Abstract:
A loop-type heat exchange device ( 10 ) includes an evaporator ( 20 ), a vapor conduit ( 30 ), a condenser ( 50 ) and a liquid conduit ( 70 ). The evaporator contains therein a working fluid. The working fluid turns into vapor in the evaporator upon receiving heat from a heat-generating component. The condenser includes a housing member ( 52 ), a plurality of tube members ( 53 ) being in fluid communication with the housing member, and a fin member ( 54 ) maintained in thermal contact with the tube members. The vapor conduit and the liquid conduit are each connected between the evaporator and the condenser. The vapor conduit conveys the vapor generated in the evaporator to the tube members of the condenser. The vapor turns into condensate in the tube members upon releasing the heat to the fin member. The condensate is conveyed back to the evaporator by the liquid conduit.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to an apparatus for dissipation of heat from heat-generating components, and more particularly to a loop-type heat exchange device suitable for removing heat from heat-generating electronic components. 
   DESCRIPTION OF RELATED ART 
   As progress continues developing in electronic industries, electronic components such as integrated circuit chips are made to have more powerful functions while maintaining an unchanged size or even a smaller size. As a result, the amount of heat generated by these electronic components during their normal operations is commensurately increased, which in turn will adversely affect their workability and stability. It is well known that cooling devices are commonly used to remove heat from heat-generating components. However, currently well-known cooling devices such as heat sinks plus electric fans are no longer qualified or desirable for removing the heat from these electronic components due to their low heat removal capacity. Conventionally, increasing the rotation speed of the cooling fan and increasing the size of the heat sink are two approaches commonly used to improve the heat dissipating performance of the cooling device involved. However, if the rotation speed of the cooling fan is increased, problems such as large noise will inevitably be raised. On the other hand, by increasing the size of the heat sink, it will make the cooling device bulky, which contravenes the current trend towards miniaturization. 
   Currently, an advantageous mechanism for more effectively removing the heat from these electronic components and overcoming the aforementioned disadvantages is adopted, which is related to use of heat pipe technology. Heat pipes are an effective heat transfer means due to their low thermal resistance. A heat pipe is usually a vacuum casing containing therein a working fluid. Preferably, a wick structure is provided inside the heat pipe, lining an inner wall of the casing. The heat pipe has an evaporating section for receiving heat from a heat-generating component and a condensing section for releasing the heat absorbed by the evaporating section. When the heat is inputted into the heat pipe via its evaporating section, the working fluid contained therein absorbs the heat and turns into vapor. Due to the difference of vapor pressure between the two sections of the heat pipe, the generated vapor moves, with the heat being carried, towards the condensing section where the vapor is condensed into condensate after releasing the heat into ambient environment by, for example, fins thermally contacting the condensing section. Due to the difference of capillary pressure developed by the wick structure between the two sections, the condensate is then drawn back by the wick structure to the evaporating section where it is again available for evaporation. 
   In the heat pipe, however, there still exists a fatal drawback awaited to be overcome. The movement of the vapor is countercurrent to that of the condensate within the casing of the heat pipe. The movement of the vapor will, to a certain extent, produce a resistance to the flow of the condensate due to an interaction between the vapor and the condensate. This negative effect will lower down the speed of the condensate in supplying to the evaporating section of the heat pipe. If the condensate is not timely sent back to the evaporating section, the heat pipe will suffer a dry-out problem at that section. 
   In order to overcome the foregoing drawback of the heat pipe, a loop-type heat exchange device has been proposed, as illustrated in  FIG. 11 . The heat exchange device includes an evaporator  1  in which a wick structure  2  saturated with a working fluid is provided, a vapor conduit  3 , a condenser  4  and a liquid conduit  5 . The working fluid in the evaporator  1  evaporates into vapor after absorbing heat from a heat source, and the generated vapor flows, via the vapor conduit  3 , to the condenser  4  where the vapor turns into condensate after releasing its latent heat of evaporation. The condensate then returns back to the evaporator  1  via the liquid conduit  5 , thus forming a heat transfer loop. The loop-type heat exchange device offers an advantage that the vapor and the condensate move along the heat transfer loop separately and do not interfere with each other. 
