Patent Publication Number: US-2013233519-A1

Title: Flat heat pipe

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to heat transfer apparatuses and, more particularly, to a flat heat pipe with enhanced heat dissipation efficiency. 
     2. Description of Related Art 
     Generally, flat heat pipes can efficiently dissipate heat from heat-generating components such as central processing units (CPU). A conventional flat heat pipe includes a hollow cover, a continuous wick structure mounted on an inner surface of the cover and a working medium contained in the wick structure. A vapor chamber is defined between an inner surface of the wick structure. When the cover absorbs heat generated from the heat-generating components, the working medium is vaporized by the heat and enters into the vapor chamber in all directions of the inner surface of the wick structure. Therefore, the vaporized working medium from different directions of the wick structure tends to interfere with each other and forms turbulence. Thus, heat dissipation efficiency and stability performance of the flat heat pipe are badly affected. 
     What is needed is a flat heat pipe which can overcome the problem of the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, isometric view of a flat heat pipe in accordance with a first embodiment of the disclosure. 
         FIG. 2  is a schematic, longitudinal cross-section view of the flat heat pipe of  FIG. 1 , taken along line II-II thereof. 
         FIG. 3  is a schematic, transverse cross-section view of the flat heat pipe of  FIG. 1 , taken along line III-III thereof. 
         FIG. 4  is a schematic, longitudinal cross-section view of the flat heat pipe of a second embodiment. 
         FIG. 5  is a schematic, transverse cross-section view of the flat heat pipe of the second embodiment. 
         FIG. 6  is a schematic, longitudinal cross-section view of the flat heat pipe of a third embodiment. 
         FIG. 7  is a schematic, transverse cross-section view of the flat heat pipe of the third embodiment. 
         FIG. 8  is a schematic, longitudinal cross-section view of the flat heat pipe of a fourth embodiment. 
         FIG. 9  is a schematic, transverse cross-section view of the flat heat pipe of the fourth embodiment. 
         FIG. 10  is a schematic, longitudinal cross-section view of the flat heat pipe of a fifth embodiment. 
         FIG. 11  is a schematic, transverse cross-section view of the flat heat pipe of the fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1-3 , a flat heat pipe  1  in accordance with a first embodiment of the disclosure includes a hollow cover  10 , a wick structure  30  mounted on an inner surface of the cover  10 , and working medium (not shown) contained in the wick structure  30 . The flat heat pipe  1  is used to contact heat-generating components (not shown) to absorb heat generated therefrom. 
     The cover  10  is integrally formed by one piece of metal such as copper or brass. The cover  10  includes an elongated front plate  11 , an elongated rear plate  13  spaced from and facing the front plate  11  and two convex connecting plates  15  located at lateral sides of the flat heat pipe  1  and interconnecting lateral edges of the front plate  11  and the rear plate  13 . Opposite ends of the front plate  11  and the rear plate  13  are pressed toward each other and sealed to form a first end  17  and a second end  19 . Inner surface of the front plate  11 , the rear plate  13  and the connecting plates  15  cooperatively define a receiving chamber  16  therebetween. One end of the flat heat pipe  1  approaching the first end  17  is an evaporating portion to absorb heat generating from the heat-generating components. The other end approaching the second end  19  is a condensing portion to condense vaporized working medium. 
