Small flow and low specific speed centrifugal pump impeller

Abstract

The present invention relates to the technical field of the design and manufacture of centrifugal pump impellers, particularly to the impeller of a small-flow and low-specific-speed centrifugal pump; it includes blades, a front cover plate, a rear cover plate, and a hub. The outlet width b2 of the blades is determined according to the following formula: Qd = k1·Qe, b2 = 0.02Ns<supgt;0.83< / supgt;(Qd / n)<supgt;1 / 3< / supgt>. The relationship between the outlet flow area A2 of the impeller and the inlet flow area A1 of the impeller is as follows: A2 = k2·A1. Windows are provided in the middle of the flow channel on the front cover plate and / or the rear cover plate, and window covers are welded on the windows. By widening the outlet width b2 of the blades, the casting difficulty of the impeller is reduced, it is easy to demold and clean the sand, the surface finish and quality are improved, and the frictional losses along the path and the disk friction losses of the small-flow and low-specific-speed centrifugal pump are greatly reduced. By restricting the outlet flow area A2 of the impeller, the diffusion loss of the flow channel can be effectively prevented. In addition, the setting of providing windows on the front cover plate and / or the rear cover plate and then welding window covers is beneficial to cleaning the sand and removing slag from the impeller flow channel after casting.

Description

Technical Field

[0001] The invention relates to the technical field of design and manufacturing of centrifugal pump impellers, in particular to a centrifugal pump impeller with small flow and low specific speed. Background Art

[0002] With the rapid development of my country's national economy, the demand for various centrifugal pumps in various industries is increasing, with an annual growth rate of about 15%. In recent years, with the continuous deepening of industrial and agricultural development, in some projects or occasions, the working conditions and medium properties of pump system devices have become more diverse and complex. In addition to requiring structural design diversity, more and more centrifugal pump application designs have a trend towards small flow and low specific speed.

[0003] The design of the traditional centrifugal pump impeller (when the specific speed NS = 30-300) is generally based on the rated operating conditions such as flow rate and head required by the user. According to the fluid machinery design theory, the blades are obtained on the axial projection of the impeller through the angle-conformal transformation method, and then the impeller flow channel is obtained according to the required number of blades array; or after obtaining the blade working surface, the thickness of the impeller blade is directly selected based on experience to obtain the back side, and then the impeller flow channel is obtained according to the required number of blades array. The blades obtained by these two methods are generally intended to reduce the thickness of the blades as much as possible under the premise of meeting the rated operating conditions and structural safety requirements, such as avoiding the blades from breaking due to excessive stress, premature corrosion damage, etc., so as to reduce the hydraulic displacement of the flow channel, improve efficiency, and reduce quality costs. However, for the narrow flow channel impeller of the small flow and low specific speed centrifugal pump, the impeller outlet width is small, casting is very difficult, sand cleaning is inconvenient, and it is easy to have defects such as pores, depressions, slag inclusions, cracks, etc. The surface is rough and the quality is very poor, which makes the hydraulic loss and disc friction loss along the small flow and low specific speed centrifugal pump very large. At the same time, due to the serious diffusion of the flow channel, the diffusion loss is also very large.

[0004] However, for small flow (Q = 2 ~ 50m 3 / h), low specific speed (NS = 10 ~ 60) centrifugal pump impeller, especially NS ≤ 30, flow rate Q ≤ 5m 3 / h, its outlet width b2 becomes very small. If calculated according to the conventional formula for calculating the impeller outlet width: when Q≤5m 3 / h, NS≤30, b2≤3mm. Such a narrow outlet width makes casting very difficult, inconvenient for sand cleaning, prone to defects such as pores, depressions, slag inclusions, cracks, etc., with a rough surface and poor quality, which makes the hydraulic loss along the process and the disc friction loss of the small flow and low specific speed centrifugal pump very large. At the same time, due to the serious diffusion of the flow channel, the diffusion loss is also very large.

[0005] Therefore, the small flow and low specific speed centrifugal pump impeller manufactured by traditional theoretical design methods and conventional casting methods can no longer meet the centrifugal pump development requirements of users' special working conditions. It is difficult to achieve a good match between the flow conditions required by the centrifugal pump impeller design and high efficiency and easy manufacturing. It is necessary to optimize the design of small flow and low specific speed centrifugal pump impellers for such projects in a targeted manner, improve the manufacturing methods, and improve the hydraulic efficiency. Summary of the invention

[0006] The present invention provides a small flow rate and low specific speed centrifugal pump impeller to solve the problem that the current small flow rate and low specific speed centrifugal pump impeller is difficult to cast, has a high product defect rate and poor quality due to narrow flow passage during casting.

