Study On Flow And Heat Transfer Performance Of Magnetic Nanofluids Based On Fe₃O₄-H₂O In Microchannels

Microchannels are of high research significance in the field of convective heat transfer,and nanofluids,due to their inherent solid-liquid two-phase mixing properties,make them promising as a new type of efficient heat transfer medium in the field of heat dissipation.The emergence of magnetic nanofluid not only has high thermal conductivity,but also can be controllable in the channel.In this paper,mainly,the flow heat transfer properties of₃₄-₂magnetic nanofluid microchannels with 1%volume fraction as the heat transfer medium and 0.8mm equivalent diameter as the experimental channel were investigated under the coupling effect of temperature field and magnetic field,and the flow heat transfer performance within the₃₄-₂magnetic nanofluid microchannels under the condition of applied magnetic field was analyzed.The reliability of the experimental platform was evaluated by the heat balance deviation,and the deviation values were all lower than 7%,so the experimental platform has high reliability and stability.The stability of nanofluid was compared with different dispersant ratios,and a more stable nanofluid ratio was obtained,which laid the foundation for the subsequent experiments.The magnetic nanofluid with 1%volume fraction of₃₄-₂was prepared as the heat transfer medium,and the effects of horizontal and vertical magnetic fields on the flow heat transfer of the magnetic nanofluid were analyzed and compared,respectively;the results showed that the nanofluid under the vertical magnetic field had better heat dissipation.The results show that the nanofluid has better heat dissipation under the vertical magnetic field.The heat dissipation performance of the nanofluid through the grid-shaped microchannel under the magnetic field of 0-700G strength is studied.The results show that the chip junction temperature of nanofluid is lower than that of deionized water by up to 2.11℃and the convective heat transfer coefficient is 1.3 times higher than that of deionized water under the condition of no magnetic field;secondly,the flow characteristics and heat transfer characteristics of nanofluid under the condition of magnetic field of 100-700G strength are analyzed.With the increase of magnetic field strength,the pressure drop and flow resistance of nanofluid showed an overall decreasing trend,and the pressure drop at 500G and 700G decreased by 19.3%and 14.51%,respectively,compared with that at 0G;the flow resistance decreased by 2.61%and 1.37%,respectively.Finally,the comprehensive performance of the nanofluid was analyzed,and the enhanced heat transfer performance under magnetic field conditions was significantly improved compared with that without magnetic field,and the average enhanced heat transfer factor was the highest and the comprehensive performance was the best when the magnetic field strength was 300G to 400G.Based on the above-mentioned experiments,a simulation of microchannel flow heat dissipation was established,and a multi-objective optimization was performed for a grid-shaped microchannel with an equivalent diameter of 0.8 mm using₃₄-₂magnetic nanofluid as the heat transfer medium,and the junction temperature,temperature gradient and pressure drop as the optimization objectives.The best multi-objective performance of the gridded microchannel was achieved with the microchannel structure parameter（wedge angle）=2°,the microchannel microstructure feature length 3.91 mm,and the magnetic nanofluid volume fraction 2.4%.