Nanofluid description

1. Technical Seminar Presentation
Technical Seminar On
NANOFLUIDS
Darshan

2. CONTENTS:
1. INTRODUCTION
2. PREPARATION METHODS FOR NANOFLUIDS
3. THERMAL CONDUCTIVITY OF NANO FLUIDS
4. MATERIALS USED FOR NANOPARTICLES AND
BASE FLUIDS
5. ADVANTAGES OF NANOFLIDS
6. LIMITATION
7. APPLICATION OF NANOFLUIDS

3. • Suspended nanoparticles in various base fluids can alter the fluid
flow and heat transfer characteristics of the base fluids. These
suspensions of nano sized particles in the base fluids are called
nanofluids.
• Nanofluids are suspensions of nanoparticles in a base fluid,
typically water. The term nanoparticle comes from the Latin
prefix „nano‟. It prefix is used to denote the 10-9 part of a unit.
• Recent development of nanotechnology brings out a new heat
transfer coolant called „nanofluids‟. These fluids exhibit larger
thermal properties than conventional coolants.
• The much larger relative surface area of nanoparticles, compared
to those of conventional particles, not only significantly improves
heat transfer capabilities, but also increases the stability of the
suspension.
What are Nanofluids ?

4. Concept of Nanofluids
0
500
1000
1500
2000
2500
1 2 3 4 5 6 7 8 9
Thermal conductivity of typical materials
Thermalconductivity(W/m-K)
Material
0.15 0.25 0.61
1-Engine Oil
2-Ethylene Glycol
3-Water
4-Alumina
5-Silicon
6-Aluminum
7-Copper
8-Silver
9-Carbon
Solids have thermal conductivities
that are orders of magnitude larger
than those of conventional heat
transfer fluids.
• Conventional heat transfer
fluids have inherently poor
thermal conductivity compared
to solids.
• Conventional fluids that contain
mm- or m-sized particles do
not work with the emerging
“miniaturized” technologies
because they can clog the tiny
channels of these devices.
• Nanofluids are a new class of
advanced heat-transfer fluids
engineered by dispersing
nanoparticles smaller than 100
nm in diameter in conventional
heat transfer fluids.

5. Nano-particles can be produced from several processes such as
gas condensation, mechanical attrition or chemical precipitation
techniques. Gas condensation processing has an advantage over
other techniques.”
Materials used for nanoparticles and base fluids:
Nanoparticle materials include:
Oxide ceramics – Al2O3, CuO
Metal carbides – Sic
Nitrides – AlN, SiN
Metals – Al, Cu
Non-metals – Graphite, carbon nanotubes
Layered – Al + Al2O3, Cu + C
Base fluids include:
Water
Ethylene- or tri-ethylene-glycols and other coolants
Oil and other lubricants
Bio-fluids
Polymer solution

6. PREPARATION METHODS FOR NANOFLUIDS
1. TWO-STEP METHOD
• Two-step method is the most widely used method for preparing
nanofluids.
• Nanoparticles, Nanofibers, nanotubes or other nanomaterials used in
this method are first produced as dry Powders by chemical or physical
methods. Then the nanosized powder will be dispersed into a fluid in
the second processing step with the help of intensive magnetic force
agitation, Ultrasonic agitation, high-shear mixing, homogenizing and
ball milling. Two-step method is the most economic method to
produce nanofluids in large scale, because nanopowder synthesis
techniques have already been scaled up to industrial production
levels. Due to the high surface area and surface activity, nanoparticles
have the tendency to aggregate.
• The important technique to enhance the stability of nanoparticles in
fluids is the use of surfactants. However the functionality of the
surfactants under high temperature is also a big concern, especially
for high temperature applications.

7. 2. SINGLE STEP METHOD

8. • To reduce the agglomeration of nanoparticles they developed a
one-step physical vapor condensation method to prepare
Cu/ethylene glycol nanofluids . The one-step process consists
of simultaneously making and dispersing the particles in the
fluid.
• In this method, the processes of drying, storage,
transportation, and dispersion of nanoparticles are avoided, so
the agglomeration of nanoparticles is minimized, and the
stability of fluids is increased . The one-step processes can
prepare uniformly dispersed nanoparticles, and the particles
can be stably suspended in the base fluid.
• However, there are some disadvantages for one-step method.
The most important one is that the residual reactants are left
in the nanofluids due to incomplete reaction or stabilization. It
is difficult to elucidate the nanoparticle effect without
eliminating this impurity effect.

