FIELD OF INVENTION
The present innovation relates to synthesis of two dimensional carbon nanomaterials
and thermal conductivity characteristics of two dimensional carbon nanomaterials
dispersed in heat-exchange fluids/radiator coolant base fluid for automotive applications.
More particularly, the invention relates a process for producing an improved heat
exchange fluid from two dimensional carbon nanomaterials.
BACKGROUND OF THE INVENTION
Heat-transfer fluids (HTFs) are used as heat carriers in many applications. HTFs usage
include but not limited to the removal or exchange of excess heat from stationary and
automotive internal combustion engines, heat generated by electrical motors and
generators, process heat and condensation heat (refineries and steam generation
plants). The most influencing characteristics involved in producing an energy-efficient
heat-transfer fluid are the thermal conductivity and heat capacity. The conventional heat
transfer liquids are water, ethylene glycol (EG), engine oil, and transformer oil. The
conventional fluids are having low thermal conductivity compared to solids (metal/metal
oxides). Therefore, the thermal conductivities of fluids that contain suspended
metal/metal oxide particles is expected to be significantly high when compared to
conventional fluids. However, bulk and micro size of solid particles if present in heat -
transfer fluids cause sedimentation, and reversely affect the heat dissipation and
thermal conductivity of a working system. In addition to these, presence of solid
particles increases the pressure drop in the working system significantly, which increases
the required pumping power and associated operating cost.
Low thermal conductivity is a primary limitation in the development of energy efficient
heat exchange fluids required in many industrial and auto-coolant applications. To
overcome this limitation, a new class of heat exchange fluids is known in the art which is
produced by suspending nanoparticles and carbon
nanomaterials (CN). S.U. Choi et A1 [1] proposed the use of nanoparticles in heat-
transfer fluids such as water, ethylene glycol and engine oil to produce a new class of
engineered fluids (nanofluids) with improved heat-transfer capabilities. Consequently,

the nanofluids possess intriguing properties such as high thermal conductivity, stability
and prevention of clogging in micro-channels. Also, heat exchange fluids with carbon
nanomaterials are expected to possess even better heat transfer properties due to the
nonspherical shape and high aspect ratio of carbon nanomaterials [2]. CNs found to
eliminate most of the problems arising with slurries like sedimentation, agglomeration,
erosion, excessive pressure drop etc. Even through carbon nantubes have promising
properties, fundamental problems still exist: how to (1) remove impurities, such as
amorphous carbons and metallic catalysts and (2) obtain uniform dispersions of the
carbon nanotubes in dispersing media. Covalent modification (chemical functionalization)
of nanomaterial was devised to achieve good dispersability and conductivity.
At present, the heat-exchange fluids/engine coolants contain additive (micro particles)
to enhance the thermal conductivity/heat transfer. It is considered that the dispersion of
a small amount of two dimensional carbon nanomaterials in heat-exchange fluids/engine
coolant base fluid normally leads to large enhancement in thermal conductivity and heat
transfer rate.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a process for producing an improved
heat exchange fluid from two dimensional carbon nanomaterials.
Another object of the invention is to propose a process for producing an improved heat
exchange fluid from two dimensional carbon nanomaterials, which can be dispersed in
heat-exchange fluids/engine coolant with out any surfactant.
Yet another object of the invention is to propose a process for producing an improved
heat exchange fluid from two dimensional carbon nanomaterials, which covalently
modify the surface of the two dimensional carbon nanomaterials by using oxidizing acid
mixture for dispersion in the coolant base fluid.
A still another object of the invention is to propose a process for producing an improved
heat exchange fluid from two dimensional carbon nanomaterials, which improves the
thermal conductivity and heat-transfer characteristics of heat-exchange fluids/engine
coolant.

SUMMARY OF THE INVENTION
According to the invention, two dimensional Graphene nanomaterials have been
synthesized by exfoliation of graphitic oxide (EG). Graphic oxide (GO) has been prepared
by Hummers method [3]. The material is characterized with different known techniques.
The synthesized Graphene is chemically functionalized with cone. H2SO4 and HNO3 to
bring on required functional groups and then dispersed in commercially available coolant
without any surfactant. The thermal conductivity and specific heat capacity of these
nanofluids for different volume fraction have been measuredby varying the temperature.
The % volume fraction varies from 0.005 to 0.035 and the temperature ranges from
30°C to 75°C. The experiments have been repeated a minimum of 5 times for
consistency and the conclusions have been drawn.
The present invention enables synthesis of heat-exchange fluids such that high thermal
conductivity/heat transfer at low volume fraction of less than 0.03% of two dimensional
carbon nanomaterials is achieved.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Graphically represents a thermal conductivity of nano-doped coolant for
different volume fraction as a function of temperature
Figure 2 - Graphically shows thermal conductivity of nano-doped coolant for
different volume fraction at room temperature
Figure 3 - Graphically shows thermal conductivity of nano-doped coolant for
different time periods
Figure 4 - Graphically represents specific heat capacity of nano-doped coolant at
varying temperature for different volume fraction.

