Hierarchically Hollow Microfibers as a Scalable and Effective Thermal Insulating Cooler for Buildings

Zhong, Hongmei; Li, Yanan; Zhang, Peng; Gao, Shouwei; Liu, Bing-Ying; Wang, Yang; Meng, Ting; Zhou, Yongsen; Hou, Huwang; Xue, Chao-Hua; Zhao, Yang; Wang, Zuankai

doi:10.1021/acsnano.1c01814

Cited by 167 publications

(114 citation statements)

References 39 publications

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“…As a result, the aerogel achieved 13 °C below ambient cooling performance around solar noon. Another approach demonstrated that radiative cooler consisting of hierarchically hollow microfibers achieved high passive cooling performance (9 °C subambient) in the summer (Figure 7c), [70] wherein hierarchically hollow microfibers with nanostructures are an efficient light scattering medium and thermal insulator, providing strong solar reflection (94%) and IR thermal emission (0.94). Simultaneously, the hollow microfiber structure with ultralow thermal conductivity (i.e., 0.014 W m −1 K −1 ) restricted heat transfer between the cooler and its surrounding environment.…”

Section: Thermal Managementmentioning

confidence: 99%

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

Zhang

Wang

et al. 2022

Small Methods

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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...

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Section: Thermal Managementmentioning

confidence: 99%

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

Zhang

Wang

et al. 2022

Small Methods

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“…The hierarchical micro- and nanostructures with mesopores of sizes broadly distributed 3–20 nm (Figs. 1 d and S9) were responsible for the excellent sunlight scattering by the composite aerogel [ 30 , 70 ]. Considering that the solar intensity varies with the wavelength, the solar intensity weighted reflectance, , was calculated by Eq.…”

Section: Resultsmentioning

confidence: 99%

Superinsulating BNNS/PVA Composite Aerogels with High Solar Reflectance for Energy-Efficient Buildings

et al. 2022

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With the mandate of worldwide carbon neutralization, pursuing comfortable living environment while consuming less energy is an enticing and unavoidable choice. Novel composite aerogels with super thermal insulation and high sunlight reflection are developed for energy-efficient buildings. A solvent-assisted freeze-casting strategy is used to produce boron nitride nanosheet/polyvinyl alcohol (BNNS/PVA) composite aerogels with a tailored alignment channel structure. The effects of acetone and BNNS fillers on microstructures and multifunctional properties of aerogels are investigated. The acetone in the PVA suspension enlarges the cell walls to suppress the shrinkage, giving rise to a lower density and a higher porosity, accompanied with much diminished heat conduction throughout the whole product. The addition of BNNS fillers creates whiskers in place of disconnected transverse ligaments between adjacent cell walls, further ameliorating the thermal insulation transverse to the cell wall direction. The resultant BNNS/PVA aerogel delivers an ultralow thermal conductivity of 23.5 mW m−1 K−1 in the transverse direction. The superinsulating aerogel presents both an infrared stealthy capability and a high solar reflectance of 93.8% over the whole sunlight wavelength, far outperforming commercial expanded polystyrene foams with reflective coatings. The anisotropic BNNS/PVA composite aerogel presents great potential for application in energy-saving buildings.

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“…With this well-established concept, people developed different types of white cooling roof to improve indoor comfort and save on energy consumed by air conditioning. 39,40 However, in cooler regions with seasonal conditions, dark roofs are more popular [Fig. 1(b)].…”

Section: Criteria Of Spectral Selectivity For Radiative Coolingmentioning

confidence: 99%

Colorful surfaces for radiative cooling

et al. 2021

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Daytime radiative cooling has attracted extensive research interest due to its potential impact for energy sustainability. To achieve subambient radiative cooling during the daytime, a white surface that strongly scatters incident solar light is normally desired. However, in many practical applications (e.g., roofing materials and car coatings), colored surfaces are more popular. Because of this, there is a strong desire to develop colorful surfaces for radiative cooling. We summarize the general design criteria of radiative cooling materials with different colors and discuss the limitations in cooling performance. Major efforts on this specific topic are reviewed with some suggested topics for future investigation.

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Hierarchically Hollow Microfibers as a Scalable and Effective Thermal Insulating Cooler for Buildings

Cited by 167 publications

References 39 publications

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

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

Superinsulating BNNS/PVA Composite Aerogels with High Solar Reflectance for Energy-Efficient Buildings

Colorful surfaces for radiative cooling

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