Patent Publication Number: US-10782076-B2

Title: Heat pipe

Description:
BACKGROUND OF THE INVENTION 
     Technical Field 
     The present invention relates to a thin heat pipe having a favorable maximum heat transport amount, low thermal resistance, and excellent heat transport characteristics. 
     Background Art 
     Electronic components, such as semiconductor elements, that are mounted on electronic devices have increased in the amount of heat generated due to higher mounting density associated with higher performance, and thus cooling of the components has become more important. One method for cooling electronic components is to use a heat pipe. 
     Due to narrowing of the installation area for the heat pipe caused by the higher mounting density of the electronic components, and due to the smaller size of the electronic components, there is demand for flat heat pipes, such as a thin heat pipe that has a thickness of 1.5 mm or below. There has been a proposal for a thin heat pipe that uses a wick having a main body and a first protruding part extending from the main body. The first protruding part divides the inside of a heat-receiving part into a first section communicating with a steam flow path and a second section communicating with a liquid return flow path, and the heat-receiving part is thermally connected to a heat generating component at a location straddling the first section and the first protruding part (Patent Document 1). 
     In Patent Document 1, the boundary between the first protruding part and second section can be disposed in a position far away from the heat generating component, which thus prevents an increase in pressure loss in this direction and the flowing of air bubbles in evaporated working fluid in this direction. By extension, this prevents a reverse flow being generated in the working fluid and inhibits a reduction in heat transport efficiency, even if a plurality of heat generating components are provided. 
     However, the thin heat pipe in Patent Document 1 is problematic in that it is not possible to attain both an improvement in the maximum heat transport amount and a reduction in thermal resistance; i.e., if the maximum heat transport amount is increased, then thermal resistance also increases, and if thermal resistance is decreased, then the maximum heat transport amount also decreases. Thus, the thin heat pipe of Patent Document 1 still had these aforementioned issues, which have a particularly marked occurrence when the heat pipe is thin. 
     RELATED ART DOCUMENT 
     Patent Document
     Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2009-204254   

