TITLE:
A method for producing nanoparticle dispersed Glycol with improved thermal property
as a potential close circuit coolant
FIELD OF INVENTION:
The present invention relates to a method for producing a particle dispersed propylene
glycol with improved thermal conductivity than the base fluid and can be used in the
close circuit cooling applications.
BACKGROUND OF INVENTION:
Conventionally, water is regarded as the best coolant for most of the close circuit
applications due to its higher specific heat, low cost, easy to use and abundant availability
factors. However, water is prone to corrosive attack in a long run and the lower freezing
point of water does not allow it to use in a wide temperature range. To mitigate such
problems of water, deionization is done to remove corrosion initiating ions from water
and further corrosion inhibitors in small quantities are added to the deionized water to
provide a full proof coolant for a long run. The low freezing point issue of water is
traditionally solved by using a glycol mixed with water preferably a ethylene glycol (EG)

or propylene glycol (PG). The ethylene glycol is best among the glycols to improve the
freezing point of water, low viscous compared to its propylene glycol counterpart.
However, ethylene glycol is toxic to use and hence in most of the cases, the safe
propylene glycol is used as a major additive in water for close circuit cooling
applications.
Most of the glycol based coolant suppliers, supply concentrated glycol with corrosion
inhibitors and the user usually dilutes the same with deionized water to maintain a
suitable composition of coolant prior to use. The corrosion inhibitors can be a single
component or a mixture of component and usually added in very small quantity.
Chemicals like, amines, borates, silicates, phosphates etc. are used in different
proportions as corrosion inhibitors depending on applications and depending on the metal
used to carry such fluids. Phosphates are not good as they release harmful ions to the
water bodies during discard and increases Biological oxygen demand (BOD) and
Chemical oxygen demand (COD) of water. Similarly, Borates are not suitable in
aluminium carriers. Amines and nitrates sometimes react forming harmful compounds
such as nitrosoamine during operation. Calcium and magnesium ions form scales during
operations. Therefore, a judicious choice of such additives depending on application has
to be formulated to get the best cooling efficiency in the closed circuit cooling
applications.

Miyake and Mori have disclosed in an European Patent EP 112290 (2001) on the use of a
formulated pre-diluted glycol based coolant with a combination of corrosion inhibitors
comprising phosphates, nitrates, benzoates and triazoles in a very small quantity. Both
ethylene glycols and propylene glycol based deionized water solutions were prepared and
tested with the combination of corrosion inhibitors and finalized the coolant composition
for potential use in as received condition in internal combustion engines. Tsujii in an
European Patent EP 1564277 (2005) has described a method with water and glycol as the
main component and added with very small amount of metal or metal oxide nanoparticles
and suitably dispersed in the base fluid. The nanofluid thus obtained also contains metal
corrosion inhibitors. The addition of nanomaterials could improve the thermal
conductivity of the base alcohol-water mixture and with suitable addition of a carboxylic
acid, the fluid can be made stable. However, with viscosity increase may limit the use of
such fluid for a long period though the thermal conductivity can be enhanced in such
fluids. Charalampos et al had reported a glycol based coolant mixture in US patent US
4810404 which are free of nitrites and phosphates and containing alkali metal salts of
bis(carboxylalkyloxyphenyl)-2-2-propane and stabilized silicate and other corrosion
inhibitors. It was pointed out that the use of phosphates can confer protection not only on
iron but also an aluminium through the formation of passivating layers especially when
the admixture water is of high hardness. The large amount of phosphate may lead to poor
heat transfer due to erosion and radiation blockage. The US patent 5330670 by BASF

corporation highlights the development of a coolant composition with polymeric
polycarboxylates which prevents precipitation due to hard water and thus avoids scale
formation. The chemical is soluble in Glycols and is very effective in silicate / phosphate
type of coolant compositions. The US patent 7718033 by Kostic et al. had described a
one step method for producing ethylene glycol based nanofluid. The process involves the
particle source evaporation and deposition of the evaporant in a base fluid such as
ethylene glycol. The nanoparticle source, like a metal, evaporates at a given rate and the
gaseous molecules deposited onto the liquid film on the surface of the revolving drum
forming a nanofluid. This is however, an expensive process and commercially difficult
to implement. A recent patent 2012/0006509 described a zinc oxide in the range of 1%
to 4.5% by volume dispersed nanofluid with a suitable dispersant for close circuit
computer cooling application. The base fluid used in this work include polyethylene
glycol and polypropylene glycol. ACTA technology Inc. has reported a method in US
patent application 20130062555 regarding the development of pyrogenic nanoparticles
such as fumed alumina, titania and iron oxide or carbon nanotubes in the range of 0.01 -
10% dispersed nanofluid with Glycols as base fluid. This nanofluid is claimed to have
application in ground source heat pump and in similar other devices. The US patent
5288419 describes a method of forming glycol based coolant composition with

