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Showing papers on "Nanofluid published in 2011"


Journal ArticleDOI
TL;DR: It has been found nan ofluids have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional fluids, which can be considered as one of the key parameters for enhanced performances for many of the applications of nanofluids.
Abstract: Nanofluids are potential heat transfer fluids with enhanced thermophysical properties and heat transfer performance can be applied in many devices for better performances (i.e. energy, heat transfer and other performances). In this paper, a comprehensive literature on the applications and challenges of nanofluids have been compiled and reviewed. Latest up to date literatures on the applications and challenges in terms of PhD and Master thesis, journal articles, conference proceedings, reports and web materials have been reviewed and reported. Recent researches have indicated that substitution of conventional coolants by nanofluids appears promising. Specific application of nanofluids in engine cooling, solar water heating, cooling of electronics, cooling of transformer oil, improving diesel generator efficiency, cooling of heat exchanging devices, improving heat transfer efficiency of chillers, domestic refrigerator-freezers, cooling in machining, in nuclear reactor and defense and space have been reviewed and presented. Authors also critically analyzed some of the applications and identified research gaps for further research. Moreover, challenges and future directions of applications of nanofluids have been reviewed and presented in this paper. Based on results available in the literatures, it has been found nanofluids have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional fluids. This can be considered as one of the key parameters for enhanced performances for many of the applications of nanofluids. Because of its superior thermal performances, latest up to date literatures on this property have been summarized and presented in this paper as well. However, few barriers and challenges that have been identified in this review must be addressed carefully before it can be fully implemented in the industrial applications.

1,558 citations


Journal ArticleDOI
TL;DR: In this article, two empirical correlations for predicting the effective thermal conductivity and dynamic viscosity of nanofluids, based on a high number of experimental data available in the literature, are proposed and discussed.

971 citations


01 Jan 2011
TL;DR: In this paper, the non-similar solutions are presented which depend on the Magnetic parameter M respectively, the obtained equations have been solved by explicit finite difference method and temperature and concentration profiles are discussed for the different values of the above parameters with different time steps.
Abstract: Unsteady heat and mass flow of a nanofluid past a stretching sheet with thermal radiation in the presence of magnetic field is studied. To obtain non-similar equation, continuity, momentum, energy and concentration equations have been non-dimensionalised by usual transformation. The non-similar solutions are presented here which depends on the Magnetic parameter M respectively . The obtained equations have been solved by explicit finite difference method. The temperature and concentration profiles are discussed for the different values of the above parameters with different time steps.

956 citations


Journal ArticleDOI
TL;DR: In this article, the stability of nanofluids is discussed as it has a major role in heat transfer enhancement for further possible applications, and general stabilization methods as well as various types of instruments for stability inspection.

948 citations


Journal ArticleDOI
TL;DR: A critical synthesis of the variants within the thermophysical properties of nanofluids is presented in this article, where the experimental results for the effective thermal conductivity and viscosity reported by several authors are in disagreement.

943 citations


Journal ArticleDOI
TL;DR: In this article, Al2O3-Cu hybrid particles have been synthesized by hydrogen reduction technique from the powder mixture of Al 2O3 and CuO in 90:10 weight proportions obtained from a chemical route synthesis and the experimental results have shown that both thermal conductivity and viscosity of the prepared hybrid nanofluids increase with the nanoparticles volume concentration.

687 citations


Journal ArticleDOI
TL;DR: Comparisons with measured extinction coefficients reveal that the approximation works well with water-based nanofluids containing graphite nanoparticles but less well with metallic nanoparticles and/or oil-based fluids.
Abstract: Suspensions of nanoparticles (i.e., particles with diameters < 100 nm) in liquids, termed nanofluids, show remarkable thermal and optical property changes from the base liquid at low particle loadings. Recent studies also indicate that selected nanofluids may improve the efficiency of direct absorption solar thermal collectors. To determine the effectiveness of nanofluids in solar applications, their ability to convert light energy to thermal energy must be known. That is, their absorption of the solar spectrum must be established. Accordingly, this study compares model predictions to spectroscopic measurements of extinction coefficients over wavelengths that are important for solar energy (0.25 to 2.5 μm). A simple addition of the base fluid and nanoparticle extinction coefficients is applied as an approximation of the effective nanofluid extinction coefficient. Comparisons with measured extinction coefficients reveal that the approximation works well with water-based nanofluids containing graphite nanoparticles but less well with metallic nanoparticles and/or oil-based fluids. For the materials used in this study, over 95% of incoming sunlight can be absorbed (in a nanofluid thickness ≥10 cm) with extremely low nanoparticle volume fractions - less than 1 × 10-5, or 10 parts per million. Thus, nanofluids could be used to absorb sunlight with a negligible amount of viscosity and/or density (read: pumping power) increase.

