FIELD OF THE INVENTION
The present invention relates to a method of producing functionalized alumina
based nanomaterial from a salt and dispersing the capped nano material in a
non-polar solvent such as oil for enhancement of thermal conductivity of the
base fluid.
BACKGROUND OF THE INVENTION
Water is the most cost effective and widely used thermal fluid and easily
controllable with high heat transfer efficiencies. However, the main limitation of
water being used as thermal fluid, is that at a temperature above 100 °C it starts
to boil, transforms to steam and hence can only be used as a pressurized
medium, which inter alia impose restrictions upon handling and use of steamed
water to ensure safe operation. Thermal oils allow use of low pressure heat
transfer medium to achieve high temperatures which otherwise would have
necessitated a high pressure steam. Oils are used as heat transfer medium in
many applications.
Nanofluids are known colloidal suspensions with dispersed nanoparticles, which
enhance thermal conductivity of a base fluid. A higher thermal conductivity
decreases winding temperature for a given load. On the other hand, load of a
particular piece of equipment retrofit with a nanofluid can be substantially
increased without exceeding the maximum load stipulated in the specifications.
Either way, the use of nanofluid as a thermal fluid greatly reduces the
maintenance and replacement costs of aging equipment. Selection of a heat
transfer media for a specific application is dependent on factors for example,
density, thermal conductivity, specific heat and viscosity. Unlike water, the

viscosity, composition and properties of oil indeed change from one application
to another. Further, water is a hydrophilic wherein oil is hydrophobic. Therefore,
the dispersion technology adopted for water as the base fluid significantly varies
as compared to oil used as a base fluid.
Nanofluids based on water as the base solvent using various types of
nanomaterials have been studied extensively worldwide in order to understand
the effect on thermal conductivity as an important parameter. The extensive
research has been carried out in Alumina-water and CuO-water systems besides
few reports in Cu-water, and carbon nanotubes (CNT) based systems. The
nanoparticles used in three main systems, such as Al203-based, CuO-based and
Cu-based nanofluids were varied in the range of 13-300, 23-29 and 50-300 nm
respectively. The improvement in the thermal conductivity in such systems was
varied in the range of 1.10-1.29, 1.07-1.54 and 1.002-1.24 respectively. Limited
reports are available in metal oxide based nanofluids in oil and ethylene glycol.
The enhancement of thermal conductivity of a base fluid is an important
requirement for the future to improve thermal efficiency of different systems.
The concept of introducing additives to cooling media to enhance thermal
conductivity is not new. However, the idea of adding nano particles to cooling
media such as transformer oil, engine oil, bearing oil and gear oil etc., was only
realized recently for example, during the last five years. Choi and Eastman in
2001 (US 6221275) experimented on Duo-seal oil and HE-200 oil among other
base fluids including water. Nanocrystalline particles such as copper, copper
oxide and aluminum oxide were produced and dispersed in the fluid by heating

the substance to be dispersed in a vacuum while passing a thin film of the fluid
near the heated substance.
Davidson and Bradshaw in their patent US 7,390,428B2 (2008) disclosed use of a
soy-based oil as the base fluid and demonstrated an oil based system which
enhanced thermal conductivity. Nano diamond with average particle size of less
than 100 nanometer was used as the additive being an inert, dielectric oil
compatible material that is dispersible and readily suspended in transformer oil.
With the addition of this property- enhancing, cost-effective dispersion, the
thermal conductivity can be directly raised resulting in increase in oil life.
Lockwood et al. (US 7,449,432 B2/2008) taught use of nanomaterials as a
viscosity modifier and thermal conductivity improver for gear oil and other
lubricating compositions. The gear oils used in the invention had higher viscosity,
higher shear stability and improved thermal conductivity compared to known
available gear oils. The preferred nanoparticles reduced the coefficient of friction,
including reduced friction in the boundary lubrication regime. These properties
are obtained by replacing part or all the polymer thickener with nanomaterials of
suitable size, shape and composition.
Zhang et al. (US 0287326 AI/2008) described a lubricant oil composition with
nanoparticles with enhanced thermal conductivity for automatic transmission
fluids, power transmission fluids and hydraulic steering applications.
Choi et al. in a Korean patent application (2009-0075989, filed on 18th Aug 2009)
disclosed a preparatory method of lubricating oil having excellent extreme

