1) Spherical ceria nanoparticles 18-25 nm in size were synthesized and dispersed in propylene glycol via ultrasonication to create stable ceria-propylene glycol nanofluids. 2) Thermal conductivity of the nanofluids increased with ceria concentration and temperature, showing up to an 18.8% enhancement over propylene glycol. 3) Viscosity of the 0.5 and 1 vol% nanofluids was lower than propylene glycol at temperatures below 80°C. Heat absorption of the nanofluids increased with ceria concentration in transient natural convection experiments.

1. Research Paper
Development and assessment of ceria–propylene glycol nanofluid as an
alternative to propylene glycol for cooling applications
M. Prabhakaran, S. Manikandan, K.S. Suganthi, V. Leela Vinodhan, K.S. Rajan ⇑
Centre for Nanotechnology & Advanced Biomaterials (CeNTAB), School of Chemical & Biotechnology, SASTRA University, Thanjavur 613401, India
h i g h l i g h t s
Stable ceria–propylene glycol nanofluids prepared by probe ultrasonication.
These nanofluids possess higher thermal conductivity volumetric specific heat.
Particle clustering Brownian motion contribute to thermal conductivity increase.
1 vol.% ceria–PG viscosity lower than PG viscosity at temperatures 80 °C.
Heat absorption by nanofluids increase with nanoparticle concentration.
a r t i c l e i n f o
Article history:
Received 24 November 2015
Accepted 27 March 2016
Available online 31 March 2016
Keywords:
Nanofluid
Ceria
Propylene glycol
Heat transfer
Natural convection
Transient
a b s t r a c t
Spherical, crystalline ceria nanoparticles of 18–25 nm were synthesized from cerium nitrate precursor.
The dispersion of as-synthesized ceria nanoparticles in propylene glycol was achieved through extended
probe ultrasonication for 14 h, leading to ceria–propylene glycol nanofluids. The influence of nanoparticle
concentration (0–1 vol.%) and temperature on viscosity and thermal conductivity of ceria–propylene gly-
col nanofluids were investigated. Our data indicate that the higher thermal conductivity enhancement at
elevated temperatures (18.8% at 80 °C for 1 vol.% nanofluid) can be attributed to the particle clustering
and Brownian-motion induced microconvection. Ceria nanoparticles interact with propylene glycol lead-
ing to disturbance in hydrogen bonding network prevalent in propylene glycol. This resulted in lower vis-
cosity of 0.5 vol.% and 1 vol.% ceria–propylene glycol nanofluids than propylene glycol over a wide range
of temperatures. The heat absorption by ceria–propylene glycol nanofluids under transient, natural con-
vective heat transfer conditions increased with ceria nanoparticle concentration. Hence ceria–propylene
glycol nanofluids are suitable for cooling applications.
Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction
The role of heat transfer in energy generation and energy con-
sumption systems is significant. For instance, the intensification
of heat transfer in collectors of solar thermal power plants can
result in higher collection efficiency [1], improved steam or vapor
generation for a fixed collector area. Heat transfer intensification in
an energy consuming system such as heat exchangers can provide
higher heat duty for a fixed heat exchanger dimensions [2]. Heat
transfer can also be intensified through use of heat transfer fluids
with favorable properties. The thermal conductivity of conven-
tional coolants can be improved by addition of nanoparticles and
maintaining the nanoparticle-liquid system in a stable, colloidal
form. Solid–liquid dispersions containing colloidally stable
nanoparticles (particle size 100 nm) in common coolants (base
fluid) are called nanofluids [3].
Metal oxides are compatible with common coolants such as
water, ethylene glycol, and propylene glycol and are preferred
choice of nanomaterial for preparation of nanofluids. Cerium oxide
(ceria) is one of the metal oxides whose potential for nanofluid
preparation has been reported in a few works only [4–6]. For a
fixed nanoparticle concentration, the thermal conductivity and vis-
cosity of nanofluids can be tuned through control of nanoparticle
aggregation. While particle clustering contributes to thermal con-
ductivity enhancement in nanofluids containing larger aggregates,
the contribution of Brownian-motion induced microconvection is
reduced in such dispersions [7]. Nanofluids with larger aggregates
are more viscous than those containing smaller aggregates at the
same nanoparticle concentration [8,9].
http://dx.doi.org/10.1016/j.applthermaleng.2016.03.159
1359-4311/Ó 2016 Elsevier Ltd. All rights reserved.
