Design method of oil tank structure, transformer and radiating fin

Abstract

The application relates to a design method of an oil tank structure, a transformer and a heat dissipation fin. The oil tank structure comprises an oil tank body and a heat dissipation fin arranged on a heat dissipation surface and protruding in a second direction intersecting the first direction. In the second direction, the outer contour of the cross section of the heat dissipation fin at any position forms a flow guide line towards the bottom of the oil tank. The flow guide line is a curve, the flow guide line is protrudingly arranged towards the top of the oil tank, and the flow guide line satisfies the brachistochrone expression. The flow guide line of the heat dissipation fin is designed as a cycloid in the oil tank structure, air can be guided to flow along the brachistochrone path, the bottom of the heat dissipation fin can guide hot air to rise along the cycloid path, hot air can be quickly guided to the side or top of the oil tank to be discharged, the accumulation of hot air under the heat dissipation fin is reduced, and the local heat dissipation efficiency is improved.

Description

Technical Field

[0001] This application relates to the field of transformer heat dissipation technology, and in particular to a design method for an oil tank structure, a transformer, and heat dissipation fins. Background Technology

[0002] Distribution transformers are key equipment in power systems, widely used in industrial, agricultural, commercial, and residential electricity consumption. Their operational reliability directly affects the safety and stability of the power grid. With the rapid development of my country's economy and society, electricity demand continues to grow, placing increasingly higher demands on the performance of distribution transformers. During operation, transformers generate a large amount of heat due to core losses and winding copper losses. If this heat cannot be dissipated effectively and promptly, it will cause the transformer temperature to rise, affecting the service life of insulation materials and, in severe cases, even leading to transformer burnout.

[0003] As the outer shell of the transformer, the oil tank not only serves to contain the transformer oil and protect the internal structure, but also plays a crucial role in heat dissipation. After absorbing internal heat, the transformer oil transfers the heat to the tank walls through convection, and then exchanges heat with the surrounding air through the outer surface of the tank, ultimately dissipating the heat.

[0004] Currently, traditional distribution transformer tanks generally employ a corrugated finned heat dissipation structure. Corrugated finned tanks are made by stamping steel plates into a corrugated shape and welding them to the tank body. The corrugated structure increases the heat dissipation area of ​​the tank, improving heat dissipation efficiency. However, during the heat dissipation process, the airflow between the corrugations creates eddies and dead zones, reducing the air's heat exchange efficiency and making it difficult to further improve the overall heat dissipation effect. Summary of the Invention

[0005] Therefore, it is necessary to provide a design method for the tank structure, transformer, and heat dissipation fins to address the problem that the airflow between the corrugations in the heat dissipation process of the corrugated sheet has eddies and dead zones, which reduces the heat exchange efficiency of the air and makes it difficult to further improve the overall heat dissipation effect.

[0006] A fuel tank structure, the fuel tank structure comprising:

[0007] The fuel tank body has a top and a bottom opposite each other in the first direction, and a heat dissipation surface is provided on its side wall;

[0008] Heat dissipation fins are disposed on the heat dissipation surface and extend outward from the heat dissipation surface along a second direction intersecting the first direction. In the second direction, the outer contour of the cross-section of the heat dissipation fins at any position forms a guide line on the side facing the bottom of the oil tank.

[0009] The guide line is curved and protrudes towards the top of the oil tank. The heat dissipation fins have a first end and a second end opposite each other in the extension direction of the guide line. The first end is located on the side of the second end closer to the top of the oil tank.

[0010] The guide line satisfies the brachistochrone expression in the rectangular coordinate system: x=r(θ-sinθ), y=r(1-cosθ), where x and y are the coordinates of any point on the guide line, r is the radius of the rolling circle that generates the cycloid, r=10mm~20mm, and θ is the rolling angle of the rolling circle.

[0011] In one embodiment, r = 15 mm.

[0012] In one embodiment, the tank structure includes a plurality of heat dissipation fins, each heat dissipation fin having a guide line, and at least a portion of the heat dissipation fins (20) having their first ends spaced apart along the first direction and aligned with each other in the first direction.

[0013] In one embodiment, a plurality of heat dissipation fins constitute a first heat dissipation unit, the first ends of all the heat dissipation fins of the first heat dissipation unit are spaced apart along the first direction, and the second ends of all the heat dissipation fins of the first heat dissipation unit are spaced apart along the first direction.

[0014] The plurality of heat dissipation fins form a second heat dissipation unit, which is located on the side of the first heat dissipation unit facing the bottom of the oil tank in the first direction. The first ends of all the heat dissipation fins of the second heat dissipation unit are arranged at intervals along the first direction, and the second ends of all the heat dissipation fins of the second heat dissipation unit are arranged at intervals along a third direction. The third direction intersects with both the first direction and the second direction and is located on a third side line.

[0015] In one embodiment, the fuel tank structure includes a plurality of heat dissipation components, each of which includes a first heat dissipation unit and a second heat dissipation unit. The plurality of heat dissipation components are arranged at intervals along a third direction on the heat dissipation surface, and the third direction intersects with both the first direction and the second direction.

[0016] In one embodiment, the length of each heat dissipation fin extending in the second direction is H. In the direction from the bottom of the oil tank to the top of the oil tank, the length of H of all the heat dissipation fins of the first heat dissipation unit gradually increases, the length of H of all the heat dissipation fins of the second heat dissipation unit gradually increases, and the length of H of all the heat dissipation fins of the first heat dissipation unit is greater than the length of H of all the heat dissipation fins of the second heat dissipation unit.

[0017] In one embodiment, an oxide film is formed on the surface of the heat dissipation fins, and the thickness of the oxide film is 10μm-25μm.

