Thermal conductivities of two types of Au nanoparticles in water and toluene were discussed. The effects of chemical factor such as direct contact of the metal surface with the solvent medium was also studied. It was found that thermal conductivity was enhanced by 5%-21% in the temperature range of 30-60°C at a loading of 0.00026.

Sarit Kumar Das

Department of Mechanical Engineering

T Sundararajan

Pradeep Thalappil

Department Of Chemistry

Hrishikesh E. Patel

Beena George

Gold

Thermal conductivity

toluene

Nanofluids

Nanostructured materials

Fulltext

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Thermal conductivities of naked and monolayer protected metal nanoparticle based nanofluids: Manifestation of anomalous enhancement and chemical effects

Applied Physics Letters

Stable surfactant-free Al2O3/deionized (DI) water nanofluids are prepared by a two-step process and are stabilized using an ultrasonic homogenizer. The thermal conductivity enhancement measured by a transient hot wire technique demonstrated a nonlinear relationship with increase in volume fraction of dispersed nanoparticles and attains a maximum enhancement of 15% for 1&nbsp;vol% of Al2O3 loading in deionized water at 70°C. The stabilized Al2O3/DI water nanofluids were employed as the working fluid in a screen mesh wick heat pipe placed horizontally. The straight heat pipe configuration is altered for more practicality in use, with crimped edges, extended conduction lengths, and minute surface depressions. The heat pipe is tested at various levels of heat inputs and concentrations of Al2O3 nanoparticles. The evaporator section is heated by circulating water through a heating chamber, and the condenser section is cooled under free convection. The experimental results show an optimum reduction of 22% in the thermal resistance value using 1&nbsp;vol% of Al2O3/DI nanofluids as compared to DI water at low heat input of 12&nbsp;W. The stabilized operation of the heat pipe is observed at high heat input of 73&nbsp;W and at low concentration of 0.005&nbsp;vol% Al2O3/DI water nanofluids. The findings emphasize potential for nanofluids as future heat pipe fluids. © 2017 Taylor &amp; Francis Group, LLC.

Heat Transfer Engineering

Augmented Thermal Performance of Straight Heat Pipe Employing Annular Screen Mesh Wick and Surfactant Free Stable Aqueous Nanofluids

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. © 2002-2012 IEEE.

IEEE Transactions on Nanotechnology

Bridging Thermal and Electrical Transport in Dielectric Nanostructure-Based Polar Colloids

Natural convection heat transfer in Al2O3/water nanofluid is analyzed using the single-component nonhomogeneous lattice Boltzmann method (SCNHLBM). There exists a contradictory observation between the numerical and experimental works in the literature with respect to the heat transfer of nanofluids in natural convection. Nanofluid is treated as a single component with nonhomogeneous particle distribution introduced by a concentration transport equation of nanoparticles by considering the Brownian and thermophoretic diffusions. The average Nusselt number is found to deteriorate with increasing nanoparticle volume fraction; thus the trend of the experimental results is captured using SCNHLBM. Addition of Brownian and thermophoretic diffusion results in additional thermal diffusion and hence reduces the convective transport of heat. The contribution of Brownian and thermophoretic diffusions in heat transfer deterioration is revealed. © 2015 Taylor and Francis Group, LLC.

Numerical Heat Transfer; Part A: Applications

A single-component nonhomogeneous lattice boltzmann model for natural convection in Al2O3/water nanofluid

Abstract: The dominant modes of charge transport in variant polar liquid-based nanoparticulate colloidal dispersions (dilute) have been theorized. Theories formulating electrical characteristics of colloids have often been found to over- or under-predict charge transport in dilute suspensions of nanoparticles in polar fluids owing to grossly different mechanistic behaviors of concentrated systems. Three major interacting modes with independent yet simultaneous existence have been proposed and found to be consistent with analyses of experimental data. Electric double layer (EDL) formation at nanoparticle–fluid interface-conjugated electrophoresis under the influence of the electric field has been determined as one important mode of charge transport. Nanoparticle polarization due to short-range field non-uniformity caused by the EDL with consequent particle motion due to inter-particle electrostatic interactions acts as another mode of transport. Coupled electro-thermal diffusion arising out of Brownian randomization in the presence of the electric field has been determined as the third dominant mode. An analytical model based on discrete interactions of the charged particle–fluid domains explains the various behavioral aspects of such dispersions, as observed and validated from detailed experimental analysis. The analysis is also predictive of the dominance and behavior of the three modes with important nanocolloidal parameters such as temperature and concentration.Graphical Abstract: [Figure not available: see fulltext]. © 2014, Springer Science+Business Media Dordrecht.

