Selection method of variable speed centrifugal pump

Abstract

The present invention relates to the technical field of centrifugal pump selection methods, specifically to a method for selecting a variable speed centrifugal pump. In this method, an operation data acquisition system of a variable speed centrifugal pump is used to collect the operation data of the required variable speed centrifugal pump, and evaluation data of the variable speed centrifugal pump is calculated through an existing formula. Tool software is used to fit the evaluation data of the variable speed centrifugal pump into a surface relationship diagram of the variable speed centrifugal pump, and a database is created. According to actual working conditions, a slicing method is used to cut the surface relationship diagram of the variable speed centrifugal pump for rough selection, the variable speed centrifugal pump characteristic equation is brought in to predict the head value for selection, and the optimal efficiency working point is calculated to compare the efficiency to determine the final model of the variable speed centrifugal pump selection method. This not only solves the problem that the original centrifugal pump flow-head characteristic curve cannot improve the efficiency evaluation of the variable speed centrifugal pump, but also provides a more accurate, convenient and fast selection method for the variable speed centrifugal pump.

Description

Technical Field

[0001] The invention relates to a method for selecting a centrifugal pump, in particular to a method for selecting a variable speed centrifugal pump. Technical Background

[0002] The traditional method of selecting a centrifugal pump is to select a centrifugal pump based on the flow and head required by the user by referring to a large number of flow-head characteristic curve charts at constant speed.

[0003] In order to adjust the flow rate or head of a centrifugal pump, the traditional selection method is based on the user flow-head, which considers installing a regulating valve on the pipeline at the centrifugal pump outlet and changing the flow-head characteristic curve of the pipeline by changing the valve opening. This method of changing the flow rate or head of the centrifugal pump by changing the pipeline characteristic curve not only increases the energy loss caused by pipeline resistance, but also causes the centrifugal pump to operate at a low efficiency point, which is economically unreasonable.

[0004] Therefore, in the existing technology, the speed of the centrifugal pump is often changed by frequency conversion speed regulation technology to achieve the regulation of the flow or head of the centrifugal pump. In modern industry, there are more and more centrifugal pump piping systems that rely on frequency converters to adjust the speed of the centrifugal pump to achieve the regulation of the flow or head of the centrifugal pump.

[0005] However, with the introduction of variable frequency speed regulation technology, the flow-head characteristic curve at constant speed that the original centrifugal pump brought with it when leaving the factory not only cannot improve the performance evaluation of variable speed centrifugal pumps but is also no longer suitable for the selection of variable speed centrifugal pumps. Summary of the Invention

[0006] In view of this, it is necessary to provide a method for selecting a variable speed centrifugal pump, including the following steps:

[0007] (1) Data acquisition: using the variable speed centrifugal pump operation data acquisition system, collect multiple sets of variable speed centrifugal pump operation data, the operation data including: the operating frequency of the centrifugal pump under test, the power of the centrifugal pump under test, the vacuum degree at the inlet of the centrifugal pump under test, the vacuum degree at the outlet of the centrifugal pump under test, and the flow rate value of the pipeline of the centrifugal pump under test;

[0008] (2) Data processing: using existing formulas to calculate and process the operating data obtained in step (1) to obtain multiple sets of evaluation data of the centrifugal pumps, and organizing the evaluation data into a table, wherein the evaluation data includes: the operating frequency of the centrifugal pump under test, the power of the centrifugal pump under test, the head of the centrifugal pump under test, the efficiency of the centrifugal pump under test, and the flow rate of the centrifugal pump under test;

[0009] (3) Surface fitting: Using tool software, the evaluation data in step (2) is fitted into frequency-power, frequency-efficiency, frequency-head, and frequency-flow curve relationship diagrams, and the corresponding curve equations are generated. To facilitate the selection of variable speed centrifugal pumps, the tool software is used again to fit the evaluation data in step (2) into frequency-flow-efficiency, frequency-flow-effective power, and frequency-efficiency-head surface relationship diagrams, and the corresponding surface equations are generated.

[0010] (4) Database creation: Repeat the above steps (1), (2), and (3) to obtain the frequency-flow-efficiency, frequency-flow-effective power, and frequency-efficiency-head surface relationship diagrams of different types of variable speed centrifugal pumps, and generate corresponding surface equations. The surface relationship diagrams and surface equations of the above different types of variable speed centrifugal pumps are combined into a variable speed centrifugal pump selection database.

[0011] (5) Selection of variable speed centrifugal pump: Based on the variable speed centrifugal pump database created in step (4), the required variable speed centrifugal pump model is finally determined after rough selection, fine selection, and optimal efficiency comparison according to the actual working conditions.

[0012] Preferably, the operation data acquisition system of the variable speed centrifugal pump in the step (1) includes: a frame, a centrifugal pump supporting platform, a pump operating frequency and power setting display module, a pump inlet vacuum acquisition display module, a pump outlet vacuum acquisition display module, a pipeline flow acquisition display module, a No. 1 power supply control module, a No. 2 power supply control module, a water tank, a pump inlet pipeline, and a pump outlet pipeline; the operation data include: the operating frequency of the centrifugal pump under test, the power of the centrifugal pump under test, the vacuum degree at the inlet of the centrifugal pump under test, the vacuum degree at the outlet of the centrifugal pump under test, and the pipeline flow value of the centrifugal pump under test; the centrifugal pump supporting platform is installed above the frame, carrying the centrifugal pump under test, and the pump The operating frequency and power setting display module is installed on the rack, located below the centrifugal pump bearing platform and can be electrically connected to the centrifugal pump under test to adjust the operating frequency and power of the centrifugal pump under test and display the corresponding operating frequency and power; the water tank is placed on a platform of appropriate height and located below the centrifugal pump bearing platform, one end of the pump inlet pipe is connected to the water inlet of the centrifugal pump under test, and the other end is inserted into the water tank, the pump inlet vacuum acquisition display module is installed on the pump inlet pipe and close to the water inlet of the centrifugal pump under test to measure the vacuum at the water inlet of the centrifugal pump under test and display it on the panel of the pump inlet vacuum acquisition display module, one end of the pump outlet pipe is connected to the water inlet of the centrifugal pump under test The centrifugal pump outlet is connected, and the other end is inserted into the water tank. The pump outlet vacuum acquisition and display module is installed on the pump outlet pipeline and close to the water outlet of the centrifugal pump to measure the vacuum at the water outlet of the centrifugal pump to be tested and display it on the panel of the pump outlet vacuum acquisition and display module; the centrifugal pump to be tested, the pump outlet pipeline, the pump inlet pipeline, and the water tank form a closed circulation pipeline. There is a height difference between the pump inlet vacuum acquisition and display module and the pump outlet vacuum acquisition and display module; the pipeline flow acquisition and display module is installed on the pump outlet pipeline close to the pipeline outlet to obtain the flow value in the pump outlet pipeline and display it on the panel of the pipeline flow acquisition and display module; No. 1 supply The electrical control module is installed on the centrifugal pump supporting platform and is located below the centrifugal pump supporting platform. The No. 1 power supply module can be electrically connected to the pump inlet vacuum acquisition and display module and the pump outlet vacuum acquisition and display module to supply power to the pump inlet vacuum acquisition and display module and the pump inlet vacuum acquisition and display module and control the operation of the pump inlet vacuum acquisition and display module and the pump outlet vacuum acquisition and display module; the No. 2 power supply control module is installed on the centrifugal pump supporting platform and is located above the centrifugal pump supporting platform. The No. 2 power supply control module can be electrically connected to the pipeline flow acquisition and display module to supply power to the pipeline flow acquisition and display module and control the operation of the pipeline flow acquisition and display module.

