- Email: [email protected]
Improving car radiator performance by using TiO2-water nanofluid
Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
Contents lists available at ScienceDirect
Engineering Science and Technology, an International Journal journal homepage: www.elsevier.com/locate/jestch
Full Length Article
Improving car radiator performance by using TiO2-water nanofluid Siraj Ali Ahmed a,⇑, Mehmet Ozkaymak a, Adnan Sözen b, Tayfun Menlik b, Abdulkarim Fahed a a b
Energy Systems Engineering, Karabuk University, Turkey Energy Systems Engineering, Gazi University, Turkey
a r t i c l e
i n f o
Article history: Received 12 January 2018 Revised 6 July 2018 Accepted 14 July 2018 Available online xxxx Keywords: Car radiator Nanofluids Performance Reynolds number TiO2-water
a b s t r a c t The most recent developments in nanotechnology have lead to improvements in original uses of nanofluids in car motor cooling. In the present study, enhancement of car engine radiator by TiO2-water nanofluid as a coolant of car engine radiator was investigated experimentally. In order to determine the effect of TiO2-water nanofluid on radiator’s performance, experiments were performed with pure water and TiO2-water nanofluid separately and results were compared with other studies on vehicle engine system FIAT DOBLO 1.3 MJTD ENG. The main objective was to check the aspects of heat transfer of the TiO2-water nanofluid as a substitution to the customary coolant system. For this purpose, experiments were carried out using a TiO2 nanofluid with 0.1, 0.2 and 0.3% volume concentrations with flow rates of 0.097 and 0.68 m3/h in laminar floe region, where Reynolds number ranged from 560 to 1650. Our results show that the friction factor decreases when Reynolds number and the volume concentration are increased. Moreover, TiO2-water nanofluid with 0.2% concentration can enhance the effectiveness of car radiator by 47% as compared to 0.1 and 0.3% concentrations and pure water as a coolant. Finally, the average heat transfer coefficient was directly affected by the increase in Reynolds number and volume concentration fraction of the nanofluid. Ó 2018 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Great efforts have been spent to improve the thermal efficiency of a number of processes with mixed success until the recent emergence of a promising new class of nano-coolants with a liquid component such as water mixed with nanoparticles started to make their way into a myriad of engineering applications. Although they are expected to provide substitutes of conventional coolants in the near future, a number of improvements are still to be made. Attempts are still being made on one hand to reduce the equipment’s size and increase the thermal exchange surface by using fins, and on the other hand to increase the thermal conductivity of fluid exchangers. Improvements in nanotechnology have enhanced our abilities to synthesize nano-scale materials, such as different types of nanoparticles including non-metallic, carbonbased and metallic ones, which have started to be used in conventional fluids such as water, ethylene glycol and oil, creating a new class of fluids called nanofluids [1]. These nanofluids have been shown to have enhanced thermal properties and potential
⇑ Corresponding author. E-mail address: [email protected] (S.A. Ahmed). Peer review under responsibility of Karabuk University.
applications in various fields such as medicine, electronics and transportation [2]. Liu Yang, and Yuhan Hu et al [3,4] summarizes recent research on TiO2 nanofluids in two reviews. The first part of the review summarizes recent study progresses on preparation, stability, and physical properties of TiO2 nanofluids, where the physical properties of TiO2 nanofluids are focused on the viscosity and surface tension. While, the application of TiO2 nanofluids and its thermal conductivity were introduced in the second part of the reviews. Therefore, TiO2 nanofluids have shown good applications in many energy-related filed. Titanium dioxide (TiO2), a stable and non-toxic material has been extensively used in nanofluids research. It has three crystalline phases, namely brookite, rutile and anatase, the last one being the most important and used for different purposes such as gas sensors, pigments, nanofluids and catalysis. In a study by Minsta et al. (2009) data were collected which established the dependence of thermal conductivity on temperature for alumina and copper oxide based nanofluids [5]. The results showed an overall predicted effect of a raise in thermal conductivity by increasing the fraction of particle volume and decreasing particle size. In addition, they also found that the relative increase in thermal conductivity was of greater significance at higher temperatures [5].
https://doi.org/10.1016/j.jestch.2018.07.008 2215-0986/Ó 2018 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
2
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
Nomenclature Cp Q _ m Dh Nu Re
Specific heat capacity J=kg K nf: nanofluid The heat transfer rate W Mass flow rate kg/s Hydraulic diameter of the tube mm Nusselt number Reynolds number
Another study by Liu Yang et al. [6] was done to improve the suspending ability of ammonia water based TiO2 nanofluids using a dynamic circulating device, and the dynamic characteristics of ammonia water based TiO2 nanofluids including suspending ability, viscosity and surface tension were investigated. The study found that the dynamic circulating process has little effect on the viscosity of TiO2 nanofluids, and the surface tension is mainly determined by the addition of sodium dodecyl benzene sulfonate (SDBS). Many aspects of nanoparticles such as volume fraction, dimension, shape and other physical properties affect nanofluid’s thermal conductivity, which is conventionally measured by the hot-wire method. Measurements have shown the increase in nanofluids’ thermal conductivity to be correlated with the volume fraction of ultra-fine particles [7]. A new correlation to estimate the thermal conductivity of Al2O3 and CuO nanofluids based on experimental data was developed and it was shown that the increase in thermal conductivity for both cases was positively correlated with temperature [8]. One of the most important tools in determining the thermophysical properties of hybrid nanofluids are mathematical models. They are, in addition, used to validate and reduce the error between predicted and experimental data [9]. Variables included in such mathematical correlations include viscosity, thermal conductivity, friction factors, Nusselt number etc. Such models show that hybrid nanofluids’ performances are determined by volume concentration, dispersion stability and mixing ratio. Usage of nanofluids in cooling systems of electronic devices offers a number of advantages and the development of this technology could be an important factor in further miniaturization as well as the increase in energy efficiency of such gadgets [10]. One of the most well-studied systems by means of Molecular Dynamic Simulations (MDS) is the layering phenomenon in which shell-like formations of water molecules cover nanoparticles’ surfaces. In these systems, metal nanoparticles (Cu) and their oxide forms (CuO) are stimulated according to the parameters of a water environment [11]. Results show ordered water molecules forming layers around nanoparticles to play an essential role in explaining experimental results of thermal conductivity for such nanofluids. In another study, the effect of water-Al2O3 nanofluid on the performance of solar collectors was determined under real weather conditions. The improvement in the efficiency of the solar collector was shown to be dependent on the concentration of nanoparticles; high nanoparticle concentration significantly reduced the device’s temperature, which was at the same time associated with increased thermal efficiency [12]. Viscosity and thermal conductivity of a number of metallic oxides such as CuO, ZnO, SiO2 and Al2O3 at different temperatures, nanoparticle concentration and shapes (spherical, platelets, blades, bricks and cylindrical) have already been modeled and determined [13]. Such studies have shown that shape has a great effect on nanofluids thermophysical properties. More importantly, thermal conductivity was enhanced by increased temperature and viscosity was positively correlated with increasing the particle volume fractions, two properties with promising applications in modern technology.
f #
q u l h
The friction factor Velocity at inlet radiator m/s Density kg=m3 Volume concentration Viscosity kg=m s The heat transfer coefficient W=m2 K
Nanofluid stability and the influence of surfactant concentration during sample preparation and sedimentation was studied to further improve the suspension stability as e means of applying it to solar plants. The long-term stability of nanofluids is extended by certain surfactants which create chemical bonds with nanoparticles in the fluid, but their thermal conductivity is not affected. Studies have shown that nanofluids in both presence and absence of surfactants show non-Newtonian behavior and they become more viscous with increasing the cluster size [14]. In another study by Gu et al. (2013) on three water based nanofluids (NFs) consisting of large aspect ratio fillers – carbon nanotubes (CNTs), silver nanowires and copper nanowires, it was found that the shape of nanoparticle had a significant effect on the suspension’s thermal effective conductivity [15]. They concluded that particle shape is an essential factor causing large changes among experimental values of thermal conductivity. Their results indicate that materials with higher thermal conductivity are not the only decisive factors in improving thermal transport profiles of nanofluids. In 2017, Liu Yang et al. [16] carried out an important and comprehensive review of both the experimental and theoretical research on the viscosity, thermal conductivity and surface tension of nanofluids. They concluded that material type has a great effect in thermal conductivity of nanofluids since thermal conductivity of Graphene, CNTs, Au; Ag etc. nanofluids is greatly higher than that of other type, such as TiO2, SiC, SiO2 nanofluids. In addition, the material type has little effect in viscosity of nanofluids because no relationship can be concluded between different particle materials. Most results show that viscosity and thermal conductivity increase as an increase in particle loading. A novel application of nanofluids is using them as a substitute for conventional coolants in car radiators, an important component of the car engine. Radiators serve as heat-exchangers for cooling the car engine conventionally using water as exchange medium. Vehicle engine’s thermal performance under the effect of nanofluids has been studied by many researchers, and the major applications of nanofluids have been as coolers and lubricants in car radiators in an attempt to increase the heat removal efficiency. Results have shown that heat transfer coefficient can be improved by more than 50% as compared to the conventional coolants but it is limited by the drop on liquid’s pressure. However, may experts agree that an optimum performance can be achieved at low nanoparticle volume fraction of less than 1% (u < 1%) [17]. In the current study, application of TiO2-water nanofluid as a car radiator cooler was investigated by measuring its viscosity and thermal conductivity. In addition, other variables such as flow rates of liquid and air, various nanoparticle concentrations and liquid inlet temperatures were studied to have a better picture of its cooling efficiency on the radiator. 2. Materials and methods 2.1. Preparation of TiO2 nanofluid Nanofluid sample preparation was carried out in a two-step process of disseminating the primarily arranged nanoparticles in
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
3
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
Fig. 1. Nanoparticles Size distribution.