DETAILED DESCRIPTION OF THE INVENTION
According to the invention exfoliated graphene (EG) is prepared from graphitic oxide
(GO). Graphic oxide is prepared by Hummers method. The as synthesized EG is found to
be insoluble in water as exfoliation takes out oxygen containing functional groups from
the sample. Now, the sample becomes hydrophobic. In order to induce hydrophilicity,
the sample is treated with cone. H2SO4: HNO3 (3:1). The acid treatment has been done
by ultrasonicating the sample for 3h and washed several times with Dl water then
filtered and dried in vacuum. The chemically functionalized EG is referred as f-EG.
Figure 1 shows the thermal conductivity chart of f-EG doped coolant for different volume
fraction as a function of temperature. Thermal conductivity measurements follows the
transient hot-wire technique [4, 5]. Thermal conductivity of base fluid coolant
(commercial coolant) and f-EG doped coolant is measured with varying temperature
from 30-75 °C. Thermal conductivity increases with temperature and maximum
enhancement is observed for volume fraction of 0.015% f-FG.
Figure 2 is a plot of thermal conductivity and volume fraction at room temperature. The
maximum enhancement has been observed for 0.015% volume fraction. And, lateral
decrease in thermal conductivity can be attributed to thermal saturation with
concentration of the dispersed nanomaterials. Figures 1 and 2 envisage utmost thermal
enhancement of f-EG doped coolant at 0.015% volume fraction.
Figure 3 above shows the stability of the solution as well as the thermal conductivity
measurement. The thermal conductivity of 0.015% volume fraction nano-coolant was
measured in an interval of 20 hrs for 120 hrs. The thermal conductivity was almost same
throughout the process (120 hrs). This indirectly shows the stability of the nano-coolant.
Figure 4 shows graphical plot of specific heat capacity with different volume fractions
and temperature. The specific heat enhancement follows similar trend to thermal
conductivity chart.

References
[1] Choi SUS Enhancing thermal conductivity of fluids with nanopartides. ASME Fluids
Eng Div (Publ) FED 231:99-105,1995.
[2] F.D.S Marquis and LP.F. Chibante Improving the Heat Transfer of Nanofluids and
Nanolubricants with Carbon Nanotubes JOM :32, 2005
[3] Hummers WS, Offeman R E Preparation of graphitic oxide. J Am Chem Soc 80: 1339,
2005.
[4] Hong TK, Yang HS, Choi CJ Study of the enhanced thermal conductivity of Fe
nanofluids J Appl Phys 97:1-4, 2005.
[5] Ding Y, Alias H, Wen D, Williams RA Heat transfer of aqueous suspensions of carbon
nanotubes (CNT nanofluids). Int J Heat Mass Transf 49:240-250, 2006.

WE CLAIM
1. A process for producing an improved heat-exchange fluid from two-dimensional
carbon nanomaterials, comprising:
- providing graphite oxide prepared by Hummers method; synthesizing the
graphite oxide to produce exfoliated graphene (EG);
- dispersing the chemically funcitionalized EG in commercially available coolant
without surfactant.
f
2. The process as claimed in claim 1, wherein the synthesized EG is treated with
concentrated H2SO4 and HNO3 (3:1) to induce hydrophilicity, and wherein the
acid treatment is conducted for at least two hours, thirty minutes, washed
several times with DI water, filtered, and dried in vacuum.
3. The process as claimed in claim 1, wherein the maximum enhancement in
thermal conductivity of the chemically functionalized EG (f-EG) is achieved at
volume fraction of 0.015% f-EG.
4. Improved heat-exchange fluid from two-dimensional carbon nanomaterial, as
substantially described and exemplified herein with reference to the
accompanying graphs.

The present invention relates to a process for producing an improved heat-exchange
fluid from two-dimensional carbon nanomaterials, comprising graphite oxide prepared by
Hummers method; synthesizing the graphite oxide to produce exfoliated graphene (EG);
dispersing the chemically functionalized EG (f-EG) in commercially coolant without
surfactant; and validating the thermal enhancement of chemically f-EG at different
temperature, concentration and time periods.