Abstract:
Provided are: a cooling device that makes it possible to achieve sufficient cooling performance even within a thin electronic device; and an electronic device that is provided with the cooling device. The cooling device is provided with: a heat reception unit that vaporizes a refrigerant; a condensation unit that condenses the vaporized refrigerant and that comprises a vapor tube through which the vaporized refrigerant moves, an inclined section that has inclines in at least two directions, and at least two members that are connected to the inclines; and a liquid tube through which the condensed liquid refrigerant moves.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a cooling device and an electronic device provided with the cooling device. 
       BACKGROUND ART 
       [0002]    In recent years, in accordance with high functionality and high integration of electronic devices represented by a server, the heating value of incorporated semiconductor devices such as CPU has increased. In these semiconductor devices, since it is impossible to maintain the performance when the temperature exceeds a predetermined value, temperature control such as cooling is required. 
         [0003]    As a background art of the present technical field, Japanese Patent Application Publication No. 2011-47616 (Patent Literature 1) is known. This publication discloses a description “provided are a cooling system utilizing a thermo-siphon with excellent energy-saving and ecological measures by efficient cooling, and a structure of electronic device appropriate to the system” (see Abstract). 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Literature 1: Japanese Patent Application Publication No. 2011-47616 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    Patent Literature 1 discloses a cooling system to condense refrigerant from vapor to liquid with a flat tube of a condenser. However, when the cooling system in Patent Literature 1 is installed in a thin electronic equipment (electronic device) such as a rack-mount type server or a blade server having a height of 1 U (1.75 inches=44.45 mm), the space in the height direction for installation of the flat tube of the condenser is very small. Since it is impossible to sufficiently condense the refrigerant with a low flat tube, the cooling performance of the cooling system is seriously lowered. 
         [0006]    Accordingly, the present invention provides a cooling device to exert sufficient cooling performance even in e.g. a thin electronic device, and an electronic device having the cooling device. 
       Solution to Problem 
       [0007]    To solve the above problem, the present invention has: a heat reception unit that vaporizes refrigerant; a condensation unit, a vapor tube through which the vaporized refrigerant moves, an inclined section having inclines in at least two directions, and two or more members connected with the inclines of the inclined section, that condenses the vapor refrigerant; and a liquid tube through which the condensed liquid refrigerant moves. 
       Advantageous Effects of Invention 
       [0008]    According to the present invention, it is possible to provide a cooling device to exert sufficient cooling performance even in e.g. a thin electronic device, and an electronic device having the cooling device. Other objects, constituent elements and advantages besides those discussed above shall be apparent from the description of preferred embodiments of the invention which follows. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  A diagram showing the entire structure of a cooling device. 
           [0010]      FIG. 2  A cross-sectional diagram showing the structure of a heat reception unit. 
           [0011]      FIG. 3  A cross-sectional diagram showing the structure of a part between a boiling heat transfer unit and a base. 
           [0012]      FIG. 4  A perspective diagram showing the structure of the boiling heat transfer unit. 
           [0013]      FIG. 5  A diagram showing the structure of a condensation unit. 
           [0014]      FIG. 6  A diagram showing the structure of a cover of the condensation unit. 
           [0015]      FIG. 7  A diagram showing the structure of a part of the cover of the condensation unit. 
           [0016]      FIG. 8  A diagram showing the structure of the condensation unit having asymmetric inclines. 
           [0017]      FIG. 9  A diagram showing the structure of the condensation unit having a radiation fin unit on the base of the chamber. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0018]    Hereinbelow, embodiments of the present invention will be described with reference to the drawings. 
         [0019]      FIG. 1  is a diagram showing the entire structure of a cooling device  100 . The cooling device  100  has a heat reception unit  101 , a vapor tube  102 , a condensation unit  103 , a liquid tube  104 , and refrigerant  107 . The heat reception unit  101  is connected with the vapor tube  102  in a first connection  112 . The heat reception unit  101  is connected with the liquid tube  104  in a second connection  113 . Further, a chamber  105  of the condensation unit  103  is connected with the vapor tube  102  in a third connection  114 . The chamber  105  is connected with the liquid tube  104  in a fourth connection  115 . 
         [0020]    A heat generating element  109  such as a semiconductor device (e.g. a processor) is mounted on a circuit board  110 . The heat reception unit  101  having the refrigerant  107  inside is attached to the surface of the heat generating element  109 . The heat generating element  109  and the heat reception unit  101  are thermally in contact with each other using TIM (Thermal Interface Material) such as thermal conductive grease. It is desirable that the first connection  112  and the second connection  113  are above the heat generating element  109  in a vertical direction. 
