Bridging Thermal and Electrical Transport in Dielectric Nanostructure-Based Polar Colloids
TL;DR: In this article, an extensional intuitive analogy to the Wiedemann-Franz law has been drawn, where mobile electrons transport both heat and charge within metallic crystal structure, and the analogy can be extended to nanocolloids, wherein the dispersed population act as the major transporter.
Abstract: Heat and charge transport characteristics of nanocolloids have been bridged from fundamental analysis. The relationship between the two transport phenomena in dielectric nanostructure-based polar colloids has been quantitatively presented. An extensional intuitive analogy to the Wiedemann–Franz law has been drawn. Derived from the fact that mobile electrons transport both heat and charge within metallic crystal structure, the analogy can be extended to nanocolloids, wherein the dispersed population act as the major transporter. The analogy allows modeling of the relationship between the two phenomena, and sheds more insight and conclusive evidence that nanoparticle traversal within the fluid domain is the main source of augmented transport phenomena exhibit by nanocolloids. Important factors, such as the thermal and dielectric responses of the nanocolloid can be quantified and bridged through the semianalytical formalism. The theoretical analysis has been validated against experimental data and variant scientific literature, and good accuracy has been observed.
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TL;DR: In this article, Graphene (Gr) nanoflakes and carbon nanotubes (CNT) have been experimentally observed for the first time to exhibit augmented dielectric breakdown strengths compared to the base transformer oils.
Abstract: Nano-oils comprising stable and dilute dispersions of synthesized Graphene (Gr) nanoflakes and carbon nanotubes (CNT) have been experimentally observed for the first time to exhibit augmented dielectric breakdown strengths compared to the base transformer oils. Variant nano-oils comprising different Gr and CNT samples suspended in two different grades of transformer oils have yielded consistent and high degrees of enhancement in the breakdown strength. The apparent counter-intuitive phenomenon of enhancing insulating caliber of fluids utilizing nanostructures of high electronic conductance has been shown to be physically consistent thorough theoretical analysis. The crux mechanism has been pin pointed as efficient charge scavenging leading to hampered streamer growth and development, thereby delaying probability of complete ionization. The mathematical analysis presented provides a comprehensive picture of the mechanisms and physics of the electrohydrodynamics involved in the phenomena of enhanced breakdown strengths. Furthermore, the analysis is able to physically explain the various breakdown characteristics observed as functions of system parameters, viz. nanostructure type, size distribution, relative permittivity, base fluid dielectric properties, nanomaterial concentration and nano-oil temperature. The mathematical analyses have been extended to propose a physically and dimensionally consistent analytical model to predict the enhanced breakdown strengths of such nano-oils from involved constituent material properties and characteristics. The model has been observed to accurately predict the augmented insulating property, thereby rendering it as an extremely useful tool for efficient design and prediction of breakdown characteristics of nanostructure infused insulating fluids. The present study, involving experimental investigations backed by theoretical analyses and models for an important dielectric phenomenon such as electrical breakdown can find utility in design of safer and more efficient high operating voltage electrical drives, transformers and machines.
37 citations
TL;DR: The hitherto unreported phenomenon of greatly enhanced thermal conductivity in such electro-active colloidal dispersions in the presence of an externally applied electric field is reported.
Abstract: Electrorheological (ER) fluids are known to exhibit enhanced viscous effects under an electric field stimulus. The present article reports the hitherto unreported phenomenon of greatly enhanced thermal conductivity in such electro-active colloidal dispersions in the presence of an externally applied electric field. Typical ER fluids are synthesized employing dielectric fluids and nanoparticles and experiments are performed employing an in-house designed setup. Greatly augmented thermal conductivity under a field's influence was observed. Enhanced thermal conduction along the fibril structures under the field effect is theorized as the crux of the mechanism. The formation of fibril structures has also been experimentally verified employing microscopy. Based on classical models for ER fluids, a mathematical formalism has been developed to predict the propensity of chain formation and statistically feasible chain dynamics at given Mason numbers. Further, a thermal resistance network model is employed to computationally predict the enhanced thermal conduction across the fibrillary colloid microstructure. Good agreement between the mathematical model and the experimental observations is achieved. The domineering role of thermal conductivity over relative permittivity has been shown by proposing a modified Hashin–Shtrikman (HS) formalism. The findings have implications towards better physical understanding and design of ER fluids from both ‘smart’ viscoelastic as well as thermally active materials points of view.