[0018] In one embodiment, the heat dissipation fins and the oil tank body are integrally formed.

[0019] A transformer comprising the tank structure as described in any of the preceding claims.

[0020] A method for designing heat dissipation fins, applied to the oil tank structure described above, the method comprising the following steps:

[0021] S1: Select the height H, spacing P and rolling circle radius r of the heat dissipation fins as the design parameters of the heat dissipation fins. H is the length of the heat dissipation fins extending out of the oil tank body, P is the spacing between two adjacent heat dissipation fins in the height direction of the oil tank body, and r is the rolling circle radius of the cycloid corresponding to the heat dissipation fins.

[0022] S2: Based on the design parameters determined in step S1, construct the experimental scheme using the full factorial experimental design method to generate multiple sets of parameter combinations;

[0023] S3: Simulation calculations are performed on all parameter combinations using a hybrid method combining finite element local simulation and analytical global analysis, and the equivalent heat dissipation coefficient corresponding to each parameter combination is obtained.

[0024] S4: Based on all the parameter combinations and all the equivalent heat dissipation coefficients, a second-order polynomial fitting method is used to establish a heat dissipation response surface model and a cost response surface model of the equivalent heat dissipation coefficient with respect to the three design parameters H, P and r.

[0025] S5: With the optimization objectives of maximizing heat dissipation and minimizing cost, multi-objective optimization is performed using the heat dissipation response surface model and cost response surface model established in step S4.

[0026] The aforementioned fuel tank structure designs the airflow guide lines of the heat dissipation fins as cycloids, which can guide the air to flow along the fastest path. This allows the bottom of the heat dissipation fins to guide the hot air to rise along the cycloid path, thereby quickly guiding the hot air to the side or top of the fuel tank for discharge, reducing the accumulation of hot air under the heat dissipation fins, and improving local heat dissipation efficiency. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the fuel tank structure in some embodiments of this application.

[0028] Figure 2 for Figure 1 A schematic diagram of the heat dissipation fins in the embodiment.

[0029] Figure 3 for Figure 2 A schematic diagram of the heat dissipation fins from another perspective in the embodiment.

[0030] Figure 4 The temperature field cloud diagrams of the heat dissipation fins in some embodiments of this application are shown.

[0031] Figure 5 for Figure 4 Streamline diagram of the heat dissipation fins in the embodiment.

[0032] Figure 6 This is a flowchart illustrating the design method of heat dissipation fins in some embodiments of this application.

[0033] Explanation of reference numerals in the attached figures:

[0034] Fuel tank body 10; heat dissipation surface 11;

[0035] Heat dissipation fins 20; airflow guide lines 21; first end 22; second end 23;

[0036] First heat dissipation unit 30;

[0037] Second heat dissipation unit 40; Third heat dissipation unit 41;

[0038] Heat dissipation component 50; heat dissipation channel 51;

[0039] First direction X; second direction Y; third direction Z. Detailed Implementation

[0040] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0041] In the description of this application, it should be understood that if terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" appear, these terms indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0042] Furthermore, where the terms "first" and "second" appear, these terms are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, where the term "multiple" appears, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0043] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0044] In this application, unless otherwise expressly specified and limited, the use of descriptions such as "above" or "below" the second feature indicates that the first and second features are in direct contact or indirect contact via an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. Similarly, "below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0045] It should be noted that if an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. If an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. If so, the terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this application are for illustrative purposes only and do not represent the only possible implementation.

[0046] See Figure 1 , Figure 1The diagram shows a schematic of the tank structure in one embodiment of this application. The tank structure provided in this embodiment includes a tank body 10 and heat dissipation fins 20 disposed on the tank body 10. The tank body 10 is used to contain transformer oil and the internal body of the transformer. The heat dissipation fins 20 are disposed on the outer wall of the tank body 10 to directly increase the contact area between the tank body 10 and the outside air, thereby improving the heat exchange efficiency between the tank body 10 and the air and ensuring that the operating temperature of the internal body of the transformer inside the tank body 10 is stable within a certain range.

[0047] The applicant discovered that air-side heat transfer is the bottleneck in the entire heat transfer process of a transformer. Traditional corrugated sheet structures are limited by stamping manufacturing processes, making it difficult to further optimize the inner diameter and wall thickness of the corrugations. The selection range for parameters such as corrugation spacing and depth is also limited, resulting in a difficulty in significantly increasing the effective heat dissipation surface area and meeting the heat dissipation requirements of transformers with higher power density. Furthermore, the regular geometry of the corrugated sheets fails to fully consider the characteristics of airflow under natural convection conditions; eddies and dead zones exist in the airflow between the corrugations, and heat transfer efficiency needs improvement.

[0048] To solve the above-mentioned technical problems, in some embodiments of this application, the fuel tank body 10 has a top and a bottom opposite each other in the first direction X, and a heat dissipation surface 11 is provided on its side wall. Heat dissipation fins 20 are provided on the heat dissipation surface 11 and extend out relative to the heat dissipation surface 11 along the second direction Y intersecting the first direction X. In the second direction Y, the outer contour of the cross section of the heat dissipation fins 20 at any position forms a guide line 21 on the side facing the bottom of the fuel tank.

[0049] In actual use, heated air tends to rise. When this hot air comes into contact with the bottom of the heat dissipation fins 20, it flows along the bottom of the fins. Therefore, the heat dissipation fins 20 also guide the hot air. To prevent hot air from accumulating at the heat dissipation fins 20, the guide line 21 is curved and protrudes towards the top of the oil tank. The heat dissipation fins 20 have a first end 22 and a second end 23 extending along the guide line 21, with the first end 22 intersecting the second end 23 closer to the top of the oil tank.