         [0021]    The condensation unit  103  has the chamber  105  having a slope shape (or taper shape), and a radiation fin unit  106  connected with the chamber  105 . A cooling fan  108  is installed in a position to generate a wind (cooling wind) and send the wind to the condensation unit  103  (especially the radiation fin unit  106 ). The direction of the wind is e.g. a direction indicated with numeral  111  in  FIG. 1 . 
         [0022]    In the cooling device  100 , the heat generated with the heat generating element  109  is transferred to the heat reception unit  101 , and the liquid refrigerant  107  is vaporized (especially boiled) with the transferred heat to vapor (first phase change). The generated vapor refrigerant  107  moves from the heat reception unit  101  to the vapor tube  102 , and further, moves through the vapor tube  102  to the chamber  105 . The direction of movement of the vapor refrigerant  107  in the vapor tube  102  is e.g. a direction indicated with numeral  117  in  FIG. 1 . 
         [0023]    The vapor refrigerant  107  in the chamber  105  is cooled with radiation with the radiation fin unit  106  or the chamber  105  which have received the wind sent from the cooling fan  108  and condensed (second phase change). Note that the heat of the vapor refrigerant  107  in the chamber  105  moves to the radiation fin unit  106  or the chamber  105 . The moved heat is radiated to the outside air of the radiation fin unit  106  or the chamber  105 . 
         [0024]    The condensed liquid refrigerant  107  moves along the incline of the slope shape (or taper shape) of the chamber  105  with the gravity to the liquid tube  104 , and returns through the liquid tube  104  to the heat reception unit  101 . The direction of movement of the liquid refrigerant  107  in the liquid tube  104  is e.g. a direction indicated with numeral  118  in  FIG. 1 . 
         [0025]    As described above, the cooling device  100  has a thermo-siphon based on a boiling cooling system which is capable of circulating the refrigerant  107  without external power such as a pump, but with the phase change (first and second phase changes) of the refrigerant  107  and the gravity. 
         [0026]    It is desirable that the position of the first connection  112  in which the heat reception unit  101  and the vapor tube  102  are connected with each other is above an interface (gas interface)  116  of the refrigerant  107  in the vertical direction in the heat reception unit  101 . Further, it is desirable that the position of the third connection  114  in which the chamber  105  and the vapor tube  102  are connected with each other is above the interface  116  of the refrigerant  107  in the vertical direction in the heat reception unit  101 . It is desirable that the position of the fourth connection  115  in which the chamber  105  and the liquid tube  104  are connected with each other is above the interface  116  of the refrigerant  107  in the vertical direction in the heat reception unit  101 . 
         [0027]    On the other hand, it is desirable that the position of the second connection  113  in which the heat reception unit  101  and the liquid tube  104  are connected with each other is below or equivalent to the interface  116  of the refrigerant  107  in the vertical direction in the heat reception unit  101 . Further, it is desirable that the position of the fourth connection  115  is above the second connection  113  in the vertical direction. 
         [0028]    As described above, the cooling device  100  cools the heat generating element  109  by the phase change of the refrigerant  107 . Accordingly, it is possible to attain high cooling efficiency by adopting e.g. water having high latent heat as the refrigerant  107 . When cooling is performed using the refrigerant  107  with a high boiling point such as water at normal temperature, it is possible to increase the cooling efficiency by reducing the pressure inside the piping forming the circulation route through which the refrigerant  107  circulates (the heat reception unit  101 , the vapor tube  102 , the chamber  105 , and the liquid tube  104 ) to lower the boiling point to promote phase change. 
         [0029]    Further, it is desirable that the heat reception unit  101 , the vapor tube  102 , the chamber  105 , and the liquid tube  104  are respectively formed with metal material (e.g. copper) having no corrosiveness (corrosion resistance) with respect to the refrigerant  107  (e.g. water). To maintain the inner pressure-reduced status, it is desirable that the respective junctions (the first connection  112 , the second connection  113 , the third connection  114 , and the fourth connection  115 ) of the heat reception unit  101 , the vapor tube  102 , the chamber  105 , and the liquid tube  104  are brazed or welded. It is desirable that the radiation fin unit  106  is formed with material with a high thermal conductivity such as copper or aluminum. 