7 citations
TL;DR: In this paper, a physically and dimensionally consistent analytical model was proposed to predict the breakdown strength of nano oils from involved constituent material properties and characteristics, such as, nanostructure type, size distribution, relative permittivity, base fluid dielectric properties, nanomaterial concentration and nano oil temperature.
Abstract: Nano oils comprising Graphene nanoflakes and CNTs have been experimentally observed for the first time to exhibit augmented dielectric breakdown strengths compared to the base transformer oils. Variant nano oils comprising different Gr and CNT samples suspended in two different grades of transformer oils have yielded consistent and high degrees of enhancement in the breakdown strength. The apparent counter intuitive phenomenon of enhancing insulating caliber of fluids utilizing nanostructures of high electronic conductance has been shown to be physically consistent thorough theoretical analysis. The crux mechanism has been pin pointed as efficient charge scavenging leading to hampered streamer growth and development, thereby delaying probability of complete ionization. The mathematical analysis presented provides a comprehensive picture of the mechanisms and physics of the electrohydrodynamics involved in the phenomena of enhanced breakdown strengths. Furthermore, the analysis is able to physically explain the various breakdown characteristics observed as functions of system parameters, such as, nanostructure type, size distribution, relative permittivity, base fluid dielectric properties, nanomaterial concentration and nano oil temperature. The mathematical analyses have been extended to propose a physically and dimensionally consistent analytical model to predict the enhanced breakdown strengths of such nano oils from involved constituent material properties and characteristics. The model has been observed to accurately predict the augmented insulating property, thereby rendering it as an extremely useful tool for efficient design and prediction of breakdown characteristics of nanostructure infused insulating fluids.
7 citations
TL;DR: In this article, a scaling analysis based on the thermophoretic and electrophoretic velocities from classical Huckel-Smoluchowski formalism is able to mathematically predict the thermal performance enhancement due to electrophoresis.
5 citations
TL;DR: In this paper, the authors report experimental evidence with a theoretical formalism on the enhancement of the dielectric breakdown strength of ferrofluids by inducing magneto-fibrillation with an external magnetic field.
Abstract: The present article reports experimental evidence with a theoretical formalism on the enhancement of the dielectric breakdown strength of ferrofluids by inducing magneto-fibrillation with an external magnetic field. The dielectric breakdown strengths of oil based ferrofluids are determined, and it is further shown that the strength enhances due to the presence of a localized magnetic field in the streamer development zones. The improvement in breakdown strength is also supplemented by improvement in the reliability of the liquid dielectrics, which is established by a two parameter Weibull analysis. It is also noted that a horizontal magnetic field is more potent toward improved breakdown strength than an equivalent vertical field. The enhanced scavenging of electrons from the streamer development zones due to localized magnetic fibrillation by the nanoparticles is proposed as the crux mechanism. Microscopy studies are conducted to provide visual evidence of the fibrillation process in the ferrofluids due to the local magnetic field. A theoretical formalism is proposed to predict the ferrohydrodynamics of fibrillation, and this is further used to develop a model to predict the increment in breakdown strengths. The proposed model predictions are noted to agree well with the experimental observations. The study may find strong implications in design and development of high voltage liquid dielectrics with tunable electrical stress bearing caliber.
