Method for calculating matching characteristics of centrifugal pump inducer and impeller

Abstract

The application discloses a kind of calculation methods of centrifugal pump inducer wheel and impeller matching characteristics;Based on the requirement that inducer wheel and impeller are connected with each other in structure when working, hydraulic performance and flow are coordinated with each other, and considering the maximum criterion of inducer wheel and impeller overlap flow area, the best axial distance of inducer wheel and impeller is obtained by inducer wheel rim exit angle and hub exit angle, combined with inducer wheel outer diameter and impeller inlet edge middle streamline radius.The method can quickly determine the axial size of inducer wheel and impeller installation, with the advantages of good adaptability, convenient calculation;The axial distance of inducer wheel and impeller determined by the method can make the flow of inducer wheel and impeller more matched, the flow area is larger, and the hydraulic loss when working can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of fluid machinery design, and specifically relates to a method for calculating the matching characteristics of the inducer and impeller of a centrifugal pump. Background Technology

[0002] Centrifugal pumps are currently the most common and widely used fluid machinery. They transfer mechanical energy to liquids, increasing the liquid's energy, and are mainly used to transport single-phase liquids, solid-liquid, and gas-liquid two-phase flows. When the centrifugal pump impeller is working, a certain range of low-pressure areas forms inside the pump body. This low pressure causes cavitation; bubbles collapse after reaching the high-pressure area as the impeller rotates, resulting in cavitation on the impeller and the inner wall of the pump body, causing irreversible damage. The most effective way to solve the cavitation cavitation problem is to add an inducer. The inducer's structure is equivalent to a low-head axial-flow impeller. Adding an inducer can reduce the required net positive suction head (NPSHr) of the centrifugal pump, thus meeting the required NPSHa of the pump system.

[0003] The inducer is positioned before the impeller inlet of the centrifugal pump. The main liquid flow from the inducer directly enters the impeller. Since the impeller inlet diameter is fixed, the size of the inducer is often limited by the pump body structure. This creates a matching problem between the inducer and the main impeller, which is directly reflected in the selection of the distance between them. Studies have found that an excessively small axial distance between the impeller and the inducer leads to unstable flow within the centrifugal impeller and degrades pump performance. Therefore, the inducer and impeller must be structurally connected, and their hydraulic performance and flow characteristics must be coordinated. Otherwise, the centrifugal pump will not only fail to fully utilize the inducer's high cavitation resistance but will also affect the pump's operational stability.

[0004] Currently, the matching of the distance between most inducer and impeller is mostly based on empirical design, and there is no better method as a design reference. Summary of the Invention

[0005] The purpose of this invention is to provide a method for calculating the distance between the inducer and the impeller based on the inducer rim outlet angle and the hub outlet angle. To achieve the above objective, this invention mainly discloses a method for calculating the matching characteristics of the inducer and impeller in a centrifugal pump. The method for calculating the optimal axial distance S between the inducer and the impeller is as follows:

[0006] S = S1 + S2;

[0007] Where: S1 is the axial distance from the point where the induced impeller outlet collides with the pipe wall to the induced impeller outlet, and S2 is the axial distance from the point where the induced impeller outlet collides with the pipe wall to the impeller inlet. The calculation methods for S1 and S2 are as follows:

[0008] S1=(D y / 4-d h / 4) / tan(90-βm ),

[0009]

[0010] In the formula D y Let d be the diameter of the inducer wheel. h R is the hub diameter. c β is the radius of the streamline at the middle of the impeller inlet edge. m The direction of the relative velocity of the liquid flow in the middle of the inducer outlet.

[0011] Furthermore, the relative velocity direction β of the liquid flow at the center of the inducer outlet m The calculation method is as follows:

[0012] β m =(β) y2 +β h2 ) / 2.

[0013] Where: β y2 β is the rim exit angle. h2 This refers to the wheel hub exit angle.

[0014] Furthermore, the calculation method takes the maximum overlapping flow area between the guide wheel and the impeller as the criterion.

[0015] Furthermore, the relative velocity direction β of the liquid flow at the center of the inducer outlet m To induce the direction of the outflow.

[0016] Furthermore, the liquid flow has a relative velocity direction β at the center of the inducer outlet. m The liquid flowing out from the induction wheel collides with the inner wall of the centrifugal pump's inlet pipe, reflects 90°, and flows into the impeller.

[0017] Furthermore, the diameter D of the inducer wheel y Hub diameter d h And the radius R of the streamline at the impeller inlet edge c The values ​​are all determined based on the actual situation.

[0018] By employing the above technical solutions, the beneficial effects of the present invention are as follows:

[0019] 1. A method for matching the spacing between the inducer and the impeller based on the inducer outlet angle is provided, which can quickly determine the axial dimensions of the inducer and the impeller, and has the advantages of good adaptability and convenient calculation;

[0020] 2. Based on the axial distance determined by this method, the flow of the inducer and the impeller can be better matched, reducing hydraulic losses when they are in sync.

[0021] To make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic axial cross-sectional view of the inducer and impeller in this embodiment.

