Composite Medium Nanofluid Solar Energy Capture And Photothermal Conversion

With the increasing depletion of fossil energy and the deterioration of ecological environment,human beings urgently need to develop the utilization of renewable energy.Among the renewable energy sources,solar energy is the most widely distributed and accessible one.In solar energy utilization,solar-thermal conversion is the most direct and practical way.By using nanofluids,which are prepared by dispersing nanomaterials in fluids,as the solar energy absorption and heat transfer media at the same time,the efficient solar energy capture and heat transfer performance can be achieved,and the high-efficiency solar-thermal utilization in the form of volumetric absorption can be realized.The solar capture performance of nanomaterials mainly depends on their own material properties and the nanostructures.According to the radiation energy distribution of sunlight in different wavelength bands,the most effective way to improve the photothermal conversion performance of nanofluids is choosing materials with light absorption properties in different wavelength bands,and designing appropriate multi-material composite nanostructures.In this way,a composite nanofluid with solar energy full spectrum absorption capacity can be obtained.Photonic nanoparticles are a new type of composite nanoparticles,in which,by combining different materials into the same nanoparticle,the spectral absorption complementarity of different materials and the near-field radiation enhancement effect between nanomaterials can be achieved.On the basis of realizing the efficient capture of sunlight,it is necessary to design a volumetric solar-thermal conversion system to realize effective heat output utilization.In view of the different temperatures and powers required by different heat utilization occasions,it is necessary to specifically analyze the solar-thermal conversion effect of the flowing nanofluid under different working conditions.Besides,nanofluid based volumetric absorption can also be applied to thermal catalysis.By dispersing the catalyst nanoparticles into the reactant liquid,the photothermal conversion and thermal catalysis of the catalyst nanoparticles can be comprehensively utilized.In this way,the conversion process of solar-thermal-chemical energy conversion based on volumetric absorption can be realized.In this paper,taking the absorption and utilization of solar energy as the background and nanofluid as the research object,the research on spectral characteristics control,heat collection performance improvement,and photothermal conversion application are carried out.The main contents include:1.Theoretical research on the method of strengthening the optical absorption characteristics of composite nanofluidsConsidering the physical process of nanofluid sunlight capture,based on electromagnetic theory,a calculation model of its spectral characteristics is established,which describes the interaction between incident light and matter.The multi-sphere T matrix method is used to analyze the light capture process of nanofluids,including the multiple interactions of light and particles,particles and particles,and particles and base fluid.Through the analysis of the spectral absorption complementarity of different nanomaterials in the solar wavelength band and the radiation synergy process in the composite nanofluid,the mechanism of the material composite on the optical capture ability of the nanofluid is analyzed.A photonic nanoparticle model is constructed to realize the full-spectrum and high-efficiency absorption of solar energy,which provides a theoretical basis for the design of composite nanofluids for volumetric absorption.2.Preparation and characterization of composite nanofluidsIn order to achieve high-efficiency solar-thermal conversion,the composite nanofluids with full-spectrum sunlight absorption capacity,stable dispersion state,and strong heat transfer performance are prepared.Different types of composite nanofluids with different materials are prepared by liquid-phase reduction method,sol-gel method,hydrothermal method,etc.The nanofluids contain core-shell structure nanofluid,direct mixed nanofluid,photonic nanofluid and so on.Through material characterization of the prepared nanoparticles,their performance stability is evaluated.Through the measurement of optical and thermal parameters,and the photothermal conversion experiment,the photothermal conversion effect of the prepared nanofluid is evaluated.By comparing the properties of the composite nanofluid and the ordinary nanofluid,the performance complementarity effect of the composite nanofluid multi-material coupling is demonstrated,and the full spectrum absorption effect of the material absorption complementarity in the photonic nanofluid is confirmed.3.The solar-thermal conversion performance of photonic nanofluids in the flowing stateBased on the heat transfer of the flowing working fluid required in the application of photothermal conversion,the photothermal conversion performance of the photonic nanofluid under the flow state is studied,and the influence of various factors on the photothermal conversion temperature and efficiency is studied.In terms of theoretical calculations,through multi-physics theoretical analysis including ray optics,computational fluid dynamics,and heat transfer,the process of solar light transfer and fluid heat transfer in concentrating heat collection is studied.In terms of experiment,the experimental system for light-concentrated volumetric solar-themal conversion is designed and built.The combination of theoretical calculations and experimental test results demonstrates that photonic nanofluids have better solar-thermal conversion performance than single-material nanofluids or binary nanofluids.The influence law and mechanism of nanofluid concentration,fluid flow rate,light intensity,and light concentration ratio on nanofluid photothermal conversion are analyzed,and the adjustment methods of photothermal conversion conditions under different heat collection requirements are explored.4.Application of photothermochemistry based on nanofluid volumetric absorption technologyBy dispersing the thermal catalytic nanoparticles in the catalytic reactant and using the catalytic nanoparticle-reactant fluid system as the volumetric absorption medium,the process of solar-thermal-chemical energy conversion is realized.Through theoretical analysis,on the basis of calculating the sunlight capture of methanol decomposition catalyst nanoparticles,the processes of methanol heating,vaporizing and decompositing after the catalyst nanoparticle heating are studied in detail.The methanol decomposition nanocatalyst is prepared by the co-precipitation method.Based on the idea of localized heating of catalyst nanoparticles,a volumetric absorption interface photothermal catalysis method for localized heating of catalysts is designed and manufactured.The experiment achieves high-efficiency solar photothermal catalysis under low concentration ratios,and explored the catalytic effect with different illumination,different reactant content,and so on.