   In practice, the condenser  4  of the heat exchange device generally takes the form of metal fins stacked along a pipe section interconnecting the vapor conduit  3  and the liquid conduit  5 . Since the pipe section has a small contacting surface area (i.e., the circumferential surface area of the pipe section) with the metal fins, this results in large interfacial resistance and spreading resistance between the pipe section and the metal fins. As a result, the heat carried by the vapor cannot be timely and effectively transferred from the pipe section to the metal fins for dissipation and the heat removal capacity of the heat exchange device as a whole is limited. Furthermore, in the heat exchange device as illustrated in  FIG. 11 , no effective mechanism is provided to maintain the unidirectional movement of the working liquid along the heat transfer loop. Frequently, a portion of the vapor generated in the evaporator  1  moves backwards towards and enters into the liquid conduit  5 . This portion of vapor flowing backwards will produce significant resistance to the condensate being conveyed from the condenser  4  to the evaporator  1  along the liquid conduit  5 . 
   Therefore, it is desirable to provide a loop-type heat exchange device which overcomes the foregoing disadvantages. 
   SUMMARY OF INVENTION 
   The present invention relates to a loop-type heat exchange device for removing heat from a heat-generating component. The heat exchange device includes an evaporator, a condenser, a vapor conduit and a liquid conduit. The evaporator contains therein a working fluid. The working fluid turns into vapor in the evaporator upon receiving the heat from the heat-generating component. The condenser includes a first housing member, a plurality of tube members being in fluid communication with the first housing member, and a fin member maintained in thermal contact with the tube members. The vapor conduit and the liquid conduit are each connected between the evaporator and the condenser. The vapor conduit conveys the vapor generated in the evaporator to the tube members of the condenser. The vapor turns into condensate in the tube members upon releasing the heat to the fin member. The condensate is conveyed back to the evaporator by the liquid conduit. 
   As further improvements, first wick structure and second wick structure are provided in the evaporator and in the liquid conduit, respectively. The evaporator has a first region for receiving the heat from the heat-generating component and a second region accommodating the first wick structure. The vapor conduit and the liquid conduit communicate with the first and second regions, respectively. A plurality of metal fins extends from an outer surface of the evaporator and is located in alignment with the second region. The evaporator has an outer wall for contacting the heat-generating component. The outer wall has first section and second section corresponding to the first and second regions of the evaporator, respectively. The first section is thicker than the second section. 
   Other advantages and novel features of the present invention will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is an isometric view of a loop-type heat exchange device in accordance with a first embodiment of the present invention; 
       FIG. 2  is a cross-sectional view of an evaporator of the heat exchange device of  FIG. 1 , taken along the line II-II thereof; 
       FIG. 3  is an isometric view of the evaporator of the heat exchange device of  FIG. 1 , with a top cover thereof being removed; 
       FIG. 4  is an isometric view of a condenser of the heat exchange device of  FIG. 1 ; 
       FIG. 5  is a cross-sectional view of the condenser of  FIG. 4 , taken along line V-V thereof; 
       FIG. 6  is an isometric view of a loop-type heat exchange device in accordance with a second embodiment of the present invention; 
       FIG. 7  is an isometric view of a loop-type heat exchange device in accordance with a third embodiment of the present invention; 
       FIG. 8  is a cross-sectional view of a condenser of the loop-type heat exchange device of  FIG. 7 , taken along line VIII-VIII thereof; 
       FIG. 9  is a fragmentary, cross-sectional view showing a condenser in accordance with another example; 
       FIG. 10  is a fragmentary, cross-sectional view showing a condenser in accordance with a further example; and 
       FIG. 11  is a schematic view showing a loop-type heat exchange device in accordance with the conventional art. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a loop-type heat exchange device  10  in accordance with a first embodiment of the present invention. The heat exchange device  10  includes an evaporator  20 , a vapor conduit  30 , a condenser  50 , a liquid conduit  70  and an electric fan  80 . The evaporator  20  preferably is made of two separable portions connected together, as will be discussed in more detail later. Two ends of each of the vapor and liquid conduits  30 ,  70  are connected to the evaporator  20  and the condenser  50 , respectively. The vapor and liquid conduits  30 ,  70  preferably are made of flexible metal or non-metal materials so that they could be bent or flattened easily in order for the heat exchange device  10  to be applicable in certain circumstances. 
