US3517821A - Deflecting element for centrifugal separators - Google Patents

Description

June 30, 1970 D. R. MONSON ETAL 3,517,321

DEFLEGTING ELEMENT FOR CENTRIFUGAL SEPARATORS Filed Nov. 29, 1968 2 Sheets-Sheet 1 PRIOR ART I N VE N TORS DONALD E. Mo/w'azv DARRYL 5'. KELLER JAMES GROTHNA/V BY MERCHANT GOULD A1 fORNEYS June 30, 1970 v D. R. MONSON ETAL 3,517,821

DEFLECTING ELEMENT FOR CENTRIFUGAL SEPARATORS.

Filed Nov. 29, 1968 2 Sheets-Sheet IN VE N TORS' -00M4L0 R. NOMSW/V 04R Yb 2.. KELLER 81.64/45! 6- RUTH/MN MERCHANT GOULD ATTORNEYS United States Patent O 3,517,821 DEFLECTING ELEMENT FOR CENTRIFUGAL SEPARATORS Donald R. Monson, West St. Paul, Darryl E. Keller,

Mound, and James C. Rothman, Rosemount, Minn., assignors to Donaldson Company, Inc., Minneapolis, Minn., a corporation of Delaware Filed Nov. 29, 1968, Ser. No. 77,759 Int. Cl. B04c /103 US. Cl. 210512 6 Claims ABSTRACT OF THE DISCLOSURE A deflecting element for a centrifugal separator having a centrally located axially extending hub with a plurality of generally helical type vanes extending radially outwardly therefrom, each vane having a camber in the high pressure surface thereof positioned so that a short portion thereof adjacent the radially extending leading edge is generally parallel with the axis of the hub and the low pressure surface of each vane has a relatively sharp break adjacent the leading edge. Further, each of the vanes includes a trailing edge formed so that the radially outermost edge of said vane has a substantially shorter length than the edge attached to the hub.

BACKGROUND OF THE INVENTION Field of the invention Centrifugal separators are utilized for a variety of separating tasks, such as separating large particles from small particles, separating solid particles from fluid particles, etc. There are a variety of centrifugal separators available which utilize a deflecting element to cause fluid entering a first tubular member to swirl about the axis of the member and force the heavier particles outwardly by centrifugal force. It is contemplated that the present deflecting element can be incorporated in substantially any separator of this type.

Description of the prior art Many types of deflecting elements are utilized in centrifugal separators, only a few of which are included in the following. Flat fins which radiate outwardly from a central hub or junction are tilted slightly at an angle to the axis to cause a swirling motion of fluid entering the tube. Generally helical shaped fins radiating outwardly from a central hub provide an increased swirling motion of the fluid. Each of these prior art devices varies somewhat in separation efficiency and in pressure drop coefficient or pressure losses.

SUMMARY OF THE INVENTION The present invention pertains to an im roved deflecting element for a centrifugal separator having a central hub element with a plurality of circumferentially spaced generally helical shaped deflecting vanes radiating outwardly therefrom with the high pressure surface of each vane having a camber in the contour thereof adjacent the leading edge and the low pressure surface having a relatively sharp break in the contour thereof adjacent the leading edge. Further, each of said vanes may include in addition to or in lieu of said modified leading edge a trailing edge formed so that the radially outermost edge of said vane has a substantially shorter length than the edge adjacent said hub element.

It is an object of the present invention to provide an improved deflecting element for centrifugal separators.

It is a further object of the present invention to provide a deflecting element having an improved efliciency and pressure drop coefficient.

