Elliptical, eccentric annular space

Abstract

The invention relates to a centrifugal pump having a housing (1) in sheet metal construction, wherein the housing (1) is designed as a deep-drawn part. The housing (1) has a pressure-side housing wall (14) on which an opening (8) for attaching a discharge port (15) is formed. An impeller wheel (3) is located within the housing (1) and is arranged in the plane of the discharge port opening (8), wherein the axis of rotation (10) of the impeller wheel (3) is eccentrically offset with respect to a centre line of the housing (1). A leading edge (7) is formed by the housing wall (14) and the discharge port (15). The housing wall (14) is designed as a lateral surface of a cylinder, wherein the cylinder has a base surface (2) which has a main axis (4) with a long extension and a secondary axis (5), which is perpendicular to the main axis (4), with a short extension.

Description

[0001] Description

[0002] Elliptical, eccentric annulus

[0003] The invention relates to a centrifugal pump with a housing in sheet metal construction, wherein the housing is designed as a deep-drawn part, wherein the housing has a pressure-side housing wall on which an opening for fastening a pressure nozzle is formed and an impeller located within the housing is arranged in the plane of the pressure nozzle opening, wherein the axis of rotation of the impeller is arranged eccentrically offset with respect to a center line of the housing and wherein a leading edge is formed by the housing wall and the pressure nozzle.

[0004] The Minimum Efficiency Index (MEI) has regulated the environmentally friendly design requirements for water pumps in the European Union since 2013. Since 2015, an MEI of 0.4 has been in effect. This means that since 2015, only pumps with an efficiency better than a reference value calculated from the worst 40% of pumps available on the market at the time may be placed on the market. It is apparent, and logical in the spirit of the energy transition, that the MEI will be raised by the European Union in the near future, thus ensuring that only pumps with the corresponding minimum efficiency will be marketable.

[0005] From a hydraulic perspective, the volute casing of a centrifugal pump is currently the most efficient geometric shape for collecting fluid after the impeller outlet and feeding it to the pump's discharge port. The simple volute is characterized by a cross-sectional profile that grows continuously around the impeller circumference, which is generally designed so that the swirl does not change along the circumference. An annular casing differs from a volute casing primarily in that the cross-sectional profile is constant around the impeller circumference. The annular space is therefore also referred to as a "pot". The geometric shape of the annular space means that the goal of constant swirl cannot be achieved with an annular casing due to the constant cross-section around the impeller circumference.Within the annular space there are areas in which the cross-section is too large or too small for the amount of fluid to be pumped and thus only a lower efficiency of the pump can be achieved due to separation and turbulence.

[0006] The annular casing is still widely used in practice because, unlike the classic spiral casing, it can be manufactured cost-effectively in sheet metal. A sheet metal annular casing typically has a smoother and higher-quality surface. This higher-quality surface is advantageous, for example, for applications with demanding hygiene conditions. At the same time, the smoother surface fundamentally reduces wall friction losses from a hydraulic perspective.

[0007] DE 199 47 720 A1 discloses a centrifugal pump with a housing made of sheet metal, wherein the housing is designed as a deep-drawn, rotationally symmetrical part in which an impeller is arranged eccentrically to the housing center axis.

[0008] Current pumps with annular casings made of sheet metal can only achieve a minimum efficiency index (MEI) of more than 0.4 within a defined or restricted operating range. If casings made of sheet metal are nevertheless required for hygiene reasons, spiral casings made of sheet metal could achieve a future-required MEI of more than 0.4 for a virtually unlimited operating range.

[0009] A sheet metal volute casing would combine the hydraulic advantages of a volute with the excellent surface finish of a sheet metal annular space, thus achieving correspondingly high levels of efficiency. At the same time, however, a sheet metal volute casing can no longer be manufactured by compression and tensile forming like a traditional annular space casing. Instead, more cost-intensive processes such as hydroforming must be used for production. The use of a sheet metal volute casing would therefore increase the pump's efficiency but also its manufacturing costs.

