Study of the Effective Thermal Conductivity of Nanofluids

2005 ◽  
Author(s):  
Ratnesh K. Shukla ◽  
Vijay K. Dhir
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Brownian Motion ◽  
Effective Thermal Conductivity ◽  
Volume Fraction ◽  
Experimental Results ◽  
Homogeneous Liquid ◽  
Size Dependent ◽  
Water Based ◽  
Base Liquid

Nanofluids, that is liquids containing nanometer sized metallic or non-metallic solid nanoparticles, show an increase in thermal conductivity compared to that of the base liquid. In this paper a model for thermal conductivity of nanofluids based on the theory of Brownian motion of particles in a homogeneous liquid combined with the macroscopic Hamilton-Crosser model is presented. The model is shown to predict a temperature and particle size dependent thermal conductivity. Comparison between the predicted and experimental results show that the model is able to accurately predict the temperature and volume fraction dependence of the thermal conductivity of water based alumina and gold nanofluids.

Parametric Analysis of Effective Thermal Conductivity Models for Nanofluids

2012 ◽  
Author(s):  
Mohsen Sharifpur ◽  
Tshimanga Ntumba ◽  
Josua P. Meyer
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Brownian Motion ◽  
Effective Thermal Conductivity ◽  
Parametric Analysis ◽  
Base Fluid ◽  
Volume Fraction ◽  
Hybrid Models ◽  
The Impact ◽  
Conductivity Models

There is a lack of reported research on comprehensive hybrid models for the effective thermal conductivity of nanofluids that takes into consideration all major mechanisms and parameters. The major mechanisms are the nanolayer, Brownian motion and clustering. The recognized important parameters can be the volume fraction of the nanoparticles, temperature, particle size, thermal conductivity of the nanolayer, thermal conductivity of the base fluid, PH of the nanofluid, and the thermal conductivity of the nanoparticle. Therefore, in this work, a parametric analysis of effective thermal conductivity models for nanofluids was done. The impact of the measurable parameters, like volume fraction of the nanoparticles, temperature and the particle size for the more sited models, were analyzed by using alumina-water nanofluid. The result of this investigation identifies the lack of a hybrid equation for the effective thermal conductivity of nanofluids and, consequently, more research is required in this field.

Thermal Conductivity of Metal-Oxide Nanofluids: Particle Size Dependence and Effect of Laser Irradiation

2006 ◽  
Vol 129 (3) ◽  
pp. 298-307 ◽  
Author(s):  
Sang Hyun Kim ◽  
Sun Rock Choi ◽  
Dongsik Kim
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Effective Thermal Conductivity ◽  
Laser Irradiation ◽  
Volume Fraction ◽  
Suspended Particle ◽  
Titanium Dioxide Nanoparticles ◽  
Size Change ◽  
Conductivity Enhancement ◽  
Wide Range

The thermal conductivity of water- and ethylene glycol-based nanofluids containing alumina, zinc-oxide, and titanium-dioxide nanoparticles is measured using the transient hot-wire method. Measurements are performed by varying the particle size and volume fraction, providing a set of consistent experimental data over a wide range of colloidal conditions. Emphasis is placed on the effect of the suspended particle size on the effective thermal conductivity. Also, the effect of laser-pulse irradiation, i.e., the particle size change by laser ablation, is examined for ZnO nanofluids. The results show that the thermal-conductivity enhancement ratio relative to the base fluid increases linearly with decreasing the particle size but no existing empirical or theoretical correlation can explain the behavior. It is also demonstrated that high-power laser irradiation can lead to substantial enhancement in the effective thermal conductivity although only a small fraction of the particles are fragmented.

Determining the Effective Thermal Conductivity of a Nanofluid Using Brownian Dynamics Simulation

2003 ◽  
Author(s):  
P. Bhattacharya ◽  
S. K. Saha ◽  
A. Yadav ◽  
P. E. Phelan ◽  
R. S. Prasher
Keyword(s):  
Thermal Conductivity ◽  
Brownian Motion ◽  
Effective Thermal Conductivity ◽  
Brownian Dynamics ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Solid Particles ◽  
Dynamics Simulation ◽  
Fluid Viscosity ◽  
Brownian Dynamics Simulation

A nanofluid is a fluid containing suspended solid particles, with sizes of the order of nanometers. Normally the fluid has a low thermal conductivity compared to the suspended particles. Therefore introduction of these particles into the fluid increases the effective thermal conductivity of the system. It is of interest to predict the effective thermal conductivity of such a nanofluid under different conditions like varying particle volume fraction, varying particle size, changing fluid conductivity or changing fluid viscosity, especially since only limited experimental data are available. Also, some controversy exists about the role of Brownian motion in enhancing the nanofluid’s thermal conductivity. We have developed a novel technique to compute the effective thermal conductivity of a nanofluid using Brownian dynamics simulation, which has the advantage of being computationally less expensive than molecular dynamics. We obtain the contribution of the nanoparticles towards the effective thermal conductivity using the equilibrium Green-Kubo method. Then we combine that with the thermal conductivity of the base fluid to obtain the effective thermal conductivity of the nanofluid, and thus are able to show that the Brownian motion contributes greatly to the thermal conductivity.

