A design method for spatial guide vanes of molten salt pumps with long and short blades

Abstract

The present invention discloses a method for designing a spatial guide vane for a molten salt pump with long and short blades. The design method includes designing a long guide vane and a short guide vane, wherein the design process of the short guide vane is as follows: determining the flow cross-section of the flow channel and calculating the flow cross-sectional area based on the axial projection of the long guide vane, making a change trend diagram of the axial direction based on the flow cross-sectional area, finding the hump position of the flow cross-sectional area based on the change trend diagram, and setting the position of the short guide vane at the rising trend of the hump position. This method accurately determines the position of the short guide vane in the guide vane based on the change trend of the flow cross-sectional area of ​​the long guide vane, providing certain theoretical guidance for the design of the guide vanes of an efficient molten salt pump. The presence of the short guide vane will effectively reduce vortices and unstable flow in the liquid flow process, thereby improving the energy conversion rate of the spatial guide vane, and ultimately improving the efficiency of the molten salt pump.

Description

Technical Field

[0001] The invention relates to a method for designing a pump space guide vane, in particular to a method for designing a molten salt pump space guide vane with long and short blades. Background Art

[0002] In the heat transfer and storage systems of CSP power plants using molten salt as a heat storage or heat transfer medium, molten salt pumps are one of the most critical pieces of equipment. Molten salt pumps are primarily used to transport high-temperature ion-exchange membrane caustic soda, carbonates, nitrates, and other media, typically at temperatures between 400 and 500°C. Molten salt pumps typically utilize a vertical, long-axis structure. Due to structural limitations, they require guide vanes to collect liquid from the impeller and redirect the flow, converting radial flow into axial flow. This results in significant energy consumption during the conversion process, leading to low overall efficiency and significant energy waste. Therefore, in order to actively support the development of energy conservation and emission reduction in my country and address the global energy crisis, there is an urgent need to improve the efficiency of molten salt pumps. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for designing spatial guide vanes of a molten salt pump with long and short blades, so as to solve the technical problem that the overall efficiency of the molten salt pump is low, resulting in a huge waste of energy.

[0004] The technical solution of the present invention is a method for designing a spatial guide vane of a molten salt pump with long and short blades. The number of short guide vanes and long guide vanes in the molten salt pump is the same, and the short blades and long blades in the spatial guide vane are alternately distributed. The design method includes the design of long guide vanes and the design of short guide vanes, wherein the design process of the short guide vanes is as follows:

[0005] (1) According to the axial projection of the long blade of the guide vane, the flow cross section of the flow channel is determined and the flow cross section area is calculated. According to the flow cross section area, a change trend diagram of the axial direction is made. The flow cross section area is shown as follows:

[0006] A i =πD i b i ,

[0007] A i is the cross-sectional area of ​​the flow, D i is the equivalent diameter of the flow section, b i is the length of the flow section;

[0008] (2) According to the change trend diagram, find the hump position of the flow cross-sectional area and set the guide vane short blade position at the rising trend of the hump position;

[0009] (3) The axial distance between the inlet position of the short guide vane and the inlet position of the long guide vane is approximately 2%-4% of the axial length of the long guide vane;

[0010] (4) The inlet edge of the guide vane short blade coincides with the flow section line at that location and the thickness of the inlet edge of the guide vane short blade is reduced to 30%-50% of the original thickness. In addition, the shape of the inlet of the guide vane short blade is circular or elliptical;

[0011] (5) The axial distance between the outlet of the short guide vane and the inlet of the long guide vane is approximately 30%-40% of the axial length of the long guide vane;

[0012] (6) The outlet edge of the guide vane short blade coincides with the flow section line at that location and the outlet thickness of the guide vane short blade is reduced to 30%-50% of the original thickness. In addition, the outlet shape of the guide vane short blade is circular or elliptical.

