JP2007297261A - Method for preparing carbon nanofluid and carbon nanofluid - Google Patents

Abstract

Carbon nanotubes are uniformly dispersed in a fluid.
The present invention provides a method for preparing a carbon nanofluid. This method is a process of preparing a base fluid, a process of preparing many carbon nanotubes, a process of mixing carbon nanotubes with the base fluid, and a process of dispersing carbon nanotubes substantially uniformly in the base fluid by a physical stirring operation. And during the physical stirring operation, a process of cooling the system performing the physical stirring operation is included. The present invention also provides carbon nanofluids that can serve as heat transfer fluids. Carbon nanofluids are approximately 99.8-98% by volume base fluid and approximately 0.2-2.0% by volume functionalized carbon nanotubes substantially evenly dispersed in the base fluid. Is included.
[Selection] Figure 1

Description

  The present invention relates to carbon nanotechnology, and more particularly, to a method for preparing a carbon nanofluid with improved thermal conductivity.

  The thermal conductivity of heat transfer fluids plays an important role in the development of energy efficient heat transfer devices in technical fields including electronics, heating, ventilation, air conditioning, cooling, and transportation. Clearly, the development of advanced heat transfer fluids is essential for improving the effective heat transfer effect of conventional heat transfer fluids. Low thermal conductivity is a major limitation for the development of energy efficient heat transfer fluids required for many industrial applications.

Patent Document 1 relating to Segal discloses an in-carrier fluid for insulating and cooling an electromagnetic device that generates heat as a result of using a large current density and a large alternative current (AC) voltage inside the electromagnetic device. Discloses a colloidal fluid having metal particles. Also, a new type of heat transfer fluid has been developed by suspending metal particles or metal oxide particles in a liquid, as disclosed in Patent Document 2 related to Choi et al. Metal particles or metal oxide particles are generated and dispersed in a vacuum while passing through a liquid film in the vicinity of a heated substrate.
US Pat. No. 6,221,275 US Pat. No. 5,863,455

  Carbon nanotechnology, an emerging technology, is promising in many aspects of engineering applications. In recent years, carbon nanotubes have been proposed with increasing popularity as stable nanomaterials with improved thermal conductivity. However, carbon nanotubes are strong and flexible, but very cohesive. This makes it difficult to evenly distribute the carbon nanotubes in the fluid in order to provide an effective heat transfer material in energy management.

  An example of the present invention provides a method for preparing or manufacturing carbon nanofluids having improved thermal conductivity or thermal conductivity. This method involves the process of preparing, preparing or providing a base fluid, the process of preparing many or multiple carbon nanotubes, the mixing or the mixing of carbon nanotubes with the base fluid. The process of combining and the process of dispersing carbon nanotubes substantially uniformly in the base fluid by physical agitation operation, and the physical operation during the physical agitation operation It includes the process of cooling the system.

  Another example of the present invention provides a method for preparing a fluid that can serve as a heat transfer agent. This method involves introducing a number or groups of functional groups onto the carbon nanotubes in order to produce or prepare functionalized or functionalized carbon nanotubes, preparing a base fluid, The process of mixing or bonding the functionalized carbon nanotubes with the base fluid, and the process of dispersing the carbon nanotubes substantially uniformly in the base fluid by an ultrasonication operation, during the sonication operation The process includes cooling the system performing the sonication operation.

  In yet another example, the present invention provides a carbon nanofluid that can be used as a heat transfer fluid. Carbon nanofluids are approximately 99.8-98% by volume base fluid and approximately 0.2-2.0% by volume functionalized carbon nanotubes substantially evenly dispersed in the base fluid. This carbon nanofluid has a thermal conductivity at least 1.3 times higher than the base fluid without any carbon nanotubes.

  In yet another example, the present invention introduces many or more functional groups onto a carbon nanotube to prepare (or prepare and provide) a functionalized carbon nanotube, Prepare and mix the functionalized carbon nanotubes with the base fluid, then disperse the carbon nanotubes substantially uniformly in the base fluid by sonication operation, and perform the sonication operation during the sonication operation A carbon nanofluid produced by a process of cooling a system is provided.

  The foregoing summary, as well as the more detailed description of the invention that follows, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.

  Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

  The present invention provides a method for preparing carbon nanofluids. This method involves preparing or preparing a base fluid, preparing or preparing a number of carbon nanotubes, mixing or combining carbon nanotubes with the base fluid, and physically stirring the carbon nanotubes into the base fluid. Including substantially evenly dispersing and cooling the system performing the physical agitation operation during the physical agitation operation.

