KR101403528B1 - Heating tube coated with carbon nano material and evaporator comprising the same - Google Patents

Abstract

Coating a composite powder composed of a carbon nanotube and a first metal powder on the surface of the heat transfer pipe by a heat transfer pipe coating method; And a sintering step of sintering the coated composite powder layer.

Description

[0001] The present invention relates to a carbon nanomaterial-coated heat transfer tube and an evaporator including the same,

The present invention relates to a carbon nanomaterial-coated heat transfer pipe coating method and a vaporizer including the same, and more particularly, to a carbon nanomaterial-coated heat transfer pipe coating method using carbon nanotubes having excellent heat transfer efficiency, And an evaporator including the same.

Energy efficiency is very important in appliances such as chillers, and energy efficiency, among other things, must promote boiling of the refrigerant and condensation heat transfer in the evaporator and condenser. Accordingly, there is a need to provide an evaporator in which the heat transfer efficiency of the evaporator is improved through the new material and the heat transfer characteristic is improved.
(Patent Document 1) KR10-2012-0037110 A

Accordingly, the present invention provides a technique for applying a carbon material such as carbon nanotubes to an evaporator or the like

According to an aspect of the present invention, there is provided a method of coating a heat transfer pipe, comprising the steps of: coating a surface of the heat transfer pipe with a composite powder of carbon nanotubes and a first metal powder; And a sintering step of sintering the coated composite powder layer.

According to an embodiment of the present invention, the method further includes coating the binder solution on the surface of the heat transfer pipe before coating the composite powder on the surface of the heat transfer pipe.

According to an embodiment of the present invention, the sintering step comprises: oxidizing the binder solution to a first temperature; And reducing the composite powder to a second temperature after the oxidizing step.

According to an embodiment of the present invention, the step of coating the composite powder on the surface of the heat transfer pipe proceeds by coating the composite powder dispersed in the solution by a powder electrostatic coating method.

According to an embodiment of the present invention, the step of coating the composite powder on the surface of the heat transfer pipe includes: a first coating of the second metal powder on the surface of the heat transfer pipe; And a second coating of the composite powder on the coated second metal powder layer.

According to an embodiment of the present invention, the first metal and the second metal are of the same kind, and the composite powder is prepared by mixing the carbon nanovube and the metal, followed by milling.

According to an embodiment of the present invention, the carbon nanotube in the composite powder is 0.5 to 30 vol%.

The present invention further provides a coated heat pipe by the above-described method.

In order to solve the above-described problems, the present invention provides a heat transfer tube using carbon nanotubes, wherein a surface of the heat transfer tube is formed with a composite metal coating layer composed of metal powder and carbon nanotubes.

According to one embodiment of the present invention, the composite metal coating layer is spray coated and then sintered.

According to an embodiment of the present invention, the heat transfer tube further includes a first metal layer formed between the composite metal coating layer and the surface of the heat transfer tube.

According to an embodiment of the present invention, the metal of the first metal layer and the metal of the composite metal coating layer are of the same kind.

According to an embodiment of the present invention, the first metal layer and the composite metal coating layer are formed by powder electrostatic painting.

According to an embodiment of the present invention, the composite gold coating layer includes two or more coating layers.

According to another aspect of the present invention, there is provided an evaporator including the heat transfer tube described above.

The present invention uses carbon nanotubes having excellent heat transfer efficiency in order to improve thermal efficiency of a heat transfer tube. Accordingly, the heat efficiency of the heat transfer pipe used in the evaporator or the like is improved, and an evaporator having excellent characteristics can be manufactured. Further, by mechanically pulverizing and mixing the metal powder and the carbon nanotubes simultaneously with the ball mill method, it is possible to form a coating layer for a heat transfer tube having improved heat conduction characteristics and pore characteristics, and further, through two or more multi- Mechanical and thermal properties can be improved.

