Materials stay cooler when water evaporates off from them but once all the water is gone, the cooling effect stops. Bearing this in mind, MIT scientists have developed a camel fur inspired material that would keep items cool without using electricity.
Although it’d initially appear to be a bare skinned camel would stay cooler overall than one covered with fur, that is not the case. The fur acts as a gas permeable insulating layer shading the animal’s skin from external heat while still allowing sweat to evaporate off from it. As a result, the evaporative cooling effect lasts longer, the camel still sweats but not much amount as the hypothetical bare-skinned one would before it become dehydrated.
MIT’s material works in a same fashion because it consists of a layer of hydrogel on the bottom, covered with a layer of porous-silica based aerogel on top. The hydrogel is made from 97% water, which evaporates when the gel heats up, thus lowering that gel’s temperature.
The aerogel has very low thermal conductivity, it means that it doesn’t absorb much heat from its environment. This suggests that the hydrogel beneath it stays cooler than it might otherwise, so its evaporative cooling effect is prolonged.
In lab tests, a bare 5 mm layer of hydrogel lost all of its water to evaporation within 40 hours, at an ambient temperature of 30 ºC (86 ºF). Once that hydrogel was covered with a 5-mm layer of the aerogel. However, it lasted for 200 hours at an equivalent temperature before becoming parched. The evaporative cooling effect lowered the composite material temperature by 7 ºC (12.6 ºF) as compared to 8 ºC (14.4 ºF) for the bare but shorter lasting plain hydrogel.
Additionally, once the hydrogel dry-out, the cooling material are often made functional again just by adding more water.
Production of the aerogel currently involves large & expensive equipment, therefore the researchers are looking into more practical, less expensive alternatives. Ultimately, it’s hoped that the camel fur-inspired material could find use in developing nations or other places lacking infrastructure for the shipping & storage of food & medicine.
The research is described in a paper that was recently published in the journal ‘Joule’.