KR101591305B1 - Method for manufacturing nanofluids containing carbon nanotubes - Google Patents

Abstract

Disclosed is a method for preparing a nanofluid comprising: a crushing step of crushing a carbon nanotube with a dispersant; and a homogenizing step of adding a solvent to the material obtained from the crushing step to be homogenized. Additionally, disclosed is the nanofluid including the carbon nanotube, the dispersant, and water, and having one or more characteristics mentioned below. i) A dispersion stability characterized by having less than 10% of a decrease rate of an extinction coefficient value over the lapse of time, compared to an initial value in the case that the nanofluid is placed at room temperature in the predetermined space for equal to or longer than 25 days. ii) A high-temperature stability characterized by having less than 10% of the decrease rate of the extinction coefficient value compared to an initial value in the case that the nanofluid is heated at 80°C for 12 hours. iii) An optical transmittance characterized by being equal to or less than 0.05 (pure water 1.0 basis) at wavelength of 200 to 1400nm measured by UV/Vis/NIR array spectrophotometer in the case that content of the carbon nanotube is present in a volume percentage of 0.003 based on the total volume of the nanofluid. iv) An optical transmittance characterized by being equal to or less than 0.02 (pure water 1.0 basis) of at wavelength of 200 to 1400nm measured by UV/Vis/NIR array spectrophotometer in the case that the content of the carbon nanotube is present in a volume percentage of 0.005 based on the total volume of the nanofluid. Thus, the nanofluid has an effect of being effectively utilized in a solar collector, especially in the direct absorption-type solar collector since the nanofluid herein is a working fluid for exchanging and storing heat and has the superior dispersion stability and a light absorbing capacity. Furthermore, the nanofluid has advantages of saving time and expense of preparing, and being prepared safely as the method for manufacturing nanofluid is simplified.

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing nanofluids containing carbon nanotubes,

Disclosed herein are nanofluids containing carbon nanotubes and methods of making the same. Also disclosed herein is a collector comprising a carbon nanotube-containing nanofluid as a working fluid.

The carbonaceous material, which has recently been undergoing much research, has a very low specific gravity and a high thermal conductivity, so that when a thermally conductive fluid composition for a heat exchanger is prepared, the thermal conductivity, heat capacity, and heat transfer coefficient of the thermally conductive fluid composition for the exchanger can be improved In addition, since it has a high surface area due to its nano-sized size, it has high dispersion stability and is suitable for producing a thermally conductive fluid composition for a heat exchanger. Of carbon materials, carbon nanotubes are in particular used. However, carbon nanotubes tend to agglomerate or collide into bundles within the matrix due to strong van der Waals forces. If the carbon nanotubes are aggregated in the matrix, the inherent characteristics of the carbon nanotubes may not be exhibited or the uniformity may be deteriorated. Although various methods have been proposed to improve this point, there have been problems in that the process is excessively complicated and dangerous, and the use of a dispersant or the like causes a remarkable decrease in light absorption ability.

Korean Patent Laid-Open No. 10-2012-0119487

In one aspect, an object of the present invention is to provide a working fluid for heat exchange and heat storage.

In one aspect, an object of the present invention is to provide a working fluid for use in a solar collector.

In one aspect, an object of the present invention is to provide a working fluid for direct absorption type solar collectors.

In one aspect, an object of the present invention is to provide a nanofluid having excellent dispersion stability and light absorbing ability.

In one aspect, an object of the present invention is to simplify the manufacturing process of nanofluids, thereby reducing time and cost.

In one aspect, an object of the present invention is to provide a safe nanofluid manufacturing method.

In one aspect, the present invention provides a method of producing a nanofluid, comprising: a pulverizing step of pulverizing a carbon nanotube together with a dispersant; And a homogenizing step of adding a solvent to the pulverized product obtained in the pulverizing step and homogenizing the pulverized product.

