KR20050017632A - Heat Pipe using Nano Fluid as working fluid - Google Patents

Abstract

PURPOSE: A heat pipe using nanofluid is provided to cool electronic appliances such as semiconductors or computers, and to improve heat exchange efficiency by injecting actuating fluid including metal nanoparticles to the enclosed pipe and by transferring heat efficiently. CONSTITUTION: A wick(5) is installed along the inner wall of an enclosed thermal conductive metal pipe(3) to induce capillary tube pressure, and actuating fluid is charged in the enclosed pipe to transfer heat from a heat exchange material by convection of actuating fluid and capillary tube pressure. A heat pipe is composed of an evaporating unit(10) absorbing heat from the heat exchange material and transferring heat from the heat exchange material to the actuating fluid in the enclosed pipe, an insulation unit(20) transmitting gas in evaporating to the upper part of the enclosed pipe, and a condensing unit(30) radiating heat from the actuating fluid to the upper part of the enclosed pipe by condensing and liquefying gas and circulating the liquefied actuating fluid to the evaporating unit along the wick with the pressure difference of capillary tube. The actuating fluid is formed of nanofluid(1) including metal nanoparticles to increase the heat capacity of fluid and the heat transfer area.

Description

Heat Pipe Using Nano Fluid as working fluid

The present invention relates to a heat pipe using nano fluid, and in particular, the heat transfer performance by forming a closed tube structure by injecting a nano fluid containing nano metal particles as the working fluid to the principle of the conventional heat pipe. The present invention relates to a heat pipe using a nanofluid, which can remarkably improve and to be able to apply such a heat pipe with nanofluid as a cooling or heat exchanger such as an electronic product.

In general, a heat pipe refers to a heat transfer device in which fluid flow occurs due to capillary pressure and density difference of a fluid formed due to thermal imbalance such as evaporation and temperature difference. The heat pipe is a tube sealed with a working fluid such as water (distilled water) or alcohol and sealed in a vacuum state. The heat pipe is divided into a condensation part, an evaporation part, and a heat insulating part connecting them, and when heat is supplied toward the evaporation part. The working fluid is evaporated to a gas is moved to the condensation unit through the heat insulating part and condenses into liquid at that point to release heat and then circulate back to the evaporator by capillary action to transfer heat.

In addition, the inner wall of the heat pipe is provided with a wick (Wick) to promote the capillary pressure on the working fluid. The wick acts as a means for inducing a capillary phenomenon for smoothly moving the working fluid in the condensation part from the condensation part to the evaporation part. Therefore, the material selection and the structural design are very important factors that influence the performance of the heat pipe. .

In general, the wick should have a good permeability in order to increase its heat transfer factor so that the fluid is uniformly distributed in any part where heat is transferred to the evaporator. To satisfy this, the smaller the radius of the capillary is advantageous. . However, if the diameter of the wick is too small, a flow resistance will be caused, and therefore an appropriate thickness must be found by an experimental method. The wick is known to be produced in the shape of a mesh by woven fine copper wire.

As described above, the heat pipe is operated by natural convection even without a separate power supply by a mechanical element such as a pump, and at present, this is a heat exchanger or a cooling device for electronic products (heat that degrades product performance due to temperature rise. It is applied to various types of cooling sinks or medical equipments to reduce the fade (heat fade) phenomenon, and its application range is continuously spreading.

However, since the conventional heat pipe uses water (distilled water) or the like as its working fluid, there is a problem in that it cannot exhibit the heat transfer performance (heat conductivity) that is expected when it is applied as a cooling device for electronic products.

In addition, in order to improve the heat transfer performance of the heat pipe at the current state of the art, the design of the wick must be made by using various working fluids or by an experimental method that undergoes a lot of trial and error. The structural optimization design to greatly increase the heat transfer area has to be made, there was a difficulty in manufacturing accordingly.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and its object is to achieve a structure in which a nanofluid containing nanoparticles of very fine metal size having high thermal conductivity in a tube is injected as a working fluid. It is possible to significantly improve heat transfer performance without considering an optimized design such as a pipe structure, and to provide a heat pipe using nanofluids that can be variously applied to a cooling or heat exchanger such as an electronic product.

