US20070068655A1

US20070068655A1 - Heat transfer device

Info

Publication number: US20070068655A1
Application number: US11/411,582
Authority: US
Inventors: Mong-Tung Lin
Original assignee: Hon Hai Precision Industry Co Ltd
Current assignee: Hon Hai Precision Industry Co Ltd
Priority date: 2005-09-29
Filing date: 2006-04-26
Publication date: 2007-03-29
Also published as: CN1940453A

Abstract

A heat transfer device includes an elongated container having an inner wall; a wick structure arranged on the inner wall of the container; a working fluid received in the container, the working fluid containing a liquid medium and a plurality of magnetic particles dispersed in the liquid medium; and at least one alternating magnetic field generator configured for applying an alternating magnetic field to the magnetic particles.

Description

BACKGROUND

1. Technical Field
The present invention relates generally to devices for transferring heat, and more particularly, to a heat transfer device having a heat pipe.
2. Discussion of Related Art
With the development of electronic apparatus recent years, heat-generating components, such as semiconductors and integrated circuits, are assembled in high density on printed circuit boards, and large numbers of these printed circuit boards may be inserted into enclosures with small spacing between them. Therefore, heat generation per unit area of the electronic apparatus has been strikingly increased. To solve this, heat pipes are now widely used in electronic apparatuses due to their efficient heat transmission, simple structure, and their quick responsiveness to heat.
Referring to FIG. 1, a conventional heat pipe 10 generally includes a sealed pipe 11, a wick structure 12 and an amount of working fluid 13. The wick structure 12 is fixedly engaged with an inner wall (not labeled) of the pipe 11. The working fluid 13 is filled in the pipe 11 and soaks the wick 12. The heat pipe 10 includes an evaporator section 10 a, a condenser section 10 b, and an adiabatic section between the evaporation section 10 a and the condenser section 10 b. In use, the evaporator section 10 a is disposed in thermal communication with an external heat source, while the condenser section 10 b is disposed in thermal communication with an external heat sink. Thus, heat absorbed at the evaporator section 10 a can be transferred to the condenser section 10 b via the adiabatic section, and then discharged at the condenser section 10 b.
The heat pipe 10 operates as follows. Heat 15 generated by an external heat source, such as a CPU, is absorbed by the evaporator section 10 a of the heat pipe 10. Thus, the working fluid 13 is heated to a high temperature. When the temperature of the working fluid 13 reaches evaporating temperature, the working fluid 13 is evaporated, i.e., the working fluid 13 changes from a liquid state to a vaporous state. The evaporated working fluid 14 is driven to the condenser section 10 b by a vapor pressure difference between the evaporator section 10 a and the condenser section 10 b. At the condenser section 10 b, the heat carried in the evaporated working fluid 14 is discharged via an external heat sink (not shown) connected with the condenser section 10 b, and the evaporated working fluid 14 is thereby transformed back into liquid form. The working fluid 13 then flows back to the evaporator section 10 a by a capillary action of the wick structure 12. This process of transmitting heat continues as long as a temperature difference exists between the evaporator section 10 a and the condenser section 10 b, and as long as the heat 15 absorbed is sufficient to vaporize the working fluid 13 at the evaporator section 10 a.
In order to ensure the effective operation of the heat pipe 10, the working fluid 13 should generally have a high vaporization heat, good fluidity, steady chemical characteristics, and low boiling point.
Conventionally, pure liquids, such as water, ethanol or acetone, have been used as working fluids. However, for many applications, thermal conductivities of these working fluids are too low, heat transfer rates of these working fluids are too slow, and an operating efficiency of the heat pipe employing such working fluids is unsatisfactory.
In order to enhance the thermal conductivity of the working fluids, metal particles having a higher thermal conductivity are mixed into the conventional working fluids. Advantageously, the metal particles are made into nanometer-sized. However, when the particle sizes of the particles are scaled down to nanometer scale, the Van Der Waals force therebetween becomes significant. The Van Der Waals force tends act as an attractive force between the nano particles, causing them to clump together. The strong attraction of the Van Der Waals force makes the nano particles difficult to uniformly disperse in the fluids. Especially when the ambient temperature rises, collisions between the particles will be increased, causing the particles to aggregate. The heat pipe will then become clogged, and eventually become unworkable.
Thus, various surfactants have been developed to prevent the aggregation of particles. However, the surfactants may unavoidably create a plurality of vapor bubbles during the operation of the heat pipe, and the vapor bubbles may adversely affect the heat transmission.
What is needed, therefore, is a heat transfer device with good heat transfer capability, and good efficiency of thermal conductivity.

