US20070240852A1 - Heat pipe with heat reservoirs at both evaporating and condensing sections thereof - Google Patents

Abstract

A heat pipe includes a hollow metal casing (10). The casing has an evaporating section (C) and a condensing section (A) at opposite ends thereof, and an adiabatic section (B) located between the evaporating section and the condensing section. A capillary wick structure (12) is arranged at an inner surface of the hollow metal casing. Two sealed heat reservoirs (20, 21) are respectively mounted on the evaporating and condensing sections of the heat pipe for increasing heat absorbing and dissipation areas of the heat pipe.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is related to co-pending U.S. patent application Ser. No. 11/309,309, entitled “HEAT PIPE”, filed on Jul. 25, 2006, and co-pending U.S. patent application Ser. No. 11/309,312, entitled “HEAT PIPE” and filed on Jul. 25, 2006. The present application and the co-pending applications are assigned to the same assignee. The disclosures of the above-identified co-pending applications are incorporated herein by reference.
1. FIELD OF THE INVENTION
• The present invention relates generally to a heat pipe as heat transfer/dissipating device, and more particularly to a heat pipe which has two heat reservoirs disposed around evaporating and condensing sections of the heat pipe, for quickly absorbing and dissipating heat from an electronic component such as a central processing unit (CPU) to increase the maximum heat transfer capacity and reduce the temperature differential across the length of the heat pipe.
2. DESCRIPTION OF RELATED ART
• It is well known that a heat pipe is essentially a vacuum-sealed pipe with a porous wick structure provided on an inner face of the pipe, and the pipe is filled with at least a phase changeable working media employed to carry heat. Generally, according to the direction from which heat is input or output, the heat pipe has three sections, an evaporating section, a condensing section, and an adiabatic section between the evaporating section and the condensing section.
• In use, the heat pipe transfers heat from one place to another place mainly through phase change of the working media taking place therein. Generally, the working media is a liquid such as alcohol, water and the like. When the working media in the evaporating section of the heat pipe is heated up, it evaporates, and a pressure difference is thus produced between the evaporating section and the condensing section in the heat pipe. As a result vapor with high enthalpy flows to the condensing section and condenses there. Then the condensed liquid reflows to the evaporating section along the wick structure. This evaporating/condensing cycle continues in the heat pipe; consequently, heat can be continuously transferred from the evaporating section to the condensing section. Due to the continual phase change of the working media, the evaporating section is kept at or near the same temperature as the condensing section of the heat pipe.
• However, during the phase change of the working media, the resultant vapor and the condensed liquid flows along two opposing directions, which reduces the speed of the condensed liquid in returning back to the evaporating section and therefore limits the maximum heat transfer capacity (Qmax) of the heat pipe. At the same time, the condensing section has a relatively small heat dissipating area. As a result, a heat pipe often suffers dry-out problems at the evaporating section as the condensed liquid cannot be quickly sent back to the evaporating section of the heat pipe. Furthermore, the heat pipe has a high ratio of length to radius so that the heat may be dissipated during transmission of the vapor and a part of the vapor may change into condensed liquid mixed in the vapor to block transfer of the vapor. Thus, thermal resistance of the heat pipe is accordingly increased and the maximum heat transfer capacity of the heat pipe is reduced. In addition, the wick structure of the heat pipe has a uniform thickness and a vapor channel of uniform dimension for passage of the vapor so that speed of the vapor transferring from the evaporating section to the condensing section is reduced, and the temperature difference (ΔT) between the evaporating section and the condensing section is increased as a result.
• A conventional method for increasing the maximum heat transfer capacity of the heat pipe consists of increasing the total thickness of the wick structure of the heat pipe to increase the quantity of the working media contained in the wick structure. However, by this method, the response time of the heat pipe for the working media at the evaporating section to become vapor is slowed and the temperature difference between the evaporating section and the condensing section is increased accordingly.
• A conventional method for reducing the temperature difference between the evaporating section and the condensing section is reducing the total thickness of the wick structure of the heat pipe to reduce the quantity of the working media contained in the wick structure. However, by this method, the maximum heat transfer capacity of the heat pipe is reduced accordingly.
