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Investigating corrosion effects and heat transfer enhancement in smaller size
radiators using CNT-nanofluids
Article in Journal of Materials Science · July 2014
DOI: 10.1007/s10853-014-8154-y
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Investigating corrosion effects and heat
transfer enhancement in smaller size
radiators using CNT-nanofluids
W. Rashmi, A. F. Ismail, M. Khalid,
A. Anuar & T. Yusaf
Journal of Materials Science
Full Set - Includes `Journal of Materials
Science Letters'
ISSN 0022-2461
J Mater Sci
DOI 10.1007/s10853-014-8154-y
1 23
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1 23
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J Mater Sci
DOI 10.1007/s10853-014-8154-y
Investigating corrosion effects and heat transfer enhancement
in smaller size radiators using CNT-nanofluids
W. Rashmi • A. F. Ismail • M. Khalid
A. Anuar • T. Yusaf
•
Received: 13 November 2013 / Accepted: 8 March 2014
Ó Springer Science+Business Media New York 2014
Abstract Nanofluids have been extensively studied in the
past to enhance the heat transfer performance and efficiency of systems. However, corrosion effects have been
paid very little attention and thus this work presents an
experimental study on the effect of carbon nanotubes
(CNT) on corrosion of three different metals under study
such as aluminium alloy, stainless steel and copper,
respectively. The work was further extended to study the
heat transfer performance in a car radiator of two different
sizes. Both the studies were performed using four different
fluids such as water, ethylene glycol, 0.02 % CNT-nanofluid and 0.1 % CNT-nanofluid, respectively. It was
observed that among the three metals, the highest rate of
corrosion occurs to aluminium, followed by stainless steel
and copper, irrespective of the fluid used. The rate of
corrosion increased with the increase in temperature
(27–90 °C) in all cases. The experimental results showed
that the stable CNT-nanofluids prepared in this work
showed better heat transfer performance in both engines.
W. Rashmi (&)
Energy Research Group, School of Engineering, Taylors
University, Subang Jaya, Malaysia
e-mail: rashmi.walvekar@gmail.com
A. F. Ismail A. Anuar
Nanoscience and Nanotechnology Research Group (NANORG),
Kulliyyah of Engineering, International Islamic University,
Gombak, Kuala Lumpur, Malaysia
M. Khalid
Division of Manufacturing and Industrial Processes, Faculty of
Engineering, University of Nottingham, Semenyih,
Kuala Lumpur, Malaysia
T. Yusaf
Department of Mechanical & Mechatronics Engineering,
University of Southern Queensland, Toowoomba, Australia
Moreover, the smaller radiator using the CNT-nanofluids
depicted enhanced heat transfer rates compared to the
standard radiator using water and ethylene glycol.
Introduction
Nanofluids have attracted a large number of scientific community since their discovery by Choi [1] in 1995, due to their
enhanced heat transfer properties and large applications
ranging from chemical and process industries, electronic
cooling, cooling of heavy vehicles, solar energy harvesting
and heat transfer applications as suitable coolants [2]. Many
review papers are available in this field with regards to the
effect of various parameters on thermal conductivity
enhancement, stability and heat transfer mechanisms and its
applications [3–7]. Carbon nanotubes (CNT) are widely being
used due to its high thermal conductivity and unique
mechanical, electrical and optical properties, respectively [8].
Previous researchers have measured the thermal conductivity
of CNT-nanofluids dispersed in various base fluids and further
reported that the CNT-nanofluids displayed significantly
higher thermal conductivities than their base fluids [9–14].
In the design of automotive systems, engineers are
exploring the idea of using nanofluids as coolants to reduce the
weight and cost of the radiator. This will result in better fuel
consumption and lower car prices in near future. Nevertheless,
not many studies have been reported to check the compatibility of nanofluids to be used as a coolant in the engine
radiator. A good quality coolant must possess a high thermal
capacity, low viscosity, and it should be non-toxic, low cost,
chemically inert, low electrical conductivity and resists oxidation. Water is a basic coolant that is commonly used as a
heat transfer fluid, due to its high thermal conductivity, cheap
and it is readily available. However, water freezing point at
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0 °C limits its capability to act as a pure coolant without any
addition of ethylene glycol. In addition, most of coolants are
blended with inhibitors to prevent corrosion in the engine
radiator. In the case of a highly corroded cooling system, the
performance of the vehicle will be severely affected. The
damage occurs due to increase in engine temperature and as
the heat that cannot be transferred directly from the engine to
the coolant effectively. Furthermore, corrosion may cause the
cavitation in the radiator that which can further restrict the
flow of coolant in the cooling system.