[0013] Preferably, in the operation data acquisition system of the variable speed centrifugal pump in step (1), the frame includes an overall load-bearing frame, a pipeline installation fixing rod, and a pump operating frequency and power setting display module installation backplate, the overall load-bearing frame is a hexahedral frame, the centrifugal pump support platform is installed on the top side of the overall weighing frame, the operating frequency and power setting display module installation backplate is installed on the back of the overall weighing frame, the operating frequency and power setting display module is installed on the operating frequency and power setting display module installation backplate to adjust the operating frequency and power of the centrifugal pump under test and display the corresponding operating frequency and power, and the pipeline installation fixing rod is installed on the back of the overall weighing frame to fix the pump inlet pipeline and the pump outlet pipeline.

[0014] Preferably, in the operation data acquisition system of the variable speed centrifugal pump in step (1), the pump inlet pipeline includes an inlet pipeline and a check valve, one end of the inlet pipeline is fixedly connected to the water inlet of the centrifugal pump to be tested, and the other end is inserted into the water tank, the pump inlet vacuum acquisition and display module is installed on the inlet pipeline and close to the water inlet of the centrifugal pump to be tested, the inlet pipeline is fixedly installed on the pipeline mounting fixing rod as a whole, and the check valve is installed on the inlet pipeline, away from the water inlet of the centrifugal pump to be tested, and placed in the water tank.

[0015] Preferably, in the operation data acquisition system of the variable speed centrifugal pump in step (1), the pump outlet pipeline includes an outlet pipeline and a valve, one end of the outlet pipeline is fixedly connected to the outlet water of the centrifugal pump under test, and the other end is inserted into the water tank, the pump outlet vacuum acquisition and display module is installed on the outlet pipeline and close to the water outlet of the centrifugal pump under test, the outlet pipeline is fixedly installed on the pipeline mounting fixing rod as a whole, and the valve is installed on the outlet pipeline and close to the water outlet of the centrifugal pump under test, and is located after the pump outlet vacuum acquisition and display module.

[0016] Preferably, in the operation data acquisition system of the variable speed centrifugal pump in step (1), the height difference between the pump inlet vacuum acquisition and display module and the pump outlet vacuum acquisition and display module is set to 0.224m.

[0017] Preferably, the data calculation formula in step (2) includes:

[0018] Calculate the speed n (rev / min):

[0019] According to the motor speed and frequency conversion formula

[0020]

[0021] Where: f is the frequency, p is the number of magnetic field poles.

[0022] Calculate lift H e (m):

[0023] According to Bernoulli's equation,

[0024]

[0025] Where:

[0026] Inlet flow rate: Unit: m / s

[0027] Outlet flow rate: Unit: m / s

[0028] The height difference between the pump inlet vacuum acquisition and display module and the pump outlet vacuum acquisition and display module:

[0029] z2-z1=0.224 m

[0030] Test bench flow resistance loss: H f Unit: m

[0031] Inlet pipe inner diameter: d1 = 0.05m

[0032] Inner diameter of outlet pipe: d1 = 0.05m

[0033] Vacuum degree at the inlet of the centrifugal pump being tested: p1 unit P a

[0034] Vacuum degree at the outlet of the centrifugal pump being tested: p1 unit P a

[0035] Measured centrifugal pump pipeline flow value: Q unit m 3 / s

[0036] Fluid density: ρ = 1000 kg / m 3

[0037] Weight unit: g = 9.81

[0038] Computational efficiency:

[0039] The known effective power calculation formula is as follows

[0040] P e =ρgQH e

[0041] In the formula: effective power: P e Unit: kW

[0042] Therefore, the efficiency calculation formula can be obtained

[0043]

[0044] Where: P a The unit is the shaft power of the motor in kW.

[0045] Preferably, the surface fitting in step (3) can be performed using a tool capable of fitting any three parameters, such as SCILAB or TableCurve3D.

[0046] Preferably, the actual working conditions include requirements a and b, and the rough selection method of the variable speed centrifugal pump in step (5) includes: when it is requirement a: cutting the frequency-flow-head surface of the corresponding model centrifugal pump in the database with the constant frequency value required for the centrifugal pump to work under the actual working conditions by a slicing method, obtaining the flow-head curve of the centrifugal pump under constant frequency, and obtaining the corresponding centrifugal pump head range according to the flow range required for the centrifugal pump to work under the actual working conditions, comparing the minimum head value within the centrifugal pump head range with the minimum head value required by the pipeline under the actual working conditions, and excluding centrifugal pumps with a head value less than the minimum head value required by the pipeline, A plurality of centrifugal pumps that meet the minimum head value required by the actual pipeline are obtained; when it is requirement b: a frequency-flow-head surface of a centrifugal pump of a corresponding model in a database is cut by a slicing method with a constant flow value required for the operation of the centrifugal pump under actual working conditions, to obtain a frequency-head curve of the centrifugal pump under constant flow, and a corresponding centrifugal pump head range is obtained according to the frequency range required for the operation of the centrifugal pump under actual working conditions, the minimum head value within the centrifugal pump head range is compared with the minimum head value required by the pipeline under actual working conditions, centrifugal pumps with a head value less than the minimum head value required by the pipeline are excluded, and a plurality of centrifugal pumps that meet the minimum head value required by the actual pipeline are obtained.

