Impellers and centrifugal pumps

Abstract

To provide an impeller and centrifugal pump capable of stable liquid delivery even at low flow rates. [Solution] The impeller 5 according to the present invention comprises a back shroud 6, a front shroud 7, and a plurality of blades 8 that partition a plurality of flow paths FL. The back shroud has a circular back shroud outer surface 6a. The blades have a positive pressure surface 81, a negative pressure surface 82, and a blade outer surface 83. The flow paths comprise a first flow path FL1 and a second flow path FL2. The shape of the blade outer surface is an arc shape arranged on a concentric circle of the back shroud outer surface. The first positive pressure surface that partitions the first flow path is arranged on a first virtual circle C1 inscribed in the blade outer surface and is a curved surface that is convex in the direction of rotation. The first negative pressure surface that partitions the first flow path is arranged on a second virtual circle C2 and is a curved surface that is concave in the direction of rotation. The distance between the second positive pressure surface and the second negative pressure surface that partition one second flow path decreases continuously as the flow moves from upstream to downstream.

Description

Technical Field

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

Background Art

[0002] Among centrifugal pumps, centrifugal pumps equipped with an impeller having an extremely low specific speed (for example, a specific speed less than 100) have begun to be used in many applications even in the operating range previously handled by conventional positive displacement pumps. In such a centrifugal pump, when the impeller is designed according to the conventional centrifugal pump design method, the blade angle at the inlet of the impeller flow path becomes shallow. As a result, the flow path from the inlet to the outlet of the impeller becomes long. Consequently, the frictional loss in the flow path increases. As a countermeasure, an impeller provided with blades ( "radial blades") extending radially from the suction port of the impeller is used (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an impeller provided with radial blades, the circumferential velocity of the flow at the outlet of the impeller flow path increases, and even if the impeller diameter is small, a change in angular momentum can be obtained. However, since the flow path is not inclined in the backward direction of the impeller rotation direction (the impeller does not have a so-called backward blade structure), the head curve (H-Q curve) slopes upward to the right, and the stability of liquid delivery in the low flow rate region decreases.

[0005] An object of the present invention is to provide an impeller and a centrifugal pump capable of stably delivering liquid even in a low flow rate region.

Means for Solving the Problems

[0006] An impeller in one embodiment of the present invention is an impeller attached to the rotating shaft of a centrifugal pump to suck in and discharge a liquid being handled, comprising: a rear shroud attached to the rotating shaft; a front shroud positioned opposite the rear shroud; and a plurality of blades arranged at equal intervals in the circumferential direction of the rotating shaft between the rear shroud and the front shroud, which together with the rear shroud and the front shroud divide a plurality of passages through which the liquid being handled flows, and the rear shroud The ud comprises a circular back shroud outer surface in an axial view of the rotating shaft, the blade comprises a positive pressure surface oriented in the direction of rotation of the rotating shaft, a negative pressure surface oriented in the opposite direction of rotation, and a blade outer surface oriented radially outward of the rotating shaft and continuous with the positive pressure surface and the negative pressure surface, the flow path comprises a flow path outlet located at the downstream end of the flow of the liquid being handled in the flow path, a first flow path located upstream of the flow from the flow path outlet and adjacent to the flow path outlet, and the first flow The system comprises a second flow path located upstream of the flow path and adjacent to the first flow path, wherein, in an axial view, the shape of the outer surface of the blade is an arc shape located on a concentric circle of the outer surface of the back shroud, the radius of curvature of the outer surface of the blade is smaller than the radius of curvature of the outer surface of the back shroud, the positive pressure surface comprises a first positive pressure surface that partitions the first flow path and a second positive pressure surface that partitions the second flow path, and the negative pressure surface comprises a first negative pressure surface that partitions the first flow path and a second negative pressure surface that partitions the second flow path The device comprises a pressure surface and a negative pressure surface, wherein, in an axial view, the first positive pressure surface is positioned on a first virtual circle inscribed in the outer circumferential surface of the blade and has a curved shape that is convex in the direction of rotation, and in an axial view, the first negative pressure surface is positioned on a second virtual circle that is larger than the first virtual circle and has a curved shape that is concave in the direction of rotation, and in an axial view, the distance between the second positive pressure surface and the second negative pressure surface that demarcate one of the second flow paths decreases continuously from upstream to downstream of the flow.

[0007] A centrifugal pump in one embodiment of the present invention comprises a motor, a rotating shaft rotated by the motor, and an impeller according to claim 1 attached to the rotating shaft. [Effects of the Invention]

[0008] The present invention provides an impeller and a centrifugal pump that can stably deliver liquid even in low flow rate ranges. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view of a centrifugal pump showing an embodiment of the centrifugal pump according to the present invention. [Figure 2] This is a partially enlarged cross-sectional view of section A in Figure 1. [Figure 3] This is a front view of an impeller showing an embodiment of the impeller according to the present invention. [Figure 4] This is a partially enlarged front view of section B in Figure 3. [Figure 5] Figure 3 is a schematic diagram illustrating the flow of the handling fluid in the impeller. [Figure 6] Figure 1 is a graph showing the head curve of the centrifugal pump. [Modes for carrying out the invention]

[0010] Embodiments of the impeller and centrifugal pump according to the present invention are described below. In the following description, the drawings are referenced as appropriate. In the drawings, the same reference numerals are used for the same members and elements, and redundant descriptions are omitted. In addition, the dimensional ratios of each element may be exaggerated for the sake of explanation and are not limited to the ratios shown in the drawings.

