KR20090090836A - Flat heat pipe - Google Patents

Abstract

A flat heat pipe having nano porous layer is provided to improve a heat transfer performance by increasing the heat transfer area. A flat heat pipe having nano porous layer is comprised of an evaporator(10), an insulating unit(20), and a condenser(30). The evaporator delivers heat from objects to actuating fluid(1) within the sealed pipe(3). The insulating unit forms a route. The route delivers gas generated with the evaporation process to the inside top of the sealed pipe. After the condenser liquefies the gas(2) with the condensation, the condenser delivers the heat from the actuating fluid of the sealed pipe to the sealed pipe outside. The condenser gets on the inner wall of the sealed pipe with the gravity and pressure difference and circulates the working fluid liquefying with evaporator. The actuating fluid is made of the filling fluid(1b) and metal nano particle(1a). The filling fluid functions as the heat transfer medium. The metal nano particle has the particle size of 1~50 nanometers. 0.0005~0.001vol.% of the metal nano particle is mixed in the filling fluid.

Description

Flat Heat Pipe with Nano Porous Layer

The present invention relates to a flat plate heat pipe having a nano-porous layer, and in particular, metal nanoparticles contained in the working fluid during the boiling of the working fluid are self-deposited in the evaporating part inside the heat pipe during the boiling process, and thus the surface inside the evaporating part. The present invention relates to a flat plate heat pipe having a nanoporous layer which forms a nanoporous layer and thereby significantly improves heat transfer performance.

In general, a heat pipe refers to a heat transfer principle (siphon action) or a device in which fluid flow is caused by a density difference of a fluid formed due to thermal imbalance such as evaporation and temperature difference.

The heat pipe is operated by natural convection without a separate power supply by a mechanical element such as a pump, and at present, this is a heat fade in which product performance is deteriorated due to a temperature rise of a heat exchanger or a cooling device of an electronic product. It has been applied to cooling heat sinks (Heat Sink) or medical equipment for reducing the fade (phenade), and the application range is continuously spreading.

However, the conventional flat plate heat pipes use water (distilled water), which is a traditional heat transfer medium, as a working fluid thereof, and thus, when applied to a cooling device of an electronic product, there is a problem that the heat transfer performance (heat conductivity) cannot be expected. In addition, in order to improve the heat transfer performance of the flat plate heat pipe at the current state of the art, it is necessary to use a variety of working fluids, or structural optimization design that greatly increases the heat transfer area of the evaporator and the condenser, so that the production There was a difficulty.

The present invention has been made to solve the above-mentioned problems, the object of the present invention is to inject a working fluid consisting of ultra-fine metal nanoparticles mixed in a filling fluid in a sealed flat plate tube, the filling During the boiling of the fluid, the metal nanoparticles are naturally deposited on the inner surface of the evaporator, thereby significantly improving heat transfer performance without considering an optimized design such as a plate structure. The present invention provides a flat heat pipe having a nano porous layer.

The flat heat pipe having the nanoporous layer according to the present invention for achieving the above object is filled with a working fluid in a metal hermetic tube forming a flat-type structure sealed in a vacuum state, so that the flow and gravity of the working fluid It forms a vertical heat transfer structure that heats the heat generated from any heat exchange object by the action to the outside, and acts in the sealed tube from the heat exchange object as a contact portion that endothermic reaction from the heat exchange object disposed on the bottom outside on the closed tube. As an evaporation unit for heat transfer to the fluid, a heat insulation unit for forming a path for transferring the gas generated by the evaporation process from the evaporation unit to the upper portion of the hermetic tube, and a contact portion for exothermic reaction on the upper side of the hermetic tube The gas delivered to the upper part through the heat insulating part is liquefied by the condensation process to the working fluid in the closed tube. In the flat heat pipe having a nano-porous layer constituting a condensation unit for heat transfer to the outside of the sealed tube and the liquefied working fluid is circulated to the evaporator by the gravity and pressure difference, the liquid The working fluid is characterized in that it consists of a filling fluid that functions as a heat transfer medium and metal nanoparticles having a particle size of 1-50 nm that is incorporated into the filling fluid by about 0.0005-0.001% by volume.