pressure load resistance and wear resistance properties.
Tingler et at. (US patent application 12/6, 93,569 filed on 26th January 2010)
disclosed a lubricating oil composition with nanoparticles for use in a submersible
electric motor.
US patent US 2012/0032543A1, taught an improved oil composition which
includes a base oil comprising a hydrocarbon and a first additive comprising a
plurality of derivatized first additive nanoparticles dispersed within the base oil to
form a modified oil comprising a stabilized suspension of the derivatized first
additive nanoparticles in the base oil. The modified thermal conductivity is
substantially greater than the base thermal conductivity by introducing the
additive content to a maximum limit of 10 %.
US patent 8076809 describes an electric submersible motor comprising a
lubricating- oil that includes a base hydrocarbon oil and a plurality of
nanoparticles. The lubricant oil preparation method with suitable functionalization
is disclosed with nanoparticles up to 30% by volume and are selected from the
group consisting of carbon nanotubes; carbon nano-onions; graphite
nanoparticles, diamond nanoparticles and derivatives thereof: silicon dioxide
nanoparticles or organic functionalized derivatives thereof; aluminium oxide
nanoparticles or organic functionalized derivatives thereof; metal oxide
nanoparticles; metal sulfonates nanoparticles; molybdenum disulfide
nanoparticles or nanotubes; tungsten disulfide nanoparticles or nanotubes;
alumoxane nanoparticles or functionalized derivatives thereof; beryllium oxide
nanoparticles and nanotubes; carbide nanoparticles; nitride nanoparticles; and

combinations thereof.
US 2012/0032543 Al describes an improved oil composition which includes a
base oil comprising a hydrocarbon and a first additive comprising a plurality of
derivatized first additive nanoparticles upto 10 vol. % dispersed within the base
oil to form a modified oil comprising a stabilized suspension of the derivatized
first additive nanoparticles in the base oil. The nanoparticles used in this work
includes fullerene, graphene, graphite, nanodiamond, metallic oxide, metal
sulfonate, molybdenum disulfide, tungsten disulfide, alumoxane, metallic carbide,
metallic nitride, and combinations thereof.
US 2011/0232940 Al, a dielectric composition is disclosed comprising an ester
liquid or water and an additive to the ester liquid having a low ionization
potential than the ionization potential of the ester liquid. The method of
preparing the dielectric fluid is disclosed wherein the additive is present at a final
concentration in a range of between about 3% to about 10% by volume.
US 20120245058, teaches a method for developing nano graphene (<50 nm
size, 0.0001 wt % to about 15 wt %.) based water and oil for oil and gas
exploration applications. Suitable graphene nanoparticles including functionalized
graphene, chemically-modified graphene, covalently-modified graphene,
graphene oxide, and combinations thereof were used for understanding
rheology, stability, lubricity, electrical properties, viscosity and thermal properties
of the base fluids.
Thus, the prior art is substantially silent on different oil. The prior patent
described hereinabove generally described physical method of dispersion using

suitable fictionalization to the nano-materials. Further, in most of the cases,
carbon based nano-materials were used, which are costly in nature. There is no
prior art available on chemical process of producing alumina based nanofluid.
Indian Patent Application number 1584/KOL/2011, teaches a method of
producing stable zircornia based nanofluid in non-polar solvent.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method of producing
functionalized alumina based nanomaterial from a salt and dispersing the nano
material in a non-polar solvent such as oil for enhancement of thermal
conductivity of the base fluid.
Another object of the invention is to propose a method of producing
functionalized alumina based nanomaterial from a salt and dispersing the nano
material in a non-polar solvent such as oil for enhancement of thermal
conductivity of the base fluid, in which different stable oil based nanofluid with
functionalized alumina for heat transport application is produced.
Yet another object of the present invention is to propose a method of producing
functionalized alumina based nanomaterial from a salt and dispersing the nano
material in a non-polar solvent such as oil for enhancement of thermal
conductivity of the base fluid, in which the thermal conductivity enhancement in
oil based nanofluids and the stability pattern, is validated.

SUMMARY OF THE INVENTION
According to the present invention, there is provided a method for producing
surface modified nano aluminum oxide based material dispersed in various oils.
Specifically, in one embodiment, a method is discussed by capping the material
with the surfactant in a reactor with a stabilizing agent. The present invention
relates, in part, to a method of dispersing the capped nanomaterial in oil
uniformly by ultrasonic disrupter. Another embodiment of the invention relates to
the dispersion stability of such fluids with different amount of nanoparticles in
oils. In another embodiment, the enhancement in thermal conductivity of such
oils has been determined. The method has been tried with different oils with
varying viscosities and the effect of such nanoparticles on the change of viscosity
is also studied.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a process flow chart depicting the method of the invention.
Figure 2 - shows a photograph of capped alumina based four different oils stable
beyond three months.
Figure 3 represents capped alumina based nanofluid in Transformer oil in a
volume fraction of 0.09 to 0.9.
Figure 4 - describes enhancement of thermal conductivity of capped alumina
based nano fluids by varying the volume fraction of nano-materials.
Figure 5 - represents the Newtonian nature of the nanofluids from the viscosity
data,
Figure 6 - shows the data representing the stability of such fluids in room
temperature for three month period