   The evaporator  20  contains therein a working fluid such as water or alcohol (not shown). As heat from a heat source (not shown) such as a central processing unit (CPU) of a computer is applied to the evaporator  20 , the working fluid contained therein evaporates into vapor after absorbing the heat. Then, the generated vapor flows, via the vapor conduit  30 , to the condenser  50  where the vapor releases its latent heat of evaporation to the condenser  50  and accordingly turns into condensate. The heat then is dissipated into the ambient environment by the condenser  50  and the electric fan  80 . The condensate resulted from the vapor at the condenser  50  returns back, via the liquid conduit  70 , to the evaporator  20  where it is again available for evaporation. In the heat exchange device  10 , the movement of the working fluid forms a heat transfer loop whereby the heat of the CPU is effectively removed away. The movements of the vapor and the condensate are carried out separately in the respective vapor and liquid conduits  30 ,  70 . 
   With reference to  FIGS. 2-3 , the evaporator  20  has a plate-type configuration, which includes a top cover  22  and a bottom cover  24 . The top and bottom covers  22 ,  24  cooperate with each other to define a chamber  26  inside the evaporator  20 . The bottom cover  24  includes a first, thicker section  24   a  and a second, thinner section  24   b  integrally extending from one side of the first section  24   a . The first section  24   a  projects downwardly to an extent below the second section  24   b  with a step (not labeled) formed between the first and second sections  24   a ,  24   b . A protrusion  28  is formed by extending further downwardly from a substantially middle portion of the first section  24   a  of the bottom cover  24  for contacting the CPU. A first wick structure  29  is arranged inside the evaporator  20 . The working fluid contained in the evaporator is saturated in the first wick structure  29 . The first wick structure  29  defines therein a plurality of micro-channels (not labeled) for storage of and providing passageways for the working fluid. The first wick structure  29  is preferably in the form of sintered powders or a screen mesh made of flexible metal wires or organic fibers. 
   The chamber  26  of the evaporator  20  includes two major regions, i.e., an evaporating region  26   a  and an adjacent liquid micro-channel region  26   b , corresponding to the first and second sections  24   a ,  24   b  of the bottom cover  24  of the evaporator  20 , respectively. The micro-channel region  26   b  is fully filled with the first wick structure  29 . Also, a portion of the first wick structure  29  extends from the micro-channel region  26   b  into a middle part of the evaporating region  26   a . This portion of the first wick structure  29  has a size substantially equal to that of the protrusion  28  of the bottom cover  24 , and is fittingly located just above and covers the protrusion  28 . Additionally, another portion of the first wick structure  29  extends from the micro-channel region  26   b  into front and rear sides of the evaporating region  26   a , as viewed from  FIG. 3 . As a result, the first wick structure  29  spans across both the micro-channel region  26   b  and the evaporating region  26   a  of the chamber  26  of the evaporator  20 . The remaining part of the evaporating region  26   a  not filled with the first wick structure  29  is provided as a vapor-gathering sub-region  26   c  for accommodating the generated vapor in the evaporator  20 . The vapor and liquid conduits  30 ,  70  are connected to the evaporating region  26   a  and the micro-channel region  26   b , respectively. The vapor-gathering sub-region  26   c  is communicated with the vapor conduit  30  so as to enable the generated vapor to leave the evaporator  20  and go into the vapor conduit  30  smoothly. 
   In order to bring the condensate from the condenser  50  back to the evaporator  20  timely, a second wick structure  72  is arranged against an inner surface of the liquid conduit  70 , as shown in  FIG. 3 . The second wick structure  72  may be fine grooves integrally formed at the inner surface of the liquid conduit  70 , screen mesh or bundles of fiber inserted into the liquid conduit  70 , or sintered powders combined to the inner surface of the liquid conduit  70 . 
