CN114329828B - Multistage centrifugal pump axial force calculation method considering mouth ring leakage - Google Patents
Multistage centrifugal pump axial force calculation method considering mouth ring leakage Download PDFInfo
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Abstract
The invention relates to a multistage centrifugal pump axial force calculation method considering mouth ring leakage, which solves the technical problem that the axial force cannot be accurately calculated by the existing multistage centrifugal pump axial force calculation method and is based on the stage number N, flow Q, single-stage lift H, rotating speed N and impeller inlet diameter D of a segmental multistage centrifugal pump 1 Diameter D of the oral ring m Hub diameter D h Equal parameters, and taking the leakage factor of the mouth ring into consideration, calculating the axial force F born by the pump A . The invention is widely applied to the field of axial force calculation of multistage centrifugal pumps.
Description
Technical Field
The invention relates to the field of axial force calculation of multistage centrifugal pumps, in particular to a multistage centrifugal pump axial force calculation method considering mouth ring leakage.
Background
Multistage centrifugal pumps generally adopt a segmented structure, and because the front cover plate and the rear cover plate of the impeller are stressed asymmetrically, the change of fluid momentum generates reaction forces on the impeller, and the axial components of the forces are called axial forces. Axial force F A Generally comprises three parts: (1) Cover force F acting on the impeller cover A1 The direction of the air inlet is directed to the impeller inlet; (2) Kinetic reaction force F caused by fluid movement A2 The direction points to the impeller back cover plate; (3) Imbalance force F acting on pump shaft due to imbalance of suction pressure and external pressure A3 The direction is related to the suction pressure, which is greater than atmospheric pressure and directed toward the back cover plate of the impeller and less than atmospheric pressure and toward the front cover plate.
The high-pressure multistage seawater desalination pump is a type of multistage centrifugal pump, and is generally of a cantilever type structure, and axial force can cause deformation increase of a pump shaft in the operation process, so that the operation stability of a pump device is affected. Calculating the axial force is the basis for designing the pump shaft and selecting the type of the bearing. Because the multistage pump has a complex structure and large axial force, the axial force is difficult to accurately measure by the existing method.
Currently, the conventional method for calculating the axial force ignores the change of the pressure distribution of the front pump cavity caused by the flow of the sealing clearance of the mouth ring, and considers that the pressure distribution functions of the front pump cavity and the rear pump cavity are consistent, which is not accurate in practical application. Meanwhile, only the change in momentum is considered when calculating the dynamic reaction force, but the calculated dynamic reaction force is lower than the actual value because the dynamic reaction force caused by the unsteady flow in the impeller is not included, so that the conventional axial force calculation method cannot accurately calculate the axial force.
Disclosure of Invention
The invention provides a multistage centrifugal pump axial force calculation method which is more accurate in calculation and takes mouth ring leakage into consideration, and aims to solve the technical problem that the axial force calculation method of the conventional multistage centrifugal pump cannot accurately calculate the axial force.
The invention provides a multistage centrifugal pump axial force calculation method considering mouth ring leakage, which comprises the following steps:
first step, calculate the cover force F A1 ：
The axial force applied by the single-stage impeller is F A1,i Is an axial force F acting on the front cover plate A1f,i And an axial force F acting on the back plate A1r,i The difference between the front pump cavity pressure distribution p f The rear pump chamber pressure profile p is considered as a linear function r Considered as a constant, calculated by the following formula:
F A1,i ＝F A1r,i -F A1f,i (1)
in the formulas (2) and (3), R is the distance from any point on the impeller cover plate in the radial direction to the axis, and the unit is m; r is R 2 ＝D 2 /2，R m ＝D m /2，R h ＝D h /2，D 2 Represents the impeller diameter, D m Diameter of the oral ring, D h Is the diameter of the hub; in formula (4), ρ represents the density of the fluid medium; k is a correction coefficient;
specific rotation speed n s Calculated by the following formula (5):
in the formula (5), Q represents the flow rate, and the unit of Q is m 3 S; n represents the rotating speed, and H represents the single-stage lift;
total cover force F A1 Calculated according to the following formula (6):
in the formula (6), F A1,1 Represents the axial force applied by the first-stage impeller, and m is more than or equal to 1 1 ≤1.2，0.96≤m 2 ≤1；
Second, the dynamic reaction force F is calculated by the following formula (7) A2 ：
In the formula (7), Q represents the flow rate, and the unit of Q is m 3 S; n represents the number of stages of the segmental multistage centrifugal pump; d (D) 1 Representing leavesWheel inlet diameter; ρ represents the density of the fluid medium; c is a correction coefficient;
third, the unbalanced force F acting on the pump shaft is calculated by the following formula (8) A3 ：
In the formula (8), D h Represents the hub diameter; p is p 1 The suction pressure is designed to be a given value; p is p a Is at atmospheric pressure;
fourth, the total axial force F is calculated by the following formula (9) A ：
F A ＝F A1 -F A2 +F A3 (9)
Preferably, k is more than or equal to 0.8 and less than or equal to 0.9, and the specific rotation speed n s When the rotation speed is less than 150, k takes a small value of 0.8, and the specific rotation speed n s And k takes a large value of 0.9 when the k is larger than 150.