[0011] ●Centrifugal pump● ● Configuration of a centrifugal pump Figure 1 is a schematic cross-sectional view of a centrifugal pump, showing an embodiment of the centrifugal pump according to the present invention. The figure shows a schematic cross-sectional view of a part of the housing 2, which will be described later, and simplifies the other parts. The figure schematically shows a longitudinal cross-section (the same applies to Figure 2) of the centrifugal pump 1 when it is cut vertically along the axial direction of the rotating shaft 4 (described later) and passing through the axial center of the rotating shaft 4.

[0012] The centrifugal pump 1 sucks in and discharges (transports) the liquid being handled. The centrifugal pump 1 comprises a housing 2, a motor 3, a rotating shaft 4, and an impeller 5.

[0013] The "handled liquid" is the liquid handled (transported) by the centrifugal pump 1. In this embodiment, the handled liquid is water.

[0014] In the following explanation, "forward direction" refers to the direction in which the impeller 5 is positioned relative to the motor 3, and "rear direction" refers to the direction in which the motor 3 is positioned relative to the impeller 5. "Axial direction" refers to the direction along the axis centerline of the rotating shaft 4 (forward-backward direction), "radial direction" refers to the radial direction of the rotating shaft 4, and "circumferential direction" refers to the circumferential direction of the rotating shaft 4. "Upstream" refers to the upstream direction in the flow of the fluid being handled within the impeller 5, and "downstream" refers to the downstream direction in the flow of the fluid being handled within the impeller 5. "Positive direction" refers to the direction of rotation of the rotating shaft 4, and "reverse direction" refers to the direction opposite to the direction of rotation of the rotating shaft 4. "Outward direction" refers to the outward direction in the circumferential direction, and "inward direction" refers to the inward direction in the circumferential direction.

[0015] The housing 2 houses the motor 3, the rotating shaft 4, and the impeller 5. The housing 2 also includes a pump chamber 21, a motor chamber 22, a suction pipe section 23, and a discharge pipe section 24.

[0016] The housing 2 comprises a pump chamber 21 housing the impeller 5 and a motor chamber 22 housing the motor 3. The pump chamber 21 is located at the front of the housing 2, and the motor chamber 22 is located at the rear of the housing 2.

[0017] The front end of the housing 2 extends cylindrically forward so as to be coaxial with the rotating shaft 4, forming a suction pipe section 23 that draws (introduces) the liquid to be handled into the pump chamber 21 (impeller 5). In addition, a portion of the housing 2 located outward from the impeller 5 extends tangentially (upward) to the impeller 5, forming a discharge pipe section 24 that discharges the liquid to be handled from the pump chamber 21 (impeller 5).

[0018] The motor 3 is a known motor including a rotor 31 attached to a rotating shaft 4 and a stator 32 for rotating the rotor 31.

[0019] The rotating shaft 4 rotates by the drive (rotation) of the motor 3 and transmits the rotational power to the impeller 5. The shape of the rotating shaft 4 is cylindrical. The rotating shaft 4 is attached to the motor 3, and the front portion 4a of the rotating shaft 4 protrudes into the pump chamber 21.

[0020] The impeller 5 sucks and discharges the liquid to be handled. The impeller 5 is attached to the front portion 4a of the rotating shaft 4 and is housed in the pump chamber 21. The impeller 5 is a so-called closed-type impeller with an extremely low specific speed (for example, the specific speed is "60"). Details of the impeller 5 will be described later.

[0021] ● Impeller ● ● Structure of the impeller Figure 2 is a partially enlarged cross-sectional view of part A in Figure 1. Figure 3 is a front view of the impeller (impeller 5) according to the present invention, showing an embodiment of the impeller 5. Figure 3 omits the illustration of the front shroud 7 (described later) of the impeller 5.

[0022] The impeller 5 includes a rear shroud 6, a front shroud 7, a plurality (8) of blades 8, and a plurality (8) of flow paths FL.

[0023] The rear shroud 6 is a plate (so-called main plate) that covers the rear direction of the blade 8. The shape of the rear shroud 6 is a ring plate shape. The rear shroud 6 includes an outer peripheral surface 6a, an inner surface 6b, a mounting hole 6c, and a hub portion 6d.

[0024] The outer peripheral surface 6a is a surface directed outward. In the axial direction view, the shape of the outer peripheral surface 6a is circular. The outer peripheral surface 6a is an example of the outer peripheral surface of the rear shroud in the present invention.

[0025] The inner surface 6b is a surface directed forward. The inner surface 6b is planar.

[0026] The mounting hole 6c is a through hole into which the front part 4a of the rotating shaft 4 is fitted. In an axial view, the mounting hole 6c is located in the center of the rear shroud 6 and penetrates the center in a cylindrical shape along the axial direction.

[0027] In an axial view, the inner edge (central part) of the rear shroud 6 protrudes cylindrically toward the rear, forming a hub portion 6d. The front portion 4a of the rotating shaft 4 is inserted through the hub portion 6d, and the impeller 5 is attached to the front portion 4a of the rotating shaft 4 by fixing the hub portion 6d to the front portion 4a of the rotating shaft 4.

[0028] The front shroud 7 is a plate (so-called side plate) that covers the front of the blades 8. The shape of the front shroud 7 is ring-shaped. The front shroud 7 is positioned in front of the rear shroud 6 so as to face the rear shroud 6. The front shroud 7 has an outer surface 7a, an inner surface 7b, and an intake port 7c.

[0029] The outer circumferential surface 7a is a surface oriented outward. In an axial view, the shape of the outer circumferential surface 7a is circular. The diameter of the outer circumferential surface 7a is the same as the diameter of the outer circumferential surface 6a.

[0030] The inner surface 7b is a surface oriented towards the rear. The inner surface 7b is planar.

[0031] In an axial view, the inner edge of the front shroud 7 protrudes cylindrically forward, coaxial with the rotation axis 4, forming a suction port 7c. The suction port 7c draws in the liquid being handled from the suction pipe section 23 and guides it to each flow path FL.