distilled water by means of ultrasonication. Particles were first reduced in size and then selected for a uniform diameter by Spex-8000 ball milling (Spex Industries, Inc., Edison, NJ), giving a normal distribution centered at an average of 44 nm and a range from 30 to 60 nm (Fig. 1). Particles’ surface morphology and microstructures were studied with scanning electron microscope (SEM) and transmission electron microscope (TEM) as shown in Figs. 2 and 3, respectively. Many previous studies have shown that increasing the nanofluid’s particle ratio leads to an increase in their precipitation. Even though we used different particle ratios in this study, the optimal one is 2% at which precipitation stays at a minimal level. Nanoparticles were suspended in deionized water which has basic properties and the mixture was further improved by addition of Triton X-100 (molecular formula: C14H22O(C2H4O)n) to final concentrations of 0.1% 0.2% and 0.3%, respectively, in order to enhance the solubility of TiO2. Triton X-100 has surfactant properties and it has been widely used in dyes and detergents for
Fig. 3. TEM of the TiO2 nanoparticle.
decreasing surface tension and contact angles, leading to an increase in the wetting ability of the material. As a result, TiO2 particulates can be suspended for longer time periods in fluids by using ball milling to provide high energy, addition of surfactant and ultrasonic bath. In order to find the optimal Triton X-100 amount, the nanofluid’s stability, foaming and aggregation were measured for different concentrations of the constituents. A concentration of 0.5% Triton X-100 was chosen for this study. Table 1 shows the characteristics of TiO2.
Table 1 Characteristics of TiO2 nanoparticles.
Fig. 2. SEM morphology of TiO2.
Parameter
Value
Purity Color Diameter SSA Shape Bulk density
99% White 44/nm 10–45/m2 g Spherical 0.460/g cm3
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
4
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
TiO2 nanoparticles dispersion in deionized water was carried out by continuous pulsing through an ultrasonic processor (Bandelin Sonorex Super RK514H) at an optimum duration. Throughout the preparation process of nanofluid, the container was constantly cooled to avoid evaporation of surface active agent. 2.2. Stability of nanofluid In order to prevent nanofluid sedimentation during the experiments, a number of steps were taken: First, TiO2 particle size was decreased to nanoscale by using high energy impacted ball milling (Spex-8000) followed by addition of Triton X-100. In addition, the nano-TiO2 obtained from the above procedures was dissolved in water by using ultrasonication. Given the huge density differences between metallic oxide nanoparticles and deionized water, two methods have been proposed to prevent sedimentation and uniformly distribute nanoparticles in nanofluids; the first one involves changing nanofluids pH and the other using surfactants [18]. Our nanofluid was prepared by using 0.1 to 0.5% surfactant, the last one giving a minimal agglomeration. In addition, particle structure is an important determinant of nanofluid stability. Active surface reagents have many characteristics such as structure, presence of many types of metal oxides for improving thermal conductivity as well as flocculation when they undergo ultrasonication, all of them making TiO2 more effective as compared to other metal oxides [19]. One of the most important features of TiO2 is high water adsorption ability making a gelly surface which increases the lubrication value. Our nanofluid maintained its stability throughout the experimental procedure in all temperatures tried (Fig. 4). The same was the case for TiO2-water nanofluid suspension which was stable and had no distillation problems throughout the whole procedure. The three fundamental thermo-physical
properties TiO2-water nanofluid were measured as shown in Table 2. 2.3. Thermophysical properties of the nanofluid The thermophysical properties of any nanofluid depend on a number of factors such as particle size, shape, whether it is metallic or non-metallic (oxide), chemistry of the solution, especially pH, and solution age. For instance, the thermal conductivity of spherical shaped nanoparticles is lower as compared to cylindrical ones, while smaller size particles have better thermal conductivity when compared to those of greater size. Additionally, metallic nanoparticles have better thermal conductivity than non-metallic ones [20]. Table 2 shows the thermo-physical properties of TiO2 and pure water at temperatures range between 20 and 80 °C. The following equations were used to show the regularity regarding viscosity, specific heat, thermal conductivity and density [21]. Nanofluid density is calculated as follows:
qnf ¼ uqp þ ð1 uÞqw
ð1Þ
2.3.1. Viscosity calculation and measurement Nanofluid viscosity is also determined by a number of factors such as the volume fraction of nanoparticles, their size and shape, base fluid, thickness of the nanolayer, dispersion technique, temperature and pH value, and nanoparticles’ Brownian motions [22–27]. Fluid viscosity is generally measured by instruments such as viscometer or rheometer, and the compiled data are compared to known correlations. The first model to measure viscosity was developed by Einstein in 1902 (Eq. (2). Particle’s spherical shape and less volume fraction are the limiting factors of this equation [28].
lnf ¼ ð1 þ 2:5uÞlw
ð2Þ
Fig. 4. TiO2-water nanofluid.
Table 2 The properties of pure water and TiO2. Working fluid
TiO2 Pure water TiO2-water u = 1% TiO2-water u = 2% TiO2-water u = 3%
Density kg/m3
4260 987.8 1044 1065 1093
Viscosity mPas 20 °C
40 °C
60 °C
80 °C
– 0.97 1.01 1.02 1.04
– 0.74 0.82 0.84 0.87
– 0.58 0.65 0.68 0.71
– 0.47 0.53 0.56 0.61
Specific heat J/kgK
Thermal conductivity W/mK
6890 4181.2 4523 4401 4366
11.7 0.645 0.728 0.737 0.751
[21]
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
5
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
A more effective formula was later derived by Brinkman called the Brickman Model [29].
lnf ¼
lbf ð1 uÞ2:5
ð3Þ
Another model considered to be more suitable for nanoparticles with volume fraction greater than 2% was derived by Nelson in 1970 and shown in Eq. (4) [30].
"
lnf ¼ ð1 þ 1:5uÞ
up eð1um Þ
#
lbf
lnf ¼ 6 4
1 34:87
6M df ¼ 0:1 Npqbf
dp df
u1:03
7 5lbf
ð5Þ
!1=3 ð6Þ
where qbf denotes the mass density of base fluid at 20 °C. In this study, nanofluid viscosity was measured by using a Brookfield Viscometer (DV-2 + Pro Programmable Viscometer) and in order to reduce uncertainty, the measured values were compared with the data in ASHARE Handbook [32]. 2.3.2. Specific heat capacity of nanofluid Specific heat is defined as the amount of heat per unit mass of a material to raise the temperature by one degree centigrade. It is one of the fundamental properties influencing the rate of heat transfer in nanofluids. Studies have shown it to vary with particle size and since smaller particles have larger specific surface areas, reducing particles size increases the effect of the surface energy on effective specific heat capacity [33,34]. In order to determine the specific heat capacity of TiO2 nanofluid, Eq. (7) was used:
Cpnf ¼
Height
Width
400 mm
200 mm
16 mm
Maxwell model knf ¼
kp þ 2kbf þ uðkp kbf Þ kbf kp þ 2kbf uðkp kbf Þ
ð8Þ
Hamilton Crosser model k nf
3
1 0:3
Length
ð4Þ
where up and um stand respectively for volume concentration and maximum volume fraction. Researchers have recently modified these models by introducing more parameters in order to increase their accuracy. One such model is the Corcione Model which has a number of advantages such as giving results with 1.84% of standard deviation as well as following boundaries of nanoparticles with diameters between 20 and 200 nm and volume fraction of 0.0001–0.071 [31].
2
Table 3 The dimensions of the selected car radiator.
uqp Cpp;n þ ð1 uÞqw Cpbf qnf
ð7Þ
2.3.3. Thermal conductivity Thermal conductivity is the ability of a material to conduct heat and it depends of many factors such as the thermal conductivities of base fluid and nanoparticles, surface area, nanoparticle shape, temperature and volume fraction. A number of theoretical and empirical models have been derived to predict the thermal conductivity of nanofluids [35–37], with Eqs. (8)–(10) representing the ones used in the current study to compare with the experimental results obtained by measuring it by KD2 Pro thermal property analyzer (Decagon, USA). This device consists of a sensor for measuring liquids thermal conductivity by using a transient line heat source and a hand-held controller. To carry out the measurements, nanofluid sample was immersed for 10 min in water bath at the desired temperature until it reached equilibrium with the medium. Four readings were taken with 15 min intervals between each at a temperature range of 20–80 °C. The thermo-physical properties of pure water and TiO2 are illustrated in Table 3.
