放射冷却と電磁波吸収のための新しいエアロゲルを開発(NUS researchers develop new aerogels for radiative cooling and the absorption of electromagnetic waves)

2024-06-05

2024-06-04 シンガポール国立大学(NUS)

In this demonstration, the white aerogel insulates the area underneath from the surrounding heat, while simultaneously cools the area through radiative cooling, as shown by the lower temperature on the upper surface of the aerogel compared to the temperature of the hot water basin.

エアロゲルは、重量管理サプリメントで脂肪球を吸収したり、持続可能な金属リサイクルを促進したりする多用途の固体材料です。シンガポール国立大学の研究チームは、このエアロゲルを放射冷却と電磁波吸収に利用する新しい応用方法を開発しました。プラスチック廃棄物を利用して作られた薄膜エアロゲルは、建物の屋根などに適用して内部温度を下げることで、エネルギーを使わない冷却を実現します。また、軽量で耐久性のあるエアロゲルは、Xバンドの電磁波を吸収し、電子機器の保護に役立ちます。これにより、エネルギー消費を抑えつつ、プラスチック廃棄物問題にも対応します。

＜関連情報＞

プラスチック廃棄物から再生した熱絶縁性ポリエチレンテレフタレートエアロゲルで亜環境放射冷却を実現 Sub-ambient radiative cooling with thermally insulating polyethylene terephthalate aerogels recycled from plastic waste

Xue Yang Goh, Jaesuk Hwang, Luon Tan Nguyen, Ren Hong Ong, Tianliang Bai, Hai M. Duong
Solar Energy Available online: 30 April 2024
DOI:https://doi.org/10.1016/j.solener.2024.112544

Abstract

We demonstrate that the aerogels produced from the polyethylene terephthalate (PET) fibers, recycled from plastic bottle wastes, can function both as a radiative cooler and a thermal insulator. An object under and in contact with the recycled PET aerogel is thermally insulated from the surroundings and, at the same time, cooled below ambient temperature via radiative cooling. These dual capabilities are tested under the warm sky of Singapore with more than 420 /2 downwelling. With a 0.48 cm thick recycled PET aerogel, a heat transfer coefficient of 1.67 /2· is measured when the object underneath is cooled by 2 °C from ambient temperature. Even under a 4.5 cm thick recycled PET aerogel, completely opaque to the thermal emission and having a heat transfer coefficient less than 1 /2·, a sub-ambient radiative cooling is observed. Our measured heat transfer coefficient is lower than that of other porous polymer materials or aerogels reported to date as a radiative cooling substrate. Our results demonstrate that the recycled PET aerogels are a multi-functional material, integrating radiative cooling and thermal insulation in a single substrate. Produced by processing waste materials, the recycled PET aerogels hold promise to be a highly scalable and sustainable thermal management solution, with a positive impact on the environment.

Xバンド電磁波を完全に吸収する軽量カーボンナノチューブ・エアロゲル複合材料のスケーラブルな製造 Scalable fabrication of lightweight carbon nanotube aerogel composites for full X-band electromagnetic wave absorption

Luon Tan Nguyen, Chong Jin Goh, Tianliang Bai, Ren Hong Ong, Xue Yang Goh, Hai M. Duong
Carbon Available online: 10 January 2024
DOI:https://doi.org/10.1016/j.carbon.2024.118811

Highlights

Non-filler porous carbon nanotube (CNT) aerogels are prepared by a simple method.
The current maximum sample size is 35 cm by 35 cm.
The aerogel absorbs 90 % of electromagnetic wave (EMW) energy in the whole X band.
Non-functionalized CNT is better for EMW absorption than COOH-functionalized CNT.
The higher aspect ratio of CNT is favourable for EMW absorption.

Abstract

Electromagnetic waves (EMWs) from advanced electronic devices can hinder normal operation of other electronic equipment, negatively affecting their performance and cause harmful impacts on human health by breaking down DNA strands and causing cancer. In this study, we thrivingly prepared new lightweight EMW absorbing aerogel composites by first blending polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), carbon nanotube (CNT), reduced graphene oxide (rGO), and carbonyl iron (CI), followed by freeze-drying. The materials are promising for up-scale production with the current pilot-scale samples sizing 35 cm × 35 cm. The effects of CNT types, CNT, rGO, CI, and crosslinker contents on EMW absorption ability are comprehensively investigated. The obtained aerogel composites exhibit a 3D porous structure with low densities (0.088–0.210 g/cm³), high thermal stability (227 °C), and high Young’s modulus (670.9 kPa) compared to past aerogels. Notably, the materials with 3.0–3.5 mm in thickness achieve the minimum reflection loss (RL_min) of up to −42 dB (99.99 % EMW energy lost) and provide coverage across the entire X-band (8.2–12.4 GHz) with RL < −10 dB, indicating a 90 % attenuation of EMW energy. Compared to commercial Ni/CNT and other existing composites, our materials boast a broader effective bandwidth of 1.2–2.2 GHz. These properties make our aerogel composites highly promising for valuable commercial use, offering lightweight, durable, and efficient EMW absorption capabilities.