• Therefore, it is desirable to provide a heat pipe which can simultaneously increase the maximum heat transfer capacity and reduce the temperature differential across the length of the heat pipe.
SUMMARY OF THE INVENTION
• The present invention relates to a heat pipe. A heat pipe includes a hollow metal casing. The casing has an evaporating section and a condensing section at respective opposite ends thereof, and an adiabatic section located between the evaporating section and the condensing section. A capillary wick structure is arranged at an inner surface of the hollow metal casing. Two sealed heat reservoirs are respectively mounted on the evaporating and condensing sections of the heat pipe for increasing heat dissipation area. The heat pipe is configured so as to reduce heat resistance thereof and enhance the maximum heat transfer capacity of the heat pipe.
• 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 THE DRAWINGS
• Many aspects of the present device can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present device. Moreover, in the drawings like reference numerals designate corresponding parts throughout the several views.
• FIG. 1 is a longitudinally cross-sectional view of a heat pipe in accordance with a first embodiment of the present invention;
• FIG. 2 is a transversely cross-sectional view taken along lines A-A ofFIG. 1;
• FIG. 3 is a transversely cross-sectional view of a heat pipe in accordance with a second embodiment of the present invention;
• FIG. 4 is a transversely cross-sectional view of a heat pipe in accordance with a third embodiment of the present invention;
• FIG. 5 is a transversely cross-sectional view of a heat pipe in accordance with a fourth embodiment of the present invention;
• FIG. 6 is a transversely cross-sectional view of a heat pipe in accordance with a fifth embodiment of the present invention;
• FIG. 7 is a longitudinally cross-sectional view of a heat pipe in accordance with a sixth embodiment of the present invention;
• FIG. 8 is a longitudinally cross-sectional view of a heat pipe in accordance with a seventh embodiment of the present invention; and
• FIG. 9 is a longitudinally cross-sectional view of a heat pipe in accordance with an eighth embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
• FIGS. 1 and 2 show a heat pipe in accordance with one embodiment of the present invention. The heat pipe has a cylindrical configuration and includes ametal casing10 made of highly thermally conductive materials such as copper or copper alloys, a first working fluid (not shown) contained in thecasing10 and a firstcapillary wick structure12 arranged in an inner surface of thecasing10. Thecasing10 includes an evaporating section C at one end, a condensing section A at the other end and an adiabatic section B arranged between the evaporating section C and the condensing section A. Sealed first andsecond heat reservoirs20,21 are mounted on the evaporating and condensing sections C, A respectively. Avapor channel14 is defined along an axial direction of the heat pipe and is located at a center of thecasing10. Thevapor channel14 is surrounded by an inner surface of the firstcapillary wick structure12 so as to guide vapor to flow therein.
• The first andsecond heat reservoirs20,21 each have a hollow cylindrical configuration and is made of highly thermally conductive materials such as aluminum or copper or copper alloys. Thefirst heat reservoir20 has a bigger radius than that of evaporating section C of the heat pipe, whilst thesecond heat reservoir21 has a bigger radius than that of condensing section A of the heat pipe. The evaporating and condensing sections C, A of the heat pipe respectively extends through the first andsecond heat reservoirs20,21, thereby positioning the first andsecond heat reservoirs20,21 thereon. The first andsecond heat reservoirs20,21 each include anouter wall211 and a pair oflateral sides221 connecting two opposite ends of theouter wall211 with the corresponding evaporating and condensing sections C, A of the heat pipe to form a sealed chamber. A secondcapillary wick structure22 is disposed on an inner surface of thefirst heat reservoir20 and an outer surface of the evaporating section C, whilst another secondcapillary wick structure22 is disposed on an inner surface of thesecond heat reservoir21 and an outer surface of the condensing section A. Second working fluids (not shown) are respectively contained in the first andsecond heat reservoirs20,21. Twovapor channels24 are respectively defined along axial directions of the first andsecond heat reservoirs20,21 and located in a center of the corresponding first andsecond heat reservoirs20,21 to guide vapor to flow therein. The first andsecond heat reservoirs20,21 are vacuum-exhausted to make the second working fluid easy to evaporate.
