Patent Publication Number: US-10330392-B2

Title: Three-dimensional heat transfer device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application is a continuation-in-part application of U.S. application Ser. No. 15/257,805, filed on Sep. 6, 2016, which claims priority under 35 U.S.C. § 119(a) to Application No. 201610082174.6 filed Feb. 5, 2016, in the Chinese National Intellectual Property Administration (CNIPA), the entire contents of both these applications are hereby incorporated by reference. This continuation-in-part application also claims priority under 35 U.S.C. § 119(a) to Application No. 201810794973.5 filed Jul. 19, 2018, in the Chinese National Intellectual Property Administration (CNIPA), the entire contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a heat transfer device and, in particular, to a three-dimensional heat transfer device. 
     BACKGROUND 
     In regard to heat transfer, in order to dissipate heat generated from heating elements, conventional heat transfer devices utilize a heat conduction plate and a heat pipe to transfer heat, and cooling devices (e.g. fins and fans) are also utilized to dissipate heat, as described below. 
     The heat conduction plate is in contact with the heating element, the heat pipe is connected between the heat conduction plate and the cooling device, so that the heat generated from the heating element is transferred to the heat conduction plate first, and then the heat is transferred from the heat conduction plate to the cooling device via the heat pipe for heat dissipation. 
     However, the heat conduction plate and the heat pipe in the conventional heat transfer device work individually, and a capillary structure of the heat conduction plate is not connected to the capillary structure of the heat pipe. As a result, the heat conduction plate or the heat pipe transfers heat individually in a plane manner instead of an overall three-dimensional manner. In other words, heat dissipation is not achieved well. 
     Accordingly, the inventor made various studies to overcome the above problems, on the basis of which the present disclosure is accomplished. 
     SUMMARY 
     According to example embodiments, a three-dimensional heat transfer device includes a vapor chamber and a heat pipe. The vapor chamber includes a chamber body and a first capillary structure, and the first capillary structure is disposed in the chamber body. The heat pipe includes a pipe body and a second capillary structure, and the second capillary structure is disposed in the pipe body. The first capillary structure is connected to the second capillary structure by metallic bonding. 
     According to example embodiments, a three-dimensional heat transfer device includes a vapor chamber, a heat pipe and a bonding layer. The vapor chamber includes a chamber body and a first capillary structure, and the first capillary structure is disposed in the chamber body. The heat pipe includes a pipe body and a second capillary structure, and the second capillary structure is disposed in the pipe body. The bonding layer is connected to the first capillary structure and the second capillary structure. The bonding layer includes a porous structure. 
     According to example embodiments, a method of manufacturing a three-dimensional heat transfer device includes providing a vapor chamber comprising a first capillary structure; providing a metal powder on at least part of the first capillary structure; contacting a heat pipe including a second capillary structure to the metal powder; and performing a sintering process to sinter the metal powder to form a bonding layer. The bonding layer is connected to the first capillary structure and the second capillary structure by metallic bonding. 
     According to example embodiments, a method of manufacturing a three-dimensional heat transfer device includes providing a vapor chamber comprising a first capillary structure, providing a metal powder on at least part of the first capillary structure, contacting a heat pipe including a second capillary structure on the metal powder, and performing a sintering process to sinter the metal powder to form a bonding layer including a porous structure. The bonding layer is connected to the first capillary structure and the second capillary structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will become more fully understood from the detailed description, and the drawings provided herein are for illustration only, and thus do not limit the disclosure, wherein: 
         FIG. 1  is a perspective exploded view according to the first embodiment of the present disclosure. 
         FIG. 2  is a perspective assembled view according to the first embodiment of the present disclosure. 
         FIG. 3  is a perspective view from another viewing angle illustrating a heat pipe according to the first embodiment of the present disclosure. 
         FIG. 4  is a cross-sectional view and also a partial enlarged view of  FIG. 2  according to the first embodiment of the present disclosure. 
         FIG. 5  is a perspective exploded view according to the second embodiment of the present disclosure. 
         FIG. 6A  is a perspective view from another viewing angle illustrating a heat pipe of the first type according to the second embodiment of the present disclosure. 
         FIG. 6B  is a perspective view from another viewing angle illustrating the heat pipe of the second type according to the second embodiment of the present disclosure. 
         FIG. 7  is a cross-sectional view and also a partially enlarged view illustrating the second embodiment of the present disclosure after assembly. 
         FIG. 8  is a perspective view of a heat transfer device according to the example embodiments. 
         FIG. 9  is an exploded view of the heat transfer device in  FIG. 8  illustrating some of the components of the heat transfer device. 
         FIG. 10  is a cross-sectional view of the heat transfer device in  FIG. 8 . 
         FIG. 11  is an enlarged view of a portion of the heat transfer device in  FIG. 10 . 
         FIG. 12  is a perspective view of a heat pipe in  FIG. 9 . 
         FIG. 13  is a perspective view of a heat pipe, according to example embodiments. 
         FIG. 14  is a perspective view of a heat pipe, according to example embodiments. 
         FIG. 15  is a perspective view of a heat pipe, according to example embodiments. 
         FIG. 16  is a perspective view of a heat pipe, according to example embodiments. 
         FIG. 17  is a perspective view of a heat pipe, according to example embodiments. 
         FIG. 18  is a perspective view of a heat pipe, according to example embodiments. 
         FIG. 19  is a perspective view of a heat pipe, according to example embodiments. 
         FIG. 20  is a perspective view of a heat pipe, according to example embodiments. 