[0050] In other words, the heat dissipation fins 20 are generally shaped to be bent upwards, and the guide lines 21 are convex toward the top of the oil tank. This means that the heat dissipation fins 20 are convex toward the top of the oil tank body 10, and the first end 22 of the heat dissipation fins 20 is higher than the second end 23. After the hot air comes into contact with the bottom of the heat dissipation fins 20, it will rise along the guide lines 21 and finally be discharged from the first end 22 of the heat dissipation fins 20. This discharges the heated air from the oil tank structure, preventing air from accumulating in the oil tank at the heat dissipation fins 20 and ensuring the heat dissipation effect.

[0051] While the hot air can be guided by the heat dissipation fins 20 to change its direction and be directed to the sides or top of the oil tank body 10 for discharge, the hot air continues to exchange heat with the air below the oil tank body 10 during its flow along the heat dissipation fins 20, generating new hot air. If the hot air is discharged too slowly along the heat dissipation fins 20, the newly generated hot air will also enter the bottom of the heat dissipation fins 20, leading to a buildup of hot air at the heat dissipation fins 20.

[0052] Therefore, considering the characteristics of airflow, the guide line 21 is controlled to satisfy the brachistochrone expression in the rectangular coordinate system: x=r(θ-sinθ), y=r(1-cosθ), where x and y are the coordinates of any point on the guide line 21, r is the radius of the rolling circle that generates the cycloid, r=10mm~20mm, and θ is the rolling angle of the rolling circle.

[0053] The "brachistochrone," also known as the cycloid, is mathematically defined as the trajectory traversed by any point P on the circumference of a circle of radius r as it rolls purely forward along a straight line. The brachistochrone exhibits isochronism, meaning that regardless of where the object begins its descent, the time to reach the endpoint is always the same and the shortest.

[0054] In natural convection cooling, the flow of air under buoyancy has a similar physical essence to the motion of a small ball in a gravitational field. In the natural convection cooling process of the fuel tank structure, the air below the heat dissipation fins 20 is heated and its density decreases, resulting in an upward flow tendency under the action of buoyancy. If we consider the heated air micro-particles as small balls and the fin surface as the curved surface constraining the motion of the small balls, then the optimal path for the air micro-particles to rise rapidly from the bottom to the top of the fins should follow a cycloidal shape.

[0055] Therefore, designing the airflow guide line 21 of the heat dissipation fin 20 as a cycloid can guide air to flow along the fastest path, allowing the bottom of the heat dissipation fin 20 to guide hot air upwards along the cycloid path, achieving rapid guidance of hot air to the side or top of the oil tank for discharge, reducing the accumulation of hot air below the heat dissipation fin 20, and improving local heat dissipation efficiency. Theoretical analysis and simulation results show that the overall heat transfer coefficient of the heat dissipation fin 20 with the airflow guide line 21 set as a cycloid is 10%-20% higher than that of the traditional straight fin. The simulated temperature field cloud map of the heat dissipation fin 20 is as follows. Figure 4 As shown, the streamline simulation of the heat sink fin 20 is as follows: Figure 5 As shown.

[0056] It should be noted that the guide line 21 satisfies the brachistochrone expression: x=r(θ-sinθ), y=r(1-cosθ). This means that when the guide line 21 formed by the heat dissipation fins 20 is placed in the first quadrant of a rectangular coordinate system, and one end of the guide line 21 is taken as the starting endpoint, θ=0, then X=0, Y=0, and this endpoint is located at (0,0). Then, by selecting the corresponding r, the values ​​of the remaining X and Y can be calculated based on the rolling angle of the rolling circle. Finally, connecting all the points forms the guide line 21. It should be noted that θ in the cycloidal equation is in radians.

[0057] In some embodiments of this application, see [reference] Figure 2 To improve the heat dissipation efficiency of the fuel tank structure, the fuel tank structure includes multiple heat dissipation fins 20. Each heat dissipation fin 20 has a guide line 21, and each heat dissipation fin 20 has a first end 22 and a second end 23 opposite to each other in the extension direction of the guide line 21. Furthermore, at least a portion of the heat dissipation fins 20 have their first ends 22 spaced apart along a first direction X and aligned with each other in the first direction X. That is, among the multiple heat dissipation fins 20, a portion of the heat dissipation fins 20 have their higher ends all along the same line, and the number of these heat dissipation fins 20 is greater than two.

[0058] As can be seen from the above, after the hot air moves along the bottom guide line 21 of the heat dissipation fin 20, it will be discharged from the first end 22 of the heat dissipation fin 20. Therefore, by setting the first ends 22 of multiple heat dissipation fins 20 on the same straight line, a vertical exhaust channel can be formed on one side of the first fin, and the hot air guided by multiple heat dissipation fins 20 can be discharged into the vertical exhaust channel together, and finally discharged from the oil tank structure along the exhaust channel.

[0059] In some embodiments, a plurality of heat dissipation fins 20 constitute a first heat dissipation unit 30. The first ends 22 of all the heat dissipation fins 20 of the first heat dissipation unit 30 are spaced apart along a first direction X, and the first ends 22 of all the heat dissipation fins 20 of the first heat dissipation unit 30 are interconnected to form a first edge line, which is parallel to the first direction X. The second ends 23 of all the heat dissipation fins 20 of the first heat dissipation unit 30 are spaced apart along the first direction X, and the second ends 23 of all the heat dissipation fins 20 of the first heat dissipation unit 30 are interconnected to form a second edge line, which can be a straight line parallel to the first direction X, or it can be a curve.

