Abrasive material testing device and testing method thereof

Abstract

According to the abrasion material testing device and the testing method thereof, the water flow speed is controlled by adjusting the rotating speed of a motor, the water level is read through a water level scale hose, and it is ensured that the testing condition is similar to the prototype engineering environment. The testing method comprises the following steps: calibrating the relationship between the near-bottom flow velocity in the device and the rotating speed of the motor, setting the control flow velocity and the punching and grinding time, carrying out a punching and grinding test, and comparing the punching and grinding effects of adding and not adding an abrasion medium to evaluate the abrasion performance of the material. By further increasing the rotating speed of the motor, optimizing the connection between the motor shaft and the stirring shaft, improving the design of the impeller, replacing a flow velocity measurement method and the like, the near-bottom flow velocity range in the device, the test accuracy and the operation safety are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydraulic engineering material performance testing, and particularly relates to an abrasion material testing device and a testing method thereof. BACKGROUND

[0002] In the process of water discharge, the sediment, large-size concrete debris and gravel carried by high-speed water flow (up to 40 m / s ~ 50 m / s) can cause abrasion damage to hydraulic structures, especially the bottom of energy dissipation facilities. Related research has found that although the inflow velocity of the water flow discharged from the hydraulic structure is large, the abrasion mainly occurs at the bottom plate of the energy dissipator, and the maximum velocity near the bottom is usually lower than 30 m / s. For example, when the inflow velocity of a certain hydropower station is 35.03 m / s, the maximum velocity near the bottom reaches 26.43 m / s. Therefore, the abrasion problem of the bottom plate of the energy dissipator is mainly concentrated in the range of 10 m / s ~ 30 m / s.

[0003] The hydraulic model test is a kind of physical model test that uses the similarity principle to restore the real hydraulic conditions of the project, and the most important hydraulic condition that determines the degree of erosion is the erosion flow velocity. The geometric scale commonly used in hydraulic models is 80, 60, 50, 30, and the range of the velocity near the bottom of the hydraulic model is 1.12 m / s ~ 5.47 m / s in the range of 30 ~ 80.

[0004] If a hydraulic model is directly built to test the applicability of the material, there are problems such as high cost, large occupation of site, long period, etc. In the practical new type CN 219161900 U, the author proposes a kind of test instrument for selecting hydraulic model abrasion material, which includes a frequency conversion motor, a test piece erosion part, and an erosion medium. The rotating speed of the frequency conversion motor is continuously adjustable in the range of 0 ~ 6000 r / min; the erosion part is composed of a double-layer steel barrel with an open bottom, a stirring shaft, an impeller, a turbine flowmeter, a steel base, a test piece groove, a model groove and the like; the motor shaft and the stirring shaft are connected through a large flange plate; the steel barrel is divided into inner and outer double layers, the outer layer is a closed steel plate, and the inner layer is a perforated steel mesh, and a turbine flowmeter is arranged between the two layers for recording the water flow velocity in the steel barrel; the stirring impeller is designed as double layers with equal size, and the blade length is 145 mm; the test piece groove is used for placing the material to be tested, and is a three-fan-shaped box fixed in the model groove. The erosion medium is an angular steel ball. The entire erosion part is placed on a movable support plate, and the erosion part steel barrel and the test piece are moved and disassembled through a hand-operated threaded rod.

[0005] The technical scheme adopted by the device mainly has the following problems:

[0006] Problem one: the perforated steel mesh is arranged in the erosion part, and the velocity difference between the inner and outer sides of the steel mesh will be large when the velocity measuring device is kept outside the steel mesh, which will cause inaccurate velocity measurement; at the same time, the perforated steel mesh will also hinder the movement of the water flow, causing energy loss; at high rotating speed, the steel ball may also damage the velocity measuring device by penetrating the steel mesh;

[0007] Problem two: the maximum rotating speed of the motor reaches 6000r / min, but relevant research shows that the maximum near-bottom flow speed in the device may reach 4.4m / s at the rotating speed of 6000r / min, without considering the influence of other design aspects, which is difficult to meet the use of the engineering flow speed above 20m / s;

[0008] Problem three: the impeller adopts a double-layer design, but the sizes are consistent, which is difficult to form an integral turbulent flow in the steel drum, so that the surface flow speed is large and the near-bottom flow speed is too small;

[0009] Problem four: the motor shaft and the stirring shaft are connected through a large flange plate, the diameter of the flange plate is large, and if the motor shaft and the stirring shaft are not uniform in material or the center line is offset, the high-speed stirring shaft is easy to shake violently, which damages the instrument and causes danger;

[0010] Problem five: the test piece groove of the device is three fan-shaped boxes, and is fixed in the model groove, with the increase of the abrasion depth, the steel ball will hit the leaked test piece groove wall, causing the medium impulse to decrease;

[0011] Problem six: the impact and abrasion medium is an angular steel ball, and the real impact and abrasion medium in the project is mostly angular sandstone, which does not completely meet the characteristics of the real impact and abrasion medium in the project.

[0012] Therefore, the cost, site and period of directly building a model to test the material performance are large, long and long. SUMMARY

[0013] The present application aims to at least solve one of the technical problems in the related art to some extent.

[0014] To this end, an embodiment of the present application proposes an abrasion material testing device based on a test instrument for selecting hydraulic model abrasion material, which improves the near-bottom flow speed range, the accuracy of the test and the safety of the operation by further improving the rotating speed of the motor, optimizing the connection between the motor shaft and the stirring shaft, improving the design of the impeller and replacing the flow speed measurement method.

[0015] Another object of the present application is to propose a method for testing the performance of model inverse abrasion material,

[0016] The abrasion material testing device of the embodiment of the present application comprises:

[0017] a frame body;

[0018] a test barrel having a barrel cavity, the bottom cavity wall of the barrel cavity being covered with an abrasion layer formed by the abrasion material;

[0019] a stirring assembly comprising an impeller and a stirring shaft, the impeller is arranged in the barrel cavity and connected with the stirring shaft, the stirring shaft is rotatably connected with the test barrel;

[0020] a driving assembly connected with the frame body, the driving assembly is used to drive the stirring shaft to rotate.

