Impeller design method for low-specific-speed fire pump

Abstract

The invention discloses an impeller design method for a low-specific-speed fire pump, which comprises the following steps of: calculating parameters of an impeller by adopting given design parameters of the fire pump, and obtaining the thickness delta 2 of an outlet side of the impeller by calculating an outlet displacement coefficient psi 2 of the impeller so as to increase the thickness delta 2 of the outlet side, so that a lift curve is suddenly reduced; noise and vibration, caused by the curve hump phenomenon, of the fire pump are effectively eliminated, the safety and reliability of the fire pump are improved, meanwhile, the outlet width b2, the outlet placement angle beta2 and the blade wrap angle # imgabs0 # of the impeller are determined within a certain range, so that the parameters of the impeller have the adjusting space, the outlet width b2 and the outlet placement angle beta2 are increased, and therefore the impeller can be adjusted conveniently. When the blade wrap angle # imgabs 1 # is reduced, the manufacturing difficulty of the impeller can be effectively reduced, the manufacturing cost is reduced, further, the impeller design method for the low-specific-speed fire pump can reduce diffusion loss in an impeller runner, and the efficiency of the impeller is effectively improved; and the pump shaft power is reduced, energy is effectively saved, and long-term stable operation of the pump is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of fire pumps, and in particular to an impeller design method for a low specific speed fire pump. Background Art

[0002] According to the provisions of my country's national standard for fire pumps GB / T6245-2006, fire pumps should meet the following requirements: (1) When meeting the rated flow rate Qn, the rated pressure Pn requirement should be met, and the working pressure should not exceed 1.05 times the rated pressure; (2) When the flow rate is 1.5Qn, the working pressure should not be less than 0.65Pn; (3) The maximum working pressure shall not exceed 1.4Pn.

[0003] At the same time, the no-overload characteristic means that the power curve rises very slowly with the increase of flow rate. More ideally, when the flow rate increases to a certain value, the power will not increase any further, but will decrease instead. In the entire range from 0 flow rate to maximum flow rate, when the fire pump is running at any operating point, the power will not exceed the motor power and cause the pump to overload, thereby improving the reliability of the fire pump.

[0004] The existing low specific speed fire pump impeller is usually directly calculated and designed according to the speed coefficient method. In order to meet the national standards to ensure that the fire pump head curve does not have a hump, and to achieve the non-overload characteristics of the low specific speed fire pump under full flow conditions, the impeller parameters are often taken as a smaller number of blades Z, a smaller outlet width b2, an outlet placement angle β2 and a larger blade wrap angle. The range of values ​​of other hydraulic parameters is often large, and it is impossible to determine whether the design scheme is overpowered, which leads to a long design cycle and high manufacturing costs. The impeller performance using this parameter is not ideal, which easily leads to a hump in the head curve, causing noise and vibration in the fire pump. At the same time, the impeller outlet width b2, outlet placement angle β2 and blade wrap angle The lack of adjustable space increases the difficulty of manufacturing the impeller, thereby making the manufacturing cost of the impeller higher.

[0005] Therefore, how to effectively improve the safety and reliability of fire pumps, make fire pumps meet the rated head and power peak requirements, and reduce the impeller manufacturing cost has become an urgent problem to be solved in this field. Summary of the invention

[0006] In view of the defects of the prior art, the purpose of the present invention is to provide an impeller design method for a low specific speed fire pump based on the existing design system, which can improve the safety and reliability of the fire pump, enable the fire pump to meet the rated head and power peak requirements, and reduce the impeller manufacturing cost.

[0007] In order to achieve the above object, the present invention provides a method for designing an impeller for a low specific speed fire pump, wherein the given design parameters of the fire pump include a rated flow rate Q n , Design pressure P n , design lift H, speed n and matching motor power p, the design method includes:

[0008] S1: Calculate the specific speed n of the fire pump according to the given design parameters of the fire pump s ,

[0009]

[0010] Among them, Q is the rated flow Q n ,

[0011] H is the design head H given by the fire pump,

[0012] S2: Determine the outer diameter D2 of the impeller,

[0013]

[0014] Among them, Q is the rated flow Q n ,

[0015] S3: Determine that the number of blades Z of the impeller is 4 to 5, and determine the blade wrap angle of the impeller It is 140°~170°.