[0060] Furthermore, a plurality of heat dissipation fins 20 form a second heat dissipation unit 40, which is located on the side of the first heat dissipation unit 30 facing the bottom of the oil tank in the first direction X. The first ends 22 of all the heat dissipation fins 20 of the second heat dissipation unit 40 are spaced apart along the first direction X, and the line connecting the first ends 22 of all the heat dissipation fins 20 of the second heat dissipation unit 40 is located on the extension line of the first side line. The second ends 23 of all the heat dissipation fins 20 of the second heat dissipation unit 40 are spaced apart along the third direction Z, and the line connecting the second ends 23 of all the heat dissipation fins 20 of the second heat dissipation unit 40 forms a third side line, which extends longitudinally along the third direction Z. The third direction Z intersects both the first direction X and the second direction Y.

[0061] In order to ensure that the second ends 23 of the second heat dissipation unit 40 are all located on the third edge line, the length of the heat dissipation fins 20 of the second heat dissipation unit 40 gradually decreases, and the closer to the first edge line, the shorter the length of the heat dissipation fins 20 of the second heat dissipation unit 40. In actual use, if all the heat dissipation fins 20 adopt the arrangement of the first heat dissipation unit 30, there will still be a large space below the lowest heat dissipation fin 20 of the fuel tank body 10 without heat dissipation fins 20, resulting in heat dissipation dead zones. By setting the second heat dissipation unit 40 below the first heat dissipation unit 30, the heat dissipation dead zones below the first heat dissipation unit 30 can be filled, ensuring the heat dissipation effect of the fuel tank body 10.

[0062] By controlling the first ends 22 of the heat dissipation fins 20 in the first heat dissipation unit 30 and the first ends 22 of the heat dissipation fins 20 in the second heat dissipation unit 40 to be located on the first sideline, both the first heat dissipation unit 30 and the second heat dissipation unit 40 can exhaust air towards the same side, ensuring the exhaust effect of hot air. Furthermore, by controlling the second ends 23 of the second heat dissipation unit 40 to be located on the third sideline, the heat dissipation fins 20 in the second heat dissipation unit 40 can be arranged more regularly. At the same time, an air inlet is formed between the second ends 23 of two connected heat dissipation units in the second heat dissipation unit 40. Since the second ends 23 are all located on the third sideline, the air inlets are also all located on the third sideline. This makes the process of air entering the two adjacent fins through each air inlet smoother, less prone to turbulence, ensuring airflow between the two adjacent heat dissipation fins 20, and thus ensuring heat dissipation efficiency.

[0063] Understandably, the first end 22 of the lowest heat dissipation fin 20 of the first heat dissipation unit 30 is located on the first side line, while the second end 23 can be located on either the second side line or the third side line. Alternatively, the first end 22 of the heat dissipation fin 20 of the second heat dissipation unit 40 closest to the second side line is located on the first side line, while the second end 23 can be located on either the second side line or the third side line.

[0064] In some embodiments, the fuel tank structure includes a plurality of heat dissipation components 50, each heat dissipation component 50 including a first heat dissipation unit 30 and a second heat dissipation unit 40. The plurality of heat dissipation components 50 are arranged at intervals along a third direction Z on the heat dissipation surface 11, and the third direction Z intersects with both the first direction X and the second direction Y. In this way, a heat dissipation channel 51 can be formed between two adjacent heat dissipation components 50. The heat dissipation channel 51 can be defined by the first edge of one heat dissipation component 50 and the second edge of another heat dissipation component 50, or it can be defined by the two first edges or the two second edges of two heat dissipation components 50. Through the heat dissipation channel 51 provided between two heat dissipation components 50, air can flow along the heat dissipation channel 51, improving the air circulation effect and thus improving the heat dissipation effect.

[0065] Furthermore, each heat dissipation component 50 also includes a third heat dissipation unit 41, which is located on the side of the first heat dissipation unit 30 facing the top of the oil tank. The third heat dissipation unit 41 includes multiple heat dissipation fins 20, and the width of all the heat dissipation fins 20 in the third direction Z of the first heat dissipation unit 30 gradually decreases in the direction facing the top of the oil tank. In this way, the space above the uppermost heat dissipation fins 20 of the first heat dissipation unit 30 can be filled by the third heat dissipation unit 41, further increasing the number of heat dissipation fins 20 and improving the heat dissipation effect.

[0066] In actual use, the internal temperature of the fuel tank body 10 is not uniform. The temperature at the bottom of the fuel tank body 10 is often lower, with less need for heat dissipation, while the temperature at the top of the fuel tank body 10 is higher, with greater need for heat dissipation. Therefore, refer to... Figure 3 Each heat dissipation fin 20 extends outward in the second direction Y for a length of H. In the direction from the bottom of the oil tank to the top of the oil tank, the length of H of all the heat dissipation fins 20 of the first heat dissipation unit 30 gradually increases, and the length of H of all the heat dissipation fins 20 of the second heat dissipation unit 40 gradually increases. Moreover, the length of H of all the heat dissipation fins 20 of the first heat dissipation unit 30 is greater than the length of H of all the heat dissipation fins 20 of the second heat dissipation unit 40.

[0067] The greater the extension length of the heat dissipation fins 20, the larger the heat exchange area between the heat dissipation fins 20 and the air, meaning that the heat dissipation effect of the heat dissipation fins 20 is better. Thus, based on the temperature distribution inside the fuel tank body 10, the lower heat dissipation fins 20 are made shorter, while the upper heat dissipation fins 20 are made longer. This reduces the material required for the heat dissipation fins 20 while ensuring the heat dissipation effect, thereby lowering the production cost of the fuel tank structure.

