Patent Publication Number: US-2010108296-A1

Title: Thin cooling device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2008-0109438, filed Nov. 5, 2008, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a vapor-liquid phase change cooling device, and more particularly, to a thin cooling device, which can be manufactured with no limitation of thickness. 
     2. Discussion of Related Art 
     In recent times, as highly efficient and reliable semiconductor devices have attracted attention, heat emitted from these devices has been considered an important issue to be solved. 
     Due to increases in performance of personal computers (PCs) and integration degree of packages, heat emitted from electronic parts such as central processing units has become significant. As high-end manufacturing technology is increasingly being applied to electronic devices as well as CPUs for PCs, emission of heat from various electronic devices is emerging as an important issue to be solved. For example, if devices such as mobile phones requiring a compact design to the extent of notebook PCs continue to develop in performance at the same rate as at present, the problems resulting from heat may become more serious. 
     With trends of various small portable electronic communication devices such as subnotebook computers, mobile phones, PMPs and game consoles decreasing in weight and thickness, an amount of heat per unit area is approaching 100 W/cm 2 . Particularly, while a current market share of the subnotebook computer is within a mere 10%, current demands of consumers can be discerned from recently-disclosed ultra-slim notebook computers, and it can be seen that these computers will continue to become slimmer. The formation of these ultra-slim devices will require high technology for miniaturization and integration of parts, and heat management design. 
     The heat management technology applied to a small device may be classified into control by a passive-type cooling device and control by an active-type cooling device. Currently, a fan-embedded passive-type cooling device is widely used. In the passive-type cooling device, a thermal conduction cooling method using a material having a high thermal conduction coefficient is generally used to dissipate to remove hot spots, and used in the range of relatively small heat flexes. On the other hand, a cooling device operated through a vapor-liquid phase change heat transfer mechanism can be used in the range of relatively high heat flexes, and can achieve more efficient heat transfer capability with a smaller thickness than that operated through the thermal conduction cooling method. This is because, while a smaller thickness gives a reduction in cross-sectional area in the thermal conduction cooling method, in the phase change heat transfer device, vapor evaporated in a phase change is rapidly transported with the latent heat, and thus thermal transport capability is high in the same cross-sectional area. 
     Current portable notebook computers have a cooling device in which a heat pipe having a diameter of 3 to 4 mm and a fan are integrated with an aluminum module. Here, the heat pipe having a diameter of 3 to 4 mm is used after being compressed to a thickness of about 2 to 2.5 mm to be packaged in a smaller space. When a heat pipe having a circular cross-sectional diameter of 3 to 4 mm is compressed to have a plate shape, heat transfer performance is reduced in a large scale. According to test results, it is reported that when a heat pipe into which a separate wick is inserted is compressed to a thickness of about 2 mm, heat transfer performance is decreased in a large scale. This is because, when a capillary structure designed to be suitable for the conventional circular cross-section is compressed, a vapor condensation space, which is a critical factor for performance, is reduced, and the capillary structure is transformed. 
     As an alternative, a planar heat pipe has recently been developed. However, the heat pipe is difficult to be installed in a very small space such as a narrow electronic package structure, even with high thermal performance. In order to install the heat pipe in a small space, the heat pipe may be compressed. However, this leads to a decrease in thermal performance. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a thin cooling device, which can be changed in thickness according to heat transfer performance. 
     One aspect of the present invention provides a thin cooling device, including: a first thin plate including a groove-shaped capillary region, an evaporator section for evaporating a working fluid injected from outside, and a condenser section having a vapor condensation space for condensing the evaporated working fluid; a second thin plate having a vapor pathway for transporting the evaporated working fluid to the condenser section; and a third thin plate having a liquid pathway for transporting the working fluid condensed in the condenser section to the evaporator section. 
     Another aspect of the present invention provides a thin cooling device, including: two thin plates each having a groove-shaped capillary region; an evaporator section for evaporating a working fluid injected from outside; and a liquid pathway for transporting condensed working fluid to the evaporator section. Here, the two thin plates are combined to face each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  shows a first thin plate of a thin cooling device according to a first exemplary embodiment of the present invention; 
         FIG. 2  shows a second thin plate of the thin cooling device according to the first exemplary embodiment of the present invention; 
         FIG. 3  shows a third thin plate of the thin cooling device according to the first exemplary embodiment of the present invention; 
         FIG. 4  shows a structure of the thin cooling device in which five thin plates are combined according to the first exemplary embodiment of the present invention; 
         FIG. 5  shows a thin plate of a thin cooling device according to a second exemplary embodiment of the present invention; and 
         FIG. 6  shows a thin cooling device in which two thin plates are combined according to the second exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, the present invention will be described with reference to the accompanying drawings in detail. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the specification. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. 
       FIG. 1  shows a first thin plate of a thin cooling device according to a first exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , the first thin plate  100  includes an evaporator section  101  disposed at one side, and a capillary region disposed in the evaporator section  101 . 
