A design method and application of a non-overload impeller for a low specific speed fire pump

Abstract

The present invention relates to a method and application for designing a non-overload impeller for a low specific speed fire pump, the method comprising: calculating the specific speed when the design point flow, design point head, and speed of the fire pump are known; using the speed coefficient method to design the impeller axial surface, including the impeller inlet diameter, impeller outlet width, impeller outlet diameter, number of blades, and blade inlet edge position; on the determined impeller axial surface, taking the front cover plate, rear cover plate, and intermediate streamlines, and dividing the impeller axial surface into streamline points; determining blade parameters, including blade inlet angle, blade outlet angle, and blade wrap angle; drawing a design streamline grid for the blade working surface and back surface respectively according to the above steps; and determining the throat area of ​​the pump body according to the designed impeller. The present invention more accurately controls the flow state of the liquid flow on the blade surface, makes the flow more closely fit the trend of the blade profile, reduces flow loss, and avoids impact and vortex; meets the requirements of high efficiency and energy saving, and realizes the stable operation of the fire pump without overload.

Description

Technical Field

[0001] The present invention relates to an impeller design method and application, and in particular to a non-overload impeller design method for a low-specific-speed fire pump, which enables the fire pump performance curve to meet the performance requirements of multiple operating points while not exceeding the design power at any point on the flow-head performance curve and its application. Background Art

[0002] As a crucial safety device in fire water supply and fire hydrant systems, fire pumps are subject to high performance requirements due to the special circumstances of their use. Different from the GB6245-2006 "Fire Pump" technical standard, the new GB50974-2014 "Technical Specification for Fire Water Supply and Fire Hydrant Systems" imposes stricter technical requirements on fire pump characteristic curves: the pump's dead-point pressure cannot exceed 140% of the design working pressure and should be greater than 120% of the design working pressure; fire pumps can operate at 150% of the design flow rate, and the outlet pressure at this time cannot be lower than 65% of the design pressure. Furthermore, the design power cannot be exceeded at any point on the flow-head performance curve.

[0003] In the design and application of fire pumps, the impeller is a core component, and its performance directly affects the efficiency and reliability of the fire pump. Especially for low-specific speed fire pumps, the traditional impeller design has certain limitations, and overload occurs at 1.5 times or even 1.3 times the flow rate.

[0004] The characteristic curve of the low specific speed centrifugal impeller is relatively flat. At present, in order to meet the steep performance curve trend of the low specific speed fire pump, a smaller outlet angle β2 is usually selected. If the traditional impeller thickening method is still used, the outlet angle on the back of the blade will be further reduced, making the flow channel of the liquid on the back of the blade narrower, intensifying the impact of the liquid flow, thereby reducing the hydraulic efficiency of the impeller and uneven pressure distribution on the back, increasing the risk of overload.

[0005] The existing technology has many shortcomings in the design of low specific speed fire pump impellers:

[0006] 1. Thickening the blades results in a smaller blade outlet angle on the back side, worsening the flow state on the back side, increasing energy loss, uneven pressure distribution causing overload risks, and increased impeller stress, shortening the service life;

[0007] 2. The no-overload characteristic of the power curve is not ideal. Even if a power extreme point appears, it often occurs at the critical point where cavitation occurs at a large flow rate. This is relatively dangerous in engineering applications and will make the operating state of the pump difficult to control.

[0008] Therefore, it is particularly important to develop a new design method for a low specific speed fire pump impeller without overload. Summary of the Invention

[0009] In response to the above problems, the main purpose of the present invention is to provide a method and application for designing a non-overload impeller for a low-specific speed fire pump, which ensures that the fire pump performance curve meets the performance requirements of multiple operating points while not exceeding the design power at any point on the flow-head performance curve.

[0010] The present invention solves the above technical problems through the following scheme: a method for designing a non-overload impeller for a low specific speed fire pump, the method comprising the following steps:

[0011] (1) Given the design point flow rate Q, design point head H, and speed n of the fire pump, calculate the specific speed n s :

[0012] ;

[0013] (2) Based on the parameters in step (1), the velocity coefficient method is used to design the impeller axial surface, including the impeller inlet diameter D1, the impeller outlet width b2, the impeller outlet diameter D2, the number of blades Z, and the blade inlet edge position;

[0014] (3) On the impeller axial surface determined in step (2), take the front cover, rear cover and middle streamlines, and divide the impeller axial surface into streamline points to provide a basis for drawing the streamline grid later;

[0015] (4) Determine the blade parameters, including the blade inlet angle β1, the blade outlet angle β2, and the blade wrap angle θ;

