Heat pipe with inner layer

[0001] 1. Field of the Invention

[0002] The present invention relates to heat pipes, and more particularly to a heat pipe which has an inner layer fixed to an inner surface of the heat pipe.

[0003] 2. Description of Related Art

[0004] Most natural substances exist in one of three states: solid, liquid, and gaseous. These three states are also called three phases: solid phase, liquid phase, and gaseous phase. Many substances can change phases repeatedly with an accompanying transfer of heat.

[0005] A heat pipe is a device utilizing phase change of working material to transfer heat from a vaporizing end of the pipe to a condensing end of the pipe. Commonly, a heat pipe connects between a heat-generating electronic device and a heat dissipation apparatus. An inner chamber of the heat pipe is substantially a vacuum, with liquid working material accommodated therein. In operation, the working material absorbs heat, becomes vaporized, and moves away from the vaporizing end. When the vaporized working material arrives at the condensing end, it condenses back to liquid form and releases heat. The condensed working material is then pumped back to the vaporizing end. This continuous cycle transfers large quantities of heat from the heat-generating electronic device.

[0006] However, a heat pipe is generally not inert to the working material. Chemical reaction occurs therebetween, particularly after prolonged use. The heat pipe is prone to dissolve and become completely damaged. In addition, gaseous by-products of such chemical reaction are generally uncondensable during normal operation of the heat pipe. The uncondensable gaseous by-products increase a pressure in the chamber of the heat pipe. This retards vaporization of the working material. Furthermore, the uncondensable gases are pushed to the condensing end of the heat pipe by vapor produced at the vaporizing end of the heat pipe. This decreases an available condensing surface area and adversely affects the heat transfer capability of the heat pipe. Over time, the uncondensable gases build up the pressure inside the chamber to a point where such pressure is equivalent to a maximum pressure at which the working material can be vaporized. At such point, the heat pipe can no longer function and must be discarded.

[0007] A further problem is that the working material tends to be partly absorbed by an inner surface of the heat pipe when it is in contact with such surface. This retards flow of the working material along such surface from the condensing end to the vaporizing end.

[0008] A still further problem is that a conventional heat pipe is made of copper. This makes the heat pipe unduly heavy, and increases manufacturing costs. Moreover, a layer of oxide is liable to be formed on an outer surface of the heat pipe. This adversely affects the heat transfer capability of the heat pipe.

[0009] It is strongly desired to provide an improved heat pipe which overcomes the above-mentioned numerous problems.

[0010] Accordingly, an object of the present invention is to provide a heat pipe which has an inner layer fixed to an inner surface of the heat pipe in order to attain optimal heat transfer capability and durability.

[0011] In order to achieve the object set out above, a heat pipe of the present invention comprises a main body, an inner layer, a chamber and working material. The main body is made of a metallic material having a high heat-transfer coefficient. The chamber is surrounded by the inner layer, and is substantially a vacuum. The working material is sealed in the chamber. The inner layer is fixed to an inner surface of the main body. The inner layer is inert to the working material, and isolates the working material from the main body. Furthermore, the working material readily globularizes when it is in contact with the inner layer.

[0012] Other objects, advantages and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

[0013] FIG. 1 is a cross-sectional side view of a heat pipe in accordance with the present invention;

[0014] FIG. 2 is a perspective view of a plurality of the heat pipes of FIG. 1 engaged with fins and a chassis to form a heat-pipe heat sink; and

[0015] FIG. 3 is a cross-sectional side view of the heat-pipe heat sink of FIG. 2, taken along line III-III thereof and showing movement of working material in the heat pipes.

[0016] Reference will now be made to the drawing figures to describe the present invention in detail.

[0017] FIG. 1 shows a heat pipe 10 of the present invention. FIG. 2 shows a plurality of the heat pipes 10 engaged with fins 20 and a chassis 30 to form a heat-pipe heat sink. The chassis 30 is attachable to a heat-generating electronic device (not shown) such as a central processing unit (CPU), for cooling the heat-generating electronic device.

