Diffuser and centrifugal pump

Abstract

This method suppresses the decrease in centrifugal pump efficiency while also suppressing the occurrence of swivel stall. [Solution] The diffuser 7 is a diffuser positioned adjacent to the impeller in the axial direction of the rotating shaft of the centrifugal pump. The diffuser comprises a flow path forming section 84 and a plurality of vanes 9 that divide a plurality of diffuser flow paths. Each vane has a positive pressure surface 91a to 98a, a negative pressure surface 91b to 98b, and a front end portion 91c to 98c, 95c to 98d. The vanes comprise a plurality of long vanes 91 to 94 and at least one short vane 95 to 98 that is shorter than the long vanes. The long vanes include at least one specific long vane positioned adjacent to the positive pressure surface side of the corresponding short vane. In the axial direction, the front end portion of the short vane is positioned further back than the front end portion of the long vane. The specific long vane has a communication flow path 91d that opens to the positive pressure surface and the negative pressure surface of the specific long vane.

Description

Technical Field

[0001] The present invention relates to a diffuser and a centrifugal pump.

Background Art

[0002] A diffuser for converting the velocity energy imparted to the liquid being handled by the impeller into pressure energy is attached to the discharge side of the impeller of a centrifugal pump. The diffuser has a plurality of vanes. The vanes form a plurality of diffuser flow paths for decelerating the liquid being discharged from the impeller and increasing the pressure. The shape of the vanes (i.e., the shape of the diffuser flow paths) is designed based on the design point of the centrifugal pump. Therefore, when the centrifugal pump is operated at a flow rate smaller than the design point, the flow of the liquid being handled in the diffuser flow paths peels off from the vane surfaces. As the area where peeling occurs increases, stall occurs where the flow in the diffuser flow paths stagnates. Stall does not occur in all the diffuser flow paths provided in the diffuser, but mainly occurs in one diffuser flow path. As a result, the symmetry of the flow of the liquid being handled with respect to the central axis of the centrifugal pump is disrupted, and a force acting in the radial direction of the rotation axis is generated on the centrifugal pump. Stall propagates to adjacent diffuser flow paths so as to swirl in the circumferential direction of the rotation axis over time. Therefore, the direction of the force acting on the centrifugal pump changes, and vibration occurs in the centrifugal pump. Such a phenomenon is called swirling stall.

[0003] In order to prevent such swirling stall, a technique is known in which slits are formed in the vanes to divide the vanes into two in the longitudinal direction of the vanes (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the technology disclosed in Patent Document 1, when a centrifugal pump is operated at a low flow rate, the forced rectification force of the vanes is reduced by the slits, thereby suppressing the occurrence of swirling stall. However, when slits are formed in the vanes, a portion of the vanes is missing, reducing the pressure-boosting function of the vanes and slightly decreasing the efficiency of the centrifugal pump. In recent years, with environmental concerns being raised, there has been a need for a method to suppress the occurrence of swirling stall while suppressing the decrease in the efficiency of centrifugal pumps.

[0006] The present invention aims to suppress the occurrence of swirling stall while suppressing the decrease in efficiency of centrifugal pumps. [Means for solving the problem]

[0007] A diffuser in one embodiment of the present invention is a diffuser arranged adjacent to an impeller in the axial direction of the rotating shaft of a centrifugal pump, wherein in the axial direction, the direction in which the impeller is arranged relative to the diffuser is the forward direction, and the direction in which the diffuser is arranged relative to the impeller is the rear direction, and comprises a flow path forming portion having a cylindrical outer surface, and a plurality of vanes arranged on the outer surface and together with the outer surface, demarcating a plurality of diffuser flow paths through which the liquid discharged from the impeller flows, wherein each of the plurality of vanes comprises a positive pressure surface, a negative pressure surface which is the surface opposite to the positive pressure surface, and a front end portion which is arranged to be continuous with the positive pressure surface and the negative pressure surface, and the plurality of vanes comprises a plurality of long vanes and at least one short vane which is shorter than the long vanes. The plurality of long vanes each include at least one specific long vane, which is positioned adjacent to the short vane corresponding to the long vane on the positive pressure side of the short vane corresponding to the long vane, wherein in the axial direction, the front end of the short vane is positioned further back than the front end of the long vane, and the specific long vane includes a communication channel that opens to the positive pressure surface of the specific long vane and the negative pressure surface of the specific long vane.

[0008] A centrifugal pump in one embodiment of the present invention comprises a motor, a rotating shaft rotated by the motor, an impeller attached to the rotating shaft, and a diffuser according to the above embodiment, which is arranged adjacent to the impeller in the axial direction of the rotating shaft. [Effects of the Invention]

[0009] This invention suppresses the occurrence of swirling stall while suppressing the decrease in efficiency of the centrifugal pump. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view of a centrifugal pump showing an embodiment of the centrifugal pump according to the present invention. [Figure 2] This is a partially schematic, enlarged cross-sectional view of the centrifugal pump shown above. [Figure 3] This is a perspective view of a diffuser, showing an embodiment of the diffuser according to the present invention. [Figure 4] This is a bottom view of the diffuser shown above. [Figure 5] This is a side view of the diffuser shown above. [Figure 6] This is a schematic diagram of the diffuser shown above. [Figure 7] This is a partially enlarged schematic diagram of the diffuser, showing the vicinity of the long vanes and short vanes of the diffuser. [Figure 8] This is a schematic diagram illustrating an example of a design method for the length of the short vanes of the diffuser described above. [Figure 9] This is a schematic diagram showing the flow of the liquid being handled in the diffuser channel formed by the diffuser described above. [Figure 10] This graph shows the measured flow rates at which swirling stall occurs in embodiments, reference examples, and comparative examples of the present invention. [Figure 11] This graph shows the measured pump efficiency at the design point for the embodiments, reference examples, and comparative examples of the present invention. [Figure 12]A graph showing the simulation analysis results of the flow rate of the diffuser flow path in the design point of the reference example of the present invention. [Figure 13] A graph showing the simulation analysis results of the flow rate of the diffuser flow path in the design point of the embodiment of the present invention. [Figure 14] A graph showing the simulation analysis results of the flow rate of the diffuser flow path in the design point of another reference example of the present invention. [Figure 15] A graph showing the simulation analysis results of the flow rate of the diffuser flow path in the design point of another embodiment of the present invention. [Figure 16] A graph showing the simulation analysis results of the flow rate of the diffuser flow path in the design point of yet another embodiment of the present invention. [Figure 17] A graph showing the simulation analysis results of the flow rate of the diffuser flow path in the design point of yet another reference example of the present invention. [Figure 18] A graph showing the simulation analysis results of the flow rate of the diffuser flow path at 30% of the flow rate of the embodiment of the present invention. [Figure 19] A graph showing the simulation analysis results of the flow rate of the diffuser flow path at 30% of the flow rate of another embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0011] Embodiments of a diffuser and a centrifugal pump according to the present invention will be described below. In the following description, the respective drawings are referred to as appropriate. In each drawing, the same members and elements are denoted by the same reference numerals, and redundant explanations are omitted. Also, the dimensional ratios of the respective elements may be exaggerated for the sake of convenience of explanation and are not limited to the ratios shown in each drawing.

[0012] In the following description, as an example of the centrifugal pump according to the present invention, a submerged pump will be described. The submerged pump is attached to a storage tank in which a liquefied gas is stored, and pumps the liquefied gas from the storage tank to the outside. That is, the submerged pump is an example of the centrifugal pump according to the present invention, and the liquefied gas is an example of the liquid to be handled in the present invention.

[0013] In the following description, "downward" is the direction of gravity and is an example of the forward direction in the present invention. "Upward" is the opposite direction of downward and is an example of the backward direction in the present invention.

[0014] ●Centrifugal pump● ●Configuration of centrifugal pump FIG. 1 is a schematic cross-sectional view of a centrifugal pump showing an embodiment of the centrifugal pump according to the present invention. The figure omits the illustration of a part of the cross-section of the centrifugal pump 1.