[0068] In some specific embodiments, each heat dissipation fin 20 is integrally formed with the fuel tank body 10. Specifically, the fuel tank structure is integrally formed using 3D-printed sand cores combined with gravity casting or low-pressure casting processes. 3D-printed sand core technology is a casting process based on additive manufacturing principles. It creates sand cores by progressively depositing binder to solidify sand particles, eliminating the need for metal molds. Design adjustments only require modifying the digital model, and the sand core manufacturing time is reduced from several weeks to 24-48 hours, adapting to the needs of multi-variety, small-batch production. Furthermore, 3D-printed sand core technology can form complex curved surfaces and irregularly shaped structures, providing process assurance for the precise forming of cycloidal fins. Gravity casting is simple and low-cost, suitable for the production of small and medium-sized fuel tanks, while low-pressure casting can produce dense castings, suitable for applications with high quality requirements.

[0069] In traditional transformers, the corrugated sheets are welded to the tank. The total length of the weld seam in a typical distribution transformer tank can reach tens of meters, with numerous weld points. During long-term operation, the weld seam area is subjected to multiple stresses: first, thermal stress, as temperature fluctuations caused by transformer load changes lead to cyclic stress in the weld seam area due to thermal expansion and contraction; second, residual stress, caused by uneven temperature fields resulting from localized heating and cooling during welding; and third, vibration fatigue, where electromagnetic and mechanical vibrations during transformer operation subject the weld seam to alternating loads. Under the combined effect of these stresses, microcracks are prone to develop in the heat-affected zone of the weld seam. These cracks gradually propagate, eventually leading to transformer oil leakage. Tank oil leakage not only causes economic losses and environmental pollution, but more seriously, it can trigger fires and other safety accidents, severely impacting the safe operation of the transformer.

[0070] The aforementioned tank structure is integrally cast with the tank body 10 via heat dissipation fins 20, fundamentally eliminating the risk of welding-induced oil leakage. Since this tank structure has no welded joints, it completely eliminates the risk of oil leakage caused by cracking in the heat-affected zone of traditional corrugated tanks. Furthermore, the cast structure has excellent integrity, with no weak weld areas, allowing it to withstand greater stress and harsher working environments, significantly improving the transformer's operational reliability and service life.

[0071] The cast heat dissipation fins 20 are solid structures, which simplify the casting process compared to hollow corrugated fin structures. Furthermore, solid fins eliminate the need for sand cores or require only simple sand cores, avoiding the manufacturing difficulties of complex, convex sand core structures and reducing casting complexity and production costs. The molten metal fills the mold smoothly, resulting in fewer casting defects and a high yield rate. Simultaneously, the application of 3D printed sand core technology further enhances process flexibility, enabling rapid response to design changes and shortening product development cycles.

[0072] In some embodiments of this application, the heat dissipation fins 20 are made of aluminum alloy, and an oxide film is formed on the surface of the heat dissipation fins 20, with a thickness of 10μm-25μm. Specifically, the fin surface undergoes anodizing treatment, which forms a dense aluminum oxide film on the surface of the aluminum alloy heat dissipation fins 20. This oxide film has the following effects: first, it increases the surface emissivity; the emissivity of the aluminum oxide film is approximately 0.8-0.9, much higher than the 0.1-0.2 of the aluminum alloy substrate, which can significantly enhance the surface radiation heat dissipation capacity; second, it improves corrosion resistance; the dense oxide film can effectively isolate the substrate from atmospheric and oil corrosion; and third, it increases surface hardness and enhances wear resistance. Controlling the oxide film thickness within the range of 10μm-25μm ensures the treatment effect without significantly affecting the thermal conductivity of the fins.

[0073] Meanwhile, due to the excellent corrosion resistance of aluminum alloy itself, combined with anodizing surface treatment, it can withstand harsh outdoor environments such as acid rain, salt spray, and high humidity. Compared to steel fuel tanks that require regular maintenance and repainting, aluminum alloy fuel tanks have lower maintenance costs and a longer service life. Furthermore, aluminum alloy materials are 100% recyclable with a high residual value, meeting the requirements of green manufacturing and the circular economy.

[0074] In some embodiments of this application, the root thickness of each heat dissipation fin 20 is 6mm-8mm, the draft angle of each heat dissipation fin 20 is 1°-3°, and the spacing between two adjacent heat dissipation fins 20 is 15mm-30mm. A reasonable draft angle is beneficial for casting demolding, ensuring the surface quality of the casting, and at the same time avoiding the impact of excessively small fin spacing on airflow. Furthermore, the spacing between two adjacent heat dissipation fins 20 gradually increases in the first direction X from the bottom to the top of the oil tank, that is, the spacing between two adjacent heat dissipation fins 20 gradually increases along the height direction to adapt to the changing velocity characteristics of hot air rising under natural convection conditions.

[0075] During natural convection cooling, the air between two adjacent heat dissipation fins 20 decreases in density after heating and rises under the influence of buoyancy. Simultaneously, as the air rises, surrounding cool air continuously replenishes it, gradually increasing the flow rate and velocity of the hot air. If the spacing between the heat dissipation fins 20 remains constant, the rising hot air will encounter increasingly greater flow resistance, affecting heat dissipation efficiency. However, by designing the spacing of the heat dissipation fins 20 to gradually increase along the height direction, matching the increasing trend of hot air flow, flow resistance can be effectively reduced, improving overall heat dissipation performance.

[0076] It should be noted that the spacing between two adjacent heat dissipation fins 20 can refer to the distance between the first ends 22 of two adjacent heat dissipation fins 20 in the first direction X. Alternatively, it can refer to the shortest distance between the lower surface of one heat dissipation fin 20 and the upper surface of the other heat dissipation fin 20.