477 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined the natural convection in an enclosure that is filled with a water-Al2O3 nanofluid and is influenced by a magnetic field, based upon numerical predictions, the effects of pertinent parameters such as the Rayleigh number (103,≤,Ra,≤ 107), the solid volume fraction (0.06), and the Hartmann number ( 0.1), on the flow and temperature fields and the heat transfer performance of the enclosure were examined.

438 citations


Journal ArticleDOI
TL;DR: Focusing mainly on dilute suspensions of well-dispersed spherical nanoparticles in water or ethylene glycol, recent experimental observations, associated measurement techniques, and new theories as well as useful correlations have been reviewed.
Abstract: Nanofluids, i.e., well-dispersed (metallic) nanoparticles at low- volume fractions in liquids, may enhance the mixture’s thermal conductivity, knf, over the base-fluid values. Thus, they are potentially useful for advanced cooling of micro-systems. Focusing mainly on dilute suspensions of well-dispersed spherical nanoparticles in water or ethylene glycol, recent experimental observations, associated measurement techniques, and new theories as well as useful correlations have been reviewed. It is evident that key questions still linger concerning the best nanoparticle-and-liquid pairing and conditioning, reliable measurements of achievable knf values, and easy-to-use, physically sound computer models which fully describe the particle dynamics and heat transfer of nanofluids. At present, experimental data and measurement methods are lacking consistency. In fact, debates on whether the anomalous enhancement is real or not endure, as well as discussions on what are repeatable correlations between knf and temperature, nanoparticle size/shape, and aggregation state. Clearly, benchmark experiments are needed, using the same nanofluids subject to different measurement methods. Such outcomes would validate new, minimally intrusive techniques and verify the reproducibility of experimental results. Dynamic knf models, assuming non-interacting metallic nano-spheres, postulate an enhancement above the classical Maxwell theory and thereby provide potentially additional physical insight. Clearly, it will be necessary to consider not only one possible mechanism but combine several mechanisms and compare predictive results to new benchmark experimental data sets.

434 citations


Journal ArticleDOI
TL;DR: In this paper, the anomalous enhancement of specific heat capacity of high-temperature nanofluids was reported, and three independent competing transport mechanisms were enumerated to explain this anomalous behavior.

430 citations


Journal ArticleDOI
TL;DR: An experimental study of nanofluids intended for enhanced oil recovery is presented in this paper, where an aqueous solution of anionic surface-active agents with addition of light non-ferrous metal nanoparticles was used as the focus of the study.

Journal ArticleDOI
TL;DR: The improvement in FC, AW, and EP properties of nanofluids is respectively by 80, 33, and 40% compared with base oil and can be attributed to the nanobearing mechanism of graphene in engine oil and ultimate mechanical strength of graphene.
Abstract: Ultrathin graphene (UG) has been prepared by exfoliation of graphite oxide by a novel technique based on focused solar radiation. Graphene based engine oil nanofluids have been prepared and their frictional characteristics (FC), antiwear (AW), and extreme pressure (EP) properties have been evaluated. The improvement in FC, AW, and EP properties of nanofluids is respectively by 80, 33, and 40% compared with base oil. The enhancement can be attributed to the nanobearing mechanism of graphene in engine oil and ultimate mechanical strength of graphene.

Journal ArticleDOI
TL;DR: In this article, a notional design of this type of nanofluid receiver is presented, and the authors show a theoretical improvement in efficiency of up to 10% as compared to surface-based collectors when solar concentration ratios are in the range of 100-1000.
Abstract: Concentrated solar energy has become the input for an increasing number of experimental and commercial thermal systems over the past 10–15 years [M. Thirugnanasambandam et al., Renewable Sustainable Energy Rev. 14 (2010)]. Recent papers have indicated that the addition of nanoparticles to conventional working fluids (i.e., nanofluids) can improve heat transfer and solar collection [H. Tyagi et al., J. Sol. Energy Eng. 131, 4 (2009); P. E. Phelan et al., Annu. Rev. Heat Transfer 14 (2005)]. This work indicates that power tower solar collectors could benefit from the potential efficiency improvements that arise from using a nanofluid working fluid. A notional design of this type of nanofluid receiver is presented. Using this design, we show a theoretical nanofluid enhancement in efficiency of up to 10% as compared to surface-based collectors when solar concentration ratios are in the range of 100–1000. Furthermore, our analysis shows that graphite nanofluids with volume fractions on the order of 0.001% or l...

Journal ArticleDOI
TL;DR: In this article, different amounts of Al2O3 nanoparticle have been added into these base fluids and its effects on the heat transfer performance of the car radiator have been determined experimentally.

