Theoretical Calculation Of Radiation Characteristics Of Multilayer Multicomponent Media Based On Monte Carlo

In recent years,the energy crisis has been highlighted,and the environmental problems caused by traditional energy are also increasingly apparent.A large number of studies involve the use of solar radiation to generate heat energy solar collectors.Flat plate collector is one of the most common types of solar collectors.It collects solar energy with high absorption rate surface to heat the working fluid in the collector.Nanofluids（suspensions of nanoparticles in the base fluid）have been used as working fluids in solar collectors to enhance light absorption characteristics.Therefore,the composition,size,inclination angle and volume concentration of the nanoparticles are the key parameters to adjust the optical absorption characteristics of the nanofluids.This project focuses on the radiation transfer characteristics of different components of nanoparticles to the direct absorption solar collector.The particles are divided into Au-Si O₂,Ag-Si O₂ and Si O₂,and the calculation model of the working fluid of the solar collector filled with different nanoparticles is established.The Monte Carlo method combined with Mie scattering theory is used to solve the radiation transfer of the working fluid of different nanoparticles.The spectral reflectance（Rsp）,spectral transmittance（T）and bidirectional reflectance distribution function（BRDF）of the nanofluids in the suspension layer of the direct absorption solar collector were calculated by compiling the program.The effects of different components of nanoparticles on the radiation characteristics of the collector were obtained.The effects of particle volume fraction,particle composition in the suspension layer,particle size and illumination angle on the spectral reflectance（Rsp）,spectral transmittance（T）and bidirectional reflectance distribution function（BRDF）were analyzed Bidirectional reflectance distribution function（BRDF）.The effects of particle volume fraction,particle composition,particle size and incident light angle on the spectral reflectance Rsp,spectral transmittance T and bidirectional reflectance distribution function（BRDF）were studied by establishing a model of Si coated solar collector.The results show that the gradual increase of the volume fraction of nanoparticles has a significant impact on the optical characteristics of the direct absorption solar collector;the change of the equivalent refractive index in the different composition of nanoparticles will affect the movement process of photons in the suspension layer,and the gradual increase of the equivalent medium absorption index will reduce the spectral transmittance in the suspension layer of nanoparticles;the direct absorption solar collector has a good performance When Si is coated on the bottom layer of the collector,the influence of different volume fraction of nanoparticles on the spectral reflectance of the suspended layer of nanoparticles is relatively weak in the 0.3-1.2μm band of incident light.In the 1.2-2.4μm band,the smaller the volume fraction of nanoparticles,the greater the spectral reflectance Rsp of the suspended layer of nanoparticles.The spectral transmittance is greatly affected by the equivalent absorption index k,and the larger the equivalent absorption index k is The smaller the spectral transmittance t is,the greater the influence of the increase of the volume fraction of nanoparticles in the suspension layer on the spectral transmittance t is,which makes the difference between the spectral transmittance T with different volume fraction of nanoparticles become larger and larger.The BRDF of incident light with wavelength of 0.3μm,1.5μm and 2.3μm decreases with the increase of nanoparticle volume fraction.