[0047] Preferably, the method for selecting the variable speed centrifugal pump in step (5) includes: selecting a centrifugal pump that meets the conditions under the condition of demand a in the rough selection of the variable speed centrifugal pump, bringing the constant frequency value required for the centrifugal pump to work under the actual working conditions and the minimum flow value required for the centrifugal pump to work under the actual working conditions into the surface equation of the variable speed centrifugal pump to obtain the minimum head prediction value of the centrifugal pump through calculation, comparing the minimum head value within the head range corresponding to the centrifugal pump that meets the conditions under the condition of demand a in the rough selection of the variable speed centrifugal pump with the minimum head prediction value of the centrifugal pump, excluding centrifugal pumps with a head value less than the minimum head prediction value of the centrifugal pump, and obtaining multiple centrifugal pumps that meet the minimum head value required by the actual pipeline and the centrifugal pump head value. A centrifugal pump with a predicted minimum head; a centrifugal pump that meets the conditions under requirement b in the rough selection of variable speed centrifugal pumps is selected, and the constant flow value required for the centrifugal pump to work under actual working conditions and the minimum frequency value required for the centrifugal pump to work under actual working conditions are substituted into the surface equation of the variable speed centrifugal pump to obtain the predicted minimum head of the centrifugal pump through calculation; the minimum head value within the head range corresponding to the centrifugal pump that meets the conditions under requirement b in the rough selection of variable speed centrifugal pumps is compared with the predicted minimum head of the centrifugal pump, and the centrifugal pumps with a head smaller than the predicted minimum head of the centrifugal pump are eliminated to obtain multiple centrifugal pumps that meet the minimum head value required by the actual pipeline and the predicted minimum head of the centrifugal pump.

[0048] Preferably, the method for comparing the optimal efficiency of the variable speed centrifugal pump in step (5) is as follows: select centrifugal pumps that meet the minimum head value required by the actual pipeline and the predicted minimum head value of the centrifugal pump from the selected variable speed centrifugal pumps, draw the flow-head characteristic curves corresponding to these centrifugal pumps and the actual pipeline characteristic curve on the same flow-head diagram, and the intersection of the flow-head characteristic curve corresponding to the centrifugal pump and the actual pipeline characteristic curve is the optimal efficiency working point of the centrifugal pump. According to the optimal efficiency working points of these centrifugal pumps, the optimal efficiency is obtained and compared, and finally the model of the variable speed centrifugal pump is determined.

[0049] In the above-mentioned variable speed centrifugal pump selection method, the operation data of the required variable speed centrifugal pump is collected by using the operation data acquisition system of the variable speed centrifugal pump, and the evaluation data of the variable speed centrifugal pump is calculated by using the existing formula, and the evaluation data of the variable speed centrifugal pump is fitted into the surface relationship diagram of the variable speed centrifugal pump using SCILAB software, and a database is created. According to the actual working conditions, the variable speed centrifugal pump surface relationship diagram is cut by the slicing method for rough selection, the variable speed centrifugal pump characteristic equation is brought into the predicted head value for selection, and the optimal efficiency working point is obtained for comparison of efficiency to determine the final model of the variable speed centrifugal pump selection method. This not only solves the problem that the original centrifugal pump flow-head characteristic curve cannot improve the efficiency evaluation of the variable speed centrifugal pump, but also provides a more accurate, convenient and fast selection method for the variable speed centrifugal pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Create a flow chart for the surface relationship diagram and surface equations of a variable speed centrifugal pump.

[0051] Figure 2 This is a flow chart for selecting a variable speed centrifugal pump.

[0052] Figure 3 This is a structural diagram of the operation data acquisition system for a variable speed centrifugal pump.

[0053] Figure 4 This is the front view of the operation data acquisition system of the variable speed centrifugal pump.

[0054] Figure 5 This is the left view of the operation data acquisition system of the variable speed centrifugal pump.

[0055] Figure 6 This is an overhead view of the operating data acquisition system for a variable speed centrifugal pump.

[0056] Figure 7 This is a bottom view of the operation data acquisition system of the variable speed centrifugal pump.

[0057] Figure 8 This is a schematic diagram of the connection between the variable frequency speed regulator and the centrifugal pump circuit under test.

[0058] Figure 9 This is a circuit connection diagram for the vacuum gauge, pressure gauge, analog-to-RS485 module, and power switch No. 1.

[0059] Figure 10 This is a schematic diagram of the circuit connection between the No. 2 power switch and the electromagnetic flowmeter.

[0060] Figure 11 Evaluation data table for the tested centrifugal pump.

[0061] Figure 12 This is the frequency-flow-head curve relationship diagram of the centrifugal pump being tested.

[0062] In the figure: frame 101, overall load-bearing frame 1011, pipeline installation fixing rod 1012, pump operating frequency and power setting display module installation backboard 1013, centrifugal pump bearing platform 102, pump operating frequency and power setting display module 103, pump inlet vacuum acquisition display module 104, pump outlet vacuum acquisition display module 105, pipeline flow acquisition display module 106, No. 1 power supply control module 107, No. 2 power supply control module 108, signal conversion module 109, water tank 110, pump inlet pipeline 111, inlet pipeline 1111, check valve 1112, pump outlet pipeline 112, outlet pipeline 1121, valve 1122, DETAILED DESCRIPTION

[0063] Please see Figure 1 and Figure 2 A method for selecting a variable speed centrifugal pump comprises the following steps:

[0064] (1) Data acquisition: using the variable speed centrifugal pump operation data acquisition system, collect multiple sets of variable speed centrifugal pump operation data, the operation data including: the operating frequency of the centrifugal pump under test, the power of the centrifugal pump under test, the vacuum degree at the inlet of the centrifugal pump under test, the vacuum degree at the outlet of the centrifugal pump under test, and the flow rate value of the pipeline of the centrifugal pump under test;

[0065] (2) Data processing: using existing formulas to calculate and process the operating data obtained in step (1) to obtain multiple sets of evaluation data of the centrifugal pumps, and organizing the evaluation data into a table, wherein the evaluation data includes: the operating frequency of the centrifugal pump under test, the power of the centrifugal pump under test, the head of the centrifugal pump under test, the efficiency of the centrifugal pump under test, and the flow rate of the centrifugal pump under test;

[0066] (3) Surface fitting: Using tool software, the evaluation data in step (2) is fitted into frequency-power, frequency-efficiency, frequency-head, and frequency-flow curve relationship diagrams, and the corresponding curve equations are generated. To facilitate the selection of variable speed centrifugal pumps, the tool software is used again to fit the evaluation data in step (2) into frequency-flow-efficiency, frequency-flow-effective power, and frequency-efficiency-head surface relationship diagrams, and the corresponding surface equations are generated.

[0067] (4) Database creation: Repeat the above steps (1), (2), and (3) to obtain the frequency-flow-efficiency, frequency-flow-effective power, and frequency-efficiency-head surface relationship diagrams of different types of variable speed centrifugal pumps, and generate corresponding surface equations. The surface relationship diagrams and surface equations of the above different types of variable speed centrifugal pumps are combined into a variable speed centrifugal pump selection database.