Journal ArticleDOI
TL;DR: In this paper, a review of the thermal conductivity of nanofluids is presented, focusing on the experimental data, proposed mechanisms responsible for its enhancement, and its predicting models.
Abstract: Nanofluids—fluid suspensions of nanometer-sized particles—are a very important area of emerging technology and are playing an increasingly important role in the continuing advances of nanotechnology and biotechnology worldwide. They have enormously exciting potential applications and may revolutionize the field of heat transfer. This review is on the advances in our understanding of heat-conduction process in nanofluids. The emphasis centers on the thermal conductivity of nanofluids: its experimental data, proposed mechanisms responsible for its enhancement, and its predicting models. A relatively intensified effort has been made on determining thermal conductivity of nanofluids from experiments. While the detailed microstructure-conductivity relationship is still unknown, the data from these experiments have enabled some trends to be identified. Suggested microscopic reasons for the experimental finding of significant conductivity enhancement include the nanoparticle Brownian motion, the Brownian-motion-induced convection, the liquid layering at the liquid-particle interface, and the nanoparticle cluster/aggregate. Although there is a lack of agreement regarding the role of the first three effects, the last effect is generally accepted to be responsible for the reported conductivity enhancement. The available models of predicting conductivity of nanofluids all involve some empirical parameters that negate their predicting ability and application. The recently developed first-principles theory of thermal waves offers not only a macroscopic reason for experimental observations but also a model governing the microstructure-conductivity relationship without involving any empirical parameter.

Journal ArticleDOI
TL;DR: In this paper, a facile technique was developed to produce ethylene glycol based nanofluids containing graphene nanosheets, and the thermal conductivity of the base fluid was increased significantly by the dispersed graphene: up to 86% increase for 5.0 vol'% graphene dispersion.

Journal ArticleDOI
TL;DR: In this article, the authors reported the flow of a nanofluid near a stagnation point towards a stretching surface and the effects of Brownian motion and thermophoresis are further taken into account.

Journal ArticleDOI
TL;DR: In this article, the thermal conductivity, viscosity, and stability of nanofluids containing multi-walled carbon nanotubes (MWCNTs) stabilized by cationic chitosan were studied.

Journal ArticleDOI
M.A.A. Hamad1
TL;DR: In this paper, the convective flow and heat transfer of an incompressible viscous nanofluid past a semi-infinite vertical stretching sheet in the presence of a magnetic field are examined.

Journal ArticleDOI
TL;DR: In this paper, forced convective heat transfer in a water based nanofluid has experimentally been compared to that of pure water in an automobile radiator, and the results showed that the water can be changed in the range of 2-5 l/min to have the fully turbulent regime.

Journal ArticleDOI
TL;DR: In this article, the authors measured the forced convective heat transfer coefficient of the nanofluids using theoretical correlations in order to compare the results with the experimental data and evaluated the effects of particle concentration and operating temperature.

Journal ArticleDOI
TL;DR: In this article, the authors review the progress made in the wetting and spreading of nanofluids over solid surfaces with an emphasis on the complex interactions between the particles in the nanoparticles and with the solid substrate.
Abstract: The wetting and spreading behavior of pure liquids over solid surfaces changes if liquids contain nanosized spherical particles or surfactant micelles, globular proteins and macromolecules. Recent studies on the spreading of nanofluids have demonstrated the inadequacy of well-known concepts of the spreading and adhesion of pure liquids on solid surfaces in understanding nanofluid spreading behavior. This paper reviews the progress made in the wetting and spreading of nanofluids over solid surfaces with an emphasis on the complex interactions between the particles in the nanofluid and with the solid substrate, as well as the spreading of thin nanofluid films containing nanoparticles on hydrophilic surfaces driven by the structural disjoining pressure gradient. The spreading droplet advances as a series of distinct nanoparticle layers.

Journal ArticleDOI
TL;DR: In this article, a review summarizes the correlations development for fluid flow and heat transfer characteristics of nanofluids in forced and free convection flows, and shows that most of the investigations recommended conventional friction factor correlation of base fluid for pressure drop prediction of the nano-fluid for both laminar and turbulent flows in minichannel as well as in microchannel.
Abstract: Nanofluids are engineered colloids made of a base fluid and nanoparticles, which become potential candidate for next generation heat transfer medium. Nanofluids have higher thermal conductivity and single-phase heat transfer coefficients than their base fluids. The heat transfer coefficient increases appear to go beyond the mere thermal conductivity effect, and cannot be predicted by traditional pure fluid correlations. This review summarizes the correlations development for fluid flow and heat transfer characteristics of nanofluids in forced and free convection flows. The review shows that most of the investigations recommended conventional friction factor correlation of base fluid for pressure drop prediction of the nanofluids for both laminar and turbulent flows in minichannel as well as in microchannel. However, the conventional correlation is not suitable for heat transfer coefficient of nanofluid and hence various correlations have been suggested for the Nusselt number for both laminar and turbulent flow. However, the large deviation of predicted values for proposed correlations has been observed may be due to strong influence of particle properties and nanofluid composition on flow and heat transfer characteristics, lack of common understanding on basic mechanism of nanofluid flow and insufficient experimental data on nanofluid heat transfer. Hence, a general framework for heat transfer correlation needs to be developed.