         [0030]    Further, when organic refrigerant having a low boiling point such as hydrofluoroether as the refrigerant  107 , it is possible to attain high cooling efficiency without pressure reduction inside the piping (the heat reception unit  101 , the vapor tube  102 , the chamber  105 , and the liquid tube  104 ) forming the circulation route for the refrigerant  107 . Further, when there is no need for pressure reduction as in this case, it is possible to use a deformable material such as a silicone tube or a rubber tube, as the vapor tube  102  and the liquid tube  104 . It is possible, by using the deformable material such as the vapor tube  102  and the liquid tube  104 , to freely change the position of the condensation unit  103  even when the heat reception unit  101  is fixed, to increase the freedom of position and range of attachment of the cooling device  100 . 
         [0031]    The material of the refrigerant  107  is not particularly limited as long as it is refrigerant which is boiled with the heat transferred from the heat generating element  109 . Further, the material used as the heat reception unit  101  and the chamber  105  is also not particularly limited as long as it has no corrosiveness (corrosion resistant) with respect to the refrigerant  107  and it has high thermal conductivity. 
         [0032]      FIG. 2  is a diagram showing the structure of the heat reception unit  101 . It is desirable that the heat reception unit  101  has a structure to promote boiling of the liquid refrigerant  107  in the heat reception unit  101  (boiling promoting structure). The structure will be described using  FIGS. 2 to 4 . 
         [0033]    The heat reception unit  101  has a cover  201 , a base  202  which is thermally in contact with the heat generating element  109 , and a boiling heat transfer unit  203  located inside the cover  201  and on the base  202 . For example, on the base  202  which is a rectangular-shaped metal member with excellent thermal conductivity formed of copper or aluminum, the cover  201  also formed by shaping metal material into a bowl shape is placed, and is brazed or welded. 
         [0034]    As the first connection  112  and the second connection  113 , through holes are formed in two upper and lower positions in a side surface of the cover  201 . The vapor tube  102  is connected with the upper through hole, and the liquid tube  104  is connected with the lower through hole. That is, the position of the first connection  112  is above the position of the second connection  113  in the vertical direction. 
         [0035]      FIG. 3  is a cross-sectional diagram showing the structure of a part between the boiling heat transfer unit  203  and the base  202 .  FIG. 4  is a perspective diagram showing the structure of the boiling heat transfer unit  203 .  FIG. 3  and  FIG. 4  lack a roof plate  204 . The boiling heat transfer unit  203  may be formed by processing the base  202 . 
         [0036]    As shown in  FIG. 2  to  FIG. 4 , the boiling heat transfer unit  203  has plural tunnel structures (tunnels)  301  having plural holes  302  in upper parts, a groove  205  deeper than the plural tunnel structures  301 , and the roof plate (plate)  204  on the groove  205 . It is desirable that the roof plate  204  is of the same metal as that of the base  202 . It is desirable that the groove  205  is located at the center of the boiling heat transfer unit  203 . It is desirable that the direction of the groove  205  is different from a tunnel direction  303  and it is more desirable the direction of the groove is orthogonal to the tunnel direction  303 . 
         [0037]    The plural tunnel structures  301  are arranged in parallel. In the tunnel structures  301 , the plural holes  302  are provided at fixed intervals in the tunnel direction  303 . The tunnel structures  301  communicate with the space in the heat reception unit  101  via the holes  302 . 
         [0038]    With this structure of the boiling heat transfer unit  203 , the bottom surface of the Groove  205  close to the heat generating element  109  is locally at a high temperature, to promote generation of bubbles as the start of boiling. The generated bubbles spread over the entire boiling surface through the tunnel structures  301  and the space formed with the groove  205  and the roof plate  204 . The spread bubbles maintain the continuous boiling through the holes  302  communicating with the tunnel structures  301 . With the above structure of the boiling heat transfer unit  203 , stable start of boiling and improvement in boiling heat transfer performance are realized. 
         [0039]      FIG. 5  is a diagram showing the structure of the condensation unit  103 .  FIG. 5  is a diagram of the condensation unit  103  and the liquid tube  104  viewed from the direction indicated with numeral  111  in  FIG. 1 . The condensation unit  103  has the chamber  105  formed in a slope shape (or taper shape) and the radiation fin unit  106  connected with the chamber  105 . 
         [0040]    The chamber  105  has a rectangular-shaped base  401  formed of metal material with excellent thermal conductivity such as copper or aluminum, and a cover  402 , brazed or welded to the base  401 , formed by shaping into a slope shape (or taper shape). The cover  402  has a side  403  connected with the base  401 , an inclined section  404  having inclines, and a bottom  405  connected with the liquid tube  104 . 
         [0041]    The liquid refrigerant  107  condensed with the condensation unit  103  moves, with the incline of the inclined section  404 , from the inclined section  404  to the bottom  405 , and further, moves to the liquid tube  104 . It is possible to efficiently move the liquid refrigerant  107  to the liquid tube  104  by connecting the bottom  405  to the liquid tube  104  in low positions in the vertical direction in the chamber  105 . 
