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New way of providing cooling without power



Two versions of the device designed by MIT researchers, using a strip of metal to prevent direct sunlight, were built and tested on the MIT building roof to confirm that they could provide cooling much lower than ambient air temperature. Picture by Bikram Bhatia
Two versions of the device designed by MIT researchers, using a strip of metal to prevent direct sunlight, were built and tested on the MIT building roof to confirm that they could provide cooling much lower than ambient air temperature.

Picture by Bikram Bhatia

MIT scientists have developed a new system that offers cooling in extreme sunny days without using power. This passive radial cooling approach exploits the impulse collection of irradiations of the sun in the air to ensure sub-ambient cooling during the day regardless of the emitter's properties in the solar spectrum.

The system can provide cooling as much as 20 degrees Celsius (36 degrees Fahrenheit) below the ambient temperature in a location such as Boston. When testing, the cooling system of 6 C (about 11 F) is proposed below the ambient temperature.

The system works by allowing heat emission to be released on a middle infrared range that can be transmitted directly through the atmosphere and spread into the space of the external space, punching through the gases that act as a greenhouse. In order to prevent heating in the direct sunlight, a small strip of metal that has been suspended over the device directly sunscreen the sun.

Scientists pointed out, "Other groups have tried to design passive cooling systems that heat heat in the form of a middle infrared light toner, but these systems are based on complex engineering photonic devices that can be expensive to make and are not readily available for a wide use. "

"Devices are complex because they have been designed to reflect every wavelength of sunlight almost perfect, and usually only to emit radiation during the infrared range. That combination of selectivity and emissivity requires multilayer material where the thickness of the layers are controlled to the detailed nanometer. "

Scientists explained, "It seems that similar solitude can be achieved by directly suspending the direct sun with a narrow strip at the right angle to cover the sun path across the air, and it does not need to be tracked actively by the device. Then a simple device built from a combination of cheap plastic film, polished aluminum, white paint, and insulation can allow the necessary emission of heat through medium infrared radiation, such as how most natural objects corrects when preventing the device from being heated by the direct sunlight. "

"In fact, radiant simple cooling systems have been used since the old time to carry out cooling at night; the problem was that such systems did not work during the day because the effect of heating the light of the sun at least 10 times stronger than possible potential cooling effect. "

Bikram Bhatia research scientist said, "But solar heating rays travel in straight lines and easily blocked – as we try, for example, stepping into the shadow of a tree on a hot day. By shadowing the device by putting an explanation on its own, adding to it with insulation around the device protecting from ambient air temperature, the researchers made passive cooling more viable. "

"We created the setup and made experiments outdoors on MIT miniature. It was made using very simple materials" and clearly demonstrates the effectiveness of the system. "

Evelyn Wang, physics professor Marin Soljačić, said: "It's really simple. By having a separate shade and emitter to the atmosphere – two separate elements that can be a relatively low cost – it is not necessary Particularly capable of emitting and absorbing system. We use an angular selection to allow direct sunblock, as we continue to spread the heavy waves to the air. "

"This would be useful for refrigeration applications, such as food storage or vaccines. The system could also be useful for some types of concentrated photovoltaic systems, where mirrors are used to focus sunlight on solar cells To increase its efficiency, but such systems can survive easily and, in general, they need operational thermal control with fluids and pumps. Instead, such backup systems could be fitted with & # 39 ; The average infrared emission surfaces used in the passive cooling system, and can control the heat without active intervention. "

Scientists are currently working on improving the system, the biggest challenge is to find ways to improve the insulation of the device, preventing from heating too much ambient air , although it does not stop its ability to separate heat.

This new system is described this week in the journal Nature Communications in a paper by the research scientist Bikram Bhatia, the graduate student, Arny Leroy, a mechanical engineering teacher and the head of department of Evelyn Wang, physics teacher Marin Soljačić, and six others in MIT.


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