[0032] The blades 8, together with the rear shroud 6 and the front shroud 7, demarcate multiple flow paths FL through which the fluid being handled flows. In the circumferential direction, the blades 8 are arranged at equal intervals. The blades 8 have a positive pressure surface 81, a negative pressure surface 82, and an outer blade surface 83. The configuration of the blades 8 in an axial view will be described in the following description. The shape of the blades 8 described below was designed, for example, by machine learning using a neural network.

[0033] Figure 4 is a partially enlarged front view of section B in Figure 3. In the following explanation, Figure 3 will be referred to as appropriate, along with Figure 4.

[0034] The positive pressure surface 81 is a surface oriented in the positive direction. The positive pressure surface 81 is broadly divided into a portion corresponding to the downstream portion of the flow path FL (hereinafter referred to as the "first positive pressure surface 81a"), a portion corresponding to the middle portion of the flow path FL (hereinafter referred to as the "second positive pressure surface 81b"), and a portion corresponding to the upstream portion of the flow path FL (hereinafter referred to as the "third positive pressure surface 81c"). In other words, the positive pressure surface 81 comprises the first positive pressure surface 81a, the second positive pressure surface 81b, and the third positive pressure surface 81c.

[0035] The shape of the first positive pressure surface 81a is a curved surface that is convex in the positive direction (i.e., a convex curved surface; the same applies hereinafter). The first positive pressure surface 81a is located on a first virtual circle C1 that is inscribed in the outer circumferential surface 83 of the blade. That is, the shape of the first positive pressure surface 81a is the same arc shape as the arc of the first virtual circle C1. The first positive pressure surface 81a is inscribed in the outer circumferential surface 83 of the blade. Therefore, at the internal contact point, the tangents of the first positive pressure surface 81a and the outer circumferential surface 83 coincide. The center point of the first virtual circle C1 (hereinafter referred to as "first center point P1") is located inside the blade 8 which has the first positive pressure surface 81a. The ratio of the radius of the first virtual circle C1 to the radius of curvature of the outer circumferential surface 83 (radius of the first virtual circle C1 / radius of curvature of the outer circumferential surface 83 of the blade) is preferably designed to be "0.15" or more and "0.25" or less.

[0036] The shape of the second positive pressure surface 81b is linear. The second positive pressure surface 81b is located upstream of the first positive pressure surface 81a and adjacent to the first positive pressure surface 81a. At the downstream end of the second positive pressure surface 81b, it coincides with the tangent to the first positive pressure surface 81a.

[0037] The shape of the third positive pressure surface 81c is a concave curved surface in the opposite direction (i.e., a concave curved surface; the same applies hereafter). The third positive pressure surface 81c is located upstream of the second positive pressure surface 81b and adjacent to the second positive pressure surface 81b. The center of curvature of the third positive pressure surface 81c is located outside the impeller 5. At the downstream end of the third positive pressure surface 81c, the tangent to the third positive pressure surface 81c coincides with the second positive pressure surface 81b.

[0038] The negative pressure surface 82 is the surface facing in the opposite direction. The negative pressure surface 82 is broadly divided into a portion corresponding to the downstream portion of the flow path FL (hereinafter referred to as the "first negative pressure surface 82a"), a portion corresponding to the middle portion of the flow path FL (hereinafter referred to as the "second negative pressure surface 82b"), and a portion corresponding to the upstream portion of the flow path FL (hereinafter referred to as the "third negative pressure surface 82c"). In other words, the negative pressure surface 82 comprises the first negative pressure surface 82a, the second negative pressure surface 82b, and the third negative pressure surface 82c.

[0039] The shape of the first negative pressure surface 82a is a curved surface that is concave in the opposite direction. The first negative pressure surface 82a is located on the second virtual circle C2. That is, the shape of the first negative pressure surface 82a is the same arc shape as the arc of the second virtual circle C2. The diameter of the second virtual circle C2 is larger than the diameter of the first virtual circle C1. The tangent to the downstream end of the first negative pressure surface 82a intersects at an acute angle with the tangent to the outer surface 6a at the same position as the downstream end. The center point of the second virtual circle C2 (hereinafter referred to as "second center point P2") is located inside the adjacent blade 8 in the opposite direction of the blade 8. The ratio of the diameter of the first virtual circle C1 to the diameter of the second virtual circle C2 (diameter of the first virtual circle C1 / diameter of the second virtual circle C2) is preferably designed to be between "0.65" and "0.85".

[0040] The shape of the second negative pressure surface 82b is linear. The second negative pressure surface 82b is located upstream of the first negative pressure surface 82a and adjacent to the first negative pressure surface 82a. The second negative pressure surface 82b is positioned along the tangential direction of the inner circumferential surface of the suction port 7c.

[0041] The shape of the third negative pressure surface 82c is curved. The third negative pressure surface 82c is located upstream of the second negative pressure surface 82b and adjacent to the second negative pressure surface 82b. The tangent to the downstream end of the third negative pressure surface 82c coincides with the second negative pressure surface 82b.

[0042] The outer surface 83 of the blade is a surface that faces outward. The shape of the outer surface 83 of the blade is a curved surface that is convex outward. The outer surface 83 of the blade is positioned on a concentric circle of the outer surface 6a. That is, the shape of the outer surface 83 of the blade is an arc that is positioned on a concentric circle of the outer surface 6a. The radius of curvature of the outer surface 83 of the blade is smaller than the radius of curvature of the outer surface 6a. At the boundary between the first positive pressure surface 81a and the outer surface 83 of the blade, the tangents of the first positive pressure surface 81a and the outer surface 83 of the blade coincide. That is, the second positive pressure surface 81b is inscribed in the outer surface 83 of the blade. The outer surface 83 of the blade is positioned to be continuous with the positive pressure surface 81 and the negative pressure surface 82.

