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Abstract
Theoretical analysis, numerical simulations, and experimental studies are used to comprehensively investigate the changes in the heat transfer characteristics of Fe3O4–water magnetic nanofluid under different types of magnetic fields and the heat transfer mechanism, providing new ideas for its practical application. By combining the fundamental conservation theorem and the Boussinesq approximation, dimensionless control equations have been established. The analysis of the variation pattern of the calculated values of the source terms under different boundary conditions, as well as the order of magnitude analysis, concludes that: the enhanced trend of Brownian motion and thermophoretic motion is the main reason for the enhanced heat transfer capability of the magnetic nanofluid; where the thermophoretic motion contributes slightly more to the heat transfer; the increase in Joule heat is the reason for the further enhancement of the heat transfer capability by the magnetic field. Volume fraction, temperature, and magnetic field strength are positively correlated with the average convective heat transfer coefficient. The reason for magnetic fields to enhance heat transfer is revealed by the deflection of the magnetic nanofluid by the magnetic body flow under local magnetic fields to form localized reflux. The alternating magnetic field further enhances the ability of magnetic fields to enhance heat transfer in magnetic nanofluids. Overall, the effect of the applied magnetic field on the motion of the magnetic nanoparticles causes the disruption of the thermal boundary layer, which is responsible for the enhanced heat transfer capacity of magnetic nanofluids.