⇑ Corresponding author. Tel.: +91 9790377951; fax: +91 4362 264120.
E-mail address: ksrajan@chem.sastra.edu (K.S. Rajan).
Applied Thermal Engineering 102 (2016) 329–335
Contents lists available at ScienceDirect
Applied Thermal Engineering
journal homepage: www.elsevier.com/locate/apthermeng

2. Propylene glycol is a food grade coolant and hence heat transfer
fluid of choice in solar water heaters and in food industries [10]. In
the present work, preparation and measurement of thermophysi-
cal properties of ceria–propylene glycol are being reported for
the first time. The capability of ceria–propylene glycol nanofluids
to absorb heat under natural convection conditions from a surface
subjected to constant heat flux has also been investigated. Such a
study would facilitate establishment of heat transfer perfor-
mance–transport properties link for ceria–propylene glycol nano-
fluid and explore the utility of single-phase heat transfer
correlations for prediction of performance of nanofluids.
2. Materials and methods
2.1. Preparation and characterization of ceria nanoparticles
Ceria nanoparticles were prepared from cerium nitrate hexahy-
drate by wet chemical synthesis, as reported elsewhere [11]. The
surface morphology of calcined powder was ascertained using a
cold field emission scanning electron microscope (JSM 6701F, JEOL,
Japan). The primary particle size was determined using transmis-
sion electron microscopy (JEM 2100F, JEOL, Japan). The powder
X-ray diffraction patterns of the calcined powder were recorded
using a X-ray diffractometer (D8Focus, Bruker, Germany).
2.2. Preparation of ceria–propylene glycol nanofluids
The maximum concentration of ceria nanoparticles was
restricted to 1 vol.% owing to requirement of larger mass of
nanoparticles due to higher density of ceria (7.65 g/cm3
) [12].
A predetermined mass of ceria nanoparticles conforming to
1 vol.% was added to propylene glycol, followed by ultrasonic
exposure in a probe ultrasonicator (Vibra-cellTM
, Sonics, USA). No
surfactant was employed as metal oxide nanoparticles can be dis-
persed in propylene glycol without surface modification or encap-
sulation [13]. The thermal conductivity of 1 vol.% dispersion was
measured at periodic intervals of probe ultrasonication to
determine the optimum ultrasonication time required. The probe
ultrasonication was discontinued, after the thermal conductivity
measurements between successive time periods of ultrasonication
were not significantly different. Ceria–propylene glycol of different
nanoparticle concentrations (0.25–1 vol.%) were prepared from
14-h ultrasonicated stock of 1 vol.% ceria–propylene glycol
nanofluid through dilution with propylene glycol as required.
2.3. Characterization of ceria–propylene glycol nanofluids
The hydrodynamic size distribution of ceria–propylene glycol
nanofluids was determined by dynamic light scattering (Nano ZS,
Malvern Instruments, UK). Thermal conductivities of propylene
glycol and ceria–propylene glycol nanofluids were determined
using transient hot-wire technique. A thermal conductivity meter
(KD2 Pro, Decagon Devices, USA) was used for this purpose. The
accuracy of thermal conductivity meter was ascertained by mea-
suring the thermal conductivity of manufacturer-supplied test
fluid (glycerine). The viscosity of propylene glycol and that of
nanofluids were measured using a viscometer (LVDV-II + Pro,
Brookfield Engineering, USA) using the S18 spindle. The accuracy
of viscosity measurement was ascertained by comparing the mea-
sured value with the manufacturer-specified value for the standard
(silicone oil). The deviations between the measured value and
manufacturer specified value for thermal conductivity and viscos-
ity were less than 2.8% and 1.84% respectively. The temperatures of
propylene glycol and ceria–propylene glycol nanofluids were
maintained at desired temperature during the measurement of
thermal conductivity in a constant temperature bath (TC-502,
Brookfield Engineering, USA). The maintenance of temperature
during the viscosity measurements was ensured through use of a
thermosel (ThermoselÒ
, Brookfield Engineering, USA). The mea-
surements of viscosity and thermal conductivity were repeated
at least thrice to ascertain reproducibility of transport property
data.
