Patent Publication Number: US-2012037344-A1

Title: Flat heat pipe having swirl core

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a heat pipe, in particular to a flat heat pipe having a swirl core. 
     2. Description of Prior Art 
     With the advancement of science and technology, the power and performance of electronic elements have increased to a greater extent, resulting in the generation of a huge amount heat during the operation of electronic elements. If the heat is not dissipated to the outside immediately and accumulated in the electronic elements, the working temperature of the electronic elements will be raised to such a high extent as to deteriorate the performance. In view of this, the manufacturers in this art continuously propose various heat-dissipating devices for electronic elements. Heat pipe is one of the common heat-dissipating devices. 
     The conventional heat pipe is substantially formed into a hollow pipe. The inner walls of the heat pipe are arranged with a wick structure made of a metallic woven mesh or metallic sintered power. The internal space of the heat pipe is filled with a working fluid. After being subjected to a vacuum-pumping process and a sealing process, a finished heat pipe can be obtained. The heat pipe is divided into an evaporating section brought into thermal contact with an electronic heat-generating element and a condensing section away from the evaporating section. The working fluid located in the evaporating section absorbs the heat of the electronic heat-generating element and is vaporized. The vapors of the working fluid flow toward the condensing section. After being heat-exchanged with the outside of the condensing section, the vapors of the working fluid condense into liquid and flows back to the evaporating section. With the circulation and phase change of the working fluid in the heat pipe, the heat of the electronic heat-generating element can be conducted to other place. 
     Since the modern electronic devices are made more and more compact, the conventional heat pipe may occupy a relatively larger height and space in such a compact electronic device. In view of this, a flat heat pipe is proposed. The interior of the flat heat pipe is substantially the same as that of the conventional tubular heat pipe. The only difference between the flat heat pipe and the conventional tubular heat pipe lies in that: the casing of the flat heat pipe is pressed to be flattened in order to reduce its height and space occupied in the height-wise direction. In this way, the requirements for compact design of the heat pipe can be conformed. 
     However, the above conventional flat heat pipe has the following problems. When the casing is pressed to be flattened, the wick structure arranged on the inner walls of the casing may be cracked or broken due to external forces, especially when the wick structure is made of sintered metallic powder. As a result, the flowing path of the working fluid in the wick structure becomes discontinuous, so that the reflow rate of the working fluid is affected. On the other hand, since the wick structure is arranged on the inner walls of the casing and the vapors of the working fluid flow to the condensing section through the space between the casing and the wick structure, the speed of the vapors flowing on a rugged porous surface of the wick structure is certainly lower than that flowing on a smooth surface. Thus, the arrangement of the wick structure inevitably makes the flowing speed of the vapors unable to be optimized. Further, in order to manufacture the wick structure, it is necessary to arrange a metallic woven mesh or metallic powder on the inner walls of the casing and perform a sintering process to make the wick structure to be adhered to the inner walls, which needs more materials and a longer procedure. 
     Therefore, it is an important issue for the present Inventor to solve the aforesaid problems in prior art. 
     SUMMARY OF THE INVENTION 
     The present invention is to provide a flat heat pipe having a swirl core, in which the swirl core made by winding a metallic woven mesh serves as a wick structure for allowing a working fluid to flow through. Thus, the cost and time for manufacturing the flat heat pie are saved while maintaining a good heat-conducting effect and confirming to the requirements for compact design. 
     The present invention provides a flat heat pipe having a swirl core, including: a flat sealed casing having smooth inner walls; a working fluid filled within the flat sealed casing; and a swirl core disposed along a central axis of the flat sealed casing to support upper and lower inner walls of the flat sealed casing, two airflow channels being formed between the swirl core and left and right inner walls of the flat sealed casing for allowing vapors of the working fluid to flow through, the swirl core being made by winding a metallic woven mesh in at least two circles for allowing the working fluid to flow through, a center of the swirl core being formed with a reflow channel. 
     In comparison with prior art, the present invention has advantageous features as follows: 
     Since the swirl core of the present invention is made by winding the metallic woven mesh in at least two circles for allowing the working fluid to flow through, the material and time for manufacturing the wick structure by a sintering process in prior art can be saved. 
