Patent Publication Number: US-2013248152-A1

Title: Heat pipe with one wick structure supporting another wick structure in position

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure generally relates to heat pipes and, particularly, to a heat pipe having two different wick structures. 
     2. Description of Related Art 
     With the continuing development of electronics technology, many electronic components are nowadays made in a small size but with a high operating frequency capability. When such electronic components operate inside a device, they generate much heat and require enhanced heat dissipation. In order to cool the electronic components, heat dissipation devices, such as heat pipes, are used to dissipate heat from the electronic components. 
     A typical heat pipe includes a tube, a wick structure received in the tube, and a working fluid sealed in the tube. The wick structure is generally attached on an entire inner wall of the tube as an elongated cylinder. The typical heat pipe has some problems which limit the heat transferring capability thereof. Firstly, when the heat pipe is manufactured, the cylindrical wick structure may not have intimate contact with the inner wall of the tube during insertion of the wick structure into the tube. Therefore after sintering (or another kind of fixing method) to attach the wick structure to the tube, some parts of the wick structure may be spaced from the inner wall of the tube. Because these parts of the wick structure are not in contact with the inner wall of the tube, such parts may significantly interrupt the capillary transport of liquid working fluid along the wick structure to an evaporating section of the heat pipe. 
     Secondly, the wick structure covers the whole inner wall of the tube, and therefore the diameter of an inner chamber of the heat pipe is reduced. The inner chamber of the heat pipe acts as a vapor passage of the heat pipe, and thus the space available for passage of vapor is reduced. For some thin heat pipes, the small space for vapor passage significantly limits transport of vaporized working fluid from the evaporating section to a condensing section of the heat pipe. Thus the heat transferring capability of the heat pipe is reduced. 
     What is needed, therefore, is a means which can address the limitations described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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 various views. 
         FIG. 1  is an abbreviated, longitudinal cross-section of a heat pipe in accordance with a first embodiment of the present disclosure. 
         FIG. 2  is a transverse cross-section of the heat pipe of  FIG. 1 , corresponding to a line II-II thereof. 
         FIG. 3  is similar to  FIG. 2 , but showing a transverse cross-section of a heat pipe in accordance with a second embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-2 , a heat pipe  100  in accordance with a first embodiment of the present disclosure is shown. The heat pipe  100  includes a longitudinal tube  10 , a first wick structure  30  and a second wick structure  40  fixed in the tube  10 , and working liquid  20  contained within the tube  10 . 
     The tube  10  is made of a heat conductive material such as copper, aluminum or alloy thereof. The tube  10  includes a bottom wall  101 , a top wall  103  parallel to the bottom wall  101 , and a first side wall  105  and a second side wall  107  interconnecting the top wall  103  and the bottom wall  101 . A distance between the top wall  103  and the bottom wall  101  is less than that between the first side wall  105  and the second side wall  107 . The tube  10  defines an elongated chamber  50  therein. The tube  10  includes an evaporating section  110  at an end thereof, a condensing section  120  at an opposite end thereof, and an adiabatic section  130  between the evaporating section  110  and the condensing section  120 . 
     The first wick structure  30  is disposed on an inner face of the tube  10  at the evaporating section  110 . The first wick structure  30  may be formed by sintering metal powder on the inner face of the tube  10 , or by inserting curved woven mesh on the inner face of the tube  10 , or by other suitable methods. In this embodiment, the first wick structure  30  is only disposed at the evaporating section  110  without extending to the adiabatic section  130  and the condensing section  120 . Thus the first wick structure  30  occupies a relatively small space of a vapor passage (i.e., the chamber  50 ) of the heat pipe  10 , and thereby facilitates the flow of vaporized working liquid  20  within the tube  10 . The first wick structure  30  has a U-shaped cross section, with a gap  301  defined between two opposite ends thereof. The first wick structure  30  partially covers the inner face of the evaporating section  110  of the tube  10 . In detail, the first wick structure  30  includes a bottom portion  302  contacting the bottom wall  101 , a side portion  304  contacting the second side wall  107 , and a top portion  303  contacting the top wall  103  of the tube  10 . The gap  301  is located between the bottom portion  302  and the top portion  303 , and is adjacent to the first side wall  105  of the tube  10 . 
     The second wick structure  40  extends throughout a length of the tube  10 , from the evaporating section  110  through the adiabatic section  130  to the condensing section  120 . The second wick structure  40  may be made of woven mesh, bunched fiber, or other suitable material. The second wick structure  40  is sandwiched between the top portion  303  and the bottom portion  302  of the first wick structure  30 , thereby providing sufficient support for the first wick structure  30 . Thus, the first wick structure  30  can intimately contact the inner face of the tube  10 , without significant spaces existing between the inner face of the tube  10  and the first wick structure  30 . The second wick structure  40  is positioned along a central axis I of the tube  10 . In one embodiment, the second wick structure  40  is hollow, and thereby defines a channel  401  therethrough. The channel  401  may function as another vapor passage within the second wick structure  40 , in addition to the vapor passage outside and surrounding the second wick structure  40 . Therefore, the vaporized working liquid  20  can be transferred to the condensing section  120  more quickly. In other embodiments, the second wick structure  40  can be a solid wick structure without the channel  401 . 
     Alternatively, the gap  301  of the first wick structure  30  may be defined in other positions of the first wick structure  30  according to different requirements. For example,  FIG. 3  shows a gap  301   a  of a first wick structure  30   a  being located at the top wall  103  adjacent to the first side wall  105  of the tube  10 . The first wick structure  30   a  includes a top portion  303   a , a side portion  304   a , a bottom portion  302   a , and another side portion  305   a . The side portion  305   a  is located opposite to the side portion  304   a , and extends from the bottom portion  302   a  towards an end of the top portion  303   a . The side portion  305   a  contacts the first side wall  105  of the tube  10 . The gap  301   a  is located between the side portion  305   a  and the end of the top portion  303   a.    
     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.