An axial ventilation convection heat exchanger using additive manufacturing

Abstract

The present invention provides an axial ventilation convection heat exchanger using additive manufacturing, which is mainly used for the internal ventilation cooling of the stator shaft of an outer rotor motor and can also be used in other similar heat dissipation occasions. The heat exchanger has a cylindrical structure and is formed by sweeping a two-dimensional circular ring-shaped planar structure. The two-dimensional circular ring-shaped planar structure includes an inner and outer shaft connection part, fins, and connecting rods. The inner and outer shaft connection part includes an inner shaft and an outer shaft respectively used for coupling with a heat source surface or other support and installation structures. The heat exchanger is made of a high thermal conductivity material and provides a unique structural design that maximizes the use of the internal space. The heat exchanger includes multiple layers of fins and multiple layers of connecting rods arranged alternately and connected to form multiple fins of the radiator. The multiple fins are connected by two rings of the inner shaft and the outer shaft. The size and number of each layer of fins have corresponding design limitations, and the adjacent inner and outer layers of fins are connected through the connecting rods of each layer. The size distribution of the fins and the air gap is uniform, and under the external condition of axial ventilation, it has good thermal conductivity and heat dissipation efficiency at the same time.

Description

Technical Field

[0001] The present invention provides an axial ventilation convection heat exchanger processed by additive manufacturing technology, which is mainly used for the internal cooling of the shaft of an outer rotor motor and can also be used for the heat dissipation of other circumferential cylindrical components, belonging to the technical field of motor manufacturing. Background Art

[0002] The main heat-generating components of a motor are the stator core and winding. For an outer rotor motor, the rotor is located on the outside and is easy to dissipate heat, but the heat of the stator core and winding is difficult to be conducted out through the air gap; currently, the stator core of an outer rotor motor is usually fixed by a stator shaft, resulting in a poor ventilation environment inside the motor, and the idea of relying on internal shaft ventilation convection heat dissipation cannot be realized. The high temperature rise of the stator assembly of an outer rotor motor severely limits the current density and output torque during the operation of the motor. Therefore, an axial ventilation convection heat exchanger processed by additive manufacturing technology is proposed, which also serves as the support structure of the stator of the outer rotor motor. Relying on its high thermal conductivity and large convective heat transfer area, the high temperature rise problem inside the motor is greatly improved, the long-time working torque of the motor is increased, and the working life of the motor is extended.

[0003] Additive manufacturing technology, that is, 3D printing, is widely used in the processing of various complex structures due to its high forming freedom and high processing accuracy. Additive manufacturing heat exchangers have been applied in the heat dissipation fields of electronic products, automobiles, aircrafts, medical devices, etc. This technology still has good research prospects in the design of motor cooling structures.

[0004] Currently, the design of similar heat exchangers mainly focuses on increasing the convective heat transfer area, and multiple branches are added to the radial fins. However, there are no specific rules for the design of the branches, and the air gap sizes between the heat dissipation fins vary greatly, resulting in insufficient utilization of the space; the flow directions of some branches are not conducive to the radial heat transfer of the heat exchanger, only increasing the convective heat transfer area. In order to increase the fins as much as possible, it is often necessary to reduce the volume of a single fin, but this will greatly affect the radial heat transfer of the heat exchanger.

[0005] Although currently there have also appeared heat exchangers with grid-like and porous-like structures, which have a large contact area with air, they require a large pressure provided by an external environment such as a fan and are not convenient for axial ventilation occasions. Therefore, traditional finned heat exchangers are still widely used, but there is a lack of design methods with high space utilization and high heat transfer efficiency. Summary of the Invention

[0006] In order to solve the problem that the heat dissipation of the stator assembly of an outer rotor motor is difficult, resulting in a low long-time working torque of the motor, the present invention provides an axial ventilation convection heat exchanger processed by additive manufacturing technology.

[0007] The specific technical solution of the present invention is as follows:

[0008] An axial ventilation convection heat exchanger using additive manufacturing, the heat exchanger being of a cylindrical structure, formed by sweeping a two-dimensional circular ring-shaped planar structure, the two-dimensional circular ring-shaped planar structure including an inner and outer shaft connection part, fins and connecting rods, the inner and outer shaft connection part including an inner shaft and an outer shaft respectively used for coupling with a heat source surface or other support and installation structures;

[0009] The fins are radially divided into m layers from the inside out, and each layer is evenly distributed with arc-edge rectangles of equivalent specifications along the circumferential direction (formed by stretching an arc with the central axis as the center of the circle radially outwards, and approximated as a rectangle due to the small central angle of the arc); the number of arc-edge rectangles in each layer increases with the increase of the radius;

[0010] The connecting rods are radially divided into n layers from the inside out, arranged alternately with the fins, and are used for connecting the fins of adjacent inner and outer layers, being polygonal, each inner side of the connecting rod corresponding to and connecting with one fin of the inner layer, and each outer side of the connecting rod corresponding to and connecting with one or two fins of the outer layer. After the connected fins and connecting rods are combined with the inner and outer shaft connection part, the two-dimensional circular ring-shaped planar structure of the heat exchanger is obtained;