[0068] (5) Selection of variable speed centrifugal pump: Based on the variable speed centrifugal pump database created in step (4), the required variable speed centrifugal pump model is finally determined after rough selection, fine selection, and optimal efficiency comparison according to the actual working conditions.

[0069] For further information, see Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 ,and Figure 7The operation data acquisition system of the variable speed centrifugal pump in the step (1) comprises: a frame 101, a centrifugal pump supporting platform 102, a pump operating frequency and power setting display module 103, a pump inlet vacuum acquisition display module 104, a pump outlet vacuum acquisition display module 105, a pipeline flow acquisition display module 106, a No. 1 power supply control module 107, a No. 2 power supply control module 108, a water tank 110, a pump inlet pipeline 111, and a pump outlet pipeline 112; the operation data comprises: the operating frequency of the centrifugal pump under test, the power of the centrifugal pump under test, the vacuum degree at the inlet of the centrifugal pump under test, the vacuum degree at the outlet of the centrifugal pump under test, and the pipeline flow value of the centrifugal pump under test; the centrifugal pump supporting platform 102 is installed above the frame, carrying the centrifugal pump under test, the pump operating frequency The frequency and power setting display module 103 is installed on the frame 101, located below the centrifugal pump bearing platform 102 and can be electrically connected to the centrifugal pump under test to adjust the operating frequency and power of the centrifugal pump under test and display the corresponding operating frequency and power; the water tank 110 is placed on a platform of appropriate height and located below the centrifugal pump bearing platform 102, one end of the pump inlet pipe 111 is connected to the water inlet of the centrifugal pump under test, and the other end is inserted into the water tank 110, the pump inlet vacuum acquisition display module 104 is installed on the pump inlet pipe 111 and close to the water inlet of the centrifugal pump under test to measure the vacuum at the water inlet of the centrifugal pump under test and display it on the panel of the pump inlet vacuum acquisition display module 104, and one end of the pump outlet pipe 112 is connected to the water outlet of the centrifugal pump under test The other end is inserted into the water tank 110, and the pump outlet vacuum acquisition and display module 105 is installed on the pump outlet pipeline 112 and close to the water outlet of the centrifugal pump to measure the vacuum at the water outlet of the centrifugal pump to be tested and display it on the panel of the pump outlet vacuum acquisition and display module 105; the centrifugal pump to be tested, the pump outlet pipeline, the pump inlet pipeline, and the water tank form a closed circulation pipeline, and there is a height difference between the pump inlet vacuum acquisition and display module 104 and the pump outlet vacuum acquisition and display module 105; the pipeline flow acquisition and display module 106 is installed on the pump outlet pipeline 112 close to the pipeline outlet to obtain the flow value in the pump outlet pipeline and display it on the panel of the pipeline flow acquisition and display module 106; the No. 1 power supply control module 107 is installed on the centrifugal pump load-bearing The platform 102 is on the centrifugal pump supporting platform 102 and is located below the centrifugal pump supporting platform 102. The No. 1 power supply control module 107 can be electrically connected to the pump inlet vacuum acquisition and display module 104 and the pump outlet vacuum acquisition and display module 105, supply power to the pump inlet vacuum acquisition and display module 104 and the pump inlet vacuum acquisition and display module 105 and control the operation of the pump inlet vacuum acquisition and display module 104 and the pump outlet vacuum acquisition and display module 105; the No. 2 power supply control module 108 is installed on the centrifugal pump supporting platform 102 and is located above the centrifugal pump supporting platform 102. The No. 2 power supply control module 108 can be electrically connected to the pipeline flow acquisition and display module 106, supply power to the pipeline flow acquisition and display module 106 and control the operation of the pipeline flow acquisition and display module 106.

[0070] Furthermore, in the operation data acquisition system of the variable speed centrifugal pump in step (1), the frame 101 includes an overall load-bearing frame 1011, a pipeline installation fixing rod 1013, and a pump operating frequency and power setting display module installation backplate 1012. The overall load-bearing frame 1011 is a hexahedral frame. The centrifugal pump support platform 102 is installed on the top side of the overall weighing frame 1011. The operating frequency and power setting display module installation backplate 1012 is installed on the back of the overall weighing frame 1011. The operating frequency and power setting display module 103 is installed on the operating frequency and power setting display module installation backplate 1012 to adjust the operating frequency and power of the centrifugal pump under test and display the corresponding operating frequency and power. The pipeline installation fixing rod 1013 is installed on the back of the overall weighing frame 1011 to fix the pump inlet pipeline 111 and the pump outlet pipeline 112 to prevent the pipeline from vibrating excessively during operation.

[0071] Furthermore, in the operation data acquisition system of the variable speed centrifugal pump in step (1), the pump inlet pipeline 111 includes an inlet pipeline 1111 and a check valve 1112. One end of the inlet pipeline 1111 is fixedly connected to the water inlet of the centrifugal pump to be tested, and the other end is inserted into the water tank 110. The pump inlet vacuum acquisition and display module 104 is installed on the inlet pipeline 1111 and close to the water inlet of the centrifugal pump to be tested. The inlet pipeline 1111 is fixedly installed on the pipeline installation fixing rod 1013 as a whole. The check valve 1112 is installed on the inlet pipeline 1111, away from the water inlet of the centrifugal pump to be tested, and placed in the water tank 110 to prevent water in the pipeline from flowing back into the water tank and causing inaccurate data. After the pipeline installation and connection are completed, waterproof glue is applied at the connection to prevent water leakage in the pipeline and causing inaccurate data.

[0072] Furthermore, in the operation data acquisition system of the variable speed centrifugal pump in step (1), the pump outlet pipeline 112 includes an outlet pipeline 1121 and a valve 1122. One end of the outlet pipeline 1121 is fixedly connected to the outlet water of the centrifugal pump to be tested, and the other end is inserted into the water tank 110. The pump outlet vacuum acquisition display module 105 is installed on the outlet pipeline 1121 and is close to the water outlet of the centrifugal pump to be tested. The outlet pipeline 1121 is fixedly installed on the pipeline installation fixing rod 1013 as a whole. The valve 1122 is installed on the outlet pipeline 1121 and is close to the water outlet of the centrifugal pump to be tested. It is located behind the pump outlet vacuum acquisition display module 105 and can change the flow rate of the pump outlet. At the same time, the pump outlet pipeline 1121 can also be closed to fill the pump to prevent the centrifugal pump from idling when it is started and damaging the centrifugal pump to be tested. After the pipeline installation and connection are completed, waterproof glue is applied at the connection to prevent the pipeline from leaking and causing inaccurate data to be obtained.