FIG. 1 is a step diagram of a method of coating a carbon nanotube / metal composite layer on a surface of a heat transfer pipe according to an embodiment of the present invention.
2 is a SEM photograph of copper powder and carbon nanotubes used in the manufacture of composite materials.
3 is a schematic view of a method of coating a heat transfer pipe according to an embodiment of the present invention.
4 is a view for explaining a method of coating the composite powder according to the present invention on the outside of the heat transfer tube.
5 to 8 are views for explaining a method of coating a composite powder on the inside of a heat transfer pipe.
9 is a photograph of a heat transfer tube coated with a carbon nanotube composite material according to the sintering process according to the present invention.
10 and 11 are TEM photographs of carbon nanotubes before and after ball milling, respectively.
12 is a graph showing the Raman component analysis results of the composite powder prepared by mixing the copper powder and 20 vol% carbon nanotube used in the present experiment with the ball mill for 4 hours.
13 is a cross-sectional and SEM image of each sample after sintering according to the coating method
14 is a high magnification FE-SEM photograph of the surface of the composite powder on the two-layer sintered coated surface.
Figures 15 and 16 are the boiling results of the coating structure and method as a result of the pool boiling of the coating surface.
17 is a SEM photograph of a surface of a carbon nanotube / copper composite powder prepared by adding carbon nanotubes at 5% to 30% vol% by sintering.
18 is a SEM photograph of the surface of the powder-expanded powder sintered with the carbon nanotube / copper composite powder prepared by adding 5% to 30% vol% of carbon nanotubes.
19 and 20 are graphs showing the influence of the carbon nanotube addition ratio on the boiling heat transfer when the carbon nanotube / copper composite powder is processed.
21 is a SEM photograph of the surface of the sintered coating with 10% carbon nanotubes / copper powder and the enlarged powder surface at 600 ° C to 800 ° C,
22 and 23 are graphs showing the effect of sintering temperature on boiling heat transfer.
24 is a graph showing the overall heat transfer coefficient variation according to the type of the heat transfer tube for the evaporator.

Hereinafter, a carbon nanomaterial-coated heat transfer tube and an evaporator including the same according to embodiments of the present invention will be described with reference to the accompanying drawings.

The following examples are intended to illustrate the present invention and should not be construed as limiting the scope of the present invention. Accordingly, equivalent inventions performing the same functions as the present invention are also within the scope of the present invention.

In addition, in adding reference numerals to the constituent elements of the drawings, it is to be noted that the same constituent elements are denoted by the same reference numerals even though they are shown in different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

In describing the components of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected to or connected to the other component, It should be understood that an element may be "connected," "coupled," or "connected."

The present invention uses carbon nanotubes having excellent heat transfer efficiency in order to improve thermal efficiency of a heat transfer tube. In the present invention, the carbon nanotube as a coating material for a heat transfer tube has an electric conductivity similar to that of copper, a strength 100 times higher than that of steel, and particularly, a thermal conductivity is the same as that of natural diamond. The carbon nanotubes of the present invention have excellent thermal conductivity and the carbon nanotubes of the present invention can be used as a multi wall carbon nanotube (MWCNT) or a single wall carbon nanotube (SWCNT) phosphor, and the metal includes all metal powders such as copper (Cu), iron (Fe), stainless steel, titanium (Ti), aluminum (Al)

FIG. 1 is a step diagram of a method of coating a carbon nanotube / metal composite layer on a surface of a heat transfer pipe according to an embodiment of the present invention.

Referring to FIG. 1, a composite powder composed of a carbon nanotube and a metal powder (first metal) is coated on the surface of the heat transfer pipe. The composite powder according to an embodiment of the present invention is manufactured by a ball milling method, and the coating proceeds by a powder electrostatic painting method using an electrostatic force. However, the scope of the present invention is not limited thereto, and various coating methods can be used.

Thereafter, the coated composite powder layer is sintered on the surface of the heat transfer tube, and the sintering according to an embodiment of the present invention proceeds with the stepwise heat treatment proceeding to the first temperature and the second temperature.

Example

Example  1-1

Composite powder manufacturing

The carbon nanotube / metal composite powder was prepared by mixing copper with multi-walled carbon nanotubes having a diameter of 5 to 20 nm and a length of 10 μm, followed by ball milling at 900 RPM for 4 hours by Attrition Milling. At this time, the mixing ratio of carbon nanotubes was varied from 5 to 30 vol%.

2 is a SEM photograph of copper powder and carbon nanotube used in accordance with the present invention.

Referring to FIG. 2, copper powder has an average particle size of 45 .mu.m, and multi-wall carbon nanotubes are intertwined with each other.

Example  1-2

Composite powder coating

3 is a schematic view of a method of coating a heat transfer pipe according to an embodiment of the present invention.