[0011] An air gap is provided between adjacent fins in each layer, and correspondingly, an air gap is provided between adjacent connecting rods in each layer, and the sizes of the two air gaps are equivalent;

[0012] The parameters of the heat exchanger are defined as follows: inner shaft diameter D1, outer shaft diameter D2, inner shaft connection thickness L1, outer shaft connection thickness L2; central angle θ of the arc of the i-th layer of fins i , radius r of the arc i , so fin arc length ε = θ i r i , fin radial length (length of the arc stretched radially) is l i , number of fins S i , i takes values from 1 to m; air gap arc length δ between the arcs of adjacent fins in each layer, radial length of the i-th layer of connecting rod is d i , numbers of the connecting rods connecting with one fin and two fins in the i-th layer are a i and b i respectively, m and n are the maximum numbers of fin layers and connecting rod layers respectively, n = m or n = m - 1.

[0013] The fin arc length ε and the air gap arc length δ match the precision of the additive manufacturing printing equipment, being respectively greater than or equal to the minimum structure size and the minimum gap size of the additive manufacturing printing equipment, and the arc length of the connecting rod is consistent with the arc lengths of the two layers of fins it connects.

[0014] Number of fins S in the i-th layer i and number of fins S in the (i + 1)-th layer i+1 are both integers, S i and Si+1 There are common factors between them, and the value is determined according to the fin density requirements, where S i (δ+ε)=2πr i , S i+1 (δ+ε)=2πr i+1 ;

[0015] By S i With S i+1 Determine the radius r of the arc i and r i+1 , further determine the radial length of the corresponding layer of fins and the radial length of the connecting rod, and select the radial length of each layer of fins and connecting rods to be equal, that is, l i =d i =(r i+1 -r i ) / 2; the arc length ε of the fin is a constant value, and each layer is equal, where ε=θ i r i ,θ i and r i Each changes, where the radius of the arc of the first layer of fins r1 = D1 / 2 + L1, thereby determining the number S1 of the first layer of fins.

[0016] The number of connecting rods in the i-th layer is equal to the number of fins in the i-th layer on the inside S i , the number of one-to-one links in the i-th layer is a i =S i -b i , the number of a pair of two-links b i =S i+1 -S i .

[0017] For the double connecting rod connected to the fins in a pair of two, a single-end structure is adopted at one end and a double-end structure at one end. The single-end side is connected to one fin of the inner layer, and the double-end end is connected to two adjacent fins of the outer layer.

[0018] The fins and connecting rods connected one to one are distributed along the same radial direction as much as possible, with a small offset angle; the inner fins of the fins and connecting rods connected one to two are located between the two outer fins; the double connecting rods in each layer of connecting rods are evenly distributed along the circular direction.

[0019] There are two forms of relationship between the number of layers of fins and connecting rods, n=m or n=m-1; when n=m, the outermost layer is the connecting rod, when n=m-1, the outermost layer is the fin, and the size of the outermost connecting rod or the outermost fin does not exceed the range of the outer shaft diameter D2.

[0020] The axial ventilation convection heat exchanger of the present invention using additive manufacturing is mainly used for the internal ventilation cooling of the stator shaft of an outer rotor motor, and can also be used in other similar heat dissipation occasions. The heat exchanger is made of high thermal conductivity materials, and a unique structural design is proposed to maximize the utilization of the internal space. The heat exchanger includes multiple layers of fins and multiple layers of connecting rods. The fins and the connecting rods are arranged alternately and connected to form multiple fins of the radiator. The multiple fins are connected by two rings, an inner shaft and an outer shaft. The size and number of each layer of fins have corresponding design limitations, and the adjacent inner and outer layers of fins are connected through the connecting rods of each layer. The size distribution of the fins and the air gap is uniform, and under the external condition of axial ventilation, it has good thermal conductivity and heat dissipation efficiency at the same time.

[0021] The present invention has the following advantages compared with the prior art:

[0022] 1. The axial ventilation convection heat exchanger of the present invention using additive manufacturing maintains the fin thickness and the air gap length basically unchanged by increasing the number of fins layer by layer, providing a design idea for fins with a high space utilization rate; the fin directions are basically distributed radially, and the number is large. Even if the volume of a single fin is small, it can still meet the radial heat transfer requirements of the heat exchanger. When manufacturing the heat exchanger, the additive manufacturing technology is introduced mainly because the designed structural dimensions are fine and the paths are complex, making it difficult to form by traditional machining; the fin arc length and the air gap arc length required in the design match the precision requirements proposed by the additive manufacturing technology, making full use of the forming advantages of the additive manufacturing technology.

[0023] 2. The heat exchanger of the present invention is installed inside the shaft of the outer rotor motor, replacing the traditional solid stator shaft structure, which can effectively reduce the overall mass of the motor and improve the ventilation environment inside the motor. The design concept of this structure is a relatively innovative cooling method for outer rotor motors. Cooperating with an end fan or applied to strong convection occasions such as aircraft electric propulsion, it has a significant heat dissipation effect.

