CA1112515A - Centrifugal pump - Google Patents

Abstract

Abstract of the Disclosure A centrifugal pump includes an impeller and a volute casing.
The impeller comprises a main disc and a plurality of vanes which project axially from at least one side of the disc. A fluid passage is formed between each pair of adjacent vanes. The passage has a constant depth and a gradually decreasing width from an inlet to an outlet thereof. Each fluid passage assures a flow of the fluid along the front surface of the associated vane and prevents the occurrence of a vortical flow therein. The volute casing has an inner surface which is substantially U-shaped in section and effectively converts the kinetic energy imparted to the fluid by the impeller into hydraulic pressures.

Description

Field of the Invention The invention relates to a centrifugal pump, and more particularly, to an improved impeller of centrifugal pump which - prevents a vortical fluid flow from occurring in passages defined between vanes.
- 20 Description of the Prior Art In the art of centrifugal pumps, an impeller of the form well known since old is ætill in use today. The impeller has a plurality of vanes which define fluid passages therebetween. The fluid passage has a width which rapidly increases from an inlet to an outlet. It is - 25 known that such impeller suffers from a significant loss head as a result of a vortical now occurring in the passage. Nevertheless the traditional form of impeller has been relied upon in practical use.
~ theoretical analysis of the action OI an impeller assumes an "ideal impeller" which has an infinite number of vanes havirlg an ,~
~n jnfinit~sim~l thit~knes.s with the tluid flnwin~ along the curved surface '~.
of vaneæ ~i~out experiencing any frictional 10SB~ Referring to Fig. 1, the ideal impeller i5 partl~ ustratedJ with fluid flowing into an inlet with an angle ~ 1 and a velocity cl. Assuming a peripheral speed ul of the impeller at thio point, the fluid has a relative velocity o wl with 5 respect to the vanes. The inlet angle ~B 1 of the vane is chosen to be ; -aligned with the direction of the relative veloci1y wl. After flowing along the curved surface of the vane, the ~luid e~its the vane outlet wi1h a relative velocity w2. If the peripheral speed of the impeller i8 U2 at the outlet, the fluid which departs from the impeller will have an absolute velocity c2, a resultant of w2 and u2, the direction of which is represented by an angle 1 2 It is presumed that particles of the fluid located on the same curved surface of the vane move in the same direction and with the same velocity. Since the fluid flow~ along the ' curved vane surface and simultaneously rotates together with the impeller, the actual path o~ movement of the fluid will be represented by a curve BlB2' starting fron- the entrance Bl, and it exits point B2' at the angle ~ 2-An increase in $he pressure head h2-hl between the outlet and the inlet of the ideal impeller will be given as follows:
,. u22 _ ul2 W22 - wl2 h2-hl = (1) 2g 2g where g represents the gravitational acceleration. An increase in the velocity head is given by ' c22 _ c12 (2) 2g The vane imparts a head to the fluid which i3 a difference between the total head at the outlet and the total head at the inlet. Thus, the theoretical head Hth will be u22 - u 2 C22 - c12 w 2 2 Hth ~ = + ~ _ _ 1 (3) 2g 2g 2g Fig. 2 shows the velocity diagrams at the inlet and the outlet.

It will be seen from these diagrams that W2 C2 + U2 - 2c2u2 cos 0~ 2 Wl = C12 + ul2 - 2ClUl C~8 ~ 1 Substitution of these expressions into the equation (3) yieldfi:
~ = U2C2 C05 a~ 2 - UlCl C0S t 1 (4) Hth .: g = 90, co~ ~ 1 = . and hence u2c2 ~os oC 2 u2c2u ,~. Hth = = (S) ~ g g The theoretical head of an actual impeller is substantially 10 reduced from the value given by the equation (5) since it has only sever~l vanes and since in most impellers of the prior art as illu~trated in Fig, 3, adjacent vanes define a passage therebetween which is broad enough to permit a free ilow, causing a complicate f:low situation.
The head of an actual pump can be represented as follows:

