Flow channel design method for low-specific-speed centrifugal pump and low-specific-speed centrifugal pump

Abstract

The invention provides a low-specific-speed centrifugal pump flow channel design method and a low-specific-speed centrifugal pump. The method comprises the following steps that flow channel inlet and outlet parameters are determined according to the rated flow, the rated lift and the rated rotating speed of the low-specific-speed centrifugal pump; the flow channel inlet and outlet parameters comprise impeller inlet and outlet diameters, flow channel inner and outer side fillets, flow channel wrap angles, flow channel inlet and outlet angles and flow channel inlet and outlet section parameters; two ends of a curve are determined through a runner inlet section and a runner outlet section, at least four transition sections are arranged between a runner inlet and a runner outlet, the runner inlet section, the transition sections and the runner outlet section are connected through an arc curve, and the runner trend and shape are determined. According to the invention, the bad flow state in the flow channel can be avoided as much as possible while the energy consumption is reduced. And the working efficiency and long-term safe and stable operation of the low-specific-speed centrifugal pump are ensured.

Description

Technical Field

[0001] The invention relates to the field of centrifugal pumps, and in particular to a flow channel design method for a low specific speed centrifugal pump and a low specific speed centrifugal pump. Background Art

[0002] Usually the specific speed n s A centrifugal pump with a specific speed of less than 30 is called a low specific speed centrifugal pump. Low specific speed centrifugal pumps have the characteristics of small flow and high head, so they are widely used. However, at the same time, low specific speed centrifugal pumps have low working efficiency due to their narrow and long flow channels and large outer diameter of impellers, and are prone to produce vortices and other undesirable flow states in the flow channels. Therefore, solving such problems has become a key point in the future development of low specific speed centrifugal pumps.

[0003] In recent years, scholars and technicians have proposed that the diffusion degree of the flow channel will affect the working efficiency of the centrifugal pump, and through the design of the impeller size, such as changing the width of the outlet blade to change the flow channel outlet area, and then calculate the ratio of the flow channel inlet and outlet areas. It is found that the ratio of the inlet and outlet areas reaching 1.2 to 1.5 can reduce the energy consumption of low specific speed centrifugal pumps and improve the working efficiency of low specific speed centrifugal pumps.

[0004] However, this method of changing the diffusion degree of the flow channel by designing the impeller size cannot effectively alleviate the current situation of unfavorable flow states such as vortices in the low specific speed flow channel. In addition, the flow channel cannot be directly and effectively controlled by designing the impeller. At the same time, the time and energy consumed by improving the working efficiency of the centrifugal pump by designing the impeller is also quite huge. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a low specific speed centrifugal pump flow channel design method and a low specific speed centrifugal pump, which can reduce energy consumption while avoiding undesirable flow patterns in the flow channel as much as possible, and ensure the working efficiency and long-term safe and stable operation of the low specific speed centrifugal pump.

[0006] The present invention achieves the above technical objectives through the following technical means.

[0007] A method for designing a flow channel of a low specific speed centrifugal pump comprises the following steps:

[0008] According to the rated flow Q of the low specific speed centrifugal pump n , Rated head H n and rated speed n, determine the flow channel inlet and outlet parameters, the flow channel inlet and outlet parameters including impeller inlet and outlet diameters, flow channel inner and outer fillets, flow channel wrap angle, flow channel inlet and outlet angles and flow channel inlet and outlet cross-sectional parameters;

[0009] The two ends of the curve are determined by the flow channel inlet section and the flow channel outlet section, at least 4 transition sections are set between the flow channel inlet and outlet, and the flow channel inlet section, transition section and flow channel outlet section are connected by arc curves to determine the flow channel direction and shape.

[0010] Furthermore, an arc curve is used to connect the flow channel inlet section, transition section and flow channel outlet section, and the flow channel direction is determined as follows:

[0011] Use arc curve to connect the flow channel inlet section and flow channel outlet section to preliminarily determine the flow channel direction

[0012] The plane perpendicular to the flow channel inlet and outlet cross-section direction and the center point of the flow channel inlet and outlet cross-section is the reference plane, the hub is the center of the circle, and the spacing between the flow channel inlet and outlet is Draw at least 4 concentric circles and make the intersections of the concentric circles and the arc curves. The intersections are the centers of the transition sections. Where: D2 is the impeller outlet diameter; r3 is the distance from the flow channel inlet margin to the axis center;

[0013] Overlap the center of the flow channel inlet section with the center of the flow channel outlet section, make the diagonal of the flow channel inlet section intersect with the flow channel outlet section, and make the major and minor axes of the flow channel outlet section intersect with the flow channel inlet section; make four equal points on the eight intersection lines respectively, and use fitting curves to connect the corresponding equal points to determine the shape of each transition section; use arc curves to connect the flow channel inlet section, transition section and flow channel outlet section to determine the flow channel direction and shape.