     SUMMARY OF THE INVENTION 
     In view of the issues described above, the present invention aims at providing a heat pipe that has excellent heat transport characteristics with a favorable maximum heat transport amount and low thermal resistance even when the heat pipe is thin. 
     Additional or separate features and advantages of the invention will be set forth in the descriptions that follow and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, in one aspect, the present disclosure provides a heat pipe having a heat receiving portion that is configured to be thermally connected to a heat generating member so as to absorb heat from the heat generating member, the heat pipe including: a flat container having a tube shape of which both ends are sealed, the flat container having a pair of flat inner surfaces that oppose each other in a vertical direction in cross sections perpendicular to a lengthwise direction of the flat container; a wick structure housed inside the flat container; and a working fluid sealed inside the flat container, wherein in at least one cross section of the flat container: the wick structure includes a first wick member and a second wick member disposed in the vertical direction, the first wick member contacts the second wick member and one inner surface of the pair of flat inner surfaces of the flat container, and both side faces of the first wick member do not contact any of the inner surfaces of the flat container, and the second wick member contacts the other inner surface of the pair of flat inner surfaces of the flat container, and both side faces of the second wick member do not contact any of the inner surfaces of the flat container, wherein the wick structure has a first wick part and a second wick part, respectively disposed in the lengthwise direction of the flat container, the second wick part being directly or indirectly connected to the first wick part and having a maximum width that is wider than a maximum width of the first wick part, and wherein the second wick part is disposed in the heat receiving portion of the heat pipe. 
     In an aspect of the heat pipe of the present invention, the maximum width of the first wick part is 40% to 60% of a maximum width of an inner space of the flat container, and the maximum width of the second wick part is 60% to 80% of the maximum width of the inner space of the flat container. 
     In the aforementioned aspect, a maximum width of the first wick part is 40% to 60% relative to the width in the direction (cross section of the flat container) orthogonal to the lengthwise direction inside the flat container; thus, on the pair of flat inner surfaces of the flat container corresponding to the position of the first wick part, there is a location that does not contact either the first wick member or the second wick member, and this location is exposed to the inner space of the flat container. Moreover, a maximum width of the second wick part is 60% to 80% relative to the width in the direction (cross section of the flat container) orthogonal to the lengthwise direction inside the flat container; thus, on the pair of flat inner surfaces of the flat container corresponding to the position of the second wick part, there is a location that does not contact either the first wick member or the second wick member, and this location is exposed to the inner space of the flat container. Furthermore, the exposed region of the flat inner surfaces of the flat container corresponding to the position of the first wick part is wider than the exposed region of the flat inner surfaces of the flat container corresponding to the position of the second wick part. 
     In an aspect of the heat pipe of the present invention, a length of the second wick part in the lengthwise direction of the flat container is 2% to 50% of a sum of a length of the first wick part in the lengthwise direction of the flat container and a length of the second wick part in the lengthwise direction of the flat container. 
     In an aspect of the heat pipe of the present invention, in the at least one cross section: a cross section of the first wick member has a convex-shaped bottom and a flat top, and a cross section of the second wick member has a flat bottom and a convex-shaped top, and the convex-shaped bottom of the first wick member contacts the convex-shaped top of the second wick member, and the flat top of the first wick member contacts the one inner surface, and the flat bottom of the second wick member contacts the other inner surface. 
     In the aforementioned aspect, the convex-shaped bottom of the first wick member and the convex-shaped top of the second wick member contact each other; thus, locations of the convex-shaped bottom and convex-shaped top other than those contacting the other convex-shaped part are exposed to the inner space of the flat container. 
     In an aspect of the heat pipe of the present invention, the second wick part of the wick structure is in the at least one cross section, and in the at least one cross section, a maximum width of the flat bottom or the convex top of the second wick member is 60% to 80% of a maximum width of an inner space of the flat container. 
     In an aspect of the heat pipe of the present invention, the first wick part is disposed on one end in the lengthwise direction of the flat container, and the second wick part is disposed on the other end in the lengthwise direction of the flat container. 
     In an aspect of the heat pipe of the present invention, there are two first wick parts, and one of the first wick parts is disposed on one end in the lengthwise direction of the flat container, and the other of the first wick parts is disposed on the other end in the lengthwise direction of the flat container, the second wick part being disposed in a center in the lengthwise direction of the flat container. 
     In an aspect of the present invention, the heat pipe further includes a third wick part disposed between the first wick part and the second wick part in the lengthwise direction of the flat container, the third wick part having a maximum width that is wider than the maximum width of the first wick part and narrower than the maximum width of the second wick part. 
     In an aspect of the heat pipe of the present invention, in the at least one cross section, the side faces of the first wick member that do not contact any of the inner surfaces of the flat container have a convex shape, and the side faces of the second wick member that do not contact any of the inner surfaces of the flat container have a convex shape. 
     In an aspect of the heat pipe of the present invention, the first wick part and the second wick part are sintered metal compacts. 
     In an aspect of the heat pipe of the present invention, the sintered metal compact of the second wick part is formed of sintered powders having a finer particle size than sintered powders of the sintered metal compact of the first wick part. 
     In an aspect of the heat pipe of the present invention, the pair of flat inner surfaces opposing each other are vertically separated by a distance of 1.5 mm or less. 
     In the aforementioned aspect, the flat container has the pair of flat inner surfaces that oppose each other (i.e., one inner surface and another inner surface that opposes the one inner surface), and the distance between the opposing flat inner faces is 1.5 mm or less. 
     In an aspect of the heat pipe of the present invention, in every cross section of the wick structure, the wick structure includes the first wick member and the second wick member disposed in the vertical direction. 