[0077] In one specific embodiment, this embodiment provides an oil tank structure suitable for a 200kVA distribution transformer. The oil tank structure is made entirely of ZL101A aluminum alloy, and the oil tank body 10 and heat dissipation fins 20 are integrally formed using a 3D-printed sand core and gravity casting process. The external dimensions of the oil tank body 10 are 1200mm in length, 800mm in width, and 1000mm in height, with a tank wall thickness of 7mm and a tank cover wall thickness of 7mm.

[0078] The outer wall of the oil tank body 10 is provided with a solid fin heat dissipation structure. The surface of the heat dissipation fins 20 is provided with guide lines 21. The outline of the guide lines 21 follows the cycloidal equation. The rolling circle radius r of the guide lines 21 corresponding to the cycloidal curve is 15mm. The root thickness of the heat dissipation fins 20 is 7mm. The draft angle of the heat dissipation fins 20 is 2°. The distance between the two bottom heat dissipation fins 20 is 15mm. The distance between the two top heat dissipation fins 20 is 25mm. The length of the heat dissipation fins 20 extending out of the heat dissipation body gradually increases from 80mm to 120mm. The total number of heat dissipation fins 20 is 40, which are evenly arranged around the oil tank.

[0079] The wall thickness parameters of the fuel tank body 10 were determined using topology optimization and response surface methodology. First, a finite element model of the fuel tank body 10 was established, and an internal pressure load of 0.05 MPa and a hoisting load under normal operating conditions were applied. Static analysis was then performed to obtain the stress distribution. Based on the analysis results, with the optimization objective of minimizing the mass of the fuel tank body 10 and the constraint that the maximum stress does not exceed the allowable stress of the material, the optimal wall thickness parameters were searched using response surface methodology. The optimized fuel tank body 10 has a mass of 138.79 kg, a 16% reduction compared to the initial design, and a maximum stress of 166.8 MPa, meeting the allowable stress requirements of ZL101A aluminum alloy.

[0080] Furthermore, after determining the shape and size of the heat dissipation fins 20, computational fluid dynamics (CFD) simulation can be used to quantitatively analyze the convective heat transfer characteristics of the heat dissipation fins 20 surface. The simulation model consists of two parts: the solid domain of the heat dissipation fins 20 and the surrounding air fluid domain. The two are coupled through a fluid-structure interaction interface to realize the interactive calculation of heat transfer and flow field information. At the same time, in order to reduce computational resource consumption and improve solution efficiency, the computational domain is simplified by taking one-quarter of the complete model as the equivalent computational domain, making full use of the geometric symmetry of the heat dissipation fins 20 structure.

[0081] The computational domain is meshed using an unstructured mesh scheme. Unstructured meshes have good geometric adaptability and can effectively fit the curved surfaces, chamfers, and local details of the fins, avoiding the mesh quality degradation problem that occurs with structured meshes in complex geometric regions. For the near-wall region near the fin surface, a dedicated boundary layer mesh is set to ensure sufficient analysis of the temperature and velocity gradients near the wall. The first layer of the mesh has a height of 0.1 mm, a growth rate of 1.2, and a total of 5 layers to ensure the analytical accuracy of heat transfer in the near-wall region.

[0082] The simulation calculation uses a pressure-based steady-state solver. The physical model is a coupled energy equation and a k-ε turbulence model. The buoyancy effect is also considered. A constant heat flux boundary condition with a heat flux density of 1000 W / m² is applied to the base of the heat sink fin 20.

[0083] Finally, simulation results show that as the length of the heat dissipation fins 20 increases, the overall heat transfer coefficient decreases, but the heat transfer area increases, resulting in an overall increase in heat transfer. Conversely, increasing the spacing of the heat dissipation fins 20 improves the heat transfer coefficient but reduces the overall heat dissipation surface area. Increasing the cycloidal circle radius corresponding to the flow guide of the heat dissipation fins 20 also improves the heat transfer coefficient and increases the heat transfer area. Based on simulation data, the equivalent heat dissipation coefficient of the heat dissipation fins 20 is calculated to be 9.7 W / (m²·K) on the vertical surface of the oil tank at the same height. Compared to a traditional corrugated fin oil tank of the same size, the heat dissipation surface area of ​​the cycloidal fin oil tank in this embodiment increases by 5.3%.

[0084] This application also provides a transformer that includes the tank structure as described in any of the above embodiments. Since the transformer includes all the technical features of the above-described tank structure, it possesses all the technical effects of the above-described tank structure, which will not be repeated here.

[0085] The above-mentioned fuel tank structure has at least the following advantages:

[0086] 1. Fundamentally eliminates the risk of welding oil leakage. The heat dissipation fins 20 of the above-mentioned oil tank structure are integrally cast with the oil tank body 10, without welding connection points, thus completely eliminating the risk of oil leakage caused by cracking of the heat-affected zone during welding in traditional corrugated oil tanks. The cast structure has good integrity, with no weak weld areas, and can withstand greater stress and harsher working environments, significantly improving the operational reliability and service life of the transformer.

[0087] 2. Excellent Casting Processability: The heat dissipation fins 20 of the aforementioned oil tank structure are solid, which simplifies the casting process compared to hollow corrugated fins. Furthermore, solid fins eliminate the need for sand cores or require only simple sand cores, avoiding the manufacturing difficulties of complex convex sand core structures and reducing casting difficulty and production costs. In addition, the solid structure of the heat dissipation fins 20 allows for smooth molten metal filling during casting, resulting in fewer casting defects and a high yield rate. The application of 3D printed sand core technology further enhances process flexibility, enabling rapid response to design changes and shortening product development cycles. Simultaneously, the solid fin structure allows for greater design freedom, achieving a larger heat dissipation surface area within the same volume, effectively breaking through the upper limit of the heat dissipation surface area of ​​traditional corrugated fins and meeting the heat dissipation requirements of higher power transformers.