3 ,5 l 7,82 l Patented June 30, 1970 BRIEF DESCRIPTION OF THE DRAWINGS Referring to the drawings, wherein like characters indicate like parts throughout the figures:

FIG. 1 is a view in perspective of a prior art deflecting element;

FIG. 2 is a view in side elevation of a first embodiment of the present deflecting element operatively mounted in a centrifugal separator, portions thereof broken away and shown in section;

FIG. 3 is a plan view of the deflecting element as seen from the leading end thereof (upper end in FIG. 2);

FIG. 4 is a plan view of the trailing end of the deflecting element (as seen from the lower end of FIG. 2);

FIG. 5 is a planar generation of one of the vanes of the deflecting element illustrated in FIG. 2 as generated at the radially outermost edge thereof;

FIG. 6 is a view similar to FIG. 2 of a second embodiment of the present deflecting element;

FIG. 7 is a view similar to FIG. 3 of the second embodiment; and

FIG. 8 is a view similar to FIG. 4 of the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 2 the numeral 10 generally designates a centrifugal separator of the uni-directional flow type having a first tubular member 11, with an upstream end 12 and an outlet end 13, a second tubular member 14 and a deflecting element 15. The second tubular member 14 has a substantially smaller diameter than the first tubular member 11 and is mounted coaxially in the outlet end 13 of the tubular element 11. The deflecting element 15 is mounted adjacent the upstream end 12 of the tubular member 11 so as to produce a swirling motion in fluid entering the upstream end 12. As the fluid passing through the centrifugal separator 10 swirls, larger particles are thrown outwardly and pass out of the tubular member 11 at the outlet end 13 thereof between the tubular member 11 and the tubular member 14. A substantial portion of the fluid flows into the tubular member 14 and out the opposite end thereof where it is separated from the flow leaving the tubular member 11 at the outlet end 13 between the tubular member 11 and the tubular member 14.

Referring to FIG. 1 a prior art deflecting element designated 15a is illustrated. The deflecting element 15a has a central elongated hub 2011 with a plurality of radially extending helical vanes 21a attached thereto in a circumferentially spaced relationship. Each of the vanes 21a is substantially similar with a leading edge 22a extending radially outwardly from the hub 20a perpendicular to the axis thereof and a trailing edge 23a extending radially outwardly from the hub 20a the same distance as the leading edge 22a but spaced axially and circumferentially therefrom. The deflecting element 15a is adapted to be mounted within a centrifugal separator in a manner and position similar to that shown in FIG. 2 for the improved deflecting element 15.

The improved deflecting element 15 includes an elongated hub member 20 having a leading end which is generally ellipsoidal in shape and a trailing end formed by a streamlined fairing 25, which is truncated to allow a free length between the end of the fairing 25 and the beginning of the tubular member 14 to allow particles which become retarded in the boundary layer of the hub member 20 to have suflicient time to be separated before they reach the tubular member 14. The fairing 25 is made with a gradually changing curve that is truncated at a point which gives the best trade-off between pressure drop, separation efliciency and length for a given application. There is no known mathematical formula for determining where this trade-off occurs in the various configurations of the hub member 20 and, consequently, the best configuration for any given application should be determined experimentally.

The hub member 20 has a plurality of generally helical shaped vanes 21 radiating outwardly therefrom in circumferentially spaced orientations. Each of the vanes 21 has a leading edge 22, a trailing edge 23, 40, an outer edge 30 and an inner edge 31 affixed to the hub member 20. In FIG. 2 the outer edge 30 and a radial extension of the portion 23 of the trailing edge 23, 40 of one of the vanes 21 is extended in dotted lines to a point at which they meet, so as to provide a trailing edge somewhat similar to the trailing edge 23a of the deflecting element 15a. The extension of the vane 21 in FIG. 2 is for explanatory purposes and to this end a planar generation of the outer edge 30 of the extended vane 21 in FIG. 2 is illustrated in FIG. 5.

Each of the vanes 21 has an upper surface 35 directed generally toward the upstream end 12 of the centrifugal separator and referred to hereinafter as a high pressure surface 35 because fluid approaching the deflecting element 15 strikes the surface 35 and is deflected in a generally spiral path thereby. Each of the vanes 21 further has a lower surface 36 directed opposite to the high pressure surface 35 and referred to hereinafter as a low pressure surface 36. Referring to FIG. 5 the high pressure surface 35 forms a generally straight line from the trailing edge 23, 40 a substantial distance toward the leading edge 22. A concavity 37 is formed in the contour of the high pressure surface 35 adjacent the leading edge 22 and generally parallel therewith so that the leading edge 22 is displaced from the helical curve (or straight line of the high pressure surface 35) toward the upstream end 12 of the tubular member 11. Referring to FIG. 2 it can be seen that each of the vanes 21 adjacent the leading edge 22 extend generally parallel with the axis of the hub member for a short distance. The concavity 37 in the high pressure surface of each of the vanes 21 is formed in a smooth curve to gradually alter the path of the fluid flowing past the deflecting element 15 into a spiral shaped path.

