JP2017048703A - Centrifugal Pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a centrifugal pump that can improve pump efficiency by reducing liquid flow separation in a flow passage.SOLUTION: A centrifugal pump according to the present invention comprises: a rotating shaft 11; and at least one impeller 1 fixed to the rotating shaft 11. The impeller 1 comprises: a hub 14; a plurality of blades 15 erected on the hub 14; and a shroud 16 that covers front surfaces of the blades 15. Regularly arranged concave parts 24c or convex parts 24b are provided on an inner surface 16a of the shroud 16.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a centrifugal pump for transferring a liquid.

  A centrifugal pump is known as a pump for transferring a liquid (for example, water). Centrifugal pumps are broadly classified into diffuser pumps in which guide vanes (diffusers or guide vanes) are provided on the radially outer side of the impeller and spiral pumps in which guide vanes are not provided on the radially outer side of the impeller. In the vortex pump, the liquid discharged from the impeller directly flows into the volute chamber, and in the diffuser pump, the liquid discharged from the impeller passes through the guide vanes, and the velocity energy of the liquid is converted into pressure energy.

  The diffuser pump includes a multistage diffuser pump in which a plurality of stages of impellers are fixed to a rotating shaft. In the multistage diffuser pump, a diffuser is provided on the radially outer side of each stage of the impeller. The diffuser has a plurality of diffuser blades, and a diffuser flow path through which liquid discharged from the impeller passes is formed between adjacent diffuser blades. The liquid passing through the diffuser flow path is guided to the next stage impeller.

  An impeller flow path through which liquid passes is formed in the impeller of these centrifugal pumps. In the multistage diffuser pump, a communication flow path for guiding the liquid that has passed through the impeller to the next-stage impeller is formed. The communication channel includes the above-described diffuser channel.

  When the liquid passes through the impeller channel and the communication channel, the liquid flows while rubbing against the wall surfaces of these channels. FIG. 11 is a schematic diagram for explaining the flow of the liquid. In FIG. 11, the liquid is flowing from the point A toward the point D, and the points B and C are intermediate points between the points A and D. The liquid passes through point A, point B, point C, and point D in this order. In FIG. 11, the velocity gradient of the liquid at the points A, B, C, and D is drawn.

  At the point A, the velocity of the liquid on the wall surface is zero, and the velocity of the liquid increases as the distance from the wall surface increases. As indicated by the velocity gradient at the point B, the velocity of the liquid flowing in the vicinity of the wall surface gradually decreases due to the friction between the liquid and the wall surface. As the liquid further flows, at the point C, the liquid in the vicinity of the wall surface has a velocity opposite to the flow direction in which the liquid should flow. That is, at the point C, the liquid in the vicinity of the wall surface flows in the direction opposite to the flow direction in which the liquid should originally flow. This phenomenon is commonly referred to as “flow separation”. At a point D downstream of the point C, a region where the liquid flows in the opposite direction (that is, a region where flow separation occurs) is enlarged. Such flow separation causes a pressure loss of the liquid and reduces the pump efficiency.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a centrifugal pump that can reduce separation of a liquid flow in a flow path and improve pump efficiency.

  One aspect of the present invention for solving the above-described problem is a centrifugal pump having a rotating shaft and at least one impeller fixed to the rotating shaft, wherein the impeller includes a hub, A plurality of wings standing on a hub; and a shroud covering a front surface of the wings, wherein a plurality of regularly arranged convex portions or a plurality of concave portions are provided on an inner surface of the shroud. It is a centrifugal pump.

In a preferred aspect of the present invention, the plurality of convex portions or the plurality of concave portions are formed on the inner surface of the shroud by attaching a sheet having a plurality of convex portions or a plurality of concave portions formed on the inner surface of the shroud. It is provided.
In a preferred aspect of the present invention, the plurality of convex portions or the plurality of concave portions are provided on the inner surface of the shroud outside of two-thirds of the radius of the impeller.

  Another aspect of the present invention is a centrifugal pump having a rotating shaft and a plurality of impellers fixed to the rotating shaft, and guides liquid discharged from the impeller to a next-stage impeller. A communication channel is provided, and the communication channel communicates with the diffuser channel formed in the diffuser disposed on the radially outer side of the impeller, the diffuser channel, and flows out of the diffuser channel. A turning flow path that changes the flow direction of the liquid to the inside in the radial direction of the impeller, and a return flow that communicates with the turning flow path and guides the liquid flowing out of the turning flow path to the next-stage impeller. And a plurality of convex portions or a plurality of concave portions regularly arranged on the inner wall surface of the diverting flow path.

