Li Xiangyu, Peoples Joseph, Yao Peiyan, Ruan Xiulin
School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907, United States.
Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, United States.
ACS Appl Mater Interfaces. 2021 May 12;13(18):21733-21739. doi: 10.1021/acsami.1c02368. Epub 2021 Apr 15.
Radiative cooling is a passive cooling technology that offers great promises to reduce space cooling cost, combat the urban island effect, and alleviate the global warming. To achieve passive daytime radiative cooling, current state-of-the-art solutions often utilize complicated multilayer structures or a reflective metal layer, limiting their applications in many fields. Attempts have been made to achieve passive daytime radiative cooling with single-layer paints, but they often require a thick coating or show partial daytime cooling. In this work, we experimentally demonstrate remarkable full-daytime subambient cooling performance with both BaSO nanoparticle films and BaSO nanocomposite paints. BaSO has a high electron band gap for low solar absorptance and phonon resonance at 9 μm for high sky window emissivity. With an appropriate particle size and a broad particle size distribution, the BaSO nanoparticle film reaches an ultrahigh solar reflectance of 97.6% and a high sky window emissivity of 0.96. During field tests, the BaSO film stays more than 4.5 °C below ambient temperature or achieves an average cooling power of 117 W/m. The BaSO-acrylic paint is developed with a 60% volume concentration to enhance the reliability in outdoor applications, achieving a solar reflectance of 98.1% and a sky window emissivity of 0.95. Field tests indicate similar cooling performance to the BaSO films. Overall, our BaSO-acrylic paint shows a standard figure of merit of 0.77, which is among the highest of radiative cooling solutions while providing great reliability, convenient paint form, ease of use, and compatibility with the commercial paint fabrication process.
辐射冷却技术是一种被动冷却技术，有望大幅降低空间冷却成本、缓解城市热岛效应并减轻全球变暖。为了实现被动日间辐射冷却，当前的先进解决方案通常采用复杂的多层结构或反射金属层，这限制了它们在许多领域的应用。人们曾尝试用单层涂料实现被动日间辐射冷却，但通常需要较厚的涂层或只能实现部分日间冷却。在这项工作中，我们通过实验证明了硫酸钡（BaSO）纳米颗粒薄膜和硫酸钡纳米复合涂料都具有出色的全天低于环境温度的冷却性能。硫酸钡具有高电子带隙，可实现低太阳吸收率，并且在9μm处存在声子共振，可实现高的天空窗口发射率。通过合适的粒径和较宽的粒径分布，硫酸钡纳米颗粒薄膜实现了97.6%的超高太阳反射率和0.96的高天空窗口发射率。在现场测试中，硫酸钡薄膜的温度比环境温度低4.5℃以上，或实现了117W/m²的平均冷却功率。通过60%的体积浓度制备了硫酸钡-丙烯酸涂料，以提高其在户外应用中的可靠性，该涂料实现了98.1%的太阳反射率和0.95的天空窗口发射率。现场测试表明其冷却性能与硫酸钡薄膜相似。总体而言，我们的硫酸钡-丙烯酸涂料的品质因数为0.77，在辐射冷却解决方案中处于最高水平之一，同时具有高可靠性、方便的涂料形式、易于使用以及与商业涂料制造工艺的兼容性。
