FIELD OF INVENTION
The present invention relates to nanofluids. More particularly, the invention
relates to a process of an a system for large scale synthesis of nano-fluids.
BACKGROUND OF INVENTION
Fluids with nano-particles suspended in them are called nano-fluids. Nano-fluids
can be considered to be the next - generation heat transfer fluids as they offer
enhanced heat transfer performance compared to pure liquids. Nano-fluids also
exhibit good lubrication performance.
Large scale preparation of nano-fluids is the first key step to make them popular
for industrial use.
Nano-fluids are not a simply liquid - solid mixture. They are produced by
dispersing nanometer - scale solid particles into base liquids such as water,
ethylene glycol (EG), oils, etc.
During the dispersion process, special technique to be adopted to prevent
agglomeration of the particles, which is a substantially difficult task.
Amongst the known to the inventors, the general state of art is defined in the
following documents:
(a) US patent 2001/6221275 by Stephen Choi and Jeffrey Eastman disclosed
a single-step technique of vacuum evaporation of particles on a running
substrate to prepare the nano-fluids.
(b) US patent WO/2007/087708 described another single-step method using
a vacuum reactor and a high energy source to produce a cloud of plasma
constituting nano-particles and dissolving the same in base fluid to
prepare nano-fluid.
There are mainly two known techniques to produce nanofluid for example, a
single-step method, and a two-step method, single step methods are energy
intensive, applicable only to low vapour pressure liquids and hence not viable for
large-scale use.
The two-step method is extensively used for synthesis or nanofluids, specially
considering easy availability of nano-powders produced and supplied by several
companies. Thus, in the two-step method, nano-particles in the form of nano-
powder are first produced or bought - out and then dispersed in the base fluids.
Generally, an ultrasonic equipment is used to intensively disperse the nano-
particles in the base fluid and simultaneously reduce the agglomeration of the
particles. For example, Eastman et al. [1], Lee et al. [2], and Wang et al. [3]
used this method to produce AI2O3 nanofluids. Also, Murshed et Al. [4] prepared
TiO2 suspension in water using the same method.
However, ultrasonic agitation has major limitations. For larger volume of
nanofluid, this process cannot completely eliminate the agglomeration. Further,
this process takes a considerable time to break the agglomerates which makes
the process only workable in a batch production. These advantages restrict the
process for adaptation in any continuous base, fluid circuit. Designing a large
ultrasonic source for industrial use in further considered as an important
economical constraint
Because of above limitations, the existing methods of preparing nano-fluids are
incapable to produce nano-fluid at a volume rate desired and/or required for
large-scale industrial production.
OBJECTS OF THE INVENTION
It is, therefore an object of the present invention to propose a two-step industrial
process for preparation of nano-fluids, which eliminates all the limitations of prior
art.
Another object of the invention is to propose a system for preparation of nano-
fluids in large volume to cater for higher capacity industrial processes.
SUMMARY OF INVENTION
Accordingly, in a first aspect of the invention there is provided a process for
large-scale manufacturing of nanofluids, comprising the steps of providing base
fluids in the mixing chamber having means for measuring temperature, pH-
concentration, and average particle size of the nanofluids; heating the base fluid
in the heating chamber; injecting nano-crystalline particles in powder form into a
system having one each mixing and heating chamber with a high-speed stirrer;
breaking of agglomerates into single particles or small clusters of primary
particles by sucking the powder through centrifugal action into a higher shear
zone of the mixing chamber; rotating the stirrer in the mixing chamber to mix
the particles with the base fluid; injecting surfactant into the mixture in the
chamber which form double layer with the dispersed particles to prevent further
agglomeration; repeating the mixing step to form a homogenous solution with
uniform physical properties; and switching off the stirrer and allow the nanofluid
to become static.
In a second aspect of the invention, there is provided A system for large-scale
manufacturer of nanofluids, comprising a heat exchanger having at least one
heating chamber, and a mixing chamber each provided with one top and one
bottom cover, with a partition in between; a dynamic light-scattering means and
a dip-in-probe provided in the mixing chamber; two RTDs disposed on the
bottom cover of each chamber, the top cover of the mixing chamber and the
heating chamber respectively having two and one RTD; a plurality of digital
display with recording means to display the temperature of a base fluid provided
being operably connected to the RTDs; at least two electrically-operated stirrers
disposed over one each in the chambers being enabled to move downward to
reach inside the chamber for rotating and mixing the basic fluid with nano
particles in the form of powder when injected through the top cover of the
chambers; and a programmable computer apparatus incorporated with a
computer program having the pre-stored data interfaced with the chambers
including the stirrer to control the operation based on comparison of the on-time
acquired data with the pre-stored data relating to temperature, pH-concentration
and average particle size of the nano-particles and the base fluid.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure - 1 schematically shows a system for large-scale preparation of nano-
fluids.