  The carbon nanotube described in the present invention includes at least one of single-walled, double-walled, and multi-walled carbon nanotubes having a plurality of functional groups thereon.

  Accordingly, the term “functionalize” or “functionalize” in the present specification means that the thermal conductivity or thermal conductivity of the carbon nanomaterial in an aqueous solution, an inorganic solution, or an organic solution, and an acid treatment that improves the solubility. It means that a plurality of functional groups are introduced on the surface of the carbon nanomaterial by chemical modification.

In one embodiment of the invention, each of the functional groups comprising COOH is treated by treating the carbon nanotubes with an acidic solution comprising at least one of H ₂ SO ₄ , HNO ₃ , HC1 and CH ₃ COOH. be introduced. The functionalized carbon nanotubes are mixed or combined with the base fluid and then dispersed substantially evenly in the base fluid by a physical stirring operation. The cooling operation can be applied to cool the system performing the physical agitation operation during the physical agitation operation.

In another embodiment of the present invention, the carbon nanotubes are surface-modified or functionalized by treating the carbon nanotubes with an acidic solution containing H ₂ SO ₄ and HNO ₃ . As a result, functional groups containing COOH are introduced onto the surface of the carbon nanotube. The functionalized carbon nanotubes can be further purified or purified by high speed centrifugation to separate the unbound acid mixture from the functionalized carbon nanotubes. Subsequently, the purified or purified carbon nanotubes are washed with the base fluid before they are combined with or combined with the base fluid and dispersed in the base fluid. The functionalized carbon nanotubes are mixed with the base fluid and then dispersed in the base fluid by a magnetic stirring operation or a physical stirring operation such as a sonication operation. The cooling operation is performed during the physical agitation operation to cool the system performing the physical agitation operation.

In a further embodiment of the invention, the carbon nanotubes are surface modified or functionalized by treating the carbon nanotubes with an acidic solution comprising H ₂ SO ₄ and HNO ₃ in a ratio of about 3: 1. The functionalized carbon nanotubes can be further purified, purified or purified by applying high speed centrifugation to separate the unbound acid mixture from the functionalized carbon nanotubes. Subsequently, the purified carbon nanotubes are washed with the base fluid before being mixed with the base fluid and dispersed into the base fluid. The purified or purified carbon nanotubes are subsequently mixed with the base fluid and dispersed into the base fluid by sonication operations. The cooling operation is performed during the sonication operation to cool the system performing the sonication operation. According to one example, the sonication operation can be performed using an ultrasonic homogenizer with a cooling system disposed adjacent to the ultrasonic homogenizer to cool the ultrasonic homogenizer.

  As explained in the above examples, it is noted that although carbon nanotubes are functionalized with an acidic solution, the present invention is not limited to functionalizing carbon nanotubes using this particular technique. Other surface modification techniques that cause the addition or introduction of functional groups onto the carbon nanotubes may be employed.

  The present invention also provides a method of preparing a fluid that can serve as a heat transfer material. The method includes introducing a number of functional groups onto the carbon nanotubes to provide functionalized carbon nanotubes, providing a base fluid, mixing the functionalized carbon nanotubes with the base fluid, and The method includes substantially uniformly dispersing the carbon nanotubes in the base fluid by an sonication operation, and cooling the system performing the sonication operation during the sonication operation.

Similarly, carbon nanotubes such as single-walled, double-walled, and multi-walled carbon nanotubes can be functionalized by treating the carbon nanotubes with an acid mixture containing H ₂ SO ₄ and HNO ₃ in a ratio of about 3: 1. Is done. The functionalized carbon nanotubes can be further purified or purified by high speed centrifugation that separates the unbound acid mixture from the functionalized carbon nanotubes. Subsequently, the purified or purified carbon nanotubes may be washed before being mixed with the base fluid and dispersed into the base fluid. Purified or purified carbon nanotubes are subsequently mixed with the base fluid and dispersed substantially evenly in the base fluid by sonication operations. And during the sonication operation, the cooling operation is applied to cool the system performing the sonication operation.

In one preferred embodiment, the functional group is treated with an acid mixture comprising H ₂ SO ₄ and HNO ₃ in a ratio of about 3: 1 by the laboratory apparatus shown in FIG. By doing so, it is introduced into the carbon nanotube. The laboratory apparatus 1 includes a beaker 10, a reflux system 11 coupled to the beaker 10, and a heating table 12. The mixture in the beaker 10 is heated on the heating table 12 and stirred. When the liquid is heated above the boiling point at which it evaporates (or boils), the reflux system 11 condenses the vaporized gas into liquid droplets that are recirculated into the beaker 10. Subsequently, the functionalized carbon nanotubes can be further purified or purified by high speed centrifugation that separates the unbound acidic mixture from the functionalized carbon nanotubes. It is. The purified or purified carbon nanotubes are washed with the base fluid before being mixed with the base fluid and dispersed into the base fluid.

