Study On The Flow And Heat Transfer Characteristics Of Magnetic Nanofluids

Magnetic nanofluid is a kind of solid-liquid two-phase suspension,which is based on a certain proportion of adding nano-sized solid particles containing magnetism in the base liquid,and making it evenly dispersed in the base liquid.In order to improve the heat transfer and flow characteristics of magnetic nanofluids,the mechanism of enhanced heat transfer of magnetic nanofluids was discussed.In this paper,two-step method was used to prepare stable Fe₃O₄-H₂O nanofluids.The physical parameters of Fe₃O₄-H₂O nanofluids were studied and the convective heat transfer was built The flow characteristics and heat transfer performance of Fe₃O₄-H₂O nanofluids were experimentally studied and theoretically analyzed.The main research contents are as follows:The preparation methods of magnetic nanofluids were analyzed and compared.Fe₃O₄-H₂O nanofluids with different concentrations were prepared by a two-step method.The stability of Fe₃O₄-H₂O nanofluids was studied by visual inspection.The physical parameters of the Fe₃O₄-H₂O nanofluid were analyzed.The density,specific heat,surface tension,viscosity,and thermal conductivity of the Fe₃O₄-H₂O nanofluid were analyzed.The surface tension,viscosity,and thermal conductivity were studied by the magnetic nanofluid volume concentration and The effect of temperature is compared and analyzed with experiments and classical models.The flow characteristics of Fe₃O₄-H₂O nanofluids were studied in a convection heat transfer experimental platform.The changes in flow pressure drop and flow resistance coefficient of magnetic nanofluids with volume concentration and the effects on the flow characteristics after applying an external magnetic field were studied.The research shows that when the Reynolds number is 4000,the flow resistance coefficient of 2% volume magnetic nanofluids is reduced by 9.12% compared with pure water,and the flow pressure drop is increased by 32.6%,but the effect on the flow characteristics after applying a magnetic field is not significant.Big.The convective heat transfer characteristics of Fe₃O₄-H₂O nanofluids under vertical magnetic fields under laminar and turbulent conditions are studied.The convective heat transfer coefficient of magnetic nanofluids increases under the influence of external magnetic fields.This is due to the nanomagnetic properties of the vertical uniform magnetic field.The particles gather along the direction of the magnetic field and function as a heat channel,thereby increasing the heat transfer coefficient of the magnetic nanofluid.The research shows that:the convective heat transfer coefficient increases with the application of the magnetic field;the convective heat transfer coefficient increases when the magnetic field strength B?600G;when the magnetic field strength B=800 and 1000G,the convective heat transfer coefficients increase by 23.89% and 26.12% on average;The enhancement of convective heat transfer coefficient under the influence of a constant magnetic field is simultaneously affected by the concentration and temperature of the nanoparticles.Temperature and concentration have a significant effect on the convective heat transfer coefficient of magnetic nanofluids.As the temperature and concentration increase,the convective heat transfer coefficient increases.When the temperature is 30? and 40?,the maximum average enhancement rates of the convective heat transfer coefficient are 4.68% And 8.38%.