Heat transfer enhancement by magnetic nanofluids—A review
TL;DR: Magnetic nanofluids (MNFs) constitute a special class of materials that exhibit both magnetic and fluid properties as discussed by the authors, and the interest in the use of MNFs as a heat transfer medium stem from a possibility of controlling its flow and heat transfer process via an external magnetic field.
Abstract: Magnetic nanofluids (MNF) constitute a special class of nanofluids that exhibit both magnetic and fluid properties The interests in the use of MNF as a heat transfer medium stem from a possibility of controlling its flow and heat transfer process via an external magnetic field This review presents recent developments in this field with the aim of identifying major affecting parameters and some novel applications This review emphasizes on thermal conductivity enhancement and thermomagnetic convection in devices using MNFs as heat transfer media
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TL;DR: In this paper, a review summarizes recent researches on synthesis, thermophysical properties, heat transfer and pressure drop characteristics, possible applications and challenges of hybrid nanofluids, and showed that proper hybridization may make the hybrid nanoparticles very promising for heat transfer enhancement, however, lot of research works are still needed in the fields of preparation and stability, characterization and applications to overcome the challenges.
Abstract: Researches on the nanofluids have been increased very rapidly over the past decade. In spite of some inconsistency in the reported results and insufficient understanding of the mechanism of the heat transfer in nanofluids, it has been emerged as a promising heat transfer fluid. In the continuation of nanofluids research, the researchers have also tried to use hybrid nanofluid recently, which is engineered by suspending dissimilar nanoparticles either in mixture or composite form. The idea of using hybrid nanofluids is to further improvement of heat transfer and pressure drop characteristics by trade-off between advantages and disadvantages of individual suspension, attributed to good aspect ratio, better thermal network and synergistic effect of nanomaterials. This review summarizes recent researches on synthesis, thermophysical properties, heat transfer and pressure drop characteristics, possible applications and challenges of hybrid nanofluids. Review showed that proper hybridization may make the hybrid nanofluids very promising for heat transfer enhancement, however, lot of research works is still needed in the fields of preparation and stability, characterization and applications to overcome the challenges.
846 citations
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TL;DR: In this article, the synthesis of hybrid nanoparticles, preparation of hybrid nanofluids, thermal properties, heat transfer, friction factor and the available Nusselt number and friction factor correlations are discussed.
Abstract: In the past decade, research on nanofluids has been increased rapidly and reports reveal that nanofluids are beneficial heat transfer fluids for engineering applications. The heat transfer enhancement of nanofluids is primarily dependent on thermal conductivity of nanoparticles, particle volume concentrations and mass flow rates. Under constant particle volume concentrations and flow rates, the heat transfer enhancement only depends on the thermal conductivity of the nanoparticles. The thermal conductivity of nanoparticles may be altered or changed by preparing hybrid (composite) nanoparticles. Hybrid nanoparticles are defined as nanoparticles composed by two or more different materials of nanometer size. The fluids prepared with hybrid nanoparticles are known as hybrid nanofluids. The motivation for the preparation of hybrid nanofluids is to obtain further heat transfer enhancement with augmented thermal conductivity of these nanofluids. This review covers the synthesis of hybrid nanoparticles, preparation of hybrid nanofluids, thermal properties, heat transfer, friction factor and the available Nusselt number and friction factor correlations. The review also demonstrates that hybrid nanofluids are more effective heat transfer fluids than single nanoparticles based nanofluids or conventional fluids. Notwithstanding, full understanding of the mechanisms associated with heat transfer enhancement of hybrid nanofluids is still lacking and, consequently it is required a considerable research effort in this area.
365 citations
TL;DR: In this paper, the fundamental physical mechanisms of switchable and nonlinear heat transfer have been harnessed to make thermal diodes, switches, and regulators, and various nonlinear and active thermal circuits are presented.
Abstract: Interest in new thermal diodes, regulators, and switches has been rapidly growing because these components have the potential for rich transport phenomena that cannot be achieved using traditional thermal resistors and capacitors. Each of these thermal components has a signature functionality: Thermal diodes can rectify heat currents, thermal regulators can maintain a desired temperature, and thermal switches can actively control the heat transfer. Here, we review the fundamental physical mechanisms of switchable and nonlinear heat transfer which have been harnessed to make thermal diodes, switches, and regulators. The review focuses on experimental demonstrations, mainly near room temperature, and spans the fields of heat conduction, convection, and radiation. We emphasize the changes in thermal properties across phase transitions and thermal switching using electric and magnetic fields. After surveying fundamental mechanisms, we present various nonlinear and active thermal circuits that are based on ana...
299 citations
TL;DR: In this paper, a review of advancements made in the field of solar thermal technology with a focus on techniques employed for its performance enhancement is presented, including geometrical modifications on the absorber plate, solar selective coatings and nanofluids.
Abstract: Given rapid depletion of conventional energy sources and environmental degradation caused by their over exploitation, the renewable energy sources are believed to be the future. Technologies utilizing renewable energy sources differ significantly from one another, not only with regard to technical and economic aspects but also in relation to their reliability, maturity, and operational experience in utility scale conditions. Technologies used to harness solar energy have emerged as the most promising and mature since solar energy is abundant, freely available, and it has commercial potential too. This paper presents a review of advancements made in the field of solar thermal technology with a focus on techniques employed for its performance enhancement. It also covers the description of different types of solar collectors to facilitate the systematic understanding of solar thermal technology and the novel modifications realized in each category of solar collectors have been highlighted to promote the use of solar energy in routine activities. Performance enhancement techniques such as geometrical modifications on the absorber plate, use of solar selective coatings and nanofluids have been given a special attention.