  In a preferred aspect of the present invention, the plurality of convex portions or the plurality of concave portions are provided on the inner wall surface by sticking a sheet having a plurality of convex portions or a plurality of concave portions formed on the surface thereof to the inner wall surface. It is characterized by that.

  According to the present invention, turbulent flow can be generated in the liquid flowing on the inner surface of the shroud by the plurality of convex portions or the plurality of concave portions provided on the inner surface of the shroud. This turbulent flow can delay the occurrence of flow separation on the inner surface of the shroud. Similarly, a turbulent flow can be generated on the inner wall surface of the turning channel by the plurality of convex portions or the plurality of concave portions provided on the inner wall surface of the turning channel. This turbulent flow can delay the occurrence of flow separation on the inner wall surface of the turning channel. As a result, the pressure loss of the liquid flowing through the centrifugal pump is reduced, so that the pump efficiency can be improved.

It is a schematic sectional drawing which shows the diffuser pump which is an example of a centrifugal pump. It is sectional drawing which shows the impeller of the diffuser pump shown by FIG. It is a perspective view which expands and shows a part of sheet | seat in which the some convex part was formed. It is a perspective view which expands and shows a part of sheet | seat in which the several recessed part was formed. It is a schematic diagram for demonstrating the principle which a some convex part or several recessed part delays generation | occurrence | production of flow separation. It is a schematic sectional drawing which shows the multistage diffuser pump which is an example of a centrifugal pump. It is a schematic sectional drawing which shows a part of multistage diffuser pump which concerns on one Embodiment of this invention. It is a cross-sectional perspective view along the AA line of FIG. It is a schematic sectional drawing which shows a part of multistage diffuser pump which concerns on another embodiment. It is a schematic sectional drawing which shows a part of multistage diffuser pump which concerns on another embodiment. It is a schematic diagram for demonstrating the flow of a liquid.

  Embodiments of the present invention will be described below with reference to the drawings. 1 to 10, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted. Moreover, the structure shown by each embodiment is applicable also to other embodiment, as long as it does not contradict each other.

  FIG. 1 is a schematic cross-sectional view showing a diffuser pump which is an example of a centrifugal pump. As shown in FIG. 1, the diffuser pump has an impeller 1 fixed to the end of the rotating shaft 11 and a casing 3 that houses the impeller 1. The rotating shaft 11 is rotated by a driving source (for example, a motor) (not shown), and the impeller 1 rotates integrally with the rotating shaft 11 in the casing 3.

  As shown in FIG. 1, the diffuser pump has a diffuser 9 disposed on the radially outer side of the impeller 1. In the diffuser 9, a plurality of diffuser blades 9a are formed, and a diffuser flow path 9b through which the liquid discharged from the impeller 1 passes is formed between adjacent diffuser blades 9a. The cross-sectional area of the diffuser channel 9b is formed so as to increase from the inlet toward the outlet, and the velocity energy of the liquid is converted into pressure energy when the liquid passes through the diffuser channel 9b.

  A volute chamber 7 is formed inside the casing 3. The volute chamber 7 has a shape surrounding the periphery of the diffuser 9. The casing 3 is formed with a cylindrical pump suction port 2 (see a dotted line in FIG. 1) extending in the axial direction of the rotary shaft 11. Further, a pump discharge port 4 is formed in the casing 3.

  When the impeller 1 is rotated, the liquid is sucked into the impeller 1 from the pump suction port 2. The liquid is given speed energy by the rotation of the impeller 1. Furthermore, when the liquid passes through the diffuser flow path 9b, the velocity energy is converted into pressure energy, and the pressure of the liquid is increased. The pressurized liquid flows along the inner wall of the volute chamber 7 and is discharged from the pump discharge port 4.

  FIG. 2 is a cross-sectional view showing the impeller 1 of the diffuser pump shown in FIG. As shown in FIG. 2, the impeller 1 includes a disk-shaped hub 14, a plurality of blades 15 standing from the hub 14, and a shroud 16 that covers the front surface of the blade 15. The wings 15 are arranged at equal intervals along the circumferential direction of the hub 14. The front end of the shroud 16 has a cylindrical shape, and the liquid inlet 1 a of the impeller 1 is formed by the front end of the shroud 16.

