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Journal of Nanomaterials
Volume 2016 (2016), Article ID 6717624, 22 pages
http://dx.doi.org/10.1155/2016/6717624
Review Article

Critical Review on Nanofluids: Preparation, Characterization, and Applications

1College of Science and Engineering, Hamad Bin Khalifa University (HBKU), Qatar Foundation, P.O. Box 5825, Doha, Qatar
2Qatar Environment and Energy Research Institute (QEERI), Hamad Bin Khalifa University (HBKU), Qatar Foundation, P.O. Box 5825, Doha, Qatar

Received 19 May 2016; Accepted 7 August 2016

Academic Editor: Bo Tan

Copyright © 2016 Mohamoud Jama et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Heat transfer fluids are a crucial parameter that affects the size and costs of heat exchangers. However, the available coolants like water and oils have low thermal conductivities, which put many limitations to the development of heat transfer to achieve high performance cooling. The need for development of new classes of fluids which enhance the heat transfer capabilities attracted the attention of many researchers. In the last few decades, modern nanotechnology developed nanoparticles, which have unique thermal and electrical properties that could help improve heat transfer using nanofluids. A “nanofluid” is a fluid with suspended fine nanoparticles which increases the heat transfer properties compared with the original fluid. Nanofluids are considered a new generation of heat transfer fluids and are considered two-phase fluids of liquid solid mixtures. The efficiency of the fluid could be improved by enhancing its thermal properties, especially the thermal conductivity, and it is expected that the nanofluids will have a greater thermal conductivity than the base fluids. This paper reviews the preparation of metallic and nonmetallic nanofluids along with the stability of the produced nanofluids. Physical and thermal properties as well as a range of applications are also discussed in detail.

1. Introduction

Heat transfer is vital area of research and study in thermal engineering. Selection of an appropriate heat transfer fluid for heat dissipation is crucial consideration in designing heat exchangers. Heat transfer fluid (HTF) is one of the critical parameters as it affects the size and cost of heat exchanger systems. Conventional HTFs like water and oils have limited heat transfer potentialities. There is urgency to develop new group of HTFs so as to reduce cost and meet the burgeoning demand of industry and commerce. Fortunately, the advances in nanotechnology have made it possible to achieve higher efficiency and cost saving in heat transfer processes. Nanoparticles are considered to be new generation materials having potential applications in the heat transfer area.

Any host liquid, either organic or inorganic, which contains nanoparticles in a suspended state, is known as nanofluid. Nanofluids are two-phase fluids of solid-liquid mixtures and are considered to be new-generation HTFs. Recently, in near past, nanofluids have developed as promising thermal fluids for heat transfer applications. Also, the thermal conductivity of nanofluids is expected to be greater than that of the base liquids [1].

When two-phase suspensions of microparticles were tested, it was reported that they produce sedimentation and obstructions to smooth fluid flow because of channel clogging and also erosion of tube materials was noticed. However, nanofluids offer many merits over single-phase pure fluids and suspensions with microparticles. The issues of particle sedimentation, clogging of microchannel passages, and erosion of tube material are mitigated largely with nanofluids. Besides, nanofluids form stable suspensions with uniform dispersion of nanoparticles in the host fluid.

Thermophysical properties of traditional heat transfer fluids such as oils, glycols, and water are well established and are available in literature and handbooks. However, similar properties of two-phase nanofluids have not been explored extensively yet. An accurate and precise measurement of properties is essential for determination of heat transfer coefficients of nanofluids. The aptness of a particular nanofluid in a heat transfer application is then analyzed on the basis of its heat transfer performance and requirement of application. Nanofluids are considered as novel alternative, new-generation liquids, for heat energy transport and can be employed as HTFs in heat exchangers, thereby replacing pure traditional fluids. The applications of nanofluids for heat transfer include radiators in automobiles, components in chemical engineering and process industries, solar water heaters, refrigeration units, and the cooling of electronics devices. The main objective of obtaining heat transfer enhancement using nanofluids is to accommodate high heat fluxes and, hence, to reduce the cost and size of heat exchangers which, in turn, results in the conservation of energy and material.

Over the last several years, substantial research has been carried out for development of heat transfer enhancement methods. Generally, many additives have been used to ameliorate the heat transfer features of base fluids. Therefore, nanofluids may be perfectly suited in actual applications as their use may have little increases in pressure drop and may positively change the heat transfer characteristics and transport properties of the fluid. Due to the fine nature of these nanoparticles, nanofluids act as a single-phase fluid instead of dual-phase mixture.

2. Preparation of Nanofluids

Preparation of nanofluids is the first key step to synthesize fluids with improved thermal conductivity. These nanofluids are obtained by suspending nanoparticles in the range of 1–100 nm in conventional regular fluids in suitable volume fractions. Theoretically, when solid particles with high thermal conductivity are added to fluids, the overall thermal conductivity is improved due to the change in flow, heat, transport, and heat transfer features of the liquid [1]. Some of the vital requirements that nanofluid must fulfill are adequate durability, even and stable suspension of particles, no chemical change of particles or fluid, and negligible agglomeration of particles. Several types of particles have been reported in literature to prepare nanofluids, which include () nonmetallic particles (SiO2 [2], SiC [84], TiO2 [68], Al2O3 [85], ZnO [28], CuO [86], Fe3O4 [14], and AlN [45]), () metallic particles (Cu [87], Ag [88], and Au [88]), and () different particle shapes such as carbon nanotubes [89], nanodroplets [90], nanofibers [67], and nanorods [91]. The base fluids commonly used are water, oil, acetone, decene, ethylene glycol, and mineral oil. Two methods have been employed in producing nanofluids which can be classified as single-step and two-step methods [1].

The single-step method involves the preparation of nanoparticles and dispersion of them in the host or base fluid simultaneously. The nanoparticles can be directly prepared via physical vapor deposition technique or liquid chemical method. Therefore, the process of drying, storage, dispersion, and transportation is avoided, so that agglomeration is minimized and, hence, nanoparticle dispersion in the host fluid is improved [15]. The main demerit of this process is that the residue of reactants is left behind in the nanofluid due to incomplete reaction or stabilization which diminishes the purity of the nanofluid [92]. Another shortage in this process is that only low vapor pressure fluids can be used, which limits the application of the method.

In the two-step method, which is the most widely used method for preparing nanofluids, the nanoparticles, nanotubes, nanofibers, or nanorods are first produced by chemical vapor deposition, inert gas condensation, or any other technique as a dry powder. The second step involves dispersing this nanopowder into the base fluid with the help of intensive magnetic force agitation, ultrasonic agitation, high shear mixing, homogenizing, and ball milling. The two-step method is more economical than the one-step method to produce nanofluids commercially. The main disadvantage of this method is that, due to the high surface area and surface attractively, the nanoparticles tend to agglomerate. The agglomeration of nanoparticles in the fluid results in decreasing the thermal conductivity and increasing the settlement and clogging of microchannels. Therefore, surfactants are widely used to stabilize nanoparticles in the fluids. Nevertheless, this method is suitable for wide range of particles such as oxide particles and carbon nanotubes and it is attractive to industry because it is simple for nanofluid preparation [93].

2.1. Stability of Nanofluids

Agglomeration of nanoparticles has severe ramifications ranging from clogging of microchannels to reduction in thermal conductivity of nanofluids. Sundry of methods have been developed to assess the stability of nanofluids and the simplest of all is sedimentation method. The nanofluids are said to be stable when their concentration remains constant. Physical inspection by naked eyes is also usually considered one of the methods for observing stability of nanofluids. Below, some methods are described for analyzing stability of nanofluids.

2.1.1. Zeta Potential Analysis

The electric potential difference between the dispersion medium and the stationary layer of fluid is termed as zeta potential. This potential is crucial for depicting the stability of colloidal suspensions. The higher zeta potential is, the more stable colloidal suspension will be and vice versa.

2.1.2. Spectral Absorbency Analysis

Spectral absorbency analysis (SAA) is another efficient way in addition to zeta potential analysis in order to assess the steadiness of nanofluids. Generally, there exists a linear relationship between concentration of nanoparticles in fluid and the absorbency intensity. If nanomaterials, which are dispersed in base fluids, possess characteristic absorption bands in the wavelength range of 190–1100 nm, then stability of nanofluids can be evaluated by using UV-vis spectroscopy reliably.

2.2. The Ways to Enhance the Stability of Nanofluids
2.2.1. Surfactants Used in Nanofluids

Surfactants or dispersants are used for increasing the stability of the nanofluids. Normally, surfactants are required in order to stabilize the nanofluid suspensions produced from two-phase method. Surfactants stabilize nanofluids by reducing the surface tension of fluids and hence are essential for increasing the stability or preventing agglomeration of nanoparticles in base fluids. Two-phase method is normally used commercially, since it is an easy and economically viable method for nanofluid production at large scale. Surfactants are composed of hydrophobic tail portion (long-chain hydrocarbon) and a hydrophilic polar head group. Surfactants help in achieving higher wettability, that is, increased contact between two materials. Water-soluble surfactants are selected when base fluid is polar solvent; otherwise, oil-soluble solvents are chosen. On the other hand, there are several issues associated with surfactants such as the fact that dispersants may contaminate the heat transfer media by producing foams while heating. Further, addition of surfactants may lead to enlargement of nanoparticles, which in turn mitigates the effective thermal conductivity of the nanofluid. Hence, the system (surfactant addition to nanofluid) needs to be optimized.

2.2.2. Surface Modification Techniques: Surfactant-Free Method

The other method which is utilization of functionalized nanoparticles is a capable way to deal with accomplishing long haul strength of nanofluid. It characterizes the surfactant-free technique. Some researchers experimented on the combination of functionalized silica (SiO2) nanoparticles by joining silanes specifically to the surface of silica nanoparticles in unique nanoparticle solutions which resulted in peculiar qualities of nanofluids in which no deposition layer formation on warmed surface after a pool bubbling procedure was observed. Some other researchers introduced hydrophilic functional groups on the surface of the nanoparticles by mechanic-chemical reaction and thus produced nanofluids, which possess qualities such as no contamination, great smoothness, low viscosity, high thermal conductivity, and high stability. These nanofluids may find applications as coolants in advanced thermal systems.

2.2.3. Stability Mechanisms of Nanofluids

Particles while in dispersion medium may pile together and agglomerate giving inflated size of particles, which may find their fate by settling down in the solution due to gravity. Steadiness of nanofluids signifies that particles do not aggregate and settle down at a noteworthy rate. The rate of aggregation is defined by the recurrence of impacts and the likelihood of union during collision. Derjaguin and his research groups’ hypothesis proposes that the stability of a particle in solution is dictated by the resultant of van der Waals attractive and electrical double layer repulsive forces that exist amongst particles as they approach each other due to the Brownian motion they are undergoing. If the attraction force is higher than the repulsion force, then the particles will collide, and the suspension will not be stable, while if the other way around was the case, then the colloidal suspensions will stay stable. Table 1 summarizes the effects of different nanoparticles types, size of nanoparticles, loading of nanoparticles, synthesis process, and dispersion method on the stability of different types of nanofluids.

Table 1: Summary of the effects of different nanoparticles types, size of nanoparticles, loading of nanoparticles, synthesis process, and dispersion method on the stability of different types of nanofluids.

3. Characterization of Nanofluids

Over the past decade, researchers have tried to improve the heat transfer properties of the nanofluids by optimizing the physical and thermal properties of the nanofluid. Experimental studies involved a wide range of nanoparticles and some correlations were established. However, they have come up with diverse results, thus making those correlations inconsistent and sometimes contradictory. In this section, the physical and thermal properties of nanofluids and their varying effect on heat transfer behavior are studied through reviewing several researches in the literature [74, 91, 94106].

3.1. Physical Properties
3.1.1. Density

The density is a factor that affects the heat transfer properties. However, reports on the effect of density are found to be scarce. Since the nanoparticle’s density is higher than liquids’, it led to believing that an increase in the volume concentration of the nanoparticles would lead to increased density values of the nanofluid. Most researchers obtain the theoretical density values from the mixing equation introduced by Pak and Cho [74].where is the density, is the volume concentration, and “” and “” subscripts are the nanofluid and base fluid, respectively. Table 2 shows the experimental results reported by Saeedinia et al. [107], which seem to be in agreement with Pak and Cho’s correlation.

Table 2: Different volume concentration and the theoretical and experimental densities.

As it is evident from the table, the above equation holds for various weight fractions with negligible differences. However, it should be noted that the difference slightly increases for 2% weight fraction, which means it could further increase at higher concentrations. Some investigations report on the effect of volume concentration and temperature on the density in water based Al2O3 nanoparticles and came up with a model that is a function of both [108].

where represents the effective density of the nanofluid, is the volume concentration, and is the temperature. The correlation shows that the density of the nanofluid is linear with volume concentration and inversely linear with increasing temperature.

Nanoparticle Concentration Effect on Density. It has been reported that increasing the volume concentration of metal oxides such as Al2O3, Sb2O5, SnO2, and ZnO with both ethylene glycol and water as base fluids leads to the increase of their densities in all of the mentioned nanofluids [109]. Furthermore, after investigating propanol based Al2O3 nanofluids, it has been proven that a linear relationship existed between the density and the volume fraction [110]. This effect is also valid for water based carbon nanotubes nanofluids, where results showed that, with 0.02 and 0.04 weight percentage of carbon nanotubes loading, the density increased by 0.01% to 0.39% [111].