[0015] The centrifugal pump 1 discharges the liquid to be handled stored in a storage tank (not shown; the same applies hereinafter) into the pump column C. The centrifugal pump 1 is housed in the lower part of the pump column C extending from the ceiling of the storage tank into the storage tank and is immersed in the liquid to be handled. The configuration of the centrifugal pump 1 is common to that of a known submerged pump except for the configuration of the diffuser 7 (described later). The centrifugal pump 1 includes an outer casing 2, a motor 3, a rotating shaft 4, two inner casings 5 (one is not shown; the same applies hereinafter), two impellers 6 (one is not shown; the same applies hereinafter), and two diffusers 7 (one is not shown; the same applies hereinafter). That is, the centrifugal pump 1 is a two-stage centrifugal pump having two impellers 6. That is, the inner casing 5, the impeller 6, and the diffuser 7 constitute the first-stage pump section M1, and the inner casing, the impeller, and the diffuser not shown constitute the second-stage pump section (not shown; the same applies hereinafter). The second-stage pump section is arranged above the first-stage pump section M1.

[0016] The external housing 2 houses the motor 3, rotating shaft 4, internal housing 5, impeller 6, and diffuser 7. The external housing 2 has a roughly cylindrical shape that follows the vertical direction. The external housing 2 is equipped with an inlet 21 and an outlet (not shown; the same applies hereinafter). The lower end of the external housing 2 is tapered in diameter, forming the inlet 21.

[0017] In the following explanation, "upstream side" refers to the upstream side of the flow of the handling fluid within the external enclosure 2, and "downstream side" refers to the downstream side of the flow of the handling fluid within the external enclosure 2.

[0018] Motor 3 is driven at a predetermined drive voltage and drive frequency to rotate the impeller 6. Motor 3 comprises a rotor 31 and a stator 32. Motor 3 is a known motor comprising a rotor 31 attached to a rotating shaft 4, and a stator 32 that rotates the rotor 31.

[0019] The rotating shaft 4 rotates due to the rotation of the motor 3, transmitting rotational power to the impeller 6. The shape of the rotating shaft 4 is cylindrical, extending in the vertical direction. The lower part 4a of the rotating shaft 4 extends downward from the motor 3 into the internal housing 5.

[0020] In the following explanation, "axial direction" refers to the axial direction (up and down direction) of the rotation axis 4.

[0021] Figure 2 is a partially schematic enlarged cross-sectional view of the centrifugal pump 1. The diagram shows the flow of the liquid being handled with arrows. In the following explanation, Figure 1 will be referred to as appropriate along with Figure 2.

[0022] The internal housing 5 holds the diffuser 7 and, together with the diffuser 7, demarcates the flow path through which the liquid discharged from the impeller 6 flows. The internal housing 5 has a roughly double-tube shape, with the upper end of a cylinder that runs vertically folded inward. That is, the internal housing 5 comprises a cylindrical outer cylinder portion 51, a cylindrical inner cylinder portion 52 located inside the outer cylinder portion 51, and a ring-shaped connecting portion 53 that connects the upper end of the outer cylinder portion 51 and the upper end of the inner cylinder portion 52. The internal housing 5 is housed in the external housing 2 and is attached to the external housing 2.

[0023] The impeller 6 imparts kinetic energy to the fluid being handled, which is drawn in from below, and discharges the fluid radially outward. The impeller 6 is housed in the external casing 2 and is attached to the lower part 4a of the rotating shaft 4. In the axial direction, the impeller 6 is positioned above the suction port 21.

[0024] The diffuser 7 slows down the fluid being handled discharged from the impeller 6 and increases its pressure, thereby converting the kinetic energy imparted to the fluid by the impeller 6 into pressure energy. The diffuser 7 is mounted on the internal housing 5 and is positioned axially above the impeller 6, adjacent to the impeller 6. In other words, the diffuser 7 is a so-called axial-type diffuser. The specific configuration of the diffuser 7 will be described later.

[0025] ●Diffuser● ● Diffuser configuration Figure 3 is a perspective view of the diffuser 7, showing an embodiment of the diffuser (diffuser 7) according to the present invention. Figure 4 is a bottom view of the diffuser 7. Figure 5 is a side view of the diffuser 7. In the following explanation, Figures 1 and 2 will be referred to as appropriate, along with Figures 3 to 5.

[0026] The diffuser 7 is made of a metal, such as an aluminum alloy. The diffuser 7 comprises a main body 8 and a number of vanes 9 (for example, 8).

[0027] The main body 8 has a bottomed cylindrical shape. The main body 8 comprises a bottom 81, an insertion hole 82, a plurality (for example, four) of rectifier plates 83 (see Figure 2; the same applies hereafter), and a cylindrical portion 84.

[0028] In the following explanation, "radial direction" refers to the direction along the diameter (radius) of the main body 8, and "circumferential direction" refers to the direction along the circumference of the main body 8.

[0029] The bottom portion 81 is roughly disc-shaped. The central part of the bottom portion 81 protrudes upward in a frustoconical shape, with a through hole 82 located in its center. A portion of the bottom portion 81 protrudes upward in a plate-like shape, forming a flow straightening plate 83.

[0030] The outer edge of the bottom portion 81 protrudes upward in a cylindrical shape, forming a cylindrical portion 84. The cylindrical portion 84 has a cylindrical outer surface 84a. A part of the outer surface 84a protrudes radially, forming a vane 9. The cylindrical portion 84 is an example of a flow path forming portion in the present invention.

[0031] Figure 6 is a schematic unfolded diagram of the diffuser 7. The figure schematically shows the diffuser 7 unfolded along the circumferential direction. In the following explanation, Figures 1 to 5 will be referred to as appropriate, along with Figure 6.

[0032] The vane 9, together with the outer cylindrical portion 51 (see Figure 2; the same applies hereafter) and the cylindrical portion 84, defines the diffuser flow path Ch. The vane 9 comprises a plurality (e.g., four) of long vanes 91, 92, 93, 94 and a plurality (e.g., four) of short vanes 95, 96, 97, 98.

[0033] In a downward view, the long vanes 91-94 and short vanes 95-98 are arranged alternately in a clockwise direction in numerical order. That is, in the circumferential direction, the long vanes 91-94 and short vanes 95-98 are arranged alternately at equal intervals on the outer surface 84a of the cylindrical portion 84. In other words, one long vane 91-94 is positioned between the short vanes 95-98 that are closest to each other in the circumferential direction.

[0034] Figure 7 is a partially enlarged schematic diagram of the diffuser 7, showing the vicinity of the long vanes 91 and short vanes 98. The figure schematically shows a portion of the diffuser 7 when it is unfolded circumferentially. The flow of the handling fluid is indicated by arrows. In the following description, Figures 3 to 6 will be referred to as appropriate, along with Figure 7.

[0035] The long vane 91 has a substantially arc-shaped plate form that extends from the lower end to the upper end of the cylindrical portion 84. The long vane 91 comprises a positive pressure surface 91a, a negative pressure surface 91b, an end surface 91c, a communication channel 91d, a first portion 91e, and a second portion 91f.

[0036] In a downward view, the positive pressure surface 91a is a surface oriented in a counterclockwise direction. The negative pressure surface 91b is the surface opposite to the positive pressure surface 91a. In a radial view, the shape of the positive pressure surface 91a is concave. In a radial view, the shape of the negative pressure surface 91b is convex, substantially following the shape of the positive pressure surface 91a. The end face 91c is the surface located furthest upstream of the long vane 91. The shape of the end face 91c is parallel to the radial direction and curved in a radial view. The end face 91c is positioned between the positive pressure surface 91a and the negative pressure surface 91b, and is continuous with both the positive pressure surface 91a and the negative pressure surface 91b. The end face 91c is an example of the "front end of the long vane" in this invention.

[0037] The communication channel 91d is a flow path for the liquid being handled, communicating with a space located on the positive pressure side 91a of the long vane 91 (first space) and a space located on the negative pressure side 91b of the long vane 91 (second space). The shape of the communication channel 91d is a slit shape that is parallel to the circumferential direction. That is, the communication channel 91d opens to the positive pressure side 91a and the negative pressure side 91b. The communication channel 91d is located at the front of the long vane 91. In the radial direction, the communication channel 91d is arranged to traverse the long vane 91 from the inner end to the outer end. That is, the communication channel 91d is arranged to divide the long vane 91 into two parts, with the communication channel 91d as the boundary. In other words, the long vane 91 is divided into a first part 91e located below (upstream of) the communication channel 91d, and a second part 91f located above (downstream of) the communication channel 91d. The communication channel 91d includes an inlet 91g located on the positive pressure surface 91a (open), and an outlet 91h located on the negative pressure surface 91b (open).