In one aspect, the invention is a nanofluid, wherein the nanofluid is a nanofluid comprising carbon nanotubes, a dispersant, and water and having one or more of the following characteristics: i) A dispersion stability with a decrease rate of the extinction coefficient value with time being less than 10% compared with the initial value; ii) high temperature stability at a heating rate of not less than 12 hours at 80 占 폚, wherein the rate of decrease of the extinction coefficient value is less than 10% compared with the initial value; iii) when the content of carbon nanotubes is 0.003% by volume based on the total volume of the nanofluid, the optical transmittance is 0.05 or less based on pure water at a wavelength of 200 to 1400 nm when measured with a UV / Vis / NIR spectrophotometer; And iv) an optical transmittance of 0.02 or less based on pure water at a wavelength of 200 to 1400 nm when measured by a UV / Vis / NIR spectrophotometer when the content of carbon nanotubes is 0.005% by volume based on the total volume of the nanofluid.

In one aspect, the present invention can provide a nanofluid having excellent dispersion stability and light absorbing ability as a working fluid for heat exchange and heat storage. Such nanofluids can be used effectively in solar collectors, especially direct absorption solar collectors.

In one aspect, the present invention can simplify the process and save time and cost, and provide a safe nanofluid manufacturing method.

FIG. 1A shows the results of measuring the dispersion stability after leaving the nanofluid prepared in Comparative Example 1, which is a conventional method, at room temperature.
FIG. 1B shows the result of measuring the dispersion stability after allowing the nanofluid prepared in Example 1 of the present invention to stand at room temperature.
FIG. 2 shows the result of observation of dispersion stability after heating the nanofluid prepared in Example 1 of the present invention at a high temperature of 80.degree. C. for 14 hours.
FIG. 3A shows the results of measurement of the optical transmittance of a nanofluid prepared according to Comparative Example 1, which is a conventional method, using a UV / Vis / NIR spectrophotometer. FIG. The optical transmittance of the fabricated nanofluid was measured using a UV / Vis / NIR spectrophotometer.
4 is a graph showing the results of comparative evaluation of the light absorption performance of a nanofluid prepared according to Example 1 of the present invention and a nanofluid prepared according to a comparative example (Comparative Example 2). The light absorption performance was evaluated by using the extinction coefficient of the nanofluid and expressed as the ratio of the extinction coefficient to the value of the extinction coefficient of the initial nanofluid, which decreases with time.
FIG. 5A is an SEM image of a nanofluid prepared according to Comparative Example 1, which is a conventional method, and FIG. 5B is an SEM image of a nanofluid manufactured according to Example 1 of the present invention.

In one aspect, the present invention provides a method of producing a nanofluid, comprising: a pulverizing step of pulverizing a carbon nanotube together with a dispersant; And a homogenizing step of adding a solvent to the pulverized product obtained in the pulverizing step and homogenizing the pulverized product.

In one aspect, the invention is a nanofluid, wherein the nanofluid is a nanofluid comprising carbon nanotubes, a dispersant, and water and having one or more of the following characteristics: i) A dispersion stability with a decrease rate of the extinction coefficient value with time being less than 10% compared with the initial value; ii) high temperature stability at a heating rate of not less than 12 hours at 80 占 폚, wherein the rate of decrease of the extinction coefficient value is less than 10% compared with the initial value; iii) when the content of carbon nanotubes is 0.003% by volume based on the total volume of the nanofluid, the optical transmittance is 0.05 or less based on pure water at a wavelength of 200 to 1400 nm when measured with a UV / Vis / NIR spectrophotometer; And iv) an optical transmittance of 0.02 or less based on pure water at a wavelength of 200 to 1400 nm when measured by a UV / Vis / NIR spectrophotometer when the content of carbon nanotubes is 0.005% by volume based on the total volume of the nanofluid.

As used herein, the term "carbon nanotube" refers to a single-walled carbon nanotube (SWCNT) having a single wall structure, a double walled carbon nanotube having a double wall structure, Various types of carbon nanotubes can be used from, but are not limited to, multi-walled carbon nanotubes (MWCNTs) and multiple carbon nanotubes, and combinations thereof. The carbon nanotubes may be prepared by a method known in the art, such as chemical vapor deposition, arc discharge, plasma torch, or ion bombardment. The carbon nanotubes may be pre-treated by conventional methods known in the art, There is no need to go through the preprocessing step. For example, the carbon nanotube may be a multi-walled carbon nanotube (MWCNT).

