Temperature-dependent rheological behavior of nanofluids rich in carbon-based nanoparticles

Abstract

Herein, the temperature-dependent viscosity of nanofluids consisting carbon-based nanoparticles (CBNs), such as graphite, graphene oxide modified with oleic acid, and reduced graphene oxide, were investigated with steady-shear viscometry. The viscosity of nanofluids relative to that of the base fluid decreased until 30 °C and increased thereafter. Moreover, the CBN nanofluids had lower dynamic viscosity than the base fluid. Particle size distribution analysis revealed a polydispersed system of nanofluids, and intrinsic viscosity studies investigated the contribution of completely nanosized particles to the viscous behavior. Based on their lateral size, the CBNs played the role of percolation participants or Brownian motion participants. It was found that the total numbers of percolation participants varied among different types of CBN nanofluids. Furthermore, the size of the percolation participants influenced to optimize the number of nanoparticles undergoing Brownian motion. Regarding size effects and the affinity of the CBNs with the base fluid, the interaction between nanoparticles with different lateral sizes induced not only temperature-dependent viscosity in the nanofluids but also a reduction in dynamic viscosity. The mechanism underlying this lower viscosity was explained by a combination of percolation effects and nanoparticle structuring. © 2020 Elsevier B.V.