scholarly journals Improved Heat Transfer in Guar Gel Composites Reinforced with Randomly Distributed Glass Microspheres

2021 ◽  
Author(s):  
Ruifeng CAO ◽  
Taotao WANG ◽  
Yuxuan ZHANG ◽  
Hui WANG
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Particle Size ◽  
Composite Materials ◽  
Effective Thermal Conductivity ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Glass Microspheres ◽  
Particle Volume ◽  
Number Of Particles

Improved heat transfer in composites consisting of guar gel matrix and randomly distributed glass microspheres is extensively studied to predict the effective thermal conductivity of composites using the finite element method. In the study, the proper and probabilistic three-dimensional random distribution of microspheres in the continuous matrix is automatically generated by a simple and efficient random sequential adsorption algorithm which is developed by considering the correlation of three factors including particle size, number of particles, and particle volume fraction controlling the geometric configuration of random packing. Then the dependences of the effective thermal conductivity of composite materials on some important factors are investigated numerically, including the particle volume fraction, the particle spatial distribution, the number of particles, the nonuniformity of particle size, the particle dispersion morphology and the thermal conductivity contrast between particle and matrix. The related numerical results are compared with theoretical predictions and available experimental results to assess the validity of the numerical model. These results can provide good guidance for the design of advanced microsphere reinforced composite materials.

Stability of Zinc Oxide Nanofluids Prepared with Aggregated Nanocrystalline Powders

2008 ◽  
Vol 8 (12) ◽  
pp. 6361-6366
Author(s):  
J. P. Leonard ◽  
S. J. Chung ◽  
I. Nettleship ◽  
Y. Soong ◽  
D. V. Martello ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Zinc Oxide ◽  
Brownian Motion ◽  
Preparation Method ◽  
Volume Fraction ◽  
High Volume ◽  
Nanocrystalline Powders ◽  
Zno Powder ◽  
20 Nm

Aqueous zinc oxide (ZnO) suspensions were prepared using a two-step preparation method in which an aggregated nanocrystalline ZnO powder was dispersed in water using a polyelectrolyte. The fluid showed anomalously high thermal conductivity when compared with the Maxwell and Hamilton-Crosser predictions. However, analysis of the particle size distribution showed that the fluid contained aggregated 20 nm crystallites of ZnO with a high volume fraction of particles larger than 100 nm. Sedimentation experiments revealed that particles settled out of the stationary fluid over times ranging from 0.1 hours to well over 10,000 hours. The size of the particles remaining in suspension agreed well with predictions made using Stoke's law, suggesting flocculation was not occurring in the fluids. Finally, a new concept of nanofluid stability is introduced based on the height of the fluid, sedimentation, Brownian motion and the kinetic energy of the particles.

Convective Heat Transfer for Water-Based Alumina Nanofluids in a Single 1.02-mm Tube

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
W. Y. Lai ◽  
S. Vinod ◽  
P. E. Phelan ◽  
Ravi Prasher
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat Transfer ◽  
Effective Thermal Conductivity ◽  
Convective Heat ◽  
Volume Fraction ◽  
Pure Water ◽  
Submicron Particles ◽  
Strong Temperature Dependence ◽  
Water Based

Nanofluids are colloidal solutions, which contain a small volume fraction of suspended submicron particles or fibers in heat transfer liquids such as water or glycol mixtures. Compared with the base fluid, numerous experiments have generally indicated an increase in effective thermal conductivity and a strong temperature dependence of the static effective thermal conductivity. However, in practical applications, a heat conduction mechanism may not be sufficient for cooling high heat dissipation devices such as microelectronics or powerful optical equipment. Thus, thermal performance under convective heat transfer conditions becomes of primary interest. We report here the heat transfer coefficient h in both developing and fully developed regions by using water-based alumina nanofluids. Our experimental test section consists of a single 1.02-mm diameter stainless steel tube, which is electrically heated to provide a constant wall heat flux. Both pressure drop and temperature differences are measured, but mostly here we report our h measurements under laminar flow conditions. An extensive characterization of the nanofluid samples, including pH, electrical conductivity, particle sizing, and zeta potential, is also documented. The measured h values for nanofluids are generally higher than those for pure water. In the developing region, this can be at least partially explained by Pr number effects.

