IIT Guwahati Researchers Develop Radiative Cooler Without Electricity Check Details

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Researchers from India’s Guwahati Institute of Technology have developed a “radiative cooler” that does not require electricity to operate. It is an affordable and efficient “passive” radiative cooling system that can be used as an alternative to air conditioners.

The radiative cooler coating material is a non-electric cooling system that can be applied to rooftops and works day or night. The chiller can act as an alternative to conventional air conditioners.

How Passive Radiative Coolers Work

Passive radiative coolers work by emitting heat absorbed from the surroundings in the form of infrared radiation which can pass through the atmosphere before being released into the cold outdoor space. Until now, most passive radiative coolers could only operate at night. To operate during the day, chillers must reflect all solar radiation. Until now, passive radiative coolers have not been able to provide sufficient cooling during the day. Therefore, researchers at IIT Guwahati set out to solve these problems and present an affordable and more efficient radiative cooling system that can operate day or night.

Researchers who designed and modeled the passive radiative cooler include Ashish Kumar Chowdhary and Professor Debabrata Sikdar, among others. The study describing their innovation was recently featured in the Current scientific reportsa column to report on scientific research in India.

Why is it difficult to design a passive radiative cooler for daytime operation?

In a statement released by IIT Guwahati, Professor Debabrata Sikdar said that designing a passive radiative cooler for daytime operation is more challenging due to the simultaneous requirement of high reflectance across the entire regime. solar spectral and high emissivity in the atmospheric transmission window. The solar spectral regime varies from 0.3 to 2.5 micrometers in wavelength. Meanwhile, the atmospheric transmission window extends from eight to 13 micrometers in wavelength.

The solar spectrum includes radio waves, microwaves, visible light, ultraviolet rays, X-rays and gamma rays. Atmospheric transmission is the process by which radiation propagates through a medium. Atmospheric transmission is the ratio between the transmitted radiation and the total incident radiation on the medium.

Why are radiative chillers the best alternatives to air conditioners?

Sikdar added that these radiative coolers requiring no external source for their operation could be one of the best alternatives to replace conventional air conditioning systems used to cool buildings and automobiles in countries experiencing hot weather, such as India. . Traditional cooling technologies dump waste into the environment. Meanwhile, radiative cooling is a unique process that cools an object on Earth by sending excess heat directly into the extremely cold universe.

Design of the new radiative cooler

According to the study, the theoretical design of the radiative cooling system is tested and verified against rigorous computer simulations. The radiative cooler is less prone to imperfections during the manufacturing process. Therefore, the cooling capacity to be obtained after construction of the chiller should correspond closely to the calculations.

This innovation is believed to encourage chiller manufacturers to explore radiative cooling to design electricity-free cooling systems. Researchers hope the radiative cooler will hit the market once full-scale prototypes are developed and tested for operational stability and durability under different climatic conditions.

Chowdhary explained the technology needed to overcome the limitations of conventional radiative coolers. He said that for a radiative cooler to work during the day, the material must reflect solar and atmospheric radiation falling on it. The materials used in conventional coolers do not work during the day because they absorb more solar radiation and emit less during the day.

How daytime cooling is achieved using the new cooler

Chowdhary said daytime cooling can be achieved using passive polymer-based radiative coolers. However, oxidation degrades the polymers resulting in a limited lifespan.

The researchers attempted to solve this problem by using thin films of silicon dioxide and aluminum nitride, which have a low optical density corresponding to the wavelength range of solar and atmospheric radiation. However, these materials have high optical density at atmospheric transmission wavelengths. A high optical density material emits all absorbed radiation as a black body, in order to remain in thermal equilibrium. A blackbody is an object that absorbs all electromagnetic radiation that falls on it. A blackbody must emit radiation at the same rate as it absorbs radiation to stay in balance.

The researchers did not use a single layer as the ground metal. Instead, they placed thin layers of silicon dioxide and aluminum nitride over a layer of silver, which was used as the ground metal. The silver layer was placed on a silicon substrate.

The radiative cooler designed by the IIT Guwahati researchers achieved 97% reflectance for solar and atmospheric radiation and 80% emissivity for radiation in atmospheric transmission wavelengths. According to the study, the net cooling power is estimated at 115 watts per square meter. This cooling power could reduce ambient temperatures up to 15 degrees below the outside temperature.

What are the main advantages of the system compared to existing technologies?

The radiative cooling system is more advantageous than existing cooking technologies. These advantages include the fact that the design is lithography-free and compatible over a large area. Lithography is a printing process that involves using a block of stone or metal on which an image has been drawn with a thick substance that attracts ink.

Large-scale compatibility is important for developing affordable and efficient large-scale radiative coolers.

The design of the radiative cooler will provide efficient cooling during the day without the need to adjust the angle or position of the cooler towards the sun.

Compared to a recent cooler design that achieves a comparable reduction in ambient temperatures, the radiative cooler provides approximately 1.6 times more cooling power.

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