Figure 7 - is the stability in turbidity value of alumina based nanofluid in
transformer oil in lower concentrations for a three month period.
DETAILED DESCRIPTION OF THE INVENTION
As shown in figure 1, Surface modified alumina based nanoparticles was
prepared by precipitating a water soluble salt of Alumina with ammonia solution
and functionalizing with oleic acid in presence of a stabilizing agent. The
functionalized precipitate was dispersed in oil by an ultrasonic disrupter. The
estimation of alumina content in the precipitate was estimated and different
volume concentration of such functionalized nanoparticles can be dispersed in
different oils of varying viscosities.
In the first step, Aluminum nitrate is reacted with ammonia solution to obtain
aluminum hydroxide which is then capped with Oleic acid in a reactor with an
amine based material as stabilizing agent to produce an Al-Oleate complex. The
final product is then dispersed in oil using an ultrasonic disrupter.
In a typical experiment, aluminum nitrate [AI(N03)3.9H20] was dissolved in water
and reacted with ammonia solution to obtain a white precipitate. The resultant
precipitate was washed with distilled water in a centrifuge at 5000 rpm for 5 min
and repeated for four times. After the 5th wash, the precipitate was collected and
diluted with water and heated to 60 °C. At this stage, required amount of Oleic
acid was added with n-Butyl amine as the stabilizing agent in excess ammonia
and manually stirred for few minutes for uniformity. The solution was then
transferred into a high pressure reactor and kept in an oven at 110 °C for 10h.

Alternately, this experiment may be carried out in an actual autoclave too. After
cooling to room temperature, the solution was removed and acetone was added
in the ratio 1:1. The resultant solution was centrifuged at 5000 rpm for 2 min.
The precipitate was removed and kept in a hot air oven at 65 °C until all the
acetone evaporated. The white color precipitate changed color to reddish brown
after drying. This was then used for dispersion in different oils in different
concentrations using ultrasonic disrupter. Figure 1 summarizes the steps involved
in this invention. Figure 2 represents the alumina based nanofluids in different
oils and figure 3 represents the alumina based nanofluids in transformer oil at
different volume fraction of nanoparticles.
The embodiment of the present invention can be better explained with suitable
examples covering preparation method, preparing different concentration of
nanoparticles in four different oils, effect of stabilizing agent and measurement
of properties.
Example 1:
About 30 g of aluminium nitrate [AI(N03)3.9H20] was dissolved in approximately
160 ml of distilled water. Once aluminium nitrate was dissolved, approximately
40 ml of ammonia solution was added in small quantities while stirring for 1 hr.
The resultant solution was washed with distilled water in a centrifuge at 5000
rpm for 5 min. This action was continued for four times. After the 5th wash, the
precipitate was collected and approximately 400 ml of distilled water was added
and the solution was heated to 60 °C. At 600 °C, 30 ml of oleic acid was added
with 30 ml of n-butyl amine and 300 ml of ammonia at a stretch with stirring.

The obtained solution was then transferred into a high pressure stainless steel
reactor and kept in an oven at 110°C for 10 hrs. After cooling to room
temperature, the solution was removed and acetone was added in the ratio 1:1.
The resultant solution was centrifuged at 5000 rpm for 2 min, followed by
washing with acetone. The precipitate was removed and kept in the hot air oven
at 65°C until all the acetone evaporated. The cycle time of drying could be
drastically reduced from lOh to 3h by drying in microwave furnace. The
precipitate which was white in colour before drying turned into reddish brown
after drying. The final product was mixed in oil with a 250 watt ultrasonic
disrupter to obtain a solid nanoparticle dispersed oil solution.
Example 2:
Stable oil based nanofluids were prepared by dispersing the varied amounts of
functionalized product in the range of 1-10 %. The estimation of nanoparticle
was carried out by heating a known quantity of functionalized product at 1000
°C. It was noted that the solid content is 30 % and accordingly the volume
fraction of nanoparticles in the oils was calculated as 0.09-0.9 vol. %. In other
words the lg of the functionalized product can result in 0.3 g of nano alumina
particles. The oils chosen in this study are transformer oil, bearing oil, gear oil
and engine oil having varying viscosities though the thermal conductivity values
were not varying significantly and lying in the range of 0.128-0.141 W/mK
compared to 0.605 for water and -40 for alumina. The varying amount of
alumina nanoparticles in such oils resulted in enhanced thermal conductivity.
Figure 4 summarizes the thermal conductivity enhancement with volume fraction
of nanoparticles in different oils. The results also revealed that the thermal