The filling fluid is preferably water.

It is preferable that the said metal material nanoparticle is any one chosen from gold, silver, and copper.

The flat heat pipe having the nanoporous layer of the present invention has a structure in which ultra-fine metal nanoparticles are injected into the working fluid in a flat tube, so that the metal nanoparticles contained in the working fluid when the working fluid is boiling, All of them are deposited to form a nanoporous layer, and only distilled water remains inside to function as a working fluid, thereby increasing the amount of bubble nuclei through the formation of the nanoporous layer without considering an optimized design such as a tube structure through an increase in heat transfer area. As a result, the heat transfer performance of the device can be remarkably improved, and when it is applied to cooling or heat exchanger devices such as various electronic products such as semiconductors and computer devices, the performance of the device can be improved, which is very useful.

Hereinafter, a planar heat pipe having a nanoporous layer according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 conceptually shows a flat heat pipe having a nanoporous layer according to the present invention.

In the planar heat pipe having the nanoporous layer according to the present invention, as shown in FIG. 1, the working fluid 1 as a heat transfer medium is filled in a vacuum in a sealed tube 3 of a metal material having good thermal conductivity. It achieves the structure sealed with. The closed tube 3 has a round flat plate shape.

The closed tube 3 is a heat insulating part 20 connecting the evaporator 10 and the condensation unit 30 with the evaporator 10 which is the bottom surface, the condenser 30 which is the upper surface according to the process of the heat transfer reaction. ).

The evaporation unit 10 is a contact portion for endothermic reaction from the heat exchange object 4 disposed outside the bottom bottom surface of the sealed tube 3, and the working fluid 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 part of the closed tube 3. This corresponds to the part forming the path through which the working fluid (1) can be heat convection. At this time, in the process of tropical flow from the evaporator 10 to the condensation unit 30, the working fluid 1 is 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. The heat transfer from the working fluid (1) to the outside of the closed tube (3) and the liquefied working fluid (1) rides on the inner wall of the closed tube (3) by gravity (G) and the pressure difference, the evaporator (10) It flows down and circulates to perform heat transfer continuously. In the condensation process by the condensation unit 30, since the liquid phase changes into liquid, the working fluid 1 is circulated while maintaining the two-phase state together with the evaporation process in the evaporation unit 10.

On the other hand, the working fluid 1 used in the present invention is filled in the heat pipe and functions as a heat transfer medium while circulating flow in two phases of gas and liquid between the evaporator 10 and the condenser 30. Filling fluid (1b) and the metal material nanoparticles (1a) having a particle size of 1-50 nm to be mixed in the fill fluid (1b) by about 0.0005-0.001% by volume.

As the filling fluid 1b, water (distilled water, 1b), which is a conventional heat transfer fluid, may be used. In addition, alcohol, an organic solvent, or the like may be used.

Gold, silver, or copper may be used as the metal nanoparticle 1a, and when a filling fluid, that is, a heat transfer fluid, that is, water 1b is absorbed from the outside of the heat pipe, that is, from the heat exchange object 4 to evaporate. As a structural characteristic that cannot be evaporated, it is deposited on the surface of the evaporation part which cannot be evaporated with the water 1b and the water 1b is boiled, and the metal material contained in the working fluid 1 as shown in FIG. 2. The nanoparticles 1a are continuously deposited on the surface of the evaporation portion of the lower portion of the nanoparticle 1a while continuously boiling, thereby forming the nanoporous layer 5, and finally only water (distilled water, 1b) is used. It functions as a working fluid.

Figure 3 is a photograph of the surface of the nano-porous layer formed on the flat heat pipe having a nano-porous layer according to the present invention, the working fluid according to the present invention, that is, the working fluid containing the metal nanoparticles boiling in the boiling process Afterwards, the surface shape of the nanoporous layer formed on the evaporation part is shown. As can be seen in Figure 3, the inner surface of the evaporator can be seen that the nano-porous layer 5 having pores formed by depositing fine metal nanoparticles (1a, the photo is silver nanoparticles) is formed.

