effects of thermal loading on nanofluid behaviour
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PaperTRANSCRIPT
International Journal of Nanoscience
Vol. 1, No. 1 (2007) 1–4
World Scientific Publishing Company
1
EFFECTS OF THERMAL LOADING ON NANOFLUID BEHAVIOUR
SUDIPTA SOM
Department of Applied Physics, Indian School of Mines
Dhanbad, Jharkhand -826004, India
SUBHRAKANTI CHAKRABORTY
R&D and Scientific Services, TATA Steel Ltd.
Jamshedpur, Jharkhand- 831001, India
SANDIP K SAHA
R&D and Scientific Services, TATA Steel Ltd.
Jamshedpur, Jharkhand- 831001, India
SUMITESH DAS
R&D and Scientific Services, TATA Steel Ltd.
Jamshedpur, Jharkhand- 831001, India
Received Day Month Year (14 November 2009)
The paper investigates the effect of thermal loading on viscosity and electrical conductivity of
weakly dosed nanofluids. Two types of thermal loadings are examined: (a) a continuous increasing
loading from sub-ambient 5 ºC to 40 ºC, (b) a heating (5 ºC → 45 ºC) followed by cooling (45 ºC → 5
ºC) loading. Results show that electrical conductivity is weakly dependent on thermal loading and is
strongly dependent on nano-particle type. Viscosity shows a strong relationship with thermal loading
but is weakly nano-particle dependent. Both electrical conductivity and viscosity show weak hysteresis
during the cyclic thermal loading for low dosages. This finding is in contrast for a strong hysteresis
pattern reported by Nguyen et al. [1] for highly dosed nanofluids.
Keywords: Nanofluids, Viscosity, Electrical conductivity, Hysteresis.
1. Introduction
Nanofluid is a mixture of solid nano particles with
average particle size smaller than 100 nm, uniformly
dispersed in a base fluid like water, ethylene glycol,
engine oil etc [2]. The nanofluid can enhance the heat
transfer performance better than any other heat transfer
fluid. Most of the research on the nanofluid as heat
transfer fluid is concentrated on its performance at
ambient and higher temperature. Although, it is more
or less obvious that at very low temperatures,
nanofluid can substantially enhance the heat transfer
(e.g. extraction) performance of system and there is a
very small amount of work available in this area.
Moreover, in authors’ knowledge, till date there is no
study reported on the properties of nanofluid even at
temperatures less than the room temperature.
The present study is aimed at the investigation on
viscosity and thermal conductivity behaviour of
metallic oxide nanofluids at moderately low
temperatures (e.g. 5 - 40 ºC). Viscosity and electrical
conductivity are two of the most important transport
2 Som et al.
properties of a colloidal dispersion. These properties
play an important role in governing the flow
behaviour, heat transfer and colloidal stability of a
dispersion. Hence, a detail analysis of these two
properties is of utmost importance for scientific
analysis of the nanofluid properties. In this study the
two transport properties, viz. electrical conductivity
and viscosity of ZnO, TiO2 and SiO2 nanofluids are
measured against the temperature variation in the sub-
ambient temperature regime. This study is also carried
out in both the heating and the cooling phases.
2. Experimental procedure
Random shape nano particles of ZnO, TiO2 and SiO2
are selected for the present study. SEM studies using
FESEM, SUPRA 25 (Ziess, Germany) reveals the
particle sizes in the following ranges:
(a) TiO2 (24- 28 nm)
(b) SiO2 (38 – 122 nm)
(c) ZnO (58 – 77 nm)
This sizes are representative of the enter material
used in the study. The appropriate quantity of nano-
particles is mixed using a ultrasonic bath for 20 mins.
No surfactants are used for the study.
A noble experimental procedure is developed to
impose the thermal loading. These are
(a) Continuous heating from a sub-ambient
temperature 5 °C to a higher temperature of 45
°C.
(b) Heating following by cooling.
The lowest temperature attempted is 5 °C that is
obtained by putting the “as-is” room temperature.
Stable nanofluid in a refrigerator for heating up and
cooling the sample and indigenous method as
schematically outlined in figure 1 is employed. The
design consists of two containers- the inner one
containing the experimental nanofluid and the outer
one contains the medium for applying the thermal
load. During the heating process the medium is heated
up using additional amount of hot water. During the
cooling process the medium is ice that is gradually
added. RTDs are used to measure the temperature of
the experimental nanofluid. A vibro-viscometer (SV-
10) and electrical conductivity meter (Cond 340i/ SBT
WTW, Germany) is used to measure the change
viscosity and electrical conductivity.
Fig. 1: Schematic diagram of experimental setup
3. Results and Discussions
The behaviour of the nanofluid subject to a single
thermal load is examined. Figure 2 shows the
nanofluid behaviour of TiO2, ZnO and SiO2 as a
function of temperature. It is observed that there is a
marginal 2~5% change in the electrical conductivity
value over the temperature range of 5- 20 ºC.