It has been found experimentally that the location of the maximum depth of the concavity 37 in the contour of the high pressure surface 35 is extremely important and greatly varies the separation efficiency and pressure drop coeflicient of the centrifugal separator 10. In general, it is preferred to locate the concavity 37 adjacent the leading edge 22 and it has been found that the maximum depth of the concavity 37 should be a distance from the leading edge 22 which is less than one-third the total length of a chord (a line drawn between the leading edge 22 and the trailing edge 23, when the centrifugal separator 10 is operating at a Reynolds number (based on chord length) approximately 2x10 For illustrative purposes, in FIG. 5 the chord has a length 0 and a line drawn perpendicular to the chord to a point at which the concavity 37 or camber is the deepest, intersects the chord a distance a from the leading edge 22. Thus, for Reynolds numbers below approximately 2X 10 the concavity 37 should be located in the contour of the high pressure surface 35 so that a/c is one-third or less.

The low pressure surface 36 of each of the vanes 21, referring to the planar generation in FIG. 5, forms a generally straight line extending a substantial distance from the trailing edge 23, 40 toward the leading edge 22. A relatively sharp break 38 is formed in the low pressure surface 36 adjacent the leading edge 22 and generally opposite the camber 37. The sharp break 38 in the contour of the low pressure surface 36 improves the pressure drop coefficient over the deflecting element 15a (which has a straight line planar generation). A strong leading edge vortex, or eddy of fluid, is produced adjacent the low pressure surface downstream of the leading edge 22a in the deflecting element 15a due to the leading edge fluid flow separation. The configuration of the low pressure surface 36 in the deflecting element 15 produces a much lower intensity vortex adjacent the low pressure surface 36 downstream of the break 38, therefore, producing lower pressure losses and an improved pressure drop coeflicient.

Referring again to FIGS. 2 through 4 a portion of each of the vanes 21 lying between the outer edge 30 and the trailing edge 23 of each thereof is removed along the edge 40. The portion of each of the vanes 21 removed provides a variation of chord length with the radial diS tance from the hub member 20. The edge 40 does not extend inwardly to the hub member 20 at which the chord is taken in this embodiment because it is desired to increase the loading mainly in the outer regions of the vanes 21. It is believed that there is an optimum chord distribution, or variation in chord length relative to the radius, which 'will provide a minimum pressure drop with little or no loss in efficiency. This optimum chord distribution must be determined for difference geometries of the upstream end 12 and various performance trade-offs between efliciency and pressure drop coeflicients can be obtained by varying the height and distribution of the trailing edge 23, 40.

From efliciency and pressure drop standpoints, the trailing edge 23, 40 is feathered, in this embodiment, to minimize the width of the wake trailing off the vanes 21. Pressure losses are contributed to the system by the wake, with the losses increasing proportional to the width of the wake. A wide wake also compromises the efliciency of separation since a short circuit flow from the high pressure area adjacent the inner surface of the tubular member 11 can pass transversely inwardly in the wake toward the low pressure area adjacent the hub 20. This short circuit flow carries particles toward the center where they have a poorer chance of being separated.