[0021] The abrasion material testing device of the embodiment of the present application can further have the following additional technical features:

[0022] In some embodiments, the test barrel comprises a barrel body, a bottom support and a cover plate, the barrel body has two oppositely arranged openings, the bottom support and the cover plate respectively seal the two openings of the barrel body to form the barrel cavity.

[0023] In some embodiments, the bottom support and the cover plate are detachably connected with the barrel body.

[0024] In some embodiments, the test barrel is arranged at the lower side of the driving assembly, and the abrasion material testing device further comprises a load wheel connected with the bottom support.

[0025] In some embodiments, the impeller comprises a connecting disc and a plurality of blades arranged along the circumference of the stirring shaft, and the plurality of blades are connected with the connecting disc.

[0026] In some embodiments, the blade has a first side surface and a second side surface arranged in a radial direction of the stirring shaft, the first side surface is attached to the stirring shaft and fixedly connected with the stirring shaft, and the second side surface is arranged in a downward direction close to the stirring shaft.

[0027] In some embodiments, the cover plate has a flow rate detection hole penetrating through the axial direction of the stirring shaft, the impeller rotation forms a stirring area, and the projection of the flow rate detection hole on the cross section of the stirring shaft is arranged in a spaced manner with the projection of the stirring area on the cross section of the stirring shaft.

[0028] In some embodiments, the abrasion material testing device further comprises a water level tube, the water level tube comprises a first tube segment and a second tube segment, the first tube segment is connected with the barrel body, the second tube segment is connected with the first tube segment, and the second tube segment extends upward along the axial direction of the barrel body.

[0029] The second tube segment comprises an observation part made of transparent material, and the observation part is provided with a water level scale.

[0030] To achieve the above-mentioned purpose, another aspect of the present application provides a method for testing the performance of abrasion material by model inversion, comprising:

[0031] Open the flow rate measuring hole cover plate, inject water flow into the abrasion material testing device from the flow rate measuring hole, calibrate the relationship between the near-bottom flow rate in the device and the motor speed, adjust the motor speed by changing the frequency converter parameters to adjust the water flow speed, measure the water flow speed in the device, and fit the measured data to obtain the fitting relationship between the near-bottom flow rate in the device and the speed;

[0032] Place the material to be tested in the material loading base, install the base, and add water to the device through the flow rate measuring hole, and read the water level from the device side water level scale hose to the preset water depth;

[0033] According to the engineering prototype flow rate, the flow rate of the hydraulic model is reduced according to the similarity principle and the flow rate scale conversion, or the near-bottom flow rate of the hydraulic model is directly measured, the control flow rate of the water flow in the device is obtained, and the speed parameter to be set of the device is determined according to the fitting relationship;

[0034] The speed parameter is directly set by controlling the frequency conversion speed of the frequency converter, the motor is started to drive the main shaft and the impeller to rotate, the water flow is driven to move, the prototype scouring time is simulated by combining the hydraulic model, the scouring time is set by controlling the frequency converter, no scouring medium is added, and continuous scouring is carried out;

[0035] Open the water release switch (as Figure 1 shown, the first pipe section 71 has a water release port 711 arranged away from the barrel body 21, a water release valve is connected at the water release port 711, the water release port 711 can be controlled to be opened or closed through the water release valve, and then the water in the barrel body 21 can be discharged through the water release port 711, that is, the first pipe section 71 is a water release pipe), the water flow in the emptying instrument is discharged, the material loading platform is disassembled, and the first scouring result is obtained by observation;

[0036] The second scouring result is determined by adding an abrasion medium;

[0037] The first scouring result and the second scouring result are compared to obtain the final test result.

[0038] The abrasion material testing device and the testing method thereof can test the applicability of various inversion abrasion materials by reducing the scale flow rate of the engineering model or the real model flow rate. The problems of high cost, long cycle, large occupied space and the like caused by directly building a hydraulic model are solved, and the deficiencies of the prior art are also made up.

[0039] The abrasion material testing device and the testing method thereof can test the applicability of various inversion abrasion materials by reducing the scale flow rate of the engineering model or the real model flow rate. The problems of high cost, long cycle, large occupied space and the like caused by directly building a hydraulic model are solved, and the deficiencies of the prior art are also made up.

[0040] For the first problem, the single-layer steel barrel body and the closed top cover are provided with a flow velocity measurement hole, and a portable flow velocity meter is used to measure the near-bottom flow velocity in the device, thereby ensuring the safety and accuracy of the velocity measurement; for the second and third problems, a motor with a speed of 50-12000 r / min and a right-angle four-leaf gradually changing impeller (crossed in top view, inverted isosceles trapezoid in side view) are used, the blades are connected to a disc, the maximum blade length is 162-172 mm, and after the scheme is used, the maximum near-bottom flow velocity in the device reaches 5.49 r / min, thereby meeting the demand of the engineering flow velocity in the range of 10-30 m / s; for the fourth problem, the scheme is that a variable-diameter joint coupling is used to connect the motor shaft and the main shaft, and the main shaft is fixed through a shaft tightening bolt, thereby solving the problem of main shaft shaking caused by large flange plate connection and ensuring the safety of the device operation; for the fifth problem, the scheme is that the material carrying bottom support is welded into one body by a bottom support and an annular groove, and no barrier is arranged in the middle, thereby increasing the contact area of the material and the impact and grinding medium and improving the impact and grinding efficiency; for the sixth problem, the scheme is that the impact and grinding medium is made of angular sandstone, and the size is determined according to the engineering prototype and the similarity principle. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a schematic diagram of the overall structure of the abrasion material testing device according to an embodiment of the present application.

[0042] Figure 2 is a schematic diagram of the coupling structure of the abrasion material testing device according to an embodiment of the present application.

[0043] Figure 3 is a schematic diagram of the bottom support structure of the abrasion material testing device according to an embodiment of the present application.

[0044] Figure 4 is a schematic diagram of the stirring assembly structure of the abrasion material testing device according to an embodiment of the present application.

[0045] Figure 5 is a schematic diagram of the cover plate structure of the abrasion material testing device according to an embodiment of the present application.