     The wick structure  50  is a screen made of wires mesh or a sintered body sintered by metal powder. The wick structure  50  has a substantially form of triangular pyramid, adhered to inner surfaces of the first end  17  and one of the connecting plate  15 . The wick structure  50  slantwise extends towards the second end  19  along a longitudinal direction of the cover  10 . A volume of the wick structure  30  is equal to a half of a cubage of the receiving chamber  16 . 
     A volume of the wick structure  30  decreases from an end contacting the first end  17  of the cover  10  to the other end contacting the second end  19  of the cover  10 . A transverse cross section of the end contacting the first end  17  is oval. The wick structure  30  has a lateral surface  31 , two side surfaces  33 , an arc-shaped connecting surface  35  and an interface  37 . The lateral surface  31  is adhered to and overspreads the inner surface of the first end  17 . The side surfaces  33  extend from opposite edges of the lateral surface  31  and are adhered to part of the inner surfaces of the front plate  11  and the rear plate  13 , respectively. A surface area of each side surface  33  is equal to a half of that of the inner surface of the front plate  11  or the rear plate  13 . A width of each side surface  33  decreases from the first end  17  to the second end  19 . 
     The connecting surface  35  extends from a top edge of the lateral surface  31  and is adhered to whole of the inner surface of the top connecting plate  15  along the longitudinal direction of the cover  10 . The interface  37  extends from another edge of the lateral surface  31  and connects ends of the side surfaces  33  near to the bottom connecting plate  15 . The interface  37 , the connecting surface  35 , and the side surfaces  33  intersect the topmost edge of the second end  19 . The interface  37  is elongated and is away from the inner surface of the second end  19  and the bottom connecting plate  15 . The interface  37 , an inner surface of the bottom connecting plate  15  away from the connecting surface  35 , and the exposed inner surfaces of the front plate  11  and the rear plates  13  cooperatively define a vapor passage  18  therebetween. A volume of the wick structure  30  is equal to a cubage of the vapor passage  18 . 
     When the evaporating portion of the flat heat pipe  1  absorbs heat generated from the heat-generating components, the absorbed heat makes the working medium in the wick structure  30  be vaporized and enter into the vapor passage  18  only from the interface  37  of the wick structure  30 . So the vaporized working medium enters into the vapor passage  18  in a smaller angle range relative to the conventional flat heat pipe. Thus, interference between the vaporized working medium in the vapor passage  18  is decreased relative to the conventional flat heat pipe. A probability of forming turbulence of the vaporized working medium is decreased. 
     Following table shows heat transfer performance of the flat heat pipe  1  via adjusting a volume proportion of the vapor passage  18  to the receiving chamber  16 . 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                   
                   
