Thermal performance analysis of tunable magnetite nanofluids for an energy system

Abstract This study is based on the effect of external magnetic field on heat transfer performance and pumping power of Fe 3 O 4 /DI-water nanofluid is experimentally investigated under both laminar and turbulent flow regimes. The magnetite ferrofluids with 0.25% and 0.50% of weight fractions are prepared by a chemical precipitating method using ammonium hydroxide reagent for maximising the stabilisation. The experiments were conducted at various mass flow rates with two different external magnets arrangements and input powers. The result shows that the enhancement in local heat coefficient was more pronounced by introducing more magnets on the tube of the test section, especially in the turbulent flow regime. The heat transfer coefficient improves with an increase in Reynolds number as well. In addition, the effect of the magnetic field was not significant on the increment of pressure loss. Therefore, the highest performance index and lowest exergy loss were found for external magnets configurations at 0.25 wt% of nanofluids. The rise in heat transfer is assumed to be an accumulation of nanoparticles near the ring magnets, which may lead to a local thermal conductivity improvement. This aggregation formation enhancing the momentum and energy transfer in the fluid flow.