[0046] Figure 6 is a schematic diagram of the flow velocity detection hole and the hole plate structure of the abrasion material testing device according to an embodiment of the present application.

[0047] Figure 7 is a flow chart of the method for testing the performance of the abrasion material according to an embodiment of the present application.

[0048] Figure 8 is a fitting relationship diagram of the rotation speed and the flow velocity according to an embodiment of the present application.

[0049] Figure 9 is a simulated relationship curve diagram of the rotation speed and the near-bottom flow according to an embodiment of the present application.

[0050] Figure 10 This is a comparison diagram of the abrasion results of an embodiment of the present invention with and without the abrasive medium.

[0051] Figure label:

[0052] 100. Testing equipment;

[0053] 1. Frame; 11. Top plate; 12. Support legs;

[0054] 2. Test barrel; 21. Barrel body; 211. First flange; 212. Second flange; 22. Base support; 221. Base plate; 222. Cylinder; 223. First rubber ring; 23. Cover plate; 231. Second rubber ring; 232. Flow rate detection hole; 232-1. Countersunk hole section; 232-2. Smooth hole section; 232-3. Annular groove; 24. Orifice plate; 25. Spindle hole;

[0055] 3. Agitator assembly; 31. Impeller; 311. Blade; 311-1. First side; 311-2. Second side; 312. Upper connecting plate; 313. Lower connecting plate; 32. Agitator shaft;

[0056] 4. Drive components; 41. Adjustable drive motor; 42. Control inverter;

[0057] 5. Coupling; 51. Upper shaft hole; 511. Keyway; 52. Lower shaft hole; 53. Locking bolt;

[0058] 6. Load-bearing wheels;

[0059] 7. Water level pipe; 71. First pipe section; 711. Outlet; 72. Second pipe section;

[0060] 200. Abrasion layer. Detailed Implementation

[0061] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0062] like Figure 1 As shown, the abrasive material testing device 100 of this embodiment includes a frame 1, a test tank 2, a stirring assembly 3, and a driving assembly 4. The test tank 2 has a cavity, and the bottom wall of the cavity is covered with an abrasive layer 200 formed by the abrasive material. The stirring assembly 3 includes an impeller 31 and a stirring shaft 32. The impeller 31 is disposed in the cavity and connected to the stirring shaft 32. The stirring shaft 32 is rotatably connected to the test tank 2. The driving assembly 4 is connected to the frame 1 and is used to drive the stirring shaft 32 to rotate.

[0063] The abrasion material testing device 100 of the embodiment of the present application firstly tests the abrasion of the abrasion layer 200 without adding the scouring medium, specifically, water is injected into the test barrel 2 to a preset water level, the stirring shaft 32 and the impeller 31 are driven to rotate by the driving assembly 4, so that the near-bottom flow rate in the test barrel 2 reaches the preset scouring flow rate, the testing device 100 is controlled to stop after running for a preset time under the preset scouring flow rate, and the water in the test barrel 2 is emptied, the abrasion layer 200 is observed and recorded as the first abrasion state. Then the abrasion of the abrasion layer 200 with the addition of the scouring medium is tested, specifically, the scouring medium is put into the test barrel 2, water is again injected into the test barrel 2 to a preset water level, and the stirring shaft 32 and the impeller 31 are driven to rotate by the driving assembly 4, so that the near-bottom flow rate in the test barrel 2 reaches the preset scouring flow rate, the testing device 100 is controlled to stop after running for a preset time under the preset scouring flow rate, and the water in the test barrel 2 is emptied, the abrasion layer 200 is observed and recorded as the second abrasion state.

[0064] The first abrasion state and the second abrasion state are compared, if the abrasion layer 200 does not produce abrasion damage in the first abrasion state, and the abrasion layer 200 produces obvious abrasion damage in the second abrasion state, it indicates that the abrasion of the abrasion layer 200 is caused by the scouring medium, then the abrasion material forming the abrasion layer 200 is suitable for the hydraulic model inversion engineering, and can assist in solving the abrasion damage problem. If the abrasion layer 200 in the first abrasion state and the abrasion layer 200 in the second abrasion state both do not produce abrasion damage, it indicates that the abrasion material forming the abrasion layer 200 is not suitable for the hydraulic model inversion engineering, thus whether the abrasion material is suitable for the hydraulic model inversion engineering can be judged.

[0065] The abrasion material testing device 100 of the embodiment of the present application can adjust the near-bottom flow rate in the test barrel 2 according to the driving assembly 4, greatly restores the scouring state of the water flow in the hydraulic model, can test the applicability of various abrasion materials (such as silk screen ink), and judge whether the abrasion material is suitable for the hydraulic model inversion engineering based on the test result, thereby reducing the problems of high cost, long cycle, large occupation of site and the like caused by directly building the hydraulic model.

[0066] The near-bottom flow rate refers to the water flow rate close to the bottom cavity wall in the barrel cavity, that is, the water flow rate directly scouring the abrasion layer 200, by controlling the near-bottom flow rate, the scouring state of the water flow in the hydraulic model can be restored to a greater extent, and the accuracy of the test result is improved.

[0067] In addition, the prototype scouring flow rate of the hydraulic model is converted based on the Froude similarity principle, the preset scouring flow rate can be obtained; the size of the prototype scouring medium is converted based on the similarity principle and the geometric scale, and the particle size of the scouring medium can be obtained.

[0068] Optionally, the impact medium is irregular angular sandstone.

[0069] Compared with the way of using steel balls as impact medium in the related art (i.e. problem six in the background art), the embodiment of the application uses angular sandstone with appropriate size as impact medium, which is more in line with the characteristics of the real impact medium in engineering, so that the test result has higher reference significance.

[0070] Optionally, the abrasive material is covered on the bottom wall of the barrel cavity in the form of brushing or spraying to form the abrasive layer 200.

[0071] Optionally, the thickness of the abrasive layer 200 is 2mm-3mm, preferably 2.5mm.

