Patent Publication Number: US-2007107878-A1

Title: Heat pipe with a tube therein

Description:
DESCRIPTION  
      1. Field of the Invention  
      The present invention relates generally to heat pipes as heat transfer/dissipating device, and more particularly to a heat pipe with a tube therein.  
      2. Description of Related Art  
      Heat pipes have excellent heat properties, and therefore are an effective means for heat transfer or dissipation from heat sources. Currently, heat pipes are widely used for removing heat from heat-generating components such as central processing units (CPUs) of computers.  FIG. 6  shows an example of a related heat pipe. The heat pipe includes a vacuum casing  10  containing a working fluid therein (not shown) and a capillary wick  20  attached to an inner surface of the casing  10 . The casing  10  includes an evaporating section  40  at one end and a condensing section  60  at the other end. An adiabatic section  50  is provided between the evaporating and condensing sections  40 ,  60 . The adiabatic section  50  is typically used for transport of the generated vapor from the evaporating section  40  to the condensing section  60 . A vapor channel  70  is formed in the central of an inside of the casing  10  and a liquid channel  80  is defined by the capillary wick  20 . As the evaporating section  40  of the heat pipe is maintained in thermal contact with a heat-generating component, the working fluid contained in the evaporating section  40  absorbs heat generated by the heat-generating component and then turns into vapor. Due to the difference of vapor pressure between the evaporating and condensing sections  40 ,  60  of the heat pipe, the generated vapor moves towards and carries the heat simultaneously to the condensing section  60  along the vapor channel  70 . The vapor is condensed into liquid at the condensing section  60  after releasing the heat into ambient environment.  FIG. 7  is a diagrammatically longitudinal cross-sectional view showing opposite flowing paths between vapor and condensed liquid of the working fluid in the casing  10  of the heat pipe. Because of contacts of the vapor and the condensed liquid, an entrainment limit caused by the opposite flowing between the vapor and the condensed liquid prevents circulations of the vapor and condensed liquid. The condensed liquid is heated before it reaches the evaporating section  40 . Accordingly, heat-transferred ability of the heat pipe is weakened and heat dissipation efficiency of the heat pipe is lowered.  
      In view of the above-mentioned disadvantage of the conventional heat pipe, there is a need for a heat pipe having a good heat transfer effect.  
     SUMMARY OF THE INVENTION  
      A heat pipe in accordance with a preferred embodiment includes a metal casing containing a working fluid therein and a capillary wick provided in an inside of the casing. The capillary wick extends in an axial direction of the casing and has a middle portion separated from an inner wall of the metal casing. A tube is provided to contact with a surface of the capillary wick to separate the capillary wick from a vapor passage in the heat pipe.  
      Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Many aspects of the present apparatus and method 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 apparatus and method. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
       FIG. 1  is a longitudinal cross-sectional view of a heat pipe in accordance with a first embodiment of the present invention;  
       FIG. 2  is a radial cross-sectional view of the heat pipe in accordance with the first embodiment, taken along line II-II of  FIG. 1 ;  
       FIG. 3  is a longitudinal cross-sectional view of a heat pipe in accordance with a second embodiment of the present invention;  
       FIG. 4  is a radial cross-sectional view of a heat pipe in accordance with a third embodiment of the present invention;  
       FIG. 5  is a radial cross-sectional view of a heat pipe in accordance with a fourth embodiment of the present invention;  
       FIG. 6  is a longitudinal cross-sectional view of a heat pipe in accordance with related art; and  
       FIG. 7  is a diagrammatically longitudinal cross-sectional view showing vapor and liquid moving paths of the related heat pipe of  FIG. 6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIGS. 1-2  show a heat pipe in accordance with a first embodiment of the present invention. The heat pipe comprises a metal casing  100  made of high thermally conductive materials such as copper or copper alloys, a working fluid (not shown) contained in the casing  100  and a capillary wick  200  arranged inside of the casing  100 . The casing  100  comprises an evaporating section  400  at one end, a condensing section  600  at the other end and an adiabatic section  500  arranged between the evaporating section  400  and the condensing section  600 . The capillary wick  200  comprises first capillary wicks  220  disposed in opposite ends of the casing  100 , respectively, and a second capillary wick  240  interconnecting with the first capillary wicks  220 . The first capillary wicks  220  are arranged on the evaporating and condensing sections  400 ,  600  of the casing  100 . The second capillary wick  240  extends in an axial direction of the casing  100 . A tube  300  surrounds the second capillary wick  240  so that an inner surface of the tube  300  is attached with an outer surface of the second capillary wick  240  in the casing  100 . The first capillary wicks  220  contact with the casing  100 , while the second capillary wick is separated from the casing  100 . A vapor passage  700  is provided between the tube  300  and an inner wall of the casing  100  and a liquid channel  800  is defined by the first and second capillary wicks  220 ,  240 . The vapor passage  700  is separated from the second capillary wick  240  by the tube  300  at the adiabatic section  500 . The tube  300  can reach the evaporating and condensing sections  400 ,  600  of the casing  100  with a proper range.  