Temperature Effect on Density. Contrary to the volume concentration, temperature has a reverse effect on density. It has been reported that the density of Al2O3 nanofluid increases with the increase of volume concentration of nanoparticle but decreases with increasing the temperature [112, 113]. This is also consistent with (2).

3.1.2. Viscosity

Researchers have found viscosity to be a key parameter in determining the convective heat transfer coefficient. However, this property is troublesome due to lack of understanding of viscosity mechanisms and lack of a general mathematical model that predicts the behavior of viscosity in nanofluids.

Several efforts were made to come up with a model that predicts the viscosity in nanofluids. The first model is Einstein’s model [71] of effective viscosity for suspended rigid spherical solids in liquids as a function of volume. The model was developed in 1906 and it was derived from linear hydrodynamic equations. Still, Einstein’s model could only predict the viscosity behavior for spherical rigid particles and for a low particle concentration of 1.0 volume percentage.

Numerous modifications of Einstein’s model were made to further enhance the viscosity correlations. Brinkman [72] developed a model based on Einstein’s equation to include higher particle concentrations, while Batchelor [73] added Brownian motion to his model. Nevertheless, experiments have shown discrepant results from the mentioned models. Researches on alumina and titania nanofluids showed higher levels of viscosity when compared with Einstein-Batchelor correlations [114]. Moreover, these models are all function of volume fraction of nanoparticles; however, they do not include the temperature effect. Researchers have continued to work on measuring the viscosity for different nanofluids and came up with their own correlations. These correlations listed in Table 3 are a function of volume fraction only, .

Table 3: Theoretical models for predicting the viscosity.

In the recent years, researches started using instruments called viscometers to measure the viscosity of nanofluids.

Nanoparticle Concentration Effect on Viscosity. Several researches have confirmed that nanoparticle volume concentration in nanofluids increases the heat transfer coefficient [115119] along with increasing the viscosity. It was found that varying the concentration of Al2O3 in water with values of 0.3, 0.5, 0.7, 1, and 2% leads to an increase of viscosity, which in turn led to increased friction factor [115]. A similar behavior was observed in both water and ethylene glycol based Al2O3 and water based SiC nanofluids [120, 121]. This trend is also true for nonmetallic nanofluids, where several studies on the rheology of carbon nanotubes nanofluids confirmed that increasing the carbon nanotubes loading increases the viscosity of the nanofluid [122124].

It is important to mention that there are some inconsistencies in the literature regarding viscosity behaviors. Pak and Cho [74] examined water based Al2O3 and TiO2 nanofluids and observed that at a volume concentration of 3% the heat transfer severely reduced and has become lower than the heat transfer of pure water.

There are factors other than volume concentration which affect the nanofluid’s viscosity such as the nanoparticle’s shape, size, and surface chemistry [114]. Similarly, a study on water based Al2O3 and TiO2 showed that the nanoparticle’s size and shape as well as the volume fraction and temperature all were important parameters for determining the viscosity. However, the mentioned factors are poorly studied in the literature and further investigations are required.

Temperature Effect on Viscosity. As mentioned before, the theoretical models for viscosity do not consider temperature. Thus, the previous models can only be true for low concentrations and at room temperature conditions, but they are not true for higher temperatures [125]. Many researches reached a consensus that viscosity decreases with increasing temperatures [120, 121, 123, 126128]. Previous studies involved CuO, Al2O3, SiC, and CNT nanofluids with the focus being on Al2O3 nanofluids. Furthermore, it has been found that viscosity decreases exponentially with temperature rise in CuO, Al2O3, and SiO2 dispersed in both water and ethylene glycol [129]. A research also concluded that if the increase in viscosity is more than the thermal conductivity of nanofluids by four times, then it is rendered useless due to the increase of friction factor [130, 131].

3.2. Thermal Properties
3.2.1. Specific Heat Capacity

Specific heat capacity measures the ability of a material to store energy in the form of heat and exchange it if a temperature difference exists [111, 112]. It is important to acquire accurate values of the specific heat as specific heat is used to calculate important properties, which include thermal conductivity, thermal diffusivity, and flow’s spatial temperature. Researchers mostly use deferential scanning calorimeter (DSC) and double hot wire to measure of nanofluids.

Several models predict the specific heat values of nanofluids at different conditions. One model was based on mixture of liquid and particle and was introduced by Pak and Cho [74]:where “” is for the specific heat, “” is the nanofluid, is the volume fraction of the nanoparticle, and “” and “” represent the base fluid and nanoparticle, respectively. Some researchers proposed a correlation that was a modification of the previous model and was based on thermal equilibrium of the nanoparticles and the base fluid [132]:where “,” “,” and “” represent the specific heat, density, and nanoparticle’s volume fraction from the nanofluid, respectively, and “,” “,” and “” represent the nanofluid, base fluid, and nanoparticle, respectively. A recent study compared the results of heat capacities of water and EG based Al, Cu, and Si nanofluids acquired from DSC with the above models, and it found that there is a significant deviation from (3) but there was an agreement with (4) [133]. This was the same case with Al2O3-water, TiO2-EG nanofluids, and ZnO with ethylene glycol and water nanofluids [134, 135].

Zhou et al. [136] further modified equation one and proposed a correlation for higher volume concentration of nanoparticleswhere “” represents the specific heat, is the density, is the nanoparticle volume fraction from the nanofluid, and “,” “,” and “” represent the nanofluid, base fluid, and nanoparticle, respectively.

A comparison study between (3) and (5) found that the latter is more suitable to use at nanofluids with higher volume concentration [137]. Many parameters affect the specific heat of nanofluids; however, nanoparticle volume concentration, type of nanoparticle, and base fluid all have higher influence than the shape, size, or the electrostatic behavior of the nanoparticles [138].

Effect of Nanoparticle’s Size and Concentration on of Nanofluids. It has been observed by many researchers that in nanofluids when the volume fraction of the nanoparticle increases the specific heat decreases due to the nanoparticles having lower heat capacities compared to their base fluid. A recent paper investigated the specific heat of five different nanofluids, which are Al2O3, ZnO, TiO2, CuO, and SiO2, with 60 : 40 ratios of propylene glycol and water, respectively. After varying the volume concentrations of the nanoparticles from 0.5% to 6% and the particle sizes from 15 nm to 76 nm, the paper reported that the size of the particle had no significant impact on the specific heat. On the other hand, the volume concentration played a big part in altering the behavior of the heat capacity. At low concentration, the reduction in specific heat was tolerable mostly because it led to increasing the thermal conductivity, which enhanced the heat transfer efficiency. However, as the volume fraction of the nanoparticle increases, the heat capacity further decreases [139]. Similarly, the specific heat of water and ethylene glycol mixture based MgO, ZnO, and ZrO2 nanofluids were investigated, and it was observed that although the nanofluids showed a 30% increase in specific heat compared to their base fluids, it still decreases with increasing nanoparticles’ volume fraction [140]. Several researchers conducted similar studies and all of them reported the same behavior across a variety of nanofluids [141144].

For carbon nanotubes nanofluids, it is reported that as the multiwalled CNT concentration in 30 : 70 EG-water increased, the specific heat decreases [145, 146]. However, in contrast, an increase in specific heat with increasing single-walled CNT concentration in water was reported [147]. It is known that carbon nanotubes (CNTs) have high specific heat capacity. It is due to this reason that increased loading leads to the increase in the specific heat, but this has not been agreed upon yet.

Temperature Effect on . Most papers in the literature have reported that the specific heat increased with increased temperature. Experiments with several nanofluids have confirmed that increasing the temperatures will lead to increased specific heat capacities [112, 139, 148]. However, a few papers have found the contrary effect and reported that specific heat capacity decreases with increased temperatures [149151]. Similar to volume concentration, when the temperature is varied, the previous behavior of specific heat does not hold for all CNT nanofluids. It was observed that specific heat of multiwalled CNT increased with increasing temperatures [146, 152], while it was the opposite in single-walled CNT nanofluid [147].

3.2.2. Thermal Conductivity ()

Thermal conductivity “” is the rate at which a material passes heat. It is a major factor in increasing nanofluid efficiency in heat transfer and researchers have extensively studied it. The rate of heat transfer through solids is much higher than that through liquids and gases; it is for this reason that nanofluids have higher “” values compared to their base fluids. There are several methods to measure the thermal conductivity of a material, but the most common method is transient hot wire method.

Several efforts have been made in order to come up with a correlation that predicts the values of thermal conductivity of nanofluids at different conditions. Using continuum equations and particle-fluid mixtures, scientists have developed equations and tested them. Some of the derived models are shown in Table 4. One of the early models is Maxwell’s [75] to determine the effective thermal conductivity of millimeter to micrometer scale spherical particle-fluid mixture. Maxwell’s equation includes the thermal conductivity of the solid particles in base fluid and its volume fraction with respect to the total fluid and it can be applied only for low concentrations of particles. Bruggeman [76] considered the interaction between randomly distributed particles and introduced a model for spherical particles. Hamilton and Crosser [77] came up with a model for any particle shape, where in their equation they included a parameter of “,” which accounts for the shape of the particle (as shown in Table 4). Further modifications were made by other scientists to enhance the prediction of thermal conductivity; however, there are none that can determine the thermal conductivity of nanofluids in high volume concentrations and temperatures.

Table 4: Theoretical models for predicting the thermal conductivity.

Volume Fraction Effect. It is reported in the literature that a higher volume fraction of the nanoparticle in the nanofluid will increase the thermal conductivity. An increase in the effective thermal conductivity of 32.4% in Al2O3 nanofluid was reported when the volume concentration was increased to 4.3% [153]. A similar behavior was reported in another research, observing a 20% increase in the effective thermal conductivity for the same volume fraction increase [154]. The enhancement is notable when compared to nanofluids’ base fluids. Moreover, after investigating Al2O3 and CuO nanofluids, their thermal conductivities were enhanced by 2% to 9.4% for a volume concentration of 1.0% and 4%, respectively, showing an increase with increasing volume concentration [80]. The same effect can be seen in single-walled CNT [147].

Particle Size Effect. The size of the nanoparticle affects the thermal conductivity of the nanofluid, where smaller particle size will have a larger surface area relative to its diameter and thus will increase the thermal conductivity. A study confirms this after testing Al2O3 and CuO with nanoparticle sizes of 28 nm and 23 nm, respectively; the results showed an improvement in the thermal conductivity for the copper oxide nanofluid because their nanoparticles were smaller compared to Al2O3 [120]. However, this effect is inconsistent in other nanofluids such as SiC nanofluid. A paper experimented SiC nanofluids with sizes of 26 nm and 600 nm. The paper reported a thermal conductivity increase of 15.8% and 22.9%, respectively. This may be due to the clustering of the nanoparticles [85].

Temperature Effect. Temperature is also a factor in determining the thermal conductivity of the nanofluid. Several papers show that increasing the temperatures will intensify the thermal conductivity of the nanofluid. This effect holds true for water based Al2O3, CuO [155], ethylene glycol based ZnO [156], and CNT nanofluids [157].

3.3. Heat Transfer Characteristics

All the previous properties affect and determine the heat transfer rate of the nanofluid. However, it is important to note that volume concentration and temperature are major factors in all of these properties as well as the heat transfer characteristics.

3.3.1. Heat Transfer Coefficient and Nusselt Number

The main objective of using nanofluids is to increase the heat transfer rate so that it can be applied in heat transfer applications. Studies have demonstrated that adding nanoparticles to base fluids would result in a nanofluid with a higher heat transfer coefficient compared with the base fluid. One study compared water based Al2O3 nanofluid with pure water; the heat transfer coefficient and the Nusselt number both increased from 399.15 W/m2 K and 367.8 to 700 W/m2 K and 587, respectively [115]. Oil based CuO also showed a 12.7% increase in the heat transfer coefficient over oil at a 0.2% volume concentration when operated in a plate heat exchanger [107]. Similarly, another study in a plate heat exchanger reported enhancements of 42% and 50% in heat transfer coefficients for aluminum oxide and carbon nanotubes nanofluids, respectively [158]. Several correlations were made in order to calculate the Nusselt number and the heat transfer coefficient, which are described in Table 5.

Table 5: Theoretical models for predicting the Nusselt number.

Effect of Volume Fraction. Several studies have shown that the volume concentration increases the heat transfer coefficient in the nanofluid. Table 6 lists some of these studies along with remarks made by their authors.

Table 6: Effect of volume fraction on heat transfer coefficient.

Some studies are inconsistent and showed different behaviors. One study confirmed an increase in the Nusselt number of SiO2 and water nanofluid as the volume concentration increased [159]. Another study also confirmed this for both water based Al2O3 and TiO2; however, it made the observation that the heat transfer coefficient decreases to less than the base fluid at a constant temperature [74]. In another paper, researchers found that although the Nusselt number increased, it only increased for volume concentrations values between 0.2 and 2% and no change was reported for values larger than what is mentioned [160].

