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Journal Article

Thermal Conductivity Enhancement of Nanofluids in Conjunction with Electrical Double Layer (EDL)

18 Nov 2007-Bulletin of the American Physical Society (American Physical Society)-Vol. 60
TL;DR: In this article, a novel expression for the thermal conductivity of nanofluids is proposed, which incorporates the kinetic theory to describe the contribution of the Brownian motion of the nanoparticles with a more realistic definition of the mean free path.
Abstract: A novel expression for the thermal conductivity of nanofluids is proposed, which incorporates the kinetic theory to describe the contribution of the Brownian motion of the nanoparticles with a more realistic definition of the mean free path, and additionally to consider the contribution of the interparticle interaction due to the existence of the electrical double layer (EDL). It is shown that this model is applied to Au/water nanofluids satisfactorily with respect to temperature, volume fraction and particle size. In the case of dense Al 2 O 3 /water nanofluids, the effect of the interparticle interaction due to EDL on enhancing the thermal conductivity is more prominent than in the case of dilute Al 2 O 3 /water nanofluids. The model proposed in this paper shows that interparticle interaction due to EDL is the most responsible for the enhancement of thermal conductivity of nanofluids.
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Dissertation
17 Aug 2013
TL;DR: In this article, the authors investigated the thermal and energy performance of a shell and tube heat exchanger and thermosyphon airpreheater operated with nanofluids.
Abstract: In recent years, there has been a substantial increase in energy demand due to industrialization. This raises concern on issues such as depletion of fossil based energy and emission of green house gasses. It is reported that a high portion of industrial energy is wasted as flue gas/hot gas from heating plants, boilers, etc. Hence, optimization of energy use through heat recovery device is one of the possible approaches to address this problem. However, conventional heat transfer fluids feature low thermal conductivity. The development in nanotechnology has enabled the introduction of nanofluids as a new generation of heat transfer fluid. Nanofluids are suspensions of nanoparticles in a base fluid. The inclusion of nanoparticles into a base fluid significantly increases the thermal conductivity of the base fluid. This study attempts to investigate the thermal and energy performance of a shell and tube heat exchanger and thermosyphon airpreheater operated with nanofluids. It focuses on recovering waste heat from hot gases/ flue gas produced by a heating plant. The analysis was conducted based on the thermophysical properties of nanofluids obtained from literatures, mathematical correlations and present experimental data. The thermo-physical properties measured in this study include thermal conductivity, viscosity and density. The study reveales that, the thermal conductivity of ethylene glycol/water based Al2O3 (0.5vol.%, partice size: 13nm) increases about 8.9% compared to base fluid. About 12.9% augmentation is also observed for water based Al2O3 (0.5vol.%, particle size :13nm). Thermal conductivity of nanofluids increases with the increase of particle volume percentage or decrease of particle size. Viscosity and density also show increasing trend with the addition of nanoparticles. The thermal performance of shell and tube heat recovery exchanger improved with the addition of nanoparticles. About 7.8% heat transfer augmentation was observed for the ethylene glycol-based nanofluids containing 1 vol.% of copper nanoparticles at 26.3 kg/s flue gasses’ mass flow rate and 111.6 kg/s coolant’s mass flow rate. For water containing 2 vol.% of copper, 4.5% heat transfer enhancement was recorded. At constant coolant mass flow rate, lower pumping power is needed when nanofluids are applied. About 10.99% less power was observed at 1vol. % of copper nanoparticle compared to ethylene glycol base fluid.The study on the size reduction of heat exchanger, implied that nanofluids provide opportunity to reduce the size of heat exchanger without decreasing its thermal performance. Analysing the total dimensionless entropy generation revealed that, 10.8% reduction is observed with an addition of 7 vol.% of Al2O3 into water. About 9.7% reduction is observed for water-based TiO2 (4 vol.%) nanofluid. Other factors that influence total dimensionless entropy generation are dimensionless temperature difference, fluid mass flow rate, tube diameter and length. Moreover, the study revealed that the change of nanofluid thermo-physical properties only plays a minor role in improving the thermal performance of the thermosyphon heat exchanger. Slight increase of overall heat transfer coefficient and cold air outlet temperatures are observed with increasing nanoparticle volume fraction. However, the thermal performance of thermosyphon heat exchanger increases when the hot air velocity elevates from 2.5 to 4.75m/s.

