Abstract:
Heat from a heat generating device such as a CPU is dissipated by a heat sink device containing a recycled two-phase vaporizable coolant. The coolant recycles inside a closed metal chamber, which has an upper section and a lower section connected by a conveying conduit, and a wick evaporator placed in the lower section. The liquid coolant in the evaporator is vaporized by the heat from the heat generating device. The coolant vapor enters the upper section and condenses therein, with the liberated latent heat dissipated out through the inner top chamber wall. The condensed coolant is then collected and flows into the lower section, and further flows back to the wick evaporator by capillary action of the evaporator, thereby recycling the coolant. Space or a piece of element with parallel grooves is used to form at least one of the sections to reduce friction in the liquid flow path.

Description:
[0001]     This is a continuation-in-part application of application Ser. No. 10/785174 filed Feb. 24, 2004, now pending. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     (1) Field of the Invention  
         [0003]     This invention relates to a heat pipe, in particular, a microchannel flat-plate heat pipe used for heat dissipation for a central processing unit (CPU) or other electronic integrated circuit (IC) chips.  
         [0004]     (2) Brief Description of Related Art  
         [0005]     The latest generation of Pentium IV CPU generates power more than 100 watts (Joule/sec). In order to maintain its normal performance and avoid overheating of the unit, more effective heat dissipating mechanism is needed. U.S. Pat. No. 5,880,524 discloses a heat pipe for spreading the heat generated by a semiconductor device as shown in  FIG. 1 . A cavity  105  is enclosed by a base metal  100  for a working liquid (not shown in the figure) to recycle. Heat sink fins  101  are arranged on the top of the base metal  100  for heat dissipation. Heat transfer medium  102  is under the base metal  100  to contact with a CPU.  
         [0006]     A two-phase vaporizable liquid resides within the cavity  105  and serves as the working fluid (the coolant) for the heat pipe. A metal wick  103  is disposed on the inner walls to form a recycling loop within cavity  105  to facilitate the flow of the working fluid within the cavity. The working liquid in the cavity  105  flows in a direction as shown in arrows in  FIG. 1 . Firstly the working liquid is absorbed in the bottom portion of the wick  103 . It evaporates when heat is transferred from the CPU and then condenses on the top portion of the wick  103 . Heat is further transferred upward to the heat sink fins  101 . The condensed liquid absorbed in the top portion of the wick  103  is then moved to the lower portion of the wick  103  due to capillary action of the wick  103 .  
       SUMMARY OF THE INVENTION  
       [0007]     An objective of this invention is to devise a coolant recycle mechanism with space passages as part of the recycling passage to decrease the friction for the coolant flow in a heat pipe. Another objective of this invention is to devise a coolant recycle mechanism with parallel grooves as a part of the passage to decrease the friction for the flow of the working fluid. A further objective of this invention is to devise a more effective heat dissipation mechanism for a heat pipe. By using space passages, parallel grooves or a combination of both as part of the passage, the friction for the liquid flow is reduced and the capillary action effectively enhances the recycling of the coolant. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  Prior art.  
         [0009]      FIG. 2  First embodiment of this invention.  
         [0010]      FIG. 3  Enlarged plane view of the recycle mechanism of  FIG. 2 .  
         [0011]      FIG. 4  Explosive perspective view of the recycle mechanism of  FIG. 2 .  
         [0012]      FIG. 5  Second embodiment of this invention.  
         [0013]      FIG. 6  Third embodiment of this invention.  
         [0014]      FIG. 7  Fourth embodiment of this invention.  
         [0015]      FIG. 8  Fifth embodiment of this invention.  
         [0016]      FIG. 9  Sixth embodiment of this invention.  
         [0017]      FIG. 10  Seventh embodiment of this invention.  
         [0018]      FIG. 11  Eighth embodiment of this invention.  
         [0019]      FIG. 12  Vertical use of the invention.  
         [0020]      FIG. 13  Ninth embodiment of this invention.  
         [0021]      FIG. 14  Tenth embodiment of this invention.  
         [0022]      FIG. 15  Eleventh embodiment of this invention.  
         [0023]      FIG. 16  Twelfth embodiment of this invention.  
         [0024]      FIG. 17  Thirteenth embodiment of this invention.  
         [0025]      FIG. 18  Fourteenth embodiment of this invention.  
         [0026]      FIG. 19  Fifteenth embodiment of this invention.  
         [0027]      FIG. 20  Sixteenth embodiment of this invention.  
         [0028]      FIG. 21  Seventeenth embodiment of this invention.  
         [0029]      FIG. 22  Eighteenth embodiment of this invention  
         [0030]      FIG. 23  Explosive perspective view of the embodiment  FIG. 22 .  
