Scientists have developed double-layer cooling technology inspired by camels to stay cool in the hot desert sun. The lower hydrogel layer of the technology behaves like the sweat glands of a camel, lowering the temperature through water vapor, while the upper airgel layer functions as a fur, insulating against external heat while allowing water vapor to pass through. The study, published today (November 11, 2020) in the journal Joule, demonstrates that the design maintains the products five times longer than conventional single-layer approaches.
“While previous passive cooling research was focused on mimicking the evaporation of mammalian sweat glands, in this work we identified the crucial role of fur insulation,” says Jeffrey Grossman, head of the Massachusetts Institute of Technology and Materials Science and Engineering. the main author of the research. “By mimicking the dual system of fur / gland in camels, we designed a double layer of vapor insulation, similar to camel, to allow a significant extension of passive steam cooling time for the same amount of water consumption.”
As the climate warms and technology becomes more and more necessary to keep buildings cool and to conserve food and pharmacy, scientists are looking for passive cooling methods that do not require an external energy source. Although approaches based on evaporation from hydrogels are one of the most promising solutions for passive cooling, they require a significant amount of water and have limited potential for long-term use.
Thinking about these issues in terms of desert animal physiology, Grossman and colleagues realized that an essential component of existing evaporation cooling technologies was missing.
“Zoologists have reported that a trimmed camel should increase sweating water expenditure by 50% compared to its natural wool coat during the day,” says Grossman. “And so to minimize water loss by maintaining the cooling power of the evaporator, and thus expanding the cooling capabilities over longer periods of time, we turned to nature.”
To mimic the fur layer of a camel, the researchers synthesized highly porous hydrophobic silica airgels about half of the air’s thermal conductivity and then combined them with hydrogels that mimic the sweat gland. The group tested a double-layer sample in a closed chamber controlled by ambient temperature and relative humidity, proving that the sample could maintain a temperature of 7 degrees. Celsius lower than its surroundings. Cooling technology with only a hydrogel layer can keep the temperature a little lower, but double-layer technology has lasted much longer. The 5 millimeter hydrogel layer covered by a 5 millimeter airgel maintained the temperature for 200 hours before the moisture ran out and had to be recharged with water, while the hydrogel layer only lasted 40 hours.
Because the object has the ability to cool for a long time without electricity, dual-layer cooling technology will allow distributors to package, transport and store products temporarily without air conditioning, a service that would be especially useful in regions of the world. where electricity is scarce.
“This technology can allow conventional evaporation technologies to be miniaturized, as it moves efficient cooling for each amount of water given over a longer period of time,” says Grossman. “It can also help the thermal management of buildings with rapidly increasing cooling demand.”
However, the aerogel layer that gives the technology an advantage limits its ability to scale so that it can now expand its use. “Although the material cost of our aircraft is low, the manufacturing cost is a bottleneck for scalability as a result of a severe point drying step,” says Grossman, noting that one of co-authors, Elise Strobach, has made a start. the company set up to build window applications to achieve scalable production of transparent airgels.
Reference: Zhengmao Lu, Elise Strobach, Ningxin Chen, Nicola Ferralis, and Jeffrey C. Grossman, “Passive Cooling Subdirector from a Transparent Layer of Double Vapor Insulation,” November 11, 2020, Joule.
DOI: 10.1016 / j.joule.2020.10.005