[0016] S4: Determine the inlet diameter D of the impeller j ,

[0017]

[0018] Among them, d h is the hub diameter of the impeller,

[0019] D0 is the inlet equivalent diameter of the impeller,

[0020] S5: Determine the outlet width b2 of the impeller,

[0021]

[0022] S6: Determine that the outlet placement angle β2 of the impeller is 14° to 16°,

[0023] S7: Determine that the thickness δ1 of the blade inlet edge of the impeller is 3 mm,

[0024] S8: Determine the thickness δ2 of the blade outlet edge of the impeller,

[0025]

[0026] Wherein, Ψ2 is the outlet displacement coefficient of the impeller,

[0027]

[0028] λ2 is the angle between the impeller outlet axial section and the streamline, and is set to λ2 = 70° to 90°.

[0029] S9: Calculate the maximum shaft power P of the fire pump max ,

[0030]

[0031] Among them, η m is the mechanical efficiency,

[0032] K3 is the correction coefficient, take K3 = 1.0 ~ 1.1,

[0033] h0 is the slip coefficient,

[0034] u2 is the circumferential velocity of the impeller outlet,

[0035] S10: Compare the maximum shaft power P of the fire pump obtained by S9 max With the given matching motor power p of the fire pump, when P max ≤p, output the outer diameter D2, number of blades Z, and blade wrap angle of the impeller Inlet diameter D j , outlet width b2, outlet placement angle β2, blade inlet edge thickness δ1 and blade outlet edge thickness δ2, otherwise repeat S1 to S10.

[0036] Further, the outlet width b2 obtained in S5 takes a larger value within the range of the outlet width b2.

[0037] Further, the outlet placement angle β2 obtained in S6 takes a larger value within the range of the outlet placement angle β2.

[0038] Further, the outlet crowding coefficient Ψ2 obtained in S8 takes a smaller value within the range of the outlet crowding coefficient Ψ2.

[0039] The impeller design method for a low specific speed fire pump provided by the present invention uses the design parameters given by the fire pump to calculate the parameters of the impeller, and obtains the outlet edge thickness δ2 of the impeller by calculating the outlet crowding coefficient Ψ2 of the impeller, so as to increase the outlet edge thickness δ2, thereby making the head curve drop steeply, effectively eliminating the noise and vibration of the fire pump caused by the curve hump phenomenon, and improving the safety and reliability of the fire pump. At the same time, the outlet width b2, outlet placement angle β2 and blade wrap angle of the impeller are Determine the value within a certain range to allow the impeller parameters to be adjusted, increase the outlet width b2, outlet placement angle β2, and reduce the blade wrap angle It can effectively reduce the difficulty of impeller manufacturing and reduce manufacturing costs.

[0040] Furthermore, the impeller design method for a low specific speed fire pump provided by the present invention can reduce diffusion losses in the impeller flow channel, effectively improve impeller efficiency; and reduce pump shaft power, effectively saving energy, which is more conducive to the long-term stable operation of the pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0042] Figure 1a , Figure 1b and Figure 1c A schematic diagram of impeller parameters in the impeller design method for a low specific speed fire pump provided by the present invention.

[0043] Figure 2 A flow chart of the impeller design method for a low specific speed fire pump provided by the present invention;

[0044] Figure 3 A schematic diagram of a blade in an embodiment of the present invention; DETAILED DESCRIPTION

[0045] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below with reference to specific diagrams.

[0046] The impeller design method for a low specific speed fire pump provided by the present invention obtains the impeller parameters according to the given design parameters of the fire pump, and obtains the outlet edge thickness δ2 of the impeller by calculating the outlet crowding coefficient Ψ2 of the impeller, so as to increase the outlet edge thickness δ2, thereby making the head curve drop steeply, effectively eliminating the noise and vibration of the fire pump caused by the curve hump phenomenon, and improving the safety and reliability of the fire pump. At the same time, the outlet width b2, outlet placement angle β2 and blade wrap angle of the impeller are Determine the value within a certain range to allow the impeller parameters to be adjusted, increase the outlet width b2, outlet placement angle β2, and reduce the blade wrap angle It can effectively reduce the difficulty of impeller manufacturing and reduce manufacturing costs.