[0088] 3. High heat dissipation efficiency: The airflow guide lines 21 of the heat dissipation fins 20 are designed as cycloids, which can guide the air to flow along the fastest path, reduce flow resistance, and improve heat transfer efficiency. Theoretical analysis and simulation results show that, under the same fin height and spacing conditions, the overall heat transfer coefficient of the cycloid fins is 10%-20% higher than that of the traditional straight fins.

[0089] 4. Excellent Structural Strength: The one-piece cast structure offers superior integrity and structural strength. The various parts are metallurgically bonded, eliminating stress concentration issues associated with welded joints. Through reasonable wall thickness design and structural optimization, the fuel tank can be lightweight while meeting strength requirements, reducing material consumption. Furthermore, the cast structure allows for easy incorporation of reinforcing ribs, fillet transitions, and other structural details, further enhancing overall rigidity and resistance to deformation.

[0090] 5. Strong Environmental Adaptability: The fuel tank body 10 and heat dissipation fins 20 are made of aluminum alloy, which has excellent corrosion resistance. After anodizing the heat dissipation fins 20, it can withstand harsh outdoor environmental conditions such as acid rain, salt spray, and high humidity. Compared to steel fuel tanks that require regular maintenance and painting, aluminum alloy fuel tanks have lower maintenance costs and a longer service life. Furthermore, aluminum alloy is 100% recyclable with a high residual value, meeting the requirements of green manufacturing and a circular economy.

[0091] This application also provides a method for designing heat dissipation fins, applied to the oil tank structure in any of the above embodiments. The method for designing heat dissipation fins includes the following steps:

[0092] S1: Select the height H, spacing P and rolling circle radius r of the heat dissipation fin 20 as the design parameters of the heat dissipation fin 20. H is the length of the heat dissipation fin 20 extending out of the oil tank body 10, P is the spacing between two adjacent heat dissipation fins 20 in the height direction of the oil tank body 10, and r is the rolling circle radius of the cycloid corresponding to the formed heat dissipation fin 20.

[0093] Specifically, in step S1, the parameter values ​​of H, P, and r are in the range of H=60mm-140mm, P=15mm-30mm, and r=10mm-20mm.

[0094] S2: Based on the design parameters determined in step S1, construct the experimental scheme using the full factorial experimental design method to generate multiple sets of parameter combinations;

[0095] Specifically, in step S2, three values ​​are selected for each of H, P, and r, and an L27(3³) orthogonal array is used to arrange the experimental scheme, and a total of 27 sets of simulation calculations are performed.

[0096] S3: Simulation calculations were performed on all parameter combinations using a hybrid method combining finite element local simulation and analytical global analysis, and the equivalent heat dissipation coefficient corresponding to each parameter combination was obtained.

[0097] Specifically, the hybrid method combining finite element method (FEM) local simulation with analytical global analysis is as follows: A high-precision FEM is used to perform detailed simulations of complex and critical local areas of the heat sink fins 20, extracting their equivalent thermal characteristic parameters. These parameters are then substituted into a global transformer temperature rise calculation model based on analytical methods for rapid and efficient iterative calculations. The specific simulation method is described above and will not be repeated here.

[0098] Based on 27 sets of simulation calculations, the specific simulation results are shown in the table below. Then, analysis of variance was used to determine the significance of each parameter's impact on heat dissipation performance for the 27 simulated structures. It was found that fin height has the most significant impact on heat dissipation, contributing 52.3%; fin spacing is second, contributing 28.7%; and the cycloidal circle radius contributes 15.4%. Increasing the spacing not only improves the heat transfer coefficient but also reduces material usage. The cycloidal circle radius angle has a positive impact on both the heat transfer coefficient and the heat dissipation area. Therefore, for economic optimization, increasing the bending radius of the cycloidal fins and widening the spacing are suitable methods.

[0099] In order to obtain more accurate design parameters, the design method of heat sink fins also includes the following steps:

[0100] S4: Based on all the parameter combinations and all the equivalent heat dissipation coefficients, a second-order polynomial fitting method is used to establish a heat dissipation response surface model and a cost response surface model of the equivalent heat dissipation coefficient with respect to the three design parameters H, P and r.

[0101] Specifically, after fitting with a second-order polynomial, when the established model's coefficient of determination (R²) reaches 0.96, it indicates that the model has high prediction accuracy and can be selected as a response surface model or a cost response surface model.

[0102] S5: With the optimization objectives of maximizing heat dissipation and minimizing cost, multi-objective optimization is performed using the heat dissipation response surface model and cost response surface model established in step S4.

[0103] S5 specifically includes:

[0104] S5-1: Establish a multi-objective optimization mathematical model with the objective functions of maximizing heat dissipation Q and minimizing cost C: maxF(H,P,r)=[Q(H,P,r),-C(H,P,r)];

[0105] Where Q(H,P,r) and C(H,P,r) are the heat dissipation response surface model and the cost response surface model established in step S4, respectively.

[0106] The constraints are H_min≤H≤H_max, P_min≤P≤P_max, r_min≤r≤r_max. The specific parameters of H, P, and r can be the parameter range selected in S1 above, that is, H=60mm-140mm, P=15mm-30mm, and r=10mm-20mm.

[0107] S5-2: The NSGA-II (non-dominated sorting genetic algorithm) is used to perform multi-objective optimization on the heat dissipation response surface model and the cost response surface model.

[0108] Among them, the NSGA-II algorithm maintains the diversity of solutions through non-dominated sorting and crowding distance mechanism. Compared with the traditional weighted single-objective optimization method, it can obtain a uniformly distributed Pareto optimal solution set in one go, avoiding the influence of subjective selection of weight coefficients on the results.