[0043] The flow path FL is the space within the impeller 5 through which the handling fluid flows. The flow path FL is partitioned by the rear shroud 6, the front shroud 7, and two adjacent blades 8 in the circumferential direction. The flow path FL comprises a flow path outlet FLo, a flow path inlet FLi, a first flow path FL1, a second flow path FL2, and a third flow path FL3.

[0044] The flow path outlet FLo is the outlet of the flow path FL (i.e., the discharge port of the impeller 5) from which the liquid being handled is discharged. The flow path outlet FLo is located at the downstream end of the flow path FL.

[0045] The channel inlet FLi is the entrance to the channel FL into which the fluid being handled is introduced. The channel inlet FLi is located at the upstream end of the channel FL.

[0046] The first flow path FL1 is the portion of the flow path FL that is demarcated by the rear shroud 6, the front shroud 7, the first positive pressure surface 81a, and the first negative pressure surface 82a which is positioned in the positive direction of the first positive pressure surface 81a. The first flow path FL1 is located upstream of the flow path outlet FLo and adjacent to the flow path outlet FLo. The shape of the first flow path FL1 is a substantially arc shape that follows the first positive pressure surface 81a and the first negative pressure surface 82a.

[0047] Here, in the first positive pressure surface 81a and the first negative pressure surface 82a that demarcate one first flow path FL1, the corresponding first center point P1 and second center point P2 are located on a radius line R1 of the outer circumferential surface 6a. The second center point P2 is located inward from the first center point P1. The distance L1 between the first center point P1 and the second center point P2 is smaller than the absolute value of the difference L2 between the radius of the first virtual circle C1 and the radius of the second virtual circle C2. The ratio of the distance L1 to the absolute value of the difference L2 (|L2| / L1) is preferably designed to be 0.2 or less. As a result, the distance between the first positive pressure surface 81a and the first negative pressure surface 82a that demarcate one first flow path FL1 decreases slightly and continuously as you move from the upstream to the downstream (flow path outlet FLo) of the first flow path FL1. Therefore, the cross-sectional area of ​​the first channel FL1 decreases slightly and continuously as you move from the upstream to the downstream (channel outlet FLo) of the first channel FL1. In one first channel FL1, the ratio of the minimum cross-sectional area to the maximum cross-sectional area (minimum / maximum) is preferably designed to be 0.8 or greater and less than 1.0. The "cross-sectional area" is the area of ​​a virtual cross-section (cross-section plane) perpendicular to the flow direction of the channel FL (first channel FL1, second channel FL2, third channel FL3).

[0048] Here, "one radius line R1" does not only mean the state in which the radius line R1 on which the first center point P1 is located and the radius line R1 on which the second center point P2 is located are perfectly aligned. That is, for example, "one radius line R1" also includes the state in which the two radius lines R1 are slightly misaligned (for example, by about 2° to 3°) due to factors such as manufacturing errors or tolerances.

[0049] The second flow path FL2 is the portion of the flow path FL that is demarcated by the rear shroud 6, the front shroud 7, the second positive pressure surface 81b, and the second negative pressure surface 82b which is positioned in the positive direction of the second positive pressure surface 81b. The shape of the second flow path FL2 is substantially straight along the second positive pressure surface 81b and the second negative pressure surface 82b.

[0050] Here, the second positive pressure surface 81b and the second negative pressure surface 82b that demarcate one second flow path FL2 are arranged non-parallel to each other. The angle between the second positive pressure surface 81b and the second negative pressure surface 82b that demarcate one second flow path FL2 is preferably designed to be 5° or less. The distance between the second positive pressure surface 81b and the second negative pressure surface 82b that demarcate one second flow path FL2 decreases continuously from upstream to downstream of the second flow path FL2. As a result, the second positive pressure surface 81b and the second negative pressure surface 82b that demarcate one second flow path FL2 decrease slightly and continuously from upstream to downstream of the second flow path FL2. Therefore, the cross-sectional area of ​​the second flow path FL2 decreases slightly and continuously from upstream to downstream of the second flow path FL2. In one second flow path FL2, the ratio of the minimum cross-sectional area to the maximum cross-sectional area (minimum / maximum) is preferably designed to be 0.8 or greater and less than 1.0. The second flow path FL2 is positioned along a direction slightly inclined in the positive direction from the tangential direction of the inner surface of the suction port 7c.

[0051] The third flow path FL3 is the portion of the flow path FL that is partitioned by the rear shroud 6, the front shroud 7, the third positive pressure surface 81c, and the third negative pressure surface 82c which is located in the positive direction of the third positive pressure surface 81c. The third flow path FL3 is positioned along the tangential direction of the inner circumferential surface of the suction port 7c.

[0052] The inner surface 6b is arranged parallel to the inner surface 7b. In one flow path FL, the shape of the cross-section of the flow path FL is designed to be, for example, close to a square. That is, for example, the ratio of the average value of the distance between the positive pressure surface 81 and the negative pressure surface 82 (width of the flow path FL) to the distance L3 between the back shroud 6 (inner surface 6b) and the front shroud 7 (inner surface 7b) (average value / distance L3) is designed to be between "0.9" and "1.1". In addition, in one flow path FL, the ratio of the minimum value of the cross-sectional area to the maximum value of the cross-sectional area (minimum value / maximum value) is preferably designed to be between "0.8" and "1.0". Furthermore, in the range from the upstream end of the second flow path FL2 (boundary between the second flow path FL2 and the third flow path FL3) to the flow path outlet FLo, the ratio of the minimum value of the cross-sectional area to the maximum value of the cross-sectional area (minimum value / maximum value) is preferably designed to be between "0.8" and "1.0". As a result, the equivalent diameter of the channel FL decreases slightly from upstream to downstream, but does not change significantly.