     Since two airflow channels are formed between the swirl core and left and right inner walls of the flat sealed casing for allowing vapors of the working fluid to flow through, the vapors of the working fluid flow on the smooth inner walls of the flat sealed casing. Thus, the speed of vapor flowing on the smooth surface is greater than that flowing on a rugged porous surface of the traditional wick structure. In this way, the heat-conducting effect of the flat heat pipe can be increased. 
     On the other hand, in the conventional heat pipe, the vapors of the working fluid flow from the evaporating section to the condensing section in only one direction. The amount of vapors in the evaporating section is often greater than that in the condensing section, so that a vapor pressure difference is generated between the evaporating section and the condensing section. If the vapors are accumulated in the condensing section due to the insufficient condensing rate, the flowability of the vapors in the heat pipe will be deteriorated and in turn the heat-conducting effect of the heat pipe will be affected. In view of this, according to the present invention, the swirl core is made by winding the metallic woven mesh in at least two circles and a reflow channel is formed in the center of the swirl core. Such a reflow channel allows a small portion of the vapors accumulated in the condensing section to flow back to the evaporating section if necessary. In this way, the flowability of the vapors flowing from the evaporating section toward the condensing section may not be deteriorated. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
         FIG. 1  is an exploded perspective view of the present invention; 
         FIG. 2  is an assembled perspective view of the present invention; 
         FIG. 3  is an axial cross-sectional view of the present invention; 
         FIG. 4  is a side cross-sectional view of the present invention; and 
         FIG. 5  is a schematic view showing the operation of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The detailed description and technical contents of the present invention will become apparent with the following detailed description accompanied with related drawings. It is noteworthy to point out that the drawings is provided for the illustration purpose only, but not intended for limiting the scope of the present invention. 
     Please refer to  FIGS. 1 to 4 . The present invention provides a flat heat pipe  1  having a swirl core for conducting the heat of an electronic heat-generating element  100  (as shown in FIG.  5 ). It can be seen from  FIG. 4  that the flat heat pipe  1  includes a flat sealed casing  10 , a working fluid  20  (indicated by dotted lines), and a swirl core  30 . Based on the functionality in heat conduction, as shown in  FIG. 5 , the flat heat pipe  1  is divided into an evaporating section  2  brought into thermal contact with the electronic heat-generating element  100  and a condensing section  3  away from the evaporating section  2 . 
     The flat sealed casing  10  is made of metallic materials having good heat conductivity. The flat sealed casing  10  has smooth inner walls and no grooves are provided on the inner walls. For better illustration, the inner walls of the flat sealed casing  10  are divided into an upper inner wall  11 , a lower inner wall  12 , a left inner wall  13  and a right inner wall  14  based on a central axis of the flat heat pipe  1 . 
     The working fluid  20  is filled within the flat sealed casing  10 . With the circulation and phase change of the working fluid  20  in the flat sealed casing  10 , the flat heat pipe  1  can continuously conduct the heat of the electronic heat-generating element  100  to the outside. As for the heat-conducting mechanism of the working fluid  20  by means of its phase change, it will be described in more detail later. 
     As shown in  FIG. 3 , the swirl core  30  is disposed along the central axis of the flat sealed casing  10  for supporting the upper inner wall  11  and the lower inner wall  12  (as shown in  FIG. 4 ) because the strength of the flat heat pipe  1  is lowest along the central axis. Thus, the arrangement of the swirl core  30  in the central axis generates a portion of supporting effect to prevent the central portion of the flat heat pipe  1  to be sunken due to external forces. 
     Two airflow channels  15  and  16  are respectively formed between the swirl core  30  and the left inner wall  13  and the right inner wall  14  for allowing the vapors of the working fluid  20  to flow from the evaporating section  2  to the condensing section  3  (as shown in dotted arrows in  FIG. 5 ). Since the vapors flow on the smooth inner walls of the flat sealed casing  10 , the flowing speed of the vapors is greater than that on a rugged porous surface of the traditional wick structure. Thus, the heat-conducting efficiency of the flat heat pipe  1  is enhanced greatly. 