¼
kp þ ðn 1Þkbf uðn 1Þðkbf kp Þ kp þ ðn 1Þkbf þ uðn 1Þðkbf kp Þ
Yuand Choi model knf ¼
kpe þ 2kb þ 2ðkpe kb Þð1 þ bÞ3 u kpe þ 2kb 2ðkpe kb Þð1 þ bÞ3 u
ð9Þ
kb ð10Þ
Table 3 shows an average specific heat of 0.09 J/kgK and an increase in specific heat capacity for TiO2-water nanofluid as compared to pure water. Similarly, it also shows that viscosity and density of TiO2-water nanofluid are higher than pure water. Given the fact that viscosity increases with temperature, the viscosity of TiO2-water nanofluid is slightly higher than pure water at all temperatures. This can be attributed to the metal particles in nanofluid which increase the density of TiO2-water mixture. According to previous studies [19,38], as the density of nanofluid increases, there is a tendency for it to flocculate. This reduces the variety of homogeneous solutions because the stability of low-density nanofluid is relatively better than the nanofluid with a higher density. 3. Experimental setup The vehicle engine system (Model FIAT DOBLO 1300 cc. MJTD) used in this study includes flow lines, a centrifugal pump, a flow meter, anemometer, tank, thermocouples, a forced draft fan and a cross flow heat exchanger, also known as automobile radiator (Fig. 5). The dimensions of the selected car radiator are shown in Table 3 and those of the car radiator tubes in Table 4. Fig. 6 shows a schematic representation and dimensions of the radiator flat tube (Table 5). Four Pico-thermocouple (display: TC-08) thermometers were used to measure the coolant temperature. In addition, a Testo-thermometer (display: 435) was connected to measure air’s input and output temperatures of back and front surfaces of the radiator. In order to avoid any potential problems during experimentation, the setup was tested first with pure water (Fig. 7). This was done to assure the stability of the experimental setup and validity of test results. The procedure was as follows: as the nanofluid goes through the pump, it is encountered by high pressures and shear; in this way grouping is expelled [38]. Furthermore, high flow rate in the radiator tubes and associated channels enhances the adjustment of the nanofluid [19]. After conducting the experiment with pure water, the test system was discharged completely and recharged to follow the same procedure for TiO2-water nanofluid. The nanofluid was used in three different concentrations: 0.1%, 0.2% and 0.3%, and was pumped through the radiator at different flow rates of 0.097 m3/h and 0.68 m3/h as working fluid. These experiments, as in pure water case, were repeated and the data were recorded.
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
6
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
Temperature Indicator
Radiator
T wall
Nanofluid Inlet Flow meter
T in Fan
200 mm
Anemometer Nanofluid Outlet
T out 400 mm
Pump
Nanofluid Tank
Engine
Power supply
Fig. 5. Schematic representation of experimental setup.
Table 4 The dimensions of the car radiator tubes. Inward measurement
Material
Number of tube
Spacing
Dh
18 19.6 295(mm)
Aluminum
33 mm
8.06
3.35 mm
Dh is the hydraulic diameter of the tube.
Fig. 6. Schematic and dimensions of the radiator flat tube.
Table 5 Technical properties, precisions and total uncertainty analysis of the equipment.
4. Theoretical analysis
Measuring device
Measuring range
Precision
Total Uncertainty
4.1. Calculation of heat transfer coefficient
Flow meter Thermometer Thermocouple Anemometer (air velocity)
2–20 m3/h 0–120 °C 0–1200 °C 0–20 m/s
±2.5% ±0.1 °C ±0.1 °C ±0.01 m/s
±0.0003125% ±0.075 °C ±0.15% ±0.012%
In order to evaluate heat transfer coefficients in the radiator, the following equations for the coolant and air were used [39].
Q ¼ hADT ¼ hAðTb Tw Þ
ð11Þ
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
7
Engine Flow meter
Radiator
Fig. 7. Photograph of the real test set up.
_ p ðTin Tout Þ Q ¼ mC
ð12Þ
where, Q is the heat transfer rate [W]; Cp is the specific heat capac_ is the mass flow rate of working fluid ity of working fluid [J/kgK]; m [kg/s]; Tin, Tout stand for inlet and outlet temperatures of coolant fluid [°C], respectively. Tb is the bulk temperature which was assumed to be the average value of inlet and outlet temperatures of the fluid moving through radiator. Tw is the tube wall temperature which is the average value of two surface thermocouples.
hexp ¼
Q AðTb Tw Þ
ð13Þ
The precision of experimental setup is crucial for any study, but of the same importance is the gathering of accurate data with the proper measuring devices. A very powerful tool in designing experiments are also uncertainty analysis since they are used to measure experimental errors which may be detrimental to data accuracy. No matter the accuracy of measuring devices, uncertainty analysis is always used to determine errors emerging from environment, test conditions, measuring devices or experimenter. In order to calculate the total uncertainty for these experiments, Eq. (19) [42,43] was used as follows:
ð14Þ
G ¼ Gðx1 ; x2 ; x3 ; . . .Þ ) W s " 2 2 2 #1=2 @G @G @G ¼ w1 þ w2 þ þ wn @x1 @x2 @xn
f
where, hexp is the heat transfer coefficient [W=m2 K]. Nusselt number (Nu) is determined as:
Nu ¼
hDh K
where, Dh is the hydraulic diameter of the tube [mm]. Finally, Reynolds number (Re) is determined as:
Re ¼
q#Dh l
ð15Þ
where, # is Velocity at inlet radiator [m=s. 4.2. Relationships for Nusselt number determination for single phase fluids Correlations for the laminar flow through pipes [40] and for the flow in the compact heat exchanger at 550 Re 1850 range were determined by wquations 16 and 17 respectively [41].
Nu ¼ 1:86
1=3 0:14 ReD Pr l ls L=Dh
P1=3 Nu ¼ 0:951 Re0:173 D r
ð16Þ ð17Þ
where ReD represents tube-side Reynolds number which is based on tube hydraulic diameter whereas Pr is Prandtl number. Although, we used a high Reynolds number as an input parameter, experimental results were compared by using the equations for friction (Eq. (18)).
f ¼
64 Re
4.3. Uncertainty analysis
ð18Þ
ð19Þ
To calculate total uncertainty, S is the necessary quantity to be determined with n independent variables affecting the quantity G as x1, x2, x3, . . .xn. The error rate for each of those independent variables as well as the total uncertainty analysis are stated as W1, W2,. . ... . ..Wn and Ws respectively. The technical qualifications, total uncertainty and precisions analysis of measuring equipment are shown in Table 4. 5. Results and discussion In Fig. 1, the distribution graph of particle size in the nanofluid according to intensity obtained by zeta-seizer on different days is shown. Figs. 2 and 3 show TEM and SEM images respectively. The distribution peak is at an almost identical horizontal position but the intensity increases vertically showing an increase in the population of aggregates. It can therefore be concluded the size of particles in TiO2-water nanofluid ranged from 30 to 60 nm with an average size of 44 nm. 5.1. Viscosity Fig. 8 shows viscosity for different volume concentrations of TiO2 (0.1, 0.2, and 0.3%) at different temperatures in order to analyze the effect of temperature on nanofluid viscosity. It can be clearly seen that increasing the inlet temperature of the nanofluid decreases its viscosity. Therefore, we can conclude that there exists
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
8
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
Viscosity (m.Pa.s)
1.1 1.0
0.1% TiO 2 0.2% TiO 2
0.9
0.3% TiO 2 Pure water
0.8 0.7 0.6 0.5 0.4 20 °C
40 °C
60 °C
80 °C
Temperature °C Fig. 8. Viscosity of TiO2-water nanofluid at different temperatures.
0.755 Experimental Setup Yu and Choi Maxwell
Thermal conductivity W/m.K
0.750
0.745
0.740
0.735
0.730
0.725
0.720 0.10
0.15
0.20
0.25
0.30
0.35
Volume concentration % Fig. 9. Thermal conductivity of TiO2 nanofluid at different volume fraction.
a direct relationship between temperature and viscosity for all experiments under all conditions as compared to the base fluid. 5.2. Thermal conductivity The experimental values of nanofluid’s thermal conductivity are in good agreement with those present in literature. It can be clearly seen from Fig. 9 that thermal conductivity increases in a nearly linear fashion with every incremental increase of volume fraction. The same figure also shows a relation of thermal conductivity to volume concentration, again in good agreement with published data [15,44,45]. Experimental values of thermal conductivity of TiO2-water nanofluids show high deviation when compared to those estimated from Maxwell Model, but they are in good agreement with estimations from Choi Model. When results of TiO2 and A12O3 [46] systems are compared by taking the base fluid as reference, the former shows significantly
higher thermal conductivity as compared to the later despite its larger particle size (mean size of 44 nm and 13 nm, respectively). These results indicate that particle’s thermal conductivity has more influence than particle size. According to a study conducted by Eastman et al. [47], metallic nanoparticle-based nanofluids show a large increase in thermal conductivity as compared to the oxide particle-based or base fluid counterparts [47]. Another study showed that nanofluids thermal conductivity was not affected by the suspended state of nanoparticles [48]. 5.3. Heat transfer coefficient In Fig. 10, nanofluid’s overall heat transfer as a function of Reynolds number at constant flow rate for different nanoparticle concentration is shown. It can be clearly seen from the figure that overall heat transfer coefficient increases with increasing Reynolds number as compared to the base fluid. The experimentally
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
9
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
Average heat transfer coefficient
2200 2000
Pure water 0.1% TiO2-water
1800
0.2% TiO2-water 0.3% TiO2-water
1600 1400 1200 1000 800 600 400 200 200
400
600
800
1000
1200
1400
1600
1800
1400
1600
Reynolds numbers Fig. 10. Average heat transfer coefficient as a function of Reynolds numbers.
3500 Base fluid 0.1vol.% 0.25vol.% 0.5vol.%
Average heat transfer coefficient
3000
2500
2000
1500
1000
500
0 0
200
400
600
800
1000
1200
Reynolds numbers Fig. 11. The experimental data of MWCNT nanofluid by [49].
obtained overall heat transfer value is 2050 W/m2K for 0.3% TiO2water. These results are in good agreement with predicted values but slightly lower when compared to vehicle radiator in which a multi-walled carbon nanotube (MWCNT) based on water/ethylene glycol is used with nanoparticle volume concentration of 0.5%, and heat transfer coefficient increase from 986.8 W/m2K to 2951 W/ m2K, for Reynolds number from 430 to 1400 (Fig. 11) [49].
nanofluids in an automobile radiator was experimentally measured as a function of concentration and temperature. It was found that the presence of TiO2 nanoparticle can significantly enhance radiator’s heat transfer rate in a manner dependent on nanoparticle quantity added to the base fluid. Heat transfer coefficient significantly improves for 0.2% nanoparticle concentration as compared to pure water. This is due to the fact that TiO2’s greater thermal conductivity, aspect ratio, lower specific gravity, thermal resistance and larger specific area as compared to pure water.