[0016] Based on the above steps (3) and (4), a streamline grid is drawn, which is a smooth curve consisting of the blade inlet angle, blade outlet angle and wrap angle, with a linear angle change from β1 to β2. The formula is as follows:

[0017] ,

[0018] ,

[0019] Where: β—angle corresponding to each streamline unit, β1—blade inlet angle, β2—blade outlet angle, Δu—streamline divided into n units of equal length, L u —Circumferential flow length (wrapped angle), L m —the length corresponding to the axial section, Δm—the spacing under the corresponding unit angle;

[0020] (5) According to the above steps, the streamline grid is drawn on the working surface and the back surface of the blade respectively, replacing the conventional blade thickening method;

[0021] (6) According to the designed impeller, determine the throat area of ​​the pump body and ensure that the area ratio Y = 0.8 ~ 1.2, where Y is the ratio of the pump body throat area to the impeller outlet area.

[0022] In a specific embodiment of the present invention, the number of blades Z in step (2) is 4 to 6.

[0023] In a specific embodiment of the present invention, the blade inlet angle β1 in step (4) is calculated based on the velocity triangle, with a value range of β1 = 15° to 35°; the impeller inlet angle of attack adopts a positive angle of attack Δβ1 = 3° to 8°.

[0024] In a specific embodiment of the present invention, the blade outlet angle β2 in step (4) ranges from 13° to 17°.

[0025] In a specific embodiment of the present invention, in step (4), according to the principle of small outlet angle and large wrap angle, the wrap angle range θ is 150° to 220°.

[0026] In a specific embodiment of the present invention, in step (5), the front cover plate streamlines, the middle streamlines and the rear cover plate streamlines are selected to draw the streamline grid according to the characteristic that the outlet width of the low specific speed impeller is relatively narrow.

[0027] In a specific implementation example of the present invention, in step (6), Y=1.0.

[0028] An application of a low-specific-speed fire pump with an overload-free impeller includes: using the low-specific-speed fire pump in fire protection systems of high-rise buildings and factories to solve the problem of continuous increase in shaft power and easy overpower leading to motor burnout when the flow rate increases under low-head conditions. The low-specific-speed fire pump can operate stably in the event of a fire, ensuring the reliability of the fire water supply.

[0029] In large complexes and smart parks, the Internet of Things fire water supply unit with this low-speed ratio fire pump as the core is used, combined with intelligent inspection and remote monitoring functions to achieve intelligent management of the fire protection system.

[0030] The positive progress of the present invention is that the design method and application of the low specific speed fire pump non-overload impeller proposed by the present invention have the following advantages:

[0031] 1. The present invention optimizes the design parameters of a low specific speed fire pump. The present invention establishes velocity triangles on the working surface and back surface of the blade respectively, draws a streamline grid, and adopts a design method in which the outlet angle of the back surface of the blade is greater than the outlet angle of the working surface of the blade, thereby replacing the conventional blade offset thickening method.

[0032] 2. By designing the working surface and back surface of the blade separately, the present invention can more accurately control the flow state of the liquid on the blade surface, make the flow more closely follow the trend of the blade profile, reduce flow loss, and avoid impact and vortex.

[0033] 3. The low-speed fire pump designed by the present invention will not have overload problems at any flow point in the full flow range. The low-speed fire pump designed by the present invention meets the requirements of high efficiency and energy saving, and realizes stable operation of the fire pump without overload. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the streamline grid in the present invention.

[0035] Figure 2 Impeller shaft cross section for the application case.

[0036] Figure 3 Blade streamline grid for application case.

[0037] Figure 4 This is the performance curve of the application case. DETAILED DESCRIPTION

[0038] The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings to illustrate the technical solutions of the present invention in detail.

[0039] Figure 1 is the streamline grid in the present invention, Figure 2 For the application case impeller shaft section, Figure 3 For the application case blade streamline grid, Figure 4 This is the performance curve of the application case. Figure 1-4 As shown: The present invention proposes a method for designing a non-overload impeller for a low specific speed fire pump, and the method comprises the following steps:

[0040] (1) Given the design point flow rate Q, design point head H, and speed n of the fire pump, calculate the specific speed n s :

[0041] ;

[0042] (2) Based on the parameters in step (1), the velocity coefficient method is used to design the impeller axial surface, including the impeller inlet diameter D1, the impeller outlet width b2, the impeller outlet diameter D2, the number of blades Z, and the blade inlet edge position;

[0043] (3) On the impeller axial surface determined in step (2), take the front cover, rear cover and middle streamlines, and divide the impeller axial surface into streamline points to provide a basis for drawing the streamline grid later;