   Referring now to  FIGS. 4-5 , the condenser  50  includes top and bottom housings  51 ,  52  and a plurality of condensing tubes  53  along which a plurality of metal fins  54  is stacked. Each of the top and bottom housings  51 ,  52  has an elongated, box-like structure. These condensing tubes  53  are located between the top and bottom housings  51 ,  52  and are positioned in parallel with each other. Two ends of each of these condensing tubes  53  are communicated with the top and bottom housings  51 ,  52 , respectively. Specifically, a bottom wall  512  of the top housing  51  and a top wall  522  of the bottom housing  52  each define therein a plurality of holes (not labeled). Top and bottom ends of these condensing tubes  53  are fixedly and hermetically positioned in these holes defined in the walls  512 ,  522 . As presenting a large heat dissipating surface area, the metal fins  54  are made of highly thermally conductive material such as copper or aluminum and are maintained in intimate thermal contact with a circumferential surface of each of the condensing tubes  53 . The bottom housing  52  has an inlet  524  and an outlet  526 , both of which are defined in a bottom wall (not labeled) of the bottom housing  52 . The inlet  524  and outlet  526  are located at opposite sides of the bottom wall and are used to connect with the vapor and liquid conduits  30 ,  70 , respectively. 
   As the vapor generated in the evaporator  20  enters into the bottom housing  52  of the condenser  50  through the inlet  524 , the vapor moves freely into the condensing tubes  53  where the vapor releases the heat carried thereby to the metal fins  54  contacting the condensing tubes  53 . With these condensing tubes  53  and metal fins  54 , the condenser  50  has a large heat removal capacity and therefore the vapor can be effectively cooled at the condenser  50 . After the vapor releases the heat in the condensing tubes  53 , it turns into the condensate. The condensate then flows towards the bottom housing  52 . Thereafter, the condensate gathered in the bottom housing  52  flows through the outlet  526  into the liquid conduit  70  through which the condensate is brought back to the evaporator  20 . As shown in  FIG. 4 , the condenser  50  is preferably positioned in an upright position with the condensing tubes  53  located perpendicularly to the liquid conduit  70  so that the condensate condensed in the condensing tubes  53  can move towards the bottom housing  52  and accordingly the liquid conduit  70  rapidly and smoothly by resorting to the weight of the condensate. In order to cause the condensate contained in the bottom housing  52  to enter into the liquid conduit  70  more rapidly and smoothly, the bottom wall of the bottom housing  52  has a slanted inner surface  527  declining from the inlet  524  towards the outlet  526  and has the lowest level at the outlet  526 . On the other hand, in order to prevent the vapor entering into the bottom housing  52  from directly entering into the liquid conduit  70  through the outlet  526  without having been condensed in the condenser  50 , a baffle  528  is placed above the outlet  526  in such a manner that it blocks a vast majority of the vapor in the bottom housing  52  to directly enter into the liquid conduit  70  but do not block the condensate in the bottom housing  52  to enter into the liquid conduit  70 . 
   In operation, the protrusion  28  of the bottom cover  24  of the evaporator  20  is maintained in thermal contact with the CPU. Preferably, a layer of thermal interface material is applied over their contacting surfaces in order to reduce thermal resistance. The heat generated by the heat source is firstly transferred to the first section  24   a  of the bottom cover  24  and then to the evaporating region  26   a  of the chamber  26  of the evaporator  20  to cause the working fluid contained in that region to evaporate into the vapor after absorbing the heat from the CPU. Due to the difference of vapor pressure between the evaporator  20  and the condenser  50 , the generated vapor moves towards the condenser  50  via the vapor conduit  30 . The vapor conduit  30  may also have a larger diameter than the liquid conduit  70  so as to enable the generated vapor in the evaporator  20  to move towards the condenser  50  smoothly. After the vapor releases its latent heat in the condenser  50  and turns into the condensate, the condensate is then rapidly and timely drawn back to the micro-channel region  26   b  of the chamber  26  of the evaporator  20  via the liquid conduit  70  under the capillary forces of the second and first wick structures  72 ,  29  as respectively provided in the liquid conduit  70  and the evaporator  20 , thereby preventing an excessive amount of the condensate from accumulating in the condenser  50  and meanwhile avoiding the potential dry-out problem occurring at the evaporator  20 . Since an inventory of working fluid in the evaporating region  26   a  is reduced due to the evaporation in that region, the condensate returned to the micro-channel region  26   b  is subsequently drawn to the evaporating region  26   a  for being available again for evaporation as a result of the capillary force of the first wick structure  29 . This cycle of the working fluid effectively takes heat away from the CPU. 