Referring to FIG. 3, in the case of the upper side, a single layer coating (coating method) of coating a carbon nanotube / copper composite powder using a powder electrostatic coater after coating a copper sample (heat transfer tube) with a binder solution having a concentration of 2 wt% layer coating method in which another metal layer (a metal layer made of the powder of the second metal) is formed on the upper side of the heat transfer tube and the composite powder is coated on the other metal layer in two or more layers. It is a schematic diagram. In the present invention, the binder solution is a liquid material serving as a pressure-sensitive adhesive. In one embodiment of the present invention, a polyvinyl alcohol (PVA) solution is used as a binder solution, but the scope of the present invention is not limited thereto.

When forming a multilayer coating, that is, a coating layer of two or more layers, in one embodiment of the present invention, the metal (first metal) of the composite powder and the second metal of another metal layer are of the same kind, Interface defects are minimized. The composite powder according to the present invention can be coated on the outer side and the inner side of the heat transfer tube, which will be described in detail below. In the case of a multilayer coating, the composite powder coating layer may include one or more coating layers.

Heat transfer pipe Outside  When coating

4 is a view for explaining a method of coating the composite powder according to the present invention on the outside of the heat transfer tube.

4, roughness is formed by sandpaper or sanding machine on the outside of the heat transfer pipe. Thereafter, a heat transfer tube rotary coating apparatus is installed in a spray booth as shown in FIG.

Thereafter, the PVA aqueous solution is first sprayed with a general air-driven spray device while rotating the heat transfer tube (low speed). Then, the pure copper powder (metal powder layer of the first metal) is coated with a powder electrostatic coater. Thereafter, the PVA aqueous solution is sprayed with a general air-driven spraying device, followed by secondary coating, and the carbon nanotube / copper composite material according to the present invention is coated with a powder electrostatic coater and is desorbed therefrom.

Heat transfer pipe  When coating inside

5 to 8 are views for explaining a method of coating a composite powder on the inside of a heat transfer pipe.

Referring to FIG. 5, the surface is roughened by using heat transfer and inner side with sandpaper or the like. Thereafter, the PVA aqueous solution was coated on the inner side of the heat transfer tube, which was covered with a plug or the like as shown in Fig. 6, the PVA aqueous solution was put in the tube, the PVA aqueous solution was uniformly coated on the inner side by rotating the both sides of the heat transfer tube, Remove the solution.

Alternatively, as shown in FIG. 7, the PVA solution may be removed by immersing the heat transfer tube in an aqueous solution of PVA and then tilting the heat transfer tube.

As shown in FIG. 8, pure metal powder is coated with a powder electrostatic coater. In detail, a heat pipe inner coating device shown in FIG. 8 is manufactured, and a heat transfer pipe with PVA is mounted on a cradle. When the copper powder is sprayed through the electrostatic coating device while sucking air through the blower, the copper powder is uniformly coated on the inside of the heat transfer pipe. In this way, pure copper powder is coated on the inner side of the heat pipe.

Then, the PVA solution as a binder is coated once more according to the method of FIGS. 6 and 7, and then a heat transfer tube is attached to the heat transfer pipe inner coating device in the same manner as in FIG. 8 to coat the optimum carbon nanotube / metal composite material with the powder electrostatic coater.

Example  1-3

Sintering

Thereafter, the binder solution such as PVA or the carbon nanotube-metal composite metal layer coated on another metal layer is sintered in a heat treatment process.

First, a coating heat transfer pipe is charged into an electric furnace. In the embodiment of the present invention, the electric furnace for the heat treatment process is a resistance furnace (indirect furnace) system. However, the induction furnace, the discharge plasma, and the arc furnace can be considered. Any type of furnace can be used in the heat treatment process according to the present invention.

Thereafter, air is supplied and heated at a rate of 20 ° C / min in an air atmosphere and maintained at 350 ° C for about 10 minutes to oxidize the binder (PVA) (first temperature heat treatment). The remaining air in the electric furnace is discharged by using a vacuum pump or nitrogen gas is supplied into the electric furnace to purge the residual air and supply the forming gas (hydrogen 10%, nitrogen 90%) to the reduction (hydrogen) Followed by reduction sintering at a high temperature for 1 hour (second temperature heat treatment). The high temperature sintering temperature is 600 ℃ ~ 800 ℃ for carbon nanotube / copper composite material and 700 ℃ ~ 1000 ℃ for carbon nanotube / steel composite material. Such a heat treatment temperature depends on the kind of the carbon nanotube-metal composite metal layer, and the scope of the present invention is not limited to the temperature condition in this embodiment.