2.4. Transient heat transfer studies
The capability of ceria–propylene glycol nanofluids to absorb
heat from a surface subjected to constant flux has been investi-
gated. The nanofluids were taken in a cylindrical container, whose
outer surface was wound with an AC electrical heating coil fol-
lowed by a layer of asbestos rope. The power supply to heating coil
was controlled using a dimmerstat. The temperature of nanofluids
was recorded at regular intervals using a ‘J’ type thermocouple
connected to a digital temperature indicator. The schematic dia-
gram of the experimental setup is shown in Fig. 1. The amount of
heat absorbed by nanofluids was calculated from their initial
($30 °C), final temperature ($50 °C) and the time taken for
increase in temperature from the initial to final values as detailed
in Section 3.4.
Nomenclature
Symbol
Cp specific heat (J/kg K)
D fractal dimension (in Eq. (5))
Da aggregate size (m)
Dp particle size (m)
g acceleration due to gravity (m/s2
)
h heat transfer coefficient (W/m2
K)
k thermal conductivity (W/m K)
kB Boltzmann constant (= 1.381 Â 10À23
) J/K
Q amount of heat transferred (W)
T temperature (°C)
t time (s)
uB Brownian velocity (m/s)
ut terminal settling velocity (m/s)
V volume (m3
)
Greek symbols
/ nanoparticle volume fraction
/a aggregate volume fraction
l viscosity (mPa s)
q density (kg/m3
)
h angle of diffraction
Subscripts
bf base fluid
BM Brownian motion
f fluid
nf,/ nanofluid of a specified nanoparticle concentration ‘/’
np nanoparticle
p particle
PG propylene glycol
r ratio
330 M. Prabhakaran et al. / Applied Thermal Engineering 102 (2016) 329–335

3. 2.5. Uncertainty analysis
The uncertainty analysis has been carried out taking into
account of random errors during the measurement (Type A uncer-
tainty). Hence, the uncertainties in measurements of thermal con-
ductivity, viscosity and amount of heat absorbed were taken as the
standard errors of the mean of respective measurements.
3. Results and discussion
3.1. Characteristics of synthesized product
The synthesized powder consisted of nanoparticles with pri-
mary particle size ranging between 18 nm and 25 nm, as evident
from scanning electron micrograph (Fig. 2a) and transmission elec-
tron micrograph (Fig. 2b). The particles were nearly spherical and
contained significant amount of aggregates (Fig. 2a). The powder
X-ray diffraction data shown in Fig. 2c revealed the presence of
crystalline ceria, as confirmed by comparison with JCPDS card
No.81-0792.
3.2. Thermal conductivity of ceria–propylene glycol nanofluids
Nanoparticles tend to agglomerate when dispersed in liquids. In
addition, ceria nanopowder too contained few aggregates as evi-
denced from scanning electron micrograph. Hence probe ultrason-
ication was utilized to achieve dispersion of ceria nanoparticles in
propylene glycol. The effect of probe ultrasonication time on ther-
mal conductivity of 1 vol.% ceria–propylene glycol nanofluids is
shown in Fig. 3. Thermal conductivity of 1 vol.% ceria–propylene
glycol nanofluids was found to increase with ultrasonication time
till about 12 h, beyond which no further increase in thermal con-
ductivity was observed.
The influence of concentration of ceria nanoparticles on thermal
conductivity of ceria–propylene glycol nanofluids at 27 °C
indicates linear increase in their thermal conductivity with ceria
concentration (Fig. 4). The thermal conductivity of 1 vol.%
ceria–propylene glycol nanofluid was higher than that of propy-
lene glycol by 10.7%. The thermal conductivity enhancement for
1 vol.% nanofluid is comparable to those already reported for opti-
mally probe ultrasonicated 1 vol.% metal oxide–propylene glycol
nanofluids such as ZnO–propylene glycol (12.5%, [14]),
MgO–propylene glycol (10.8%, [13]), sand–propylene glycol
(11.5%, [15]), and Fe2O3–propylene glycol (10.5%, [16]) nanofluids.
The hydrodynamic size distribution of 1 vol.% ceria–propylene
glycol nanofluids revealed the average particle size to be
70 ± 1.8 nm. The average hydrodynamic size is about 3 times the
Fig. 1. Schematic diagram of the experimental setup.
Fig. 2. (a) Scanning electron micrograph of ceria nanoparticles. (b) Transmission electron micrograph of ceria nanoparticles. (c) Powder X-ray diffraction pattern of ceria
nanoparticles.