[0013] In the aforementioned method for designing the spatial guide vanes of a molten salt pump with long and short blades, the design of the long guide vanes includes the following steps:

[0014] (1) The inlet diameter of the long blade of the guide vane is approximately 1.0-1.1 times the outlet diameter of the impeller;

[0015] (2) The inlet width of the guide vane is approximately 1.0-1.2 times the outlet width of the impeller;

[0016] (3) The axial length of the long blade of the guide vane is approximately 0.7 to 1.2 times the impeller outlet diameter;

[0017] (4) The blade wrap angle of the long guide vane is 60-100°;

[0018] (5) The guide vane long blade inlet placement angle α3;

[0019]

[0020] Where v m3 ——Axial velocity at the calculation point of the guide vane’s long blade inlet; v u3 ——Circumferential component velocity at the inlet calculation point of the guide vane long blade;

[0021]

[0022] Where F3 is the cross-sectional area of ​​the axial liquid flow at the calculation point of the guide vane inlet edge, F3=2πR c b; Q - molten salt pump volume flow, m 3 / s; ψ3——the inlet displacement coefficient of the guide vane; R c ——the inlet radius of the guide vane, m; b——the length of the flow section line segment;

[0023]

[0024] Where Z is the number of blades of the guide vane; D3 is the inlet diameter of the guide vane, m; S U3 ——the circumferential thickness of the guide vane long blade inlet, m;

[0025]

[0026] Where S3 is the thickness of the flow surface at the inlet calculation point of the guide vane long blade; α3 is the inlet angle of the guide vane long blade;

[0027] The inlet angle of the long blade of the guide vane is: α3 = α′3 + Δα, where the angle of attack Δα = 0° to 8°;

[0028] (6) The outlet angle of the long blade of the guide vane is α4, α4 = 90°;

[0029] (7) Determine the design parameters of the long guide vane and make a hydraulic diagram of the long guide vane.

[0030] The beneficial effects of the present invention are as follows: compared with the prior art, since the flow area inside the limited space guide vane of the molten salt pump structure shows a trend of first increasing and then decreasing, less energy is consumed in the process of the liquid flow area changing from large to small, but in the process of the liquid flow area changing from small to large, especially in the area where the flow cross-sectional area changes greatly, vortices and unstable flows will be generated, and this process will greatly cause energy consumption and waste. To address this problem, a design method for a molten salt pump space guide vane with long and short blades is proposed. This method accurately determines the position of the short guide vane in the guide vane according to the changing trend of the flow cross-sectional area of ​​the long guide vane, and provides certain theoretical guidance for the guide vane design of a high-efficiency molten salt pump. The presence of the short guide vane will effectively reduce the vortex and unstable flow in the liquid flow process, thereby improving the energy conversion rate of the space guide vane, and ultimately improving the efficiency of the molten salt pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the axial projection diagram of the long guide vane and the short guide vane;

[0032] Figure 2 This is the trend diagram of the flow cross-sectional area change of the long blade of the guide vane;

[0033] Figure 3 This is the guide vane long blade space guide vane structure diagram;

[0034] Figure 4 This is the guide vane structure diagram of the long and short blades;

[0035] Figure 5 are the external characteristic curves under different guide vane structures. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to the accompanying drawings and examples, but they are not intended to limit the present invention.

[0037] The embodiment of the present invention: The following is a detailed description of the implementation process of the present invention through a specific example. Take a certain model molten salt pump as an example, its basic parameters are flow rate 25m 3 / h, lift 8m, speed 1450r / min.

[0038] Step 1: Design the guide vane long blade steps:

[0039] (1) The dimensional parameters of the impeller are:

[0040] Impeller inlet diameter (mm) Impeller outlet diameter (mm) Impeller outlet width (mm) 71 174 12

[0041] (2) The inlet diameter of the guide vane is slightly larger than the outlet diameter of the impeller, which is about 1.0-1.1 times the outlet diameter of the impeller, so that the fluid flowing out of the impeller outlet can fully enter the guide vane. Therefore, the inlet diameter of the guide vane is set to 178 mm. In addition, if the gap between the impeller outlet and the long blade inlet of the guide vane is too small, it will cause large pressure pulsation, which is not conducive to the stable operation of the molten salt pump. Too large a gap will cause more energy loss, which leads to reduced efficiency of the molten salt pump.

