Heat pipe
By designing a combination of three-dimensional and two-dimensional capillary structures in the heat pipe, the problems of large thermal resistance, large space occupation, difficult process and low compatibility in existing heat pipes are solved, and more efficient heat dissipation and better heat source compatibility are achieved.
Patent Information
- Application Number
- CN202421755924.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-23
- Publication Date
- 2025-06-24
- Estimated Expiration
- 2034-07-23
AI Technical Summary
The capillary structure in existing heat pipes has a large thermal resistance, too much space in the pipe body, difficult process, and low compatibility with different heat sources, making it difficult to effectively improve heat dissipation capabilities.
A heat pipe is designed, and the pipe body has a hollow structure, and a first capillary structure with a three-dimensional structure and a second capillary structure with a two-dimensional structure are provided. The first capillary structure extends axially along the tube body, and the second capillary structure surrounds the first capillary structure and attaches to the tube wall of the tube body. The two are connected to one outside the tube body and are then arranged in the hollow structure.
With this design, the thermal resistance from the evaporation section to the heat dissipation section is reduced, the maximum heat transfer is improved, and the compatibility of the heat pipe with different heat sources is improved, while simplifying the process and saving material costs.
Smart Images
Figure CN223021014U_ABST
Abstract
Description
Technical Field
[0001] This application relates to a heat pipe, and more particularly to a heat pipe having a capillary structure therein. Background Art
[0002] Known heat pipes mainly consist of a closed tube body, a capillary structure disposed within the tube body, and a heat transfer fluid filled within the tube body. The heat pipe can be divided into an evaporation section and a heat dissipation section. In use, the evaporation section of the heat pipe is placed close to the heat source. The heat generated by the heat source causes the heat transfer fluid in the evaporation section to evaporate and gasify. The generated vapor flows to the heat dissipation section, where it releases latent heat and condenses back into a liquid, and then the liquid is guided back to the evaporation section through the capillary structure. Thus, the heat pipe can achieve the purpose of dissipating heat from the heat source.
[0003] Currently, it is known to use woven mesh and fiber technologies in heat pipes to form capillary structures. However, the known capillary structures have disadvantages such as relatively large thermal resistance, occupying too much internal space of the tube body, difficult processes, and low compatibility with different heat sources.
[0004] Therefore, how to increase the heat transfer space and improve the heat dissipation ability without affecting the process has become an important issue. Summary of the Utility Model
[0005] According to some embodiments of the present application, there is provided a heat pipe, including: a tube body, a first capillary structure, and a second capillary structure. The tube body has a hollow structure. The first capillary structure is disposed in the tube body, extends along an axial direction of the tube body, and has a three-dimensional structure. The second capillary structure surrounds the first capillary structure, adheres to a tube wall of the tube body, and has a two-dimensional structure. The first capillary structure and the second capillary structure are connected into one body outside the tube body first, and then disposed in the hollow structure. The second capillary structure has an opening, the first capillary structure is exposed through the opening, and the exposed part of the first capillary structure contacts the tube wall.
[0006] In some embodiments, the length of the second capillary structure extending along the tube wall is three-quarters of the perimeter of the cross-section of the tube body in a direction perpendicular to the axial direction.
[0007] In some embodiments, the tube body includes an evaporation section and two heat dissipation sections. The evaporation section is located between the two heat dissipation sections. The evaporation section corresponds to one or more heat sources outside the heat pipe.
[0008] In some embodiments, the first capillary structure is located in the evaporation section and the two heat dissipation sections, and the second capillary structure is only located in the evaporation section.
[0009] In some embodiments, the part of the first capillary structure located in the two heat dissipation sections only contacts the tube wall on one side.
[0010] In some embodiments, the two heat dissipation sections, the first capillary structure, and the second capillary structure are all line-symmetric with respect to a central line of the evaporation section.
[0011] In some embodiments, the length of the opening of the second capillary structure in the axial direction corresponds to the length of one or more heat sources.
[0012] In some embodiments, the width of the opening of the second capillary structure in a direction perpendicular to the axial direction is greater than the diameter of the first capillary structure.
[0013] In some embodiments, the second capillary structure further has a support portion disposed in the middle part of the opening, separating the opening into a first opening and a second opening.
