Abstract:
A loop heat pipe structure includes an evaporator and a first pipe. The evaporator has a first chamber, a first wick layer, and a bottom. The first wick layer is provided in the first chamber. The first pipe includes a first inlet and a first outlet communicably connected to the evaporator. The first inlet internally defines a second chamber communicable with the first wick layer. By providing the second chamber outside the evaporator, the evaporator can have a reduced overall height without creating very high vapor pressure in the evaporator, enabling the loop heat pipe structure to have upgraded heat dissipation efficiency.

Description:
This application claims the priority benefit of China patent application number 201110110326.6 filed on Apr. 29, 2011. 
     FIELD OF THE INVENTION 
     The present invention relates to a loop heat pipe structure, and more particularly to a loop heat pipe structure that includes an evaporator with largely reduced height to thereby overcome the problem of limited space available in an electronic device and to effectively prevent the occurrence of heat leak. 
     BACKGROUND OF THE INVENTION 
     Due to the progress in the semiconductor technology, integrated circuit (IC) chips have been widely used in various electronic apparatus, such as personal computers, notebook computers and network servers. While the IC chips have significantly increased computing speed and functions, they also generate correspondingly increased waste heat. Such waste heat must be effectively removed to protect the electronic apparatus against failure. Various heat dissipation means are therefore developed to achieve effective removal of the heat generated by the IC chips. 
     One of the heat dissipation means is loop heat pipe (LHP). In a conventional loop heat pipe structure, there is included a reservoir or a compensation chamber for storing an adequate amount of working fluid, so that the evaporator for the loop heat pipe structure can be properly furnished with the working fluid and adapt to the volume change of the working fluid caused by density change thereof. The reservoir or compensation chamber also filters gas or bubbles in the working fluid, so that the working fluid is not interfered and damaged by the contained gas or bubbles. 
     While the conventional loop heat pipe structure provides a lot of advantages, it has a cylindrical evaporator that occupies a relatively large space and fails to directly contact with the heat source due to the round outer surface thereof. To overcome such disadvantages, a flat plate loop heat pipe (FPLHP) structure has been developed. In the currently available flat plate loop heat pipe structure, the compensation chamber is located above a wick structure provided inside the evaporator. The loop heat pipe structure with the compensation chamber provided above the wick structure in the evaporator tends to have serious heat leak, which brings difficulty in the start-up of the flat plate loop heat pipe structure and leads to increased total thermal resistance. 
     Moreover, the currently available flat plate loop heat pipe structure usually has an evaporator made of only one type of material for both of its wall portions and bottom. However, the bottom of the evaporator in contact with the heat source should have higher thermal conductivity than the wall portions of the evaporation. Further, due to the special construction of the flat plate loop heat pipe structure, when the bottom of the evaporator is in contact with the heat source, the heat is also transferred via the wall portions of the evaporator to heat the working fluid in the reservoir or compensation chamber. In some cases, the amount of heat transferred to the reservoir or compensation chamber is even equal to that causing the heat leak via the wick structure in the evaporator. A combined effect of the above two conditions badly affects the thermal performance of the flat plate loop heat pipe structure to even offset the advantages thereof. 
     Furthermore, the currently available electronic devices are so designed that they have constantly reduced size, volume and weight, and accordingly, largely reduced internal space. As a result, it has become the most important task to design a heat dissipation device that has small size and low profile to adapt to the limited inner space of the current electronic devices. 
     SUMMARY OF THE INVENTION 
     A primary object of the present invention is to provide a loop heat pipe structure capable of preventing the occurrence of heat leak and accordingly having upgraded heat dissipation performance. 
     Another object of the present invention is to provide a loop heat pipe structure that includes an evaporator with reduced overall height, and accordingly, can be used in electronic devices having narrow internal space. 
     To achieve the above and other objects, the loop heat pipe structure according to the present invention includes an evaporator and a first pipe. The evaporator has a first chamber, a first wick layer, a bottom, and a plurality of grooves. The first wick layer is provided in the first chamber to thereby define a first main chamber and a first secondary chamber in the first chamber. The first wick structure is filled with a working fluid. The grooves are selectively provided on the first wick layer or the bottom. The first pipe has a first inlet and a first outlet. The first inlet internally defines a second chamber, and is connected to a wall of the evaporator to communicate with the first wick layer. The first outlet is connected to another wall of the evaporator to communicate with the first secondary chamber. 
