Abstract:
The circulative cooling apparatus has a first chamber, a second chamber, a first pipe, and a second pipe. There are porous structures on internal walls of the first chamber and the second pipe. There is work fluid in the second chamber and the porous structures. The work fluid is evaporated by heat in the first chamber, and owing to the pressure drop the vapor of the work fluid moves to the second chamber through the first pipe. Then the vapor of the work fluid condenses into the work fluid in the second chamber. Afterward the work fluid is transported back to the first chamber through the second pipe using the porous structures thereof, thus forming a circulative cooling apparatus.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to a heat dissipation device. More particularly, the present invention relates to a circulative cooling apparatus. 
   2. Description of Related Art 
   Electronic devices are developed to have smaller volume, lighter weight, and lower power consumption as science and technology makes tremendous progress. Energy utility rates of electronic devices are not completely utilized since a lot of energy is consumed as heat energy. The heat energy arises a temperature inside an electronic system. When the temperature inside the electronic system is higher than that can be tolerated by the electronic devices thereof, the physical characteristics of the electronic devices are changed by the high surrounding temperature and the electronic system becomes abnormal, generates errors, or is halted. Furthermore, the temperature inside the electronic system is raised and the breakdown rate of the electronic system is higher. 
   A main object of heat dissipation is to enhance reliability of a system. A temperature surrounding the electronic devices inside the system has a great effect on the reliability of the system. The temperature inside the system must be maintained at a lower degree to obtain a higher reliability of the system. Heat dissipation devices are therefore used to lower the temperature inside the system to an ideal operating temperature range for the electronic devices inside the system. Heat dissipation device design concerns an operating environment of the system, operating conditions, and allowed operating temperatures of the system. A structure of the system with good heat dissipation shapes or apparatus can dissipate heat outside the system and maintain a constant temperature therein to keep the system stable. 
   In conventional systems, heat dissipation of electronic devices usually uses fans driven by electric power to dissipate heat absorbed by heat sinks, so as to force airflows surrounding electronic devices to convect. But disadvantages of this method are large power consumption, noise and vibration that affects operations of electronic devices. Therefore, various apparatus have been developed to replace conventional fans/heat sinks combinations, such as a heat dissipation apparatus using phase changes of materials. 
   The heat transferring efficiency of two phase flow heat removal is higher than the heat transferring efficiency of single phase flow heat removal. A feature of the two phase flow heat removal is use of the latent heat between two phases of a work fluid to remove rapidly a great amount of heat energy. Some conventional apparatus, such as heat pipes and vapor chambers, utilizes this method. The following description explains them respectively. 
     FIG. 1  is a schematic view of a structure of a conventional heat pipe  100  and operating processes thereof. As shown in  FIG. 1 , the heat pipe  100  is a hollow container with low pressure therein. Materials, such as sintered metal, or feltmetal, are used to make a porous structure  114  on internal walls of a pipe case  112 . The porous structure  114  is soaked in a work fluid. The work fluid can be water, mercury, Freon, sodium, potassium or silver, depending upon what working temperature is needed. 
   A side of the heat pipe  100  is an evaporation section  102 . The evaporation section  102  contacts heat energy  126  of a heat source, and the work fluid within the evaporation section  102  is evaporated to become vapor because of absorbing heat energy  126  from the heat source. Owing to the pressure drop the vapor forms a vapor flow flowing to a condensation section  104 , and then condenses into the original work fluid. The condensed work fluid falls to the porous structure  114  inside the condensation section  104 , and afterward forms fluid flow  124  to flow back to evaporation section  102  due to capillary action. Evaporation and condensation are repeated to dissipate heat. 
     FIG. 2  is a schematic view of a structure of a conventional vapor chamber  200  and operating processes thereof. As shown in  FIG. 2 , the vapor chamber  200  is a hollow container with a low pressure therein. Internal walls of the vapor chamber  200  are like the heat pipe  100  as illustrated in  FIG. 1 , having a porous structure  214 , and the porous structure  214  is also soaked in a work fluid. A side of the vapor chamber  200  is an evaporation section  202 . 
