Patent Publication Number: US-2006016578-A1

Title: [high-performance two-phase flow evaporator]

Description:
BACKGROUND OF INVENTION  
      1. Field of the Invention  
      The present invention relates generally to an evaporator and more particularly to a high-performance two-phase flow evaporator, which effectively dissipates heat energy from an electronic device by mans of the continuously alternating phase changing action between vapor phase and liquid phase of a working fluid.  
      2. Description of the Related Art  
      Following fast development of high technology, electronic devices are made in a mini scale, and have enhanced performance. However, an advanced electronic device releases much heat energy during operation. High temperature causes an advanced electronic device to release free electrons and thermal stress, resulting in working instability and shortening of service life. Therefore, it is important to dissipate heat energy from a working electronic device for preventing an overheat of the working electronic device. Because personal computer is popular and the life cycle of computer generation is short, the elimination ration of CPU is relatively increased. Improving the function and accelerating the speed of a CPU will relatively cause the CPU to produce much heat energy. Within the surface area of a CPU, the working temperature of a CPU is about 60˜95° C. Continuous working may cause increasing of the working temperature. Without cooling means to dissipate heat energy may result in abnormality of the CPU. Therefore, it is important to improve the heat dissipation efficient of CPU cooling means.  
      Under the circumstances in view, two-phase flow evaporator (s) are developed for use to dissipate heat energy from an electronic device. A conventional two-phase flow evaporator is comprised of a hollow metal container and radiation fins at the topside of the metal container. When in use, the bottom wall of the metal container is kept in contact with the electronic device, enabling heat energy to be transferred from the electronic device through the bottom wall to the inside of the metal container. The metal container has a capillary structure inside the surface metal, and the inside space of the metal container is drawn into a vacuum status. During transferring of heat energy from the electronic device to the metal container, a part of heat energy is transmitted to the whole metal container, and the rest of heat energy is transferred through the contact area between the electronic device and the metal container to the inside space of the metal container. Because the inside space of the metal container is maintained in a vacuum status, the working fluid in the capillary structure is caused to change the phase when hot, i.e., the working fluid is changed from liquid status into vapor status, thereby producing bubbles. Because the inside pressure of the bubbles is relatively greater, the bubbles move over the capillary structure to the space above the capillary structure, and then touch the cold top wall of the metal container. When touching the cold top wall of the metal container, heat energy is transferred from vapor to the top wall of the metal container for dissipation into the outside open air by the radiation fins, and at the same time vapor is condensed into liquid, which is transferred to the hot side by means of the capillary action of the capillary structure. Because reversible liquid-vapor phase change absorbs or releases a big amount of heat energy, this design of two-phase flow evaporator has the characteristic of transferring heat energy rapidly at a big volume, keeping the working temperature of the electronic device stable.  
      Conventionally, a metal container for two-phase flow evaporator is made by welding two open metal casing together, or welding two metal plates to the two ends of a metal column. Before welding or vacuum process, metal powder may be sintered to form the desired capillary structure. A two-phase flow evaporator made according to this design is heavy and expensive. When installing the retaining devices during assembly of a two-phase flow evaporator with an electronic device, the metal container may be deformed, thereby breaking the capillary structure. Damage to the capillary structure may lower heat transfer efficiency, or cause the working fluid unable to return to the hot side, thereby resulting in dry out. Further, because heat energy is transmitted from the electronic device to the whole metal container, less amount of heat energy is transferred by phase change, the working efficiency of the two-phase flow evaporator is greatly reduced.  
      Therefore, it is desirable to provide a high-performance two-phase flow evaporator that eliminates the aforesaid drawbacks.  
