Patent Publication Number: US-2006000581-A1

Title: Cylindrical heat pipes

Description:
BACKGROUND  
      The invention relates to heat pipes, and in particular to cylindrical heat pipes or heat columns.  
      In the continued development of electronic devices, the number of transistors per unit area in an electronic device has increased to improve performance. External fans and heat-dissipation devices are normally installed in electronic devices to dissipate excess heat and maintain an acceptable working temperature. Since heat dissipation of the electronic devices can increase effective chip speeds, fan speed is increased to accelerate heat conduction. Power consumption and noise level, however, both increase accordingly. Additionally, heat-dissipation device such as heat-dissipation fin, while improving heat conduction, reduce the available internal space. Thus, currently, a heat pipe with a small cross section and low temperature differential is often used to provide a relatively long distance for heat conduction without requiring an additional power supply. The smaller heat pipe occupies little internal space, and thus, is widely used in electronic devices.  
      A heat pipe comprises a hollow body with two sealed ends, a wick structure, and working fluid. The heat pipe is a vacuumed vessel charged with a working fluid. The walls of the heat pipe are lined with the wick structure that allows working fluid to travel from one end of the heat pipe to the other via capillary action. The conventional heat pipe is manufactured by sealing an end of the pipe, forming the wick structure, adding working fluid, and vacuuming. Alternatively, the pipe can be vacuumed before adding working fluid. Finally, the other end of the pipe is sealed. In a cylindrical heat pipe comprising a cover and an additional hollow body in the center thereof, the cover seals the pipe opening after adding working fluid and vacuums through the hollow body.  
       FIG. 1A  is a schematic view showing a conventional heat pipe with an open end.  FIG. 1B  is a cross section of the cylindrical heat pipe of  FIG. 1A . The cylindrical heat pipe  1  with an open end comprises a hollow body  10 . An interior wall  14  of the hollow body  10  has a gradient, shown in  FIG. 1B  for use in a subsequent process. After formation of the wick structure, a cover  11  is disposed in the hollow body  10  to form a closed space. The gradient on the interior wall  14  allows the cover  11  to be positioned thereon. The cover  11  comprises a small hollow tube  12  passing through the center thereof. The hollow body  10  can be filled with a working fluid through the hollow tube  12 , which is the only injection inlet of the heat pipe  1 . After vacuuming and adding working fluid, the hollow tube  12  is sealed. A sealant fills a space  15  between the open end  13  and the cover  11  to ensure the pipe is adequately sealed. Thus, production of a cylindrical heat pipe  1  is completed.  
      Since the distance between the open end  13  and the cover  11  is long, however, heat-dissipation space of the heat pipe is reduced, thereby reducing heat conductivity and heat-dissipation efficiency. Moreover, due to the combination of the hollow tube  12  and the cover  11 , the hollow tube  12  must be sealed after working fluid is added. Thus, the procedure becomes complicated and reduces reliability.  
     SUMMARY  
      Embodiments of the invention provide a cylindrical heat pipe. The cylindrical heat pipe comprises a hollow cylindrical body, a cover, and a hollow tube. The cylindrical body includes a sealed bottom, a top portion and an inner wall. The cover includes an elevated portion, and the hollow tube penetrates the cover. The cover seals the hollow cylindrical body and guides a working fluid passing therethrough into the heat pipe. The inner wall of the hollow cylindrical body comprises a stepped portion or at least one protrusion for fixing and supporting the cover. After the working fluid is added and the heat pipe is vacuumed, the hollow tube is sealed, and the elevated portion enlarges the heat-dissipation space of the cylindrical heat pipe.  
      Embodiments of the invention further provide another cylindrical heat pipe. The cylindrical heat pipe comprises a hollow cylindrical body and a cover. The cover comprises a center with an opening defined thereon. The cover seals the hollow cylindrical body and guides a working fluid passing therethrough into the heat pipe. The inner wall of the hollow cylindrical body comprises a stepped portion or at least one protrusion for fixing and supporting the cover. After the working fluid is added through the opening of the cover, the heat pipe is vacuumed, and the opening is sealed by a block. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:  
       FIG. 1A  is a schematic view of a conventional heat pipe with an open end;  
       FIG. 1B  is a cross-sectional view of the cylindrical heat pipe of  FIG. 1A ;  
       FIG. 2A  is a schematic view of a cover according to a first embodiment of the invention;  
       FIG. 2B  is a cross-sectional view of a cylindrical heat pipe with the cover of  FIG. 2A ;  
       FIG. 3A  is a cylindrical heat pipe of a second embodiment of the invention;  
       FIG. 3B  is a cross-sectional view of the cylindrical heat pipe of  FIG. 3A ;  
       FIG. 4A  is a schematic view of a cylindrical heat pipe of a third embodiment when an end thereof is not sealed;  
       FIG. 4B  is a cross section of the cylindrical heat pipe of  FIG. 4A ;  
       FIG. 4C  is a top view of the cylindrical heat pipe of  FIG. 4A ;  
       FIG. 4D  is a cross-sectional view of a cylindrical heat pipe with the cover of  FIG. 2B ; and  
       FIG. 4E  is a cross-sectional view of a cylindrical heat pipe with the cover of  FIG. 3B . 
