US3006534A - Centrifugal fans - Google Patents

Description

Oct. 31, 1961 Filed Nov. 2, 1959 J. E. M DONALD CENTRIFUGAL FANS 2 Sheets-Sheet l Oct. 31, 1961 J. E. MCDONALD CENTRIFUGAL FANS 2 Sheets-Sheet 2 Filed Nov. 2, 1959 II I I l l l mm m H0 0 0 on H E u H vm H I o 0 e 0 VM III I r n N n u Wm H lm E MN om Iwezzi'ofi- JomEZ lIcDonaZd, y

diffoflney United States Patent Ofiice 3,006,534 Patented Oct. 31, 1961 3,006,534 CENTRIFUGAL FANS John E. McDonald, Newton, Mass, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 2, 1959, Ser. No. 850,234 4 Claims. (Cl. 230-134) This invention relates to centrifugal fans, and relates more particularly to centrifugal fans having backwardly curved, airfoil blades.

This application is a continuation-in-part of my copending application, Serial No. 789,937 which was filed January 29, 1959, now abandoned.

Centrifugal fans having backwardly curved, airfoil blades are widely used for heavy duties such as forced draft for the boilers of steam plants. Such fans are usually driven by constant speed induction motors, and are usually selected to handle the maximum loads expected to be encountered. However, an engineer may underestimate the maximum load so that the selected fan is too small, or a change may be made in a system requiring the use of a larger fan. Many engineers, therefore, select oversize fans as a factor of safety, but such oversize fans result in undesired increased capital and operating cost.

I have found that I can increase the capacity of such a fan by adding a simple, inexpensive wedge to the driving face of each blade at the blade tip, which deflects the streamline flow along the driving face, forwardly in the direction of rotation, at the blade tip. The capacity of such a fan can be increased as much as 30% by the use of such wedges. Such a wedge preferably is constructed so that normally, it is retracted so that it does not interfere with the streamline flow along the driving face of a blade. With the wedges on all blades of such a fan so retracted, the fan would deliver its ordinarily designed pressure and volume. Then, when an increase in capacity is required, the wedges can easily be advanced. Thus, a fan selected to handle a given load, can easily be adjusted in the field to handle a larger load if the necessity arises.

In one embodiment of this invention, such a wedge is a sheet of spring metal, cantilever supported at its forward end to a blade, with its free end adjustable manually to a retracted position where it has no appreciable effect on the streamline flow along the driving face of the blade, or to an advanced position where it deflects the air or other gas flowing along the driving face of the blade, forwardly at the blade tip.

An object of this invention is to increase the capacity of a centrifugal fan above its ordinary design capacity.

Another object of this invention is to provide means which can easily be adjusted at slight expense to positions where the capacity of a centrifugal fan is not affected, or to positions where the capacity of the fan is increased.

Another object of this invention is to provide a wedge at the tip of the driving face of a backwardly inclined blade of a centrifugal fan which can be manually adjusted through a clean-out opening in the casing of the fan, to a position where it has no appreciable effect on the air or other gas flowing along the driving face of the blade, or to a position where it deflects the gas forwardly at the tip of the blade.

This invention will now be described with reference to the annexed drawings, of which:

FIG. 1 is a fragmentary front view of the rotor of a centrifugal fan embodying this invention, with the front plate omitted, and the blades shown in section;

FIG. 2 is a plan view of the rotor of FIG. 1;

FIG. 3 is an enlarged sectional viewof an airfoil fan blade embodying this invention;

FIG. 4 is an enlarged sectional view of the tip end portion of another airfoil 'blade embodying this invention;

FIG. portion tion;

FIG. portion tion;

FIG. portion tion;

FIG. portion tion;

FIG. 9 is an enlarged sectional view of another airfoil blade embodying this invention, and

FIG. 10 is an end view, looking at the tip of the blade of FIG. 9.

The illustrated fan rotor is a double-inlet one having a center-plate 20 on a rotary shaft 21, and having front or inlet plates 22 with axial inlet openings 23. The rotor has spaced-apart, backwardly curved, backwardly inclined, airfoil blades 24 which have their noses adjacent to the peripheries of the inlets 23, and which have their tips adjacent to the periphery of the rotor. The rotor is designed to rotate in a counterclockwise direction, looking at FIG. 1.

The blades of FIGS. 1-10 have convex driving (gas impacting) faces, and have concave trailing faces. The blades shown in FIG. 1 are the same as the one shown by FIG. 3, although the blades of FIGS. 4-9 could be used.

Each blade 24 of FIGS. 1, 2 and 3 has riveted to its driving face, slightly forwardly of its tip, the forward end of a sheet or strip of spring metal 25 having a bent portion 26 which can be manually lifted so that the outer end of the portion 26 can be placed on the driving face of the blade at its tip as shown by the solid lines of FIG. 3, or can manually be placed as shown by the dashed lines of FIG. 3 so that the strip 25 lies flush against the driving face of the blade. In the latter position, the bent strip portion 26 extends slightly beyond the trailing face of the blade at its tip, but this has no appreciable effect on the performance of the blade.