     In an aspect of the heat pipe of the present invention, in every cross section of the wick structure: the wick structure includes the first wick member and the second wick member disposed in the vertical direction; the first wick member contacts the second wick member and the one inner surface of the pair of flat inner surfaces of the flat container, and the side faces of the first wick member do not contact any of the inner surfaces of the flat container; and the second wick member contacts the other inner surface of the pair of flat inner surfaces of the flat container, and the side faces of the second wick member do not contact any of the inner surfaces of the flat container. 
     In an aspect of the heat pipe of the present invention further includes a thermally conductive member attached to the heat receiving portion of the heat pipe so as to be thermally connected to the heat generating member. 
     In an aspect of the heat pipe of the present invention, in a cross section of the heat receiving portion of the heat pipe that is different from the at least one cross section: the wick structure includes the first wick member and the second wick member disposed in the vertical direction; the first wick member contacts the one inner surface of the pair of flat inner surfaces of the flat container, and the side faces of the first wick member do not contact any of the inner surfaces of the flat container; the second wick member contacts the other inner surface of the pair of flat inner surfaces of the flat container, and the side faces of the second wick member do not contact any of the inner surfaces of the flat container; and the first wick member does not contact the second wick member. 
     According to an aspect of the present invention, when a heat pipe has a first wick part and a second wick part that has a wider maximum width than the first wick part, and a location of the heat pipe contacting a heat generating member is regarded as a heat receiving portion, the positioning of the second wick part at the heat receiving portion makes it possible to obtain, even if the heat pipe is thin, excellent heat transport characteristics with an excellent maximum heat transport amount and reduced thermal resistance. 
     According to an aspect of the present invention, the heat pipe has the first wick part and the second wick part that is formed as the heat receiving portion, wherein the first wick part has a maximum width of 40% to 60% relative to the maximum width of a cross section of a flat container, and the second wick part has a maximum width that is wider than the first wick part and 60% to 80% relative to the maximum width of the cross section of the flat container; thus, even if the heat pipe is thin, it is possible to obtain even better heat transport characteristics with reduced thermal resistance and an excellent maximum heat transport amount. 
     According to an aspect of the present invention, the length of the second wick part in the lengthwise direction of the flat container is 2% to 50% of the sum of the length of the first wick part and the length of the second wick part in the lengthwise direction of the flat container, thus making it possible to further reduce thermal resistance while improving the maximum heat transport amount. 
     According to an aspect of the present invention, the cross section of the first wick member has a convex-shaped bottom side part and a flat top side part, and the cross section of the second wick member has a flat bottom side part and a convex-shaped top side part, and the maximum width of the bottom side part or top side part of the second wick part is 60% to 80% relative to the maximum width of the cross section of the flat container, thus making it possible to further reduce thermal resistance while improving the maximum heat transport amount. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a planar cross-sectional view of a heat pipe according to Embodiment 1 of the present invention,  FIG. 1B  is a cross-sectional view along a-a in  FIG. 1A , and  FIG. 1C  is a cross-sectional view along b-b in  FIG. 1A . 
         FIG. 2A  is a planar cross-sectional view of a heat pipe according to Embodiment 2 of the present invention,  FIG. 2B  is a cross-sectional view along a-a in  FIG. 2A , and  FIG. 2C  is a cross-sectional view along b-b in  FIG. 2A . 
         FIG. 3  is a planar cross-sectional view of a heat pipe according to Embodiment 3 of the present invention. 
         FIG. 4  is a planar cross-sectional view of a heat pipe according to Embodiment 4 of the present invention. 
         FIG. 5A  is a side view of a heat pipe according to another embodiment of the present invention,  FIG. 5B  is a cross-sectional view along a-a in  FIG. 5A , and  FIG. 5C  is a cross-sectional view along b-b in  FIG. 5A . 
         FIG. 6A  is a side view of a heat pipe according to another embodiment of the present invention,  FIG. 6B  is a cross-sectional view along a-a in  FIG. 6A , and  FIG. 6C  is a cross-sectional view along b-b in  FIG. 6A . 
         FIG. 7  is a diagram for explaining a heat pipe according to another embodiment of the present invention. 
         FIG. 8A  is a side view of a heat pipe according to another embodiment of the present invention,  FIG. 8B  is a cross-sectional view along a-a in  FIG. 8A , and  FIG. 8C  is a cross-sectional view along b-b in  FIG. 8A . 
         FIG. 9A  is a side view of a heat pipe according to another embodiment of the present invention,  FIG. 9B  is a cross-sectional view along a-a in  FIG. 9A , and  FIG. 9C  is a cross-sectional view along b-b in  FIG. 9A . 
         FIG. 10A  is a side view of a heat pipe according to another embodiment of the present invention,  FIG. 10B  is a cross-sectional view along a-a in  FIG. 10A , and  FIG. 10C  is a cross-sectional view along b-b in  FIG. 10A . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A heat pipe according to Embodiment 1 of the present invention will be described below with reference to the drawings. 
     As shown in  FIGS. 1A to 1C , a heat pipe  1  according to Embodiment 1 includes a tube shaped flat container  10  having one flat inner surface  11  and another flat inner surface  12  opposing the one flat inner surface  11 , a first wick member  21  disposed on the one flat inner surface  11 , a second wick member  22  disposed on the other flat inner surface  12 , and a working fluid (not shown) sealed inside the flat container  10 . 
     As shown in  FIGS. 1B and 1C , the flat container  10  is a sealed straight tube member that has the one flat inner surface  11  and the other flat inner surface  12  opposing the one flat inner surface  11 , and curved sections  13  and  13 ′ formed between the one flat inner surface  11  and the other flat inner surface  12 . The cross-sectional shape of the flat container in a direction orthogonal to the lengthwise direction (i.e., the cross-sectional shape perpendicular to the lengthwise direction) is a flat shape. In other words, the flat container  10  has a pair of flat inner surfaces that oppose each other in the vertical direction in a cross section perpendicular to the lengthwise direction. The entirety of the flat container  10  in the lengthwise direction thereof is a flat shape. Furthermore, the cross-sectional area of the inner space of the flat container  10  in the direction orthogonal to the lengthwise direction is the same at all locations, and the one flat inner surface  11  is formed in a direction parallel to the other flat inner surface  12 . Moreover, the distance between the one flat inner surface  11  and the other flat inner surface  12  is not particularly limited, but is 1.5 mm or less in the flat container  10 , or in particular, a thin shape of 1.0 mm or less. The heat transport direction of the heat pipe  1  is the lengthwise direction of the flat container  10 . 
