几种材料的辐射制冷实验效果研究

对4种可以用于辐射制冷的化合物进行了辐射制冷效果的对比试验,并测定了其吸收比和法向发射比.结果表明,4种化合物都具有很高的辐射率,且与其辐射制冷实验结果表现出一致.首次提出CaF2用于辐射制冷,实现了制冷空间温度比环境温度低8～11℃的结果.     

一种新型铝基功能复合材料的研究

采用铸造凝固复合法将铝和在４￣１４μｍ波长范围内具有强辐射能力的ＴＭ颗粒复合在一定，制成Ａｌ／ＴＭ红外辐射功能复合材料，Ａｌ／ＴＭ复合材料组织致密，颗粒分布均匀。研究发现，Ａｌ／ＴＭ复合材料在红外光谱４￣１４μｍ的光谱辐射率和光谱辐射度比铝有很大提高。     

日间辐射制冷材料研究进展

辐射制冷是一种备受关注的新型降温方式,该方式利用大气透明窗口(ATW)向外太空辐射传热,实现被动降温.一般日间辐射制冷材料应在8～13μm波段内具有高发射率,在太阳光谱波段吸收率低于5％.辐射制冷研究可以绿色低耗的方式为建筑节能、服饰降温、冷藏冷凝、电池降温等提供方案,有着广阔的应用前景.如何使辐射材料较好地匹配理想辐射光谱是目前最主要的问题.近年来研究者多从辐射材料结构入手,在提高8～13μm窗口波段发射率的同时,通过构建具备光子带隙或发生Mie散射的结构等方式,减少太阳辐射吸收,并取得了显著成果.通过高聚物掺杂纳米粒子、不同折射率材料堆叠等结构设计,使辐射制冷材料的红外选择性得到了显著提升.一些高聚物在8～13μm波段内具有高发射率,同时可有效隔绝体系外的热量输入.将高聚物与发射光谱互补的掺杂纳米粒子相结合,可覆盖整个目标波段,提高其制冷性能.层堆叠模式参考了光子晶体阻断特定波长电磁波传播的特性,设计了不同折射率层交替排列,在不影响高发射层向外辐射红外能量的同时降低了材料对太阳光的吸收.本文主要综述了近年日间辐射制冷材料的研究进展,按其结构形态,将前沿辐射制冷材料分为薄膜类、涂层类、织物类和块材类,并阐述了辐射制冷器在建筑、电池降温等方面的实际应用.     

材料的红外光谱透反射性能测量研究

近年来,红外光源、红外纤维、红外冷热光镜、红外隐身材料等各类红外产品层出不穷。红外材料在医疗、光纤通信、军事等众多领域得到了越来越广泛的应用。作为红外材料的两个极其重要的基本参量——反射比和透射比的精确测量就显得十分重要。因此,研究材料的中远红外反射比和透射比的测量方法很有实际意义。一、几个容易混淆的概念1.反射比、镜面反射比与漫反射比材料的反射比是指材料表面反射的辐射光通量与入射到材料表面的辐射光通量之比。镜面反射又称镜反射或规则反射,是在无漫反射的情况下,按照几何光学定律进行的反射。漫反射则是宏观…     

氰基联苯乙烯类双光子吸收材料的合成

合成了一种新型双光子吸收材料氰基联苯乙烯类化合物,通过元素分析、电喷雾质谱、1H NMR和红外对其进行表征.测试了紫外吸收光谱、单光子荧光光谱、单光子荧光寿命和双光子荧光光谱.其双光子吸收截面为1.32×10-48cm4·s·photon-1,是潜在应用前景的双光子吸收材料.     

SiC和Si_3N_4粉体的太赫兹时域光谱研究

采用太赫兹时域光谱装置测试SiC和Si3N4粉体在0.4～2.4 THz的透射光谱,研究SiC和Si3N4粉体对太赫兹波的吸收性能与其电导率的关系,分析SiC和Si3N4粉体对太赫兹波的散射特性。结果表明,SiC是一种半导体材料,其内部含有较多可以自由移动的载流子,对太赫兹波的吸收较强;Si3N4是绝缘性很好的材料,对太赫兹波的吸收很小;SiC和Si3N4粉体对太赫兹波的散射作用属于瑞利散射,但是测试波长比粉体粒径大得多,散射效果不明显。     

硫酸铜分子结构及热变性的红外光谱

采用中红外(MIR)光谱技术开展了硫酸铜分子结构的研究.试验发现:在303 K的温度条件下,硫酸铜分子的红外吸收模式主要包括:νOH、δH2O、νasSO4、νsSO4和δasSO4.采用变温中红外(TD-MIR)光谱,开展了硫酸铜热变性的研究.试验发现:在303～573 K的温度范围内,随着测定温度的升高,硫酸铜分子...     