         [0031]      FIG. 24  Nineteenth embodiment of this invention.  
         [0032]      FIG. 25  Twentieth embodiment of this invention.  
         [0033]      FIG. 26  Twenty-first embodiment of this invention.  
         [0034]      FIG. 27  Twenty-second embodiment of this invention.  
         [0035]      FIG. 28  Twenty-third embodiment of this invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0036]     The principle of this invention is to use space passages, parallel grooves or a combination of both as part of the passage for the flow of the working liquid within a flat-plate heat pipe.  FIG. 2  shows the first embodiment of this invention. Cavity  105  is enclosed by a base metal  100 . Multiple sections are divided in the cavity  105  for the recycling of the working liquid. The working liquid moves in a direction following the arrows shown in the figure.  
         [0037]      FIG. 3  shows an enlarged plane view of the recycle mechanism in the cavity  105  of  FIG. 2 . There are four sets of parallel grooves shown in this design. A first set of left parallel grooves  201  and a second set of left parallel grooves  202  are arranged on the left of the wick  203 . A third set of right parallel grooves  201  and a fourth set of right parallel grooves  202  are arranged on the right side of the wick  203 . The two sets of grooves  201  and  202  are separated with an isolation plate  205 . The recycling principle for the left two sets of grooves  201  and  202  is exactly the same as that for the right-side two sets of grooves  201  and  202 , and therefore only two left-side grooves are described below.  
         [0038]     Working liquid (not shown) is absorbed in the wick  203 . The wick  203  can be made of sintered copper (Cu) powder, sintered nickel (Ni) powder, or sintered stainless-steel powder. Alternatively, the wick  203  can be made of single-layer or multi-layer of metal wire mesh (not shown) or metal wire cloth (not shown). When the heat pipe is attached to a heat generating unit such as a central process unit (CPU), a certain amount of the working liquid in the wick  203  is heated and vaporized as shown by the arrows. Part of the vapor condenses on the inner top surface within the cavity  105 , which is enclosed by the base metal  100 . Part of the vapor enters a first set of parallel grooves  201  to condense. The condensed liquid is collected in the corners of the parallel grooves. The liquid is then driven by the vapor flow and the capillary action to a second set of parallel grooves  202  under the first set of parallel grooves  201  through a slot  204 . The conveying slot  204  is located at a common end of the two sets of grooves to connect the two sets of grooves  201  and  202 . The wick  203  is located on the other end of the grooves  202  and has a height no less than the height of the grooves  202 . The evaporation of the liquid in the wick  203  leads to a liquid-vapor interface within the wick  203 . This liquid-vapor interface results in a capillary pulling force on the working liquid in grooves  202  toward the wick  203  to make a full cycle: liquid→vapor→cooling→liquid, following the arrows as shown in  FIG. 3 .  
         [0039]      FIG. 4  shows the explosive perspective view of the recycle mechanism of  FIG. 2 . The parallel grooves  201  and  202  can be made separately before being connected together. Alternatively, the parallel grooves  201  and  202  can also be made integrally as a single body by molding or extrusion, or by etching, cutting, or machining on a metal plate. The cross-sectional shape of the grooves is triangular as illustrated, or of other shapes, such as rectangular or trapezoidal, etc. The base material for grooves  201  and  202  can be metal or nonmetal such as silicon or plastics, etc. may also be used.  
         [0040]     In this embodiment, the grooves  201  and  202  are essentially independent of each other except being communicated by the slot  204  so that the liquid flowing in grooves  202  is not dragged by the vapor flow in grooves  201  in the opposite direction.  
         [0041]     In order for effective condensation of the vapor molecules in the first set of parallel grooves  201 , single-sided grooves in contact with the inner top surface of the cavity is desired for the first set of parallel grooves  201 . However, for the second set of parallel grooves  202  where condensed liquid flows, either a set of single-sided grooves or a set of double-sided grooves works equally well. Double-sided grooves can be made using a corrugated sheet (not shown). Single-sided grooves  202  are shown in  FIG. 4 . They can be made by the way of molding, extrusion, or by etching, cutting, or machining on a metal plate.  
         [0042]      FIG. 5  shows a second embodiment of this invention. This embodiment includes a vertical guiding plate  207  above the wick  203  to bridge the wick  203  and the inner top surface of the base metal  100 . The guiding plate  207  allows part of the condensed liquid on the inner top surface to flow downward back to the wick  203  directly. The guiding plate  207  also serves as a strengthener against the inward pressure when the cavity  105  is evacuated.  
         [0043]      FIG. 6  shows a third embodiment of this invention. This embodiment uses an elongated grooves  201 B over the top of the wick  203 .  