         [0042]    The radiation fin unit  106  is connected with the chamber  105  by brazing or welding. It has plural fins of metal with excellent thermal conductivity. It is desirable that the respective fins of the radiation fin unit  106  have a length variable in accordance with inclination angle of the inclined section  404 . It is desirable that the respective fins are set with the respective fin directions along the vertical direction. 
         [0043]    The position at which a fin positioned close to the liquid tube  104  (or the bottom  405 ) is connected with the inclined section  404  is below the position at which a fin in a farther position is connected with the inclined section  404  (or in a position close to the circuit board  110 ) in the vertical direction. It is desirable that the fin close to the liquid tube  104  (or the bottom  405 ) has a length shorter than that of the fin in the farther position in the vertical direction. With this configuration, e.g. when the height positions in the vertical direction in which the fins are connected with the circuit board  101  (or an installation part for installation on the circuit board  101 ) are aligned with each other, the installation of the radiation fin unit  106  on the circuit board  101  (or an installation part for installation on the circuit board  101 ) is facilitated. The fins may be connected with the bottom  405 . 
         [0044]    In another embodiment, it may be configured such that the respective fins of the radiation fin unit  106  have a slope shape along the incline of the inclined section  404  and are connected with the inclined section  404 . In the other embodiment, regarding the connection positions between the respective fins and the inclined section  404 , the connection position of a fin closer to the liquid tube  104  (or the bottom  405 ) is lower. In this embodiment, in the respective fins, to facilitate installation on the circuit board  101  (or an installation part for installation on the circuit board  101 ), it is desirable that the length of a fine closer to the liquid tube  104  (or the bottom  405 ) is shorter in the vertical direction. 
         [0045]    In the cover  402 , through holes are formed in the side  403  and the bottom  405  as the third connection  114  and the fourth connection  115 . The vapor tube  102  is connected with the upper through hole, and the liquid tube  104  is connected with the lower through hole. That is, the position of the third connection  114  is above the position of the fourth connection  115  in the vertical direction. 
         [0046]    The vapor refrigerant  107  moves through the vapor tube  102  into the chamber  105  and is condensed. The condensed liquid refrigerant  107  moves smoothly by the gravity along the incline of the inclined section  404 . Further, the refrigerant moves through the bottom  405  to the liquid tube  104  (is transported). With this structure, since the condensed liquid refrigerant  107  does not stay in the condensation heat transfer surface (e.g. the inclined section  404 ), it is possible to improve the condensation performance. 
         [0047]    The inclined section  404  has two or more inclines in different directions. For example, it has two inclines symmetrically or asymmetrically on the both sides of the liquid tube  104  (or the bottom  405 ). For example, when the chamber  105  has a conic shape or pyramid shape, the inclined section  404  has a large number of inclines in different directions. 
         [0048]      FIG. 6  is a diagram showing the structure of the cover  402  of the condensation unit  103 .  FIG. 7  is a diagram showing the structure of a part  602  in  FIG. 6 . 
         [0049]    The inclined section  404  has plural fine grooves  601  (e.g. having a depth of 0.1 mm, a width of 0.1 mm, and a pitch of 0.3 mm) along a direction where the condensed liquid refrigerant  107  flows, i.e., inclination direction of the inclined section  404 . With the chamber  105  provided with the fine grooves  601  in its inner wall, the movement (transport) of the condensed liquid refrigerant  107  is promoted with the capillary force of the fine grooves  601 . Further, since the wet condition is always maintained inside the grooves  601 , it is possible to suppress the growth of droplet of the condensed refrigerant  107  and to improve the condensation thermal conductivity. 
         [0050]    According to the structure of the condensation unit  103  according to the present embodiment, one chamber structure has three functions: a function of receiving the vapor refrigerant  107  from the vapor tube  102 ; a function of condensing (radiating) the vapor refrigerant  107 ; and a function of collecting the condensed liquid refrigerant  107  and send it to the liquid tube  104 . 
         [0051]    Since the cooling device  100  according to the present embodiment realizes three functions with one condensation unit  103  as described above, the space is saved. Further, the saved space may be used for enlargement of the radiation fin unit  106 . Accordingly, in comparison with the conventional cooling device in e.g. Patent Literature 1, it is possible to greatly improve the cooling performance. Note that in the conventional cooling device in e.g. Patent Literature 1 these three functions are realized by respectively using the three structures, the upper header, the flat tube (cooling tube), and the lower header. 