4. Applications of Nanofluids

In the previous sections, characteristics, preparation, and properties of nanofluids have been discussed. In this section, the focus will be on application of nanofluids. Nanofluids are used in several industries such as the automobile sector and the energy industry. Specific applications include cooling in electrical, electronic, and mechanical machines or devices, efficient heat transfer in energy generation and process industries, energy recovery from flue gases, cooling and heating of buildings, thermal storage, solar energy systems, desalination, refrigeration, space and defense, and lubrication in moving parts of machines and biomedical equipment. In the following sections, the role of nanofluids in these applications is discussed in detail.

4.1. Nanofluids in Cooling Applications

The use of water as a cooling medium has many limitations; thus there is a need for fluids with higher heat transfer efficiencies [161]. It is known that solids have higher thermal conductivities than fluids; this suggests that they provide improved thermal properties [162164]. Since fluids are required to substitute water and coolants, nanofluids are the best candidates because they provide the necessary properties for better heat transfer properties. Nanoparticle concentration has a direct effect on nanofluid’s thermal conductivity, heat transfer, and viscosity [165, 166]. Therefore, the effects must be considered before utilizing nanofluids in any applications. There are various cooling applications of nanofluids, which are described below.

4.2. Nanofluids in Vapor Compression Cycles

Water based nanofluids can achieve enhanced high heat flux cooling while keeping the benefits of water [99]. Many studies were performed on household fridges utilizing nanorefrigerants. One study utilized R134a as a refrigerant and a blend of mineral POE oil mixed with TiO2 nanoparticles as a lubricant. It was found that energy consumption decreased by 26% in comparison to R134a and regular POE oil lubricant. Likewise, there was a significant decrease in the power utilization and a large change in freezing capacity. The change in the cycle performance was related to the improvements in the thermophysical characteristics of the lubricant in addition to the presence of nanoparticles with the R134a [167]. In later studies, tests were performed on a household fridge utilizing TiO2-R600a nanorefrigerant as working liquid. The study demonstrated that utilizing TiO2 with the R600a refrigerant makes the system perform regularly and productively in the icebox. Furthermore, energy consumption decreased by up to 10% [123, 167174]. Similarly, a study was conducted to investigate the performance of a residential fridge, which utilized Al2O3-R134a nanorefrigerant as the working fluid. It was found that the Al2O3-R134a system performance was superior to the system with lubricant and R134a working fluid mentioned before. The system consumed 10.30% less energy with 0.2% volume concentration. Moreover, by utilizing nanosized Al2O3, an increase was noticed in the heat transfer coefficient [175].

Another study focused on the performance of a household fridge utilizing TiO2-R12 nanorefrigerant as the working fluid in a household fridge. The experiment discovered that the freezing capacity enhanced while 3.6% of enhancement was recorded in the heat transfer coefficient by using nanofluids. A decrease of 11% in the pressure work and an increase of 17% in the coefficient of performance by adding nanoparticles to the lubricant were also observed [176].

In another study, TiO2 nanoparticles were added to R600a and were used as the working fluid; the energy saving and coefficient of performance increase were found to be 11% and 19%, respectively [177]. A CFD study used a working fluid consisting of CuO-R134a as a part of the vapor compression system. The study reported an increase in the evaporator heat transfer coefficient by adding CuO nanoparticles [178]. The conventional refrigerant and lubricant were replaced with a hydrocarbon refrigerant and mineral lubricant that contains Al2O3 nanoparticles in order to enhance the grease and heat transfer characteristics. The authors concluded that a volume concentration of 0.1 wt.% Al2O3 nanoparticle and a 60% R134a refrigerant were ideal and had decreased energy consumption by around 2.4% while increasing the coefficient of performance by 4.4% [179].

In addition to metal oxide nanofluids, several studies investigated the potential of CNT nanofluids. CNTs were added to the polyester oil by concentrations of 0.01–0.1 wt.% and were experimented with R134a refrigerant as the base fluid. The authors showed that 0.1 wt% was ideal, achieving the higher values of heat transfer improvement as well as increasing the coefficient of performance by 4.2% [180]. CNTs were noticed to have higher thermal conductivity (~3000 W/mK) over other nanoparticles such as CuO, Al2O3, SiO2 diamond, and TiO2 [181]. In a study, CNT nanofluid with R113a as the base refrigerant was utilized and notable enhancements of the system were observed. This recent study has also found that CNT based nanofluid has higher thermal conductivity when compared with ordinary refrigerants [182].

Nanofluids are expected to contribute largely in decreasing energy consumption as well as emissions in industrial air conditioning applications [183]. It was estimated that savings of 1 trillion Btu can be saved in the energy sector within US by replacing water with nanofluids in cooling and heating applications [184]. Similarly, about 10–30 trillion Btu can be saved annually by utilizing nanofluids in closed loop cooling cycles. Furthermore, this would reduce the related emissions of carbon dioxide, nitrogen oxides, and sulfur dioxide by 5.6 million metric tons, 8,600 metric tons, and 21,000 metric tons, respectively [183].

4.3. Nanofluids in Microchips and Server Cooling

Efficient cooling in electronics is necessary to maintain their performance. Alumina nanofluid was tested in microchannels and has been shown to improve heat transfer. It has been also shown to be effective in microchips cooling applications [185, 186]. A new design for a cooler containing microchannel heat sink was tested using nanofluid and the results showed a decrease in heat resistance as well as temperature gradient between the warmed microchannel walls and the coolant [88].

The heat transfer enhancement of water-Al2O3 nanofluid at various concentrations was investigated using a cooler designed with microchannel heat sink [187]. Similarly, a heat sink of silicon microchannels was used to analyze the performance of Cu nanoparticles [188].

4.4. Nanofluids in Automotive Cooling

Nanofluids dispersed in ethylene glycol have pulled in great attention in motor cooling applications [189]. Increment in the conventional coolant working temperature and the heat rejection rate can be done by utilizing nanofluids within the current motor cooling system [190]. A study used a 3.5% volume fraction of aluminum oxide nanoparticles dispersed in a standard motor coolant in a standard car engine and recorded enhanced thermal conductivity of 10.41% at room temperature [191]. A nanofluid composed of CuO and Al2O3 nanoparticles was used in the engine transmission oil as a coolant for automatic transmission systems. The outcomes demonstrated that CuO nanofluids lead to a reduced transmission temperature at different turning speeds [192]. The mentioned results show that using nanofluids in transmission systems may have a significant potential.

4.5. Nanofluids in Aerospace and Defense Cooling

Various military equipment needs sufficient amount of cooling in the order of Mw/m2. Using conventional fluids for cooling in these sectors would require large and heavy operations. An example of military equipment cooling is the cooling requirement in direct energy weapons, high power laser diodes, and submarines. Transformer cooling in order to reduce the size and weight is necessary in naval and energy industries. Retrofitting conventional fluids in transformer may lead to large cost savings. It has been experimentally proven that, with nanofluids, the magnitude of critical flux in pool boiling increases manifold in comparison to the conventional fluids. The high levels of critical flux will help in simplifying cooling requirements in space such as space shuttle or space suits [193].

4.6. Nanofluids in Heat Exchanger Applications

The replacement of conventional heat transfer fluids by nanofluids in heat exchangers is promising [194]. The development of new, highly efficient heat exchanger fluids is an important requirement for heat exchanger design [195]. Nanofluids can improve the heat transfer process more than twice with small volume fraction under 0.3% [196]. One study focused on thoroughly characterizing all the properties of the nanofluid in order to determine its suitability in a particular heat exchanger. The latest experimental work related to the utilization of nanofluids in heat exchangers claimed that the flow type within the heat exchanger is a vital concern in the suitability of a nanofluid [119, 197]. In situations where the heat exchanger works under turbulent conditions, the use of nanofluids is helpful if it is accommodated by a minimum increase fluid viscosity which appears to be extremely hard to accomplish. Yet, improvement in the Nusselt number was achieved by using alumina-water and Titania-water nanofluids in fluids where the flow was described as turbulent [198]. A study showed improvements in the critical convective heat transfer of MWCNTs scattered in water. It was noticed that the improvement relied on the flow conditions and volume concentration [199]. The conductive heat transfer in turbulent flows using copper/water nanofluid was investigated. The study showed an improvement of more than 39% with a volume concentration of 1.5% [200]. Another study found that, by adding 0.2% volume concentration of TiO2 nanoparticles, an upgrade of 11% in the convective heat transfer coefficient is possible [201]. On the other hand, if a laminar flow exists in the heat exchanger, the utilization of nanofluids appears to be favorable with the main obstacles being the cost and the particles suspension concerns when compared to pure fluids [194]. A study investigated the use of nanofluid under laminar flow and reported a 41% improvement in heat transfer characteristics in the entry region [202]. Similarly, graphite nanofluids were utilized in a horizontal circular tube to study the laminar convective heat transfer performance and were proven to be effective [203].

4.7. Biomedical Applications of Nanofluids

Medical science is also not aloof from technological advancement. The growing field of nanofluids finds many applications in the biomedical industry. One example is the use of nanofluids in order to minimize the side effects of traditional radiation cancer therapy, in which iron based nanoparticles can help in delivering drugs or radiation to the targeted cells (nanofluids can be guided in blood stream with magnets outside) without actually damaging the healthy cells [203]. Moreover, undergoing surgery is an unpleasant experience. However, with help of nanofluids, the effective cooling can be achieved around the surgical area, thus improving the chance of survival for the patient and mitigating the danger of organ damage. On the other hand, nanofluids (heating mode) can also be used for killing tumors or cancerous cells without affecting neighboring healthy cells. Furthermore, researches have confirmed antibacterial properties of nanofluids. ZnO nanofluids are helpful in killing Escherichia coli (E. coli) bacteria [204]. Increasing nanoparticles volume fraction and decreasing their size were shown to increase the antibacterial activity. In addition, nanofluids also help in nanodrug delivery systems in order to supply controlled dose of drug over desired period of time.

4.8. Application in Mechanical Processes Energy Industry

Heat transfer value may be of a great benefit to the final quality of a product or process in industry. This increase may help in reducing pumping power and in turn may help in saving energy in HVAC systems. In the energy sector, nanofluids can enhance the heat transfer, which in turn will lead to higher temperatures in turbines and more power outputs. In cooling systems such as refrigeration or process of cooling applications, nanofluids are equally trustworthy. Nanofluid coolants can be used in several applications like chemical, food and drinks, and oil and gas industries. In addition, The Massachusetts Institute of Technology (MIT) has a multidiscipline center to research the application of nanofluids in nuclear energy industry. Currently, potential impacts of using nanofluids in nuclear systems on safety, economic performance, and neutronic are under study [203].

4.9. Solar Energy and Desalination Applications

The major problem with solar or other forms of renewable energies is their availability at irregular intervals and the energy cannot be fetched from renewables round the clock. Therefore, storing energy becomes necessary to meet the demand in a more appropriate fashion. With this concept of storage, the technology of solar thermal energy cropped up. However, this technology still faces some serious problems with thermal energy storage for longer durations. The molten salts used for storing energy have certain drawbacks associated with them. The salts have freezing point of about 200°C and, below this temperature, they precipitate down in the system and clog the entire plant within fraction of seconds. Nanofluids prove to be trustworthy for storing energy as nanofluids PCMs (Phase Change Materials) possess extremely high thermal conductivities compared to the base material. Recently, researchers have tested nanofluid based PCMs by suspending nanoparticles from titanium oxide in saturated barium chloride aqueous solution and the result showed that the nanofluid based PCMs possessed considerably high thermal properties.

Solar energy is the major form of renewable energy and has the potential to supply the entire world’s demand. Many researchers have proven that installing solar thermal power plants in arid regions of the globe will help in meeting the demands of entire world. The only problem with solar thermal energy is storage for a consistent base load, peak load, and intermediate load power generation. With nanofluids this problem of storage may be sorted out. Recent study from scientists has shown that nanofluid based concentrating solar thermal power plants can improve the efficiency by 10% and installing these nanofluid based plants in solar resource areas of Tucson, Arizona, and Algeria can lead to $3.5 million more earnings per year per 100 MWe.

On the other hand, world is also facing water shortages and in particular the arid regions of globe are water stress zones. Implementing nanofluid based solar thermal power plants along with solar thermal desalination systems will help in solving the problems of water along with electricity or energy. With nanofluids, more heat transfer capacities will be obtained which in turn will give more power output and more potable water. Implementing MED (Multieffect Distillation) systems with solar thermal power plant based on nanofluids energy storage will provide uninterrupted, round the clock water and energy supply [204].

4.10. Optical Application

Optical filters are used to choose various wavelengths of light. A ferrobased nanofluid can help in selecting several bands of the wavelength of the spectrum such as infrared, ultraviolet, or even the visible region. The required wavelengths range in addition to their bandwidths along with reflectivity can be managed by using properly customized ferrofluid emulsions [204].