[0018] The heat pipe 10 comprises a main body 12, an inner layer 16, a chamber 13, and working material 18. The chamber 13 is surrounded by the inner layer 16, and is substantially a vacuum. The working material 18 is sealed in the chamber 13. The working material 18 is a liquid at room temperature and pressure, has low viscosity, and is chemically stable. The working material 18 in liquid form has great heat absorption characteristics, and a low phase-change threshold temperature. Water is suitable working material 18. The main body 12 is made of metallic material having a high heat-transfer coefficient, such as aluminum or high carbon steel. The main body 12 has a low weight, and is resistant to physical and chemical deterioration. The inner layer 16 is a thin layer fixed to an inner surface of the main body 12 by electroplating, displacement, or other suitable means. The inner layer 16 has a high heat-transfer coefficient for quickly conducting heat to the main body 12. Accordingly, the inner layer 16 is made of copper, nickel or other suitable material. The inner layer 16 is inert to the working material 18. That is, no chemical reaction occurs between the inner layer 16 and the working material 18, even during operation of the heat pipe 10. Furthermore, the working material 18 readily globularizes when it is in contact with the inner layer 16. That is, the working material 18 is not absorbed by the inner layer 16 when it is in contact with the inner layer 16. This allows the working material 18 to readily flow along a surface of the inner layer 16. The inner layer 16 comprises a plurality of protrusions (not shown) that cooperatively form a wicking structure in the heat pipe 10, for facilitating recirculation of condensed working material 18.

[0019] Referring also to FIG. 3, vaporizing ends of the heat pipes 10 are fixed in the chassis 30 such that the heat pipes 10 are oriented perpendicular to the chassis 30. A plurality of the fins 20 is stacked at uniform intervals on the chassis 30. The fins 20 are parallel to each other and to the chassis 30, and abuttingly surround the heat pipes 10. The fins 20 provide ample surface area for dissipation of heat into surrounding air. The working material 18 is located at the condensing ends of the heat pipes 10.

[0020] During operation of each heat pipe 10, heat is transferred from the heat-generating electronic device to the chassis 30. The working material 18 absorbs heat from the chassis 30, and is vaporized. Therefore, a temperature of the chassis 30 is decreased. The vaporized working material 18 then travels to a distal condensing end of the heat pipe 10, whereat a slightly lower temperature causes the vaporized working material 18 to condense back to liquid form and release its latent heat of vaporization to the fins 20. The vaporized working material 18 is then pumped back to the vaporizing end by capillary forces of the wicking structure, and by the force of gravity. This continuous cycle of the working material 18 in the chamber 13 transfers large quantities of heat from the chassis 30 to the fins 20. Thus, reliable heat transfer from the heat-generating electronic device is achieved.

[0021] In the present invention, the inner layer 16 is fixed to the inner surface of the main body 12 to isolate the working material 18 from the main body 12. The inner layer 16 is inert to the working material 18. No chemical reaction can occur between the working material 18 and the main body 12. This protects the main body 12 from deterioration, even after prolonged operation of the heat pipe 10. Because no chemical reaction occurs, no uncondensable gaseous by-products are produced. Vaporized working material 18 can freely condense back to liquid form. A maximum condensing surface is utilized in the chamber 13, and pressure in the chamber 13 is maintained at a low level substantially that of a vacuum. Vaporization of the liquid working material 18 can readily take place. In addition, because the working material 18 readily globularizes when it is in contact with the inner layer 16, condensed working material readily flows along the surface of the inner layer 16 from the condensing end of the heat pipe 10 to the vaporizing end thereof. Accordingly, the heat pipe 10 can maintain great heat transfer capability even after prolonged use. Furthermore, the main body 12 has low weight, and is resistant to physical and chemical deterioration. The main body 12 provides more advantage compared with typical heat pipes made of copper.

[0022] 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.