[0024] 3. Since the available space inside the motor is small and the size of the heat exchanger is small, it is necessary to rely on additive manufacturing technology to complete the processing. According to the minimum structural size and the minimum gap size recommended by this technology, the fin thickness and the air gap length of the heat exchanger are determined, and as much as possible, the solid heat transfer part and the air convection space are retained under the limited size, ensuring the heat transfer and heat dissipation capabilities of the heat exchanger. Description of the Drawings

[0025] Figure 1 It is a schematic diagram of the coupled installation of the heat exchanger and the stator structure of the outer rotor motor;

[0026] Figure 2 It is a schematic diagram of the whole heat exchanger;

[0027] Figure 3 It is a schematic flow diagram of the manufacturing process of the heat exchanger;

[0028] Figure 4 Schematic diagram of the connection structure and parameters of the inner and outer shaft connection part

[0029] Figure 5 Schematic diagram of the local structure and parameters of the fin

[0030] Figure 6 Schematic diagram of the local structure and parameters of the connecting rod

[0031] Figure 7 Entity diagram of the heat exchanger formed by the two-dimensional structure

[0032] In the figure, 1: heat exchanger; 2: motor stator; 3: inner and outer shaft connection part, 3-1: inner shaft, 3-2: outer shaft; 4: fin, 4-1 to 4-m: the 1st to mth layer of fins; 5: connecting rod, 5-1 to 5-n: the 1st to nth layer of connecting rods; 6: air gap arc; in the partial enlarged view, O represents the coordinate origin.

[0033] Description of each parameter: D1, inner shaft diameter; D2, outer shaft diameter; L1, inner shaft thickness; L2, outer shaft thickness; ε, fin arc length; m, maximum number of fin layers; θ i , central angle of the arc of a single fin in the ith layer; r i , fin arc radius in the ith layer; l i , radial length of the fin in the ith layer; S i , number of fins in the ith layer; δ, air gap arc length; n, maximum number of connecting rod layers; d i , radial length of the connecting rod in the ith layer; a i , number of one-to-one form connecting rods in the ith layer; b i , number of one-to-two form connecting rods in the ith layer. Detailed implementation method

[0034] The present invention will be further described below in conjunction with the drawings and embodiments

[0035] Embodiment 1:

[0036] As Figure 1 shown, the heat exchanger designed by the present invention is in direct contact with the outer rotor motor stator. The figure shows the installation schematic diagram. For specific installation, appropriate mechanical measures can be selected at the end or contact surface of the motor stator 2 to fix the heat exchanger 1, such as slotting and threading. Figure 1 Show the cross-sectional structure of the installation of the two.

[0037] Figure 2 Show the contour diagrams of the three main structures before sharing topological combination in the implementation case of the present invention.

[0038] The axial ventilation convection heat exchanger of the present invention adopts additive manufacturing. The overall structure of the heat exchanger is cylindrical, and is formed by sweeping a two-dimensional circular ring-shaped planar structure to form a three-dimensional structure. The two-dimensional circular ring-shaped planar structure includes an inner and outer shaft connection part 3, fins 4 and connecting rods 5. The inner and outer shaft connection part 3 includes an inner shaft 3-1 and an outer shaft 3-2 respectively used for coupling with a heat source surface or other support and installation structures;

[0039] As Figure 5 shown, the fins 4 are radially divided into m layers from the inside to the outside, namely 4-1 to 4-m. Each layer is evenly distributed with arc-edge rectangles of equivalent specifications along the circumferential direction. The arc-edge rectangle is formed by stretching an arc with the central axis as the center of the circle radially outwards. Since the central angle of the arc is small, it is approximately a rectangle. The number of arc-edge rectangles increases with the increase of the radius for each layer.

[0040] As Figure 6 shown, the connecting rods 5 are radially divided into n layers from the inside to the outside, namely 5-1 to 5-n. Each layer is arranged in a circle along the circumferential direction and is arranged alternately with the fins 4 for connecting the fins of adjacent inner and outer layers. They are polygonal. The inner side of each connecting rod is correspondingly connected to one fin of the inner layer, and the outer side of each connecting rod is correspondingly connected to one or two fins of the outer layer. After the connected fins and connecting rods are combined with the inner and outer shaft connection parts, the two-dimensional circular ring-shaped planar structure of the heat exchanger is obtained. The fins and connecting rods are arranged alternately and connected to form multiple fins of the radiator. The multiple fins are connected by two rings of the inner shaft and the outer shaft.

[0041] An air gap 6 is provided between adjacent fins of each layer. Correspondingly, an air gap is provided between adjacent connecting rods of each layer, and the sizes of the two air gaps are quite the same; the arc length of the connecting rod is the same as the arc length of the fin or the corresponding arc lengths of two fins;

[0042] The definitions of the parameters of the heat exchanger are as follows: the inner shaft diameter D1, the outer shaft diameter D2, the inner shaft connection thickness L1, the outer shaft connection thickness L2; the central angle θ of the arc of the i-th layer of fins i , the radius r of the arc i , so the fin arc length ε = θ i r i , the radial length of the fin is l i , this length is the length of the arc stretched radially; the number of fins S i , i takes values from 1 to m. The air gap arc length δ between the arcs of adjacent fins of each layer, the radial length of the i-th layer of connecting rod is d i , the numbers of the connecting rods connecting to one fin and two fins of the i-th layer are a i and b i respectively, and m and n are the maximum numbers of fin layers and connecting rod layers respectively, and n = m or n = m - 1.