                 Average of the max load 
                 Average of thermal 
               
               
                 Proportion 
                 Number 
                 of heat transfer (W) 
                 resistance (° C./W) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 0.45 
                 30 
                 31.5 
                 0.45 
               
               
                 0.5 
                 30 
                 32 
                 0.2 
               
               
                 0.67 
                 30 
                 31 
                 0.15 
               
               
                 0.7 
                 30 
                 25 
                 0.13 
               
               
                   
               
               
                 Remarks: 1: A length of the flat heat pipe is 160 mm, before pressed, a height of the heat pipe is 6 mm, and after pressed, a height of the flat heat pipe is 1.5 mm. 
               
               
                 2: The working temperature is 50 Celsius degrees. 
               
               
                 3: A number of the tested flat heat pipes is 30. 
               
            
           
         
       
     
     It can be concluded from the above table, the flat heat pipe  1  has a smaller liquid resistance and greater capillary force when the cubage of the vapor passage  18  is equal to a half of that of the receiving chamber  16 . 
     Referring to  FIGS. 4-5 , a flat heat pipe  1   a  of a second embodiment is shown. The flat heat pipe  1   a  is similar to the flat heat pipe  1  of the first embodiment, except that the flat heat pipe  1   a  has a wick structure  30   a  different from the wick structure  30 . The wick structure  30   a  has a substantially triangular prism and includes a lateral surface  31   a , a first connecting surface  35   a , a second connecting surface  36   a , two side surfaces  33   a , and an interface  37   a . The lateral surface  31   a  is adhered to and overspreads the inner surface of the first end  17 . The first connecting surface  35   a  and the second connecting surface  36   a  extend from top and bottom edges of the lateral surface  31   a  and are respectively adhered to part of the inner surfaces of the connecting plates  15 . The first connecting surface  35   a  and the second connecting surface  36   a  respectively cover right parts of the inner surfaces of the connecting plates  15  along the longitudinal direction of the cover  10 . The second connecting surface  36   a  is longer than the first connecting surface  35   a  along the longitudinal direction of the cover  10 . The side surfaces  33   a  extend opposite edges of the lateral surface  31   a  and are respectively adhered to part of the inner surfaces of the front plate  11  and the rear plate  13 . The interface  37   a  connects the side surfaces  33   a , the first connecting surface  35   a  and the second connecting surface  36   a . The interface  37   a , the side surfaces  33   a , the first connecting surface  35   a  and the second connecting surface  36   a  intersect a line  34   a  away from and at a right side of the topmost edge of the inner surface of the second end  19 . The interface  37   a , the exposed inner surfaces of the connecting plates  15 , the front plate  11  and the rear plate  13  cooperatively define a vapor passage  18   a  therebetween. 
     Referring to  FIGS. 6-7 , a flat heat pipe  1   b  of a third embodiment is shown. The flat heat pipe  1   b  is similar to the flat heat pipe  1  of the first embodiment, except that the flat heat pipe  1   b  has a wick structure  30   b  different from the wick structure  30 . In this embodiment, the wick structure  30   b  has a substantially form of triangular pyramid and is adhered to and overspreads the inner surfaces of the top connecting plate  15  and the front plate  11 . The wick structure  30   b  slantwise extends from the first end  17  to the second end  19  along the longitudinal direction of the cover  10 . The wick structure  30   b  is spaced from the bottom connecting plate  15  and the rear plate  13 . An interface  37   b  of the wick structure  30   b  is formed at a bottom end of the wick structure  30   b  oriented towards the bottom connecting plate  15  and the rear plate  13 . The interface  37   a , the inner surfaces of the bottom connecting plate  15  and the rear plate  13  cooperatively define a vapor passage  18   b  therebetween. 
     Referring to  FIGS. 8-9 , a flat heat pipe  1   c  of a fourth embodiment is shown. The flat heat pipe  1   c  is similar to the flat heat pipe  1  of the first embodiment, except that the flat heat pipe  1   c  has a wick structure  30   c  different from the wick structure  30 . In this embodiment, the wick structure  30   c  has a substantially form of cube and is adhered to and overspreads the inner surface of the top connecting plate  15 . The wick structure  30   c  evenly extends towards the bottom connecting plate  15  along a transverse direction of the cover  10  until fills of a top half of the receiving chamber  16 . The wick structure  30   c  evenly extends from the first end  17  to the second end  19  along the longitudinal direction of the cover  10 . An interface  37   c  is formed on a bottom ends of the wick structure  30   c  facing the bottom connecting plate  15 . The interface  37   c , the inner surface of the bottom connecting plate  35   c , and the exposed inner surface of the front plate  11  and rear plate  13  cooperatively define a vapor passage  18   c  therebetween. 
     Referring to  FIGS. 10-11 , a flat heat pipe  1   d  of a fifth embodiment is shown. The flat heat pipe  1   d  is similar to the flat heat pipe  1  of the first embodiment, except that the flat heat pipe  1   d  has a wick structure  30   d  different from the wick structure  30 . In this embodiment, the wick structure  30   d  is substantially cubical and arranged on a central of the cover  10  along the longitudinal direction of the cover  10  to divide the receiving chamber  16  into three parts. Two vapor passages  18   d  are defined between the connecting plates  15  and top and bottom ends of the wick structure  30   d . Lateral surfaces  31   e ,  31   d  of the wick structure  30   d  are respectively adhered to a central portion of the inner surface of the first end  17  and the second end  19 . Side surfaces  33   d  connect the lateral surfaces  31   e ,  31   d  and are respectively adhered to central portions of the front plate  11  and the rear plate  13 . The wick structure  30   d  evenly extends from the first end  17  to the second end  19  along the longitudinal direction of the cover  10 . 
     It is believed that the disclosed embodiment(s) 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 disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the disclosure.