     Since the second chamber is located outside the evaporator, the condition of heat leak from the first wick layer in the first chamber into the second chamber can be effectively prevented. That is, the working fluid in the second chamber will not be overheated to form vapor-liquid phase equilibrium and produce high saturation vapor pressure in the second chamber, and the liquid-phase working fluid in the first pipe would not be stopped from returning to the second chamber. Further, with the second chamber located outside the evaporator, the evaporator can have a largely reduced overall height, allowing the loop heat pipe structure to be used in an electronic device with limited internal space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein 
         FIG. 1  is an exploded perspective view of a loop heat pipe structure with low-profile evaporator according to a first embodiment of the present invention; 
         FIG. 2  is an assembled view of  FIG. 1 ; 
         FIG. 3   a  is a sectional view taken along line A-A of  FIG. 2 ; 
         FIG. 3   b  is another sectional view taken along line A-A of  FIG. 2  according to a variant of the first embodiment of the present invention; 
         FIG. 3   c  is a sectional view taken along line C-C of  FIG. 3   b;    
         FIG. 4   a  is a sectional view taken along line B-B of  FIG. 2 ; 
         FIG. 4   b  is another sectional view taken along line B-B of  FIG. 2  according to a variant of the first embodiment of the present invention; 
         FIG. 5   a  is an exploded perspective view of a loop heat pipe structure with low-profile evaporator according to a second embodiment of the present invention; 
         FIG. 5   b  is an exploded perspective view of a variant of the second embodiment of the present invention; 
         FIG. 6  is an assembled perspective view of the loop heat pipe structure with low-profile evaporator according to the second embodiment of the present invention; 
         FIG. 7  is an assembled perspective view of a loop heat pipe structure with low-profile evaporator according to a third embodiment of the present invention; 
         FIG. 8  is an assembled perspective view of a loop heat pipe structure with low-profile evaporator according to a fourth embodiment of the present invention; 
         FIG. 9   a  is a sectional view taken along line D-D of  FIG. 8 ; 
         FIG. 9   b  is another sectional view taken along line D-D of  FIG. 8  according to a variant of the fourth embodiment of the present invention; 
         FIG. 10  is an exploded perspective view of a loop heat pipe structure with low-profile evaporator according to a fifth embodiment of the present invention; 
         FIG. 11  is an assembled perspective view of a loop heat pipe structure with low-profile evaporator according to a sixth embodiment of the present invention; 
         FIG. 12  is an assembled perspective view of a loop heat pipe structure with low-profile evaporator according to a seventh embodiment of the present invention; and 
         FIG. 13  is an assembled sectional view of a loop heat pipe structure with low-profile evaporator according to an eighth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described with some preferred embodiments thereof and with reference to the accompanying drawings. For ease of understanding, elements that are the same in the preferred embodiments are denoted by the same reference numerals. 
     Please refer to  FIGS. 1 and 2  that are exploded and assembled perspective views, respectively, of a loop heat pipe structure with low-profile evaporator according to a first embodiment of the present invention. For the purpose of conciseness, the present invention is also briefly referred to as a “loop heat pipe structure” herein. As shown, in the first embodiment, the loop heat pipe structure includes an evaporator  1  and a first pipe  2 . 
     The evaporator  1  has a first chamber  11 , a first wick layer  12 , a bottom  13 , and a plurality of grooves  14 . The first wick layer  12  is provided in the first chamber  11  to define a first main chamber  111  and a first secondary chamber  112  in the first chamber  11 . A working fluid  3  is filled in the first wick layer  12 . While the first embodiment is illustrated with the grooves  14  provided on the first wick layer  12  as can be seen from  FIG. 3   a , it is understood the grooves  14  can be selectively provided on any one of the first wick layer  12  and the bottom  13 . For example, in a variant of the first embodiment as shown in  FIG. 3   b , the grooves  14  are provided on the bottom  13 . Please refer to  FIG. 3   c , which is a sectional view taken along line C-C of  FIG. 3   b , the grooves  14  provided on the bottom  13  are spaced from one another. 
