Diffuser and centrifugal pump

Abstract

When this centrifugal pump is operating in a flow rate range lower than a designed point, the occurrence of stalling that occurs in the flow of a handled liquid in a diffuser flow passage provided with the centrifugal pump is reduced.　A diffuser 6 according to the present invention comprises a diffuser body 7 and a diffuser housing 8 that houses the diffuser body. The diffuser body comprises a cylindrical outer peripheral surface 71a and a plurality of vanes 72 extending outward from the outer peripheral surface. The diffuser housing comprises a cylindrical inner peripheral surface 81b disposed so as to face the outer peripheral surface of the diffuser body. Together with the outer peripheral surface of the diffuser body and the plurality of vanes, the inner peripheral surface of the diffuser housing forms a plurality of diffuser flow passages DL through which the handled liquid flows. At least one of the outer peripheral surface of the diffuser body and the inner peripheral surface of the diffuser housing is provided with a recessed and protruded surface 9 having at least one of a plurality of recess portions and a plurality of protrusion portions.

Description

Diffusers and centrifugal pumps

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

[0002] A centrifugal pump is known that includes an impeller that draws in a pumped liquid and a diffuser that is located downstream of the impeller in the flow of the pumped liquid. The diffuser converts velocity energy imparted to the pumped liquid by the impeller into pressure energy. That is, the diffuser reduces the flow velocity of the pumped liquid discharged from the impeller, thereby increasing the pressure of the pumped liquid. As a result, the suction performance of the centrifugal pump is improved (see, for example, Patent Document 1).

[0003] The diffuser includes a diffuser body and a diffuser housing that houses the diffuser body. The diffuser body includes a cylindrical outer peripheral surface and a plurality of vanes that extend radially outward from the outer peripheral surface. The diffuser housing is disposed opposite the outer peripheral surface of the diffuser body. The inner peripheral surface of the diffuser housing, together with the outer peripheral surface of the diffuser body and the plurality of vanes, form a plurality of diffuser flow paths through which the treated liquid flows.

[0004] JP 2017-20431 A

[0005] The shape of the diffuser is designed based on the design point of the centrifugal pump. Therefore, when the centrifugal pump is operating at a flow rate lower than the design point, a stall can occur, which stagnates the flow of the handled liquid in the diffuser passage. Stall can cause rotating stall, which generates vibrations in the centrifugal pump. In the low flow rate range where rotating stall occurs, the suction performance of the centrifugal pump also decreases.

[0006] An object of the present invention is to reduce the occurrence of stall that occurs in the flow of handled liquid in a diffuser passage provided in a centrifugal pump when the centrifugal pump is operating in a flow rate range lower than the design point.

[0007] In one embodiment of the present invention, the diffuser is disposed adjacent to an impeller in the axial direction of a rotating shaft of a centrifugal pump, and includes a diffuser body and a diffuser housing that houses the diffuser body, wherein the diffuser body has a cylindrical outer peripheral surface and a plurality of vanes extending outward from the outer peripheral surface in a radial direction of the outer peripheral surface, and the diffuser housing has a cylindrical inner peripheral surface that is disposed opposite the outer peripheral surface, and the inner peripheral surface, together with the outer peripheral surface and the plurality of vanes, form a plurality of diffuser flow paths through which the handled liquid discharged from the impeller flows, and at least one of the outer peripheral surface and the inner peripheral surface has an uneven surface having at least one of a plurality of concave portions and a plurality of convex portions.

[0008] In one embodiment of the present invention, a centrifugal pump includes a motor, a rotary shaft rotated by the motor, an impeller attached to the rotary shaft, and the diffuser described in the above-described embodiment, which is arranged adjacent to the impeller in the axial direction of the rotary shaft.

[0009] According to the present invention, when the centrifugal pump is operating in a flow rate range lower than the design point, the occurrence of stall occurring in the flow of the handled liquid in the diffuser passage of the centrifugal pump is reduced.

[0010] 1. A schematic cross-sectional view of a centrifugal pump showing an embodiment of the present invention. 2. A perspective view of a diffuser showing an embodiment of the present invention. 3. A side view of a diffuser body with the diffuser housing of the diffuser removed. 4. A partially enlarged cross-sectional view of the centrifugal pump showing the flow of handled liquid flowing inside the impeller and diffuser provided in the centrifugal pump of FIG. 1. 5. A schematic diagram explaining the flow of handled liquid in a diffuser flow path formed by the diffuser of FIG. 2, in which (a) is a schematic diagram showing a state in which the centrifugal pump is operating at a design point, and (b) is a schematic diagram showing a state in which the centrifugal pump is operating in a flow rate range lower than the design point. 6. A list of patterns of uneven surfaces showing modified examples of the diffuser provided in the centrifugal pump of the present invention. 7. A schematic diagram showing the shape of the unevenness of the uneven surface shown in FIG. 6 and the arrangement surface of the uneven surface. 8. A schematic diagram showing the pattern shape of the uneven surface shown in FIG. 6. 9. A schematic diagram showing the pitch of the unevenness in the uneven surface shown in FIG. 6. 6 is a graph showing the head capacity of the centrifugal pump for each of the modified examples (No. 1 to No. 12) shown in FIG. 6. FIG. 7 is a graph showing the pump efficiency of the centrifugal pump for each of the modified examples (No. 1 to No. 12) shown in FIG. 6. FIG. 8 is a graph showing the backflow rate of the diffuser flow passage for each of the modified examples (No. 1 to No. 12) shown in FIG. 6. FIG. 9 is a graph showing the number of diffuser flow passages in which backflow occurs for each of the modified examples (No. 1 to No. 12) shown in FIG. 6. FIG. 10 is a table of concave-convex surface patterns showing another modified example of a diffuser provided in a centrifugal pump according to the present invention. FIG. 11 is a graph showing the head capacity of the centrifugal pump for another modified example (No. 13) shown in FIG. 14. FIG. 12 is a graph showing the pump efficiency of the centrifugal pump for another modified example (No. 13) shown in FIG. 14. FIG. 13 is a graph showing the backflow rate of the diffuser flow passage for another modified example (No. 13) shown in FIG. 15 is a graph showing the number of diffuser passages in which backflow occurs in another modified example (No. 13) shown in FIG. 14 .

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

[0012] In the following description, the centrifugal pump according to the present invention is attached to a storage tank that mainly stores liquefied gas. The centrifugal pump is described as a submerged motor pump that pumps liquefied gas from the storage tank to the outside. The centrifugal pump is housed in a pump column. The pump column housing the centrifugal pump extends from the ceiling of the storage tank into the storage tank. The submerged motor pump is an example of the centrifugal pump according to the present invention. Liquefied gas is an example of the handled liquid in the present invention.

[0013] In the following description, "downward" refers to the direction of gravity, and "upward" refers to the opposite direction of "downward."

[0014] Centrifugal Pump Configuration of Centrifugal Pump The configuration of the centrifugal pump according to the present invention (hereinafter referred to as "the pump") will be described below.

[0015] FIG. 1 is a schematic cross-sectional view of the pump according to an embodiment of the present invention.

