Abstract:
An exemplary method for manufacturing a heat pipe includes the following steps: providing a tube, a mandrel and an artery pipe, the tube defining an opening at one end thereof, a wick structure being positioned on an inner surface of the tube, a slot being defined in an outer surface of the mandrel; inserting the mandrel and the artery pipe into the tube via the opening, the artery pipe being received in the slot; baking the tube with the mandrel and the artery pipe to make the artery pipe join the wick structure; drawing the mandrel out of the tube via the opening; and injecting a working media into the tube, and evacuating and sealing the tube.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The disclosure generally relates to a method for manufacturing a heat pipe, and particularly to a method for manufacturing a heat pipe with an artery pipe. 
         [0003]    2. Description of Related Art 
         [0004]    Heat pipes are widely used in various fields for heat dissipation purposes due to their excellent heat transfer performance. Currently, a typical heat pipe includes a sealed tube made of thermally conductive material and a working fluid contained in the tube. The working fluid is employed to carry heat from one end of the tube, typically called an “evaporator section,” to the other end of the tube, typically called a “condenser section.” Preferably, a wick structure is provided inside the heat pipe, lining an inner wall of the tube, for drawing the working fluid back to the evaporator section after it is condensed at the condenser section. 
         [0005]    During operation, the evaporator section of the heat pipe is maintained in thermal contact with a heat-generating component. The working fluid contained at the evaporator section absorbs heat generated by the heat-generating component and then turns into vapor. Due to the difference of vapor pressure between the two sections of the heat pipe, the generated vapor moves and thus carries the heat towards the condenser section where the vapor is condensed into condensate after releasing the heat into ambient environment via, for example, fins thermally contacting the condenser section. Due to the difference in capillary pressure which develops in the wick structure between the two sections, the condensate is then drawn back by the wick structure to the evaporator section where it is again available for evaporation. 
         [0006]    Usually, an artery pipe is provided inside the heat pipe. The artery pipe enhances the capillary force to draw the condensate back and thereby avoid dry-out of the heat pipe. The artery pipe is sealed within the tube of the heat pipe, but is unfixed and can move freely in the tube. This can adversely affect vapor flow in the heat pipe. In addition, when such a heat pipe needs to be flattened to increase a contact surface with the heat-generating component, it is impracticable to ensure that the artery pipe is attached on a portion of the tube of the heat pipe aligning with the heat-generating component. Thus the performance of the heat pipe may be adversely affected. 
         [0007]    What is needed, therefore, is a method for manufacturing a heat pipe which can overcome the described limitations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0009]      FIG. 1  is a flow chart showing a method for manufacturing a heat pipe in accordance with one embodiment of the disclosure. 
           [0010]      FIG. 2  is an exploded, isometric view of a tube, a cylindrical mandrel and an artery pipe used for manufacturing the heat pipe of  FIG. 1 . 
           [0011]      FIG. 3  is similar to  FIG. 2 , but showing the cylindrical mandrel inserted in the tube, and the artery pipe still out of the tube. 
           [0012]      FIG. 4  is similar to  FIG. 3 , but showing the artery pipe inserted in the tube after the cylindrical mandrel has been inserted in the tube. 
           [0013]      FIG. 5  is a cross sectional view of the tube of  FIG. 4 , taken along line V-V thereof. 
           [0014]      FIG. 6  is similar to  FIG. 4 , but with the cylindrical mandrel have been removed from the tube, and showing the tube marked. 
           [0015]      FIG. 7  is similar to  FIG. 6 , but showing the tube flattened. 
           [0016]      FIG. 8  is a cross sectional view of the tube of  FIG. 7 , taken along line VIII-VIII thereof. 
           [0017]      FIG. 9  is an isometric view of a tube, a cylindrical mandrel and artery pipes used for manufacturing a heat pipe with a plurality of artery pipes. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  summarizes a method for manufacturing a heat pipe in accordance with one embodiment of the disclosure. The method is explained in detail as follows: 
         [0019]    Referring also to  FIG. 2 , firstly, a tube  10 , a cylindrical mandrel  20  and an artery pipe  30  are provided. The tube  10  is hollow and cylindrical, and is made of highly heat conductive metal, such as copper, and so on. The tube  10  defines an opening  11  at one end thereof. A wick structure  12  is layered on an inner surface of the tube  10 . The wick structure  12  can be fine grooves defined in the inner surface of the tube  10 , screen mesh or fiber inserted into the tube  10  and held against the inner surface of the tube  10 , or sintered powders bonded to the inner surface of the tube  10  by a sintering process. The cylindrical mandrel  20  is made of metal which has high rigidity, a high melting point and low reactivity, such as steel, and so on. The mandrel  20  defines a longitudinal slot  21  in an outer surface thereof. The slot  21  extends through to both a front end surface and a rear end surface of the mandrel  20 . A cross section of the slot  21  defines part of an ellipse. An outer diameter of the mandrel  20  is substantially equal to an inner diameter of the tube  10  with the wick structure  12  therein, and a length of the mandrel  20  is greater than that of the tube  10 . The artery pipe  30  is hollow and cylindrical, and defines a channel  31  therein. A cross section of the artery pipe  30  is annular. The artery pipe  30  has an outer diameter slightly less than a width of the slot  21  of the mandrel  20 , but greater than a depth of the slot  21  of the mandrel  20 . The artery pipe  30  has a length substantially equal to that of the tube  10 . The artery pipe  30  is formed by a plurality of copper wires woven together, each of the copper wires having a diameter of about 0.05 mm. 