Figure 3 shows the viscosity behaviour as a function
of rising temperature. The effect here is of the order of
35- 48 ºC as the temperature rises from 5- 25 ºC. The
effect of nanoparticle type is slightly pronounced at
higher temperature.
The results of the cycle thermal load are presented
next. Here the nanofluid is first heated up using the
procedure outlined in the earlier section. Figure 4
shows the behaviour of electrical conductivity in
thermal loading. The nanoparticle type effect is similar
to that in figure 3. Only a weak hysteresis is observed
for the ZnO nanofluid. Figure 5 shows the effect on
viscosity for the cyclic loading condition. There is a
prominent hysteresis loop for all nanofluids including
DM water.
Nguyen et al. conducted experiments with Al2O3 at
higher concentrations of 7% and reported a hysteresis
effect. Table 1 compares the different experimental
conditions used by Nguyen et al. and the present
authors. Two observations are pertinent:
(a) The time taken for heating and cooling is
substantially higher than the present study.
(b) A higher concentration of 1~7% compare to
0.025% in the present study.
Effect of nanoparticles on electrical conductivity and viscosity under cyclic temperature pattern 3 Temperature Vs. Electrical conductivity graph
0
200
400
600
800
1000
0 5 10 15 20 25
Temperature(oC)
Ele
ctr
ical
co
nd
ucti
vit
y (
mic
ro S
/Cm
)
TiO2DM waterZnOSiO2
Fig. 2: Temperature variation of electrical conductivity during
heating cycle
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Temperature ( oC)
Vis
co
sit
y (
m P
a.S
)
TiO2
ZnO
DM Water
SiO2
Fig. 3: Temperature variation of viscosity during heating cycle
0
100
200
300
400
500
600
700
800
900
0 5 10 15 20 25 30 35 40 45 50
Temperature (oC)
Ele
ctri
cal
Co
nd
uct
ivit
y (
mic
ro S
/Cm
)
ZnO
SiO2
TiO2
DM Water
Fig. 4: Temperature variation of electrical conductivity during
heating and cooling cycle
Figure 6 compares the findings of the present author
with those of Nguyen et al. The hysteresis loop is only
for the higher concentration of 7% and above. Time
for supplying the thermal load in terms of heating and
cooling rates does not affect the hysteresis pattern.
This is observed for the low concentration of 1% and
4% Al2O3 in the experiments of Nguyen et al.
Fig. 5: Temperature variation of viscosity during heating and
cooling cycle Temp. vs viscosity graph
0
0.5
1
1.5
2
2.5
0 10 20 30 40 50 60 70
Temperature(oC)
Vis
cosi
ty(m
Pa.S
)
TiO2
1 % Al2O3
4 % Al2O3
7% Al2O3
Fig. 6: Heating-cooling comparison curve for viscosity variation
with Al2O3 and TiO2 nanofluids
Table 1: Comparison between Nguyen et al. and the present
experiments
Experiment
performed by
Nguyen et al.
Present experiment
Time taken for
heating
(approximately)
240 mins 10 mins
Time taken for
cooling
(approximately)
300 mins 50 mins
Temperature
range
20 0C to 80 0C 5 0C to 40 0C /20 0C
Particle used Al2O3 SiO2, ZnO, TiO2
Particle size 47 nm TiO2 (24- 28 nm)
SiO2 (38 – 122 nm)
ZnO (58 – 77 nm)
Concentration
(in volume
fraction)
7% 0.025%
4 Som et al.
4. Conclusions
In the present paper, the effect of temperature on
electrical conductivity and viscosity of three
nanofluids (TiO2, SiO2 and ZnO) as compared with the
base fluid (i.e. D.M water) is investigated. The
following conclusions can be drawn,
(a) The electrical conductivity is weakly dependent
on thermal loading
(b) Electrical conductivity is a strong function of
nanoparticle type.
(c) On the other hand, the viscosity of nanofluids is a
strong function of temperature (variation is 35-
48%), which decreases with increase in
temperature in the sub-ambient range.
(d) Low concentration shows negligible amount of
hysteresis in a temperature cycle for the range of
volume fraction tested.
Acknowledgement
The authors acknowledge Dr. D. Rautray and Dr.
Sachin Parashar, TATA Chemicals innovation cenre
for supply of ZnO and SiO2 sample for the present
study. The authors also acknowledge TATA Steel Ltd.
for the permission to publish the research work.
References
1. C. T. Nguyen et al., (2008), International Journal of
Thermal Sciences, 47, 103–111.
2. S. K. Das, S. U. S. Choi and H. B. Patil, (2006), Heat
transfer Engg., 295, 3-19.