[0044] (4) Determine the blade parameters, including the blade inlet angle β1, the blade outlet angle β2, and the blade wrap angle θ;

[0045] On the basis of the above steps (3) and (4), a streamline grid is drawn, i.e., a smooth curve consisting of the blade inlet angle, blade outlet angle, and wrap angle, which changes linearly from β1 to β2. The formula is as follows:

[0046] ,

[0047] ,

[0048] Where: β—angle corresponding to each streamline unit, β1—blade inlet angle, β2—blade outlet angle, Δu—streamline divided into n units of equal length (usually Δu=5mm), L u —Circumferential flow length (wrapped angle), L m —The length of the axial section (the projection of the streamline in the axial section), Δm—the spacing under the corresponding unit angle;

[0049] (5) According to the above steps, the streamline grid is drawn on the working surface and the back surface of the blade respectively, replacing the conventional blade thickening method;

[0050] (6) According to the designed impeller, determine the throat area of ​​the pump body and ensure that the area ratio Y = 0.8 ~ 1.2, where Y is the ratio of the pump body throat area to the impeller outlet area.

[0051] In a specific implementation process, the number of blades Z in the above step (2) is 4 to 6.

[0052] The blade inlet angle β1 in the above step (4) can be calculated based on the velocity triangle, with a value range of β1 = 15° to 35°. At the same time, in order to improve the anti-cavitation ability of large flow rates, the impeller inlet angle adopts a positive angle Δβ1 = 3° to 8°.

[0053] In the above step (4), the blade outlet angle β2 directly affects the changing trend of the power curve. The smaller the blade outlet angle β2 is, the flatter the power curve is, and it is very easy for the power extreme point to appear in the large flow range. However, the blade outlet angle β2 is not the smaller the better. Too small β2 will lead to an increase in the outer diameter of the impeller, thereby increasing the friction loss of the disk. Here, it is recommended that the value range of β2 be 13° to 17°.

[0054] In the above step (4), according to the principle of small outlet angle and large wrap angle, the wrap angle range is θ = 150° ~ 220°.

[0055] In the above step (5), according to the relatively narrow outlet width of the low specific speed impeller, the front cover streamlines, the middle streamlines and the rear cover streamlines are usually selected to draw the streamline grid.

[0056] The above step (6) specifies the ratio of the pump throat area to the impeller outlet area. The throat area is one of the key channels for liquid flow in the pump. Although a throat area that is too small can easily cause the flow head curve to reach a steep drop, it will limit the amount of liquid passing through, not only making it more likely for cavitation to occur at high flow rates, but also causing greater hydraulic losses, reducing overall efficiency, and making it more likely to overload. This design concept does not recommend using a smaller throat area to control the flow head curve trend.

[0057] The following are specific implementation examples:

[0058] The invention proposes a design method for a non-overload impeller of a low specific speed fire pump. Figure 2 For the application case impeller shaft section, Figure 3 For the application case blade streamline grid, Figure 4 This is the performance curve of the application case.

[0059] The design flow rate is 80L / s, the design head is 153m, and the design speed is 2960r / min.

[0060] ;

[0061] Determine the impeller shaft section design parameters according to the speed coefficient method:

[0062] The optimal number of blades Z=5;

[0063] The preferred throat area ratio Y=1.1.

[0064] Since this design method is to design the working surface and back surface of the blade separately, the blade parameters of the working surface and back surface need to be determined separately:

[0065] Working surface parameters are determined: inlet angle β1=20, outlet angle β2=14

[0066] Back parameter determination: inlet angle β1=17, outlet angle β2=17

[0067] Wrap angle θ = 205°

[0068] Based on the determined blade parameters and the front cover streamlines, middle streamlines, and rear cover streamlines of the impeller shaft section, the streamline grids of the blade working surface and back surface are drawn using the formula provided in step (4), as follows Figure 3 shown.

[0069] Figure 4 This is the test performance curve of the fire pump using this design method. The design point head H = 156.7m, the dead point head H0 = 180m, and 1.5 times the design point head H 1.5 =107.6m, H1.5 / H=107.6 / 156.7=0.69, H0 / H=180 / 156.7=1.15, power extreme value P max =187.1Kw, the flow rate at the power extreme point is 1.6 times the design flow rate, which fully meets the requirement that the pump pressure at the dead point cannot be higher than 140% of the design working pressure, and the pump operates at 150% of the design flow rate, and the outlet pressure at this time is not lower than 65% of the design pressure. At the same time, the design power cannot be exceeded at any point on the flow-head performance curve.