Preferably, c is 2.8, which is a large value of 2.8 when the actual flow is not equal to the design flow.
The axial force calculation method has the advantages of being capable of accurately calculating the axial force, simple and convenient in calculation process, high in practicality and convenient to apply.
Further features and aspects of the present invention will become apparent from the following description of specific embodiments with reference to the accompanying drawings.
Drawings
FIG. 1 is a schematic structural view of a segmented multistage centrifugal pump;
FIG. 2 is a schematic illustration of impeller stress for a segmented multistage centrifugal pump;
FIG. 3 is a schematic illustration of the radial dimension of an impeller of a segmented multistage centrifugal pump;
fig. 4 is a schematic illustration of impeller sizing and pressure direction.
Detailed Description
In the prior art, a common method for calculating the axial force ignores the change of the pressure distribution of the front pump cavity caused by the flow of the sealing clearance of the mouth ring, and considers that the pressure distribution functions of the front pump cavity and the rear pump cavity are consistent, which is not accurate in practical application. Meanwhile, when calculating the dynamic reaction force, only the change in momentum is considered, but the dynamic reaction force due to the unsteady flow inside the impeller is not included, and the calculated dynamic reaction force is lower than the actual value.
According to the stage number N, flow Q, single stage lift H, rotating speed N and impeller inlet diameter D of a segmental multistage centrifugal pump 1 Diameter D of the oral ring m Hub diameter D h Equal parameters, calculating the axial force F applied by the pump A . The method comprises the following specific steps:
first step, calculate the cover force F A1 。
The axial force applied by the single-stage impeller is F A1,i Is an axial force F acting on the front cover plate A1f,i And an axial force F acting on the back plate A1r,i And (3) a difference. The pump orifice ring seal leakage loss is considered, so that the pressure distribution p of the front pump cavity can be realized f As a linear function; the rear pump cavity pressure distribution p is realized due to the fact that the rear pump cavity is extremely small in leakage r And is considered as a constant. Thus, the following calculation formula is derived:
F A1,i ＝F A1r,i -F A1f,i (1)
in the formulas (2) and (3), R is the distance from any point on the impeller cover plate in the radial direction to the axis, and the unit is m; r is R 2 ＝D 2 /2，R m ＝D m /2，R h ＝D h /2，D 2 Represents the impeller diameter, D m Diameter of the oral ring, D h Is the hub diameter. In the formula (4), ρ represents the density of the fluid mediumA degree; considering the leakage of the sealing of the mouth ring, the force acting on the front cover plate is corrected by adopting the coefficient k, wherein k is more than or equal to 0.8 and less than or equal to 0.9, and the specific rotation speed n s When the rotation speed is less than 150, k takes a small value of 0.8, and the specific rotation speed n s And k takes a large value of 0.9 when the k is larger than 150.
Specific rotation speed n s Calculated by the following formula (5):
in the formula (5), Q represents the flow rate, and the unit of Q is m 3 S; n represents the rotation speed, and H represents the single-stage lift.
Considering that the pre-rotation exists at the inlet of the secondary impeller, the single-stage performance is reduced, and the total cover plate force F A1 Calculated according to the following formula:
in the formula (6), F A1,1 Represents the axial force applied by the first-stage impeller, and m is more than or equal to 1 1 ≤1.2，0.96≤m 2 ≤1。
Second, the dynamic reaction force F is calculated by the following formula (7) A2 。
In the formula (7), Q represents the flow rate, and the unit of Q is m 3 S; n represents the number of stages of the segmental multistage centrifugal pump; d (D) 1 Representing the impeller inlet diameter; ρ represents the density of the fluid medium; 2.3<c<2.8, considering the unsteady flow in the impeller, adopting a coefficient c for correction, and taking a large value of 2.8 when the actual flow is not equal to the design flow, namely, when the actual flow deviates from the design working condition.
Third, the unbalanced force F acting on the pump shaft is calculated by the following formula (8) A3 。
In the formula (8), D h Represents the hub diameter; p is p 1 The suction pressure is designed to be a given value; p is p a Is at atmospheric pressure.
