Microchannel heat pipe with parallel grooves for recycling coolant

Heat from a heat generating device such as 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 connection with 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 at least one of the sections to reduce friction in the liquid flow path.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to a heat pipe, in particular, a microchannel heat pipe used for heat dissipation for a central processing unit (CPU) or other electronic integrated circuit (IC) chips.

(2) Brief Description of Related Art

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 inFIG. 1. A cavity105is enclosed by a base metal100for a working liquid (not shown in the figure) to recycle. Heat sink pipes101are arranged on the top of the base metal100for heat dissipation. Heat transfer medium102is under the base metal100to contact with a CPU.

A two-phase vaporizable liquid resides within the cavity105and serves as the working fluid (the coolant) for the heat pipe. A wick103in the form of a mesh is disposed on the inner walls to form a recycling loop within cavity105to facilitate the flow of the working fluid within the cavity. The working liquid in the cavity105flows in a direction as shown in arrows inFIG. 1. Firstly the working liquid is absorbed in the bottom portion of the wick103. It evaporates when heat is transferred from the CPU and then condenses on the top portion of the wick103. Heat is further transferred upward to the heat sink pipes101. The condensed liquid absorbed in the top portion of the wick103is then moved to the lower portion of the wick103due to capillary action in the mesh of the wick103.

SUMMARY OF THE INVENTION

An object of this invention is to devise a coolant recycle mechanism with space passages as part of the recycling passage to decrease the friction during the coolant flowing. Another object of this invention is to devise a coolant recycle mechanism with parallel grooves as a part of the passage to decrease the friction during flowing of the working liquid. A further object of this invention is to devise a more effective heat dissipation mechanism.

The above objects can be achieved by using space passages, parallel grooves or a combination of both to be part of the passage for liquid flowing to reduce friction. By using space passages and/or parallel grooves, the friction is reduced and the capillary action effectively enhances the flow of the coolant.

DETAILED DESCRIPTION OF THE INVENTION

The principle of this invention is to use space passages or parallel grooves as part of the passage for a working liquid to flow within a cavity105in a heat pipe.FIG. 2shows the first embodiment of this invention. Cavity105is enclosed by a base metal100. Multiple sections are divided in the cavity105for the recycling of the working liquid. The working liquid moves in a direction following the arrows shown in the figure.

FIG. 3shows an enlarged plane view of the recycle mechanism in the cavity105ofFIG. 2. There are four sets of parallel grooves shown in this design. A first set of left parallel grooves201and a second set of left parallel grooves202arranged on the left of the wick203. A third set of right parallel grooves201and a fourth set of right parallel grooves202arranged on the right side of the wick203. The recycling principle for the left two set grooves201and202is exactly the same as that for the right-side two sets grooves201and202, and therefore only two left side grooves are described below.

Working liquid (not shown) is absorbed in the wick203. The wick203can be made of sintered copper (Cu) powder, sintered nickel (Ni) powder, or sintered stainless-steel powder. Alternatively, wick203can be made of single-layer or multi-layer of metal mesh (not shown) or metal cloth (not shown). When the heat pipe is attached to a heat generating unit such as a central process unit (CPU), the work liquid in the wick203is heated to evaporate and gives vapors upward as shown in the arrows. Part of the vapor condenses on the inner top surface within the cavity105, which is enclosed by the base metal100. Part of the vapor goes into a first set of parallel grooves201to condense. The condensed liquid is conveyed to a second set of parallel grooves202under the first set of parallel grooves201through a slot204. The conveying slot204is located at a common end of the two sets of grooves to connect the two grooves201and202. The wick203is located on the other end of the grooves202to form a recycle loop. The upward evaporation from the wick203results in a capillary pulling force to the working liquid in grooves202toward wick203to make a full cycle: liquid→vapor→cooling→liquid, following the arrows as shown inFIG. 3.

The following several figures show the recycle mechanism of this invention within the cavity105.

FIG. 4shows the explosive perspective view of the recycle mechanism ofFIG. 2. The parallel grooves201and202can be made separately before being connected together. Alternatively, the parallel grooves201and202can be also made integrally to be a single body by molding, extrusion, etching, cutting, or machining on a metal plate.

In order to insure the recycle to operate in a smooth loop, single way forward movement is desired for the first set of parallel grooves201which accommodates essentially vapor molecules. For this purpose, single-sided grooves are desired for the first set of parallel grooves201. However, for the second set of parallel grooves202where condensed liquid flows, either a single-sided grooves or a double-sided grooves works the equally well. Double-sided grooves can be made by a folded metal sheet (not shown). Single sided grooves202are shown inFIG. 4. They can be made by the way of molding, extrusion, etching, cutting, or machining on a metal plate.

In this embodiment, the grooves201and202are essentially independent of each other except being communicated by the slot204so that the liquid flowing in grooves202is not dragged by the vapor flow in the opposite direction.

Part of the vapor entering the first set of the parallel grooves201condenses to liquid, and is gathered in the corners of the triangular microchannels of the grooves201. A conveying slot204is placed on one end of the first set of parallel grooves201. 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 grooves201and202is illustrated with metal. However, nonmetal material such as silicon or plastics . . . etc. may also be used.

A second set of parallel grooves202is arranged under the first set of parallel grooves201. The conveying slot204is at the first end of the second set of parallel grooves202. The wick203is placed in the second end of the second set of parallel grooves and has a height no less than the height of the grooves202so as to generate a pulling force from grooves202toward the wick203when the working fluid evaporates from the wick203. A dividing plate205is used to separate the first set of parallel grooves201and the second set of parallel grooves202.

