Effect of the mixture of mineral/sunflower oil based ferrofluid on thermal and flow properties

Ferrofluids were prepared by adding γ-Fe₂O₃ nanoparticles, which was synthesized by co-precipitation method, into a blend of 1:1 ratio of mineral/sunflower oil. The structure, morphology and crystal size of nanoparticles were analyzed by FTIR, SEM, XRD and nanosizer. The crystal size of the nanoparticles was 12 nm calculated by using Debye–Scherer equation. The results via nanosizer showed that the mean diameter of nanoparticles was ∼59 nm at 100% intensity. The viscosity and thermal conductivity of the mineral oil, sunflower oil and different ratios of mineral/sunflower oil mixtures were investigated. Mineral oil has high thermal conductivity; however it requires high energy consumption for circulation due to its high viscosity. Although the viscosity of sunflower oil is low, its thermal conductivity is not sufficient for heat transfer applications. The results showed that 1:1 ratio of mineral/sunflower oil has a practical viscosity with low thermal conductivity. The addition of the synthesized γ-Fe₂O₃ nanoparticles into the mixture resulted in obtaining a ferrofluid with higher thermal conductivity. An average enhancement of 51% in the thermal conductivity of ferrofluid at 1.5 (w/v)% concentrations of γ-Fe₂O₃ nanoparticles was achieved as compared to the 1:1 ratio of mineral/sunflower oil. This ferrofluid may have practical applications in computer appliances, bearings, transducers, coolant, shielding and others. (paper)