  The sonication operation dissipates the heat generated by the ultrasonic homogenizer 2 to cool the base fluid and is adjacent to a dual tube heat exchanger 3. This is carried out using an ultrasonic homogenizer 2 arranged in the manner described above. Referring to FIG. 2, the ultrasonic homogenizer 2 includes an ultrasonic probe 20 and a power source 21 that is connected to the ultrasonic probe 20 and supplies electric power necessary for the ultrasonic processing operation. The ultrasonic probe 20 is arranged such that the tip 20a of the ultrasonic probe 20 is immersed in the base fluid so as to provide dispersion. The double-pipe heat exchanger 3 has an inner portion or inner tube 30 that receives the base fluid, and an outer portion or outer tube 31 that surrounds the inner tube 30. The outer tube 31 is filled with a fluid that dissipates or removes heat generated by the ultrasonic probe 20. As shown in FIG. 2, the outer tube 31 has an inlet 311 disposed at the bottom end and an outlet 312 disposed at the top end, and the fluid passes through the inlet 311 and flows into the outer tube. 31 is discharged through the outlet 312 to cool the ultrasonic homogenizer 2. Therefore, the ultrasonic processing operation is not interrupted as a result of the ultrasonic probe 20 being overheated by the substantially high power supplied to the ultrasonic probe 20 over a period of time. This ensures that a high power constant output during the sonication operation achieves an optimal dispersion effect.

  According to another preferred embodiment of the present invention, the cooling system includes a double pipe heat exchanger 3 and a cooling circulation system 4 as shown in FIG. Referring to FIG. 3, the double-tube heat exchanger 3 is cooled and circulated in such a manner that the fluid flowing out of the outer tube 31 is recirculated by returning to the outer tube 31 through the pipe 40 so as to dissipate heat. Connected to system 4. Furthermore, the pipe 40 is connected to a cooling bath 41 to further cool the fluid in the pipe 40 before the fluid is redirected back to the outer tube 31 of the double tube heat exchanger 3. Also good. Thus, the cooling system shown in FIG. 3 efficiently recirculates fluid to achieve heat dissipation or cooling of the ultrasonic homogenizer without wasting too much fluid. Thus, the total cost of nanofluid preparation is effectively reduced.

  It should be noted that the cooling system in the present invention is not limited to the specific apparatus or means described in the above embodiment. For example, the cooling system may be modified or improved in the knowledge of a technician skilled in heat exchange technology to achieve a similar cooling effect in the ultrasonic probe and ultrasonic homogenizer.

  In view of the preparation methods described above, the present invention further provides carbon nanofluids that can serve as heat transfer fluids. The carbon nanofluid comprises approximately 99.8-98% by volume of the base fluid and approximately 0.2-2.0% by volume of carbon nanotubes substantially evenly dispersed within the base fluid. This carbon nanofluid has a thermal conductivity that is at least 1.3 times higher than the base fluid without any carbon nanotubes.

  The present invention further introduces a number of functional groups onto the carbon nanotubes to provide functionalized carbon nanotubes, prepares or prepares the base fluid, mixes the functionalized carbon nanotubes with the base fluid, Provides carbon nanofluids produced by a process that disperses carbon nanotubes substantially uniformly in the base fluid by sonication operation and cools the system performing the sonication operation during the sonication operation To do.

  According to the present invention, the base fluid includes, but is not limited to, organic solvents, inorganic solvents, and aqueous solutions that disperse carbon nanotubes substantially evenly to serve as a heat transfer material. Further, depending on the actual application, the base fluid includes at least one of ethylene glycol, water and oil. The invention also includes carbon nanofluids mixed with surfactants or dispersants and methods for their preparation, but confining carbon nanotubes to mask or reduce high thermal conductivity, or More preferably, the fluid complex or carbon nanofluid is prepared without the addition of a surfactant or dispersant to be coated.

  The invention will now be described in further detail with the following specific, non-limiting examples.

Preparation of carbon nanofluids Single-walled, double-walled and multi-walled carbon nanotubes are commercially available (Nanotech Port, Shenzhen, China) and purchased in powder form. The carbon nanotubes were functionalized or surface modified by treatment with an acidic solution containing H ₂ SO ₄ and HNO ₃ in a ratio of approximately 3: 1 in the laboratory apparatus shown in FIG. Subsequently, the functionalized carbon nanotubes can be further purified or purified by high speed centrifugation that separates the unbound acid mixture from the functionalized carbon nanotubes. The purified or purified carbon nanotubes were washed with the working fluid before being dispersed into the base fluid by sonication.