     The first wick member  21  has a first curved section  23 , which is a convex-shaped bottom side part of a convex shape protruding from the one flat inner surface  11 , and a flat top side part  25 , which contacts part of the one flat inner surface  11 . In the heat pipe  1 , the flat top side part  25  is adhered to the one flat inner surface  11 . The first wick member  21  is provided in the center of the flat container  10  in the direction orthogonal to the lengthwise direction of the flat container  10  (in a cross section of the flat container  10 ). In the heat pipe  1 , the cross-sectional shape of the first wick member  21  in the direction orthogonal to the lengthwise direction of the flat container  10  is a semi-elliptical shape. 
     The second wick member  22  has a second curved section  24 , which is a convex-shaped top side part of a convex shape opposing the first curved section  23  that is the convex-shaped bottom side part of the convex shape protruding from the other flat inner surface  12 , and a flat bottom side part  26 , which contacts part of the other flat inner surface  12 . In the heat pipe  1 , the flat bottom side part  26  is adhered to the other flat inner surface  12 . The second wick member  22  is provided in the center of the flat container  10  in the direction orthogonal to the lengthwise direction of the flat container  10 . In the heat pipe  1 , the cross-sectional shape of the second wick member  22  in the direction orthogonal to the lengthwise direction of the flat container  10  is a semi-elliptical shape. 
     In the heat pipe  1 , the region of the one flat inner surface  11  of the flat container  10  not contacting the flat top side part  25  of the first wick member  21 , and the region of the other flat inner surface  12  of the flat container  10  not contacting the flat bottom side part  26  of the second wick member  22 , and the curved sections  13  and  13 ′ of the flat container  10 , are all exposed to the inner space of the flat container  10 . 
     The first curved section  23  of the first wick member  21  contacts the second curved section  24  of the second wick member  22 . In the heat pipe  1 , the bottom of the first curved section  23  and the top of the second curved section  24  contact each other. The bottom of the first curved section  23  and the top of the second curved section  24  are both in a state of pressure contact with each other. Accordingly, the bottom of the first curved section  23  and the top of the second curved section  24  are compressed and deformed. This can further improve the capillary pressure of the first wick member  21  and the second wick member  22  and cause the working fluid in the liquid phase to circulate more smoothly. 
     As shown in  FIG. 1B , on one end of the flat container  10 , a first wick part  31  made of the first wick member  21  and the second wick member  22  is formed. The maximum widths of the flat top side part  25  and flat bottom side part  26  in the first wick part  31  in the direction orthogonal to the lengthwise direction of the flat container  10  are 40% to 60% of the maximum width of the inner space of the flat container  10  in the direction orthogonal to the lengthwise direction of the flat container. The first wick part  31  of the heat pipe  1  has a cross-sectional shape in the direction orthogonal to the lengthwise direction of the flat container  10  that has approximately the same shape and dimensions at all locations in the lengthwise direction of the flat container  10 . Accordingly, the widths of the flat top side part  25  and flat bottom side part  26  in the direction orthogonal to the lengthwise direction of the flat container are approximately uniform in the first wick part  31  along the lengthwise direction of the flat container  10 . 
     In contrast, as shown in  FIG. 1C , on the other end of the flat container  10 , a second wick part  32  made of the first wick member  21  and the second wick member  22  is formed. Accordingly, the wick structure, which is made of the first wick member  21  and the second wick member  22 , has the first wick part  31  and the second wick part  32 . The maximum widths of the flat top side part  25  and flat bottom side part  26  in the second wick part  32  in the direction orthogonal to the lengthwise direction of the flat container  10  are 60% to 80% of the maximum width of the inner space of the flat container  10  in the direction orthogonal to the lengthwise direction of the flat container. Moreover, the above-mentioned widths (in the direction orthogonal to the lengthwise direction of the flat container) of the flat top side part  25  and flat bottom side part  26  of the second wick part  32  are always wider than the widths (in the direction orthogonal to the lengthwise direction of the flat container) of the flat top side part  25  and flat bottom side part  26  of the first wick part  31 . The second wick part  32  of the heat pipe  1  has a cross-sectional shape in the direction orthogonal to the lengthwise direction of the flat container  10  that has approximately the same shape and dimensions at all locations in the lengthwise direction of the flat container  10 . Accordingly, the widths of the flat top side part  25  and flat bottom side part  26  are also approximately uniform at the second wick part  32  in the lengthwise direction of the flat container  10 . 
     As shown in  FIG. 1A , in the heat pipe  1 , the first wick part  31  made of the first wick member  21  and second wick member  22  is formed at a location between one end and another end of the flat container  10 , or namely, is formed in the center of the flat container  10  in a similar manner to the one end of the flat container  10 . 
     In the heat pipe  1 , a portion of the flat container  10  that has the second wick part  32  is a heat receiving portion of the heat pipe  1 , and a portion of the flat container  10  that has the first wick part  31  is a heat dissipating part of the heat pipe  1 . In order to function as a heat receiving portion, a heat generating member (not shown) is thermally connected to a prescribed location of the flat container  10 . When thermally connecting the heat generating member to the prescribed location of the flat container  10 , a thermally conductive member such as a metal heat receiving plate, thermally conductive rubber, or thermal rubber may be provided between the prescribed location and the heat generating member as necessary. Furthermore, in order to function as a heat dissipating part, a heat exchange member (not shown) such as heat radiating fins or heat sink, for example, is thermally connected to a prescribed location of the flat container  10 . 
     In the heat pipe  1 , the width of the second wick part  32  in the direction orthogonal to the lengthwise direction of the flat container is greater than the width of the first wick part  31  in the direction orthogonal to the lengthwise direction of the flat container. Furthermore, the width of the second wick part  32  in the direction orthogonal to the lengthwise direction of the flat container is 60% to 80% relative to the width of the flat container  10 , and the width of the first wick part  31  in the direction orthogonal to the lengthwise direction of the flat container is 40% to 60% relative to the width of the flat container  10 . This makes it possible to achieve excellent heat transport characteristics with reduced thermal resistance and an excellent maximum heat transport amount, even if the container is thin. 