4.11. Friction Reduction

The major concern of any mechanical industry ranging from manufacturing companies to railways is wear and tear, life, and reliability of moving parts. Nanoparticles have excellent load bearing capabilities and can withstand high pressures, thereby reducing wear and tear in moving parts of machines. Tribology is the science of bearing and it greatly emphasizes the mitigation of friction and wear. Lubrication provided by conventional fluids is not as efficient as lubrication provided by nanofluids. This is shown in the evaluation of tribological behavior of Cu based nanofluids; results have confirmed that the Cu nanofluid showed increased friction reduction as well as antiwear properties even at high loads. In addition, nanofluids proved to be valuable in machining operations such as cutting, grinding, and tapering. Better surface finish was achieved and prevented the burning of the workpiece and the tool [204].

4.12. Magnetic Sealing

In comparison to mechanical sealing, magnetic ones are more cost-effective and provide environment friendly and hazard proof sealing to large number of rotational equipment in the industry. They have low frictional resistance, long life, and high reliability and are capable of withstanding high speeds. Magnetic nanofluids are stable emulsions of magnetic particles like magnetite (Fe3O4). The developed seal of magnetic fluid operated for 286 days in constant flow state. Ferrocobalt magnetic fluid can withstand 25 times the pressure when compared with traditional magnetite sealing [204].

4.13. Nanofluid Detergent

In order to discover the method of dispersing dynamics in nanofluids of polystyrene, reflected-light digital video microscopy was used and it was demonstrated that nanofluids can act as a detergent; however, more work is required in this area. Commercial extraction of oil and oil spills removal can also be an application for the same nanofluid type [193].

4.14. Application in Geothermal Energy Extraction

Using zinc oxide nanofluids increases heat transfer ability of geothermal systems. Nanofluids usage increases the efficiency of entire power generation cycle based on geothermal energy. Out of the many renewable energy sources available, geothermal energy is a rarely used source. So far, only 1.5% of the available geothermal energy resource is extractable globally. However, nanofluids can help in extracting more geothermal energy and producing power in a Rankine cycle more efficiently. Moreover, nanofluids can be put in place to cool the pipes, which carry geothermal fluid at high temperatures, that is, in the range between 500°C and 1000°C. Furthermore, nanofluids behave as “fluid superconductors” and hence might be utilized as a working fluid to convert energy into useful form [205].

5. Conclusion

In this paper, the goal was to present an overview of the recent developments in the field of nanofluids. Preparation, characteristics, and applications of nanofluids have been discussed in detail. It is important to mention that thermophysical properties vary with the volume concentration, temperature, and flow rate. However, more research is required to study the effect of nanoparticle’s shape, size, and surface chemistry on the properties of nanofluids. In general, the increase of volume fraction of the nanoparticles increases the density, viscosity, and thermal conductivity of the nanofluid. In the case of heat transfer coefficient and Nusselt number, studies showed that there is a limit to enhancement and an optimum volume fraction exists. The application of nanofluids appears promising in a wide range of fields; however, more work is required in some areas such as the stability of these nanofluids in various applications, the use of hybrid nanofluids, and effect of working conditions on the properties of these nanofluids. Furthermore, the experimental and lab scale results must be scaled up to the prototype level in order to evaluate the results and implement them commercially in various fields such as water desalination, power generation, mechanical devices, defense, and space applications. Finally, environmental consequences of nanofluids must be investigated and analyzed using cradle to grave approach or LCA (Life Cycle Assessment) method.

Competing Interests

The authors declare that they have no competing interests.

Acknowledgments

The authors would like to thank Qatar Environment and Energy Research Institute under Hamad Bin Khalifa University and Qatar Foundation for funding this work through Project QEERI-TI-PP-8000-00.

