Thermophysical Investigations of Ultrasonically Assisted Magnetic Nanofluids for Heat Transfer

The NiFe2O4 magnetic nanoparticles synthesized and used to prepare stable water-based magnetic nanofluids of various concentrations by ultrasonically assisted two-step techniques. Thermophysical investigations are made on the nanofluids at different temperatures ranging from 20 to 80 degrees C. The measurements revealed that the thermal conductivity of nanofluids significantly enhances with an increase in the percentage of nanoparticle volume fraction. The thermal conductivity measurements showed that the maximum enhancement is 32.65% achieved at 1% nanoparticle volume fraction and at 80 degrees C. Specific heat of nanofluids was decreased with increasing nanoparticle volume fractions, and it augments with increasing temperature. Viscosity measurements showed that nanofluid had a Newtonian behavior at all nanoparticle volume fractions and temperatures considered. The viscosity of the nanofluid increased with increasing nanoparticle concentration and decreasing temperature. Experimental results revealed that the viscosity sensitivity to temperature variation is minor, while it is more sensitive to the variations of nanoparticle volume fraction. The density of nanofluids was increased with increasing nanoparticle volume fractions and decreased with increasing temperature. Lastly, efforts were made to provide a precise correlation to estimate the thermal conductivity, as well as other thermophysical properties at various temperatures and volume fractions of nanoparticles. The comparison between the results and the correlation results showed a good agreement.