2 citations
References
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23,110 citations
Book•
01 Jan 1953
TL;DR: In this paper, the Hartree-Fock Approximation of many-body techniques and the Electron Gas Polarons and Electron-phonon Interaction are discussed.
Abstract: Mathematical Introduction Acoustic Phonons Plasmons, Optical Phonons, and Polarization Waves Magnons Fermion Fields and the Hartree-Fock Approximation Many-body Techniques and the Electron Gas Polarons and the Electron-phonon Interaction Superconductivity Bloch Functions - General Properties Brillouin Zones and Crystal Symmetry Dynamics of Electrons in a Magnetic Field: de Haas-van Alphen Effect and Cyclotron Resonance Magnetoresistance Calculation of Energy Bands and Fermi Surfaces Semiconductor Crystals I: Energy Bands, Cyclotron Resonance, and Impurity States Semiconductor Crystals II: Optical Absorption and Excitons Electrodynamics of Metals Acoustic Attenuation in Metals Theory of Alloys Correlation Functions and Neutron Diffraction by Crystals Recoilless Emission Green's Functions - Application to Solid State Physics Appendix: Perturbation Theory and the Electron Gas Index.
21,954 citations
TL;DR: In this paper, it was shown that a "nanofluid" consisting of copper nanometer-sized particles dispersed in ethylene glycol has a much higher effective thermal conductivity than either pure or pure glycol or even polyethylene glycol containing the same volume fraction of dispersed oxide nanoparticles.
Abstract: It is shown that a “nanofluid” consisting of copper nanometer-sized particles dispersed in ethylene glycol has a much higher effective thermal conductivity than either pure ethylene glycol or ethylene glycol containing the same volume fraction of dispersed oxide nanoparticles. The effective thermal conductivity of ethylene glycol is shown to be increased by up to 40% for a nanofluid consisting of ethylene glycol containing approximately 0.3 vol % Cu nanoparticles of mean diameter <10 nm. The results are anomalous based on previous theoretical calculations that had predicted a strong effect of particle shape on effective nanofluid thermal conductivity, but no effect of either particle size or particle thermal conductivity.
3,551 citations
"Bridging Thermal and Electrical Tra..." refers background in this paper
...THERMAL and electrical transport properties of nanocolloids [1], [2] have been topics of intensive research over...
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...The particle diameter dnp maintains an inverse relationship with the thermal conductivity of the nanocolloid [1], [4], [8], [11], [16], kc ....
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TL;DR: In this article, the authors present a procedure for preparing a nanofluid which is a suspension consisting of nanophase powders and a base liquid, and their TEM photographs are given to illustrate the stability and evenness of suspension.
2,341 citations
"Bridging Thermal and Electrical Tra..." refers background in this paper
...The particle diameter dnp maintains an inverse relationship with the thermal conductivity of the nanocolloid [1], [4], [8], [11], [16], kc ....
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...This is in fact established by detailed experimental reports [4], [26]....
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TL;DR: In this article, the authors investigated the increase of thermal conductivity with temperature for nano fluids with water as base fluid and particles of Al 2 O 3 or CuO as suspension material.
Abstract: Usual heat transfer fluids with suspended ultra fine particles of nanometer size are named as nanofluids, which have opened a new dimension in heat transfer processes. The recent investigations confirm the potential of nanofluids in enhancing heat transfer required for present age technology. The present investigation goes detailed into investigating the increase of thermal conductivity with temperature for nano fluids with water as base fluid and particles of Al 2 O 3 or CuO as suspension material. A temperature oscillation technique is utilized for the measurement of thermal diffusivity and thermal conductivity is calculated from it
2,177 citations
"Bridging Thermal and Electrical Tra..." refers background in this paper
...This in essence provides a quantitative reasoning of the similar response of the thermal and electrical transport properties of nanocolloids to temperature [3], [9]....
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...the past decade and a half, and the phenomena have been experimentally observed [3]–[8], and mathematically modeled [9]– [13]....
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