By retracting the strips 25 as shown by the dashed lines of FIG. 3, a fan rotor with the blades 24 would deliver its ordinary design pressure and volume. By extending each strip 25 as shown by the solid lines of FIG. 3, so that its trailing portion protrudes forwardly, a substantially larger pressure and volume are provided. In the field, one can reach into the usual clean-out opening provided in the casings of such fans, and retract or extend the strips While the fan rotor is slowly rotated to present the blade tips in succession.

FIGS. 41() show other forms of adjustable wedges. The wedge of FIG. 3 is an on-off wedge. The wedge strip 25A of FIG. 4 can be adjusted to provide a wide range of pressures. The strip 25A is riveted at its forward end to the driving face of blade 24A, forwardly of the tip of the blade, and is so spring biased that its trailing end can protrude forwardly of the tip of the driving face of the blade as shown by the solid lines of FIG. 4. The threaded shank of a machine screw 27 extends through the strip 25A, and is threaded into the trailing face of the blade. The screw 27 can be adjusted to place the strip 25A flush against the driving face of the blade as shown by the dashed lines of FIG. 4, where the strip 27 has no appreciable effect on the gas passing the blade. By backing off the screw 27, the strip 25A can 5 is an enlarged sectional view of the tip end of another airfoil blade embodying this inven- 6 is an enlarged sectional view of the tip end of another airfoil blade embodying this inven- 7 is an enlarged sectional View of the tip end of another airfoil blade embodying this inven- 8 is an enlarged sectional view of the tip end of another airfoil blade embodying this inven- 3 be extended forwardly to provide different degrees of pressure increase.

FIG. 5 shows another form of two-position or on-off wedge in which a strip 253 of spring metal has its inner or forward end riveted to the trailing face of a blade 24B forwardly of its tip, and which has a trailing end portion 26B bent at about an angle of 90 to the main body of the strip. The strip portion 268 can be pulled down manually and its upper end placed in a transverse groove 283 in the trailing face of the blade 24B as shown by the solid lines of FIG. 5', in which position it has no practical effect on the gas passing the blade, or it can be withdrawn manualiy from this position, and placed in the position shown by the dashed lines of FIG. 5 Where the portion 2613 forms a wedge extending at an angle of 90 to the tip of the driving face of the blade, forwardly beyond such tip.

FIG. 6 shows a blade 24C having a spring strip 250 having its forward end riveted to the trailing face of the blade adjacent its tip, and having its trailing end portion turned upwardly at an angle of 90 to the main body portion of the strip 25C. A machine screw 270 is threaded into the driving face of the blade, and its shank extends through a clearance opening in the trailing face of the blade and bears against the upper surface of the strip 25C. The strip 25C is spring biased towards the extended position shown by the dashed lines of FIG. 6, and can be forced from this position by screwing in the screw 27C to variably retract the strip portion 260, one retracted position being shown by the solid lines of FIG. 6. 7

FIG. 7 shows a blade 24D having a spring strip 25D lying flush at all times with the trailing portion of the trailing face of the blade, the strip 25D having a trailing end portion 26D which can extend upwardly at an angle of 90 to the main body portion of the strip 25D as shown by the full or solid lines of FIG. 7, at which position maximum pressure is provided, and which can be bent forwardly around the tip of the blade to positions 26DA, 26DB or 26DC shown by the dashed lines of FIG. 7. Position 26DA would provide reduced pressure increase, position 26DB would provide still less pressure increase, and position 26DC in which the trailing end portion of the strip 25D lies flush against the trailing portion of the driving face of the blade, providing no pressure increase. The blade of FIG. 7 is provided where a fan having an excess capacity is shipped from the factory, and where the capacity can be reduced after installation of the fan by forcing as by hammering, the strip portions forwardly to a position 26DA, 26DB, 26DC or positions therebetween as dictated by the fan capacity desired.

FIG. 8 shows a blade 24E having a spring strip 25E riveted at its forward end to the driving face of the blade, and having its free-trailing end bendable upwardly by hand or a tool to positions such as positions 25EA and 251313 shown by the dashed lines of FIG. 8, the position 25EB providing the greater pressure increase. With the strip 25E lying flush with the driving face of the blade as shown by the full lines of FIG. 8, no pressure increase is provided.