[0073] Furthermore, in the operation data acquisition system of the variable speed centrifugal pump in step (1), the height difference between the pump inlet vacuum acquisition and display module 104 and the pump outlet vacuum acquisition and display module 105 is set to 0.224 to more accurately calculate the efficiency of the centrifugal pump being tested.

[0074] Furthermore, preferably, the data calculation formula in step (2) includes:

[0075] Calculate the speed n (rev / min):

[0076] According to the motor speed and frequency conversion formula

[0077]

[0078] Where: f is the frequency, p is the number of magnetic field poles.

[0079] Calculate lift H e (m):

[0080] According to Bernoulli's equation,

[0081]

[0082] Where:

[0083] Inlet flow rate: Unit: m / s

[0084] Outlet flow rate: Unit: m / s

[0085] The height difference between the pump inlet vacuum acquisition and display module and the pump outlet vacuum acquisition and display module: z2-z1=0.224 m

[0086] Test bench flow resistance loss: H f Unit: m

[0087] Inlet pipe inner diameter: d1 = 0.05m

[0088] Inner diameter of outlet pipe: d1 = 0.05m

[0089] Vacuum degree at the inlet of the centrifugal pump being tested: p1 unit P a

[0090] Vacuum degree at the outlet of the centrifugal pump being tested: p1 unit P a

[0091] Measured centrifugal pump pipeline flow value: Q unit m 3 / s

[0092] Fluid density: ρ = 1000 kg / m 3

[0093] Weight unit: g = 9.81

[0094] Computational efficiency:

[0095] The known effective power calculation formula is as follows

[0096] P e =ρgQH e

[0097] In the formula: effective power: P e Unit: kW

[0098] Therefore, the efficiency calculation formula can be obtained

[0099]

[0100] Where: P a is the shaft power of the motor, in kW.

[0101] The variable speed centrifugal pump operation data acquisition system in the above steps provides manufacturers with an experimental method and acquisition tools for obtaining the surface relationship diagram of the centrifugal pumps they produce. Through the above steps, the variable speed centrifugal pump operation data acquisition system is used for calculation processing and surface fitting, and the variable speed centrifugal pump surface relationship diagram and surface equation obtained can be used for flow and head design calculation during variable frequency speed regulation, and can provide efficiency-related data, which is conducive to achieving the selection goal of energy conservation and emission reduction.

[0102] Furthermore, the surface fitting in step (3) can be performed using a tool capable of fitting any three parameters, such as SCILAB or TableCurve3D.

[0103] Furthermore, the rough selection method of the variable speed centrifugal pump in step (5) includes: requirement a: cutting the frequency-flow-head curve of each model of centrifugal pump in the database with the constant frequency value required for the centrifugal pump to work under actual working conditions by a slicing method, obtaining the flow-head curve of the centrifugal pump under constant frequency, and obtaining the corresponding centrifugal pump head range according to the flow range required for the centrifugal pump to work under actual working conditions, comparing the minimum head value within the centrifugal pump head range with the minimum head value required by the pipeline under actual working conditions, excluding centrifugal pumps with a head value less than the minimum head value required by the pipeline, and obtaining multiple centrifugal pumps that meet the actual working conditions. A centrifugal pump with the minimum head value required for the pipeline; Requirement b: The frequency-flow-head curves of various models of centrifugal pumps in the database are cut by the slicing method with the constant flow value required for the centrifugal pump to work under actual working conditions, and the frequency-head curves of the centrifugal pump under constant flow are obtained. The corresponding centrifugal pump head range is obtained according to the frequency range required for the centrifugal pump to work under actual working conditions, and the minimum head value within the centrifugal pump head range is compared with the minimum head value required for the pipeline under actual working conditions. The centrifugal pumps with a head value less than the minimum head value required for the pipeline are eliminated, and multiple centrifugal pumps that meet the minimum head value required for the actual pipeline are obtained.

[0104] Furthermore, the method for selecting the variable speed centrifugal pump in step (5) includes: selecting a centrifugal pump that meets the conditions under the condition of demand a in the rough selection of the variable speed centrifugal pump, bringing the constant frequency value required for the centrifugal pump to work under the actual working conditions and the minimum flow value required for the centrifugal pump to work under the actual working conditions into the surface equation of the variable speed centrifugal pump to obtain the minimum head prediction value of the centrifugal pump through calculation, comparing the minimum head value within the head range corresponding to the centrifugal pump that meets the conditions under the condition of demand a in the rough selection of the variable speed centrifugal pump with the minimum head prediction value of the centrifugal pump, excluding centrifugal pumps with a head value less than the minimum head prediction value of the centrifugal pump, and obtaining multiple centrifugal pumps that meet the minimum head value and the minimum head value required by the actual pipeline. The minimum head prediction value of the centrifugal pump is obtained by calculating the minimum head prediction value of the centrifugal pump; the centrifugal pump that meets the conditions under the condition of demand b in the rough selection of the variable speed centrifugal pump is selected, and the constant flow value required for the centrifugal pump to work under the actual working conditions and the minimum frequency value required for the centrifugal pump to work under the actual working conditions are substituted into the surface equation of the variable speed centrifugal pump to obtain the minimum head prediction value of the centrifugal pump; the minimum head value within the head range corresponding to the centrifugal pump that meets the conditions under the condition of demand b in the rough selection of the variable speed centrifugal pump is compared with the minimum head prediction value of the centrifugal pump, and the centrifugal pumps with a head smaller than the minimum head prediction value of the centrifugal pump are eliminated to obtain multiple centrifugal pumps that meet the minimum head value required by the actual pipeline and the minimum head prediction value of the centrifugal pump.

[0105] Furthermore, the optimal efficiency comparison method of the variable speed centrifugal pump in step (5) is as follows: select centrifugal pumps that meet the minimum head value required by the actual pipeline and the predicted minimum head value of the centrifugal pump from the selected variable speed centrifugal pumps, draw the flow-head characteristic curves corresponding to these centrifugal pumps and the actual pipeline characteristic curve on the same flow-head diagram, and the intersection of the flow-head characteristic curve corresponding to the centrifugal pump and the actual pipeline characteristic curve is the optimal efficiency working point of the centrifugal pump. According to the optimal efficiency working points of these centrifugal pumps, the optimal efficiency is obtained and compared, and finally the model of the variable speed centrifugal pump is determined.

[0106] The above selection method can utilize the variable speed centrifugal pump surface relationship diagram and surface equation to select the required centrifugal pump model according to the actual working conditions. It not only provides a convenient, fast and accurate selection method for centrifugal pump purchasers, but also provides manufacturers with a selection method and selection tool development ideas using the variable speed centrifugal pump characteristic surface, thereby increasing product outlets.