• As thefirst heat reservoir20 at the evaporating section C of the heat pipe absorbs heat from a heat source (not shown), the second working fluid contained in thefirst heat reservoir20 absorbs the heat and evaporates, and simultaneously transfers the heat to the evaporating section C of the heat pipe. The evaporating section C of the heat pipe absorbs the heat from thefirst heat reservoir20, and the first working fluid contained in the evaporating section C absorbs the heat and evaporates, and then carries the heat to the condensing section A in the form of vapor. Then, the heat is carried by the first working fluid in the form of vapor to the condensing section A where the heat is transferred to thesecond heat reservoir21. The second working fluid contained in thesecond heat reservoir21 absorbs the heat and evaporates. The first andsecond heat reservoirs20,21 have so big heat dissipating areas that the heat pipe can quickly and largely absorb and dissipate heat, thereby reducing the heat resistance of the heat pipe and enhancing the maximum heat transfer capacity of the heat pipe. The temperature differential across the length of the heat pipe is therefore reduced.
• Alternatively, there may be a cylinder inner wall (not shown) formed in each of the first andsecond heat reservoirs20,21. The oppositelateral sides221 of thefirst heat reservoir20 interconnects theouter wall211 with the inner wall thereof to form a sealed chamber, whilst the oppositelateral sides221 of thesecond heat reservoir21 interconnects theouter wall211 with the inner wall thereof to form another sealed chamber. The evaporating and condensing sections C, A of the heat pipe are respectively inserted into the first andsecond heat reservoirs20,21, and interferentially engage with the inner walls of the first andsecond heat reservoirs20,21, whereby the first andsecond heat reservoirs20,21 are positioned on evaporating and condensing sections C, A of the heat pipe. Alternatively, the first andsecond heat reservoirs20,21 are positioned on the evaporating and condensing sections C, A of the heat pipe by metallurgical or adhesive means.
• FIG. 3 illustrates a heat pipe according to a second embodiment of the present invention. The heat pipe of the second embodiment is similar to that of the previous first embodiment. However, twoheat reservoirs201 with square-shaped cross sections replace the first andsecond heat reservoirs20,21 of the first embodiment. That is, the cross section of each of theheat reservoirs201 has a circular-shaped inner wall (outer wall of the casing101) and a square-shapedouter wall212.
• FIG. 4 illustrates a heat pipe according to a third embodiment of the present invention. In this embodiment, the heat pipe has a similar structure to the heat pipe of the previous first embodiment. However, acasing102 with a square-shaped cross section replaces thecasing10 of the previous first embodiment. That is, the cross section of each of theheat reservoirs202 has a square-shaped inner wall (outer wall of the casing102) and a circular-shapedouter wall213.
• FIG. 5 illustrates a heat pipe according to a fourth embodiment of the present invention. In this embodiment, the heat pipe has a similar structure to the heat pipe of the previous first embodiment. However, twoheat reservoirs203 with triangular-shaped cross sections replace the first andsecond heat reservoirs20,21 of the first embodiment. That is, the cross section of each of theheat reservoirs203 has a circular-shaped inner wall (outer wall of the casing103) and a triangular-shapedouter wall214.
• FIG. 6 illustrates a heat pipe according to a fifth embodiment of the present invention. In this embodiment, the heat pipe has a similar structure to the heat pipe of the previous third embodiment. However, twoheat reservoirs204 with square-shaped cross sections replace theheat reservoirs202 of the previous third embodiment. That is, the cross section of each of theheat reservoirs204 has a square-shaped inner wall (outer wall of the casing104) and a square-shapedouter wall215.
• FIG. 7 illustrates a heat pipe according to a sixth embodiment of the present invention. The heat pipe has a similar structure to the heat pipe of the above-mentioned embodiments. In this embodiment, a plurality offins26 is mounted on the outer wall of thesecond heat reservoir21ato increase the heat dissipating area of the heat pipe.
• FIG. 8 illustrates a heat pipe according to a seventh embodiment of the present invention. The heat pipe has a similar structure to the heat pipe of the first to fifth embodiments. In this embodiment, a sealedvacuum casing30, which has a bigger radius than that of the adiabatic section B of the heat pipe, is disposed around the adiabatic section B of the heat pipe. The adiabatic section B of the heat pipe is therefore with enhanced adiabatic effectiveness from surrounding environment, which reduces the heat dissipation during the transmission of the vapor. Accordingly, the heat resistance of the heat pipe is further reduced and the maximum heat transfer capacity of the heat pipe is enhanced. In addition, the sealedvacuum casing30 connects thefirst heat reservoir20 with thesecond heat reservoir21 and has a same cross section as the first andsecond heat reservoirs20,21.
• FIG. 9 illustrates a heat pipe according to an eighth embodiment of the present invention. The heat pipe has a similar structure to the heat pipe of the sixth embodiment. In this embodiment, a sealed vacuum casing30a, which has a bigger radius than that of the adiabatic section B of the heat pipe, is disposed around the adiabatic section B of the heat pipe, to insulate the adiabatic section B of the heat pipe from the surrounding environment.
• 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.