SUMMARY

In a preferred embodiment, a heat transfer device includes an elongated container having an inner wall; a wick structure arranged on the inner wall of the container; a working fluid received in the container, the working fluid containing a liquid medium and a plurality of magnetic particles dispersed in the liquid medium; and at least one alternating magnetic field generator configured for applying an alternating magnetic field to the magnetic particles.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the heat transfer device can be better understood with reference to the following drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present heat transfer device. Moreover, in the drawing, like reference numerals designate corresponding parts throughout the several views.
FIG. 1 is a schematic, cross-sectional view of a conventional heat pipe;
FIG. 2 is a schematic view of a heat transfer device in accordance with a first preferred embodiment of the invention;
FIG. 3 is a cut-away view of the heat transfer device in FIG. 2;
FIG. 4 is an explanatory view explaining the operation of the magnetic particles; and
FIG. 5 is a schematic, cut-away view of a heat transfer device in accordance with a second preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiment of the present heat transfer device will now be described in detail below and with reference to the drawings.
Referring to FIGS. 2 to 4, a heat transfer device 20 of the first preferred embodiment includes an elongated container 21, a wick structure 22, a working fluid 23 (denoted as an arrow in FIG. 3), and an alternating magnetic field generator 24.
The elongated container 21 includes an inner wall 211 for defining an inner space therein. The wick structure 22 is arranged on the inner wall 211 of the elongated container 21. The working fluid 23 is received in the inner space of container 21 and soaks the wick structure 22. The working fluid 23 contains a liquid medium 231 and a plurality of magnetic particles 232 dispersed therein. The alternating magnetic field generator 24 surrounds the elongated container 21 and generates an alternating magnetic field. The alternating magnetic field generator 24 includes an alternating current (AC) power source 240, and a coil of wire 241. The coil of wire 241 surrounds around the elongated container 21, and is electrically connected to the AC power source. The coil of wire 241 is wound evenly around the elongated container 21.
The elongated container 21 may be made from copper, aluminum, steel, carbon steel, stainless steel, iron, nickel, titanium, or any appropriate alloy of these materials. A cross-sectional shape of the elongated container 21 may be formed into a desired shape according to actual need. For example, the shape may be circular, square, triangular, trapezoidal, or semicircular. In the present preferred embodiment, the cross-sectional shape of the elongated container 21 is circular. A diameter of the elongated container 21 may be in the range from 2 to 200 millimeters, and a length of the elongated container 21 may be as little as a few several millimeters and as much as a hundred meters or more.
The wick structure 22 can be a groove, mesh, or porous sintered structure.
The liquid medium 231 is selected from the group consisting of water, ammoniated water, methanol, alcohol, acetone, and heptane. The magnetic particles 232 contain a material selected from the group consisting of iron, cobalt, nickel, and any alloy of these materials. The magnetic particles 232 may have an average particle size in the range from about 1 to 100 nanometers, and with a percentage by weight approximate to 0.1% to 3% of the working fluid 23. Preferably, the working fluid 23 may further contains a stabilizing agent. The stabilizing agent contains a material selected from the group consisting of citric acid, citrate, polyvinyl alcohol, or polyvinyl pyrrolidine.
In operation, when the AC power source 240 is supplied, an alternating current passes through the coil of wire 241, and an alternating magnetic field is generated. The magnetic particles 232 in the working fluid 23 are subjected to the alternating magnetic field and are driven to move along an alternating direction of the alternating magnetic field. Thus, the liquid medium 231 is also driven along with the magnetic particles 232. Once the magnetic particles 232 collide with the inner wall 211 of the elongated container 21, especially the evaporator section thereof, the magnetic particles 232 will bombard vapor bubbles 25 therewith (see FIG. 4), which produced due to heat absorbed by the evaporator section. Vapor bubbles 25 being bombarded will detach from the evaporator section, vaporize, and move to the condenser section in the vaporized form. In this way, the rate of heat transmission will be promoted.
Furthermore, the magnetic particles 232 driven by the alternating magnetic force move back and forth, with the liquid medium 231 moving along therewith. As such, flow of the working fluid 23 becomes turbulent, thus preventing the magnetic particles 232 from aggregating, and accordingly avoiding the clogging of the heat transfer device 20.
A magnetic strength of the alternating magnetic field can be controlled by adjusting the alternating current applied to the coil of wire 241 surrounding the elongated container 21. Accordingly, the magnetic force applied to the working fluid 23 can be adjusted with respect to the magnetic strength of the magnetic field.
FIG. 5 shows a heat transfer device 30 of a second preferred embodiment. The heat transfer device 30 is essentially similar to the heat transfer device 20 illustrated in the first preferred embodiment. The heat transfer device 30 includes an elongated container 31, a wick structure 32, a working fluid 33 (denoted as an arrow in FIG. 5), and two alternating magnetic field generators 34.
The elongated container 31 includes an inner wall 211 for defining an inner space therein. The wick structure 32 is arranged on the inner wall 211 of the main member 31. The working fluid 23 is received in the inner space of the elongated container 21 and is soaked into the wick 22. The working fluid 33 includes a liquid medium and a plurality of magnetic particles (not show) dispersed therein. The two alternating magnetic field generators 34 are symmetrically disposed around the main member 31 for applying an alternating magnetic field to the magnetic particles in the elongated container 31.
Each of the alternating magnetic field generator 34 includes a AC power source 340, a core 342, and a coil of wire 341 surrounding the core 342, the coil of wire 341 being electrically connected to the AC power source 340. The core 342 can be an iron core.
Alternatively, the heat transfer device 30 may include only one alternating magnetic field generator 34 disposed adjacent to the elongated container 31, along a direction substantially parallel to a longitudinal direction of the elongated container 31, or a plurality of alternating magnetic field generators 34 symmetrically disposed around the main member 31.
It is understood that the above-described embodiment are intended to illustrate rather than limit the invention. Variations may be made to the embodiments and methods without departing from the spirit of the invention. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