[0038] The communication channel 91d (at least the outlet 91h) in the long vane 91 is located within the range from the upstream limit position P1 to the downstream limit position P2. In this embodiment, the outlet 91h of the communication channel 91d passes through the lowest end (bottom surface 98d: described later) of the short vane 98 corresponding to the long vane 91, and is located below the imaginary line C1 along the circumferential direction, adjacent to the imaginary line C1. In other words, the outlet 91h is located at a position adjacent to the position where the communication channel 91d is located in the axial direction, and adjacent in the circumferential direction. The imaginary line C1 is an example of a specific imaginary line in the present invention.

[0039] The "upstream limit position P1" is the upstreammost position among the positions where the flow of the liquid being handled F2, which has passed through the communication channel 91d, can merge with the flow of the liquid being handled F1 that flows into the diffuser channel Ch1. Here, "the position where flow F2 can merge with flow F1" means the position where the majority of flow F2 (for example, 80% or more) can flow into the diffuser channel Ch1 together with flow F1.

[0040] The "downstream limit position P2" is the furthest downstream position among the positions upstream of the vortex V (described later; the same applies hereafter). Here, "a position upstream of the vortex V" means a position where the flow F3 of the liquid being handled, based on the vortex V, does not directly flow into the communication channel 91d.

[0041] In this invention, the communication channel 91d (particularly the outlet 91h) in the long vane 91 is preferably located near the position P3 closest to the end face 98c of the corresponding short vane 98, and more preferably located at position P3. Here, "located at position P3" means that the outlet 91h is located such that it includes position P3.

[0042] The configuration of the long vanes 92 to 94 is the same as that of the long vane 91. Therefore, in the following description, a detailed explanation of each of the long vanes 92 to 94 will be omitted. The long vane 92 comprises a positive pressure surface 92a, a negative pressure surface 92b, an end face 92c, a communication channel 92d, a first part 92e, and a second part 92f. The long vane 93 comprises a positive pressure surface 93a, a negative pressure surface 93b, an end face 93c, a communication channel 93d, a first part 93e, and a second part 93f. The long vane 94 comprises a positive pressure surface 94a, a negative pressure surface 94b, an end face 94c, a communication channel 94d, a first part 94e, and a second part 94f.

[0043] The shape of the short vane 95 is a roughly arc-shaped plate extending from the lower end to the upper end of the cylindrical portion 84. The short vane 95 has a shape as if the long vane 91 had been cut upward from the end face 91c of the long vane 91 at a predetermined length position (position of the imaginary line C1). Here, the "predetermined length position" is the position where the communication channel 91d is located. Therefore, the shape of the short vane 95 is the same as the shape of the second portion 91f of the long vane 91. The short vane 95 comprises a positive pressure surface 95a, a negative pressure surface 95b, an end face 95c, and a lower surface 95d.

[0044] In a downward view, the positive pressure surface 95a is the surface oriented counterclockwise. The negative pressure surface 95b is the surface opposite to the positive pressure surface 95a. In a radial view, the shape of the positive pressure surface 95a is concave. In a radial view, the shape of the negative pressure surface 95b is convex, substantially following the positive pressure surface 95a. The end face 95c is the surface located furthest upstream of the short vanes 95. The end face 95c is positioned between the positive pressure surface 95a and the bottom surface 95d, and is continuous with both the positive pressure surface 95a and the bottom surface 95d. The shape of the end face 95c is a curved surface parallel to the radial direction. The bottom surface 95d is the surface oriented downward. The shape of the bottom surface 95d is a planar surface parallel to the circumferential and radial directions. The lower surface 95d is positioned between the negative pressure surface 95b and the end surface 95c, and is continuous with the negative pressure surface 95b and the end surface 95c. In the axial direction, the end surface 95c and the lower surface 95d are positioned above the end surfaces 91c to 94c. The end surface 95c and the lower surface 95d are examples of the "front end portion of the short vane" in this invention.

[0045] Figure 8 is a schematic diagram of the diffuser 7, illustrating an example of a design method for the positions of the end face 95c and the bottom face 95d (i.e., the length of the short vane 95). The dashed lines in the figure indicate the positions of the end face 95c and the bottom face 95d of the short vane 95. In the following explanation, Figures 3 to 7 will be referred to as appropriate, along with Figure 8.

[0046] The positions of the end face 95c and the bottom face 95d (i.e., the length of the short vane 95) are designed based on the ratio of the second length L2 to the first length L1 (L2 / L1: hereinafter referred to as the "throat ratio").

[0047] "First length L1" is the radial length of the inlet Chi of the diffuser flow path Ch (diffuser flow path Ch2) located on the negative pressure surface 95b side of the short vane 95. "Inlet Chi" is the narrowest part of the diffuser flow path Ch. The cross-sectional area perpendicular to the direction of flow of the liquid being handled in the diffuser flow path Ch is smallest at inlet Chi and increases as the position of the cross-sectional area moves downstream. When the bottom surface 95d is located upstream of the end surface 91c, the first length L1 is the length of the imaginary line segment connecting the end surface 91c and the negative pressure surface 95b by the shortest distance. When the bottom surface 95d is located downstream of the end surface 91c, the first length L1 is the length of the imaginary line segment connecting the positive pressure surface 91a and the boundary between the negative pressure surface 95b and the bottom surface 95d by the shortest distance. The first length L1 changes depending on the position of the end surface 95c.

[0048] The "second length L2" is the length of the inlet Chi of the diffuser flow path Ch (diffuser flow path Ch3) located on the positive pressure surface 95a side of the short vane 95. The second length L2 is the length of the imaginary line segment connecting the end face 95c and the negative pressure surface 92b by the shortest distance. The second length L2 changes depending on the position of the end face 95c.

[0049] The throat ratio increases (greater than "1") as the positions of the end face 95c and bottom face 95d of the short vane 95 move downstream, reaching a maximum when these positions are at a predetermined position (hereinafter referred to as the "maximum position"), and decreasing as these positions move downstream from the maximum position. The positions of the end face 95c and bottom face 95d should be such that the throat ratio is "1" or greater and the required static pressure capacity for the diffuser 7 can be maintained. Preferably, these positions should be above the position of the end face 92c of the long vane 92 corresponding to the short vane 95, and within the range up to the maximum position, and more preferably at the maximum position.

[0050] The configuration of short vanes 96-98 is the same as that of short vane 95. Therefore, the following description omits specific details for each of the short vanes 96-98. Short vane 96 comprises a positive pressure surface 96a, a negative pressure surface 96b, an end surface 96c, and a bottom surface 96d. Short vane 97 comprises a positive pressure surface 97a, a negative pressure surface 97b, an end surface 97c, and a bottom surface 97d. Short vane 98 comprises a positive pressure surface 98a, a negative pressure surface 98b, an end surface 98c, and a bottom surface 98d.

[0051] Of the vanes 9, the long vanes 91 to 94 correspond to the short vanes 95 to 98 that are positioned adjacent to each other on the negative pressure surfaces 91b to 94b. Therefore, the long vanes 91 to 94 are positioned adjacent to the corresponding short vanes 95 to 98 on the positive pressure surfaces 95a to 98a of the corresponding short vanes 95 to 98. That is, long vane 91 corresponds to short vane 98, long vane 92 corresponds to short vane 95, long vane 93 corresponds to short vane 96, and long vane 94 corresponds to short vane 97. In other words, long vanes 91 to 94 are examples of specific long vanes in the present invention.

[0052] The main body 8 is attached to the inner housing 5 with the lower part 4a of the rotating shaft 4 inserted through the insertion hole 82. At this time, the outer cylinder portion 51 of the inner housing 5 is positioned radially outward relative to the cylindrical portion 84 so as to face the outer circumferential surface 84a of the cylindrical portion 84. That is, in the circumferential direction, the space between adjacent long vanes 91-94 and short vanes 95-98 is covered by the outer cylinder portion 51. As a result, the opposing positive pressure surfaces 91a-98a and negative pressure surfaces 91b-98b, the outer circumferential surface 84a, and the outer cylinder portion 51 form a diffuser flow path Ch that slows down and increases the pressure of the liquid discharged from the impeller 6. In other words, the vanes 9, together with the inner housing 5 and the outer circumferential surface 84a of the cylindrical portion 84, define the diffuser flow path Ch. In the following description, when each of the diffuser flow paths Ch is particularly distinguished, the symbols "1" to "8" are appended to the end of their names.

[0053] Diffuser channel Ch1 is located between the long vane 91 and the short vane 98. Diffuser channel Ch2 is located between the long vane 91 and the short vane 95. Diffuser channel Ch3 is located between the long vane 92 and the short vane 95. Diffuser channel Ch4 is located between the long vane 92 and the short vane 96. Diffuser channel Ch5 is located between the long vane 93 and the short vane 96. Diffuser channel Ch6 is located between the long vane 93 and the short vane 97. Diffuser channel Ch7 is located between the long vane 94 and the short vane 97. Diffuser channel Ch8 is located between the long vane 94 and the short vane 98.