There are also many studies reported to investigate the
effect of coolant especially ethylene glycol (EG) towards
different materials used in the cooling system. Some of the
common metals used to manufacture the cooling system are
aluminium, steel, cast iron and copper. The corrosive effects
of EG on steel and copper were investigated by Khomomi
et al. [15] and May et al. [16], whereas Liu and Cheng [17–
19] and Niu and Cheng [20] studied the corrosion effects on
aluminium. All of the tests were mostly restricted to EG with
different inhibitors and concentrations. Celata et al. [21]
conducted erosion tests on aluminium, stainless steel and
copper using TiO2, Al2O3, SiC and ZrO2 nanofluids. The
results showed that the mechanical effects strongly depended
on the target material and type of nanoparticle material.
Among all, Al2O3 has proved to give a largest damage to the
gears followed by SiC, ZrO2 and TiO2 being the last. In
addition, it is also reported that the use nanofluids in radiators
can lead to a reduction in the frontal area of the radiator up to
10 % and the fuel saving up to 5 % due to the reduction in
aerodynamic drag [22].
Thus, this study aims to study the corrosion effects of
CNT-nanofluids using water and EG as base fluids. Two
different CNT concentrations have been studied, 0.02 and
0.1 wt%, respectively. Further, these nanofluids are applied
in two different size radiators to test their heat transfer
performance and efficiency.
adding them to the respective measured amount of base
fluid. Optimum amount of gum Arabic (GA) dispersant
was added to stabilize the CNT in base fluid. The solution
was further homogenized using high shear homogenizer
(Fluko, Germany) at 28000 rpm for 10 min, respectively.
This was done in order to break the agglomerates and
homogenize the suspension. The solution was immediately
sonicated in a water bath sonicator at 25 °C for 4 h. During
the sonication process, the CNTs which are initially
entangled gets separated due to the effect of ultrasonic
vibration and a thin layer of GA is coated on the CNT
surface which will prevent the agglomeration and sedimentation. From, our previous studies, it is reported that
the optimum amount of GA for 0.02 wt% CNT is 1.0 wt%
and for 0.1 wt% CNT is 2.5 wt%, respectively. Further, 4 h
sonication was found to be optimum as increasing the
sonication time would damage the CNT structure and
morphology. More details on stability of CNT-nanofluids
can be found in our previously published paper [13].
Corrosion test method
Specimen preparation
Metal specimens were prepared before being used as the
working electrode (Fig. 1). Prior to testing, cutting,
grinding, polishing, washing and drying of the metal
specimens were carried out. The specimen of copper,
stainless steel and aluminium alloy plate were cut with
dimension of 1 9 1 cm2 with metal scissors. The metals
are then ground with different grades of emery paper from
100 degrees of fineness and increasing up to 800 degrees of
fineness. Since the samples are small in size, they are first
mounted together before grinding as shown in Fig. 2.
The metal pieces were mounted with copper wire connected to the metal. The copper wire was used as a wire
connection of the working electrode to the circuit. The
mounted metal mould makes the grounding process easier.
Experimental procedure
Materials
Multiwalled CNTs were used in the present work with size
of 20–30 nm OD and 5–10 nm ID, a length of approximately 30 lm and the purity of the CNT was greater than
95 %. CNT was purchased from Sab Bayan Enterprise,
Klang Malaysia. Ethylene glycol used in this work was
purchased from Chemolab, Malaysia.