[0047] Specifically, the given design parameters of the fire pump include the rated flow rate Q n , Design pressure P n , design lift H, speed n and matching motor power p, combined Figure 1a to Figure 1c , this design method includes:

[0048] S1: Calculate the specific speed n of the fire pump based on the given design parameters of the fire pump s ,

[0049]

[0050] Among them, Q is the rated flow Q given by the fire pump n , H is the given design head H of the fire pump,

[0051] S2: The specific speed n of the fire pump obtained according to S1 s Determine the outer diameter D2 of the impeller,

[0052]

[0053] Among them, Q is the rated flow Q n ,

[0054] S3: Determine the number of impeller blades Z to be 4 to 5, and determine the impeller blade wrap angle It is 140°~170°.

[0055] Most existing low specific speed pumps have 6 blades. In this design method, in order to obtain a steeply falling HQ curve (corresponding to a flat shaft power curve), reducing the number of blades Z is one of the effective measures. In low specific speed pumps, due to the small outlet placement angle β2, the blade wrap angle Too many blades Z will lead to a narrow and long flow channel and serious blockage; too few blades Z will not be able to effectively control the fluid, resulting in unsatisfactory impeller performance. Therefore, selecting 4 to 5 impeller blades Z can satisfy the requirement of a relatively flat shaft power curve while effectively controlling the fluid.

[0056] In order to obtain a steeply falling HQ curve, a smaller number of blades Z and a smaller outlet placement angle β2 are selected so that the blade wrap angle Larger, but the blade angle Too large will lead to complicated manufacturing and increase manufacturing costs. Therefore, the blade wrap angle is selected When the angle is 140° to 170°, the performance and manufacturing cost of the impeller are ideal.

[0057] S4: Determine the impeller inlet diameter D j ,

[0058]

[0059] Among them, d h is the hub diameter of the impeller,

[0060] D0 is the equivalent diameter of the impeller inlet. The area of ​​the circle with D0 as the diameter is equal to the effective area of ​​the impeller inlet after removing the hub, that is, From this we can get

[0061] S5: Determine the outlet width b2 of the impeller,

[0062]

[0063] Among them, the outlet width b2 takes a larger value within the range of outlet width b2 to increase the outlet flow of the impeller, reduce the fluid volume borne by each blade, increase the water pressure, increase the head, and thus improve the efficiency of the fire pump. At the same time, appropriately increasing the outlet width b2 reduces the fluid velocity, thereby reducing the noise level, reducing the vibration and wear of the fire pump, and making the impeller easier to manufacture.

[0064] S6: Determine the impeller outlet placement angle β2 to be 14° to 16°,

[0065] The outlet installation angle β2 takes a larger value within the range of the outlet installation angle β2. The outlet installation angle β2 is appropriately increased to improve the lift and efficiency of the fire pump and reduce the manufacturing difficulty of the impeller.

[0066] S7: To reduce manufacturing costs and ensure that the impeller inlet edge thickness δ1 can meet the impeller inlet inflow conditions, the impeller blade inlet edge thickness δ1 is determined to be 3 mm.

[0067] S8: Determine the impeller blade outlet edge thickness δ2.

[0068] Since the outlet displacement coefficient Ψ2, that is, the ratio of the fluid volume displaced by the blade at a certain inlet flow rate and speed, is an important parameter for measuring the impeller's drainage capacity and the efficiency of the fire pump, the outlet edge thickness δ2 of the blade is determined by the outlet displacement coefficient Ψ2.

[0069] Specifically, the export crowding coefficient Ψ2 is

[0070]

[0071] The smaller the outlet displacement coefficient Ψ2 is, the less fluid the blades displace, and the fire pump can transport the fluid more efficiently. In order to obtain a steep head curve and a power curve with a peak value, the outlet displacement coefficient Ψ2 takes a smaller value in the range of the outlet displacement coefficient Ψ2.

[0072] Furthermore, the blade outlet edge thickness δ2 is determined by the outlet crowding coefficient Ψ2, and the blade outlet edge thickness δ2 is

[0073]

[0074] Among them, λ2 is the angle between the impeller outlet axial section and the streamline, and λ2=70°~90°,

[0075] At the same time, in order to obtain a steep head curve and a power curve with a peak value, the blade outlet edge thickness δ2 takes a larger value within the blade outlet edge thickness δ2 range, and the blade outlet edge thickness δ2 is appropriately thickened to make the blade inlet to outlet evenly thickened to block part of the impeller flow channel, reduce the vortex flow area in the blade wake area, make the flow between the blades tend to be consistent, improve the fluid flow state, and help improve the efficiency of the fire pump.