[0016] This pump 1 pumps pumped liquid. This pump 1 sucks pumped liquid stored in a storage tank (not shown) from below. This pump 1 pumps the sucked pumped liquid upward. This pump 1 is housed at the lower end of a pump column C. This pump 1 is immersed in the pumped liquid in the storage tank within the pump column C. This pump 1 discharges the pumped liquid stored in the storage tank into the pump column C. The discharged pumped liquid flows within the pump column C. The configuration of this pump 1 is the same as that of a known submerged motor pump, except for the configuration of a diffuser 6, which will be described later.

[0017] The pump 1 includes a housing 2 , a motor 3 , a rotating shaft 4 , an impeller 5 , and a diffuser 6 .

[0018] The housing 2 houses the motor 3, the rotary shaft 4, the impeller 5, and the diffuser 6. The housing 2 is housed inside the pump column C. The housing 2 is substantially cylindrical in shape. The housing 2 has a suction port 21 and a discharge port (not shown). The lower end of the housing 2 has a reduced diameter, forming the suction port 21.

[0019] In the following description, the "upstream side" refers to the upstream side in the flow of the pumped liquid being pumped to the pump 1. The "downstream side" refers to the downstream side in the flow of the pumped liquid.

[0020] The motor 3 is driven at a predetermined drive voltage and drive frequency to rotate the impeller 5, which will be described later. The motor 3 has a rotary shaft 4 at its rotational center. The motor 3 is a known motor that includes a rotor 31 attached to the rotary shaft 4 and a stator 32 that rotates the rotor 31. The motor 3 is connected to a power source (not shown) that operates the motor 3. The motor 3 is also connected to a control device (not shown) that controls the rotation of the motor 3.

[0021] The rotary shaft 4 rotates due to the rotation of the motor 3 and transmits rotational power to the impeller 5. The rotary shaft 4 has a cylindrical shape. A tip end 41 of the rotary shaft 4 extends downward from the motor 3.

[0022] The impeller 5 delivers the pumped fluid at a flow rate that corresponds to the rotation of the motor 3. The impeller 5 draws in the pumped fluid as the motor 3 rotates. The impeller 5 imparts velocity energy to the pumped fluid drawn in from below, and discharges the pumped fluid radially outward. In other words, the impeller 5 discharges the drawn pumped fluid toward the diffuser 6. The impeller 5 is attached to the rotating shaft 4. The impeller 5 is disposed downstream of the suction port 21 in the axial direction of the rotating shaft 4.

[0023] Diffuser Configuration Fig. 2 is a perspective view of a diffuser showing an embodiment of the diffuser according to the present invention. Fig. 3 is a side view of the diffuser body with the diffuser housing removed. In the following description, Fig. 1 will be referenced as appropriate.

[0024] The diffuser 6 reduces the flow velocity of the treated fluid discharged from the impeller 5 to increase the pressure of the treated fluid. That is, the diffuser 6 converts the velocity energy imparted to the treated fluid by the impeller 5 into pressure energy. The diffuser 6 is disposed adjacent to the impeller 5 in the axial direction of the rotary shaft 4. The diffuser 6 is disposed downstream of the impeller 5. The diffuser 6 is a so-called axial type diffuser. The diffuser 6 is made of a metal such as an aluminum alloy. The diffuser 6 includes a diffuser main body 7 and a diffuser housing 8.

[0025] In the following description, the “radial direction” refers to a direction along the radius of the diffuser 6. The “circumferential direction” refers to a direction along the circumference of the diffuser 6.

[0026] The diffuser body 7 constitutes a part of the flow path through which the treated liquid flows. The diffuser body 7 has a cylindrical shape with a bottom. The diffuser body 7 includes an inner tubular portion 71, vanes 72, a bottom portion 73, and support holes 74.

[0027] The inner cylinder portion 71 has an outer peripheral surface 71a, an inner peripheral surface 71b (see FIG. 4), a lower end portion 71c, and a rear end portion 71d. The inner cylinder portion 71 is cylindrical in shape. In the radial direction of the inner cylinder portion 71, the outer peripheral surface 71a is the outer surface of the inner cylinder portion 71. In the radial direction of the inner cylinder portion 71, the inner peripheral surface 71b is the inner surface of the inner cylinder portion 71. In a diffuser flow path DL (described below), the lower end portion 71c is the upstream end of the flow of the pumped fluid and is the end on the inlet side. In the diffuser flow path DL, the rear end portion 71d is the downstream end of the flow of the pumped fluid and is the end on the discharge port side. The inner cylinder portion 71 has an internal space 711 (see FIG. 4) on its inner side. The outer peripheral surface 71a has an uneven surface 9 (described below).

[0028] The vanes 72 extend outward from the outer circumferential surface 71a in the radial direction of the outer circumferential surface 71a. The diffuser body 7 includes eight vanes 72 (721 to 728). In the following description, when the vanes 721 to 728 are not particularly distinguished from one another, the vanes 721 to 728 and the components of each of the vanes 721 to 728 are denoted by the reference numeral "72" instead of the reference numerals "721 to 728."

[0029] The vanes 721 to 728 are arranged at equal angular intervals in the circumferential direction on the outer peripheral surface 71a of the inner cylindrical portion 71. Each of the vanes 721 to 728 protrudes radially from the outer peripheral surface 71a. When viewed from the bottom, the vanes 721 to 728 are arranged clockwise in the order indicated by their reference numerals.

[0030] The vane 72 has a pressure surface 72e and a suction surface 72f. The configuration of the vane 72 is the same as the configuration of vanes included in known diffusers. When viewed in the radial direction, the vane 72 has a generally arcuate plate shape extending from the lower end 71c of the inner cylindrical portion 71 to the rear end 71d. The pressure surface 72e is the upper surface of the vane 72. The suction surface 72f is the lower surface of the vane 72. When viewed in the radial direction, the positive pressure surface 72e has a concave shape. The suction surface 72f is the surface opposite to the positive pressure surface 72e. When viewed in the radial direction, the suction surface 72f has a convex shape that generally follows the shape of the positive pressure surface 72e.

[0031] The bottom 73 is connected to the lower end 71c of the inner cylindrical portion 71. The inner cylindrical portion 71 is arranged to extend upward from the outer edge of the bottom 73. The bottom 73 is generally disk-shaped. The center of the bottom 73 protrudes upward in a mountain-like shape. A support hole 74 is arranged in the center of the bottom 73. The support hole 74 is a hole into which the rotating shaft 4 is rotatably inserted. The bottom 73 is equipped with a rectifying plate 731 (see FIG. 4) that rectifies the flow of the treated fluid. The rectifying plate 731 extends upward in a plate-like shape (see FIG. 4). The rectifying plate 731 is arranged in the internal space 711.

[0032] The diffuser housing 8 accommodates the diffuser body 7. The diffuser housing 8 constitutes a part of the flow path through which the treated liquid flows. The diffuser housing 8 includes an outer cylinder portion 81 and a connecting portion 82.

[0033] The outer cylinder portion 81 has an outer peripheral surface 81a and an inner peripheral surface 81b. The outer cylinder portion 81 is cylindrical in shape. In the radial direction of the outer cylinder portion 81, the outer peripheral surface 81a is the surface on the outer side of the outer cylinder portion 81. In the radial direction of the outer cylinder portion 81, the inner peripheral surface 81b is the surface on the inner side of the outer cylinder portion 81. The inner peripheral surface 81b of the outer cylinder portion 81 is disposed so as to face the outer peripheral surface 71a of the diffuser body 7.