[0054] For each of the long vanes 91-94 and short vanes 95-98, the diffuser flow path Ch located on the positive pressure side 91a-98a functions as a positive pressure side diffuser flow path. For each of the long vanes 91-94 and short vanes 95-98, the diffuser flow path Ch located on the negative pressure side 91b-98b functions as a negative pressure side diffuser flow path. That is, for example, diffuser flow path Ch2 functions as a positive pressure side diffuser flow path for the long vane 91 and as a negative pressure side diffuser flow path for the short vane 95. In other words, the diffuser flow path Ch includes both a positive pressure side diffuser flow path and a negative pressure side diffuser flow path.

[0055] Furthermore, the connecting portion 53 of the internal housing 5 is positioned above the vane 9 and the cylindrical portion 84, and radially, the inner cylinder portion 52 of the internal housing 5 is positioned inward of the cylindrical portion 84. As a result, the inner cylinder portion 52, the connecting portion 53, and the cylindrical portion 84 form a flow path that guides the liquid being handled, which has flowed out from the diffuser flow path Ch, to the inside of the cylindrical portion 84. In addition, the bottom portion 81, the rectifier plate 83, and the inner cylinder portion 52 form a flow path that guides the liquid being handled, which has been guided to the inside of the cylindrical portion 84, to the second-stage pump section.

[0056] The configuration of the second-stage pump section is the same as that of the first-stage pump section M1. Therefore, the description of the internal housing, impeller, and diffuser (not shown) that constitute the second-stage pump section is omitted.

[0057] ● Operation of the centrifugal pump Next, the operation of the centrifugal pump 1 will be described below, focusing on the flow of the handled fluid in the diffuser 7 (particularly near the long vanes 92 and short vanes 95). Figures 1 to 8 will be referred to as appropriate in the following description.

[0058] Figure 9 is a schematic diagram illustrating the flow of the liquid being handled in the diffuser channel Ch. The diagram shows the flow of the handling fluid with arrows. The diagram schematically shows a portion of the diffuser 7 in a state where it is unfolded along the circumferential direction.

[0059] The handling fluid drawn into the impeller 6 is discharged radially outward from the impeller 6. The handling fluid discharged from the impeller 6 has its flow direction changed upward by the external housing 2 and flows into each diffuser flow path Ch while swirling circumferentially.

[0060] When the centrifugal pump 1 is operating at the design point, the inflow angle "α" of the liquid being handled flowing into the diffuser flow path Ch is adjusted to be close to the appropriate design angle (for example, α ≈ β1: a range where the angle of attack is a few degrees) relative to the inlet angle "β1" of the long vanes 91 to 94. As mentioned above, the shape of the short vane 95 is the same as the shape of the second part 92f of the long vane 92. Therefore, the inlet angle "β2" of the short vanes 95 to 98 is slightly larger (for example, about 1° to 10°) than the inlet angle "β1" of the long vanes 91 to 94.

[0061] The handling fluid flows into diffuser channels Ch2 and Ch3. As mentioned above, the long vane 91 is positioned on the negative pressure side 95b of the short vane 95, and the long vane 92 is positioned on the positive pressure side 95a. Therefore, the inlet Chi of the diffuser channel Ch3 on the positive pressure side 95a of the short vane 95 is larger than the inlet Chi of the diffuser channel Ch2 on the negative pressure side 95b. As a result, the flow rate of the handling fluid flowing into the diffuser channel Ch3 is greater than the flow rate of the handling fluid flowing into the diffuser channel Ch2. In other words, the diffuser 7 is designed so that the flow rate of the handling fluid flowing into the diffuser channel Ch3 is greater than the flow rate of the handling fluid flowing into the diffuser channel Ch2 (a high flow rate).

[0062] A portion of the handling fluid also flows into the connecting channel 92d. The flow of handling fluid F2 that flows out from the outlet 92h upstream of the inlet Chi of the diffuser channel Ch3 merges with the flow of handling fluid F1 that flows into the diffuser channel Ch3 upstream. Therefore, the flow rate of the handling fluid flowing into the diffuser channel Ch3 increases by the amount of this merger. The handling fluid that flows into the diffuser channels Ch2 and Ch3 is decelerated and pressurized as it passes through the diffuser channels Ch2 and Ch3. As shown in Figure 2, the handling fluid that has passed through the diffuser channels Ch2 and Ch3 is guided into the respective channels, which are composed of the inner cylinder section 52, the connecting section 53, the bottom section 81, and the cylindrical section 84, and introduced into the second-stage pump section. The handling fluid discharged from the second-stage pump section is discharged into the pump column C from the discharge port and flows upward within the pump column C.

[0063] The inlet 92g of the connecting channel 92d opens onto the positive pressure surface 92a. Therefore, a portion of the handling fluid flowing into the diffuser channel Ch4 flows into the connecting channel 92d. As a result, the effect of increasing the pressure of the handling fluid in the diffuser channel Ch4 may be slightly reduced. Also, the flow of the handling fluid flowing into the diffuser channel Ch3 may be slightly disturbed. However, the diffuser channel Ch3 is designed to have a large flow rate. Therefore, the influence of the handling fluid flow F2 from the connecting channel 92d on the handling fluid flow F1 flowing into the diffuser channel Ch3 is reduced. As a result, the pump efficiency of centrifugal pump 1 is improved compared to the pump efficiency of a conventional centrifugal pump equipped only with conventional vanes without a connecting channel (hereinafter referred to as "conventional pump A") and a conventional centrifugal pump equipped only with vanes (long vanes) with a connecting channel (hereinafter referred to as "conventional pump B").

[0064] Next, when the centrifugal pump 1 is operating at a flow rate lower than the design point, the inflow angle "α" of the liquid being handled into the diffuser flow path Ch becomes smaller, and the difference between the inflow angle "α" and the inlet angles "β1" and "β2" becomes larger (the angle of attack becomes larger). As a result, in the region in contact with the negative pressure surfaces 92b and 95b, separation of the liquid being handled occurs, starting from the upstream end of the negative pressure surfaces 92b and 95b.

[0065] Generally, when the angle of attack increases and separation occurs, the area where separation occurs (hereinafter referred to as the "separation area") increases over time. At this time, downstream of the diffuser channel Ch where separation is occurring, a phenomenon occurs that resembles a backflow of some of the handling fluid that has flowed out from the adjacent diffuser channel Ch located on the negative pressure surface 91b~98b side relative to the diffuser channel Ch where separation is occurring. At this time, a vortex V is formed downstream of the diffuser channel Ch due to the backflow. Ultimately, the diffuser channel Ch can become blocked by the separation area, and a stall may occur where the flow in the diffuser channel Ch becomes stagnant.

[0066] In this embodiment, the flow rate of the handling liquid flowing into the diffuser channel Ch3 is increased by the short vane 95 and the connecting channel 92d. That is, the flow of the handling liquid in the diffuser channel Ch3 is strong. Therefore, even if delamination occurs in the diffuser channel Ch3, the delamination area does not increase, and the diffuser channel Ch3 is not blocked by the delamination area. In addition, the flow of the handling liquid that has flowed out of the diffuser channel Ch3 downstream of the diffuser channel Ch3 becomes stronger. Therefore, the inflow (backflow) of the handling liquid that has flowed out of the diffuser channel Ch3 downstream of the diffuser channel Ch2 is also suppressed. As a result, in the diffuser channel Ch2, the delamination area does not increase to the point of blocking the diffuser channel Ch2, and the diffuser channel Ch2 is not blocked by the delamination area.

[0067] Furthermore, a vortex V is formed in the diffuser channel Ch3 due to backflow. The position of this vortex V is not significantly affected by increases or decreases in the flow rate of the centrifugal pump 1, and remains approximately the same regardless of the flow rate. As mentioned above, the communication channel 92d is located upstream of the vortex V. Therefore, the flow F3 of the liquid being handled, based on the vortex V, does not flow directly into the communication channel 91d. Consequently, the communication channel 91d is not blocked by flow F3, and flow F2 is not obstructed by flow F3.