[0043] The fin arc length ε and the air gap arc length δ match the accuracy of the additive manufacturing printing equipment, being respectively greater than or equal to the minimum structure size and the minimum gap size of the additive manufacturing printing equipment. The connecting rod arc length is consistent with the fin arc lengths of the two layers it connects.

[0044] The number of fins S in the i-th layer i and the number of fins S in the (i + 1)-th layer i+1 are both integers. There is a common factor between S i and S i+1 , and the value is specifically determined according to the requirement of fin density. Among them, S i (δ + ε) = 2πr i , S i+1 (δ + ε) = 2πr i+1 ; r i is reserved to two decimal places when determined according to the formula.

[0045] From S i and S i+1 , the radius r of the arc is determined i and r i+1 . Further, the radial lengths of the fins and the connecting rods in the corresponding layers are determined. Generally, the radial lengths of the fins and the connecting rods in each layer are selected to be equal, that is, l i = d i = (r i+1 - r i ) / 2; the fin arc length ε is a fixed value and is equal in each layer, where ε = θ i r i , and θ i and r i vary respectively.

[0046] In the heat exchanger structure, the first layer on the inner shaft side is fins, and then fins and connecting rods are arranged alternately layer by layer. Among them, the radius r1 of the arc of the first layer of fins is r1 = D1 / 2 + L1, from which the number S1 of the first layer can be determined; the number of connecting rods in the i-th layer is equal to the number S of fins in the i-th layer on the inner side i , the number a of one-to-one connecting rods in the i-th layer i = S i - b i , and the number b of one-to-two connecting rods i = S i+1 - S i .

[0047] For the double connecting rod with a one-to-two connection to the fin, it adopts a structure with one single-end and one double-end. The single-end side is connected to one fin in the inner layer, and the double-end side is connected to two adjacent fins in the outer layer. As Figure 6 shown, the double connecting rod with a one-to-two connection is in a nearly V shape. The double-head part at the upper part of the V shape has the same arc length as the adjacent outer-layer fins and is connected;

[0048] The fins and connecting rods with one-to-one connection are preferably distributed along the same radial direction with a small offset angle; for the fins and connecting rods with one-to-two connection, the inner fins are located in the middle of the two outer fins; in each layer of connecting rods, the double connecting rods are evenly distributed along the circumferential direction.

[0049] There are two forms of the layer relationship between the fins and the connecting rods, n = m or n = m - 1; when n = m, the outermost layer is the connecting rod, and when n = m - 1, the outermost layer is the fin. The size of the outermost connecting rod or the outermost fin does not exceed the range of the outer shaft diameter D2.

[0050] The multiple layers of fins and multiple layers of connecting rods of the heat exchanger are arranged alternately and connected to form multiple fins of the radiator, and the multiple fins are connected by two rings of the inner shaft and the outer shaft. The size and number of fins in each layer have corresponding design limitations, and the adjacent inner and outer layers of fins are connected through the connecting rods of each layer. The size distribution of the fins and the air gap is uniform, and under the external condition of axial ventilation, it has good heat conduction performance and heat dissipation efficiency at the same time.

[0051] Embodiment 2:

[0052] Figure 3 For the design process of the two-dimensional structure proposed by the present invention, the following will specifically describe each part in combination with other drawings and implementation processes. Figure 3 Specific descriptions will be made for each part.

[0053] As Figure 3 , first, the connection structure of the inner shaft and the outer shaft is as Figure 4 shown, and the two together constitute the general framework of the two-dimensional plane of the heat exchanger. D1 and D2 are mainly determined by the application scenario of the heat exchanger, while L1 and L2 need to consider the mechanical strength of the heat exchanger or whether there is a margin in the installation structure, and the present invention does not make strict restrictions. In this example, the inner shaft diameter D1 is 30 mm, the outer shaft diameter D2 is 70 mm, and the connection thicknesses L1 and L2 are 1.3 mm and 1.5 mm respectively.

[0054] Furthermore, it is necessary to determine the fin arc length ε and the air gap arc length δ. The purpose of the process of the present invention is to process using additive manufacturing technology and make full use of the limited space. Therefore, ε and δ should be equal to the recommended minimum structure size and the minimum gap size of this technology processing respectively. In actual applications, other external factors such as mechanical strength and pressure loss may need to be considered, and the implementer can limit the sizes of ε and δ as needed. The significance of the present invention is that the designed structure size is closely related to these two, the size distribution of the fins and the air gap is uniform, and through variance analysis verification by the inventor, the sizes of these two have the greatest impact on the working performance of the heat exchanger. This implementation case is an application case optimized by the inventor through orthogonal experiments, and both ε and δ are determined to be 0.8 mm.