polymeric polycarboxylate additives as corrosion inhibitors. Choi et al in US patent
6221275 have described a method and apparatus for enhancing heat transfer in fluids
such as water, oil and glycols by dispersing suitable nanoparticles such as copper, copper
oxide, aluminium oxide etc. Nanoparticles are produced and dispersed in the base fluid
by vacuum heating the dispersed substance while passing a thin film of the base fluid
near the heated substance. Kostic et al. have described a one step method and system in
US 20100171068 for producing nanofluids by an evaporation-deposition technique. The
base fluid such as glycol is placed in a rotating cylindrical drum having an adjustable
heater boat evaporator and heat exchanger cooler apparatus. As the drum rotates, a thin
liquid layer is formed on the inside surface of the drum. The material evaporates forming
nanoparticles which is absorbed by the liquid film to form the nanofluid. In the patent
application WO 2013030845, the authors have described a method for producing stable
nanofluid based on glycol by dispersing nano metal oxide powder like alumina in the
base fluid with a suitable dispersant. The method further includes grinding the primary
mixture to obtain a concentrated nanoparticle suspension where the dispersant is added to
the primary mixture during the grinding after every predetermined time period. In a
patent US 2013 0056675 filed, the inventors have claimed the development of a high
volume alumina dispersed water upto 58.8% with 30-160 nm particle size. The dispersed

coolant finds application in nuclear reactor back up cooling. In a recent patent, MnC>2
nanotubes were dispersed in water and glycol based base fluids to produce stable fluids
using a chemical method comprising of solution and precipitation. The dopant
concentration was varied from 0.0001 -0.1 vol. % and the solution was claimed to be an
effective coolant.
Most of the inventions described above are either follows lengthy procedure such as
chemical methods, uses expensive nanoparticles like nanotubes or uses extensive
equipment like evaporation and condensation systems etc. to produce suitable nanofluids.
Further, in most of the inventions, the stability of the fluid is not elaborated. Therefore,
the present invention will deal with a very simple method of dispersing metal oxide
nanoparticles in propylene glycol and study its stability and thermal characteristics. The
developed fluid has significant potential as coolant in close circuit electronic applications.
OBJECTS OF THE INVENTION:
An object of the present invention is to propose a method of producing metal oxide nano
ceramic particle dispersed fluid in propylene glycol.
Another object of the present invention is to stabilize the suspension at least for two
months for use in practical applications.

A still another object of the present invention is to demonstrate thermal conductivity
enhancement of base fluid propylene glycol based suspension.
Further object of the present invention is to study the corrosion behavior of such fluids
with different metals.
BRIEF DESCRIPTION OF THE INVENTION:
According to the present invention there is provided a method for producing a nano
particle dispersed in a propylene glycol. A method for producing nano particle dispersed
glycol with improved thermal property comprising the steps of:
a) mixing of nanoparticles in the base fluid with magnetic stirring to form a
suspension;
b) subjecting the said suspension to the step of ultrasonication for 10-20h and
c) stabilizing the suspension without any surface active agent.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 summarizes the increase in viscosity of glycol based nanofluid with increase in
nanoparticle concentration. This limits the use of nanofluids with high nanoparticle
concentration. Figure 2 depicts the effect of thermal conductivity enhancement with
increasing the sonication time. With increasing sonication, the dispersion of nanoparticles
improves resulting in increase in thermal conductivity of the fluid. Figure 3 depicts the
thermal conductivity enhancement behavior increasing with rise in test temperature.
Figure 4 depicts the corrosion of different metals with stable PG based nanofluid. It was
observed that the MS is highly corrosive and SS and Cu are suitable as carrier for these
coolants. Figure 5 highlights the change in enhancement of thermal conductivity of 0.037
vol.% nanofluid with time. It was observed that the nanofluid can be made stable at least
for 90 days with at least 6% enhancement.

DETAILED DESCRIPTION OF THE PRESENT INVENTION.
The present invention is focused on developing a propylene Glycol based base fluid
dispersed with nano alumina particles by ultrasonication method. In the typical method,
the base fluid was taken in a beaker and was ultrasonicated with the requisite quantity of
nanomaterials with average particle size in the range of 20-30 nm. Various dispersing
agents were used to stabilize the nanomaterial suspension in propylene glycol, but none
of them resulted in long term stability. Further, various chemical methods were also
attempted such as reflux method for capping, but the stability of nanofluid produced by
these methods were not more than one week. Therefore, the physical process with
ultrasonication in absence of surface active agents was stabilized and varying the
sonication time in the range of 2-20h. It was noted that 10 h sonication of a 100 ml,
solution using a 250 watt sonicator is ideal for stabilizing the suspension for more than 90
days. However, high power sonicator may be used to reduce such sonication time and to
use larger amount of suspension.
The nanofluid was demonstrated to provide higher thermal conductivity than the base
fluid. The stability of the base fluid was monitored. The corrosion behavior of such
developed fluid was also studied. The effect of thermal conductivity of the nanofluid was
also observed with varying the nanoparticle content in the base fluid. The thermal
conductivity behavior at high temperature was also examined. The developed nanofluid is
a potential candidate as coolant in close circuit electronic systems.