DETAIL DESCRIPTION OF INVENTION
According to the invention the process of large-scale preparation of nanofluids
basically comprises four steps for example, Breaking of agglomerates,
Dispersion, Mixing, and Characterization.
In a first step, nanoparticles in powder form are sucked into a high shear zone
at the system by centrifugal action. This prevents formation of lumps and
facilitates the dispersing action. This also provides the agglomerates a high
impact velocity.
In a second step, the powders drawn the top of the system get wetted and
deagglomerated by passing through the high shear zone between a stirrer and
the chambers of the system.
The shear force builds high shear rate on the agglomerates. At high shear strain
rates, fracture and shattering occurs at a high rate, causing the agglomerates to
break into single particles or small clusters of primary particles.
Each of these particles instantaneously form double layer with the surfactant
molecules, which prevents further agglomeration.
In a third step, the individual particles/clusters flow radially and readily get mixed
with water. The mixing action is repeated till the stirrer is switched off.
Recurrent mixing action ensures the homogeneity of the solution and uniform
physical property. In a fourth step, the rotor is switched off and the nanofluid is
static.
According to the invention, the nano-crystalline particles in powder form are
distinctly injected in the high shear zone comprised of a stirrer assembly. The
angular speed of the stirrer is selected depending on the type of nano-particle,
surfactant and the base fluid. A clearance between the stirrer and the base of
the chamber is maintained. This inventive process is implementable : with (a)
base fluids such as water (H2O), heavy water (D2O), ethylene glycol, oils other
organic liquids, (b) all nano-particles of sizes from 1 nm to 1000 nm and shapes
as shares tube, rod/whisker and cube, (c) all anionic, cationic, zwitterionic and
non-ionic surfactants. The mixing vessel of the invention is equipped with means
to measure temperature, pH, concentration, average particles size of the
nanofluid. A semi-empirical model is used to estimate the thermal properties of
the fluid from the above measured data.
Figure 1 illustrates a system for large-scale manufacture of nano-fluids. The
system is enabled to be interfaced with a computer apparatus incorporated with
a computer program. A heat exchanger made of stainless steel where at least
two chambers are configured. One chamber, named as a heating chamber, and
is built for heating of the fluid or water, and the other chamber id for exchanging
the heat using the nanofluid. Two chambers made of stainless steel, are
separated by a stainless steel plate.
The first chamber is provided with a heater for heating water in the hot
chamber. The first heater is disposed in a space-apart relationship with any
adjoining surface of the chamber without touching the Plexiglas surface to avoid
the heat exchanger. Each chamber has one each top cover and bottom cover.
Two RTDs on the bottom side of each of the two chambers for example, the
heating and cooling chamber, are installed. The heating chamber is provided
with one RTD at the top through the top cover of the chamber, while the top
side of the cooling chamber is provided with two RTDs, as shown in the figure.
Total numbers of RTDs are five for the two chambers for measuring
temperature. The RTD at the top covers dip inside the water for a specific
distance of 15 to 20% of the depth of the chambers, while the bottom RTDs
protrude upward upto a height of no more than 15 to 20% of the height of the
chambers from the bottom surface.
A plurality of digital display with provision for display of the temperature of all
the RTDs are provided in the display board with means for recording of RTD data
from digital display to a datalogger.
A controller for cut off of the heater after a set value of temperature has been
attained is attached along with a relay for control of the temperature.
Temperature of water in the hot chamber during heating is allowed to fluctuate
beyond +/-0.5 °C. The relay for the cut-off value is guided by the temperature
recorded by the fourth RTD located a the top cover surface of the hot chamber,
as shown in the attached figure.
