Elliptical, eccentric annulus

Abstract

The invention relates to a centrifugal pump with a housing (1) made of sheet metal, 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) is formed for attaching a pressure port (15). An impeller (3) located within the housing (1) is arranged in the plane of the pressure port opening (8), wherein the axis of rotation (10) of the impeller (3) is arranged eccentrically offset with respect to a center line of the housing (1). A leading edge (7) is formed by the housing wall (14) and the pressure port (15). The housing wall (14) is designed as the outer 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) perpendicular to the main axis (4) with a short extension.

Description

[0001] The invention relates to a centrifugal pump with a housing made of sheet metal construction, wherein the housing is formed as a deep-drawn part, wherein the housing has a pressure-side housing wall on which an opening for attaching a pressure port is formed, and an impeller located within the housing is arranged in the plane of the pressure port opening, wherein the axis of rotation of the impeller is arranged eccentrically offset from a centerline of the housing, and wherein a leading edge is formed by the housing wall and the pressure port. Furthermore, the invention relates to the use of a corresponding centrifugal pump.

[0002] 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 likely, 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.

[0003] From a hydraulic perspective, the volute casing of a centrifugal pump represents the most efficient geometry currently available 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 steadily increases over the impeller circumference, which is generally designed to ensure that the swirl does not change over the circumference.

[0004] An annular casing differs from a volute casing primarily in that its cross-sectional area is constant across the impeller circumference. The annular casing is therefore also referred to as a "pot." Due to the geometric shape of the annular casing, the goal of achieving a constant swirl cannot be achieved with an annular casing due to the constant cross-section across the impeller circumference. Within the annular casing, there are areas where the cross-section is either too large or too small for the fluid volume to be pumped, and thus, due to separation and turbulence, only a lower pump efficiency can be achieved.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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 tensile compression forming like a conventional 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.

[0009] 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 capable of high-quality, cost-effective production and large-scale production. The centrifugal pump with the sheet metal housing should be capable of achieving a fluid flow with a predominantly constant swirl.

[0010] 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.

[0011] According to the invention, the housing wall is designed as a lateral 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.

[0012] 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 is exposed to the fluid 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.

[0013] In this respect, the definition of the cylinder used here is that of a general mathematical cylinder.

[0014] 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 extent of the ellipse in a given direction, causing 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 predefined points are represented 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.

[0020] The position of the foci relative to the major and minor axes of an ellipse depends on the eccentricity of the ellipse. If the eccentricity is zero, the foci are at the center of the major axis and coincide with the center of the ellipse. The greater the eccentricity, the farther the foci are from the center of the major axis.

[0021] 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 spiral casing, thus achieving a particularly high and advantageous level of efficiency.

[0022] 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°.

[0023] 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.

[0024] 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.

[0025] 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 reduction in the cross-section is minimal, allowing the flow to flow at a nearly constant swirl.

[0026] However, the housing of the centrifugal pump does not have to be manufactured using a complex process such as hydroforming, but can be designed as a deep-drawn sheet metal component, for example, which means that the housing can be manufactured cost-effectively and in large quantities.

[0027] 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 the 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.

[0028] 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.

[0029] The elliptical eccentric annular casing of a centrifugal pump represents an excellent solution for the task of manufacturing the casing in sheet metal construction and at the same time achieving a high minimum efficiency index MEI. On the one hand, the eccentricity and the elliptical shape approximate a spiral contour and thus significantly improve the flow guidance, while on the other hand, the favorable manufacturability even in high quantities is ensured by tensile compression forming.

[0030] For example, the fluid flowing through the centrifugal pump has a swirl, whereby the swirl is largely constant in the flow direction between the spur and the discharge nozzle opening.

[0031] 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 at this location and, for example, welded to the housing wall.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The eccentricity of the impeller in the casing stabilizes the swirl of the fluid flow in the area of ​​the spur. In the elliptically eccentric annular casing, the swirl distribution almost completely approximates the constant swirl pattern of a volute casing.

[0036] In a variant of the invention, the main axis is rotated by an angle α 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 continuously increasing cross-section of the space between the impeller and the casing wall, thus achieving fluid flow with constant swirl.

[0037] For example, the angle α 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°.

[0038] 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.

[0039] 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 housing center, and the value e = 1 when the impeller has a contact point with the housing wall.

[0040] In some variants of the invention, it is provided that the axis of rotation of the impeller is arranged in an eccentricity range which 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.

[0041] For example, a split ring is arranged eccentrically on the housing between the impeller and the casing.

[0042] Due to the difference in pressure 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.

[0043] To match the eccentrically positioned impeller, a suction port on the casing is positioned concentrically to the impeller's axis of rotation. This ensures ideal axial fluid flow into the impeller of the centrifugal pump, even when the impeller is positioned off-center in the casing.

[0044] 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.

[0045] 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.

[0046] Further features and advantages of the invention will become apparent from the description of embodiments with reference to the drawings and from the drawings themselves.

[0047] It shows: Fig. 1 a plan view of an elliptically eccentric casing of the centrifugal pump, Fig. 2 a longitudinal section through the housing of the centrifugal pump.

[0048] Fig. Figure 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.

[0049] 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.

[0050] 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 α, 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 shifted in the radial direction from the intersection point 12 of the main axis 4 with the secondary axis 5.

[0051] 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 the amount of angle α 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 swirl of the fluid is maintained at a largely constant level thanks to the special design of the centrifugal pump.

[0052] The discharge port opening 8 extends clockwise from the leading edge 7 across a quadrant of the housing wall 14 of the housing 1. As a result, 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.

[0053] 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 spiral casing made of sheet metal.

[0054] The 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.

[0055] A split ring 13 is arranged eccentrically on the housing 1 between the impeller 3 and the housing 1. The split ring 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.

[0056] 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 nozzle 15 is formed on the housing wall 14, with the pressure nozzle 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 1 housing 2 floor space 3 wheel 4 Main axis 5 Minor axis 6 rooms 7 Leading edge 8 Pressure port opening 9 horizontal 10 axis of rotation 11 Suction nozzle opening 12 Intersection 13 Split ring 14 Housing wall 15 pressure nozzles

Claims

[1] Centrifugal pump with a casing (1) in sheet metal construction, - wherein the housing (1) is designed 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 by that the housing wall (14) is designed as a jacket 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) perpendicular to the main axis (4) with a short extension. [2] Centrifugal pump according to claim 1, characterized by that the base area (2) is elliptical. [3] Centrifugal pump according to claim 1 or 2, characterized by in that in a space (6) formed between an outlet edge of the impeller (3) and the casing wall (14), the cross section of the space (6) in the flow direction between the leading edge (7) and the discharge 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 by that the fluid flowing through the centrifugal pump has a swirl, wherein the swirl is 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 by that the main axis (4) is rotated by an angle α relative to a horizontal (9). [6] Centrifugal pump according to one of claims 1 to 5, characterized by that the pressure port 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 by 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 by 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 by 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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