lS~; U2C2 COS ~1 2 H = - (6) ~ g where g; represents a coefficient having a magnitude which depends on the configuration and the number of ~anes and the specific speed of the impeller and which usually rangeæ from 0. 5 to 0. 8.
In known impeller constructions, the broad passages formed between adjacent vanes fail to provide a fluid ~low along the curved vane surface, resulting in non-uniform velocity and pressure distribution along the curved surface. Because the velocity and pressure are higher at ~e ~ront surface than at the rear surface of the valle, the pressure and speed differentials across the vanes cause a kind of complicate vortical flow. This will be considered in more detail with reference to Fig. 3. A conventional centrifugal pump includes an impeller 10 having a plurality of vanes 11 of substantially uniform thickness. Each vane 11 is disposed on a side o~ a main disc 12 ; 30 having a boss 13 which is firmly mounted on a drive shaft 14. As is well ~ 4 --known, the impeller 10 is received in a body 17 having a volute ca~ing 16 which defines a spiral space 15 around the impeller. Fluid is admitted a2dally around the boss 13 as the impeller 10 rotates, and is delivered to the spiral space 15 through passages 18 defined between adjacent 5 vanes 11. Fluid obtains kinetic energy during itæ passage through the passages 18, and the kinetic energy is converted into hydraulic pressures in the spiral space 15. As mentioned, in the conventional pump, the passage 18 of the impeller 10 has an inlet 19 which is restricted and an outlet 20 which has an increased opening size, giving rise to a ; 10 vortical flow within the passages 18, such flow being iLlustratively shown by arrows c.

. .
Such vortical flow has inlluences upon the actual velocity diagrams a~ indicated by broken lines in Fig. 1. Specifically, while the velocity diagram of the ideal impeller at the outlet is represented by A2B2D2, the actual impeller will have a velocity diagram A2'B2D2, involving a flow slip caused by vortical flow A2A2' . Similar slip also occurs at the inlet, but can be neglected because of the reduced magnitude. Taking into consideration the entire flow slip at the outl~t~
the theoretical head of the actual impeller iæ given by the following 20 expreæsion:
U2Cz~l C05 t 2 U2 (C2 C0S C~ 2 - k2U2) Hth = = (7) g g ' where k2u2 represents the flow slip at the ou1~et, and k2 a coefficient.
As discussed above, it is found that the principal loss head of 25 conventional impellers is caused by a flow slip which occurs as a result of a kind of vortical flow which exists within the passages between adjacent vanes. In order to prevent vortical flows from occurring in the passages formed between adjacent vanes and to assure a uniform flow of fluid along the curved surface of vanes as it is assumed in the 30 ideal impeller, the inventor has proposed a uniform width and depth of passages in Japanese Laid_open Patent Application No. 49-114,101, - which was laid open on October 31, 1974. The width of pasBage as ; termed herein refers to the spacing between the front surface of a vane and the rear surface of an adjacent vane while the depth of passage - 5 refers to the a~ial dimension of a vane. The proposed arrangementsuffered from th~ disadvantage however that the constant cross-sectional area of the passage over the entire leng~ thereof cannot accommodate a flow of fluid having a velocity which increases from the inlet toward - the outlet.
An isnproved impeller has been subsequently proposed in Japanese Utility Model Application No. 50-26, 323, which was filed on February 10, 1975 in which the width of the passage remains constant while the depth decreaæes gradually from the inlet toward the outlet.
The improved impeller e~hibited an excellent efficiency and an actual head which i8 significantly higher than that of the conventional design, but stiLI calmot be fu~ly satisfactory.
;~ Summary of the Invention It is an object of the invention to provide a centrifugal pump which haæ a low loss and produces an increased head. -It is a specific object of the învention to provide an impeller for a centrifugal pump which is substantially ~ree from a vortical flow in its passages defined between adjacent vanes, allowing a fluid flow along the curved surface of the vanes.
In accordance with the invention, there is provided a centrifugal pump comprising a drive shaft, an impeller firmly mounted on the drive shaft, and a body including an inlet path communicating with the impeller a~d also including a volute casing which defines a spiral space around the impeller~ the impeller including a main disc ha~ing a boss which is fitted over the shaft and a plurality of vanes which are disposed at an - 30 equal spacing from each other and axially project Erom at least one side 5.~ ~