References

  1. Y. Li, J. Zhou, S. Tung, E. Schneider, and S. Xi, “A review on development of nanofluid preparation and characterization,” Powder Technology, vol. 196, no. 2, pp. 89–101, 2009. View at Publisher · View at Google Scholar · View at Scopus
  2. X.-F. Yang and Z.-H. Liu, “Pool boiling heat transfer of functionalized nanofluid under sub-atmospheric pressures,” International Journal of Thermal Sciences, vol. 50, no. 12, pp. 2402–2412, 2011. View at Publisher · View at Google Scholar · View at Scopus
  3. I. Tavman and A. Turgut, “Experimental investigation of viscosity and thermal conductivity of suspensions containing nanosized ceramic particles,” Archives of Materials Science and Engineering, vol. 34, no. 2, pp. 99–104, 2008. View at Google Scholar
  4. N. Jamshidi, M. Farhadi, D. D. Ganji, and K. Sedighi, “Experimental investigation on the viscosity of nanofluids,” International Journal of Engineering, Transactions B: Applications, vol. 25, no. 3, pp. 201–209, 2012. View at Publisher · View at Google Scholar · View at Scopus
  5. E. V. Timofeeva, D. S. Smith, W. Yu, D. M. France, D. Singh, and J. L. Routbort, “Particle size and interfacial effects on thermo-physical and heat transfer characteristics of water-based α-SiC nanofluids,” Nanotechnology, vol. 21, no. 21, pp. 215703–215710, 2010. View at Publisher · View at Google Scholar
  6. E. V. Timofeeva, W. Yu, D. M. France, D. Singh, and J. L. Routbort, “Base fluid and temperature effects on the heat transfer characteristics of SiC in ethylene glycol/H2O and H2O nanofluids,” Journal of Applied Physics, vol. 109, no. 1, Article ID 014914, 2011. View at Publisher · View at Google Scholar · View at Scopus
  7. N. Nikkam, M. Saleemi, E. B. Haghighi et al., “Fabrication, characterization and thermo- physical property evaluation of SiC nanofluids for heat transfer applications,” Nano-Micro Letters, vol. 6, no. 2, pp. 178–189, 2014. View at Publisher · View at Google Scholar · View at Scopus
  8. K. Abdul Hamid, W. H. Azmi, R. Mamat, N. A. Usri, and G. Najafi, “Effect of titanium oxide nanofluid concentration on pressure drop,” ARPN Journal of Engineering and Applied Sciences, vol. 10, no. 17, pp. 7815–7820, 2015. View at Google Scholar · View at Scopus
  9. T. Kavitha, A. Rajendran, and A. Durairajan, “Synthesis, characterization of TiO2 nano powder and water based nanofluids using two step method,” European Journal of Applied Engineering & Scienctific Research, vol. 1, pp. 235–240, 2012. View at Google Scholar
  10. A. L. Subramaniyan, S. Lakshmi Priya, and R. Ilangovan, “Energy harvesting through optical properties of TiO2 and C- TiO2 nanofluid for direct absorption solar collectors,” International Journal of Renewable Energy Research, vol. 5, no. 2, pp. 542–547, 2015. View at Google Scholar · View at Scopus
  11. A. R. Sajadi and M. H. Kazemi, “Investigation of turbulent convective heat transfer and pressure drop of TiO2/water nanofluid in circular tube,” International Communications in Heat and Mass Transfer, vol. 38, no. 10, pp. 1474–1478, 2011. View at Publisher · View at Google Scholar · View at Scopus
  12. W. D. S. Wongwises, “Heat transfer enhancement and pressure drop characteristics of TiO2-water nanofluid in a double-tube counter flow heat exchanger,” International Journal of Heat and Mass Transfer, vol. 38, no. 10, pp. 1474–1478, 2011. View at Publisher · View at Google Scholar
  13. M. H. Kayhani, H. Soltanzadeh, M. M. Heyhat, M. Nazari, and F. Kowsary, “Experimental study of convective heat transfer and pressure drop of TiO2/water nanofluid,” International Communications in Heat and Mass Transfer, vol. 39, no. 3, pp. 456–462, 2012. View at Publisher · View at Google Scholar · View at Scopus
  14. H. Zhu, C. Zhang, S. Liu, Y. Tang, and Y. Yin, “Effects of nanoparticle clustering and alignment on thermal conductivities of Fe3O4 aqueous nanofluids,” Applied Physics Letters, vol. 89, no. 2, Article ID 023123, pp. 1–3, 2006. View at Publisher · View at Google Scholar · View at Scopus
  15. Y. Lv, Y. Zhou, C. Li, Q. Wang, and B. Qi, “Recent progress in nanofluids based on transformer oil: preparation and electrical insulation properties,” IEEE Electrical Insulation Magazine, vol. 30, no. 5, pp. 23–32, 2014. View at Publisher · View at Google Scholar · View at Scopus
  16. S. Lee, S. U.-S. Choi, S. Li, and J. A. Eastman, “Measuring thermal conductivity of fluids containing oxide nanoparticles,” Journal of Heat Transfer, vol. 121, no. 2, pp. 280–289, 1999. View at Publisher · View at Google Scholar · View at Scopus
  17. K. B. Anoop, T. Sundararajan, and S. K. Das, “Effect of particle size on the convective heat transfer in nanofluid in the developing region,” International Journal of Heat and Mass Transfer, vol. 52, no. 9-10, pp. 2189–2195, 2009. View at Publisher · View at Google Scholar · View at Zentralblatt MATH · View at Scopus
  18. J. Qu, H.-Y. Wu, and P. Cheng, “Thermal performance of an oscillating heat pipe with Al2O3-water nanofluids,” International Communications in Heat and Mass Transfer, vol. 37, no. 2, pp. 111–115, 2010. View at Publisher · View at Google Scholar · View at Scopus
  19. M. Chandrasekar, S. Suresh, and A. C. Bose, “Experimental investigations and theoretical determination of thermal conductivity and viscosity of Al2O3/water nanofluid,” Experimental Thermal and Fluid Science, vol. 34, no. 2, pp. 210–216, 2010. View at Publisher · View at Google Scholar · View at Scopus
  20. S. Soltani, S. G. Etemad, and J. Thibault, “Pool boiling heat transfer of non-Newtonian nanofluids,” International Communications in Heat and Mass Transfer, vol. 37, no. 1, pp. 29–33, 2010. View at Publisher · View at Google Scholar · View at Scopus
  21. P. E. Gharagozloo and K. E. Goodson, “Temperature-dependent aggregation and diffusion in nanofluids,” International Journal of Heat and Mass Transfer, vol. 54, no. 4, pp. 797–806, 2011. View at Publisher · View at Google Scholar · View at Scopus
  22. S. Suresh, P. Selvakumar, M. Chandrasekar, and V. S. Raman, “Experimental studies on heat transfer and friction factor characteristics of Al2O3/water nanofluid under turbulent flow with spiraled rod inserts,” Chemical Engineering and Processing: Process Intensification, vol. 53, pp. 24–30, 2012. View at Publisher · View at Google Scholar · View at Scopus
  23. Y.-H. Hung, T.-P. Teng, and B.-G. Lin, “Evaluation of the thermal performance of a heat pipe using alumina nanofluids,” Experimental Thermal and Fluid Science, vol. 44, pp. 504–511, 2013. View at Publisher · View at Google Scholar · View at Scopus
  24. W. Yu, H. Xie, L. Chen, and Y. Li, “Investigation of thermal conductivity and viscosity of ethylene glycol based ZnO nanofluid,” Thermochimica Acta, vol. 491, no. 1-2, pp. 92–96, 2009. View at Publisher · View at Google Scholar · View at Scopus
  25. U. Bhagat, P. More, and P. Khanna, “Study of zinc oxide nanofluids for heat transfer application,” SAJ Nanoscience and Nanotechnology, vol. 1, no. 1, pp. 1–7, 2015. View at Google Scholar
  26. K. S. Suganthi and K. S. Rajan, “Temperature induced changes in ZnO-water nanofluid: Zeta potential, size distribution and viscosity profiles,” International Journal of Heat and Mass Transfer, vol. 55, no. 25-26, pp. 7969–7980, 2012. View at Publisher · View at Google Scholar · View at Scopus
  27. M. T. Zafarani-Moattar and R. Majdan-Cegincara, “Effect of temperature on volumetric and transport properties of nanofluids containing ZnO nanoparticles poly(ethylene glycol) and water,” Journal of Chemical Thermodynamics, vol. 54, pp. 55–67, 2012. View at Publisher · View at Google Scholar · View at Scopus
  28. M. Kole and T. K. Dey, “Thermophysical and pool boiling characteristics of ZnO-ethylene glycol nanofluids,” International Journal of Thermal Sciences, vol. 62, pp. 61–70, 2012. View at Publisher · View at Google Scholar · View at Scopus
  29. S. W. Lee, S. D. Park, and I. C. Bang, “Critical heat flux for CuO nanofluid fabricated by pulsed laser ablation differentiating deposition characteristics,” International Journal of Heat and Mass Transfer, vol. 55, no. 23-24, pp. 6908–6915, 2012. View at Publisher · View at Google Scholar · View at Scopus
  30. K. Rohini Priya, K. S. Suganthi, and K. S. Rajan, “Transport properties of ultra-low concentration CuO-water nanofluids containing non-spherical nanoparticles,” International Journal of Heat and Mass Transfer, vol. 55, no. 17-18, pp. 4734–4743, 2012. View at Publisher · View at Google Scholar · View at Scopus
  31. J. J. Michael and S. Iniyan, “Performance analysis of a copper sheet laminated photovoltaic thermal collector using copper oxide—water nanofluid,” Solar Energy, vol. 119, pp. 439–451, 2015. View at Publisher · View at Google Scholar · View at Scopus
  32. S. Harikrishnan and S. Kalaiselvam, “Preparation and thermal characteristics of CuO-oleic acid nanofluids as a phase change material,” Thermochimica Acta, vol. 533, pp. 46–55, 2012. View at Publisher · View at Google Scholar · View at Scopus
  33. M. Karami, M. A. Akhavan-Behabadi, M. Raisee Dehkordi, and S. Delfani, “Thermo-optical properties of copper oxide nanofluids for direct absorption of solar radiation,” Solar Energy Materials and Solar Cells, vol. 144, pp. 136–142, 2016. View at Publisher · View at Google Scholar · View at Scopus
  34. N. Kannadasan, K. Ramanathan, and S. Suresh, “Comparison of heat transfer and pressure drop in horizontal and vertical helically coiled heat exchanger with CuO/water based nano fluids,” Experimental Thermal and Fluid Science, vol. 42, pp. 64–70, 2012. View at Publisher · View at Google Scholar · View at Scopus
  35. S. M. Fotukian and M. Nasr Esfahany, “Experimental study of turbulent convective heat transfer and pressure drop of dilute CuO/water nanofluid inside a circular tube,” International Communications in Heat and Mass Transfer, vol. 37, no. 2, pp. 214–219, 2010. View at Publisher · View at Google Scholar · View at Scopus
  36. M. Sheikhbahai, M. Nasr Esfahany, and N. Etesami, “Experimental investigation of pool boiling of Fe3O4/ethylene glycol-water nanofluid in electric field,” International Journal of Thermal Sciences, vol. 62, pp. 149–153, 2012. View at Publisher · View at Google Scholar · View at Scopus
  37. Q. Li, Y. Xuan, and J. Wang, “Experimental investigations on transport properties of magnetic fluids,” Experimental Thermal and Fluid Science, vol. 30, no. 2, pp. 109–116, 2005. View at Publisher · View at Google Scholar · View at Scopus
  38. W. Yu, H. Xie, L. Chen, and Y. Li, “Enhancement of thermal conductivity of kerosene-based Fe3O4 nanofluids prepared via phase-transfer method,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 355, no. 1–3, pp. 109–113, 2010. View at Publisher · View at Google Scholar · View at Scopus
  39. M. Abareshi, S. H. Sajjadi, S. M. Zebarjad, and E. K. Goharshadi, “Fabrication, characterization, and measurement of viscosity of α-Fe2O3-glycerol nanofluids,” Journal of Molecular Liquids, vol. 163, no. 1, pp. 27–32, 2011. View at Publisher · View at Google Scholar · View at Scopus
  40. F. Asadzadeh, M. N. Esfahany, and N. Etesami, “Natural convective heat transfer of Fe3O4/ethylene glycol nanofluid in electric field,” International Journal of Thermal Sciences, vol. 62, pp. 114–119, 2012. View at Publisher · View at Google Scholar · View at Scopus
  41. L. S. Sundar, M. T. Naik, K. V. Sharma, M. K. Singh, and T. C. S. Reddy, “Experimental investigation of forced convection heat transfer and friction factor in a tube with Fe3O4 magnetic nanofluid,” Experimental Thermal and Fluid Science, vol. 37, pp. 65–71, 2012. View at Publisher · View at Google Scholar · View at Scopus
  42. Y. Vermahmoudi, S. M. Peyghambarzadeh, S. H. Hashemabadi, and M. Naraki, “Experimental investigation on heat transfer performance of Fe2O3/water nanofluid in an air-finned heat exchanger,” European Journal of Mechanics—B/Fluids, vol. 44, pp. 32–41, 2014. View at Publisher · View at Google Scholar · View at Scopus
  43. S. Sen, E. Moazzen, S. Aryal, C. U. Segre, and E. V. Timofeeva, “Engineering nanofluid electrodes: controlling rheology and electrochemical activity of γ-Fe2O3 nanoparticles,” Journal of Nanoparticle Research, vol. 17, article 437, pp. 1–10, 2015. View at Publisher · View at Google Scholar · View at Scopus
  44. A. Karimi, M. Goharkhah, M. Ashjaee, and M. B. Shafii, “Thermal conductivity of Fe2O3 and Fe3O4 magnetic nanofluids under the influence of magnetic field,” International Journal of Thermophysics, vol. 36, no. 10-11, pp. 2720–2739, 2015. View at Publisher · View at Google Scholar · View at Scopus
  45. M. Wozniak, A. Danelska, D. Kata, and M. Szafran, “New anhydrous aluminum nitride dispersions as potential heat-transferring media,” Powder Technology, vol. 235, pp. 717–722, 2013. View at Publisher · View at Google Scholar · View at Scopus
  46. W. Yu, H. Xie, Y. Li, and L. Chen, “Experimental investigation on thermal conductivity and viscosity of aluminum nitride nanofluid,” Particuology, vol. 9, no. 2, pp. 187–191, 2011. View at Publisher · View at Google Scholar · View at Scopus
  47. M. Dong, L. P. Shen, H. Wang, H. B. Wang, and J. Miao, “Investigation on the electrical conductivity of transformer oil-based AlN nanofluid,” Journal of Nanomaterials, vol. 2013, Article ID 842963, 7 pages, 2013. View at Publisher · View at Google Scholar
  48. P. Hu, W.-L. Shan, F. Yu, and Z.-S. Chen, “Thermal conductivity of AlN-ethanol nanofluids,” International Journal of Thermophysics, vol. 29, no. 6, pp. 1968–1973, 2008. View at Publisher · View at Google Scholar
  49. Y. Xuan and Q. Li, “Heat transfer enhancement of nanofluids,” International Journal of Heat and Fluid Flow, vol. 21, no. 1, pp. 58–64, 2000. View at Publisher · View at Google Scholar · View at Scopus
  50. H. Peng, G. Ding, and H. Hu, “Effect of surfactant additives on nucleate pool boiling heat transfer of refrigerant-based nanofluid,” Experimental Thermal and Fluid Science, vol. 35, no. 6, pp. 960–970, 2011. View at Publisher · View at Google Scholar · View at Scopus