[0034] The connecting portion 82 guides the treated fluid discharged from a diffuser flow path DL (described later) to the inside (internal space 711) of the inner cylindrical portion 71. The connecting portion 82 is connected to the upper end of the outer cylindrical portion 81. The connecting portion 82 is disposed above the vane 72 and the inner cylindrical portion 71. In other words, the connecting portion 82 is disposed on the discharge port side of the diffuser flow path DL.

[0035] 4 is a partially enlarged cross-sectional view of the pump 1 showing the flow of the pumped liquid through the impeller 5 and the diffuser 6 of the pump 1. In the following description, FIGS. 1 to 3 will be referred to as appropriate.

[0036] The inner circumferential surface 81b of the diffuser housing 8 is disposed to face the outer circumferential surface 71a of the diffuser body 7. That is, the space between adjacent vanes 72, 72 in the circumferential direction is covered by the diffuser housing 8. As a result, the opposing positive pressure surfaces 72e and negative pressure surfaces 72f of adjacent vanes 72, 72, the outer circumferential surface 71a of the diffuser body 7, and the inner circumferential surface 81b of the diffuser housing 8 form a diffuser flow path DL.

[0037] The diffuser flow passage DL reduces the flow velocity of the pumped fluid discharged from the impeller 5 and increases the pressure of the pumped fluid. The diffuser flow passage DL is a flow passage for the pumped fluid separated by multiple vanes 72 within the diffuser 6. Specifically, the diffuser flow passage DL is defined by the outer peripheral surface 71a of the diffuser body 7, the multiple vanes 72, and the inner peripheral surface 81b of the diffuser housing 8. The diffuser 6 has eight diffuser flow passages DL. Specifically, each diffuser flow passage DL is surrounded by the outer peripheral surface 71a of the diffuser body 7, the positive pressure surface 72e and the negative pressure surface 72f of the vane 72, and the inner peripheral surface 81b of the diffuser housing 8. The pumped fluid discharged from the impeller 5 flows through the diffuser flow passage DL. In the diffuser flow passage DL, the cross-sectional area perpendicular to the flow direction of the pumped fluid is smallest at the inlet (upstream side) and increases downstream.

[0038] As described above, the uneven surface 9 is disposed on the outer peripheral surface 71a of the diffuser body 7. The uneven surface 9 has a plurality of recesses disposed over substantially the entire surface of the outer peripheral surface 71a. The recesses of the uneven surface 9 are hemispherical in shape. The recesses are hemispherical in shape with a diameter of 4 mm and a radius (depth) of 2 mm. The recesses protrude inward in the radial direction. The uneven surface 9 is formed by molding.

[0039] The uneven surface 9 may be provided on at least one of the outer peripheral surface 71 a of the diffuser body 7 and the inner peripheral surface 81 b of the diffuser housing 8. The outer peripheral surface 71 a of the diffuser body 7 and / or the inner peripheral surface 81 b of the diffuser housing 8 may be provided with at least one of a plurality of recesses and a plurality of protrusions. The uneven surface 9 is disposed over the entire outer peripheral surface 71 a of the diffuser body 7 and / or the entire inner peripheral surface 81 b of the diffuser housing 8.

[0040] The control device (not shown) controls the operation of the motor 3 to control the flow rate (discharge flow rate) of the pumped fluid discharged from the pump 1. The control device includes a control unit (not shown), a memory unit (not shown), and a display unit (not shown).

[0041] The control unit controls the operation of the pump 1. The control unit acquires flow rate information of the pump 1 and rotation information of the motor 3 as sensor information via a sensor (not shown). The flow rate information is information related to the flow rate of the pumped liquid being discharged from the pump 1. The rotation information is information related to the rotation of the rotating shaft 4 of the motor 3. The control unit controls the operation of the motor 3 to obtain the flow rate of the pump 1 based on the sensor information. The control unit stores the measured sensor information and control information for controlling the rotation of the rotating shaft 4 of the motor 3 in the memory unit. The control unit transmits the sensor information and control information to the display unit. The control unit is connected to the memory unit and the display unit.

[0042] The control unit is composed of, for example, a processor such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), or DSP (Digital Signal Processor), a volatile memory such as RAM (Random Access Memory) that functions as the processor's working area, and a non-volatile memory such as ROM (Read Only Memory) that stores various information such as control of data analysis processing.

[0043] The storage unit stores the sensor information and the control information. The storage unit is connected to the display unit. The storage unit may be, for example, a portable storage medium such as a hard disk drive (HDD), a solid state drive (SSD), or a flash memory, or other non-transitory storage medium, or a RAM or other temporary storage medium.

[0044] The display unit displays sensor information and control information. The display unit is a touch panel. A user of the pump 1 controls the operation of the pump 1 by operating the operation screen displayed on the display unit.

[0045] Operation of the Centrifugal Pump Next, the operation of the present pump 1 will be explained below. In the following explanation, reference will be made to Figures 1 to 4 as appropriate.

[0046] 5A and 5B are schematic diagrams illustrating the flow of pumped liquid in the diffuser flow path DL formed by the diffuser 6. Fig. 5A is a schematic diagram illustrating the pump 1 operating at a design point. Fig. 5B is a schematic diagram illustrating the pump 1 operating in a flow rate range lower than the design point. These figures are schematic diagrams illustrating the diffuser 6 deployed in the circumferential direction.

[0047] The design point refers to a point on the performance curve of the discharge amount, head, etc. at which the pump 1 operates most efficiently.

[0048] As described above, the pump 1 draws the pumped liquid stored in the storage tank from below and pumps it upward. The pump 1 draws the pumped liquid through the suction port 21 of the housing 2 as the impeller 5 rotates.

[0049] The pumped fluid sucked into the impeller 5 is discharged radially outward from the impeller 5. The pumped fluid discharged from the impeller 5 has its flow direction changed upward by the housing 2 and flows into the diffuser flow path DL while swirling in the circumferential direction.

[0050] FIG. 5A shows the pump 1 operating at its design point. The inflow angle "α" of the pumped liquid flowing into the diffuser flow passage DL is adjusted to be close to a suitable design angle (e.g., α≒β: a range in which the angle of attack is several degrees) relative to the inlet angle "β" of the vane 72. The pumped liquid passes through the diffuser flow passage DL, whereby its flow velocity is reduced and its pressure is increased. As shown in FIG. 4, the pumped liquid that has passed through the diffuser flow passage DL is guided into the internal space 711 of the inner tubular portion 71 via the connecting portion 82. The pressurized pumped liquid is discharged from a discharge port (not shown) into the pump column C and flows upward within the pump column C.

[0051] 5B shows the pump 1 operating at a flow rate lower than the design point. The inflow angle "α" of the pumped liquid flowing into the diffuser flow passage DL decreases, and the difference between the inflow angle "α" and the inlet angle "β" of the vane 72 increases (the angle of attack increases). As a result, in the region in contact with the suction surface 72f of the vane 72, separation of the pumped liquid occurs, starting from the upstream end of the suction surface 72f. When separation occurs, the region where separation occurs (hereinafter referred to as the "separated region PA") expands over time.

[0052] The separation region PA is a region in the diffuser flow path DL where separation of the pumped fluid occurs, starting from the upstream end of the negative pressure surface 72 f of the vane 72 .