         FIG. 21  is a perspective view of a heat pipe, according to example embodiments. 
         FIG. 22  is a perspective view of a heat pipe, according to example embodiments. 
         FIG. 23  is a perspective view of a heat pipe, according to example embodiments. 
         FIG. 24  is a perspective view of a heat pipe, according to example embodiments. 
         FIG. 25  is a cross-sectional view of the heat pipe in  FIG. 24 ; 
         FIG. 26  is a cross-sectional view of the heat pipe in  FIG. 24  connected to a vapor chamber, according to example embodiments. 
         FIG. 27  is a cross-sectional view of the heat pipe coupled to a vapor chamber, according to example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Detailed descriptions and technical contents of the present disclosure are illustrated below in conjunction with the accompany drawings. However, it is to be understood that the descriptions and the accompany drawings disclosed herein are merely illustrative and exemplary and not intended to limit the scope of the present disclosure. 
     The present disclosure provides a three-dimensional heat transfer device.  FIGS. 1 to 4  show the first embodiment of the present disclosure, and  FIGS. 5 to 7  show the second embodiment of the present disclosure. 
     As shown in  FIGS. 1 to 4 , according to the first embodiment of the present disclosure, the three-dimensional heat transfer device includes a vapor chamber  1 , at least one heat pipe  2  and a working fluid flowing inside the vapor chamber  1  and the heat pipe  2 . 
     The vapor chamber  1  has a first plate  11  and a second plate  12  opposite to each other, and a cavity  10  is formed between the first plate  11  and the second plate  12 . The vapor chamber  1  can be an integral structure and also can be a combined structure. In the present embodiment, the combined structure disclosed therein is merely representative for purposes of describing an example of the present disclosure. That is to say, the second plate  12  can be assembled to the first plate  11  to form the vapor chamber  1  having the cavity  10  inside. 
     A first capillary structure  13  is disposed on an inner surface of the first plate  11 , a third capillary structure  14  (see  FIG. 4 ) is disposed on an inner surface of the second plate  12 , and the first and third capillary structures  13 ,  14  face each other. The first and third capillary structures  13 ,  14  can include sintered powder, sintered ceramic powder, metal web, or metal groove, and the present disclosure is not limited in this regard. However, in some embodiments, an inner surface of the second plate  12  is not disposed with the third capillary structure  14 . In other words, only the inner surface of the first plate  11  is disposed with the capillary structure (i.e. the first capillary structure  13 ). 
     The second plate  12  forms at least one insertion hole  121 . In the present embodiment, there are multiple insertion holes  121  for purposes of describing an example. Therefore, there are also multiple heat pipes  2  corresponding in number to the number of the insertion holes  121 . Furthermore, a flange  122  in a circular form extends outwardly from a periphery of each insertion hole  121 , thereby facilitating fixed connection with the heat pipe  2 . 
     The heat pipe  2  is a hollow tube which has a second capillary structure  21  disposed inside, and the second capillary structure  21  has a contact portion  212  extending out of the heat pipe  2  to be exposed. In the present embodiment, one end (hereinafter referred to as the insertion end but not labelled) of the heat pipe  2  forms an opening  22  (see  FIG. 3 ), the second capillary structure  21  includes two capillary elements  211  (see  FIG. 4 ) arranged spaced apart and side by side so as to form a vapor passage  23  between the two capillary elements  211 . Each of the two capillary elements  211  includes an exposed section  2111 , the contact portion  212  consists of the exposed section  2111  of each of the two capillary elements  211 , and thereby the vapor passage  23  of the heat pipe  2  communicates with the cavity  10  by means of the contact portion  212 . The second capillary structure  21  can include sintered powder, ceramic powder, metal web or metal grooves, and the present disclosure is not limited in this regard. In the present embodiment, the second capillary structure  21  includes sintered powder for purposes of describing an example of the present disclosure. 
     Each heat pipe  2  is inserted through each insertion hole  121  correspondingly to be erected on the second plate  12 , and the insertion end of the heat pipe  2  is utilized for insertion, so that the opening  22  is exposed within the cavity  10 . The contact portion  212  of the second capillary structure  21  extends out from the opening  22  to be exposed, so the contact portion  212  extends into the cavity  10  to be connected to the first capillary structure  13 , and thereby the first and second capillary structures  13 ,  21  communicate with each other. 
     In the present embodiment, for purposes of describing clear examples, the insertion end of the heat pipe  2  is inserted into the cavity  10  to contact a bottom thereof, so as to make the contact portion  212  in stable contact with the first capillary structure  13 , and thereby the first and second capillary structures  13 ,  21  communicate with each other. 
     Each heat pipe  2  is inserted through the second plate  12  for fixed connection therewith by any suitable method such as making an outer wall surface of each heat pipe  2  in contact with the flange  122  and soldered thereto, thereby enhancing structural stability between the heat pipe  2  and the vapor chamber  1 . Each heat pipe  2  is vertically inserted through the second plate  12 , or the heat pipe  2  can form an included angle of 70 to 110 degrees with the second plate  12 . The heat pipe  2  intersects the second plate  12 , no matter whether the heat pipe  2  is vertically inserted or forms the included angle. 
     As shown in  FIGS. 2 and 4 , the heat pipe  2  inserted into the cavity of the vapor chamber  1  is in an erected condition, and the second capillary structure  21  inside the heat pipe  2  and the first capillary structure  13  inside the vapor chamber  1  contact and communicate with each other. As a result, an overall three-dimensional heat transfer effect can be achieved, thus desired ideal heat dissipation can be effected. 