[0053] ● Operation of the centrifugal pump Next, the operation of the centrifugal pump 1 will be explained below, focusing on the flow of the liquid being handled in the impeller 5. Figures 1 to 4 will be referred to as appropriate in the following explanation.

[0054] Figure 5 is a schematic diagram illustrating the flow of the handling fluid in the impeller 5. The diagram shows the flow of the liquid being handled with arrows.

[0055] When the centrifugal pump 1 is operating, the impeller 5 rotates in the forward direction, drawing in and discharging the fluid being handled. Specifically, the fluid is drawn in from the suction port 7c in a swirling motion in the forward direction and flows into each flow path FL from each flow path inlet FLi. The fluid that has flowed into the flow path FL flows along the flow path FL from upstream to downstream. At this time, the peripheral velocity, static pressure, and total pressure of the fluid being handled in each flow path FL increase as the flow path FL moves from upstream to downstream.

[0056] As mentioned above, the cross-sectional shape of the flow path FL is close to a square. Generally, when the cross-section is rectangular, the fluid loss of the liquid flowing through the flow path decreases as the aspect ratio approaches "1.0" (as the shape of the cross-section approaches a square). Therefore, the liquid being handled flows efficiently even if the cross-section of the flow path FL is rectangular. Furthermore, when the spacing between adjacent vanes 8 in the circumferential direction (width of the flow path FL) is narrowed, the swirling vortices generated between the vanes of the so-called radial vanes are prevented. As a result, fluid loss is reduced.

[0057] Furthermore, as mentioned above, the equivalent diameter of the flow path FL decreases slightly from upstream to downstream, but does not change significantly. Therefore, the peripheral velocity, static pressure, and total pressure of the fluid being handled in each flow path FL increase smoothly from upstream to downstream.

[0058] Furthermore, as mentioned above, the second positive pressure surface 81b is continuous with the first positive pressure surface 81a and the third positive pressure surface 81c, respectively, with their tangents coinciding. Similarly, the second negative pressure surface 82b is continuous with the first negative pressure surface 82a and the third negative pressure surface 82c, respectively, with their tangents coinciding. In other words, the positive pressure surface 81 and the negative pressure surface 82 are formed smoothly without any corners. As a result, fluid loss is suppressed and separation of the handled fluid is suppressed at both the positive pressure surface 81 and the negative pressure surface 82.

[0059] Here, in the circumferential direction, the length of the outer surface 83 of the blade is larger than the length of the same part of a typical impeller. That is, in the circumferential direction, the spacing between the flow outlets FLo is larger than the spacing of the same part of a typical impeller. Therefore, the outer surface 83 of the blade has a shape that makes it easy for the handling fluid to separate. However, as mentioned above, the first positive pressure surface 81a is inscribed in the outer surface 83 of the blade. Also, as mentioned above, the radius of curvature of the outer surface 83 of the blade is smaller than the radius of curvature of the outer surfaces 6a and 7a. Therefore, the handling fluid is discharged from the flow outlet FLo along the first positive pressure surface 81a and the outer surface 83 of the blade, and separation of the handling fluid on the outer surface 83 of the blade is suppressed. In addition, the flow F1 (relative flow) of the handling fluid discharged from the flow outlet FLo can merge smoothly with the outward flow F2 (flow along the positive direction: absolute flow) of the handling fluid from the blade 8 without significantly disturbing each other's flows F1 and F2.

[0060] Furthermore, as mentioned above, the first positive pressure surface 81a is inscribed within the outer surface 83 of the blade. As a result, the relative flow F1 of the handled liquid discharged from the flow outlet FLo flows near the outer surface 83 of the blade in the opposite direction. That is, the direction of the relative flow F1 of the handled liquid (opposite direction) is opposite to the direction of the absolute velocity of the handled liquid flow F2 (positive direction). Therefore, when the discharge flow rate of the centrifugal pump 1 (discharge flow rate of the impeller 5) is low, the relative velocity of the relative flow F1 (relative to the handled liquid flow F2) in the handled liquid flow F2, which is moving in the opposite direction, becomes small. As a result, the peripheral velocity component becomes dominant in the handled liquid flow F2, and the absolute velocity becomes large. As a result, the head becomes large according to Eulerhead's equation. On the other hand, when the discharge flow rate of the centrifugal pump 1 (discharge flow rate of the impeller 5) is large, the aforementioned relative velocity becomes large in the handled liquid flow F2. As a result, the absolute velocity in the handled liquid flow F2 becomes small, and the head becomes small. In other words, in centrifugal pump 1, the head decreases as the discharge flow rate increases (and increases as the discharge flow rate decreases).

[0061] Figure 6 is a graph showing the head curve of centrifugal pump 1. The figure shows the head curve of centrifugal pump 1 obtained from simulation analysis. The vertical axis of the figure represents the head, and the horizontal axis represents the discharge flow rate. The figure shows that the head curve (HQ curve) of centrifugal pump 1 slopes downward to the right. As a result, the stability of liquid delivery in the low flow rate range is improved in centrifugal pump 1.