[0068] Furthermore, the handling fluid flowing out from the communication channel 92d rectifies a portion of the separation region, suppressing its enlargement. As a result, the size of the separation region is kept to a size that does not cause stall. Therefore, the occurrence of swirling stall is suppressed. At this point, a portion of the handling fluid collides with the end face 95c of the short vane 95. At this time, the fluid pressure around the end face 95c decreases. Therefore, the closer the outlet 92h is to the end face 95c, the easier it is for the handling fluid to flow out of the communication channel 92d and to flow into the communication channel 92d.

[0069] ●Examples● Next, embodiments of the present invention will be described below, along with reference examples and comparative examples. In each of the following embodiments, some components of the pump device differ from those of centrifugal pump 1. Therefore, the reference numerals assigned to each component are omitted, except for the diffuser flow path Ch. ●Examples 1-3 (Comparison of flow rate at which swirling stall occurs and pump efficiency) Figure 10 is a graph showing the measured flow rates at which swirling stall occurs in embodiments, reference examples, and comparative examples of the present invention. Figure 11 is a graph showing the measured pump efficiency at the design point for the embodiments, reference examples, and comparative examples of the present invention. In Figure 10, the "flow rate at which a swing stall occurs" is the ratio of the flow rate at the design point to the flow rate at which a swing stall occurs, with the flow rate at the design point being set to 100%.

[0070] In these figures, in Examples 1-3, the number of short vanes is set to one, two, and three. In the axial direction, the position of the lower surface of the short vanes is set to the same position as 11 mm (throat ratio: 2.61) from the lowest end of the long vanes (the upstream end of the long vanes: the lower end of the cylindrical part of the diffuser). Here, the width of the communication channel is set to 2 mm, and the length of the cylindrical part in the axial direction is set to 76 mm. In the axial direction, the position of the upper end of the communication channel is set to the same position as the position of the lower surface of the short vanes. In Reference Examples 1-4 and 8, the number of short vanes is set to one, two, three, four, and eight. No communication channel is provided. In Comparative Example 1, neither short vanes nor a communication channel are provided. That is, the pump device of Comparative Example 1 is the same as conventional pump A. In Comparative Example 2, no short vanes are provided. The width of the communication channel is set to 2 mm. That is, the pump device of Comparative Example 2 is the same as conventional pump B.

[0071] As shown in Figure 10, in Examples 1 and 2, swirling stall did not occur even when the flow rate was 0% (the discharge side of the pump device was shut off). In other words, swirling stall did not occur. In Example 3, the flow rate at which swirling stall occurred was reduced to 2%. On the other hand, in Comparative Example 1, swirling stall occurred when the flow rate was 50% or less. In Comparative Example 2, the flow rate at which swirling stall occurred was reduced compared to Comparative Example 1, but swirling stall occurred when the flow rate was 44% or less.

[0072] Reference Examples 1-4 and 8 examine the effect of the number of short vanes on the flow in the diffuser channel Ch. As shown in Reference Examples 1-4, with 1 to 3 short vanes, the flow rate at which swirling stall occurs was reduced to 8%. Even with 4 short vanes, the flow rate at which swirling stall occurs was reduced to 14%. On the other hand, as shown in Reference Example 8, when there were 8 short vanes, i.e., all vanes were short vanes, swirling stall occurred at a flow rate near the design point (90%). These phenomena are presumed to occur because, as the number of short vanes increases, the flow rate at the design point increases, and when the number of short vanes exceeds half of the total number of vanes, the design point changes to a large flow rate corresponding to the short vanes (the influence of short vanes on the flow of the handled fluid becomes more dominant than the influence of long vanes). Therefore, in order to suppress swirling stall, it is preferable that the number of short vanes be less than or equal to half of the total number of vanes.

[0073] As shown in Figure 11, in Examples 1-3, the pump efficiency increased as the number of short vanes increased, exceeding the pump efficiency of Comparative Examples 1-2. In Reference Examples 1-4 and 8, the pump efficiency increased as the number of short vanes increased up to three, and then decreased as the number of short vanes increased thereafter. The pump efficiency increased up to four short vanes, exceeding the pump efficiency of Comparative Examples 1-2. The presence of a connecting flow path in the vanes slightly reduced the pump efficiency.

[0074] These results show that, by combining short vanes and a connecting flow path, the present invention was able to suppress the decrease in centrifugal pump efficiency and the occurrence of swirling stall compared to conventional pumps A and B.

[0075] ●Reference Examples 1-8 (Comparison of Diffuser Flow Rates: Design Points) Figure 12 is a graph showing the simulation analysis results of the flow rate of each diffuser flow path at the design point of the reference examples of the present invention (Reference Examples 1 to 8). For ease of explanation, the diagram labels each diffuser channel "Ch1~Ch8" (the same applies to Figures 13~19). The diagram shows the position of the short vanes with thick dashed lines (the same applies to Figures 13~19). The diagram also shows the results of Comparative Example 1 for comparison. In the diagram, the vertical axis represents the flow rate of the handled liquid passing axially through the cross section along the circumferential direction of each diffuser channel Ch1~Ch8 at the downstream end of each diffuser channel Ch1~Ch8 (the same applies to Figures 13~19). In Reference Examples 5~7, the number of short vanes is set to three types: 5, 6, and 7. No connecting channels are provided.

[0076] As shown in Figure 12, when the number of short vanes is four or less (when the number of short vanes is less than half the total number of vanes), a tendency was observed in which the flow rates of diffuser channels Ch1, Ch3, Ch5, and Ch7 located on the positive pressure side of the short vanes increased, and the flow rates of diffuser channels Ch2, Ch4, Ch6, and Ch8 located on the negative pressure side of the short vanes decreased. On the other hand, when the number of short vanes is five or more (when the number of short vanes is greater than the total number of vanes), variability was observed in the aforementioned tendency. This result indicates that for controlling the flow rates of diffuser channels Ch1 to Ch8, it is preferable that the number of short vanes be less than half the total number of vanes.

[0077] ●Examples 1-3 (Comparison of diffuser flow rates: design point) Figure 13 is a graph showing the simulation analysis results of the flow rate of each diffuser flow path at the design points of Embodiments 1 to 3 of the present invention. The figure also shows the results for Reference Examples 1-3 for comparison.

[0078] As shown in Figure 13, the flow rates of the diffuser channels Ch3, Ch5, and Ch7 in Examples 1-3 were higher than those of the diffuser channels Ch3, Ch5, and Ch7 in Comparative Examples 1-3. In other words, this result indicates that the flow rates of the diffuser channels Ch3, Ch5, and Ch7 located on the positive pressure side of the short vanes are increased by arranging the communication channels between the long vanes and the short vanes.

[0079] ●Reference Example 9 (Comparison of flow rates in diffuser channels: Design point) Figure 14 is a graph showing the simulation analysis results of the flow rate of each diffuser flow path at the design point of a different reference example of the present invention (Reference Example 9). The figure also shows the results of Reference Example 2 for comparison. In Reference Example 9, there are two short vanes, and they are arranged adjacent to each other.

[0080] As shown in Figure 14, the flow rate in the diffuser channel Ch5 located between the short vanes and the long vanes increased compared to the same flow rate in Reference Example 2, but the flow rate in the diffuser channel Ch4 located between the short vanes decreased compared to the same flow rate in Reference Example 2. This result indicates that the flow rate in a specific diffuser channel Ch5 increases even when two short vanes are placed adjacent to each other, and that it is preferable to place one long vane between two short vanes.

[0081] ●Example 4 (Comparison of flow rates in diffuser channels: design point) Figure 15 is a graph showing the simulation analysis results of the flow rate of each diffuser flow path at the design point of another embodiment of the present invention (Embodiment 4). The figure also shows the results of Example 3 for comparison. In Example 4, three short vanes are arranged alternately with long vanes. The outlet of the communication channel is located downstream (position P3) than in Example 3.

[0082] As shown in Figure 15, the flow rates of the diffuser channels Ch3, Ch5, and Ch7 located on the positive pressure side of the short vane increased slightly when the outlet of the connecting channel was positioned closest to the lower end of the corresponding short vane. This result indicates that the flow rates of the diffuser channels Ch3, Ch5, and Ch7 located on the positive pressure side of the short vane increase as the outlet of the connecting channel approaches position P3.

[0083] ●Examples 5-10 (Comparison of diffuser flow rates: design point) Figure 16 is a graph showing the simulation analysis results of the flow rate of each diffuser flow path at the design point of yet another embodiment of the present invention (Embodiments 5 to 10). The figure also shows the results of Examples 1 and 3 for comparison. In Examples 5 to 7, there is one short vane. In Examples 8 to 10, there are three short vanes. In Examples 5 to 10, the lower surface of the short vane is positioned in the same location as the long vane, at 5.5 mm (throat ratio: 1.83), 22 mm (throat ratio: 2.38), and 33 mm (throat ratio: 2.22) from the lowest end of the long vane in the axial direction.