[0109] The specific settings for the algorithm parameters are as follows: Set the population size and number of iterations to obtain the Pareto optimal solution set. Set the population size to 100-200 individuals (preferably 100 or 200) and the maximum number of iterations to 300-500 generations.

[0110] S5-3: Based on the actual needs of the project, such as prioritizing heat dissipation performance or cost control, select the optimal compromise solution from the Pareto solution set.

[0111] The above-mentioned design method for heat dissipation fins clarifies the influence of three key parameters: fin height, fin spacing, and cycloidal circle radius. This provides a quantitative basis for parameter control in engineering design. Furthermore, through orthogonal experimental design, it avoids the limitations of single-factor experiments and significantly improves the reliability of parameter influence law evaluation.

[0112] The simulation results for 27 groups are shown below:

[0113]

[0114] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0115] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A fuel tank structure, characterized in that, The fuel tank structure includes: The fuel tank body (10) has a top and bottom opposite each other in the first direction (X), and a heat dissipation surface (11) is provided on its side wall. Heat dissipation fins (20) are disposed on the heat dissipation surface (11) and extend out relative to the heat dissipation surface (11) along a second direction (Y) intersecting the first direction (X). In the second direction (Y), the outer contour of the cross section of the heat dissipation fins (20) at any position forms a guide line (21) on the side facing the bottom of the oil tank. The guide line (21) is curved and protrudes towards the top of the oil tank. The heat dissipation fins (20) have a first end (22) and a second end (23) opposite each other in the extension direction of the guide line (21). The first end (22) is closer to the top of the oil tank than the second end (23). The guide line (21) satisfies the brachistochrone expression in the rectangular coordinate system: x=r(θ-sinθ), y=r(1-cosθ), where x and y are the coordinates of any point on the guide line (21), r is the radius of the rolling circle that generates the cycloid, r=10mm~20mm, and θ is the rolling angle of the rolling circle.

2. The fuel tank structure according to claim 1, characterized in that, r=15mm.

3. The fuel tank structure according to claim 1, characterized in that, The oil tank structure includes a plurality of heat dissipation fins (20), each heat dissipation fin (20) having a guide line (21), and at least a portion of the heat dissipation fins (20) having their first ends (22) spaced apart along the first direction (X) and aligned with each other in the first direction (X).

4. The fuel tank structure according to claim 3, characterized in that, The plurality of heat dissipation fins (20) constitute a first heat dissipation unit (30), the first ends (22) of all the heat dissipation fins (20) of the first heat dissipation unit (30) are arranged at intervals along the first direction (X), and the second ends (23) of all the heat dissipation fins (20) of the first heat dissipation unit (30) are arranged at intervals along the first direction (X). The plurality of heat dissipation fins (20) constitute a second heat dissipation unit (40), which is located on the side of the first heat dissipation unit (30) facing the bottom of the oil tank in the first direction (X). The first ends (22) of all the heat dissipation fins (20) of the second heat dissipation unit (40) are arranged at intervals along the first direction (X), and the second ends (23) of all the heat dissipation fins (20) of the second heat dissipation unit (40) are arranged at intervals along the third direction (Z).

5. The fuel tank structure according to claim 4, characterized in that, The fuel tank structure includes multiple heat dissipation components (50), each heat dissipation component (50) includes a first heat dissipation unit (30) and a second heat dissipation unit (40), and the multiple heat dissipation components (50) are arranged at intervals along a third direction (Z) on the heat dissipation surface (11), and the third direction (Z) intersects with both the first direction (X) and the second direction (Y).

6. The fuel tank structure according to claim 4, characterized in that, Each of the heat dissipation fins (20) extends by a length H in the second direction (Y). In the direction from the bottom of the oil tank to the top of the oil tank, the length H of all the heat dissipation fins (20) of the first heat dissipation unit (30) gradually increases, the length H of all the heat dissipation fins (20) of the second heat dissipation unit (40) gradually increases, and the length H of all the heat dissipation fins (20) of the first heat dissipation unit (30) is greater than the length H of all the heat dissipation fins (20) of the second heat dissipation unit (40).

7. The fuel tank structure according to claim 1, characterized in that, An oxide film is formed on the surface of the heat dissipation fins (20), and the thickness of the oxide film is 10μm-25μm.

8. The fuel tank structure according to claim 1, characterized in that, The heat dissipation fins (20) and the oil tank body (10) are integrally formed.

9. A transformer, characterized in that, Includes the fuel tank structure as described in any one of claims 1-8.

10. A method for designing heat dissipation fins, applied to the fuel tank structure as described in any one of claims 1-8, characterized in that, The design method for the heat dissipation fins includes the following steps: S1: Select the height H, spacing P and rolling circle radius r of the heat dissipation fins as the design parameters of the heat dissipation fins. H is the length of the heat dissipation fin (20) extending out of the oil tank body (10), P is the spacing between two adjacent heat dissipation fins (20) in the height direction of the oil tank body (10), and r is the rolling circle radius of the cycloid corresponding to the heat dissipation fin (20). S2: Based on the design parameters determined in step S1, construct the experimental scheme using the full factorial experimental design method to generate multiple sets of parameter combinations; S3: Simulation calculations are performed on all parameter combinations using a hybrid method combining finite element local simulation and analytical global analysis, and the equivalent heat dissipation coefficient corresponding to each parameter combination is obtained. S4: Based on all the parameter combinations and all the equivalent heat dissipation coefficients, a second-order polynomial fitting method is used to establish a heat dissipation response surface model and a cost response surface model of the equivalent heat dissipation coefficient with respect to the three design parameters H, P and r. S5: With the optimization objectives of maximizing heat dissipation and minimizing cost, multi-objective optimization is performed using the heat dissipation response surface model and cost response surface model established in step S4.

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