The role of several heat transfer mechanisms on the enhancement of thermal conductivity in nanofluids

Abstract

A modelling of the thermal conductivity of nanofluids based on extended irreversible thermodynamics is proposed with emphasis on the role of several coupled heat transfer mechanisms: liquid interfacial layering between nanoparticles and base fluid, particles agglomeration and Brownian motion. The relative importance of each specific mechanism on the enhancement of the effective thermal conductivity is examined. It is shown that sizes of the nanoparticles and the liquid boundary layer around the particles play a determining role. For nanoparticles close to molecular range, the Brownian effect is important. At nanoparticles of the order of 1-100 nm, both agglomeration and liquid layering are influent. Agglomeration becomes the most important mechanism at nanoparticle sizes of the order of 100 nm and higher.The theoretical considerations are illustrated by three case-studies: suspensions of alumina rigid spherical nanoparticles in water, ethylene glycol and a 50/50 w% water/ethylene-glycol mixture, respectively, good agreement with experimental data is observed.

A thermodynamic model of nanofluid viscosity based on a generalized Maxwell-type constitutive equation

“…Here for simplicity , we limit our developments to the use of P and P (3) as flux state variables but there will be no difficulty to include higher order tensors as P (4) , … P (N) as done previously in the problem of non-local heat conduction wherein an infinite number of extra fluxes have been introduced [30][31][32]. From the kinetic theory point of view, P (2) and P (3) represent the second and third order moments of the velocity distribution.…”

Heat Transfer Enhancement by Coupling of Carbon Nanotubes and SiO2 Nanofluids: A Numerical Approach

“…Lately, Hamilton and Crosser [4], came up with a modified version of Maxwell's model, which demonstrated the influence of particle shape and volume fraction, on the thermal efficiency of the fluid containing nanometer sized structures. Further studies have exposed a diverse class of models, which incorporates different features of nanomaterials, like Brownian motion [5], nanoparticles size [6,7], shapes [8], liquid layering [9], and particles agglomeration [10,11], in order to examine the variations in thermo-physical characteristics of nanofluid.…”

Thermophysical Analysis of Water Based (Cu–Al2O3) Hybrid Nanofluid in an Asymmetric Channel with Dilating/Squeezing Walls Considering Different Shapes of Nanoparticles

“…More studies in this area introduce a variety of models which examined the effects of nanoparticles type [6][7][8], particle shapes [9] and particles size [10,11] etc. Moreover, various heat transfer mechanisms including Brownian movement of particles [12], particles agglomeration [13,14] and liquid layering [15] would also gain the attention of many scientists.…”