[0084] As shown in Figure 16, in Examples 1, 5 to 7, when the position of the lower surface of the short vane was within the range of 5.5 mm to 33 mm, the flow rate of the diffuser channel Ch3 located on the positive pressure side of the short vane increased compared to the flow rate of the other diffuser channels Ch. Similarly, in Examples 3, 8 to 10, when the position of the lower surface of the short vane was within the range of 5.5 mm to 33 mm, the flow rates of the diffuser channels Ch3, Ch5, and C7 located on the positive pressure side of the short vane increased compared to the flow rate of the other diffuser channels Ch. In addition, in Examples 1, 5 to 7, when the position of the lower surface of the short vane moved from 5.5 mm to 11 mm (when the short vane became shorter), the flow rate of the diffuser channel Ch3 increased. At positions of the lower surface of the short vane at 11 mm and 22 mm, the flow rate of the diffuser channel Ch3 was approximately the same. When the position of the lower surface of the short vane moved from 22 mm to 33 mm (the short vane became shorter), the flow rate of the diffuser channel Ch3 decreased. On the other hand, in Examples 3, 8 to 10, when the position of the lower surface of the short vane moved from 5.5 mm to 11 mm, the flow rates of the diffuser channels Ch3, Ch5, and Ch7 located on the positive pressure side of the short vane increased slightly. Within the range of 11 mm to 33 mm for the position of the lower surface of the short vane, the flow rates of the diffuser channels Ch3, Ch5, and Ch7 decreased as the position of the lower surface of the short vane moved upward. The rate of decrease in the flow rate of the diffuser channel Ch3 (Ch3, Ch5, Ch7) located on the positive pressure side of the short vane when the position of the lower surface of the short vane moved from 22 mm to 33 mm decreased as the number of short vanes increased. Here, the throat ratio is maximized when the position of the lower surface of the short vane is within the range of 11 mm to 16.5 mm from the lowest end of the long vane. These results indicate that if the position of the lower surface of the short vane is at the maximum position where the throat ratio is maximized, or below (upstream) the maximum position, the flow rate of the diffuser channels Ch3, Ch5, and Ch7 located on the positive pressure side of the short vane increases. Furthermore, these results indicate that even if the position of the lower surface of the short vane is above (downstream) the maximum position, the flow rate of the diffuser channels Ch3, Ch5, and Ch7 located on the positive pressure side of the short vane increases if the throat ratio is 2 or greater.

[0085] ●Reference Examples 10-15 (Comparison of Diffuser Flow Rates: Design Point) Figure 17 is a graph showing the simulation analysis results of the flow rate of each diffuser flow path at the design point of yet another reference example of the present invention (Reference Examples 10-15). The figure also shows the results of Reference Examples 1 and 3 for comparison. In Reference Examples 10 to 12, there is one short vane. In Reference Examples 13 to 15, there are three short vanes. In Reference Examples 10 to 15, the position of the lower surface of the short vane in the axial direction is the same as the positions of the long vane at 5.5 mm (throat ratio: 1.83), 22 mm (throat ratio: 2.38), and 33 mm (throat ratio: 2.22) from the lowest end of the long vane.

[0086] As shown in Figure 17, in Reference Examples 1, 10, and 11, the flow rate of the diffuser channel Ch3 located on the positive pressure side of the short vane was approximately the same. On the other hand, in Reference Example 12, the same flow rate was significantly lower than that of Reference Examples 1, 10, and 11. In Reference Examples 3, 13 to 15, the flow rates of the diffuser channels Ch3, Ch5, and Ch7 located on the positive pressure side of the short vane decreased as the position of the lower surface of the short vane moved upward. In particular, the flow rate decreased significantly when the position of the lower surface of the short vane was 22 mm or more from the lowest end of the long vane. The flow rate of the diffuser channel Ch3 (Ch3, Ch5, Ch7) located on the positive pressure side of the short vane decreased compared to the same flow rate in Examples 5 to 10. This result indicates that the flow rate of the diffuser channel Ch3 (Ch3, Ch5, Ch7) located on the positive pressure side of the short vane increases due to the connecting channel.

[0087] ●Examples 1-3 (Comparison of diffuser flow rates: 30% flow rate) Figure 18 is a graph showing the simulation analysis results of the flow rate of each diffuser channel at 30% flow rate in Examples 1 to 3 of the present invention. The figure also shows the results of Reference Examples 1-3 and Comparative Example 1 for comparison.

[0088] As shown in Figure 18, in Examples 1 to 3, the flow rates of the diffuser channels Ch3, Ch5, and Ch7 located on the positive pressure side of the short vanes increased compared to the flow rates of the diffuser channels Ch2, Ch4, and Ch6 located on the negative pressure side of the short vanes. On the other hand, in Reference Examples 1 to 3, this increase in flow rate was not obtained except in Reference Example 3. This result indicates that by arranging a connecting channel in the long vanes corresponding to the short vanes, the flow rates of the diffuser channels Ch3, Ch5, and Ch7 located on the positive pressure side of the short vanes increase even at low flow rates.

[0089] ●Example 4 (Comparison of diffuser flow rates: 30% flow rate) Figure 19 is a graph showing the simulation analysis results of the flow rate of each diffuser channel at 30% flow rate in another embodiment of the present invention (Embodiment 4). The figure also shows the results of Example 3 for comparison.

[0090] As shown in Figure 19, because the outlet of the connecting channel is located closest to the lower end of the corresponding short vane, the flow rates of the diffuser channels Ch3, Ch5, and Ch7, which are located on the positive pressure side of the short vane, increased slightly even at a 30% flow rate. This result indicates that as the outlet of the connecting channel approaches position P3, the flow rates of the diffuser channels Ch3, Ch5, and Ch7, which are located on the positive pressure side of the short vane, increase even at low flow rates.

[0091] ●Summary According to the embodiment described above, the vanes 9 of the diffuser 7 include long vanes 91 to 94 and short vanes 95 to 98. Each of the long vanes 91 to 94 is positioned adjacent to the corresponding short vanes 95 to 98 on the positive pressure surface 95a to 98a side of the corresponding short vanes 95 to 98. In the axial direction, the end faces 95c to 98c and the lower faces 95d to 98d of the short vanes 95 to 98 are positioned above the end faces 91c to 94c of the long vanes 91 to 94. The long vanes 91 to 94 are provided with communication channels 91d to 94d that open to the positive pressure surface 91a to 94a and the negative pressure surface 91b to 94b.

[0092] With this configuration, the flow rate of the handling fluid flowing into the diffuser channels Ch1, Ch3, Ch5, and Ch7, which are located on the positive pressure surface 95a to 98a side of the short vanes 95 to 98, increases. Therefore, even if delamination occurs in the diffuser channels Ch1, Ch3, Ch5, and Ch7, the delamination area does not increase, and the diffuser channels Ch1, Ch3, Ch5, and Ch7 are not blocked by the delamination area. The inflow (backflow) of the handling fluid that has flowed out from the diffuser channels Ch1, Ch3, Ch5, and Ch7 to the downstream side of the diffuser channels Ch2, Ch4, Ch6, and Ch8 is also suppressed. As a result, in the diffuser channels Ch2, Ch4, Ch6, and Ch8, the delamination area does not increase to the point of blocking the diffuser channels Ch2, Ch4, Ch6, and Ch8, and the diffuser channels Ch2, Ch4, Ch6, and Ch8 are not blocked by the delamination area.

[0093] Furthermore, the diffuser channels Ch1, Ch3, Ch5, and Ch7 are designed to handle large flow rates. As a result, the influence of the liquid flow F2 from the connecting channels 91d to 94d on the liquid flow F1 flowing into the diffuser channels Ch1, Ch3, Ch5, and Ch7 is reduced. Consequently, the pump efficiency of centrifugal pump 1 is improved compared to conventional pumps A and B.

[0094] In this way, centrifugal pump 1 suppresses the decrease in efficiency while also suppressing the occurrence of swirling stall.

[0095] Furthermore, according to the embodiment described above, the number of short vanes 95-98 is half (or less) of the total number of vanes 9. With this configuration, the influence of the long vanes 91-94 on the flow of the liquid being handled becomes more dominant than the influence of the short vanes 95-98. Therefore, the design point can be set to a flow rate corresponding to the long vanes. In addition, controlling the flow rate of the diffuser flow path Ch at the design point becomes easier.