     In addition, the two capillary elements  211  of the second capillary structure  21  and the two exposed sections  2111  thereof are spaced apart to form the vapor passage  23 , so when the contact portion  212  of the heat pipe  2  is in contact with the first capillary structure  13 , vapor can circulate via the vapor passage  23 , and a hollow space inside the heat pipe  2  communicates with the cavity  10  of the vapor chamber  1 , thereby enhancing heat dissipation. Certainly, after the contact portion  212  extending out of the heat pipe  2  and exposed therefrom is inserted into the cavity  10 , a portion of the heat pipe  2 , having the contact portion  212  extending out, also communicates with the cavity  10 , thus having a function similar to the vapor passage  23 . 
     In addition to contacting and communicating with the first capillary structure  13 , the second capillary structure  21  of each heat pipe  2  can also connect and communicate with the third capillary structure  14 . In fact, just by making the second capillary structure  21  contact and communicate with the first capillary structure  13 , the second capillary structure  21  can dissipate heat properly. 
     Furthermore, as shown in  FIG. 2 , the three-dimensional heat transfer device can further include a fin set  3 . The fin set  3  is assembled onto the heat pipe  2 , so that the heat of the heat pipe  2  can be transferred to the fin set  3 , thereby facilitating dissipating the heat of the fin set  3  by a fan not illustrated in the drawing. 
       FIGS. 5 to 7  illustrate the three-dimensional heat transfer device according to the second embodiment of the present disclosure. The second embodiment is similar to the first embodiment with the difference that the heat pipe  2   a  in the second embodiment is different from the heat pipe  2  in the first embodiment, as more fully detailed below. 
     The heat pipe  2   a  (see  FIG. 7 ) includes an inner section  2711  inside the cavity  10 , an outer section  2712  outside the cavity  10 , and an insertion section (not labelled) connected between the inner section  2711  and the outer section  2712  and fixed to the flange  122 . A portion of the inner section  2711  forms an opening  22 , and the opening  22  can be circular, rectangular or can be of a tear drop shape; the present disclosure is not limited in this regard. The opening  22  can be enlarged from a tube end (i.e. the insertion end) of the heat pipe  2   a  to a tube body to also permit circulation of the vapor (as shown in  FIG. 6A ). Alternatively, the opening  22  can be formed first, and then a plurality of gaps  24  (as shown in  FIG. 5  or  FIG. 6B ) are formed directly on the tube body, so that the gaps  24  can serve as a vapor opening for the vapor to circulate therethrough. To be specific, the opening  22  is formed at a free end (i.e. the insertion end of the heat pipe  2   a ) of the inner section  2711 , each gap  24  is formed at the inner section  2711  (which is also the tube body of the heat pipe  2   a ), and the gaps adjoin the opening  22  to communicate with each other, so the gaps  24  can serve as the vapor opening for the vapor to circulate therethrough. 
     The heat pipe in the second embodiment can be the heat pipe  2   a  of the first type in  FIG. 6A  and can also be the heat pipe  2   a  of the second type in  FIG. 6B ; the present disclosure is not limited in this regard, although for the purpose of describing the second embodiment, the heat pipe  2   a  of the second type shown in the  FIG. 6B  is taken as an example. 
     The second capillary structure  27  includes a contact portion  272  which is arranged in the opening  22  and exposed. In the present embodiment, the contact portion  272  is a rim of the second capillary structure  27 , which is exposed corresponding to the opening  22 . The contact portion  272  can be flush with or slightly shrink inwardly into the free end (or into the insertion end of the heat pipe  2   a ) of the inner section  2711 . 
     The heat pipe  2   a  is vertically inserted through the second plate  12 , and the inner section  2711  extends into the cavity  10 , so that the contact portion  272  can be connected to the first capillary structure  13  via the opening  22  to make the first and second capillary structures  13 ,  27  communicate with each other. To be specific, the inner section  2711  contacts, by its free end, the first capillary structure  13 , and therefore the contact portion  272  together with the inner section  2711  contacts the first capillary structure  13 . 
     In summary, compared with conventional techniques, the present disclosure provides the following advantages. By making the second capillary structure  21 ,  27  of the heat pipe  2 ,  2   a  connected and communicating with the first capillary structure  13  of the vapor chamber  1 , overall three-dimensional heat transfer is achieved, and a desired optimized heat dissipation effect can be obtained when the vapor chamber  1  collaborates with the heat pipe  2 ,  2   a.    
     The present disclosure further has other advantages. By spacing the two capillary elements  211  to be apart from each other to form the vapor passage  23  or by forming the opening  22  of the heat pipe  2   a , a hollow space inside the heat pipe  2 ,  2   a  is in communication with the cavity  10  of the vapor chamber  1 , thereby promoting heat dissipation. Certainly, after the contact portion  212  extending out of the heat pipe  2  and exposed therefrom is inserted into the cavity  10 , a portion of the heat pipe  2 , having the contact portion  212  extending out, also communicates with the cavity  10 , thus achieving an effect similar to the vapor passage  23 . 
       FIG. 8  is a perspective view of a heat transfer device  10   a , according to the example embodiments.  FIG. 9  is an exploded view of the heat transfer device  10   a  in  FIG. 8  illustrating some of the components of the heat transfer device  10   a .  FIG. 10  is a cross-sectional view of the heat transfer device  10   a  in  FIG. 8 .  FIG. 11  is an enlarged view of a portion of the heat transfer device  10   a  in  FIG. 10 .  FIG. 12  is a perspective view of a heat pipe  200   a  in  FIG. 9 . 