6. Conclusion Acknowledgements In the current study, usage of TiO2-water nanofluid’s as a cooler in car engine radiator was studied. Based on the experimental results, TiO2-water nanofluid offers a better overall performance than base fluid. The overall heat transfer coefficient of TiO2
The authors would like to acknowledge the funding from Libyan Government and the Faculty of Technology in Karabuk University, and especially adviser Professor Mehmet Ozkaymak.
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
10
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
References [1] S.U. Choi, J.A. Eastman, Enhancing Thermal Conductivity of Fluids with Nanoparticles, Argonne National Lab, IL (United States), 1995. [2] M. Leena, S. Srinivasan, Synthesis and ultrasonic investigations of titanium oxide nanofluids, J. Mol. Liq. 206 (2015) 103–109. [3] L. Yang, Y. Hu, Toward TiO2 nanofluids—part 1: preparation and properties, Nanoscale Res. Lett. 12 (1) (2017) 417. [4] L. Yang, Y. Hu, Toward TiO2 nanofluids—part 2: applications and challenges, Nanoscale Res. Lett. 12 (1) (2017) 446. [5] H.A. Mintsa et al., New temperature dependent thermal conductivity data for water-based nanofluids, Int. J. Therm. Sci. 48 (2) (2009) 363–371. [6] L. Yang et al., Dynamic characteristics of an environment-friendly refrigerant: ammonia-water based TiO2 nanofluids, Int. J. Refrig. 82 (2017) 366–380. [7] Y. Xuan, Q. Li, Heat transfer enhancement of nanofluids, Int. J. Heat Fluid Flow 21 (1) (2000) 58–64. [8] L.S. Sundar et al., Experimental thermal conductivity of ethylene glycol and water mixture based low volume concentration of Al2O3 and CuO nanofluids, Int. Commun. Heat Mass Transfer 41 (2013) 41–46. [9] M.H. Hamzah et al., Factors affecting the performance of hybrid nanofluids: a comprehensive review, Int. J. Heat Mass Transfer 115 (2017) 630–646. [10] G. Colangelo et al., Cooling of electronic devices: nanofluids contribution, Appl. Therm. Eng. 127 (2017) 421–435. [11] M. Milanese et al., An investigation of layering phenomenon at the liquid–solid interface in Cu and CuO based nanofluids, Int. J. Heat Mass Transfer 103 (2016) 564–571. [12] G. Colangelo, M. Milanese, A. De Risi, Numerical simulation of thermal efficiency of an innovative Al2O3 nanofluid solar thermal collector, Therm. Sci. 21 (6B) (2017) 2769–2779. [13] O.A. Alawi et al., Thermal conductivity and viscosity models of metallic oxides nanofluids, Int. J. Heat Mass Transfer 116 (2018) 1314–1325. [14] G. Colangelo et al., Thermal conductivity, viscosity and stability of Al2O3diathermic oil nanofluids for solar energy systems, Energy 95 (2016) 124–136. [15] B. Gu et al., Thermal conductivity of nanofluids containing high aspect ratio fillers, Int. J. Heat Mass Transfer 64 (2013) 108–114. [16] L. Yang et al., Recent developments on viscosity and thermal conductivity of nanofluids, Powder Technol. 317 (2017) 348–369. [17] N.A.C. Sidik, M.N.A.W.M. Yazid, R. Mamat, Recent advancement of nanofluids in engine cooling system, Renewable Sustainable Energy Rev. 75 (2017) 137– 144. [18] A. Sözen et al., Utilization of fly ash nanofluids in two-phase closed thermosyphon for enhancing heat transfer, Exp. Heat Transfer 29 (3) (2016) 337–354. [19] A.A. Minea, Advances in New Heat Transfer Fluids: From Numerical to Experimental Techniques, CRC Press, 2017. [20] W. Duangthongsuk, S. Wongwises, Measurement of temperature-dependent thermal conductivity and viscosity of TiO2-water nanofluids, Exp. Therm Fluid Sci. 33 (4) (2009) 706–714. [21] S. Devireddy, C.S.R. Mekala, V.R. Veeredhi, Improving the cooling performance of automobile radiator with ethylene glycol water based TiO2 nanofluids, Int. Commun. Heat Mass Transfer 78 (2016) 121–126. [22] H. Masuda, A. Ebata, K. Teramae, Alteration of thermal conductivity and viscosity of liquid by dispersing ultra-fine particles. Dispersion of Al2O3, SiO2 and TiO2 ultra-fine particles, 1993. [23] A. Turgut et al., Thermal conductivity and viscosity measurements of waterbased TiO2 nanofluids, Int. J. Thermophys. 30 (4) (2009) 1213–1226. [24] M. Bahiraei et al., Using neural network for determination of viscosity in water-TiO2 nanofluid, Adv. Mech. Eng. 4 (2012) 742680. [25] X. Fan et al., Potential of ‘nanofluids’ to further intensify microreactors, Green Chem. 10 (6) (2008) 670–677.
[26] A. Ghadimi, I.H. Metselaar, The influence of surfactant and ultrasonic processing on improvement of stability, thermal conductivity and viscosity of titania nanofluid, Exp. Therm. Fluid Sci. 51 (2013) 1–9. [27] T. Yiamsawas et al., Measurement and correlation of the viscosity of waterbased Al2O3 and TiO2 nanofluids in high temperatures and comparisons with literature reports, J. Dispersion Sci. Technol. 34 (12) (2013) 1697–1703. [28] A. Einstein, Eine neue Bestimmung der Moleküldimensionen, Annalen der Physik 324 (2) (1906) 289–306. [29] H. Brinkman, The viscosity of concentrated suspensions and solutions, J. Chem. Phys. 20 (4) (1952). 571-571. [30] L.E. Nielsen, Generalized equation for the elastic moduli of composite materials, J. Appl. Phys. 41 (11) (1970) 4626–4627. [31] M. Corcione, Empirical correlating equations for predicting the effective thermal conductivity and dynamic viscosity of nanofluids, Energy Convers. Manage. 52 (1) (2011) 789–793. [32] A.F. Handbook, American Society of Heating, Refrigerating and AirConditioning Engineers, Inc., Atlanta, GA, USA, 2009. [33] X.-Q. Wang, A.S. Mujumdar, Heat transfer characteristics of nanofluids: a review, Int. J. Therm. Sci. 46 (1) (2007) 1–19. [34] S. Eiamsa-Ard, K. Kiatkittipong, W. Jedsadaratanachai, Heat transfer enhancement of TiO2/water nanofluid in a heat exchanger tube equipped with overlapped dual twisted-tapes, Eng. Sci. Technol. Int. J. 18 (3) (2015) 336–350. [35] J.C. Maxwell, A Treatise on Electricity and Magnetism, Clarendon Press, Oxford, 1873. [36] R.L. Hamilton, O. Crosser, Thermal conductivity of heterogeneous twocomponent systems, Ind. Eng. Chem. Fundam. 1 (3) (1962) 187–191. [37] W. Yu, S. Choi, The role of interfacial layers in the enhanced thermal conductivity of nanofluids: a renovated Maxwell model, J. Nanopart. Res. 5 (1–2) (2003) 167–171. [38] M. Nasiri, S.G. Etemad, R. Bagheri, Experimental heat transfer of nanofluid through an annular duct, Int. Commun. Heat Mass Transfer 38 (7) (2011) 958–963. [39] A.M. Hussein et al., Experimental measurement of nanofluids thermal properties, Int. J. Automot. Mech. Eng. 7 (2013) 850. [40] E.N. Sieder, G.E. Tate, Heat transfer and pressure drop of liquids in tubes, Ind. Eng. Chem. 28 (12) (1936) 1429–1435. [41] M. Dehghandokht et al., Flow and heat transfer characteristics of water and ethylene glycol–water in a multi-port serpentine meso-channel heat exchanger, Int. J. Therm. Sci. 50 (8) (2011) 1615–1627. [42] J.P. Holman, W.J. Gajda, in: Experimental Methods for Engineers, 8 ed., McGraw-Hill, New York, 2012, p. 8. [43] M. Aktasß et al., Performance analysis and modeling of a closed-loop heat pump dryer for bay leaves using artificial neural network, Appl. Therm. Eng. 87 (2015) 714–723. [44] K. Abdul Hamid et al., Thermal conductivity enhancement of TiO2 nanofluid in water and ethylene glycol (EG) mixture, Indian J. Pure Appl. Phys. (IJPAP) 54 (10) (2016) 651–655. [45] M. Arulprakasajothi et al., Heat transfer study of water-based nanofluids containing titanium oxide nanoparticles, Mater. Today: Proc. 2 (4–5) (2015) 3648–3655. [46] N. Usri et al., Thermal conductivity enhancement of Al2O3 nanofluid in ethylene glycol and water mixture, Energy Proc. 79 (2015) 397–402. [47] J.A. Eastman et al., Anomalously increased effective thermal conductivities of ethylene glycol-based nanofluids containing copper nanoparticles, Appl. Phys. Lett. 78 (6) (2001) 718–720. [48] D.-H. Yoo, K. Hong, H.-S. Yang, Study of thermal conductivity of nanofluids for the application of heat transfer fluids, Thermochim. Acta 455 (1–2) (2007) 66–69. [49] B. M’hamed et al., Experimental study on thermal performance of MWCNT nanocoolant in Perodua Kelisa 1000cc radiator system, Int. Commun. Heat Mass Transfer 76 (2016) 156–161.