of the disc, each vane having a front and a rear surface, part of the rear surface being opposite to and spaced from the boss in surrounding relationship therewith, a fluid passage being formed between the front surface of each vane and the remainder of the rear surface of its 5 adjacent vane and e:~tending from a region around the boss to the outer periphery of the disc, each vane having a constant axial thickness, the most parts of the front surface of a vane and the rear surface of an !
adjacent vane which form together a passage therebetween being segments of circles struck from dif~erent points on the disc and of 10 different radii so that the passage formed therebetween have a constant depth and a width which gradually decreases from said region toward the outer periphery of the disc.
In the centrifugal pump of the invention, the fluid passages formed between adjacent vanes have a cross-sectional area which 15 gradua~ly deerease6 from the inlet toward the outlet. Since the depth of the passage remains constant, the fluid flows along the front surface of the associated vane, whereby the centrifugal force of the vane imparts kinetic energy to the fluid. The occurrence of a vortical flow, cavity or air bubble~ within the fluid passage is substantia~ly eliminated 20 inasmuch as the fluid ilows while filling the passage defined by arcuate surfaces having different radii of curvature. As a consequence, the loss head in the impeller which is caused by a vortieal flow is almost eliminated, providing a pump with an increased head. Fluid containing a significant amount of air or of a relatively high temperature can be 25 pumped without causing a cavitation.
In a preferred embodiment of the invention, the volute casing which defines the spiral space around the impeller has an inner surface which i6 U-shaped in longitudinal section. Admittedly, the theoretical design of a volute casin~ has been very difficult, which prevented the 30 functional analysis of the volute casing. This is why conventional - 7 _ 5~.5 - centrifugal pumps traditionally employ a volute casing which defines a spiral space which is circular in longitudinal section. Such volute -~; casing has been advantageous in providing a com~utation of a fluid flow, as it exits the vane outlets, which assumes a complicate flow pattern as a result of the presence of vortical flows. However, the complicate flow pattern within the casing causes a non-uniform velocit"v profile, resulting in an increased iluid resistance. By contrast, the substantial absence of vortical flow in the fluid as it leaves the vane outlets removes the necessity of a commutation which is provided by 10 the volute casing, the principal objective of which is then to achieve a high efficiency in converting the kinetic energy of the fluid into .: ~
pressures. It is found that the volute casing defining a spiral space which i8 U-shaped in longitudinal section achieves a high conversion ,: , efficiency.
Brief Description of the Drawings - Fig. 1 is a velocity diagram of a centrifugal pump;
Fig. 2 shows the velocity triangles;
Fig. 3 is an elevational section of a conventional centrifugal p~ p;
.
Fig. 4 is an elevational section of the centrifugal pump of the invention;
Fig. 5 is a cro~s section of the pump shown in Fig. 4;
Fig. 6 is a perspective view of the impeller shown in Figs. 4 and 5;
~ig. 7 is a diagrammatic side elevation of the impeller shown 25 in Fig 6; and Figs, 8a and 8b graphically illustrate the comparative performance of a commercially available standard centrifugal pump and the pump OI ~he invention in which the impeller of the former pump is replaced by the impeller of a corresponding slze which is constructed - 30 in accordance with the invention.

zs~

Description of Preferred Embodiment Referring to Figs. 4 to 7 inclusively, there is shown a centrifugal pump constructed according to one embodiment of the ` invention. The pump includes an impeller 30 comprising a main disc 31 having a boss 32, and a plurality of vanes 33 which axially project from the opposite sides of the disc and which are disposed at an equal angular spacing. The vanes disposed on one side of the disc may be circumferentially aligned with or phase displaced from those disposed on the other side. The impeller also includes side boards 34 which are firmly secured to the opposite æides of the disc. It is to be understood however that the vanes 33 may be disposed on only one side of the disc 31 and that the invention is equa~ly applicable to an impeller of semi-open type having no side boards. These are a matter of design, and do not form part of 1~e invention.
Referring to Fig. 73 each vane 33 of the impeller 30 has a circumferential surface 35 which substantially coincides with the outer periphery of the diæc 31, and a front surface 36 and a rear ~urface 37 which are located at an advanced position and at a retarded position, respectively, as viewed in the direction of rotation of the impeller.
Part of the rear surface is disposed opposite to but spaced from the boss 32, thlls partly surrounding it. Fluid passage 38 is formed between l~e fro~ surface 36 of each vane 33 and 1~e rear surface 37 OI
an adjacent vane. The nuid passage 38 extendæ from a vane inlet 39 located around the boss 32 to a vane outlet 40 located along the outer periphery of the impeller 30. The passage 38 has a width W which gradually decreases from the inlet 39 toward the outlet 40. However, the depth D of the passage 38, that is, the thickness of vane 33 correspond~ng to the spacing between the disc 31 and side board 34, remains constant. The all or most parts of the front surface 36 OI
; 30 a particular vane and the rear surface 37 of an adjacent vane, which _ g _ $,-~ !