  In the impeller 1, an impeller channel 12 is formed between the inner surface 14 a of the hub 14 and the inner surface 16 a of the shroud 16. The liquid sucked from the liquid inlet 1a receives a centrifugal force by the rotating impeller 1 and moves in the impeller channel 12 to the outside in the radial direction of the impeller 1. The sectional area of the impeller channel 12 at the outer peripheral end of the impeller 1 is larger than the sectional area of the impeller channel 12 at the liquid inlet 1 a of the impeller 1. Therefore, the flow velocity of the liquid flowing through the impeller channel 12 is gradually decreased, and the velocity energy of the liquid is converted into pressure energy.

  In the impeller channel 12, the speed of the liquid flowing along the inner surface 16 a of the shroud 16 is slower than the speed of the liquid flowing along the inner surface 14 a of the hub 14, so the pressure of the liquid flowing along the inner surface 16 a of the shroud 16 is The pressure of the liquid flowing along the inner surface 14a of the hub 14 becomes larger. For this reason, friction between the inner surface 16 a of the shroud 16 and the liquid greatly affects the liquid, and flow separation is likely to occur on the inner surface 16 a of the shroud 16.

  In order to suppress the occurrence of such flow separation, a plurality of regularly arranged convex portions are formed on the inner surface 16 a of the shroud 16 in the present embodiment. More specifically, a sheet 24 in which a plurality of convex portions are regularly arranged on the surface thereof is affixed to the inner surface 16 a of the shroud 16. By sticking this sheet 24 to the inner surface 16 a of the shroud 16, a plurality of convex portions are provided on the inner surface 16 a of the shroud 16.

  FIG. 3 is an enlarged perspective view showing a part of the sheet 24 on which a plurality of convex portions 24b are formed. As shown in FIG. 3, the sheet 24 includes a sheet base 24a and a plurality of convex portions 24b protruding from the surface of the sheet base 24a. The plurality of convex portions 24b shown in FIG. 3 are regularly arranged on the sheet base portion 24a like a two-dimensional square lattice.

  In the embodiment shown in FIG. 3, a plurality of protrusions 24 b arranged in each column are arranged in a straight line at equal intervals, and the protrusions 24 b arranged in each row are arranged in a straight line at equal intervals. The parts 24b are arranged on the surface of the sheet base 24a. An interval D1 between adjacent convex portions 24b in the row is equal to an interval D2 between adjacent convex portions 24b in the vertical row.

  The interval D1 and the interval D2 are preferably 1 mm or more and 10 mm or less. The distance D1 and the distance D2 are usually several mm. The height H of the protrusion 24b (that is, the distance from the surface of the sheet base 24a to the top of the protrusion 24b) is preferably 0.5 mm or more and 2 mm or less. The height H of the convex part 24b is usually about 1 mm. Although the convex part 24b shown in FIG. 3 has a conical shape, it may have a pyramid shape, a cylindrical shape, or a prism shape. When the thickness t of the seat base 24a is too large, the cross-sectional area of the impeller channel 12 is narrowed, which may deteriorate the pump performance. Therefore, the range of the thickness t of the sheet base 24a is preferably 0.3 mm or more and 1 mm or less. The sheet 24 is preferably made of a resin material such as PTFE.

  Further, the plurality of convex portions 24b may be regularly arranged according to a two-dimensional lattice other than the square lattice. For example, the convex portions 24b may be arranged according to an equilateral triangular lattice, an oblique lattice, or a parallel lattice.

  As shown in FIG. 4, instead of the plurality of convex portions 24b, a plurality of regularly arranged concave portions 24c may be formed on the surface of the sheet base portion 24a. FIG. 4 is an enlarged perspective view showing a part of the sheet 24 in which a plurality of recesses 24c are formed. The concave portions 24c shown in FIG. 4 are regularly formed in the sheet base portion 24a like a two-dimensional square lattice. Like the convex portion 24b described with reference to FIG. 3, the interval D3 between the adjacent concave portions 24c in the row is equal to the interval D4 between the adjacent concave portions 24c in the column, and the interval D3 and the interval D4 are 1 mm or more and 10 mm. It is preferable that: The distance D3 and the distance D4 are usually several mm. The depth d of the recess 24c depends on the thickness t of the sheet base 24a. As described above, since the thickness t of the sheet base 24a is preferably 0.3 mm or more and 1 mm or less, the depth d of the recess 24c is also preferably 0.3 mm or more and 1 mm or less.

  The shape of the recess 24 c is not limited to the embodiment shown in FIG. 4, and may be a mortar-like recess or a hemispherical recess. Further, the plurality of recesses 24c may be regularly arranged on the surface of the sheet base 24a according to a two-dimensional lattice other than a square lattice. For example, the concave portions 24c may be arranged according to an equilateral triangular lattice, an oblique lattice, or a parallel lattice.