FIGS. 9 and 10 show a blade 24F having a spring strip 25F having its forward portion riveted to the trailing face of the blade, and having its free, trailing end portion 26F turned upwardly at 90 to the main body portion of the strip. The trailing end or tip of the blade is arranged to receive spaced-apart pins 39 which are adapted to be placed in circular openings 35, 36 or 37 in the strip portion 26F, the openings 36 being aligned above aligned openings 35, and the openings 37 being aligned above the openings 36. When the pins 39 are in the openings 35 as shown by FIGS. 9 and 10, the strip portion 26F is extended fully forwardly for providing maximum pressure increase. When the pins 39 are in the openings 36, less pressure increase is provided since the strip portion 26F is extended less, and when the pins 39 are in the open- 4 ings 37, the strip portion 26F is fully retracted and provides no pressure increase. The strip 25F can easily be bent by hand to line up the openings 35, 36 or 37 with the pin receiving openings in the tip of the blade 24F In working models, the wedges such as are shown by FIGS. 5, 6, 7, 9'and 10 provided maximum pressure increase when fully extended, and are preferred. A 90 wedge is believed to deflect the air or other gas passing in streamline flow along the driving face of a blade from its nose to its tip, abruptly forwardly in jet flap action at the tip of the blade, the action being somewhat similar to projecting a jet of gas from the interior of an airfoil blade, through a slot in the driving face of the blade adjacent to its tip as is disclosed in my copending application, Serial No. 627,459 which was filed December 10, 1956, now Patent No. 2,935,245.

In FIGS. 4 and 6, more than one screw such as screw 27 in FIG. 4 and 27C in FIG. 6, could be used to adjust the associated wedge strips.

The wedges which, when retracted, extend rearwardly of trailing faces of the blades as shown by FIGS. 3, 5, 6 and 9, have no adverse effect upon performance other than the creation of slight turbulence. Turbulence and some loss in efliciency result when the wedge strips are extended forwardly of the driving faces of the blades, but the slight loss in efliciency is more than justified by being able easily to increase the pressure from a fan above its design pressure.

A center plate of a double inlet fan, is, of course, the back plate of each rotor section, and corresponds to the back plate of a single inlet fan.

In the annexed claims, forward means in the direction of rotation of the rotor.

What is claimed is:

1. In a rotor for a centrifugal fan, said rotor having a back plate, having a front plate with an axial gas inlet opening, and having a plurality of spaced-apart, backwardly inclined blades supported between said plates with their leading edges adjacent to said opening and their trailing edges adjacent to the periphery of said rotor, the improvement comprising the addition to said blades of metal gas deflection strips having leading ends cantilever supported to said blades between said leading and trailing edges and having trailing ends which extend to said trailing edges of said blades. and at said trailing edges of said blades project forwardly of the driving faces of said blades into the gas passing said driving faces for deflecting the 'gas passing said driving faces forwardly of said trailing edges of said blades, said trailing ends of said strips being adjustable to positions where they do not project forwardly of said driving faces.

2. In a rotor for a centrifugal fan, said rotor having a back plate, having a front plate with an axial gas inlet opening, and having a plurality of backwardly inclined blades supported between said plates with their leading edges adjacent to said opening and their trailing edges adjacent to the periphery of said rotor, the improvement comprising the addition to said blades of metal gas de flection strips cantilever supported at their leading ends to said blades between said leading and trailing edges, said strips having free trailing ends at said trailing edges of said blades, said free ends of said strips being movable to positions where they project forwardly of the driving faces of said blades into the gas passing said driving faces or to positions where they do not project forwardly of said driving faces.

3. In a rotor for a centrifugal fan, said rotor having a back plate, having a front plate with an axial gas inlet opening, and having a plurality of backwardly inclined blades supported between said plates with their leading edges adjacent to said opening and their trailing edges adjacent to the periphery of said rotor, the improvement comprising the addition to said blades of gas deflection strips of spring metal cantilever supported at their leading ends to said blades between said leading and trailing edges of said blades, said strips having trailing ends at said trailing edges of said blades, said trailing ends of said strips extending substantially perpendicular to said strips.

4. In a rotor for a centrifugal fan, sm'd rotor having a back plate, having a front plate with an axial gas inlet opening, and having a plurality of backwardly inclined blades supported between said plates with their leading edges adjacent to said opening and their trailing edges adjacent to the periphery of said rotor, the improvement comprising the addition to said blades of gas deflection strips of spring metal cantilever Supported at their leading ends to said blades between the said leading and trailing edges of said blades, said stn'ps having free trailing ends at said trailing edges of said blades, and means for 15 6 adjusting said free ends to positions where they project forwardly into the gas passing the driving faces of said blades or to positions where they do not project forwardly into the gas passing said driving faces.

References Cited in the file of this patent UNITED STATES PATENTS 1,869,655 Beebe Aug. 2, 1932 1,948,949 Stockton Feb. 27, 1934 2,351,516 Jandasek June 13, 1944 FOREIGN PATENTS 214,419 Australia Apr. 8, 1958 653,161 Great Britain May 9, 1951

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