Preparation of CNT-nanofluid
Stable CNT-nanofluids of 0.02 and 0.1 wt% were prepared
by measuring the correct amount of CNT nanoparticles and
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Fig. 1 Copper, aluminium alloy and stainless steel in 1 9 1 cm2 size
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Fig. 2 a Metal pieces connected to copper wire to be mounted together. b Mounted specimen with copper wire
Fig. 3 Polarization test setup
Then, the specimens were polished with aluminium oxide
on the horizontal polishing machine manually. This was
done to remove all the scratch marks on the metal surfaces
thus making the surface smooth. These mounted metals
were polished until they looked like a mirror image. The
shinier the metal surfaces, the more easy reading can be
taken. Next, the metals were washed with distilled water
twice to remove any metal residue. Finally, the specimens
were dried with a hair dryer to remove the moisture.
Polarization test
Before carrying out the polarization test, all of the equipment and samples were prepared in advance and test setup
is done as shown in Fig. 3. A 50 ml solution of water is
placed in a 100-ml beaker which acts as the electrolyte.
While making sure the working electrode is fully immersed
in the electrolyte, the other two electrodes that are counter
electrode and reference electrode were also connected to
the circuit. The reference electrode that is used here is
saturated calomel electrode (SCE) and the counter electrode is the platinum plate (Fig. 4). After all of the electrodes are connected to the circuit system, the computer to
run the test was turned on. The constant maximum and
minimum voltage of ?2 and -2 mV were applied to the
circuit system. This is the potential limit for the circuit.
The polarization test was carried out by varying the
temperature of the nanofluid keeping the solution static
(magnetic stirrer was set off). The nanofluid was heated
using the hot plate. After it reached the desired temperature, the polarization test was conducted on the metal and
solution. During the experiment, the temperature was varied from 27 to 90 °C by 10 °C increment. Readings were
tabulated and plotted for every measurement.
Radiator test
Engine specifications and dimensions
Two different sizes of radiators were tested with a 1.5 L
Proton Wira engine at idle conditions. Tables 1 and 2 list
the dimensions of both the standard radiator used for the
engine and the smaller radiator used as its replacement.
Where L, H and W denotes the length, height and width of
the radiators, tubes and fins, and N is the number of tubes
and fins used in both radiators. While the width of both
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Fig. 4 Images of metals. a Counter electrode; platinum and nickel. b Aluminium alloy, copper and stainless steel. c Saturated calomel electrode
(SCE) as the reference electrode
Table 1 Standard radiator
dimensions for the 1.5 L Proton
Wira
Table 2 Smaller radiator
dimensions used as the
replacement
Lradiator
(mm)
Hradiator
(mm)
Wradiator
(mm)
Wtube
(mm)
Htube
(mm)
Lfin
(mm)
Wfin
(mm)
Hfin
(mm)
Ntube
Nfin
678
375
40
25.4
2.11
3.96
58.42
0.0762
45
188
Lradiator
(mm)
Hradiator
(mm)
Wradiator
(mm)
Wtube
(mm)
Htube
(mm)
Lfin
(mm)
Wfin
(mm)
Hfin
(mm)
Ntube
Nfin
318
350
40
25.4
2.11
3.96
58.42
0.0762
28
168
radiators is the same, the length and the height of the
smaller radiator are approximately 47 and 9 % less than
that of standard radiator, respectively. The engine specification is listed in Table 3.
Test procedure
Half cut car which is Proton Wira using the Magma engine
12 valves is used in this experiment as shown in Fig. 5 to
determine the heat transfer of the cooling system. Custom
made connectors or radiator hoses are connected from the
engine to the radiator. Thermocouples were attached to the
connectors by using epoxy resin to gain a strong bond that
can withstand high temperature and pressure of coolant.
Later, the thermocouple probes were connected to the
thermocouple to measure and record the coolant temperature. Initially, water as a coolant was poured into the
radiator and the engine was started. After 10 min, the
temperature readings for the coolant inlet and outlet of the
radiator were recorded with every 5 s increment until 60 s
123
for every 1000, 2000 and 3000 rpm. Tables 4 and 5 give
the summary of the experimental values through smaller
and standard radiators, respectively.
Strobotest was used to indicate rpm reading for every
throttle position. Finally, the coolant was flushed out from
the radiator. This procedure was repeated for other types of
coolant, which are the ethylene–glycol, CNT-nanofluids
0.1 wt% and CNT-nanofluids 0.02 wt%, respectively.
