Abstract:
A heat pipe has a wick of capillary structure formed on the inner wall of the heat pipe so as to form a working fluid path in the heat pipe, wherein the wick of the capillary structure is un-ringlike or various radially. The cross-section of the working fluid path in the heat pipe is in various shapes, such as in a shape of polygon, poly-petal, poly-serration, arc or semicircle. Thus, the thickness of the capillary wick structure on the inner wall of the heat pipe is various due to the shape of the working fluid path.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a heat pipe with a capillary structure, and in particular, relates to a heat pipe with a wick of a capillary structure at the inner wall of the pipe, in which the thickness of the wick is un-ringlike or various radially. 
         [0003]    2. Description of the Related Art 
         [0004]    A conventional method for manufacturing a heat pipe comprises the steps of positioning a mandrel in a tube, filling metal powder into the space between the mandrel and inner wall of the tube, sintering the metal powder and removing out the mandrel. A heat pipe  10  with a capillary structure is thus formed with a concentric and ringlike wick  16 , as shown in  FIG. 1 . The heat pipe is performed further processes for the specific uses, such as cutting, bending, or pressing processes. The capillary wick structure is unavoidably damaged during the processes and the properties thereof is thus adversely affected, for example, the capillarity of the heat pipe is decreased, which results in a decrease of the performance of the vapor and working fluid in the heat pipe. Thus, the application of the heat pipe is limited. 
         [0005]    Therefore, a heat pipe is demanded, in which the damage to the capillary wick of a heat pipe is limited during the manufacturing processes. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is to provide a heat pipe with a wick of capillary structure, in which the thickness of the capillary wick structure is various radially. The cross-sectional of working fluid path in the heat pipe is in various shapes, such as in a shape of polygon, poly-petal, poly-serration, arc, or semicircle. Thus, the thickness of the capillary wick structure on the inner wall of the heat pipe is various due to the shape of the working fluid path. 
         [0007]    In one embodiment of the present invention, the capillary wick structure is at part of the axial semicircle or arc of the heat pipe. In another one embodiment of present invention, the working fluid path of the present heat pipe is a combination of sections with different radius, such as two sections respectively with different radius. 
         [0008]    A reinforced layer, such as mesh, fibers, a porous material, is provided to be formed at the inner wall of the heat pipe to incorporate into the capillary wick structure for reinforcing the capillary wick structure and enhancing the capillary transferring function thereof. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]    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: 
           [0010]      FIG. 1  is a perspective view of a conventional heat pipe with a capillary wick; 
           [0011]      FIG. 2  is a perspective view of an embodiment of a heat pipe with a capillary wick according to the present invention; 
           [0012]      FIG. 3  is a perspective view of another embodiment of a heat pipe with a capillary wick according to the present invention; 
           [0013]      FIG. 4  is a perspective view of another embodiment of a heat pipe with a capillary wick according to the present invention; 
           [0014]      FIG. 5  is a perspective view of another embodiment of a heat pipe with a capillary wick according to the present invention; 
           [0015]      FIG. 6  is a perspective view of another embodiment of a heat pipe with a capillary wick according to the present invention; 
           [0016]      FIG. 7A  is a perspective view of an embodiment of a mandrel for using in manufacturing of a capillary wick according to the present invention; 
           [0017]      FIG. 7B  is a perspective view of another embodiment of a mandrel for using in manufacturing of a capillary wick according to the present invention; 
           [0018]      FIG. 8  is a perspective view of another embodiment of a heat pipe with a capillary wick according to the present invention; 
           [0019]      FIG. 8A  is a perspective view of another embodiment of a heat pipe with a capillary wick according to the present invention; 
           [0020]      FIG. 8B  is a perspective view of another embodiment of a heat pipe with a capillary wick according to the present invention; 
           [0021]      FIG. 9  is a perspective view of another embodiment of a heat pipe with a capillary wick according to the present invention; 
           [0022]      FIG. 10  is a perspective view of another embodiment of a heat pipe with a capillary wick according to the present invention; 
           [0023]      FIG. 11  is a perspective view of a continuous U-shape tube made from the heat pipe of  FIG. 8  according to the present invention; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The present invention is to provide a heat pipe  20  with a capillary wick structure  26 . Referring to  FIG. 2 , a mandrel of rectangular shape (not shown in the drawings) is inserted into a tube  22  for forming a working fluid path  24  in the heat pipe. A metal powder is filled into the space between the mandrel and the inner wall of the tube. After sintering process is complete, the metal powder is sintered to form a capillary wick structure  26  on the inner wall of the tube. Thus, a heat pipe  20  with a working fluid path  24  of rectangular shape in cross section is constructed. This heat pipe  20  with rectangular working fluid path  24  is able to be pressed into a flat tube without damaging the capillary structure during the pressing process because the thickness of the capillary wick  26  is radially various. 
         [0025]    As shown in  FIG. 3 , a heat pipe  30  with a penta-petalous working fluid path  34  is constructed by the above described method. A capillary wick  36  is formed on the tube wall with a radially various thickness. When the heat pipe  30  is pressed into a flat tube, the thinner portion of the wick  36  is born with the stress damage. However, the thicker portion of the wick  36  is not damaged and keeps the original axial capillarity for the application of the heat pipe  30 , such as used as a heat pipe for vaporization. 