[0042] (3) The inlet width of the long guide vane is slightly larger than the outlet width of the impeller, which is about 1.0-1.2 times the outlet width of the impeller. Therefore, the inlet width of the long guide vane is set to 12.6 mm, so that the fluid flowing out of the impeller outlet can smoothly enter the guide vane. In addition, if the difference between the impeller outlet and the inlet width of the long guide vane is too small, it will cause a large pressure pulsation. If the difference is too large, it will cause more volume loss, which will lead to a decrease in the efficiency of the molten salt pump.

[0043] (4) The axial length of the long blade of the guide vane is about 0.7 to 1.2 times the impeller outlet diameter, so the axial length of the long blade of the guide vane is 130 mm;

[0044] (5) The wrap angle of the long blade of the guide vane is 60°-100°; therefore, the wrap angle of the long blade of the guide vane is 70°;

[0045] (6) Guide vane long blade inlet placement angle α3;

[0046]

[0047] Where v m3 ——Axial velocity at the calculation point of the guide vane’s long blade inlet;

[0048] v u3 ——Circumferential component velocity at the inlet calculation point of the guide vane long blade;

[0049]

[0050] Where F3 is the cross-sectional area of ​​the axial liquid flow at the inlet of the guide vane; ψ3 is the inlet displacement coefficient of the guide vane; Q is the volume flow rate of the molten salt pump, m 3 / s.

[0051] F3=2πR c b

[0052] Where R c is the inlet radius of the guide vane, m; b is the length of the flow section line segment;

[0053]

[0054] Where S U3 is the circumferential thickness of the guide vane long blade at the inlet; Z is the number of blades of the guide vane long blade; D3 is the inlet diameter of the guide vane long blade, m.

[0055]

[0056] Where S3 is the flow surface thickness of the axis of the guide vane long blade inlet calculation point, m; α3 is the guide vane long blade inlet angle.

[0057] The guide vane inlet angle α3 = α′3 + Δα, where the attack angle Δα = 0° to 8°, so the guide vane blade inlet placement angle is taken as 10°.

[0058] (7) Guide vane outlet angle α4. Considering that the normal direction of the liquid flow at the outlet of the long guide vane is optimal, the guide vane outlet placement angle is set to α4 = 90°.

[0059] (8) The number of long guide vane blades is selected as 10.

[0060] The various dimensional parameters of the guide vane long blades are determined accordingly.

[0061] Step 2: Design the short guide vane steps:

[0062] The design process of the guide vane short blade is as follows:

[0063] (1) According to the axial projection of the long blade of the guide vane, the flow section of the flow channel is determined and the flow section area is calculated. According to the flow section area, a trend diagram of its change along the axial direction is formed, such as Figure 1 and Figure 2 shown.

[0064] (2) Due to the limited space of the molten salt pump structure, the flow area inside the guide vane shows a trend of first increasing and then decreasing, forming a change trend similar to a "hump". The energy consumed in the process of the liquid flow area changing from large to small is relatively small, but in the process of the liquid flow area changing from small to large, especially when the flow area changes greatly, vortices and unstable flow will be generated. This process will greatly cause energy consumption and waste. Therefore, the position of the short blade of the guide vane is set at the rising trend of the hump position to reduce the flow loss at this position and play a rectifying role. The position of the hump is determined according to the change trend diagram of the flow cross-sectional area of ​​the long blade of the guide vane.

[0065] (3) The axial distance between the inlet position of the short guide vane is about 2 mm, which is within the range of 4%-10% of the axial length of the long guide vane. The inlet edge of the short guide vane is too close to the inlet edge of the long guide vane, which may cause large dynamic and static interference and pressure pulsation between the impeller and the guide vane. The distance between the inlet edge of the short guide vane and the inlet edge of the long guide vane is too far, which cannot effectively eliminate the vortex and secondary flow at this location.

[0066] (4) In order to reduce the loss of flow at the blade inlet, the inlet edge of the guide vane short blade coincides with the flow section line at that location and the thickness of the inlet edge of the guide vane short blade is thinned to 30%-50% of the original thickness. In addition, the shape of the inlet of the guide vane short blade is circular or elliptical.