[0053] When the separation area PA increases, a backflow of the pumped liquid occurs downstream of the diffuser flow path DL where the separation occurs.

[0054] The backflow is a flow in the diffuser flow passage DL in the opposite direction to the flow of the pumped liquid (the assumed normal flow) when the pump 1 is operating at the design point.

[0055] The backflow area BA is an area in the diffuser flow passage DL where a backflow occurs.

[0056] The backflow occurs on the suction surface 72f side of the diffuser flow passage DL where separation is occurring, downstream of the diffuser flow passage DL. As a result, the diffuser flow passage DL is blocked by the separation area PA and the backflow area BA. When the diffuser flow passage DL is blocked, a stall occurs, where the flow in the diffuser flow passage DL stagnates.

[0057] Stall is a phenomenon in which the flow of the handled liquid in the diffuser flow passage DL is stagnated.

[0058] The stall occurs mainly in one of the diffuser passages DL of all the diffuser passages DL included in the diffuser 6. As a result, the symmetry of the flow of the pumped liquid relative to the central axis of the pump 1 is lost. When the flow symmetry is lost, a force acting on the pump 1 in the radial direction of the rotating shaft 4 is generated. Over time, this force acts in a rotating manner around the circumferential direction of the rotating shaft 4. The stall propagates to the adjacent diffuser passage DL, rotating around the circumferential direction of the rotating shaft 4 over time. When the diffuser passage DL in which the stall occurs is replaced by another diffuser passage DL, the direction of the force acting on the pump 1 changes, causing vibrations in the pump 1. In this way, when the pump 1 is operating in a low flow rate range, a rotating stall that causes vibrations in the pump 1 can occur.

[0059] The diffuser 6 has an uneven surface 9 composed of a plurality of recesses on the outer peripheral surface 71a of the diffuser body 7. A portion of the treated liquid discharged from the impeller 5 flows along this uneven surface 9. The treated liquid flowing along the uneven surface 9 forms a vortex following the shape of the uneven surface 9.

[0060] The vortex flow is a flow of the handled fluid that flows along the shape of the uneven surface 9. The vortex flow includes flows in multiple directions. The vortex flow interferes with the flow in the separation region PA and the flow in the reverse flow region BA, which cause stall, and disrupts the flow in the separation region PA and the flow in the reverse flow region BA. In other words, the collision of the vortex flow with the separation flow and the reverse flow generates turbulence in the separation region PA and the reverse flow region BA. This turbulence reduces the occurrence of stall, thereby suppressing the occurrence of rotating stall in the present pump 1.

[0061] The diffuser 6 suppresses the occurrence of rotating stall in the pump 1 even when the pump 1 operates in a flow rate range lower than the design point. Therefore, the reduction in the suction performance of the pump 1 equipped with the diffuser 6 according to the present invention is reduced.

[0062] Modification (1) Next, a modification of the diffuser 6 included in the pump 1 will be described. In this modification, the arrangement and shape of the uneven surface 9 of the diffuser 6 differ from those of the previously described embodiment. In the following modification, reference will be made to Figures 1 to 5 as appropriate.

[0063] Fig. 6 is a list of patterns of the diffuser 6. The list shows the arrangement surface, surface irregularities, pattern shape, diameter, depth, and pitch for each of 12 types of diffuser 6 patterns. Fig. 7 is a schematic diagram showing the shape of the irregularities of the irregular surface 9 and the arrangement surface of the irregular surface 9. Fig. 8 is a schematic diagram showing the pattern shape of the irregular surface 9. Fig. 9 is a schematic diagram showing the pitch of the irregularities on the irregular surface 9.

[0064] The 12 types of diffusers 6 shown in Fig. 6 are compared with a comparative example (Base). The 12 types of diffusers 6 are identified by numbers No. 1 to No. 12. The diffuser 6 of the previously described embodiment corresponds to No. 4.

[0065] The "arrangement surface" in the table indicates whether the uneven surface 9 is arranged on either the outer peripheral surface 71a of the diffuser main body 7 or the inner peripheral surface 81b of the diffuser housing 8. For the outer peripheral surface of the main body, the uneven surface 9 is arranged on the outer peripheral surface 71a of the diffuser main body 7. For the inner peripheral surface of the housing, the uneven surface 9 is arranged on the inner peripheral surface 81b of the diffuser housing 8. The uneven surface 9 is arranged over substantially the entire surface of either the outer peripheral surface 71a or the inner peripheral surface 81b.

[0066] In the table, "surface unevenness" indicates whether the surface of the uneven surface 9 is concave or convex. That is, the surface unevenness indicates whether a concave portion is formed radially inward from the outer peripheral surface 71 a of the diffuser body 7, or whether a convex portion is formed radially outward from the outer peripheral surface 71 a of the diffuser body 7. Alternatively, the surface unevenness indicates whether a concave portion is formed radially outward from the inner peripheral surface 81 b of the diffuser housing 8, or whether a convex portion is formed radially inward from the inner peripheral surface 81 b of the diffuser housing 8.

[0067] In the present invention, the unevenness of the surface is not limited to only recesses or protrusions, and may be, for example, a mixture of recesses and protrusions.

[0068] The "pattern shape" in the table refers to the shape of the recesses or protrusions of the uneven surface 9. As shown in Fig. 8, A indicates a hemispherical shape, B indicates a triangular prism shape, and C indicates a quadrangular prism shape.

[0069] The "diameter" in the table indicates the size of the recesses or protrusions of the uneven surface 9. The diameter is expressed in millimeters. The diameter is based on the size of a square having vertical and horizontal lengths. That is, the diameter is the vertical and horizontal size of a circle for a hemispherical shape (A), an equilateral triangle for a triangular prism shape (B), and a rectangle for a quadrangular prism shape (C). For example, a diameter of 4 mm for a circle indicates that the pattern fits exactly in a circle with a diameter of 4 mm. A regular triangle of 4 mm indicates that the pattern fits exactly in a square with 4 mm length and width. A rectangle of 4 mm indicates that the pattern is a square with 4 mm length and width.

[0070] The "depth" in the table refers to the depth of the recesses and / or the height of the protrusions of the uneven surface 9. That is, the depth indicates the length from the outer peripheral surface 71a of the diffuser body 7 and / or the inner peripheral surface 81b of the diffuser housing 8 to the bottom of the recesses or the top of the protrusions. The depth of the recesses and / or the height of the protrusions are indicated in mm.

[0071] "Pitch" in the table indicates the pitch (denseness) between the projections and recesses. "Standard" indicates that the length between adjacent projections and recesses is a standard length. In the standard case, the length between the bottoms or peaks of adjacent projections and recesses is approximately twice the diameter. In the standard case, multiple recesses or multiple peaks are alternately arranged in the axial direction of the diffuser 6. "Alternate" indicates that multiple recesses or multiple peaks are arranged with an alternating offset in the axial direction of the diffuser 6. "Wide" indicates that the length between adjacent projections and recesses is longer than the standard length. In the wide case, the length between the bottoms or peaks of adjacent projections and recesses is approximately three times the diameter.

[0072] Basic operating environment of the pump 1 Next, the basic operating environment of the pump 1 will be explained. In this embodiment, the handled liquid is water. The temperature of the water is set to 25°C. The density of water is 997 kg / m ３The dynamic viscosity of water is 0.0008899 kg / (m·s). The inlet condition is static pressure, and the outlet condition is set as mass flow rate.