[0014] Further, according to the rated flow Q of the low specific speed centrifugal pump n , Rated head H n And rated speed n, determine the impeller inlet and outlet diameters, specifically:

[0015] Impeller inlet diameter D j Determined by the following formula:

[0016]

[0017] Where: D0 is the equivalent diameter of the impeller inlet, m;

[0018] k0 is the coefficient, k0=4.0~4.5;

[0019] Q n is the rated flow rate, m 3 / s;

[0020] n is the pump speed, r / min;

[0021] d h is the hub diameter, m;

[0022] D jis the impeller inlet diameter, m;

[0023] The impeller outlet diameter D2 is determined by the following formula:

[0024]

[0025] Where: μ d is the correction coefficient of the impeller outlet diameter D2, when n s When ≤30, take μ d =1.175~1.247, when n s When n is larger, it takes a smaller value. s When it is smaller, take the larger value;

[0026] n s is the specific speed,

[0027] D2 is the impeller outlet diameter, m.

[0028] Further, according to the impeller inlet diameter D of the low specific speed centrifugal pump j , impeller outlet diameter D2 and hub diameter d n , determine the inner and outer fillets of the flow channel, specifically:

[0029] The range of the inner fillet r1 of the flow channel can be determined by the following formula and then rounded off, specifically:

[0030]

[0031] Where: σ1 is the correction coefficient, taking σ1 = 0.85 ~ 1.1;

[0032] D2 is the impeller outlet diameter, m;

[0033] D j is the impeller inlet diameter, m;

[0034] d h is the hub diameter, m;

[0035] The range of the outer fillet r2 of the flow channel can be determined by the following formula and then rounded, specifically:

[0036] r2=σ2(D j -d n )≤r3

[0037] Where: σ2 is the correction coefficient, taking σ2 = 0.9 ~ 1.5;

[0038] D j is the impeller inlet diameter, m;

[0039] d h is the hub diameter, m;

[0040] r3 is the distance from the flow channel inlet edge to the axis, m; it is determined by the following formula:

[0041] r3=k c (r1+D j )

[0042] Where: k c is the r3 correction coefficient, take k c =1.05~1.25;

[0043] r1 is the inner fillet of the flow channel, m.

[0044] Furthermore, the flow channel wrap angle and the flow channel inlet and outlet angles are determined according to the impeller outlet diameter D2 of the low specific speed centrifugal pump and the distance r3 from the flow channel inlet margin to the axial center, specifically:

[0045] The flow channel wrap angle α is calculated according to the following formula:

[0046]

[0047] in:

[0048] D2 is the impeller outlet diameter, m;

[0049] r3 is the distance from the flow channel inlet edge to the axis, m;

[0050] The flow channel outlet angle β2 ranges from 50° to 60°;

[0051] The flow channel inlet angle β1 is controlled by the flow channel wrap angle α and the flow channel outlet angle β2, and the range is 75° to 85°.

[0052] Furthermore, the flow channel inlet and outlet cross-sectional parameters include the number of flow channels, the flow channel inlet area and the flow channel outlet area, which are specifically determined as follows:

[0053] The number of flow channels Z0 is determined by the following formula:

[0054]

[0055] Where: K is the coefficient, K = 6.0 ~ 8.5;

[0056] D2 is the impeller outlet diameter, m;

[0057] D j is the impeller inlet diameter, m;

[0058] α is the flow channel wrap angle;

[0059] Assume the flow channel inlet area is A1, and the flow channel outlet area is A2.

[0060] Among them, the inlet area A1 of the flow passage between the two blades is determined by the following formula:

[0061]

[0062] Where: r3 is the distance from the flow channel inlet edge to the axis, m;

[0063] b1 is the blade inlet width, m;

[0064] ψ1 is the flow channel area utilization rate;

[0065] Z0 is the number of flow channels;

[0066] According to the ratio of the flow channel inlet and outlet areas Determine the flow channel outlet area as A2;

[0067] The flow channel outlet cross section is an elliptical cross section, the major semi-axis of the elliptical cross section is a1, and the minor semi-axis of the elliptical cross section is a2.

