US2441411A - Centrifugal fan - Google Patents

Description

' MW 1, 1948. 1-1. F1 HAGEN cnnmxruou. n11

Filed April 8, 1944 7 Sheets-Sheet 2 myavmiz. Hana/.01; M4624! v May 11, 1948. H. F. HAGEN CEN'I'RIFUGAL FAN Filed April 8, 1944 7 Sheets-Sheet 5 INVENTOR. F. H465.

May 11, 1948. H. F. HAGEN 2,441,411

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May 11, 1948.

H. F. HAGEN CENTRIFUGAL FAN '7 Sheets-Sheet 7 Filed April 8, 1944 v INVENTO? Heeow #1 H465 8y M J ATTORA/Ey Patented May 11, 1948 CENTRIFUGAL FAN Harold F. Hagen,

Wellesley, Mass., assignor, by

mesne assignments, to Westinghouse Electric Corporation, a corpora tion of Pennsylvania Application April 8, 1944, Serial No. 530,114 16 Claims. (Cl. 230-134) This invention relates to cen rifugal fans and has as objects, improvements in the efliciency of, and increases in the structural strength of, such fans.

The relatively high pressures required for certain duties from centrifugal fans result in high rotational velocities of the blades and in correspondingly high centrifugal forces. For limiting the stresses due to centrifugal forces to a minimum, it is desirable to have all elements of the fan blades extend in lines radiating fromthe center line of the fan shaft. My U. S. Patents Nos. 2,082,955 and Re. 20,409 disclose such constructions.

eflicient. All elements of the blades extend in radial lines or substantially so, with the result the blades have the desired strength, while the curvature of all elements of the blades is such that high efficiencies result.

A feature of this invention is that all elements of the fan blades are so curved at every radius, that the air particles upon which they act, are

directed in streamline flow from the axial inlet to the radial outlet. Streamline air flow has previously been accomplished in propeller type fans which have axial outlets as well as axial inlets,

the blade during its rotation, with a plane perpendicular to the center line of the fan shaft;

Fig.2 is a view similar to Fig. 1 but with the hub and inlet guide omitted, illustrating the first graphical step in the conformal plotting for determining the correct shape for the blade along the streamline paths, and shows lines of projection carried over to Fig. 3;

Fig. 3 is a. view corresponding to Fig. 2 but is a view looking axially at the streamline path of Fig. 2 following rotation thereof, and illustrates another step in the conformal plotting; I

Fig. 4 is a vector diagram illustrating how the resultant velocity vector at the entrance of the streamline path of Fig, 2 is determined for application to Fig. 6, and illustrates another step in the conformal plotting;

Fig. 5 is a vector diagram illustrating how the resultant velocity vector at the point N on the streamline path of Fig. 2 is determined for application to Fig. 6, and illustrates another step in the conformal plotting;

Fig. 6 is a conformal plot illustrating how, through use of the resultant velocity vectors obtained from Figs. 4 and-5, the streamline path C-C shown by Figs. 3 and 8 is obtained;

Fig. 7 is a view similar to Fig. 2 but with more streamline paths added at other radii, with lines of projection carried over to Figs. 8 and 9;

Fig. 8 is a view similar to Fig. 3 but with more streamline paths added;

Fig. 9 is a view showing how one of the dashdot lines of Fig. 10 which illustrates the lines of but so far as is known, this has not been accomplished in centrifugal fans in which the air particles, due to the radial delivery, have radial as well as axial and tangential velocities. The shapes of the prior centrifugal fan blades have been such that the .air particles have been forced out of streamline flow paths with the result that the blades have done excessive work with resulting decreased efliciency.