9 is a photograph of a heat transfer tube coated with a carbon nanotube composite material according to the sintering process according to the present invention.

Experimental Example

Composite powder characteristics

10 and 11 are TEM photographs of carbon nanotubes before and after ball milling, respectively.

Referring to FIG. 10, long multi-walled carbon nanotubes are shown. In FIG. 11, however, long carbon nanotubes entangled with each other are briefly boiled after ball milling and embedded in copper powder.

12 is a graph showing the Raman component analysis results of the composite powder prepared by mixing the copper powder and 20 vol% carbon nanotube used in the present experiment with the ball mill for 4 hours.

12, when the D band near 1350cm ^-1 and 1580cm ^-1 near the G band. The Raman peak of the carbon nanotube according to the present invention is characterized by a typical crystallized graphite peak (G Peak) mainly at 1580 cm ^-1 and a peak indicating a carbonaceous impurity form such as amorphous carbon and catalyst at the vicinity of 1350 cm ^-1 D Peak appears. Therefore, as shown in the figure, the particle size of the composite powder is larger than that of the carbon nanotube, so that the intensity of the band of 20 vol% carbon nanotube s / copper composite powder is much stronger than that of the original carbon nanotube. The D band and G band ratio of the 20vol% carbon nanotube / copper composite powder are different from those of the original carbon nanotube.

Also, as shown in Table 1 below, the IG / ID value of 20 vol% carbon nanotube / copper composite powder is lower than that of the original carbon nanotube. This is because the length of the carbon nanotubes is shortened and the structure is partially damaged due to collision and friction between the ball and the copper and the carbon nanotube during the ball mill process.

[Table 1]

Tissue and Heat Transfer Characteristics by Coating Method

13 is a cross-sectional and SEM image of each sample after sintering according to the coating method

(A, b), single-layer sintered coating (c, d) with carbon nanotube / copper composite powder, pure carbon nanotube s / copper composite powder on pure copper powder (E, f) in the case of a two-layer coating with a sinter coating.

It can be seen from Fig. 13 that the two-layer coating rather than the monolayer coating has a high porosity which is favorable for pool boiling heat transfer in cross-section and surface photographs. It can be seen that the porosity of the surface coated with the composite powder is higher than that of the pure copper powder coated sintered surface.

Table 2 below shows the PSA (Pore Size Analyzer) analysis results.

[Table 2]

13 (a) and (b) show the pore size, porosity, and pore density of each sample through Table 2, wherein the copper coated through the sintering process is composed of copper particles As a result, the largest average pore diameter is shown and the porosity is the lowest. 13 (c) and (d), however, show that when the carbon nanotube / copper composite powder is sintered in a single layer, the size of powder in the ball mill process becomes small and the pore size is small due to the interface between the carbon nanotubes and the copper particles It can be seen that the porosity is increased and the porosity density is increased. 13 (e) and (f) show the smallest pore size, the largest pore size, and the highest pore density as a two-layer structure.

14 is a high magnification FE-SEM photograph of the surface of the composite powder on the two-layer sintered coated surface.

Referring to FIG. 14, it can be seen that the carbon nanotube is embedded in the surface of the copper powder and there are fine pores favorable to boiling heat transfer.

Figures 15 and 16 are the boiling results of the coating structure and method as a result of the pool boiling of the coating surface.

As can be seen in Figures 15 and 16, boiling heat transfer occurs first on a single or double coated carbon nanotube / copper coated surface rather than on a smooth copper surface. That is, when the initial boiling heat transfer occurs at the time of simple copper powder coating, the superheat degree is about 2 ° C, while the surface of single-wall carbon nanotube / copper coating is 0.65 ° C and the surface of double coating is 0.45 ° C. It can be seen that the boiling starts at a lower superheat than the copper powder coating.

