LOOP HEAT PIPE

Abstract

A loop heat pipe for heat dissipating to a heat source including a first pipe, a first capillary structure, a second capillary structure, a second pipe, and a working fluid is provided. The first pipe has an evaporating portion adjacent to the heat source and a condensing portion. The first capillary structure is disposed on an inner surface of the first pipe and extends from the evaporating portion to the condensing portion. The second capillary structure is disposed on the inner surface and located within the evaporating portion. The second pipe is connected between the evaporating portion and the condensing portion. The working fluid disposed in the first pipe and the second pipe is capable of being transferred from the evaporating portion to the condensing portion via the second pipe, and is capable of being transferred from the condensing portion to the evaporating portion in the first.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 97123967, filed on Jun. 26, 2008. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a heat pipe, and more particularly, to a loop heat pipe.

2. Description of Related Art

Along with the rapid developments of computers, communication, information and the relevant industries in recent years, the electronic products and the electronic components are designed more following the light-slim-short-small tendency, which leads to gradually increasing the generated heat and the heat density therewithin. To solve the problems in this regard, a heat pipe device based on the phase transition principle has been broadly used.

FIG. 1 is a structure diagram of a conventional heat pipe. Referring to FIG. 1, a heat pipe 100 includes a closed metallic pipe 110, a capillary structure 120 disposed on the inner wall of the metallic pipe 110 and a working fluid disposed in the metallic pipe 110 and in the interstices of the capillary structure 120. The capillary structure 120 herein is fabricated by sintered body made of metal powder.

When a heated end of the metallic pipe 110 contacts a heat source, the heat of the heat source is transferred into the capillary structure 120 via the metallic pipe 110 so as to evaporate the working fluid in liquid state in the interstices of the capillary structure 120. At the time, the working fluid in liquid state in the interstices of the capillary structure 120 durably flows from a cooling end of the metallic pipe 110 to the heated end thereof due to capillarity, and the working fluid in gas state durably flows towards the cooling end of the metallic pipe 110 via the hollow portion of the metallic pipe 110.

Meanwhile, the heat of the working fluid in gas state located at the cooling end is dissipated out of the metallic pipe 110 via the pipe wall thereof. As a result, the working fluid in gas state located at the cooling end is gradually condensed in the interstices of the capillary structure 120. In this way, the heat pipe 100 dissipates the heat of the heat source through the phase transition and flowing of the working fluid.

Note that during the heat pipe 100 dissipates the heat of the heat source, the working fluid in gas state and the working fluid in liquid state respectively have a flowing direction opposite to each other. Therefore, the working fluid flowing in the metallic pipe 110 encounters a larger resistance. On the other hand, it is known that the heat pipe 100 disposed inside an electronic device is usually bent or flattened in the process thereof to fit the internal space of the electronic device, which likely destroys the capillary structure 120 and accordingly prevents the working fluid in liquid state from smoothly flowing in the interstices of the capillary structure 120 due to poor capillarity.

FIG. 2 is a structure diagram of a conventional loop heat pipe. Referring to FIG. 2, a loop heat pipe 200 includes an evaporator 210, a connection pipe 220 to form a closed loop together with the evaporator 210, a condenser 230 disposed on the connection pipe 220 and a working fluid suitable for flowing in the evaporator 210 and the connection pipe 220. The evaporator 210 includes an outer pipe 212, an inner pipe 214 disposed in the outer pipe 212 and having a plurality of capillary structures, a liquid channel 216 formed in the inner pipe and a vapour channel 218 formed between the outer pipe 212 and the inner pipe 214.

The working fluid in liquid state in the liquid channel 216 can be infiltrated into the vapour channel 218 via the capillary structures of the inner pipe 214 and converted into gas state by absorbing the heat energy of the heat source. Then, the working fluid in gas state flows into the connection pipe 220 via the vapour channel 218. After that, the working fluid in gas state flowing in the connection pipe 220 is cooled by a condenser 230, converted into liquid state and refluxes back to the evaporator 210. In this way, the working fluid functions to durably dissipate heat on the heat source.

In the loop heat pipe 200, the flowing directions of the working fluid in gas state and the working fluid in liquid state are almost the same, so that the working fluid in liquid state in the connection pipe 220 flows towards the evaporator 210 through the capillarity, and the working fluid in gas state during flowing due to a pressure difference is able to further push on the working fluid in liquid state for flowing. In comparison with the heat pipe 100, the working fluid in the loop heat pipe 200 encounters a less resistance during flowing.

Although the working fluid in the loop heat pipe 200 encounters a less resistance during flowing, however, the working fluid in gas state after passing the condenser 230 must be completely condensed into the working fluid in liquid state so as to be refluxed back to the evaporator 210 through the capillarity. And in this way, the loop heat pipe 200 is able to durably dissipate heat on the heat source through the phase transition and the flowing of the working fluid. In addition, in comparison with the heat pipe 100, it is more difficult to control the heat balance and the working temperature of the loop heat pipe 200.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a loop heat pipe with a better heat transfer efficiency and higher operation stability.

The present invention provides a loop heat pipe suited for heat dissipating to a heat source. The loop heat pipe includes a first pipe, a first capillary structure, a second capillary structure, a second pipe and a working fluid. The first pipe has an evaporating portion and a condensing portion, wherein the evaporating portion is adjacent to the heat source. The first capillary structure is disposed on an inner surface of the first pipe and extends from the evaporating portion to the condensing portion. The second capillary structure is disposed on the inner surface and located in the evaporating portion. The second pipe is connected between the evaporating portion and the condensing portion. The working fluid is disposed in the first pipe and the second pipe, wherein the working fluid is capable of being transferred from the evaporating portion to the condensing portion through the second pipe and is capable of being transferred from the condensing portion to the evaporating portion in the first pipe.

In an embodiment of the present invention, the above-mentioned first capillary structure is a plurality of grooves formed on the inner surface, and the above-mentioned second capillary structure is a sintering structure.

In an embodiment of the present invention, the above-mentioned first capillary structure and second capillary structure are formed as an integrative sintering structure.

In an embodiment of the present invention, the above-mentioned second capillary structure has an exhaust end and a reflux end, and the heat source and the second pipe are adjacent to the exhaust end.

In an embodiment of the present invention, the above-mentioned exhaust end is an open end and the above-mentioned reflux end is a close end.

In an embodiment of the present invention, the thickness of the above-mentioned exhaust end is less than the thickness of the reflux end.

In the loop heat pipe of the present invention, the flowing directions of the working fluid in liquid state and the working fluid in gas state are almost the same; therefore, the working fluid flowing in the first pipe and the second pipe encounters a less resistance. In addition, the working fluid in gas state after passing the condensing portion is not required to be completely converted into the working fluid in liquid state. In other words, the working fluid flowing from the condensing portion towards the evaporating portion in the first pipe can be in a liquid-gas coexistence status. Therefore, the heat balance and the working temperature of the invented loop heat pipe are easier to be controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a structure diagram of a conventional heat pipe.

FIG. 2 is a structure diagram of a conventional loop heat pipe.

FIG. 3 is a structure diagram of a loop heat pipe according to an embodiment of the present invention.

FIG. 4 is the sectional view along A-A line in FIG. 3.

FIG. 5 is the sectional view along B-B line in FIG. 3.

DESCRIPTION OF THE 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.

FIG. 3 is a structure diagram of a loop heat pipe according to an embodiment of the present invention. Referring to FIG. 3, a loop heat pipe 300 is suited for heat dissipating to a heat source, wherein the heat source is, for example, a central processing unit (CPU) or other electronic components. The loop heat pipe 300 includes a first pipe 310, a first capillary structure 320, a second capillary structure 330, a second pipe 340 and a working fluid.

Both opposite ends of the first pipe 310 are respectively an evaporating portion 312 and a condensing portion 314, wherein the evaporating portion 312 is adjacent to the heat source. The first capillary structure 320 is disposed on an inner surface of the first pipe 310 and extends from the evaporating portion 312 to the condensing portion 314. The second capillary structure 330 is disposed on the inner surface and located in the evaporating portion 312. The second pipe 340 is connected between the evaporating portion 312 and the condensing portion 314, and the working fluid is suited for flowing in the first pipe 310 and the second pipe 340.