An energy meter is provided for recording the energy input to the heater during
heating for a predefined period. For better mixing and stirring in the chambers,
at least two stirrers are placed vertically which pass through he top cover of each
of the chamber. Each stirrer is driven by a motor and the shaft rod of the stirrer
does not touch the top cover of the chambers. The shaft rod is kept separated
from the motor so that the stirrer can be removed at any stage during the
operation form the chambers. A regulator for each motor is provided to control
the rotation or speed of the motor of each stirrer.
A hole at the top cover of each chamber enables pouring of either water or any
liquid during the process operation. Each cover of the top and bottom of each
chamber allows the passage of the RTDs, the stirrers, and the heaters.
A drain is configured on the chamber for draining out of any liquid inside the
chambers through the bottom of each chamber, as shown in figure-1. The drain
at the base of each chamber is installed with a valve so as that the chamber can
be emptied when necessary.
The base of the heat exchanger having the two chamber is located at a level
higher than the ground level such that drainage of the liquid from each chamber
can be facilitates. A separate mounting / framework holds the motor-stirrer
assembly, which allows an easy removal of the plexiglass chamber assembly.
The open outer surface of each chamber is insulated to ensures a minimum heat
loss. Electrical switches connecting means to operate the RTDs, the heater and
the stirrers are provided.
The temperature of the fluid is measured by at least five RTD placed inside the
system. The pH is measured by a dip-in probe provided inside the mixing
chamber.
A dynamic light scattering technique is inbuilt in the system, which provides the
particles count and average particle size distribution across the height of the
vessel.
All these data are then logged in a computer program. This program has pre-
recorded thermal conductivity values against semi-empirical relations containing
temperature, pH, concentration and average particle size.
The present values are compared with stored ones and the thermal conductivity
of the present nano-fluid is determined. Based on the thermal conductivity value,
the system also estimates how much nano-fluid is required for a specific
application.
Based on this calculation, an electrically flow-control valve regulates the flow of
nanofluid to the industrial process.
WE CLAIM
1. A process for large-scale manufacturing of nanofluids, comprising the
steps of:
- providing base fluids in the mixing chamber having means for measuring
temperature, pH-concentration, and average particle size of the
nanofluids;
- heating the base fluid in the heating chamber;
- injecting nano-crystalline particles in powder form into a system having
one each mixing and heating chamber with a high-speed stirrer;
- breaking of agglomerates into single particles or small clusters of primary
particles by sucking the powder through centrifugal action into a higher
shear zone of the mixing chamber;
- rotating the stirrer in the mixing chamber to mix the particles with the
base fluid;
- injecting surfactant into the mixture in the chamber which form double
layer with the dispersed particles to prevent further agglomeration;
- repeating the mixing step to form a homogenous solution with uniform
physical properties; and
- switching off the stirrer and allow the nanofluid to become static.
2. A system for large-scale manufacturer of nanofluids, comprising:-
- a heat exchanger having at least one heating chamber, and a mixing
chamber each provided with one top and one bottom cover, with a
partition in between;
- a dynamic light-scattering means and a dip-in-probe provided in the
mixing chamber;
- two RTDs disposed on the bottom cover of each chamber, the top cover
of the mixing chamber and the heating chamber respectively having two
and one RTD;
- a plurality of digital display with recording means to display the
temperature of a base fluid provided being operably connected to the
RTDs;
- at least two electrically-operated stirrers disposed over one each in the
chambers being enabled to move downward to reach inside the chamber
for rotating and mixing the basic fluid with nano particles in the form of
powder when injected through the top cover of the chambers; and
- a programmable computer apparatus incorporated with a computer
program having the pre-stored data interfaced with the chambers
including the stirrer to control the operation based on comparison of the
on-time acquired data with the pre-stored data relating to temperature,
pH-concentration and average particle size of the nano-particles and the
base fluid.
3. A process for large-scale manufacturing of nanofluids, as substantially
described and illustrated herein with reference to the accompanying
drawings.
4. A system for large-scale manufacturer of nanofluids, as substantially
described and illustrated herein with reference to the accompanying
drawings.

This invention is directed to a system for large scale synthesis of nanofluids.
Nanoparticles (with surfactants or dispersants) are first mixed with the base fluid
in a system constituting a high shear mixer machine. The system is further
equipped with means to measure temperature, concentration, pH and average
particle size in nanofluid. The measured data are fed in a computer program to
estimate the thermal properties of the produced nanofluid.
The invention further relates to a process for large-scale synthesis of nanofluids.