         [0026]    A heat pipe  40  with an octagonal working fluid path  44 , as shown in  FIG. 4 , is constructed by the above described method. The thickness of the wick  46  is various according to the shape of the octagonal mandrel. Thus, when the heat pipe  40  is pressed into a flat tube, the working fluid path  44  is deformed into a poly-serration shape in cross section, as shown in  FIG. 5 . Due to the octagonal shape of the working fluid path, the damage to the capillary wick structure is limited during the pressing process. 
         [0027]    As described above, the non-circle mandrel is provided to form a capillary wick with different thickness radially. The different thickness of wicks is provided to meet the different requirements in different application of the present heat pipes. However, when a heat pipe is pressed for forming a specific shape, the capillary wick is stressed and thus is damaged. To minimize this possible defect to the capillary wick, the present invention is to provide a reinforced capillary structure, as shown in  FIG. 6 . A reinforce material  67  is applied to the inner wall of the tube  60 . The reinforced material is a mesh, fibers, a porous material and the likes, which are well known to the skilled in the art. Optionally, a plurality of slots can be formed on the inner wall for strengthening the capillary wick structure. The reinforced material or the plurality of the slots are able to reinforce the capillary wicks  66 , especially in the case that the working fluid path  64  is non-circle shape in cross-section. Particularly, when the thickness of the capillary wick  66  is various radially, the reinforced means is able to compliment the thinner portion of the capillary wick  66  to be against the pressing stress. 
         [0028]    For a various requirements of heat pipes, the mandrel can be in various shapes, such as described above, in rectangular, penta-petalous, octagonal and the likes. Optionally, the mandrel is able to be a combination of sections with different radius, as shown in  FIG. 7 . In one embodiment of the  FIG. 7A , one end  71   a  of the mandrel  71  is smaller than the other end  71   b , wherein the end  71   a  is in a conical shape and gradually extends toward the end  71   b.  The other embodiment as shown in  FIG. 7B , the mandrel  73  is a combination of two sections, or multi-sections with different radius. When the mandrel of  FIGS. 7A and 7B  are used to manufacture heat pipes, the thickness of capillary structure on the inner wall of the tube is axially various at the ends thereof. Thus, this heat pipe is able to be used for specific applications. 
         [0029]    In general, heat pipes contact a heat source at one side only. Thus, the capillary wick structure can be sintered at one side of the tube for meeting the high heat transfer efficiency request. As shown in  FIG. 8 , the capillary structure  86  is at the half side of the heat pipe  80  for concentrating the capillary function. The working fluid path  84  is at the other half side for the vapor of working fluid in the heat pipe  80 . A reinforced layer  87 , such as in mesh, fibers, a porous material, is formed at all over the inner wall of the heat pipe  80 . The reinforced layer  87  is performed as a secondary capillary structure for enhancing the radial capillary function in heat pipe  80 . The heat pipe  80  can be further conducted to be pressed into a flat tube, as shown in  FIGS. 8   a  and  8   b.  In  FIG. 8   a , the pressed capillary structure  86   a  is thus at the horizontal side of the heat pipe  80   a.  In  FIG. 8   b , the pressed capillary structure  86   b  is thus at the longitudinal side. The pressed secondary capillary layers  87   a ,  87   b  still cover the inner wall the heat pipe  80   a  and  80   b.    
         [0030]    Referring to  FIG. 9 , the curve heat pipe  90  is shown. Since the capillary structure will be significantly damaged if a tube with capillary sintering layer is bended. In such a situation, the tube is conducted a bending process and then, is sintering a wick of capillary structure  96 . 
         [0031]    In another one embodiment of the present invention, a capillary structure of a heat pipe  100  is manufactured as an axially various thickness. As shown in  FIG. 10 , the thickness of the capillary structure is gradually increased from the end  111  toward the end  112 . Due to the space variation between the end  111  to end  112 , the working fluid path  140  and the capillary wick  160  can effectively transfer the heat via the capillary wick  160  and the working fluid path  140 . 
         [0032]      FIG. 11  shows a continuous U-shape tube  110  made from a heat pipe  80  of the embodiment of  FIG. 8  according to the present invention. In conventional, when a heat pipe is subjected to a 180° bending process, the capillary structure is damaged and the thermal resistance is very high. Thus, the continuous U-shape tube made from a conventional heat pipe is unable to perform the desired heat transfer function. The present invention is to provide a method to avoid the defeat to the capillary structure of heat pipe. In present invention, a tube is bended to form a continuous 180° U-shape tube and then, is sintered to form a wick of capillary structure, such as mesh, fibers, porous layer, as shown in  FIG. 8 , so as to afford the capillary function to the tube. 
         [0033]    Accordingly, the present invention provides a novel mandrel for using in the sintering of the capillary structure of a heat pipe. Due to the various shape of the mandrel, the capillary wick sintering thereby is in various thicknesses. Thus, the pressing damage to the capillary structure will be minimized 
         [0034]    As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrative of the present invention rather than limiting of the present invention. It is intended that various modifications and similar arrangements be included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures.