Thermal Conductivity, Rheology and Electrical Conductivity of Water- and Ethylene Glycol-Based Nanofluids with Copper and Aluminum Particles

Nanoparticles are mesoobjects that occupy an intermediate position in size between ordinary molecules and macroscopic particles. Suspensions with nanoparticles, called nanofluids, are also specific mesoscopic suspensions. Today it is known that their thermophysical and mechanical properties are not described by classical theories. The unusual properties of these dispersed fluids make them extremely popular in a wide variety of applications. However, successful use of nanofluids involves the prediction of their properties, which in turn requires systematic studies. This paper presents an experimental study on the thermophysical properties of water- and ethylene glycol-based nanofluids with aluminum and copper particles. The thermal conductivity, rheology and electrical conductivity of the nanofluids were systematically studied. The weight concentration of nanoparticles varied from 2.5 to 20%. It was shown that the thermal conductivity of the nanofluids significantly exceeds that of nanofluids with oxide particles. Its higher values are determined by the size of the nanoparticles and the thermal conductivity of the base fluid. The nanofluids studied are either pseudoplastic or viscoplastic. Their rheology is determined by the concentration and size of nanoparticles. The smaller the size of nanoparticles and the higher their concentration, the more likely the change in rheology is. Correlation curves were constructed for the rheological parameters of nanofluids versus the concentration and size of nanoparticles. It was found that the electrical conductivity of nanofluids increases almost linearly with increasing nanoparticle concentration and strongly depends on the nanoparticle size. The electrical conductivity mechanisms of nanofluids were discussed. The speed of sound in the nanofluid and its dependence on particle size were measured.