JCBPS; Section A; November 2015 – January 2016, Vol. 6, No. 1; 043-051
E- ISSN: 2249 –1929
Journal of Chemical, Biological and Physical Sciences
Available online atwww.jcbsc.org
Section A: Chemical Sciences
CODEN (USA): JCBPAT
Research Article
An International Peer Review E-3 Journal of Sciences
Experimental Investigation of Heat Transfer Enhancement
of Non-Newtonian Nanofluids (CMC)
Abinaya K.*, Thirumarimurugan M., Kannadasan T.
Department of Chemical Engineering, Coimbatore Institute of Technology, Coimbatore,
Tamil Nadu, India
Received: 01 May 2015; Revised: 01 November 2015; Accepted: 06 November 2014
Abstract: Development of high performance thermal systems has increased interest in heat
transfer enhancement techniques. Heat transfer by nanofluids gained remarkable interest
among researchers owing to its enhanced thermal conductivity. The efficiacy of nanofluids
such as alumina dispersed in Carboxy Methyl Cellulose (CMC) nonNewtonian fluid in
spiral type heat exchanger resulting in enhancement of turbulent heat transfer was
investigated. The experiment was carried out for various flow rates and for various
Reynolds number. Results show that heat transfer enhancement is promoted due to the
presence of alumina but enhancement is minimized due to increase in concentration of
CMC.
Keywords: alumina, heat transfer enhancement, nanofluids, non-Newtonian fluids, spiral type
heat exchanger, CMC.
INTRODUCTION
Efficient energy transfer is vital to render processes economically viable. More efficient heat exchangers
are essential to make this possible. Various engineering techniques have been proposed since 1950’s to
reduce the size and cost of the equipment, to enhance the heat transfer rate thus saving up energy. One of
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Experimental …
Abinaya et al.
the innovative techniques recently proposed is the use of nanofluids. The concept that thermal conductivity
for solids is higher than liquids, it is expected that thermal performance will be augmented
January 2016; Vol.6, No.1;053-051.
significantly by addition of nanoparticles to heat transfer fluids. Such fluids containing well dispersed
nanoparticles into the base fluid is termed as nanofluids. Main reason for higher thermal conductivity of
nanofluids is due to Brownian motion and better effective mixing. It should be noted that the size of
nanoparticles plays an important role in the enhancement of thermal conductivity of nanofluid. Nanofluid
is prepared by adding metals, metal oxides, carbon nanotubes or any other solid nanomaterials to a base
fluid like water, ethylene glycol or engine oil. Solid nanoparticles can be directly produced in a base fluid
through chemical techniques1-6. Enhancement characteristics for various nanoparticles have been studied
by various researchers. The materials which are commonly used as nanoparticles include chemically stable
metals (e.g., gold, copper), metal oxides (e.g., alumina, silica, zirconia, titania), oxide ceramics (e.g., Al2O3,
CuO), metal carbides (e.g., SiC), metal nitrides (e.g., AlN, SiN), carbon in various forms (e.g., diamond,
graphite, carbon nanotubes) and functionalized nanoparticles7.
The early studies considered suspensions of millimeter or micrometer size particles which show some
enhancements. However, if solid particles of millimeter, even micrometer magnitude are added into
the base fluids to make slurries, the increase in thermal conductivity of the slurries is
insignificant even at high particle loading. Due to which, the method of enhancing the thermal
conductivity of the traditional heat transfer fluids by adding solid particles is not preferred. Predicted
values of the heat transfer coefficient of nanofluids using conventional correlations for the heat transfer of
single-phase fluids are generally much smaller than the values observed experimentally. It was believed
that the enhancement in the thermal conductivity of nanofluids would be mostly responsible for the
improvement in the convective heat transfer coefficient of nanofluids 8. Choi9 in 1995 at the Argonne
National Laboratory, USA invented nanometer size suspended particles in a solution and showed
increase of thermal conductivity compared to traditional or base fluid. The thermal conductivity of
nanofluids varies with the size, shape, and material of nanoparticles dispersed in the base fluids. Past studies
showed that nanofluids exhibit enhanced thermal properties, such as higher thermal conductivity and
convective heat transfer coefficients compared to the base fluid10-13.