M. Prabhakaran et al. / Applied Thermal Engineering 102 (2016) 329–335 331

4. primary particle size, which indicates that nanofluid contained
colloidally-stable aggregates. In the absence of net attractive
forces, the ratio of Brownian velocity (uB) to terminal settling
velocity (ut) of aggregates provides an indication about the col-
loidal stability of dispersion. Higher the Brownian-to-settling
velocity ratio (uB/ut), better is the colloidal stability. Brownian
velocity (uB) and terminal settling velocity (ut) of aggregates in
ceria–proylene glycol nanofluid were calculated using the follow-
ing formulae [17]:
uB ¼
2kBT
plD2
p
ð1Þ
ut ¼
ðqp À qf ÞgD2
p
18l
ð2Þ
Brownian-to-terminal settling velocity ratio (uB/ut) was esti-
mated to be 30,000, which is high enough to ensure that the ran-
dom motion of particles overcomes settling of particles by
gravity. This was confirmed visually as there was no phase separa-
tion between nanoparticles and the base fluid. The nanofluids were
stable for more than a month despite repeated heating and cooling.
Thermal conductivity of 1 vol.% ceria–propylene glycol nano-
fluid varied very little with temperature (27–80 °C), with mini-
mum and maximum thermal conductivities within this
temperature range differing from average thermal conductivity in
this temperature range by less than 1% (Fig. 5). The thermal con-
ductivity of propylene glycol was found to decrease with temper-
ature when heated above 50 °C (Fig. 5). However, the thermal
conductivity of 1 vol.% ceria–propylene glycol nanofluid did not
decrease. Hence thermal conductivity ratio, defined as the ratio
of thermal conductivity of 1 vol.% ceria–propylene glycol nanofluid
to propylene glycol, was found to increase with temperature
(Fig. 6). The thermal conductivity ratio increased from 1.107 at
27 °C to 1.188 at 80 °C, corresponding to 10.7% and 18.8% enhance-
ments in thermal conductivity at 27 and 80 °C respectively. Such
higher thermal conductivity ratio at higher temperatures has been
reported for several water-based nanofluids systems [18,19] attrib-
uted to increased Brownian motion at elevated temperatures,
enabled by higher thermal energy and lower liquid viscosity.
The thermal conductivity enhancement for 1 vol.% ceria–propy-
lene glycol nanofluid at the lowest temperature investigated
(27 °C) is 10.7%, which is greater than the thermal conductivity
enhancement (3%) predicted by the simplified Hamilton–Crosser
model. The nanofluid viscosity at 27 °C was measured to be
30.53 cP, considered high enough to reduce the impact of Brown-
ian motion on thermal conductivity enhancement. Therefore, the
fact that the actual higher thermal conductivity enhancement even
at 27 °C was found to be higher than that predicted by simplified
Hamilton–Crosser model points out to the role of other possible
mechanisms in thermal conductivity modulation of 1 vol.% ceria–
propylene glycol nanofluid.
It may be recalled that the ceria–propylene glycol nanofluid
contained stable aggregates whose diameter was three times the
primary particle size. These stable aggregates form longer path of
heat conduction than those with individual particles [20]. The
effective volume fraction of aggregates (/a) may be related to
aggregate size (Da), primary particle size (Dp) and volume fraction
of nanoparticles (/) as [21]:
/a
/
¼
Da
Dp
3ÀD
ð3Þ
The value of fractal dimension (D) ranges from 2 to 2.2 for rate-
limited aggregation [21].
The simplified Hamilton–Crosser model can be modified to
account for the effect of particle clustering on thermal conductivity
ratio (kr) by replacing the nanoparticle volume fraction (/) by the
effective volume fraction of aggregates (/a) as follows [22]:
kr ¼ 1 þ 3/a ð4Þ
Eliminating ‘/a’ from Eq. (4) using Eq. (3) leads to
kr ¼ 1 þ 3/
Da
Dp
3ÀD
ð5Þ
Fig. 3. Effect of ultrasonication time on thermal conductivity of 1 vol.% ceria-
propylene glycol nanofluid.
Fig. 4. Influence of concentration of ceria nanoparticles on thermal conductivity of
ceria–propylene glycol nanofluids at 27 °C.
Fig. 5. Influence of temperature on thermal conductivity of base fluid and 1 vol.%
ceria717 propylene glycol nanofluid.
