Design Of Micro-Nano Structure Of Polymer For Radiative Cooling

The majority of conventional cooling methods employ gas compression technology,necessitating electric power and utilizing refrigerants that have detrimental effects on the environment.Passive radiative cooling represents a pollution-free cooling strategy that exploits the atmospheric transparent window to facilitate the transfer of thermal energy from ground objects to the frigid outer space through spontaneous radiation,resulting in temperature reduction.Daytime radiative cooling has garnered considerable interest due to its ability to overcome the limitations associated with cooling solely during nighttime.Previous studies have explored various approaches for daytime radiative cooling,including photonic films and metamaterials.However,many of these approaches are characterized by complex structures,challenging fabrication processes,and high costs.The polymer-based radiative cooler has emerged as a prominent research topic in recent years,owing to its remarkable infrared radiation properties and feasibility for mass production.Nonetheless,the high transmittance of polymers poses challenges to the cooling structure,including the requirement for a backing metal substrate,excessive thickness,and insufficient cooling power during daylight hours.In this paper,we address the aforementioned challenges by proposing two novel polymer radiative cooling structures that eliminate the need for a metal substrate and by optimizing the structural parameters.Through extensive numerical simulations,we demonstrate that these structures exhibit highly efficient cooling performance throughout the day.The specific research objectives and methodologies are outlined as follows:1.A porous polymer radiative cooling structure was designed utilizing polymethyl methacrylate(PMMA)as the matrix material.The research findings demonstrate that the structure achieves a remarkable net cooling power of up to 171.5 W/m2 at 300K during the day.Throughout the design process,we conducted simulations to analyze the spectral radiation characteristics of the structure within the solar spectrum and atmospheric transparent window.We specifically examined the impact of various structural parameters,including aperture radius(r),porosity(p),structural thickness(h),and the distribution of nanopores within the aperture range,on the cooling efficiency.By optimizing these structural parameters,we significantly enhanced the cooling performance of the polymer radiative cooling structure.After optimization,the average solar reflectance of the structure reaches an impressive value of 0.97,indicating its strong ability to reflect solar radiation.Moreover,the average emissivity within the atmospheric transparent window exceeds 0.93,ensuring efficient thermal radiation.Additionally,the emissivity remains above 0.85 even when the incident angle of infrared radiation is less than 65°.These results highlight the structure’s capability to maintain high emissivity across a wide range of angles,further contributing to its enhanced cooling performance.2.By utilizing polydimethylsiloxane(PDMS)as the matrix material and incorporating Al2O3 particles,a novel polymer radiative cooling structure was developed.The simulation results demonstrate its remarkable cooling capabilities,achieving a net cooling power of 131.8 W/m2 during daytime and 221.9 W/m2 during nighttime at ambient temperature.Notably,this structure eliminates the need for a metal substrate to reflect sunlight and possesses a reduced thickness of only 300 μm.Compared to previous radiative coolers,the design presented in this study exhibits significantly improved cooling performance while maintaining a simplified and lightweight construction.During the research,the influence of particle size(d),volume fraction(fv),and thickness(h)on the radiation characteristics of the designed structure was investigated.The spectral characteristics of the structure in two wavelength bands,namely 0.3～2.5 μm and 7～25 μm,were simulated to analyze their effects.Subsequently,the parameters were optimized to enhance the performance of the structure.The optimized structure has a broadband emissivity,insensitivity to the angle of incident light,an average atmospheric emissivity of 0.96,and a solar reflectance of 0.91.It effectively emits thermal radiation across a wide range of wavelengths,ensuring consistent cooling performance regardless of the orientation.The structure’s high atmospheric emissivity indicates its ability to emit thermal radiation to the surrounding environment,while its solar reflectance minimizes solar heat absorption.