     SUMMARY OF INVENTION  
      The present invention has been accomplished under the circumstances in view. According to one aspect of the present invention, the high-performance two-phase flow evaporator comprises an electronic device, a non-metal casing, a heat sink device provided at the top side of the non-metal casing and defining with the non-metal casing an enclosed chamber, a working fluid contained in the enclosed chamber, and a heat conductivity member formed of higher heat conductivity material (k&gt;100 W/m.K) in the bottom side of the non-metal casing and disposed in contact between the electronic device and the working fluid for transferring heat energy from the electronic device to the working fluid to heat the working fluid to give off steam so that heat energy is quickly dissipated from the electronic device into the outside open air through the heat sink device. According to another aspect of the present invention, the casing can be directly injection-molded from plastics on the heat conductivity member of higher heat conductivity material (k&gt;100 W/m.K) to reduce the weight of the evaporator for preventing breaking or damage of the electronic device due to a heavy load. After molding of the casing on the heat conductivity member, the casing is assembled with the heat sink device. This manufacturing method is practical for mass production at a high manufacturing speed to reduce the cost. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is an elevational view of a high-performance two-phase flow evaporator according to the first embodiment of the present invention.  
       FIG. 2  is an exploded view of the high-performance two-phase flow evaporator according to the first embodiment of the present invention.  
       FIG. 3  is a schematic sectional side view of the first embodiment of the present invention, showing the high-performance two-phase flow evaporator in operation (I).  
       FIG. 4  is a schematic sectional side view of the first embodiment of the present invention, showing the high-performance two-phase flow evaporator in operation (II).  
       FIG. 5  is a sectional side view of showing the operation of a high-performance two-phase flow evaporator according to the second embodiment of the present invention.  
       FIG. 6  is a sectional side view of showing the operation of a high-performance two-phase flow evaporator according to the third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
      Referring to FIGS.  1 ˜ 3 , a high-performance two-phase flow evaporator in accordance with the first embodiment of the present invention is shown comprised of a casing  1 , a working fluid  2 , and an electronic device  3 .  
      The casing  1  is a non-metal member defining an enclosed chamber  11  for accommodating the working fluid  2 . The inside pressure of the enclosed chamber  11  is lower than the atmospheric pressure, i.e., the enclosed chamber  11  is maintained in a vacuum status. The casing  1  has a heat conductivity member  12  formed of higher heat conductivity material (k&gt;100 W/m.K) in the bottom side of the enclosed chamber  11 . The heat conductivity member  12  has a bottom contact surface  121  disposed in contact with the electronic device  3 , and a top heating surface  122  disposed in contact with the working fluid  2 . The topside of the enclosed chamber  11  is a metal heat sink device  13 . The heat sink device  13  comprises a flat base  131  that closes the topside of the casing  1 , and a plurality of radiating fins  132  upwardly extended from the top wall of the flat base  131 .  
      The working fluid  2  is held in the enclosed chamber  11  inside the casing  1 . The working fluid  2  can be water, alcohol, acetone, or their mixture.  
      The electronic device  3  is disposed in contact with the bottom contact surface  121  of the heat conductivity member  12 .  
      Referring to  FIGS. 3 and 4 , when the electronic device  3  is releasing heat energy during operation, the heat conductivity member  12  absorbs heat energy from the electronic device  3  and transfers absorbed heat energy to the working fluid  2 . Because the casing  1  is made of non-metal material and the heat conductivity member  12  is formed of higher heat conductivity material (k&gt;100 W/m.K), heat energy does not disperse and is gathered at the top heating surface  122  to heat the working fluid  2 . By controlling the enclosed chamber  11  in a vacuum status to lower the boiling point of the working fluid  2 , the working fluid  2  can be quickly heated by the top heating surface  122  to give off steam that flows toward the heat sink device  13  (see hollow arrow signs in  FIG. 3 ), enabling heat energy of steam to be absorbed by the flat base  131  of the heat sink device  13  and than transferred to the radiating fins  132 , so that heat energy can be quickly dissipated into the outside open air. When heat energy of steam was absorbed by the heat sink device  13 , steam is condensed into liquid status and returned to the bottom side of the enclosed space  11  due to the effect of gravity or capillary action. (see the hollow arrow signs in  FIG. 4 ). When returned to liquid status, the working fluid  2  absorbs heat energy from the top heating surface  122  and is heated to give off steam again. This liquid-vapor phase alternation continues, and therefore heat energy is efficiently dissipates from the electronic device  3  into the outside open air through the heat sink device  13  via the casing  1  and the working fluid  2 .  