[0096] Furthermore, according to the embodiment described above, one long vane 91-94 is arranged between each of the short vanes 95-98 in the circumferential direction. With this configuration, the flow rates of the diffuser channels Ch1, Ch3, Ch5, and Ch7 on the positive pressure surface 95a-98a side of the short vanes 95-98 are reliably increased.

[0097] Furthermore, according to the embodiment described above, the outlets 91h to 94h of the communication channels 91d to 94d are located within the range from the upstream limit position P1 to the downstream limit position P2. With this configuration, flow F2 reliably merges with flow F1. Therefore, the flow rates of the diffuser channels Ch1, Ch3, Ch5, and Ch7 on the positive pressure surfaces 95a to 98a of the short vanes 95 to 98 are reliably increased by flow F2. In addition, the communication channels 91d to 94d are not blocked by the flow based on the vortex V.

[0098] Furthermore, according to the embodiment described above, the outlets 91h to 94h of the communication channels 91d to 94d are located below the virtual line C1 and adjacent to the virtual line C1. With this configuration, flow F2 reliably merges with flow F1. Therefore, the flow rates of the diffuser channels Ch1, Ch3, Ch5, and Ch7 on the positive pressure surfaces 95a to 98a of the short vanes 95 to 98 are reliably increased by flow F2.

[0099] Furthermore, according to the embodiments described above, the end faces 95c to 98c and the lower faces 95d to 98d of the short vanes 95 to 98 are positioned forward of the position where the throat ratio is maximized. With this configuration, the required static pressure capacity of the diffuser 7 is reliably maintained. Also, flow F2 reliably merges with flow F1. Therefore, the flow rates of the diffuser flow paths Ch1, Ch3, Ch5, and Ch7 on the positive pressure surfaces 95a to 98a of the short vanes 95 to 98 are reliably increased.

[0100] Furthermore, according to the embodiments described above, each of the long vanes 91 to 94 is provided with a communication channel 91d to 94d. With this configuration, the flow F2 merges with the flow F1 that flows into the diffuser channels Ch1, Ch3, Ch5, and Ch7 on the negative pressure surfaces 91b to 94b of all the long vanes 91 to 94. As a result, the flow rates of the diffuser channels Ch1, Ch3, Ch5, and Ch7 are reliably increased.

[0101] Furthermore, according to the embodiments described above, the shape of each of the communication channels 91d to 94d is a slit shape that divides the long vanes 91 to 94 into two parts, with the communication channels 91d to 94d as the boundary. With this configuration, the communication channels 91d to 94d can be easily formed simply by forming slits in the vanes of the existing diffuser.

[0102] Furthermore, according to the embodiments described above, the long vanes 91 to 94 include first parts 91e to 94e positioned below the communication channels 91d to 94d, and second parts 91f to 94f positioned above the communication channels 91d to 94d. The shape of the short vanes 95 to 98 is the same as the shape of the second parts 91f to 94f. With this configuration, the short vanes 95 to 98 can be easily formed by simply removing a portion of the vanes of an existing diffuser (the portion corresponding to the first parts 91e to 94e and the communication channels 91d to 94d).

[0103] Furthermore, according to the embodiments described above, the centrifugal pump 1 is equipped with a diffuser 7. With this configuration, the centrifugal pump 1 suppresses the decrease in efficiency while suppressing the occurrence of swirling stall.

[0104] ●Other Embodiments● In this invention, the centrifugal pump 1 does not necessarily have a second pump section, or it may have a third or more pump sections.

[0105] Furthermore, in the present invention, the number of vanes 9 is not limited to "8".

[0106] Furthermore, in the present invention, it is sufficient that at least one of the long vanes 91 to 94, corresponding to any of the short vanes 95 to 98, is provided with a communication channel 91d to 94d, and some of the long vanes 91 to 94 do not need to be provided with a communication channel 91d to 94d.

[0107] Furthermore, in the present invention, the shape of the communication channels 91d to 94d is not limited to a slit shape. That is, for example, the shape of the communication channels 91d to 94d may be one or more tubular shapes (through holes) that penetrate the long vanes 91 to 94.

[0108] Furthermore, in the present invention, the communication channels 91d to 94d do not necessarily have to be arranged parallel to each other in the circumferential direction.

[0109] Furthermore, in the present invention, the positions of the axial communication channels 91d to 94d may be different.

[0110] Furthermore, in this invention, the number of short vanes 95 to 98 is not limited to "4" and is only required to be less than or equal to half the total number of vanes 9. That is, for example, the number of short vanes 95 to 98 could be "1" to "3".

[0111] Furthermore, in the present invention, the positions of the end faces 95c to 98c and the lower faces 95d to 98d of the short vanes 95 to 98 (length of the short vanes 95 to 98) are not limited to the positions in this embodiment.

[0112] Furthermore, in the present invention, the shape of the lower surfaces 95d to 98d of the short vanes 95 to 98 is not limited to a planar shape parallel to the circumferential and radial directions. That is, for example, the shape of the lower surfaces 95d to 98d may be a curved surface that is convex downwards.

[0113] Furthermore, in the present invention, two or more of the short vanes 95 to 98 may be arranged adjacent to each other.

[0114] Furthermore, in this invention, the lengths of the short vanes 95 to 98 may be different.

[0115] Furthermore, in the present invention, the diffuser channel Ch may be divided into two circumferentially on the downstream side within the diffuser channel Ch.

[0116] Furthermore, in the present invention, the diffuser channel Ch may merge with an adjacent diffuser channel Ch downstream of the diffuser channel Ch.

[0117] ●Embodiments of the present invention● Next, embodiments of the present invention as understood from the embodiments described above will be described below, with reference to the terms and reference numerals described in each embodiment.

[0118] A first embodiment of the present invention is a diffuser (e.g., diffuser 7) arranged adjacent to an impeller (e.g., impeller 6) in the axial direction of the rotating shaft (e.g., rotating shaft 4) of a centrifugal pump (e.g., centrifugal pump 1), wherein in the axial direction, the direction in which the impeller is positioned relative to the diffuser is the forward direction (e.g., downward direction), and the direction in which the diffuser is positioned relative to the impeller is the rear direction (e.g., upward direction), and comprises a flow path forming portion (e.g., cylindrical portion 84) having a cylindrical outer surface (e.g., outer surface 84a), and a plurality of vanes (e.g., vanes 9) arranged on the outer surface and together with the outer surface, demarcate a plurality of diffuser flow paths (e.g., diffuser flow path Ch) through which the liquid discharged from the impeller flows, and each of the plurality of vanes has a positive pressure surface (e.g., positive pressure surfaces 91a~98a) and a negative pressure surface which is the surface opposite to the positive pressure surface. For example, comprising a negative pressure surface (91b-98b) and a front end portion (e.g., end faces 91c-98c, bottom faces 95d-98d) arranged to be continuous with the positive pressure surface and the negative pressure surface, wherein the plurality of vanes comprises a plurality of long vanes (e.g., long vanes 91-94) and at least one short vane (e.g., short vanes 95-98) shorter than the long vanes, wherein the plurality of long vanes have the corresponding short vanes on the positive pressure surface side, A diffuser comprising at least one specific long vane (e.g., long vanes 91-94) arranged adjacent to the short vanes corresponding to the long vanes, wherein in the axial direction, the front end of the short vane is positioned further back than the front end of the long vane, and the specific long vane is provided with a communication channel (e.g., communication channel 91d-94d) opening to the positive pressure surface and the negative pressure surface of the specific long vane. This configuration suppresses the decrease in efficiency in the centrifugal pump while also suppressing the occurrence of swirling stall.

[0119] A second embodiment of the present invention is a diffuser in which, in the first embodiment, the number of short vanes is less than or equal to half the total number of vanes. This configuration makes it easier to control the flow rate of the diffuser channel at the design point.

[0120] A third embodiment of the present invention is a diffuser in which, in the second embodiment, the plurality of vanes comprises a plurality of short vanes, and in the circumferential direction of the outer surface, one long vane is arranged between two of the plurality of short vanes. With this configuration, the flow rate in the diffuser channel on the positive pressure side of the short vane is guaranteed to increase.

[0121] A fourth embodiment of the present invention is a diffuser in which, in the second embodiment, the plurality of vanes comprises a plurality of short vanes, wherein two of the short vanes are arranged adjacent to each other in the circumferential direction of the outer surface. With this configuration, the flow rate in the diffuser channel on the positive pressure side of the short vane is reliably increased by the flow out of the connecting channel.