     The swirl core  30  is made by winding a metallic woven mesh  31  in at least two circles for allowing the working fluid  30  to flow through. It can be seen from  FIG. 4  that the swirl core  30  is made by winding the metallic woven mesh  31  in three circles. A gap G is formed between adjacent two circles of the metallic woven mesh  31 . In other word, adjacent two circles of the metallic woven mesh  31  are not tightly adhered to each other. The gap G allows a small portion of the vapors of the working fluid  20  to flow from the condensing section  3  back to the evaporating section  2 . 
     It should be noted that, according to the present invention, the center of the swirl core  30  is formed with a reflow channel  32 , so that the center of the swirl core  30  is not solid. The reflow channel  32  also allows a small portion of the vapors to flow from the condensing section  3  back to the evaporating section  2  (as shown in the arrows in  FIG. 5 ), thereby preventing the accumulation of excess vapors in the condensing section  3  to deteriorate the flowability of the vapors in the flat heat pipe  1 . 
     With reference to  FIG. 5 , the operating principle of the flat heat pipe  1  of the present invention will be described as follows. The evaporating section  2  is brought into thermal contact with the electronic heat-generating element  100 . The working fluid near the evaporating section  2  absorbs the heat generated by the electronic heat-generating element  100  and is vaporized. The thus-formed vapors rapidly flow to the condensing section  3  through the airflow channels  15  and  16  formed between the swirl core  30  and the left inner wall  13  and the right inner wall  14  of the flat sealed casing  10 . Since the vapors flow on the smooth inner walls of the flat sealed casing  10  toward the condensing section  3 , the flowing speed of the vapors of the working fluid  20  is increased greatly, thereby generating a better heat-conducting effect. 
     A heat-dissipating fin asset  200  may be further connected to the outer surface of the condensing section  3  of the flat heat pipe  1 , thereby dissipating the heat of the condensing section  3  to the outside. If the vapors are accumulated in the condensing section  3  because of the insufficient condensing rate of the vapors, the vapor pressure between the evaporating section  2  and the condensing section  3  will force a portion of the vapors in the condensing section  3  to flow back to the evaporating section  2  through the reflow channel  32 , thereby preventing the accumulation of excess vapors in the condensing section  3  to deteriorate the flowability of the vapors in the flat heat pipe  1 . 
     In comparison with prior art, the present invention has advantageous features as follows: 
     Since the swirl core  30  of the present invention is made by winding the metallic woven mesh  31  in at least two circles for allowing the working fluid  20  to flow through, the material and time for manufacturing the wick structure by a sintering process in prior art can be saved. 
     Since the two airflow channels  15  and  16  are formed between the swirl core  30  and left and right inner walls  13  and  14  of the flat sealed casing  10  for allowing vapors of the working fluid  20  to flow through, the vapors of the working fluid  20  flow on the smooth inner walls of the flat sealed casing  10 . Thus, the speed of vapor flowing on the smooth surface is greater than that flowing on a rugged porous surface of the traditional wick structure. In this way, the heat-conducting effect of the flat heat pipe  1  can be increased. 
     On the other hand, in the conventional heat pipe, the vapors of the working fluid flow from the evaporating section to the condensing section in only one direction. The amount of vapors in the evaporating section is often greater than that in the condensing section, so that a vapor pressure difference is generated between the evaporating section and the condensing section. If the vapors are accumulated in the condensing section due to the insufficient condensing rate, the flowability of the vapors in the heat pipe will be deteriorated and in turn the heat-conducting effect of the heat pipe will be affected. In view of this, according to the present invention, the swirl core  30  is made by winding the metallic woven mesh  31  in at least two circles and a reflow channel  32  is formed in the center of the swirl core  30 . Such a reflow channel  32  allows a small portion of the vapors accumulated in the condensing section  3  to flow back to the evaporating section  2 . In this way, the flowability of the vapors flowing from the evaporating section  2  toward the condensing section  3  may not be deteriorated. 
     Although the present invention has been described with reference to the foregoing preferred embodiments, it will be understood that the invention is not limited to the details thereof. Various equivalent variations and modifications can still occur to those skilled in this art in view of the teachings of the present invention. Thus, all such variations and equivalent modifications are also embraced within the scope of the invention as defined in the appended claims.