[0072] Specifically, as shown in Figure 1 The frame body 1 includes a top plate 11 and four legs 12, the top plate 11 is rectangular, and the four legs 12 are respectively arranged at the four corner positions of the lower side of the top plate 11 and are welded and fixed with the top plate 11, so as to form a frame body 1 with stable structure. The driving assembly 4 is arranged on the upper side of the top plate 11, and the test barrel 2 is arranged on the lower side of the top plate 11. The stirring shaft 32 penetrates through the top wall of the test barrel 2 and is connected with the output shaft of the driving assembly 4. The driving assembly 4 can be used to drive the stirring shaft 32 to rotate and adjust the rotating speed of the stirring shaft 32 and the impeller 31.

[0073] The driving assembly 4 includes an adjustable driving motor 41 and a control frequency converter 42, both of which are fixedly connected with the top plate 11 and are connected through three-phase lines. The control frequency converter 42 can control the voltage or current to adjust the frequency or rotating speed, so that the rotating speed of the adjustable driving motor 41 can be continuously adjusted in the range of 50r / min-12000r / min, and the near-bottom flow rate in the test barrel 2 is 0.376r / min-5.49r / min, so as to meet the demand of the abrasive material test device 100 for the impact flow rate.

[0074] Preferably, the adjustable driving motor 41 is a Korean three-phase asynchronous motor, which has a variable frequency speed regulation function, has 2 poles, has a rated power of 7.5KW, and has a rated voltage of 380V.

[0075] Preferably, the control frequency converter 42 is a V / F general type control frequency converter 42.

[0076] Optionally, the output shaft of the adjustable driving motor 41 is connected with the stirring shaft 32 through the shaft coupling 5.

[0077] Specifically, as shown in Figure 2As shown, the coupling 5 is a variable-diameter joint coupling 5, the outer diameter of the coupling 5 is 54 mm, the length is 90 mm, the coupling 5 has an upper shaft hole 51 and a lower shaft hole 52, the hole diameter of the upper shaft hole 51 is 42 mm, the depth is 45 mm, the hole diameter of the lower shaft hole 52 is 40 mm, the depth is 45 mm, the upper shaft hole 51 is used to connect the output shaft of the adjustable driving motor 41, and the lower shaft hole 52 is used to connect the stirring shaft 32; the hole wall of the upper shaft hole 51 has a key groove 511, the width of the key groove 511 is 8 mm, and the depth is 5 mm, the output shaft of the adjustable driving motor 41 is arranged in the upper shaft hole 51 and connected through the key groove 511.

[0078] In addition, the coupling 5 is connected with four locking bolts 53, the four locking bolts 53 are arranged in the axial direction of the coupling 5, the upper two locking bolts 53 are used to lock the output shaft of the adjustable driving motor 41, and the lower two locking bolts 53 are used to lock the stirring shaft 32, so as to realize the connection of the output shaft of the adjustable driving motor 41 and the stirring shaft 32, and the stirring shaft 32 can be driven to rotate by the adjustable driving motor 41, and then the impeller 31 is driven to rotate.

[0079] Compared with the connection mode of the motor shaft and the stirring shaft through a large flange plate in the related art (i.e., problem four in the background art), the output shaft of the adjustable driving motor 41 and the stirring shaft 32 are connected through the coupling 5 in the embodiment of the application, so that the problem of shaking of the stirring shaft 32 can be solved, and the operation safety of the device is improved.

[0080] In some embodiments, the test barrel 2 includes a barrel body 21, a bottom support 22 and a cover plate 23, the barrel body 21 has two openings arranged oppositely, and the bottom support 22 and the cover plate 23 respectively block the two openings of the barrel body 21 to form the barrel cavity.

[0081] Specifically, as shown in Figure 1 The bottom support 22 and the cover plate 23 are respectively arranged on the upper and lower sides of the barrel body 21 and block the two openings on the upper and lower sides of the barrel body 21, so as to form a cylindrical test barrel 2, the upper surface of the bottom support 22 forms the bottom cavity wall of the barrel cavity, the lower surface of the cover plate 23 forms the top cavity wall of the barrel cavity, and the inner side surface of the barrel body 21 forms the side cavity wall of the barrel cavity.

[0082] In some embodiments, the bottom support 22 and the cover plate 23 are detachably connected with the barrel body 21.

[0083] Specifically, as shown in Figure 1 and Figure 3As shown, the bottom support 22 includes a bottom plate part 221 and a cylinder part 222, the bottom plate part 221 blocks the lower opening of the barrel 21, the bottom plate part 221 has a plurality of first through holes uniformly distributed along the circumference thereof, the lower end of the barrel 21 is welded with a first flange 211, the first flange 211 also has a plurality of first through holes uniformly distributed along the circumference thereof, the first through holes of the bottom plate part 221 and the first through holes of the first flange 211 correspond one by one, and the bottom plate part 221 and the first flange 211 can be detachably connected through a bolt assembly. The cylinder part 222 is welded and fixed with the bottom plate part 221, the outer diameter of the cylinder part 222 matches the inner diameter of the barrel 21, when the bottom plate part 221 is fixedly connected with the barrel 21, the cylinder part 222 is inserted into the barrel 21; the upper plate surface of the bottom plate part 221 is the bottom cavity wall of the barrel cavity, covering the erosion material on the bottom cavity wall of the barrel cavity can form the erosion layer 200, the cylinder part 222 surrounds a circular test piece groove, the impact erosion medium is placed in the test piece groove, when the water flow forms a vortex, the impact erosion medium can be driven to rotate and move with the vortex, and the erosion layer 200 is impacted and eroded.

[0084] The test piece groove in the related art is three fan-shaped boxes, and there is a partition plate between adjacent two test piece grooves, the impact erosion medium collides with the partition plate during the impact erosion process, the impact energy of the impact erosion medium is reduced, and the erosion effect is poor (i.e., problem five in the background art). The test piece groove in the embodiment of the present application is not provided with a partition plate, the impact erosion medium is placed in the test piece groove surrounded by the cylinder part 222, the situation that the impact energy of the impact erosion medium is reduced due to collision can be prevented, at the same time, the contact area between the impact erosion medium and the erosion layer is increased, and the impact erosion efficiency is improved.