  As shown in FIG. 2, the sheet 24 is preferably attached to the outer peripheral region of the inner surface 16 a of the shroud 16. For example, it is preferable to affix to the inner surface 16a of the shroud 16 outside the two-thirds of the radius r of the impeller 1. The sheet 24 may be attached to the inner surface 16a of the shroud 16 on the inner side of the two-thirds of the radius r of the impeller 1.

  In many cases, the inner surface 16a of the shroud 16 of the impeller 1 of a centrifugal pump, particularly a multistage diffuser pump, which will be described later, is a flat surface outside two-thirds of the radius r of the impeller 1. Since the sheet 24 can be easily attached to the flat surface, the sheet 24 is preferably attached to the inner surface 16a of the shroud 16 outside the two-thirds of the radius r of the impeller 1.

  By affixing the sheet 24 having the plurality of regularly arranged convex portions 24b or the plurality of concave portions 24c to the inner surface 16a of the shroud 16, the occurrence of flow separation on the inner surface 16a can be delayed. FIG. 5 is a schematic diagram for explaining the principle that the plurality of convex portions 24b or the plurality of concave portions 24c can delay the occurrence of flow separation.

  In FIG. 5, the liquid is flowing from the point A toward the point D, and the points B and C are intermediate points between the points A and D. The liquid passes through point A, point B, point C, and point D in this order. A plurality of convex portions or a plurality of concave portions are provided on the wall surface downstream from the point E located between the points B and C. In FIG. 5, the velocity gradient of the liquid at the point A, the point B, the point C, and the point D is drawn.

  At the point A, the velocity of the liquid on the wall surface is zero, and the velocity of the liquid increases as the distance from the wall surface increases. As indicated by the velocity gradient at the point B, the velocity of the liquid flowing in the vicinity of the wall surface gradually decreases due to the friction between the liquid and the wall surface. When the liquid reaches a plurality of convex portions or a plurality of concave portions, a turbulent flow of the liquid occurs as indicated by the velocity gradient at the point C. This turbulent flow makes it difficult for the liquid flow reversal phenomenon, that is, flow separation to occur. In the example shown in FIG. 5, the separation of the flow and the expansion thereof are also suppressed at the point D.

  Thus, according to the present embodiment, a turbulent flow can be intentionally created on the inner surface 16a of the shroud 16 by the plurality of convex portions 24b or the plurality of concave portions 24c provided on the inner surface 16a of the shroud 16. . Due to this turbulent flow, it is possible to delay the occurrence of separation of the liquid flowing in the impeller channel 12 on the inner surface 16a of the shroud 16. As a result, the pressure loss of the liquid is reduced, so that the pump efficiency can be improved.

  Instead of the sheet 24, the inner surface 16a of the shroud 16 may be directly machined (for example, by grinding) to provide a plurality of regularly arranged convex portions or a plurality of concave portions on the inner surface 16a. Also in this case, since machining can be easily performed on the flat surface, a plurality of protrusions formed by machining are formed on the inner surface 16a of the shroud 16 outside the two-thirds of the radius r of the impeller 1. It is preferable to provide a portion or a plurality of recesses.

  FIG. 6 is a schematic cross-sectional view showing a multistage diffuser pump which is an example of a centrifugal pump. The multistage diffuser pump shown in FIG. 6 includes a rotating member 30 and a stationary member 40. The rotating member 30 includes a rotating shaft 11 and a plurality of impellers 1 fixed to the rotating shaft 11. Both ends of the rotating shaft 11 are rotatably supported by bearings. The stationary member 40 includes a cylindrical outer cylinder 25 having a pump suction port 2 and a pump discharge port 4, and a suction side plate 18 and a discharge side plate 19 that close both ends of the outer drum 25. The stationary member 40 further includes a plurality of middle cylinders (casings) 3 disposed inside the outer cylinder 25.

  An impeller 1 and a diffuser 9 are arranged on each middle drum 3. The impeller 1 and the diffuser 9 arranged in each middle cylinder 3 form a boosting section at each stage. The impeller 1 constitutes a part of the rotating member 30 as described above, while the diffuser 9 is fixed to the inner drum 3 and constitutes a part of the stationary member 40. Further, in the multistage diffuser pump, a communication flow path 20 (described later) that guides the liquid discharged from the impeller 1 to the next-stage impeller 1 is formed. The liquid boosted by the booster is supplied to the next-stage impeller 1 (that is, the next-stage booster) through the communication channel 20 and further boosted there. As described above, the liquid flowing into the multi-stage diffuser pump through the pump suction port 2 is sequentially boosted by the boosting unit of each stage and discharged from the pump discharge port 4.