FIG. 5shows a second embodiment of this invention. This embodiment shows a vertical guiding plate207added above the wick203to bridge the wick203and the inner top surface of the base metal100within the cavity105. The guiding plate207allows part of the condensed liquid on the inner top surface to flow downward back to the wick203. The guiding plate207also serves as a strengthener against the inward pressure when the cavity105is evacuated.

FIG. 6shows a third embodiment of this invention. This embodiment shows an elongated grooves201B arranged over the top of the wick203.

FIG. 7shows a fourth embodiment of this invention. This embodiment shows that the first set of parallel grooves and the conveying slot204are integrated with the top part of the base metal100to form a top metal base201C. Parallel grooves2011and the conveying slot204can be fabricated by molding, cutting, scribing, or etching, etc. directly on the base metal100.

FIG. 8shows a fifth embodiment of this invention. Similar to the fourth embodiment ofFIG. 7, the second set of parallel grooves202and the conveying slot204can be integrated with the bottom part of the base metal100to form the bottom metal base201C. Parallel grooves2021and the conveying slot204can be fabricated by molding, cutting, scribing, or etching, etc. directly on the base metal100.

FIG. 9shows a sixth embodiment of this invention. This embodiment shows the wick203in the previous embodiments is replaced with a pin-array block203B. The spaces between the pins are used to absorb the working liquid by capillary attraction. These vertical spaces allow 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 wick203. This design shows better efficiency in liquid flow compared with the sintered-metal-powder or mesh wick203to enhance the cooling effectiveness.

FIG. 10shows a seventh embodiment of this invention. This embodiment shows a different shape of folded metal207B being used. A square folded metal207B is used in this embodiment, which differs from the V-shape folded metal207inFIG. 5. Other folded metals are also usable, such as spiral folding, S shaped folding, . . . etc., and are not exhaustive in this specification.

FIG. 11shows an eighth embodiment of this invention. This embodiment shows that a meshed metal207C is used as the guiding plate, which differs from the non-meshed guiding plate207B used inFIG. 10.

FIG. 12shows a ninth embodiment of this invention. This embodiment shows that this invention as shown inFIG. 3can be used in a vertical direction. Part of the vapor from the wick203condenses directly on the inner wall opposite to the wick203or enters the first set of bottom parallel grooves201and 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. With the combined capillary action of the wick203and of the parallel grooves202, the working liquid is pulled up back to the wick203.

Part of the vapor from the wick203goes up to the first set of top parallel groves201and condensed herein. Some of the condensed liquid may drop into the first set of bottom parallel grooves201. Some of the condensed liquid is driven upward by the vapor flow to enter the top conveying slot and then the second set of parallel grooves202, before it finally flows back to the wick203.

In order to enhance the capillary action to increase the pulling force to 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 grooves202are made smaller than those of the first set of parallel grooves201.

FIG. 13shows a ninth embodiment of this invention. This embodiment is a modified version ofFIG. 12. The first set of top parallel grooves201inFIG. 12is omitted and replaced with a space A. As the vapor from the wick203enters space A, part of it condenses on the inner wall of the metal base100. The condensed liquid either drops to the first set of bottom parallel grooves201or is driven upward by the vapor flow across the conveying slot204into the second set of top parallel grooves202. The liquid in the grooves202then flows back to the wick203by gravity in addition to the capillary action of the wick203.

FIG. 14shows a tenth embodiment of this invention. This embodiment is a modified version ofFIG. 12. The second set of top parallel grooves202inFIG. 12is omitted and replaced with a space B. The space B functions as a passage for the condensed liquid to flow back to the wick203by gravity in addition to the capillary action of the wick203.

FIG. 15shows an eleventh embodiment of this invention. This embodiment is a modified version ofFIG. 12. The first set of top parallel grooves201inFIG. 12is omitted and replaced with a space A; the second set of top parallel grooves202is omitted and replaced with a space B. The space B functions as a passage for the condensed liquid to flow back to the wick203by gravity in addition to the capillary action of the wick203.

FIG. 16shows a twelfth embodiment of this invention. This embodiment is a simplified version ofFIG. 3orFIG. 4. A single first set of parallel grooves201and a single second set of parallel grooves202is used. The recycle mechanism is exactly the same as described inFIG. 3orFIG. 4.

FIG. 17shows a thirteenth embodiment of this invention. This embodiment is a modified version ofFIG. 16. The first set of parallel grooves201inFIG. 16is omitted and replaced with a space A. As the vapor form the wick203enters space A, part of it condenses on the inner wall of the metal base100. The condensed liquid is driven by the vapor flow across the conveying slot204into the second set of parallel grooves202. The second set of parallel grooves202functions as a passage for the condensed liquid to flow back to the wick203by capillary action of the wick203.

FIG. 18shows a fourteenth embodiment of this invention. This embodiment is a modified version ofFIG. 16. The second set of parallel grooves202inFIG. 16is omitted and replaced with a space B. The space B functions as a passage for the condensed liquid to flow back to the wick203by capillary action of the wick203.

FIG. 19shows a fifteenth embodiment of this invention. This embodiment is a modified version ofFIG. 16. The first set of parallel grooves201inFIG. 16is omitted and replaced with a space A; the second set of parallel grooves202is omitted and replaced with a space B. As the vapor form the wick203enters space A, part of it condenses on the inner wall of the metal base100. The condensed liquid is driven by the vapor flow across the conveying slot204into the second set of parallel grooves202The space B functions as a passage for the condensed liquid to flow back to the wick203by the capillary action of the wick203.

FIG. 20shows a sixteenth embodiment of this invention. This embodiment is a modification to all the previous embodiments.FIG. 20shows a second wick204B inserted into the slot204to smooth the liquid flow. The capillary action within204B grabs the condensed liquid stronger than a slot204as shown in the previous embodiments. This design prevents the vapor from entering the second set of parallel grooves202and, therefore, leads to a smoother liquid flow.

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.