[0055] According to Figure 3, Further, determine that the radius of the first - layer fin arc \(r1 = D1 / 2+L1 = 16.3\mathrm{mm}\), and the central angle of a single fin arc in the first layer \(\theta1 = 2.81^{\circ}\). To satisfy \(S\) i (\(\delta+\varepsilon\)) = \(2\pi r\) i , the number of single fin arcs in the first layer \(S1 = 64\), that is, the first - layer fin structure is composed of 64 arc - edged rectangles.

[0056] If the X - axis is taken as the starting point and the counter - clockwise rotation is in the positive order, for the first fin in the \(i\) - th layer of fins, the included angle between its central axis and the X - axis is \(180^{\circ} / S\) i , and the remaining fins in this layer are symmetrically distributed along the X - axis in a counter - clockwise rotation. Therefore, in this example, the included angle between the central axis of the first fin and the X - axis is \(180^{\circ} / S1 = 2.8125^{\circ}\). Thus, first design the arc edges of the 64 fins in the first layer. At this time, judge whether the radius of the fin arc exceeds the limit, \(r1\lt D2 / 2 - L2 = 33.5\mathrm{mm}\), and since it does not exceed the limit, enter the loop part.

[0057] According to Figure 3 , determine the parameters of the fin arc of the next layer. Assume that the greatest common divisor of \(S\) i and \(S\) i+1 is \(x\) i . Theoretically, the number of fins \(S\) i and the greatest common divisor \(x\) i of each subsequent layer can be determined by themselves. However, according to the relationship

[0058]

[0059] When \((\delta+\varepsilon)\) is a fixed value, if the difference between \(S\) i+1 and \(S\) i is small, it will lead to a small radial length of each layer of fins and connecting rods, resulting in poor heat - conduction ability; if it is large, it will lead to a long radial length, large air - gap changes, and insufficient space utilization. When designing the values, the working effect of the heat exchanger needs to be considered, and appropriate \(S\) i+1 and \(x\) i should be selected. According to the above content, it is easy to infer that \(b\) i should be an integer multiple of \(x\) i , but should try to satisfy \(x\) i = \(S\) i+1 - \(S\) i = \(b\) i .

[0060] In this example, first take \(S2 = 72\), and correspondingly take \(x1 = b1 = 8\). Similarly, according to \(S\) i (\(\delta+\varepsilon\)) = \(2\pi r\) i, it is determined that r2 is 18.33 mm, θ2 is 2.50°, and the included angle between the central axis of the first fin and the X-axis is 180° / S2 = 2.5°. Thus, the arc structure of the second layer of fins can be designed.

[0061] According to Figure 3 , the relevant parameters of the radial length between the first layer and the second layer of fins are determined next. According to d i +l i =r i+1 -r i , to ensure the uniformity of the air gap, generally l i =d i =(r i+1 -r i ) / 2, l1 = d1 = (r2 - r1) / 2 = 1.02 mm. Further, the first layer of fins can be formed by stretching the first layer of arc according to l1.

[0062] According to Figure 3 , the design of the first layer of connecting rod structure is carried out next. Connect the tail of the stretched first layer of fins and the arc of the second layer of fins with a polygon to form the first layer of connecting rods. A one-to-one connecting rod is composed of the connecting line of two fin arcs and their endpoints at the corresponding positions; a one-to-two connecting rod is composed of the sequential connecting lines of three fin arcs and their endpoints at the corresponding positions, approximately trapezoidal. Further, a fillet with the air gap arc length as the diameter is opened at the connection between the two outer fin arcs to form an outer double-head structure.

[0063] There is a periodic distribution of each layer of connecting rods, with a total of x i cycles. In each cycle, there are S i / x i inner fins connected to S i+1 / x i outer fins. The one-to-one connecting rod structure appears at the position where the offset angle between adjacent layers of fins is small, and the one-to-two connecting rod structure appears at the position where the offset angle is large and a certain inner fin is located between two outer fins. And the quantities a i and b i should satisfy the relationship of a i +b i =S i , a i +2b i =S i+1 .

[0064] When S1 and S2 are known to be 64 and 72 respectively, the selected common factor x1 is 8. Each cycle of the first-layer connecting rod should connect 64 / 8 = 8 first-layer fins and 72 / 8 = 9 second-layer fins, forming 7 one-to-one connecting rods and 1 one-to-two connecting rod. Taking the counterclockwise direction of the X-axis as the positive sequence, the 4th and 5th fins of the first layer are respectively located between the 4th and 5th and the 5th and 6th fins of the second layer. In this example, it is selected to use the one-to-two connecting rod to connect the 5th fin of the first layer and the 5th and 6th fins of the second layer. In addition, a fillet with the diameter of the air-gap arc length is cut at the tail of the one-to-two connecting rod. The 8 connecting rods repeat x1 = 8 cycles along the circumference, that is, a1 = 56, b1 = 8, satisfying the above relationship. The design of the first-layer connecting rod is completed.