[0062] ●Summary According to the embodiment described above, the centrifugal pump 1 comprises a motor 3, a rotating shaft 4, and an impeller 5. The radius of curvature of the outer surface 83 of the impeller blade is smaller than the radius of curvature of the outer surface 6a. In an axial view, the shape of the outer surface 83 of the impeller blade is an arc shape located on a concentric circle of the outer surface 6a. The first positive pressure surface 81a is located on a first virtual circle C1 inscribed in the outer surface 83 of the impeller blade and is a curved surface that is convex in the positive direction. The first negative pressure surface 82a is located on a second virtual circle C2 which is larger than the first virtual circle C1 and is a curved surface that is concave in the positive direction. The distance between the second positive pressure surface 81b and the second negative pressure surface 82b that demarcate one second flow path FL2 decreases continuously from upstream to downstream. With this configuration, the handling fluid discharged from the flow path outlet FLo is smoothly discharged onto the outer surface 83 of the impeller blade. As a result, separation of the handling fluid on the outer surface 83 of the impeller blade is suppressed. Furthermore, the relative flow F1 of the handled liquid discharged from the flow path outlet FLo can smoothly merge with the outward flow F2 of the handled liquid (flow along the positive direction) of the impeller 8. In addition, the head curve (HQ curve) of the centrifugal pump 1 becomes downward sloping to the right, improving the stability of liquid delivery in the low flow rate range of the centrifugal pump 1. In other words, an impeller 5 and centrifugal pump 1 capable of stable liquid delivery even in the low flow rate range can be obtained.

[0063] Furthermore, according to the embodiment described above, the second positive pressure surface 81b and the second negative pressure surface 82b that demarcate one second flow path FL2 are non-parallel to each other and are in a straight line. With this configuration, the peripheral velocity, static pressure, and total pressure of the fluid being handled in the second flow path FL2 increase from upstream to downstream.

[0064] Furthermore, according to the embodiments described above, the angle between the second positive pressure surface 81b and the second negative pressure surface 82b that demarcate one second flow path FL2 is preferably 5° or less. With this configuration, the cross-sectional area of ​​the second flow path FL2 does not change significantly. Therefore, the equivalent diameter of the second flow path FL2 decreases slightly from upstream to downstream, but does not change significantly. As a result, the peripheral velocity, static pressure, and total pressure of the fluid being handled in the second flow path FL2 increase smoothly from upstream to downstream.

[0065] Furthermore, according to the embodiment described above, in the first positive pressure surface 81a and the first negative pressure surface 82a that demarcate one first flow path FL1, the first center point P1 and the second center point P2 are located on a radius line R1 of the outer peripheral surface 6a. The second center point P2 is located inward from the first center point P1. With this configuration, the cross-sectional area of ​​the first flow path FL1 decreases from upstream to downstream. Therefore, the liquid being handled is accelerated in the first flow path FL1. As a result, the head curve (HQ curve) of the centrifugal pump 1 tends to slope downward to the right.

[0066] Furthermore, according to the embodiments described above, the distance L1 between the first center point P1 and the second center point P2 is smaller than the absolute value of the difference L2 between the radius of the first virtual circle C1 and the radius of the second virtual circle C2. With this configuration, the first flow path FL1 is reliably formed all the way to the flow path outlet FLo.

[0067] Furthermore, according to the embodiments described above, the ratio of the distance L1 between center points to the absolute value of the difference L2 (|L2| / L1) is preferably set to "0.2" or less. With this configuration, the cross-sectional area of ​​the first flow path FL1 does not change significantly. Therefore, the equivalent diameter of the first flow path FL1 decreases slightly from upstream to downstream, but does not change significantly. As a result, the peripheral velocity, static pressure, and total pressure of the liquid being handled in the first flow path FL1 increase smoothly from upstream to downstream.

[0068] Furthermore, according to the embodiments described above, the cross-sectional area of ​​the flow path FL decreases continuously from the upstream end of the second flow path FL2 toward the flow path outlet FLo. In the range from the upstream end of the second flow path FL2 toward the flow path outlet FLo, the ratio of the minimum cross-sectional area to the maximum cross-sectional area (minimum / maximum) is preferably designed to be 0.8 or greater and less than 1.0. Therefore, the equivalent diameters of the first flow path FL1 and the second flow path FL2 decrease slightly from upstream to downstream, but do not change significantly. As a result, the peripheral velocity, static pressure, and total pressure of the fluid being handled in the first flow path FL1 and the second flow path FL2 increase smoothly from upstream to downstream.

[0069] ●Other Embodiments● In this invention, the specific speed of the impeller 5 is not limited to "60" and may be less than "100".

[0070] Furthermore, in the present invention, the second center point P2 may be located at the same position as the first center point P1 (they may coincide). In this case, the cross-sectional area of ​​the first flow path FL1 is the same from upstream to downstream.

[0071] Furthermore, in the present invention, the first center point P1 and the second center point P2 do not necessarily have to be located on a single radius line R1.

[0072] Furthermore, in the present invention, the ratio of the distance L1 between center points to the absolute value of the difference L2 (|L2| / L1) is less than 1.0, and may be designed to be 0.2 or greater. In this case, in one first flow path FL1, the ratio of the minimum value of the cross-sectional area to the maximum value of the cross-sectional area (minimum value / maximum value) may be designed to be less than 0.8.

[0073] Furthermore, in the present invention, the center of curvature of the third positive pressure surface 81c may be located inside the impeller 5.

[0074] Furthermore, in the present invention, the second negative pressure surface 82b does not have to be arranged along the tangential direction of the inner circumferential surface of the suction port 7c.

[0075] Furthermore, in the present invention, the ratio of the minimum value of the cross-sectional area to the maximum value of the cross-sectional area (minimum value / maximum value) in the range from the upstream end of the second flow channel FL2 to the flow channel outlet FLo may be designed to be less than "0.8".

[0076] Furthermore, in the present invention, the second flow path FL2 does not necessarily have to be arranged along a direction that is slightly inclined in the positive direction from the tangential direction of the inner circumferential surface of the suction port 7c.

[0077] Furthermore, in the present invention, the second flow path FL2 may be arranged along the tangential direction of the inner circumferential surface of the suction port 7c.