Later, similar procedure is repeated for different radiator
sizes.
Results and discussion
Corrosion rates
The corrosion rates of aluminium alloy, stainless steel and
copper, using 0.1 wt% CNT-nanofluid at different temperatures are presented in Fig. 5. Tables 4, 5, and 6 present
the corrosion rates of four different coolants measured at
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Table 3 Engine specification
Table 4 Summary of heat transfer test for smaller radiator
Code
Type of
coolant
4G15
Manufacturer
Mitsubishi
Type
S-4
SOHC
12 valves
Water
75.5 9 82 mm2
Bore/stroke ratio
0.92
Displacement
1468 cc
Unitary capacity
367 cc/cylinder
Density ratio
9.20:1
Fuel system
Aspiration
MPFi
Normal
Intercooler
No
Catalytic converter
Yes
Maximum output
89.2 PS (88.0 bhp) (65.6 kW) @ 6000 rpm
Maximum torque
126.0 Nm (93 lbft) (12.8 kgm) @ 3000 rpm
Specific output
59.9 bhp/l
Specific torque
85.83 m/l
different temperatures and different metals used, respectively. As observed from Fig. 6, copper shows the lowest
corrosion rate value compared with the other two metals.
The highest corrosion rate at a fixed temperature is
obtained by aluminium alloy in all of the coolants as
depicted by the results in Tables 4, 5, and 6. This can be
explained by the galvanic series for metal and alloy, where
aluminium alloy position is the nearest to the active side of
metals. For all coolants, the stainless steel corrosion rates
are between copper and aluminium alloy. The results also
demonstrate that the rate of corrosion increases with the
increase in temperature in all cases.
For water, Table 6 indicates that the corrosion rate for
aluminium alloy varies from 3.01 9 10-2 mm/year at 27 °C
to 9.75 9 10-2 mm/year at 90 °C. Meanwhile, the corrosion
rates for stainless steel (Table 7) and copper (Table 8) vary
Mass
flow
rate, m_
(kg/s)
Specific
heat, Cp
(J/kg C)
Temp
difference,
DT (°C)
Heat
transfer
rate,
Q_ (kW)
1000
0.066
4191
16.217
4.485
2000
3000
0.066
0.066
4198
4203
16.267
16.308
4.507
4.524
1000
0.071
3583
19
4.833
2000
0.071
3583
19.025
4.840
3000
0.071
3598
22.108
5.648
CNTnanofluids
0.02
1000
0.142
4129
21.842
12.595
2000
0.142
4134
23.15
13.590
3000
0.142
4139
24.533
14.419
CNTnanofluids
0.01
1000
0.142
3851
23.017
12.586
2000
0.142
3856
24.517
13.424
3000
0.142
3860
25.5
13.977
3 valves/cylinder
Bore 9 stroke
rpm
Ethylene–
glycol
from 1.59 9 10-2 mm/year to 8.60 9 10-2 mm/year and
1.06 9 10-2 mm/year to 7.97 9 10-2 mm/year, respectively. It is further observed that aluminium alloy has the
highest corrosion rate compared to stainless steel and copper
in both CNT-nanofluids with the value from 3.95 9
10-5 mm/year (at 27 °C) to 2.54 9 10-4 mm/year (at 90 °C)
for 0.1 wt% CNT-nanofluid and from 9.23 9 10-5 mm/year
(at 27 °C) to 6.66 9 10-3 mm/year (at 90 °C) for 0.02 wt%
CNT-nanofluid.
