The rheological and thermal behavior of CuO in ethylene glycol - water nanofluids

In this work, copper oxide nanofluids have been prepared by adding 2%, 4% and 6% (vol/vol) into the ethylene glycol/water mixture (60:40) for measuring the viscosity and thermal experiments. The mixing section was carried out by ultrasonic bath. By using the well-known hot wire method the thermal behavior of nanofluids has been studied. The results show that the ratio of thermal conductivity reaches to 1.15, 1.26 and 1.31 after adding 2%, 4% and 6% nanoparticles, respectively. The thermal behavior of nanofluids was studied by Maxwell, Bruggeman and Koo and Klenstreuer models. Among the applied models, the latter one can better predict the experimental data. In another part of this work, the viscosity of samples was measured by a modern Brookfield rheometer at ranging from 5 s-1 to 200 s-1 and from -5°C to 40°C. The results indicate that the base flow shows Newtonian behavior over the whole range of shear rates and temperatures. But the nanofluids are switching to Non-Newtonian behavior. This effect can be enhanced at lower temperatures. The viscosity/shear rate data was modeled by Sisko model and then the parameter of n, K and infinite viscosity has been calculated. The viscosity is going to decrease by increasing the temperature. At the end, this behavior was studied by exponential form which suggested by Namburu et al. Based on this model, the fitting parameters of A and B were then extracted that can predict the experimental data very well.