A low specific speed canned motor pump and an axial clearance collaborative optimization design method thereof

Abstract

The application relates to a low specific speed shield pump and an axial gap collaborative optimization design method thereof, and relates to the technical field of water pumps. The shield pump comprises a pump body, an impeller and a rear pump cavity, the axial gap range of the rear pump cavity is 1.2mm-2.2mm, the specific speed ns of the shield pump is less than or equal to 40, and the shield pump is free of a rear port ring sealing structure. The application has the advantages that the optimal axial gap range is solved by constructing a double-target optimization function containing disc friction loss minimization and cooling flow guarantee and combining with CFD numerical simulation, and the motor cooling effect is guaranteed on the premise of reducing the disc friction loss.

Description

Technical Field

[0001] This application relates to the technical field of water pumps, and in particular to a low specific speed canned pump and its axial clearance co-optimization design method. Background Technology

[0002] Low specific speed (ns≤40) canned motor pumps are widely used in chemical, pharmaceutical, nuclear power, and household appliance (such as gas water heater) fields, with their core advantage being absolute leak-free operation. However, the impellers of low specific speed pumps are characterized by large outer diameter and narrow outlet width, resulting in a significantly higher proportion of disc friction loss to total power. Literature research shows that when the specific speed ns=30, disc friction loss can reach 30% of the effective power.

[0003] The disc friction loss mainly occurs in the rear pump chamber between the impeller rear cover and the pump cover. Reducing the axial clearance of the rear pump chamber can effectively reduce the disc friction loss, but it will also reduce the motor cooling circulation flow, which may lead to motor overheating. Conversely, increasing the clearance is beneficial for cooling, but it can easily generate a huge vortex ring in the rear pump chamber, which will drastically increase the disc friction loss.

[0004] In existing technologies, the design of low specific speed canned motor pumps often considers disc friction loss and cooling requirements separately, lacking a method to optimize both synergistically. Therefore, minimizing disc friction loss while ensuring motor cooling is a pressing technical problem to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, one of the objectives of this application is to provide a low specific speed canned pump and its axial clearance co-optimization design method, which has the advantage of ensuring cooling effect while reducing disc friction loss.

[0006] The above-mentioned objective of this application is achieved through the following technical solution: A low specific speed canned motor pump includes a pump body, an impeller, and a rear pump chamber, wherein the axial clearance of the rear pump chamber is in the range of 1.2mm-2.2mm; wherein the specific speed of the canned motor pump is ns≤40, and there is no rear inlet ring seal structure.

[0007] This application also discloses a collaborative optimization design method for the axial clearance of a low specific speed canned motor pump: This method, used to design the aforementioned low specific speed canned motor pump, includes the following steps: Evaluation step: Establishing evaluation equations, Where S is the axial clearance of the rear pump chamber (mm), w1 is the weighting coefficient for disc friction loss, w2 is the weighting coefficient for cooling flow rate, 0≤w1, w2≤1, w1+w2=1, P df (S) represents the power loss due to disk friction under gap S, in W / P. df0 is the disk friction loss power at the reference clearance S0, unit: W, Q cool (S) is the cooling flow rate of the rear pump chamber at clearance S, unit m 3 / s, Q cool 0 is the cooling flow rate of the rear pump chamber at the reference clearance S0, unit m 3 / s, ; Steps of establishing the relationship equation between disk friction loss and clearance: , , where, C M is the friction torque coefficient, D2 is the outer diameter of the impeller, unit: m, Re is the rotational Reynolds number, P df is the disk friction loss power, unit: W, ρ is the fluid density, unit Kg / m 3 , ω is the angular velocity of impeller rotation, unit: rad / s; Steps of establishing the relationship between cooling flow rate and clearance: , where, Q cool is the cooling flow rate of the rear pump chamber, unit m 3 / s, k is the flow coefficient, S m is the axial clearance of the rear pump chamber, unit: m, which satisfies S m =S / 1000; S is the axial clearance of the rear pump chamber, unit: mm; V avg is the average flow velocity in the rear pump chamber, unit: m / s; Solving step, the optimal clearance S that maximizes F(S) is solved through the formulas in the above steps.

[0008] The present application may be further configured in a preferred example as: , where, v is the kinematic viscosity of the fluid, unit: m 2 / s.

[0009] The present application may be further configured in a preferred example as: , where, α is the velocity coefficient, for a canned pump without balance holes, the value range of α is 0.3-0.5; ω is the angular velocity of impeller rotation, unit: rad / s.