[0078] Furthermore, in the present invention, the shape of the second positive pressure surface 81b and / or the second negative pressure surface 82b may be a curved surface such that the distance between the second positive pressure surface 81b and the second negative pressure surface 82b decreases continuously from upstream to downstream. In this case, the angle between the second positive pressure surface 81b and the second negative pressure surface 82b is determined based on an imaginary line segment (chord) connecting the upstream end and the downstream end of the curved second positive pressure surface 81b and / or the second negative pressure surface 82b.

[0079] Furthermore, in the present invention, the ratio of the minimum cross-sectional area to the maximum cross-sectional area in one second channel FL2 (minimum / maximum) may be designed to be less than "0.8".

[0080] Furthermore, in the present invention, the shapes of the third positive pressure surface 81c and the third negative pressure surface 82c do not necessarily have to be curved.

[0081] Furthermore, in the present invention, the third flow path FL3 does not have to be arranged along the tangential direction of the inner circumferential surface of the suction port 7c.

[0082] Furthermore, in the present invention, the ratio of the minimum cross-sectional area to the maximum cross-sectional area in one flow path FL (minimum / maximum) may be designed to be less than "0.8".

[0083] Furthermore, in the present invention, the inner surfaces 6b and 7b may be arranged non-parallel to each other. That is, for example, the distance L3 between the inner surfaces 6b and 7b may decrease slightly from the inner edge to the outer edge.

[0084] Furthermore, in the present invention, the number of blades 8 is not limited to "8".

[0085] ●Embodiments of the present invention● Next, embodiments of the present invention as understood from the embodiments described above will be described below, with reference to the terms and reference numerals described in each embodiment.

[0086] A first embodiment of the present invention is an impeller (e.g., impeller 5) attached to the rotating shaft (e.g., rotating shaft 4) of a centrifugal pump (e.g., centrifugal pump 1) for sucking in and discharging a liquid being handled, comprising: a rear shroud (e.g., rear shroud 6) attached to the rotating shaft; a front shroud (e.g., front shroud 7) positioned opposite the rear shroud; and a plurality of flow channels (e.g., For example, the back shroud has a plurality of vanes (e.g., vane 8) that demarcate the flow path FL, and the back shroud has a circular back shroud outer surface (e.g., outer surface 6a) in an axial view of the rotation shaft, and the vanes have a positive pressure surface (e.g., positive pressure surface 81) oriented in the direction of rotation of the rotation shaft, a negative pressure surface (e.g., negative pressure surface 82) oriented in the opposite direction of rotation, and a vane outer surface (e.g., vane outer surface 83) oriented radially outward of the rotation shaft and continuous with the positive pressure surface and the negative pressure surface, and the flow path is downstream of the flow of the liquid being handled in the flow path. The system comprises a flow channel outlet located at the end (e.g., flow channel outlet FLo), a first flow channel (e.g., first flow channel FL1) located upstream of the flow channel outlet and adjacent to the flow channel outlet, and a second flow channel (e.g., second flow channel FL2) located upstream of the flow channel and adjacent to the first flow channel, wherein, in the axial view, the shape of the outer surface of the blade is an arc shape located on a concentric circle of the outer surface of the back shroud, the radius of curvature of the outer surface of the blade is smaller than the radius of curvature of the outer surface of the back shroud, and the positive pressure surface is a first flow channel that demarcates the first flow channel. The negative pressure surface comprises a positive pressure surface (e.g., a first positive pressure surface 81a) and a second positive pressure surface (e.g., a second positive pressure surface 81b) that demarcates the second flow path, and the negative pressure surface comprises a first negative pressure surface (e.g., a first negative pressure surface 82a) that demarcates the first flow path and a second negative pressure surface (e.g., a second negative pressure surface 82b) that demarcates the second flow path, and in the axial view, the first positive pressure surface is positioned on a first virtual circle (e.g., a first virtual circle C1) that is inscribed in the outer circumferential surface of the blade and is a curved surface that is convex in the direction of rotation, and in the axial view, the first negative pressure surface is positioned on a second virtual circle (e.g.,An impeller positioned on a second virtual circle C2), having a concave curved surface in the direction of rotation, wherein, in the axial view, the distance between the second positive pressure surface and the second negative pressure surface that demarcate one of the second flow paths decreases continuously from upstream to downstream of the flow. This configuration provides an impeller and centrifugal pump capable of stable liquid delivery even at low flow rates.

[0087] A second embodiment of the present invention is an impeller in which, in the first embodiment, the second positive pressure surface and the second negative pressure surface that demarcate one of the second flow paths are in a non-parallel straight line in an axial view. In this configuration, the peripheral velocity, static pressure, and total pressure of the fluid being handled in the second flow path increase from upstream to downstream.

[0088] A third embodiment of the present invention is an impeller, in the second embodiment, wherein, in an axial view, the angle between the second positive pressure surface and the second negative pressure surface that demarcate one of the second flow paths is 5° or less. With this configuration, the peripheral velocity, static pressure, and total pressure of the fluid being handled in the second flow path increase smoothly from upstream to downstream.

[0089] A fourth embodiment of the present invention is an impeller in which, in the first embodiment, the first positive pressure surface and the first negative pressure surface that demarcate one of the first flow paths, the first center point of the first virtual circle (e.g., first center point P1) and the second center point of the second virtual circle (e.g., second center point P2) are located on one radius line (e.g., radius line R1) of the outer circumferential surface of the back shroud, and in the radial direction, the second center point coincides with the first center point or is located inward from the first center point. With this configuration, the head curve (HQ curve) of the centrifugal pump tends to be downward sloping.