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
Contents lists available at ScienceDirect
Engineering Science and Technology, an International Journal journal homepage: www.elsevier.com/locate/jestch
Full Length Article
Improving car radiator performance by using TiO2-water nanofluid Siraj Ali Ahmed a,⇑, Mehmet Ozkaymak a, Adnan Sözen b, Tayfun Menlik b, Abdulkarim Fahed a a b
Energy Systems Engineering, Karabuk University, Turkey Energy Systems Engineering, Gazi University, Turkey
a r t i c l e
i n f o
Article history: Received 12 January 2018 Revised 6 July 2018 Accepted 14 July 2018 Available online xxxx Keywords: Car radiator Nanofluids Performance Reynolds number TiO2-water
a b s t r a c t The most recent developments in nanotechnology have lead to improvements in original uses of nanofluids in car motor cooling. In the present study, enhancement of car engine radiator by TiO2-water nanofluid as a coolant of car engine radiator was investigated experimentally. In order to determine the effect of TiO2-water nanofluid on radiator’s performance, experiments were performed with pure water and TiO2-water nanofluid separately and results were compared with other studies on vehicle engine system FIAT DOBLO 1.3 MJTD ENG. The main objective was to check the aspects of heat transfer of the TiO2-water nanofluid as a substitution to the customary coolant system. For this purpose, experiments were carried out using a TiO2 nanofluid with 0.1, 0.2 and 0.3% volume concentrations with flow rates of 0.097 and 0.68 m3/h in laminar floe region, where Reynolds number ranged from 560 to 1650. Our results show that the friction factor decreases when Reynolds number and the volume concentration are increased. Moreover, TiO2-water nanofluid with 0.2% concentration can enhance the effectiveness of car radiator by 47% as compared to 0.1 and 0.3% concentrations and pure water as a coolant. Finally, the average heat transfer coefficient was directly affected by the increase in Reynolds number and volume concentration fraction of the nanofluid. Ó 2018 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Great efforts have been spent to improve the thermal efficiency of a number of processes with mixed success until the recent emergence of a promising new class of nano-coolants with a liquid component such as water mixed with nanoparticles started to make their way into a myriad of engineering applications. Although they are expected to provide substitutes of conventional coolants in the near future, a number of improvements are still to be made. Attempts are still being made on one hand to reduce the equipment’s size and increase the thermal exchange surface by using fins, and on the other hand to increase the thermal conductivity of fluid exchangers. Improvements in nanotechnology have enhanced our abilities to synthesize nano-scale materials, such as different types of nanoparticles including non-metallic, carbonbased and metallic ones, which have started to be used in conventional fluids such as water, ethylene glycol and oil, creating a new class of fluids called nanofluids [1]. These nanofluids have been shown to have enhanced thermal properties and potential
⇑ Corresponding author. E-mail address: [email protected] (S.A. Ahmed). Peer review under responsibility of Karabuk University.
applications in various fields such as medicine, electronics and transportation [2]. Liu Yang, and Yuhan Hu et al [3,4] summarizes recent research on TiO2 nanofluids in two reviews. The first part of the review summarizes recent study progresses on preparation, stability, and physical properties of TiO2 nanofluids, where the physical properties of TiO2 nanofluids are focused on the viscosity and surface tension. While, the application of TiO2 nanofluids and its thermal conductivity were introduced in the second part of the reviews. Therefore, TiO2 nanofluids have shown good applications in many energy-related filed. Titanium dioxide (TiO2), a stable and non-toxic material has been extensively used in nanofluids research. It has three crystalline phases, namely brookite, rutile and anatase, the last one being the most important and used for different purposes such as gas sensors, pigments, nanofluids and catalysis. In a study by Minsta et al. (2009) data were collected which established the dependence of thermal conductivity on temperature for alumina and copper oxide based nanofluids [5]. The results showed an overall predicted effect of a raise in thermal conductivity by increasing the fraction of particle volume and decreasing particle size. In addition, they also found that the relative increase in thermal conductivity was of greater significance at higher temperatures [5].
https://doi.org/10.1016/j.jestch.2018.07.008 2215-0986/Ó 2018 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
2
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
Nomenclature Cp Q _ m Dh Nu Re
Specific heat capacity J=kg K nf: nanofluid The heat transfer rate W Mass flow rate kg/s Hydraulic diameter of the tube mm Nusselt number Reynolds number
Another study by Liu Yang et al. [6] was done to improve the suspending ability of ammonia water based TiO2 nanofluids using a dynamic circulating device, and the dynamic characteristics of ammonia water based TiO2 nanofluids including suspending ability, viscosity and surface tension were investigated. The study found that the dynamic circulating process has little effect on the viscosity of TiO2 nanofluids, and the surface tension is mainly determined by the addition of sodium dodecyl benzene sulfonate (SDBS). Many aspects of nanoparticles such as volume fraction, dimension, shape and other physical properties affect nanofluid’s thermal conductivity, which is conventionally measured by the hot-wire method. Measurements have shown the increase in nanofluids’ thermal conductivity to be correlated with the volume fraction of ultra-fine particles [7]. A new correlation to estimate the thermal conductivity of Al2O3 and CuO nanofluids based on experimental data was developed and it was shown that the increase in thermal conductivity for both cases was positively correlated with temperature [8]. One of the most important tools in determining the thermophysical properties of hybrid nanofluids are mathematical models. They are, in addition, used to validate and reduce the error between predicted and experimental data [9]. Variables included in such mathematical correlations include viscosity, thermal conductivity, friction factors, Nusselt number etc. Such models show that hybrid nanofluids’ performances are determined by volume concentration, dispersion stability and mixing ratio. Usage of nanofluids in cooling systems of electronic devices offers a number of advantages and the development of this technology could be an important factor in further miniaturization as well as the increase in energy efficiency of such gadgets [10]. One of the most well-studied systems by means of Molecular Dynamic Simulations (MDS) is the layering phenomenon in which shell-like formations of water molecules cover nanoparticles’ surfaces. In these systems, metal nanoparticles (Cu) and their oxide forms (CuO) are stimulated according to the parameters of a water environment [11]. Results show ordered water molecules forming layers around nanoparticles to play an essential role in explaining experimental results of thermal conductivity for such nanofluids. In another study, the effect of water-Al2O3 nanofluid on the performance of solar collectors was determined under real weather conditions. The improvement in the efficiency of the solar collector was shown to be dependent on the concentration of nanoparticles; high nanoparticle concentration significantly reduced the device’s temperature, which was at the same time associated with increased thermal efficiency [12]. Viscosity and thermal conductivity of a number of metallic oxides such as CuO, ZnO, SiO2 and Al2O3 at different temperatures, nanoparticle concentration and shapes (spherical, platelets, blades, bricks and cylindrical) have already been modeled and determined [13]. Such studies have shown that shape has a great effect on nanofluids thermophysical properties. More importantly, thermal conductivity was enhanced by increased temperature and viscosity was positively correlated with increasing the particle volume fractions, two properties with promising applications in modern technology.
f #
q u l h
The friction factor Velocity at inlet radiator m/s Density kg=m3 Volume concentration Viscosity kg=m s The heat transfer coefficient W=m2 K
Nanofluid stability and the influence of surfactant concentration during sample preparation and sedimentation was studied to further improve the suspension stability as e means of applying it to solar plants. The long-term stability of nanofluids is extended by certain surfactants which create chemical bonds with nanoparticles in the fluid, but their thermal conductivity is not affected. Studies have shown that nanofluids in both presence and absence of surfactants show non-Newtonian behavior and they become more viscous with increasing the cluster size [14]. In another study by Gu et al. (2013) on three water based nanofluids (NFs) consisting of large aspect ratio fillers – carbon nanotubes (CNTs), silver nanowires and copper nanowires, it was found that the shape of nanoparticle had a significant effect on the suspension’s thermal effective conductivity [15]. They concluded that particle shape is an essential factor causing large changes among experimental values of thermal conductivity. Their results indicate that materials with higher thermal conductivity are not the only decisive factors in improving thermal transport profiles of nanofluids. In 2017, Liu Yang et al. [16] carried out an important and comprehensive review of both the experimental and theoretical research on the viscosity, thermal conductivity and surface tension of nanofluids. They concluded that material type has a great effect in thermal conductivity of nanofluids since thermal conductivity of Graphene, CNTs, Au; Ag etc. nanofluids is greatly higher than that of other type, such as TiO2, SiC, SiO2 nanofluids. In addition, the material type has little effect in viscosity of nanofluids because no relationship can be concluded between different particle materials. Most results show that viscosity and thermal conductivity increase as an increase in particle loading. A novel application of nanofluids is using them as a substitute for conventional coolants in car radiators, an important component of the car engine. Radiators serve as heat-exchangers for cooling the car engine conventionally using water as exchange medium. Vehicle engine’s thermal performance under the effect of nanofluids has been studied by many researchers, and the major applications of nanofluids have been as coolers and lubricants in car radiators in an attempt to increase the heat removal efficiency. Results have shown that heat transfer coefficient can be improved by more than 50% as compared to the conventional coolants but it is limited by the drop on liquid’s pressure. However, may experts agree that an optimum performance can be achieved at low nanoparticle volume fraction of less than 1% (u < 1%) [17]. In the current study, application of TiO2-water nanofluid as a car radiator cooler was investigated by measuring its viscosity and thermal conductivity. In addition, other variables such as flow rates of liquid and air, various nanoparticle concentrations and liquid inlet temperatures were studied to have a better picture of its cooling efficiency on the radiator. 2. Materials and methods 2.1. Preparation of TiO2 nanofluid Nanofluid sample preparation was carried out in a two-step process of disseminating the primarily arranged nanoparticles in
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
3
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
Fig. 1. Nanoparticles Size distribution.
distilled water by means of ultrasonication. Particles were first reduced in size and then selected for a uniform diameter by Spex-8000 ball milling (Spex Industries, Inc., Edison, NJ), giving a normal distribution centered at an average of 44 nm and a range from 30 to 60 nm (Fig. 1). Particles’ surface morphology and microstructures were studied with scanning electron microscope (SEM) and transmission electron microscope (TEM) as shown in Figs. 2 and 3, respectively. Many previous studies have shown that increasing the nanofluid’s particle ratio leads to an increase in their precipitation. Even though we used different particle ratios in this study, the optimal one is 2% at which precipitation stays at a minimal level. Nanoparticles were suspended in deionized water which has basic properties and the mixture was further improved by addition of Triton X-100 (molecular formula: C14H22O(C2H4O)n) to final concentrations of 0.1% 0.2% and 0.3%, respectively, in order to enhance the solubility of TiO2. Triton X-100 has surfactant properties and it has been widely used in dyes and detergents for
Fig. 3. TEM of the TiO2 nanoparticle.
decreasing surface tension and contact angles, leading to an increase in the wetting ability of the material. As a result, TiO2 particulates can be suspended for longer time periods in fluids by using ball milling to provide high energy, addition of surfactant and ultrasonic bath. In order to find the optimal Triton X-100 amount, the nanofluid’s stability, foaming and aggregation were measured for different concentrations of the constituents. A concentration of 0.5% Triton X-100 was chosen for this study. Table 1 shows the characteristics of TiO2.