[0010] The object of the invention is to provide a centrifugal pump with a sheet metal housing that exhibits a favorable minimum efficiency index (MEI). At the same time, the pump housing should be high-quality, cost-effective, and capable of being manufactured in large quantities. The centrifugal pump with the sheet metal housing should be able to achieve a fluid flow with a predominantly constant swirl.

[0011] This object is achieved according to the invention by a centrifugal pump with a housing of sheet metal construction according to the features of claim 1. Preferred variants can be found in the independent main claims, the subclaims, the description and the drawings.

[0012] According to the invention, the housing wall is designed as a jacket surface of a cylinder, wherein the cylinder has a base surface which has a main axis with a long extension and a secondary axis perpendicular to the main axis with a short extension.

[0013] The outer surface of a cylinder is the total surface area of ​​the cylinder, excluding the two end surfaces. It consists of the cylinder's lateral surface, which is usually rectangular in shape. The outer surface of the cylinder is therefore the part of the casing wall that the fluid flows against after exiting the impeller and that limits the fluid flow. In this respect, the casing wall of a cylinder differs fundamentally from the design of a volute casing, which usually has defined curves and radii.

[0014] In this respect, the definition of the cylinder used here is that of a general mathematical cylinder. For example, the base of the cylinder is elliptical. The elliptical shape of the base results in a centrifugal pump housing that supports the formation of a fluid flow with a constant swirl throughout the flow path within the centrifugal pump.

[0015] An ellipse is a closed, curved geometric shape that differs from a circle in that it has two foci, and the sum of the distances from any point on the ellipse to these two foci is constant.

[0016] The major axis of an ellipse is one of the two axes that characterize an ellipse. The major axis is the longer of the two axes and extends from one end of the ellipse to the other, passing through the center of the ellipse. The major axis determines the greatest extension of the ellipse in a given direction, which causes the base of the housing wall to have a long extension along the major axis.

[0017] The minor axis of an ellipse is one of the two axes that characterize an ellipse. In contrast to the major axis, which is the longer of the two axes, the minor axis is the shorter of the two. The minor axis extends perpendicular to the major axis and passes through the center of the ellipse. It determines the smallest extension of the ellipse in a given direction, which means that the base of the housing wall has a short extension along the minor axis. Together with the major axis, the minor axis forms the coordinate system of the ellipse.

[0018] In a variant of the invention, the sum of the distances of a point on the housing wall from two predetermined points is the same for all points on the housing wall.

[0019] For example, these given points are designed as foci. The foci of an ellipse are two defined points inside the ellipse, which characterize the following important geometric property of the ellipse: The sum of the distances from any point on the ellipse to the two foci is constant and equal to the length of the major axis of the ellipse. The position of the foci relative to the major axis and the minor axis of an ellipse depends on the eccentricity of the ellipse. If the eccentricity is zero, the foci are in the center of the major axis and coincide with the center of the ellipse. The greater the eccentricity, the further the foci are from the center of the major axis.

[0020] In a variant of the invention, the cross-section of the space formed between the trailing edge of the impeller and the casing wall increases almost continuously in the direction of flow between the spur and the discharge port opening. The special, elliptical shape of the centrifugal pump casing, combined with the eccentrically arranged impeller, creates a fluid flow that is almost identical to the fluid flow in a volute casing, thus achieving a particularly high and advantageous level of efficiency.

[0021] For example, in a space formed between a trailing edge of the impeller and the casing wall, the cross-section of the space in the flow direction between the leading edge or the spur and the discharge nozzle opening is continuously increasing in a range of up to 270°.

[0022] In an advantageous variant of the invention, the area of ​​continuous cross-sectional increase between leading edge and discharge nozzle opening is 270° in the flow direction.

[0023] In an alternative variant of the invention, the area of ​​continuous increase in space begins approximately 10° offset in the direction of flow after the spur and ends at the transition to the pressure nozzle.