    
    
     DETAILED DESCRIPTION  
     First Embodiment  
       FIG. 2A  is a schematic view of a cover according to a first embodiment of the invention. The cover  21  comprises an elevated portion  26 , and a hollow tube  22  penetrates at the center of the cover  21  as the only injection inlet when the hollow tube  22  guides a working fluid therethrough into the cylindrical heat pipe in a sequential procedure. Referring to  FIG. 2B , it is a cross-sectional view of a cylindrical heat pipe with the cover of  FIG. 2A . The cylindrical heat pipe  2  comprises a hollow body  20 . The hollow body  20  comprises a sealed bottom, a top portion  23 , and an inner wall  24 . The inner wall comprises a stepped portion for fixing and supporting the cover  21 .  
      After a wick structure is formed on the inner wall  24  of the hollow body  20 , the cover  21  is disposed in the hollow body  20  for sealing the pipe. Then a working fluid is added into the hollow body  20  of the cylindrical heat pipe  2  through the hollow tube  22 . After the hollow body  20  is vacuumed, the hollow tube  22  is sealed. Thus, process of manufacturing the cylindrical heat pipe  2  is completed. Further, a sealant (or vacuum gel) is filled in a space  25  between the cover  21  and the top portion  23 , for ensuring adequately sealing the pipe. The sealant comprises epoxy or thermosetting gel.  
      Comparing to the conventional heat pipe, a periphery of the cover  21  is raised by the elevated portion  26  from position S 1  of the conventional heat pipe to a higher position S 2 . Thus, the space close to the periphery of the cover  21  is enlarged owing to the elevated portion  26 . As a result, the heat-dissipation space is increased and heat conductivity of the cylindrical heat pipe  2  is improved.  
     Second Embodiment  
       FIG. 3A  is a cylindrical heat pipe  3  of a second embodiment of the invention.  FIG. 3B  is a cross-sectional view of the cylindrical heat pipe  3  of  FIG. 3A . The cylindrical heat pipe  3  comprises a hollow body  30  having a sealed bottom, a top portion  33 , and an inner wall  34 . The inner wall  34  comprises a stepped portion for fixing and supporting the cover  31 .  
      After a wick structure is formed on the inner wall  34  of the hollow body  30 , the cover  31  is disposed in the hollow body  30  for sealing the pipe. The center of the cover  31  has an opening  37  defined thereon, and a Working fluid is added into the hollow body  30  of the cylindrical heat pipe  3  through the opening  37 . After the hollow body  30  is vacuumed, the opening  37  is sealed. Thus, process of manufacturing the cylindrical heat pipe  3  is completed. Further, a sealant is filled in a space  35  between the cover  31  and the top portion  33 , for ensuring adequately sealing the pipe. The sealant comprises epoxy or thermosetting gel.  
      The method of sealing the opening  37  is not limited in the invention. For example, the opening  37  can be sealed by a block  38  with a radius slightly larger than the opening  37 . The block  38  is pressed and deformed by stress to completely seal the opening  37 . The block  38  can be a copper ball, or the block  38  can comprise other materials or have different shapes as long as the opening  37  of the cover  31  can be sealed. Moreover, the opening  37  may be sealed with a copper ball by welding, soldering, brazing, or gluing.  
      In this embodiment, because adding a working fluid or vacuuming is performed through the opening instead of using a conventional hollow tube, and the pipe is then sealed. Thus, the bottom level of the cover  31  can be raised from the conventional position S 1  to a higher position S 2 . As a result, the heat-dissipation space is increased and heat conductivity of the cylindrical heat pipe  3  is improved.  
     Third Embodiment  
       FIG. 4A  is a schematic view of a cylindrical heat pipe of a third embodiment when an end thereof is not sealed.  FIG. 4B  is a cross-sectional view of the cylindrical heat pipe of  FIG. 4A .  FIG. 4C  is a top view of a cylindrical heat pipe of  FIG. 4A . Referring to  FIG. 4A  to  FIG. 4C , the cylindrical heat pipe  4  comprises a hollow body  40  having a sealed bottom, a top portion  43 , and an inner wall  44 .  
