Active control of near-field radiative heat transfer by coating-twisting method

工作温度下光谱发射率测量对确定太阳能选择性涂层效率的重要性

Importance of the spectral emissivity measurements at working temperature to determine the efficiency of a solar selective coating

本研究针对太阳能集热器总发射率计算问题，指出需用工作温度下的光谱发射率测量值计算而非室温外推值，并分析了仅靠普朗克函数引入温度依赖的估算不确定性，对提升太阳能热发电经济性有重要意义。

An Optimized Self-Adaptive Thermal Radiation Turn-Down Coating with Vanadium Dioxide Nanowire Array

High performance metasurfaces for thermal radiative cooling applications can be identified using computational optimization methods. This work has identified an easy-to-fabricate temperature phase transition VO2 nanowire array laid atop dielectric BaF2 Fabry-Perot cavity-on-metal with total coating thickness of 2 um. This optimized structure has ability to self-adaptively switch between high reflectance at low temperature to high emissivity at high temperature in the broad thermal infrared spectrum. This design demonstrates exceptional turn-down figure-of-merit compared to previously realized …

Passive radiative cooling impact on commercial crystalline silicon-based photovoltaics

The radiative cooling of objects during daytime under direct sunlight has recently been shown to be significantly enhanced by utilizing nanophotonic coatings. Multilayer thin film stacks, 2D photonic crystals, etc. as coating structures improved the thermal emission rate of a device in the infrared atmospheric transparency window reducing considerably devices' temperature. Due to the increased heating in photovoltaic (PV) devices, that has significant adverse consequences on both their efficiency and life-time, and inspired by the recent advances in daytime radiative cooling, we developed a co…

热辐射阻挡涂层材料中的光吸收效应

Optical Absorption Effects in Thermal Radiation Barrier Coating Materials

本文利用双通量热传递模型研究热障涂层的光学吸收与散射特性，发现高归一化吸收率可降低界面温度，提出增强光吸收以减少冷却需求并提升燃气轮机效率。

纳米粒子与石墨烯光栅之间的近场辐射换热

Near-field radiative heat transfer between a nanoparticle and a graphene grating

本研究开发散射矩阵方法，探究纳米粒子与石墨烯光栅间的近场辐射换热，发现石墨烯涂层可提升热通量85%，光栅化因等离激元模式拓扑转变进一步增强换热，并揭示横向偏移对热通量的影响及临界几何因子。

Mechanically Tunable Radiative Cooling for Adaptive Thermal Control

Passive radiative cooling is currently the frontier technology in renewable-energy research. In terms of extraterrestrial applications, radiative cooling is a critical component to the thermal management system of a spacecraft, where the extreme environment of space can cause large temperature variations that can break and damage equipment. For terrestrial applications, nocturnal or daytime radiative cooling is expected to lead to cost-effective passive heat management without the need of inefficient and costly artificial refrigeration technologies. However, most currently available radiative …

Beam-controlled spectral-selective architecture with planar polydimethylsiloxane/metal-films for all-day radiative cooling

Radiative cooling is a passive cooling strategy with zero consumption of electricity. Although this technology can work well during optimal atmospheric conditions at nighttime, it is essential to achieve efficient radiative cooling during daytime when peak cooling demand actually occurs. In this article, we report an inexpensive planar polydimethylsiloxane (PDMS)/metal thermal emitter, i.e., a thin film structure fabricated using fast solution coating process that is scalable for large area manufacturing. By manipulating the beaming effect of the thermal radiation, temperature reduction of 9.5…

Radiative thermal switch via asymmetric black phosphorus gratings

Active control of heat transfer at the nanoscale has great potentials in thermal logic and energy conversion devices. In the present work, we theoretically propose a radiative thermal switch (RTS) composed of a pair of asymmetric black phosphorus (BP) gratings, with BP nanoribbons periodically patterned in different directions. The simply mechanical rotation between the gratings enables substantial modulation of near-field radiative heat transfer, especially when combined with the use of non-identical parameters, i.e., filling factors and electron densities of BP. Among all the cases including…

The gray body approximation for radiative heat transfer in evacuated tube solar collectors: Effects of envelope infrared transparency

A theoretical and experimental analysis is carried out of radiative heat transfer in the coaxial geometry of evacuated tube solar collectors. The gray body approximation implicit in the use of an effective emissivity does not strictly apply to evacuated tube solar collectors due to selective absorber coating and partially transmitting outer glass in the thermal infrared, especially when constructed from borosilicate. We develop analytic expressions for the heat transfer through the outer envelope and show the equations no longer follow a simple form where an effective emissivity for the system…

Thermal Insulating Polymer-Air Multilayer for Window Energy Efficiency

Polymer-air multilayer (PAM) was developed to decrease the heat loss through window glass panes. A PAM consists of a few polymer films separated from each other by air gaps. Thanks to the excellent optical properties of the polymer films, the visual transmittance of PAM is higher than 70%, and the haze is less than 2%. PAM not only has mechanisms to reduce the conductive and convective heat transfer, but also can obstruct the radiative heat transfer. With a 4~6 mm thick PAM coating, the U-factor of a glass pane can be lowered from above 1 Btu/{{h}{ft}^2{°F}} to 0.5~0.6 Btu/{{h}{ft}^2{°F}} .PAM…

具有DBR工程化色彩选择性的被动式日间彩色辐射冷却器

A Passive Daytime Colored Radiative Cooler with DBR-Engineered Color Selectivity

本文提出一种无需光刻的被动式日间彩色辐射冷却器，通过DBR与MgF2间隔层实现CMY色彩生成，PDMS层提供强热发射，日间可降温约12℃，适用于多种户外节能热管理场景。

Self-cleaning and self-cooling paper

The technique of passive daytime radiative cooling (PDRC) is used to cool an object down by simultaneously reflecting sunlight and thermally radiating heat to the cold outer space through the Earth's atmospheric window. However, for practical applications, current PDRC materials are facing unprecedented challenges such as complicated and expensive fabrication approaches and performance degradation arising from surface contamination. Here, we develop a scalable paper-based material with excellent self-cleaning and self-cooling capabilities, through air-spraying ethanolic polytetrafluoroethylene…

用于全方位热管理的具有可切换太阳透射率的光学木材

Optical wood with switchable solar transmittance for all-round thermal management

本研究开发出具有可切换太阳透射率的光学木材，可通过苯乙醇浸渍切换状态，分别实现夏季高效辐射制冷与冬季日光加热，为全季节建筑热管理提供低成本可持续方案。