[0065] According to Figure 3 , next, it is necessary to judge whether the radius of the second-layer arc exceeds the limit and enter the loop accordingly.

[0066] According to the above design process of the first-layer fins and connecting rods, the fins of the remaining layers are designed as Figure 5 shown, and the connecting rods of each layer are as Figure 6 shown. In this example, the number of layers S3 to S8 are determined to be 81, 90, 100, 110, 121, 132 in sequence, and the corresponding x2 to x7 and b2 to b7 are selected as 9, 9, 10, 10, 11, 11. After S8 is determined, r8 is determined to be 33.61 mm, and in this example, D2 / 2 - L2 = 33.5 mm, satisfying D2 / 2 - L2 < r8 < D2 / 2. Therefore, Figure 3 the loop in i ends, and at the same time, m = 7 is determined, and the 8th-layer fin cannot appear as the final structure. In addition, according to the selection in this example, taking l i = d i+1 = (r i - r m ) / 2 and the values of S3 to S7, r3 to r7 are 20.63 mm, 22.92 mm, 25.46 mm, 28.01 mm, 30.81 mm respectively. Based on this, θ3 to θ7 are 2.22°, 2.00°, 1.80°, 1.64°, 1.49° respectively, and l2 to l7 are 1.15 mm, 1.15 mm, 1.27 mm, 1.28 mm, 1.40 mm, 1.40 mm respectively.

[0067] In terms of the number of layers of fins and connecting rods, when n = m, it is necessary to satisfy r m + l m < D2 / 2 - L2, D2 / 2 - L2 < r m+1 < D2 / 2. At this time, the (m + 1)th-layer fin only exists for generating the part of the mth-layer connecting rod, and still satisfies d m + l m = r m+1 - r m, and is not used to generate the final two-dimensional structure; when n = m - 1, it is necessary to satisfy r m <D2 / 2 - L2, D2 / 2 - L2 ≤ r m +l m <D2 / 2, and at the same time d n = d m-1 = r m -r m-1 -l m-1 .

[0068] Figure 2 The relationship of m = n = 7 in this example is shown in ,

[0068] , Figure 2 . On the outer side of the seventh-layer connecting rod, that is, the arc size of the eighth-layer fin satisfies D2 / 2 - L2 < r8 < D2 / 2. Therefore, the eighth-layer fin is not designed when generating the heat exchanger structure, but the seventh-layer connecting rod structure is still constructed with the seventh-layer fin and the arc of the eighth-layer fin.

[0069] Figure 7 The physical diagram in ,

[0069] , Figure 7 is generated by sweeping the two-dimensional structure constructed in this example along the Z-axis by 30 mm. The two-dimensional structures applied to other examples can also generate different three-dimensional physical objects along different directions and with different extension lengths.

[0070] Orthogonal test content:

[0071] Adopting the design method of the second embodiment of the present invention, four main parameters affecting the structure are selected, namely the fin arc length ε, the air gap arc length δ, the average fin radial length l ave and the average connecting rod radial length d ave . Since the radial lengths of the fins and connecting rods of each layer are different, the average values are used to reflect.

[0072] Taking these four parameters as factors, a traditional orthogonal test is designed. Each of the four factors takes 4 variables, forming 16 groups of orthogonal test samples, as shown in Table 1 specifically.

[0073] Table 1 Orthogonal test table

[0074]

[0075] For the 16 groups of samples in Table 1, the design method of the present invention is respectively adopted to design different heat exchanger models, and axial ventilation simulations are respectively carried out on them. Three values of wind speed are set, which are 1 m / s, 2 m / s and 3 m / s respectively. The statistics of the simulation results are as follows.

[0076] Three performance indicators are mainly observed: the average temperature, which reflects the overall heat dissipation ability. The lower the temperature, the better the heat dissipation ability; the maximum temperature, which reflects the heat transfer ability. The lower the temperature, the better the heat transfer ability; the pressure loss, which reflects the pressure that the inlet fan needs to provide at the same wind speed.

[0077] Statistically analyze the three performance indicators of 16 groups of sample tests under three wind speed conditions respectively, and organize them in Table 2.

[0078] Table 2 Results of Orthogonal Experiment

[0079]

[0080]

[0081] According to Table 2, calculate the average value of each factor under each performance indicator respectively. For example, for the first factor ε of samples 1, 2, 3, and 4, which are all 0.8 mm, calculate the average value of the three performance indicators of samples 1, 2, 3, and 4. And so on, the statistics are shown in Table 3.

[0082] Table 3 Average Value Table

[0083]

[0084] Under each wind speed condition and each observation index, select the optimal value of each factor and combine them, which is the best combination under each condition.

[0085] As can be seen from Table 3, when the wind speed is 1 m / s, the factor value combination to ensure the lowest average temperature is ε = 0.8 mm, δ = 1.1 mm, l ave = 2.0 mm, d ave = 1.2 mm; the combination to ensure the lowest maximum temperature is 0.8, 1.1, 1.2, 1.2; the combination to ensure the minimum pressure loss is 0.8, 1.4, 1.2, 1.2. Similarly, for 2 m / s, the combinations to ensure the best of the three are 0.8, 0.8, 1.2, 0.8; 0.8, 0.8, 2.0, 2.0 and 0.8, 1.4, 1.2, 1.2 respectively. When the wind speed is 3 m / s, the optimal combinations are 0.8, 0.5, 1.2, 0.8; 0.8, 0.5, 2.0, 2.0 and 0.8, 1.4, 1.2, 1.2 respectively.