According to this invention, the theoretically correct streamline flow paths at different radii are determined through conformal plotting, and

the fan blades are shaped to conform to suchpaths. An example of the use of conformal plotting in fan design is disclosed in my U. S. Patent No. 2,322,357. 1

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

Fig. 1 is a view illustrating the path swept by a selected fan blade between an inlet guide and a hub having a backplate, and may be considered as illustrating an intersection of the outline of interception of a blade surface with surfaces of cylinders, is determined;

Fig. 10 is a view illustrating the lines of interception of' a blade surface with the surfaces of six different cylinders of different radii, concentric with the center line of the fan shaft;

Fig. 11 is an end view of a blade and a portion of a hub and 'back plate as seen looking axially into the inlet of the fan wheel;

Fig. 12 is a plan view looking downwardly upon the blade and a portion of the hub and backplate of Fig. 11;

Fig. 13 is a side elevation of the blade of Figs. 11 and 12, and

Fig. 14 is a side elevation with a portion in vertical section, of an assembled, double inlet fan embodying this invention.

In the description of the procedure in conformal plotting:

V=the velocity of the air relative a blade element.

WX=the axial component of velocity.

WR=the radial component of velocity.

wR=the tangential component of velocity (from wheel rotation) WS=the tangential spin component.

(wRWS)=the total tangential component of velocity relative the blade.

U=the resultant of the radial and axial velocities.

R=the radius of the cylinder upon which the conformal plot is made.

C-C' is the mean streamline path of an air particle as selected for explaining the process of conformal plotting-C being the inlet point on the streamline and C being the outlet point on the Streamline.

AS=the linear distance between the point C, the inlet point on the mean streamline C-C' of Fig. 2, and a point N located a small distance downstream on the streamline.

r=the mean radius of the circular are between the points C-N of Fig. 3.

A9=the small angle between radial lines drawn through C and N.

E=the symbol for summation.

The subscript N indicates the velocities at the point N on the streamline -0.

The subscript C indicates entering velocities at the point C on the streamline C-C', and the subscript C indicates leaving velocities at the point C' on the streamline C--C'.

In designing a fan wheel, the air pressures and volumes to be provided, are of course, known as are other working conditions such as the type and speed of drive and the limitations of space and materials. The blade diameters and surface areas for a desired rotational speed are determined by standard procedures and knowing these and the pressure to be provided, the velocities along the blade elements can be determined.

With reference now to Fig. 1, a smoothly curved air passage through the wheel is desired for efli cient flow. The inlet guide l5 provides the outer wall of this passage and the curved hub l6 provides its inner wall. The outer end I! of the hub forms the backplate of the wheel. The curved line connecting the points E and E defines the outer contour of the path swept by the outer edges of the inner portion of a. fan blade, and the curved line connecting the points E and A defines the outer contour of the path swept by the outer edges of the outer portion of the blade.

The path swept by the blade is reproduced on Fig. 2, and the mean streamline C-C' is drawn in, C being the inlet point on the streamline and C being the outlet point. The point N is selected on the streamline, a small distance downstream of the point C. The reference cylinder on which the conformal plot is to be made, is given the radius R.

With reference to Fig. 4, the resultant velocity at the point C is determined as Uc through drawing in the known radial velocity vector WRc and the known axial velocity vector WXo. Then V0 is determined from drawing in the known velocity vector WRc and the vector Uc. The velocity vectors described as known are calculated from knowledge of the rotational velocity of the blade and of the shape of the passage through the wheel.

Then with reference to Fig. 5, the resultant velocity UN at the point N is determined from the vectors WRn and WXN and the vector VN is determined from Us and (kvRxv-WSN).

The velocity vectors Co' at C and the corresponding velocity vectors at any number of points along the streamline C-C' can be determined in the same way. v

With reference now to Fig. 6, which is the conformal chart, the ordinates are ZXRAG) and the abscissas are I X(7AS The point C is laid out with a zero ordinate value and a zero abscissa value. The velocity vector V0 is drawn in on Fig. 6, it being the resultant of U0 and as described in connection with Fig. 4. The abscissa values for the points N and C are known as are the angles as determined by velocity diagrams such as Fig. 5. A curve having a suitable parabolic curvature as recommended by the National Advisory Committee for Aeronautics, is then drawn in tangent to the velocity vector V0 and to the vectors Va and V0 and is the solid line curve 0-0 of Fig. 6. Other points on the curve CC could be determined for more accurately plotting the curve C--C of Fig. 6,

As is known, in conformal plotting such as illustrated by Fig. 6, the angles plotted are true angles. The velocity vectors represent true velocities. Therefore, the solid line curve C-C' represents correctly the streamline path CC of Fig. 2 in its relation to the velocity forces involved.