[0107] In this embodiment, the operation data acquisition system of the variable speed centrifugal pump in step (1), the pump operating frequency and power setting display module 103 is a variable frequency speed regulator, model Delta EV4300-0.75G1, input voltage 200-240V, frequency 50-60Hz, output voltage 0-240V, power 0.75kW, which can be electrically connected to the centrifugal pump under test to adjust the operating frequency and power of the centrifugal pump under test and display the corresponding operating frequency and power, so that the evaluator can obtain and record the operating frequency and power of the centrifugal pump under test; the pump inlet vacuum acquisition display module 104 is a digital pressure transmitter, model 208, range -0.1-0.1MPa, output 4-20mA, accuracy 0.5 level, to measure the vacuum at the water inlet of the centrifugal pump under test and display it on the panel, so that the evaluator can obtain and record the vacuum at the water inlet of the centrifugal pump under test. The vacuum degree at the outlet is obtained and recorded. After the digital pressure transmitter is installed, waterproof glue is applied at the connection to prevent inaccurate readings caused by water leakage; the pump outlet vacuum degree acquisition and display module 105 is a digital pressure transmitter, model 208, range 0~0.1MPa, output 4~20mA, accuracy 0.5 level, to measure the vacuum degree at the outlet of the centrifugal pump under test and display it on the panel, so that the evaluator can obtain and record the vacuum degree at the inlet and outlet of the centrifugal pump under test. After the digital pressure transmitter is installed, waterproof glue is applied at the connection to prevent inaccurate readings caused by water leakage; the pipeline flow acquisition and display module 106 is an electromagnetic flowmeter 106, model LD-DN15, voltage 220V, nominal diameter 15mm, instrument coefficient 1.004, rated pressure 1.6MPa, lining material is PTFE, accuracy grade 0.5 level, motor material 316L, flow range 0.4~4m 3 / h, to obtain the flow value in the pump outlet pipeline and display it on the panel, so that the assessor can obtain and record the flow value in the pump outlet pipeline; the No. 2 power supply control module 108 is an S-100-24 type power switch, with an input voltage of 100~120V current 3.0A / 200~240V current 1.5A, an input frequency of 50 / 60Hz, and an output of 24V. The No. 2 power switch can be electrically connected to the electromagnetic flowmeter and control the operation of the electromagnetic flowmeter; the No. 1 power supply control module is an S-200-24 type power switch, with an input voltage of 190~240V frequency 50 / 60Hz, an output voltage of 24V, and a current of 8.3A. The No. 1 power switch can be electrically connected to the digital pressure gauge at the water inlet of the centrifugal pump being tested and the digital pressure gauge at the water outlet of the centrifugal pump being tested, and control the operation of the digital pressure gauge at the water inlet of the centrifugal pump being tested and the digital pressure at the water outlet of the centrifugal pump being tested.

[0108] Furthermore, in this embodiment, the operation data acquisition system of the variable speed centrifugal pump in step (1) is further provided with a signal conversion module 109 in order to more intuitively reflect the changes in the vacuum degree at the inlet of the centrifugal pump being measured, the vacuum degree at the outlet of the centrifugal pump being measured, and the fluid flow value in the pipeline at the pump outlet. The signal conversion module 109 is an analog-to-RS485 module with a power supply voltage of 9 to 24 V, a collection signal of 0 to 20 mA / 0 to 10 V, and 4 channels. The input end of the analog-to-RS485 module can be electrically connected to the input end of the No. 1 power supply control module 107. The No. 1 power supply control module 107 supplies power to the analog-to-RS485 module and controls the operation of the analog-to-RS485 module. The output end of the RS485 module can be electrically connected to the pump inlet vacuum acquisition and display module 104, the pump outlet vacuum acquisition and display module 105, and the pipeline flow acquisition and display module 106 to receive the vacuum degree at the inlet of the centrifugal pump under test, the vacuum degree at the outlet of the centrifugal pump under test, and the flow rate value in the pump outlet pipeline output by the pump inlet vacuum acquisition and display module 104, the pump outlet vacuum acquisition and display module 105, and the pipeline flow acquisition and display module 106, and convert them into analog signals for collection to the computer. The computer displays the received analog signals in the form of a waveform graph, so that the evaluator can more intuitively observe the changes in the vacuum degree at the inlet of the centrifugal pump under test, the vacuum degree at the outlet of the centrifugal pump under test, and the flow rate value in the pump outlet pipeline.

[0109] Furthermore, in this embodiment, the specific circuit connection of the variable speed centrifugal pump operation data acquisition system in step (1) is shown in FIG. Figure 8 、 Figure 9 and Figure 10 .

[0110] This embodiment illustrates the method of using the operation data acquisition system of the variable speed centrifugal pump in step (1):

[0111] (1) The assessor shall install the centrifugal pump to be tested on the centrifugal pump support platform, correctly connect the pipelines and circuits, and take waterproof measures at the pipeline connections.

[0112] (2) The assessor plugs the frequency converter, power switch No. 1, and power switch No. 2 into the power supply, presses the "Run" button on the frequency converter control panel, and runs it for more than ten minutes to preheat the electromagnetic flowmeter, and waits for the electromagnetic flowmeter reading to stabilize.

[0113] (3) The assessor adjusts the output frequency using the knob on the frequency converter control panel. The initial frequency is set to 50 Hz, and the frequency is adjusted according to the required frequency change. The set frequency and corresponding power are recorded.

[0114] (4) After the adjustment is completed, wait for a while, and the evaluator observes the display panel of the digital pressure transmitter at the pump inlet, the digital pressure transmitter at the pump outlet, and the electromagnetic flowmeter. After the readings are stable, read and record the vacuum degree at the inlet of the measured centrifugal pump, the vacuum degree at the outlet of the measured centrifugal pump, and the flow value in the pump outlet pipeline at the set frequency.

[0115] (5) After completing the required operating data recording of the centrifugal pump under test, press the "Stop" button on the frequency converter control panel, confirm that the motor of the centrifugal pump under test has stopped running, and then unplug it.

[0116] (6) Remove the centrifugal pump under test and clean the experimental device.

[0117] Furthermore, in this embodiment, the variable speed centrifugal pump operation data acquisition system in step (1) is used to collect the centrifugal pump operation data, which is processed and sorted into the centrifugal pump evaluation data table. Figure 11 .