     As shown in  FIG. 1A , in the heat pipe  1 , the first wick member  21  and second wick member  22  (not shown in  FIG. 1A ) both extend in a straight line in a direction from one end to the other end of the flat container  10 , or namely, in the direction parallel to the lengthwise direction of the flat container  10 . Both the first wick member  21  and second wick member  22  (not shown in  FIG. 1A ) are configured such that the width of the second wick part  32  in the direction orthogonal to the lengthwise direction of the flat container  10  is wider than the width of the first wick part  31  and a step  33  is formed at the boundary between the first wick part  31  and the second wick part  32 . The boundary between the first wick part  31  and the second wick part  32  need not be a step, and the width may gradually change instead. 
     The length of the second wick part  32  in the lengthwise direction of the flat container  10  has no particular limitations, but is preferably 2% to 50% of the sum of the length of the first wick part  31  and the length of the second wick part  32  in the lengthwise direction of the flat container  10 , so as to have a favorable balance between the increase in maximum heat transport amount and decrease in thermal resistance. Furthermore, the lengths in the lengthwise direction of the flat container  10  of the flat top side part  25  and flat bottom side part  26  of the second wick part  32  have no particular limitations, but are preferably 1.0 to 5.0 times the length of the heat generating member thermally connected to the heat receiving portion, so as to have a favorable balance between the increase in maximum heat transport amount and decrease in thermal resistance. Moreover, the widths of the flat top side part  25  and flat bottom side part  26  of the second wick part  32  in the direction orthogonal to the lengthwise direction of the flat container  10  have no particular limitations, but are preferably 0.50 to 1.5 times the width of the heat generating member thermally connected to the heat receiving portion, so as to have a favorable balance between the increase in maximum heat transport amount and decrease in thermal resistance. 
     As shown in  FIGS. 1A to 1C , the locations in the inner space of the flat container  10  where the first wick member  21  and second wick member  22  are not disposed function as a steam flow path  34  for the working fluid in the gas phase. In other words, the steam flow path  34  is formed from the region of the one flat inner surface  11  not contacting the first wick member  21 , the surface of the first curved section  23 , the region of the other flat inner surface  12  not contacting the second wick member  22 , the surface of the second curved section  24 , and the curved sections  13  and  13 ′ of the flat container  10 . Accordingly, the steam flow path  34  extends in a straight line in the direction parallel to the lengthwise direction of the flat container  10 , and the steam flow path  34  on the first wick part  31  side is wider than the steam flow path  34  on the second wick part  32 , with the step  33  as the boundary. The steam flow path  34  is provided on both sides of the first wick member  21  and the second wick member  22 . 
     The material of the flat container  10  has no particular limitations, and can be copper, to have excellent thermal conductivity; aluminum, to be lightweight; stainless steel, to improve strength; or the like. The material of the first wick member  21  and second wick member  22  has no particular limitations, and can be a metal powder such as copper powder or stainless steel powder, carbon powder, a mixed powder of copper powder and carbon powder, nanoparticles of the aforementioned powders, a sintered compact such as a composite alloy in which a metal mesh and metal powder have been combined, or the like. The sintered compact can be manufactured by sintering the aforementioned powders or composite metal to bond the powder, and forming a porous structure having capillary pressure by sintering. It is preferable that the sintered metal compact of the second wick part  32  be formed of a sintered powder having a finer particle size than the sintered metal compact of the first wick part  31 , in order to improve the capillary force of the second wick part  32  over the capillary force of the first wick part  31  and to smoothly circulate the working fluid in the liquid phase to the heat receiving portion. 
     The working fluid sealed in the flat container  10  can be selected as appropriate based on compatibility with the material of the flat container  10 , and examples of the working fluid include water, alternative chlorofluorocarbon, perfluorocarbon, or cyclopentane. 
     Next, the heat transport mechanism of the heat pipe  1  according to Embodiment 1 of the present invention will be explained. When the heat pipe  1  receives heat from the heat generating member thermally connected at the heat receiving portion, the working fluid changes phases from a liquid phase to a gas phase at the heat receiving portion. The gas phase working fluid flows through the steam flow path  34  from the heat receiving portion to the heat dissipating part in the lengthwise direction of the flat container  10 , thereby transporting the heat from the heat generating member to the heat dissipating part from the heat receiving portion. The heat from the heat generating part that has been transported from the heat receiving portion to the heat dissipating part changes phases from a gas phase working fluid to a liquid phase working fluid at the heat dissipating part provided with the heat exchange member, thus being discharged as latent heat. The latent heat discharged at the heat dissipating part is discharged from the heat dissipating part to the external environment of the heat pipe  1  via the heat exchange member provided to the heat dissipating part. The working fluid that has changed phases to a liquid phase at the heat dissipating part is taken into the first wick member  21  and second wick member  22  and is returned from the heat dissipating part to the heat receiving portion by the capillary pressure of the first wick member  21  and the second wick member  22 . 
     Next, a heat pipe according to Embodiment 2 of the present invention will be described below with reference to the drawings. The same reference characters are used for the same components as the heat pipe of Embodiment 1. 
     In the heat pipe  1 , the first wick part  31  was disposed at one end and the center in the lengthwise direction of the flat container  10 , and the second wick part  32  was disposed at the other end. Instead of this configuration, in the heat pipe  2  of Embodiment 2, as shown in  FIGS. 2A to 2C , a second wick part  32  is disposed in the center in the lengthwise direction of the flat container  10 , and first wick parts  31  are respectively disposed at both ends in the lengthwise direction of the flat container  10 . In other words, there are two first wick parts  31 . Accordingly, in the heat pipe  2 , the center in the lengthwise direction of the flat container  10  is the heat receiving portion, and the one end and other end in the lengthwise direction of the flat container  10  are heat dissipating parts. The first wick parts  31  are provided on both ends of the second wick part  32 ; thus, there are two boundaries between the first wick parts  31  and second wick part  32 , and thus there are two steps  33  formed. 
     The heat pipe  2  also makes it possible to achieve excellent heat transport characteristics with reduced thermal resistance and an excellent maximum heat transport amount. Furthermore, in the heat pipe  2 , a plurality (two in the drawings) of heat dissipating parts can be provided, which further improves the cooling efficiency of the heat generating member. 