  The sonication process was performed using an ultrasonic homogenizer in the presence of a cooling system such as the double-tube heat exchanger shown in FIG. 3 that can dissipate the heat generated by the sonication process. Thus, when the carbon nanotubes were dispersed into the base fluid by sonication, the heat generated by the ultrasound probe could be immediately dissipated as a result of the fluid flowing through the outer tube. This ensures stable operation of the ultrasonic homogenizer even if high power of approximately 300 to 600 W is supplied to the ultrasonic probe over a period of time during the ultrasonic processing operation. Accordingly, a substantially high power constant output was provided to disperse the carbon nanotubes into the base fluid substantially evenly during the sonication operation.

Measurement of Thermal Conductivity The thermal conductivity (k) of carbon nanofluids, as described in (Lee et al., Journal of Heat Transfer, Vol. 121, p. 280 (1999)), Measured with specially designed computer controlled equipment. Thermal conductivity was measured at room temperature as a function of nanotube volume content. In the thermal conductivity measurement, the carbon nanofluid was filled into a vertical, cylindrical glass container of a transient hot wire system. This long glass container has an inner diameter of 19 mm and a length of 240 mm. Within the transient hot wire system, a platinum wire having a diameter of approximately 76.2 μm was immersed in the carbon nanofluid. Platinum wire was used simultaneously as a heater and an electrical resistance thermometer for carbon nanofluids. The surface of the platinum wire was coated with a thin electrically insulating epoxy to prevent the platinum wire from shorting out. The temperature change of the platinum wire was obtained as a result of the change in electrical resistance over time. Thereafter, the thermal conductivity was estimated from Fourier's law. The thermal conductivity of the carbon nanofluid was inversely proportional to the temperature vs. time response slope of the platinum wire. The transient hot wire system was calibrated with deionized water and ethylene glycol at room temperature. The measurement uncertainty was less than 2%.

  Example 1: Nanofluid A (carbon nanotube / ethylene glycol)

  Nanofluid A was prepared by dispersing multi-walled carbon nanotubes in ethylene glycol. No surfactant was added to Nanofluid A. Furthermore, the carbon nanotubes were mixed with ethylene glycol and dispersed in ethylene glycol by a sonication operation at 600 W for approximately 1 hour. During the sonication operation, the cooling operation is performed using a double tube heat exchanger as shown in FIG. 2 to cool the nanofluid A during the sonication operation performed by the ultrasonic homogenizer. Applied.

表 １
The nanofluid A was then subjected to thermal conductivity measurements as described above. As described in Table 1 below, the thermal conductivity (indicated by the k value) is 0.01 (1 for the carbon nanotube / ethylene glycol suspension compared to ethylene glycol alone. It increased by 12.4% in the volume part of volume percent (vol.%). Thus, the small amount of carbon nanotubes dispersed according to the present invention significantly increased the thermal conductivity of the base fluid.

Table 1

  Example 2: Nanofluid B (carbon nanotube / water)

  Nanofluid B was prepared by dispersing multi-walled carbon nanotubes in water. No surfactant was added to Nanofluid B. Furthermore, the carbon nanotubes were mixed with water and dispersed in water by sonication operation at 600 W for approximately 1 hour. During the sonication operation, the cooling operation is performed using a double tube heat exchanger as shown in FIG. 2 to cool the nanofluid B during the sonication operation performed by the ultrasonic homogenizer. Applied.

表 ２
Nanofluid B was then subjected to thermal conductivity measurements as described above. As described in Table 2 below, the thermal conductivity is 0.015 (1.5 volume percent (vol.%) For the carbon nanotube / water suspension compared to water alone. ) Increased by 17.8%. Thus, the small amount of carbon nanotubes dispersed according to the present invention significantly increased the thermal conductivity of the working fluid.

Table 2

  Example 3: Nanofluid C (carbon nanotube / synthetic engine oil)

  Nanofluid C was prepared by dispersing multi-walled carbon nanotubes in a synthetic engine oil. N-hydroxysuccinimide (NHS) was added to Nanofluid C. Furthermore, the sonication operation at 600 W for approximately 1 hour combined the carbon nanotubes with the synthetic engine oil and dispersed within the synthetic engine oil. During the sonication operation, the cooling operation is performed using a double tube heat exchanger as shown in FIG. 2 to cool the nanofluid C during the sonication operation performed by the ultrasonic homogenizer. Applied.