[0085] In addition, a first rubber ring 223 is arranged between the bottom plate part 221 and the lower end surface of the barrel 21, the first rubber ring 223 is sleeved on the cylinder part 222, and when the bottom support 22 is connected with the barrel 21, the first rubber ring 223 can be compressed to play a sealing role.

[0086] The bottom support 22 and the barrel 21 are detachably connected, the bottom support 22 can be detached to observe the erosion condition of the erosion layer 200; at the same time, the tested erosion material on the bottom support 22 can be cleaned after the bottom support 22 is detached, and another kind of erosion material can be covered on the bottom support 22 to test a plurality of erosion materials.

[0087] As shown in the drawings, Figure 1 and Figure 4As shown, the cover plate 23 has a plurality of second through holes uniformly distributed along the circumference thereof, the upper end of the barrel 21 is welded with a second flange 212, the second flange 212 also has a plurality of second through holes uniformly distributed along the circumference thereof, the plurality of second through holes of the cover plate 23 correspond to the plurality of second through holes of the second flange 212 one by one, and the cover plate 23 and the second flange 212 can be detachably connected through a bolt assembly, so as to realize the detachable connection of the cover plate 23 and the barrel 21. In addition, a second rubber ring 231 is arranged between the lower plate surface of the cover plate 23 and the upper end surface of the barrel 21, so as to play a sealing role.

[0088] The cover plate 23 has a main shaft hole 25 arranged therethrough, the stirring shaft 32 passes through the main shaft hole 25, and the hole diameter of the main shaft hole 25 is 2mm-3mm larger than the diameter of the stirring shaft 32.

[0089] In some embodiments, the test barrel 2 is arranged on the lower side of the driving assembly 4, and the abrasion material testing device 100 further comprises a load wheel 6 connected with the bottom support 22.

[0090] The load wheel 6 is more conducive to controlling the movement of the test barrel 2, so as to facilitate the disassembly of the bottom support 22 and the like, thereby improving the operation convenience of the testing device 100.

[0091] Specifically, as shown in the drawings, Figure 1 The load wheel 6 is a universal wheel, and the number of the load wheels 6 is multiple, for example, four, and the four universal wheels are uniformly distributed along the circumference of the test barrel 2, so as to provide stable support for the test barrel 2. In addition, the load wheel 6 can be locked during the operation of the stirring assembly 3, so as to realize the fixation of the test barrel 2.

[0092] In some embodiments, the impeller 31 comprises a connecting disc and a plurality of blades 311 arranged along the circumference of the stirring shaft 32, and the plurality of blades 311 are all connected with the connecting disc.

[0093] In some embodiments, the blade 311 has a first side surface 311-1 and a second side surface 311-2 arranged in a radial direction of the stirring shaft 32, the first side surface 311-1 is attached to the stirring shaft 32 and is fixedly connected with the stirring shaft 32, and the second side surface 311-2 is arranged in a downwardly inclined manner towards the stirring shaft 32.

[0094] Specifically, as shown in the drawings, Figure 4As shown, the impeller 31 is arranged at the lower side of the stirring shaft 32, the number of the blades 311 is four, and the four blades 311 are uniformly distributed along the circumference of the stirring shaft 32, so that the projection of the four blades 311 on the cross section of the stirring shaft 32 is in the shape of a "cross"; the blade 311 is in the shape of a right trapezoid, two bottom sides of the right trapezoid form the upper side and the lower side of the blade 311 respectively, two waist sides of the right trapezoid form the first side 311-1 and the second side 311-2 of the blade 311 respectively, the first side 311-1 is parallel to the axis of the stirring shaft 32 and is welded and fixed with the stirring shaft 32, and the second side 311-2 is arranged to be inclined from top to bottom to the direction close to the stirring shaft 32.

[0095] It is known that the opening of the vortex has the characteristics of being large at the top and small at the bottom, the impeller with a double-layer design and consistent size is adopted in the related art, the contact area of the upper end of the impeller with the upper side opening of the vortex is small, and it is difficult to form an integrated turbulent flow, and the motor with a rotating speed of 6000 r / min is adopted in the related art, and the maximum near-bottom flow speed can only reach 4.4 m / s, which is difficult to meet the case of engineering flow speed above 30 m / s (i.e. problems two and three in the background art). The rotating speed of the adjustable driving motor 41 is 50-12000 r / min, the impeller 31 is large at the top and small at the bottom, and can be matched with the vortex with the opening large at the top and small at the bottom, the contact area of the upper end of the impeller 31 with the water flow is increased, which is more conducive to forming an integrated turbulent flow, so as to increase the near-bottom flow speed to 5.49 r / min, and can meet the demand of engineering flow speed in the range of 10-30 m / s; at the same time, the size of the lower side of the impeller 31 is small, which can reduce the overall weight of the impeller 31, and further reduce the load of the shaft coupling 5, and improve the operation stability of the stirring assembly 3.

[0096] As shown in the figure, Figure 4 the maximum distance between the second side 311-2 of the blade 311 and the axis of the stirring shaft 32 is the first distance, and the minimum distance is the second distance; the number of the connecting discs is two, which are the upper connecting disc 312 and the lower connecting disc 313, the diameter of the upper connecting disc 312 is equal to the first distance, and the radius of the lower connecting disc 313 is equal to the second distance; the upper side of the four blades 311 is fixedly connected with the upper connecting disc 312, and the lower side is fixedly connected with the lower connecting disc 313, so that the parts of the impeller 31 are integrated, and the stability of the rotation of the impeller 31 is improved.

[0097] Optionally, the first distance D is 162-172 mm, the second side 311-2 forms an angle a with the axis of the stirring shaft 32, and 0°<a<4°.

[0098] As an example, the first distance is 168 mm, the second distance is 120 mm, the distance between the upper side and the lower side of the blade 311 is 145 mm, and the thickness of the blade 311 is 5 mm.

[0099] Optionally, the second side surface 311-2 of the impeller 31 is arranged spaced apart from the side cavity wall of the barrel cavity.

[0100] Thus, the rotation resistance of the impeller 31 can be reduced, the stirring loss is reduced while ensuring the near-bottom flow rate, and the stirring efficiency is improved.