     Next, a heat pipe according to Embodiment 3 of the present invention will be described below with reference to the drawings. The same reference characters are used for the same components as the heat pipes of Embodiments 1 and 2. 
     In the heat pipe  1  according to Embodiment 1, the first wick member  21  and second wick member  22  were not provided at both end faces in the lengthwise direction of the flat container  10 , but rather the entirety of both end faces was exposed to the inner space of the flat container  10 ; however, instead of this configuration, in the heat pipe  3  of Embodiment 3, as shown in  FIG. 3 , a first wick member  21  and a second wick member  22  (not shown) extend up to both end faces  14  in the lengthwise direction of the flat container  10 . Accordingly, both end faces of the first wick member  21  and the second wick member  22  in the lengthwise direction of the flat container  10  contact both end faces  14  in the lengthwise direction of the flat container  10 . 
     The heat pipe  3  also makes it possible to achieve excellent heat transport characteristics with reduced thermal resistance and an excellent maximum heat transport amount. 
     Next, a heat pipe according to Embodiment 4 of the present invention will be described below with reference to the drawings. The same reference characters are used for the same components as the heat pipes of Embodiments 1 to 3. 
     In the heat pipe  2  according to Embodiment 2, the first wick member  21  and second wick member  22  were not provided at both end faces in the lengthwise direction of the flat container  10 , but rather the entirety of both end faces was exposed to the inner space of the flat container  10 ; however, instead of this configuration, in the heat pipe  4  of Embodiment 4, as shown in  FIG. 4 , a first wick member  21  and a second wick member  22  (not shown) extend up to both end faces  14  in the lengthwise direction of the flat container  10 . Accordingly, both end faces  14  of the first wick member  21  and the second wick member  22  in the lengthwise direction of the flat container  10  contact both end faces in the lengthwise direction of the flat container  10 . 
     The heat pipe  4  also makes it possible to achieve excellent heat transport characteristics with reduced thermal resistance and an excellent maximum heat transport amount. 
     Next, an example of a method of manufacturing the heat pipe of the present invention will be described. The method of manufacturing has no particular limitations; however, as an example, for the heat pipe according to Embodiment 1, a core rod having a cutout of a prescribed shape is inserted along the lengthwise direction of a round tube member, and a metal material in powdered form, which will become the first wick member and second wick member, is filled into a cavity between the inner wall faces of the tube member and the outer faces of the cutout. The cutout of the core rod has a small cutout corresponding to the position of the first wick part and a large cutout corresponding to the position of the second wick part. Next, a thermal treatment is applied to form a precursor of the first wick member and a precursor of the second wick member. Thereafter, the core rod is removed from the small cutout side and the tube member is flattened to manufacture a heat pipe having the first wick member and the second wick member. 
     The heat pipe according to Embodiment 2 can be manufactured in a similar manner to the heat pipe according to Embodiment 1, but instead of the core rod used in the heat pipe of Embodiment 1, a first core rod having a small cutout corresponding to the position of the first wick part and a large cutout corresponding to the position of the second wick part is inserted from one end of the round tube member up to the center in the lengthwise direction, and a second rod part having a small cutout corresponding to the position of the first wick part is inserted from the other end of the round tube member. After the filling of the powdered metal material and heat treatment, the first core rod is removed from the small cutout side at the one end side of the tube member, and the second core rod is removed from the other end side, thus making it possible to manufacture the heat pipe of Embodiment 2. 
     Next, other embodiments of the present invention will be explained. In the heat pipes of the respective embodiments above, a second wick part having a wide width in the direction orthogonal to the lengthwise direction of the flat container was disposed adjacent to a first wick part for which the width is narrow, but instead of this configuration, a third wick part for which the width is wider than the first wick part and narrower than the second wick part may be provided between the first wick part and the second wick part. The width of the third wick part may be uniform, or may gradually expand from the first wick part to the second wick part. 
     In the heat pipe of Embodiment 1, the first wick part for which the width is narrow was formed in the center of the flat container in a similar manner to the one end of the flat container, but instead of this configuration, a second wick part for which the width is wide may be formed in a similar manner to the other end of the flat container. In the heat pipes of the respective embodiments above, the first wick part and the second wick part each had, in the lengthwise direction of the flat container, a width of the flat top side part and width of the flat bottom side part in the direction orthogonal to the lengthwise direction of the flat container that were approximately uniform, but instead of this configuration, the widths need not necessarily be approximately uniform, and may gradually widen, or may repeatedly widen and contract, or the like, for example, as long as the widths are within the numerical ranges described above. 
     In the heat pipes of the respective embodiments above, the entirety of the container in the lengthwise direction was a flat shape, but instead of this configuration, a part in the lengthwise direction may be a flat shape. 
     In the heat pipes of the respective embodiments above, the cross-sectional shape of the first wick member and second wick member was a semi-elliptical shape, but the shape has no particular limitations and may be rectangular, for example. In the heat pipes of the respective embodiments above, the first wick member and the second wick member were both provided in the center position in the direction orthogonal to the lengthwise direction of the flat container, but the first wick member and second wick member are not limited to these positions, and may be provided outside the center (at the ends, for example), or the first wick member and the second wick member may be provided at differing positions from each other (for example, one of the first wick member and the second wick member may be provided in the center, and the other at the end). In the heat pipes of the respective embodiments above, the bottom of the convex-shaped bottom side part and the top of the convex-shaped top side part pressure contacted each other, but instead of this configuration, the parts may contact each other without pressure. 
     In the heat pipes of the respective embodiments above, the bottom of the convex-shaped bottom side part and the top of the convex-shaped top side part pressure contacted each other, but instead of this configuration, a configuration is possible in which the bottom of the convex-shaped bottom side part and the top of the convex-shaped top side part of the first wick part contact each other, and the bottom of the convex-shaped bottom side part and the top of the convex-shaped top side part of the second wick part do not contact each other, or a configuration in which the bottom of the convex-shaped bottom side part and the top of the convex-shaped top side part of the second wick part, which requires high capillary pressure, contact each other, and the bottom of the convex-shaped bottom side part and the top of the convex-shaped top side part of the first wick part do not contact each other. 