Fourth, the total axial force F is calculated by the following formula (9) A 。
F A ＝F A1 -F A2 +F A3 (9)
The pump stage number n=6 is taken as an example, and a single stage lift h=50m and a flow q=100deg.m are designed 3 /h, rotational speed n=2950r/min, D 1 ＝132mm，D 2 ＝220mm，D m ＝145mm，D h =80 mm, the suction pressure is atmospheric pressure. The medium is clear water, the density rho=1000 kg/m3, and the gravity acceleration g is 9.81m/s 2 。
(1) Calculating the cover plate force F A1 ：
Specific rotation speed n s Taking k=0.8,
taking m 1 ＝1.05，m 2 ＝0.96，
F A1 ＝1.05×7743+0.96×5×7743＝45297N
(2) Calculating dynamic reaction force F A2 ：
Taking the value of c=2.5,
(3) Calculating unbalance force F acting on pump shaft A3 ：
(4) Calculating the total axial force F A ：
F A ＝F A1 -F A2 +F A3 ＝45297-30447＝14850N
The above example is more accurate by comparison with test and numerical simulation results.
The above description is only for the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art.
Claims (3)
1. The multistage centrifugal pump axial force calculation method considering the leakage of the orifice ring is characterized by comprising the following steps of:
first step, calculate the cover force F A1 ：
The axial force applied by the single-stage impeller is F A1,i Is an axial force F acting on the front cover plate A1f,i And an axial force F acting on the back plate A1r,i The difference between the front pump cavity pressure distribution p f The rear pump chamber pressure profile p is considered as a linear function r Considered as a constant, calculated by the following formula:
F A1,i ＝F A1r,i -F A1f,i (1)
in the formulas (2) and (3), R is the distance from any point on the impeller cover plate in the radial direction to the axis, and the unit is m; r is R 2 ＝D 2 /2，R m ＝D m /2，R h ＝D h /2，D 2 Represents the impeller diameter, D m Diameter of the oral ring, D h Is the diameter of the hub; in formula (4), ρ represents the density of the fluid medium; k (k)Is a correction coefficient; g represents gravitational acceleration;
specific rotation speed n s Calculated by the following formula (5):
in the formula (5), Q represents the flow rate, and the unit of Q is m 3 S; n represents the rotating speed, and H represents the single-stage lift;
total cover force F A1 Calculated according to the following formula (6):
in the formula (6), F A1,1 Represents the axial force applied by the first-stage impeller, and m is more than or equal to 1 1 ≤1.2，0.96≤m 2 ≤1；
Second, the dynamic reaction force F is calculated by the following formula (7) A2 ：
In the formula (7), Q represents the flow rate, and the unit of Q is m 3 S; n represents the number of stages of the segmental multistage centrifugal pump; d (D) 1 Representing the impeller inlet diameter; ρ represents the density of the fluid medium; c is a correction coefficient;
third, the unbalanced force F acting on the pump shaft is calculated by the following formula (8) A3 ：
In the formula (8), D h Represents the hub diameter; p is p 1 The suction pressure is designed to be a given value; p is p a Is at atmospheric pressure;
fourth, the total axial force F is calculated by the following formula (9) A ：
F A ＝F A1 -F A2 +F A3 (9)。
2. The method for calculating axial force of multistage centrifugal pump taking into account leakage of orifice ring according to claim 1, wherein k is 0.8.ltoreq.k.ltoreq.0.9, specific rotation speed n s When the rotation speed is less than 150, k takes a small value of 0.8, and the specific rotation speed n s And k takes a large value of 0.9 when the k is larger than 150.
3. The method for calculating the axial force of the multistage centrifugal pump considering the leakage of the orifice ring according to claim 2, wherein c is 2.8 which is a large value when the actual flow is not equal to the design flow, and c is 2.3< c < 2.8.
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Citations (4)
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| CN102322443A (en) * | 2011-09-08 | 2012-01-18 | 浙江工业大学 | Single-stage centrifugal pump with balanced axial force |
| CN104196752A (en) * | 2013-12-31 | 2014-12-10 | 江苏大学 | Multi-working-condition hydraulic design method of centrifugal pump with eccentrically placed impeller |
| CN107461361A (en) * | 2017-09-20 | 2017-12-12 | 江苏大学 | A kind of design method of multistage pump first-stage double suction impeller |
| CN108223459A (en) * | 2017-06-23 | 2018-06-29 | 闫龙 | The stuck method for maintaining of multistage Rule pumping hole ring is solved using the not mode of disintegrating |
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Patent Citations (4)
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|---|---|---|---|---|
| CN102322443A (en) * | 2011-09-08 | 2012-01-18 | 浙江工业大学 | Single-stage centrifugal pump with balanced axial force |
| CN104196752A (en) * | 2013-12-31 | 2014-12-10 | 江苏大学 | Multi-working-condition hydraulic design method of centrifugal pump with eccentrically placed impeller |
| CN108223459A (en) * | 2017-06-23 | 2018-06-29 | 闫龙 | The stuck method for maintaining of multistage Rule pumping hole ring is solved using the not mode of disintegrating |
| CN107461361A (en) * | 2017-09-20 | 2017-12-12 | 江苏大学 | A kind of design method of multistage pump first-stage double suction impeller |
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