The carbon nanotubes preferably have an outer diameter of 1 to 100 nm and a length of 0.5 to 30 탆. Carbon nanotubes having an outer diameter and a length within the above ranges are excellent in thermal stability as well as thermal conductivity. When the outer diameter of the carbon nanotube is more than 100 nm or the length is more than 30 탆, it may be difficult to disperse the sonanotube. When the length of the carbon nanotube is less than 0.5 탆, Performance may not be effective.

As used herein, the term "dispersant" is any dispersant that can disperse carbon nanotubes in an aqueous solution. For example, sodium dodecylbenzenesulfate (SDBS), sodium dodecylsulfate (SDS), sodium chlorate, cetyltrimethyl ammonium bromide (CTAB), TX-100, poly One of polyoxyethylene, oleyl ether, poly (vinylpyrrolidone), PVP, gum arabic, and mixtures thereof may be used. For example, the dispersing agent may be sodium dodecylbenzenesulfate (SDBS).

In one embodiment, the grinding step may be to perform grinding by grinding. In another embodiment, the grinding may be wet grinding with a small amount of the base fluid. The amount of the basic fluid can be appropriately adjusted depending on the amount of the carbon nanotube and / or the dispersant. For example, a small amount of basic fluid may be water of 20 cc or less. For example, it may be 1 to 20 cc of water. The amount of basic fluid is 20cc or less, 19cc or less, 18cc or less, 17cc or less, 16cc or less, 15cc or less, 14cc or less, 13cc or less, 12cc or less, 11cc or less, 10cc or less, 9cc or less, 8cc or less, 7cc or less, Or less, or 4cc or less, or 3cc or less.

In one embodiment, the base fluid can be used without limitation as long as it is a solvent suitable for crushing carbon nanotubes and a dispersant. For example, the base fluid may be water.

In one embodiment, the wet grinding is not limited to a specific method of grinding. For example, the grinding may be performed by putting the carbon nanotubes and the dispersant into a mortar and grinding them into a pestle. More specifically, the wet grinding can be performed by putting the carbon nanotubes, the dispersant, and the base fluid in a mortar and grinding them into a mortar.

In one embodiment, milling can be performed for 1 to 30 minutes. For example, milling can be performed for 30 minutes or less, 25 minutes or less, 20 minutes or less, 15 minutes or less, or 10 minutes or less. On the other hand, in another embodiment, the pulverization can be performed for at least 1 minute, at least 3 minutes, at least 5 minutes, at least 7 minutes, at least 9 minutes, or at least 11 minutes. For example, the milling may be carried out for 5 to 15 minutes. Through this process, the carbon nanotubes can be broken down and easily dispersed compared to the untreated carbon nanotubes. In addition, the surface of the hydrophobic carbon nanotubes is coated with a hydrophilic dispersing agent, thereby reducing the van der Waals attractive force generated between the carbon nanotubes, thereby making it possible to disperse the carbon nanotubes more effectively in the distilled water.

In one embodiment, the homogenization step may be one or more of mechanical agitation and sonication. For example, the homogenization step may be performed while performing ultrasonic treatment and mechanical stirring. Mechanical stirring and sonication can be carried out according to conventional methods using equipment known in the art. For example, a mixed solution of a carbon nanotube and a dispersant may be mixed with distilled water, and homogenized by an ultrasonic water bath and a mechanical stirrer at the same time.

In one embodiment, mechanical agitation may be performed at 100 to 500 rpm. The mechanical stirring may be performed at 500 rpm or less, 450 rpm or less, 400 rpm or less, 350 rpm or less, 300 rpm or less, 250 rpm or less, 200 rpm or 150 rpm or less. In another embodiment, the agitation may be performed at 100 rpm or more, 150 rpm or more, 200 rpm or more, 250 rpm or more, 300 rpm or more, 350 rpm or more, or 400 rpm or more.

In one embodiment, the ultrasonic treatment can be performed at a frequency of 20 to 40 kHz. In one embodiment, the ultrasound treatment may be performed at a frequency of 40 kHz or less, 38 kHz or less, 36 kHz or less, 34 kHz or less, 32 kHz or less, 30 kHz or less, 28 kHz or less, or 26 kHz or less. In another embodiment, the ultrasonic treatment may be performed at a frequency of 20 kHz or higher, 22 kHz or higher, 24 kHz or higher, 26 kHz or higher, 28 kHz or higher, 30 kHz or higher, 32 kHz or higher or 34 kHz or higher.

