patented Apr. 20, 1948 CENTRIFUGAL BLOWER Charles F. Jenkins, Laughlintown, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 28, 1943, Serial No. 496,404

4 Claims. 1

My invention relates to centrifugal blowers of the curved-blade variety, and it has particular relation to exhauster-type blowers having a multiple-scroll frame. By an exhauster-type blower, I mean a type of blower which draws or exhausts air out of a machine or space to be Ventilated, and discharges the air outwardly away from the circumference of the blower in all directions into the surrounding atmosphere.

The principal object of my invention is to provide a blower, of the above-mentioned type, which is capable of delivering air at a greatly increased rate of air-fiow, and at a very considerably increased pressure-head, in an extremely compact blower-design which not only occupies little space, but is also light in weight and very inexpensive to manufacture. While my invention is capable of various applications, the application for which it was primarily designed is in connection with the ventilation of unidirectional railway motors for use on trolleys or trolley-buses having single-end operation.

An object of my invention is to provide a novel combination of a centrifugal fan having a plurality of forwardly curved blades, and a multiple-scroll frame surrounding the same. Certain forwardly curved blade-shapes, and certain types of multiple-scroll fan-housings, have both been known in the past, but, so far as I am aware, they have not heretofore been utilized together, in my particular combinations.

A multiple-scroll housing, when utilized with radial-bladed fans, produces some slight benefit, as distinguished from a fan having no housing, but the benefit is only slight, so much so that in'most cases it has not been considered worth while, in the past, to add the scroll-housing to such radial-bladed centrifugal fans.

It has also been known, heretofore, that more air could be delivered, at a greater pressure, by slightly forwardly curving the blades of the centrifugal fan,. in the direction of rotation, but here again, certain disadvantages have been encountered, not only in the loss of either-direction operativeness of the fan, but also, if the blades are curved very sharply forwardly in an effort to increase the advantage, the air had a discouraging tendency to rotate around with the periphery of the fan, so that very great difficulty was ex perienced in making the air lift off and discharge away from the outer periphery of the fan.

I have found that my multiple-scroll housin with a number of radially short, forwardl inclined, flared guide-vanes, when properly designed, serves admirably to lift the air away from the periphery of the curved-bladed fan, and to thus bring up the air-volume and the air-pressure in a very remarkable degree.

I have also discovered certain advantageous relationships in the design of forwardly-curved fan-blades, which make it possible for me to obtain the same air-flow and air-pressure, with a number of fan-blades which is very much smaller than the number of blades which have heretofore been required, in centrifugal fans, my bladenumber being just about halved, or more than halved, as compared to previous practice, thus resulting in a circumferential spacing or separation of the blades by a distance sufficient to provide room for a welding-tool, so that it becomes feasible to weld the blades in place, thus making possible an inexpensive welded design, as distinguished from the cast fan-blade structures, or extremely complicated fabricated constructions, which have heretofore been necessary.

With the foregoing and other objects in view, my invention consists in the parts, elements, combinations, systems and methods hereinafter described and claimed and illustrated in the accompanying drawing, wherein:

Figure 1 is a fragmentary longitudinal sectional view, on the line I-I of Fig. 2, showing an exhauster-type blower of my invention, as applied to a direct-current motor for a trolleybus designed for single-end operation;

Fig. 2 is a cross-sectional view on the line II-II of Fig. 1, showing the shape of the fanblades, and also the shape of the diffusers or guide-vanes of the multiple-scroll housing; and

Fig. 3 is a diagrammatic sketch illustrative of the fan-construction and, operation.

In Fig. 1, I have illustrated my invention as being applied to a unidirectional direct-current railway-type motor having a salient-pole statormember 4 having a plurality of field-coils 5 thereon, and a rotor-armature 6 with an armature-winding i thereon. A characteristic feature of railway-type or traction-motors and generators is the ever-present requirement for an extremely compact design, so that there is very little room for the ventilating air to pass around the field-coils 5, or through the narrow air-gap 8, or through the rotor-ventilating open ings 9, so that, unlike ordinary commercial motors, a railway machine requires a rather considerable pressure-head to drive or draw any considerable volume of ventilating-air therethrough. For this reason, it is particular desirable, in this type of motor, to have a blower which is capable of developing a rather moderate air-pressure, in exhausting the air from the motor.

I have shown the rear end of the motor, in

Fig. 1, as being equipped with an exhauster-typeblower of my invention. This blower comprises the combination of a rotatable centrifugal fan i l and a multiple-scroll frame or housing I2. The fan II' is mounted on a rotatable annular plate or disc i3, by which I mean a flat, sheet-like, m mber having a substantially plane surface which is bounded by two concentric circles, marking its inner and outer peripheries, respectively. This annular member is carried by the motor-rotor 6, at substantially right angles to the shaft, so that it is substantially radially disposed. It has a plurality of circumfercntially spaced, forwardly curved blades i i, secured thereto in a ring-formation, preferably near the periphery of the annular plate 83. Esually, as illustrated, the fan-blades it are mounted between the radially extending annular plate i3 and a second ring-member i5, also radially er:- tending, to provide an outer bafile plate and a rigid blade-construction. The blades are bent. rectangular plates, having substantially parallel, axially extending inner and outer edges, as-shown in Fig. l, and having a curved fan-blade shape, 'as illustrated in Fig. 2, and the direction of ro-- tation is indicated by the arrow it.