332 M. Prabhakaran et al. / Applied Thermal Engineering 102 (2016) 329–335

5. It may be recalled that the average aggregate and primary par-
ticle sizes were 70 and 23 nm respectively. Substituting the values
of ‘Da/Dp’ and D (fractal dimension) as 3 and 2 respectively in Eq.
(5), results in
kr ¼ 1 þ 9/ ð6Þ
Eq. (6) accounts for thermal conductivity enhancement due to
nanoparticle addition (effective-medium approximation) and par-
ticle clustering.
For a fixed nanoparticle concentration, the influence of temper-
ature on Brownian motion-induced thermal conductivity enhance-
ment can be expressed as [19,23]:
kr;BM ¼ fðTÞ ð7Þ
Taking into account of role of particle clustering and Brownian
motion on thermal conductivity enhancement, thermal conductiv-
ity ratio–temperature relationship for 1 vol.% ceria–propylene gly-
col nanofluid may be expressed as:
kr ¼ 1 þ 9/ þ fðTÞ ð8Þ
An expression for f(T) was obtained as follows through regres-
sion analysis of kr–T data in accordance with the form of Eq. (8):
fðTÞ ¼ 6:067 Â 10À5
T1:66
ð9Þ
Combining Eqs. (8) and (9)
kr ¼ 1 þ 9/ þ 6:067 Â 10À5
T1:66
ð27 T 40
CÞ ð10Þ
3.3. Viscosity of ceria–propylene glycol nanofluids
The influence of temperature and nanoparticle concentration on
the viscosity of nanofluids prepared from 14 h-ultrasonicated stock
is shown in Fig. 7. It is clear from Fig. 7 that the viscosity of 0.5 vol.
% and 1 vol.% ceria–propylene glycol nanofluid decreased with
temperature, qualitatively matching the viscosity–temperature
relationship for propylene glycol (base fluid). The qualitative sim-
ilarity between viscosity–temperature profiles of ceria–propylene
glycol nanofluid and propylene glycol indicates that the magnitude
of intermolecular attractive forces decreased in nanofluids as well
over the entire temperature and concentration ranges investigated.
It may also be observed from Fig. 7 that the viscosities of 0.5 vol.%
and 1 vol.% ceria–propylene glycol nanofluids were lower than that
of propylene glycol in the temperature range of 30–70 °C. It is
widely believed and reported that viscosity of nanofluid is greater
than that of the liquid in which the nanoparticles are dispersed
(base fluid).
In nanofluid systems with no chemical interactions between
nanoparticles and liquid, the viscosity of nanofluid can be esti-
mated using the viscosity models [24] that account for increased
viscous dissipation due to nanoparticles. However when metal
oxide nanoparticles are dispersed in strongly-hydrogen bonded
liquids, strong interactions originate between liquid and nanopar-
ticles on particles’ surface. These interactions seem to interfere
with the hydrogen bonding network of liquid, leading to reduction
in viscosity [15,25], as confirmed by FTIR spectra (data not shown
to maintain brevity). Hence the viscosity change caused by the
addition of nanoparticles is attributable to both the increased vis-
cous dissipation that causes viscosity increase and the disturbance
to hydrogen bonding network in base fluid that causes viscosity
reduction.
3.4. Heat transfer performance of ceria–propylene glycol nanofluids
The temporal variation of temperature of ceria–propylene gly-
col nanofluids of different concentrations is shown in Fig. 8. The
rate of change of temperature of 1 vol.% ceria–propylene glycol
nanofluids was the highest among different nanofluid concentra-
tions investigated as evident from the slope of temperature–time
data (Fig. 8). The quantity of heat transferred to nanofluids or heat
absorbed by nanofluids was calculated from the initial and final
temperature as follows:
Qnf ¼ Vnf Cp;nf qnf
dT
dt
ð11Þ
The product of specific heat and density of nanofluid was esti-
mated using the following equation [26]:
Fig. 6. Thermal conductivity ratio–temperature data for 1 vol.% ceria–propylene
nanofluid.
Fig. 7. Influence of temperature on the viscosity of ceria-propylene glycol
nanofluids 30–70 °C.
Fig. 8. Transient response 723 of ceria-propylene glycol nanofluids.