  FIG. 7 is a schematic cross-sectional view showing a part of a multistage diffuser pump according to an embodiment of the present invention. In FIG. 7, the upper half of the impeller 1 fixed to the rotating shaft 11 is shown. As shown in FIG. 7, a diffuser 9 is provided outside the impeller 1 in the radial direction. The rotating shaft 11 is rotated by a driving source (for example, a motor) (not shown), and the impeller 1 rotates integrally with the rotating shaft 11 in the middle body (casing) 3.

  8 is a cross-sectional perspective view taken along line AA in FIG. In FIG. 8, in order to clearly show the diffuser 9, illustration of the impeller 1, the return vane 17, and the rotating shaft 11 is omitted except for the liquid inlet 1 a of the impeller 1 arranged in the next stage. The diffuser 9 has a plurality of diffuser blades 9a, and a diffuser flow path 9b through which the liquid discharged from the impeller 1 passes is formed between adjacent diffuser blades 9a. The cross-sectional area of the diffuser channel 9b is formed so as to increase from the inlet toward the outlet, and the velocity energy of the liquid is converted into pressure energy when the liquid passes through the diffuser channel 9b. The liquid that has passed through the diffuser flow path 9b flows through the communication flow path 20 along the arrow shown in FIG. 8, and is guided to the liquid inlet 1a of the impeller 1 at the next stage.

  As shown in FIG. 7, the communication flow path 20 that guides the liquid discharged from the impeller 1 to the next stage impeller 1 is a diffuser flow path 9 b (see FIG. 8) formed in the diffuser 9. A diverting flow path 21 that communicates with the diffuser flow path 9b and changes the flow direction of the liquid flowing out of the diffuser flow path 9b to the inside in the radial direction of the impeller 1, and a diverting flow path 21 that communicates with the diverting flow path 21. The return flow path 22 guides the liquid flowing out from the path 21 to the impeller 1 at the next stage. A return blade 17 is disposed in the return flow path 22.

  The sheet 24 described with reference to FIGS. 2 to 4 is attached to the inner surface 16a of the shroud 16 of each stage of the impeller 1, or machining (for example, grinding) is performed directly on the inner surface 16a of the shroud 16. ) To provide a plurality of convex portions or a plurality of concave portions regularly arranged. Similarly, in the present embodiment, turbulent flow can be intentionally created on the inner surface 16a of the shroud 16 by the plurality of convex portions 24b or the plurality of concave portions 24c. This turbulent flow can delay the occurrence of flow separation on the inner surface 16a of the shroud 16. As a result, the pressure loss of the liquid is reduced, so that the pump efficiency can be improved.

  FIG. 9 is a schematic cross-sectional view showing a part of a multistage diffuser pump according to another embodiment. In FIG. 9, the upper half of the impeller 1 fixed to the rotating shaft 11 is shown. In the multistage diffuser pump shown in FIG. 9, the sheet 24 described with reference to FIGS. 2 to 4 is attached to the inner wall surface 21 a of the turning channel 21. The inner wall surface 21 a of the turning channel 21 is a wall surface constituting the inner side surface of the turning channel 21 that is curved. The outer wall surface 21b of the turning channel 21 is a wall surface constituting the outer surface of the turning channel 21 and is located outside the inner wall surface 21a. The inner wall surface 21a of the turning channel 21 is disposed closer to the impeller 1 than the outer wall surface 21b. In the present embodiment, the sheet 24 is provided with a plurality of convex portions 24 b or a plurality of concave portions 24 c arranged regularly on the inner wall surface 21 a of the turning channel 21.

  The flow direction of the liquid flowing out from the diffuser flow path 9 b is changed to the inside in the radial direction of the impeller 1 by the turning flow path 21, and the liquid passing through the turning flow path 21 flows into the return flow path 22. That is, in the turning channel 21, the flow direction of the liquid is greatly changed. In this case, the velocity of the liquid flowing along the inner wall surface 21 a of the turning channel 21 is slower than the velocity of the liquid flowing along the outer wall surface 21 b of the turning channel 21. As a result, the pressure of the liquid flowing along the inner wall surface 21 a of the turning channel 21 becomes larger than the pressure of the liquid flowing along the outer wall surface 21 b of the turning channel 21. Therefore, friction between the inner wall surface 21 a of the turning channel 21 and the liquid greatly affects the liquid, and flow separation is likely to occur on the inner wall surface 21 a of the turning channel 21.