Several researches have been carried out in Newtonian fluids such as water, ethylene glycol whereas very
few researches alone have been carried out by the use of non-Newtonian nanofluids. Non-Newtonian
nanofluids are widely encountered in many industrial and technology applications, such as melts of
polymers, biological solutions, paints, tars, asphalts, and glues. High heat transfer capacity and low
pumping power of some non-Newtonian fluids make them attractive as a coolant for various applications
such as microchannel heat exchangers. Non-Newtonian fluids exhibit a non-linear relation between shear
stress and shear rate. In this study, heat transfer characteristics of alumina nanoparticles dispersed in
non-Newtonian nanofluids is investigated and their enhancement in heat transfer is also investigated.
SAMPLE PREPARATION
Carboxy Methyl Cellulose (CMC) was obtained from SDFCL fine chem. limited. 0.01%, 0.05%, 0.1%
CMC was prepared in deionized water. Each sample of the mixture is agitated by mechanical stirrer for
15 min to disperse uniformly. The experiment was repeated for 0.01% alumina (20 - 30 nm) nonNewtonian
nanofluids. The fluids are stirred to obtain homogenous suspension. Since no sedimentation is observed,
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Experimental …
Abinaya et al.
the experiments are repeated by using same nanofluids. In order to test stability, density of samples of
nanofluids was measured before and after test which no significant change is observed.
EXPERIMENTAL SETUP
A Spiral heat exchanger that consists of a copper coil of height 150 mm spiral with a gap of 10 mm
approximately is taken for experimental studies. The experiments are carried out for spiral heat exchangers
both in parallel and counter flow patterns for non-Newtonian fluids with an without nanoparticles. One
centrifugal pump of 0.5 hp , two instant water heaters(3kW), three rotameters an three storage vessel of 100
liter capacity are installed for carrying out the experiment. The experimental setup of the spiral type heat
exchanger with all accessories is shown in Fig. 1.
Fig. 1: Spiral Type Heat Exchanger Experimental Set up.
EXPERIMENTAL PROCEDURE
The experimental studies involve the determination of outlet temperature of both cold and hot fluids for
various flow rates. The hot fluid used here is water. The fluid on cold side is non-Newtonian fluid of various
concentrations. Cold fluid (CMC) is pumped at an inlet temperature of 31 ± 3˚C and hot fluid
(Water) is pumped at an inlet temperature of 60 ± 3˚C. Constant hot water flow rate of 4LPM is maintained
throughout the experiment. Flow of rate of cold fluid is varied from 2 LPM to 8 LPM and corresponding
inlet and outlet temperatures are noted. Times taken for filling definite volume are noted at the exit to reduce
uncertainity in flow measurements. The system is allowed to reach steady state condition before the
temperatures are noted. For each test fluids, the experiments are repeated for few readings to minimize the
uncertainty in measured experimental parameters and reproducibility were found to be within ± 2%
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DATA ANALYSIS
Abinaya et al.
Thermo-physical properties of test fluids are assumed to be constant along the length of the spiral and
evaluated at the average temperature. Physical properties of non-Newtonian fluids such as density, thermal
conductivity and specific heat were taken to be same as that of water, as taken by Rajasekharan et. al.14 All
Nano fluids used exhibit shear thinning behavior. Physical Properties of nanofluids at average bulk
temperatures are calculated from base fluids and nanofluids properties by following correlation15
The base fluids follow power law model. The base fluids and all nanofluids employed in this study
exhibiting the power-law rheological behavior expressed as
For purely non-Newtonian fluid (pseudoplastic), dimensionless numbers are defined as follows
Convective heat transfer coefficient for nanofluids is calculated as follows
RESULTS AND DISCUSSION
To evaluate the accuracy and reliability of the experimental data, measurements were first carried out using
de-ionized water. The Nusselt number calculated using the experimental data were compared with the
Nusselt numbers predicted by well accepted Dittus Boelter equations for turbulent flow, given by the
following equations
The results of this comparison are presented in Fig. 2 This figure shows very good agreement between the
results of the present study and those predicted by the Dittus-Boelter equation. Thus it gives an assurance
that the experimental setup and procedure can provide reliable heat transfer for experiments that were be
conducted in this investigation. Fig. 3(a-f) shows variation of heat transfer coefficient for non-Newtonian
nanofluid of Alumina nanoparticle concentration of 0.01% and 0.05% by weight as a function of various
Reynolds numbers and different CMC concentrations (0.01%, 0.05%, 0.1%) for both parallel and counter
flow arrangements. Results clearly show that addition of nanoparticles increases significantly the heat
transfer coefficient of the fluids and enhancement in the heat transfer coefficient increases with increase in
the Reynolds number. It can also be observed that for a given Reynolds number, the heat transfer coefficient
decreases with increase in non-Newtonian fluid concentration.