[0086] From the optimal combinations, if only considering the heat dissipation capacity and heat transfer capacity and ignoring the pressure loss index, among many combinations, both factors ε and δ take relatively small values. And under the wind speeds of 1 m / s, 2 m / s, and 3 m / s, the value of the air gap arc length δ is affected to a certain extent, because the wind speed also belongs to other factors in practical applications. However, even if the optimal value of δ is different under different wind speeds, it is still more reasonable for δ to take a relatively small value, because among the 16 combinations, the combination with the maximum value of δ set to 1.4 mm is not the optimal under any conditions.

[0087] So far, it is sufficient to show that by using the method of the present invention to determine the minimum values of ε and δ is the optimal design considering the heat transfer and heat dissipation capabilities of the heat exchanger.

[0088] Continue the analysis of variance. Calculate the variance by using the average value of each factor under each index and the total average value of all samples under each index. For example, for the fin arc length factor, the average temperatures at 1 m / s are 106.01, 109.86, 112.09, and 116.47 respectively. Calculate the variance using these four values and the total average temperature of 111.11. And so on, to obtain Table 4.

[0089] Table 4 Variance Table

[0090]

[0091] The variance table reflects the degree to which the corresponding index deviates from the average level when each factor changes. In other words, it reflects the influence degree of each factor on a single index. The larger the variance under the same index, the greater the influence of the factor on the index.

[0092] It can be seen that for each index, the influence of the air gap arc length δ is the greatest, followed by the fin arc length ε, and the two radial lengths l ave and d ave have comparable influence, and are far less than the influence of the other two.

[0093] So far, it can be seen that in the design method proposed in the present invention, δ and ε have the greatest influence on the performance of the heat exchanger in various aspects. Especially in the two indexes of average temperature and maximum temperature, it can be seen the influence of δ and ε on the heat dissipation and heat transfer performance. As mentioned in the analysis of Table 3, both δ and ε should be minimized as much as possible.

[0094] Therefore, the inventor concludes that when not considering the influence of other external factors, δ and ε are the main parameters affecting the heat transfer and heat dissipation performance of the heat exchanger, and should be minimized as much as possible; while the influence of the average radial lengths l ave and d ave is relatively small, and can be determined according to the mathematical relationship in the invention design process.

[0095] For the example selection of the present invention, the inventor considered comprehensive factors such as wind speed and pressure loss, and finally determined the four indexes as 0.8, 0.8, 1.2, and 1.2, without choosing the minimum size restricted by additive manufacturing processing.

[0096] To verify the above conclusion, the inventor also designed a combination with δ and ε being 0.8 and 0.6 respectively. In Table 5, the inventor compared three combinations. The three combinations are: ① δ = 0.8, ε = 1.2; ② δ = 0.8, ε = 0.8; ③ δ = 0.8, ε = 0.6; ④ δ = 0.5, ε = 0.8. Among them, Scheme ① is the scheme adopted by the inventor in the initial stage of this invention, and Scheme ② is the optimized scheme after the above orthogonal test work. Scheme ③ is the scheme proposed by the inventor to verify that when the fin arc length ε is smaller, the heat dissipation and heat transfer ability are better. Scheme ④ is based on Scheme ②, keeping ε unchanged and reducing δ to 0.5 mm.

[0097] Table 5 Simulation Comparison of Several Schemes

[0098]

[0099]

[0100] It can be seen that when the values of δ and ε are relatively small, better results will indeed be obtained.

[0101] Comparing Schemes ①②③, it is reflected that when δ remains unchanged and ε is smaller, the average temperature is lower, indicating better heat dissipation, and the highest temperature is lower, indicating better heat conduction.

[0102] Comparing Scheme ② and Scheme ④, it is reflected that when keeping ε unchanged and reducing δ, the heat dissipation and heat transfer ability of the heat exchanger become worse at low wind speeds, but become better at high wind speeds, and there is still room for further increase in wind speed. Therefore, generally speaking, the smaller the air gap arc length, the better the performance of the heat exchanger.

[0103] However, from the results of pressure loss, it is consistent with the previous orthogonal test analysis. When considering pressure loss, the air gap arc length is not the smaller the better, and reducing the air gap arc length will bring a large pressure loss. When the air gap arc length remains unchanged and the fin arc length decreases, the space occupied by the air gap becomes larger, which will reduce the pressure loss.

[0104] From the above comparison work, the heat exchangers designed according to this invention generally have good effects. When only considering the heat transfer and heat dissipation capabilities, the smaller the values of δ and ε, the better the performance of the heat exchanger. Therefore, it is proposed that the minimum values of δ and ε be determined based on the processing accuracy, and by designing the heat exchanger according to this invention, the optimal results can be obtained. When considering other factors such as wind speed and pressure loss, too small values of δ and ε will have a certain negative impact on the effect of the heat exchanger, but it can be seen from the orthogonal test and variance analysis that δ and ε cannot be too large, because these two have a huge impact on the performance of the heat exchanger.