As shown in Figs. 1 and 2, the multiple-scroll frame i2 is composed of a plurality of circumferentially-spaced, forwardly inclined, flared guidevanes H, which are suitably mounted between annular end-members it. Each of the guidevanes ii is preferably of a flared or V-construction, having a long under-surface 2b which extends forwardly at a relatively small angle with respect to the tangential direction, and an outersurface 2i whch is directed outwardly at an angle with respect to the under-surface 2B, so that the outer-surface 2|! of one guide-vane H is approximately parallel to the discharge-end of the undersurface 26 of the next guide=vane behind it, or preferably, as shown, the two surfaces 28 and 28, between the two adjacent guide-vanes, may provide a gas-flow space which flares into an expanding-nozzle formation, having an included angle of the order of 6 therebetween, or of the order of from to 12", as indicated by the angle A in Fig. 2. The inner or under-surface 2b of each flared guide-vane may often advantageously include a spiral-shaped portion 22, as indicated in Fig. 2.

In operation, as diagrammatically illustrated in Fig. 3, the curved-bladed fan It produces airjets which are discharged forwardly from the discharging ends of the inner, forwardly curved surfaces 23 of the blades, so that these air-jets have a velocity and direction, with respect to the blades, as approximately determined by the direction of the discharge-ends of these inner, forwardly curved surfaces 23, at the outer periphery of the fan, as indicated by the velocityvector 24 in Fig. 3. To this velocity-vector 24 must be added the tangential or peripheral velocity 25 due to the rotation of the fan-blades, resulting in a resultant air-velocity 28, in space, which is inclined at a relatively small angle B with respect to the tangential direction.

It will be understood that the magnitude of the velocity-vector 24 with respect to the fanblades will vary in accordance with the rate of air-flow, which is, in turn, dependent upon the amount of resistance to air-flow which is encountered in the motor or other apparatus being ventilated, and it is also dependent upon the amount of air-pressure developed by the fan itself. The peripheral velocity 25 is, of course, dependent upon the speed of rotation of the fan. It follows, therefore, that the precise magnitude and direction of the resultant air-velocity 26 is variable, under different operating-conditions of the fan.

The design is such that under certain particular operating-conditions, at which the max mum benefit from the scroll-housing is desired, the actual air velocity 26 will be in such direction that it will be substantially parallel to the entrance-portion 27 of the inner, forwardly inclined surface 28 of each diifuser or guide-vane ill. Consequently, the air will flow outwardly along this surface 27, and will thus be drawn away from the periphery of the fan, breaking the suction which would otherwise tend to draw the peripherally discharged fan-air circularly around the outer periphery of the rotating fan. Thus, if the air should try to break away from the surface of the entrance-portion 2'! of the guide-vane, it would create a low-pressure area between itself and that surface, thus drawing the air back again to the surface.

In this manner, the air is discharged, with little or no change in volume or cross-sectional area, from the outer periphery of the fan H to the air-flow spaces between successive flared guide-vanes ill. By gently outwardly flaring these air-flow spaces between successive guidevanes if, as indicated by the angle A, the discharged air or gas may be somewhat expanded, thus recovering some of the velocity-head of the discharged air, and thereby increasing the efficiency of the fan.

In order to obtain the best benefits from the operation just described, it is obviously necessary that there shall be a plurality of the stationary scroll-means or flared guide-vanes H. The distributed effect of the plurality of guide-vanes begins to be observable significantly when the vane-number is as small as 3, although, usually, a larger number, such as 6 or 8, is desirable, or even a larger number of guide-vanes may be utilized.

My invention works best in a combination in which the fan-blades id are rather drastically curved, in the forward direction, or in the direction of rotation, so that the discharge-surfaces 23 of the fan-blades, which have a direction corresponding to the air-velocity vector 24, shall be inclined by the angle C, which is at least greater than 25, with respect to the radial direction, and which is preferably between the limits of 45 and with respect to the radial direction.

I also prefer to give the fan-blades M a sufficient radial depth, between their outer and inner peripheries, as well as a sufiicient forward curvature, as indicated by the angle C, and a sufficient circumferential spacing between successive blades, so as to produce a smooth air-flow which substantially fllls the entire space between successive blades at the point of exit from the blades, in the operation of the fan.

Thus the air enters the fan between any pair of blades at the inner periphery of the fan, as indicated at D Fig. 3, and leaves the restricted area between the blades at E. Since all portions of each blade have the same radial depth, and since the lateral edges of the blades are parallel, as bounded by the radially disposed rings l3 and I5, respectively, it is possible to treat the linear dimensions D, E and P, of Fig. 3, as representing the cross-sectional airflow-areas at these places, respectively. The exit area E is taken substantially at right angles to the air-velocity vector 24, or substantially at right angles to the inner discharge-surface 23 of the blade, immediately before this exit-point. M. is the midpoint between blades in the plane of E, and P is the tangential area between blades at right angles to a radius through the exit-area midpoint M.