;; ~ combine together to form a particular passage 38, have different radii of curvature rl, r2 struck from different pointq Pl, P2 . which have coordinates X1, Y1 and X2, Y2 as refere~eed to the origin located at the center of the impeLler and which are disposed on circles struck ;; 5 from the origin and having radii Rl, R2, respectively. Preferred values of these coordinates will be given later, but it is to be noted here that radius of curvature rl is less than radius of curvature r2 while radius Rl is greater than radius R2. It should be noted, however, that the front surface 3¢ of a particular vane and the rear surface 37 of an adjacent vane, which combine together to form a particular pa sage 38, respectively may have at the vicinity of a particular inlet 39 a radius of curvature differe~t from said radii of curvature rl, r2. Side boards 34 are firmly welded to the vanes 33, and are formed with openings 41 which communicate with the inlets 3g of individual passages 38.
The impeller 30 is mou ted on the end of a drive shaft 42 and is secured thereto by a nut 43. The combination of the impeller and the shaft is assembled into a pump body 44, which include~ a pair of inlet paths 45 communicating with the openings 41 and which i~ provided wi~ a volute casing 47 which defines a gradu~lly enlarging æpiral space 4B around the impeller 30. The side boards 34 are formed with ' annular Iip9 48 around the openings 41J and rings 49 having a reduced frictional resistance are placed between the lips 48 and the body 44.
The volute casing 47 has an inner surface which is U-shaped in longitudinal section, and the spiral space 46 has an opening of ~a width which i8 substantially equal t~ the thickness of l;he impeller 30 and has a gradually increasing depth It will be understood that the spiral space 46 leads to a discharge port.
- In operati~n, as the impeller 30 rotates, fluid is admitted into 30 the openings 41 through inlet path 45, and is then forced through 5~

the passageæ 38 into the spiral space 46. The centrifugal force of the vane6 33 impart kinetic energy to the fluid flow. No substantial vortical flow occurs within the passages 38 from the inlets 39 to the outletæ 40 thereof as a result of the gradual decrease in the width combined with the uniform depth of the passages, thus contributing to r ' enhancing the magnetic of the kinetic energy imparted to the flow.
Thifi result has been demonstrated by a comparative performance test using a commercially available standard centrifugal pump of the known type as illustrated in Fig. 3 and the same pump in which the original impeller is replaced by the impeller of the invention, the both pumps being operated under equal operating conditions. The test has been performed generally in conformity to the Japan Industrial Standards (JIS B 8301). Referring to Fig. 8a where the efficiency E, shaft power P, total head H aDd number of revolutions R, all taken on the '~ 15 ordinate, are plotted against the flow rate F shown on the abscissa, .
` the performance of standard pump A is shown in dotted lines while the performance of the corresponding pump A' modified according to the invention is shown in solid line. The test also covered another ,. .
standard pump B supplied by a different manufacturer, and the test ,.
results are shown in dotted lines in Fig. 8b in the same manner as in Fig. 8a, The solid line curves in Fig. 8b show the performance of .
a pump B' which corresponds to the standard pump B, but is modified according to the invention. It will be seen that both the head and the efficiency are significantly improved.
It i8 to be noted that since the pump of ~e invention permits the fluid to flow in a given direction while filling the passage 38 and without producing a vortical ilow, there can be achieved a complete pressure isolation between the inlét path 45 and the spiral space 46, and the negative pressure in the inlet path 45 reaches 700 to 750 mm Hg.
While the elimination of the vortical flow within the impeller 30 has been demonstrated to proudce a significant contribution to the improvement of the performance, it i8 found that the particular configuration of the volute casing, namely, its inner surface which - ~ is U-shaped in longitudinal section, contributes to a further 5 improvement of l~e performance. While no theoretical explanation can be given, it is believed that since the absence of the vortical flow avoids the need for the pump to provide a commutation effect, the conversion of the kinetic energy into the hydraulic pressures of the fluid is the only function required of the pump, which is optimally 10 accompli6hed with the described configuration.
In the embodiment shown, the impeller 30 is of dual inlet type and carries si~ vanes 33 on each side which form six passages 38.
~; While this represents a preferred arrangement, it i8 to be understood ,;::
; that the invention is not limited thereto. In this respect, it wi~l be 15 understood that the nllmber of vanes 33~ ~e diameter and the thickness of the impeller 30 are a matter of design as recognized in the art.
Similarly, the specific size of the fluid passages 38 is to be determined by a design engineer. However, several specific values of the radii of curvature of the fluid passages 38 will be given below for different 20 values of the depth D of the passa~es assuming that the diameter of . .
- the i~npeller i6 conætant. As recognized, the diameter of the impeller relates to the discharge head while the depth D relates to the aperture ;~ or the discharge flow rate. The values given below are for an impeller of dual inlet type having a diameter of 148 ~ and having si~ vanes i.
25 on each side. Reference characters used can be understood by reference to Fig. 7. A~l figures are in millimeters. I

