A comprehensive theoretical model which explains the enhancement in thermal conductivity of a nanofluid with respect to variation in the particle size, particle volume fraction and temperature. It was shown that in nanoparticle suspensions, the large enhancement of the heat transfer rate occured due to the large surface area offered by the nanoparticles. The temperature dependence was attributed to the variation of Brownian motion velocity for the particles. The enhancement was found to be linearly proportional to nanoparticle concentration, for small concentrations.

T Sundararajan

Department of Mechanical Engineering

Pradeep Thalappil

Department Of Chemistry

Sarit Kumar Das

Hrishikesh E. Patel

Brownian movement

Concentration (process)

Heat conduction

Heat transfer

Mathematical models

Particle size analysis

Thermal effects

velocity

conductivity enhancement

MOVING PARTICLE MODELS

Nanofluids

STOKES-EINSTEIN FORMULA

Thermal conductivity

article

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

Physical Review Letters

In this experimental work, three different types of nanofluids were evaluated for their stability using dynamic light scattering and particle morphological study using scanning electron microscopy. The nanofluids used in this study are zinc oxide (ZnO) nanoparticle in water and 5 wt% polyvinylpyrrolidone (PVP) as a dispersant, and ZnO with polyethylene glycol (PEG 600) and CuO with PEG 600 with 5 wt% PVP at different concentration of 0.1, 0.3 and 0.5 wt%. Thermal and electrical conductivities were determined by KD-2 Pro® and PC 700 Eutech®. The result shows better enhancement in the thermal and electrical conductivity in the ZnO+PVP+Water system, followed by the CuO+PVP+PEG and ZnO+PEG systems. The highest percentage enhancement in thermal conductivity found to be 35.5% of ZnO+ PVP+water systems. The thermal conductivity results were compared with a theoretical model and show good agreement with results predicted by the model. The proposed model of Nan et al. (1997) is based on a hypothesis regarding the physical mechanism in heat transfer for nanofluids. This study is expected to form the basis for the development of nanoﬂuid-based technologies with PEG as the primary additive in the upstream oil and gas industry especially in gas hydrates and drilling technology. © 2019, © 2019 Indian Institute of Chemical Engineers.

Indian Chemical Engineer

Investigations on the thermal and electrical conductivity of polyethylene glycol-based CuO and ZnO nanofluids

WC-Co cermets (ceramic-metal composites) were ground by a resin bonded diamond grinding wheel using hexagonal boron nitride (hBN) nano-aerosol to improve the grindability. This is a new generation grinding fluid and was produced by dispersing nano-sized hBN platelets in deionized water. Small quantity cooling-lubrication (SQCL) technology was employed to deliver hBN nanofluid in the form of nano-aerosol so that volumetric consumption rate could be kept at a very low value of 200 ml/h. The nanofluid, when separately characterized, demonstrated good lubrication and heat dissipation capability in reference with soluble oil, which is a commonly used cutting fluid for grinding. The superior tribological characteristics of hBN nanofluid were more pronounced at a high sliding speed of 1 m/s, as observed during a ball-on-disc test. However, the beneficial effect of using hBN nanofluid could be extracted more efficiently only in aggressive grinding condition. A clear drop in specific energy, favourable values of residual stress indicate the same. Prevalence of low grinding zone temperature was reflected through low specific energy values and finer but complex chip micromorphology. Overall the aqueous hBN nanofluid was proven to be a high performing grinding fluid suitable for SQCL application and WC-Co cermet grinding. © 2018 Elsevier Ltd

International Journal of Refractory Metals and Hard Materials

Grinding of WC-Co cermets using hexagonal boron nitride nano-aerosol

Optofluidic manipulation using lasers and colloidal systems have immense applications in microscale thermofluidic devices. The present study analyses the effect of laser as an external optical source in modulating the evaporation characteristics of pendent nanofluid microdroplets (which are free from substrate effects) so as to capture the physics behind the interfacial mass transport. The study analyses the effect of the power of laser, nature and concentration of the particle on evaporation rate of the complex fluids. Evidence of internal circulation was observed with Particle Image Velocimetry (PIV) technique in colloidal systems which together with the volumetric heat generation due to laser irradiation can be attributed to be the cause behind the enhanced evaporation rate. The nanoparticles are observed to efficiently convert the energy of radiant photons to heat while water is observed to show poor evaporative performance under laser irradiation. Theoretical analysis of the evaporation rate with the classical diffusion driven evaporation model is found to fall short in predicting the evaporation rate in colloidal systems, even in the absence of laser irradiation. Thermal Marangoni and Rayleigh numbers are calculated from the theoretical examination and are found not potent enough to induce the circulation in such systems which could improve evaporation. Hence the observed weak internal circulation can be attributed to the solutal Marangoni arising out of the local concentration gradients of nanoparticles in the droplet and the enhanced Thermophoretic drift and Brownian dynamics of the nanoparticles. Also the enhancement in the diffusion coefficient and its strong dependence with the particle concentration is also contributing to the enhancement in enhanced evaporation rate in nanocolloidal systems. The augmentation in the evaporative process under laser radiation is found to be governed majorly by the optical heat generation with weak solutal Marangoni and a scaling model is able to accurately predict the experimental observations. The present findings could have implications in modulation of thermofluidic and species transport phenomena in microscale devices. © 2017 Elsevier Ltd