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Abinaya et al.
120
100
Dittus boltus
Equation
80
Nu 60
40
Experimental
20
0
0
2000
4000
6000
Re
Fig. 2: Nusselt number of water vs. Reynolds number.
For example, for Reynolds number of about 812.16, heat transfer coefficient for nanofluid containing CMC
of concentration 0.01% counter flow is found to be 1198 W/m2 K whereas for CMC of concentration 0.05%,
heat transfer coefficient is found to be 829 W/m2 K and for 0.1%, heat transfer coefficient decreases to 617
W/m2 K., Whereas heat transfer coefficient increases with increase in nanoparticle concentration. For
Reynolds number of about 812.16 heat transfer coefficient of 0.01% alumina nanofluids is increased to
1227 W/m2 K and for 0.05% alumina nanofluids heat transfer coefficient is about 1583 W/m2 K. An increase
in thermal conductivity is an effective reason for increase in heat transfer coefficient of nanofluids. However
enhancement is attributed to various other properties like density, Specific heat. But increase in nonNewtonian fluid concentration decreases the effect of nanoparticles as it leads to increase in apparent
viscosity leading to decrease in heat transfer coefficient.
Experimental heat transfer coefficient varies greatly with theoretical heat transfer coefficient. The reason is
that properties of nanofluids are not known accurately till date and attempts to study its properties should
be carried out. The non-Newtonian behavior of nanofluids also influences the heat transfer coefficient. For
pseudoplastic fluids, because the shear rate close to the wall is large, the apparent viscosity is small which
leads to a smaller boundary layer thickness. The thermal dispersion due to the inherent random motion of
particles also contributes to this enhancement, which, in turn, contributes to flatten the temperature profile.
As a result, the heat transfer rate at the wall increases16, 17.
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0.01% CMC
Counter Flow
5000
4500
4000
3500
3000
h 2500
2000
1500
1000
500
0
CMC
0.01% Alumina
0.05% Alumina
0
2000
4000
Re
6000
8000
( a)
0.01% CMC
Parallel Flow
3500
3000
2500
h
2000
CMC
1500
0.01% Alumina
1000
0.05% Alumina
500
0
0
2000
4000
Re
6000
8000
(b)
0.05 % CMC
Counter Flow
3000
2500
2000
h 1500
1000
500
CMC
0.01% Alumina
0.05% Alumina
0
0
48
2000
4000
Re
6000
8000
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(c)
0.05 % CMC
Parallel Flow
2000
1800
1600
1400
1200
CMC
h 1000
0.01% Alumina
800
0.05% Alumina
600
400
200
0
0
2000
4000
Re
6000
8000
(d)
0.1% CMC
Counter Flow
2500
2000
1500
h
CMC
1000
0.01% Alumina
0.05% Alumina
500
0
0
2000
4000
Re
6000
8000
(f)
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( e)
0.1% CMC
Parallel Flow
2000
1800
1600
1400
1200
h 1000
800
CMC
0.01% Alumina
600
0.05% Alumina
400
200
0
0
2000
4000
Re
6000
8000
Fig. 3(a-f): Heat transfer coefficient of nanofluids compared with various concentrations of CMC
as a function of the Reynolds number.
CONCLUSION
This paper presented results of an experimental investigation on the convective heat transfer in turbulent
flow regime under constant wall temperature boundary conditions for non-Newtonian nanofluid consisting
of suspensions of Al2O3 in Carboxy Methyl Cellulose. Addition of nanoparticles increases significantly the
heat transfer coefficient of the fluids and enhancement in the heat transfer coefficient increases with increase
in the Reynolds number. It can also be observed that for a given Reynolds number, the heat transfer
coefficient decreases with increase in non-Newtonian fluid concentration. It is expected that enhancement
will be still higher for higher concentration of nanoparticles.
NOMENCLATURE
ρ
•
•
density (kg/m3)
CP
specific heat (kJ/kg K)
D
equivalent diameter (m)
u
velocity of fluid (m/s)
k
thermal conductivity (W/m K)
K
consistency index (Pa sn)
h
heat transfer coefficient (W/m2 K)
n
power law index (dimensionless)
Nu
Pr
Re
Nusselt number (dimensionless)
Prandtl number (dimensionless)
Reynolds number (dimensionless)
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* Corresponding author: Abinaya K; Department of Chemical Engineering, Coimbatore
Institute of Technology, Coimbatore, Tamil Nadu, India
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