  In the present embodiment, by sticking the sheet 24 to the inner wall surface 21a of the turning channel 21, the occurrence of flow separation on the wall surface 21a can be delayed. As a result, the pressure loss of the liquid is reduced, so that the pump efficiency can be improved. By directly machining (for example, grinding) the inner wall surface 21a of the turning flow path 21 without attaching the sheet 24, the plurality of regularly arranged convex portions or the plurality of recessed portions are changed to the turning flow path. 21 may be provided on the inner wall surface 21a.

  FIG. 10 is a schematic cross-sectional view showing a part of a multistage diffuser pump according to still another embodiment. In the multistage diffuser pump shown in FIG. 10, the sheets 24 are respectively attached to both the inner surface 16 a of the shroud 16 and the inner wall surface 21 a of the turning channel 21. As described above, a plurality of concave portions 24 c or a plurality of convex portions 24 c may be provided on both the inner surface 16 a of the shroud 16 and the inner wall surface 21 a of the turning channel 21. By attaching a sheet 24 to one of the inner surface 16a of the shroud 16 and the inner wall surface 21a of the turning channel 21, and directly machining the other (for example, grinding), a plurality of convex portions or a plurality of projections A recess may be provided. Alternatively, a plurality of concave portions may be provided on one of the inner surface 16a of the shroud 16 and the inner wall surface 21a of the turning channel 21, and a plurality of convex portions may be provided on the other.

  According to the present embodiment, it is possible to delay the occurrence of flow separation on both the inner surface 16a of the shroud 16 and the inner wall surface 21a of the turning channel 21. As a result, the pump efficiency of the multistage diffuser pump can be further improved.

  The embodiment described above is described for the purpose of enabling the person having ordinary knowledge in the technical field to which the present invention belongs to implement the present invention. Various modifications of the above embodiment can be naturally made by those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Accordingly, the present invention is not limited to the described embodiments, but is to be construed in the widest scope according to the technical idea defined by the claims.

DESCRIPTION OF SYMBOLS 1 Impeller 2 Pump suction port 3 Casing 4 Pump discharge port 9 Diffuser 9a Diffuser blade 9b Diffuser flow path 11 Rotating shaft 12 Impeller flow path 14 Hub 15 Blade 16 Shroud 16a Inner surface 17 Return blade 18 Suction side plate 19 Discharge side plate 20 Communication flow path DESCRIPTION OF SYMBOLS 21 Turning flow path 21a Inner wall surface 21b Outer wall surface 22 Return flow path 24 Sheet 24a Sheet base part 24b Convex part 24c Concave part 25 Outer trunk 30 Rotating member 40 Static member

Claims (5)

A rotation axis;
A centrifugal pump having at least one impeller fixed to the rotating shaft,
The impeller has a hub, a plurality of wings standing on the hub, and a shroud covering a front surface of the wings,
A centrifugal pump characterized in that a plurality of regularly arranged convex portions or a plurality of concave portions are provided on the inner surface of the shroud.   The plurality of convex portions or the plurality of concave portions are provided on the inner surface of the shroud by attaching a sheet having a plurality of convex portions or a plurality of concave portions formed on the inner surface of the shroud. The centrifugal pump according to claim 1.   3. The centrifugal pump according to claim 1, wherein the plurality of convex portions or the plurality of concave portions are provided on an inner surface of the shroud outside of two-thirds of the radius of the impeller. . A rotation axis;
A centrifugal pump having a plurality of impellers fixed to the rotating shaft,
A communication channel for guiding the liquid discharged from the impeller to the next stage impeller is provided;
The communication channel is
A diffuser flow path formed in a diffuser disposed radially outward of the impeller;
A diverting channel that communicates with the diffuser channel and changes the flow direction of the liquid flowing out of the diffuser channel to the radially inner side of the impeller; and
A return flow path that communicates with the turning flow path and guides the liquid flowing out of the turning flow path to the impeller of the next stage,
A centrifugal pump characterized in that a plurality of convex portions or a plurality of concave portions regularly arranged are provided on an inner wall surface of the turning channel.   The plurality of convex portions or the plurality of concave portions are provided on the inner wall surface by sticking a sheet having a plurality of convex portions or a plurality of concave portions formed on a surface thereof to the inner wall surface. 4. The centrifugal pump according to 4.

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