[0105] The requirements that δ and ε should meet are as follows: Considering only the influence of machining accuracy, the minimum value restricted by machining accuracy should be taken; considering other factors, after analysis by the implementer, the minimum value that meets the restrictions of each index should be selected.

Claims

1. An axial ventilation convection heat exchanger using additive manufacturing, characterized in that: The heat exchanger has a cylindrical structure, which is formed by sweeping a two-dimensional circular ring-shaped planar structure. The two-dimensional circular ring-shaped planar structure includes an inner and outer shaft connection part, fins, and connecting rods. The inner and outer shaft connection part includes an inner shaft and an outer shaft; the fins are radially divided into m layers from the inside to the outside, and each layer is evenly distributed with arc-edge rectangles of equivalent specifications along the circumferential direction; the number of arc-edge rectangles in each layer increases as the radius increases. The connecting rods are radially divided into n layers from the inside to the outside, arranged alternately with the fins, and are used for connecting the fins of two adjacent inner and outer layers. The connecting rods are polygonal. The inner side of each connecting rod is correspondingly connected to one fin of the inner layer, and the outer side of each connecting rod is correspondingly connected to one or two fins of the outer layer. After the connected fins and connecting rods are combined with the inner and outer shaft connection part, the two-dimensional circular ring-shaped planar structure of the heat exchanger is obtained. An air gap is provided between adjacent fins in each layer. Correspondingly, an air gap is provided between adjacent connecting rods in each layer, and the sizes of the two air gaps are equivalent. The definitions of the parameters of this heat exchanger are as follows: the inner shaft diameter D1, the outer shaft diameter D2, the inner shaft connection thickness L1, the outer shaft connection thickness L2; the central angle θ of the fin arc of the i-th layer i , the radius r of the arc i , so the fin arc length ε = θ i r i , the fin radial length is l i , the number of fins S i , i takes values from 1 to m; the air gap arc length δ between two adjacent fin arcs of each layer, the radial length of the connecting rod of the i-th layer is d i , the numbers of the connecting rods connecting the i-th layer to one fin and two fins are a i and b i , m and n are the maximum numbers of fin layers and connecting rod layers respectively, n = m or n = m - 1.

2. The axial ventilation convection heat exchanger using additive manufacturing according to claim 1, characterized in that: The arc length ε of the fins and the arc length δ of the air gap match the accuracy of the additive manufacturing printing equipment, and are respectively greater than or equal to the minimum structure size and the minimum gap size of the additive manufacturing printing equipment. The arc length of the connecting rod is consistent with the arc lengths of the two layers of fins it connects.

3. The axial ventilation convection heat exchanger using additive manufacturing according to claim 1, characterized in that: The number of fins S in the i-th layer i and the number of fins S in the (i + 1)-th layer i+1 are both integers. There is a common factor between S i and S i+1 , and the specific value is determined according to the requirement of fin density. Among them, S i (δ + ε) = 2πr i , S i+1 (δ + ε) = 2πr i+1 ; From S i and S i+1 Determine the radius r of the arc i and r i+1 , further determine the radial length of the corresponding layer of fins and the radial length of the connecting rod, and select the radial lengths of each layer of fins and the connecting rod to be equal, that is, l i = d i = (r i+1 - r i ) / 2; the arc length ε of the fins is a fixed value and is equal for each layer, where ε = θ i r i , θ i and r i vary independently; where the radius r1 of the arc of the fins in the first layer = D1 / 2 + L1, from which the number S1 in the first layer can be determined.

4. The axial ventilation convection heat exchanger using additive manufacturing according to claim 1, characterized in that: The number of linkages in the i-th layer is equal to the number S of fins in the inner i-th layer i , the number a of one-to-one linkages in the i-th layer i = S i - b i , the number b of one-to-two linkages i = S i+1 - S i .

5. The axial ventilation convection heat exchanger using additive manufacturing according to claim 1, characterized in that: For the double connecting rods with a one-to-two connection to the fins, a one-end single-head and one-end double-head structure is adopted. The single-head side is connected to one fin of the inner layer, and the double-head end is connected to two adjacent fins of the outer layer. The fins and connecting rods with a one-to-one connection are preferably distributed along the same radial direction with a small offset angle; for the fins and connecting rods with a one-to-two connection, the inner fin is located in the middle of the two outer fins; the double connecting rods in each layer of connecting rods are evenly distributed along the circumferential direction.

6. The axial ventilation convection heat exchanger using additive manufacturing according to claim 1, characterized in that: There are two forms of the layer relationship between the fins and the connecting rods, n = m or n = m - 1; when n = m, the outermost layer is a connecting rod, and when n = m - 1, the outermost layer is a fin. The sizes of the outermost connecting rod or the outermost fin do not exceed the range of the outer shaft diameter D2.

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