[0010] Further, the weight coefficients w1 and w2 are determined according to the motor heating characteristics and application scenarios: when the motor cooling demand is urgent (for example, the ambient temperature is higher than a set value (the set value can be set as required) and / or the heat dissipation condition is poor, that is, the heat dissipated per unit time is less than a preset value (the preset value is set as required)), take w1<w2; when the motor cooling is sufficient, take w1>w2. The typical value range is w1=0.3-0.7, w2=0.7-0.3.

[0011] The present application has the following advantages: For the first time, a dual-objective collaborative optimization framework is proposed: In response to the long-standing contradiction between "disc friction loss" and "motor cooling" in the design of the axial clearance of the pump chamber after low specific speed shielded pumps, a dual-objective optimization function that simultaneously includes both is constructed for the first time, realizing the collaborative optimization of the two.

[0012] Provides a quantifiable optimal clearance range: Through numerical simulation, the specific optimal clearance range (1.2mm-2.2mm) for a specific speed of 35.29 and a shielded pump without a rear inlet ring is given, providing a quantitative basis for the design of similar pumps.

[0013] Balancing efficiency and reliability: While ensuring motor cooling, the disc friction loss is effectively reduced, improving the overall efficiency of the pump, while avoiding the risk of motor overheating and improving system reliability. Attached Figure Description

[0014] Figure 1 This is a cross-sectional structural diagram of this application.

[0015] Figure 2 This is a schematic diagram of the water pump's performance after the rear cover plate is installed.

[0016] Figure 3 This is a schematic diagram of the water pump's performance without the rear cover installed. Detailed Implementation

[0017] The present application will be further described in detail below with reference to the accompanying drawings.

[0018] exist Figure 2 and Figure 3 middle, Figure 2 The red and blue dots are both higher than the black cross marker, which meets the design requirements. Figure 3 The red and blue intersection point is below the black crosshair cursor, which does not meet the design requirements.

[0019] Reference Figure 1 The present application discloses a water pump that reduces the axial clearance of the rear pump chamber, including a rear pump chamber, and a rear cover plate is installed in the rear pump chamber so that the axial clearance of the rear pump chamber is in the range of 1.2mm (inclusive) to 2.2mm (inclusive).

[0020] This application also discloses a design method for a water pump that reduces the axial clearance of the rear pump chamber: the method for designing the aforementioned water pump with reduced axial clearance of the rear pump chamber includes the following steps: Evaluation steps: Establish evaluation equations, (1) Where S is the axial clearance of the rear pump chamber (mm), w1 is the weighting coefficient for disc friction loss, w2 is the weighting coefficient for cooling flow rate, 0≤w1, w2≤1, w1+w2=1; P df(S) represents the power loss due to disk friction under gap S, in W; P df 0 represents the disk friction loss power under the reference gap S0, in W; Q cool (S) represents the cooling flow rate of the rear pump chamber under gap S, in m³ / s. 3 / s;Q cool 0 represents the cooling flow rate of the rear pump chamber under the reference gap S0, in m³ / s. 3 / s.

[0021] Steps to establish the relationship between disk friction loss and clearance: (2) (3) Among them, C M P is the friction torque coefficient, dimensionless; df D2 is the power loss due to friction of the impeller (W); D2 is the impeller outer diameter (m); Re is the rotating Reynolds number (dimensionless); ρ is the fluid density (kg / m³). 3 ω is the angular velocity of the impeller, in rad / s; Steps to establish the relationship between cooling flow rate and clearance: (4) Among them, Q cool This refers to the cooling flow rate of the rear pump chamber, in meters. 3 / s, k is the flow coefficient, S m The axial clearance of the rear pump chamber, in meters (m), satisfies S. m =S / 1000; S is the axial clearance of the rear pump chamber, unit: mm; V avg The average flow velocity within the rear pump chamber, in m / s; The solution steps involve using the formulas described above to select at least three different gap values ​​for numerical simulation, thereby obtaining P for each gap. df (S) and Q cool (S); Substitute the calculation results into equation (1) to solve for the optimal gap S that maximizes F(S).