(1) D = 2. 5 (aperture 32) P1 = Xl ' Y1 = 23 26 ~1 53 R1 = 35 P2 X2 ' Y2 = 15, 5 23 r2 = 57 R2 = 30

(2) D = 3 5 (aperture 40) . ~

Pl = Xl Yl = 23 28 rl = 53 Rl = 35 P2 X2 Y2 = 18 23, 5 r2 = 59 R2 = 30

(3) D = 8 (aperture 50) Pl = Xl Yl = 22 28 rl = 50 Rl = 36 P2 = X2 Y2 = 17 24 r2 = 58 R2 = 30

(4) D = 20 (aperture 100) Pl = Xl Yl = 35 20 rl = 65 Rl = 40 P2 = X2 Y2 = 23 19 r2 = 67. S R2 = 30 VVhile the invention has been described in detail with reference 10 to a particular embodiment, it should be understood that it is e2~emplary ` only, and not limitative of the invention. Ratl~er, a number of changes and modifications can be made therein as mention. Therefore, it is intended that the invention be solely defined by the appended claims.

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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A centrifugal pump comprising a drive shaft, an impeller firmly mounted on the drive shaft, and a body including an inlet path communicating with the impeller and also including a volute casing which defines a spiral space around the impeller, the impeller including a main disc having a boss which is fitted over the shaft and a plurality of vanes which are disposed at an equal spacing from each other and axially project from at least one side of the disc, each vane having a front and a rear surface, part of the rear surface being opposite to and spaced from the boss in surrounding relationship therewith, a fluid passage being formed between the front surface of each vane and the remainder of the rear surface of its adjacent vane and extending from a region around the boss to the outer periphery of the disc, each vane having a constant axial thickness, the most parts of the front surface of a vane and the rear surface of an adjacent vane which form together a passage therebetween being segments of circles struck from different points on the disc and of different radii so that the passage formed therebetween have a constant depth and a width which gradually decreases from said region toward the outer periphery of the disc, the front surface of each vane having a radius of curvature which is less than that of the rear surface of the adjacent vane with which it forms the passage and which is struck from a point further spaced from the axis of the impeller than a point from which the radius of curva-ture of the rear surface of said adjacent vane is struck, said boss being positioned substantially completely within all of the circles along which lie the respective vane front surfaces.

2. A centrifugal pump according to Claim 1 in which the volute casing has an inner surface which is U-shaped in longit-udinal section and the spiral space includes an opening of a width which is substantially equal to the thickness of the impeller.

3. A centrifugal pump according to Claim 1 in which the impeller has another plurality of vanes located on the other side of the disc which are disposed symmetrically with the first mentioned vanes.

4. A centrifugal pump according to Claim 1 in which the impeller includes a side board which is rigidly secured to the side of the vanes, the side board having an opening which provides a fluid communication between the inlet path and the fluid passages.

5. A centrifugal pump according to Claim 1 in which said boss is positioned entirely within all of the circles along which lie the respective vane front surfaces.

6. An impeller for a centrifugal pump or the like com-prising: a main disc having a center opening; an annular boss on at least one side of the disc and surrounding the center opening for attaching the impeller to a rotary shaft inserted into the center opening; and means defining a plurality of circumferentially equi-spaced fluid passages on at least one side of the disc having inlets which open at a circular open region at the disc center for admitting fluid into the passages and outlets which open at the disc periphery for discharging fluid from the passages during rotation of the impeller, said fluid passages having a constant depth and a gradually decreas-ing width in the direction from their inlet to their outlet and having an arcuate shape and location effective to impart increasing kinetic energy to the fluid during its flow through the passages while effectively preventing formation of fluid vortices throughout the entire length of the passages from the inlets to the outlets., said means defining said plurality of fluid passages comprising a plurality of similarly shaped vanes disposed in equi-spaced apart relation from one another about at least one side of the disc such that each two spaced-apart vanes define therebetween one fluid passage, each vane having a front surface and a rear surface with respect to the direction of rotation of the impeller, the front surface of each vane being spaced from and opposite the rear surface of an adjacent vane to define therebetween one fluid passage, at least the major part of the front and rear surfaces of the vanes lying along imaginary circles of different radii, and the radii of the front surfaces being less than the radii of the rear surfaces, and wherein said boss is positioned sub-stantially completely within all of the imaginary circles along which lie the vane front surfaces.

7. An impeller according to Claim 6, wherein the entire length of the front and rear surfaces of the vanes lie along said imaginary circles.