On the other hand, in the case As shown in 16, the boiling heat transfer coefficient when a heat transfer boiling starts also be simple copper powder coatings are single-walled carbon nanotubes on the other hand it is about 2,000 W / m ² ℃ tube / copper coated surface is about 10,000 W / m ² ℃ , The two-layer coated surface is about 14,000 W / m ² ° C, indicating that the carbon nanotube / copper coating has a much higher boiling heat transfer coefficient than a simple copper powder coating. In the case of single-walled carbon nanotube / copper coating, the superheat is reduced by about 68% and the heat transfer coefficient is increased about 5 times when the initial bubbles are generated, and the superheating degree of the double coating surface is reduced by about 78% To about 7 times the increase. This increases the fine pores of the carbon nanotube / copper composite powder on the surface of the coating, thereby providing a large number of bubble generating sites required for the nucleate boiling. Also, due to the excellent heat transfer characteristics of the carbon nanotubes, bubbling occurs well during the boiling process and boiling heat transfer Especially, it is considered that the surface of the two - layer coating greatly increases the pore density required for bubble generation, thereby increasing the rate of bubble formation, and accordingly, the superheating degree of the surface is decreased, and the boiling heat transfer is greatly improved.

As shown in FIG. 16, the heat transfer coefficient of the two-layer coating surface is maintained at the initial high at a low superheating degree, but the film boiling is formed as the superheating degree is increased, and the heat transfer coefficient is gradually decreased. It can be seen that the smooth copper surface and the simple copper powder coated surface gradually increase the heat transfer coefficient as the superheat degree increases. That is, the sintered coating of the carbon nanotube / copper composite exhibits a boiling heat transfer characteristic that is very good at low superheat than a smooth copper surface. Thus, it can be seen that the microstructure coated with carbon nanotube / copper composite powder is more advantageous than the case of plate or simple copper powder coating in boiling heat transfer with low superheat.

Tissue and Heat Transfer Characteristics by Carbon Nanotube Addition Rate

17 is a SEM photograph of a surface of a carbon nanotube / copper composite powder prepared by adding carbon nanotubes in an amount of 5% to 30% vol% ((a) 5 vol%; (b) 10 vol%; ) 20 vol%); (d) 30 vol%).

Referring to FIG. 17, the carbon nanotube / copper composite particles in the ball mill process are reduced to a smaller size because the relative content of copper decreases as the carbon nanotube addition ratio increases. In addition, the size of the pores decreases as the carbon nanotube addition ratio increases from 5 to 20% on the sintered coating surface of the carbon nanotubes, and when the sintering temperature is more than 30%, the size of the pores increases suddenly and large cracks are observed .

Table 3 shows the average pore size, porosity and pore density of the coating with increasing carbon nanotube addition ratio.

[Table 3]

Referring to Table 3 and FIG. 17, when the carbon nanotube ratio is 5% and 10%, the average pore size and porosity are similar to each other. When the carbon nanotubes are 20% in size, the size of the composite particles becomes smaller, and the porosity at the time of sintering is about 5% lower than that of the carbon nanotubes containing 10%. When the size of the pores is reduced to about 2 times, It can be seen that the doubling degree is increased. As a result, it can be seen that when the content of carbon nanotubes in the composite powder is 5 to 30 vol%, it is possible to provide a source of bubbles required for further boiling heat transfer. At 30% of carbon nanotubes, the content of copper particles is the lowest, resulting in poor intergranular agglomeration during sintering and cracking on the surface. That is, when the carbon nanotube content exceeds 30%, the pore size is increased by about 4 times as compared with 20%, but the porosity is reduced by about 3.6%, and the pore density is decreased by about 100 times or more.

18 is a SEM photograph of the surface of the powder-coated powder sintered with the carbon nanotube / copper composite powder having a carbon nanotube content of 5 to 30 vol%.

Referring to FIG. 18, as the content of carbon nanotubes increases, the morphology of carbon nanotubes becomes more apparent. Especially, when the content of carbon nanotubes is 30 vol%, the interfacial densities disappear during sintering, and as the carbon nanotubes cohere with each other, the interface with copper particles becomes larger. As a result, it can be observed that uniform bonding is difficult on the whole.

19 and 20 are graphs showing the influence of the carbon nanotube addition ratio on the boiling heat transfer when the carbon nanotube / copper composite powder is processed.

As can be seen from FIGS. 19 and 20, when the content of the carbon nanotubes is 5% to 20%, it can be seen that boiling heat transfer enhancement increases with an increase in the carbon nanotube addition ratio. 20% Carbon Nanotubes Coated surfaces exhibit lower superheat and higher heat transfer coefficients than other coated surfaces. This is because, as shown in Table 3, when the carbon nanotube content is 20 vol%, it has the largest number of pores and the carbon nanotubes are uniformly dispersed, thereby promoting boiling heat transfer. In the case of adding 30% carbon nanotubes, Is lowered. This is because as shown in FIG. 16 and Table 3, due to the influence of a large amount of carbon nanotube particles, agglomeration between particles during sintering becomes poor, and boiling heat transfer due to cracking is reduced, and the boiling heat transfer promotion phenomenon is reduced .

