Experimental And Theoretical Research On A Superhydrophobic Radiative Cooling Paint

With the development of the economy and the improvement of living standards,the consumption of energy is increasing day by day,and the demand for cooling is also more urgent.Radiative cooling technology is a new type of passive cooling method without energy consumption.Compared with traditional cooling methods,it has the advantages of no pollution and no emissions.It is of great significance in energy saving and emission reduction and carbon neutrality.The practical application of radiative cooling has always been faced with the problems of high manufacturing cost and complicated processing,which hinders the practical application and large-scale industrialization of the technology.In addition,radiative cooling materials are exposed to outdoor working environment for a long time,facing challenges of wind and rain erosion and dust pollution,which can cause damage to their spectral performance,greatly weaken radiative cooling performance,and even shorten their service life.Based on these issues,this paper focuses on two key issues of practicality and anti-pollution,and designs a superhydrophobic radiative cooling paint with potential for scalable production,and conducts experimental and simulation studies as follows:1.A layered structure design concept was proposed,in which a radiative cooling layer and a superhydrophobic self-cleaning layer were separately designed to simplify the production difficulty.Firstly,aiming to produce paint,TiO2 nanoparticles were doped in acrylic resin to construct Mie scattering effect,which can reduce the production cost and process difficulty while meeting the spectral requirements of radiative cooling materials Secondly,a superhydrophobic thin layer was constructed by spraying nano-SiO2/P(VdF-HFP)and modifying with a hydrophobic agent.The superhydrophobic layer has a positive synergistic effect on the spectral characteristics of the radiative cooling layer.The Mie scattering effects of TiO2 and SiO2 particles with different particle sizes in resin and air were explored by simulation methods,and the optimal particle sizes were selected as 500 nm for both TiO2 and SiO2.2.Based on the above design idea,a superhydrophobic radiative cooling paint with both radiative cooling and superhydrophobic self-cleaning functions was prepared,and its morphology,spectral characteristics,and superhydrophobic properties were characterized and analyzed.The superhydrophobic radiative cooling paint modified with a hydrophobic agent can achieve a superhydrophobic effect with an average contact angle of 158.9° and a rolling angle of 7°,and has excellent performance in selfcleaning of pollutants.At the same time,the superhydrophobic thin layer formed by spraying has a synergistic enhancement effect on the spectral characteristics of the paint.It can effectively improve the spectral defects caused by TiO2 intrinsic absorption,increase the reflectivity of the basic paint in the ultraviolet short-wave band to above 85%,and make the solar reflectivity of the superhydrophobic radiative cooling paint reach 94%and the mid-infrared band emissivity reach 97.1%.3.A outdoor radiative cooling experimental system was set up and established,and the all-weather outdoor radiative cooling performance was tested under two conditions:with and without windscreen protection in Hefei.Uncoated radiative cooling paint,commercial paint,and aluminum plate were used as controls.The experimental results demonstrate that the superhydrophobic radiative cooling paint maintains a lower stagnation temperature during the day compared to the uncoated radiant cooling paint and commercial paint,indicating superior radiant cooling performance.Furthermore,with a windscreen,the superhydrophobic radiative cooling paint can achieve a temperature that is 3℃ lower than the local environment temperature during the day.Even without a windscreen,the paint can achieve an allday radiative cooling effect that is lower than the ambient temperature,while the temperatures of other materials remain higher than the ambient temperature.4.The heat transfer model of radiative cooling based on superhydrophobic radiative cooling paint was established,and the outdoor cooling performance of superhydrophobic radiative cooling paint under different climatic conditions was analyzed.The results showed that the superhydrophobic radiative cooling paint could achieve all-day cooling effect lower than the ambient temperature in tropical and midlatitude summer conditions with high cooling demand.Taking four typical locations,Hefei,Urumqi,Singapore,and Phoenix,as examples and combining with meteorological annual data,the monthly radiative cooling potential of the paint in these locations was simulated and analyzed.The results showed that the superhydrophobic radiative cooling paint exhibited significant cooling potential in all zones.Among the four cities,the lowest cooling potential was in humid and hot Singapore,whose annual cooling power was 1068.07 MJ/m2,while the highest cooling potential was in Phoenix with desert climate,whose annual cooling power was 2562.71 MJ/m2.