In more detail, the heat produced by the heat source can be transferred into the first capillary structure 320 and the second capillary structure 330 of the evaporating portion 312 via the first pipe 310 so as to evaporate the working fluid in liquid state located in the first capillary structure 320 and the second capillary structure 330. Meanwhile, the working fluid in gas state located in the condensing portion 314 is cooled and then condensed into liquid on the inner surface of the first pipe 310. As a result, the working fluid in gas state located in the evaporating portion 312 would be gradually increased and the working fluid in gas state located in the condensing portion 314 would be gradually decreased. In this way, the working fluid in gas state is able to flow from the evaporating portion 312 to the condensing portion 314 through the second pipe 340 due to a pressure difference; meanwhile, the working fluid in liquid state is able to durably flow in the interstices of the first capillary structure 320 from the condensing portion 314 towards the evaporating portion 312 due to capillarity; and the loop heat pipe 300 of the present invention functions to durably dissipate heat on the heat source through the phase transition and the flowing of the working fluid.

Note that the working fluid in liquid state flows in the interstices of the first capillary structure 320 from the condensing portion 314 towards the evaporating portion 312 through capillarity. Therefore, the partial working fluid in gas state which is not yet condensed into liquid state in the condensing portion 314 can flow from the condensing portion 314 towards the evaporating portion 312 in a hollow portion 316 of the first pipe 310. In other words, even though the working fluid in gas state is not completely condensed into the working fluid in liquid state in the condensing portion 314, but the invented loop heat pipe 300 can still durably dissipate heat on the heat source; and thereby, in comparison with the conventional loop heat pipe 200, the heat balance and the working temperature of the invented loop heat pipe 300 is easier to be controlled.

Additionally, the working fluid in gas state and the working fluid in liquid state in the loop heat pipe 300 of the present invention have almost the same flowing directions; thus, the working fluid in liquid state is able to durably flow in the interstices of the first capillary structure 320 from the condensing portion 314 towards the evaporating portion 312 not only through capillarity, but also by the assistance of the working fluid in gas state which is able to push on the working fluid in liquid state for flowing when the working fluid in gas state flows in the hollow portion 316 of the first pipe 310 from the condensing portion 314 towards the evaporating portion 312. Accordingly, in comparison with the conventional heat pipe 100, the working fluid of the invented loop heat pipe 300 encounters a less resistance during flowing in the first pipe 310.

FIG. 4 is the sectional view along A-A line in FIG. 3 and FIG. 5 is the sectional view along B-B line in FIG. 3. Referring to FIGS. 3 and 4, in the embodiment, the first pipe 310 is, for example, a pipe with grooves, and the first capillary structure 320 is just the plurality of grooves formed on the inner surface of the first pipe 310. The second pipe 340 is, for example, a smooth pipe which enables the working fluid in gas state flowing in the second pipe 340 to have a better flowing efficiency. In other unshown embodiments, the first pipe 310 and the second pipe 340 can be formed as an integrative pipe with grooves so as to shorten the process of the loop heat pipe 300.

Referring to FIGS. 3 and 5, the second capillary structure 330 herein is, for example, a tubular sintering structure formed on the inner surface of the first pipe 310; especially, the second capillary structure 330 can be formed by sintering metal powder. In addition, the second capillary structure 330 can have an exhaust end E and a reflux end I, and the heat source is adjacent to the exhaust end E.

Note that the thickness of the exhaust end E is made less than the thickness of the reflux end I when forming the second capillary structure 330; that is to say the remaining inner diameter of the second capillary structure 330 at the exhaust end E is greater than the remaining inner diameter thereof at the reflux end I. In this way, the working fluid in gas state located in the evaporating portion 312 has a less resistance during passing the exhaust end E than that during passing the reflux end I. Therefore, when the working fluid in gas state located in the evaporating portion 312 is gradually increased, the working fluid in gas state flows almost towards the second pipe 340, which avoids the working fluid in gas state and the working fluid in liquid state in the first pipe 310 from flowing towards two directions opposite to each other.