Sintering temperature analysis

FIG. 21 is a SEM photograph of a surface of a sintered coating with a 10% carbon nanotube / copper powder at 600 ° C. to 800 ° C. and an enlarged powder surface (a) (b) 600 ° C. (c) (d) 700 ° C.; (e) (f) 800 < 0 > C).

Referring to FIG. 21, it can be seen that as the sintering temperature is increased, the porosity between the powders becomes smaller and the overall porosity decreases. That is, as the surface of the powder increases in sintering temperature, the interface between the copper particles becomes smaller and the porosity decreases.

22 and 23 are graphs showing the effect of sintering temperature on boiling heat transfer.

22 and 23, it can be seen that the carbon nanotube / copper composite powder has a boiling heat transfer characteristic superior to that of a smooth copper surface.

In FIG. 22, it can be seen that the superheat degree of the boiling surface decreases as the sintering temperature decreases at the same heat flux. That is, when the sintering temperature is 600 ° C., the lowest initial bubble generation superheat is exhibited, and the difference is not large when the heat flux is high.

23, the heat transfer coefficient increases with decreasing sintering temperature at the same superheating degree when the superheating degree is 7 ° C or less, but the superheating degree is not significantly different when the superheating degree is 7 ° C or more. This is because the sintered coating surface at low temperature has sufficient porosity to promote boiling heat transfer. However, as the sintering temperature increases during coating, the atoms diffuse at the interface between the copper particles to increase the melting degree and decrease the partial pores, It is considered that the characteristics are poor.

Heat pipe heat  Comparison of efficiency

FIG. 24 is a graph showing the overall heat transfer coefficient change according to the type of the heat transfer tube for the evaporator. In the case where the cold water inlet temperature is 10 ° C., 12 ° C., and 14 ° C. in the refrigerant R134a, excel E tube, the same spiral processing inside the tube), sintered coating tube (spiral processing inside the tube), and smooth tube (tube side tube).

Referring to FIG. 24, when the carbon nanotube + copper is sintered (2 layers coating) (present invention), the heat transfer performance is about 40% higher than that of the existing heat transfer tube (dotted line).

 The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas falling within the scope of the same shall be construed as falling within the scope of the present invention.

Claims (16)

A method for coating an evaporation tube,
A first coating of a second metal powder on the surface of the heat transfer pipe;
A second coating of a composite powder of carbon nanotubes and a first metal powder on the coated second metal powder layer; And
Sintering the coated composite powder layer,
Wherein the first metal and the second metal are copper (Cu) of the same kind,
Wherein the coating layer is coated in a multi-layer structure. The evaporation transport tube coating method according to claim 1,
Further comprising the step of applying a binder solution to the second metal powder coating layer before coating the composite powder on the surface of the heat transfer tube. 3. The method of claim 2,
Wherein the sintering step comprises: oxidizing the binder solution to a first temperature; And
And reducing the composite powder to a second temperature after the oxidizing step. 3. The method of claim 2, wherein coating the composite powder on the surface of the heat transfer pipe comprises:
Wherein the composite powder dispersed in the solution is coated by a powder electrostatic coating method. delete delete The method according to claim 1,
Wherein the composite powder is prepared by mixing the carbon nanotubes with a metal and then milling the mixture. The method according to claim 1,
Wherein the carbon nanotube in the composite powder is 20 vol%. delete As an evaporation heat transfer tube,
A second metal powder layer that is first coated on the surface of the heat transfer tube;
A composite metal coating layer is formed on the second metal powder layer in the state of the first metal powder and the carbon nanotube,
Wherein the first metal and the second metal are copper (Cu) of the same kind and are coated in a multilayered manner. 11. The method of claim 10,
Wherein the composite metal coating layer is spray coated and then sintered. delete delete 12. The method of claim 11,
Wherein the second metal powder layer and the composite metal coating layer are formed by a powder electrostatic coating method. delete An evaporator comprising an evaporation heat transfer tube according to any one of claims 10, 11 and 14.

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