   The evaporation section  202  contacts heat energy  226  of a heat source, and the work fluid within the evaporation section  202  is evaporated to become vapor by absorbing heat energy  226  from the heat source. The vapor moves upward and contacts an upper chamber wall  212  on the top of the evaporation section  202 , and then dissipates heat therein and condenses back to the original work fluid. The condensed work fluid falls back to the evaporation section  202  due to gravity or other reasons. Evaporation and condensation are repeated to dissipate heat. 
   The method of two phase flow heat removal continuously removes heat energy from a heat source by a successive circulation of a work fluid. The work fluid absorbs and dissipates latent heat of phase change to transfer heat energy, and the thermal conductivity thereof is a hundred or thousands of times greater than that of the thermal conductivities of silver or copper. For example, a effective thermal conductivity of a simplest sodium heat pipe (using stainless steel as it&#39;s the pipe case, rolling stainless steel net as it&#39;s the porous structure, and sodium as it&#39;s the work fluid) is over 418 J/(cm·s·° C.), but a thermal conductivity of copper is only 3.8 J/(cm·s·° C.). 
   However, since the work fluid and the vapor thereof both exist in the same space, when the evaporation rate of the vapor and the condensation rate of the work fluid reach critical values, entrainment and counter current flow are generated. These increase the instability between the work fluid and the vapor, and further decrease the condensed work fluid that should flow back to the evaporation section for a next evaporation procedure. If the work fluid cannot flow back to the evaporation section successfully, the heat energy of the evaporation section does not dissipate by the circulative work fluid. Then the temperature of the evaporation is continuously raised until the pipe is dried out and disabled. 
   SUMMARY OF THE INVENTION 
   It is therefore an objective of the present invention to provide a circulative cooling apparatus that satisfies the need to improve the dry-out problem of conventional heat pipes and vapor chambers. 
   In accordance with the foregoing and other objectives of the present invention, a circulative apparatus is described. The circulative cooling apparatus includes two chambers and two pipes. An evaporation chamber receives heat energy from a heat source, and a porous structure thereof contains saturated work fluid. The work fluid is evaporated to vapor by heat energy, and owing to the pressure drop the vapor of the work fluid moves to a condensation chamber through a vapor pipe. Then the vapor of the work fluid condenses into the work fluid because of the lower temperature of the condensation chamber. The condensation chamber is storage for the work fluid, and the work fluid is transported back to the evaporation chamber through a fluid pipe, thus forming a circulative cooling apparatus. 
   In one preferred embodiments of the present inventions, a gas channel is located inside the evaporation chamber that forces the vapor of the work fluid to flow according to a direction of the gas channel. Besides the direction for vapor flow, the gas channel also enlarges the unit air pressure inside the evaporation chamber to improve the vapor flow efficiency, so as to enhance the heat dissipation efficiency of the invention. 
   Furthermore, the work fluid stored in the condensation chamber is a buffer for the method of two phases flow removing heat, and prevents the apparatus from drying out. In addition, in this preferred embodiment, a position of the condensation chamber is lower than a position of the evaporation chamber, and gravity thus does not slow the capillary attraction of the porous structure, thus preserving the efficiency of the invention. 
   In another preferred embodiments of the present inventions, two dissipation devices, such as dissipation fins or dissipation fans, are installed on the evaporation chamber and the condensation chamber, so as to facilitate heat dissipation thereby. 
   The invention works on the principle of two phase flow heat removal; the thermal conductivity thereof is superior, heat response thereof is fast, and the heat transferring efficiency thereof is high. Furthermore, the invention uses the condensation chamber as storage for the work fluid, so the work fluid stored therein is a buffer to prevent the conventional drying out problem due to cooling too slowly. The operation lifetime of the invention is thereby extended. The invention also balances temperature of the chambers to decrease the spreading resistance effect. 
   The invention is a self-circulating cooling apparatus, and operates on its own without any additional power. Besides saving power, the invention also avoids the electronic elements attached thereto from overheating and then being burned due to the power devices or power transmission devices malfunctioning. The invention is not limited by the inner space of the system, and therefore can configure the invention according to the practical system design. Furthermore, the two chambers of the invention can be separated by a distance, so that the condensation chamber is distant from the heat source, thus enhancing the condensation efficiency of the work fluid and improving the heat dissipation efficiency of the invention. 