[0122] A fifth embodiment of the present invention is a diffuser in which, in the first embodiment, the communication channel comprises an outlet (e.g., outlets 91h to 94h) located on the negative pressure surface, the outlet being located within a range from an upstream limit position (e.g., upstream limit position P1) to a downstream limit position (e.g., downstream limit position P2), the upstream limit position being a position where the flow of the handling liquid (e.g., flow F2) flowing out from the outlet can merge with the flow of the handling liquid (e.g., flow F1) flowing into the diffuser channel (e.g., diffuser channels Ch1, Ch3, Ch5, Ch7) located on the negative pressure surface side of the specific length vane, and the downstream limit position being a position in the diffuser channel located on the negative pressure surface side of the specific length vane, upstream of the vortex (e.g., vortex V) formed by the backflow of the handling liquid in the diffuser channel. With this configuration, the flow out of the connecting channel reliably merges with the flow flowing into the diffuser channel.

[0123] A sixth embodiment of the present invention is, in the fifth embodiment, the upstream limit position is a position in which the outlet is located adjacent to a specific virtual line (e.g., virtual line C1) in a forward direction, and the specific virtual line is a diffuser that passes through the front end of the short vane corresponding to the specific long vane and along the circumferential direction of the outer surface. With this configuration, the flow out of the connecting channel reliably merges with the flow flowing into the diffuser channel.

[0124] A seventh embodiment of the present invention is a diffuser in which, in the sixth embodiment, the short vanes have end faces (e.g., end faces 95c to 98c) located furthest upstream in the flow of the liquid being handled in the first diffuser channel relative to the short vanes, and the outlet is located at the position (e.g., position P3) closest to the end faces among the short vanes corresponding to the specific long vanes. With this configuration, the liquid being handled can easily flow out of the connecting channel and easily flow into the connecting channel.

[0125] An eighth embodiment of the present invention is a diffuser in which the front end of the short vane is positioned forward from a position (e.g., maximum position) where the ratio (e.g., throat ratio) of the length of the inlet of the diffuser flow channel (e.g., inlet Chi) located on the positive pressure side of the short vane to the length (e.g., first length L1) of the inlet of the diffuser flow channel (e.g., inlet Chi) located on the negative pressure side of the short vane is maximized. With this configuration, the required static pressure capacity for the diffuser is reliably maintained.

[0126] A ninth embodiment of the present invention is a diffuser in which, in the first embodiment, each of the long vanes is provided with the communication channel. With this configuration, the flow rate in the diffuser channel on the negative pressure side of all long vanes is reliably increased.

[0127] A tenth embodiment of the present invention is a diffuser in which, in the first embodiment, the shape of each of the communication channels is a slit shape that divides the specific-length vane into two parts with respect to the communication channel. With this configuration, a communication channel can be easily formed in an existing diffuser.

[0128] An eleventh embodiment of the present invention is a diffuser in which, in the tenth embodiment, the specific-length vane comprises a first part (e.g., first parts 91e to 94e) positioned forward of the communication channel and a second part (e.g., second parts 91f to 94f) positioned backward of the communication channel, wherein the shape of the short vane corresponding to the specific-length vane is the same as the shape of the second part. With this configuration, short vanes can be easily formed in existing diffusers.

[0129] A twelfth embodiment of the present invention is a centrifugal pump (e.g., centrifugal pump 1) comprising a motor (e.g., motor 3), a rotating shaft (e.g., rotating shaft 4) rotated by the motor, an impeller (e.g., impeller 6) attached to the rotating shaft, and a diffuser (e.g., diffuser 7) according to the first embodiment, which is arranged adjacent to the impeller in the axial direction of the rotating shaft. This configuration suppresses the decrease in efficiency in the centrifugal pump while also suppressing the occurrence of swirling stall. [Explanation of symbols]

[0130] 1. Centrifugal pump 3 motors 4 rotation axes 6 impellers 7 Diffuser 84 Cylindrical section 84a Outer surface 9. Bane 91-94 Long vanes 91a~94a Positive pressure side 91b~94b Negative pressure side 91c~94c End face (front end) 91d~94d Connecting channel 91e~94e Part 1 91f~94f Part 2 91h~94h Exit 95-98 Short vanes 95a~98a Positive pressure side 95b~98b Negative pressure side 95c~98c End face (front end) 95d~98d Lower surface (front end) Ch Diffuser channel Chi entrance C1 virtual line F1 flow F2 flow P1 Upstream limit position P2 Downstream limit position P3 position L1 First length L2 Second length V vortex

Claims

1. A diffuser positioned adjacent to the impeller in the axial direction of the rotating shaft of a centrifugal pump, In the axial direction, the direction in which the impeller is positioned relative to the diffuser is the forward direction, and the direction in which the diffuser is positioned relative to the impeller is the rear direction. A channel forming portion having a cylindrical outer surface, A plurality of vanes are arranged on the outer circumferential surface and, together with the outer circumferential surface, demarcate a plurality of diffuser channels through which the liquid discharged from the impeller flows, It has, Each of the multiple vanes is, Positive pressure surface and, The negative pressure surface is the surface opposite to the positive pressure surface, A front end portion is arranged to be continuous with the positive pressure surface and the negative pressure surface, Equipped with, The multiple vanes are, Multiple long vanes, At least one short vane that is shorter than the aforementioned long vane, Equipped with, The multiple long vanes are, On the positive pressure side of the short vane corresponding to the long vane, at least one specific long vane is arranged adjacent to the short vane corresponding to the long vane, Equipped with, In the axial direction, the front end of the short vane is positioned further back than the front end of the long vane. The aforementioned specific length vane is A communication channel opening to the positive pressure surface of the specified length vane and the negative pressure surface of the specified length vane, Equipped with, Diffuser.

2. The number of the short vanes is less than or equal to half the total number of vanes. The diffuser according to claim 1.

3. The multiple vanes are, Multiple short vanes, Equipped with, In the circumferential direction of the outer surface, one long vane is arranged between two of the multiple short vanes. The diffuser according to claim 2.

4. The multiple vanes are, Multiple short vanes, Equipped with, In the circumferential direction of the outer surface, two of the multiple short vanes are arranged to be adjacent to each other. The diffuser according to claim 2.

5. The aforementioned communication channel is An outlet located on the negative pressure surface, Equipped with, The aforementioned outlet is located within the range from the upstream limit position to the downstream limit position. The upstream limit position is a position where the flow of the handling fluid discharged from the outlet can merge with the flow of the handling fluid flowing into the diffuser channel located on the negative pressure side of the specific-length vane. The downstream limit position is a position in the diffuser flow path, located on the negative pressure side of the specific-length vane, that is upstream of the vortex formed by the backflow of the fluid being handled within the diffuser flow path. The diffuser according to claim 1.

6. The upstream limit position is a position where the outlet is located ahead of the specific virtual line and adjacent to the specific virtual line. The aforementioned specific virtual line passes through the front end of the short vane corresponding to the specific long vane and runs along the circumferential direction of the outer surface. The diffuser according to claim 5.

7. The aforementioned short vane is The end face located furthest upstream in the flow of the liquid being handled within the first diffuser channel relative to the short vane, Equipped with, The outlet is positioned among the short vanes corresponding to the specific long vane, closest to the end face. The diffuser according to claim 6.

8. The front end of the short vane is positioned forward from the position where the ratio of the length of the inlet of the diffuser flow channel located on the positive pressure side of the short vane to the length of the inlet of the diffuser flow channel located on the negative pressure side of the short vane is maximized. The diffuser according to claim 1.

9. Each of the aforementioned long vanes is, The aforementioned communication channel, Equipped with, The diffuser according to claim 1.

10. The shape of each of the aforementioned communication channels is a slit shape that divides the specific-length vane into two parts with the communication channel as the boundary. The diffuser according to claim 1.

11. The aforementioned specific length vane is A first part positioned forward of the aforementioned communication channel, A second part is positioned behind the aforementioned communication channel, Equipped with, The shape of the short vane corresponding to the specified long vane is the same as the shape of the second part. The diffuser according to claim 10.

12. Motor and, A rotating shaft that is rotated by the aforementioned motor, An impeller attached to the aforementioned rotating shaft, A diffuser according to claim 1, which is arranged adjacent to the impeller in the axial direction of the rotating shaft, Having, Centrifugal pump.

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