M. Prabhakaran et al. / Applied Thermal Engineering 102 (2016) 329–335 333

6. Cp;nf qnf ¼ Cp;PGqPGð1 À /Þ þ Cp;npqnp/ ð12Þ
The density and specific heat of propylene glycol are 1040 kg/
m3
[27] and 2500 J/kg K [28] respectively, while those of ceria
are 7650 kg/m3
[12] and 390 J/kg K [29]. Hence with increase in
nanoparticle concentration, the volumetric specific heat (qnf cp,nf)
of ceria–propylene glycol nanofluid increased due to higher volu-
metric specific heat of particles.
The higher slope (dT/dt) of temperature–time data and higher
volumetric specific heat (qnf cp,nf) at higher nanoparticle
concentration resulted in improved heat absorption for 1 vol.%
ceria–propylene glycol nanofluid when compared to those of 0.5
and 0.25 vol.% ceria–propylene glycol nanofluid as shown in Fig. 9.
The amount of heat absorbed by nanofluids is related to
nanoparticle volume fraction as
Qnf;/ ¼ 17:65/ þ 0:8785 ð13Þ
Qnf;/
0:8785
¼
17:65
0:8785
/ þ 1 ð14Þ
From Eq. (14), / ? 0, Qnf,0 = 0.8785. Therefore, Eq. (14) can be
re-written as
Qnf;/
Qnf;0
¼ 20:09/ þ 1 ð15Þ
From Eq. (15), it may be understood that the addition of ceria
nanoparticles to propylene glycol at the concentration of 1 vol.%
would result in $20% enhancement in quantity of heat absorbed.
Under the experimental conditions employed in the present study,
the predominant mode of heat transfer is natural convection. The
natural convective heat transfer coefficient is related to specific
heat, density, viscosity and thermal conductivity as [30]:
hnf /
Cp;nf q2
nf
lnf knf
!n
knf ð16Þ
The value of ‘n’ is 0.25 for conditions of the present study [30].
The quantity of heat absorbed by nanofluids (Qnf,/) is propor-
tional to natural convective heat transfer coefficient (hnf). Therefore,
Qnf;/ / hnf ð17Þ
Combining Eqs. (16) and (17), the ratio of heat absorbed by
nanofluids to heat absorbed by nanoparticle-free fluid (base fluid)
may be calculated as:
Qnf;/
Qnf;0
/
Cp;nf q2
nf
lnf knf
!0:25
knf
8
:
,
Cp;nf;0q2
nf;0
lnf;0knf;0
!0:25
knf;0
9
=
;
ð18Þ
The
Qnf ;1%
Qnf ;0
and
Qnf ;0:5%
Qnf;0
ratios calculated using Eq. (18) were found to
be 1.096 and 1.191. These ratios were closer to the ones deter-
mined from heat transfer experiments (1.10 and 1.201 for 0.5 vol.
% and 1 vol.% ceria–propylene glycol nanofluids respectively) in
accordance with Eq. (15). Hence it may be concluded that the
improvement in thermophysical properties of ceria–propylene gly-
col nanofluids were reflected in their heat absorption performance
under natural convective conditions.
4. Conclusions
Ceria–propylene glycol nanofluid with high colloidal stability
was prepared by dispersing surfactant-free ceria nanoparticles of
18–25 nm diameter in propylene glycol using probe ultrasonica-
tion for 14 h. The thermal conductivity of 1 vol.% ceria–propylene
glycol nanofluid was higher than that of propylene glycol by
10.7% and 18.8% at temperatures of 27 °C and 80 °C respectively.
Brownian motion-induced microconvection and particle clustering
were found to be major contributors for thermal conductivity
enhancement of ceria–propylene glycol nanofluid. The viscosities
of 1 vol.% and 0.5 vol.% ceria–propylene glycol nanofluids were
lower than that of pure propylene glycol at temperatures below
80 °C, due to ceria nanoparticles-induced perturbations in inter-
molecular hydrogen bonding of propylene glycol. The improved
thermophysical properties (higher volumetric specific heat, higher
thermal conductivity and lower viscosity) of 1 vol.% ceria–propy-
lene glycol nanofluid resulted in $20% improvement in quantity
of heat absorption under transient, natural-convective constant
wall heat flux conditions.
Acknowledgements
This work was supported by (i) PG teaching grant No: SR/NM/
PG-16/2007 of Nano Mission Council, Department of Science
Technology (DST), India, (ii) Grant No: SR/FT/ET-061/2008, DST,
India, (iii) INSPIRE fellowship (Reg Nos: IF110312 and IF130529)
of Department of Science and Technology (DST), India and (iv)
Research Modernization Project #1, SASTRA University, India.
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