   It is to be understood that both the foregoing general description and the following detailed description are examples, and are intended to provide further explanation of the invention as claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
       FIG. 1  is a schematic view of a structure of a conventional heat pipe and operating processes thereof; 
       FIG. 2  is a schematic view of a structure of a conventional vapor chamber and operating processes thereof; 
       FIG. 3A  illustrates a schematic view of one preferred embodiment of the invention; 
       FIG. 3B  is a top view of an internal structure of the preferred embodiment in  FIG. 3A ; 
       FIG. 3C  is a side view of the preferred embodiment in  FIG. 3A ; and 
       FIG. 4  is a schematic view of another preferred embodiment of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
   The present invention provides a circulative cooling apparatus to improve the dry-out problem of conventional heat pipes and vapor chambers. 
   The invention provides a circulative cooling apparatus including two chambers and two pipes. An evaporation chamber receives heat energy from a heat source, and a porous structure thereof contains saturated work fluid. The work fluid is evaporated to vapor by heat energy, and owing to the pressure drop the vapor of the work fluid moves to a condensation chamber through a vapor pipe. Then the vapor of the work fluid condenses into the work fluid because of the lower temperature of the condensation chamber. The condensation chamber is storage for the work fluid, and the work fluid is transported back to the evaporation chamber through a fluid pipe, thus forming a circulative cooling apparatus. 
   The condensation chamber contains a lot of work fluid, and the porous structure inside the evaporation chamber contains saturated work fluid. When the work fluid inside the evaporation chamber is evaporated to vapor by heat energy and then moves to the condensation chamber, the porous structure inside the evaporation chamber becomes unsaturated. At this time the work fluid stored inside the condensation chamber moves back to the evaporation chamber by capillary attraction of the porous structure until the porous structure of the evaporation chamber becomes saturated again. 
   A gas channel is located inside the evaporation chamber and forces the vapor of the work fluid to flow according a direction of the gas channel. Besides the direction for flowing the vapor, the gas channel also enlarges the unit air pressure inside the evaporation chamber to improve the vapor flowing efficiency, so as to enhance the heat dissipation efficiency of the invention. Furthermore, the work fluid stored in the condensation chamber is a buffer for the method of two phases flow removing heat, and prevents the apparatus from drying out and prolongs the operating lifetime thereof. 
     FIG. 3A  illustrates a schematic view of one preferred embodiment of the invention. As shown in  FIG. 3A , an evaporation chamber  302  is connected to a condensation chamber  304  by a vapor pipe  306  and a fluid pipe  308 . A heat source is located below the evaporation chamber  302  to provide heat energy  326  to the evaporation chamber  302 . The evaporation chamber  302 , the condensation chamber  304 , the vapor pipe  306  and the fluid pipe  308  can be integrally or separately formed. 
     FIG. 3B  is a top view of an internal structure of the preferred embodiment in  FIG. 3A . As shown in  FIG. 3B , internal walls of the evaporation chamber  302  have a porous structure  312 , and the porous structure  312  is made from sintered metal, or feltmetal. The porous structure  312  contains saturated work fluid. A gas channel  314  lacking the porous structure  312  is located inside the evaporation chamber  302 , and the vapor inside the evaporation chamber  302  flows from the gas channel to the condensation chamber  304  through the vapor pipe  306 . 
   In this preferred embodiment, the gas channel  314  is E-shaped, mainly to make the gas channel  314  spread everywhere inside the evaporation chamber  302 . However, the shape of the gas channel  314  can be any other shape that spreads everywhere inside the evaporation chamber  302  to collect the vapor of the work fluid everywhere inside the evaporation chamber  302 . Moreover, a volume of the gas channel is designed to be less than a volume of the vapor of the work fluid contained by the porous structure  312  inside the evaporation chamber  302 . Thus, a unit air pressure of the gas channel  314  is enlarged to improve the efficiency of the vapor flowing from the evaporation chamber  302  to the condensation chamber  304 , so as to enhance the heat dissipation efficiency of the invention. 