[0101] Optionally, the lower connecting disc 313 is arranged spaced apart from the bottom cavity wall of the barrel cavity, and the spacing between the lower surface of the lower connecting disc 313 and the bottom cavity wall of the barrel cavity is 80 mm.

[0102] In some embodiments, the cover plate 23 has a flow rate detection hole 232 penetrating in the axial direction of the stirring shaft 32, the impeller 31 rotates to form a stirring area, and the projection of the flow rate detection hole 232 on the cross section of the stirring shaft 32 is arranged spaced apart from the projection of the stirring area on the cross section of the stirring shaft 32.

[0103] Through the above arrangement, the near-bottom flow rate in the barrel body 21 can be measured in real time when the impeller 31 and the stirring shaft 32 rotate, so as to ensure that the near-bottom flow rate in the barrel cavity reaches the preset scouring flow rate, and the accuracy of the test result is ensured. In addition, the flow rate detection hole 232 can also be used to inject water and add scouring medium into the barrel cavity.

[0104] Specifically, as shown in Figure 1 , Figure 5 and Figure 6 , the number of flow rate detection holes 232 is two, and the two flow rate detection holes are oppositely arranged on both sides of the main shaft hole 25; the flow rate detection hole 232 includes a counterbore section 232-1 and a light hole section 232-2, the depth of the counterbore section 232-1 is 4 mm, the hole diameter of the light hole section 232-2 of the flow rate detection hole 232 is 110 mm, the bottom wall of the counterbore section 232-1 has a ring groove 232-3, and a third rubber ring is arranged in the ring groove 232-3; the abrasion material testing device 100 further includes a hole plate 24, the hole plate 24 is arranged in the counterbore section 232-1, and the hole plate 24 is detachably connected to the bottom wall of the counterbore section 232-1 through four bolt assemblies; the near-bottom flow rate of the barrel cavity can be measured by detaching the hole plate 24.

[0105] The impeller 31 rotates to form a stirring area in the shape of a truncated cone, the flow rate detection hole 232 is arranged on the outside of the stirring area, the projection of the flow rate detection hole 232 on the cross section of the stirring shaft 32 has a certain spacing with the projection of the stirring area on the cross section of the stirring shaft 32, and the safe range of flow rate measurement is 0 mm-57 mm from the side cavity wall of the barrel cavity. Within this range, the near-bottom flow rate is measured, which can prevent the flow rate meter from colliding with the impeller 31 and ensure safe measurement.

[0106] Compared with the prior art of arranging the flow measuring device outside the protective steel mesh (i.e., the problem one in the background art), the embodiment of the present application directly inserts the flow meter into the barrel cavity to measure the near-bottom flow rate, which can ensure safe measurement while improving the accuracy of flow rate measurement.

[0107] In some embodiments, the abrasion material testing device 100 further comprises a water level pipe 7, which comprises a first pipe section 71 connected with the barrel body 21 and a second pipe section 72 connected with the first pipe section 71 and extending upward along the axial direction of the barrel body 21; the second pipe section 72 comprises an observation part made of transparent material and provided with a water level scale.

[0108] Specifically, as shown in Figure 1 , the first pipe section 71 has a spacing of 52 mm from the first flange 211, and has a diameter of 12 mm and extends along the radial direction of the barrel body 21; the second pipe section 72 is perpendicular to the first pipe section 71 and is a water level scale hose made of transparent material and provided with a water level scale, so that the water level in the barrel cavity can be detected through the water level scale hose.

[0109] Optionally, the first pipe section 71 has a water outlet 711 arranged away from the barrel body 21, and a water outlet valve is connected at the water outlet 711, so that the water outlet 711 can be controlled to be opened or closed through the water outlet valve, and in turn the water in the barrel body 21 can be discharged through the water outlet 711, in other words, the first pipe section 71 is a water discharge pipe.

[0110] To achieve the above-mentioned embodiments, as shown in Figure 7 , the present embodiment further provides a method for model inversion abrasion material performance testing, comprising:

[0111] S1, open the flow rate measuring hole cover plate, inject water flow from the flow rate measuring hole into the abrasion material testing device, calibrate the relationship between the near-bottom flow rate and the motor speed in the device, adjust the motor speed by changing the frequency converter parameters to adjust the water flow speed, measure the water flow rate in the device, and fit the measured data to obtain the fitting relationship between the near-bottom flow rate and the speed in the device.

[0112] Specifically, open the flow rate measuring hole cover plate, inject water flow from the flow rate measuring hole into the device, observe and record the water level hose liquid level scale H0. Start the drive motor, control the speed from the initial value N0 (N0 = 50 r / min) by the frequency converter, increase by ΔN = 50 r / min, after the water flow is stable for 60 s, use the LS300-A portable flow meter to collect the near-bottom flow rate of the water flow in the steel barrel for three times in succession, record the measurement values V i1 , V i2 , V i3 , take the arithmetic mean as the calibration flow rate at this speed Record water level scale H i , if AH / H i > 5% immediately terminate data collection. According to the collected data to establish a logarithmic model:

[0113] V = aln (N / N0) + b (N0 = 1 r / min)

[0114] Define the independent variable X i = ln (N i ), Y i = V i , calculated by least squares:

[0115]

[0116] The determination coefficient R 2 = 0.9.

[0117] S2, the material to be measured is placed in the load bottom support, the bottom support is installed, and water is added to the device through the flow rate measuring hole, and the water depth is read from the device side water level scale hose to the preset water depth.

[0118] S3, according to the prototype flow rate, according to the similarity principle and the flow rate scale conversion, the hydraulic model flow rate is reduced or the hydraulic model near-bottom flow rate is directly measured, the control flow rate of the water flow in the device is obtained, and the speed parameter to be set by the device is determined according to the fitting relationship.

[0119] Specifically, the near-bottom flow rate V p (unit: m / s) of the prototype is obtained by field measurement or hydrological data, and the near-bottom flow rate of the hydraulic model is converted and reduced or directly measured according to the Froude similarity principle, to obtain the control flow rate of the water flow in the device:

[0120]

[0121] Wherein, V control is the near-bottom flow rate required to be controlled in the device, V P is the near-bottom flow rate of the prototype, V m is the near-bottom flow rate of the hydraulic model, λ V is the flow rate scale, and λ L is the geometric scale. According to the fitting relationship between the motor speed and the near-bottom flow rate of the water flow in the device of the present application:

[0122] V = aln (N / N0) + b (N0 = 1 r / min)

[0123] Determine the speed parameter N to be set by the device.