      The inner wall  44  of the hollow body  40  having a stepped portion is formed by a lathe. The inner wall  44  is partially cut, forming the stepped portion, such that the cover can be fixed and supported by the stepped portion. Alternatively, several protrusions  48  or a circular flange can be directly formed on the inner wall  44  of the hollow body  40  by a mold at a predetermined location. As shown in  FIGS. 4B and 4C , four protrusions  48  are preferably formed at the location S 2  by a jig or molding such that the protrusions  48  can serve as fixing points for supporting the cover. The width and thickness of the flange or quantity and shape of the protrusions are not limited in the invention as long as support for the cover is provided.  
      In the subsequent processes, several different covers and various sealing method are applied to the hollow body  40  with protrusions  48  thereon. For example, as shown in  FIG. 4D , a cover  41  is disposed in the hollow body  40 . The cover  41  is similar to the cover  21  of  FIG. 2B  in the first embodiment. Also, the sealing method is similar to that of the first embodiment. A working fluid is added through the hollow tube  42  into the internal space of the hollow body  40  of the cylindrical heat pipe  4 . After vacuuming, the hollow tube  42  is sealed. Thus, process of manufacturing the cylindrical heat pipe  4  is completed. Further, a sealant is filled in a space  45  between the cover  41  and the top portion  43 , for ensuring adequately sealing the pipe. The sealant comprises epoxy or thermosetting gel.  
      Comparing to the conventional heat pipe, a periphery of the cover  41  is raised by the elevated portion  46  from the conventional position S 1  to a higher position S 2 . Thus, the space close to the periphery of the cover  41  is enlarged owing to the elevated portion  46 . As a result, the heat-dissipation space is increased and heat conductivity of the cylindrical heat pipe  4  is improved.  
      Furthermore,  FIG. 4E  is a cross-sectional view of a cylindrical heat pipe  4  with the cover of  FIG. 3B . As shown in  FIG. 4E , the cover  51  is the same as that in  FIG. 3B  of the second embodiment. The center of the cover  51  has an opening  57  defined therein, so that a working fluid can be added through the opening  57  into the hollow body  40  of the cylindrical heat pipe  4 . The opening  57  is sealed after the hollow body  40  is vacuumed, thereby completing the formation of the cylindrical heat pipe  4 . Further, a sealant is filled in a space  55  between the cover  51  and the top portion  43 , for ensuring sealing adequately sealing the pipe. The sealant comprises epoxy or thermosetting gel.  
      The method of sealing the opening  57  is not limited in the present invention. For example, the opening  57  can be sealed by a block  58  with a radius slightly larger than the opening  57 . The block  58  is pressed and deformed by stress to completely seal the opening  57 . The block  58  can be a copper ball, or the block  38  can comprise other materials or have different shapes as long as the opening  57  of the cover  51  can be sealed. Moreover, the opening  57  may be sealed with a copper ball by welding, soldering, brazing, or gluing.  
      In this embodiment, because adding a working fluid or vacuuming is performed through the opening  57  instead of using a conventional hollow tube, and the pipe is then sealed. Thus, the bottom level of the cover  31  can be raised from the conventional position S 1  to a higher position S 2 . As a result, the heat-dissipation space is increased and heat conductivity of the cylindrical heat pipe  3  is improved.  
      In the above-disclosed embodiments, the wick structure can comprise mesh, fiber, sinter, or grooved wick, formed by sintering, gluing, filling, or deposition. The working fluid can comprise inorganic compounds, water, alcohol, liquid metal such as mercury, ketone, refrigerant such as HFC-134a, or other organic compounds. Typically, the most frequently used working fluid is water. The surface tension between corresponding working fluids differs with wick structures. The sequence of adding the working fluid and vacuuming can be interchanged, followed by sealing the opening. The cylindrical heat pipe of embodiments of the invention can be applied in any heat-dissipation module of any electronic device and can be shaped to meet requirements of the heat-dissipation module.  
      In conclusion, the disclosed cylindrical heat pipe of the invention comprises a cover with an elevated portion, wherein a working fluid can be added not only through a hollow tube, but also through an opening in the cover such that the bottom level of the cover can be elevated. Moreover, the inner wall of the hollow body has a stepped portion or at least one protrusion for fixing and supporting the cover. Embodiments of the invention maintain or increase the space of the heat-dissipation region by forsaking conventional using a hollow tube to add a working fluid and vacuum. Thus, the heat-dissipation region of the cylindrical heat pipe according to embodiments of the invention can be enlarged, thereby increasing heat conductivity.  
      While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.