[0068] A2=a1a2π

[0069] The minor semi-axis a2 of the elliptical cross section at the flow channel outlet should be approximately equal to the distance c2 between the front and rear cover plates of the impeller. The distance c2 between the front and rear cover plates of the impeller is determined by the following formula:

[0070]

[0071] Where: k b is the correction coefficient, and its value range is k b =1.09~1.152, when n s When k is larger, b Take a small value; when n s When k is small, b Take the larger value;

[0072] Q n is the normal working flow, m 3 / s;

[0073] n is the pump speed, r / min.

[0074] Furthermore, a horizontal straight line is introduced at the inlet of the flow channel, and the length of the straight line d1 is determined by the following formula:

[0075] d1=(0.7~0.9)D j

[0076] Where: D j is the impeller inlet diameter, m.

[0077] A low specific speed centrifugal pump uses the low specific speed centrifugal pump flow channel design method.

[0078] The beneficial effects of the present invention are:

[0079] 1. The low specific speed centrifugal pump flow channel design method and the low specific speed centrifugal pump described in the present invention directly control the ratio of the flow channel inlet and outlet areas between two blades through the design of the flow channel inlet and outlet, thereby minimizing the loss between the flow channels and increasing the working efficiency of the centrifugal pump.

[0080] 2. The low specific speed centrifugal pump flow channel design method and the low specific speed centrifugal pump described in the present invention can effectively avoid the complicated design when designing the blades by directly designing the flow channel, reduce the trial and error cost in the design process, and can more easily avoid the adverse flow state in the flow channel of the low specific speed centrifugal pump in the design of the flow channel, thereby extending the service life of the centrifugal pump and ensuring that the water pump can operate safely and efficiently for a longer period of time.

[0081] 3. The low specific speed centrifugal pump flow channel design method and the low specific speed centrifugal pump described in the present invention can enable such centrifugal pumps to achieve better working efficiency and operate more safely and effectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. The drawings described below are some embodiments of the present invention. For ordinary technicians in this field, it is obvious that other drawings can be obtained based on these drawings without paying any creative work.

[0083] Figure 1 It is a cross-sectional view of the flow passage of the low specific speed centrifugal pump of the present invention.

[0084] Figure 2 This is a cross-sectional view of the impeller flow channel described in the present invention.

[0085] Figure 3 This is a flow channel transition surface diagram of the present invention.

[0086] Figure 4 This is a 3D schematic diagram of the present invention.

[0087] Figure 5 A schematic diagram showing the diagonal lines drawn to overlap the center of the flow channel inlet section and the center of the flow channel outlet section.

[0088] Figure 6 This is a simulation diagram of the impeller of a traditional low specific speed centrifugal pump.

[0089] Figure 7 This is a simulation diagram of the impeller of a low specific speed centrifugal pump according to an embodiment of the present invention.

[0090] In the figure:

[0091] 1- impeller inlet; 2- impeller outlet; 3- flow channel. DETAILED DESCRIPTION

[0092] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0093] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "axial", "radial", "vertical", "horizontal", "inner", "outer" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0094] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0095] like Figure 4 As shown in the figure, the inlet and outlet cross-sectional area ratio of the flow passage between the two blades of the low specific speed centrifugal pump in the embodiment is controlled at 1.2, and the outlet cross-sectional shape is controlled to be an elliptical outlet cross-sectional shape. The flow passage design method of the low specific speed centrifugal pump specifically includes the following steps:

[0096] According to the rated flow Q of the low specific speed centrifugal pump n , Rated head H n and rated speed n, determine the flow channel inlet and outlet parameters, the flow channel inlet and outlet parameters include impeller inlet and outlet diameters, flow channel inner and outer fillets, flow channel wrap angle, flow channel inlet and outlet angles and flow channel inlet and outlet cross-sectional parameters, such as Figure 1 As shown, specifically:

[0097] Impeller inlet diameter D jDetermined by the following formula:

[0098]

[0099] Where: D0 is the equivalent diameter of the impeller inlet, m;

[0100] k0 is a coefficient. Based on statistical data, k0=4.0~4.5 is selected mainly considering efficiency and cavitation;

[0101] Q n is the rated flow rate, m 3 / s;

[0102] n is the pump speed, r / min;

[0103] d h is the hub diameter, m;

[0104] D j is the impeller inlet diameter, m;

[0105] The impeller outlet diameter D2 is determined by the following formula:

[0106]

[0107] Where: μ d is the correction coefficient of the impeller outlet diameter D2, when n s When ≤30, take μ d =1.175~1.247, when n s When n is larger, it takes a smaller value. s When n is smaller, it takes a larger value; that is, when n s When the value is close to 30, μ d Take the lower limit (such as a value near 1.175), and similarly when n s The further away from 30 the value is, the d Take the upper limit value.