         [0052]    For example, in a rack server in the minimum unit size of 1 U (1.75 inch=44.45 mm) determined with the Electronics Industries Alliance (EIA), considering the heights of the circuit board and the CPU socket, the space allowed for the cooling device is about 30 mm. In the cooling device  100  according to the present embodiment, in e.g. the condensation unit  103 , about 10 mm space is used for the chamber  105  installed in the upper part, and all the remaining space of about 20 mm, for installation space of the radiation fin unit  106 , as shown in  FIG. 1 . 
         [0053]    Further, in the cooling device  100  according to the present embodiment, it is possible to fully utilize the space allowed by changing the lengths of the respective fins of the radiation fin unit  106  in accordance with the incline (taper) of the inclined section  404  and aligning the directions in the vertical direction. As a result, it is possible to incorporate the cooling device  100  in a thin type electronic device such as a server in thickness size of 1 U (44.45 mm) or a thin blade server. 
         [0054]      FIG. 8  is a diagram showing another embodiment in the structure of the condensation unit  103 . Regarding the incline of the inclined section  404  of the chamber  105 , a lower end of the incline (or the bottom  405 ) is shifted from the center of the chamber  105 . In the condensation unit  103 , the inclined section  404  has two or more inclines at different angles. The inclined section  404  has asymmetric inclines on the both sides of the bottom  405  (or the liquid tube  104 ). 
         [0055]    As shown in  FIG. 8 , it is possible to control the connection position of the vapor tube  102  or the liquid tube  104  by changing e.g. the position or angle of the incline (taper) of the inclined section  404 . Accordingly, it is possible to freely design the installation position or size of the condensation unit  103  in accordance with electronic equipment in which the unit is installed. 
         [0056]    Note that when a rectangular parallelepiped chamber, in an inclined status, is installed, and the vapor tube is connected with the upper part and the liquid tube is connected with the lower part, the position where the rectangular parallelepiped chamber is connected with the vapor tube (or the liquid tube) is limited. Accordingly, in comparison with the structure of the condensation unit  103  according to the present embodiment, the freedom of design is low. 
         [0057]    Further, in the rectangular parallelepiped chamber structure, since the bottom surface of the chamber is inclined in only one direction, when the height of the cooling device is lowered in accordance with reduction of height and thickness of the electronic device, the inclination is limited to small. Accordingly, refrigerant does not efficiently flow, and the condensation performance is lowered. On the other hand, in the structure of the condensation unit  103  according to the present embodiment, since there are two or more inclines in different directions, it is possible to increase the inclination of the inclined section  404  and to efficiently flow the refrigerant  107  to the liquid tube  104 . Accordingly, it is possible to maintain or improve the condensation performance even when the height and thickness of the electronic device are reduced. 
         [0058]      FIG. 9  is a diagram showing the structure of the condensation unit  103  having the radiation fin unit  106  on the base  401 . In the condensation unit  103 , the radiation fin unit  106  having plural fins is provided on the base  401  on the chamber  105 . That is, in the condensation unit  103 , the radiation fin unit  106  is installed in the inclined section  404 , the bottom  405  or the base  401  in the chamber  105 . It is possible to freely design the shape of the radiation fin unit  106  in accordance with electronic device in which it is installed. 
         [0059]    In the cooling device  100  according to the present embodiment, the circulation route for the refrigerant  107  is formed with the heat reception unit  101 , the vapor tube  102 , the condensation unit  103 , and the liquid tube  104 . The refrigerant  107  is circulated by phase change of the refrigerant  107  inside the cooling device  100 . The condensation unit  103  has the chamber  105  connected with the vapor tube  102  and the liquid tube  103  and the radiation fin unit  106  connected with the chamber  105 . The bottom surface of the chamber  105  is formed in a slope shape (or taper shape). 
         [0060]    In the cooling device  100  according to the present embodiment, even when it is installed in an e.g. thin electronic device and the height (vertical direction) is low, since the inclined section  404  has two or more inclines (or tapers) in different directions, sufficient space in which the condensation unit  103  (especially the inclined section  404  and the radiation fin unit  106 ) is installed is ensured in accordance with the position, angle and size of the inclines. It is possible to exert sufficient cooling performance. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               100 : cooling device,  101 : heat reception unit,  102 : vapor tube,  103 : condensation unit,  104 : liquid tube,  105 : chamber,  106 : radiation fin unit,  107 : refrigerant,  108 : cooling fan,  109 : heat generating element,  110 : circuit board,  401 : base,  402 : cover,  403 : side,  404 : inclined section, and  405 : bottom.