The curve C-C of Fig. 6 therefore determines I the correct blade curvature along the selected streamline, and since the blades used will have finite thicknesses whether of airfoil shape or of sheet metal having uniform thickness, should be considered as illustrating the center line of the blade element which will move air particles along the streamline CC' of Fig. 2, in its true relation to the velocity vectors and their angles.

Due to the fact that there are a finite number of blades (eight in the embodiment of the invention illustrated), the air between the blades will not follow the blade angles and it is necessary to rotate the blades through a selected angle of attack for providing the necessary average change of direction for the whole mass of air. The proper angle of attack is determined from published data such as the N. A. C. A. reports, on blades or airfoils having approximately the same camber, and the blades are rotated in the direction of wheel rotation through the selected angle of attack. With reference now to Fig. 6, the point C may be considered to be rotated about the point C, in a counter clockwise direction for providing, the blade shape adjusted for the angle of attack. The dashed line curve C-C of Fig. 6 illustrates the solid line curve CC' rotated through an angle of attack. The rotated curve C--C' in Fig. 6 is then transferred to Fig. 3 by determining the value of A9 from Fig. 6 for any point on CC', say point N.

The value of A6 together with RN will locate point N on Fig. 3.

Figs. 2 and 3 illustrate conditions during blade rotation. An air particle is moved along the streamline 0-0 of Fig. 2 by a blade element position of the streamline 0-6 of Fig. 3 was determined as described in the foregoing.

A cylinder having the radius RF is drawn in Figs. 7 and 8, and appears as a straight line parallel to the center line of the fan shaft, extending through the point A in Fig. 7, and as a circular arc with center on the center line of the fan shaft, in Fig. 8.

The lines of intersection of this cylinder with the streamlines AA, B--B, C-C', D-D, and EE are projected vertically downward throu h Fig. 9 and appear there as vertical lines. Then with reference to Fig. 8, the cylinder intersects the streamline EE' at e, the streamline DD' at d, the streamline C--C' at c, the streamline BB' at b, and the streamline A-A' at a. The circular distance E-e is scaled off and plotted to scale below the reference line of Fig. 9 along the vertical lines extending through the intersecw tion of the cylinder with the streamline E-E' on Fig. 7. Likewise the circular distances D-d, Cc, Bb, and A-a are scaled from Fig. 8 and plotted to scale below the reference line of Fig. 9 on the vertical lines drawn through the intersec tions of the cylinder with the streamlines D-D', CC', BB' and AA' respectively of Fig. 7.

The curve F-F' is then drawn through the points sealed off on Fig. 9 and is a curve showing the interception of the blade surface with the surface of a cylinder having the radius Rs.

' Fig. 10 illustrates interceptions of the blade surface with other cylinders having other radii.

The curves F'-F', G-G', H-H', I-I', J.J', and KK' are the interceptions of the blade surface with the surfaces of cylinders having the radii, F, G, H, I, J, and K, respectively, of Figs. 1 and 11. The lengths of these lines of interception are substantially correct and they are lined up along the radial line XX which is the line X-X of Figs. 11 and 13. These lines of interception, in their true relation, which is not correctly illustrated by Fig. 10, are also to be considered as lined up so that the points where they cross the line X-X, coincide: It would be difficult to illustrate this since the lines would appear as merged at many points. The lines of interception are shown in other views by Figs. 11 and 13.

The portions of the blade to the left (facing the drawings) of the radial lines X-X of Figs. 11 and 13 are the outlet or delivery portions.