The ultrasonic treatment and mechanical stirring may be performed for 1 to 2 hours.

In one embodiment, the solvent of the homogenization step, that is, the solvent of the nanofluid, may be any of those known in the art, but it is preferably water, ethylene glycol, and polyethylene glycol, or a mixture thereof Can be used. In another aspect, the solvent can be boiling, including water, ethanol, methanol, acetone, ammonia, freon refrigerant, non-refrigerant refrigerant, antifreeze, oil, and any solvent that can be used for boiling heat transfer.

In another embodiment, the solvent includes water, alcohols such as methanol, ethanol, isopropyl alcohol, propyl alcohol and butanol; Ketones such as acetone, methyl ethyl ketone, ethyl isobutyl ketone and methyl isobutyl ketone; Glycols such as ethylene glycol, ethylene glycol methyl ether, ethylene glycol mono-n-propyl ether propyl ether propylene glycol, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether and propylene glycol propyl ether; Amides such as dimethylformamide and dimethylacetoamide; Pyrrolidones such as N-methyl pyrrolidone and N-ethyl pyrrolidone; Hydroxy esters such as dimethyl sulfoxide,? -Butyrolactone, methyl lactate, ethyl lactate, methyl? -Methoxyisobutyrate and? -Hydroxyisobutyrate; Propylene glycol monomethyl ether acetate (PGMEA), N-methyl-2-pyrrolidone (NMP), and the like can be used as the aniline, such as aniline, N-methyl aniline and the like, hexane, terpineol, chloroform, toluene, , But are not limited thereto.

For example, the solvent may be water. For example, the solvent may be distilled water.

In one embodiment, the nanofluid of the present invention can be 0.001 to 10 wt% of the dispersant based on the total weight of the total nanofluid composition.

On the other hand, the carbon nanotubes may be 0.000001 to 5% by volume based on the total weight of the entire nanofluid composition. For example, the carbon nanotubes may be present in an amount of 0.000001% by volume, 0.00001% by volume, 0.0001% by volume, 0.001% by volume, 0.002% by volume, 0.003% by volume, 0.004% by volume or more based on the total weight of the nanofluid composition, 0.005% by volume or more. For example, the carbon nanotubes may be present in an amount of up to 5 vol%, up to 4 vol%, up to 3 vol%, up to 2 vol%, up to 1 vol%, up to 0.1 vol%, or up to 0.01 vol% ≪ / RTI >

The solvent may be 85 to 99.989% by volume based on the total volume of the total nanofluid composition.

In one embodiment, the mixing weight ratio of the carbon nanotubes to the dispersant may be 1: 0.001 to 1:10.

When CNT: dispersant: solvent is expressed by weight, it may be 1: 1-20: 1-10000.

In one embodiment, the nanofluid may further comprise a binder or other organic additive.

In one embodiment, the nanofluid may be a heat transfer working fluid for heat exchange. For example, it may be a working fluid of a direct absorption type solar collector. Direct absorptive solar collectors are collectors that collect solar heat by absorbing solar energy directly into the working fluid for heat exchange, unlike conventional solar collectors. The direct absorption type solar collector has a merit that it has less heat loss than the conventional method using the heat collecting plate and can mechanically collect the heat collecting system. Direct absorption type solar collectors include not only solar collectors for hot water hot water but also concentrated solar collectors for electric power generation.

In the present specification, the term "extinction coefficient" means a value calculated by the Lambert-Beer law. For example, the values measured using an extinction coefficient measuring apparatus composed of a He-Ne laser ( ? = 632.8 nm), a sample nanofluid as a light source, a photodiode and a power meter for measurement are substituted into the following equations Lt; RTI ID = 0.0 >

(Equation 1)

I, I ₀ , l , λ and σ are the transmitted light intensity, the incident light intensity, the path length, the wavelength, and the extinction coefficient, respectively.

In the present specification, the "rate of decrease of extinction coefficient value with time" means a rate of change of extinction coefficient with time. For example, the performance degradation ratio ( ε ) may be a value obtained by dividing an initial extinction coefficient value by an extinction coefficient value that changes with time as shown in the following Equation (2).