On the other hand, the heat source in the embodiment is more close to the exhaust end E than the reflux end I so that the working fluid in liquid state at the exhaust end E has a greater evaporation rate than that at the reflux end I. When the remaining inner diameter of the second capillary structure 330 at the reflux end I is extremely small, the hole with the extremely small diameter at the reflux end I may be filled up with the working fluid in liquid state accumulated in the interstices of the second capillary structure 320, which further avoids the working fluid in gas state and the working fluid in liquid state in the first pipe 310 from flowing towards two directions opposite to each other.

In other unshown embodiments, the exhaust end E can be an open end and the reflux end I can be a close end, which forces the working fluid in gas state in the evaporating portion 312 flowing towards the second pipe 340 only.

Note that the first capillary structure 320 in the embodiment is a plurality of grooves formed on the inner surface of the first pipe 310; thus, even though a user makes the first pipe 310 bent or flattened in the process thereof, the working fluid in liquid state is still able to flow basically in the grooves through capillarity. In comparison with the conventional heat pipe 100, the loop heat pipe 300 of the present invention is more suitable to be re-processed to fit the assembly space.

In addition, in other unshown embodiments, where the loop heat pipe 300 is not bent or flattened in the processing thereof, the first capillary structure 320 and the second capillary structure 330 can be formed as an integrative sintering structure.

In summary, in the loop heat pipe of the present invention, the working fluid in liquid state and the working fluid in gas state have almost the same flowing directions, so that the working fluid in liquid state flows not only through capillarity, but also by the assistance of the flowing working fluid in gas state which is able to push on the working fluid in liquid state for flowing. Thus, in comparison with the heat pipe in the prior art, the working fluid in the loop heat pipe of the present invention encounters a less resistance in flowing.

Furthermore, when the working fluid passes through the condensing portion, the working fluid condensed into liquid state can flow through capillarity in the interstices of the first capillary structure from the condensing portion towards the evaporating portion, while the rest working fluid in gas state can flow in the hollow portion of the first pipe from the condensing portion towards the evaporating portion. Therefore, even though the working fluid in gas state is not yet completely condensed into liquid state in the condensing portion, the loop heat pipe of the present invention still can durably dissipate heat on the heat source; and in comparison with the conventional heat pipe, the heat balance and the working temperature of the invented loop heat pipe is easier to be controlled.

Moreover, the loop heat pipe of the present invention can take a structure with grooves to replace a part of the sintering structure, so that even though a user makes the first pipe bent or flattened in the process thereof, the working fluid in liquid state is able to flow basically in the grooves through capillarity. In comparison with the conventional heat pipe, the loop heat pipe of the present invention is more suitable to be re-processed to fit the assembly space.

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.

Claims

1. A loop heat pipe, suitable for heat dissipating to a heat source; the loop heat pipe comprising:

a first pipe, having an evaporating portion and a condensing portion, wherein the evaporating portion is adjacent to the heat source;

a first capillary structure, disposed on an inner surface of the first pipe and extending from the evaporating portion to the condensing portion;

a second capillary structure, disposed on the inner surface and located in the evaporating portion;

a second pipe, connected between the evaporating portion and the condensing portion; and

a working fluid, disposed in the first pipe and the second pipe, wherein the working fluid is capable of being transferred from the evaporating portion to the condensing portion via the second pipe and is capable of being transferred from the condensing portion to the evaporating portion in the first pipe.

2. The loop heat pipe according to claim 1, wherein the first capillary structure is a plurality of grooves formed on the inner surface, and the second capillary structure is a sintering structure.

3. The loop heat pipe according to claim 1, wherein the first capillary structure and the second capillary structure are formed as an integrative sintering structure.

4. The loop heat pipe according to claim 1, wherein the second capillary structure has an exhaust end and a reflux end, and the heat source and the second pipe are adjacent to the exhaust end.

5. The loop heat pipe according to claim 4, wherein the exhaust end is an open end and the reflux end is a close end.

6. The loop heat pipe according to claim 4, wherein the thickness of the exhaust end is less than the thickness of the reflux end.