Numerical Simulation Study On Heat Transfer Enhancement Of Nanofluid Under The Action Of Magnetic Field

As a relatively new technological product,nanofluid are developing very well,and especially in the recent period of rapid development,nanofluid as a mixed liquid,because of its excellent performance in heat transfer performance,it receives special attention from domestic and foreign researchers.In this paper,simulation software in computational fluid dynamics is used to simulate nanofluid,and the Discrete Phase Model is used to calculate.Firstly,a three-dimensional circular pipe is selected,the three parts of the circular tube are located in the three plane spaces X,Y,and Z,and each segment has the same length,then,the research is carried out around the various physical properties of nanofluid,including the volume share of nanoparticle,particle diameter,particle type,Reynolds number,etc.,to study the interference and excitation of these physical characteristics on the flow of nanofluid in three-dimensional pipes and the forced convection heat transfer process,and finally applied magnetic fields of different directions and different sizes to the nanofluid in the three-dimensional round tube,and explore the interference and influence of magnetic fields on the above process.Cu-H₂O nanofluid and Al-H₂O nanofluid with volume fractions of 0.5%,1%and 2%and particle diameters of 500nm,200nm and 100nm are used in the simulation,to research these two nanofluid under different conditions that flow and heat transfer behavior.Within a certain range,along with Reynolds number increases,reduce the thickness of the three-dimensional pipeline boundary layer,and increased turbulence disturbance,so energy exchange is increased.For every1%increase in volume,the temperature increases by 17.3%,the reason is that when the volume share increases,it is equivalent to increasing the overall number of particles.The decrease in particle diameter reduces the Nusselt number and heat transfer coefficient,at the same concentration,the Cu-H₂O nanofluid with a particle diameter of 100nm has an average increase of 6.5%in heat transfer coefficient and Nusselt number than the Cu-H₂O nanofluid with a particle diameter of 200nm.Because of the small size of the nanoparticles makes the interaction between the two stronger and makes the energy transfer rate faster.Because of the novelty and particularity of this model,three magnetic fields must be applied separately to make the nanofluid in each part of the pipeline be subjected to the Magnetic force,therefore,this article applies magnetic fields of different magnitudes from three directions.The results show that when the diameter of granule is 100nm,the magnetic field along the Z axis changes the heat transfer ability of the nanofluid the most,the heat transfer performance of the Cu-H₂O nanofluid and the Al-H₂O nanofluid are on average different than that without the magnetic field increased by 8.66%and 7.95%;the magnetic field along the Y axis makes the heat transfer capability of the nanofluid slightly smaller than that of the Z axis.The heat transfer performance of Cu-H₂O nanofluid and Al-H₂O nanofluid is averagely different than that without a magnetic field.The heat transfer performance of Cu-H₂O nanofluid and Al-H₂O nanofluid is increased by 6.94%and 6.13%on average,respectively,by the magnetic field along the X-axis,compared with the other two directions,the increase in heat transfer capacity has the smallest change.Because the Lorentz force of the magnetic field along the X axis does not act on the middle part of the three-dimensional pipe,thus the magnetic field force is interrupted,the disturbance of the particles is reduced,and the energy exchange is reduced.When the magnetic field strength is 0.5T,it is most suitable for fluid flow and heat exchange.At this time,the convective heat transfer coefficient and Nusselt number ratio of Cu-H₂O nanofluid and Al-H₂O nanofluid with the same particle size under the same volume fraction When there is no magnetic field,the average increase is 9.87%,7.52%and 5.96%,6.52%respectively.The low magnetic field strength has little effect on the heat transfer performance of the fluid,and the high magnetic field strength does not significantly improve the heat transfer performance of the fluid with a magnetic field strength of 0.5T.