284 citations
Cites background from "Heat transfer enhancement by magnet..."
...[97] Magnetic nanofluid Solar radiation could be completely absorbed in a magnetic nanofluid layer with about 10-mm thickness...
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...…[96] Applications in solar energy Need to find the optimum volume fraction Vagaries in effect of particle size on the efficiency of collectors Nkurikiyimfura et al. (2013) [97] Magnetic nanofluid Solar radiation could be completely absorbed in a magnetic nanofluid layer with about 10-mm…...
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...[97] reviewed the advancement in heat transfer enhancement by magnetic nanofluids and suggested that solar thermosyphons where the fluid flow and heat transfer process may be completely controlled by an external magnetic field could be the future design....
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TL;DR: In this article, a brief overview of evolution in the use of nanofluids in some applications has been presented, and enhancements recorded experimentally are reviewed and summarized, including: nanoparticle concentration, size, shape and thermal conductivity.
Abstract: In many applications, there is a critical need for enhancing the poor thermal conductivity of conventional fluids in order to develop efficient heat transfer fluids. This requirement can be met through dispersing nanometric particles in a given base fluid such as water, ethylene glycol, oil or air. The resulting nanofluids enhanced thermal conductivity of the base fluids. In order to evaluate this enhancement, nanofluid thermal conductivity is required to be measured. Several methods and techniques are covered in the present contribution. In addition, enhancements recorded experimentally are reviewed and summarized. Different parameters affecting on such enhancement are covered, including: nanoparticle concentration, size, shape and thermal conductivity. In addition, base fluid type, nanofluid bulk temperature and dispersion techniques are also covered parameters. However, nanofluids have the potential to contribute in several practical applications including solar thermal, transportation, electronic cooling, medical, detergency and military applications. In the present work, a brief overview of evolution in the use of nanofluids in some applications has been presented. According to this contribution, there is a critical need for further fundamental and applications of nanofluids studies in order to understand the physical mechanisms of using nanofluids as well as explore different aspects of applications of nanofluids.
249 citations
References
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TL;DR: A review on fluid flow and heat transfer characteristics of nanofluids in forced and free convection flows is presented in this article, where the authors identify opportunities for future research.
1,988 citations
TL;DR: This Review provides a critical examination of the various interparticle forces (van der Waals, electrostatic, magnetic, molecular, and entropic) that can be used in nanoscale self-assembly.
Abstract: The ability to assemble nanoscopic components into larger structures and materials depends crucially on the ability to understand in quantitative detail and subsequently "engineer" the interparticle interactions. This Review provides a critical examination of the various interparticle forces (van der Waals, electrostatic, magnetic, molecular, and entropic) that can be used in nanoscale self-assembly. For each type of interaction, the magnitude and the length scale are discussed, as well as the scaling with particle size and interparticle distance. In all cases, the discussion emphasizes characteristics unique to the nanoscale. These theoretical considerations are accompanied by examples of recent experimental systems, in which specific interaction types were used to drive nanoscopic self-assembly. Overall, this Review aims to provide a comprehensive yet easily accessible resource of nanoscale-specific interparticle forces that can be implemented in models or simulations of self-assembly processes at this scale.
1,344 citations
Book•
01 Mar 1994
TL;DR: In this article, the authors evaluated two-phase heat exchangers for single-phase flows and showed that they can achieve state-of-the-art performance in terms of heat transfer.
Abstract: Heat Transfer Fundamentals Performance Evaluation for Single-Phase Flows Performance Evaluation Criteria for Two-Phase Heat Exchangers Plate-and-Fin Extended Surfaces Externally Finned Tubes Insert Devices for Single-Phase Flow Internally Finned Tubes and Annuli Integral Roughness Fouling on Enhanced Surfaces Pool Boiling Vapor Space Condensation Convective Vaporization Convective Condensation Enhancement Using Electric Fields Simultaneous Heat and Mass Transfer Additives for Gases and Liquids Problem Supplement Index.
1,296 citations
TL;DR: In this article, a thermal conductivity model for nanofluids has been developed, which takes the effects of particle size, particle volume fraction and temperature dependence as well as properties of base liquid and particle phase into consideration by considering surrounding liquid traveling with randomly moving nanoparticles.
Abstract: In a quiescent suspension, nanoparticles move randomly and thereby carry relatively large volumes of surrounding liquid with them. This micro-scale interaction may occur between hot and cold regions, resulting in a lower local temperature gradient for a given heat flux compared with the pure liquid case. Thus, as a result of Brownian motion, the effective thermal conductivity, keff, which is composed of the particles’ conventional static part and the Brownian motion part, increases to result in a lower temperature gradient for a given heat flux. To capture these transport phenomena, a new thermal conductivity model for nanofluids has been developed, which takes the effects of particle size, particle volume fraction and temperature dependence as well as properties of base liquid and particle phase into consideration by considering surrounding liquid traveling with randomly moving nanoparticles.
964 citations
TL;DR: In this paper, Oleic acid (OA)-coated magnetite nanoparticles of 7 and 19 µm were obtained by the seed-mediated high temperature thermal decomposition of iron(III) acetylacetonate (Fe(acac) 3 ) precursor method.
859 citations