         [0020]    Referring also to  FIG. 3 , the mandrel  20  is inserted into the tube  10  via the opening  11 , with one end of the mandrel  20  exposed out of the tube  10 . An outer circumferential surface of the mandrel  20  is intimately in contact with the wick structure  12  of the tube  10 . In particular, when the wick structure  12  is a screen mesh or fiber wick, or a sintered powder wick, the mandrel  20  can provide required pressure to compel the wick structure  12  to intimately contact the inner surface of the tube  10 . Thus, heat generated by a heat-generating component (not shown) is transferred to the wick structure  12  from the tube  10  more easily. 
         [0021]    Referring also to  FIG. 4 , the artery pipe  30  is horizontally inserted into the slot  21  and then moves along the slot  21  into the tube  10 . Since the diameter of the artery pipe  30  is slightly greater than the depth of the slot  21 , when the artery pipe  30  enters the tube  10 , the artery pipe  30  is pressed by both the wick structure  12  and the mandrel  20  and thereby deforms slightly. Thus, when the artery pipe  30  is inserted in the tube  10 , the artery pipe  30  is deformed to intimately contact with the wick structure  12 . Referring also to  FIG. 5 , after the artery pipe  30  is inserted in the tube  10 , the artery pipe  30  has an elliptic cross-section, and forms an arcuate contact surface  33  abutting the wick structure  12 . A contact area between the contact surface  33  of the artery pipe  30  and the wick structure  12  is increased after the artery pipe  30  is deformed, whereby the capillary force generated by the artery pipe  30  and the wick structure  12  is improved. 
         [0022]    The tube  10  with the mandrel  20  and the artery pipe  30  is then heated in a high temperature furnace (not shown) to make the artery pipe  30  join with the wick structure  12 . During heating, the mandrel  20  is kept in the tube  10  to ensure that the artery pipe  30  is straight and extends along a longitudinal direction of the tube  10 , and further ensure that the artery pipe  30  intimately contacts the wick structure  12 . 
         [0023]    Referring to  FIG. 6 , after the artery pipe  10  is baked to combine with the wick  12  of the tube  10 , the mandrel  20  is drawn out of the tube  10  via the opening  11  of the tube  10 . A marking  40  is engraved on an outer circumferential surface of each end of the tube  10 , corresponding to a position of the artery pipe  30 . Alternatively, the marking  40  can be formed on only one end of the tube  10  or at a middle of the tube  10 . 
         [0024]    Subsequent processes such as injecting a working media into the tube  10 , and evacuating and sealing the tube  10 , can be performed using conventional methods. Thus, a straight circular heat pipe is attained. A portion of the tube  10 , where the markings  40  are formed, is finally flattened to form a flat-type heat pipe  50  which has a rectangular cross-section, as shown in  FIGS. 7 and 8 . The heat pipe  50  includes a top surface  51 , and a bottom surface  52  in parallel with the top surface  51 . The top and bottom surfaces  51 ,  52  are planar. The markings  40  are located on a middle axis (not shown) of the top surface  51 , and the artery pipe  30  is aligned with the middle axis of the top surface  51 . 
         [0025]    In use, the top surface  51  of the heat pipe  50 , with the markings  40 , is attached to the heat-generating component. At this time, the artery pipe  30  aligns with the heat-generating component. 
         [0026]    In the present method for manufacturing the heat pipe  50 , the slot  21  is defined in the mandrel  20 . Thus, the artery pipe  30  is accurately fixed on the wick structure  12  of the tube  10 , in an orientation whereby a length of the artery pipe  30  is fixed along a corresponding length of the wick structure  12 . The artery pipe  30  cannot move freely in the tube  10 . This increases the flow of the working media in the tube  10 , and improves the heat transfer performance of the heat pipe  50 . In addition, the markings  40  are formed on the circumferential surface of the tube  10 , and align with the artery pipe  30 . Accordingly, it is easy to ascertain the position of the artery pipe  30  according to the markings  40 . In use, the position of the heat pipe  50  can be adjusted to make sure that the artery pipe  30  aligns with the heat-generating component, by using the markings  40  as guides. This further ensures the best heat transfer performance of the heat pipe  50 . 
         [0027]    In alternative embodiments, the shape and size of the slot  21  of the mandrel  20  can be varied, thereby forming different kinds of artery pipes  30  in the heat pipe  50  to satisfy different heat dissipation requirements. Furthermore, the mandrel  20  can have more than one slot  21 , so that more than one artery pipe  30  is fixed in the tube  10 . The embodiment described below includes one example of such variations. 
         [0028]    Referring to  FIG. 9 , in this embodiment, a mandrel  20   a  longitudinally defines three slots  21   a  in an outer circumferential surface thereof. Two of the slots  21   a  are at one end of the mandrel  20   a , and the other slot  21   a  is at the other opposite end of the mandrel  20   a . Each of the slots  21   a  has a length less than that of the mandrel  20   a . Each of the slots  21   a  accommodates one artery pipe  30   a . Thus, the heat pipe manufactured via this method includes three artery pipes  30   a  in the tube  10 , wherein two artery pipes  30   a  are attached to one end of the wick structure  12 , and another artery pipe  30   a  is attached to the other opposite end of the wick structure  12 . 
         [0029]    It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.