   In the present heat exchange device  10 , the two-section design of the bottom cover  24  with different thicknesses is aimed to reduce an amount of the heat of the CPU to be conducted from the first section  24   a  to the second section  24   b  and finally to the micro-channel region  26   b  of the evaporator  20 . Since the first section  24   a  has a larger thickness than the second section  24   b , the heat conducted laterally from the first section  24   a  towards the second section  24   b  is reduced in comparison with a bottom cover with a uniform thickness. Accordingly, the heat transferred to the micro-channel region  26   b  of the evaporator  20  from the bottom cover  24  is also effectively reduced, the condensate in the micro-channel region  26   b  is less likely to be heated directly in that region and excessive vapor is thus prevented from being formed and accumulated in the micro-channel region  26   b.    
     FIG. 6  shows a second embodiment of the present invention, in which a plurality of metal fins  82  is provided on an outer surface of the evaporator  20 . The metal fins  82  are aligned with the micro-channel region  26   b  of the chamber  26  of the evaporator  20 . The vapor and liquid conduits  30 ,  70  are connected to a sidewall (not labeled) of the bottom housing  52  of the condenser  50 . The other structure of this embodiment is the same as that of the first embodiment described above, and its description is omitted. In this embodiment, the metal fins  82  are provided as a cooling device to lower the temperature of the micro-channel region  26   b  and at the same time to prevent vapor from being formed and accumulated in that region. Since the micro-channel region  26   b  is connected with the adjacent evaporating region  26   a,  a portion of the vapor generated in the evaporating region  26   a  will “creep” from the evaporating region  26   a  into the micro-channel region  26   b  due to a large vapor pressure in the vapor-gathering sub-region  26   c.  Additionally, the temperature in the micro-channel region  26   b  will also gradually increase, subject to a relatively high temperature and a flow of the vapor in the evaporating region  26   a.  The metal fins  82  are applied to directly condense the vapor entering into the micro-channel region  26   b  and simultaneously to dissipate the heat transferred to the micro-channel region  26   b  from the adjacent evaporating region  26   a  or the second, thinner section  24   b  of the bottom cover  24 . Thus, due to the presence of the metal fins  82 , the vapor potentially to be formed and accumulated in the micro-channel region  26   b  is greatly reduced. 
     FIGS. 7-8  show a third embodiment of the present invention, in which the vapor and liquid conduits  30 ,  70  are connected to the top and bottom housings  51 ,  52  of the condenser  50 , respectively. In this embodiment, since the vapor transferred by the vapor conduit  30  enters into the condenser from the top housing  51 , the baffle  528  (see  FIG. 5 ) as provided in the bottom housing  52  as required by the first and second embodiments is no longer needed. The other structure of this embodiment is substantially the same as that of the second embodiment described above, and its description is omitted. 
   Referring now to  FIGS. 9-10 , in order to further increase the heat exchange capability of the condenser  50 , a vapor dispenser  90  is provided in the bottom housing  52  for distributing the vapor entering into the bottom housing  52  over the condensing tubes  53  of the condenser  50  evenly. The inlet  524  of the bottom housing  52  is connected with the vapor dispenser  90 . The vapor dispenser  90  is provided with a plurality of openings  94  oriented towards the condensing tubes  53  of the condenser  50  so that the vapor can be uniformly divided by these openings  94  into many small portions for successively entering into these condensing tubes  53 . As shown in  FIG. 9 , the inlet  524  is connected to a middle portion of the vapor dispenser  90 . In  FIG. 10 , the inlet  524  is shown as connected to one end of the vapor dispenser  90  and the outlet  526  of the bottom housing  52  is located at a middle portion of the bottom housing  52 . Due to the presence of the vapor dispenser  90 , the baffle  528 , as shown in  FIG. 5 , is no longer required. Although in  FIGS. 9-10  the vapor dispenser  90  is shown as provided in the bottom housing  52  of the condenser  50 , it should be recognized that if the vapor enters into the condenser  50  from the top housing  51  thereof as shown in  FIGS. 7-8  of the third embodiment, the vapor dispenser  90  is expected to be provided in the top housing  51 . 
   It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.