         [0044]      FIG. 7  shows a fourth embodiment of this invention. Shown herein is a half-cut piece, with the front surface representing the mid-plane cross-section of the whole unit. This embodiment shows that the first set of parallel grooves and the conveying slot  204  can be integrated with the top part of the base metal  100  to form a top metal base  201 C. The parallel grooves  2011  and the conveying slot  204  can be fabricated by molding, or by cutting, scribing, or etching the base metal  100 .  
         [0045]      FIG. 8  shows a fifth embodiment of this invention. Shown herein is also a half-cut piece, with the front surface representing the mid-plane cross-section of the whole unit. Similar to the fourth embodiment of  FIG. 7 , the second set of parallel grooves  202  and the conveying slot  204  can be integrated with the bottom part of the base metal  100  to form the bottom metal base  202 B. Parallel grooves  2021  and the conveying slot  204  can be fabricated by molding, or by cutting, scribing, or etching the base metal  100 .  
         [0046]      FIG. 9  shows a sixth embodiment of this invention. This embodiment shows that the wick  203  in the previous embodiments can be replaced with a pin-array block  203 B. The space between the pins is used to absorb the working liquid by capillary attraction. The vertically open space allows for easy escape of bubbles once they are formed under high heat power conditions. This design is aimed at extending the dry-out limits of the working liquid in the wick  203 .  
         [0047]      FIG. 10  shows a seventh embodiment of this invention. This embodiment uses a different shape of corrugated metal  207 B. The square corrugated metal  207 B used herein differs from the V-shaped corrugated metal  207  in  FIG. 5 . Other forms of corrugation are also usable, such as spiral corrugation, S-shaped corrugation, etc., and are not exhaustive in this specification.  
         [0048]      FIG. 11  shows an eighth embodiment of this invention. This embodiment uses a meshed metal  207 C as the guiding plate, rather than the non-meshed guiding plate  207 B in  FIG. 10 .  
         [0049]      FIG. 12  shows that the invention as shown in  FIG. 3  can be used in a vertical direction. Part of the vapor from the wick  203  condenses directly on the inner wall opposite to the wick  203  or enters the first set of bottom parallel grooves  201  and condenses herein. The condensed liquid flows downward, driven by the vapor flow as well as the gravity, into the liquid pool at the bottom end (not shown). With the combined capillary action of the wick  203  and of the parallel grooves  202 , the working liquid is pulled up back to the wick  203 .  
         [0050]     Part of the vapor from the wick  203  goes up to the first set of top parallel groves  201  and condensed herein. Some of the condensed liquid may drop into the first set of bottom parallel grooves  201 . Some of the condensed liquid is driven upward by the vapor flow to enter the top conveying slot  204  and then the second set of parallel grooves  202 , before it finally flows back to the wick  203 .  
         [0051]     In order to enhance the capillary pulling force on the recycled liquid for those embodiments where two sets of parallel grooves are used, the hydraulic diameters (or the cross-sectional areas of the flow path) of the second set of parallel grooves  202  are made smaller than those of the first set of parallel grooves  201 .  
         [0052]      FIG. 13  shows a ninth embodiment of this invention. This embodiment is a modified version of  FIG. 12 . The first set of top parallel grooves  201  in  FIG. 12  is replaced with a space A. As the vapor from the wick  203  enters space A, part of it condenses on the inner wall of the metal base  100 . The condensed liquid either drops to the first set of bottom parallel grooves  201  or is driven upward by the vapor flow across the conveying slot  204  into the second set of top parallel grooves  202 . The second set of parallel grooves  202  functions as a passage for the condensed liquid to flow back to the wick  203  by the capillary force provided by the micro grooves  202  and the wick  203 .  
         [0053]      FIG. 14  shows a tenth embodiment of this invention. This embodiment is a modified version of  FIG. 12 . The second set of top parallel grooves  202  in  FIG. 12  is replaced with a space B. The space B functions as a passage for the condensed liquid to flow back to the wick  203  by gravity and the capillary force provided by the thin space B and the wick  203 .  
         [0054]      FIG. 15  shows an eleventh embodiment of this invention. This embodiment is a modified version of  FIG. 12 . The first set of top parallel grooves  201  in  FIG. 12  is replaced with a space A; while the second set of top parallel grooves  202  is replaced with a space B. The space B functions as a passage for the condensed liquid to flow back to the wick  203  by gravity and the capillary force provided by the thin space B and the wick  203 .  
         [0055]      FIG. 16  shows a twelfth embodiment of this invention. This embodiment is a simplified version of  FIG. 3  or  FIG. 4 . A single first set of parallel grooves  201  and a single second set of parallel grooves  202  are used. The recycle mechanism is exactly the same as described in  FIG. 3  or  FIG. 4 .  