[0014] In some embodiments, the lengths of the first opening and the second opening in the axial direction are different and respectively correspond to the lengths of a plurality of heat sources outside the heat pipe. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] As will be best understood from the following detailed description when reading the accompanying drawings. It should be noted that, according to the standard operating mode in the industry, the various features are not necessarily drawn to scale. In fact, the dimensions of the various features may be arbitrarily enlarged or reduced for clear illustration.
[0016] Figure 1A FIG. 21 is a longitudinal sectional view of the heat pipe observed perpendicular to the axial direction according to some embodiments of the present application.
[0017] Figures 1B to 1D FIG. 25 is a radial sectional view of the heat pipe observed along the axial direction according to some embodiments of the present application.
[0018] Figure 2A FIG. 29 is a schematic diagram showing the relative positions of the heat pipe and the heat source according to some embodiments of the present application.
[0019] Figure 2B FIG. 33 is a schematic diagram showing the connection manner of the first capillary structure and the second capillary structure according to some embodiments of the present application.
[0020] Figure 2C FIG. 37 is a schematic diagram showing the connection manner of the first capillary structure and the second capillary structure according to some other embodiments of the present application.
[0021] Figure 3A FIG. 41 is a schematic diagram showing the relative positions of the heat pipe and the heat source according to some other embodiments of the present application.
[0022] Figure 3B FIG. 45 is a schematic diagram showing the connection manner of the first capillary structure and the second capillary structure according to some embodiments of the present application.
[0023] Figure 3CSchematic diagram showing the connection mode of the first capillary structure and the second capillary structure according to still other embodiments of the present application.
[0024] Figure 4A Line graph showing the influence of different capillary structures on the maximum heat transfer amount.
[0025] Figures 4B to 4D For Figure 4A Schematic diagrams of three different capillary structures shown in
[0026] Figure 5 Schematic diagram showing the state of the connection of the first capillary structure and the second capillary structure outside the tube according to still other embodiments of the present application.
[0027] Figure 6 Schematic diagram showing the configuration of the first capillary structure and the second capillary structure in the tube according to still other embodiments of the present application.
[0028] Explanation of reference numerals
[0029] 100: Heat pipe
[0030] 110: Tube body
[0031] 111: Hollow structure
[0032] 112: Tube wall
[0033] 120: First capillary structure
[0034] 130, 130', 130": Second capillary structure
[0035] 135: Opening
[0036] 136: Support part
[0037] 137: First opening
[0038] 138: Second opening
[0039] 200: Heat source
[0040] 201: First heat source
[0041] 202: Second heat source
[0042] A: Axial direction
[0043] C: Heat dissipation section
[0044] D: Diameter
[0045] E: Evaporation section
[0046] L1, L2, L3, L4, L5, L6, L7: Length
[0047] M1: Center line,
[0048] M2: Section line of the heat dissipation section,
[0049] M3: Section line of the heat dissipation section,
[0050] P: Connection point,
[0051] W: Width. Detailed implementation manners
[0052] The following presented content provides many different embodiments or examples, and describes specific examples of each component and arrangement manner to implement different features of the present application. For example, if the present specification describes that a first feature is formed "on" or "above" a second feature, it means that embodiments including direct contact between the first feature and the second feature can be included, and embodiments in which additional features are formed between the first feature and the second feature and the first feature and the second feature are not in direct contact can also be included.
[0053] Relative spatial related terms may be used in the embodiments. For example, terms such as "below", "above", etc. are used to facilitate the description of the relationship between components or features in the drawings and other components or features. Except for the orientations shown in the drawings, these spatial related terms are intended to include different orientations of the device during use or operation. If the device is turned to different orientations (rotated 90 degrees or other orientations), the spatial related terms used herein can also be interpreted in the same way.
[0054] First, please refer to Figures 1A to 1D . Figures 1A to 1D For some embodiments of the present application, it is a schematic diagram showing the cross-section of the heat pipe 100. Among them Figure 1A is a longitudinal cross-sectional view of the heat pipe 100 observed perpendicular to the axial direction A, Figures 1B to 1D is a radial cross-sectional view of the heat pipe 100 observed along the axial direction A.
[0055] It can be seen from Figure 1A that the heat pipe 100 mainly includes a pipe body 110, a first capillary structure 120, and a second capillary structure 130.