     In such a case, as shown in  FIGS. 5A to 5C , for example, a configuration is possible in which the thickness of the flat container changes at the center in the lengthwise direction of the flat container  10 : at the thicker end of the flat container  10  (as shown in  FIG. 5B , the end to which heat radiating fins  101  are thermally connected), the first curved section  23  of the first wick member  21  and the second curved section  24  of the second wick member  22  of the first wick part  31  do not contact each other, but rather, at the thinner end of the flat container  10  (as shown in  FIG. 5C , the end to which a heat generating member  102  is thermally connected), the first curved section  23  of the first wick member  21  and the second curved section  24  of the second wick member  22  of the second wick part  32  contact each other. 
     Moreover, as shown in  FIGS. 6A to 6C , a configuration is possible in which the thickness of the flat container changes at the center in the lengthwise direction of the flat container  10 : at the thicker end of the flat container  10  (as shown in  FIG. 6C , the end to which a heat generating member  102  is thermally connected), the first curved section  23  of the first wick member  21  and the second curved section  24  of the second wick member  22  of the second wick part  32  do not contact each other, but rather, at the thinner end of the flat container  10  (as shown in  FIG. 6B , the end to which heat radiating fins  101  are thermally connected), the first curved section  23  of the first wick member  21  and the second curved section  24  of the second wick member  22  of the first wick part  31  contact each other. 
     In the heat pipes of the respective embodiments above, the flat container is a tube member, and the cross-sectional shape thereof is a substantially elliptical shape having a pair of flat inner surfaces that vertically oppose each other, but there are no particular limitations on the cross-sectional shape of the flat container, and the shape may be a rectangle with corners, for example. 
     Furthermore, in the heat pipes of the respective embodiments above, the tube member flat container was a straight shape, but there are no particular limitations on the shape in the lengthwise direction shape of the tube member; as shown in  FIG. 7 , for example, the tube container  10  may be bent into an L-shape or the like, and a heat exchange member such as the heat radiating fins  101  may be thermally connected to one end, and a heat generating member  102  may be thermally connected to the other end. 
     In addition, as shown in  FIG. 8A  through  FIG. 9C , the shape of the flat container  10 , which has a uniform thickness, may have a step-like location  15  in the center in the lengthwise direction of the flat container  10 . In such a case, at the end of the flat container  10  to which the heat generating member  102  is thermally connected, the first curved section  23  of the first wick member  21  and the second curved section  24  of the second wick member  22  of the second wick part  32  may contact each other, as shown in  FIG. 8C , or may not contact each other, as shown in  FIG. 9C . In a similar manner, at the end of the flat container  10  to which the heat exchange member such as the heat radiating fins  101  is thermally connected, the first curved section  23  of the first wick member  21  and the second curved section  24  of the second wick member  22  of the first wick part  31  may not contact each other, as shown in  FIG. 8B , or may contact each other, as shown in  FIG. 9B . 
     In the heat pipes of Embodiments 1 and 2, the cross section of the first wick member and the cross section of the second wick member were approximately the same size (i.e., the width of the flat top side part and the width of the bottom side part were approximately the same), but instead of this configuration, as shown in  FIGS. 10A to 10C , the cross section of the first wick member  21  may differ in size from the cross section of the second wick member  22 , or in other words, the width of the flat top side part  25  may differ from the width of the flat bottom side part  26 . In such a case, if the maximum width of the second wick part  32  is greater than the maximum width of the first wick part  31 , then as shown in  FIGS. 10B and 10C , the cross section of the first wick member  21  may be larger than the cross section of the second wick member  22 , or namely, the width of the flat top side part  25  may be wider than the width of the flat bottom side part  26 , or the cross section of the second wick member  22  may be larger than the cross section of the first wick member  21 , or namely, the width of the flat bottom side part  26  may be wider than the width of the flat top side part  25 . In such a configuration, it is possible to improve the contact area of the first wick member  21  and second wick member  22  with the working fluid while more reliably securing the steam flow passage  34 , thus further improving heat transport characteristics of the heat pipe. 
     In the heat pipes of Embodiments 1 and 2, the distance between one flat inner surface of the flat container and the other flat inner surface, or namely, the thickness of the flat container, was uniform, but instead of this configuration, the distance need not be uniform; for example, the thickness of the flat container corresponding to the position of the first wick part may differ from the thickness of the flat container corresponding to the position of the second wick part (e.g., the thickness of the flat container corresponding to the position of the second wick part may be thinner than the thickness of the flat container corresponding to the position of the first wick part). 
     In the heat pipe of Embodiment 2, one second wick part was disposed in the center, but there are no particular limitations to the number of second wick parts, and a plurality may be provided instead. In such a case, the first wick part and/or third wick part would be disposed between the adjacent second wick parts. 
     Working Example 
     Next, a working example of the present invention will be described, but the present invention is not limited to this example. 
     As a working example, a configuration having the same structure as the heat pipe of Embodiment 1 was used. However, the maximum widths of the first wick part and second wick part were modified as indicated in Table 1 below. For the container, a tube member with a length of 200 mm and φ of 8 mm was flattened to 1 mm A 10 mm×20 mm and 15 W member was used as the heat generating member. The heat generating member was made to contact the other end of the container (heat pipe) where the second wick part was formed, a thermocouple was installed at a location of 15 mm from the one end of the container (heat pipe) where the first wick part was formed, and ΔT was measured. 
     ΔT was evaluated as “A” when 0° C. to 5° C., “B” when exceeding 5° C. but not more than 8° C., “C” when exceeding 8° C. but not more than 10° C., and “D” when exceeding 10° C. 
     The evaluation results are shown in Table 1 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                   
                 Maximum Width of First Wick Part 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 35% 
                 40% 
                 45% 
                 50% 
                 55% 
                 60% 
                 65% 
               