Thermal Conductivity Affected by Temperature and Particle Size in Al2O3-Water Nanofluids

2011 ◽  
Author(s):  
D. Kwek ◽  
A. Crivoi ◽  
Fei Duan
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Effective Thermal Conductivity ◽  
Experimental Results ◽  
Al2o3 Nanoparticles ◽  
Particle Sizes ◽  
Transient Hot Wire ◽  
Hot Wire ◽  
Nanoparticle Concentration ◽  
Wire Method

The effective thermal conductivity of Al2O3-water nanofluids has been measured using a transient hot wire method. Experimental results demonstrate that the thermal conductivity of Al2O3 nanofluids increases linearly with increasing nanoparticle concentration. Adding 5 vol % of Al2O3 nanoparticles in water increases the effective thermal conductivity of the nanofluids by 20%. Thermal conductivity of Al2O3 nanofluids increases with an increase of temperature. The enhancement is around 1.7% at 15 °C in comparison with around 16% at 55 °C in a 1 vol % nanofluid. The particle size is another important parameter for the effective thermal conductivity. The increase of thermal conductivity reduces from 30% to 10% as the particle sizes increase from 10 nm to 35 nm. The increase of the effective thermal conductivity starts as the particle size increases above 35 nm, reaching about 27.5% in the nanofluid with the particle size at 150 nm.

Investigation on Thermal Conductivity of Low Concentration AlN/EG Nanofluids

2013 ◽  
Vol 546 ◽  
pp. 112-116
Author(s):  
Yan Jiao Li ◽  
Chang Jiang Liu ◽  
Zhi Qing Guo ◽  
Qiu Juan Lv ◽  
Fang Xie
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Volume Fraction ◽  
Maxwell Model ◽  
Experimental Results ◽  
Effect Of Temperature ◽  
Transient Hot Wire ◽  
Hot Wire ◽  
Wire Method ◽  
Nanoparticles Volume Fraction

The thermal conductivity of AlN/EG nanofluids was investigated by transient hot-wire method. Experimental results indicated that the thermal conductivity of AlN/EG nanofluids increase nearly linear with the increase of nanoparticles volume fraction, and the results can’t be predicted by conditional Maxwell model. The effect of temperature on effective thermal conductivity of AlN/EG nanofluids was investigated. Result indicated that the thermal conductivity of AlN/EG nanofluids increased with the increase of temperature.

Effective thermal conductivity of silicone/phosphor composites

2011 ◽  
Vol 45 (23) ◽  
pp. 2465-2473 ◽  
Author(s):  
Qin Zhang ◽  
Zhihua Pi ◽  
Mingxiang Chen ◽  
Xiaobing Luo ◽  
Ling Xu ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Effective Thermal Conductivity ◽  
Volume Fraction ◽  
Numerical Study ◽  
Element Model ◽  
Interfacial Thermal Resistance ◽  
Conductivity Measurements ◽  
The Monte Carlo Method ◽  
Random Particle

The effective thermal conductivity of silicone/phosphor composites is studied experimentally and numerically. Thermal conductivity measurements are conducted from 30°C to 150°C for the composites with phosphor volume fraction up to 40%. In the numerical study, a finite element model with empirical particle size distribution and random particle position is constructed using a probability density function and the Monte Carlo method, and the interfacial thermal resistance layer between phases also introduced in the model. The results indicate that when phosphor concentration is below 25 vol.%, the conductivity of the composite increases slightly with either phosphor volume fraction or temperature, and the Kapitza radius of the composite is 0.8 µm. When phosphor concentration is above 25 vol.%, the increase of conductivity correlates positively with phosphor volume fraction significantly but negatively with the temperature, and the Kapitza radius is 0.032 µm.

scholarly journals An extended irreversible thermodynamic modelling of size-dependent thermal conductivity of spherical nanoparticles dispersed in homogeneous media

2015 ◽  
Vol 471 (2182) ◽  
pp. 20150144 ◽  
Author(s):  
G. Lebon ◽  
H. Machrafi ◽  
M. Grmela
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Phonon Scattering ◽  
Volume Fraction ◽  
Irreversible Thermodynamic ◽  
Irreversible Thermodynamics ◽  
Point Of View ◽  
Size Dependent ◽  
Si Nanoparticles ◽  
Homogeneous Media

The effective thermal conductivity of nanocomposites constituted by nanoparticles and homogeneous host media is discussed from the point of view of extended irreversible thermodynamics. This formalism is particularly well adapted to the description of small length scales. As illustrations, dispersion of Si nanoparticles in Ge (respectively, SiO 2 in epoxy resin) homogeneous matrices is investigated, the nanoparticles are assumed to be spherical with a wide dispersion. Four specific problems are studied: the dependence of the effective thermal conductivity on the volume fraction of particles, the type of phonon scattering at the interface particle–matrix, the radius of the nanoparticles and the temperature.

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