The thermal conductivity of the suspension was measured using the concept of transient
heat technique method. The enhancement of thermal conductivity was measured by
comparing the data with that of base fluid. The viscosity of base fluid (propylene glycol)
was measured using Brookfield viscometer with spindle speed ranging from 0.3 - 12
rpm. Viscosities at different rpm were noted down and plotted against shear rate. In case
of Newtonian fluids, the viscosity remains constant with respect to shear rate. But base
fluid showed a non-newtonian behaviour in which decrease in viscosity with increase in
shear rate was observed. This implied propylene glycol is pseudoplastic or shear rate
thinning fluid. The viscosity of the nanofluid was found to be increased (figure 1) with
increasing nanoparticle concentration. However, higher particle concentration in the base
fluid makes the suspension not only lowers the stability but also not fit to use in
application. Therefore, low concentration of nanoparticles are suitable for making
nanofluids which will be stable and provide significant improvement in thermal
conductivity over a long period due to less chance of agglomeration of nanoparticles in
such condition.
The figure 2 summarizes the effect of ultrasonication time on the stability pattern of
alumina based nanofluid in PG. It was observed that more than10h is required to
stabilize the suspension for atleast one month. The effect of sonication time increasing to
20h was also compared with that of 10h sonicated suspension. It was noted that the
enhancement of thermal conductivity can be achieved from 6 % with 5h ultrasonication
to nearly 16% with 20 h of ultrasonication. The process breaks the agglomerates of
nanoparticles and allows them to disperse uniformly in the suspension contributing to the
improvement in heat transfer process. The particle size distribution of such nanoparticle
suspension as carried out by a Dynamic nanosizer revealed that inspite of lOh

ultrasonication the agglomerates size was in the range of 1 micron. Therefore, the
agglomerates size needs to be reduced and this can only be achieved by the synthesis of
such nanofluids by chemical methods starting from the precursors. This has been
confirmed by us in a separate work that the agglomeration size of alumina synthesized by
a reactor method in propylene glycol can be brought down to < 200nm. However, since
this process is lengthy and cumbersome, it was not followed in the study. Further, the
stability and thermal conductivity enhancement were not high and hence not continued
further.
Thermal conductivities of nanofluids were studied in a temperature range 30 to 50°C.
They were determined for every 5°C rise in temperature. Thermal conductivity was found
to increase with increase in temperature for both base fluid as well as for nanofluids
(figure 3). The variation of thermal conductivity for nanofluids found to follow the trend
of base fluid as shown in the figure below.
The corrosion study was carried out following ASTM D1384 (2012) guidelines by
inserting pre-weighed metallic pieces into the suspension of different nanoparticle
concentrations and maintained at 90 C using a hot water bath insulated with mineral
wool. The metal pieces were removed from the suspension after every 25h, washed in
water, dried and measured the weight loss or gain during such process. This was
continued for 200h and table 1 summarizes the loss or gain of four different metals
namely aluminium, copper, mildsteel and stainless steel (SS 304) during the entire
duration of the experiment. By comparing the pictures of metals which had been taken

before and after corrosion test, it was found that nanofluids changed their colour after
testing for corrosion. A gradual change of colour from white to brown was observed in
nanofluid to which mild steel was put. Copper had changed the color of sample light
yellow. There was no change of color in solutions, to which stainless steel and
aluminium metals were added. The % loss in weight of metal was determined using the
formula,

Where W1, W2 were the weight of metals before and after corrosion test respectively or
(W2-W1) represents the loss in the metal. The average loss or gain was estimated and
plotted in figure 4. The results indicated that the corrosion rate is lowest in SS 304 and
highest in MS. Therefore, the piping material to hold the coolant should be SS or in
some cases may be copper but never MS.
Ageing studies were done to know the shelf life of the nanofluid and to check any
deterioration of thermal properties with time. In the present study thermal conductivity
was determined for every 5 days and plotted against number of days. 0.0307, 0.176 and
0.263 vol% of nanofluids were kept in a capped 30 ml tube. Ageing studies were carried
out for 2-3 months and thermal conductivity was found to decrease with time. It was

