Experimental Characterization of Magnetic Field Waveform Effects on Heat Transfer and Entropy Generation of Fe3O4-MgO

Magnetic hybrid nanofluids (MHNFs), also known as ferrofluids, exhibit increased efficiency under an appropriate magnetic field. This work explores the effectiveness of heat transfer in MHNFs across various nanoparticle concentrations and magnetic field waveforms in both turbulent and transitional flow regimes. Five nanoparticle volume fractions (0.00625 % to 0.1 %) were tested under square, sine, and triangular magnetic fields across a Reynolds number (Re) spectrum of 1000 to 8000. Compared to DIW in the transitional regime, MHNFs showed up to 5.2 % improvement in the convective heat transfer coefficient at a 0.0125 % volume fraction, with average Nusselt number (Nu) increases of up to 5.1 %. The square wave magnetic field was particularly effective, enhancing performance by 8.8 % at 0.0125 % and 7.9 % at 0.00625 % in the turbulent phase. In the transition phase, Nu enhancements reached up to 31.38 % at 0.0125 % volume fraction without a magnetic field, with the square wave field achieving 36.1 % improvement, a 15.0 % increase compared to the no field case. Triangular waves induced the earliest transition onset at Re 2495.12 for 0.1 % volume fraction. The highest thermal performance factor (TPF) was 1.9789 for the turbulent regime and 4.2297 for the transitional regime. Triangular wave fields were most effective at reducing entropy generation, especially at high velocities.