[0024] In one variant of the invention, the cross-section at the transition to the discharge nozzle can be designed to be non-increasing due to the design. For example, the cross-section reduction is minimal, allowing the flow to flow at a nearly constant swirl. However, the housing of the centrifugal pump does not have to be manufactured using a complex process such as hydroforming, but can be constructed, for example, as a deep-drawn sheet metal component, allowing the housing to be manufactured cost-effectively and in high volumes.

[0025] Deep drawing is a metalworking process used to draw flat metal sheets into three-dimensional, hollow, or deep shapes. According to DIN 8584, deep drawing is the tensile and compressive forming of a sheet metal blank into a hollow body that is open on one side. First, a flat metal sheet is cut to the correct size and shape. The forming tool has the desired shape of the final product, while the die has a recess for the sheet. The sheet is placed between the forming tool and die. Using a hydraulic or mechanical press, the flat metal sheet is drawn into the forming tool. The pressure and speed are carefully controlled to ensure that the sheet is drawn evenly into the mold. The pressure forces the metal sheet into the desired shape and forms it. It takes on the contour of the forming tool, thus forming the finished part.After the deep drawing process is completed, the formed part is removed from the mold.

[0026] Deep drawing offers the advantage of producing complex and precise shapes that are lightweight yet strong. It is a cost-effective process for mass production of parts because it minimizes material waste.

[0027] The elliptical, eccentric annular casing of a centrifugal pump represents an excellent solution for the task of manufacturing the casing from sheet metal while simultaneously achieving a high minimum efficiency index (MEI). On the one hand, the eccentricity and elliptical shape approximate a spiral contour, thus significantly improving flow guidance. On the other hand, it allows for favorable manufacturing, even in high volumes, through tensile-compression forming. For example, the fluid flowing through the centrifugal pump exhibits a swirl, with the swirl remaining largely constant in the flow direction between the spur and the discharge port opening.

[0028] In one embodiment of the invention, a flattened housing with a pressure port opening is arranged on the housing wall. The pressure port component can be inserted into this location and, for example, welded to the housing wall.

[0029] For example, the discharge port opening is positioned on the housing wall in such a way that, starting from the elliptical base of the pump housing, the cross-section for the fluid flow flows into the discharge port with a constant swirl, so that the cross-section increases continuously up to the discharge port. The flow-optimized design of the housing, in conjunction with the eccentric arrangement of the impeller, can almost fully adapt the advantages of a volute casing, namely its increasing flow cross-section, which promotes pressure buildup. Due to the flattening of the housing wall, the discharge port opening has a leading edge that approximates the spur of a volute casing.

[0030] The described casing design in no way compromises the advantages of a casing made of deep-drawn sheet metal in terms of manufacturing and rigidity. At the same time, the combination with an eccentric impeller arrangement significantly approximates the advantages of a volute casing in terms of efficiency and radial force distribution.

[0031] Swirl, or swirling flow, is a flow rotating around an axis with circumferential components. The flow vectors can have both axial and radial components. The flowing particles then move along helical paths. The swirl of a fluid is linked to its angular momentum. Angular momentum is a measure of the rotational motion of a body. In a flow, swirl contributes to the conservation of angular momentum. The eccentricity of the impeller in the casing stabilizes the swirl of the fluid flow in the region of the spur. In the elliptically eccentric annular casing, the swirl distribution almost completely approximates the constant swirl pattern of a volute casing.

[0032] In a variant of the invention, the main axis is oriented at an angle a relative to a horizontal line, which, for example, extends from the impeller axis to the base of the discharge nozzle. This further supports the formation of the steadily increasing cross-section of the space between the impeller and the casing wall, thus achieving fluid flow with constant swirl.

[0033] For example, the angle a is more than 5°, preferably more than 7.5°, in particular more than 10°, and / or less than 25°, preferably less than 20°, in particular less than 15°.

[0034] In one variant, the discharge port opening extends from the spur across an entire quadrant of the casing wall. This ensures that the discharge port opening is sufficiently large so that the steadily increasing flow cross-section does not taper at the discharge port opening, which would adversely affect the flow with constant swirl in terms of increased efficiency.