Er3+:LiYF4单晶生长与光谱特性

采用坩埚下降法在非真空密闭条件下生长出尺寸为φ9mm×68mm的1mol%Er3+:LiYF4单晶材料,测试了样品的折射率、透过光谱、吸收光谱、以及在980nm和792nm激光泵浦下的近红外和中红外荧光光谱.应用Judd-Ofelt理论计算了Er3+离子在LiYF4晶体材料中的强度参数(Ωt,t=2,4,6)、能级跃迁振子强度(fcal)、自发辐射跃迁几率(A)、荧光分支比(β)、辐射寿命(τrad)等光谱参数,讨论了其近红外和中红外的荧光特性.结果表明,在980nm和792nm激光泵浦下观察到了1.5μm近红外荧光和3.0μm中红外荧光,分别对应于Er3+:4I13/2→4I15/2和4I11/2→4I13/2跃迁,并分析了3.0μm中红外荧光强度较弱的可能原因.     

天空辐射制冷技术发展现状与展望

天空辐射制冷技术是指地球表面物体通过“大气窗口”波段(主要在8～13μm)向宇宙发射红外辐射以实现自身降温的过程。作为一种无需能量输入的制冷技术,天空辐射制冷可为应对能源危机及全球变暖提供一种新的思路。从发展历程看,传统的辐射制冷技术应用仅限于夜间。近年来,随着纳米光子学及超材料领域的发展,日间辐射制冷技术的优势已经得到验证。本文对天空辐射制冷技术的发展现状进行了回顾,涉及基本原理、材料与结构,分析了其潜在应用前景,并重点讨论了该技术当前研究与应用中面临的挑战。在能源形势与环境问题日益严峻的今天,探索天空辐射制冷技术在不同场景的应用,如建筑节能、减轻城市热岛效应、缓解水资源短缺、提高光伏发电效率等,有望助力我国的碳达峰、碳中和事业发展。     

一种基于GA-NSVM的自适应洛伦兹分峰拟合识别红外光谱吸收重叠峰的方法

提出一种基于遗传算法-非线性支持向量机的自适应洛伦兹分峰拟合识别红外光谱吸收重叠峰的方法。利用单质特征吸收线型的根本性差异,将混合物光谱分解为满足特征吸收线型的多个洛伦兹单峰,采用非线性支持向量机对多个拟合单峰进行多分类筛选确定特定目标组分的谱峰。采集了400个混合烷烃气体样本的红外光谱数据,论证了该方法在高相似分子结构的光谱识别分类的可行性。实验结果表明该方法能有效分离烷烃中甲烷、乙烷、丙烷的红外吸收单峰,具有良好的准确性和鲁棒性,模型参数的解释能力更强。该方法能够加速光谱检测技术在生物制药、食品化工、油气勘探等领域的应用,尤其是在含同系有机物混合物的分析及应用场合。     

建筑材料日间曝晒和夜间辐射致冷热效果的研究

研究了常见建筑材料和一些其它材料日间曝晒和夜间辐射致冷的热效果.结果表明,材料日间曝晒效果主要受其太阳吸收率的影响,与发射率无关;材料夜间辐射致冷效果则与发射率相关,而与太阳吸收率无关;不同地区建筑对建筑材料热物性有不同的要求.     