     Here, the capillary region filling the space in the evaporator section  101  has a plurality of grooves (hereinafter, referred to as “capillary grooves”;  102 ), which are aligned in regular widths, depths and intervals. 
     The capillary grooves  102  have smaller widths than a plurality of grooves formed in a liquid pathway of the thin cooling device. In the first exemplary embodiment of the present invention, the capillary grooves  102  are formed to pass through the first thin plate  100 . 
     The capillary grooves  102  formed in the first thin plate  100  are crosslinked with the liquid pathway when combined with a third thin plate. When a liquid transported to the evaporator section  101  through the liquid pathway is uniformly distributed in a saturated state, a vapor-liquid interface (meniscus) is formed along a wall of the capillary groove  102 . Afterward, according to an input of heat applied to the evaporator section  101 , vapor is generated from the vapor-liquid interface (meniscus). 
     At the other side of the first thin plate  100 , a condenser section  103  is disposed, and a vapor condensation space  104  is formed therein. 
     The vapor condensation space  104  is used as a space for easy flow of vapor transported from the condenser section  103  before condensing. The vapor condensation space  104  corresponds to a size of the condenser section  103  for condensing vapor having latent heat, which is transported from the evaporator section  101 . 
     The first thin plate  100  also includes a vapor-liquid separation layer  105  for separating the evaporator section  100  from the condenser section  103 , and a through hole  106  for injecting a working fluid from outside at the end of the vapor condensation space  104 . 
       FIG. 2  shows a second thin plate of the thin cooling device according to the first exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , most of the second thin plate  200  is an empty space except for a first bridge  201  for preventing compression in an evaporator section, and a second bridge  202  used for a vapor pathway  203 . 
     The vapor pathway  203  of the second thin plate  200  acts as a pathway for transporting vapor evaporated from capillary grooves in the evaporator section to the condenser section. 
     The vapor pathway  203  is formed lengthwise from the evaporator section to the condenser section due to the second bridge  202  formed at regular intervals in the second thin plate  200 , and the second bridge  202  prevents compression due to vacuum and expansion due to internal high pressure. 
     Here, the second bridge  202  is disconnected at the end of the evaporator section, which prevents back flow of a working fluid distributed in the evaporator section toward the condenser section along the second bridge  202 . 
     In order to prevent compression in the evaporator section formed in the first thin plate and expansion due to internal high pressure when the second thin plate  200  is combined with the first thin plate, the first bridge  201  is formed in a portion in which the evaporator section of the first thin plate is disposed. 
     At one end of the second thin plate  200  having the vapor pathway  203 , a through hole  204  is formed to inject the working fluid from outside, and the through hole is formed to correspond to the through hole in the first thin plate. While, in the first exemplary embodiment of the present invention, the through holes are disposed in one end of the first thin plate and in one end of the second thin plate, respectively, the through holes may be disposed not only at sides of the first and second thin plates, but also disposed on upper or lower portions of the first and second thin plates depending on a formation process and application of the cooling device. 
       FIG. 3  shows a third thin plate constituting the thin cooling device according to the first exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , the third thin plate  300  disposed at the outermost of the thin cooling device includes a liquid pathway  301  for transporting a working fluid. 
     The liquid pathway  301  of the third thin plate  300  is formed between the evaporator section and the condenser section of the first thin plate, and transports the working fluid condensed in the condenser section of the first thin plate to the evaporator section of the first thin plate. 
     The liquid pathway  301  has a plurality of grooves formed lengthwise by engraving the third thin plate  300  to a predetermined thickness, and the grooves may be formed in a semi-circular shape by wet etching. 
     Here, the plurality of grooves forming the liquid pathway  301  are formed with regular width and depth and at regular intervals, and have a larger width than the capillary grooves formed in the evaporator section of the first thin plate. 
     Meanwhile, in each of four outer corners of the third thin plate  300 , holes  302  are formed to align the first and second thin plates when they are combined. 
       FIG. 4  shows a structure of the thin cooling device in which five thin plates are combined according to the first exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , the thin cooling device  400  according to the first exemplary embodiment of the present invention includes the first to third thin plates  100  to  300 , which are formed by separate processes. 
     The cooling device  400  has a combined structure of first, second and third thin plates  100  to  300 . It includes the second thin plate  200  having the vapor pathway, as a middle plate; two first thin plates  100  having the capillary grooves at both ends and the vapor condensation space in the condenser section above and below the second thin plate  200 ; and the third thin plates  300  having the liquid pathway above and below the first plates  100 . While the first exemplary embodiment of the present invention shows the thin cooling device having a maximum of five thin plates, the number of the thin plates may be changed within five according to the total thickness of the thin cooling device, and thus the present invention is not limited to this number of the thin plates. If the cooling device  400  is formed by combining one first thin plate  100 , one second thin plate  200  and one third thin plate  300 , one side of the second thin plate  200  is preferably closed. 
     The cooling device  400  in which the first to third thin plates  100  to  300  are combined has a hermetically sealed structure in which a vacuum state is maintained. A working fluid is injected into the cooling device  400 , and then the cooling device  400  is sealed to complete the cooling device. 