On the other hand, lower corrosion rates are produced
when EG and the CNT-nanofluids are being used as the
solution. The reason for this is the existent of inhibitor in
EG that prevents corrosion from happening. Interestingly,
the corrosion rates of metals using the CNT-nanofluid are
the lowest compared to the corrosion rates using pure water
and ethylene glycol. This could be explained on the basis
that nanofluids show lower and more stable friction coefficients and they also have self-healing lubricating effects
[23]. This could be the main reason for low corrosion rate
of metals in nanofluids. It has been reported that the stable
Fig. 5 Experimental setup with Magma engine 12 value and thermocouple probe placement
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Table 5 Summary of heat transfer test for bigger radiator
Type of
coolant
rpm
Temp
difference,
DT (°C)
Table 7 Corrosion rate of stainless steel (mm/year)
Heat
transfer
rate, Q_
(kW)
Mass
flow
rate, m_
(kg/s)
Specific
heat, Cp
(J/kg C)
1000
0.041
4198
20.442
3.518
2000
3000
0.041
0.041
4198
4198
21.85
22.708
3.761
3.908
1000
0.044
3583
22.417
3.534
2000
0.044
3583
23.317
3.676
3000
0.044
3622
23.708
3.778
CNTnanofluids
0.02
1000
0.089
4129
25.075
9.215
2000
0.089
4139
25.017
3000
0.089
4139
31.5
CNTnanofluids
0.01
1000
0.089
3851
26.942
2000
0.089
3856
27.092
9.307
3000
0.089
3860
32.492
11.162
Water
Ethylene–
glycol
9.234
Temperature
(°C)
Water
Ethylene
glycol
Nanofluid
0.1 wt%
Nanofluid
0.02 wt%
27
3.01E-02
1.85E-02
3.95E-05
9.23E-05
40
3.64E-02
2.01E-02
4.49E-05
1.36E-04
50
60
3.94E-02
4.15E-02
2.39E-02
3.02E-02
6.29E-05
7.47E-05
1.64E-03
1.74E-03
70
6.99E-02
3.72E-02
9.29E-05
4.82E-03
80
7.88E-02
3.84E-02
2.24E-04
6.09E-03
90
9.75E-02
4.15E-02
2.54E-04
6.66E-03
Corrosion Rate (mm/year)
Copper
Stainless Steal
Aluminium Alloy
0.00025
0.0002
0.00015
0.0001
0.00005
0
0
20
40
60
80
100
Temperature (°C)
Fig. 6 Corrosion rates of metals using 0.1 wt% CNT-nanofluid
and homogeneously dispersed nanoparticles in mineral oils
are effective in reducing wear and increasing load carrying
capacity. Furthermore, the friction can be reduced between
the moving mechanical parts. The corrosion rates produced
123
Water
Ethylene
glycol
Nanofluid
0.1 wt%
Nanofluid
0.02 wt%
27
1.59E-02
1.42E-02
2.48E-05
3.32E-05
40
2.01E-02
1.76E-02
3.53E-05
3.59E-05
50
2.03E-02
1.94E-02
3.66E-05
4.85E-05
60
3.68E-02
2.47E-02
5.14E-05
7.11E-05
70
3.94E-02
2.91E-02
7.81E-05
7.66E-05
80
8.31E-02
3.90E-02
1.03E-04
9.73E-05
90
8.60E-02
4.03E-02
2.46E-04
1.41E-04
9.215
11.604
Table 6 Corrosion rate of aluminium alloy (mm/year)
0.0003
Temperature
(°C)
Table 8 Corrosion rate of copper (mm/year)
Temperature
(°C)
Water
Ethylene
glycol
Nanofluid
0.1 wt%
Nanofluid
0.02 wt%
27
1.06E-02
1.46E-03
8.54E-06
4.56E-05
40
1.30E-02
1.57E-03
1.03E-05
5.64E-05
50
1.57E-02
1.59E-03
1.07E-05
5.94E-05
60
2.17E-02
4.18E-03
1.13E-05
7.10E-05
70
2.89E-02
2.01E-02
1.16E-05
7.10E-05
80
3.72E-02
3.17E-02
1.35E-05
9.16E-05
90
7.97E-02
3.81E-02
1.43E-05
1.01E-04
by the 0.1 wt% CNT-nanofluid and 0.02 wt% CNT-nanofluid are very similar.
Another reason for the low corrosion rates of both CNTnanofluids under study is the presence of additive (GA) in
the solution. It has been widely known that GA is commonly used as an inhibitor and its function is to prevent or
slow down the corrosion process [24–26]. GA is a natural
biopolymer which contains hydroxyls, aldehydes, ketones,
carboxyls, double bonds, ester, ether and other functional
groups. These functional groups impart good adhesion and
corrosion resistance performance to the substrate. As these
CNT-nanofluids uses GA as dispersant, indirectly the
inhibitor characteristics of the nanofluids are enhanced. As
a result, lower corrosion rates of metals are recorded in the
experiment using the CNT-nanofluids.
