反斯托克斯荧光及辐射制冷涂料的研究

Cooling is a significant end-use of energy globally. Air conditioning accounts for approximately 15% of the world-wide energy used by buildings. Therefore, a passive cooling strategy that cools without any cryogen and electricity input could have a significant impact on global energy consumption. Because peak cooling demand generally occurs during the daytime, sub-ambient daytime cooling under direct sunlight has become a hot research topic recently. Sub-ambient cooling has been demonstrated to be achieved either by radiative cooling mechanism or by anti-Stokes fluorescent cooling mechanism. However, silver must be used to maximally reflect sunlight to attain meaningful sub-ambient daytime radiative cooling and a pump laser needs to be employed to excite the cooling elements to achieve observable fluorescent cooling. .In this study, we will demonstrate that, without silver or a pump laser, integrating these two cooling mechanisms into a single-layer paint coating will enable us to achieve pronounced sub-ambient daytime cooling under direct sunlight. The contents and novelties of this study will include (1) a demonstration, for the first time to our knowledge, that radiative and fluorescent cooling can be integrated into a single-layer coating for realizing sub-ambient daytime cooling; (2) in contrast to studies published in the literature, the fluorescent cooling effect of the coating will be observed in an open environment rather than in a vacuum chamber, which is of practical significance; (3) an experimental demonstration, again for the first time to our knowledge, of achieving net anti-Stokes fluorescent cooling using sunlight rather than a pump laser to excite a coating with a phosphor; and (4) a systematic investigation of anti-Stokes fluorescent cooling mechanism excited by sunlight.

建筑制冷能耗约占全球总能耗的15%。因此，既无需氟利昂又不损耗电能的制冷技术对于降低全球总能耗具有重要的意义。鉴于夏季制冷用电需求高峰出现在白天，因此，白天低于气温的制冷技术已成为当前研究的热点。研究结果表明，利用辐射制冷或反斯托克斯荧光制冷机理均可以使材料的表面温度低于环境温度，但前者需要银，后者需要泵浦激光。通过本研究，我们将证明，无须贵金属银或泵浦激光，将辐射制冷和反思托克斯荧光制冷两种制冷机理集成于一单层涂层体系，完全可以实现白天阳光直射下明显低于气温的制冷。本研究的主要内容和创新之处在于（1）世界范围内，首次证明可以将辐射和荧光制冷机理有机整合于单一涂层体系；（2）不同于现有文献，荧光制冷是在敞开环境而非真空腔室中实现和观察到的，具有实际意义；（3）世界范围内，首次试验证明可以用阳光而非泵浦激光激发具有荧光中心的制冷单元以实现荧光制冷；（4）阳光激发下荧光制冷机理的研究。

建筑能耗约占全球能源总消耗的35~40％，随着人们对建筑环境舒适度的要求不断提高，暖通空调系统在建筑能耗中所占的比重不断增加。传统的主动制冷技术需电能驱动，耗能较大，日间低于环境温度的辐射制冷技术的出现解决了这一难题。目前，实现日间低于气温的辐射制冷普遍采用的方法是最大限度的减少制冷材料对太阳辐射的吸收，并提高大气窗口的选择性发射率，极大限制了材料的选择，不利于大规模应用。.本课题将粒子散射、广谱红外辐射与太阳光激发荧光发射相结合，提出一种实现阳光直射下表面温度恒低于气温（SDRC）的新途径，并在此基础上进行了进一步升级，开发出具有超双疏功能的纯辐射制冷涂料。具体研究内容及结果如下：.（1）采用传统的低成本商用原材料制备出具有SDRC效果的荧光及辐射制冷涂料（FR制冷涂料），可由太阳光激发发射出荧光，使涂层的有效太阳反射率突破传统上限，达到实现SDRC的水平。.（2）设计制作了一种SDRC检测设备，对FR制冷涂料在充分隔热条件下的制冷性能进行了研究。研究结果表明，在北京等典型温带季风气候区，该涂料对多种基材均表现出明显的SDRC效应，且太阳辐射越强制冷效果越好。.（3）通过比例模型房和工程示范，对FR制冷涂料在不同的基材、气候条件以及不同季节等实际条件下的制冷性能进行了研究。实验证明，FR制冷涂料在混凝土模型房上具有更明显的SDRC效果。此外，空气湿度和云层对制冷效果具有抑制作用，在夏季炎热、潮湿、多云的地区制冷效果有所降低。在气候干燥寒冷的北方，冬季制冷温差低于夏季，采暖高峰时段仅使室内温度降低1.5~1.6 ℃，不会大幅增加采暖能耗。.（4）开发出一种具有超双疏功能的辐射制冷涂料，并将其成功应用于通讯基站、粮仓、冷库、储罐、建筑、生活设施等八大领域，取得了显著的制冷和节能效果。.本课题提出一种简单、普适的SDRC实现方法，大大拓展了SDRC技术的选材范围，从而促进了该技术的大规模应用。