(445d) Numerical Investigation of Rheological Properties of Nanofluids Containing Organic Modified Nanoparticles

Nanofluids are colloidal suspensions of nanoparticles and have attracted much attention in various fields. For example, nanofluids are expected to be applied as refrigerant, coolant and nano-ink for printed electronics. Nanoparticles in nanofluids are required to keep a dispersed state, but nanoparticles usually form aggregates in solvent because of their high surface energy. In order to deal with this problem, organic modified nanoparticles of single nanometer size have been synthesized by the supercritical hydrothermal method. This method makes it possible to design the nanoparticles which can be well-dispersed in organic solvent even at high concentration by selecting the appropriate organic molecules.

In this study, for contributions to design and control of nanofluids containing the organic modified nanoparticles, the dispersion and aggregation behavior of the organic modified nanoparticles in shear flow are investigated by numerical simulation. In this simulation, the discrete element method-computational fluid dynamics (DEM-CFD) model is used and the motion of nanoparticles and the flow field in solvent are coupled. Furthermore, as the interaction forces between nanoparticles, the forces caused by organic modifiers are considered in addition to van der Waals force, contact force and hydrodynamic force.

The effects of organic modifier and volume fraction of nanoparticles on the dispersion and aggregation behavior of nanoparticles are investigated when the organic solvent is toluene, the nanoparticle is an alumina nanoparticle with a diameter of 25 nm and the organic modifiers are decanoic acid, tetradecanoic acid and oleic acid. In addition, the relationship between the apparent viscosity of nanofluids and the dispersion and aggregation behavior of organic modified nanoparticles in toluene are revealed. In the case of nanoparticles modified by oleic acid which has high affinity for toluene, the nanoparticles are well-dispersed at high volume fraction of nanoparticles. On the other hand, in the case of decanoic acid which has low affinity for toluene, nanoparticles tend to form aggregates even at low volume fraction. In addition, the viscosity of nanofluids containing decanoic acid-modified nanoparticles is larger than that of nanofluids containing oleic acid-modified nanoparticles. Furthermore, in the case of decanoic acid-modified nanoparticles, the viscosity of nanofluids increases markedly with volume fraction of nanoparticles.