Scalable Bacterial Cellulose-Based Radiative Cooling Materials with Switchable Transparency for Thermal Management and Enhanced Solar Energy Harvesting

Radiative cooling materials that can dynamically control solar transmittance and emit thermal radiation into cold outer space are critical for smart thermal management and sustainable energy-efficient buildings. This work reports the judicious design and scalable fabrication of biosynthetic bacterial cellulose (BC)-based radiative cooling (Bio-RC) materials with switchable solar transmittance, which are developed by entangling silica microspheres with continuously secreted cellulose nanofibers during in situ cultivation. Theresulting film shows a high solar reflection (95.3%) that can be facilely switched between an opaque state and a transparent state upon wetting. Interestingly, the Bio-RC film exhibits a high mid-infrared emissivity (93.4%) and an average sub-ambient temperature drop of ≈3.7 °C at noon. When integrating with a commercially available semi-transparent solar cell, the switchable solar transmittance of Bio-RC film enables an enhancement of solar power conversion efficiency (opaque state: 0.92%, transparent state: 0.57%, bare solar cell: 0.33%). As a proof-of-concept illustration, an energy-efficient model house with its roof built with Bio-RC-integrated semi-transparent solar cell is demonstrated. This research can shine new light on the design and emerging applications of advanced radiative cooling materials.     

Flexible and Dual-Sided Available Colored Films for Efficient Daytime Radiative Cooling

Passive daytime radiative cooling (PDRC) is a promising strategy to realize surface cooling of objects without any external energy consumption. While such materials typically exhibit dazzling white appearances, developing pleasingly looking colored radiative cooling materials is greatly significant but remains an arduous challenge. Herein, self-standing, flexible colored films available on both sides are prepared by using a facile and scalable strategy. The films are asymmetrically designed. One side is SiO₂-filled porous structure with highly reflective pigment distributed that can selectively reflect solar light to generate specific color, and the other side is hierarchically porous three-phase composite with less SiO₂, which maximizes the solar reflection. The breathable film achieves a relatively high near infrared reflectance on the colored side (up to 89%), and a broadband solar reflectance on the reverse side. Moreover, both sides exhibit extremely high mid-infrared emissivity (98%) allowing significant radiative heat loss. With the diverse but efficient reflectance and emittance, different sides of three colored films yield temperature drops ranging from 2.0 to 11.1 °C during daytime. Building energy simulation indicates that 655 MJ m⁻² energy can be saved over the whole summer if the dual-sided available colored film is deployed in China.     

Multidisciplinary approach to materials selection for bipropellant thrusters using ablative and radiative cooling

Reduction of costs is a main consideration in every space mission, and propulsion system is an important subsystem of those missions where orbital maneuvers are considered. Lighter propulsions with higher performance are necessary to reduce the mission costs. Bipropellant propulsions have been widely used in launch vehicles and upper-stages as well as deorbit modules because of better performances in comparison with other propulsion systems. Unfortunately heat transfer and thermal control limit bipropellant propulsion performance and maximum performance cannot be achieved. Well-known cooling methods such as regenerative and film cooling increase the cost using extra equipment and high temperature materials. In this paper, a new approach for cooling is presented based on combined ablative and radiative cooling. Governing equations are derived for two or three layers of thermal protection system (TPS) to optimize the TPS mass. The first layer is used as an ablative layer to control the temperature where the second and third layers are used as an insulator to control the heat fluxes. Proposed cooling method has been applied for two real bipropellant thrusters. According to the results, the presented algorithm can suitably predict the heat fluxes and satisfy the wall temperature constraint. Then, the algorithm has been used to minimize the wall temperatures as low as possible and replace high temperature materials (platinum alloy) with common materials (composite or steel). It is shown that selection of TPS materials affects the TPS mass and Isp simultaneously, but conversely. Best solution should be derived by trading off between structure temperature (cost), Isp (performance), and TPS thicknesses (geometry). Multidisciplinary approach to TPS and structure material selection of a bipropellant thruster is presented for a case study. It has been shown that mass and performance penalties of using TPS are acceptable, considering the advantages of using steel alloy instead of platinum alloy.     