     The cooling device may be manufactured to a thickness of 1.5 mm or less, and simultaneously perform functions of heat dissipation and heat transport in electronic devices. When heat is applied to the evaporator section side of the cooling device, the working fluid saturated in the capillary groove of the first thin plate  100  is evaporated, and the vapor having latent heat is transported toward the condenser section side through the vapor pathway in the second thin plate  200 . Here, the transported vapor dissipates the latent heat and is then condensed into a liquid in the condenser section, and the condensed liquid flows back to the evaporator section side along the liquid pathway in the third thin plate  300 , and is then re-saturated in the capillary groove of the evaporator section, which is called circulation. Thus, through the repeated circulations, the cooling device dissipates and transfers heat. 
     Accordingly, the thin cooling device, in which the first to third thin plates  100  to  300  are combined, transfers heat from one side to another without supply of external power. 
       FIG. 5  shows a thin plate of a thin cooling device according to a second exemplary embodiment of the present invention. 
     Referring to  FIG. 5 , the thin cooling device according to the second exemplary embodiment of the present invention includes a thin plate  500 . An evaporator section is disposed at one side of the thin plate  500 . The evaporation section has a capillary region having a plurality of grooves  501  (hereinafter, referred to as “capillary grooves”). The capillary grooves  501 , which are formed with regular width and depth in the thin plate  500 , are aligned with each other at regular intervals. 
     A plurality of bridges  503  is formed lengthwise in the thin plate  500  at regular intervals, except for the evaporator section area, to prevent compression due to vacuum and expansion due to high temperature and pressure. 
     Grooves of a liquid pathway  502  are formed between the plurality of bridges  503  formed in the thin plate  500 , and have differences in size and shape from the capillary grooves  501  in the evaporator as shown in  FIG. 5 . 
     Here, the capillary grooves  501  in the evaporator section have smaller widths and depths than the grooves of the liquid pathway  502 , which can generate high capillary action. 
     The plurality of grooves forming the liquid pathway  502  may be formed in a semi-circular shape by wet etching, and the capillary grooves  501  may be formed using a laser. 
     After forming the capillary grooves  501  and the grooves of the liquid pathway  502 , the bridges  503  are formed by stamping. However, if the capillary grooves  501  are prone to damage, the order of the processes may be changed. While, in the second exemplary embodiment of the present invention, the capillary grooves  501 , the liquid pathway  502  and the bridges  503  can be formed by the above-mentioned processes, the present invention is not limited thereto. 
     As shown in  FIG. 5 , step differences are created between the capillary grooves  501  in the evaporator section, the liquid pathway  502  and the bridges  503  of the thin plate  500 , and a space created by the step differences is utilized as a vapor pathway (not shown) for transporting vapor evaporated from the capillary grooves  501  in the evaporator section to the condenser section and a vapor condensation space (not shown) in the condenser section. 
       FIG. 6  shows a structure of the thin cooling device in which two thin plates are combined according to the second exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , the two thin plates  500  formed by separate processes as shown in  FIG. 5  are combined to face each other, and thus the cooling device  600  according to the second exemplary embodiment of the present invention is completed. 
     The cooling device  600  including the two thin plates  500  is formed in a hermetically sealed structure, inside of which a vacuum state is maintained. A working fluid is injected into the cooling device  600  formed of the two thin plates  500 , and then the cooling device  600  is hermetically sealed to be completed. 
     The cooling device  600  formed of the two thin plates  500  may simultaneously perform the functions of heat dissipation and heat transport of the electronic parts and equipment. 
     When heat is applied to the evaporator section side of the cooling device  600  formed of the two thin plates  500 , the working fluid included in the capillary grooves of the thin plate  500  is evaporated to produce evaporated vapor, which has latent heat and is transported to the condenser section side through the vapor pathway in the thin plate  500 . The transported vapor dissipates the latent heat and is condensed into a liquid in the condenser section, and the condensed liquid flows back to the evaporator section side along the liquid pathway in the thin plate  500  and then is re-saturated in the capillary groove of the evaporator section, which process is called circulation. Through repeated circulations, the cooling device  600  dissipates and transfers heat. 
     An operation mechanism of the cooling device  600  formed of the two thin plates  500  is to transfer heat from one side to another without supply of external power. 
     As described above, since the cooling device includes several stacked thin plates, it can be manufactured with no limitation of thickness. 
     Unlike configurations of conventional circular and planar cooling devices, the present invention can provide a thin cooling device manufactured by stacking several thin plates with no limitation of thickness. 
     The present invention can also overcome a limitation of heat transfer performance associated with the thickness of the conventional circular cooling device, which is formed by compression, or the conventional planar cooling device, which is formed by drawing and extruding, and ensure a maximum size of an internal vapor pathway even with a thin structure of 1.5 mm or less, simplify a formation process, and reduce production costs. 
     In addition, the thin cooling device can be used as a heat control device for various electronic and communication devices having lightweight, compact and slim structures. 
     While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.