      As the evaporating section  400  of the heat pipe is maintained in thermal contact with a heat-generating component (not shown), the working fluid contained in the evaporating section  400  absorbs heat generated by the heat-generating component and then turns into vapor. Due to the difference of vapor pressure between the evaporating and condensing sections  400 ,  600  of the heat pipe, the generated vapor moves along the vapor passage  700  and carries the heat simultaneously to the condensing section  600 . The vapor is condensed into liquid at the condensing section  600  after releasing the heat into ambient environment. Because of an arrangement of the tube  300  attached on the second capillary wick  240  at the adiabatic section  500 , the vapor flows only along the vapor passage  700  toward the condensing section  600  and the liquid flows only in the liquid channel  800  towards the evaporating section  400  when they flow in the adiabatic section  500 . The vapor and the liquid in the adiabatic section  50  are separated by the metal tube  300 , which can avoid the adverse contact between the vapor and liquid. Thus, the condensed working fluid from the condensing section  600  can smoothly reach the evaporating section  400  and is prevented from being heated by the high temperature vapor at the adiabatic section  500 . Abilities of heat-absorption and heat-dissipation of the working fluid of the heat pipe is enhanced and heat-transfer efficiency of the heat pipe is accordingly improved.  
       FIG. 3  illustrates a heat pipe according to a second embodiment of the present invention. Main differences between the second and first embodiments are that in the second embodiment the capillary wick  200  further comprises a third capillary wick  230  attached on the inner wall of the casing  100  at the evaporating section  400 . The third capillary wick  230  is a thin layer extending from an end of the first capillary wick  220  at the evaporating section  400  of the casing  100 . The third capillary wick  230  is so thin that it can guide the vapor at the evaporating section  400  into the vapor passage  700  quickly. Portions of the first capillary wicks  220  near the second capillary wick  240  each have a graduated thickness: the thickness at the evaporating section  400  is gradually decreased along a direction from the evaporating section  400  toward the adiabatic section  500 , and at the condensing section  600  is gradually increased from the adiabatic section  500  toward the condensing section  600 . The third capillary wick  230  is much thinner than that of the first and second capillary wicks  220 ,  240 . As the evaporating section  400  of the heat pipe absorbs the heat generated by the heat-generating component, the heated working fluid can turn into vapor quickly and then flow into the vapor passage  700  towards the condensing section  600  of the casing  100 . The vapor passage  700  is separated from the second capillary wick  240  by the tube  300 . A liquid channel  820  is defined by the first, second and third capillary wicks  220 ,  240  and  230 . The condensed liquid in the condensing section  600  flows along the liquid channel  820  and is drawn back to the evaporating section  400  under capillary pressure developed by the first and second capillary wicks  220 ,  240  to achieve a thermal circulation.  
       FIG. 4  illustrates a heat pipe according to a third embodiment of the present invention. Four spaced ribs  310  are disposed between an outer wall of the tube  300  and the inner wall of the casing  100  so as to reinforce the heat pipe. The other structure of the heat pipe of the third embodiment is similar to that of the first embodiment.  
       FIG. 5  illustrates a heat pipe according to a fourth embodiment of the present invention. Four-spaced small pipes  320  are disposed surrounding the tube  300  and an inner surface of each small pipe  320  is filled with a supplementary second capillary wick  240 . Each small pipe  320  extends in a longitudinal direction of the casing  100  and is sandwiched between an outer wall of the tube  300  and the inner wall of the casing  100 . The vapor passage  700  is enclosed by the inner wall of the casing  100  and defined between the tube  300  and the small pipes  320 . The supplementary second capillary wick  240  interconnects the first wick structures at the evaporating section and at the condensing section. The other structure of the heat pipe of the fourth embodiment is similar to that of the first embodiment.  
      The tube  300  and the pipes  320  in the preferred embodiments are made of metal sheet. Alternatively, they can be made of metal mesh. The tube  300  and the pipes  320  are made of metal materials such as copper or aluminum. Alternatively they can be made of non-metal material such as plastics or resin. A cross-sectional area of the tube  300  or the pipes  320  can also be square or rectangular, according to the shape of heat pipe.  
      It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.