[0076] Furthermore, the blade outlet edge thickness δ2 is appropriately increased to reduce the impeller planar flow area. In order to maintain sufficient flow area, the impeller outlet width b2 determined in S5 and the outlet placement angle β2 determined in S5 are also appropriately increased, so that S5, S6 and S8 cooperate to calculate the impeller outlet width b2, outlet placement angle β2 and blade outlet edge thickness δ2. While maintaining sufficient flow area, it can also improve the impeller manufacturing process and improve manufacturing efficiency.

[0077] S9: Calculate the maximum shaft power P of the fire pump max .

[0078]

[0079] Among them, η m is the mechanical efficiency,

[0080] k3 is the correction coefficient, take K3 = 1.0 ~ 1.1,

[0081] h0 is the slip coefficient,

[0082] u2 is the circumferential velocity of the impeller outlet,

[0083] S10: Compare the maximum shaft power P of the fire pump obtained by S9 max The matching motor power p given with the fire pump.

[0084] In order to achieve energy-saving and efficient use of fire pumps, fire pumps should be operated at their rated operating point (i.e., the highest efficiency point) as much as possible. At the same time, the shaft power of the fire pump will change with the increase and decrease of flow or head. Therefore, the maximum shaft power P of the fire pump max It must be no greater than the power p of the matching motor given by the fire pump so that the fire pump can maintain stable operation even when operating under non-optimal conditions.

[0085] Therefore, combined with Figure 2 , when P max ≤p, the impeller parameters meet the fire pump operation requirements, the output impeller outer diameter D2, blade number Z, blade wrap angle Inlet diameter D j, outlet width b2, outlet placement angle β2, blade inlet edge thickness δ1 and blade outlet edge thickness δ2,

[0086] If the maximum shaft power of the fire pump P max Does not satisfy P max When ≤p, repeat S1 to S10 to adjust the impeller parameters until the impeller parameters meet the fire pump operation requirements.

[0087] Furthermore, the impeller parameters can be max Under the condition of ≤p, adjustments are made within a certain range to reduce the difficulty and cost of impeller manufacturing.

[0088] Combination Figure 3 The following examples illustrate the working process of the present invention in a specific application. It should be noted that the content described below is only a specific application example of the present solution and does not constitute a limitation to the present solution.

[0089] In this example, the design parameters of the fire pump are: design pressure P n =1.86MPa, rated flow rate Q n =144m3 / h, speed n=2960rpm, matching motor power p=160kW.

[0090] Impeller design methods include:

[0091] S1: Calculate the specific speed n of the fire pump s ,

[0092]

[0093] S2: Determine the outer diameter D2 of the impeller,

[0094] Take D2 = 395 mm;

[0095] S3: Determine the number of impeller blades Z and blade wrap angle Select the number of blades Z as 5 and the blade wrap angle is 150°;

[0096] S4: Determine the impeller inlet diameter D j ,

[0097] Take the impeller hub diameter d h =60mm,

[0098] Impeller inlet equivalent diameter

[0099] thus, Take the impeller inlet diameter D j =120mm;

[0100] S5: Determine the outlet width b2 of the impeller,

[0101]

[0102] Take the larger value of the outlet width b2 within the range, that is, take the outlet width b2 = 12mm;

[0103] S6: Determine that the blade outlet placement angle β2 is 14° to 16°, and select the largest value of the outlet placement angle β2 within the range of 16°;

[0104] S7: Determine that the thickness δ1 of the impeller blade inlet edge is 3 mm;

[0105] S8: Determine the impeller blade outlet edge thickness δ2:

[0106] First, calculate the export crowding-out coefficient Ψ2,

[0107] Depend on It can be obtained that 0.84≤Ψ<1,

[0108] Take the smaller value of the export crowding coefficient Ψ2 within the range, that is, take the export crowding coefficient Ψ2 = 0.84,

[0109] Take the angle λ2 between the impeller outlet axial section and the streamline as 90°.

[0110] From this we can get, Take δ2 = 15 mm,

[0111] S9: Calculate the maximum shaft power P of the fire pump max .