  51. R. Kathiravan, R. Kumar, A. Gupta, and R. Chandra, “Preparation and pool boiling characteristics of copper nanofluids over a flat plate heater,” International Journal of Heat and Mass Transfer, vol. 53, no. 9-10, pp. 1673–1681, 2010. View at Publisher · View at Google Scholar · View at Scopus
  52. R. R. Riehl and N. dos Santos, “Water-copper nanofluid application in an open loop pulsating heat pipe,” Applied Thermal Engineering, vol. 42, pp. 6–10, 2012. View at Publisher · View at Google Scholar · View at Scopus
  53. M. Kole and T. K. Dey, “Thermal performance of screen mesh wick heat pipes using water-based copper nanofluids,” Applied Thermal Engineering, vol. 50, no. 1, pp. 763–770, 2013. View at Publisher · View at Google Scholar · View at Scopus
  54. M. Khoshvaght-Aliabadi, S. Pazdar, and O. Sartipzadeh, “Experimental investigation of water based nanofluid containing copper nanoparticles across helical microtubes,” International Communications in Heat and Mass Transfer, vol. 70, pp. 84–92, 2016. View at Publisher · View at Google Scholar · View at Scopus
  55. E. Tamjid and B. H. Guenther, “Rheology and colloidal structure of silver nanoparticles dispersed in diethylene glycol,” Powder Technology, vol. 197, no. 1-2, pp. 49–53, 2010. View at Publisher · View at Google Scholar · View at Scopus
  56. M. Hari, S. A. Joseph, S. Mathew, B. Nithyaja, V. P. N. Nampoori, and P. Radhakrishnan, “Thermal diffusivity of nanofluids composed of rod-shaped silver nanoparticles,” International Journal of Thermal Sciences, vol. 64, pp. 188–194, 2013. View at Publisher · View at Google Scholar · View at Scopus
  57. T. Parametthanuwat, S. Rittidech, and A. Pattiya, “A correlation to predict heat-transfer rates of a two-phase closed thermosyphon (TPCT) using silver nanofluid at normal operating conditions,” International Journal of Heat and Mass Transfer, vol. 53, no. 21-22, pp. 4960–4965, 2010. View at Publisher · View at Google Scholar · View at Scopus
  58. R. Hajian, M. Layeghi, and K. A. Sani, “Experimental study of nanofluid effects on the thermal performance with response time of heat pipe,” Energy Conversion and Management, vol. 56, pp. 63–68, 2012. View at Publisher · View at Google Scholar · View at Scopus
  59. J. John, L. Thomas, B. Rajesh Kumar, A. Kurian, and S. D. George, “Shape dependent heat transport through green synthesized gold nanofluids,” Journal of Physics D: Applied Physics, vol. 48, no. 33, Article ID 335301, 2015. View at Publisher · View at Google Scholar
  60. S. Soltaninejad, M. S. Husin, A. R. Sadrolhosseini et al., “Thermal diffusivity measurement of Au nanofluids of very low concentration by using photoflash technique,” Measurement, vol. 46, no. 10, pp. 4321–4327, 2013. View at Publisher · View at Google Scholar · View at Scopus
  61. L. Chen, H. Xie, Y. Li, and W. Yu, “Nanofluids containing carbon nanotubes treated by mechanochemical reaction,” Thermochimica Acta, vol. 477, no. 1-2, pp. 21–24, 2008. View at Publisher · View at Google Scholar · View at Scopus
  62. P. Garg, J. L. Alvarado, C. Marsh, T. A. Carlson, D. A. Kessler, and K. Annamalai, “An experimental study on the effect of ultrasonication on viscosity and heat transfer performance of multi-wall carbon nanotube-based aqueous nanofluids,” International Journal of Heat and Mass Transfer, vol. 52, no. 21-22, pp. 5090–5101, 2009. View at Publisher · View at Google Scholar · View at Scopus
  63. T. X. Phuoc, M. Massoudi, and R.-H. Chen, “Viscosity and thermal conductivity of nanofluids containing multi-walled carbon nanotubes stabilized by chitosan,” International Journal of Thermal Sciences, vol. 50, no. 1, pp. 12–18, 2011. View at Publisher · View at Google Scholar · View at Scopus
  64. M. Zhaoguo, W. Daxiong, L. Wang, H. Zhu, and Q. Li, “Carbon nanotube glycol nanofluids: photo-thermal properties, thermal conductivities and rheological behavior,” Particuology, vol. 10, no. 5, pp. 614–618, 2012. View at Publisher · View at Google Scholar
  65. M. Xing, J. Yu, and R. Wang, “Experimental study on the thermal conductivity enhancement of water based nanofluids using different types of carbon nanotubes,” International Journal of Heat and Mass Transfer, vol. 88, pp. 609–616, 2015. View at Publisher · View at Google Scholar · View at Scopus
  66. C. K. Kim, G.-J. Lee, and C. K. Rhee, “A study on heat transfer characteristics of spherical and fibrous alumina nanofluids,” Thermochimica Acta, vol. 542, pp. 33–36, 2012. View at Publisher · View at Google Scholar · View at Scopus
  67. I. S. Mohamad, S. T. Chitrambalam, and S. B. A. Hamid, “Investigations on the thermo-physical properties of nanofluid-based carbon nanofibers under modified testing conditions,” International Journal of Nanoelectronics and Materials, vol. 5, no. 1, pp. 25–30, 2012. View at Google Scholar · View at Scopus
  68. S. M. S. Murshed, K. C. Leong, and C. Yang, “Enhanced thermal conductivity of TiO2—water based nanofluids,” International Journal of Thermal Sciences, vol. 44, no. 4, pp. 367–373, 2005. View at Publisher · View at Google Scholar · View at Scopus
  69. H. X. Wang, H. Zhao, and S. Liu, “Preparation and thermal conductivity of nanofluids consisting of SiO2-organic composite nanorods,” Journal of Inorganic and Organometallic Polymers and Materials, vol. 21, no. 4, pp. 946–949, 2011. View at Publisher · View at Google Scholar · View at Scopus
  70. N. Li, Y.-X. Zeng, Z.-Q. Liu, X.-W. Zhong, and S. Chen, “Nanofluids containing stearic acid-modified CuO nanorods and their thermal conductivity enhancements,” Nanoscience and Nanotechnology Letters, vol. 7, no. 4, pp. 314–317, 2015. View at Publisher · View at Google Scholar · View at Scopus
  71. A. Einstein, “Eine neue Bestimmung der Moleküldimensionen,” Annalen der Physik, vol. 324, no. 2, pp. 289–306, 1906. View at Publisher · View at Google Scholar
  72. H. C. Brinkman, “The viscosity of concentrated suspensions and solutions,” The Journal of Chemical Physics, vol. 20, no. 4, p. 571, 1952. View at Publisher · View at Google Scholar
  73. G. K. Batchelor, “The effect of Brownian motion on the bulk stress in a suspension of spherical particles,” Journal of Fluid Mechanics, vol. 83, no. 1, pp. 97–117, 1977. View at Publisher · View at Google Scholar
  74. B. C. Pak and Y. I. Cho, “Hydrodynamic and heat transfer study of dispersed fluids with submicron metallic oxide particles,” Experimental Heat Transfer, vol. 11, no. 2, pp. 151–170, 1998. View at Publisher · View at Google Scholar
  75. J. C. Maxwell, A Treatise on Electricity and Magnetism, Clarendon, Oxford, UK, 1873.
  76. D. A. Bruggeman, “Berechnung verschiedener physikalischer Konstanten von heterogenen Substanzen. I. Dielektrizitätskonstanten und Leitfähigkeiten der Mischkörper aus isotropen Substanzen,” Annalen der Physik, vol. 416, no. 7, pp. 636–664, 1935. View at Publisher · View at Google Scholar
  77. R. L. Hamilton and O. K. Crosser, “Thermal conductivity of heterogeneous two-component systems,” Industrial & Engineering Chemistry Fundamentals, vol. 1, no. 3, pp. 187–191, 1962. View at Publisher · View at Google Scholar
  78. W. Duangthongsuk and S. Wongwises, “An experimental study on the heat transfer performance and pressure drop of TiO2-water nanofluids flowing under a turbulent flow regime,” International Journal of Heat and Mass Transfer, vol. 53, no. 1–3, pp. 334–344, 2010. View at Publisher · View at Google Scholar · View at Scopus
  79. S. El Bécaye Maïga, S. J. Palm, C. T. Nguyen, G. Roy, and N. Galanis, “Heat transfer enhancement by using nanofluids in forced convection flows,” International Journal of Heat and Fluid Flow, vol. 26, no. 4, pp. 530–546, 2005. View at Publisher · View at Google Scholar · View at Scopus
  80. S. K. Das, N. Putra, P. Thiesen, and W. Roetzel, “Temperature dependence of thermal conductivity enhancement for nanofluids,” Journal of Heat Transfer, vol. 125, no. 4, pp. 567–574, 2003. View at Publisher · View at Google Scholar · View at Scopus
  81. M. Haghshenas Fard, M. N. Esfahany, and M. R. Talaie, “Numerical study of convective heat transfer of nanofluids in a circular tube two-phase model versus single-phase model,” International Communications in Heat and Mass Transfer, vol. 37, no. 1, pp. 91–97, 2010. View at Publisher · View at Google Scholar · View at Scopus
  82. S. Z. Heris, S. G. Etemad, and M. N. Esfahany, “Experimental investigation of oxide nanofluids laminar flow convective heat transfer,” International Communications in Heat and Mass Transfer, vol. 33, no. 4, pp. 529–535, 2006. View at Publisher · View at Google Scholar · View at Scopus
  83. M. Corcione, “Heat transfer features of buoyancy-driven nanofluids inside rectangular enclosures differentially heated at the sidewalls,” International Journal of Thermal Sciences, vol. 49, no. 9, pp. 1536–1546, 2010. View at Publisher · View at Google Scholar · View at Scopus
  84. H. Q. Xie and J. C. Wang, “Study on the thermal conductivity of SiC nanofluids,” Journal of the Chinese Ceramic Society, vol. 29, pp. 361–364, 2001. View at Google Scholar
  85. H. Xie, J. Wang, T. Xi, Y. Liu, F. Ai, and Q. Wu, “Thermal conductivity enhancement of suspensions containing nanosized alumina particles,” Journal of Applied Physics, vol. 91, no. 7, pp. 4568–4572, 2002. View at Publisher · View at Google Scholar · View at Scopus
  86. X. Zhang, H. Gu, and M. Fujii, “Experimental study on the effective thermal conductivity and thermal diffusivity of nanofluids,” International Journal of Thermophysics, vol. 27, no. 2, pp. 569–580, 2006. View at Publisher · View at Google Scholar · View at Scopus
  87. J. A. Eastman, S. U. S. Choi, S. Li, W. Yu, and L. J. Thompson, “Anomalously increased effective thermal conductivities of ethylene glycol-based nanofluids containing copper nanoparticles,” Applied Physics Letters, vol. 78, no. 6, pp. 718–720, 2001. View at Publisher · View at Google Scholar · View at Scopus
  88. H. E. Patel, S. K. Das, T. Sundararajan, A. Sreekumaran Nair, B. George, and T. Pradeep, “Thermal conductivities of naked and monolayer protected metal nanoparticle based nanofluids: manifestation of anomalous enhancement and chemical effects,” Applied Physics Letters, vol. 83, no. 14, pp. 2931–2933, 2003. View at Publisher · View at Google Scholar · View at Scopus
  89. H. Xie, H. Lee, W. Youn, and M. Choi, “Nanofluids containing multiwalled carbon nanotubes and their enhanced thermal conductivities,” Journal of Applied Physics, vol. 94, no. 8, pp. 4967–4971, 2003. View at Publisher · View at Google Scholar · View at Scopus
  90. B. Yang and Z. H. Han, “Thermal conductivity enhancement in water-in-FC72 nanoemulsion fluids,” Applied Physics Letters, vol. 88, no. 26, Article ID 261914, 2006. View at Publisher · View at Google Scholar · View at Scopus
  91. J. Jeon, S. Park, and B. J. Lee, “Optical property of blended plasmonic nanofluid based on gold nanorods,” Optics Express, vol. 22, no. 4, pp. A1101–A1111, 2014. View at Publisher · View at Google Scholar · View at Scopus
  92. W. Yu and H. Xie, “A review on nanofluids: preparation, stability mechanisms, and applications,” Journal of Nanomaterials, vol. 2012, Article ID 435873, 17 pages, 2012. View at Publisher · View at Google Scholar
  93. A. Ghadimi, R. Saidur, and H. S. C. Metselaar, “A review of nanofluid stability properties and characterization in stationary conditions,” International Journal of Heat and Mass Transfer, vol. 54, no. 17-18, pp. 4051–4068, 2011. View at Publisher · View at Google Scholar · View at Scopus
  94. M.-S. Liu, M. C.-C. Lin, C. Y. Tsai, and C.-C. Wang, “Enhancement of thermal conductivity with Cu for nanofluids using chemical reduction method,” International Journal of Heat and Mass Transfer, vol. 49, no. 17-18, pp. 3028–3033, 2006. View at Publisher · View at Google Scholar · View at Scopus
  95. Y. Xuan and Q. Li, “Heat transfer enhancement of nanofluids,” Journal of Applied Physics, vol. 97, pp. 1–4, 2005. View at Google Scholar
  96. T.-K. Hong, H.-S. Yang, and C. J. Choi, “Study of the enhanced thermal conductivity of Fe nanofluids,” Journal of Applied Physics, vol. 97, no. 6, Article ID 064311, 2005. View at Publisher · View at Google Scholar · View at Scopus
  97. A. S. Putnam, D. G. Cahill, and P. V. Braun, “Thermal conductivity of nanoparticle suspensions,” Journal of Applied Physics, vol. 99, pp. 1–6, 2006. View at Google Scholar
  98. M.-S. Liu, M. Ching-Cheng Lin, I.-T. Huang, and C.-C. Wang, “Enhancement of thermal conductivity with carbon nanotube for nanofluids,” International Communications in Heat and Mass Transfer, vol. 32, no. 9, pp. 1202–1210, 2005. View at Publisher · View at Google Scholar · View at Scopus
  99. S. U. S. Choi, Z. G. Zhang, W. Yu, F. E. Lockwood, and E. A. Grulke, “Anomalous thermal conductivity enhancement in nanotube suspensions,” Applied Physics Letters, vol. 79, no. 14, pp. 2252–2254, 2001. View at Publisher · View at Google Scholar · View at Scopus
  100. V. Segal, A. Hjortsberg, A. Rabinovich, D. Nattrass, and K. Raj, “AC (60 Hz) and impulse breakdown strength of a colloidal fluid based on transformer oil and magnetite nanoparticles,” in Proceedings of the IEEE International Symposium on Electrical Insulation, pp. 619–622, Arlington, Va, USA, June 1998. View at Publisher · View at Google Scholar
  101. P. P. Sartoratto, A. V. Neto, E. C. Lima, A. L. R. de Sá, and P. C. Morais, “Preparation and electrical properties of oil-based magnetic fluids,” Journal of Applied Physics, vol. 97, no. 10, pp. 10Q917.1–10Q917.3, 2005. View at Publisher · View at Google Scholar
  102. J. Li, Z. Zhang, P. Zou, S. Grzybowski, and M. Zahn, “Preparation of a vegetable oil-based nanofluid and investigation of its breakdown and dielectric properties,” IEEE Transactions on Dielectrics and Electrical Insulation, vol. 28, no. 8, pp. 43–50, 2012. View at Publisher · View at Google Scholar