Claims

1. A heat transfer device comprising:

an elongated container having an inner wall;

a wick arranged on the inner wall of the container;

a working fluid received in the container, the working fluid containing a liquid medium and a plurality of magnetic particles dispersed in the liquid medium; and

at least one alternating magnetic field generator configured for applying an alternating magnetic field to the magnetic particles.

2. The heat transfer device as claimed in claim 1, wherein the liquid medium is selected from the group consisting of water, ammonia water, methanol, alcohol, acetone, and heptane.

3. The heat transfer device as claimed in claim 1, wherein the magnetic particles contain a material selected from the group consisting of iron, cobalt, nickel, and any appropriate alloy of these materials.

4. The heat transfer device as claimed in claim 1, wherein the magnetic particles have an average particle size in the range from 1 to 100 nanometers.

5. The heat transfer device as claimed in claim 1, wherein the magnetic particles have a percentage by weight in the range from 0.1% to 3% in the working fluid.

6. The heat transfer device as claimed in claim 1, wherein the working fluid further contains a stabilizing agent.

7. The heat transfer device as claimed in claim 6, wherein the stabilizing agent contains a material selected from the group consisting of citric acid, citrate, polyvinyl alcohol, and polyvinyl pyrrolidine.

8. The heat transfer device as claimed in claim 1, wherein the alternating magnetic field generator comprises an alternating current power source, and a coil of wire surrounding the container, the coil being electrically connected to the alternating current power source.

9. The heat transfer device as claimed in claim 1, wherein the alternating magnetic field generator comprises an alternating current power, an iron core, and a coil of wire surrounding the iron core, the coil being electrically connected to the current power source.

10. The heat transfer device as claimed in claim 1, wherein the at least one alternating magnetic field generator is disposed adjacent to the container, and is configured for applying the alternating magnetic field to the magnetic particles along a direction substantially parallel to a longitudinal direction of the container.

11. The heat transfer device as claimed in claim 1, wherein the at least one alternating magnetic field generator comprises a plurality of the alternating magnetic field generators, the alternating magnetic field generators are symmetrically disposed around the container.