For reference, the correlation between the increase in the amount of bubble nucleation due to boiling heat transfer and nuclear boiling on the surface and the improvement of heat transfer performance will be explained based on the general theory.

n " = N _c (1-cos θ ) ( T _w - T _sat ) ---------- (1)

Since the role of bubbles in boiling heat transfer plays a role of transferring heat at the surface, an increase in the amount of bubble generation leads to an improvement in heat transfer performance. In Equation (1), n " is the amount of bubble nuclei, N _c is the space for generating bubbles, that is, the number of bubble nuclei. Θ is the bubble contact angle of the surface, T _w is the surface temperature, and T _sat is the Saturation temperature. As can be seen in Eq. (1), the increase of N _c , that is, the increase of nucleation space, that is, the increase of small nanoporous layer, leads to the increase of n " (bubble nucleation) and the formation of nanoporous layer. As the pore size of the surface decreases, the contact angle θ increases, which also increases the n "

Therefore, the flat heat pipe having the nanoporous layer 5 of the present invention is formed by forming a nanoporous layer by self-deposition of the metal nanoparticles contained in the working fluid and increasing the amount of bubbles according to the present invention. Compared to the device, it can contribute greatly to improving heat transfer performance and heat transfer thresholds.

는 발열부와 냉각부의 온도차이로 온도차가 크면 열전달이 일어나지 않기에 온도만 상승하는 것이고, 열전달이 빨리 일어날수록 열이 방출되어 온도차는 떨어지게 되며, 가로축은 Q(W)는 히트파이프 밑면 증발부에 공급하는 열량{보통, 와트(Watt)단위로 정의함}을 의미한다. Figure 4 is a graph for comparing the heat transfer effect of the flat heat pipe having a nano-porous layer according to the present invention, Figure 4 (A) is a heat transfer of a heat pipe using only distilled water as a working fluid without any metal nanoparticles 4B shows the nanoporous layer 5 in the evaporation section by the working fluid 1 containing the metal nanoparticles (silver nanoparticles) according to the present invention, and again the 4 is a graph showing a heat transfer effect when the heat transfer performance experiment is performed by putting distilled water 1b therein, and FIG. 4C is a metal nanoparticle (silver nanoparticle) injected into the heat pipe in the present invention. The result shows the heat transfer effect of the working fluid higher than the concentration. In the graph above,

Is a temperature difference between the heat generating part and the cooling part, so that only the temperature rises because no heat transfer occurs, and as the heat transfer occurs, heat is released and the temperature difference decreases, and the horizontal axis is Q (W) at the bottom of the heat pipe. The amount of heat supplied (usually defined in watts).

Referring to Figure 4, the experiment on pure distilled water (1b) was shown that the heat transfer performance is significantly reduced as shown in the results of the graph (A), the graph of the experiment (B) according to the present invention is a graph (A) It was observed that the heat transfer effect is significantly improved than in the case, which can be seen that the heat transfer performance is improved by the formation of the nano-porous layer (5), which can be seen that the present invention has a significant effect on improving the heat transfer performance. In addition, the heat transfer effect of the experiment (C) may be expected to improve some of the heat transfer effect by the nano-porous layer formed by the metal nanoparticles, but some data show that the heat transfer effect is significantly reduced than that of the experiment (B) It was confirmed that the results were different depending on the degree of formation of the nanoporous layer by the metal nanoparticles in the evaporation part or the degree of aggregation of the metal nanoparticles in the form of agglomerates in the inside of the heat pipe.

On the other hand, in the working fluid used in the present invention, the ratio of the metal nanoparticles to water is preferably contained in the water in the metal nanoparticles having a particle size of 1-50 nm in a volume ratio of about 0.0005-0.001%.