(Equation 2)

In one embodiment, the nanofluid may have a dispersion stability with an elapsed time-dependent decrease rate of the extinction coefficient value of less than 10% compared with the initial value at a temperature of 25 days or more at room temperature. For example, the nanofluid exhibits a rate of decrease in extinction coefficient over time at a temperature of 25 days or more, 26 days, 27 days, 28 days, 29 days, 30 days, or 31 days And may have a dispersion stability of less than 10% relative to the initial. In another embodiment, the nanofluid is at a temperature of extinction coefficient at a temperature of at least 1 month, at least 2 months, at least 3 months, at least 4 months, at least 5 months, at least 6 months, or at least 7 months May have a dispersion stability of less than 10% as compared with the initial. The dispersion stability is such that the degradation rate of the extinction coefficient value over time is less than 50%, less than 40%, less than 30%, less than 20%, less than 10%, less than 9%, less than 8% Less than 7 wt%, less than 6 wt%, less than 5 wt%, less than 4 wt%, less than 3 wt%, less than 2 wt%, less than 1 wt%, less than 0.5 wt%, less than 0.4 wt% Less than 0.2% by weight, less than 0.1% by weight, less than 0.05% by weight, less than 0.01% by weight, less than 0.005% by weight, or less than 0.001% by weight. In another embodiment, the nanofluid may have high temperature stability such that less than 10% of the change in light absorption performance is precipitated upon heating at 80 DEG C for 12 hours or more. In one embodiment, the nanofluid has a pH of at least 12 hours, at least 13 hours, at least 14 hours, at least 15 hours, at least 16 hours, at least 17 hours, at least 18 hours, at least 19 hours, at least 20 hours, at least 21 hours , The lowering rate of the extinction coefficient value is less than 10% when heated for more than 22 hours, more than 23 hours, more than 24 hours, more than 2 days, more than 3 days, more than 4 days or more than 5 days. In one embodiment, the high temperature stability is such that upon heating at 80 DEG C for at least 12 hours at 80 DEG C, the rate of decrease of the extinction coefficient value is less than 50%, less than 40%, less than 30%, less than 20%, less than 10% Less than 9 wt%, less than 8 wt%, less than 7 wt%, less than 6 wt%, less than 5 wt%, less than 4 wt%, less than 3 wt%, less than 2 wt% , Less than 0.4 wt%, less than 0.3 wt%, less than 0.2 wt%, less than 0.1 wt%, less than 0.05 wt%, less than 0.01 wt%, less than 0.005 wt%, or less than 0.001 wt%.

In one embodiment, the nanofluid may be one having excellent light absorption performance. For example, when the content of carbon nanotubes is 0.003% by volume based on the total volume of the nanofluid, the optical transmittance is 0.05 or less based on pure water at a wavelength of 200 to 1400 nm when measured with a UV / Vis / NIR spectrophotometer, and / When the content of the tube is 0.005% by volume based on the total volume of the nanofluid, the optical transmittance may be 0.02 or less based on pure water at a wavelength of 200 to 1400 nm when measured with a UV / Vis / NIR spectrophotometer. For example, when the content of the carbon nanotubes is 0.003% by volume based on the total volume of the nanofluid, the nanofluid has an optical transmittance of 0.05 or less based on pure water over a wavelength of 200 to 1400 nm when measured with a UV / Vis / NIR spectrophotometer 0.045 or less, 0.04 or less, 0.035 or less, or 0.03 or less. In another embodiment, the nanofluid is an optical fiber having a carbon nanotube content of 0.005% by volume based on the total volume of the nanofluid, and having a ratio of carbon nanotubes of 0.005% by volume based on the total volume of the nanofluid to a wavelength of 200 to 1400 nm measured by a UV / Vis / NIR spectrophotometer The transmittance may be 0.02 or less, 0.018 or less, 0.016 or less, 0.014 or less, or 0.012 or less.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not intended to limit the scope of the present invention, and the scope of the present invention is defined by the following claims.