[0108] n s is the specific speed,

[0109] D2 is the impeller outlet diameter, m.

[0110] Determine the inner and outer fillets of the flow channel, specifically:

[0111] The range of the inner fillet r1 of the flow channel can be determined by the following formula and then rounded off, specifically:

[0112]

[0113] Where: σ1 is the correction coefficient, taking σ1 = 0.85 ~ 1.1;

[0114] D2 is the impeller outlet diameter, m;

[0115] D j is the impeller inlet diameter, m;

[0116] d h is the hub diameter, m;

[0117] The range of the outer fillet r2 of the flow channel can be determined by the following formula and then rounded, specifically:

[0118] r2=σ2(D j -d n )≤r3

[0119] Where: σ2 is the correction coefficient, taking σ2 = 0.9 ~ 1.5;

[0120] D j is the impeller inlet diameter, m;

[0121] d h is the hub diameter, m;

[0122] r3 is the distance from the flow channel inlet edge to the axis, m; it is determined by the following formula:

[0123] r3=k c (r1+D j )

[0124] Where: k c is the r3 correction coefficient, take k c =1.05~1.25;

[0125] r1 is the inner fillet of the flow channel, m.

[0126] Determine the flow channel wrap angle and flow channel inlet and outlet angles, specifically:

[0127] The flow channel wrap angle α is calculated according to the following formula:

[0128]

[0129] in:

[0130] D2 is the impeller outlet diameter, m;

[0131] r3 is the distance from the flow channel inlet edge to the axis, m;

[0132] The flow channel outlet angle β2 ranges from 50° to 60°;

[0133] The flow channel inlet angle β1 is controlled by the flow channel wrap angle α and the flow channel outlet angle β2, and the range is 75° to 85°.

[0134] The flow channel inlet and outlet cross-sectional parameters include the number of flow channels, the flow channel inlet area and the flow channel outlet area, which are specifically determined as follows: The number of flow channels Z0 is determined by the following formula:

[0135]

[0136] Where: K is a coefficient, and its value varies according to the material, and K is taken as 6.0 to 8.5;

[0137] D2 is the impeller outlet diameter, m;

[0138] D j is the impeller inlet diameter, m;

[0139] α is the flow channel wrap angle;

[0140] Assume that the flow channel inlet area is A1 and the flow channel outlet area is A2, where the flow channel inlet area A1 between the two blades is determined by the following formula:

[0141]

[0142] Where: r3 is the distance from the flow channel inlet edge to the axis, m;

[0143] b1 is the blade inlet width, m;

[0144] ψ1 is the flow channel area utilization rate;

[0145] Z0 is the number of flow channels;

[0146] According to the ratio of the flow channel inlet and outlet areas Determine the flow channel outlet area as A2;

[0147] The flow channel outlet cross section is an elliptical cross section, the major semi-axis of the elliptical cross section is a1, and the minor semi-axis of the elliptical cross section is a2.

[0148] A2=a1a2π

[0149] The minor semi-axis a2 of the elliptical cross section at the flow channel outlet should be approximately equal to the distance c2 between the front and rear cover plates of the impeller. The distance c2 between the front and rear cover plates of the impeller is determined by the following formula:

[0150]

[0151] Where: k b is the correction coefficient, and its value range is k b =1.09~1.152, when n s When k is larger, b Take a small value; when n s When k is small, b Take a large value; that is, when n s When the value is close to 30, k bTake the lower limit (such as a value near 1.09), and similarly when n s The further away from 30 the value is, the d Take the upper limit value.

[0152] Q n is the normal working flow, m 3 / s;

[0153] n is the pump speed, r / min.

[0154] A horizontal straight line is introduced at the inlet of the flow channel, and the length of the straight line d1 is determined by the following formula:

[0155] d1=(0.7~0.9)D j

[0156] Where: D j is the impeller inlet diameter, m.