Heat pipe using a nanofluid according to the present invention for achieving the above object, the wick (Wick) is installed that can induce capillary pressure along the inner wall of the metal sealed tube excellent in thermal conductivity sealed in a vacuum state A predetermined working fluid is filled in the hermetic pipe to form a heat transfer structure for transferring heat generated from any heat exchange object to the outside by the action of tropical flow and capillary pressure of the working fluid to the outside. An evaporation unit for transferring heat from the heat exchange object to the working fluid in the hermetic tube from the heat exchange object, and a path for transferring gas generated by the evaporation process from the evaporation unit to the upper part of the hermetic tube. A heat insulating portion and a contact portion that exothermicly reacts to the outside of the upper portion of the hermetic pipe. The heat constituting the condensation unit to liquefy the gas delivered to the negative portion by the condensation process to heat the fluid from the working fluid in the closed tube to the outside of the closed tube, and to circulate the liquefied working fluid to the evaporator along the wick by capillary pressure difference. In the pipe, the working fluid, characterized in that the nanofluid consisting of a predetermined filling fluid containing a predetermined amount of extremely fine metal particles of nano-unit size to increase the heat transfer area and the heat capacity of the fluid.

Here, the nanoparticles are preferably made of any one metal selected from gold, silver, and copper having excellent thermal conductivity.

In addition, the size of the nanoparticles is preferably 100nm or less.

Hereinafter, a heat pipe using a nanofluid according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 conceptually illustrates a heat pipe using a nanofluid according to the present invention.

In the heat pipe using the nanofluid according to the present invention, as shown in the drawing, a wick 5 capable of inducing capillary pressure along the inner wall of the closed tube 3 of a metal material having good thermal conductivity is installed. The sealed tube 3 is filled with a nanofluid 1 as a heat transfer medium to form a sealed structure in a vacuum state. On the drawing, the shape of the closed tube 3 has a vertical rod-like structure, but is not limited thereto.

The closed tube 3 is divided into an evaporator 10, a condenser 30, and a heat insulating part 20 connecting the evaporator 10 and the condenser 30 according to a heat transfer reaction. .

The evaporation unit 10 is a contact portion for endothermic reaction from the heat exchange object 4 disposed on the bottom outside of the sealed tube 3, and the nanofluid 1 in the sealed tube 3 from the heat exchange object 4. Corresponds to the part that heats up with).

The heat insulating part 20 communicates the evaporator 10 and the condenser 30 so that the gas generated by the evaporation process from the evaporator 10 is condensed in the upper portion of the closed tube 3 ( 30) corresponds to the part forming the path through which the nanofluid 1 can be heat convection. At this time, in the process of tropical flow from the evaporator 10 to the condensation unit 30, the nanofluid 1 is phase-changed into a gas (vapor) (2).

The condensation unit 30 is a contact portion that exothermicly reacts to the outside of the upper side of the sealing tube 3, and liquefies the gas delivered to the upper portion through the heat insulating part 20 by the condensation process. In addition to the heat transfer from the nanofluid (1) to the outside of the closed tube (3), the liquefied nanofluid (1) flows along the wick (5) toward the evaporator (10) by the capillary pressure difference and circulates and heat transfer The action is carried out continuously. In the condensation process by the condensation unit 30, the phase change to liquid is performed, and the nanofluid 1 is circulated while maintaining the state of the two phases together with the evaporation process in the evaporation unit 10.

On the other hand, the nanofluid (1) is made of distilled water, that is, the filling fluid (1a) containing a small amount of metal nanoparticles (1b) to increase the heat transfer area and the heat capacity of the fluid. However, it is not necessary to use distilled water as the filling fluid (1a), it is clear that any liquid can be applied as long as it can activate the heat transfer performance.

In addition, said nanoparticle 1b means the particle whose physicochemical property changes with size. For example, in the case of gold particles, the melting point is 1,063 ° C. when the size is μm, but the melting point is reduced to 300 ° C. when the particle size is 5 nm (5 × 10 ⁻⁹ m). This is because as the ratio of the surface to mass of the particles increases, the surface chemical per unit mass and the surface energy of the particles also increase, changing the physicochemical properties. In other words, the smaller the particle size, the larger the surface area on the same volume basis, resulting in completely different properties from those of the conventional materials.

In the present invention, metal nanoparticles (1b) such as gold (Au), silver (Ag), copper (Cu), and the like, which have particularly good conductivity among various metals and have a particle size of about 1 to 100 nm, are applied.

The nanofluid 1 of the present invention is produced using the nanoparticles 1b. That is, the nanofluid 1 as a working fluid injected into the heat pipe of the present invention is prepared by mixing a small amount of the nanoparticles 1b with water (distilled water), which is a conventional heat transfer fluid.

The nanofluid (1), by increasing the heat transfer area and the heat capacity (Heat Capacity) of the fluid by the nanoparticles (1b) mixed therein to improve the effective conductivity of the fluid, the nanoparticles (1b) and the filling fluid ( Not only enhances the interaction and fusion in the flow area between 1a), but also enhances mixing and turbulent flowability of the filling fluid 1a, and inverses of the filling fluid 1a by diffusion of the nanoparticles 1b. It is possible to reduce the temperature gradient and the like.