     Referring to  FIGS. 8-12 , the three-dimensional (3D) heat transfer device  10   a  includes a vapor chamber  100   a , multiple heat pipes  200   a , and a fin assembly  400   a  including a plurality of fins. The vapor chamber  100   a  and the heat pipes  200   a  are configured to allow working fluid (e.g., vapor, in this case, but can be any liquid or gas) to flow in the vapor chamber  100   a  and the heat pipes  200   a.    
     The vapor chamber  100   a  includes a chamber body  110   a  and a first capillary structure  120   a . The chamber body  110   a  includes a first (or bottom) plate  111   a  and a second (or top) plate  112   a . The first plate  111   a  includes a bottom part  115  and sidewalls  113  arranged along the periphery of the bottom part  115 . The bottom part  115  and the sidewalls  113  thus define the general shape of the first plate  111   a . The bottom part  115  is a generally planar structure and the sidewalls  113  are generally vertical structures arranged along the periphery of the bottom part  115 . The second plate  112   a  is connected to the sidewalls  113  of the first plate  111   a  along the periphery thereof (e.g., along the edges of the second plate  112   a ), and the first plate  111   a  and the second plate  112   a  jointly define a cavity S. The cavity S is configured to accommodate the working fluid. In an example, and as illustrated, the first plate  111   a  and the second plate  112   a  are shown as separate components that are assembled together to form the chamber body  110   a , but embodiments are not limited in this regard. In some other embodiments, the chamber body  110   a  is a unitary structure wherein the first plate  111   a  is integrally formed with the second plate  112   a.    
     The first capillary structure  120   a  is disposed in the cavity S and on the bottom part  115  of the first plate  111   a . In an embodiment, and as illustrated, the first capillary structure  120   a  is disposed on the entire bottom part  115 ; however, in other embodiments, the first capillary structure  120   a  may be disposed in a portion of the bottom part  115 . The vapor chamber  100   a  further includes a third capillary structure  130   a  disposed in the cavity S and on a bottom surface  117  of the second plate  112   a  facing the first plate  111   a . However, in other embodiments of the vapor chamber, the third capillary structure  130   a  is omitted, and the vapor chamber includes only the first capillary structure  120   a . In an embodiment, the first capillary structure  120   a  and the third capillary structure  130   a  are selected from the group consisting of metal mesh, sintered metal powder, sintered ceramic, micro grooves, and combination thereof. 
     The second plate  112   a  includes multiple through holes  1121   a , each including a flange  1122   a  along the edges of the through holes  1121   a  and that projects vertically upward from a top surface  119  of the second plate  112   a  opposite the bottom surface  117 . The through holes  1121   a  are arranged in a pattern on the second plate  112   a ; however, the arrangement of the through holes  1121   a  is not limited in this regard. The number of the through holes  1121   a  is equal to the number of the heat pipes  200   a . For example, when the 3D heat transfer device  10   a  includes single heat pipe  200   a , the second plate  112   a  includes a single through hole  1121   a . Each flange  1122   a  is connected to the edge of the corresponding through hole  1121   a  and is shaped and sized, or otherwise configured, for receiving a heat pipe  200   a  therewithin. 
     Referring to  FIGS. 10-12 , each of the heat pipes  200   a  includes a pipe body  210   a  and a second capillary structure  220   a  disposed along the inner circumferential surface  211   a  of the pipe body  210   a . In an embodiment, and as illustrated, the pipe body  210   a  is a generally cylindrical hollow tube. Each pipe body  210   a  includes an open end  212   a  and a closed end  213   a  opposite the open end  212   a . The open end  212   a  of the pipe body  210   a  includes an opening  214   a  ( FIGS. 11 and 12 ) of the pipe body  210   a  and an edge  215   a  of the pipe body  210   a  that defines the opening  214   a . The second capillary structure  220   a  includes two capillary elements  2200   a  disposed on and lining the inner circumferential surface  211   a . The two capillary elements  2200   a  are arranged circumferentially and radially spaced apart (e.g., non-contacting) from each other to define a vapor passage  1123 . Each capillary element  2200   a  includes a curved or arched surface that contacts the inner circumferential surface  211   a  and a planar surface that faces the interior of the pipe body  210   a  and defines the vapor passage  1123 . An axial end  2207  of each capillary element  2200   a  contacts the interior of the pipe body  210   a  at the closed end  213   a , and the opposite axial end  2209  of each capillary element  2200   a  includes a contact portion  221   a  extending axially out of the pipe body  210   a  a certain distance from the edge  215   a  of the pipe body  210   a . The contact portion  221   a  thus forms an exposed portion of the capillary element  2200   a . In an embodiment, the second capillary structure  220   a  is a sintered solid part including metal powder, but embodiments are not limited in this regard. In some other embodiments, the second capillary structure is selected from the group consisting of metal mesh, sintered metal powder, sintered ceramic, micro grooves, and combination thereof. 
     Each heat pipe  200   a  is inserted in the through hole  1121   a , and each capillary element  2200   a  of the second capillary structure  220   a  is connected to the first capillary structure  120   a  by metallic bonding. Referring to  FIGS. 10 and 11 , the 3D heat transfer device  10   a  further includes a bonding layer  300   a  including gold powder, silver powder, copper powder, iron powder, a combination thereof, and the like. The powder(s) is/are sintered to form the bonding layer  300   a  including a porous structure. One surface of the bonding layer  300   a  is connected to the first capillary structure  120   a  by metallic bonding, and the other opposite surface of the bonding layer  300   a  is connected to the second capillary structure  220   a  by metallic bonding. 