表 ３
Nanofluid C was then subjected to thermal conductivity measurements as described above. As described in Table 3 below, the thermal conductivity is 0.02 (2.0 volume percent (vol.) For the carbon nanotube / synthetic engine oil suspension compared to the oil alone. %)) By 30.3%. Thus, the small amount of carbon nanotubes dispersed according to the present invention significantly increased the thermal conductivity of the working fluid.

Table 3

  In spite of the above examples, in view of the carbon nanofluids and preparation methods described in the present invention, those skilled in the art will recognize whether carbon nanomaterials are incorporated into the interior, whether functionalized or not. It is understood that other base fluids that disperse can fall within the scope of the present invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be exemplary only, and that the true scope and spirit of the invention be considered as being indicated in the claims.

  Those skilled in the art will appreciate that modifications can be made to the described embodiments without departing from the broader concepts of the present invention. Accordingly, it is to be understood that the invention is not limited to the particular embodiments disclosed, but is intended to cover modifications within the spirit and scope of the invention as defined by the claims.

1 is a schematic diagram illustrating an experimental apparatus for producing functionalized carbon nanotubes, according to one embodiment of the present invention. It is the schematic which shows the ultrasonic homogenizer arrange | positioned adjacent to the double pipe | tube type heat exchange system based on the other Example of this invention. FIG. 2 is a schematic diagram illustrating a dual tube heat exchange system according to a further embodiment of the present invention.

Explanation of symbols

  1 laboratory apparatus, 2 ultrasonic homogenizer, 3 double tube heat exchanger, 4 cooling circulation system, 10 beaker, 11 reflux system, 12 heating table, 20 ultrasonic probe, 21 power supply, 30 inner tube, 31 outer tube , 40 pipes, 41 cooling tanks.

Claims (15)

A method of preparing a carbon nanofluid comprising:
Preparing the base fluid; and
The process of preparing many carbon nanotubes,
Mixing the carbon nanotubes with the base fluid;
A process of substantially uniformly dispersing the carbon nanotubes in the base fluid by a physical stirring operation;
Cooling the system performing the physical stirring operation during the physical stirring operation.   The method according to claim 1, wherein the physical stirring operation includes sonication.   The carbon nanotube comprises at least one of single-walled, double-walled and multi-walled carbon nanotubes having a plurality of functional groups introduced thereon. the method of.   The method of claim 3, wherein each of the functional groups comprises COOH.   The method of claim 1, wherein the base fluid comprises at least one of ethylene glycol, water, and oil. A method of preparing a fluid that can be used as a heat transfer medium, comprising:
Introducing a number of functional groups onto the carbon nanotubes to produce functionalized carbon nanotubes;
Preparing the base fluid; and
Mixing the functionalized carbon nanotubes with the base fluid;
A process of dispersing the carbon nanotubes substantially uniformly in the base fluid by an ultrasonic treatment operation;
Cooling the system performing the sonication operation during the sonication operation. The process of introducing the functional groups, the H ₂ SO ₄ and HNO ₃ to about 3: characterized in that it comprises a step of treating with an acidic solution containing 1 ratio The method of claim 6.   The method of claim 7, further comprising the step of purifying the functionalized carbon nanotubes by high speed centrifugation prior to mixing the carbon nanotubes with the base fluid.   9. The method of claim 8, wherein the carbon nanotubes comprise at least one of single-walled, double-walled and multi-walled carbon nanotubes.   9. A method according to claim 8, characterized in that each of the functional groups comprises COOH.   9. The method of claim 8, wherein the base fluid comprises at least one of ethylene glycol, oil, and water. A carbon nanofluid that can be used as a heat transfer fluid,
(A) a base fluid of approximately 99.8-98% by volume;
(B) approximately 0.2-2.0% by volume functionalized carbon nanotubes substantially uniformly dispersed in the base fluid;
A carbon nanofluid characterized by having a thermal conductivity at least 1.3 times higher than that of a base fluid having no carbon nanotubes.   The functionalized carbon nanotubes described above comprise at least one of single-walled, double-walled and multi-walled carbon nanotubes having a number of functional groups introduced thereon, Item 13. The carbon nanofluid according to Item 12.   The carbon nanofluid according to claim 12, wherein the base fluid includes at least one of ethylene glycol, water, and oil. Introducing a number of functional groups onto the carbon nanotubes to produce functionalized carbon nanotubes;
Preparing the base fluid; and
Mixing the functionalized carbon nanotubes with the base fluid;
A process of dispersing the carbon nanotubes substantially uniformly in the base fluid by sonication operation;
A carbon nanofluid manufactured by a method including a step of cooling a system performing the ultrasonic treatment operation during the ultrasonic treatment operation.

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