[0035] For example, the impeller's rotational axis is arranged in an eccentricity range with a value of e = 0.05 - 0.40 in the radial direction. The value e = 0 when the impeller center coincides with the casing center, and the value e = 1 when the impeller has a contact point with the casing wall.

[0036] In some variants of the invention, the rotational axis of the impeller is arranged in an eccentricity range that has a value of 0.10 to 0.35 in the radial direction, preferably a value of 0.15 to 0.30, in particular a value of 0.20 to 0.25. For example, a split ring is arranged eccentrically on the housing between the impeller and the housing.

[0037] Due to the pressure difference upstream and downstream of the impeller, a portion of the pumped fluid, which has already been brought to a higher static pressure, flows back through the gap between the stationary and rotating parts of the pump. By installing a wear ring, the loss through the gap can be significantly minimized. In one embodiment of the invention, an eccentrically arranged or eccentrically designed wear ring carrier can create a narrow gap for sealing between the rotating impeller and the stationary, elliptically eccentric annular housing.

[0038] To match the eccentrically positioned impeller, a suction port on the casing is positioned concentrically to the impeller's rotational axis. This ensures ideal axial fluid flow into the impeller of the centrifugal pump, even if the impeller is positioned off-center in the casing.

[0039] According to the invention, a centrifugal pump with a casing made of sheet metal construction, with an eccentrically arranged impeller and a casing with an elliptical base area is used to achieve high energy efficiency in fluid conveyance.

[0040] A centrifugal pump with an elliptically eccentric annular casing achieves the efficiency level of a smooth spiral casing and thus represents a cost-effective and at the same time efficient alternative to the sheet metal spiral casing.

[0041] Further features and advantages of the invention will become apparent from the description of embodiments based on the drawings and from the drawings themselves.

[0042] Fig. 1 is a plan view of an elliptical eccentric casing of the centrifugal pump,

[0043] Fig. 2 shows a longitudinal section through the housing of the centrifugal pump.

[0044] Fig. 1 shows a plan view of a housing 1 with an elliptical base 2 and an eccentrically arranged impeller 3. The housing 1 is formed as a deep-drawn part. The elliptical base 2 has a main axis 4 with a long extension and a secondary axis 5 with a short extension, perpendicular to the main axis 4.

[0045] In the space 6, which is formed between an outlet edge of the impeller 3 and a housing wall 14 of the housing 1, the cross-section of a space 6 increases almost continuously in the flow direction between a leading edge 7, which is designed as a spur, and a discharge port opening 8. As a result, the swirl of the fluid flowing through the centrifugal pump is largely constant in the flow direction between the leading edge 7 and the discharge port opening 8.

[0046] In this embodiment, the center line of the housing 1 corresponds to the main axis 4. The main axis 4 of the housing 1 is rotated relative to a horizontal line 9 by an angle e, which in the embodiment shown is 12°. The axis of rotation 10 of the impeller 3 is arranged in an eccentricity range with a value of e = 0.2 in the radial direction. The axis of rotation 10 of the impeller 3 is offset in the radial direction from the intersection point 12 of the main axis 4 with the secondary axis 5.

[0047] The area of ​​chamber 6 with a continuous cross-sectional increase, formed between an outlet edge of impeller 3 and a casing wall 14 of casing 1, begins approximately at an angle ε in the direction of flow. At the transition to the discharge nozzle 15, the continuous cross-sectional increase of chamber 6 cannot be fully realized due to the design. Nevertheless, the fluid swirl is maintained at a largely constant level thanks to the special design of the centrifugal pump.

[0048] The discharge port opening 8 extends clockwise from the leading edge 7 across a quadrant of the housing wall 14 of the housing 1. This ensures that the discharge port opening 8 is sufficiently large so that the continuously increasing cross-section of the chamber 6 does not taper at the discharge port opening 8. This promotes the formation of a flow with constant swirl and advantageously increases the efficiency of the centrifugal pump.

