Easy Way to Achieve Self-Adaptive Cooling of Passive Radiative Materials

et al. 2022

Small Methods

the terrestrial radiation with a temperature of ≈300 K at the Earth's surface is concentrated at wavelengths ranging from 2.5 to 50 µm. Meanwhile, the combined effects from all atmospheric components result in that the special atmospheric window between 8 and 13 µm that is highly transparent. Hence, most terrestrial areas can effectively radiate heat through the transparent atmospheric window to the cold universe to maintain a relatively stable temperature. To this end, radiative coolers should have high emissivity in the transparent atmospheric window (8-13 µm), which is transparent in this region and allows infrared (IR) light to pass through. In this regard, various materials and structures have been designed in the past few decades and have exhibited promising passive cooling performance at night. [8,9] However, during the daytime, the Sun heats the radiative coolers, which seriously compromises the cooling effect. To resolve this problem, the cooler should radiate more heat to the cold universe while reflecting sunlight to avoid solar heating. Fan and co-workers [10] first designed multilayer photonic materials and achieved daytime radiative cooling to a temperature below ambient conditions when subjected to direct sunlight. Since then, various materials have been demonstrated to realize subambient daytime radiative cooling and have shown great potential for practical applications. [11][12][13] Before some reviews have summarized these developments in radiative cooling, [14][15][16][17] but the limited net cooling power and instability of radiative cooling hinder its practical wide applications. In this review, by summarizing the state-of-the-art research and development in passive daytime radiative cooling (PDRC), we first propose three critical components for PDRC: 1) spectral design in the mid-IR range, 2) structure design for enhancing solar reflectance, and 3) thermal management. Second, we introduce various applications of PDRC, such as building cooling, solar cell cooling, water harvesting, clothing, and electricity generation (Figure 1). Finally, the remaining challenges and opportunities of PDRCs are also discussed. Fundamental Mechanisms of PDRC PDRC ConceptBased on Kirchhoff's law, an object with a temperature higher than 0 K continuously exchanges heat with other objects by absorbing Passive daytime radiative cooling (PDRC) is emerging as a promising cooling technology. Owing to the high, broadband solar reflectivity and high mid-infrared emissivity, daytime radiative cooling materials can achieve passive net cooling power under direct sunlight. The zero-energy-consumption characteristic enables PDRC to reduce negative environmental issues compared with conventional cooling systems. In this review, the development of advanced daytime radiative cooling designs is summarized, recent progress is highlighted, and potential correlated applications, such as building cooling, photovoltaic cooling, and electricity generation, are introduced. The remaining challenges and opportunities of PDRCs are also in...

Section: Discussionmentioning

confidence: 99%

Recent Progress in Daytime Radiative Cooling: Advanced Material Designs and Applications

Zhang

et al. 2022

Small Methods

“…When T c > T ct , the coating operates as a cooling device, and when T c < T ct , the coating stays in the heating mode. Switchable coatings based on vanadium dioxide (VO 2 ), 86,90–93 which exhibit an insulator‐to‐metal transition at T ct = 68°C, have been developed 94 . For example, a self‐adaptive coating based on VO 2 was theoretically designed; the coating can adaptively turn “on” and “off” radiative cooling in the LWIR atmospheric window while the solar reflectance is unchanged (

{\overset{true¯}{R}}_{solar}

~ 1) by a spectrally selective filter, depending on the ambient temperature without any extra energy input for switching, as shown in Figure 13A 86 .…”

Section: Materials Designs For Pdrcmentioning

confidence: 99%

Passive daytime radiative cooling: Fundamentals, material designs, and applications

Chen

Pang

Chen

et al. 2021

EcoMat

Passive daytime radiative cooling (PDRC) dissipates terrestrial heat to the extremely cold outer space without using any energy input or producing pollution. It has the potential to simultaneously alleviate the two major problems of energy crisis and global warming. In this review, we summarize general strategies implemented for achieving PDRC and various applications of PDRC technologies. We first introduce heat transfer processes involved in PDRC, including radiative and nonradiative heat transfer processes, to evaluate the PDRC performance. Subsequently, we summarize the general material designs used for controlling PDRC performance, such as tuning the thermal mid-infrared emittance and solar reflectance. Finally, we discuss the diverse applications of PDRC technologies to overcome problems in space cooling, solar cell cooling, water harvesting, and electricity generation.

“…Thus, the Janus material can realize cooling and heating functions within the same film by simply flipping the sides and does not require any additional energy input, such as fossil fuels or electricity. The significant thermal load range can be tuned with both states because the sun absorption and infrared radiation are both controlled rather than only one of them. ,, …”

Section: Resultsmentioning

confidence: 99%

“…We designed and fabricated this film, as shown in Figure . The Janus material was achieved with common materials and simply a multilayer structure, which is attractive for large-scale fabrication compared to special materials and a complex structure. ,− The materials were chosen according to the solar absorption, infrared radiation, and heat conduction property, as shown in Table . Three materials Si 3 N 4 , SiO 2 , and PDMS were chosen for the cooling side to broaden the range of the emission.…”

Section: Resultsmentioning

confidence: 99%

Janus Multilayer for Radiative Cooling and Heating in Double-Side Photonic Thermal System

Zou

ACS Appl. Mater. Interfaces

et al. 2021

The temperature of outdoor structures, such as automobiles, buildings, and clothing, can be tuned by designing photonic properties. However, particular challenges arise when considering the temperature of an object itself rather than the enclosure in these outdoor structures. We present a double-side photonic thermal (DSPT) system. In the DSPT system, the tunable range of photonic thermal load for heating and cooling functions is calculated by designing the absorption spectra of both sides to adapt to different temperature conditions. These include the proper photonic design of not only the side facing outward but also the inner side and more complex temperature conditions of the object, enclosures, and atmosphere. According to the DSPT mechanisms, we developed a Janus material that can achieve the opposite functions (cooling and heating) with one film by simply flipping the sides of the Janus material, which does not require any additional energy input. The Janus material is designed and fabricated by common materials and a simple multilayer structure, which is attractive for large-scale fabrication. The thermal experiment proved the Janus multilayer could achieve a high temperature in the heating mode and a low temperature in the cooling mode, and the range of the tunable temperature would be wider with stronger sun radiation. The Janus material can passively achieve more efficient temperature control in enclosures while offering both side photonic design comparable to conventional radiative coolers and heaters.