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Researchers at the Massachusetts Institute of Technology have created an electric-free cooling system. The technique, known as ‘passive cooling,’ could preserve food crops and supplement conventional air conditioners in buildings while using only a small amount of water to operate.
The system, which combines radiative cooling, evaporative cooling, and thermal insulation in a small housing that resembles a solar panel, has a cooling capacity of 9.3 degrees Celsius. It is composed of three layers of material: an aerogel sponge-like polyethylene layer, a hydrogel layer, and a reflective layer.

About the system

The aerogel is highly insulating while also allowing water vapour to pass through and cool the system; below that is the hydrogel, which is another sponge-like material with pore spaces filled with water rather than air and serves as the water source for evaporative cooling. The mirror-like layer then reflects any incoming sunlight that has reached it, redirecting it through the device rather than allowing it to heat up the materials and thus reducing their thermal load.
The system was tested in a small enclosure only 10 centimetres across, which the researchers claim demonstrates its effectiveness in less-than-ideal conditions.
“This technology combines some of the good features of previous technologies such as evaporative cooling and radiative cooling,” MIT postdoctoral researcher Zhengmao Lu said.
This combination “demonstrates that significant food life extension can be achieved even in areas with high humidity,” which limits the capabilities of conventional evaporative or radiative cooling systems. It is claimed that cooling could be used to store food for up to 40% longer in humid conditions and three times longer in dry conditions.
The aerogel, on the other hand, is expensive to produce due to the fact that it requires special equipment to remove solvents without damaging it. It’s possible that freeze-drying or using different materials could provide a similar function for less money.
“The aerogel is the only material that’s a product from the lab that requires further development in terms of mass production,” Mr Lu said, but it is unclear how long such research would take.
“By combining evaporative cooling, radiative cooling, and insulation, it has a better cooling performance and can be effective in a wider range of climates than evaporative cooling or radiative cooling alone,” said Xiulin Ruan, a professor of mechanical engineering at Purdue University.
“The work could attract significant practical applications, such as in food preservation, if the system can be made at reasonable cost.”

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