[0118] Furthermore, in this embodiment, the frequency-flow-head curve relationship diagram formed by the MATLAB software curve fitting is shown in FIG. Figure 12 , its surface equation is:

[0119] f(x,y)=7.388-0.7871x+6.999y+0.01921x 2 -0.2361xy

[0120] -0.003202y 2 +0.0008479x 2 y+0.005725xy 2 -0.006991y 3

[0121] Where x is the frequency value of the centrifugal pump, y is the flow value of the centrifugal pump, and f(x,y) is the head value of the centrifugal pump.

[0122] Furthermore, in this embodiment, in order to facilitate the selection of the variable speed centrifugal pump in step (5), a function calculation interface is created using Python's pyqt5 to obtain the value of f(x, y) by inputting the values ​​of x and y.

Claims

1. A method for selecting a variable speed centrifugal pump, comprising the following steps: (1) Data acquisition: using the variable speed centrifugal pump operation data acquisition system, collect multiple sets of variable speed centrifugal pump operation data, the operation data including: the operating frequency of the centrifugal pump under test, the power of the centrifugal pump under test, the vacuum degree at the inlet of the centrifugal pump under test, the vacuum degree at the outlet of the centrifugal pump under test, and the flow rate value of the pipeline of the centrifugal pump under test; (2) Data processing: using existing formulas to calculate and process the operating data obtained in step (1) to obtain multiple sets of evaluation data of the centrifugal pumps, and organizing the evaluation data into a table, wherein the evaluation data includes: the operating frequency of the centrifugal pump under test, the power of the centrifugal pump under test, the head of the centrifugal pump under test, the efficiency of the centrifugal pump under test, and the flow rate of the centrifugal pump under test; (3) Surface fitting: Using tool software, the evaluation data in step (2) is fitted into frequency-power, frequency-efficiency, frequency-head, and frequency-flow curve relationship diagrams, and the corresponding curve equations are generated. To facilitate the selection of variable speed centrifugal pumps, the tool software is again used to fit the evaluation data in step (2) into frequency-flow-efficiency, frequency-flow-effective power, and frequency-efficiency-head surface relationship diagrams, and the corresponding surface equations are generated; (4) Database creation: Repeat the above steps (1), (2), and (3) to obtain the frequency-flow-efficiency, frequency-flow-effective power, and frequency-efficiency-head surface relationship diagrams of different types of variable speed centrifugal pumps, and generate corresponding surface equations. The surface relationship diagrams and surface equations of the above different types of variable speed centrifugal pumps are combined into a variable speed centrifugal pump selection database; (5) Selection of variable speed centrifugal pump: Based on the variable speed centrifugal pump database created in step (4), the required variable speed centrifugal pump model is finally determined after rough selection, fine selection, and optimal efficiency comparison according to the actual working conditions.

2. The method for selecting a variable speed centrifugal pump according to claim 1, characterized in that: The operation data acquisition system of the variable speed centrifugal pump in the step (1) comprises: a frame, a centrifugal pump supporting platform, a pump operating frequency and power setting display module, a pump inlet vacuum acquisition display module, a pump outlet vacuum acquisition display module, a pipeline flow acquisition display module, a No. 1 power supply control module, a No. 2 power supply control module, a water tank, a pump inlet pipeline, and a pump outlet pipeline; the operation data comprises: the operating frequency of the centrifugal pump under test, the power of the centrifugal pump under test, the vacuum degree at the inlet of the centrifugal pump under test, the vacuum degree at the outlet of the centrifugal pump under test, and the flow value of the pipeline of the centrifugal pump under test; the centrifugal pump supporting platform is installed above the frame, carrying the centrifugal pump under test, the pump operating frequency The frequency and power setting display module is installed on the rack, located below the centrifugal pump bearing platform and can be electrically connected to the centrifugal pump under test to adjust the operating frequency and power of the centrifugal pump under test and display the corresponding operating frequency and power; the water tank is placed on a platform of appropriate height and located below the centrifugal pump bearing platform, one end of the pump inlet pipe is connected to the water inlet of the centrifugal pump under test, and the other end is inserted into the water tank, the pump inlet vacuum acquisition display module is installed on the pump inlet pipe and close to the water inlet of the centrifugal pump under test to measure the vacuum at the water inlet of the centrifugal pump under test and display it on the panel of the pump inlet vacuum acquisition display module, one end of the pump outlet pipe is connected to the centrifugal pump under test The water outlet is connected, and the other end is inserted into the water tank. The pump outlet vacuum acquisition and display module is installed on the pump outlet pipeline and close to the water outlet of the centrifugal pump to measure the vacuum at the water outlet of the centrifugal pump to be tested and display it on the panel of the pump outlet vacuum acquisition and display module; the centrifugal pump to be tested, the pump outlet pipeline, the pump inlet pipeline, and the water tank form a closed circulation pipeline. There is a height difference between the pump inlet vacuum acquisition and display module and the pump outlet vacuum acquisition and display module; the pipeline flow acquisition and display module is installed on the pump outlet pipeline close to the pipeline outlet to obtain the flow value in the pump outlet pipeline and display it on the panel of the pipeline flow acquisition and display module; No. 1 power supply The control module is installed on the centrifugal pump supporting platform and is located below the centrifugal pump supporting platform. The No. 1 power supply module can be electrically connected to the pump inlet vacuum acquisition and display module and the pump outlet vacuum acquisition and display module to supply power to the pump inlet vacuum acquisition and display module and the pump inlet vacuum acquisition and display module and control the operation of the pump inlet vacuum acquisition and display module and the pump outlet vacuum acquisition and display module; the No. 2 power supply control module is installed on the centrifugal pump supporting platform and is located above the centrifugal pump supporting platform. The No. 2 power supply control module can be electrically connected to the pipeline flow acquisition and display module to supply power to the pipeline flow acquisition and display module and control the operation of the pipeline flow acquisition and display module.

3. The method for selecting a variable speed centrifugal pump according to claim 2, characterized in that: The operation data acquisition system of the variable speed centrifugal pump in the step (1) comprises a frame including an integral load-bearing frame, a pipeline mounting fixing rod, and a pump operating frequency and power setting display module mounting backplate. The integral load-bearing frame is a hexahedral frame. The centrifugal pump support platform is mounted on one side of the top of the integral weighing frame. The operating frequency and power setting display module mounting backplate is mounted on the back of the integral weighing frame. The operating frequency and power setting display module is mounted on the operating frequency and power setting display module mounting backplate to adjust the operating frequency and power of the centrifugal pump under test and display the corresponding operating frequency and power. The pipeline mounting fixing rod is mounted on the back of the integral weighing frame to fix the pump inlet pipeline and the pump outlet pipeline.