[0007] In order to achieve the above functions, the technical solution provided by the present invention is:

[0008] A small flow and low specific speed centrifugal pump impeller comprises blades, a front cover plate, a rear cover plate and a hub, wherein the outlet width b2 of the blades is determined according to the following formula:

[0009] Qd=k1·Qe,

[0010] b2=0.02Ns 0.83 (Qd / n) 1 / 3 ,

[0011] Where:

[0012] Qe - original design rated flow, unit is m 3 / h, and 2≤Qe≤50;

[0013] Qd - new rated flow, in m 3 / h;

[0014] k1 - empirical coefficient, k1 = 1.1 ~ 1.25, take the larger value when Ns is small, and take the smaller value when Ns is large;

[0015] b2 - blade outlet width, in mm;

[0016] Ns - specific speed, no unit, Ns = 10 ~ 60;

[0017] n - rotation speed, in revolutions per minute.

[0018] Preferably, the relationship between the outlet flow cross-sectional area A2 of the impeller and the inlet flow cross-sectional area A1 of the impeller is as follows:

[0019] A2=k2·A1,

[0020] Where:

[0021] K2 - empirical coefficient, k2 = 1.05 ~ 1.25, take the larger value when Ns is small, and take the smaller value when Ns is large.

[0022] Preferably, the blade is provided with a cavity.

[0023] Preferably, the front cover plate and / or the rear cover plate is provided with a window in the middle of the flow channel, and a window cover is welded on the window.

[0024] Preferably, the two edges of the window adjacent to the blade working surface and the blade back surface are respectively obtained by offsetting the blade working surface and the blade back surface toward the flow channel side by a welding distance γ; the arc edge of the window close to the impeller inlet has a diameter of 1.2*D1; the arc edge of the window close to the impeller outlet has a diameter of 0.8*D2; wherein D1 is the impeller inlet diameter, and D2 is the impeller outlet diameter.

[0025] Preferably, a boss is provided at the edge of the window, and a groove corresponding to the boss is provided at the edge of the window cover.

[0026] The beneficial effects of the present invention are:

[0027] 1. By widening the blade outlet width b2, the casting difficulty of the impeller is reduced, demolding and sand cleaning are facilitated, the surface finish and quality are improved, and the hydraulic loss and disc friction loss along the centrifugal pump with small flow and low specific speed are greatly reduced;

[0028] 2. By limiting the impeller outlet flow cross-sectional area A2, it can effectively prevent the problem of serious flow channel diffusion loss;

[0029] 3. By setting cavities in the blades, it is convenient to demould and clean sand, reduce casting defects such as pores, depressions, slag inclusions, cracks, etc., and reduce the thickness of the blades, reduce weight, and reduce manufacturing costs. In addition, after the impeller is reduced in weight, the unbalanced force and centrifugal force of the pump rotor during operation can be reduced, thereby reducing the vibration and noise of the pump rotor, making the pump operation more stable, reliable, and safe, and extending its service life;

[0030] 4. The impeller with small flow and low specific speed has high head, and its outer diameter D2 is generally large. Its flow channel is very narrow and long. Traditional closed impellers are prone to casting defects such as slag inclusion in the flow channel. The tool probe cannot be inserted into it, and it is impossible to clean the sand and slag and polish it smooth. By opening windows on the front cover and / or the rear cover, the slag inclusion in the flow channel can be effectively reduced, which is convenient for sand cleaning and polishing, greatly improving efficiency. Most of the impeller is cast, and it is only partially welded, so its structural strength is almost not reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a plan projection diagram of the impeller of the present invention;

[0032] Figure 2 for Figure 1 Axial section view of

[0033] Figure 3 It is a plane projection diagram of a traditional impeller;

[0034] Figure 4 for Figure 5 Axial section view of

[0035] Figure 5 This is a comparison chart of the performance curves of the new impeller and the traditional impeller. DETAILED DESCRIPTION

[0036] The following is combined with Figure 1 To Attachment Figure 5 The present invention is further described:

[0037] like Figure 1 and Figure 2 The impeller of a centrifugal pump with a small flow rate and a low specific speed shown comprises blades 1, a front cover plate 2, a rear cover plate 3 and a hub 4, wherein the impeller blades 1, the front cover plate 2, the rear cover plate 3 and the hub 4 are manufactured by integral casting.