In the case where the volume ratio of the metal nanoparticles is less than 0.0005%, the deposition degree of the metal nanoparticles 1a is generally decreased, resulting in a nonuniform distribution of the nanoporous layer 5 on the surface, which is a large improvement in heat transfer performance. It will not bring any improvement.

In addition, when the volume ratio of the metal nanoparticles of the working fluid containing the metal nanoparticles is 0.001% or more, due to the characteristics of the working fluid 1 containing the metal nanoparticles, the mean free path between the metal nanoparticles is reduced. The mutual access force between the particles increases, and thus the cohesion between particles increases, rather than the deposition of particles, metal nanoparticles grow due to coagulation and fail to deposit inside the heat pipe, which remains as a barrier to flow due to internal heat transfer. It will work.

In general, as the number of bubble nuclei increases during boiling, as in Equation (1), the amount of bubbles increases to help improve heat transfer performance. At high concentrations (0.001% or more), the amount of deposition increases, so that the thickness of the nanoporous layer 5 increases. It can be expected to increase, but rather the heat of the aggregates of the metal nanoparticles increases and the metal nanoparticles (1a) do not grow to be deposited so that only distilled water remains and remain as impurities, not a heat transfer medium, requiring smooth circulation of the working fluid. Due to the structure of the pipe, it acts as a blocker for fluid flow, which in turn acts as a heat transfer inhibitor. This is a common disadvantage that occurs due to aggregation of nanofluids during operation, which is aggravated with increasing concentrations.

In addition, the metal nanoparticles mixed in the working fluid in the present invention preferably has a size in the range of 1-50nm.

When the size of the metal nanoparticles exceeds 50nm, the attraction force between particles increases, which increases the possibility of forming agglomerates of particles at the same concentration. In addition, when the size of the metal nanoparticles is 1nm or less, it will be impossible to manufacture the metal nanoparticles due to the difficulty of dispersing the nanoparticles.

1 is a conceptual diagram showing the structure of a flat heat pipe having a nano porous layer according to the present invention,

2 is a partially enlarged view of FIG. 1;

3 is a photograph of the surface of the nano-porous layer formed on the flat heat pipe having a nano-porous layer according to the present invention,

Figure 4 is a graph for comparing the heat transfer effect of the flat heat pipe having a nano-porous layer according to the present invention.

<Description of Symbols for Major Parts of Drawings>

1: working fluid 1a: nanoparticle

1b: Filling fluid 2: Gas (vapor)

3: sealed tube 4: heat exchange object

5: nano porous layer 10: evaporation part (heat absorption part)

20: heat insulation part 30: condensation part (heat dissipation part)

G: gravity

Claims (3)

The working fluid is filled in the metal hermetic tube forming the flat plate-type structure sealed in a vacuum state to form an upper and lower heat transfer structure which heats heat generated from any heat exchange object to the outside by the tropical flow and gravity action of the working fluid. However, the evaporation unit for heat transfer from the heat exchange object to the working fluid in the hermetic tube as the end portion endothermic reaction from the heat exchange object disposed on the bottom outside on the closed tube, and the gas generated by the evaporation process from the evaporation unit A heat insulating part forming a path for delivery to the upper part of the closed tube and a contacting part exothermicly reacting to the outside of the upper part of the closed tube and liquefying the gas delivered to the upper part through the heat insulating part by a condensation process from the working fluid in the closed tube. In addition to the heat transfer to the outside of the closed tube, the liquefied working fluid In riding on the inner wall of the closing plate type heat pipe having a nano-porous layer constituting the condensation such that the circular portion evaporation, The working fluid comprises a nanoporous layer comprising a filling fluid that functions as a heat transfer medium and metal particles having particle sizes of 1-50 nm that are incorporated in the filling fluid by about 0.0005-0.001% by volume. Having a flat heat pipe. The method of claim 1, The filling fluid is a flat bottom pipe having a nano-porous layer, characterized in that the water. The method of claim 1, The metal nanoparticle is a flat bottom pipe having a nanoporous layer, characterized in that any one selected from gold, silver, copper.

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