4. The method for selecting a variable speed centrifugal pump according to claim 3, wherein: The operation data acquisition system of the variable speed centrifugal pump in step (1) comprises an inlet pipeline and a check valve, one end of the inlet pipeline is fixedly connected to the water inlet of the centrifugal pump to be tested, and the other end is inserted into the water tank, the pump inlet vacuum acquisition and display module is installed on the inlet pipeline and close to the water inlet of the centrifugal pump to be tested, the inlet pipeline is fixedly installed on the pipeline mounting fixing rod as a whole, and the check valve is installed on the inlet pipeline, away from the water inlet of the centrifugal pump to be tested, and placed in the water tank.

5. The method for selecting a variable speed centrifugal pump according to claim 4, characterized in that: The operation data acquisition system of the variable speed centrifugal pump in step (1) comprises an outlet pipeline and a valve, one end of the outlet pipeline is fixedly connected to the outlet water of the centrifugal pump under test, and the other end is inserted into the water tank, a pump outlet vacuum acquisition and display module is installed on the outlet pipeline and close to the water outlet of the centrifugal pump under test, the outlet pipeline is fixedly installed on the pipeline mounting fixing rod as a whole, and the valve is installed on the outlet pipeline and close to the water outlet of the centrifugal pump under test, and is located after the pump outlet vacuum acquisition and display module.

6. The method for selecting a variable speed centrifugal pump according to claim 5, characterized in that: In the operation data acquisition system of the variable speed centrifugal pump in step (1), the height difference between the pump inlet vacuum acquisition and display module and the pump outlet vacuum acquisition and display module is set to 0.224m.

7. The method for selecting a variable speed centrifugal pump according to claim 1, wherein: The data calculation formula in step (2) includes: Calculate the speed n (rev / min): According to the motor speed and frequency conversion formula Where: f is the frequency, p is the number of magnetic field poles, Calculate lift H e (m): According to Bernoulli's equation, Where: Inlet flow rate: Unit: m / s Outlet flow rate: Unit: m / s The height difference between the pump inlet vacuum acquisition and display module and the pump outlet vacuum acquisition and display module: z2-z1=0.224 m Test bench flow resistance loss: H f Unit: m Inlet pipe inner diameter: d1 = 0.05m Outlet pipe inner diameter: d1 = 0.05m Vacuum degree at the inlet of the centrifugal pump being tested: p1 unit P a Vacuum degree at the outlet of the centrifugal pump being tested: p1 unit P a Measured centrifugal pump pipeline flow value: Q unit m 3 / s Fluid density: ρ = 1000 kg / m 3 Weight unit: g = 9.81 Computational efficiency: The calculation formula for effective power is as follows: P e =ρgQH e In the formula: effective power: P e Unit: kW Therefore, the efficiency calculation formula can be obtained Where: P a is the shaft power of the motor, in kW.

8. The method for selecting a variable speed centrifugal pump according to claim 1, wherein: The rough selection of variable speed centrifugal pumps in step (5) includes: requirement a: cutting the frequency-flow-head curve of each type of centrifugal pump in the database with the constant frequency value required for the centrifugal pump to work under actual working conditions by a slicing method, obtaining the flow-head curve of the centrifugal pump under constant frequency, and obtaining the corresponding centrifugal pump head range according to the flow range required for the centrifugal pump to work under actual working conditions, comparing the minimum head value within the centrifugal pump head range with the minimum head value required by the pipeline under actual working conditions, excluding centrifugal pumps with a head value less than the minimum head value required by the pipeline, and obtaining multiple centrifugal pumps that meet the actual pipeline requirements. A centrifugal pump with a minimum head value; Requirement b: The frequency-flow-head curves of various types of centrifugal pumps in the database are cut by the slicing method with the constant flow value required for the centrifugal pump to work under actual working conditions, and the frequency-head curves of the centrifugal pump under constant flow are obtained. The corresponding centrifugal pump head range is obtained according to the frequency range required for the centrifugal pump to work under actual working conditions, and the minimum head value within the centrifugal pump head range is compared with the minimum head value required by the pipeline under actual working conditions. The centrifugal pumps with a head value less than the minimum head value required by the pipeline are eliminated, and multiple centrifugal pumps that meet the minimum head value required by the actual pipeline are obtained.

9. The method for selecting a variable speed centrifugal pump according to claim 8, characterized in that: The selection of the variable speed centrifugal pump in the step (5) includes: selecting a centrifugal pump that meets the conditions under the condition of demand a in the rough selection of the variable speed centrifugal pump, bringing the constant frequency value required for the centrifugal pump to work under the actual working condition and the minimum flow value required for the centrifugal pump to work under the actual working condition into the surface equation of the variable speed centrifugal pump to obtain the minimum head prediction value of the centrifugal pump through calculation, comparing the minimum head value within the head range corresponding to the centrifugal pump that meets the conditions under the condition of demand a in the rough selection of the variable speed centrifugal pump with the minimum head prediction value of the centrifugal pump, excluding centrifugal pumps with a head value less than the minimum head prediction value of the centrifugal pump, and obtaining multiple centrifugal pumps that meet the minimum head value required by the actual pipeline and the minimum head value of the centrifugal pump. Centrifugal pump with predicted head value; select the centrifugal pump that meets the conditions under the condition of requirement b in the rough selection of variable speed centrifugal pumps, bring the constant flow value required for the centrifugal pump to work under actual working conditions and the minimum frequency value required for the centrifugal pump to work under actual working conditions into the surface equation of the variable speed centrifugal pump, and calculate to obtain the predicted minimum head value of the centrifugal pump; compare the minimum head value within the head range corresponding to the centrifugal pump that meets the conditions under the condition of requirement b in the rough selection of variable speed centrifugal pumps with the predicted minimum head value of the centrifugal pump, exclude the centrifugal pumps with a head value less than the predicted minimum head value of the centrifugal pump, and obtain multiple centrifugal pumps that meet the minimum head value required by the actual pipeline and the predicted minimum head value of the centrifugal pump.

10. The method for selecting a variable speed centrifugal pump according to claim 9, characterized in that: The method for comparing the optimal efficiency of the variable speed centrifugal pump in step (5) is as follows: select centrifugal pumps that meet the minimum head value required by the actual pipeline and the predicted minimum head value of the centrifugal pump from the selected variable speed centrifugal pumps, plot the flow-head characteristic curves corresponding to these centrifugal pumps and the actual pipeline characteristic curve on the same flow-head diagram, and the intersection of the flow-head characteristic curve corresponding to the centrifugal pump and the actual pipeline characteristic curve is the optimal efficiency working point of the centrifugal pump. The optimal efficiency is obtained and compared based on the optimal efficiency working points of these centrifugal pumps, and the model of the variable speed centrifugal pump is finally determined.

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