[0124] S4, by controlling the frequency conversion of the frequency converter, the rotating speed parameter is directly set, the motor is started to drive the rotation of the main shaft and the impeller, the water flow is driven to move, the prototype scouring time is simulated by combining the hydraulic model, the scouring time is set by controlling the frequency converter, no scouring medium is added, and continuous scouring is carried out.

[0125] Specifically, the power supply is connected, the rotating speed parameter is directly set by controlling the frequency conversion of the frequency converter, the motor is started to drive the rotation of the main shaft and the impeller, the water flow is further driven to move, the prototype scouring time is simulated by combining the hydraulic model, the scouring time is set by controlling the frequency converter, no scouring medium is added, and continuous scouring is carried out.

[0126] S5, the water discharge switch is opened, the water flow in the instrument is emptied, and the loading platform is disassembled, and the first scouring result is obtained.

[0127] Specifically, the water discharge pipe is opened, the water flow in the steel barrel is emptied, the loading platform bolt is disassembled, and the first scouring result is obtained.

[0128] It can be understood that the device structure of the embodiment of the application has been clearly described in the above device, and no redundant description is made here.

[0129] S6, adding an erosion medium to determine a second scouring result.

[0130] Specifically, the erosion medium is added, and steps S2 to S5 are repeated until the second scouring result is determined.

[0131] S7, comparing the first scouring result and the second scouring result to obtain a final test result.

[0132] Specifically, the erosion effects of the first scouring result and the second scouring result are compared, if no erosion damage occurs on the surface of the material without adding the scouring medium, and obvious erosion damage occurs on the surface of the material after adding the scouring medium, it is indicated that the erosion of the material is caused by the medium, and the material can be used for the problem of erosion damage in the hydraulic model inversion engineering.

[0133] In summary, the erosion material testing device comprises an adjustable driving motor, a control frequency converter, a motor fixing frame, a variable diameter joint coupling, a main shaft, a rotating impeller, a steel barrel body, a steel barrel closed top cover, and a loading bottom support. The adjustable motor is connected with the control frequency converter through three-phase lines and is placed at the top end of the motor fixing frame. The steel barrel top cover is connected with the steel barrel body through bolts. The loading bottom support is fixed in the groove at the bottom of the steel barrel through bolts. Universal load-bearing wheels are welded at the lower end of the steel barrel body at equal intervals. The adjustable driving motor is connected with the upper end of the main shaft through the variable diameter joint coupling. The main shaft penetrates through the steel barrel top cover. The rotating impeller is fixed at the lower end of the main shaft through bolts. The clearance distance between the main shaft end and the loading bottom support is 80mm. The scouring medium is irregular angular sandstone, and the size is determined according to the similarity principle and the engineering prototype.

[0134] When using the device and method, the relationship between the near-bottom flow rate in the device and the motor speed needs to be calibrated. The flow rate measuring hole cover plate is opened, water flow is injected into the instrument, the water depth value in this example is 40 mm, the motor speed is adjusted by changing the frequency converter parameters to adjust the water flow rate, the LS300-A portable flowmeter is used to measure the water flow rate in the device, the initial value of the speed in this example is 50 r / min, the speed is measured every 50 r / min, the data is collected three times each time and the weighted average value is obtained, the collection is terminated when the water level appears to drop, the actual measurement range in this example is 50 r / min-400 r / min, the measurement results are shown in Table 1, the measured data is fitted, and the relationship between the water flow in the device and the motor speed is obtained; v=0.9577ln(r)-3.5068, the correlation coefficient is 0.9696, and the fitting relationship curve is shown in Figure 8 The simulation curve of 450 r / min-12000 r / min is constructed from the fitting curve, as shown in Figure 9 According to the simulation curve, the near-bottom flow rate in the device ranges from 0.376 m / s to 5.49 m / s (speed of 50 r / min-12000 r / min).

[0135] Table 1

[0136]

[0137] The self-prepared silk screen ink is brushed into the carrier bottom support, the thickness of the silk screen ink in this example is controlled to be 3.5 mm, and the bottom support is installed after drying and solidification; water is added to the device through the flow rate measuring hole, and the water level is read to 40 cm from the water level scale hose on the side of the device; it is assumed that the prototype scouring flow rate of a certain project is 26.4 m / s, the prototype scouring medium size is 30 cm, and the geometric scale of the hydraulic model is 50, according to the similarity principle and the flow rate scale conversion, the hydraulic model flow rate is reduced to 3.73 m / s, which is the flow rate that needs to be controlled in the device; the power supply is connected, the motor speed and the fitting relationship between the near-bottom flow rate in the device and the fitting relationship: v=0.9577ln(r)-3.5068, the speed parameter is directly set to 1904 r / min by controlling the frequency conversion speed function of the frequency converter; the scouring time is set to 3h, no scouring medium is added, and the water scouring is carried out; the water discharge switch is opened, the water flow in the instrument is emptied, the carrier platform is disassembled, and direct observation is carried out. Add the erosion medium, the particle size of the scouring medium is determined according to the geometric similarity, which is 6 mm, and the scouring is carried out again, and the scouring result is directly observed. The comparison of the two results is shown below Figure 10 , Figure 10 (a) in the above table is the erosion result without adding the erosion medium, Figure 10 (b) in the above table is the erosion result after adding the erosion medium. This kind of material will not be damaged by water scouring, and the erosion damage is caused by the scouring medium. After testing, the performance of this kind of material can be applied to the inversion of engineering erosion damage of the hydraulic model.

[0138] The method for model inversion abrasion material performance test according to the embodiment of the present application can test the applicability of various inversion abrasion materials by reducing the scale flow velocity of the engineering model or the real model flow velocity, and solves the problems of high cost, long cycle and large occupied space caused by directly building a hydraulic model, and makes up for the deficiencies of the prior art.

