Nano carbon materials for enhancing thermal transfer in fluids

Details Nano carbon materials for enhancing thermal transfer in fluids Nano carbon materials for enhancing thermal transfer in fluids

2002-01-29

2004-02-24

Green, Anthony J. (Department: 1755)

Compositions

Frost-preventing, ice-thawing, thermostatic, thermophoric,...

C165S104190

Reexamination Certificate

active

06695974

ABSTRACT:

BACKGROUND OF THE INVENTION
Improvements in the heat transfer ability of working fluids in thermally-based energy systems can lead to increased conversion efficiencies, lower pollution, decreased costs including operation and maintenance cost, improved reliability, and could facilitate the miniaturization of energy systems. Traditional heat transfer fluids, such as water, oils, ethylene glycol and its mixtures are inherently poor heat transfer fluids, but they have been the classics as nothing better existed. There is a strong need to develop advanced heat transfer fluids, with significantly higher thermal conductivities that achieves improved heat transfer characteristics than are presently available. Despite considerable previous research and development focusing on industrial heat transfer requirements, major improvements in heat transfer capabilities have been held back because of a fundamental limit in the thermal conductivity of conventional fluids. Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids that are required in a plethora of heat transfer applications.
It has been demonstrated that the addition of metal and oxide nanoparticles that are small enough to remain in suspension in a fluid can substantially enhance the thermal conductivities of the fluid and thus substantially enhance heat transfer. See Choi,
“Enhancing Thermal Conductivity of Fluids with Nanoparticles,” Developments and Applications of Non-Newtonian Flows,
eds. Siginer et al.,
The American Society of Mechanical Engineers
, New York, FED-Vol. 66, pp. 99-105 (Nov. 1995); Lee et al.(I),
“Application of Metallic Nanoparticle Suspensions in Advanced Cooling Systems,” Recent Advances in Solids/Structures and Application of Metallic Materials,
eds. Kwon et al.,
The American Society of Mechanical Engineers
, New York, PVP-Vol. 342/MD-Vol. 72, pp. 227-234 (Nov. 1996); Eastman et al.(I),
“Enhanced Thermal Conductivity through the Development of Nanofluids,”
Invited paper presented at
Materials Research Society
1996
Fall Meeting
, Boston, Dec. 2-6, 1996, also published in
Proceedings of Symposium on Nanophase and Nanocomposite Materials II, Materials Research Society
, Boston, Vol. 457, pp. 3-11 (1997); Lee et al.(II),
“Measuring Thermal Conductivity of Fluids Containing Oxide Nanoparticles,” ASME Tran. J. Heat Transfer,
Vol. 121, pp. 280-289 (1999); Wang et al.,
“Thermal Conductivity of Nanoparticle-Fluid Mixture,” J. of Thermophysics and Heat Transfer
, Vol. 13, No. 4, pp. 474-480, October-December (1999); Eastman et al.(II),
“Anomalously Increased Effective Thermal Conductivities of Ethylene Glycol-Based Nanofluids Containing Copper Nanoparticles,”
To appear in
Applied Physics Letters,
2001
; and Masuda et al.,
“Alteration of Thermal Conductivity and Viscosity of Liquid by Dispersing Ultra-Fine Particles
(
Dispersion of g-Al
2
O
3
, SiO
2
and TiO
2
Ultra-Fine Particles
),” Netsu Bussei (Japan), Vol 4, No. 4, pp. 227-233 (1993). The smaller the particle size the greater the effect of increasing the nanofluid thermal conductivity as well as the higher the thermal conductivity of the nanoparticle. For example, the thermal conductivity of a nanoparticle copper in a fluid provides a higher thermal conductivity than aluminum oxide because copper metal has a higher thermal conductivity than aluminum oxide.
To improve the suspension of copper in ethylene glycol, Eastman et al II, supra, found that the addition of thioglycolic acid substantially enhanced thermal conductivity of the nanofluid.
BRIEF STATEMENT OF INVENTION
An ideal nanoparticle which has high thermal conductivity is carbon in the structure or type of nanotube or diamond. Nanotubes can be produced in the architecture of single wall, double wall and multiwall. These forms of carbon can be chemically modified by addition of select chemicals that absorb or chemically attach to the carbon surface as well as functionally bond to the surface to provide a stable nanosuspension.
Briefly stated, the present invention is concerned with the provision of a novel heat transfer agent in the form of a fluid complex comprising a body of heat transfer fluid having suspended therein carbon nanoparticles in a quantity sufficient to enhance the thermal conductivity of the heat transfer complex, as compared to that of the body of heat transfer fluid per se.
The novel heat transfer agent, comprising the complex of a nanoparticle suspension in the heat transfer fluid provides improved heat transfer in a method wherein the fluid heat transfer agent is caused to flow in a closed path between first and second bodies, such as an evaporator and condenser of a heat exchange system, with which the fluid passes in heat exchange relationship as it flows through the closed system, thereby transferring heat energy from the warmer to the cooler of said bodies when at different temperatures.
Advantageously, the carbon nanoparticles are selected from carbon in the forms of sp
2
and sp
3
bonding types, which includes graphite and fullerenes, as well as diamonds.
The preferred form of carbon includes nanotubes, both single-walled and multi-walled.
Advantageously, the invention further involves the use of one or more coupling agents to further enhance the effectiveness of the carbon nanoparticles in the fluid heat exchange complex. Such coupling agents may be chemically bonded to the nanoparticle and may be organic radicals or compounds, organo-metallic radicals or compounds, or individual elements, such as those set forth below in this specification.
When the nanoparticles are of elongated form, such as a nanotube or elongated fullerene, as distinguished from a buckeyball form, the length to diameter ratio (l/d) should be greater than one (1) and preferably greater than two (2).
In one specific embodiment, the suspended nanoparticles consist essentially of fullerenes in the form of a fullerene epoxide and the body of heat transfer fluid comprises water in which the epoxide is soluble.
In another specific example, the suspended nanoparticles consist essentially of nanotubes having an organic coupling agent attached thereto and the body of heat transfer fluid comprises ethylene glycol.
In certain embodiments of the invention, the coupling agent may be incorporated within the molecular structure of the nanotube, which may be a fullerene or nanotube that comprises an endohedral compound encapsulating the coupling agents. Furthermore, the endohedral molecular structures comprising the nanotube may also be modified on its exterior by the provision of one or more coupling agents which, for example, may be radicals or compounds molecularly bonded thereto.
Advantageously, the nanotubes suspended in the fluid complex should have a maximum cross sectional size of about 100 nanometers and preferably of about 25 nanometers.
DESCRIPTION OF PREFERRED EMBODIMENTS
Carbon nanofluids will result in significant energy and cost savings for heat transfer thermal management, and will support the current trend toward miniaturization by enabling the design of smaller and lighter heat exchanger systems. Thermal resistances are reduced and power densities can be increased while dramatically reducing heat exchange pumping power with the use of nanofluids.
The connective heat transfer coefficient can be greatly increased in a solid-fluid two-phase system by adding carbon-based nanoparticles. Some of the reasons heat performance of carbon based nanoparticles in a fluid improve thermal conductivity or heat transfer of the fluid are:
1. The suspended carbon nanoparticles increase the surface area and the heat capacity of the fluid.
2. The suspended carbon nanoparticles increase the effective (or apparent) thermal conductivity of the fluid.
3. The interaction and collision among carbon particles, fluid and the flow passage surface are intensified.
4. The mixing fluctuation and turbulence of the fluid are intensified.
5. The dispersion of carbon nanoparticles flattens the transverse temperature gradient of the fluid.
Some additional factors whi

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