[0067] (5) The axial distance of the outlet position of the short blade of the guide vane is about 60 mm, which is within the range of 30%-40% of the axial length of the long blade of the guide vane.

[0068] (6) In order to reduce the flow loss at the blade outlet, the outlet edge of the guide vane short blade coincides with the flow section line at that location and the thickness of the guide vane short blade outlet is thinned to 30%-50% of the original thickness. In addition, the shape of the guide vane short blade outlet is circular or elliptical.

[0069] (7) The number of the short guide vanes and the long guide vanes is the same, which is 10, and the short blades and the long blades are distributed alternately in the spatial guide vanes.

[0070] (8) Figure 5 As shown in Figure 2, numerical simulation shows that the efficiency and head of the guide vanes with long and short blades at various flow rates are improved to a certain extent compared with the guide vanes with long blades.

Claims

1. A method for designing spatial guide vanes for a molten salt pump with long and short blades, characterized by: The number of short guide vanes and long guide vanes in the molten salt pump is the same, and the short blades and long blades are distributed alternately in the spatial guide vanes. The design method includes the design of long guide vanes and the design of short guide vanes, wherein the design process of short guide vanes is as follows: (1) According to the axial projection of the long blade of the guide vane, the flow cross section of the flow channel is determined and the flow cross section area is calculated. According to the flow cross section area, a change trend diagram of the axial direction is made. The flow cross section area is shown as follows: A i =πD i b i , A i is the cross-sectional area of ​​the flow, D i is the equivalent diameter of the flow section, b i is the length of the flow section; (2) According to the change trend diagram, find the hump position of the flow cross-sectional area and set the guide vane short blade position at the rising trend of the hump position; (3) The axial distance between the inlet position of the short guide vane and the inlet position of the long guide vane is approximately 2%-4% of the axial length of the long guide vane; (4) The inlet edge of the guide vane short blade coincides with the flow section line at that location and the thickness of the inlet edge of the guide vane short blade is reduced to 30%-50% of the original thickness. In addition, the shape of the inlet of the guide vane short blade is circular or elliptical; (5) The axial distance between the outlet of the short guide vane and the inlet of the long guide vane is approximately 30%-40% of the axial length of the long guide vane; (6) The outlet edge of the guide vane short blade coincides with the flow section line at that location and the thickness of the guide vane short blade outlet is reduced to 30%-50% of the original thickness. In addition, the shape of the guide vane short blade outlet is circular or elliptical; The design of the long guide vane comprises the following steps: (1) The inlet diameter of the long blade of the guide vane is approximately 1.0-1.1 times the outlet diameter of the impeller; (2) The inlet width of the guide vane is approximately 1.0-1.2 times the outlet width of the impeller; (3) The axial length of the long blade of the guide vane is approximately 0.7 to 1.2 times the impeller outlet diameter; (4) The blade wrap angle of the long guide vane is 60-100°; (5) The guide vane long blade inlet placement angle α3; Where v m3 ——Axial velocity at the calculation point of the guide vane’s long blade inlet; v u3 ——Circumferential component velocity at the inlet calculation point of the guide vane long blade; Where F3 is the cross-sectional area of ​​the axial liquid flow at the calculation point of the guide vane inlet edge, F3=2πR c b; Q - molten salt pump volume flow, m 3 / s; ψ3——the inlet displacement coefficient of the guide vane; R c ——the inlet radius of the guide vane, m; b——the length of the flow section line segment; Where Z is the number of blades of the guide vane; D3 is the inlet diameter of the guide vane, m; S U3 ——the circumferential thickness of the guide vane long blade inlet, m; Where S3 is the thickness of the flow surface at the inlet calculation point of the guide vane long blade; α3 is the inlet angle of the guide vane long blade; The inlet angle of the long blade of the guide vane is: α3 = α'3 + Δα, where the angle of attack Δα = 0° to 8°; (6) The outlet angle of the long blade of the guide vane is α4, α4 = 90°; (7) Determine the design parameters of the long guide vane and make a hydraulic diagram of the long guide vane.

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