  103. M. Hanai, S. Hosomi, H. Kojima, N. Hayakawa, and H. Okubo, “Dependence of TiO2 and ZnO nanoparticle concentration on electrical insulation characteristics of insulating oil,” in Proceedings of the IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP '13), pp. 780–783, IEEE, Shenzhen, China, October 2013. View at Publisher · View at Google Scholar · View at Scopus
  104. Y. Du, Y. Lv, C. Li et al., “Effect of electron shallow trap on breakdown performance of transformer oil-based nanofluids,” Journal of Applied Physics, vol. 110, no. 10, Article ID 104104, pp. 1–4, 2011. View at Publisher · View at Google Scholar · View at Scopus
  105. Y. Zhong, Y. Lv, C. Li et al., “Insulating properties and charge characteristics of natural ester fluid modified by TiO2 semiconductive nanoparticles,” IEEE Transactions on Dielectrics and Electrical Insulation, vol. 20, no. 1, pp. 135–140, 2013. View at Publisher · View at Google Scholar · View at Scopus
  106. J. Liu, L. J. Zhou, G. N. Wu, Y. F. Zhao, P. Liu, and Q. Peng, “Dielectric frequency response of oil-paper composite insulation modified by nanoparticles,” IEEE Transactions on Dielectrics and Electrical Insulation, vol. 19, no. 2, pp. 510–520, 2012. View at Publisher · View at Google Scholar · View at Scopus
  107. M. Saeedinia, M. A. Akhavan-Behabadi, and P. Razi, “Thermal and rheological characteristics of CuO-Base oil nanofluid flow inside a circular tube,” International Communications in Heat and Mass Transfer, vol. 39, no. 1, pp. 152–159, 2012. View at Publisher · View at Google Scholar · View at Scopus
  108. C. J. Ho, W. K. Liu, Y. S. Chang, and C. C. Lin, “Natural convection heat transfer of alumina-water nanofluid in vertical square enclosures: an experimental study,” International Journal of Thermal Sciences, vol. 49, no. 8, pp. 1345–1353, 2010. View at Publisher · View at Google Scholar · View at Scopus
  109. R. S. Vajjha, D. K. Das, and B. M. Mahagaonkar, “Density measurement of different nanofluids and their comparison with theory,” Petroleum Science and Technology, vol. 27, no. 6, pp. 612–624, 2009. View at Publisher · View at Google Scholar · View at Scopus
  110. A. D. Sommers and K. L. Yerkes, “Experimental investigation into the convective heat transfer and system-level effects of Al2O3-propanol nanofluid,” Journal of Nanoparticle Research, vol. 12, no. 3, pp. 1003–1014, 2010. View at Publisher · View at Google Scholar · View at Scopus
  111. T. P. Teng, C. M. Cheng, and F. Y. Pai, “Preparation and characterization of carbon nanofluid by a plasma arc nanoparticles synthesis system,” Nanoscale Research Letters, vol. 6, article 293, 2011. View at Publisher · View at Google Scholar
  112. R. Vajjha and D. Das, “Measurements of specific heat and density of Al2O3 nanofluid,” in Proceedings of the Mesoscopic, Nanoscopic and Macroscopic Materials: Proceedings of the International Workshop on Mesoscopic, Nanoscopic and Macroscopic Materials (IWMNMM '08), vol. 40, pp. 361–371, Bhubaneswar, India, January 2008. View at Publisher · View at Google Scholar
  113. I. M. Mahbubul, R. Saidur, and M. A. Amalina, “Thermal conductivity, viscosity and density of R141b refrigerant based nanofluid,” Procedia Engineering, vol. 56, pp. 310–315, 2013. View at Publisher · View at Google Scholar
  114. A. T. Utomo, H. Poth, P. T. Robbins, and A. W. Pacek, “Experimental and theoretical studies of thermal conductivity, viscosity and heat transfer coefficient of titania and alumina nanofluids,” International Journal of Heat and Mass Transfer, vol. 55, no. 25-26, pp. 7772–7781, 2012. View at Publisher · View at Google Scholar · View at Scopus
  115. J. Albadr, S. Tayal, and M. Alasadi, “Heat transfer through heat exchanger using Al2O3 nanofluid at different concentrations,” Case Studies in Thermal Engineering, vol. 1, no. 1, pp. 38–44, 2013. View at Publisher · View at Google Scholar · View at Scopus
  116. M. M. Heyhat, F. Kowsary, A. M. Rashidi, S. Alem Varzane Esfehani, and A. Amrollahi, “Experimental investigation of turbulent flow and convective heat transfer characteristics of alumina water nanofluids in fully developed flow regime,” International Communications in Heat and Mass Transfer, vol. 39, no. 8, pp. 1272–1278, 2012. View at Publisher · View at Google Scholar · View at Scopus
  117. A. Zamzamian, S. N. Oskouie, A. Doosthoseini, A. Joneidi, and M. Pazouki, “Experimental investigation of forced convective heat transfer coefficient in nanofluids of Al2O3/EG and CuO/EG in a double pipe and plate heat exchangers under turbulent flow,” Experimental Thermal and Fluid Science, vol. 35, no. 3, pp. 495–502, 2011. View at Publisher · View at Google Scholar · View at Scopus
  118. Q. Li and Y. Xuan, “Convective heat transfer and flow characteristics of Cu-water nanofluid,” Science in China Series E: Technolgical Science, vol. 45, no. 4, pp. 408–416, 2002. View at Publisher · View at Google Scholar
  119. Y. Xuan and Q. Li, “Investigation on convective heat transfer and flow features of nanofluids,” Journal of Heat Transfer, vol. 125, no. 1, pp. 151–155, 2003. View at Publisher · View at Google Scholar · View at Scopus
  120. X. Wang, X. Xu, and S. U. S. Choi, “Thermal conductivity of nanoparticle—fluid mixture,” Journal of Thermophysics and Heat Transfer, vol. 13, no. 4, pp. 474–480, 1999. View at Publisher · View at Google Scholar
  121. S. W. Lee, S. D. Park, S. Kang, I. C. Bang, and J. H. Kim, “Investigation of viscosity and thermal conductivity of SiC nanofluids for heat transfer applications,” International Journal of Heat and Mass Transfer, vol. 54, no. 1–3, pp. 433–438, 2011. View at Publisher · View at Google Scholar · View at Scopus
  122. B. Aladag, S. Halelfadl, N. Doner, T. Maré, S. Duret, and P. Estellé, “Experimental investigations of the viscosity of nanofluids at low temperatures,” Applied Energy, vol. 97, pp. 876–880, 2012. View at Publisher · View at Google Scholar · View at Scopus
  123. Y. Ding, H. Alias, D. Wen, and R. A. Williams, “Heat transfer of aqueous suspensions of carbon nanotubes (CNT nanofluids),” International Journal of Heat and Mass Transfer, vol. 49, no. 1-2, pp. 240–250, 2006. View at Publisher · View at Google Scholar · View at Scopus
  124. Z. Wu, L. Wang, B. Sundén, and L. Wadsö, “Aqueous carbon nanotube nanofluids and their thermal performance in a helical heat exchanger,” Applied Thermal Engineering, vol. 96, pp. 364–371, 2016. View at Publisher · View at Google Scholar · View at Scopus
  125. K. Khanafer and K. Vafai, “A critical synthesis of thermophysical characteristics of nanofluids,” International Journal of Heat and Mass Transfer, vol. 54, no. 19-20, pp. 4410–4428, 2011. View at Publisher · View at Google Scholar · View at Scopus
  126. P. K. Namburu, D. P. Kulkarni, D. Misra, and D. K. Das, “Viscosity of copper oxide nanoparticles dispersed in ethylene glycol and water mixture,” Experimental Thermal and Fluid Science, vol. 32, no. 2, pp. 397–402, 2007. View at Publisher · View at Google Scholar · View at Scopus
  127. C. T. Nguyen, F. Desgranges, G. Roy et al., “Temperature and particle-size dependent viscosity data for water-based nanofluids—hysteresis phenomenon,” International Journal of Heat and Fluid Flow, vol. 28, no. 6, pp. 1492–1506, 2007. View at Publisher · View at Google Scholar · View at Scopus
  128. C. T. Nguyen, F. Desgranges, N. Galanis et al., “Viscosity data for Al2O3-water nanofluid—hysteresis: is heat transfer enhancement using nanofluids reliable?” International Journal of Thermal Sciences, vol. 47, no. 2, pp. 103–111, 2008. View at Publisher · View at Google Scholar · View at Scopus
  129. D. P. Kulkarni, D. K. Das, and R. S. Vajjha, “Application of nanofluids in heating buildings and reducing pollution,” Applied Energy, vol. 86, no. 12, pp. 2566–2573, 2009. View at Publisher · View at Google Scholar · View at Scopus
  130. E. V. Timofeeva, J. L. Routbort, and D. Singh, “Particle shape effects on thermophysical properties of alumina nanofluids,” Journal of Applied Physics, vol. 106, no. 1, Article ID 014304, 2009. View at Publisher · View at Google Scholar · View at Scopus
  131. T. Yiamsawas, A. S. Dalkilic, O. Mahian, and S. Wongwises, “Measurement and correlation of the viscosity of water-based Al2O3 and TiO2 nanofluids in high temperatures and comparisons with literature reports,” Journal of Dispersion Science and Technology, vol. 34, no. 12, pp. 1697–1703, 2013. View at Publisher · View at Google Scholar · View at Scopus
  132. Y. Xuan and W. Roetzel, “Conceptions for heat transfer correlation of nanofluids,” International Journal of Heat and Mass Transfer, vol. 43, no. 19, pp. 3701–3707, 2000. View at Publisher · View at Google Scholar · View at Scopus
  133. H. O'Hanley, J. Buongiorno, T. McKrell, and L.-W. Hu, “Measurement and model validation of nanofluid specific heat capacity with differential scanning calorimetry,” Advances in Mechanical Engineering, vol. 4, Article ID 181079, 2012. View at Publisher · View at Google Scholar
  134. S. M. S. Murshed, “Determination of effective specific heat of nanofluids,” Journal of Experimental Nanoscience, vol. 6, no. 5, pp. 539–546, 2011. View at Publisher · View at Google Scholar · View at Scopus
  135. Y. Li, J. Fernández-Seara, K. Du, Á. Á. Pardiñas, L. L. Latas, and W. Jiang, “Experimental investigation on heat transfer and pressure drop of ZnO/ethylene glycol-water nanofluids in transition flow,” Applied Thermal Engineering, vol. 93, pp. 537–548, 2016. View at Publisher · View at Google Scholar · View at Scopus
  136. L.-P. Zhou, B.-X. Wang, X.-F. Peng, X.-Z. Du, and Y.-P. Yang, “On the specific heat capacity of CuO nanofluid,” Advances in Mechanical Engineering, vol. 2, Article ID 172085, 2010. View at Publisher · View at Google Scholar
  137. S. Zhou and R. Ni, “Measurement of the specific heat capacity of water-based Al2O3 nanofluid,” Applied Physics Letters, vol. 92, no. 9, Article ID 093123, 2008. View at Publisher · View at Google Scholar
  138. E. V. Timofeeva, W. Yu, D. M. France, D. Singh, and J. L. Routbort, “Nanofluids for heat transfer: an engineering approach,” Nanoscale Research Letters, vol. 6, article 182, 7 pages, 2011. View at Publisher · View at Google Scholar · View at Scopus
  139. J. R. Satti, D. K. Das, and D. Ray, “Specific heat measurements of five different propylene glycol based nanofluids and development of a new correlation,” International Journal of Heat and Mass Transfer, vol. 94, pp. 343–353, 2016. View at Publisher · View at Google Scholar · View at Scopus
  140. D. Cabaleiro, C. Gracia-Fernández, J. L. Legido, and L. Lugo, “Specific heat of metal oxide nanofluids at high concentrations for heat transfer,” International Journal of Heat and Mass Transfer, vol. 88, pp. 872–879, 2015. View at Publisher · View at Google Scholar · View at Scopus
  141. J. Choi and Y. Zhang, “Numerical simulation of laminar forced convection heat transfer of Al2O3-water nanofluid in a pipe with return bend,” International Journal of Thermal Sciences, vol. 55, pp. 90–102, 2012. View at Publisher · View at Google Scholar · View at Scopus
  142. T. L. Bergman, “Effect of reduced specific heats of nanofluids on single phase, laminar internal forced convection,” International Journal of Heat and Mass Transfer, vol. 52, no. 5-6, pp. 1240–1244, 2009. View at Publisher · View at Google Scholar · View at Zentralblatt MATH · View at Scopus
  143. J. Lee and I. Mudawar, “Assessment of the effectiveness of nanofluids for single-phase and two-phase heat transfer in micro-channels,” International Journal of Heat and Mass Transfer, vol. 50, no. 3-4, pp. 452–463, 2007. View at Publisher · View at Google Scholar · View at Scopus
  144. M. N. Pantzali, A. G. Kanaris, K. D. Antoniadis, A. A. Mouza, and S. V. Paras, “Effect of nanofluids on the performance of a miniature plate heat exchanger with modulated surface,” International Journal of Heat and Fluid Flow, vol. 30, no. 4, pp. 691–699, 2009. View at Publisher · View at Google Scholar · View at Scopus
  145. S. Sonawane, K. Patankar, A. Fogla, B. Puranik, U. Bhandarkar, and S. Sunil Kumar, “An experimental investigation of thermo-physical properties and heat transfer performance of Al2O3-Aviation Turbine Fuel nanofluids,” Applied Thermal Engineering, vol. 31, no. 14-15, pp. 2841–2849, 2011. View at Publisher · View at Google Scholar · View at Scopus
  146. V. Kumaresan and R. Velraj, “Experimental investigation of the thermo-physical properties of water-ethylene glycol mixture based CNT nanofluids,” Thermochimica Acta, vol. 545, pp. 180–186, 2012. View at Publisher · View at Google Scholar
  147. Z. Said, R. Saidur, M. A. Sabiha, N. A. Rahim, and M. R. Anisur, “Thermophysical properties of Single Wall Carbon Nanotubes and its effect on exergy efficiency of a flat plate solar collector,” Solar Energy, vol. 115, pp. 757–769, 2015. View at Publisher · View at Google Scholar · View at Scopus
  148. E. De Robertis, E. H. H. Cosme, R. S. Neves et al., “Application of the modulated temperature differential scanning calorimetry technique for the determination of the specific heat of copper nanofluids,” Applied Thermal Engineering, vol. 41, pp. 10–17, 2012. View at Publisher · View at Google Scholar · View at Scopus
  149. M. Saeedinia, M. A. Akhavan-Behabadi, and M. Nasr, “Experimental study on heat transfer and pressure drop of nanofluid flow in a horizontal coiled wire inserted tube under constant heat flux,” Experimental Thermal and Fluid Science, vol. 36, pp. 158–168, 2012. View at Publisher · View at Google Scholar · View at Scopus
  150. D. Gangacharyulu, Preparationg and Characterization of Nanofluids and Some Investigation in Biological Applications, Mechanical Engineering Carbondale Southern Illinois University, 2010.
  151. M. X. Ho and C. Pan, “Optimal concentration of alumina nanoparticles in molten hitec salt to maximize its specific heat capacity,” International Journal of Heat and Mass Transfer, vol. 70, pp. 174–184, 2014. View at Publisher · View at Google Scholar · View at Scopus