Emerging Materials and Strategies for Passive Daytime Radiative Cooling

In recent decades, the growing demands for energy saving and accompanying heat mitigation concerns, together with the vital goal for carbon neutrality, have drawn human attention to the zero-energy-consumption cooling technique. Recent breakthroughs in passive daytime radiative cooling (PDRC) might be a potent approach to combat the energy crisis and environmental challenges by directly dissipating ambient heat from the Earth to the cold outer space instead of only moving the heat across the Earth's surface. Despite significant progress in cooling mechanisms, materials design, and application exploration, PDRC faces potential functionalization, durability, and commercialization challenges. Herein, emerging materials and rational strategies for PDRC devices are reviewed. First, the fundamental physics and thermodynamic concepts of PDRC are examined, followed by a discussion on several categories of PDRC devices developed to date according to their implementation mechanism and material properties. Emerging strategies for performance enhancement and specific functions of PDRC are discussed in detail. Potential applications and possible directions for designing next-generation high-efficiency PDRC are also discussed. It is hoped that this review will contribute to exciting advances in PDRC and aid its potential applications in various fields.     

Feasibility evaluation of intracavity solid state laser cooling to cryogenic temperatures

The requirements for obtaining cryogenic temperatures (i.e. 150 K and below) by anti-Stokes fluorescence cooling are analysed for a dielectric cooling medium located inside the cavity of a diode-pumped solid state laser. The cooling efficiency is derived in terms of pump beam parameters, intracavity loss associated with the cooling medium, reabsorption and saturation effects in the gain medium, radiative and conductive heat load on the cooling medium, and finally bulk and surface heating effects. Using experimental data for a Yb³⁺:ZrF₄–BaF₂–LaF₃–AlF₃–NaF [ZBLAN] cooling medium and a Yb³⁺:KY(WO4)₂ [KYW] gain medium, the conditions for optimum cooling efficiency are obtained. Based on realistic materials properties, the analysis shows that it is feasible to obtain a cooling efficiency (i.e. cooling power per input diode pump power) of approximately 0.1% at an operating temperature of 150 K, with a heat lift up to 30 mW.     

Radiative Properties of Silica Nanoporous Matrices

Superinsulating materials are currently of much interest because of the price of energy on the one hand and CO₂ emissions attributed to offices and houses cooling and heating on the other hand. In this work, we aim at understanding and modeling the radiative transfer within silica nanoporous matrices that are the principal components of nanoporous superinsulating materials. We first elaborate samples of various thicknesses from a pyrogenic silica powder. These samples are characterized using two spectrophotometers on the whole wavelength range [250 nm; 20 μm]. Using a parameter identification technique, we compute the radiative properties of the various samples. Then, our samples being made of packed quasi-spherical particles, we use the Mie theory to model the radiative properties of these materials. Due to the observed discrepancies between the experimental radiative properties and those computed from the Mie theory with a uniform value of 10 nm for the scatterer diameter (value derived from TEM images), we determine an effective scatterer diameter that allows a good agreement between the experimental radiative properties and the Mie results. Nevertheless, in the short wavelength range, the Mie theory gives results that significantly differ from the experimental radiative properties. This behavior is attributed to structure effects as the wavelength is of the same order of magnitude as the diameter of the scatterer that is now regarded as an aggregate of nanoparticles. Hence, to take into account these effects, we use the discrete dipole approximation (DDA). The DDA extinction coefficient spectra appear to be much closer to the experimental results than the Mie spectra, and these first results are quite encouraging.     

Comparison of radiative transfer Monte Carlo and volume integral equation methods of studying the clustering of small scatterers

The effect of clustering of small scatterers on optical properties was studied by creation of a Poisson distributed plane-parallel geometry and slow cooling of the particle system in the sense of simulated annealing in an attempt to minimize the assumed total potential energy and sample the spatial distribution during the process. The optical properties were calculated by the volume integral equation method (VIEM). The scattering results for unclustered structures with different size parameters and packing densities were also compared with those given by Monte Carlo simulation for radiative transfer. In particular, measuring the intensity distribution of the VIEM is well suited to the classic radiative transfer approach.     

Near-field radiative cooling of nanostructures

We measure near-field radiative cooling of a thermally isolated nanostructure up to a few degrees and show that in principle this process can efficiently cool down localized hotspots by tens of degrees at submicrometer gaps. This process of cooling is achieved without any physical contact, in contrast to heat transfer through conduction, thus enabling novel cooling capabilities. We show that the measured trend of radiative cooling agrees well theoretical predictions and is limited mainly by the geometry of the probe used here as well as the minimum separation that could be achieved in our setup. These results also pave the way for realizing other new effects based on resonant heat transfer, like thermal rectification and negative thermal conductance.