9. Structure of Nanofluids
Figure 1: ZrO2 in water that
produced
with Two Step method
Figure 2: Cu nanoparticles in ethylene
glycol produced with One Step
method

10. THERMAL CONDUCTIVITY OF NANO FLUIDS
The fluids that have been traditionally used for heat transfer
applications have a rather low thermal conductivity. Taking
into account the rising demands of modern technology, it has
been recently proposed that dispersion of small amounts of
nanometres-sized solids in the fluid called nanofluids can
enhance the thermal conductivity of the fluids.
This increase in the thermal conductivity is predicted to be
because of the following reasons:
1. Brownian motion
2. Interfacial layer
3. Volume fraction of particles

11. 1. Brownian motion

12. It has been found that the Brownian motion of nanoparticles at the
molecular and nanoscale level is a key mechanism governing the
thermal behavior of nanoparticle–fluid suspensions ("nanofluids").
The enhancement in the effective thermal conductivity of nanofluids
is due mainly to the localized convection caused by the Brownian
movement of the nanoparticles.
• It is postulated that the enhanced thermal conductivity of a
nanofluids when
Compared to conventional predictions, is mainly due to
• Brownian motion which produces micro-mixing.
• This effect is additive to the thermal conductivity of a static dilute
suspension.
• Keff = kstatic + kbrownian
• Since the speed of thermal wave propagation is much faster than
the particle Brownian motion, the static part cannot be neglected

13. 2. Interfacial layer
Fig: Schematic cross section of
nanofluids structure consisting of
nanoparticles, bulk liquid, and
nanolayers at solid/liquid
interface
Fig: Single spherical
particle with interfacial
layer in a fluid medium.

14. • Although liquid molecules close to a solid surface are known
to form Layered structures, little is known about the
connection between this Nanolayer and the thermal
properties of solid/liquid suspensions. It is assumed that the
solid-like nanolayer acts as a thermal bridge between a solid
nanoparticle and a bulk liquid and so is key to Enhancing
thermal conductivity.
• From this thermally bridging nanolayer idea, a structural
model of nanofluids that consists of solid was suggested.
Nanoparticles, bulk liquid and solid-like nanolayers.
• Conventional pictures of solid/liquid suspensions do not
have this nanolayer. The thermal conductivity of the
nanolayer on the surface of the nanoparticle is not known.
However, because the layered molecules are in an
intermediate

15. 3. Volume fraction
Highly conductive nanoparticles of very low volume fractions
distributed in a quiescent liquid (called „nanofluids‟) may
measurably increase the effective thermal conductivity of
the suspension when compared to the pure liquid.

16. ADVANTAGES OF NANOFLUIDS
 High specific surface area and therefore more heat
transfer surface between particles and fluids.
 High dispersion stability with predominant
Brownian motion of particles.
 Reduced pumping power as compared to pure
liquid to achieve equivalent heat transfer
intensification.
 Reduced particle clogging as compared to
conventional slurries, thus promoting system
miniaturization.
 Adjustable properties, including thermal
conductivity and surface wet ability, by varying
particle concentrations to suit different
applications.

17. LIMITATION
• Lower specific heat
From the literatures, it is found that specific heat of nanofluids is
lower than base fluid . Namburu et al reported that CuO/ethylene
glycol nanofluids, SiO2/ethylene glycol nanofluids and
Al2O3/ethylene glycol nanofluids exhibit lower specific heat
compared to base fluids. An ideal coolant should possess higher
value of specific heat which enable the coolant to remove more
heat.
• High cost of nanofluids
Higher production cost of nanofluids is among the Reasons that
may hinder the application of nanofluids in industry. Nanofluids
can be produced by either one step or two steps methods.
However both methods require advanced and sophisticated
equipment's.

18. • Difficulties in production process
 Another difficulty encountered in nanofluid manufacture is
nanoparticles‟ tendency to agglomerate into larger
particles, which limits the benefits of the high surface area
nanoparticles. To counter this tendency, particle dispersion
additives are often added to the base fluid with the
nanoparticles.
 Unfortunately, this practice can change the surface
properties of the particles, and nanofluids prepared in this
way may contain unacceptable levels of impurities.
 Most studies to date have been limited to sample sizes less
than a few hundred milliliters of nanofluids. This is
problematic since larger samples are needed to test many
properties of nanofluids and, in particular, to assess their
potential for use in new applications

19. APPLICATIONS
 Electronic applications
 Transportation
 Industrial cooling applications
 Nuclear systems cooling
 Space and Defence
 Medical application
 Cooling of Microchips

20. Studies of nanofluids reveals high thermal
conductivities and heat transfer coefficients
compared to those of conventional fluids.
These characteristic features of nanofluids
make them suitable for the next generation of
flow and heat-transfer fluids.
Pioneering nanofluids research has inspired
physicists, chemists, and engineers around the
world.
CONCLUSIONS

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