Thursday , June 30 2022

A new way to provide cooling without power



[ad_1]

Two versions of the device designed by MIT researchers, using a strip of & # 39; metal to block direct sun light, have been built and tested on the roof of & # 39; MIT building to confirm that cooling can provide far below the temperature of the ambient air. Photo by Bikram Bhatia
Two versions of the device designed by MIT researchers, using a strip of & # 39; metal to block direct sun light, have been built and tested on the roof of & # 39; MIT building to confirm that cooling can provide far below the temperature of the ambient air.

Photo by Bikram Bhatia

Scientists of MIT have developed a new system that offers cooling in & # 39; extreme sunny days without using energy. This approach & # 39; passive cooling exploits the angular radius isolation & # 39; irradiation from the sun in the sky to achieve sub-ambient cooling throughout the day regardless of the issuing properties in solar spectrum.

The system can & # 39; & # 39 provides cooling; Size 20 degrees Celsius (36 degrees Fahrenheit) below the ambient temperature at & # 39; place like Boston. When tested, the system offered to cool 6 C (about 11 F) below the ambient temperature.

The system works by allowing the emission of & # 39; & # 39 in heat; range & # 39; Infrared light can & # 39; passes through the atmosphere and spreads in cold & # 39; space & # 39; abroad, punching well above act as greenhouse gases. To avoid heating in direct sun light, small strip of & # 39; metal suspended on the device blocking direct sunlight.

Scientists have observed that "Other groups have tried to design a & # 39 systems, passive cooling to spread heat in & # 39; form & # 39; wavelengths & # 39; infrared & # 39; half-light, but they systems were based on complex photonic devices can be expensive and not readily available for use ".

"The devices are complex because they are designed to reflect the length of & # 39; all waves of sunlight almost perfectly, and only to emit radiation at & # 39; mid-infrared, at the most. that combination & # 39; reflectivity and emissivity requires selective material with & # 39; many layers where the thickness of the layers of nanometer are checked for accuracy. "

Scientists explained, "It turns out that such selectivity can & # 39; achieved by simply blocking the light direct sunlight with a narrow strip placed just at the right angle to cover the sun's path through the sky, not require active tracking of the device. Then, a simple device built from a combination of & # 39; inexpensive plastic film, polished aluminum, white paint and insulation can & # 39; allowing the required emission of heat through & # 39; middle radiation & # 39; the infrared, which is how most natural objects while keeping cool than heated by direct sunlight. "

"In fact, simple systems & # 39; radiant cooling have been used since ancient times to achieve cooling at night; the problem was that such systems do not work during the day due to the heating effect of sunlight was at least 10 times more b & # 39; his health than the maximum effect that can & # 39; to achieve.

The scientist & # 39; research Bikram Bhatia said, "But the heat rays of the sun traveling at & # 39; straight lines and are easily blocked – as we have experienced, for example, by going into the shade & # 39; tree in & # 39; hot day. by stripping device essentially put umbrellas on, and supplement that with & # 39; insulation around the equipment to protect it from ambient temperature air, researchers have made more viable passive-cooling.

"We have built the setup and did outdoor experiments on the roof of MIT. This was done using the & # 39; very simple materials" and showed b & # 39; clearly the effectiveness of the system. "

Evelyn Wang, professor of marine physics Soljačić said, "It's kind of & # 39; deceptively simple. By having a separate shadow issuer in the atmosphere – two separate components that can be relatively low cost – the system does not require capacity special to throw and absorb b & # 39; selectively. We have been using the angular selectivity to allow the blocking direct sunlight, as we continue to throw the wavelengths carrying heat to the sky. "

"This is useful for applications & # 39; refrigeration, such as storage & # 39; food or vaccines. The system can & # 39 well, be useful for some types & # 39; photovoltaic concentrated systems, where mirrors used to focus sunlight on a solar cell to increase its efficiency. But such systems can easily overheat and generally require active thermal management with fluids and pumps. Instead, side & # 39; after & # 39; of & # 39 systems, such concentration they can & # 39; complete with emissive surface middle infrared used in the & # 39; passive cooling system, and can control without intervention warming active. "

Scientists are currently working to improve the system, the biggest challenge is to find ways to improve the insulation of the device, to prevent heating much of the surrounding air, while not to block its ability to throw heat.

The new system is described this week in Nature journal Communications in & # 39; format of the scientist from the research Bikram Bhatia, a graduate student Arny Leroy, professor of mechanical engineering and head of the department Evelyn Wang, professor Marin physical Soljačić and six others at MIT.

[ad_2]
Source link