All elements of the fan blades of this invention curve in axial, radial and tangential directions so that it is impossible to represent their shape by the usual sections. Therefore, to manufacture the blade, a pattern maker has to be given curves suchas shown by Figs. 9 and 10. He cuts the surfaces of wooden cylinders to follow the curves, and then dies are made to conform with the outlines of the cylinder surfaces as modified.

The curved dash-dot lines F-F', G-G', H-H', I-I', JJ', and K-K, of Fig. 11 in this view, not'only represent arcs of cylinders but also represent the lines of interception of the surfaces of the cylinders with the blade surface.

Fig. 12 is a plan view looking downwardly upon the blade of Fig. 11 and illustrates thereverse curvature of the blade as do the lines of interception of Fig. 10.

The curved lines F-F', G-G', H-H', I-I', J-J', and KK' of Fig. 13 are the projections on a plane perpendicular to the center line of the fan shaft, of the interceptions of the blade surface with the surfaces of the cylinders which have the radii: RF, Ra, Ra, R1, R1, and Rx respectively.

The outer elements of the blades, those farther from the axis of the fan wheel, extend substantially on radial lines extending through corresponding inner elements, those nearer said axis. It is sometimes necessary slightly to modify the blade shape when determined as described in the foregoing, in order for the outer elements to line up radially and this is done when necessary, for minimizing the stresses due to centrifugal forces, but the change is so slight that the departure of the air particles from streamline flow is of no practical consequence. Fig. 13 illustrates radial lines U--U, V-V, W-W, and 2-2 upon which the corresponding inner'and outer elements of the blades substantially fall.

While for clearness, Figs. 11, 12 and 13 have shown but one blade, the wheel for which the blade was designed would have eight equally spaced blades.

Fig. 14 illustrates a double inlet fan having two fan wheels, each wheel having shown thereon, twoopposed blades 20. The other blades are not shown. The hubs I6 have the common shaft 2i supported by theend bearings 22, the back plates I'l being placed back to back as is usual in double inlet fans. Thecasing 23 has the usual scroll shaped walls forming a common outlet for the two wheels. The inlet guides l5 are continued from around the inlet portions of the blades to the exterior of thecasing 23 and then curve rearwardly to form thesemicircular sections 24. The spin vanes 25 are pivoted in the guides and in thevane adjusting housings 26.

The blades may be formed separately with their root edges attached to the curved hub as illustrated by Figs. 11-14, as by welding, or they may be cast integral with the hub. The root edges of the blades are those nearest the axis of the fan wheel.

Characteristics of the blades of this invention are that they conform to streamline paths between the axial inlet and the radial outlet. This results in the delivery portions of the blades illustrated, being backwardly curved so that less spin is produced in the air leaving the blades than in the prior blades such as are disclosed in my said patents. This also results in the inlet portions of the blades being forwardly curved for the desired propeller action,

As illustrated best by Fig. 11, the blades have increasing radial depth and area from their inlet edges to their delivery portions while the delivery portions of the blade have decreasing radial depth and area towards the backplates for the reasons explained in detail in my said Patent No. 2,082,955.

Another advantage of this fan is that it does not pulsate at any point in its operating range.

While one embodiment ofthe invention has been described for the purpose of illustration, it should be understood that the invention is not limited to the methods of procedure or the details of design disclosed, as modifications thereof may be suggested by those skilled in the art, without departure from the essence of the invention.

What is claimed is:

1. A fan wheel for a centrifugal fan, comprising a back plate for turning the air from said wheel so as. to be discharged substantially perpendicular to the axis thereof, a hub, and a blade attached along its root edge to said hub, said blade having a forwardly curved inlet portion and a. backwardly curved outlet portion, the radial depth of said blade increasing from its inlet edge to wards said back plate, the outer elements of said blade and the corresponding inner elements extending substantially in radial lines.