         [0056]      FIG. 17  shows a thirteenth embodiment of this invention. This embodiment is a modified version of  FIG. 16 . The first set of parallel grooves  201  in  FIG. 16  is replaced with a space A. As the vapor form the wick  203  enters space A, part of it condenses on the inner wall of the metal base  100 . The condensed liquid is driven by the vapor flow across the conveying slot  204  into the second set of parallel grooves  202 . The liquid in the grooves  202  then flows back to the wick  203  by gravity and the capillary force provided by the micro grooves  202  and the wick  203 .  
         [0057]      FIG. 18  shows a fourteenth embodiment of this invention. This embodiment is a modified version of  FIG. 16 . The second set of parallel grooves  202  in  FIG. 16  is replaced with a space B. The space B functions as a passage for the condensed liquid to flow back to the wick  203  by the capillary force provided by the thin space B and the wick  203 .  
         [0058]      FIG. 19  shows a fifteenth embodiment of this invention. This embodiment is a modified version of  FIG. 16 . The first set of parallel grooves  201  in  FIG. 16  is replaced with a space A; while the second set of parallel grooves  202  is replaced with a space B. As the vapor form the wick  203  enters space A, part of it condenses on the inner wall of the metal base  100 . The condensed liquid is driven by the vapor flow across the conveying slot  204  into the space B. The space B functions as a passage for the condensed liquid to flow back to the wick  203  by the capillary force provided by the thin space B and the wick  203 .  
         [0059]      FIG. 20  shows a sixteenth embodiment of this invention. This embodiment is a modification to all the previous embodiments.  FIG. 20  shows a second wick  204 B inserted into the slot  204  to smooth the liquid flow. The capillary action within  204 B grabs the condensed liquid stronger than a slot  204  as shown in the previous embodiments. This design prevents the vapor from entering the second set of parallel grooves  202  and, therefore, leads to a smoother liquid flow.  
         [0060]      FIG. 21  shows a seventeenth embodiment of this invention. This embodiment is a modification to  FIG. 3  by replacing the grooves  202  in the lower section with a space B. The space B functions as a passage for the condensed liquid to flow back to the wick  203  by the capillary force provided by the thin space B and the wick  203 .  
         [0061]      FIG. 22  shows an eighteenth embodiment of this invention. This embodiment uses an elongated wick  203 C as wide as that of the lower section. The middle part of the elongated wick  203 C is used as an evaporator to absorb the heat from a heat-generating device attached below it (not shown). The other parts under the grooves  201  are used as a passage for the liquid to flow back to the middle part of the wick  203 C The wick  203 C can be sintered metal powder, metal wire mesh or metal wire cloth.  
         [0062]      FIG. 23  is the explosive perspective view of the embodiment in  FIG. 22 . Two sets of parallel grooves  201  are placed in the two sides of the upper section of the cavity  105  to help collect the condensed liquid.  
         [0063]      FIG. 24  shows a nineteenth embodiment of this invention. A V-shaped corrugated metal  207  is placed on top of the wick  203 C and between the two sets of parallel grooves  201 .  FIG. 25  shows a twentieth embodiment of this invention. This embodiment uses a set of elongated grooves  201 B over the top of the long wick  203 C. An isolation plate  205  made of a metal or nonmetal sheet is placed in between the elongated grooves  201 B and the long wick  203 C except for a space  300  arranged for the vapor to enter the grooves  201 B. In this embodiment, the isolation plate  205  can alternatively be made of wire mesh or wire cloth so that a part of the condensed liquid collected in the grooves  201 C can enter the wick  203 C directly without flowing through the conveying slot  204   
         [0064]      FIG. 26  shows a twenty-first embodiment of this invention. This embodiment shows that a V-shaped corrugated wire mesh  302  is used to replace the elongated grooves  201 B in the previous embodiment. The isolation plate  205  can alternatively be made pf wire mesh or wire cloth in this embodiment.  
         [0065]      FIG. 27  shows a twenty-second embodiment of this invention. This embodiment shows that the elongated wick  203 C as in  FIG. 25  can be replaced with a corrugated metal wire mesh  302 .  
         [0066]      FIG. 28  shows a twenty-third embodiment of this invention. This embodiment shows that a sheet of wire mesh  304  can be added above the corrugated metal mesh  302  to enhance capillary force, especially for the evaporator.  
         [0067]     While the preferred embodiment of the invention have been described, it will be apparent to those skilled in the art that various modifications may be made without departing from the spirit of the present invention. Such modifications are all within the scope of this invention.