Rheological and flow characteristics of nanofluids: Influence of electroviscous effects and particle agglomeration

Abstract

Nanofluids have shown remarkable attraction in heat transfer community due to its reported enhanced thermal properties. One factor which can restrict nanofluids in heat transfer application is the increased viscosity value (compared to classical predictions). Particle aggregation occurring was the major reason for this observation. Even though majority of the aqueous nanofluids prepared in literature were stabilized electrostatically by adjusting the pH, studies on the effect of the electrical double layer thus created and its influence on viscosity increase has not been investigated for these nanofluids so far. Thus, in the present paper, rheological properties of alumina-water nanofluids, which are electrostatically stabilized, are measured and the increase in suspension viscosity due to presence of this electrical double layer causing additional electroviscous effects is brought out. Based on dynamic light scattering studies, particle agglomeration and its subsequent effect in increasing the viscosity of alumina-ethylene glycol nanofluid, where electroviscous effects are absent, are also considered. It is noted that the understanding of electroviscous effect is equally important as understanding the particle agglomeration effect and understanding both the effects is central to revealing the physics of nanofluid rheology. Further, hydrodynamic experiments are made, which show that nanofluids behaves almost like a homogeneous fluids under flow conditions, and by knowing their properties, such as viscosity and density, pressure drop can be predicted.

Effect of volume-fraction dependent agglomeration of nanoparticles on the thermal conductivity of nanocomposites: Applications to epoxy resins, filled by SiO2, AlN and MgO nanoparticles

“…The first one is linked to the use of EIT leading to the establishment of relation (22), the second one is that the degree of agglomeration is explicitly expressed as a (power-law) function of the volume fraction (see Eq. (23)).…”

“…propose , ≈ 3 , while Anoop et al [22] [20]. In the forthcoming, we consider AlN and MgO nanoparticles for which experimental gyration radii have been measured in our laboratory (see Section 4).…”

“…For the sake of simplicity, the particles are supposed to be spherical and monodisperse. Many experiments have been performed on investigating the role of agglomeration [18][19][20][21][22], which will therefore be given a special attention. The majority of models taking into account nanoparticles' agglomeration introduce an agglomerate radius that is kept fixed [23] or consider a change in agglomerate's size due to aging [21], without examining the influence of volume fraction on the degree of agglomeration.…”

Determination of the packing fraction of silica nanoparticles from the rheological and viscoelastic measurements of nanofluids

“…The effect influencing the fluidity limit is the secondary electroviscous effect. It produces an increase of the viscosity due to the overlap of electrical double layers, modifyin the final packing fraction of the particles at the jamming point (Anoop et al, 2009;Hunter, 1988). In this way high repulsions generate loose structures with low packing.…”

Group analysis and numerical computation of magneto-convective non-Newtonian nanofluid slip flow from a permeable stretching sheet

“…They considered the rheology of seven different fluids that include dispersions of metal-oxide nanoparticles in water, and in synthetic oil, elaborating on the effects of particle shape and concentration on the viscosity of these same nanofluids and benchmarking computations with classical theories on suspension rheology. Further significant studies exploring the non-Newtonian characteristics of nanofluids include Anoop et al (2009) who considered agglomeration. Kim et al (2011) showed that rod-like alumina nanoparticles have a sol-or weakly flocculated gel-structure depending on particle concentration and that thermal conductivity rate is enhanced with concentration and is markedly faster in the sol state than in the weakly flocculated gel state.…”