Radiator performance
Figure 7 indicates the temperature difference between the
inlet and outlet as a function of the engine speed for the
standard size radiator using the four different types of
coolants used in this work. It is observed that the temperature difference increases with the increase in rpm. For all
rpms, the highest temperature difference is produced by the
0.1 wt% CNT-nanofluid followed by 0.02 % CNT-nanofluid, EG and water. These results prove that the CNT-
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Water
Ethylene Glycol
0.02% CNT-Nanofluid
0.1%CNT-Nanofluid
30
Water
Ethylene Glycol
0.02%CNT Nanofluid
0.1%CNT Nanofluid
14
Heat Transfer Rate (kW)
Temperature Difference (°C)
35
25
20
15
12
10
8
6
4
2
10
0
500
1000
1500
2000
2500
3000
3500
0
0
RPM
500
1000
1500
2000
2500
3000
3500
3000
3500
RPM
Fig. 7 Temperature difference between inlet and outlet temperatures
for the standard radiator
Water
Ethylene Glycol
0.02% CNT-nanofluid
0.1% CNT-nanofluid
30
Water
Ethylene Glycol
16
25
20
15
10
0
500
1000
1500
2000
2500
3000
3500
RPM
Heat Transfer Rate (kW)
Temperature Difference (°C)
35
Fig. 9 Heat transfer rates for the standard radiator
0.02%CNT Nanofluid
0.1%CNT Nanofluid
14
12
10
8
6
4
2
0
0
Fig. 8 Temperature difference between inlet and outlet temperatures
for the smaller radiator
500
1000
1500
2000
2500
RPM
Fig. 10 Heat transfer rates for the smaller radiator
nanofluids have greater thermal conductivity that can
absorb and transfer more heat to the surroundings.
The temperature difference between the inlet and outlet
temperatures as a function of the engine speed for the
smaller radiator is shown in Fig. 8. The plots reveal similar
trends depicted in Fig. 7. Comparing the values of the
results in Figs. 7 and 8, it can be seen that the temperature
difference (between 22 and 25 °C) obtained using CNTnanofluids in the smaller radiator match the temperature
difference obtained using EG or water in the standard size
radiator.
Figures 9 and 10 demonstrate the heat transfer rates as a
function of the engine speed rpm for the standard radiator
and the smaller radiator, respectively. For both radiators,
the heat transfer rate for water and ethylene–glycol demonstrates almost similar values for each rpm. The two
different CNT-nanofluids used in this study show similar
heat transfer rates which are higher than those of water and
ethylene glycol. This is expected due to the higher thermal
properties of the CNT-nanofluids and the results suggest
that 0.02 wt% CNT concentration is adequate to enhance
the heat transfer rates. Overall, the heat transfer rates
increase with the increase of the engine speeds, since more
heat needs to be dissipated at higher rpm.
Comparing the results in Figs. 9 and 10, the heat transfer
rates produced by the two CNT-nanofluids in the smaller
radiator are much higher that the rates obtained by either
water or EG in the standard radiator.
Conclusion
Corrosion rates using three different metals and heat
transfer studies in two different size radiators have been
performed using water, EG and two different CNT-water
nanofluids. The results indicated that the corrosion rates of
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the three metals are found to be lower using CNT-nanofluids under study. Aluminium alloy showed the highest
corrosion rate compared to stainless steel and copper in
both sets of CNT-nanofluids demonstrating their selfhealing lubricating properties. Moreover, the addition of
GA not only enhanced the stability of the CNT-nanofluid
but also improved the corrosion resistance. The results on
heat transfer rates and the temperature difference using
CNT-nanofluids in the smaller radiator were found to be
similar or higher than those using water or EG in the
standard radiator. Thus, proving that the smaller radiator
can be deployed using the nanofluids in the car cooling
system. This will further lead to improved system that will
provide better engine performance as well as lower fuel
consumption in the automotive industry. The results of this
study should promote further investigations on the optimum operating process conditions using the CNTnanofluids.
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