     In conventional heat transfer devices, metal bonding layer is not included between capillary structures, and the capillary structures directly contact each other. The bonding layer  300   a , according to example embodiments, provides a metallic bonding between the first capillary structure  120   a  and the second capillary structure  220   a  and improves the flow rate of the working fluid between the second capillary structure  220   a  and the first capillary structure  120   a , thereby increasing a heat dissipation efficiency of the 3D heat transfer device  10   a.    
     A method of manufacturing the 3D heat transfer device  10   a  includes providing a vapor chamber  100   a  including a first capillary structure  120   a . At least part of the first capillary structure  120   a  includes a metal powder. The method then includes contacting a second capillary structure  220   a  of a heat pipe  200   a  with the first capillary structure  120   a . A sintering process is then performed to sinter the metal powder to form the bonding layer  300   a . The bonding layer  300   a  is connected to the first capillary structure  120   a  and the second capillary structure  220   a  by metallic bonding. 
     According to example embodiments, the 3D heat transfer device  10   a  includes multiple (four, in this case) heat pipes  200   a , but embodiments are not limited thereto. In some other embodiments, the 3D heat transfer device  10   a  includes a single heat pipe  200   a  or more than four heat pipes  200   a . The multiple heat pipes  200   a , and the corresponding through holes  1121   a , can be arranged in any desired manner on the vapor chamber  100   a.    
     According to example embodiments, the second capillary structure  220   a  of the heat pipe  200   a  is connected to the first capillary structure  120   a  by metallic bonding, while metallic bonding is absent between the first capillary structure  120   a  and the third capillary structure  130   a . However, embodiments are not limited in this regard. In other embodiments, the second capillary structure  220   a  is connected to both the first capillary structure  120   a  and the third capillary structure  130   a  by metallic bonding. 
     Referring to  FIG. 8 , the fin assembly  400   a  including a plurality of fins disposed on the heat pipes  200   a  improves the heat dissipation efficiency of the 3D heat transfer device  10   a . Herein, the heat generated by a heat source is transferred through the heat pipes  200   a  to the fin assembly  400   a , thereby increasing the surface area for heat dissipation and providing increased heat dissipation in a relatively smaller area. 
       FIGS. 13-19  illustrate different embodiments of heat pipes  200   b - 200   h , each of which may be used in place of the heat pipe  200   a.    
       FIG. 13  is a perspective view of a heat pipe  200   b  according to example embodiments. The heat pipe  200   b  may be similar in some respects to the heat pipe  200   a  in  FIG. 12 , and therefore may be best understood with reference thereto where like numerals designate like components not described again in detail. As illustrated, the heat pipe  200   b  includes a second capillary structure  220   b  disposed on and lining the inner circumferential surface  211   a  of the pipe body  210   a . The second capillary structure  220   b  includes two capillary elements  2200   b  similar to the capillary elements  2200   a . Each capillary element  2200   b  is disposed on and lines (contacts) the inner circumferential surface  211   a , and is circumferentially spaced apart from the other capillary element  2200   b . An axial end  2207  of each capillary element  2200   b  inside the pipe body  210   a  is axially spaced from the closed end  213   b , and the other opposite axial end  2209  of each capillary element  2200   b  includes a contact portion  221   a  extending axially out of the pipe body  210   a  a certain distance from the edge  215   a  of the pipe body  210   a  and thereby exposed. In an embodiment, the length (e.g., axial extent) of each capillary element  2200   b  is about half of the length (e.g., axial extent) of the pipe body  210   a , and the axial end  2207  is located below the mid-point of the heat pipe  200   b . However, embodiments are not limited in this regard. In an embodiment, the length of each capillary element  2200   b  is greater than half the length of the pipe body  210   a , but the capillary element  2200   b  does not contact the closed end  213   a . In another embodiment, the length of each capillary element  2200   b  is less than half the length of the pipe body  210   a . In yet another embodiment, the two capillary elements  2200   b  may have different lengths. 
       FIG. 14  is a perspective view of a heat pipe  200   c  according to example embodiments. The heat pipe  200   c  may be similar in some respects to the heat pipe  200   a  in  FIG. 12 , and therefore may be best understood with reference thereto where like numerals designate like components not described again in detail. As shown in  FIG. 14 , the heat pipe  200   c  includes a second capillary structure  220   c  disposed on and lining the inner circumferential surface  211   a  of the pipe body  210   a . The second capillary structure  220   c  includes two capillary elements  2200   c  similar to the capillary elements  2200   a . Each capillary element  2200   c  is disposed on and lines the inner circumferential surface  211   a , and is circumferentially and radially spaced apart from the other capillary element  2200   c . The axial end  2207  of each capillary element  2200   c  inside the pipe body  210   a  contacts the interior of the pipe body  210   a  at the closed end  213   a , and the other opposite end  2209  of each capillary element  2200   c  is flush with the edge  215   a . In an embodiment, the length (e.g., axial extent) of the capillary element  2200   c  is substantially equal to the length (e.g., axial extent) of the pipe body  210   a  including projections  217   c  (see below). However, in other embodiments, the capillary elements  2200   c  may have different lengths, wherein the end  2207  of a capillary element  2200   c  is axially spaced from the pipe body  210   a  at the closed end  213   a.    