Referring to FIGS. 6-8, a second embodiment of the deflecting element is illustrated wherein the deflecting element is incorporated in a reverse flow type of centrifugal separator. The various parts illustrated in the FIGS. 6-8 similar to parts of the embodiment illustrated in FIGS. 2-5 are designated with similar numerals having a prime added. In the embodiment illustrated in FIGS. 6-8 the hub element is actually the tubular member 14'. Also, while in both embodiments illustrated herein the vanes 21 and 21' are connected to the hub element 20 and the inner tubular member (hub element) 14', it should be understood that the vanes would also operate it they were connected to a separate sleeve, to the outer tubular member 11, 11, etc. The operation of the reverse flow separator is such that the majority of the fluid reverses the axial direction of flow in the lower tapered portion, or outlet 13, of the tubular member 11 and flows out through the tubular member 14' while a small amount of fluid and the majority of the foreign matter flows out through the tapered opening or outlet 13 of the tubular member 11'. It should be understood that the present invention might be incorporated in many other embodiments known to those skilled in the art.

Thus, an improved deflecting element for centrifugal separators is disclosed which has an improved or lower pressure drop coeflicient and an improved or higher efficiency. Further, utilizing the modified leading edge and/ or the modified trailing edge of the vanes in the deflecting element as previously described, and positioning the modifications according to the configuration of the centrifugal separator and the desired results will greatly improve the pressure drop coeflicient and/ or the efficiency of the centrifugal separator, depending upon the particular application and the desired results.

What is claimed is:

1. In a centrifugal separator an improved deflecting element comprising:

(a) a central hub member;

(b) a plurality of circumferentially spaced deflecting vanes positioned adjacent to said hub member in an outwardly radiating orientation therewith and each extending a substantial distance in a generally axial direction;

(0) each of said vanes being generally helical in shape with a leading edge and a high pressure surface directed generally upstream within the separator and a low pressure surface directed generally in the opposite direction;

(d) each said high pressure surface having a concavity in the contour thereof adjacent the leading edge positioned so that the leading edge is displaced from the helical curve of the vane generally in an upstream direction; and

(e) each said low pressure surface having a relatively sharp generally radially extending break in the contour thereof adjacent the leading edge and spaced generally axially therefrom.

2. In a centrifugal separator an improved deflecting element as set forth in claim 1 wherein the hub member extends axially a substantial distance with the upstream end being formed as a portion of an ellipsoid and the opposite end having a streamlined fairing attached thereto.

3. In a centrifugal separator an improved deflecting element as set forth in claim 1 wherein each of the deflecting vanes has a feathered trailing edge.

4. In a centrifugal separator an improved deflecting element as set forth in claim 1 wherein the camber in the contour of the high pressure surface is further characterized by being located so that a line drawn perpendicular to a chord, which chord is drawn between a point on the leading edge and a point on the trailing edge of a planar generation equidistant from the axis of the hub, at the point along said chord of maximum camber intersects said chord at a point spaced from the leading edge a distance less than one-third the total length of said chord.

5. In a centrifugal separator an improved deflecting element comprising:

(a) a central hub member;

(b) a plurality of circumferentially spaced deflecting vanes positioned adjacent to said hub member in an outwardly radiating orientation therewith and each extending a substantial distance in a generally axial direction;

(c) each of said vanes being generally helical in shape;

and

((1) each of said vanes having an outermost peripheral edge formed so that the radially outermost edge of said vane has a substantially shorter length that the edge attached to said hub member.

6. In a centrifugal separator an improved deflecting element comprising:

(a) a central hub member;

(b) a plurality of circumferentially spaced deflecting vanes positioned adjacent to said hub member in an outwardly radiating orientation therewith and each extending a substantial distance in a generally axial direction;

(c) each of said vanes being generally helical in shape with a leading edge and a high pressure surface directed generally upstream within the separator and a low pressure surface directed generally in the opposite direction;

(d) each said high pressure surface having a concavity in the contour thereof adjacent the leading edge positioned so that the leading edge is displaced from the helical curve of the vane generally in an upstream direction;

(e) each said low pressure surface having a relatively sharp generally radially extending break in the contour thereof adjacent the leading edge and spaced generally axially therefrom; and

(f) each of said vanes having an outermost peripheral edge formed so that the radially outermost edge of said vane has a substantially shorter length than the edge attached to said hub member.

References Cited UNITED STATES PATENTS 379,009 3/ 1888 De Rycke -457 X JAMES L. DECESARE, Primary Examiner I US. 01. X.R. ss 457; 209-211

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