[0139] In the description of the present application, it needs to be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0140] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise explicitly specified and limited.

[0141] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integrated; can be mechanical connection, can also be electrical connection or communication with each other; can be directly connected, or indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0142] In the present application, unless otherwise explicitly specified and limited, the first feature "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature "above", "over" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "under" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0143] In this disclosure, the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" mean that a particular feature, structure, material, or characteristic is included in at least one embodiment or example of the present application. The illustrative appearances of the above-mentioned terms in various places in the specification are not necessarily referred to the same embodiment or example. Moreover, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. Furthermore, the terms "comprising", "containing", "having" and "including" and their grammatical variations are intended to be open-ended terms that do not preclude the possibility of additional features, structures, materials, or characteristics.

[0144] Although the embodiments of the present application have been shown and described above, it is understood that the above-mentioned embodiments are exemplary, and are not to be construed as limiting the present application, and the ordinary skilled in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments within the scope of the present application.

Claims

1. An abrasion material testing device characterized by, include: Frame; A test barrel having a cavity, the bottom wall of which is covered with an abrasive layer formed by the abrasive material; A stirring assembly, comprising an impeller and a stirring shaft, wherein the impeller is disposed within the chamber of the test vessel and connected to the stirring shaft, and the stirring shaft is rotatably connected to the test vessel; A drive assembly is connected to the frame and is used to drive the stirring shaft to rotate.

2. The abrasion material testing device of claim 1, wherein, The test bucket includes a bucket body, a base, and a cover plate. The bucket body has two openings arranged opposite to each other. The base and the cover plate respectively block the two openings of the bucket body to form the bucket cavity.

3. The abrasion material testing device of claim 2, wherein, Both the base and the cover are detachably connected to the barrel body.

4. The abrasion material testing device of claim 3, wherein, The test barrel is located on the lower side of the drive assembly, and the abrasive material testing device also includes a load-bearing wheel, which is connected to the base.

5. The abrasion material testing device of any of claims 2-4, wherein, The impeller includes a connecting disc and a plurality of blades arranged circumferentially along the stirring shaft, and the plurality of blades are all connected to the connecting disc.

6. The abrasion material testing device of claim 5, wherein, The blade has a first side and a second side arranged radially at intervals along the stirring shaft. The first side is attached to and fixedly connected to the stirring shaft, and the second side is inclined from top to bottom toward the stirring shaft.

7. The abrasion material testing device of claim 5, wherein, The cover plate has a flow rate detection hole that extends through the axial direction of the stirring shaft. The impeller rotates to form a stirring zone. The projection of the flow rate detection hole on the cross-section of the stirring shaft and the projection of the stirring zone on the cross-section of the stirring shaft are arranged at intervals.

8. The abrasion material testing device of claim 1, wherein, The abrasive material testing device also includes a water level pipe, which includes a first pipe section and a second pipe section. The first pipe section is connected to the barrel body, and the second pipe section is connected to the first pipe section. The second pipe section extends upward along the axial direction of the barrel body. The second pipe section includes an observation section made of transparent material, which is equipped with a water level scale.

9. A method for model inversion attrition material performance testing, characterized by, include: Open the flow velocity measurement hole cover and inject water into the abrasive material testing device through the flow velocity measurement hole. The relationship between the near bottom flow velocity and the motor speed in the device is calibrated. The motor speed is adjusted by changing the frequency converter parameters to adjust the water flow velocity. The water flow velocity in the device is measured, and the measured data is fitted to obtain the fitting relationship between the near bottom flow velocity and the speed in the device. Place the material to be tested in the material carrier, install the carrier, and add water into the device through the flow rate measuring hole. Read the water level from the water level scale hose on the side of the device to the preset water depth. Based on the flow velocity of the engineering prototype, the flow velocity of the hydraulic model is reduced by conversion according to the similarity principle and flow velocity scale, or the bottom flow velocity of the hydraulic model is directly measured to obtain the control flow velocity of the water flow in the device, and the rotational speed parameters to be set in the device are determined according to the fitting relationship. The speed parameters are directly set by controlling the variable frequency speed control of the frequency converter, the motor is started to drive the main shaft and impeller to rotate, and the water flow is driven. Combined with the hydraulic model to simulate the prototype grinding time, the grinding time is set by controlling the frequency converter, and continuous grinding is carried out without adding grinding media. Open the drain valve to drain the water from the instrument, disassemble the material platform, and observe to obtain the first grinding result; The results of the second grinding process were determined by adding abrasive media. The first and second results are compared to obtain the final test result.

10. The method of claim 9, wherein, Open the flow rate measurement hole cover plate, inject water flow into the abrasion material testing device from the flow rate measurement hole, observe and record the water level hose liquid level scale H0, start the drive motor, control the rotating speed from the initial value N0 by the frequency converter, increase by the gradient ΔN=50 r / min, after the water flow is stable for 60 s, collect the near-bottom flow rate in the steel drum for 3 times continuously by using the LS300-A portable flow rate meter, and record the measurement value V i1 , V i2 , V i3 Take the arithmetic average value as the calibration flow rate under the rotating speed Record the water level scale H i If ΔH / H i >5%, immediately terminate the data collection.

11. The method of claim 10, wherein, A logarithmic model is established according to the collected data: V = a ln(N / N0) + b (N0 = 1 r / min) Definition of independent variable X i = ln(N i ), Y i = V i , calculated by least squares R 2 ≧ 0.

9.

12. The method of claim 11, wherein, The flow velocity near the bottom of the prototype is obtained by field measurement or hydrological data p According to the Froude similarity principle, the flow velocity near the bottom of the reduced hydraulic model is converted or directly measured to obtain the control flow velocity of the water flow in the device: where V control is the near-bed velocity to be controlled in the device, V P is the near-bed velocity of the prototype, V m is the near-bed velocity of the hydraulic model, λ V is the velocity scale, λ L is the geometric scale; According to the fitting relationship between the motor speed and the near-bottom flow velocity in the device: V = a ln(N / N0) + b (N0 = 1 r / min) Determine the speed parameter N to be set for the device.

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