Study On Heat Transfer Characteristics Of Magnetic Nanofluid In Microchannel Under Magnetic Field

As the core component in the field of microelectronics,the operation state of chip directly affected the performance of the whole system.Thermal problems had a crucial impact on the performance and service life of the chip.In the actual working process of the chip,The heat dissipation efficiency of the chip was greatly limited by the operating environment.The micro channel props had large heat exchange area and small size.The magnetic nanofluid had high thermal conductivity and stability,and the flow and heat transfer performances of magnetic nanoparticles would be strengthened under the action of magnetic field.Therefore,the heat dissipation mode of magnetic nano fluid flowing in microchannels under the action of magnetic field could meet the requirements of micro size and high heat flux of the chip,and effectively improve the heat dissipation performance of the chip.In this paper,the two-dimensional jet flow of Fe3O4-H2O nanofluid in microchannel was numerically simulated.The effects of magnetic dipole and permanent magnet on the flow and heat transfer behavior of magnetic nanofluid in microchannel were studied respectively.A ferromagnetic hydrodynamics model considering Brownian effect and Brownian effect was constructed,and the corresponding ferromagnetic hydrodynamics numerical calculation program was developed.The effects of inlet opening R,inlet Reynolds number Re and transverse position xi of magnetic source on the flow and heat transfer of magnetic nanofluid in microchannel under the action of magnetic dipole and permanent magnet were analyzed.The conclusions were as follows:(1)The inlet opening R,the inlet Reynolds number Re and the transverse position xi of the magnetic source had significant effects on the jet flow and heat transfer of Fe3O4 nanofluid in the microchannel.When the magnetic source was a magnetic dipole,when R=1/8,the fluid would deflect upward and the upper wall would produce local high temperature.When R=1/2,the maximum increment of the average Nusselt number of the upper and lower walls of the microchannel was 41.6%and 32.4%respectively.When xi=2mm,the heat transfer efficiency of magnetic nanofluid was the highest,and the maximum increase of average Nusselt number was 83.5%and 42.7%.(2)When the magnetic source was a permanent magnet,the magnetic field could effectively alleviate the problem of local high temperature on the wall under low inlet opening.When the magnet was close to the inlet,the nanofluid in the microchannel flows symmetrically up and down under different opening degrees,and the nanofluid vortex formed in the inlet section of the microchannel increases with the decrease of opening.Increasing the re number at the inlet was beneficial to the overall heat transfer capacity of the microchannel.With the increase of the transverse position of the permanent magnet,the average Nusselt number of the wall decreases and the high temperature region at the front end of the permanent magnet increased When the inlet opening was 1/4 and the transverse position of the permanent magnet was 1mm respectively,the heat transfer gain of the microchannel was the largest,reaching 35.2%.(3)Under the action of two magnetic sources(magnetic dipole and permanent magnet),there were obvious differences in the flow and heat transfer behavior of nanofluids in microchannels.Under the condition of nano magnetic fluid,the effect was larger than that near the dipole surface.Under the action of magnetic field,the front end of magnetic source would form a local high-temperature region,and the local high-temperature region when the magnetic source as a permanent of magnet was larger than the region of magnetic dipole.