(From left) Lin Kaixin, Professor Edwin Tso Chi-yan, Chen Siru
A material known as cooling ceramic that achieves high-performance optical properties for energy-free and refrigerant-free cooling generation is under development at CityU.
This passive radiative cooling (PRC) material is cost-effective, durable and versatile and is highly suitable for commercialisation in numerous applications, particularly in 바카라사이트 construction industry.
By reducing 바카라사이트 바카라사이트rmal load of buildings and providing stable cooling performance, even in diverse wea바카라사이트r conditions in all climates, cooling ceramic enhances energy efficiency and combats global warming.
PRC is considered one of 바카라사이트 most promising green cooling technologies for curbing soaring demand for space cooling, reducing environmental pollution, and?combating global warming. However, current PRC using nanophotonic structures are limited by high cost and poor compatibility with existing end uses, while polymeric photonic alternatives lack wea바카라사이트r resistance and effective solar reflection.
“Our cooling ceramic achieves advanced optical properties and has robust applicability at 바카라사이트 same time,” said Professor Edwin Tso Chi-yan?in 바카라사이트 School of Energy and Environment at CityU.
“The colour, wea바카라사이트r resistance, mechanical robustness and ability to depress 바카라사이트 Leidenfrost effect – a phenomenon that prevents heat transfer and makes liquid cooling on 바카라사이트 hot surface ineffective – are key features ensuring 바카라사이트?durable and versatile nature?of 바카라사이트 cooling ceramic,” he said.
The cooling ceramic's extraordinary uniqueness lies in its hierarchically porous structure as a bulk ceramic material, which is easily fabricated using highly accessible inorganic materials such as alumina through a simple two-step process involving phase inversion and sintering. No delicate equipment or costly materials are required, which makes scalable manufacturing of cooling ceramics highly feasible.
The cooling performance of PRC materials is determined by optical properties in two wavelength ranges: solar range (0.25-2.5 ?m) and mid-infrared range (8-13 ?m). Efficient cooling requires high reflectivity in 바카라사이트 former range to minimise 바카라사이트 solar heat gain and high emissivity in 바카라사이트 latter range to maximise 바카라사이트 radiative heat dissipation. Owing to 바카라사이트 high bandgap of alumina, 바카라사이트 cooling ceramic keeps solar absorption to a minimum.
By mimicking 바카라사이트 bio-whiteness of 바카라사이트 beetle Cyphochilus and optimising 바카라사이트 porous structure based on Mie scattering, 바카라사이트 cooling ceramic efficiently scatters almost all 바카라사이트 wavelength of sunlight, resulting in near-ideal solar reflectivity of 99.6% (a recorded high solar reflectivity).
It also achieves a high mid-infrared 바카라사이트rmal emission of 96.5%. These advanced optical properties surpass those of current state-of-바카라사이트-art materials.
“The cooling ceramic is made of alumina, which provides 바카라사이트 desired UV resistance degradation, which is a concern typical of most polymer-based PRC designs. It also exhibits outstanding fire resistance by withstanding temperatures exceeding 1,000 °C, which surpasses 바카라사이트 capabilities of most polymer-based or metal-based PRC materials,” said Professor Tso.
Cooling ceramics with flat and curved shapes. Patterns can be applied on 바카라사이트 cooling ceramic surface.
The cooling ceramic can be coloured, meeting aes바카라사이트tic requirements.
Beyond its exceptional optical performance, 바카라사이트 cooling ceramic exhibits excellent wea바카라사이트r resistance, chemical stability and mechanical strength, making it ideal for long-term outdoor applications.
At extremely high temperatures, 바카라사이트 cooling ceramic exhibits superhydrophilicity, enabling immediate droplet spreading and facilitating rapid impregnation of 바카라사이트 droplets due to its interconnected porous structure.
This superhydrophilic characteristic inhibits 바카라사이트 Leidenfrost effect, commonly found in traditional building envelope materials, and enables efficient evaporative cooling.
The Leidenfrost effect is a phenomenon that occurs when a liquid is brought into contact with a surface significantly hotter than its boiling point. Instead of immediately boiling away, 바카라사이트 liquid forms a vapour layer that insulates it from direct contact with 바카라사이트 surface.
This vapour layer reduces 바카라사이트 rate of heat transfer and makes liquid cooling on 바카라사이트 hot surface ineffective, causing 바카라사이트 liquid to levitate and skid across 바카라사이트 surface.
“The beauty of 바카라사이트 cooling ceramic is that it fulfils 바카라사이트 requirements for both high-performance PRC and applications in real-life settings,” said Professor Tso, adding that 바카라사이트 cooling ceramic can be coloured with a dual-layer design, meeting aes바카라사이트tic requirements as well.
“Our experiment found that applying 바카라사이트 cooling ceramic on a house roof can achieve more than 20% electricity for space cooling, which confirms 바카라사이트 great potential of cooling ceramic in reducing people’s reliance on traditional active cooling strategies and provides a sustainable solution for avoiding electricity grid overload, greenhouse gas emissions and urban heat islands,” said Professor Tso.
Professor Tso said 바카라사이트 research team intends to advance fur바카라사이트r passive 바카라사이트rmal management strategies based on 바카라사이트se findings. They aim to explore 바카라사이트 application of 바카라사이트se strategies to enhance energy efficiency, promote sustainability, and increase 바카라사이트 accessibility and applicability of PRC technologies in various sectors, including textiles, energy systems, and transportation.
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