[0157] In the embodiment, the two ends of the curve are determined by the flow channel inlet section and the flow channel outlet section, four transition sections are set between the flow channel inlet and outlet, and arc curves are used to connect the flow channel inlet section, transition section and flow channel outlet section to determine the flow channel direction and shape. Figure 2 As shown, a, b, c and d represent 4 cross sections.

[0158] Determine the flow path direction as follows:

[0159] Use arc curve to connect the flow channel inlet section and flow channel outlet section to preliminarily determine the flow channel direction;

[0160] The plane perpendicular to the flow channel inlet and outlet cross-section direction and the center point of the flow channel inlet and outlet cross-section is the reference plane, the hub is the center of the circle, and the spacing between the flow channel inlet and outlet is Draw 4 concentric circles and make the intersections of the concentric circles and the arc curves. The intersections are the centers of the transition sections. Where: D2 is the impeller outlet diameter; r3 is the distance from the flow channel inlet margin to the axis center;

[0161] Overlap the center of the flow channel inlet section with the center of the flow channel outlet section, make the diagonal of the flow channel inlet section intersect with the flow channel outlet section, and make the major and minor axes of the flow channel outlet section intersect with the flow channel inlet section, such as Figure 5 As shown; the eight intersection lines are divided into four equal points, and the corresponding equal points are connected with the fitting curve to determine the shape of each transition section, as shown in Figure 3 As shown; arc curves are used to connect the flow channel inlet section, transition section and flow channel outlet section to determine the flow channel direction and shape.

[0162] Figure 6 and Figure 7 The fluid distribution of the internal liquid of the impeller of the embodiment of the present invention and the traditional impeller of the same type under large flow conditions, such as Figure 6 As shown in the figure, the conventional impeller generates obvious fluid turbulence and vortex after entering the blades, which significantly reduces its flow capacity. Figure 7 As shown, the impeller fluid distribution of the embodiment of the present invention is smooth, without obvious vortex, has better flow capacity, reduces the occurrence of undesirable flow states, and increases the working efficiency of the centrifugal pump.

[0163] A low specific speed centrifugal pump uses the low specific speed centrifugal pump flow channel design method.

[0164] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0165] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for designing a flow channel of a low specific speed centrifugal pump, characterized in that: The steps include: According to the rated flow Q of the low specific speed centrifugal pump n , Rated head H n and rated speed n, determine the flow channel inlet and outlet parameters, the flow channel inlet and outlet parameters including impeller inlet and outlet diameters, flow channel inner and outer fillets, flow channel wrap angle, flow channel inlet and outlet angles and flow channel inlet and outlet cross-sectional parameters; The two ends of the curve are determined by the flow channel inlet section and the flow channel outlet section, at least 4 transition sections are set between the flow channel inlet and outlet, and the flow channel inlet section, transition section and flow channel outlet section are connected by arc curves to determine the flow channel direction and shape.

2. The method for designing a flow channel of a low specific speed centrifugal pump according to claim 1, characterized in that: The arc curve is used to connect the flow channel inlet section, transition section and flow channel outlet section, and the flow channel direction is determined as follows: Use arc curve to connect the flow channel inlet section and flow channel outlet section to preliminarily determine the flow channel direction; The plane perpendicular to the flow channel inlet and outlet cross-section direction and the center point of the flow channel inlet and outlet cross-section is the reference plane, the hub is the center of the circle, and the spacing between the flow channel inlet and outlet is Draw at least 4 concentric circles and make the intersections of the concentric circles and the arc curves. The intersections are the centers of the transition sections. Where: D2 is the impeller outlet diameter; r3 is the distance from the flow channel inlet margin to the axis center; Overlap the center of the flow channel inlet section with the center of the flow channel outlet section, make the diagonal of the flow channel inlet section intersect with the flow channel outlet section, and make the major and minor axes of the flow channel outlet section intersect with the flow channel inlet section; make four equal points on the eight intersection lines respectively, and use fitting curves to connect the corresponding equal points to determine the shape of each transition section; use arc curves to connect the flow channel inlet section, transition section and flow channel outlet section to determine the flow channel direction and shape.