Journal ArticleDOI
TL;DR: In this paper, the viscosity of the stable nanofluids, prepared by dispersing 40-nm diameter spherical CuO nanoparticles in gear oil, was investigated.

Journal ArticleDOI
TL;DR: In this article, the shape and size of SiC nanoparticles were characterized using transmission electron microscopy and scanning electron microscope images to evaluate the properties of the SiC/deionized water (DIW) nanofluids.

Journal ArticleDOI
TL;DR: In this paper, an Eulerian two-fluid model is considered to simulate the nanofluid flow inside the microchannel and the governing mass, momentum and energy equations for both phases are solved using the finite volume method.

Journal ArticleDOI
TL;DR: In this paper, a review of research and development made in these areas of nanofluids is presented together with exhaustive review of these important cooling features, including boiling, spreading, and convective heat transfers.
Abstract: Nanofluids have evoked immense interest from researchers of multi-disciplines from around the globe due to their fascinating thermophysical properties and numerous potential benefits and applications in important fields such as microelectronics, microfluidics, transportation, and biomedical. However, there are many controversies and inconsistencies in reported arguments and experimental results on various thermal characteristics such as effective thermal conductivity, convective heat transfer coefficient and boiling heat transfer rate of nanofluids. As of today, researchers have mostly focused on anomalous thermal conductivity of nanofluids. Although investigations on boiling, droplet spreading, and convective heat transfer are very important in order to exploit nanofluids as the next generation coolants, considerably less efforts have been made on these major features of nanofluids. In this paper, these important cooling features—boiling, spreading, and convective heat transfers of nanofluids are presented together with exhaustive review of research and development made in these areas of nanofluids.

Journal ArticleDOI
TL;DR: In this article, thermal properties of nanoparticles suspended in refrigerant and lubricating oil of refrigerating systems were reviewed and review results are presented as well, and challenges and future direction of nanofluids/nanorefrigerants have been reviewed and presented in this paper.
Abstract: Recently scientists used nanoparticles in refrigeration systems because of theirs remarkable improvement in thermo-physical, and heat transfer capabilities to enhance the efficiency and reliability of refrigeration and air conditioning system. In this paper thermal–physical properties of nanoparticles suspended in refrigerant and lubricating oil of refrigerating systems were reviewed. Heat transfer performance of different nanorefrigerants with varying concentrations was reviewed and review results are presented as well. Pressure drop and pumping power of a refrigeration system with nanorefrigerants were obtained from different sources and reported in this review. Along with these, pool boiling heat transfer performance of CNT refrigerant was reported. Moreover, challenges and future direction of nanofluids/nanorefrigerants have been reviewed and presented in this paper. Based on results available in the literatures, it has been found that nanorefrigerants have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional refrigerant. This can be considered as one of the key parameters for enhanced performance for refrigeration and air conditioning systems. Because of its superior thermal performances, latest upto date literatures on this property has been summarized and presented in this paper as well. The results indicate that HFC134a and mineral oil with TiO2 nanoparticles works normally and safely in the refrigerator with better performance. The energy consumption of the HFC134a refrigerant using mineral oil and nanoparticles mixture as lubricant saved 26.1% energy with 0.1% mass fraction TiO2 nanoparticles compared to the HFC134a and POE oil system. It was identified that fundamental properties (i.e. density, specific heat capacity, and surface tension) of nanorefrigerants were not experimentally determined yet. It may be noted as well that few barriers and challenges those have been identified in this review must be addressed carefully before it can be fully implemented in refrigeration and air conditioning systems.

Journal ArticleDOI
TL;DR: In this paper, turbulent forced convection flow of water-Al2O3 nanofluid in a circular tube, subjected to a constant and uniform heat flux at the wall, is numerically analyzed.

Journal ArticleDOI
TL;DR: In this paper, the dispersion and stability of nanofluids obtained by dispersing CuO nanoparticles (obtained from different sources) in water have been analyzed, and the volumetric behavior up to high pressures (45 MPa) and atmospheric pressure viscosity were experimentally determined.