I believe it is a significant feature of my invention that! so choose the depth and the thickness of the fan-blades, and the spacing between the blades, and also the amount of forward curvature of the fan-blades, so that the transverse exit-section E of the air-stream between adjacent blades, as it is discharged from the fan, is related to the tangential section or area P between adjacent blades at the discharge-end thereof, in approximately the same ratio as the cosine of the angle C between the radial direction at the exitpoint and the air-velocity vector 24 or the inner discharge-surface 23 of the blade immediately before this exit-point. Thus, if the radial component of the air-velocity is indicated by the vector 28 in Fig. 3, and if the exit-velocity with respect to the fan-blades is indicated by the vector 24, the ratio of the areas may be expressed by the equation,

area E velocity 28 area P velocity 24 within approximately :20 percent.

Obviously this relation is the only one which satisfies the vector diagram, for uniform air-flow. For instance, suppose that the area E should be increased by changing the shape and proportions of the blades in such manner that the exitangle C remains the same. At the same volume of air delivered by the fan, the radial component 20 would remain unchanged. Likewise, the velocity 24 parallel to the blades at exit would have to remain the same, to satisfy the vector-relations. However, the average velocity through the increased area E would have to be reduced. The result would be a non-uniform flow, where various portions of the discharged air would be moving at different velocities.

By observing the fan-blade design-precautions just explained, I not only increase the smoothness and efficiency of air-flow between the fanblades, but I also considerably increase the circumferential spacing between the blades, using deeper blades than have heretofore been customary, and using a much smaller number of blades, although the blade-number will still be in excess of ii, and usually considerably in excess of 8, depending somewhat upon the radius of the fan.

An important result of a reduction in the number of blades necessary to obtain any given airvolume, or rate of air-flow, is a rather considerable decrease in the cost of manufacturing and assembling the blades, when a fabricated construction is utilized. In previous designs, with a very large number of blades, very close together, there simply has not been room to inexpensively fabricate the fan, and in most cases welding has been quite out of the question, because of the very restricted spaces. In my design, I provide sufficient blade-spacing to make welding possible, and a reduced number of blades which reduces the required number of welding-operations or other blade-fastening operations.

While I have illustrated my invention in a pref erred form of embodiment, and described it with reference to this particular form of embodiment, I wish it to be understood that such illustration and description are only illustrative, and that various changes in proportions and other designdetails may be made by those skilled in the art without departing from the essential features of my invention. I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their lemm- I claim as my invention:

1. An exhauster-type blower comprising the combination of a rotatable centrifugal fan and a scroll-housing surrounding the fan, characterized by said fan comprising a substantially radially disposed, rotatable annular plate and a plurality of circumferentially spaced, substantially rectangularly shaped, formerly curved blades secured thereto in a ring-formation, the inner dischargesurface of each fan-blade, immediately before the exit-point, being inclined forwardly, in the direction of rotation, at an inclination-angle with respect to the radial direction, the exit-area between adjacent blades, measured at right angles to said inner discharge-surface, immediately before the exit-point, being related to the tangential area between the blades, measured at right angles to the radius at the mid-point of said exit-area, in approximately the same ratio as the cosine of said inclination-angle within approximately plus or minus 20%, so as to produce a smooth air-flow which substantially fills the entire space between successive blades, at all times.

2. A blower as defined in claim 1, characterized by the inner discharge-surfaces of said forwardly curved blades being inclined by an inclination angle between 45 and with respect to the radial direction.

3. An exhauster-type blower comprising the combination of a rotatable centrifugal fan and a multiple-scroll frame surrounding the fan, characterized by said fan comprising a substantially radially disposed, rotatable annular plate and a plurality of circumferentially spaced substantially rectangulariy shaped, forwardly curved blades secured thereto in a ring-formation, and said frame comprising more than two circumferentially spaced, forwardly inclined, flared guide= vanes, the inner discharge-surface of each fanblade, immediately before the exit-point, being in clined forwardly, in the direction of rotation, at an inclination-angle with respect to the radial directlon, the exit-area between adjacent blades, measured at right angles to said inner dischargesurface, immediately before the exit-point, being related to the tangential area between the blades, measured at right angles to the radius at the mid= point of said exit-area, in approximately the same ratio as the cosine of said inclination-angle within approximately plus or minus 20%, so as to produce a smooth air-flow which substantially fills the entire space between successive blades, at all times.

4. A blower as defined in claim 3, characterized by the inner discharge-surfaces of said forwardly curved blades being inclined by an inclination angle between 45 and 75 with respect to the radial direction.

CHARLES F. JENKINS. REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,201,867 McMahan May 21, 1940 FOREIGN PATENTS Number Country Date 338,436 Germany June 18, 1920

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