conductivity does not change with room temperature varying from 22 to 32 °C in
the three month measurement period especially for high volume concentrations.
Example 3:
The thermal conductivity was measured using a KD2 Pro probe. It was noted
that the thermal conductivity can be enhanced with increasing functionalized
nanoparticles in oils. This has been represented in figure 2. The figure represents
the effective enhancement in thermal conductivity of oil with the varying
nanoparticle concentration. The enhancement in transformer oil based nanofluid
was in the range of 2-10 % for an effective nano solid content in the oil ranging
0,09- 0.9 vol, %. However, the enhancement was limited to 3 % with 0.4 vol. %
nanoparticles in other high viscous oils. The higher volume of functionalized
nanoparticles increased the viscosity content of the oils beyond 0.4 vol. % as
represented in figure 5, which may make ineffective for the intended application.
Therefore, an optimum concentration of nanoparticles in oil is desirable and
hence only transformer oil was studied further for stability and viscosity studies.
The Newtonian behavior of transformer oil could be maintained even with 0.9
vol. % alumina nanoparticle addition as revealed in figure 5.
Example 4
The stability of such nanofluids as depicted in figure 6 for transformer oil with
different volume fraction of nanoparticles have been observed over a long period
of time in many of these oils with suitable nanoparticles dispersion. Unlike
physical dispersion of nanomaterials in oil which make the nanofluid unstable

after a short time, the method adopted here can make stable nanofluid for a
much longer period of time as described in figure 6. The results demonstrated
that more than 90 days of stability of transformer oil based nanofluid can be
achieved, which can further be improved using this method with higher thermal
conductivity than the base fluid. The effect of stabilizing agent has also been
studied and an optimum concentration has been finalized. Further, the turbidity
of such nano fluids was found to be constant as depicted in figure 7 confirming
the stability of such fluids for the minimum 90 days period.
The above examples are not limited to the invention and are exemplary in
nature. Many experiments have been carried out in the laboratory by varying the
above procedure for preparation of functionalized product, dispersion
characteristics in different oils (figure 5), effect of stabilizing agents on the
stability of nanofluids, variation of viscosity with increase in volume fraction of
functionalized nanoparticles etc. The detailed experiments indicated that the
reactor method is suitable for effective functionalization of alumina based
nanomaterials and for enhancement of thermal conductivity of alumina based
nanofluid in low viscous oils like Transformer oil. This method can be tried out
with water soluble salts of other ceramic materials and further, this method can
be scaled up for large scale nanofluid preparation.
While preferred embodiments have been shown and described, it should be
understood that changes and modifications can be made therein without
departing from the invention in its broader aspects. Various features of the
invention are defined in the following claims:

WE CLAIM
1. A novel method of producing functionalized alumina based nanomaterial
from a salt and dispersing the nano material in a non-polar solvent such
as oil for enhancement of thermal conductivity of the base fluid, the
method comprising the steps of:-
- mixing a water soluble salt of alumina with ammonia solution to form a
precipitate;
- forming an aluminum Oleate complex by "adding oleic acid to the
mixture with a stabilizing agent and heating the mixture;
- extracting the Al-Oleate complex to acetone and centrifuged to obtain
the functionalized alumina based nanomaterial, followed by drying to
remove the acetone; and
- dispersing of the final functionalized product in oil by an ultrasonic
disrupter for 30-400 min. depending on the concentration of
nanoparticles.
2. A method as claimed in claim 1, wherein, a nitrate salt of aluminum is used
for producing the functionalized product.
3. A method as claimed in claim 1, wherein, the functionalization of the salt
is carried out in a stainless steel reactor at 110 °C for 6-10h.
4. A method as claimed in claim 1, wherein the stabilizing agent is n-Butyl
amine.

5. A method as described in claim 1, wherein stable nanofluids are obtained
in four different oils of varying viscosities in particular with low viscous oil
such as transformer off with nanoparticle concentration in a range of
0.09- 0.9 vol. %.
6. A method as claimed in claim 1, wherein, the thermal conductivity
enhancement is in the range of 2-10 % for transformer oil based
nanofluid.
7. A method as claimed in claim 1 wherein the alumina based nanofluids with
solid concentration in the range of 0.09-0.9 vol. % maintain Newtonian
behavior.

ABSTRACT

The present invention relates to a method for the preparation of alumina based
nanofluid in different oils. The method comprises a converting a water soluble
salt of alumina to a final product and functionalize the same in -situ prior to
dispersing in oil resulting stable nanofluids. The properties for example
enhancement of thermal conductivity, viscosity, stability over a period of time are
studied. The method disclosed herein can produce alumina based nanofluids
which can be stable at least for 90 days without significant deterioration in
thermal conductivity. The method is suitable for low viscous oils like transformer
oil and bearing oil to high viscous oils for example Gear oil and engine oil, with
more suitable in Transformer Oil.