     At the open end  212   a , the pipe body  210   a  includes recesses  216   c  (two shown) extending axially from the edge  215   a , and projections  217   c  (two shown) formed by the recesses  216   c  at the open end  212   a . As illustrated, each capillary element  2200   c  extends from the closed end  213   a  to the edge  215   a  included in a projection  217   c  and flush with the edge  215   a . In an embodiment, and as illustrated, the capillary elements  2200   c  do not extend into the recesses  216   c . The recesses  216   c  are in fluid communication with the opening  214   a  and thereby with the vapor passage  1123 . Each recess  216   c  is shaped and sized, or otherwise configured, to provide a fluid path through which working fluid, such as vapor, flows. 
       FIG. 15  is a perspective view of a heat pipe  200   d  according to example embodiments. The heat pipe  200   d  may be similar in some respects to the heat pipe  200   c  in  FIG. 14 , and therefore may be best understood with reference thereto where like numerals designate like components not described again in detail. As illustrated in  FIG. 15 , the heat pipe  200   d  includes a second capillary structure  220   d  disposed on and lining the inner circumferential surface  211   a . The second capillary structure  220   d  includes two capillary elements  2200   d  disposed on and lining the inner circumferential surface  211   a , and spaced apart from each other. The end  2207  of each capillary element  2200   d  inside the pipe body  210   a  is axially spaced from the closed end  213   d , and the opposite axial end  2209  of the capillary element  2200   d  is flush with the edge  215   a . In an embodiment, the length (e.g., axial extent) of each capillary element  2200   d  is about half of the length (e.g., axial extent) of the pipe body  210   a . However, embodiments are not limited in this regard. In an embodiment, the length of each capillary element  2200   d  is greater than half the length of the pipe body  210   a , but the capillary element  2200   d  does not contact the closed end  213   a . In another embodiment, the length of each capillary element  2200   d  is less than half the length of the pipe body  210   a . In yet another embodiment, the capillary elements  2200   d  may have different lengths. 
       FIG. 16  is a perspective view of a heat pipe  200   e  according to example embodiments. The heat pipe  200   e  may be similar in some respects to the heat pipe  200   a  in  FIG. 12 , and therefore may be best understood with reference thereto where like numerals designate like components not described again in detail. As illustrated in  FIG. 16 , the heat pipe  200   e  includes a second capillary structure  220   e  disposed on and lining the inner circumferential surface  211   a.    
     As illustrated, the second capillary structure  220   e  lines the entire inner circumferential surface  211   a . The second capillary structure  220   e  is a generally tubular structure having an outer circumferential surface contacting the inner circumferential surface  211   a  and an inner circumferential surface that defines the vapor passage  1123  that extends the axial length of the second capillary structure  220   e . One end of the second capillary structure  220   e  contacts the interior surface of the pipe body  210   a  at the closed end  213   e , and the other opposite end of the second capillary structure  220   e  includes contact portion  221   a  extending axially out of the pipe body  210   a  a certain distance from the edge  215   a  of the pipe body  210   a , and is thereby exposed. Specifically, the length of the second capillary structure  220   e  is substantially equal to the length of the pipe body  210   e . In an embodiment, the contact portion  221   a  includes two (or more) projections  223  circumferentially separated from each other by recesses  225  (two shown) defined in the second capillary structure  220   e . Each recess  225  may extend axially from an axial end of the second capillary structure  220   e  in the contact portion  221   a , and a bottom of each recess  225  is flush with the edge  215   a  of the pipe body  210   a.    
       FIG. 17  is a perspective view of a heat pipe  200   f  according to example embodiments. The heat pipe  200   f  may be similar in some respects to the heat pipe  200   e  in  FIG. 16 , and therefore may be best understood with reference thereto where like numerals designate like components not described again in detail. As illustrated in  FIG. 17 , the heat pipe  200   f  includes a second capillary structure  220   f  disposed on and lining an inner circumferential surface  211   a . The second capillary structure  220   f  is similar to the second capillary structure  220   e  in  FIG. 16 , except that the axial end  2207  of the second capillary structure  220   f  inside the pipe body  210   a  is axially spaced from the closed end  213   a . In an embodiment, the length (e.g., axial extent) of the second capillary structure  220   f  is about half of the length of the pipe body  210   a . However, embodiments are not limited in this regard. In an embodiment, the length of the second capillary structure  220   f  is greater than half the length of the pipe body  210   a , but the second capillary structure  220   f  does not contact the closed end  213   a . In another embodiment, the length of the second capillary structure  220   f  is less than half the length of the pipe body  210   a.    
       FIG. 18  is a perspective view of a heat pipe  200   g  according to example embodiments. The heat pipe  200   g  may be similar in some respects to the heat pipes  200   c  and  200   e  in  FIGS. 14 and 16 , respectively, and therefore may be best understood with reference thereto where like numerals designate like components not described again in detail. As illustrated in  FIG. 18 , the heat pipe  200   g  includes a second capillary structure  220   g  disposed on and lining the entire inner circumferential surface  211   a  of the pipe body  210   a . The open end  212   a  of the pipe body  210   a  includes recesses  216   c  and two projections  217   c  similar to the heat pipe  200   c  in  FIG. 14  The second capillary structure  220   g  includes two projections  223  circumferentially separated from each other by recesses  225  defined in the second capillary structure  220   g  at the open end  212   a  The second capillary structure  220   g  is flush with the pipe body  210   a  in the recesses  216   c . The projections  223  of the second capillary structure  220   g  also line the inner circumferential surface  211   a  of the pipe body  210   a  in the projections  217   c . The number of projections  223  correspond to the number of projections  217   c . The projections  223  of the second capillary structure  220   g  are flush with the projections  217   c  of the pipe body  210   a.    