   The work fluid  322  fills the condensation chamber  304 . A drawing area  320  is located inside the condensation chamber  304 , and the drawing area  320  is connected to fluid pipe  308 . The drawing area  320  and the fluid pipe  308  both have the porous structure inside. After the evaporation chamber  302  receiving the heat energy  326  of the heat source (as illustrated in  FIG. 3A ), the work fluid contained by the porous structure  312  of the evaporation chamber  302  is evaporated to vapor by heat energy and then flows according the direction of the gas channel  314 . An end  316  of the gas channel  314  which is near the fluid pipe  308  is closed by the porous structure  312 , and another end  318  of the gas channel  314  which is near the vapor pipe  306  is connected to the vapor pipe  306  to limit the flow direction of the vapor in the gas channel  314 . Owing to the pressure drop between the two chambers  302  and  304 , the vapor moves from the evaporation chamber  302  to the condensation chamber  304  through a vapor pipe  306 , and then is condensed to the work fluid because of the lower temperature. 
   A condensed chamber  304  serves as storage for the work fluid  322 , which stores a lot of work fluid  322 , and the porous structure  312  inside the evaporation chamber  302  contains the saturated work fluid. When the work fluid inside the evaporation chamber  302  is evaporated to vapor by heat energy and then moves to the condensation chamber  304 , the porous structure  312  inside the evaporation chamber  302  becomes unsaturated. At this time the work fluid stored inside the condensation chamber  304  moves back to the evaporation chamber  302  by a capillary attraction of the porous structure  312  until the porous structure  312  of the evaporation chamber  302  becomes saturated again. 
     FIG. 3C  is a side view of the preferred embodiment in  FIG. 3A . As shown in  FIG. 3C , the evaporation chamber  302  receives the heat energy  326  of the heat source (not illustrated in  FIG. 3C ). After the work fluid inside evaporates into vapor, the vapor not only is condensed on the upper section of the evaporation chamber  302  to dissipate heat energy  328 , but also moves to the condensation chamber  304  through the vapor pipe  306  and dissipates heat energy  328  by the condensation chamber  304 . In addition, in this preferred embodiment, a position of the condensation chamber  304  is lower than a position of the evaporation chamber  302 , and gravity thus does not slow the capillary attraction of the porous structure  312 , so as to maintain the work efficiency of the invention. 
     FIG. 4  is a schematic view of another preferred embodiment of the invention. Two dissipation devices  402 , such as dissipation fins or dissipation fans, are installed on the preferred embodiment in  FIG. 3  to facilitate the evaporation chamber  302  and condensation chamber  304  to dissipate heat. Thus enhances the heat dissipation efficiency of the invention, prolongs the operating lifetime of it, and avoids the invention drying out. 
   In conclusion, the invention has following advantages: 
   1. The invention works on the principle of two phase flow heat removal, and the thermal conductivity of it is superior, heat response of it is fast, and the heat transferring efficiency of it is high. Furthermore, the invention uses the condensation chamber as storage for the work fluid, so the work fluid stored therein is a buffer to avoid the conventional drying out problem due to cooling too slowly, and thus prolongs the operating lifetime of the invention. The invention also balances temperature of the chambers to decrease the spreading resistance effect. 
   2. The shape of the invention is simple and easy to manufacture, thus improves the yield thereof. Further, the internal structure of the invention is simple, without any complicated elements therein, so the breakdown rate thereof is lower. The invention is a self-circulating cooling apparatus, and operates on its own without any additional power. Besides saving power, the invention can prevent the electronic elements attached thereto from overheating then being burned due to the power devices or power transmission devices malfunctioning. 
   3. Conventional solid heat transferring efficiency is generally inversely proportional to the length of the transferring path. In other words, when the transferring path is longer, the solid heat transferring efficiency is lower. However, the invention does not have the foregoing disadvantages of the solid heat transferring, and is not limited by the length of the transferring path. Moreover, the invention also is not limited by the system inner space, and the invention can therefore be configured according to the practical system design. Furthermore, the two chambers of the invention can be separated by a distance, so the condensation chamber is distant from the heat source, thus enhancing the condensation efficiency of the work fluid and improving the heat dissipation efficiency of the invention. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.