[0038] The impeller outlet width is b2, the impeller outlet flow cross-sectional area is A2, and the impeller inlet flow cross-sectional area is A1. Among them, the blade outlet width b2 is determined according to the following formula:

[0039] Qd=k1·Qe,

[0040] b2=0.02Ns 0.83 (Qd / n) 1 / 3 ,

[0041] Where:

[0042] Qe - original design rated flow, unit is m 3 / h, and 2≤Qe≤50;

[0043] Qd - new rated flow, in m 3 / h;

[0044] k1 - empirical coefficient, k1 = 1.1 ~ 1.25, take the larger value when Ns is small, and take the smaller value when Ns is large;

[0045] b2 - blade outlet width, in mm;

[0046] Ns - specific speed, no unit, Ns = 10 ~ 60;

[0047] n - rotation speed, in revolutions per minute.

[0048] Through the above formula, the impeller outlet width b2 can be calculated, and other geometric parameters of the impeller can be calculated according to fluid machinery design theory.

[0049] By redesigning the blade outlet width b2, the blade outlet width b2 is widened, thereby reducing the difficulty of impeller casting, facilitating demoulding and sand cleaning, improving surface finish and quality, and greatly reducing the hydraulic loss along the process and disc friction loss of the small flow and low specific speed centrifugal pump.

[0050] Since the impeller of the present invention increases the rated flow rate Qd of the centrifugal pump impeller, in order to prevent serious flow channel diffusion loss problems, the impeller outlet flow cross-sectional area A2 and the impeller inlet flow cross-sectional area A1 are designed according to A2=k2·A1.

[0051] Where:

[0052] K2 - empirical coefficient, k2 = 1.05 ~ 1.25, take the larger value when Ns is small, and take the smaller value when Ns is large.

[0053] The other flow passage sections are gradually transitioned, so that the design obtains the best blade back. The impeller of the present invention can greatly improve the efficiency of the centrifugal pump impeller by increasing the flow design and maintaining the flow passage area ratio design. When designing, the values ​​of K1 and K2 are mainly determined based on the principle of taking a larger value when Ns is small and a smaller value when Ns is large, and then the initial values ​​of K1 and K2 are determined, and then modified based on design experience and CFD simulation calculation analysis results.

[0054] like Figure 1 As shown, the impeller blade 1 adopts a straight blade, and the blade 1 is provided with a cavity 11. This arrangement is conducive to demolding and sand cleaning, and reduces casting defects such as pores, depressions, slag inclusions, cracks, etc. At the same time, it reduces the thickness of the blade 1, reduces the weight, and reduces the manufacturing cost. Secondly, after the impeller is reduced in weight, the unbalanced force and centrifugal force of the pump rotor during operation can be reduced, thereby reducing the vibration and noise of the pump rotor, making the machine pump operation more stable, reliable, and safe, and extending its service life. In this embodiment, a wall thickness of δ is reserved between the blade 1 and the flow passage, and the other parts are hollowed out. The wall thickness is the same as the wall thickness of the front cover plate 2 and the rear cover plate 3.

[0055] like Figure 1 and Figure 2 As shown, the front cover plate 2 and / or the rear cover plate 3 are provided with a window in the middle of the flow channel, and a window cover 5 is welded on the window. In this embodiment, the front cover plate 2 is provided with a window.

[0056] The shape of the window is determined by the following conditions:

[0057] The two edges of the window adjacent to the working surface and the back of the blade are obtained by offsetting the working surface and the back of the blade to the flow channel side by a welding distance γ; the arc edge close to the impeller inlet has a diameter of 1.2*D1; the arc edge close to the impeller outlet has a diameter of 0.8*D2. That is, the two arc edges are obtained by offsetting the impeller inlet and outlet diameters by a distance of 1.2*D1 and 0.8*D2. Among them, D1 is the impeller inlet diameter, and D2 is the impeller outlet diameter. The shape of the window cover 5 is the same as that of the window, and the two are clearance-matched, and then fixed and sealed by welding. The welding distance γ is generally 3 to 7 mm, and is preferably 5 mm in this embodiment.