Example 1: Preparation of nanofluids

Multi-Walled Carbon Nanotubes [Multi-walled carbon nanotubes (C- _tube 120); CNT Co., Ltd. , Korea] was mixed with sodium dodecylbenzenesulfate (SDBS) dispersant [sodium dodecylbenzenesulfate; Sigma-Aldrich, UK] in a weight ratio of 1:20, and then 10 cc of water was added thereto. It was then wet-ground for 10 minutes in a mortar. Then, the wet-ground mixture was mixed with distilled water to adjust the concentrations of the carbon nanotubes to 0.0005%, 0.0002%, 0.001%, 0.002%, 0.003%, 0.004% and 0.005% by volume, respectively, The nanofluid was prepared by treating ultrasonic waves of 40 kHz for 1 hour while stirring at 300 rpm.

Comparative Example 1: Preparation of Conventional Nanofluid

The carbon nanotubes were milled for 48 hours by a tumbling ball mill and a mono-planer mill, and the ground carbon nanotubes were immersed in M-chloroperbenzoic acid to be subjected to a surface treatment. The immersed carbon nanotubes were separated, , And the dried carbon nanotubes were heated to a temperature of 500 DEG C and heat-treated. 5 parts by weight of the heat-treated carbon nanoparticles were mixed with 95 parts by weight of an aqueous solution obtained by mixing 0.05 mol of sodium hydrogencarbonate with 200 mL of purified water, 20 kHz and an amplitude of 48.8 micrometer was irradiated for 1 hour to prepare a nanofluid containing metal-treated carbon nanoparticles.

Comparative Example 2: Preparation of Conventional Nanofluid

Carbon nanotubes (CNTs) were obtained from Tsinghua Nafine Nano-Powder Commercialization Engineering Center (China), and SDBS was dispersed in Sigma-Aldrich, UK. The mixing ratio of CNT and dispersant was used at a weight ratio of 1: 0.2. CNT applied ultrasonic energy for 36 hours before mixing with the basic fluid. The CNT thus pretreated was mixed with water and subjected to ultrasonic energy for 24 hours. Finally, a high speed magnetic stirrer was used for an additional 1 hour to complete the nanofluid. The concentration was 0.2% by weight.

Experimental Example 1: Measurement of dispersion stability at room temperature

Each of the nanofluids of Example 1 (0.005 vol%) and Comparative Example 1 was left at room temperature for 120 hours after the preparation. The precipitates were measured immediately after nanofluid production, after 1 hour, 5 hours, 24 hours, 120 hours, and 1 month, respectively. The results are shown in Figs. 1A and 2B. As shown in Fig. 1A, in the nanofluid of Comparative Example 1, it was observed that almost all the solids precipitated within 30 minutes. On the other hand, as shown in Fig. 1B, the nanofluid of Example 1 did not show sedimentation until 120 hours.

Experimental Example 2: Measurement of high-temperature stability

Each of the nanofluids of Example 1 (0.005% by volume) and Comparative Example 2 was heated in a bath for 14 hours at 80 ° C. As a result, it was found that the nanofluid of Comparative Example 2 was precipitated while the dispersion stability of the nanofluid of Example 1 was maintained (FIG. 2).

Considering that the operating temperature of the flat panel type collector is around 80 ° C, the nanofluid according to the present invention shows excellent performance as a working fluid for a flat panel type collector.

Experimental Example 3: Measurement of Optical Transmittance

The optical transmittance of each nanofluid of Example 1 and Comparative Example 1 was measured using a UV / Vis / NIR spectrophotometer (manufactured by Varian; Model name: Cary5000). As a result, it was found that the nanofluid of Example 1 was significantly superior in light absorption performance to the nanofluid of Comparative Example 1 (FIG. 3A) (FIG. 3B).

On the other hand, the extinction coefficient was calculated by the Lambert-Beer law. Specifically, the values measured using an extinction coefficient measuring apparatus composed of a He-Ne laser ( λ = 632.8 nm), a sample nanofluid as a light source, a photodiode and a power meter for measurement are shown in the following equations The extinction coefficient was calculated by substitution:

(Equation 1)

I , I ₀ , l , λ and σ are the transmitted light intensity, the incident light intensity, the path length, the wavelength, and the extinction coefficient, respectively.