[0024] In the figure, the sum of S1 and S2 is the optimal axial distance S between the inducer and the impeller, and the direction of the relative velocity of the liquid flow in the middle of the inducer outlet is β. m The arrow points in the direction of the relative velocity of the liquid flow at the center of the inducer outlet. (D) y Let d be the diameter of the inducer wheel. h Let R be the hub diameter, and R be the radius of the streamline at the impeller inlet edge. c . Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that in the description of this invention, the terms "first," "second," etc., are used only for descriptive purposes and to distinguish similar objects; there is no order between them, nor should they be construed as indicating or implying relative importance. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0027] Example: Combining Figure 1 As shown in this embodiment, a method for calculating the matching characteristics of the inducer and impeller of a centrifugal pump is disclosed. This method is based on the requirements of structural interconnection, hydraulic performance, and flow coordination between the inducer and impeller. Taking the maximum overlapping flow area of ​​the inducer and impeller as the criterion, the optimal axial distance between the inducer and impeller is calculated using the inducer rim outlet angle, inducer hub outlet angle, inducer outer diameter, and the streamline radius at the impeller inlet edge. The calculation method includes the following steps:

[0028] Through the rim exit angle β of the inducer y2 and hub exit angle β h2 Calculate the direction of relative velocity β of the fluid flow at the middle of the inducer outlet. m ;

[0029] According to β m Calculate the axial distance S1 from the point of collision between the induced impeller outlet and the pipe wall to the induced impeller outlet, and the axial distance S2 from the point of collision between the induced impeller outlet and the pipe wall to the impeller inlet, where:

[0030] S1=(D y / 4-d h / 4) / tan(90-β m ),

[0031]

[0032] In the formula D y Let d be the diameter of the inducer wheel. h R is the hub diameter. c The radius of the streamline at the middle of the impeller inlet edge;

[0033] Determine the optimal axial distance S between the inducer and the impeller, where S = S1 + S2.

[0034] If the flow matching and coordination between the inducer and the impeller are required, the liquid flow must not be misaligned or have a large gap during the process from the inducer to the impeller inlet. Otherwise, the collision between the liquid flow and the impeller inlet edge will cause a large hydraulic loss and affect the performance of both.

[0035] In this embodiment, the maximum overlapping flow area of ​​the liquid flow from the inducer outlet to the impeller inlet is taken as the benchmark. The inducer and impeller rotate coaxially, and the influence is achieved through the inducer hub outlet angle β. h2 rim exit angle β y2 Calculate the direction of relative velocity β of the fluid flow at the middle of the inducer outlet. m This direction is the direction of induced outflow. The fluid flow follows a β-axis. m After being reflected 90° by the inner wall of the inlet pipe of the centrifugal pump, the fluid flows into the impeller. The axial distance from the outlet edge of the guide wheel to the starting point of the streamline at the middle of the impeller inlet edge is the optimal axial distance S between the inducer and the impeller. At this point, the overlapping flow area of ​​the fluid flow from the outlet of the inducer to the inlet of the impeller is the largest, and the fluid flow is smooth with minimal hydraulic loss in this section.

[0036] The optimal axial spacing S can be calculated using trigonometric functions. The optimal axial spacing S is divided into two segments, S1 and S2. S1 and S2 can be determined by the outer diameter of the inducer wheel and the relative velocity direction β. m Radius R of the starting point of the streamline at the middle of the inlet side cCalculate. Where: S1 is the axial distance from the point where the induced impeller outflow collides with the pipe wall to the induced impeller outlet, and S2 is the axial distance from the point where the induced impeller outflow collides with the pipe wall to the impeller inlet.

[0037] In this example, β y2 =13°, β h2 =30°.

[0038] The direction of relative velocity β of the liquid flow at the middle of the inducer outlet m The calculation method is as follows:

[0039] β m =(β) y2 +β h2 ) / 2,

[0040] The direction of the relative velocity of the liquid flow in the middle of the inducer outlet can be obtained as: β m =(β) y2 +β h2 ) / 2=21.5°.

[0041] The axial distance S1 from the point where the induced flow collides with the pipe wall to the induced flow outlet is calculated as follows:

[0042] S1=(D y / 4-d h / 4) / tan(90-β m ),

[0043] In this example, D y =204mm, d h =75mm; therefore:

[0044] S1 = 11.8 mm.

[0045] The axial distance S2 from the point where the induced flow collides with the pipe wall to the impeller inlet is calculated as follows:

[0046]

[0047] In this example, R c =82mm, therefore:

[0048] S2 = 45.7 mm.

[0049] Determine the axial distance S between the inducer and the impeller:

[0050] S = S1 + S2,

[0051] The result is S = 57.5 mm.

[0052] It should be noted that the axial distance S can be adjusted appropriately according to structural requirements.

[0053] The embodiments described in this specification are merely examples of specific implementations of the inventive concept. The scope of protection of this invention should not be considered as limited to the specific forms described in the embodiments, but also includes equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. A method for calculating the optimal axial distance between the inducer and impeller of a centrifugal pump, characterized in that: The optimal axial distance S between the inducer and the impeller is calculated as follows: ＝ + ； in: The axial distance from the point where the induced flow collides with the pipe wall to the outlet of the induced flow wheel is given. S1 and S2 are the axial distances from the point where the induced flow collides with the pipe wall to the impeller inlet; the calculation methods are as follows: ； ； In the formula The diameter of the inducer wheel, The diameter of the wheel hub. The radius of the streamline at the middle of the impeller inlet edge. The direction of the relative velocity of the liquid flow at the middle of the inducer outlet; the direction of the relative velocity of the liquid flow at the middle of the inducer outlet. The calculation method is as follows: ； Where: β y2 For the rim exit angle, This refers to the wheel hub exit angle.

2. The method for calculating the optimal axial distance between the centrifugal pump inducer and impeller according to claim 1, characterized in that: The calculation method is based on maximizing the overlapping flow area between the inducer and the impeller.

3. The method for calculating the optimal axial distance between the centrifugal pump inducer and impeller according to claim 1, characterized in that: The relative velocity direction of the liquid flow at the middle of the inducer outlet To induce the outflow direction.

4. The method for calculating the optimal axial distance between the centrifugal pump inducer and impeller according to claim 3, characterized in that: The fluid flow is directed in the direction of relative velocity β at the center of the inducer outlet. m The liquid flowing out from the induction wheel collides with the inner wall of the centrifugal pump's inlet pipe, reflects 90°, and flows into the impeller.

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