[0090] A fifth embodiment of the present invention is an impeller in which, in the fourth embodiment, the second center point is positioned radially inward from the first center point, and the distance between the first and second center points (e.g., distance L1) is smaller than the absolute value of the difference between the radius of the first virtual circle and the radius of the second virtual circle (e.g., difference L2). With this configuration, the first channel is reliably formed all the way to the channel outlet.

[0091] A sixth embodiment of the present invention is an impeller in which, in the fifth embodiment, the ratio of the distance between center points to the absolute value is "0.2" or less. With this configuration, the peripheral velocity, static pressure, and total pressure of the fluid being handled in the first flow path increase smoothly from upstream to downstream.

[0092] A seventh embodiment of the present invention is an impeller in which, in the fifth embodiment, the cross-sectional area of ​​the flow path decreases continuously from the upstream end of the flow of the second flow path toward the outlet of the flow path, and in the range from the upstream end to the outlet of the flow path, the ratio of the minimum value of the cross-sectional area to the maximum value of the cross-sectional area is 0.8 or more and less than 1.0. With this configuration, the peripheral velocity, static pressure, and total pressure of the fluid being handled in the first and second flow paths increase smoothly from upstream to downstream.

[0093] An eighth embodiment of the present invention is a centrifugal pump (e.g., centrifugal pump 1) comprising a motor (e.g., motor 3), a rotating shaft (e.g., rotating shaft 4) rotated by the motor, and an impeller (e.g., impeller 5) as described in the first embodiment, attached to the rotating shaft. This configuration provides an impeller and centrifugal pump capable of stable liquid delivery even at low flow rates. [Explanation of Symbols]

[0094] 1. Centrifugal pump 3 motors 4 rotation axes 5 Impellers 6. Rear shroud 6a Outer surface 7 Front Shroud 7a Outer surface 8 feathers 81 Positive pressure surface 81a First positive pressure surface 81b 2nd pressure surface 82 Suction surface 82a 1st suction surface 82b 2nd suction surface 83 Outer surface of the blade C1 First Virtual Circle C2 Second Virtual Circle FL channel FL1 First channel FL2 Second channel F Lo channel outlet L1 Distance between center points L2 difference L3 Interval P1 1st center point P2 2nd center point R1 Radius Line

Claims

1. An impeller attached to the rotating shaft of a centrifugal pump, which sucks in and discharges the liquid being handled, A rear shroud attached to the aforementioned rotating shaft, A front shroud is positioned opposite the aforementioned rear shroud, A plurality of vanes are arranged between the rear shroud and the front shroud at equal intervals in the circumferential direction of the rotation axis, and together with the rear shroud and the front shroud, divide a plurality of flow paths through which the handling fluid flows, It has, The aforementioned rear shroud is, In the axial view of the aforementioned rotating shaft, the outer peripheral surface of the circular back shroud, Equipped with, The aforementioned feathers are, A positive pressure surface oriented in the direction of rotation of the aforementioned rotating shaft, A negative pressure surface oriented in the opposite direction to the rotational direction, The outer circumferential surface of the blade is oriented radially outward from the rotation axis and is continuous with the positive pressure surface and the negative pressure surface, Equipped with, The aforementioned flow path is A flow channel outlet is located at the downstream end of the flow of the liquid being handled in the aforementioned flow channel, A first channel is located upstream of the channel outlet, adjacent to the channel outlet, A second channel is arranged upstream of the first channel and adjacent to the first channel, Equipped with, In the axial view, the shape of the outer surface of the blade is an arc shape arranged on a concentric circle of the outer surface of the back shroud, The radius of curvature of the outer surface of the blade is smaller than the radius of curvature of the outer surface of the back shroud. The aforementioned positive pressure surface is A first positive pressure surface that defines the first flow path, A second positive pressure surface that demarcates the second flow path, Equipped with, The negative pressure surface is A first negative pressure surface that defines the first flow path, A second negative pressure surface that demarcates the second flow path, Equipped with, In the axial view, the first positive pressure surface is positioned on a first virtual circle inscribed in the outer circumferential surface of the blade and has a curved shape that is convex in the direction of rotation. In the axial view, the first negative pressure surface is positioned on a second virtual circle that is larger than the first virtual circle, and has a concave curved surface in the rotational direction. In the axial view, the distance between the second positive pressure surface and the second negative pressure surface that demarcate one of the second flow channels decreases continuously as the flow moves from upstream to downstream. Impeller.

2. In the axial view, the second positive pressure surface and the second negative pressure surface that demarcate one of the second flow paths are in a straight line that is not parallel to each other. The impeller according to claim 1.

3. In the axial view, the angle between the second positive pressure surface and the second negative pressure surface that demarcate one of the second flow paths is 5° or less. The impeller according to claim 2.

4. In the first positive pressure surface and the first negative pressure surface that demarcate one of the first flow paths, the first center point of the first virtual circle and the second center point of the second virtual circle are arranged on one radius line of the outer circumferential surface of the back shroud, In the radial direction, the second center point is located either at the same time as the first center point or inward from the first center point. The impeller according to claim 1.

5. In the radial direction, the second center point is positioned inward from the first center point. The distance between the first center point and the second center point is less than the absolute value of the difference between the radius of the first virtual circle and the radius of the second virtual circle. The impeller according to claim 4.

6. The ratio of the distance between the center points to the absolute value is 0.2 or less. The impeller according to claim 5.

7. The cross-sectional area of ​​the channel decreases continuously from the upstream end of the flow in the second channel toward the channel outlet. In the range from the upstream end to the outlet of the flow path, the ratio of the minimum value of the cross-sectional area to the maximum value of the cross-sectional area is 0.8 or more and less than 1.

0. The impeller according to claim 5.

8. Motor and, A rotating shaft that is rotated by the aforementioned motor, The impeller according to claim 1, which is attached to the aforementioned rotating shaft, Having, Centrifugal pump.

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