International Journal of Heat and Mass Transfer

Optical thermogeneration induced enhanced evaporation kinetics in pendant nanofluid droplets

While a body of literature on the spreading dynamics of surfactants and a few studies on the spreading dynamics of nanocolloids exist, to the best of the authors' knowledge, there are no reports on the effect of presence of surfactants on the spreading dynamics of nanocolloidal suspensions. For the first time the present study reports an extensive experimental and theoretical study on the effect of surfactant impregnated nanocolloidal complex fluids in modulating the spreading dynamics. A segregation analysis of the effect of surfactants alone, nanoparticle alone, and the combined effect of nanoparticle and surfactants in altering the spreading dynamics have been studied in detail. The spreading dynamics of nanocolloidal solutions alone and of the surfactant impregnated nanocolloidal solutions are found to be grossly different, and particle morphology is found to play a predominant role. For the first time the present study experimentally proves that the classical Tanner's law is disobeyed by the complex fluids in the case of particle alone and combined particle and surfactant case. We also discuss the role of imbibitions across the particle wedge in the precursor film in tuning spreading dynamics. We propose an analytical model to predict the nature of dependency of contact radius on time for the complex colloids. A detailed theoretical examination of the governing factors, the interacting forces at the three phase contact line, and the effects of interplay of surfactants and the nanoparticles at the precursor film in modulating the spreading dynamics has been presented for such complex colloids. © 2017 American Chemical Society.

Langmuir

Effect of Interaction of Nanoparticles and Surfactants on the Spreading Dynamics of Sessile Droplets

(Graph Presented) Even though there are quite large studies on wettability of aqueous surfactants and a few studies on effects of nanoparticles on wettability of colloids, to the best of authors' knowledge, there is no study reported on the combined effect of surfactant and nanoparticles in altering the wettability. The present study, for the first time, reports an extensive experimental and theoretical study on the combined effect of surfactants and nanoparticles on the wettability of complex fluids such as nanocolloids on different substrates, ranging from hydrophilic with a predominantly polar surface energy component (silicon wafer and glass) to near hydrophobic range with a predominantly dispersive component of surface energy (aluminum and copper substrates). Systematically planned experiments are carried out to segregate the contributing effects of surfactants, particles, and combined particle and surfactants in modulating the wettability. The mechanisms and the governing parameters behind the interactions of nanocolloids alone and of surfactant capped nanocolloids with different surfaces are found to be grossly different. The article, for the first time, also analyzes the interplay of the nature of surfaces, surfactant and particle concentrations on contact angle, and contact angle hysteresis (CAH) of particle and surfactant impregnated colloidal suspensions. In the case of nanoparticle suspensions, the contact angle is observed to decrease for the hydrophobic system and increase for the hydrophilic systems considered. On the contrary, the combined particle and surfactant colloidal system shows a quasi-unique wetting behavior of decreasing contact angle with particle concentration on all substrates. Also interestingly, the combined particle surfactant system at all particle concentrations shows a wetting angle much lower than that of the only-surfactant case at the same surfactant concentration. Such counterintuitive observations have been explained based on the near-surface interactivity of the particle, fluid, and surfactant molecules based on effective slip length considerations. The CAH analyses of colloidal suspensions at varying surfactant and particle concentrations reveal in-depth physical insight into contact line pinning, and a unique novel relationship is established between the contact angle and differential energy for distorting the instantaneous contact angle for a pinned sessile droplet. A detailed theoretical analysis of the governing parameters influencing the wettability has been presented invoking the principles of DLVO (Derjaguin-Landau-Verwey-Overbeek), surface energy and interaction parameters influencing at the molecular scale, and the theoretical framework is found to support the experimental observations. © 2017 American Chemical Society.

Journal of Physical Chemistry B

Wettability of Complex Fluids and Surfactant Capped Nanoparticle-Induced Quasi-Universal Wetting Behavior

Water Science and Technology

Rainwater harvesting - an alternative for securing food production under climate variability

Genetical Research

Books Received

Physics Letters A

Model for effective thermal conductivity of nanofluids

Macroscopic modelling of heat transfer in composites with interfacial thermal barrier

Model for heat conduction in nanofluids

Journal	Data powered by TypesetPhysical Review Letters
Publisher	Data powered by TypesetAmerican Physical Society
ISSN	00319007
Open Access	No