Journal of Nanoparticle Research

Trimodal charge transport in polar liquid-based dilute nanoparticulate colloidal dispersions

The absorbance and the fluorescence intensity of dye have been found to decrease on increasing the concentration of either (i) functionalized hydrogen-induced exfoliated multilayer graphene (f-HEG) or (ii) silver nanoparticles (AgNP). The observed static-quenching is due to the weak interaction between the dye and the AgNP or f-HEG in the ground state. In contrast, the spectra of the dye are unaffected by the presence of AgNP-decorated graphene. Pre-existing charge transfer interaction between the metal nanoparticles and graphene has been proposed to be mechanism responsible for this behavior. © 2011 Elsevier B.V. All rights reserved.

Chemical Physics Letters

Restricting charge transfer in dye-graphene system

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 Al2O3 or CuO as suspension material. A temperature oscillation technique is utilized for the measurement of thermal diffusivity and thermal conductivity is calculated from it. The results indicate an increase of enhancement characteristics with temperature, which makes the nanofluids even more attractive for applications with high energy density than usual room temperature measurements reported earlier.

Journal of Heat Transfer

Temperature dependence of thermal conductivity enhancement for nanofluids

Alkanethiol-protected silver clusters of average diameter 4.0 ± 0.5 nm form single-phase superlattice solids, and their X-ray powder diffractograms have been fully indexed to single cubic unit cells. Whereas alkanethiols with five or more carbon atoms form superlattices, the corresponding cluster with four carbons yield only separated clusters. The superlattice solids can be recrystallized from nonpolar solvents. No such superlattices are seen for the corresponding gold clusters. The superlattice collapses upon heating, but the solid retains the structure even at 398 K, much above the melting point of crystalline alkanes and the corresponding self-assembled monolayer. In situ variable-temperature X-ray diffraction investigations did not show any solid-state phase transitions in the superlattice. Temperature-dependent infrared spectroscopy reveals the melting of the alkyl chain, and it is seen that the chain as a whole achieves rotational freedom prior to the collapse of the superlattice. Calorimetric investigations show distinct monolayer and superlattice melting transitions. The chemical nature of the cluster-molecule interaction is similar to that of the previously investigated gold and silver systems, as revealed by NMR, mass, infrared, and X-ray photoelectron spectroscopies and thermogravimetry analyses. Conductivity measurements clearly manifest the superlattice melting transition. Diffusion constants in solution measured by NMR show that the relative decrease in the diffusion constant with increasing monolayer chain length is smaller for silver than for gold, suggested to be a signature of intercluster interaction even in solution. Corroborative evidence is provided by the variable-temperature UV/vis investigations of the clusters.

Chemistry of Materials

Monolayer-protected cluster superlattices: Structural, spectroscopic, calorimetric, and conductivity studies

Monolayer-protected Au, Ag, and Au:Ag alloy nanoclusters have been synthesized using octanethiol and octadecanethiol as capping agents. The particle-size distribution is narrow with an average core size of 3-4 nm. Optical nonlinearity induced by 35 ps pulses at 532 nm has been investigated in these samples using the Z-scan technique. It is found that in general, they behave either as saturable absorbers or reverse saturable absorbers depending on the intensity of excitation. Au and Ag clusters show nearly the same efficiency for optical limiting, but the alloy clusters are found to be less efficient in limiting and are less photostable. The observed effects are explained in terms of the electron dynamics of the excited-state species.

Journal	Applied Physics Letters
ISSN	00036951
Open Access	No