(455h) An Eyring-Based Model to Estimate the Dynamic Viscosity of Nanofluids

Nanofluids are a new class of heat transfer fluids obtained by suspending nano-sized particles into a base liquid. It has been shown¹ that an uniform dispersion of low concentrations of nanoparticles (e.g. TiO₂, CuO, Al₂O₃) into a conventional liquid such as water may yield a significant enhancement in the thermal performance of the resulting suspension. Another important transport property that also undergoes a substantial change is the dynamic viscosity of the nanofluid. In fact, the increase in viscosity of nanofluids may occur thus leading to serious operating limitations in terms of increased pressure drops and therefore costly pumping requirements. Consequently, the importance of accurately calculating the effective dynamic viscosity of a nanofluid seems paramount in establishing if its use is indeed advantageous with respect to its pure base liquid. Well-known colloid dispersion theories by Einstein^2,3, Brinkman⁴ and Lundgren⁵ have been recently used to predict the dynamic viscosity of nanofluids; however, all these theories significantly under-estimate this property. The aim of this work is to present the development of a viscosity model under the basis of the Eyring theory to properly estimate the effective dynamic viscosity of nanoparticle suspensions (aqueous and non-aqueous) within sufficiently wide ranges of temperature, particle volume fraction and particle diameter.

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