Numerical Simulation Of Radiation Cooling Based On Generalized Lorenz–Mie Theory

With the development of society,people’s demand for refrigeration is increasing.The energy consumption of cooling and refrigeration equipment accounts for about 27%of the total energy consumption every year,which causes environmental pollution problems such as greenhouse effect and air pollution.Therefore,it is urgent to obtain an efficient and environmentally friendly energy-saving way.Radiation refrigeration is a zero-energy-consuming and renewable passive refrigeration method.The radiation cooler with nanoparticles has several advantages,such as simple fabrication,low cost,and can be used day and night.It has great potential for industrial application.At present,polymers are usually considered as non-absorbent media,but they have absorption properties in practice.In this paper,we use generalized Mie theory to solve the spectral characteristics of particle system in absorptive media,and then use Monte Carlo method to solve the optical transmission process of nanoparticles in thin films,and calculate the radiation characteristics of micro/nanoparticles-absorptive medium thin films.On this basis,the radiation characteristics of nanoparticles with different particle sizes were investigated,including single particle sizes,hierarachical particle sizes and non-uniform particle size,and the cooling power of the film structure was analyzed.（1）For the structure of single-particle polymer films,CaCO₃ and ZnO nanoparticles were added into three kinds of absorbent media（PMMA,PDMS and TPX）,respectively.The spectral characteristics of the films in the 0.2-20 um band were simulated,and the effects of particle size,particle volume fraction and film thickness were investigated.Finally,the optimized structure is obtained:PMMA and PDMS thin films have similar radiation cooling performance and are superior to TPX thin films.The cooling power of ZnO-PMMA film is 167.41W/m² in daytime and 216.55W/m² at night,which is similar to that of CaCO₃-PMMA film.The cooling power of ZnO-PDMS is 171.48W/m² in daytime and 215.26W/m² at night,which is obviously better than that of CaCO₃-PDMS film.CaCO₃-TPX film can not be used in daytime,while the cooling power of ZnO-TPX film is 59.91W/m² in daytime and 212.19W/m² at night.（2）For the structure of multi-particle polymer films,CaCO₃ and ZnO nanoparticles were added to PMMA and PDMS respective ly.The spectral radiation characteristics of mixed particle size system,non-uniform particle size system and the corresponding radiation refrigeration problems were investigated.The design idea of mixed particle size combination is to use the particles with the highest reflectivity in vis ible band as the main part,and doped with the particles with higher reflectivity in ultraviolet and near infrared band.Usually,the particle combination with adjacent particle size will get the best optimization effect.The absorption coefficient and scattering coeffic ient of uniform structure and non-uniform particle size are obviously different,and the maximum relative error is 61.54%.In the solar radiation band,the reflectivity of uniform structure is higher than non-uniform structure.For the atmospheric window,the difference of emissivity is very small.The radiation refrigeration effect of uniform structure in daytime is stronger than non-uniform structure.