Literature Review on the enhancement of rate of heat transfer using nano fluids.

1. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 1
ABSTRACT
Nanofluid is a multiphase material that is macroscopically uniform. Well dispersed
metallic nanoparticles at low-volume fractions in liquids enhance the mixture’s thermal
conductivity over conventional. They are potentially useful for advanced cooling of micro-
systems. Dilute suspensions of well-dispersed spherical nanoparticles in water or ethylene
glycol. Fluids containing solid particles enhance thermal conductivity, relative to pure fluids.
Fluids containing nanometer-sized particles could be a new class of engineered fluids with high
thermal conductivity. Brownian motion of nanoparticles, particle size, effect of surfactants,
dispersion of particles, and thermal properties of dispersed particles, have been expected to
influence the thermal properties of nanofluids. These properties make them useful in many
applications in heat transfer including microelectronics, fuel cells, pharmaceutical processes, and
hybrid-powered engines, engine cooling/vehicle thermal management, domestic refrigerator,
chiller, heat exchanger, in grinding, machining and in boiler flue gas temperature reduction.
Nanofluids exhibit enhanced thermal conductivity and the convective heat transfer coefficient
compared to the base fluid.
KEYWORDS: nanofluid, thermal conductivity, Brownian motion, convective heat transfer,
specific surface area

2. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 2
INTRODUCTION
Nanofluid is a newkind of heat transfer medium, containing nanoparticles (1–100 nm)
which are uniformly and stably distributed in a base fluid. The efficiency of the heat transfer
fluids can be increased by enhancing the thermal conductivity and heat transfer properties. These
distributed nanoparticles, generally a metal or metal oxide greatly enhance the thermal
conductivity of the nanofluid, increases conduction and convection coefficients, allowing for
more heat transfer. Efficient heat transfer systems are preferred because increasing
miniaturization, and the increasing heat flux. In many industrial processes, including power
generation, chemical processes, heating or cooling processes, and microelectronics, heat transfer
fluids such as water, mineral oil, and ethylene glycol always play vital roles.
The thermal conductivity in these can be improved by suspending ultrafine metallic or
nonmetallic solid powders into the traditional fluids. Thermal conductivity is an important
parameter responsible for the enhancement of heat transfer. Due to their microscopic size they
have enhanced characters such as increased Brownian motion, aggregation qualities and high
viscous properties when introduced with the base fluid. Nanofluids deliver greater rate of heat
transfer compared to the conventional fluids used in heat transfer. With the advancing
technology nanofluids serve as one of the most futuristic option in heat transfer.
Deionized water, ethylene glycol, glycerol, silicone oil are used as base fluids. Al2O3 ,SiC
,MgO, ZnO, SiO2, Fe3O4, TiO2 , diamond ,and carbon nanotubes are used as nanoparticle
additives. Nanofluids are deagglomerated by intensive ultrasonication by mixing with the base
fluid, and then the suspensions are homogenized by magnetic force agitation. The thermal
conductivities of these nanofluids are measured by transient hot wire (THW) method or short hot
wire (SHW) technique.TiO2 nanoparticles with diameters of 21 nm dispersed in water with
volume concentrations of 0.2–2% showed that the heat transfer coefficient of nanofluid was
higher than that of the base liquid and increased with increasing the Reynolds number and
particle concentrations.

3. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 3
PRINCIPLE
• Liquid dispersions of nanoparticles exhibit higher thermal conductivities than those of the
base fluids.
• Physical and chemical factors, like volume fraction, the size, the shape, and the species of
the nanoparticles, pH value and temperature of the fluids, the Brownian motion of the
nanoparticles, and the aggregation of the nanoparticles, are responsible for increased
thermal conductivity. FIG 2
• Nanoparticles have unique properties, such as large surface area to volume ratio,
dimension-dependent physical properties, and lower kinetic energy, which can be
exploited by the nanofluids. Also, the large surface area makes nanoparticles better and
more stably dispersed in base fluids. FIG 1
• Even by the addition of small amount of nanoparticle, they show anomalous
enhancement in thermal conductivity.
• The large surface area of nanoparticles per unit volume allows for more heat transfer
between solids particles and base fluids.
• High mobility of the nanoparticles due to the tininess, introduces micro-convection in
fluids to further stimulate heat transfer.
• The thermal conductivity of the most used conventional heat transfer fluid, water, is
about 0.6 W/m · K at room temperature, while that of copper is higher than 400 W/m · K.
There-fore, particle loading would be the chief factor that influences the thermal transport
in nanofluids. As expected, the thermal conductivities of the nanofluids have been
increased over that of the base fluid with the addition of a small amount of nanoparticle.
Fig 1 efficiency of NF over conventional base fluids Fig 2 aggregation of particles

4. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 4
EXPERIMENTATION
• Preparation of nanofluids containing oxide NPs like Al2O3, ZnO, MgO, TiO2, and SiO2
nanoparticles is prepared by first phase method obtained commercially and is dispersed
into a base fluid in a mixing container. The nanoparticles are de-agglomerated by
intensive ultrasonication after being mixed with the base fluid, and then the suspensions
were homogenized by magnetic force agitation
• Phase transfer method is used to prepare stable kerosene based Fe3O4 magnetic nanofluid.
The first step is synthesizing Fe3O4 nanoparticles in water by co precipitation. Oleic acid
is added. When kerosene is added to the mixture with slow stirring, the phase transfer
takes place.
• Nanofluids containing copper nanoparticles are prepared by direct chemical reduction
method. Stable nanofluids are obtained by the addition of polyvinylpyrrolidone (PVP).
• SiC nanoparticles are heated in air to remove the excess free carbon and their surfaces
modified to enhance their dispersibility.
• Surface modification is used to enhance the dispersibility of nanoparticles in the
preparation of nanofluids. Thermal conductivity of nanofluids is enhanced like volume
fraction of the dispersed nanoparticle, temperature, thermal conductivity of the base fluid,
size of the dispersed nanoparticles, the pretreatment process, and the additives of the
fluids.
• In the preparation of nanofluids, solid additives are subjected to various pretreatment
procedures. It is to tailor the surfaces of the nanoparticles to enhance their dispersibility,
thereby to enhance the thermal conductivity of the nanofluids.
• To make a nanofluid homogeneous and long-term stable, it is subjected to intensive
agitation like magnetic stirring and sonication to destroy the aggregation of the suspended
nanoparticles.
• The transient short hot wire (SHW) method is used to measure the thermal conductivity
and thermal diffusivity of nanofluids . Experimental apparatus consists of a short hot wire
probe and a teflon cell of 30 cm3
volume. FIG 1

5. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 5
Fig 1 dimensions of SHW
• SHW probe is mounted on the teflon cap of the cell. A short platinum wire of length
14.5 mm and 20 μm diameter is welded at both ends to platinum lead wires of 1.5 mm in
diameter.
• The platinum probe is coated with 1 μm of alumina for insulation, thus preventing
electrical leakage. Before and after the application of the Al2O3 film coating, the effective
length and radius of the hot wire and the thickness of the Al2O3 insulation film are
calibrated.
• Two thermocouples are located at the upper and lower welding spots of the hot wire and
lead wires, respectively which monitor the temperature homogeneity. The temperature
fluctuations are minimized by placing the hot wire cell in a thermostatic bath at the
measurement temperature.
• the dimensionless volume-averaged temperature rise of the hot wire is given by
θv=[ (Tv - Ti)/(qvr2/λ)] where, Ti and Tv are the initial liquid temperature and volume
averaged hot-wire temperature. qv the heat rate generated per unit volume, r the
radius of the SHW, t is the time, and λ is thermal conductivity.
• Thermal conductivity is calculated using the Fourier’s law
k= q /4π (T2−T1)*l n(t2/t1) ,where T1 and T2 are the temperatures at times, t1 and t2.
• Experimentation is conducted at different size, temperature, base fluids to see rate of heat
transfer at different parameter.

6. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 6
EXPERIMENT AS A NEW COOLANT FOR CAR RADIATORS
• TiO2 nanoparticles are mixed with 1, 1, 1, 3, 3, 3, hexamethyldisilane (C6H19NSi2) in a
mass fraction ratio of 2:1. The resulting mixture is sonicated at 30 °C for 1 h using
ultrasonic vibration at sound frequency of 40 kHz.
• The soaked nanoparticles were dried with a rotary evaporation apparatus. Nanoparticles
are mixed with distilled water as the base fluid to make nanofluids in particular volume
fractions. The suspensions were subjected to ultrasonic vibration at 400W and 24 kHz for
3–5 h to obtain uniform suspensions and break down the large agglomerations. Fig 1
Fig 1 FESEM image TiO2 of nanoparticles after dispersion.
• The experimental system includes flow lines, a storage tank, a heater, a centrifugal pump,
a flow meter, a forced draft fan and a cross flow heat exchanger (an automobile radiator).
Fig 1
• The pump gives a variable flow rate of 90-120 l/min; the flow rate is regulated by
adjusting of a globe valve.
• For heating the working fluid, an electrical heater and a controller were used to maintain
the temperature between 40 and 80 0C.
• The working fluid fills 25% of the storage tank whose total volume is 30 L (height of 35
cm and diameter of 30 cm).
• Two thermocouples (J-type and K-type) are used for radiator wall temperature
measurement. These thermocouples are installed at the center of the radiator surfaces
(both sides).
• The temperatures from the thermocouples and RTDs are measured by two digital
multimeters of high accuracy.

7. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 7
• Automobile radiator used is louvered fin-and tube type, with 34 vertical tubes with
stadium-shaped cross section. The fins and the tubes are made with aluminum. Fig 2.
• Constant velocity and temperature of the air are considered throughout.
• For cooling the liquid, a forced fan (1400 rpm) is installed close and face to face to the
radiator.
Fig 1 Experimental setup Fig 2 louvered fin radiator
• Heat transfer coefficient and corresponding Nusselt number are calculated using:
a. q= hAdt = hA( Tb-Tw )
b. q= mcpdT = mcp(Tin-Tout)
c. Nu= (hexpdhy) / k = mcp (Tin-Tout) / A(Tb-Tw)
Nu = average Nusselt number for the whole radiator.
m = mass flow rate which is the product of density and volume flow rate of fluid.
Cp = fluid specific heat capacity.
A = peripheral area of radiator tubes.
Tin and Tout are inlet and outlet temperatures,
Tb = bulk temperature which is assumed to be the average values of inlet and
outlet temperature of the fluid moving through the radiator.
Tw is tube wall temperature which is the mean value by two surface
thermocouples. In this equation, k is fluid thermal conductivity
dhy is hydraulic diameter of the tube.
`

8. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 8
RESULT
• Aggregation of nanoparticles increases the thermal conductivity enhancement . This
implies that the positive influence of the aggregation surpasses the negative influence of
the aspect ratio deterioration.
• Hydration forces among particles increase with the increasing difference of the pH value
of a suspension, which results in the enhanced mobility of nanoparticles in the
suspension. The microscopic motions of the particles cause micro-convection that
enhances the heat transport process. Thermal conductivity enhancement increases with
pH values in the range of 7.0-8.
• The surfactant added in the nanofluids acts as stabilizer and improves the stability of the
nanofluids. Excess surfactant addition inhibits thermal conductivity enhancement of the
nanofluids.
• Al2O3-water under constant wall temperature with 0.22.5 vol. % of nanoparticle for
Reynolds number varying between700 and 2050. The Nusselt number for the nanofluid
was found to be greater than that of the base fluid. FIG 1
• A great improvement in thermal conductivity of nanofluid is seen for a base fluid with
lower thermal conductivity.
• CuO (27nm) particles in deionized water show that the convective heat transfer
coefficient and Nusselt number of nanofluids increase compared to base fluid .
• Thermal conductivity and viscosity of copper nano particles in ethylene glycol, with
water as the solvent, shows increase in thermal conductivity.
• The enhancement of thermal conductivity is directly proportional to the particle volume
concentration.
Fig 1 Temp vs volume

9. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 9
• The thermal conductivity ratio has been observed to increase linearly with increase in
concentration and the maximum level of enhancement observed is 26% at 0·8 vol%
concentration. Thermal conductivity of a Fe nano fluid is increased non linearly upto
18%as the volume fraction of particles is increased upto 0.55 vol %. FIG 2
Fig 2 variation with respect to Reynolds number
• It is found that the thermal conductivity enhancements of nanofluids mightbe influenced
by multi-faceted factors including the volume fraction of the dispersed nanofluids, the
tested temperature, the thermal conductivity of the base fluid, the size of the dispersed
nanoparticles, the pretreatment process, and the additives of the fluids.
• The presence of TiO2 nanoparticle in water can enhance the heat transfer rate of the
automobile radiator. The degree of the heat transfer enhancement depends on the amount
of nanoparticle added to pure water. Ultimately, at the concentration of 1 vol. %, the heat
transfer enhancement of 40-45% compared to pure water is recorded. FIG 3
• Increasing the flow rate of working fluid enhances the heat transfer coefficient for both
pure water and nanofluid considerably.
• The increase in the effective thermal conductivity and the variations of the other physical
properties are not responsible for the large heat transfer enhancement. Brownian motion
of nanoparticles maybe one of the factors in the enhancement of heat transfers.
• TiO2 nanoparticles with diameters of 21 nm dispersed in water with volume
concentrations of 0.2–2%. Their results showed that the heat transfer coefficient of
nanofluid was higher than that of the base liquid and increased with increasing in
Reynolds number and particle concentrations.

10. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 10
Fig 3 variation of thermal conductivity and heat transfer coefficient with respect to volume
fraction
• . The Nusselt number for the nanofluid was found to be greater than that of the base fluid;
and the heat transfer coefficient increased with an increase in particle concentration. The
ratio of the measured heat transfer coefficients increases with the Peclet number as well
as nanoparticle concentrations. FIG 4
Fig 4 variatrion of peclet number with respect to over all heat transfer

11. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 11
APPLICATION
• Nanofluids have applications in heat transfer, including microelectronics, fuel cells,
pharmaceutical processes, and hybrid-powered engines, engine cooling/vehicle thermal
management, domestic refrigerator, chiller, heat exchanger, in grinding, machining and in
boiler flue gas temperature reduction.
• A nanofluid coolant could flow through tiny passages in MEMS to improve its efficiency.
• Nanofluids can effectively use in a variety of industries, ranging from transportation to
energy production and in electronics systems like microprocessors, micro-Electro-
Mechanical systems and in the field of biotechnology.
• In industrial heat exchangers, refrigeration.
• In space applications, cooling of engine parts and propulsion parts.
• Nanofluids can be used in high viscous operations where conventional base fluids are
added with microscopic nanoparticles which enhances the thermal properties and hence
rate of heat transfer.
• Nanofluids in solar collectors is another application where nanofluids are employed for
their tunable optical properties.
Fig 1 Fig 2
Nanofluid coolant in radiators and electronic devices such as mems

12. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 12
MERITS
• High specific surface area and hence more heat transfer 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. Better stability of nanofluids will prevent rapid settling and reduce
clogging in the walls of heat transfer devices.
• Adjustable properties, including thermal conductivity and surface wettability, by varying
particle concentrations to suit different applications.
• The high thermal conductivity of nanofluids facilitates higher energy efficiency, better
performance, and lower operating costs. They can reduce energy consumption for pumping
heat transfer fluids. Thermal systems can be smaller and lighter due to nanofluids in
vehicles, smaller components result in better gasoline mileage, fuel savings, lower
emissions, and a cleaner environment.
DEMERITS
• Abnormal variation of heat transfer is found in some metallic nanofluids.
• Overuse of surfactant reduces the thermal conductivity.
• Nanofluids have a life span after which their properties diminish and loose efficiency.
• Production and infrastructure costs for making nanoparticles is high as of now.

13. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 13
CONCLUSION
Nanofluids have great potential for heat transfer enhancement and are highly suited to
application in practical heat transfer processes. The improved thermal transport properties of
nanofluids improve the efficiency of heat exchanging, reduce the size of the systems, save pump
power, reduce operational cost and provide much greater safety margins. This provides
promising ways for engineers to develop highly compact and effective heat transfer equipment’s.
Nusselt number for the dispersed fluids increased with increasing volume concentration as well
as Reynolds number. The thermal characteristics of nanofluids might be manipulated by means
of controlling the morphology of the inclusions.
The additives like acid, base, or surfactant play considerable roles on the thermal
conductivity enhancement of nanofluids. Higher heat transfer coefficients obtained by using
nanofluid instead of water allow the working fluid in the automobile radiator to be cooler. The
addition of nanoparticles to the water has the potential to improve automotive and heavy-duty
engine cooling rates and remove the engine heat with a reduced-size coolant system. Smaller
coolant systems result in smaller and lighter radiators, which in turn benefit almost every aspect
of car and truck performance and lead to increased fuel economy. Having all the desirable
properties which are not found in conventional base fluids, thus giving promising results and
efficiency over the conventional.

14. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 14
SUGGESTIONS
• Particle agglomeration and coagulation is undesirable. If the nanoparticles can be
prevented from agglomerating and coagulating, the dispersion behavior of them improves
substantially.
• Surface treatment of nanoparticles is a better way to improve the dispersion in fluids
instead of using surfactants.
• Phase change nanoparticles can be useful to improve the thermal conductivity of
nanofluids and further increase the heat transfer efficiency.
• Nanoparticle geometry has influence on the effectiveness. Hence incorporating the best
structure of the nanoparticle further enhances rate of heat transfer.

15. ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS
DEPARTMENT OF MECHANICAL ENGINEERING, VVCE MYSURU Page 15
REFERENCES
1. Xie Discussion on the thermal conductivity enhancement of nanofluids Nanoscale
Research Letters 2011, 6:124 http://www.nanoscalereslett.com/content/6/1/124
2. Experimental Study of Heat Transfer Enhancement Using Water Based Nanofluids as a
New Coolant for Car Radiators- International Journal of Emerging Technology and
Advanced Engineering.
3. Xie HQ, Gu H, Fujii M, Zhang X: Short hot wire technique for measuring thermal
conductivity and thermal diffusivity of various materials. Meas Sci Technol 2006,
17:208.
4. Yu W, Xie H, Li Y, Chen L: Investigation of thermal conductivity and viscosity of
ethylene glycol based ZnO nanofluid. Thermochimica Acta 2009, 491:92.
5. Yu W, Xie HQ, Chen LF, Li Y: Enhancement of thermal conductivity of kerosene-based
magnetic nanofluids prepared via phase-transfer method. Colloids Surf A 2010, 355:109.