Claims (13)

1. A heat pipe comprising:

a hollow metal casing having an evaporating section for receiving heat and a condensing section for releasing the heat, and an adiabatic section located between the evaporating section and the condensing section;

a first working fluid contained in the metal casing;

a first capillary wick structure arranged at an inner surface of the hollow metal casing; and

two sealed heat reservoirs respectively mounted on the evaporating and condensing sections of the heat pipe for increasing heat absorbing and dissipation areas.

2. The heat pipe ofclaim 1, wherein the evaporating and condensing sections of the heat pipe are inserted into the heat reservoirs and engaged with the corresponding heat reservoirs.

3. The heat pipe ofclaim 1, wherein second capillary wick structures are arranged at inner surfaces of the heat reservoirs and corresponding outer surfaces of the evaporating and condensing sections of the heat pipe.

4. The heat pipe ofclaim 2, wherein a second working fluid is contained in the heat reservoir.

5. The heat pipe ofclaim 1, wherein each of the heat reservoirs comprises an outer wall spacing a distance from an outer surface of each of the evaporating and condensing sections and a pair of opposite lateral sides connected with two opposite ends of the outer wall.

6. The heat pipe ofclaim 5, wherein an inner wall is formed in each of the heat reservoirs, and the evaporating and condensing sections of the heat pipe are inserted into the heat reservoirs and engage with corresponding inner walls of the heat reservoirs.

7. The heat pipe ofclaim 1, wherein the heat pipe and at least one of the heat reservoirs have circular cross sections.

8. The heat pipe ofclaim 1, wherein the heat pipe has one of a circular and a square cross section, and at least one of the heat reservoirs has the other one of the circular and square cross section.

9. The heat pipe ofclaim 1, wherein the heat pipe has a circular cross section and at least one of the heat reservoirs has a triangular cross section.

10. The heat pipe ofclaim 1, wherein the heat pipe and at least one of the heat reservoirs have square cross sections.

11. The heat pipe ofclaim 1, wherein a plurality of fins are mounted on an outer surface of one of the heat reservoirs mounted on the condensing section.

12. The heat pipe ofclaim 1, wherein a vacuum casing is disposed on the adiabatic section of the heat pipe.

13. The heat pipe ofclaim 12, wherein a plurality of fins are mounted on an outer surface of one of the heat reservoirs mounted on the condensing section.

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