       FIG. 19  is a perspective view of a heat pipe  200   h  according to example embodiments. The heat pipe  200   h  may be similar in some respects to the heat pipe  200   g  in  FIG. 18 , and therefore may be best understood with reference thereto where like numerals designate like components not described again in detail. As illustrated in  FIG. 19 , the heat pipe  200   h  includes a second capillary structure  220   h  disposed on and lining an inner circumferential surface  211   a . The second capillary structure  220   h  is similar to the second capillary structure  220   g  in  FIG. 18 , except that the axial end  2207  of the second capillary structure  220   h  inside the pipe body  210   a  is axially spaced from the closed end  213   a . In an embodiment, the length (e.g., axial extent) of the second capillary structure  220   h  is about half of the length of the pipe body  210   a . However, embodiments are not limited in this regard. In an embodiment, the length of the second capillary structure  220   h  is greater than half the length of the pipe body  210   a , but the second capillary structure  220   h  does not contact the closed end  213   a . In another embodiment, the length of the second capillary structure  220   h  is less than half the length of the pipe body  210   a.    
       FIG. 20  is a perspective view of a heat pipe  200   i  according to the example embodiments. As illustrated in  FIG. 20 , the heat pipe  200   i  includes a pipe body  210   i  and a second capillary structure  220   i . The pipe body  210   i  is a generally cylindrical hollow tube that includes an open end  212   i  and an axially opposite closed end  213   i . The open end  212   i  of the pipe body  210   i  includes an edge  215   i . The second capillary structure  220   i  is disposed on and lines an entire inner circumferential surface  211   i  of the pipe body  210   i  and defines the vapor passage  1123 . In an embodiment, the second capillary structure  220   i  includes multiple micro grooves  2215   i . The micro grooves  2215   i  extend axially along the inner circumferential surface  211   i  between the closed end  213   i  and open end  212   i . An axial end  2213  of each micro groove  2215   i  contacts the interior surface of the pipe body  210   i  at the closed end  213   i , and the other axially opposite end  2217  of each micro groove  2215   i  is flush with the edge  215   i . In an embodiment, the micro grooves  2215   i  extend an entire axial length of the pipe body  210   i . The pipe body  210   i  includes multiple (two shown) recesses  216   i  extending axially from the edge  215   i . The recesses  216   i  define projections  217   i  at the open end  212   i . It will thus be understood that, the micro grooves  2215   i  that end in the recesses  216   i  have a smaller length that the micro grooves  2215   i  that end at the edges  215   i.    
       FIG. 21  is a perspective view of a heat pipe  200   j  according to example embodiments. The heat pipe  200   j  may be similar in some respects to the heat pipe  200   i  in  FIG. 20 , and therefore may be best understood with reference thereto where like numerals designate like components not described again in detail. As illustrated, the end  2213  of each micro groove  2215   i  is axially spaced from the closed end  213   j , and the axially opposite end  2217  of the micro grooves  2215   i  is flush with the edge  215   j  or with the recess  216   i . In an embodiment, the length of the micro groove  2215   i  extending along the inner circumferential surface  211   i  and along the projections  217   i  is about half of the length of the pipe body  210   j.    
       FIG. 22  is a perspective view of a heat pipe  200   k  according to example embodiments. The heat pipe  200   k  may be similar in some respects to the heat pipe  200   i  in  FIG. 20 , and therefore may be best understood with reference thereto where like numerals designate like components not described again in detail. As illustrated in  FIG. 22 , the heat pipe  200   k  includes a second capillary structure  220   k  similar to the second capillary structure  220   i , except that the second capillary structure  220   k  includes two capillary elements  2200   k  disposed on and lining the inner circumferential surface  211   i  of the pipe body  210   k . The two capillary elements  2200   k  are circumferentially and radially spaced apart from each other, and define vapor passage  1123  therebetween. Each capillary element  2200   k  includes a plurality of micro grooves  2215   i . An end  2213  of the micro grooves  2215   i  contacts the interior surface of the heat pipe  200   k  at the closed end  213   k , and the micro grooves  2215   i  extend on the projections  217   i  and the axially opposite end of the micro grooves  2215   i  is flush with the edge  215   i  of the pipe body  210   i  in the projections  217   i . In an embodiment, the length of each micro groove  2215   i  is substantially equal to the length of the pipe body  210   i  including the projections  217   i . As illustrated, the micro grooves  2215   i  are absent in the axial portion of the pipe body  210   i  between the recess  216   i  and the closed end  213   i.    