[0073] Comparison of Modification (1) with Comparative Example Next, a comparison between a modification of the diffuser 6 provided in the present pump 1 and a comparative example will be described. First, the relationship between the head of the modification of the diffuser 6 provided in the present pump 1 and the head of the comparative example will be described.

[0074] FIG. 10 is a graph showing the head capacity of the pump 1 for each of the modified examples (No. 1 to No. 12).

[0075] In FIG. 10, the horizontal axis represents the flow rate (m ３ / h). The vertical axis indicates the head (m) of this pump 1 against the flow rate.

[0076] Each variant of this pump 1 is 40 m ３ / h~65m ３ When operated at a flow rate of 25 m / h, the head of each of the modified examples is smaller than the head of the comparative example. ３ When operated at a flow rate of around 20 m / h, the head of each of the modified examples begins to increase more than the head of the comparative example. ３ When operated at a flow rate of 1 / h, the head of all the variants is greater than the head of the comparative example. That is, in each variant of the present pump 1, the head is increased in the low flow rate range.

[0077] Next, the relationship between the pump efficiency of a modified example of the diffuser 6 provided in the pump 1 and the pump efficiency of a comparative example will be described.

[0078] FIG. 11 is a graph showing the pump efficiency of the pump 1 for each of the modified examples (No. 1 to No. 12).

[0079] In FIG. 11, the horizontal axis represents the flow rate (m ３ / h). The vertical axis shows the pump efficiency (%) of this pump 1 against the flow rate. Pump efficiency is calculated by hydraulic power (kW) ÷ shaft power (kW) × 100 (%). Hydraulic power is calculated by density of handled liquid × flow rate × total head. Shaft power refers to the power that the motor 3 gives to this pump 1 when it is operated.

[0080] Each variant of this pump 1 is 40 m ３ / h~65m ３ When operated at a flow rate of 25 m / h, the pump efficiency of each modified example is lower than that of the comparative example. ３ When operated at a flow rate of around 20 m / h, the pump efficiency of each variant shows some increases and some decreases compared to the pump efficiency of the comparative example. ３ When operated at a flow rate of 1 / h, the pump efficiency of each variant is sometimes higher than that of the comparative example, and sometimes lower. That is, in each variant of the present pump 1, the pump efficiency is increased in the low flow rate range.

[0081] Next, the relationship between the backflow amount of the pumped fluid in the diffuser flow passage DL in the modified example of the diffuser 6 of the pump 1 and the backflow amount of the pumped fluid in the diffuser flow passage DL in the comparative example will be described.

[0082] The backflow amount is the amount of backflow of the handled liquid flowing through the diffuser flow passage DL.

[0083] FIG. 12 is a graph showing the backflow amount in the diffuser flow passage DL for each of the modified examples (No. 1 to No. 12).

[0084] In FIG. 12, the horizontal axis represents the flow rate (m ３ The vertical axis represents the backflow rate (kg / s) of the treated liquid in the diffuser flow path DL.

[0085] Each variant of this pump 1 is 40 m ３ / h~65m ３ When operated at a flow rate of 40 m / h, no backflow occurs in either variant. ３When the pump 1 is operated at a flow rate less than 40 m / h, a backflow occurs. ３ This occurs when the pump 1 is operated at a flow rate less than 25 m / h. ３ When operated at a flow rate of around 20 m / h, the backflow rate of all the modified examples is smaller than that of the comparative example. ３ When operated at a flow rate of 1 / h, the backflow rate of each of the modified examples is sometimes greater than that of the comparative example, and sometimes less than that. That is, each of the modified examples of the present pump 1 has a reduced backflow rate in the low flow rate range.

[0086] Next, the relationship between the number of diffuser flow passages DL in which backflow occurs in the modified example of the diffuser 6 included in the pump 1 and the number of diffuser flow passages DL in which backflow occurs in the comparative example will be described.

[0087] FIG. 13 is a graph showing the number of diffuser passages DL in which backflow occurs for each of the modified examples (No. 1 to No. 12).

[0088] In FIG. 13, the horizontal axis represents the flow rate (m ３ / h). The vertical axis indicates the number of diffuser passages DL where backflow occurs.

[0089] Each variant of this pump 1 is 40 m ３ / h~65m ３ When operated at a flow rate of 40 m / h, no backflow occurs in either variant. ３ When the pump 1 is operated at a flow rate less than 1 / h, a backflow occurs. That is, the diffuser flow path DL where the backflow occurs is 40 m. ３ This occurs when the pump 1 is operated at a flow rate less than 25 m / h. ３ When operated at a flow rate of around 20 m / h, the number of diffuser passages DL where backflow occurs in each of the modified examples except for No. 12 is smaller than the number in the comparative example. ３When operated at a flow rate of 1 / h, the number of diffuser passages DL where backflow occurs in each of the modified examples except for No. 12 is smaller than the number in the comparative example. That is, in each of the modified examples of the present pump 1 except for No. 12, the number of diffuser passages DL where backflow occurs is reduced in the small flow rate range.

[0090] Summary (1) According to the embodiment described above, the diffuser 6, together with the outer peripheral surface 71a of the diffuser body 7, the plurality of vanes 72, and the inner peripheral surface 81b of the diffuser housing 8, defines the plurality of diffuser flow passages DL through which the treated fluid discharged from the impeller 5 flows. At least one of the outer peripheral surface 71a and the inner peripheral surface 81b has an uneven surface 9 having at least one of a plurality of recesses and a plurality of protrusions. With this configuration, a portion of the treated fluid flowing through the diffuser flow passages DL flows onto the uneven surface 9. The treated fluid flowing onto the uneven surface 9 forms a vortex along the shape of the uneven surface 9. The vortex collides with the treated fluid flow in the diffuser flow passage DL, inhibiting the separation flow and the backflow (increase). That is, the vortex collides with the flow in the separation region PA and the flow in the backflow region BA, which cause stall, generating turbulence in the separation region PA and the backflow region BA. This turbulence reduces the occurrence of stall, and the occurrence of rotating stall in the present pump 1 is suppressed.

[0091] According to the embodiment described above, the uneven surface 9 of the diffuser 6 is disposed over the entire outer circumferential surface 71a of the diffuser body 7 and / or the entire inner circumferential surface 81b of the diffuser housing 8. With this configuration, a portion of the treated fluid flowing through the diffuser flow passage DL flows onto the uneven surface 9. The treated fluid flowing onto the uneven surface 9 forms vortices along the shape of the uneven surface 9. The vortices collide with the treated fluid flow in the diffuser flow passage DL, inhibiting the increase of separated flows and reverse flows. Specifically, the vortices collide with the flows in the separation region PA and the reverse flow region BA, which cause stall, generating turbulence in the separation region PA and the reverse flow region BA. This turbulence reduces the occurrence of stall, thereby suppressing the occurrence of rotating stall in the pump 1.

[0092] Furthermore, according to the embodiment described above, the uneven surface 9 of the diffuser 6 is disposed only on the outer peripheral surface 71a of the diffuser body 7. This configuration reduces the number of processing steps and processing costs compared to processing both the outer peripheral surface 71a of the diffuser body 7 and the inner peripheral surface 81b of the diffuser housing 8.

