When water is evaporating off materials, they remain cooler, but the cooling effect stops once that water runs out. On the other hand, camels have evolved a thick coat of insulating fur to keep cool while conserving water in scorching desert environments. MIT scientists have turned to camel-fur for inspiration on making a material that could keep items, such as fresh produce or pharmaceuticals, cool in hot regions without needing to use electricity.
As strange as it sounds, a camel covered in fur stays cooler than a bare-skinned camel. The fur shades the animal’s skin from external heat while simultaneously allowing sweat to evaporate off of it, causing the evaporative cooling effect to last longer.
The furry camel may still sweat but not as much as the bare-skinned one. According to the researchers, tests have shown that a shaved camel loses 50% more moisture than an unshaved one under the same conditions.
The MIT team produced a material that uses the same approach. It consists of a bottom layer of a hydrogel with a top layer of porous silica-based aerogel. As the gel on top heats up, the hydrogel – composed of 97% water – starts to evaporate, and as it does, it lowers the gel’s temperature.
The aerogel has an ultra-low thermal conductivity that keeps it from absorbing too much heat from its surroundings. Therefore, the hydrogel underneath it stays cooler longer, and its evaporative cooling effect is extended.
When the material was tested in the lab, a 5mm layer of the hydrogel lost all of its water to evaporation within 40 hours, at temperatures of 86°F (30°C). However, once that hydrogel was covered with a 5mm layer of the aerogel, it lasted up to 200 hours at the same temperature. Overall, the evaporative cooling effect lowered the material’s temperature by 12.6°F (7°C) instead of 14.4°F (8°C) for the plain hydrogel. Once the hydrogel dries out, the material can be reused by simply adding more water.
The only downfall is that the production of the aerogel involves massive and expensive equipment. The MIT researchers are currently searching for more practical and in-expensive alternatives. Their ultimate goal is that the material could find use in developing countries that lack infrastructure for shipping and storing food or medicine.
The MIT team published their findings on November 11 in the journal Joule.
