Abstract
The dynamic viscosity and rheological properties of two different non-aqueous graphene nano-plates-based nanofluids are experimentally investigated in this paper, focusing on the effects of solid volume fraction and shear rate. For each nanofluid, four solid volume fractions have been considered ranging from 0.1% to 1%. The rheological characterization of the suspensions was performed at 20 C, with shear rates ranging from to , using a cone-plate rheometer. The Carreau–Yasuda model has been successfully applied to fit most of the rheological measurements. Although it is very common to observe an increase of the viscosity with the solid volume fraction, we still found here that the addition of nanoparticles produces lubrication effects in some cases. Such a result could be very helpful in the domain of heat extraction applications. The dependence of dynamic viscosity with graphene volume fraction was analyzed using the model of Vallejo et al.
Highlights
This paper presents an experimental study of the rheological properties of two thermal nanofluids based on an allotropic variety of graphene nanoparticles, called graphene nanoplatelets (GNPs)
To study the state of dispersion of the nano-particles in the base fluid and to evaluate the presence and size of graphene aggregates [33,44,45,46,47], samples of each suspension were analyzed by scanning electron microscope (SEM) after drying (Figure 3 shows an example of nanofluid based on ethylene glycol, for a solid volume fraction φ = 0.25%: Ethylene glycol (EG)-GNPs-0.25)
An experimental study of the rheological properties of two different graphene based nanofluids was presented for the following base fluids: ethylene glycol and an industrial lubricating oil
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Kole et al [34] examined and evaluated the effect of graphene nano-sheets, added to the base fluid (distilled water + ethylene glycol) Their results showed a non-Newtonian behavior with the appearance of a reduction in viscosity by shearing, and an increase of 100% compared to the basic fluid for a graphene volume fraction of 0.395%. The addition of nanoparticles to a base fluid can significantly alter its rheological properties, inducing, for example, non-Newtonian behaviors, and, it can lead to a significant increase of head losses These pressure losses and rheological behavior alterations can represent a serious limitation to the industrial use of thermal nanofluids [32]. Experimental results are presented and analyzed in terms of the influence of solid volume fraction and shear rate on the rheological properties of the two graphene-based suspensions (Results and Discussion). Conclusions and perspectives for future investigations are proposed (Conclusions and Perspectives)
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