Patent Application
20060207750
The present invention relates generally to a heat transfer apparatus, and more particularly to a heat pipe having composite capillary wick structure.
As a heat transfer apparatus, heat pipes can transfer heat rapidly and therefore are widely used in various fields for heat dissipation purposes. Fox example, in electronic field, heat pipes are commonly applied to transfer heat from heat-generating electronic components, such as central processing units (CPUs), to heat dissipating devices, such as heat sinks, to thereby remove the heat away. A conventional heat pipe generally includes a sealed casing made of thermally conductive material and a working fluid contained in the casing. The working fluid is employed to carry heat from one end of the casing, typically called as “evaporating section”, to the other end of the casing, typically called as “condensing section”. Specifically, when the evaporating section of a heat pipe is thermally attached to a heat-generating electronic component, the working fluid receives heat from the electronic component and evaporates. Then, the generated vapor moves towards the condensing section of the heat pipe under the vapor pressure gradient between the two sections. In the condensing section, the vapor is condensed to liquid state by releasing its latent heat to, for example, a heat sink attached to the condensing section. Thus, the heat is removed away from the electronic component.
In order to rapidly return the condensed liquid back from the condensing section to the evaporating section to start a next cycling of evaporation and condensation, a capillary wick is generally provided in an inner surface of the casing in order to accelerate the return of the liquid. In particular, the liquid is drawn back to the evaporating section by a capillary force developed by the capillary wick. The capillary wick may be a plurality of fine grooves defined in its lengthwise direction of the casing, a fine-mesh wick, or a layer of sintered metal or ceramic powders. However, the capillary force derived from each type of these wicks is generally different, and meanwhile, the flow resistance provided by each type of wick may also be different. The general rule is that larger an average capillary pore size a wick has, smaller a capillary force it develops and lower a flow resistance it provides.
In view of the above-mentioned disadvantage of the conventional heat pipe, there is a need for a heat pipe having a good heat transfer effect.
The present invention relates to a heat pipe. In one embodiment, the heat pipe includes a metal casing having an evaporating section and a condensing section. A first type of capillary wick is provided in the evaporating section and a second type of capillary wick is provided in the condensing section. The average capillary pore size of the second type of capillary wick is larger than that of the first type of capillary wick.
As compared with the conventional heat pipe, the heat pipe in accordance with the present invention incorporates a composite capillary wick structure and therefore has many advantages. The second type of capillary wick provides a low flow resistance so that the liquid condensed in a condensing end of the condensing section, i.e., an extremity of the condensing section remote from the evaporating section can more easily flow through the condensing section to reach the evaporating section. Meanwhile, the first type of capillary wick develops a large capillary force to draw the liquid from the condensing section to flow through the evaporating section and return its original position, i.e., an extremity of the evaporating section remote from the condensing section. Thus, the condensed liquid is brought back from the condensing section to the evaporating section in an accelerated manner, thereby increasing the total 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 the preferred embodiment when taken in conjunction with the accompanying drawings, in which:
The working fluid functions as a heat carrier for transferring heat from the evaporating section 70 to the condensing section 80. In particular, the working fluid contained in the evaporating section 70 absorbs heat from heat source and evaporates, and then carries the heat to the condensing section 80 in the form of vapor. Then, the vapor releases its heat to ambient environment and is condensed back to liquid state. The condensed liquid is then brought back to the evaporating section 70 via the composite capillary wick.
The composite capillary wick includes a plurality of fine grooves 241 (hereinafter referring to as “groove-type wick”) defined in the condensing and dielectric sections 80, 90 and a layer of porous sintered powders 242 (hereinafter referring to as “sintered-type wick”) formed in the evaporating section 70 by sintering process. The grooves 241 extend in the lengthwise direction of the casing 22 and may be formed by mechanical machining. The sintering process typically involves steps of filling metal or ceramic powders into the casing 22 by using a mandrel to control the thickness of the sintered-type wick and sintering the powders under a high temperature to thereby form the sintered-type wick with porosity.
In this embodiment, the composite capillary wick has different types of capillary wick disposed in different sections of the heat pipe 20. The groove-type wick 241 has a relatively large average capillary pore size and therefore provides a relatively low flow resistance to the condensed liquid to flow therethrough, and meanwhile, the sintered-type wick 242 has a relatively small average capillary pore size and accordingly develops a relatively large capillary force to the liquid. As a result, the groove-type wick 241 reduces the flow resistance the condensed liquid encounters when flowing through the condensing and dielectric sections 80, 90, and the sintered-type wick 242 has a large capillary force and therefore the liquid is then rapidly drawn back to the evaporating section 70 from the dielectric section 90 as the liquid reaches to a position adjacent to the evaporating section 70. The condensed liquid is returned back from the condensing section 80 in an accelerated manner. After the condensed liquid is returned back to the evaporating section 70, a next phase-change cycling will then begin. Thus, as a whole, the cycling of the working fluid is accelerated and therefore the total heat transfer capacity of the heat pipe 20 is enhanced. On the other hand, the small-sized sintered-type wick 242 has a large surface area for contacting with the working fluid, and meanwhile maintains a large contact surface between the casing 22 and the wick 242, thereby facilitating the transport of heat from the heat-generating component into the heat pipe 20.
Except for the sintered-type wick 242, some other types of capillary wick can also be provided in the evaporating section 70 so long as they have a relatively small average pore size. For example,
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 94108395 | Mar 2005 | TW | national |
