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Taking inspiration from evolution, scientists have developed a new cooling technology using the same method that camels prevent themselves from overheating in the desert.
The way camels (and other animals, and humans too) cool off is usually by sweating. When the core body temperature rises, the sweat glands in the skin begin to produce sweat. This salt water is found on the skin and the difference in humidity between that and dry air evaporates the sweat in the form of water vapor, taking heat with it, in the form of energy.
By studying this process, scientists developed technology that mimicked the work of the sweat glands by using a hydrogel, which is a gel-like material designed to hold large amounts of water. A single layer of this hydrogel could keep something cool by releasing its water over the course of about 40 hours, after which it had to be replenished with more “sweat”.
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To increase the amount of time the hydrogel could keep something fresh, the scientists again looked at the camel.
“Zoologists have reported that a shorn camel has to increase water bills to sweat by 50 percent during the day compared to a natural wool coat,” said Jeffrey Grossman, senior author of the study. This means that the animal with less hair had to produce more sweat to stay cool. Thus, a hydrogel without an insulating layer on top would lose water faster than one with something acting as “fur”.
To do this, scientists from the Massachusetts Institute of Technology designed an airgel layer that would let water vapor through.
“Imitating the double fur / gland system in camels, we have designed a double layer of evaporation insulation, which, like the camel, allows for a significant extension of passive evaporative cooling time for the same amount of water consumption.” Grossman said.
The team’s dual-layer design kept a sample 7 ° C below the surrounding temperature for 200 hours before it needed to be “refilled” with more water, five times longer than the single-layer approach.
Unlike cooling systems based on air conditioners and refrigerators, hydrogel-airgel technology does not use electricity, making it more appropriate for the millions of people around the world who lack access to electricity.
“We want this to be green technology,” said study lead author Zhengmao Lu. “Once the hydrogel is completely dry [out], can be immersed in water (not necessarily clean) and becomes hydrated and functional again, for multiple cooling cycles. “
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However, the cost of manufacturing the technology is currently the bottleneck for scalability, Grossman said. But with news that the Pfizer / BioNTech coronavirus vaccine may need to be kept at -70 ° C, low-cost portable cooling technology is in demand.
“One important thing we learn in this paper is the benefit of adding porous insulation, which I think will also be useful for regulating the temperature of the coronavirus vaccine,” said Lu. “Sure, with our current set of materials. , where the main heat removal mechanism is still the evaporation of water, it is unlikely to reach such low temperatures. “
Using their discovery, Lu says a solution to the problem could be to couple dry ice with porous insulation.
“To some extent, people already do this with existing dry ice packs. To reach temperatures even lower than those, it is necessary to optimize the design of the insulation material. At this point, we expect this to take a few years’ effort. “
Reader’s Questions and Answers: Why do we sweat when we’re anxious?
Asked by: Kanika Ahuja, Winchester
This is part of our fight or flight response and occurs when our sympathetic nervous system releases hormones, including adrenaline, which activates the sweat glands.
Brain scans reveal that smelling someone else’s panic-induced sweat illuminates the regions of the brain that handle emotional and social signals. So one theory is that this sweating is an evolved behavior that makes other people’s brains more alert and ready for whatever makes us anxious – useful if there is a predatory tiger on the loose.
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