Research On Radiative Cooling Polymer Based On Fillable Particles

With the rapid development of society,the energy crisis and greenhouse effect have become increasingly serious.Traditional active refrigeration consumes a large amount of electricity and emits a large amount of greenhouse gases.Radiative cooling is a very environmentally friendly and efficient passive cooling method,which achieves object cooling by radiating heat to outer space through the atmospheric window,with the characteristics of zero energy consumption and zero pollution.The development of nano-optical materials has made it possible to massproduce micro/nano particle-polymer materials.Particle-polymer materials have relatively low preparation costs and show good cooling potential.However,existing radiative cooling materials based on particle-polymer still have some problems,such as relying on a metallic substrate to reflect sunlight to ensure cooling effect,which brings higher costs,and the lack of metal-free particle-polymer materials results in low cooling power.Based on this,this paper carries out research on the particle-polymer radiative cooling structure without a metallic substrate,and proposes multiple micro/nano particle-polymer structures with high cooling performance and practicality.The specific work is as follows:(1)Based on FDTD(Finite Difference Time Domain)method,a hybrid particle radiation cooling polymer structure was designed and studied in this work.The structure showed excellent cooling performance,achieving an average solar reflectance of 91%and an average emissivity of 94%within the atmospheric window.Its net cooling power during the day at ambient temperature was 199.5W/m2,capable of achieving temperatures below 23 ℃ lower than the ambient temperature.By verifying the reflection characteristics of BaSO4 particles and the optical loss characteristics of the polymer,the structure was determined to contain complementary emission spectra of BaSO4 and SiO2 particles,as well as PDMS polymer.Through the optimization of various parameters,the structure exhibited ideal radiation characteristics within the range of 0～30μm,with the optimal parameters being a radius of 0.2 μm and a volume fraction of 40%for BaSO4 particles,a radius of 0.4 μm and a volume fraction of 10%for SiO2 particles,and a thickness of only 300μm.(2)Based on the generalized Mie theory and the Monte Carlo ray tracing algorithm,we studied three sets of single-particle-polymer radiation cooling structures,including SiC-PMMA,Ta2O5-PMMA,and Si3N4-PMMA.By optimizing the parameters of particle size,volume fraction,and thickness,the radiation characteristics of 0～20μm were calculated.Among them,the SiC-PMMA cooling effect was the mostideal,achieving an average solar reflectivity of 96%and an average atmospheric window emissivity of 93%,with a net cooling power of 156.1W/m2 in daylight at ambient temperature,and a temperature lower than the ambient temperature of 21℃ could be achieved.The Si3N4-PMMA structure had a moderate cooling effect,with a net cooling power of 62 W/m2 in daylight at ambient temperature,and a temperature lower than the ambient temperature of 7℃ could be achieved.The Ta2O5-PMMA had a poor effect and was not conducive to radiation cooling.In addition,we studied the effect of particle size distribution type on the optimal SiC-PMMA structure.When the particle size followed a normal distribution with different standard deviations σ,the solar reflectivity was almost the same as that of a single peak particle size;when the particle size followed a lognormal distribution,the solar reflectivity was lower than that of a single peak particle size,and the best effect was obtained when the log standard deviation σ was less than 0.3nm.Furthermore,we studied the angle sensitivity of SiC-PMMA,which maintained a high reflectivity of over 96%at 0-800 and a high emissivity in the atmospheric window at 0-60°,enabling radiation cooling at a wide range of incidence angles.