[0093] Furthermore, according to the embodiment described above, the uneven surface 9 of the diffuser 6 is disposed only on the inner circumferential surface 81b of the diffuser housing 8. This configuration reduces the number of processing steps and processing costs compared to processing both the outer circumferential surface 71a of the diffuser body 7 and the inner circumferential surface 81b of the diffuser housing 8.

[0094] Modified Example (2)

[0095] Next, another modification of the diffuser 6 included in the pump 1 will be described. This modification differs from the previously described embodiment in that the uneven surface 9 of the diffuser 6 is disposed on a portion of the outer circumferential surface 71a of the diffuser body 7. In the following modification, reference will be made to FIGS. 1 to 9 as appropriate.

[0096] 14 is a table of patterns of another modified example of the diffuser 6. The table shows the arrangement surface, surface irregularities, arrangement region, pattern shape, diameter, depth, and pitch of the pattern of another modified example of the diffuser 6. The arrangement surface, surface irregularities, pattern shape, diameter, depth, and pitch in the table are the same as those in the previous modified example (1).

[0097] The diffuser 6 shown in Figure 14 is compared with a comparative example (Base). The diffuser 6 is identified by the number No. 13.

[0098] The "arrangement region" in the table refers to a partial region where the uneven surface 9 is arranged on the outer peripheral surface 71a of the diffuser body 7 and the inner peripheral surface 81b of the diffuser housing 8. The arrangement region is a predetermined region where the uneven surface 9 is arranged to reduce the occurrence of stall.

[0099] The arrangement surface of the modified example (No. 13) is the outer peripheral surface 71a of the diffuser body 7. The unevenness of the uneven surface 9 of the modified example (No. 13) forms recesses radially inward from the outer peripheral surface 71a of the diffuser body 7.

[0100] In Modification Example No. 13, the arrangement region is located on the outer peripheral surface 71a of the diffuser body 7. The arrangement region is located on the downstream side of the diffuser flow path DL. The area of ​​the arrangement region is approximately one-third of the area of ​​the outer peripheral surface 71a of the diffuser body 7 in the diffuser flow path DL. In other words, the uneven surface 9 is located on approximately one-third of the outer peripheral surface 71a of the diffuser body 7 on the downstream side of the diffuser flow path DL.

[0101] In the irregular surface 9 of the modified example (No. 13), multiple recesses are arranged only on the downstream side of the outer peripheral surface 71a. The recesses of the irregular surface 9 are hemispherical in shape. The recesses are hemispherical in shape, with a diameter of 4 mm and a radius (depth) of 2 mm. The pitch length between adjacent irregularities is approximately twice the diameter.

[0102] Basic Operating Environment of the Pump 1 In this embodiment, the basic operating environment of the pump 1 is the same as that of the previous modification (1).

[0103] Comparison of Modification (2) with Comparative Example Next, a comparison between a modification of the diffuser 6 provided in the present pump 1 and a comparative example will be described. First, the relationship between the head of the modification of the diffuser 6 provided in the present pump 1 and the head of the comparative example will be described.

[0104] FIG. 15 is a graph showing the head capacity of the pump 1 according to the modified example (No. 13).

[0105] In FIG. 15, the horizontal axis represents the flow rate (m ３ / h). The vertical axis indicates the head (m) of this pump 1 against the flow rate.

[0106] The modified example of this pump 1 (No. 13) is 65 m ３ When operated at a flow rate of 45 m / h, the head of the modified example (No. 13) is reduced compared to the head of the comparative example. ３When operated at a flow rate of 25 m / h, the head of the modified example (No. 13) is approximately the same as that of the comparative example. ３ When operated at a flow rate of around 20 m / h, the head of the modified example (No. 13) begins to increase more than the head of the comparative example. ３ When operated at a flow rate of 1 / h, the head of the modified example (No. 13) is increased over the head of the comparative example.

[0107] Next, the relationship between the pump efficiency of a modified example of the diffuser 6 provided in the pump 1 and the pump efficiency of a comparative example will be described.

[0108] FIG. 16 is a graph showing the pump efficiency of the present pump 1 according to the modified example (No. 13).

[0109] In FIG. 16, the horizontal axis represents the flow rate (m ３ / h). The vertical axis indicates the pump efficiency (%) of the pump 1 relative to the flow rate.

[0110] Pump 1 variant (No. 13) is 65 m ３ When operated at a flow rate of 45 m / h, the pump efficiency of the modified example (No. 13) is reduced compared to the pump efficiency of the comparative example. ３ When operated at a flow rate of 25 m / h, the pump efficiency of the modified example (No. 13) is approximately the same as that of the comparative example. ３ When operated at a flow rate of around 20 m / h, the pump efficiency of the modified example (No. 13) is higher than that of the comparative example. ３ When operated at a flow rate of 1 / h, the pump efficiency of the modified example (No. 13) is reduced compared to the pump efficiency of the comparative example.

[0111] Next, the relationship between the backflow amount of the pumped fluid in the diffuser flow passage DL in the modified example of the diffuser 6 of the pump 1 and the backflow amount of the pumped fluid in the diffuser flow passage DL in the comparative example will be described.

[0112] FIG. 17 is a graph showing the backflow amount in the diffuser flow path DL of the modified example (No. 13).

[0113] In FIG. 17, the horizontal axis represents the flow rate (m ３ The vertical axis represents the backflow rate (kg / s) of the treated liquid in the diffuser flow path DL.

[0114] The modified example (No. 13) of this pump 1 is 40 m ３ / h~65m ３ When operated at a flow rate of 40 m / h, no backflow occurs in the modified example (No. 13). ３ When the pump 1 is operated at a flow rate less than 40 m / h, a backflow occurs. ３ This occurs when the pump 1 is operated at a flow rate less than 25 m / h. ３ When operated at a flow rate of around 20 m / h, the backflow rate of the modified example (No. 13) is smaller than that of the comparative example. ３ When operated at a flow rate of 1 / h, the backflow amount of the modified example (No. 13) is greater than that of the comparative example.

[0115] Next, the relationship between the number of diffuser flow passages DL in which backflow occurs in the modified example of the diffuser 6 included in the pump 1 and the number of diffuser flow passages DL in which backflow occurs in the comparative example will be described.

[0116] FIG. 18 is a graph showing the number of diffuser passages DL in which backflow occurs in the modified example (No. 13).

[0117] In FIG. 18, the horizontal axis represents the flow rate (m ３ / h). The vertical axis indicates the number of diffuser passages DL where backflow occurs.

[0118] The modified example (No. 13) of this pump 1 is 40 m ３ / h~65m ３ When operated at a flow rate of 40 m / h, no backflow occurs in the modified example (No. 13). ３When the pump 1 is operated at a flow rate less than 1 / h, a backflow occurs. That is, the diffuser flow path DL where the backflow occurs is 40 m. ３ This occurs when the pump 1 is operated at a flow rate less than 25 m / h. ３ When the pump 1 is operated at a flow rate of around 20 m / h, the number of diffuser passages DL where backflow occurs in the modified example (No. 13) is smaller than the number in the comparative example. ３ When operated at a flow rate of 1 / h, the number of diffuser passages DL in which backflow occurs in the modified example (No. 13) is the same as the number in the comparative example.