These characteristics of the nanofluid (1) is clearly demonstrated through the performance comparison test results for the present invention and the conventional heat pipe. That is, according to the performance comparison test results, it was found that the thermal conductivity of the nanofluid 1 was about three times larger than that of the conventional working fluid, thereby significantly improving the heat transfer performance.

For reference, the correlation between the heat conductivity and the heat transfer coefficient for the fluid flowing in the pipe will be described based on the general theory.

Turbulent heat transfer coefficient (h) in the pipe,

----------------------- [One]

Is displayed. Where V is the flow rate and k is the thermal conductivity of the fluid.

According to the above formula [1], it can be seen that the heat transfer coefficient h can be changed depending on the flow rate V and the thermal conductivity k of the fluid. In particular, it can be seen that the heat transfer coefficient h is proportionally changed in accordance with the change in the thermal conductivity k, assuming that the flow rate V is kept constant. In the case of the present invention using the nanofluid 1 as the working fluid, it is known that the (convective) heat transfer coefficient increases by about 4.6 times when the thermal conductivity is increased by 10 times.

On the other hand, the velocity effect in the sealed tube 3 in the heat pipe using the conventional general working fluid is obtained by introducing a fanning friction factor into the turbulent pressure drop relation in the sealed tube 3 as follows. It can be expressed by the expression of pumping power.

----------------------- [2]

Where h _o is the initial heat transfer coefficient, P _o is the initial pump power, and P is the changed pump power. According to Equation [2], in the heat pipe using a general working fluid, the heat transfer coefficient h increases 1.9 times when the pump power P is increased 10 times.

That is, according to the calculation results according to the above formulas [1] and [2], in order to increase the heat transfer capacity by 2 times in the conventional heat pipe, the pump power (P) must be increased by 10 times, but the nanofluid (1) In the vertical bar type heat pipe of the present invention, the same effect can be obtained by merely increasing the thermal conductivity k by about three times.

Therefore, the heat pipe using nanofluid as in the present invention can greatly contribute to improving the heat transfer performance compared to the conventional device.

As described above, the heat pipe using the nanofluid of the present invention forms a structure in which a nanofluid containing nanoparticles of ultra-fine metals having high thermal conductivity in a hermetic tube is injected as a working fluid. It is possible to remarkably improve the heat transfer performance of the device by the tropical flow action by the nanofluid without considering the optimized design, and the performance of the device when it is applied to cooling or heat exchanger of various electronic products such as semiconductors or computer devices It is very useful because it can be improved.

Although the present invention has been described with reference to one embodiment shown in the accompanying drawings, which may be regarded as illustrative, and those skilled in the art will come up with various modifications and equivalent embodiments therefrom. As such, it should be considered that such equivalent embodiments are also included within the claims of the present invention. Therefore, the true scope of protection of the present invention should be determined only by the appended claims.

1 is a conceptual diagram showing the structure of a heat pipe to which a nanofluid according to the present invention is applied.

<Description of Symbols for Major Parts of Drawings>

One ; Nanofluid 1a; Filling fluid

1b; Nanoparticles 2; Gas (Steam)

3; Closed tube 4; Heat exchange object

5; Wick 10; Evaporator (Heat Absorption)

20; Thermal insulation 30; Condensation unit (heat dissipation unit)

Claims (3)

A wick which is capable of inducing capillary pressure is installed along the inner wall of the metal sealed tube having excellent thermal conductivity and sealed in a vacuum state, and a predetermined working fluid is filled in the sealed tube to prevent tropical and capillary pressure of the working fluid. A heat transfer structure that heats heat generated from an arbitrary heat exchange object by an action to the outside, and is a contact portion that endothermic reacts from a heat exchange object disposed on the bottom outside of the sealed tube, and the working fluid in the sealed tube from the heat exchange object. An evaporation unit that heats the furnace, a heat insulation unit that forms a path for transferring a gas generated by the evaporation process from the evaporation unit to an upper portion of the sealed tube, and a contact portion that exothermicly reacts to the outside of the upper side of the sealed tube. The gas delivered to the upper part through the heat insulating part is liquefied by the condensation process, and is pushed from the working fluid in the closed tube. In the heat pipe constituting the condensation unit for the heat transfer to the outside of the closed pipe and liquefied working fluid is circulated to the evaporation unit along the wick by the capillary pressure difference, The working fluid is a heat pipe using a nanofluid, characterized in that the nanofluid consisting of a predetermined fill fluid containing a predetermined amount of extremely fine metal particles having a nano unit size so as to increase a heat transfer area and a heat capacity of the fluid. The method of claim 1, The nanoparticles are heat pipes using nanofluids, characterized in that made of any one metal selected from gold, silver, and copper having excellent thermal conductivity. The method according to claim 1 or 2, The nanoparticles are heat pipes using nanofluids, the size of which is 100 nm or less.