Review of Heat Conduction in Nanofluids

Abstract

Nanofluids—fluid suspensions of nanometer-sized particles—are a very important area of emerging technology and are playing an increasingly important role in the continuing advances of nanotechnology and biotechnology worldwide. They have enormously exciting potential applications and may revolutionize the field of heat transfer. This review is on the advances in our understanding of heat-conduction process in nanofluids. The emphasis centers on the thermal conductivity of nanofluids: its experimental data, proposed mechanisms responsible for its enhancement, and its predicting models. A relatively intensified effort has been made on determining thermal conductivity of nanofluids from experiments. While the detailed microstructure-conductivity relationship is still unknown, the data from these experiments have enabled some trends to be identified. Suggested microscopic reasons for the experimental finding of significant conductivity enhancement include the nanoparticle Brownian motion, the Brownian-motion-induced convection, the liquid layering at the liquid-particle interface, and the nanoparticle cluster/aggregate. Although there is a lack of agreement regarding the role of the first three effects, the last effect is generally accepted to be responsible for the reported conductivity enhancement. The available models of predicting conductivity of nanofluids all involve some empirical parameters that negate their predicting ability and application. The recently developed first-principles theory of thermal waves offers not only a macroscopic reason for experimental observations but also a model governing the microstructure-conductivity relationship without involving any empirical parameter.

An improved model for thermal conductivity of nanofluids with effects of particle size and Brownian motion

“…Many researchers attributed the impact of Brownian motion on the heat conduction to the dynamic thermal conductivity [4,16,17], which was reflected mainly by the microconvection of the fluids. However, the dynamic thermal conductivity models contain some empirical relations and coefficients, which may not conducive to practical application.…”

“…The heat transport can be improved up to 20% by adding nanoparticles with volume fraction less than 4% [3]. The main four factors contributing to thermal conductivity enhancement include the adsorbed liquid layer at the interface, the nanoparticle aggregation, the nanoparticle Brownian motion and the Brownian motion-induced microconvection [4]. The dynamic enhancement mechanism mainly stems from Brownian motion.…”

The shape effects of nanoparticles suspended in HFE-7100 over wedge with entropy generation and mixed convection

“…Typical thermal conductivity of spherical particles enhancements is in the range 15-40 % over the base fluid and heat transfer coefficient enhancements have been found up to 40 % (Yu et al 2008). In the literature, different authors investigate the thermal properties of cylindrical structures nanoparticle, namely single or multiwall nanotubes suspensions in a variety of solvents (Eastman et al 2004;Fan and Wang 2011;Keblinski et al 2008;Kleinstreuer and Feng 2011). Owing to different aspect ratios, solvents, and type of nanotubes (single or multiwall), there is considerable spread in the data.…”

An experimental study of thermal diffusivity of Au nanoparticles: effects of concentration particle size

“…In addition, the nature of the surface, such as charge, its distribution, and the presence of surfactant plays an important role [11,12]. The subject of heat transport through dilute suspensions of solid particles has received a renewed boost owing to the reports of enhancement in thermal conductivity of suspensions carrying nanoparticles [13][14][15][16].…”