Characterization Of Enhanced Convective Heat Transfer In Fe₃O₄-Water Nanofluid Under Magnetic Excitation

With the development of modern vehicles,the traditional heat transfer fluids are nearly unable to meet the increasingly demanding heat transfer requirements,so this dissertation proposes a method to replace the traditional heat transfer masses with Fe₃O₄-water nanofluids.Using the controlled effect of Fe₃O₄ nanoparticles under magnetic excitation,the enhanced convective heat transfer characteristics of Fe₃O₄-water nanofluid under magnetic excitation are investigated by numerical simulation combined with experimental approach and the mechanism of its enhanced convective heat transfer under magnetic excitation is explored.The stability theory,thermal conductivity theory and mechanism of enhanced convective heat transfer of Fe₃O₄-water nanofluid under magnetic excitation are analyzed,and it is proved that the Lorentz force on Fe₃O₄ nanoparticles plays a dominant role in the enhanced convective heat transfer.The flow model,heat transfer model,DPM model and MHD model in CFD software Fluent are used to numerically simulate the convective heat transfer of Fe₃O₄-water nanofluid under magnetic excitation.The mass fraction and inlet temperature of Fe₃O₄-water nanofluid under multi-physics field coupling;the effects of magnetic excitation direction,magnetic field strength and alternating frequency on the enhanced convective heat transfer characteristics are investigated.It is concluded that increasing the mass fraction and inlet temperature of Fe₃O₄-water nanofluid can enhance the performance of enhanced convective heat transfer.Under magnetic excitation,a magnetic field horizontal to the flow direction deteriorates the performance of convective heat transfer of Fe₃O₄-water nanofluid;a perpendicular magnetic field enhances its convective heat transfer performance,and the enhancement is proportional to the magnetic field strength and Re.The excitation of alternating magnetic field in vertical direction further enhances the performance of convective heat transfer of Fe₃O₄-water nanofluid,and the enhancement is proportional to the magnetic field intensity and inversely proportional to the alternating frequency and Re.An experimental system for convective heat transfer of Fe₃O₄-water nanofluid under magnetic excitation was designed and built to study the effects of magnetic excitation on convective heat transfer and flow resistance characteristics of Fe₃O₄-water nanofluid.The mass fraction and inlet temperature of Fe₃O₄-water nanofluid under magnetic excitation;the direction of magnetic excitation,magnetic field strength and alternating frequency on the enhanced convective heat transfer of Fe₃O₄-water nanofluid have the same trend as the results of numerical simulation.The excitation of the perpendicular alternating magnetic field leads to a maximum increase of 24.69%in the convective heat transfer coefficient h for Fe₃O₄-water nanofluid compared to the base fluid.The use of Fe₃O₄-water nanofluid will increase the flow resistance,which is proportional to the mass fraction of Fe₃O₄-water nanofluid and the magnetic field intensity with a maximum increase of 13.9%in the flow resistance coefficient f.The excitation of the alternating magnetic field can reduce the flow resistance,and the reduction of the flow resistance decreases with the increase of the alternating frequency,and the flow resistance tends to the same intensity of the constant magnetic field.The results of numerical simulation and experiment are compared,and the maximum error between numerical simulation and experiment is 6.59%,which indicates that the numerical simulation basically meets the requirement of accuracy,and the reasons for the error between the simulated and experimental values are analyzed.