       FIG. 23  is a perspective view of a heat pipe  200   m  according to example embodiments. The heat pipe  200   m  may be similar in some respects to the heat pipe  200   j  in  FIG. 21 , and therefore may be best understood with reference thereto where like numerals designate like components not described again in detail. As illustrated, the heat pipe  200   m  includes a second capillary structure  220   m  similar to the second capillary structure  220   i  in  FIG. 21 , except that the second capillary structure  220   m  includes two capillary elements  2200   m  disposed on and lining the inner circumferential surface  211   i  of the pipe body  210   m . The two capillary elements  2200   m  are circumferentially and radially spaced apart from each other. Each capillary element  2200   m  includes multiple micro grooves  2215   i . An end  2213  of each micro groove  2215   i  is axially spaced from the closed end  213   i , and the other axially opposite end  2217  of each micro groove  2215   i  is flush with the edge  215   i  of the pipe body  210   i  in the projections  217   i . In an embodiment, the length of the micro grooves  2215   i  is about half of the length of the pipe body  210   i  including the projections  217   i . However, embodiments are not limited in this regard. In an embodiment, the length of micro grooves  2215   i  is greater than half the length of the pipe body  210   a , but the micro grooves  2215   i  do not contact the closed end  213   i . In another embodiment, the length of the micro grooves  2215   i  is less than half the length of the pipe body  210   a . In yet another embodiment, the micro grooves  2215   i  in one capillary element  2200   m  and the micro grooves  2215   i  in the other capillary element  2200   m  may have different lengths. 
     In the aforementioned embodiments of the heat pipes in  FIGS. 13-23 , the second capillary structures may include either a metal mesh, a sintered solid part made of metal powder, a sintered ceramic, multiple micro grooves, a combination thereof, and the like. 
       FIG. 24  is a perspective view of a heat pipe  200   n  according to example embodiments.  FIG. 25  is a cross-sectional view of the heat pipe  200   n  in  FIG. 24 . The heat pipe  200   n  may be similar in some respects to the heat pipe  200   k  in  FIG. 22 , and therefore may be best understood with reference thereto where like numerals designate like components not described again in detail. 
     Referring to  FIGS. 24 and 25 , the heat pipe  200   n  includes a second capillary structure  220   n  that includes two capillary elements  2200   n  disposed on and contacting the inner circumferential surface  211   i  of the pipe body  210   i.    
     The second capillary structure  220   n  is a composite capillary structure. Each capillary element  2200   n  includes a curved or arched surface  2203  contacting the inner circumferential surface  211   i  and a generally planar surface  2205  extending between ends of the curved surface  2203 . The capillary element  2200   n  includes a first layer  2201   n  disposed on the curved surface  2203  and a second layer  2202   n  disposed on the first layer  2201   n  and including the planar surface  2205 . The first layer  2201   n  includes multiple micro grooves  2215   i . An axial end  2213  of the first layer  2201   n  contacts the interior surface of the heat pipe  200   n  at the close end  213   n , and the other axially opposite end  2217  of the first layer  2201   n  is flush with the edge  215   n  of the pipe body  210   n . The second layer  2202   n  includes a metal mesh, a sintered solid part made of metal powder or a sintered ceramic. An axial end  2219  of the second layer  2202   n  contacts the interior surface of the heat pipe  200   n  at the close end  213   n , and the other axially opposite end  2221  of the second layer  2202   n  is flush with the edge  215   n  of the pipe body  210   n.    
       FIG. 26  is a cross-sectional view of the heat pipe  200   n  in  FIG. 24  connected to a vapor chamber, according to example embodiments. In an embodiment, the vapor chamber may be similar in some respects to the vapor chamber  100   a  in  FIGS. 8-11 . In an embodiment, the heat pipe  200   n  is inserted through a through hole  1121   n  of second plate  112   a . Both the first layer  2201   n  and the second layer  2202   n  of the second capillary structure  220   n  are connected to the first capillary structure  120   a  ( FIG. 8 ) via bonding layer  300   a . More specifically, the bonding layer  300   a  is connected to the first capillary structure  120   a  and the second capillary structure  220   n  by metallic bonding. 
       FIG. 27  is a cross-sectional view of the heat pipe  200   n  coupled to a vapor chamber  100   p , according to example embodiments. The vapor chamber  100   p  may be similar in some respects to the vapor chamber  100   a  in  FIGS. 8-11 , and therefore may be best understood with reference thereto where like numerals designate like components not described again in detail. The vapor chamber includes a first capillary structure  120   p  in the first plate  111   a . The first capillary structure  120   p  is a composite capillary structure including a first layer  1201   p  and a second layer 1202p. The first layer  1201   p  contact the bottom part  115  of the first plate  111   a , and the second layer  1202   p  is disposed on the first layer  1201   p . The first layer  1201   p  includes multiple micro grooves, and the second layer  1202   p  of the first capillary structure  120   p  includes a metal mesh, a sintered solid part made of metal powder or a sintered ceramic. Both a first layer  2201   n  and a second layer  2202   n  of a second capillary structure  220   n  are connected to the second layer  1202   p  of the first capillary structure  120   p  via a bonding layer  300   a . More specifically, the bonding layer  300   p  is connected to the first layer  2201   n , the second layer  2202   n , and the second layer  1202   p  by metallic bonding. 
     In a conventional heat dissipation devices, the first capillary structure merely contacts the second capillary structure without metal bonding, and the working fluid is retained in the second capillary structure due to an adhesive force between the working fluid and the second capillary structure. According to example embodiments, the first capillary structure is coupled to the second capillary structure by metallic bonding. The metallic bonding encourages flow of the working fluid from the second capillary structure into the first capillary structure. Therefore, a flow rate of the working fluid is increased and the heat dissipation efficiency of the 3D heat transfer device is improved. 
     It is to be understood that the above descriptions are merely the preferable embodiment of the present disclosure and are not intended to limit the scope of the present disclosure. Equivalent changes and modifications made in the spirit of the present disclosure are regarded as falling within the scope of the present disclosure.