3. A fan wheel for a centrifugal fan, comprising a back plate for turning the air from said wheel so as to be discharged substantially perpendicular to the axis thereof, a, hub, and a blade attached along its root edge to said hub, said blade having a forwardly curved inlet portion and a backwardly curved outlet portion, the area of said blade increasing from its inlet edge to said outlet portion and then decreasing towards said back plate.

4. A fan wheel for a centrifugal fan, comprising a back plate for turning the air from said wheel so as to be discharged substantially perpendicular to the axis thereof, a hub, and a blade attached along its root edge to said hub, said blade having a forwardly curved inlet portion and a backwardly curved outlet portion, the-area of said blade increasing from its inlet edge to said outlet portion and then decreasing towards said back plate, the outer elements of said blade and the corresponding inner elements extending substantially in radial lines.

5. A fan blade for a centrifugal fan having elements with center lines formed substantially tangent at their inlet edges to the velocity vectors which are the resultants of the velocity vectors U and 10B, and being formed substantially tangent at their outlet edges to the velocity vectors which are the resultants of the velocity vectors U and (wR-WS), the vectors U being the resultants of the velocity vectors WR and WK, where wR=the tangential velocity components WX=the axial velocity-components WR=the radial velocity components WS=the tangential spin components.

6. A fan blade for a centrifugal fan having elements with center lines formed substantially tangent at their inlet edges to the velocity vectors which are the resultants of the velocity vectors U and :13, and being formed substantially tangent between their inlet edges and their outlet edges to the velocity vectors which are the resultants of the velocity vectors U and (wR-WS), the vectors U being the resultants of the velocity vectors WR and WK, where wR=the tangential velocity components WX=the axial velocity components WR=the radial velocity components WS=the tangential spin components.

7. A fan blade for a centrifugal fan having elements with center lines formed substantially tangent at their inlet edges to the velocity vectors which are the resultants of the velocity vectors U and wR, and being formed substantially tangent between their inlet edges and their outlet wR=the tangential velocity components WX=the axial velocity components WR=the radial velocity components WS=the tangential spin components.

8. A fan wheel according to claim 1 in which the radial depth of the blade decreases to zero depth at the back plate.

9. A fan wheel according to claim 2 in which the radial depth of the blade decreases to zero depth at the back plate.

10. A fan wheel according to claim 3 in which the radial depth of the blade decreases to zero depth at the back plate.

11. A centrifugal fan comprising a fan wheel having an axial inlet and a peripheral outlet, a curved hub having diameters which increase progressively from the upstream end to the downstream end of said wheel, a plurality of fan blades having forwardly curved inlet portions and backwardly curved outlet portions attached along their root edges to said hub, the curvature of said hub being such at said downstream end of said wheel that it turns the air discharged from said blades substantially perpendicular to the axis of said wheel,

12. A centrifugal fan according to claim 11 in which the tips of said blades merge with the surface of said hub at said downstream end of said wheel.

13. A centrifugal fan according to claim 11 in which the tips of said blades merge with the surface of said hub at the downstream end of said hub.

14. A centrifugal fan according to claim 11 in which the radial depths of said blades decrease in said outlet portions towards said downstream end of said wheel.

15. A centrifugal fan according to claim 11 in which the radial depths of said blades decrease in said outlet portions towards said downstream end of said wheel and their tips merge with the surface of said hub at said downstream end of said wheel.

16. A centrifugal fan according to claim 11 in which the radial depths of said blades decrease in said outlet portions towards, the downstream end of said hub and their tips merge with the surface of said hub at the downstream end thereof.

HAROLD F. HAGEN.

REFERENCES CITED The following references are of record in the file of this patent:

. UNITED STATES PATENTS Number Name Date 1,042,506 DeVallat Oct. 29, 1912 1,075,300 Moss Oct. 7, 1913 1,161,926 Criqui Nov. 30, 1915 1,167,152 Criqui Jan. 4, 1916 1,240,949 Criqui Sept. 25, 1917 1,314,049 Criqui Aug. 26, 1919 1,959,703 Birmann May 22, 1934 2,240,653 Jenkins et al May 6, 1941

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