[0056] The pipe body 110 is formed into a closed tubular shape, in which a hollow structure 111 is formed, and the hollow structure 111 is surrounded by a pipe wall 112. A heat transfer fluid (not shown) is filled in the hollow structure 111, and heat dissipation can be achieved through the cycle of gasification and liquefaction in the pipe body 110. And, as Figure 1A shown, the pipe body 110 may include an evaporation section E and two heat dissipation sections C. The evaporation section E is located between the two heat dissipation sections C. In some embodiments, the evaporation section E may correspond to one or more heat sources outside the heat pipe 100 (for example: Figure 2AThe heat source 200 shown or Figure 3A the first heat source 201 and the second heat source 202 shown).
[0057] The first capillary structure 120 is disposed in the tube body 110, extends along an axial direction A of the tube body 110, and has a three-dimensional structure. In some embodiments, the first capillary structure 120 may be a fibrous structure and is formed in a long strip shape. As Figure 1A shown, the first capillary structure 120 is located in the evaporation section E and the two heat dissipation sections C of the tube body 110. In other words, the first capillary structure 120 is provided in all sections of the tube body 110.
[0058] The second capillary structure 130 is also disposed in the tube body 110, surrounds the first capillary structure 120 (as Figure 1C shown), adheres to the tube wall 112 of the tube body 110, and has a two-dimensional structure. In some embodiments, the second capillary structure 130 may be a woven mesh structure and is formed in a thin sheet shape (as Figure 2B shown). The structure of the second capillary structure 130 will be further described in detail below. As Figure 1A shown, the second capillary structure 130 is only located in the evaporation section E of the tube body 110, which is beneficial to improving the heat absorption efficiency of the evaporation section E and retaining the internal space of the tube body in the heat dissipation section C.
[0059] Figures 1B to 1D Shows the internal structure of the heat pipe 100 in the evaporation section E and the heat dissipation section C when observed along the axial direction A. Figure 1B , Figure 1D Are respectively cross-sectional views formed by the heat dissipation section profile line M2 and the heat dissipation section profile line M3 along Figure 1A . Figure 1C Is a cross-sectional view formed along the center line M1 of Figure 1A .
[0060] As Figure 1B , Figure 1D shown, the part of the first capillary structure 120 located in the two heat dissipation sections C only contacts the tube wall 112 on one side (the lower side in the drawing). In this way, in addition to improving the heat dissipation efficiency of the contact side, it can also ensure that there is enough space inside the tube body in the heat dissipation section C for the steam to flow. In addition, the part of the first capillary structure 120 located in the evaporation section E also contacts the tube wall 112 on one side to improve the heat dissipation efficiency.
[0061] As Figure 1C shown, in the evaporation section E, the second capillary structure 130 surrounds the first capillary structure 120 and adheres to the tube wall 112. In some embodiments, the length ([[]] Figure 2B shown as the length L1) that the second capillary structure 130 extends along the tube wall 112 is approximately the cross-section of the tube body 110 perpendicular to the axial direction A (as Figure 1CThree quarters of the perimeter of the (displayed cross-section). In this way, the thermal resistance can be effectively reduced, and the maximum heat transfer amount can be increased in a limited space.
[0062] Next, please refer to Figures 2A to 2C and Figures 5 to 6 . Figure 2A FIG. is a schematic diagram showing the relative positions of the heat pipe 100 and the heat source 200 according to some embodiments of the present application. Figure 2B FIG. is a schematic diagram showing the connection manner of the first capillary structure 120 and the second capillary structure 130 according to some embodiments of the present application.
[0063] Figure 2C FIG. is a schematic diagram showing the connection manner of the first capillary structure 120 and the second capillary structure 130' according to some other embodiments of the present application. Among them, Figure 2B and Figure 2C The structures shown are applicable to the heat pipe 100 shown in Figure 2A FIG. Figure 5 FIG. is a schematic diagram showing the state where the first capillary structure 120 and the second capillary structure 130' are connected outside the pipe body 110 according to some other embodiments of the present application. Figure 6 FIG. is a schematic diagram showing the configuration of the first capillary structure 120 and the second capillary structure 130' in the pipe body 110 according to some embodiments of the present application.