[0119] From the above, compared to variant (1) in which the uneven surface 9 is arranged over almost the entire surface, variant (No. 13) suppresses the decrease in head and pump efficiency of this pump 1 even in a flow rate range close to the set point.

[0120] Other Embodiments: In the present invention, the uneven surface 9 is disposed on approximately the downstream one-third of the outer peripheral surface 71a of the diffuser body 7. However, the uneven surface 9 may be disposed on only another portion of the outer peripheral surface 71a if the occurrence of stall can be reduced. That is, for example, the uneven surface 9 may be disposed in a position adjacent to an area where separation of the treated fluid flowing through the diffuser flow passage DL from the suction surface 72f occurs. More specifically, the uneven surface 9 is disposed at the end on the suction surface 72f side. For example, the uneven surface 9 may be disposed at a position that obstructs backflow of the treated fluid flowing through the diffuser flow passage DL from the downstream end of the treated fluid flow to the upstream end of the flow. More specifically, the uneven surface 9 is disposed at the downstream end of the treated fluid flowing through the diffuser flow passage DL.

[0121] In the present invention, the uneven surface 9 is disposed on only a portion of the outer peripheral surface 71a of the diffuser body 7, but the uneven surface 9 may be disposed on only a portion of the inner peripheral surface 81b of the diffuser housing 8. The uneven surface 9 may be disposed on both a portion of the outer peripheral surface 71a of the diffuser body 7 and a portion of the inner peripheral surface 81b of the diffuser housing 8.

[0122] Furthermore, in the present invention, the method for forming the uneven surface 9 in the diffuser 6 is not limited to molding, as long as it can form a plurality of recesses and / or a plurality of protrusions. That is, for example, the uneven surface 9 may be formed by pressing or shot peening. In such a case, the uneven surface 9 is formed so that the depth (height) is 0.25 mm or more.

[0123] Furthermore, in the present invention, the shape of the recesses and / or protrusions of the uneven surface 9 may be any shape that can generate a vortex flow. That is, for example, the shape of the recesses and / or protrusions may be polygonal, irregular (random uneven shape, shape with varying size), etc.

[0124] Furthermore, in the present invention, the size of the recesses and / or protrusions of the uneven surface 9 may be any size that can generate vortex flows. Preferably, for example, the average size of the recesses and / or protrusions in the axial and circumferential directions of the diffuser 6 is 0.5 mm or more and 8 mm or less.

[0125] Furthermore, in the present invention, the depth of the recesses and / or the height of the protrusions of the uneven surface 9 may be sufficient as long as they are deep enough to generate a vortex flow. Preferably, for example, the average depth of the recesses and / or the average height of the protrusions is 0.25 mm or more and 4 mm or less.

[0126] Summary (2) In the embodiment described above, each of the vanes 72 in the diffuser 6 has a concave pressure surface 72e and a convex suction surface 72f when viewed in the radial direction of the outer peripheral surface 71a of the diffuser body 7. The uneven surface 9 of the diffuser 6 is located at the end on the suction surface 72f side. With this configuration, vortex flows collide primarily with the flow in the separation region PA, generating turbulence. This turbulence reduces the occurrence of stall, thereby suppressing the occurrence of rotating stall in the pump 1.

[0127] Furthermore, according to the embodiment described above, the uneven surface 9 of the diffuser 6 is positioned in a region (separation region PA) where separation of the pumped liquid from the suction surface 72f occurs in the diffuser flow passage DL. With this configuration, vortex flows collide with the flow in the separation region PA, generating turbulence. This turbulence reduces the occurrence of stall, thereby suppressing the occurrence of rotating stall in the pump 1. By pinpointing the uneven surface 9 in the region where separation occurs, a decrease in the head and pump efficiency of the pump 1 is suppressed, even in a flow rate range close to the set point.

[0128] Furthermore, according to the embodiment described above, the uneven surface 9 of the diffuser 6 is located at the downstream end of the flow of the treated liquid through the diffuser flow passage DL. With this configuration, the vortex flows collide primarily with the flow in the backflow area BA, generating turbulence. This turbulence reduces the occurrence of stall, thereby suppressing the occurrence of rotating stall in the pump 1.

[0129] Furthermore, according to the embodiment described above, the uneven surface 9 of the diffuser 6 is positioned to block the reverse flow of the treated fluid flowing through the diffuser flow passage DL from the downstream end of the treated fluid flow toward the upstream side of the flow. With this configuration, vortex flows collide with the flow in the reverse flow region BA, generating turbulence. This turbulence reduces the occurrence of stall, thereby suppressing the occurrence of rotating stall in the pump 1. By pinpointing the uneven surface 9 at a position that blocks the reverse flow, a decrease in the head and pump efficiency of the pump 1 is suppressed, even in a flow rate range close to the set point.

[0130] Furthermore, according to the embodiment described above, the average size of the recesses and / or protrusions is 0.5 mm or more and 8 mm or less in the circumferential and axial directions on the outer peripheral surface 71 a of the diffuser body 7. With this configuration, vortices are formed along the shape of the uneven surface 9.

[0131] Furthermore, according to the embodiment described above, the average depth of the recesses and / or the average height of the protrusions is 0.25 mm or more and 4 mm or less. With this configuration, vortex flows are formed along the shape of the uneven surface 9.

[0132] Embodiments of the Present Invention Next, embodiments of the present invention that can be understood from the embodiments described above will be described below, using the terms and symbols described in each embodiment.

[0133] A first embodiment of the present invention is a diffuser (e.g., diffuser 6) disposed adjacent to an impeller (e.g., impeller 5) in the axial direction of a rotary shaft (e.g., rotary shaft 4) of a centrifugal pump (e.g., this pump 1), the diffuser comprising a diffuser body (e.g., diffuser body 7) and a diffuser housing (e.g., diffuser housing 8) that houses the diffuser body, the diffuser body having a cylindrical outer peripheral surface (e.g., outer peripheral surface 71a) and a radially extending portion extending outward from the outer peripheral surface. a plurality of vanes (e.g., vane 72), the diffuser housing having a cylindrical inner circumferential surface (e.g., inner circumferential surface 81b) disposed opposite the outer circumferential surface, the inner circumferential surface, together with the outer circumferential surface and the plurality of vanes, forming a plurality of diffuser flow paths (e.g., diffuser flow paths DL) through which the treated liquid discharged from the impeller flows, and at least one of the outer circumferential surface and the inner circumferential surface has an uneven surface (e.g., uneven surface 9) having at least one of a plurality of recesses and a plurality of protrusions. With this configuration, when the centrifugal pump is operating in a flow rate range lower than a design point, stalling of the treated liquid in the diffuser flow paths provided in the centrifugal pump is reduced.

[0134] A second embodiment of the present invention is a diffuser according to the first embodiment, wherein, when viewed in the radial direction of the outer circumferential surface, each of the plurality of vanes has a concave pressure surface (e.g., pressure surface 72 e) and a convex suction surface (e.g., suction surface 72 f) opposite to the pressure surface, and the concave / convex surface is disposed at an end of the suction surface. With this configuration, when the centrifugal pump is operating at a flow rate lower than the design point, vortex flow mainly interferes with the flow in separation region PA, thereby reducing the occurrence of stall in the flow of the handled liquid in the diffuser flow path of the centrifugal pump.