[0070] The present invention proposes an application of a low-specific-speed fire pump with an overload-free impeller. The application includes: using the low-specific-speed fire pump in fire protection systems of high-rise buildings and factories can solve the problem of continuous increase in shaft power and easy overpower leading to motor burning when the flow rate increases under low-head conditions. The pump can operate stably when a fire occurs, ensuring the reliability of fire water supply.

[0071] In large complexes and smart parks, the Internet of Things fire water supply unit with this low-speed ratio fire pump as the core is used, combined with intelligent inspection and remote monitoring functions to achieve intelligent management of the fire protection system.

[0072] The present invention optimizes the design parameters of a low specific speed fire pump. The present invention establishes velocity triangles on the working surface and back surface of the blade respectively, draws a streamline grid, and adopts a design method in which the outlet installation angle of the back surface of the blade is greater than the outlet installation angle of the working surface of the blade, thereby replacing the conventional blade offset thickening method.

[0073] By designing the working surface and back surface of the blade separately, the present invention can more accurately control the flow state of the liquid on the blade surface, make the flow more closely follow the trend of the blade profile, reduce flow loss, and avoid impact and vortex.

[0074] The low specific speed fire pump designed by the present invention can operate at any flow point within the full flow range without overload problems. The low specific speed fire pump designed by the present invention meets the requirements of high efficiency and energy saving, and realizes stable operation of the fire pump without overload.

[0075] The basic principles, main features and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention, which is defined by the appended claims and their equivalents.

Claims

1. A method for designing a non-overload impeller for a low specific speed fire pump, characterized by: The design method of the non-overload impeller of the low specific speed fire pump includes the following steps: (1) Given the design point flow rate Q, design point head H, and speed n of the fire pump, calculate the specific speed n s : ； (2) Based on the parameters in step (1), the velocity coefficient method is used to design the impeller axial surface, including the impeller inlet diameter D1, the impeller outlet width b2, the impeller outlet diameter D2, the number of blades Z, and the blade inlet edge position; (3) On the impeller axial surface determined in step (2), take the front cover, rear cover and middle streamlines, and divide the impeller axial surface into streamline points to provide a basis for drawing the streamline grid later; (4) Determine the blade parameters, including the blade inlet angle β1, the blade outlet angle β2, and the blade wrap angle θ; Based on the above steps (3) and (4), a streamline grid is drawn, which is a smooth curve consisting of the blade inlet angle, blade outlet angle and wrap angle, with a linear angle change from β1 to β2. The formula is as follows: ， ， Where: β—angle corresponding to each streamline unit, β1—blade inlet angle, β2—blade outlet angle, Δu—streamline divided into n units of equal length, L u —Circumferential flow length, L m —the length corresponding to the axial section, Δm—the spacing under the corresponding unit angle; (5) According to the above steps, streamline grids are drawn on the working surface and back surface of the blade respectively, replacing the conventional blade thickening method; (6) According to the designed impeller, determine the throat area of ​​the pump body and ensure that the area ratio Y = 0.8 ~ 1.2, where Y is the ratio of the pump body throat area to the impeller outlet area.

2. The method for designing a non-overload impeller for a low specific speed fire pump according to claim 1, characterized in that: In step (2), the number of leaves Z is 4 to 6.

3. The method for designing a non-overload impeller for a low specific speed fire pump according to claim 1, characterized in that: In step (4), the blade inlet angle β1 is calculated based on the velocity triangle, and the value range is β1 = 15° to 35°; the impeller inlet angle of attack adopts the positive angle Δβ1 = 3° to 8°.

4. The method for designing a non-overload impeller for a low specific speed fire pump according to claim 1, characterized in that: The blade outlet angle β2 in step (4) ranges from 13° to 17°.

5. The method for designing a non-overload impeller for a low specific speed fire pump according to claim 1, characterized in that: In the step (4), according to the principle of small outlet angle and large wrap angle, the wrap angle range θ is 150° to 220°.

6. The method for designing a non-overload impeller for a low specific speed fire pump according to claim 1, characterized in that: In the step (5), according to the characteristic that the outlet width of the low specific speed impeller is relatively narrow, the front cover streamlines, the middle streamlines and the rear cover streamlines are selected to draw the streamline grid.

7. The method for designing a non-overload impeller for a low specific speed fire pump according to claim 1, characterized in that: In step (6), Y=1.

0.

8. Application of a low specific speed fire pump non-overload impeller designed by the design method of any one of claims 1 to 7, characterized in that: The applications include: using the low-speed ratio fire pump in fire protection systems of high-rise buildings and factories; and using an IoT fire water supply unit with the low-speed ratio fire pump as the core in large complexes and smart parks.

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