The performance degradation ratio ( ε ) over time is obtained by dividing the initial extinction coefficient value by the extinction coefficient value which changes with time as shown in the following Equation 2.

(Equation 2)

The results are shown in Fig. In Example 1 (0.0002% by volume), the rate of decrease of the extinction coefficient was less than 10% in 30 days, whereas in Comparative Example 1, the extinction coefficient dropped sharply compared to the initial value, It was found that it reached as much as 70%.

Experimental Example 4: SEM image capture of nanofluid

Each nanofluid of Example 1 and Comparative Example 1 was photographed by SEM. The results are shown in Fig. 5A (Comparative Example 1) and Fig. 5B (Example 1). As shown in the figure, it can be seen that the nanofluid of Example 1 is finer than the nanofluid of Comparative Example 1 in size. The more scattered surfaces of the carbon nanotubes were, the larger the dispersive energy for dispersing the particles was.

Claims (21)

A method for producing a nanofluid,
The method
A pulverizing step of pulverizing the carbon nanotubes together with the dispersant; And
And a homogenizing step of adding a solvent to the pulverized product obtained in the pulverizing step and homogenizing the pulverized product. 2. The method of claim 1, wherein the grinding is performed by grinding. 3. The method of claim 2, wherein the grinding is wet grinding with a base fluid of greater than 0 and less than 20 cc. 4. The method of claim 3, wherein the base fluid is water. 4. The method of manufacturing a nanofluid according to claim 3, wherein the wet grinding is performed by putting the carbon nanotube, the dispersant, and the base fluid into a mortar and grinding the pellet. The method of claim 1, wherein the carbon nanotubes are multi-walled carbon nanotubes. The method of claim 1, wherein the dispersant is sodium dodecylbenzenesulfate (SDBS). 2. The method of claim 1, wherein the homogenizing step performs at least one of mechanical agitation and ultrasonic treatment. The method of manufacturing a nanofluid according to claim 8, wherein the homogenizing step is performed while performing ultrasonic treatment and mechanical stirring. 9. The method of claim 8, wherein the mechanical agitation is performed at 100 to 500 rpm. 9. The method of manufacturing a nanofluid according to claim 8, wherein the ultrasonic treatment is performed at a frequency of 20 to 40 kHz. The method of claim 1, wherein the solvent in the homogenization step is water. 10. The method of claim 9, wherein the ultrasonic treatment and the mechanical stirring are performed for 1 to 2 hours. The method of claim 1, wherein the nanofluid is a working fluid of a direct absorption type solar collector. As nanofluids,
Wherein the nanofluid comprises carbon nanotubes, a dispersant and water,
Nanofluids having one or more of the following characteristics:
i) a dispersion stability with a decrease rate of the value of the extinction coefficient over time of less than 10% compared to the initial value at a temperature of 25 days or more at room temperature;
ii) high temperature stability at a heating rate of not less than 12 hours at 80 占 폚, wherein the rate of decrease of the extinction coefficient value is less than 10% compared with the initial value;
iii) a characteristic that the optical transmittance of the carbon nanotube is 0.003% by volume based on the total volume of the nanofluid, and the optical transmittance is more than 0 and less than 0.05 at a wavelength of 200 to 1400 nm based on pure water when measured with a UV / Vis / NIR spectrophotometer; And
iv) a characteristic that the optical transmittance of the carbon nanotube is 0.005% by volume based on the total volume of the nanofluid, and the optical transmittance is more than 0 and less than 0.02 when measured with a UV / Vis / NIR spectrophotometer at a wavelength of 200 to 1400 nm. 16. The method of claim 15,
Wherein the carbon nanotube is a multi-walled carbon nanotube. 16. The nanofluid of claim 15, wherein the dispersant is sodium dodecylbenzenesulfate (SDBS). 16. The nanofluid of claim 15, wherein the nanofluid is a heat transfer fluid for heat exchange. 19. The nanofluid according to claim 18, wherein the nanofluid is a working fluid of a direct absorption type solar collector. 16. The nanofluid of claim 15, wherein the nanofluid is produced by the process of any one of claims 1 to 14. 18. A direct absorption type solar collector comprising a nanofluid according to any one of claims 15 to 18 as a working fluid.

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