Study On Regulation And Application Of Thermal Transport Characteristics Of Ferroferric Oxide Based Nanoparticle Suspension

Due to the rapid growth of energy demand in the 21 st century,solving the energy problem is the first priority around the world.The key to an efficient thermal conversion system is to develop advanced functional working fluids that match the heat transfer requirements.As a typical working medium for heat transfer,magnetic nanoparticle suspension has both the properties of solid magnetism and liquid fluidity,which has considerable academic value and application prospects.However,the premise of these applications requires the effective regulation of thermal transport characteristics based on magnetic nanoparticle suspensions.Therefore,based on the magnetic nanoparticle suspension,this work regulates its magnetic properties and thermophysical properties,and studies its thermal transport characteristics and applications.Fe₃O₄,Fe₃O₄@CNT,and Fe₃O₄@Ti O2 nanoparticles are prepared by different methods.Effects of reaction time,temperature,and concentration on the structure and morphology of nanoparticles are studied.Considering heat transfer performance of magnetic nanoparticle suspension,the magnetic properties and thermophysical properties（thermal conductivity,viscosity and specific heat capacity）of nanoparticle suspension are measured.As for catalytic properties,the magnetic properties and optical properties of nanoparticle suspension are measured.The results show that,with less impact on the viscosity and specific heat capacity,the magnetic nanoparticle suspension,which has magnetization characteristics,can significantly enhance the thermal conductivity of the based fluid.It has the potential to control its transport and enhance the flow and heat transfer under the magnetic field,providing material and basic physical parameters for further research on convective heat transfer,photothermal conversion,and photothermal energy storage characteristics of magnetic nanofluids.Based on magnetohydrodynamic（MHD）,a magnetic-heat-flow coupling model of multi-physics fields is established.Then,a method of enhancing heat transfer is proposed.Natural convection and forced convection effect of the magnetic nanofluid are studied experimentally and numerically,and the local heating characteristics of the flow system are effectively regulated.The magnetic field distribution is obtained by solving Maxwell equation,and the magnetic field force exerted on the fluid is calculated.Then the heat transfer state of the flow is changed.For the restricted natural convection area,the magnetic enhancement heat transfer strategy improves the heat transfer efficiency,and reduces the temperature gradient of the heating wall surface in contact with the nanoparticle suspension,thus achieving more accurate heat transfer enhancement.Regarding the forced convection in straight round tube,the effect of the magnetic field on the heat transfer characteristics is mainly at the local area.Under the external magnetic field,the average heat transfer efficiency increases by 12.2 %,and the local heat transfer efficiency increases by 30.2 %.Based on the magnetic nanoparticle suspension,a magnetic-responsive rapid heating/cooling method is proposed.Based on the theory of nanoparticle movement and droplet deformation,a rapid heat channel between the heat source and the radiator is established.It is proved that the magnetic-responsive heat switch has several good characteristics,such as magnetic susceptibility,adjustability of heat transfer,and cyclicity.The overheating protection experiment shows that the proposed method can effectively reduce the working temperature of electronic components.Compared with base fluid,the stable temperature of electronic components decreases by 22.6 %.A magnetic enhancer is presented to achieve a controllable heat exchange characteristic by adjusting the magnetic distribution and material properties,and a thermal management system based on the spacecraft is proposed.The heat tran sfer effect of the magnetic nanoparticle suspension system increases by 30.6 %,and the heat transfer effect after adding the magnetic field increases by 96.8 %.Based on the evaluation model photo-thermal conversion performance,steamgenerating devices and catalytic devices of photo-thermal conversion are designed.Furthermore,this work analyzed the photo-thermal conversion characteristics of magnetic nanoparticle suspensions.The effects of solar intensity,reactant concentration,and particle material on photo-thermal conversion are studied.The photo-thermal steam-generating experiments reveal that the magnetic nanoparticle suspensions have a higher temperature and a lower evaporation rate at low concentrations.The photo-thermal catalytic experiments show that the ability of the magnetic catalyst to generate and transport photogenerated carriers can be improved by increasing the reaction area and Lorentz force.The magnetic field strength increases from 25 m T to 100 m T,and the recovery efficiency of Fe₃O₄@Ti O2 magnetic nanoparticle suspension increases from 47.4 % to 94.0 %,which indicates the faster separation speed and better recovery effect of Fe₃O₄@CNT nanoparticle suspensions.Therefore,the recovery speed and efficiency can be adjusted from the material properties and external magnetic field.Based on the magnetic composite phase change material,a photo-thermal storage evaluation model,an experiment platform,and a magnetically-enhanced photo-thermal energy storage method are established.Then,under various magnetic field strength,experimental and numerical studies about the solid-liquid phase transition characteristics of magnetic phase change materials are carried out.And the thermal resistance network of the nanoparticle system is establis hed to explain the mechanism of the magnetically-enhanced photo-thermal energy storage.The heat storage capacity of magnetic composite material is nearly 40 % higher than that of paraffin at 400 m T,and the highest heat storage efficiency is about 4.5 tim es that of paraffin.The application research of magnetic-enhanced photo-thermal energy storage power generation shows that the magnetic field can further increase the temperature difference of the thermoelectric module by enhancing the temperature rise effect of phase change materials.Compared with the case under the non-magnetic field,the voltage of the thermoelectric module increases by 50 % under the magnetic field by increasing the temperature difference.The latent heat and the average temperature have undergone 6 circular experiments,indicating that the magnetic phase change composite material has good stability in the photo-thermal storage utilization.