3. The method for designing a flow channel of a low specific speed centrifugal pump according to claim 1, characterized in that: According to the rated flow Q of the low specific speed centrifugal pump n , Rated head H n And rated speed n, determine the impeller inlet and outlet diameters, specifically: Impeller inlet diameter D j Determined by the following formula: Where: D0 is the equivalent diameter of the impeller inlet, m; k0 is the coefficient, k0=4.0~4.5; Q n is the rated flow rate, m 3 / s; n is the pump speed, r / min; d h is the hub diameter, m; D j is the impeller inlet diameter, m; The impeller outlet diameter D2 is determined by the following formula: Where: μ d is the correction coefficient of the impeller outlet diameter D2, when n s When ≤30, take μ d =1.175~1.247, when n s When n is larger, it takes a smaller value. s When it is smaller, take the larger value; n s is the specific speed, D2 is the impeller outlet diameter, m.

4. The method for designing a flow channel of a low specific speed centrifugal pump according to claim 3, characterized in that: According to the impeller inlet diameter D of the low specific speed centrifugal pump j , impeller outlet diameter D2 and hub diameter d n Determine the inner and outer fillets of the flow channel, specifically: The range of the inner fillet r1 of the flow channel can be determined by the following formula and then rounded off, specifically: Where: σ1 is the correction coefficient, taking σ1 = 0.85 ~ 1.1; D2 is the impeller outlet diameter, m; D j is the impeller inlet diameter, m; d h is the hub diameter, m; The range of the outer fillet r2 of the flow channel can be determined by the following formula and then rounded, specifically: r2=σ2(D j -d n )≤r3 Where: σ2 is the correction coefficient, taking σ2 = 0.9 ~ 1.5; D j is the impeller inlet diameter, m; d h is the hub diameter, m; r3 is the distance from the flow channel inlet edge to the axis, m; it is determined by the following formula: r3=k c (r1+D j ) Where: k c is the r3 correction coefficient, take k c =1.05~1.25; r1 is the inner fillet of the flow channel, m.

5. The method for designing a flow channel of a low specific speed centrifugal pump according to claim 3, characterized in that: According to the impeller outlet diameter D2 of the low specific speed centrifugal pump and the distance r3 from the flow channel inlet edge to the axial center, the flow channel wrap angle and the flow channel inlet and outlet angles are determined, specifically: The flow channel wrap angle α is calculated according to the following formula: in: D2 is the impeller outlet diameter, m; r3 is the distance from the flow channel inlet edge to the axis, m; The flow channel outlet angle β2 ranges from 50° to 60°; The flow channel inlet angle β1 is controlled by the flow channel wrap angle α and the flow channel outlet angle β2, and the range is 75° to 85°.

6. The method for designing a flow channel of a low specific speed centrifugal pump according to claim 3, characterized in that: The flow channel inlet and outlet cross-sectional parameters include the number of flow channels, the flow channel inlet area and the flow channel outlet area, which are specifically determined as follows: The number of flow channels Z0 is determined by the following formula: Where: K is the coefficient, K = 6.0 ~ 8.5; D2 is the impeller outlet diameter, m; D j is the impeller inlet diameter, m; α is the flow channel wrap angle; Assume the flow channel inlet area is A1, and the flow channel outlet area is A2. Among them, the inlet area A1 of the flow passage between the two blades is determined by the following formula: Where: r3 is the distance from the flow channel inlet edge to the axis, m; b1 is the blade inlet width, m; ψ1 is the flow channel area utilization rate; Z0 is the number of flow channels; According to the ratio of the flow channel inlet and outlet areas Determine the flow channel outlet area as A2; The flow channel outlet cross section is an elliptical cross section, the major semi-axis of the elliptical cross section is a1, and the minor semi-axis of the elliptical cross section is a2. A2=a1a2π The minor semi-axis a2 of the elliptical cross section at the flow channel outlet should be approximately equal to the distance c2 between the front and rear cover plates of the impeller. The distance c2 between the front and rear cover plates of the impeller is determined by the following formula: Where: k b is the correction coefficient, and its value range is k b =1.09~1.152, when n s When k is larger, b Take a small value; when n s When k is small, b Take the larger value; Q n is the normal working flow, m 3 / s; n is the pump speed, r / min.

7. The method for designing a flow channel of a low specific speed centrifugal pump according to claim 3, characterized in that: A horizontal straight line is introduced at the inlet of the flow channel, and the length of the straight line d1 is determined by the following formula: d1=(0.7~0.9)D j Where: D j is the impeller inlet diameter, m.

8. A low specific speed centrifugal pump, characterized in that: The flow channel is designed using the low specific speed centrifugal pump flow channel design method described in any one of claims 1 to 7.

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