               
                   
               
               
                 Maximum 
                 55% 
                 C 
                 C 
                 C 
                 C 
                 C 
                 — 
                 — 
               
               
                 Width of 
                 60% 
                 C 
                 B 
                 B 
                 B 
                 B 
                 C 
                 — 
               
               
                 Second 
                 65% 
                 C 
                 B 
                 A 
                 A 
                 A 
                 B 
                 C 
               
               
                 Wick Part 
                 70% 
                 C 
                 B 
                 A 
                 A 
                 A 
                 B 
                 C 
               
               
                   
                 75% 
                 C 
                 B 
                 A 
                 A 
                 A 
                 B 
                 C 
               
               
                   
                 80% 
                 C 
                 B 
                 B 
                 B 
                 B 
                 B 
                 C 
               
               
                   
                 85% 
                 C 
                 C 
                 B 
                 D 
                 D 
                 C 
                 D 
               
               
                   
               
            
           
         
       
     
     From Table 1, it can be seen that when a maximum width of the first wick part relative to the maximum width in the direction (cross section) orthogonal to the lengthwise direction of the flat container is 40% to 60% and a maximum width of the second wick part relative to the maximum width in the direction (cross section) orthogonal to the lengthwise direction of the flat container is 60% to 80%, it gives at least evaluation B, which offers excellent heat transport characteristics with a favorable maximum heat transport amount and reduced thermal resistance. In particular, when a maximum width of the first wick part relative to the maximum width in the direction (cross section) orthogonal to the lengthwise direction of the flat container is 45% to 55% and a maximum width of the second wick part relative to the maximum width in the direction (cross section) orthogonal to the lengthwise direction of the flat container is 65% to 75%, it gives evaluation A, which offers extremely excellent heat transport characteristics. 
     INDUSTRIAL APPLICABILITY 
     The heat pipe of the present invention has, even when thin, excellent heat transport characteristics with a favorable maximum heat transport amount and low thermal resistance; thus, the heat pipe of the present invention has a high utilization value in fields such as the cooling of thin electronic components or the cooling of electronic components mounted at a high density, for example. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents. In particular, it is explicitly contemplated that any part or whole of any two or more of the embodiments and their modifications described above can be combined and regarded within the scope of the present invention.