noted from figure 5 that the initial high thermal conductivity value falls down with time
and gets stable after a certain period of time. The stability of such fluid thus can be
confirmed with substantial improvement in thermal conductivity over a time period with
low volume fraction of nanoparticles.
In summary, the propylene glycol based nanofluid with enhanced thermal conductivity by
stabilizing the dispersion of ceramic nanoparticles can be used as potential coolant in
close circuit cooling applications by mixing with water.
The present invention can better be explained with few suitable examples
Example 1: Three different volume fractions of alumina nanoparticles were separately
dispersed in propylene glycol by ultrasonication. The effect of sonication was studied by
varying the sonication time from 5 h to 20 h and the percentage enhancement in thermal
conductivity was monitored. This has been depicted in figure 2 and revealed that the
higher concentration of nanoparticles does not have much effect on the enhancement in
thermal conductivity of glycol nanofluid studied in this work. However, the enhancement
in thermal conductivity increased from ~ 6% with 5h ultrasonication time to ~ 15 % with
20 h of ultrasonication time. As the sonication time increases, more and more
agglomerates break up resulting more particles to contribute in thermal conductivity
enhancement. This experiment revealed that it is better to work on low volume fraction of
nanoparticles for better application of the nanofluid.

Example 2 : Three different volume fractions of alumina nanoparticles were separately
dispersed in propylene glycol by ultrasonication. The effect of temperature on thermal
conductivity enhancement was studied and summarized in figure 2. The experiment was
carried out by inserting the nanofluids in a closed test tube inside a hot water bath
insulated from outside with mineral wool. The thermal conductivity meter probe was
inserted into the fluid and measured the parameter at different intervals of time and also
at different temperature. The data in the figure 3 indicated that there is not much effect
on the improvement in thermal conductivity by increasing the nanoparticle content.
However, the thermal conductivity increased with increase in temperature. The viscosity
of all such fluids was also measured at room temperature. It was found that the viscosity
increased with nanoparticle concentration. Therefore, it is advisable not to use high
concentration of nanoparticles which are difficult to use for practical applications.
Example 3 : Three different volume fractions of alumina nanoparticles were separately
dispersed in propylene glycol by ultrasonication. Four different metal strips were added
separately to the test tube containing the nanofluids with varying nanoparticle
concentration. The suspensions sere heated in an insulated water bath at 90 deg C
following the guidelines of ASTM standard D 1384 (2012). After every 25 h, the
variation in weight of the metals were calculated after removing from the suspension and
drying. After 200 h of treatment, the average loss or gain was estimated for each of the
four metals namely : stainless steel (SS 304), aluminium, Mild steel and copper. It was
observed that in some cases, there was weight gain in the metal pieces due to oxidation
and in other cases, there was reduction in weight due to corrosion as depicted in figure 4.

However, the average loss/gain in weight after 200h treatment was plotted in figure and it
was noted that 0.037 % nanoparticle concentration is lower in both scale formation and
corrosion. This has been also summarized in the table 1. Therefore, it is essential to load
lower volume fraction of nanoparticles for better dispersion in the base fluid.
Example 4 : In this experiment, the variation in thermal conductivity was monitored for
all the three volume fraction of samples. It was noted that the initial high thermal
conductivity of nanofluid was reduced in all the cases and the enhancement of approx. 6
% was maintained for 0.037 vol. % suspension studied in this work after 30 days as
depicted in figure 5. However, for higher concentration suspensions, the stability could
not be maintained after 30 days and a separation of nanoparticle layer was obtained and
the enhancement in thermal conductivity was lowered. This experiment confirmed the
need for lower concentration of nanoparticles in the base fluid to improve substantially
the thermal conductivity. Therefore, 0.037 vol. % of alumina nanoparticles was chosen
as the optimum concentration in the propylene glycol based nanofluid.

WE CLAIM:
1. A method for producing nano particle dispersed glycol with improved thermal property
comprising the steps of:
a) mixing of nanoparticles in the base fluid with magnetic stirring to form a
suspension;
b) subjecting the said suspension to the step of ultrasonication for 10-20h and
c) stabilizing the suspension without any surface active agent.
2. The method as claimed in claim 1, wherein the nanoparticles are alumina nanoparticles
in the range of 30-40 nm and the concentration varies from 0.03 to 0.26 vol. %.
3. The method as claimed in claim 1, wherein for uniform dispersion of nanoparticles
ultrasonication probe of 250 watt is used to break the agglomerates of nanoparticles with
ultrasonication time varying in the range of 5-20 h.
4. The method as claimed in claim 1, wherein the enhanced thermal conductivity >
10 % was achieved with low fraction of nanoparticles of 0.037 vol. %.
5. The method as claimed in claim 1 wherein the stability of the fluid with 0.037 vol.
% nanoparticles more than 90 days was confirmed with 6% enhancement.

6. The method as claimed in claim 1, wherein the least corrosion with 0.037 vol. %
nanoparticles in stainless steel is confirmed compared to that with other metals such as
copper, aluminum and mild steel.