4 citations

References
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Journal ArticleDOI
TL;DR: In this article, an innovative new class of heat transfer fluids can be engineered by suspending metallic nanoparticles in conventional heat-transfer fluids, which are expected to exhibit high thermal conductivities compared to those of currently used heat transfer fluid, and they represent the best hope for enhancing heat transfer.
Abstract: Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids that are required in many industrial applications. In this paper we propose that an innovative new class of heat transfer fluids can be engineered by suspending metallic nanoparticles in conventional heat transfer fluids. The resulting {open_quotes}nanofluids{close_quotes} are expected to exhibit high thermal conductivities compared to those of currently used heat transfer fluids, and they represent the best hope for enhancement of heat transfer. The results of a theoretical study of the thermal conductivity of nanofluids with copper nanophase materials are presented, the potential benefits of the fluids are estimated, and it is shown that one of the benefits of nanofluids will be dramatic reductions in heat exchanger pumping power.

4,634 citations

Journal ArticleDOI
TL;DR: In this paper, the Brownian motion of nanoparticles at the molecular and nanoscale level is a key mechanism governing the thermal behavior of nanoparticle-fluid suspensions (nanofluids).
Abstract: We have found that the Brownian motion of nanoparticles at the molecular and nanoscale level is a key mechanism governing the thermal behavior of nanoparticle–fluid suspensions (“nanofluids”). We have devised a theoretical model that accounts for the fundamental role of dynamic nanoparticles in nanofluids. The model not only captures the concentration and temperature-dependent conductivity, but also predicts strongly size-dependent conductivity. Furthermore, we have discovered a fundamental difference between solid/solid composites and solid/liquid suspensions in size-dependent conductivity. This understanding could lead to design of nanoengineered next-generation coolants with industrial and biomedical applications in high-heat-flux cooling.

1,459 citations

01 Jan 1873
TL;DR: A Treatise on Electricity and Magnetism by James Clerk-Maxwell as mentioned in this paper was published in 1873, and has been widely cited as a seminal work in the history of physics.
Abstract: IN his deservedly celebrated treatise on “Sound,” the late Sir John Herschel felt himself justified in saying, “It is vain to conceal the melancholy truth. We are fast dropping behind. In Mathematics we have long since drawn the rein and given over a hopeless race.” Thanks to Herschel himself, and others, the reproach, if perhaps then just, did not long remain so. Even in pure mathematics, a subject which till lately has not been much attended to in Britain, except by a few scattered specialists, we stand at this moment at the very least on a par with the élite of the enormously disproportionate remainder of the world. The discoveries of Boole and Hamilton, of Cayley and Sylvester, extend into limitless regions of abstract thought, of which they are as yet the sole explorers. In applied mathematics no living men stand higher than Adams, Stokes, and W. Thomson. Any one of these names alone would assure our position in the face of the world as regards triumphs already von in the grandest struggles of the human intellect. But the men of the next generation—the successors of these long-proved knights—are beginning to win their spurs, and among them there is none of greater promise than Clerk-Maxwell. He has already, as the first holder of the new chair of Experimental Science in Cambridge, given the post a name which requires only the stamp of antiquity to raise it almost to the level of that of Newton. And among the numerous services he has done to science, even taking account of his exceedingly remarkable treatise on “Heat,” the present volumes must be regarded as pre-eminent.A Treatise on Electricity and Magnetism.By James Clerk-Maxwell, Professor of Experimental Physics in the University of Cambridge. (Clarendon Press Series, Macmillan & Co., 1873.)

1,419 citations

Journal ArticleDOI
TL;DR: In this paper, an experimental correlation for the thermal conductivity of Al2O3 nanofluids as a function of nanoparticle size over a wide range of temperature (from 21 to 71°C).
Abstract: In this letter, we report an experimental correlation [Eqs. (1a) and (1b) or (1c)] for the thermal conductivity of Al2O3 nanofluids as a function of nanoparticle size (ranging from 11nmto150nm nominal diameters) over a wide range of temperature (from 21to71°C). Following the previously proposed conjecture from the theoretical point-of-view (Jang and Choi, 2004), it is experimentally validated that the Brownian motion of nanoparticles constitutes a key mechanism of the thermal conductivity enhancement with increasing temperature and decreasing nanoparticle sizes.

1,188 citations