Photo-thermal Conversion Performance Of Hybrid Nanofluids-based Direct Absorption Solar Collectors

Sustainable development is the eternal theme of the development and progress of human society.China has entered a stage of rapid development.The clean and efficient use of energy has become an important way to maintain the earth’s environment.The massive use of traditional fossil fuels such as coal and petroleum has caused a huge burden on the earth’s environment and aggravated the greenhouse effect.In recent years,renewable energy has gradually entered everyone’s field of vision.Among them,solar energy has attracted widespread attention due to its green,clean and renewable characteristics.However,the current utilization efficiency of solar energy is still at a low level and needs to be optimized and improved.In order to realize the efficient utilization of solar energy,this paper focuses on the nanofluids-based direct absorption solar collector（DASC）,which aims at the deficiency of low matching degree between solar absorption performance of mono nanofluid and solar spectrum.The spectral regulation strategy of hybrid nanoparticles with different light absorption characteristics based on the characteristics of solar spectrum distribution was explored.The preparation,optical properties characterization,photo-thermal conversion performance testing and stability evaluation of hybrid nanofluids were carried out.The main research contents of this paper are as follows:（1）A“two-step method”was used to prepare mono MWCNT nanofluid.The optical properties of nanofluids with different mass fractions were measured and analyzed.The photo-thermal conversion performance system of direct absorption solar collector based nanofluid was built.The photo-thermal conversion performance of MWCNT mono nanofluid was explored.The result shows that when the illumination time was 2000s,the photo-thermal conversion efficiency of the 10ppm MWCNT nanofluid is improved by 7.2%compared with the base fluid.（2）The optical properties and photo-thermal conversion properties of the three types of composite nanofluids,MWCNT-TiN,MWCNT-Zr C,and MWCNT-Fe₃O₄,were studied respectively.The result shows that the optical properties of the three types of composite nanofluids are improved due to the superposition of the extinction coefficients of the composite nanoparticle.However,due to the different absorption effects of different kinds of nanoparticles on solar radiation energy,only the MWCNT-TiN nanofluid had better photo-thermal conversion performance than the mono MWCNT nanofluid.After receiving solar radiation for 2000s,the photo-thermal conversion efficiency of the 10ppm MWCNT-10ppm TiN hybrid nanofluid increases by 8.18%compared with the base fluid.（3）The stability and steady-state photo-thermal conversion performance of the MWCNT-TiN composite nanofluids were mainly studied.The static sedimentation experiment,Zeta potential test and morphology characterization results show that the composite nanofluid has good stability.After multiple rounds of heating-cooling cycle test,the10ppm MWCNT-10ppm TiN composite nanofluid still maintains steady photo-thermal conversion performance.In this study,the solar radiation absorption properties and photo-thermal conversion properties of the MWCNT-TiN hybrid nanofluid were further improved compared with that of MWCNT mono nanofluid,which confirms the feasibility of regulating the optical and photo-thermal conversion properties of nanofluids by composite nanoparticles with different light absorption properties.In addition,the composite nanofluids have steady cyclic stability.This study can provide some guidance for the selection of working medium and optimization of photo-thermal conversion performance of direct absorption solar collector.