     Please refer to  FIG. 4   a , which is a sectional view taken along line B-B of  FIG. 2 . The first pipe  2  has a first inlet  21  and a first outlet  22 . The first inlet  21  internally defines a second chamber  211  and is connected to one wall of the evaporator  1  to communicate with the first wick layer  12  in the evaporator  1 . The first outlet  22  is connected to another wall of the evaporator  1  to communicate with the first secondary chamber  112 . According to a variant of the first embodiment, the second chamber  211  is internally provided with a second wick layer  2111 , as shown in  FIG. 4   b.    
     While the first embodiment is illustrated with the first wick layers  12  being a sintered powder body, it is understood the first wick layer  12  can be any one of a sintered powder body, a net-like body, carbon fibers, and graphite. 
     The evaporator  1  further includes a working pipe  15 , which has an end communicating with the first chamber  11 . 
     Please refer to  FIGS. 5   a  and  6  that are exploded and assembled perspective views, respectively, of a heat pipe structure according to a second embodiment of the present invention, and to  FIG. 5   b  that is an exploded perspective view of a variant of the second embodiment. As shown, the second embodiment is generally structurally similar to the first embodiment, except that, in the second embodiment, the evaporator  1  includes a cover  1   a  and a bottom plate  1   b  correspondingly closed to each other and the first wick layer  12  is provided on the bottom plate  1   b  to define the first main chamber  111  and the first secondary chamber  112  between the cover  1   a  and the bottom plate  1   b . While the second embodiment is illustrated with the grooves  14  provided on the bottom plate lb as can be seen from  FIG. 5   a , it is understood the grooves  14  can be selectively provided on any one of the first wick layer  12  and the bottom plate  1   b . For example, in a variant of the second embodiment as shown in  FIG. 5   b , the grooves  14  are provided on the first wick layer  12 . 
       FIG. 7  is a perspective view of a loop heat pipe structure according to a third embodiment of the present invention. As shown, the third embodiment is generally structurally similar to the first embodiment, except that, in the third embodiment, the first pipe  2  is extended through a plurality of radiating fins  4 . 
       FIG. 8  is an assembled perspective view of a loop heat pipe structure according to a fourth embodiment of the present invention, and  FIG. 9   a  is a sectional view taken along line D-D of  FIG. 8 . As shown, the fourth embodiment is generally structurally similar to the first embodiment, except that, in the fourth embodiment, a second pipe  5  is further provided. The second pipe  5  has a second inlet  51  and a second outlet  52 . The second inlet  51  internally defines a third chamber  511 , and is connected to one wall of the evaporator  1  to communicate with the first wick layer  12 . The second outlet  52  is connected to another wall of the evaporator  1  to communicate with the first secondary chamber  112 . According to a variant of the fourth embodiment, the third chamber  511  is internally provided with a third wick layer  512 , as shown in  FIG. 9   b.    
       FIG. 10  is an exploded perspective view of a loop heat pipe structure according to a fifth embodiment of the present invention. As shown, the fifth embodiment is generally structurally similar to the second embodiment, except that, in the fifth embodiment, a fourth wick layer  16  is further provided to one side of the first wick layer  12 . 
       FIG. 11  is a perspective view of a loop heat pipe structure according to a sixth embodiment of the present invention. As shown, the sixth embodiment is generally structurally similar to the fourth embodiment, except that, in the sixth embodiment, the first pipe  2  and the second pipe  5  are extended through a condensing device  6 . 
       FIG. 12  is a perspective view of a loop heat pipe structure according to a seventh embodiment of the present invention. As shown, the seventh embodiment is generally structurally similar to the fourth embodiment, except that, in the seventh embodiment, the first pipe  2  and the second pipe  5  are extended through a water-cooled device  7 . 
     In the embodiments of the present invention, the second and the third wick layer  2111 ,  512  have permeability larger than that of the first wick layer  12 , and the first and the second inlet  21 ,  51  respectively have a flat configuration. 