[0064] In some embodiments, the heat source 200 is generally located at the central position of the heat pipe 100. Figure 2A and Figure 6 The heat pipes 100 shown in FIG. have a bent structure corresponding to the heat source 200, but the shape of the heat pipe 100 is not limited thereto and can be determined according to requirements. In Figures 2A to 2C FIG., the section of the heat pipe 100 corresponding to the heat source 200 is the evaporation section E, and the section not corresponding to the heat source 200 is the two heat dissipation sections C.
[0065] In some embodiments, the first capillary structure 120 and the second capillary structure 130 are first connected into one body outside the pipe body 110 and then disposed in the hollow structure 111. For example, Figure 2B FIG. shows the state before the first capillary structure 120 and the second capillary structure 130 are disposed into the pipe body 110. At this time, the second capillary structure 130 is simply fixed on the first capillary structure 120. As shown in Figure 2B FIG., the second capillary structure 130 may have an opening 135, and the first capillary structure 120 is exposed from the opening 135. After the first capillary structure 120 and the second capillary structure 130 are disposed in the hollow structure 111, the exposed part of the first capillary structure 120 contacts the pipe wall 112 (as shown in Figures 1B to 1D FIG.) to improve the heat dissipation efficiency.
[0066] In some embodiments, the length of the opening 135 of the second capillary structure 130 in the axial direction A( Figure 1A ) corresponds to the length of the heat source 200. For example, in Figure 2B , the length L2 of the opening 135 corresponds to the length L5 of the heat source 200. In other words, the length of the opening 135 of the second capillary structure 130 can be determined according to the length of the heat source and can be adjusted according to actual needs. Thereby, the compatibility of the heat pipe 100 is improved.
[0067] In some embodiments, the width of the opening 135 of the second capillary structure 130 in a direction perpendicular to the axial direction A( Figure 1A ) is greater than the diameter of the first capillary structure 120. For example, in Figure 2B , the width W of the opening 135 is greater than the diameter D of the first capillary structure 120. In this way, it can be ensured that the first capillary structure 120 has sufficient area exposed from the opening 135, effectively reducing the thermal resistance.
[0068] In Figure 2C and Figure 5 , another embodiment is shown, in which the second capillary structure 130’ has a different structure from the second capillary structure 130 of Figure 2B . Compared with the second capillary structure 130, the second capillary structure 130’ further has a support portion 136 disposed in the middle part of the opening 135, dividing the opening into a first opening 137 and a second opening 138. Similar to the opening 135 of the second capillary structure 130, the first capillary structure 120 can also be exposed from the first opening 137 and the second opening 138 of the second capillary structure 130’.
[0069] Figure 5 Shows the state before the first capillary structure 120 and the second capillary structure 130’ are disposed into the tube body 110. The operator can fix the first capillary structure 120 and the second capillary structure 130’ together in advance and then dispose both of them into the tube body 110. Specifically, as shown in Figure 5 , the operator can pass the first capillary structure 120 upward through the first opening 137 of the second capillary structure 130’, bypass the support portion 136, and then pass downward through the second opening 138. In this way, the bonding force between the first capillary structure 120 and the second capillary structure 130’ can be improved, effectively fixing the two and enhancing the reliability.
[0070] After the first capillary structure 120 and the second capillary structure 130’ are disposed into the tube body 110, in order to fix the second capillary structure 130’, the upper and lower ends of the sheet-like second capillary structure 130’ are joined together so that it adheres to the tube wall 112. Specifically, Figure 2BThe shown connection point P is the joint of the second capillary structure 130. An operator can surround the first capillary structure 120 with the second capillary structure 130 and connect the connection points P at the upper and lower ends together. Figure 1C The shown connection point P is Figure 2B the position where the two connection points P overlap. The second capillary structure 130' is also joined in the same way.
[0071] The state after the first capillary structure 120 and the second capillary structure 130' are arranged inside the tube body 110 is as Figure 6 shown. Figure 6 What is shown is the state where the tube body 110 is cut open and lifted upward. Figure 6 The upper half shows the tube body 110 (only the part of the tube wall 112), and the lower half shows the first capillary structure 120 and the second capillary structure 130' arranged in the tube body 110. As Figure 6 can be seen, as described above, the first capillary structure 120 can be exposed through the first opening 137 and the second opening 138 to contact the upper tube wall 112, so as to reduce the thermal resistance and increase the maximum heat transfer amount.