[0049] The centrifugal pump shown with an elliptically eccentric casing 1 achieves the efficiency level of a smooth spiral casing and thus represents a cost-effective and at the same time efficient alternative to the sheet metal spiral casing.

[0050] Fig. 2 shows an embodiment in which the suction nozzle opening 11 on the housing 1 is arranged concentrically to the axis of rotation 10 of the impeller 3.

[0051] A split ring 13 is arranged eccentrically on the housing 1 between the impeller 3 and the housing 1. The split 13 forms a sealing gap between the impeller 3 and the interior of the housing 1. This prevents fluid escaping from the impeller 3 from flowing back to the suction port opening 11.

[0052] The housing 1 is formed as a deep-drawn part and has a pressure-side housing wall 14. An opening 8 for attaching a pressure port 15 is formed on the housing wall 14, with the pressure port 15 being welded to the housing wall 14. The housing wall 14 is designed as the outer surface of a cylinder. List of reference symbols

[0053] 1 housing 10 rotation axis

[0054] 2 Base area 11 Suction nozzle opening

[0055] 3 Impeller 12 Intersection

[0056] 4 Main axis 13 Cleavage

[0057] 5 Minor axis 14 Housing wall

[0058] 6 Room 15 Pressure nozzle

[0059] 7 Leading edge

[0060] 8 Pressure port opening

[0061] 9 horizontal

Claims

Patent claims 1. Centrifugal pump with a casing (1) made of sheet metal, - wherein the housing (1) is formed as a deep-drawn part, - wherein the housing (1) has a pressure-side housing wall (14) on which an opening (8) for fastening a pressure nozzle (15) is formed, - and an impeller (3) located within the housing (1) is arranged in the plane of the discharge nozzle opening (8), - wherein the axis of rotation (10) of the impeller (3) is arranged eccentrically offset from a center line of the housing (1), - wherein a leading edge (7) is formed by the housing wall (14) and the pressure nozzle (15), characterized in that the housing wall (14) is designed as a jacket surface of a cylinder, the cylinder having a base surface (2) which has a main axis (4) with a long extension and a secondary axis (5) perpendicular to the main axis (4) with a short extension.

2. Centrifugal pump according to claim 1, characterized in that the base surface (2) is elliptical.

3. Centrifugal pump according to claim 1 or 2, characterized in that in a space (6) which is formed between an outlet edge of the impeller (3) and the housing wall (14), the cross section of the space (6) in the flow direction between the leading edge (7) and the pressure nozzle opening (8) is continuously increasing in a range of up to 270 °.

4. Centrifugal pump according to one of claims 1 to 3, characterized in that the fluid flowing through the centrifugal pump has a swirl, the swirl being largely constant in the flow direction between the leading edge (7) and the discharge nozzle opening (8).

5. Centrifugal pump according to one of claims 1 to 4, characterized in that the main axis (4) is aligned rotated by an angle ε relative to a horizontal (9).

6. Centrifugal pump according to one of claims 1 to 5, characterized in that the pressure nozzle opening (8) extends from the leading edge (7) over an entire quadrant of the housing wall (14).

7. Centrifugal pump according to one of claims 1 to 6, characterized in that the axis of rotation (10) of the impeller (3) is arranged in an eccentricity range which has a value e of 0.05 to 0.40 in the radial direction.

8. Centrifugal pump according to one of claims 1 to 7, characterized in that a split ring (13) is arranged eccentrically on the housing (1) between the impeller (3) and the housing (1).

9. Centrifugal pump according to one of claims 1 to 8, characterized in that a suction nozzle opening (11) on the housing (1) is arranged concentrically to the axis of rotation (10) of the impeller (3).

10. Use of a centrifugal pump according to one of claims 1 to 9 with a housing (1) in sheet metal construction, with an eccentrically arranged impeller (3) and a housing (1) with an elliptical base area (2) to achieve high energy efficiency in fluid conveyance.

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