Table 1 Characteristics of TiO2 nanoparticles.
Fig. 2. SEM morphology of TiO2.
Parameter
Value
Purity Color Diameter SSA Shape Bulk density
99% White 44/nm 10–45/m2 g Spherical 0.460/g cm3
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
4
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
TiO2 nanoparticles dispersion in deionized water was carried out by continuous pulsing through an ultrasonic processor (Bandelin Sonorex Super RK514H) at an optimum duration. Throughout the preparation process of nanofluid, the container was constantly cooled to avoid evaporation of surface active agent. 2.2. Stability of nanofluid In order to prevent nanofluid sedimentation during the experiments, a number of steps were taken: First, TiO2 particle size was decreased to nanoscale by using high energy impacted ball milling (Spex-8000) followed by addition of Triton X-100. In addition, the nano-TiO2 obtained from the above procedures was dissolved in water by using ultrasonication. Given the huge density differences between metallic oxide nanoparticles and deionized water, two methods have been proposed to prevent sedimentation and uniformly distribute nanoparticles in nanofluids; the first one involves changing nanofluids pH and the other using surfactants [18]. Our nanofluid was prepared by using 0.1 to 0.5% surfactant, the last one giving a minimal agglomeration. In addition, particle structure is an important determinant of nanofluid stability. Active surface reagents have many characteristics such as structure, presence of many types of metal oxides for improving thermal conductivity as well as flocculation when they undergo ultrasonication, all of them making TiO2 more effective as compared to other metal oxides [19]. One of the most important features of TiO2 is high water adsorption ability making a gelly surface which increases the lubrication value. Our nanofluid maintained its stability throughout the experimental procedure in all temperatures tried (Fig. 4). The same was the case for TiO2-water nanofluid suspension which was stable and had no distillation problems throughout the whole procedure. The three fundamental thermo-physical
properties TiO2-water nanofluid were measured as shown in Table 2. 2.3. Thermophysical properties of the nanofluid The thermophysical properties of any nanofluid depend on a number of factors such as particle size, shape, whether it is metallic or non-metallic (oxide), chemistry of the solution, especially pH, and solution age. For instance, the thermal conductivity of spherical shaped nanoparticles is lower as compared to cylindrical ones, while smaller size particles have better thermal conductivity when compared to those of greater size. Additionally, metallic nanoparticles have better thermal conductivity than non-metallic ones [20]. Table 2 shows the thermo-physical properties of TiO2 and pure water at temperatures range between 20 and 80 °C. The following equations were used to show the regularity regarding viscosity, specific heat, thermal conductivity and density [21]. Nanofluid density is calculated as follows:
qnf ¼ uqp þ ð1 uÞqw
ð1Þ
2.3.1. Viscosity calculation and measurement Nanofluid viscosity is also determined by a number of factors such as the volume fraction of nanoparticles, their size and shape, base fluid, thickness of the nanolayer, dispersion technique, temperature and pH value, and nanoparticles’ Brownian motions [22–27]. Fluid viscosity is generally measured by instruments such as viscometer or rheometer, and the compiled data are compared to known correlations. The first model to measure viscosity was developed by Einstein in 1902 (Eq. (2). Particle’s spherical shape and less volume fraction are the limiting factors of this equation [28].
lnf ¼ ð1 þ 2:5uÞlw
ð2Þ
Fig. 4. TiO2-water nanofluid.
Table 2 The properties of pure water and TiO2. Working fluid
TiO2 Pure water TiO2-water u = 1% TiO2-water u = 2% TiO2-water u = 3%
Density kg/m3
4260 987.8 1044 1065 1093
Viscosity mPas 20 °C
40 °C
60 °C
80 °C
– 0.97 1.01 1.02 1.04
– 0.74 0.82 0.84 0.87
– 0.58 0.65 0.68 0.71
– 0.47 0.53 0.56 0.61
Specific heat J/kgK
Thermal conductivity W/mK
6890 4181.2 4523 4401 4366
11.7 0.645 0.728 0.737 0.751
[21]
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
5
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
A more effective formula was later derived by Brinkman called the Brickman Model [29].
lnf ¼
lbf ð1 uÞ2:5
ð3Þ
Another model considered to be more suitable for nanoparticles with volume fraction greater than 2% was derived by Nelson in 1970 and shown in Eq. (4) [30].
"
lnf ¼ ð1 þ 1:5uÞ
up eð1um Þ
#
lbf
lnf ¼ 6 4
1 34:87
6M df ¼ 0:1 Npqbf
dp df
u1:03
7 5lbf
ð5Þ
!1=3 ð6Þ
where qbf denotes the mass density of base fluid at 20 °C. In this study, nanofluid viscosity was measured by using a Brookfield Viscometer (DV-2 + Pro Programmable Viscometer) and in order to reduce uncertainty, the measured values were compared with the data in ASHARE Handbook [32]. 2.3.2. Specific heat capacity of nanofluid Specific heat is defined as the amount of heat per unit mass of a material to raise the temperature by one degree centigrade. It is one of the fundamental properties influencing the rate of heat transfer in nanofluids. Studies have shown it to vary with particle size and since smaller particles have larger specific surface areas, reducing particles size increases the effect of the surface energy on effective specific heat capacity [33,34]. In order to determine the specific heat capacity of TiO2 nanofluid, Eq. (7) was used:
Cpnf ¼
Height
Width
400 mm
200 mm
16 mm
Maxwell model knf ¼
kp þ 2kbf þ uðkp kbf Þ kbf kp þ 2kbf uðkp kbf Þ
ð8Þ
Hamilton Crosser model k nf
3
1 0:3
Length
ð4Þ
where up and um stand respectively for volume concentration and maximum volume fraction. Researchers have recently modified these models by introducing more parameters in order to increase their accuracy. One such model is the Corcione Model which has a number of advantages such as giving results with 1.84% of standard deviation as well as following boundaries of nanoparticles with diameters between 20 and 200 nm and volume fraction of 0.0001–0.071 [31].
2
Table 3 The dimensions of the selected car radiator.
uqp Cpp;n þ ð1 uÞqw Cpbf qnf
ð7Þ
2.3.3. Thermal conductivity Thermal conductivity is the ability of a material to conduct heat and it depends of many factors such as the thermal conductivities of base fluid and nanoparticles, surface area, nanoparticle shape, temperature and volume fraction. A number of theoretical and empirical models have been derived to predict the thermal conductivity of nanofluids [35–37], with Eqs. (8)–(10) representing the ones used in the current study to compare with the experimental results obtained by measuring it by KD2 Pro thermal property analyzer (Decagon, USA). This device consists of a sensor for measuring liquids thermal conductivity by using a transient line heat source and a hand-held controller. To carry out the measurements, nanofluid sample was immersed for 10 min in water bath at the desired temperature until it reached equilibrium with the medium. Four readings were taken with 15 min intervals between each at a temperature range of 20–80 °C. The thermo-physical properties of pure water and TiO2 are illustrated in Table 3.
¼
kp þ ðn 1Þkbf uðn 1Þðkbf kp Þ kp þ ðn 1Þkbf þ uðn 1Þðkbf kp Þ
Yuand Choi model knf ¼
kpe þ 2kb þ 2ðkpe kb Þð1 þ bÞ3 u kpe þ 2kb 2ðkpe kb Þð1 þ bÞ3 u
ð9Þ
kb ð10Þ
Table 3 shows an average specific heat of 0.09 J/kgK and an increase in specific heat capacity for TiO2-water nanofluid as compared to pure water. Similarly, it also shows that viscosity and density of TiO2-water nanofluid are higher than pure water. Given the fact that viscosity increases with temperature, the viscosity of TiO2-water nanofluid is slightly higher than pure water at all temperatures. This can be attributed to the metal particles in nanofluid which increase the density of TiO2-water mixture. According to previous studies [19,38], as the density of nanofluid increases, there is a tendency for it to flocculate. This reduces the variety of homogeneous solutions because the stability of low-density nanofluid is relatively better than the nanofluid with a higher density. 3. Experimental setup The vehicle engine system (Model FIAT DOBLO 1300 cc. MJTD) used in this study includes flow lines, a centrifugal pump, a flow meter, anemometer, tank, thermocouples, a forced draft fan and a cross flow heat exchanger, also known as automobile radiator (Fig. 5). The dimensions of the selected car radiator are shown in Table 3 and those of the car radiator tubes in Table 4. Fig. 6 shows a schematic representation and dimensions of the radiator flat tube (Table 5). Four Pico-thermocouple (display: TC-08) thermometers were used to measure the coolant temperature. In addition, a Testo-thermometer (display: 435) was connected to measure air’s input and output temperatures of back and front surfaces of the radiator. In order to avoid any potential problems during experimentation, the setup was tested first with pure water (Fig. 7). This was done to assure the stability of the experimental setup and validity of test results. The procedure was as follows: as the nanofluid goes through the pump, it is encountered by high pressures and shear; in this way grouping is expelled [38]. Furthermore, high flow rate in the radiator tubes and associated channels enhances the adjustment of the nanofluid [19]. After conducting the experiment with pure water, the test system was discharged completely and recharged to follow the same procedure for TiO2-water nanofluid. The nanofluid was used in three different concentrations: 0.1%, 0.2% and 0.3%, and was pumped through the radiator at different flow rates of 0.097 m3/h and 0.68 m3/h as working fluid. These experiments, as in pure water case, were repeated and the data were recorded.