[0072] In addition, in Figure 2C the shown embodiment, in the axial direction A ( Figure 1A ), the length of the first opening 137 is the same as the length of the second opening 138, and the total length of the first opening 137 and the second opening 138 can correspond to the length L5 ( Figure 2A ) of the heat source 200.
[0073] In Figures 2A to 2C the shown embodiment, the two heat dissipation sections C, the first capillary structure 120 and the second capillary structure 130 (or the second capillary structure 130') are all line-symmetric with respect to the center line (such as Figure 1A the center line M1 shown) of the evaporation section E. The symmetric structure has the advantage that the temperature difference at both ends of the heat pipe 100 is similar.
[0074] Next, please refer to Figures 3A to 3C . Figure 3A FIG. is a schematic diagram showing the relative positions of the heat pipe 100, the first heat source 201 and the second heat source 202 according to some other embodiments of the present application. Figure 3B FIG. is a schematic diagram showing the connection manner between the first capillary structure 120 and the second capillary structure 130 according to some embodiments of the present application. Figure 3C FIG. is a schematic diagram showing the connection manner between the first capillary structure 120 and the second capillary structure 130'' according to still some other embodiments of the present application. Among them, Figure 3B and Figure 3C the shown structures are applicable to Figure 3A the heat pipe 100 shown.
[0075] Figures 3A to 3C The illustrated embodiment is similar to Figures 2A to 2C the illustrated embodiment, and one of the differences is that Figure 3A it includes multiple heat sources instead of a single heat source.
[0076] In some embodiments, the evaporation section E of the heat pipe 100 can correspond to multiple heat sources, such as Figure 3A the first heat source 201 and the second heat source 202 shown. At this time, as Figure 3B shown, the length of the opening 135 of the second capillary structure 130 in the axial direction A ( Figure 1A ) can correspond to the total length of multiple heat sources (for example: the length L6 of the first heat source 201 plus the length L7 of the second heat source 202).
[0077] In Figure 3C another embodiment is shown, in which the second capillary structure 130” has a different structure from Figure 2C the second capillary structure 130’ of. Compared with the second capillary structure 130’, although the second capillary structure 130” also has a support portion 136, a first opening 137 and a second opening 138, the lengths of the first opening 137 and the second opening 138 of the second capillary structure 130” in the axial direction A ( Figure 1A ) are different, and respectively correspond to the lengths of multiple different heat sources. For example, as Figure 3A and Figure 3C shown, the length L3 of the first opening 137 of the second capillary structure 130” corresponds to the length L6 of the first heat source 201, and the length L4 of the second opening 138 corresponds to the length L7 of the second heat source 202. However, the above term “corresponds to” does not mean that the length L3 is equal to the length L6 and the length L4 is equal to the length L7, but rather that in the case where the length L6 of the first heat source 201 is greater than the length L7 of the second heat source 202, the length L3 of the first opening 137 can also be greater than the length L4 of the second opening 138, and vice versa. Therefore, by setting openings with adjustable lengths, the compatibility of the second capillary structure 130 with different heat sources can be further improved.
[0078] In addition, although not shown, in other embodiments, the second capillary structure 130 may also include multiple support portions 136, so that the opening 135 is divided into more than two openings, which can not only further enhance the bonding force between the first capillary structure 120 and the second capillary structure 130, but also adapt to different heat source configurations or quantities.
[0079] Figure 4A is a line graph showing the influence of different capillary structures on the maximum heat transfer amount (Qmax). As Figure 4A shown, the maximum heat transfer amounts achieved by three different capillary structures are compared. Figure 4AThe "woven mesh '0'" shown in [Figure] represents Figure 4B the capillary structure without the second capillary structure 130 shown, which has the lowest maximum heat transfer capacity. Figure 4A The "woven mesh '1 / 2'" shown in [Figure] represents Figure 4C the capillary structure where the second capillary structure 130 only adheres to half of the circumference of the tube wall, which has the second highest maximum heat transfer capacity. Figure 4A The "woven mesh '3 / 4'" shown in [Figure] represents Figure 4D the capillary structure where, according to the present application, the second capillary structure 130 adheres to three - quarters of the circumference of the tube wall, which has the highest maximum heat transfer capacity. Thus, it can be seen that the capillary structure according to the present application can indeed improve the maximum heat transfer capacity in the heat pipe. According to some embodiments of the present application, the maximum heat transfer capacity of the heat pipe can be increased by 10%.