     Please refer to  FIG. 13  that is an assembled sectional view of a loop heat pipe structure according to an eighth embodiment of the present invention. As shown, the eighth embodiment is generally structurally similar to the first embodiment, except that, in the eighth embodiment, the first secondary chamber  112  has a first end  1121  coupled with the first outlet of the first pipe and an opposite second end  1122  adjacent to the first chamber. The first end  1121  and the second end  1122  communicate with each other, and the first secondary chamber  112  is tapered from the second end  1122  toward the first end  1121 . 
     The second wick layer  2111  has an effective capillary radius larger than or equal to that of the first wick layer  12 , and has thermal conductivity lower than that of the first wick layer  12 . 
     Please refer to  FIGS. 1 through 13 . In practical implementation of the loop heat pipe structure of the present invention, the first wick layer  12  has an effective capillary radius smaller than that of the second wick layer  2111 , and has thermal conductivity higher than that of the second wick layer  2111 . With this design, the thermal resistance between the evaporator  1  and the second chamber  211  can be increased to reduce the heat reversely permeating from the evaporator  1  to the second chamber  211  during operation of the evaporator  1 . Further, since the second chamber  211  is located outside the evaporator  1 , the condition of heat leak from the first wick layer  12  in the first chamber  11  into the second chamber  211  can be effectively prevented. That is, the working fluid  3  in the second chamber  211  will not be overheated to form vapor-liquid phase equilibrium and produce high saturation vapor pressure in the second chamber  211 , and the liquid-phase working fluid  3  in the first pipe  2  would not be stopped from returning to the second chamber  211 . 
     In conclusion, the above-described structural design is able to create better heat lock effect. 
     The above-described structure can provide sufficient capillary force required by the whole loop heat pipe structure to work normally under both standard and anti-gravity conditions with reduced local thermal resistance. 
     The loop heat pipe structure according to the present invention provides the following advantages: 
     (1) Only the first wick layer  12  and the grooves  14  are provided inside the evaporator  1  while the second chamber  211  and the third chamber  511  of the loop heat pipe structure are located outside the evaporator  1 . That is, the second and the third chambers  211 ,  511 , respectively are located outside two walls of the evaporator  1  that are perpendicular to the direction in which the grooves  14  are extended. 
     (2) The second and the third chambers  211 ,  511 , respectively can be located outside any walls of the evaporator  1  that are not provided with any outlet for vapor-phase working fluid, i.e. located outside any of three walls of the evaporator  1  that are not connected to the first secondary chamber  112 . 
     (3) The first inlet  21  of the first pipe  2  and the second inlet  51  of the second pipe  5  may be configured as a diameter-expanded round pipe, a width-increased flat pipe, a rectangular chamber, or a space in any other suitable cross-sectional shape. 
     (4) The first inlet  21  and the second inlet  51  respectively have an internal design fulfilling the design requirement for the first wick layer. 
     (5) The second chamber  211  and the third chamber  511  are sized to adapt to any fluctuation in the volume of the working fluid caused by changes in temperature. 
     (6) By providing the second and the third chamber  211 ,  511  outside the evaporator  1 , there are only considerably small contact areas between the walls of the evaporator  1  and each of the second and third chambers  211 ,  511 . Therefore, the amount of heat leaked from the evaporator  1  into the second and third chambers  211 ,  511  is relatively low. That is, the saturated vapor pressure difference between the evaporator  1  and the second and third chambers  211 ,  511  is sufficient to satisfy the start-up requirement for the loop heat pipe structure. 
     (7) With the loop heat pipe structure according to the present invention, the evaporator  1  has an effectively reduced volume. That is, the evaporator  1  can have a reduced height or a reduced surface area in parallel with the heat source. 
     (8) The total thermal resistance of the loop heat pipe structure of the present invention can be controlled and limited to a relatively small range, as long as the second and third chambers  211 ,  511  have well designed volumes. 
     (9) Since the second chamber  211  is located outside the evaporator  1 , the evaporator  1  can have a largely reduced overall height, allowing the loop heat pipe structure to have increased flexibility in its applications. 
     The present invention has been described with some preferred embodiments thereof and it is understood that many changes and modifications in the described embodiments can be carried out without departing from the scope and the spirit of the invention that is intended to be limited only by the appended claims.