[0058] like Figure 2 As shown, a boss is provided at the edge of the window, and a groove corresponding to the boss is provided at the edge of the window cover 5.

[0059] The above-mentioned window design makes the impeller blades easier to cast, and is conducive to sand cleaning and smoothing of the flow channel, improving the surface quality of the flow channel and making the hydraulic efficiency higher. Secondly, although the window design is used in the middle cover of the flow channel, most of the impeller parts are still integrally cast, which improves the strength and rigidity of the impeller structure. It is more powerful and stable than other semi-open or fully split impellers, and its strength is equivalent to that of traditional closed impellers. This makes the operation of the centrifugal pump more stable, reliable and safe, and extends its service life.

[0060] Based on the customer's required flow rate Q = 12m 3 / h, head H = 65m, speed n = 2900rpm, Ns = 26.6 as an example, the impeller obtained by the traditional design method (hereinafter referred to as: traditional impeller) has the following shape Figure 3 and Figure 4 As shown, its parameters are:

[0061] Qe=12m 3 / h, He=65m, n=2900rpm, D12=62mm, D22=228mm, b22=5mm,

[0062] A12=265mm 2 ,A22=395mm 2 ,λ=5mm,ηe=46%.

[0063] The impeller of the present invention (hereinafter referred to as the new impeller) has the following parameters: Qd = 14m 3 / h, Hd=65m, n=2900rpm, D1=62mm, D2=228mm, b2=6mm, A1=265mm 2 ,A2=305mm 2 ,δ=5mm,γ=5mm,1.2*D1=75mm,

[0064] 0.8*D2=182mm,ηd=51%.

[0065] From the above parameters, we can see that the outlet width of the two impellers b22<b2. It can be seen that the outlet width of the new impeller is wider, which is more conducive to casting. Figure 5 As shown in the figure, under the premise of meeting the design flow and head requirements, the performance curve of the new impeller is better than that of the traditional impeller as a whole. The performance curve of the new impeller can obtain a wide range of high-efficiency areas under flow conditions, and the efficiency of the performance curve of the new impeller at the equivalent flow point Q=Qe is more than 3% higher than the efficiency value of the original traditional design impeller at Qe, which significantly improves the efficiency.

[0066] The above-described embodiments are only preferred examples of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, any equivalent changes or modifications made according to the structures, features and principles described in the scope of the patent application of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A small flow and low specific speed centrifugal pump impeller, comprising blades, a front cover plate, a rear cover plate and a hub, Features: The outlet width b2 of the blade is determined according to the following formula: Qd = k1·Qe, <h2 style=";text-align:left;direction:ltr">b2=0.02Ns<h2 style=";text-align:left;direction:ltr"> 0.83 <h2 style=";text-align:left;direction:ltr"> (Qd / n)<h2 style=";text-align:left;direction:ltr"> 1 / 3 <h2 style=";text-align:left;direction:ltr"> , Where: Qe - original design rated flow, unit is m 3 / h, and 2≤Qe ≤50; Qd - new rated flow, in m 3 / h; k1 - empirical coefficient, k1 = 1.1 ~ 1.25, take the larger value when Ns is small, and take the smaller value when Ns is large; b2 - blade outlet width, in mm; Ns - specific speed, no unit, Ns = 10 ~ 60; n - speed, in revolutions per minute; The relationship between the impeller outlet flow cross-sectional area A2 and the impeller inlet flow cross-sectional area A1 is as follows: A2= k2•A1, Where: K2 - empirical coefficient, k2 = 1.05 ~ 1.25, take the larger value when Ns is small, and take the smaller value when Ns is large; The blade is provided with a cavity, the front cover plate and / or the rear cover plate is provided with a window in the middle of the flow channel, and a window cover is welded on the window.

2. The small flow and low specific speed centrifugal pump impeller according to claim 1, Features: The two edges of the window adjacent to the blade working surface and the blade back are obtained by offsetting the blade working surface and the blade back toward the flow channel by a welding distance γ; the arc edge of the window close to the impeller inlet has a diameter of 1.2*D1; the arc edge of the window close to the impeller outlet has a diameter of 0.8*D2; wherein D1 is the impeller inlet diameter, and D2 is the impeller outlet diameter.

3. The small flow and low specific speed centrifugal pump impeller according to claim 1, Features: The edge of the window is provided with a boss, and the edge of the window cover is provided with a groove corresponding to the boss.

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