IIT Guwahati’s Radiative Cooler

By Aaryaa Padhyegurjar

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Ever imagined an AC that runs without electricity? Researchers at IIT Guwahati have created a substitute for an air conditioner that, according to their claims, is not only reasonably priced and effective, but also runs without power!

The “Radiative Cooler” coating material is a new invention that can be used as an alternative to traditional air conditioners. It can be applied to rooftops and works both during the day and at night. Systems that use passive radiative cooling work by releasing heat that has been absorbed from the environment as infrared radiation, which can pass through the atmosphere before being released into the frigid outer space. The majority of passive radiative coolers only work at night. Current cooling technologies have not yet been able to cool buildings enough throughout the day.

IIT Guwahati’s new radiative cooling system’s theoretical design has been put to the test and confirmed by meticulous computer simulations. According to the IIT, this pattern-free radiative cooler design is large-area compatible and thus less prone to flaws during the fabrication process.

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Explaining the technology to overcome the limitations of conventional radiative coolers, Mr. Ashish Kumar Chowdhary said, “For a radiative cooler to work during the daytime, the material should reflect the solar and atmospheric radiations falling on it. Since the materials used in conventional coolers absorb more solar radiation and emit less during the day, they do not work during the daytime. While daytime cooling can be achieved using polymer-based passive radiative coolers, oxidation degrades the polymers resulting in a limited lifespan.”

The inventors thought about employing silicon dioxide and aluminium nitride thin films to address this. The wavelength range of solar and atmospheric radiations are matched by the low optical density of these materials. But they have a high optical density at wavelengths where there is atmospheric transmission. When optical density is high, radiations penetrate a medium more slowly and are absorbed more fully. The substance emits all absorbed radiations like a black body to maintain thermal equilibrium.

“Instead of a single layer, the team cascaded silicon dioxide and aluminum nitride thin film layers on a silver layer, used as a ground metal, placed over a silicon substrate. The cooler they designed achieved about 97 per cent reflectance for solar and atmospheric radiations and 80 per cent emissivity for radiations in atmospheric transmittance wavelengths. The net cooling power is estimated to be 115 Wm−2 which could reduce ambient temperature up to 15 degrees below the outside temperature,” said the IIT in a statement.


 

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