[0022] Rotating Reynolds Number Where v is the kinematic viscosity of the fluid, in m³. 2 / s Average flow velocity in the rear pump chamber Where α is the velocity coefficient, which is dimensionless; ω is the angular velocity of the impeller, in rad / s. The weight coefficients w1 and w2 are determined according to the motor heating characteristics and application scenarios: when the motor cooling demand is tight (for example, the ambient temperature is higher than a set value (the set value can be set as needed) and / or the heat dissipation condition is poor, that is, the heat dissipated per unit time is less than a preset value (the preset value is set as needed)), w1<w2 is adopted; when the motor cooling is sufficient, w1>w2 is adopted. A typical value range is w1=0.3-0.7, w2=0.7-0.3.

[0023] For the structure of a canned pump with an impeller outer diameter of 58mm, a rotational speed of 7780rpm, a specific speed of 35.29, and no rear sealing ring, the optimized optimal axial clearance range is 1.2mm-2.2mm.

[0024] The implementation principle of this embodiment is: by setting the axial clearance range of the rear pump chamber to 1.2mm-2.2mm, the purposes of reducing disc friction loss and ensuring the cooling effect can be both achieved.

[0025] All the embodiments in this specific implementation are preferred embodiments of the present application, and are not intended to limit the protection scope of the present application. Therefore, all equivalent changes made according to the structure, shape and principle of the present application shall be covered within the protection scope of the present application.

Claims

1. A design method for co-optimizing the axial clearance of a low specific speed canned motor pump, characterized in that: To design a low specific speed canned motor pump, the low specific speed canned motor pump includes a rear pump chamber, the axial clearance of which is in the range of 1.2mm-2.2mm; the specific speed of the canned motor pump is ≤ 40 ns, and it has no rear end ring seal structure, the following steps are included: Evaluation steps: Establish evaluation equations, （1） Where S is the axial clearance of the rear pump chamber (mm), w1 is the weighting coefficient for disc friction loss, w2 is the weighting coefficient for cooling flow rate, 0≤w1, w2≤1, w1+w2=1; P df (S) represents the power loss due to disk friction under gap S, in W; P df 0 represents the disk friction loss power under the reference gap S0, in W; Q cool (S) represents the cooling flow rate of the rear pump chamber under gap S, in m³ / s. 3 / s;Q cool 0 represents the cooling flow rate of the rear pump chamber under the reference gap S0, in m³ / s. 3 / s; Steps to establish the relationship between disk friction loss and clearance: （2） C M =f( ,Re)(3) Among them, S m The axial clearance of the rear pump chamber, in meters (m), satisfies S. m =S / 1000; S is the axial clearance of the rear pump chamber, unit: mm; C M P is the friction torque coefficient, dimensionless; df D2 is the power loss due to friction of the impeller (W); D2 is the outer diameter of the impeller (m); Re is the rotating Reynolds number (dimensionless); ρ is the fluid density (kg / m³). 3 ω is the angular velocity of the impeller, in rad / s; Steps to establish the relationship between cooling flow rate and clearance: ； Among them, Q cool This refers to the cooling flow rate of the rear pump chamber, in meters. 3 / s, k is the flow coefficient, S m The axial clearance of the rear pump chamber, in meters (m), satisfies S. m =S / 1000; S is the axial clearance of the rear pump chamber, unit: mm; V avg The average flow velocity within the rear pump chamber, in m / s; The solution steps involve using the formulas described above to select at least three different gap values ​​for numerical simulation, thereby obtaining P for each gap. df (S) and Q cool (S); Substitute the calculation results into equation (1) to solve for the optimal gap S that maximizes F(S).

2. The design method for axial clearance co-optimization of a low specific speed canned pump according to claim 1, characterized in that: Rotating Reynolds Number Where v is the kinematic viscosity of the fluid, in m³. 2 / s.

3. The design method for axial clearance co-optimization of a low specific speed canned motor pump according to claim 1, characterized in that: Average flow velocity V in the rear pump chamber avg =α*ωD2 / 2, where α is the velocity coefficient, dimensionless; ω is the angular velocity of the impeller, in rad / s.

4. The design method for axial clearance co-optimization of a low specific speed canned motor pump according to claim 1, characterized in that: The weighting coefficients w1 and w2 are determined based on the motor's heating characteristics and application scenario: when the motor's cooling demand is tight, w1 < w2 is taken; when the motor's cooling is sufficient, w1 > w2 is taken.

5. The design method for axial clearance co-optimization of a low specific speed canned motor pump according to claim 1, characterized in that: For a canned pump structure with an impeller outer diameter of 58mm, a rotational speed of 7780rpm, a specific speed of 35.29, and no rear inlet ring, the axial clearance range is 1.2mm-2.2mm.

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