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
6
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
Temperature Indicator
Radiator
T wall
Nanofluid Inlet Flow meter
T in Fan
200 mm
Anemometer Nanofluid Outlet
T out 400 mm
Pump
Nanofluid Tank
Engine
Power supply
Fig. 5. Schematic representation of experimental setup.
Table 4 The dimensions of the car radiator tubes. Inward measurement
Material
Number of tube
Spacing
Dh
18 19.6 295(mm)
Aluminum
33 mm
8.06
3.35 mm
Dh is the hydraulic diameter of the tube.
Fig. 6. Schematic and dimensions of the radiator flat tube.
Table 5 Technical properties, precisions and total uncertainty analysis of the equipment.
4. Theoretical analysis
Measuring device
Measuring range
Precision
Total Uncertainty
4.1. Calculation of heat transfer coefficient
Flow meter Thermometer Thermocouple Anemometer (air velocity)
2–20 m3/h 0–120 °C 0–1200 °C 0–20 m/s
±2.5% ±0.1 °C ±0.1 °C ±0.01 m/s
±0.0003125% ±0.075 °C ±0.15% ±0.012%
In order to evaluate heat transfer coefficients in the radiator, the following equations for the coolant and air were used [39].
Q ¼ hADT ¼ hAðTb Tw Þ
ð11Þ
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
7
Engine Flow meter
Radiator
Fig. 7. Photograph of the real test set up.
_ p ðTin Tout Þ Q ¼ mC
ð12Þ
where, Q is the heat transfer rate [W]; Cp is the specific heat capac_ is the mass flow rate of working fluid ity of working fluid [J/kgK]; m [kg/s]; Tin, Tout stand for inlet and outlet temperatures of coolant fluid [°C], respectively. Tb is the bulk temperature which was assumed to be the average value of inlet and outlet temperatures of the fluid moving through radiator. Tw is the tube wall temperature which is the average value of two surface thermocouples.
hexp ¼
Q AðTb Tw Þ
ð13Þ
The precision of experimental setup is crucial for any study, but of the same importance is the gathering of accurate data with the proper measuring devices. A very powerful tool in designing experiments are also uncertainty analysis since they are used to measure experimental errors which may be detrimental to data accuracy. No matter the accuracy of measuring devices, uncertainty analysis is always used to determine errors emerging from environment, test conditions, measuring devices or experimenter. In order to calculate the total uncertainty for these experiments, Eq. (19) [42,43] was used as follows:
ð14Þ
G ¼ Gðx1 ; x2 ; x3 ; . . .Þ ) W s " 2 2 2 #1=2 @G @G @G ¼ w1 þ w2 þ þ wn @x1 @x2 @xn
f
where, hexp is the heat transfer coefficient [W=m2 K]. Nusselt number (Nu) is determined as:
Nu ¼
hDh K
where, Dh is the hydraulic diameter of the tube [mm]. Finally, Reynolds number (Re) is determined as:
Re ¼
q#Dh l
ð15Þ
where, # is Velocity at inlet radiator [m=s. 4.2. Relationships for Nusselt number determination for single phase fluids Correlations for the laminar flow through pipes [40] and for the flow in the compact heat exchanger at 550 Re 1850 range were determined by wquations 16 and 17 respectively [41].
Nu ¼ 1:86
1=3 0:14 ReD Pr l ls L=Dh
P1=3 Nu ¼ 0:951 Re0:173 D r
ð16Þ ð17Þ
where ReD represents tube-side Reynolds number which is based on tube hydraulic diameter whereas Pr is Prandtl number. Although, we used a high Reynolds number as an input parameter, experimental results were compared by using the equations for friction (Eq. (18)).
f ¼
64 Re
4.3. Uncertainty analysis
ð18Þ
ð19Þ
To calculate total uncertainty, S is the necessary quantity to be determined with n independent variables affecting the quantity G as x1, x2, x3, . . .xn. The error rate for each of those independent variables as well as the total uncertainty analysis are stated as W1, W2,. . ... . ..Wn and Ws respectively. The technical qualifications, total uncertainty and precisions analysis of measuring equipment are shown in Table 4. 5. Results and discussion In Fig. 1, the distribution graph of particle size in the nanofluid according to intensity obtained by zeta-seizer on different days is shown. Figs. 2 and 3 show TEM and SEM images respectively. The distribution peak is at an almost identical horizontal position but the intensity increases vertically showing an increase in the population of aggregates. It can therefore be concluded the size of particles in TiO2-water nanofluid ranged from 30 to 60 nm with an average size of 44 nm. 5.1. Viscosity Fig. 8 shows viscosity for different volume concentrations of TiO2 (0.1, 0.2, and 0.3%) at different temperatures in order to analyze the effect of temperature on nanofluid viscosity. It can be clearly seen that increasing the inlet temperature of the nanofluid decreases its viscosity. Therefore, we can conclude that there exists
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
8
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
Viscosity (m.Pa.s)
1.1 1.0
0.1% TiO 2 0.2% TiO 2
0.9
0.3% TiO 2 Pure water
0.8 0.7 0.6 0.5 0.4 20 °C
40 °C
60 °C
80 °C
Temperature °C Fig. 8. Viscosity of TiO2-water nanofluid at different temperatures.
0.755 Experimental Setup Yu and Choi Maxwell
Thermal conductivity W/m.K
0.750
0.745
0.740
0.735
0.730
0.725
0.720 0.10
0.15
0.20
0.25
0.30
0.35
Volume concentration % Fig. 9. Thermal conductivity of TiO2 nanofluid at different volume fraction.
a direct relationship between temperature and viscosity for all experiments under all conditions as compared to the base fluid. 5.2. Thermal conductivity The experimental values of nanofluid’s thermal conductivity are in good agreement with those present in literature. It can be clearly seen from Fig. 9 that thermal conductivity increases in a nearly linear fashion with every incremental increase of volume fraction. The same figure also shows a relation of thermal conductivity to volume concentration, again in good agreement with published data [15,44,45]. Experimental values of thermal conductivity of TiO2-water nanofluids show high deviation when compared to those estimated from Maxwell Model, but they are in good agreement with estimations from Choi Model. When results of TiO2 and A12O3 [46] systems are compared by taking the base fluid as reference, the former shows significantly
higher thermal conductivity as compared to the later despite its larger particle size (mean size of 44 nm and 13 nm, respectively). These results indicate that particle’s thermal conductivity has more influence than particle size. According to a study conducted by Eastman et al. [47], metallic nanoparticle-based nanofluids show a large increase in thermal conductivity as compared to the oxide particle-based or base fluid counterparts [47]. Another study showed that nanofluids thermal conductivity was not affected by the suspended state of nanoparticles [48]. 5.3. Heat transfer coefficient In Fig. 10, nanofluid’s overall heat transfer as a function of Reynolds number at constant flow rate for different nanoparticle concentration is shown. It can be clearly seen from the figure that overall heat transfer coefficient increases with increasing Reynolds number as compared to the base fluid. The experimentally
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
9
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
Average heat transfer coefficient
2200 2000
Pure water 0.1% TiO2-water
1800
0.2% TiO2-water 0.3% TiO2-water
1600 1400 1200 1000 800 600 400 200 200
400
600
800
1000
1200
1400
1600
1800
1400
1600
Reynolds numbers Fig. 10. Average heat transfer coefficient as a function of Reynolds numbers.
3500 Base fluid 0.1vol.% 0.25vol.% 0.5vol.%
Average heat transfer coefficient
3000
2500
2000
1500
1000
500
0 0
200
400
600
800
1000
1200
Reynolds numbers Fig. 11. The experimental data of MWCNT nanofluid by [49].
obtained overall heat transfer value is 2050 W/m2K for 0.3% TiO2water. These results are in good agreement with predicted values but slightly lower when compared to vehicle radiator in which a multi-walled carbon nanotube (MWCNT) based on water/ethylene glycol is used with nanoparticle volume concentration of 0.5%, and heat transfer coefficient increase from 986.8 W/m2K to 2951 W/ m2K, for Reynolds number from 430 to 1400 (Fig. 11) [49].
nanofluids in an automobile radiator was experimentally measured as a function of concentration and temperature. It was found that the presence of TiO2 nanoparticle can significantly enhance radiator’s heat transfer rate in a manner dependent on nanoparticle quantity added to the base fluid. Heat transfer coefficient significantly improves for 0.2% nanoparticle concentration as compared to pure water. This is due to the fact that TiO2’s greater thermal conductivity, aspect ratio, lower specific gravity, thermal resistance and larger specific area as compared to pure water.