      Referring to  FIG. 5 , the flat base  131  of the heat sink device  13  has a capillary structure  14  that increases the contact area to accelerate liquid-vapor phase changing speed. An electric fan  4  is provided at the topside of the radiation fins  132  and adapted to cause currents of air toward the radiation fins  132 . Besides, a steam guide device  111  is provided inside the enclosed chamber  11  and adapted to guide steam from the working fluid  2  to the flat base  131  of the heat sink device  13 .  
      Referring to  FIG. 6 , because the shell of the electric device  3  is made of higher heat conductivity material and the heat conductivity member  12  forms with the casing  1  a recessed hole, the electronic device  3  is directly inserted into the recessed hole and firmly secured thereto so that heat energy from the electronic device  3  can directly heat the working fluid  2  to give off steam, preventing accumulation of heat energy in the electronic device  3 . Therefore, this design enhances the stability of the electronic device  3  and extends the service life of the electronic device  3 . Further, the electronic device  3  can be a CPU (central processing unit).  
      Further, the top wall of the flat base  131  of the heat sink device  13  can be made having a corrugated or serrated face to increase contact area to air and to further accelerating condensing of vapor into liquid. The non-metal material of the casing  1  can be plastics or ceramics. The higher heat conductivity material (k&gt;100 W/m.K) of the heat conductivity member  12  can be copper or aluminum alloy, ceramic material such as graphite, silicon carbide, aluminum nitride, or boron nitride, or compound material such as aluminum and silicon carbide compound, graphite and copper compound, graphite and aluminum compound. The casing  1  can be injection molded from plastics on the heat conductivity member  12  of higher heat conductivity material (k&gt;100 W/m.K), and then assembled with the heat sink device  13  that is extruded from aluminum or made through a different manufacturing process. This manufacturing method is practical for mass production at a high manufacturing speed to reduce the cost.  
      Further, metal, ceramic, or non-metal balls and/or powder of density ratio higher than the working fluid  2  may be added to the working fluid  2  in the enclosed chamber  11  to enhance heat transfer efficiency or to lift the water lever of the working fluid  2  for enabling the heat conductivity member  12  to be fully covered by the working fluid  2  without affecting the performance of the heat sink device  13 .  
      In general, the high-performance two-phase flow evaporator of the present invention has the following features.  
      1. The invention provides a heat conductivity member  12  of higher heat conductivity material (k&gt;100 W/m.K) and a metal heat sink device  13  at the bottom and top sides of the non-metal casing  1  so that released heat energy from the electronic device  3  can be almost fully absorbed by the heat conductivity member  12  and transferred upwards through the top heating surface  122  to heat the working fluid  2  to give off steam. Due to minor pressure difference, steam flows upwards to the heat sink device  13 , and the heat sink device  13  efficiently transfers heat energy from steam to the outside air, causing steam to be quickly condensed into liquid status. Because heat energy is quickly dissipated from the electronic device  3  into the outside open air through the working fluid  2  and the heat sink device  13 , the invention prevents accumulation of heat energy at the electronic device  3 , and therefore enhancing the working stability of the electronic device  3  and extending the service life of the electronic device  3 .  
      2. Because the casing  1  is made of non-metal material, the weight of the evaporator can greatly be reduced, preventing breaking or damage of the electronic device  3  due to a heavy load. The casing  1  can be directly injection-molded from plastics on the heat conductivity member  12 , and then assembled with the heat sink device  13 . Therefore, this manufacturing method is practical for mass production at a high manufacturing speed to reduce the cost.  
      Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.