[0080] In addition, Figure 5 and Figure 6 although the combination of the first capillary structure 120 and the second capillary structure 130' is shown, it should be understood that in Figure 5 and Figure 6 the embodiments shown, the second capillary structure 130 or the second capillary structure 130" or other woven mesh structures with suitable sizes can also be used to replace the second capillary structure 130', and it is not limited to the form presented in the present application.
[0081] In summary, the present application provides a heat pipe 100, which has a first capillary structure 120 and a second capillary structure 130 pre - connected and integrated outside the tube body 110. In addition to reducing the process difficulty, saving material costs, and enhancing reliability, it also reduces the thermal resistance from the evaporation section to the heat dissipation section through the opening design to improve the maximum heat transfer capacity. Furthermore, the opening of the second capillary structure 130 can change its form according to the actual heat source configuration, effectively improving the compatibility with different heat sources. And, the second capillary structure 130 of the embodiments of the present application only needs to be arranged in the evaporation section E at the center of the heat pipe 100, which can ensure that there is enough heat transfer space in the heat dissipation section C and improve the heat dissipation capacity.
[0082] Although the embodiments of the present application and their advantages have been shown as above, it should be understood that any person of ordinary skill in the art can make changes, substitutions, and modifications without departing from the spirit and scope of the present application. In addition, the protection scope of the present application is not limited to the processes, machines, manufactures, compositions of matter, devices, methods, and steps in the specific embodiments described in the specification. Any person of ordinary skill in the art can understand the processes, machines, manufactures, compositions of matter, devices, methods, and steps developed currently or in the future from the disclosure of the present application. As long as they can perform substantially the same functions or obtain substantially the same results in the embodiments described herein, they can be used according to the present application. Therefore, the protection scope of the present application includes the above-mentioned processes, machines, manufactures, compositions of matter, devices, methods, and steps. In addition, each claim for patent constitutes an individual embodiment, and the protection scope of the present application also includes the combination of each claim for patent and the embodiments.
Claims
1. A heat pipe, wherein: include: A tube body having a hollow structure; a first capillary structure, disposed in the tube body, extending along an axial direction of the tube body, and having a three-dimensional structure; and a second capillary structure, surrounding the first capillary structure, attached to a tube wall of the tube body, and having a two-dimensional structure; The first capillary structure and the second capillary structure are first connected to form a whole outside the tube body and then arranged in the hollow structure. The second capillary structure has an opening, the first capillary structure is exposed from the opening, and the exposed portion of the first capillary structure contacts the tube wall.
2. The heat pipe according to claim 1, wherein: The length of the second capillary structure extending along the tube wall is three quarters of the circumference of the cross section of the tube body perpendicular to the axial direction.
3. The heat pipe according to claim 1, wherein: The pipe body includes an evaporation section and two heat dissipation sections, wherein the evaporation section is located between the two heat dissipation sections, wherein the evaporation section corresponds to one or more heat sources outside the heat pipe.
4. The heat pipe according to claim 3, wherein: The first capillary structure is located in the evaporation section and the second heat dissipation section, and the second capillary structure is only located in the evaporation section.
5. The heat pipe according to claim 4, wherein: The portion of the first capillary structure located at the second heat dissipation section contacts the tube wall only from one side.
6. The heat pipe according to claim 5, wherein: The two heat dissipation sections, the first capillary structure and the second capillary structure are all linearly symmetrical relative to a center line of the evaporation section.
7. The heat pipe according to claim 3, wherein: The length of the opening of the second capillary structure in the axial direction corresponds to the length of the one or more heat sources.
8. The heat pipe according to claim 7, wherein: A width of the opening of the second capillary structure in a direction perpendicular to the axial direction is greater than a diameter of the first capillary structure.
9. The heat pipe according to claim 1, wherein: The second capillary structure also has a supporting portion, which is arranged at the middle part of the opening to separate the opening into a first opening and a second opening.
10. The heat pipe according to claim 9, wherein: The first opening and the second opening have different lengths in the axial direction, respectively corresponding to the lengths of a plurality of heat sources outside the heat pipe.