  152. M. Fakoor Pakdaman, M. A. Akhavan-Behabadi, and P. Razi, “An experimental investigation on thermo-physical properties and overall performance of MWCNT/heat transfer oil nanofluid flow inside vertical helically coiled tubes,” Experimental Thermal and Fluid Science, vol. 40, pp. 103–111, 2012. View at Publisher · View at Google Scholar · View at Scopus
  153. H. Masuda, A. Ebata, K. Teramae, and N. Hishinuma, “Alteration of thermal conductivity and viscosity of liquid by dispersing ultra-fine particles. dispersion of Al2O3, SiO2 and TiO2 ultra-fine particles,” Netsu Bussei, vol. 7, no. 4, pp. 227–233, 1993. View at Publisher · View at Google Scholar
  154. S. Lee, S. U.-S. Choi, S. Li, and J. A. Eastman, “Measuring thermal conductivity of fluids containing oxide nano particles,” Journal of Heat Transfer, vol. 121, no. 2, pp. 280–289, 1999. View at Publisher · View at Google Scholar
  155. C. H. Li and G. P. Peterson, “Experimental investigation of temperature and volume fraction variations on the effective thermal conductivity of nanoparticle suspensions (nanofluids),” Journal of Applied Physics, vol. 99, no. 8, Article ID 084314, 2006. View at Publisher · View at Google Scholar · View at Scopus
  156. H. Li, L. Wang, Y. He, Y. Hu, J. Zhu, and B. Jiang, “Experimental investigation of thermal conductivity and viscosity of ethylene glycol based ZnO nanofluids,” Applied Thermal Engineering, vol. 88, pp. 363–368, 2014. View at Publisher · View at Google Scholar · View at Scopus
  157. W. Rashmi, A. F. Ismail, I. Sopyan et al., “Stability and thermal conductivity enhancement of carbon nanotube nanofluid using gum arabic,” Journal of Experimental Nanoscience, vol. 6, no. 6, pp. 567–579, 2011. View at Publisher · View at Google Scholar · View at Scopus
  158. T. Maré, S. Halelfadl, O. Sow, P. Estellé, S. Duret, and F. Bazantay, “Comparison of the thermal performances of two nanofluids at low temperature in a plate heat exchanger,” Experimental Thermal and Fluid Science, vol. 35, no. 8, pp. 1535–1543, 2011. View at Publisher · View at Google Scholar · View at Scopus
  159. M. Jahanshahi, S. F. Hosseinizadeh, M. Alipanah, A. Dehghani, and G. R. Vakilinejad, “Numerical simulation of free convection based on experimental measured conductivity in a square cavity using water/SiO2 nanofluid,” International Communications in Heat and Mass Transfer, vol. 37, no. 6, pp. 687–694, 2010. View at Publisher · View at Google Scholar · View at Scopus
  160. A. G. A. Nnanna, “Experimental model of temperature-driven nanofluid,” Journal of Heat Transfer, vol. 129, no. 6, pp. 697–704, 2007. View at Publisher · View at Google Scholar · View at Scopus
  161. M. Abbas, R. G. Walvekar, M. T. Hajibeigy, and F. S. Javadi, Efficient Air—Condition Unit By Using Nano—Refrigerant, pp. 87–88, 2013
  162. A. Amiri, M. Shanbedi, H. Eshghi et al., “Highly dispersed multiwalled carbon nanotubes decorated with ag nano particles in water and experimental investigation of the thermophysical properties,” The Journal of Physical Chemistry, vol. 116, no. 5, pp. 3369–3375, 2012. View at Publisher · View at Google Scholar
  163. T. R. Barrett, S. Robinson, K. Flinders, A. Sergis, and Y. Hardalupas, “Investigating the use of nanofluids to improve high heat flux cooling systems,” Fusion Engineering and Design, vol. 88, no. 9-10, pp. 2594–2597, 2013. View at Publisher · View at Google Scholar · View at Scopus
  164. S. Bi, K. Guo, Z. Liu, and J. Wu, “Performance of a domestic refrigerator using TiO2-R600a nano-refrigerant as working fluid,” Energy Conversion and Management, vol. 52, no. 1, pp. 733–737, 2011. View at Publisher · View at Google Scholar · View at Scopus
  165. S. Bi, L. Shi, and L. Zhang, “Application of nano particles in domestic refrigerators,” Applied Thermal Engineering, vol. 28, no. 14-15, pp. 1834–1843, 2008. View at Publisher · View at Google Scholar
  166. R. Chein and J. Chuang, “Experimental microchannel heat sink performance studies using nanofluids,” International Journal of Thermal Sciences, vol. 46, no. 1, pp. 57–66, 2007. View at Publisher · View at Google Scholar · View at Scopus
  167. Y. Hwang, J. K. Lee, C. H. Lee et al., “Stability and thermal conductivity characteristics of nanofluids,” Thermochimica Acta, vol. 455, no. 1-2, pp. 70–74, 2007. View at Publisher · View at Google Scholar · View at Scopus
  168. G. Colangelo, E. Favale, A. De Risi, and D. Laforgia, “A new solution for reduced sedimentation flat panel solar thermal collector using nanofluids,” Applied Energy, vol. 111, pp. 80–93, 2013. View at Publisher · View at Google Scholar · View at Scopus
  169. G. Colangelo, E. Favale, A. de Risi, and D. Laforgia, “Results of experimental investigations on the heat conductivity of nanofluids based on diathermic oil for high temperature applications,” Applied Energy, vol. 97, pp. 828–833, 2012. View at Publisher · View at Google Scholar · View at Scopus
  170. T. Coumaressin and K. Palaniradja, “Performance analysis of a refrigeration system using nano fluid,” International Journal of Advanced Mechanical Engineering, vol. 4, no. 4, pp. 459–470, 2014. View at Google Scholar
  171. S. Eiamsa-ard, K. Kiatkittipong, and W. Jedsadaratanachai, “Heat transfer enhancement of TiO2/water nanofluid in a heat exchanger tube equipped with overlapped dual twisted-tapes,” Engineering Science and Technology, vol. 18, no. 3, pp. 336–350, 2015. View at Publisher · View at Google Scholar
  172. R. Hajian, M. Layeghi, and K. Abbaspour Sani, “Experimental study of nanofluid effects on the thermal performance with response time of heat pipe,” Energy Conversion and Management, vol. 56, pp. 63–68, 2012. View at Publisher · View at Google Scholar · View at Scopus
  173. Y. He, Y. Jin, H. Chen, Y. Ding, D. Cang, and H. Lu, “Heat transfer and flow behaviour of aqueous suspensions of TiO2 nanoparticles (nanofluids) flowing upward through a vertical pipe,” International Journal of Heat and Mass Transfer, vol. 50, no. 11-12, pp. 2272–2281, 2007. View at Publisher · View at Google Scholar · View at Scopus
  174. Y. J. Hwang, Y. C. Ahn, H. S. Shin et al., “Investigation on characteristics of thermal conductivity enhancement of nanofluids,” Current Applied Physics, vol. 6, no. 6, pp. 1068–1071, 2006. View at Publisher · View at Google Scholar · View at Scopus
  175. S. P. Jang and S. U. S. Choi, “Cooling performance of a microchannel heat sink with nanofluids,” Applied Thermal Engineering, vol. 26, no. 17-18, pp. 2457–2463, 2006. View at Publisher · View at Google Scholar · View at Scopus
  176. C.-S. Jwo, L.-Y. Jeng, T.-P. Teng, and H. Chang, “Effects of nanolubricant on performance of hydrocarbon refrigerant system,” Journal of Vacuum Science & Technology B, vol. 27, no. 3, pp. 1473–1477, 2009. View at Publisher · View at Google Scholar
  177. P. Keblinski, J. A. Eastman, and D. G. Cahill, “Nanofluids for thermal transport,” Materials Today, vol. 8, no. 6, pp. 36–44, 2005. View at Publisher · View at Google Scholar · View at Scopus
  178. D. S. Kumar and R. Elansezhian, “Experimental study on Al2O3-R134a nano refrigerant in refrigeration system,” International Journal of Modern Engineering Research, vol. 2, no. 5, pp. 3927–3929, 2012. View at Google Scholar
  179. R. R. Kumar, K. Sridhar, and M. Narasimha, “Heat transfer enhancement in domestic refrigerator using R600a/mineral oil/nano-Al2O3 as working fluid,” International Journal of Computational Engineering Research, vol. 3, no. 4, pp. 42–50, 2013. View at Google Scholar
  180. J. H. Lee, K. S. Hwanga, S. P. Jang et al., “Effective viscosities and thermal conductivities of aqueous nanofluids containing low volume concentrations of Al2O3 nano particles,” International Journal of Heat and Mass Transfer, vol. 51, no. 11-12, pp. 2651–2656, 2008. View at Publisher · View at Google Scholar
  181. C.-Y. Lin, J.-C. Wang, and T.-C. Chen, “Analysis of suspension and heat transfer characteristics of Al2O3 nanofluids prepared through ultrasonic vibration,” Applied Energy, vol. 88, no. 12, pp. 4527–4533, 2011. View at Publisher · View at Google Scholar · View at Scopus
  182. M. Kole and T. K. Dey, “Thermal conductivity and viscosity of Al2O3 nanofluid based on car engine coolant,” Journal of Physics D: Applied Physics, vol. 43, no. 31, Article ID 315501, 2010. View at Publisher · View at Google Scholar · View at Scopus
  183. M. Mehrali, E. Sadeghinezhad, M. A. Rosen et al., “Heat transfer and entropy generation for laminar forced convection flow of graphene nanoplatelets nanofluids in a horizontal tube,” International Communications in Heat and Mass Transfer, vol. 66, pp. 23–31, 2015. View at Publisher · View at Google Scholar · View at Scopus
  184. C. T. Nguyen, G. Roy, N. Galanis, and S. Suiro, “Heat transfer enhancement by using Al2O3-water nanofluid in a liquid cooling system for microprocessors,” in Proceedings of the 4th International Conference on Heat Transfer, Thermal Engineering And Environment (WSEAS '06), pp. 103–108, Elounda, Greece, August 2006.
  185. B. C. Pak and Y. I. Cho, “Hydrodynamic and heat transfer study of dispersed fluids with submicron metallic oxide particles,” Experimental Heat Transfer, vol. 11, no. 2, pp. 151–170, 1998. View at Publisher · View at Google Scholar · View at Scopus
  186. M. N. Pantzali, A. A. Mouza, and S. V. Paras, “Investigating the efficacy of nanofluids as coolants in plate heat exchangers (PHE),” Chemical Engineering Science, vol. 64, no. 14, pp. 3290–3300, 2009. View at Publisher · View at Google Scholar · View at Scopus
  187. A. de Risi, M. Marco, C. Gianpiero, and L. Domenico, “High efficiency nanofluid cooling system for wind turbines,” Thermal Science, vol. 18, no. 2, pp. 543–554, 2014. View at Publisher · View at Google Scholar
  188. R. K. Sabareesh, N. Gobinath, V. Sajith, S. Das, and C. B. Sobhan, “Application des nanoparticules de TiO2 en tant que lubrifiant et additif dans les systémes frigorifiques à compression de vapeur—une étude expérimentale,” International Journal of Refrigeration, vol. 35, no. 7, pp. 1989–1996, 2012. View at Publisher · View at Google Scholar
  189. R. Saidur, K. Y. Leong, and H. A. Mohammad, “A review on applications and challenges of nanofluids,” Renewable and Sustainable Energy Reviews, vol. 15, no. 3, pp. 1646–1668, 2011. View at Publisher · View at Google Scholar · View at Scopus
  190. A. Sergis and Y. Hardalupas, “Revealing the complex conduction heat transfer mechanism of nanofluids,” Nanoscale Research Letters, vol. 10, no. 1, article 250, 2015. View at Publisher · View at Google Scholar · View at Scopus
  191. H. Shokouhmand, M. Ghazvini, and J. Shabanian, “Performance analysis of using nanofluids in microchannel heat sink in different flow regimes and its simulation using artificial neural network,” in Proceedings of the World Congress on Engineering (WCE '08), vol. 3, pp. 4–9, London, UK, July 2008.
  192. S.-C. Tzeng, C.-W. Lin, and K. D. Huang, “Heat transfer enhancement of nanofluids in rotary blade coupling of four-wheel-drive vehicles,” Acta Mechanica, vol. 179, no. 1-2, pp. 11–23, 2005. View at Publisher · View at Google Scholar · View at Zentralblatt MATH · View at Scopus
  193. D. T. Wasan and A. D. Nikolov, “Spreading of nanofluids on solids,” Nature, vol. 423, no. 6936, pp. 156–159, 2003. View at Publisher · View at Google Scholar · View at Scopus
  194. D. Wen and Y. Ding, “Experimental investigation into convective heat transfer of nanofluids at the entrance region under laminar flow conditions,” International Journal of Heat and Mass Transfer, vol. 47, no. 24, pp. 5181–5188, 2004. View at Publisher · View at Google Scholar · View at Scopus
  195. K. V. Wong and O. D. Leon, “Applications of nanofluids: current and future,” Advances in Mechanical Engineering, vol. 2, Article ID 519659, 2010. View at Publisher · View at Google Scholar
  196. H. Xie and L. Chen, “Adjustable thermal conductivity in carbon nanotube nanofluids,” Physics Letters A, vol. 373, no. 21, pp. 1861–1864, 2009. View at Publisher · View at Google Scholar · View at Scopus
  197. Y. Xuan and Q. Li, “Heat transfer enhancement of nanofluids,” International Journal of Heat and Fluid Flow, vol. 21, no. 1, pp. 58–64, 2000. View at Publisher · View at Google Scholar · View at Scopus
  198. Y. Xuan and W. Roetzel, “Conceptions for heat transfer correlation of nanofluids,” International Journal of Heat and Mass Transfer, vol. 43, no. 19, pp. 3701–3707, 2000. View at Publisher · View at Google Scholar · View at Zentralblatt MATH · View at Scopus
  199. Q.-Z. Xue, “Model for effective thermal conductivity of nanofluids,” Physics Letters A, vol. 307, no. 5-6, pp. 313–317, 2003. View at Publisher · View at Google Scholar · View at Scopus
  200. Y. Yang, Z. G. Zhang, E. A. Grulke, W. B. Anderson, and G. Wu, “Heat transfer properties of nanoparticle-in-fluid dispersions (nanofluids) in laminar flow,” International Journal of Heat and Mass Transfer, vol. 48, no. 6, pp. 1107–1116, 2005. View at Publisher · View at Google Scholar · View at Scopus
  201. W. Yu, D. M. France, S. U. S. Choi, and L. J. Routbort, Review and Assessment of Nanofluid Technology For Transportation and Other Applications, 2007.
  202. W. Yu and H. Xie, “A review on nanofluids: preparation, stability mechanisms, and applications,” Journal of Nanomaterials, vol. 2012, Article ID 435873, 17 pages, 2012. View at Publisher · View at Google Scholar · View at Scopus
  203. X.-Q. Wang and A. S. Mujumdar, “A review on nanofluids—part II: experiments and applications,” Brazilian Journal of Chemical Engineering, vol. 25, no. 4, pp. 631–648, 2008. View at Publisher · View at Google Scholar · View at Scopus
  204. D. K. Devendiran and V. A. Amirtham, “A review on preparation, characterization, properties and applications of nanofluids,” Renewable & Sustainable Energy Reviews, vol. 60, pp. 21–40, 2016. View at Publisher · View at Google Scholar · View at Scopus
  205. http://www.discoversensors.ie/ProjectDocumentation/Nanofluids-to-Improve-Efficiency-of-Geothermal-Model.pdf