[0135] In a third aspect of the present invention, the vanes are arranged in a radial direction of the outer circumferential surface of the centrifugal pump, and each of the vanes has a concave pressure surface (e.g., a positive pressure surface 72 e) and a convex suction surface (e.g., a suction surface 72 f) opposite to the positive pressure surface, and the concave and convex surfaces are arranged in contact with a region where separation of the treated fluid from the suction surface occurs. With this configuration, when the centrifugal pump is operating at a flow rate lower than a design point, vortex flow interferes with the flow in the separation region PA, reducing stall in the treated fluid flow in the diffuser flow path of the centrifugal pump.

[0136] In a fourth aspect of the present invention, in the first aspect, the uneven surface is a diffuser disposed at an end on the downstream side of the flow of the treated liquid flowing through the diffuser passage. With this configuration, when the centrifugal pump is operating in a flow rate range lower than the design point, the vortex flow mainly interferes with the flow in the backflow area BA, thereby reducing the occurrence of stall in the flow of the treated liquid in the diffuser passage provided in the centrifugal pump.

[0137] A fifth aspect of the present invention is a diffuser according to the first aspect, wherein the uneven surface is disposed at a position that obstructs a backflow of the treated fluid flowing through the diffuser passage from a downstream end of the treated fluid flow toward an upstream end of the treated fluid flow. With this configuration, when the centrifugal pump is operating in a flow rate range lower than the design point, the vortex flow interferes with the flow in the backflow area BA, thereby reducing the occurrence of stall in the treated fluid flow in the diffuser passage provided in the centrifugal pump.

[0138] A sixth aspect of the present invention is a diffuser according to any one of the first to fifth aspects, wherein the uneven surface is disposed on the entire outer circumferential surface and / or the entire inner circumferential surface. With this configuration, when the centrifugal pump is operating in a flow rate range lower than the design point, the vortex flow interferes with the flow in the separation region PA and the flow in the backflow region BA, thereby reducing the occurrence of stall in the flow of the handled liquid in the diffuser flow path provided in the centrifugal pump.

[0139] A seventh aspect of the present invention is the diffuser of the first aspect, wherein the uneven surface is disposed only on the outer peripheral surface. With this configuration, the number of processing steps and processing costs can be reduced compared to processing both the outer peripheral surface of the diffuser body and the inner peripheral surface of the diffuser housing.

[0140] An eighth aspect of the present invention is the diffuser of the first aspect, wherein the uneven surface is disposed only on the inner peripheral surface. With this configuration, the number of processing steps and processing costs can be reduced compared to processing both the outer peripheral surface of the diffuser body and the inner peripheral surface of the diffuser housing.

[0141] A ninth aspect of the present invention is the diffuser of the first aspect, wherein an average size of the recesses and / or the protrusions in the circumferential direction and the axial direction of the outer peripheral surface is 0.5 mm to 8 mm. With this configuration, a vortex is formed along the shape of the uneven surface.

[0142] A tenth aspect of the present invention is the diffuser of the first aspect, wherein the average depth of the recesses and / or the average height of the protrusions is 0.25 mm or more and 4 mm or less. With this configuration, vortices are formed along the shape of the uneven surface.

[0143] An eleventh embodiment of the present invention is a centrifugal pump comprising a motor (e.g., motor 3), a rotary shaft (e.g., rotary shaft 4) rotated by the motor, an impeller (e.g., impeller 5) attached to the rotary shaft, and a diffuser (e.g., diffuser 6) according to the first embodiment, disposed adjacent to the impeller in the axial direction of the rotary shaft. This configuration reduces stall occurrence in the flow of the handled liquid in the diffuser passage of the centrifugal pump when the centrifugal pump is operating in a flow rate range lower than the design point. The reduced stall reduces the deterioration of the suction performance of the centrifugal pump.

[0144] DESCRIPTION OF SYMBOLS 1 Centrifugal pump (this pump) 2 Housing 21 Suction port 3 Motor 31 Rotor 32 Stator 4 Rotating shaft 41 Tip portion 5 Impeller 6 Diffuser 7 Diffuser body 71 Inner cylindrical portion 71a Outer peripheral surface 71b Inner peripheral surface 71c Lower end portion 71d Rear end portion 711 Internal space 72 Vane 72e Positive pressure surface 72f Negative pressure surface 73 Bottom portion 731 Flow straightening plate 74 Support hole 8 Diffuser housing 81 Outer cylindrical portion 81a Outer peripheral surface 81b Inner peripheral surface 82 Connecting portion 9 Uneven surface C Pump column DL Diffuser flow path PA Separation region BA Backflow region

Claims

1. A diffuser arranged adjacent to an impeller in the axial direction of a rotating shaft of a centrifugal pump, comprising: a diffuser body; and a diffuser housing that houses the diffuser body, wherein the diffuser body has a cylindrical outer peripheral surface and a plurality of vanes extending outward from the outer peripheral surface in the radial direction of the outer peripheral surface, and the diffuser housing has a cylindrical inner peripheral surface that is arranged opposite the outer peripheral surface, and the inner peripheral surface, together with the outer peripheral surface and the plurality of vanes, forms a plurality of diffuser flow paths through which the handled liquid discharged from the impeller flows, and at least one of the outer peripheral surface and the inner peripheral surface has an uneven surface having at least one of a plurality of concave portions and a plurality of convex portions.

2. A diffuser as set forth in claim 1, wherein, when viewed radially from the outer circumferential surface, each of the plurality of vanes comprises: a concave pressure surface; and a convex suction surface opposite the positive pressure surface, the concave surface being located at the end on the suction surface side.

3. A diffuser according to claim 1, wherein, when viewed radially from the outer circumferential surface, each of the plurality of vanes comprises a concave positive pressure surface and a convex negative pressure surface opposite the positive pressure surface, and the concave and convex surfaces are positioned in contact with an area where separation of the handled liquid flowing through the diffuser flow path from the negative pressure surface occurs.

4. The diffuser according to claim 1, wherein the uneven surface is disposed at an end on the downstream side of the flow of the treated liquid flowing through the diffuser flow path.

5. A diffuser according to claim 1, wherein the uneven surface is positioned so as to obstruct a reverse flow of the treated fluid flowing through the diffuser flow path from the downstream end of the treated fluid flow toward the upstream end of the treated fluid flow.

6. A diffuser according to any one of claims 1 to 5, wherein the uneven surface is disposed over the entire outer circumferential surface and / or the entire inner circumferential surface.

7. The diffuser according to claim 1, wherein the uneven surface is disposed only on the outer peripheral surface.

8. The diffuser according to claim 1, wherein the uneven surface is disposed only on the inner circumferential surface.

9. A diffuser according to claim 1, wherein the average size of the recesses and / or the average size of the protrusions in the circumferential direction and the axial direction of the outer peripheral surface is 0.5 mm or more and 8 mm or less.

10. A diffuser according to claim 1, wherein the average depth of the recesses and / or the average height of the protrusions is 0.25 mm or more and 4 mm or less.

11. A centrifugal pump comprising: a motor; a rotary shaft rotated by said motor; an impeller attached to said rotary shaft; and the diffuser according to claim 1, which is disposed adjacent to said impeller in the axial direction of said rotary shaft.

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