Enhancement of rate of heat transfer using nano fluids

VISVESVARAYA TECHNOLOGICAL UNIVERSITY, BELGAUM
“ENHANCEMENT OF RATE OF HEAT TRANSFER USING NANOFLUIDS”
A Seminar report submitted in partial fulfillment of the requirements for the award of the degree of
Bachelor of Engineering
in
Mechanical Engineering
Submitted by
M.S. SHARATH KUMAR
4VV11ME039
Under the valuable guidance of
Prof. GANESH B.B
Assistant professor
Mechanical engineering, VVCE
DEPARTMENT OF MECHANICAL ENGINEERING
VIDYAVARDHAKA COLLEGE OF ENGINEERING
MYSURU
2014-2015

CHAPTER
NO.
CONTENTS PAGE
NO.
1.
ABSTRACT
INTRODUCTION.
I
II
2.
PRINCIPLES
3
3.
4.
EXPERIMENTATION
EXPERIMENT AS CAR COOLANT IN RADIATOR
RESULTS.
4
6
9
5.
APPLICATIONS.
12
6.
MERITS AND DEMERITS.
13
7.
CONCLUSION.
14
8.
9.
SUGGESTIONS/INFERENCE
REFERENCES
15
16
CONTENTS

The efficiency of the heat transfer fluids can be increased by enhancing the thermal
conductivity and heat transfer properties. The distribution of nanoparticles, generally a metal or
metal oxide greatly enhance the thermal conductivity of the nanofluid. It increases conduction
and convection coefficients, allowing for more heat transfer.
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.
Al2O3 ,SiC ,MgO, ZnO, SiO2, Fe3O4, TiO2 , diamond ,and carbon nanotubes are used as
nanoparticles. Nanofliuids 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 short hot wire (SHW) technique.
INTRODUCTION

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.
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 called brownian motion due to the tininess, introduces
micro-convection in fluids to further stimulate heat transfer.
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 make nanoparticles better and more stably dispersed in
base fluids.
PRINCIPLE

EXPERIMENTATION
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. nanoparticles are de-
agglomerated by intensive ultrasonication after being mixed with the base fluid, and then the
suspensions are homogenized by magnetic force agitation.
Second Phase transfer method is used to prepare stable kerosene-based Fe3O4 nanofluid.
Nanofluids containing copper nanoparticles are prepared by direct chemical reduction method.
To make a nanofluid homogeneous and long-term stable, it is subjected to intensive agitation like
magnetic stirring and sonication.
SiC nanoparticles are heated in air to remove the excess free carbon and their surfaces modified to
enhance their dispersibility.
The transient short hot wire (SHW) method is used to measure the thermal conductivity and
thermal diffusivity of nanofluids .
Experimentation is conducted at different size, temperature ,base fluids to see rate of heat
transfer at different parameter.

DIMENSIONS OF SHORT HOT WIRE
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,
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.

EXPERIMENT AS A NEW COOLANT FOR CAR
RADIATORS
TiO2 nanoparticles are mixed with 1, 1, 1, 3, 3, 3, hexamethyldisilazane (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.
PREPARATION OF NANOFLUID
FESEM IMAGE OF TIO2 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).
The pump gives a variable flow rate of 90-120 l/min adjusted by a globe valve.
Electrical heater and a controller are used to maintain the temperature between 40
and 80 oC.
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.
The temperatures from the thermocouples are measured by two digital multimeters of
high accuracy.
EXPERIMENTAL SETUP

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
For cooling the liquid, a forced fan (1400 rpm) is installed close and face to face
to the radiator .
Heat transfer coefficient and corresponding Nusselt number are calculated
using:
q= hAdt = hA( Tb-Tw )
q= mcpdT = mcp(Tin-Tout)
Nu= (hexpdhy) / k = mcp (Tin-Tout) / A(Tb-Tw)

Aggregation of nanoparticles increases the thermal conductivity enhancement.
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. due to hydration forces.
The surfactant added in the nanofluids acts as stabilizer and improves the stability
of the nanofluids.
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.
RESULTS

CuO (27nm) particles in deionized water show that the convective heat
transfer coefficient and Nusselt number of nanofluids increase compared to
base fluid .
The enhancement of thermal conductivity is directly proportional to the
particle volume concentration.
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.

The presence of TiO2 nanoparticle in water can enhance the heat transfer rate of the
automobile radiator. concentration of 1 vol. %, the heat transfer enhancement of 40-
45% compared to pure water is recorded.
TiO2 nanoparticles with diameters of 21 nm dispersed in water with volume
concentrations of 0.2–2% show 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.
Increasing the flow rate of working fluid enhances the heat transfer coefficient for
both pure water and nanofluid considerably.
RESULT AS A RADIATOR
COOLANT

Nanofluids can effectively used in a variety of industries, energy production and in
electronics systems like microprocessors and micro-Electro-Mechanical systems .
Nanofluids can be used in high viscous operations which enhances the thermal properties
and hence rate of heat transfer.
As a coolant in radiators.
A nanofluid coolant could flow through tiny passages in MEMS to improve its efficiency.
In space and rocket propulsion applications, cooling of engine and propulsion.
Nanofluids in solar collectors is another application where nanofluids are employed for
their tunable optical properties.
APPLICATIONS

MERITS
High dispersion stability with predominant Brownian motion of particles.
Reduced pumping power as compared to pure liquid
Reduced particle clogging as compared to conventional slurries
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.
Nanofluids have a life span after which their properties diminish and loose
efficiency.
Abnormal variation of heat transfer is found in some metallic nanofluids.
DEMERITS

Nanofluids have great potential for heat transfer enhancement and are highly
suited to application in practical heat transfer processes.
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.
The thermal characteristics of nanofluids might be manipulated by means of
controlling the morphology of the inclusions
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.
Having all the desirable properties which are not found in conventiaonl base
fluids, it gives promising results and efficiency over the conventional.
CONCLUSION

Enhancement of rate of heat transfer using nano fluids

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