[0112] Mechanical efficiency

[0113] Correction coefficient K3 = 1.0 ~ 1.1, take K3 = 1.1,

[0114] Slip coefficient

[0115] Impeller outlet peripheral speed

[0116] From this we can get,

[0117] S10: P max ≤p, output impeller parameters: impeller outer diameter D2 = 395mm, blade number Z is 5, blade wrap angle is 150°, the impeller inlet diameter D j =120mm, outlet width b2=12mm, outlet placement angle β2=16°, blade inlet edge thickness δ1=3mm, blade outlet edge thickness δ2=15mm.

[0118] Therefore, the impeller parameters are determined by this design method.

[0119] In order to specifically illustrate that the impeller parameters determined by this design method can obtain a steep head curve and a relatively flat shaft power curve, and improve efficiency, the impeller parameters in this example are compared with the impeller parameters directly obtained by the existing design method according to the speed coefficient method. The specific comparison results are as follows:

[0120] Table 1. Fire pump design parameter comparison table

[0121]

[0122] Table 2. Impeller parameter comparison table

[0123]

[0124] Table 3. Fire pump performance comparison table

[0125]

[0126] Among them, Table 1 shows the fire pump design parameters corresponding to the impeller parameters of this example and the existing impeller parameters, respectively; Table 2 shows the impeller parameters determined by the present design method and the impeller parameters directly determined by the existing design method according to the speed coefficient method in this example, respectively; Table 3 shows the fire pump performance corresponding to the impeller parameters of this example and the existing impeller parameters, respectively.

[0127] From Tables 1 to 3, it can be seen that in this example, the fire pump corresponding to the impeller parameters obtained by the present design method, compared with the fire pump corresponding to the existing impeller parameters, under the same flow rate, the impeller parameters of this example can achieve a steep head, and the shaft power is relatively flat, and the efficiency is high. Therefore, the impeller parameters obtained by the present design method can effectively improve the performance of the fire pump, obtain a steep head curve and a relatively flat shaft power curve, and improve efficiency.

[0128] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for designing an impeller for a low specific speed fire pump, characterized in that: The given design parameters of the fire pump include the rated flow rate Q n , Design pressure P n , design lift H, speed n and matching motor power p, the design method includes: S1: Calculate the specific speed n of the fire pump according to the given design parameters of the fire pump s , Among them, Q is the rated flow Q n , H is the design head H given by the fire pump, S2: Determine the outer diameter D2 of the impeller, Among them, Q is the rated flow Q n , S3: Determine that the number of blades Z of the impeller is 4 to 5, and determine the blade wrap angle of the impeller It is 140°~170°. S4: Determine the inlet diameter D of the impeller j , Among them, d h is the hub diameter of the impeller, D0 is the inlet equivalent diameter of the impeller, S5: Determine the outlet width b2 of the impeller, S6: Determine that the outlet placement angle β2 of the impeller is 14° to 16°, S7: Determine that the thickness δ1 of the blade inlet edge of the impeller is 3 mm, S8: Determine the thickness δ2 of the blade outlet edge of the impeller, Wherein, Ψ2 is the outlet displacement coefficient of the impeller, λ2 is the angle between the impeller outlet axial section and the streamline, and is set to λ2 = 70° to 90°. S9: Calculate the maximum shaft power P of the fire pump max , Among them, η m is the mechanical efficiency, K3 is the correction coefficient, take K3 = 1.0 ~ 1.1, h0 is the slip coefficient, u2 is the circumferential velocity of the impeller outlet, S10: Compare the maximum shaft power P of the fire pump obtained by S9 max With the given matching motor power p of the fire pump, when P max ≤p, output the outer diameter D2, number of blades Z, and blade wrap angle of the impeller Inlet diameter D j , outlet width b2, outlet placement angle β2, blade inlet edge thickness δ1 and blade outlet edge thickness δ2, otherwise repeat S1 to S10.

2. The impeller design method for a low specific speed fire pump according to claim 1, characterized in that: The outlet width b2 obtained in S5 takes a larger value within the range of the outlet width b2.

3. The impeller design method for a low specific speed fire pump according to claim 1, characterized in that: The outlet placement angle β2 obtained in S6 takes a larger value within the range of the outlet placement angle β2.

4. The impeller design method for a low specific speed fire pump according to claim 1, characterized in that: The outlet crowding coefficient Ψ2 obtained in S8 takes a smaller value within the range of the outlet crowding coefficient Ψ2.

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