6. Conclusion Acknowledgements In the current study, usage of TiO2-water nanofluid’s as a cooler in car engine radiator was studied. Based on the experimental results, TiO2-water nanofluid offers a better overall performance than base fluid. The overall heat transfer coefficient of TiO2
The authors would like to acknowledge the funding from Libyan Government and the Faculty of Technology in Karabuk University, and especially adviser Professor Mehmet Ozkaymak.
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008
10
S.A. Ahmed et al. / Engineering Science and Technology, an International Journal xxx (2018) xxx–xxx
References [1] S.U. Choi, J.A. Eastman, Enhancing Thermal Conductivity of Fluids with Nanoparticles, Argonne National Lab, IL (United States), 1995. [2] M. Leena, S. Srinivasan, Synthesis and ultrasonic investigations of titanium oxide nanofluids, J. Mol. Liq. 206 (2015) 103–109. [3] L. Yang, Y. Hu, Toward TiO2 nanofluids—part 1: preparation and properties, Nanoscale Res. Lett. 12 (1) (2017) 417. [4] L. Yang, Y. Hu, Toward TiO2 nanofluids—part 2: applications and challenges, Nanoscale Res. Lett. 12 (1) (2017) 446. [5] H.A. Mintsa et al., New temperature dependent thermal conductivity data for water-based nanofluids, Int. J. Therm. Sci. 48 (2) (2009) 363–371. [6] L. Yang et al., Dynamic characteristics of an environment-friendly refrigerant: ammonia-water based TiO2 nanofluids, Int. J. Refrig. 82 (2017) 366–380. [7] Y. Xuan, Q. Li, Heat transfer enhancement of nanofluids, Int. J. Heat Fluid Flow 21 (1) (2000) 58–64. [8] L.S. Sundar et al., Experimental thermal conductivity of ethylene glycol and water mixture based low volume concentration of Al2O3 and CuO nanofluids, Int. Commun. Heat Mass Transfer 41 (2013) 41–46. [9] M.H. Hamzah et al., Factors affecting the performance of hybrid nanofluids: a comprehensive review, Int. J. Heat Mass Transfer 115 (2017) 630–646. [10] G. Colangelo et al., Cooling of electronic devices: nanofluids contribution, Appl. Therm. Eng. 127 (2017) 421–435. [11] M. Milanese et al., An investigation of layering phenomenon at the liquid–solid interface in Cu and CuO based nanofluids, Int. J. Heat Mass Transfer 103 (2016) 564–571. [12] G. Colangelo, M. Milanese, A. De Risi, Numerical simulation of thermal efficiency of an innovative Al2O3 nanofluid solar thermal collector, Therm. Sci. 21 (6B) (2017) 2769–2779. [13] O.A. Alawi et al., Thermal conductivity and viscosity models of metallic oxides nanofluids, Int. J. Heat Mass Transfer 116 (2018) 1314–1325. [14] G. Colangelo et al., Thermal conductivity, viscosity and stability of Al2O3diathermic oil nanofluids for solar energy systems, Energy 95 (2016) 124–136. [15] B. Gu et al., Thermal conductivity of nanofluids containing high aspect ratio fillers, Int. J. Heat Mass Transfer 64 (2013) 108–114. [16] L. Yang et al., Recent developments on viscosity and thermal conductivity of nanofluids, Powder Technol. 317 (2017) 348–369. [17] N.A.C. Sidik, M.N.A.W.M. Yazid, R. Mamat, Recent advancement of nanofluids in engine cooling system, Renewable Sustainable Energy Rev. 75 (2017) 137– 144. [18] A. Sözen et al., Utilization of fly ash nanofluids in two-phase closed thermosyphon for enhancing heat transfer, Exp. Heat Transfer 29 (3) (2016) 337–354. [19] A.A. Minea, Advances in New Heat Transfer Fluids: From Numerical to Experimental Techniques, CRC Press, 2017. [20] W. Duangthongsuk, S. Wongwises, Measurement of temperature-dependent thermal conductivity and viscosity of TiO2-water nanofluids, Exp. Therm Fluid Sci. 33 (4) (2009) 706–714. [21] S. Devireddy, C.S.R. Mekala, V.R. Veeredhi, Improving the cooling performance of automobile radiator with ethylene glycol water based TiO2 nanofluids, Int. Commun. Heat Mass Transfer 78 (2016) 121–126. [22] H. Masuda, A. Ebata, K. Teramae, Alteration of thermal conductivity and viscosity of liquid by dispersing ultra-fine particles. Dispersion of Al2O3, SiO2 and TiO2 ultra-fine particles, 1993. [23] A. Turgut et al., Thermal conductivity and viscosity measurements of waterbased TiO2 nanofluids, Int. J. Thermophys. 30 (4) (2009) 1213–1226. [24] M. Bahiraei et al., Using neural network for determination of viscosity in water-TiO2 nanofluid, Adv. Mech. Eng. 4 (2012) 742680. [25] X. Fan et al., Potential of ‘nanofluids’ to further intensify microreactors, Green Chem. 10 (6) (2008) 670–677.
[26] A. Ghadimi, I.H. Metselaar, The influence of surfactant and ultrasonic processing on improvement of stability, thermal conductivity and viscosity of titania nanofluid, Exp. Therm. Fluid Sci. 51 (2013) 1–9. [27] T. Yiamsawas et al., Measurement and correlation of the viscosity of waterbased Al2O3 and TiO2 nanofluids in high temperatures and comparisons with literature reports, J. Dispersion Sci. Technol. 34 (12) (2013) 1697–1703. [28] A. Einstein, Eine neue Bestimmung der Moleküldimensionen, Annalen der Physik 324 (2) (1906) 289–306. [29] H. Brinkman, The viscosity of concentrated suspensions and solutions, J. Chem. Phys. 20 (4) (1952). 571-571. [30] L.E. Nielsen, Generalized equation for the elastic moduli of composite materials, J. Appl. Phys. 41 (11) (1970) 4626–4627. [31] M. Corcione, Empirical correlating equations for predicting the effective thermal conductivity and dynamic viscosity of nanofluids, Energy Convers. Manage. 52 (1) (2011) 789–793. [32] A.F. Handbook, American Society of Heating, Refrigerating and AirConditioning Engineers, Inc., Atlanta, GA, USA, 2009. [33] X.-Q. Wang, A.S. Mujumdar, Heat transfer characteristics of nanofluids: a review, Int. J. Therm. Sci. 46 (1) (2007) 1–19. [34] S. Eiamsa-Ard, K. Kiatkittipong, W. Jedsadaratanachai, Heat transfer enhancement of TiO2/water nanofluid in a heat exchanger tube equipped with overlapped dual twisted-tapes, Eng. Sci. Technol. Int. J. 18 (3) (2015) 336–350. [35] J.C. Maxwell, A Treatise on Electricity and Magnetism, Clarendon Press, Oxford, 1873. [36] R.L. Hamilton, O. Crosser, Thermal conductivity of heterogeneous twocomponent systems, Ind. Eng. Chem. Fundam. 1 (3) (1962) 187–191. [37] W. Yu, S. Choi, The role of interfacial layers in the enhanced thermal conductivity of nanofluids: a renovated Maxwell model, J. Nanopart. Res. 5 (1–2) (2003) 167–171. [38] M. Nasiri, S.G. Etemad, R. Bagheri, Experimental heat transfer of nanofluid through an annular duct, Int. Commun. Heat Mass Transfer 38 (7) (2011) 958–963. [39] A.M. Hussein et al., Experimental measurement of nanofluids thermal properties, Int. J. Automot. Mech. Eng. 7 (2013) 850. [40] E.N. Sieder, G.E. Tate, Heat transfer and pressure drop of liquids in tubes, Ind. Eng. Chem. 28 (12) (1936) 1429–1435. [41] M. Dehghandokht et al., Flow and heat transfer characteristics of water and ethylene glycol–water in a multi-port serpentine meso-channel heat exchanger, Int. J. Therm. Sci. 50 (8) (2011) 1615–1627. [42] J.P. Holman, W.J. Gajda, in: Experimental Methods for Engineers, 8 ed., McGraw-Hill, New York, 2012, p. 8. [43] M. Aktasß et al., Performance analysis and modeling of a closed-loop heat pump dryer for bay leaves using artificial neural network, Appl. Therm. Eng. 87 (2015) 714–723. [44] K. Abdul Hamid et al., Thermal conductivity enhancement of TiO2 nanofluid in water and ethylene glycol (EG) mixture, Indian J. Pure Appl. Phys. (IJPAP) 54 (10) (2016) 651–655. [45] M. Arulprakasajothi et al., Heat transfer study of water-based nanofluids containing titanium oxide nanoparticles, Mater. Today: Proc. 2 (4–5) (2015) 3648–3655. [46] N. Usri et al., Thermal conductivity enhancement of Al2O3 nanofluid in ethylene glycol and water mixture, Energy Proc. 79 (2015) 397–402. [47] J.A. Eastman et al., Anomalously increased effective thermal conductivities of ethylene glycol-based nanofluids containing copper nanoparticles, Appl. Phys. Lett. 78 (6) (2001) 718–720. [48] D.-H. Yoo, K. Hong, H.-S. Yang, Study of thermal conductivity of nanofluids for the application of heat transfer fluids, Thermochim. Acta 455 (1–2) (2007) 66–69. [49] B. M’hamed et al., Experimental study on thermal performance of MWCNT nanocoolant in Perodua Kelisa 1000cc radiator system, Int. Commun. Heat Mass Transfer 76 (2016) 156–161.
Please cite this article in press as: S.A. Ahmed et al., Improving car radiator performance by using TiO2-water nanofluid, Eng. Sci. Tech., Int. J. (2018), https:// doi.org/10.1016/j.jestch.2018.07.008