The Evapolar evaCHILL personal air conditioner isn't a new concept. Water requires a significant amount of energy to change phases from liquid to gas, and it takes that energy from its surroundings. This process is called evaporative cooling. The more water that evaporates (changes from liquid to gas) the more cooling you will get.
Because the rate of evaporation is highly dependent on how saturated the air currently is with water (the humidity), the effectiveness of an evaporative cooler will vary wildly with your environment. The other downside is that if you use an evaporative cooler in an enclosed space it will quickly raise the humidity of that space and therefore lower its own effectiveness. Because of this, evaporative coolers are sometimes called "Swamp Coolers", because they can make the air feel "Swampy" (overly humid).
I live in Florida, an area known for it's high temperatures and even higher humidity, so I didn't have high hopes for the effectiveness of this product, but, I have used it significantly more than I expected.
The evaCHILL is an incredibly simple device: A 120mm DC cooling fan, a water reservoir, and a special filter material that wicks water into the airflow. It costs around $80, which I feel is a bit steep for what you're actually getting, but it has one huge advantage over the $50 swamp coolers that they sell at Walmart here in the US: The evaCHILL runs on 5V and takes a standard USB-C connection meaning it can be run off of a standard power USB power bank. After not initially seeing much use for it, I found myself bringing my evaCHILL camping, to summer block parties, and it even saved my sanity one day when the air conditioning was broken at work. It doesn't provide the same level of cooling as a typical air conditioner, but it does make stiflingly hot environments significantly more tolerable.
But it's not all good. Other than the price issue that I already mentioned, the evaCHILL has one huge drawback: It uses a paper like (which according to their documents is 100% free of organic material) filter to wick the water up from the filter... this paper-like filter remains very damp in already humid environments which could lead to growth of mold and mildew. I've been super careful not to leave water in the reservoir and I always run the fan until the filter is completely dry, and while I can't see any visible mold on the filter the air coming evaCHILL has a bit of a funky smell to it after just a few months and a dozen or so uses. It's not bad enough that I won't use it, but just enough that I wonder whether I'm spewing mold spores into the air around me. Again, the documentation says that the specially designed filters do not harbor the growth of mold and mildew, but it doesn't smell the same as it did when I first got it.
I'm not sure how much of the cost of the evaCHILL is for the filter, but if they sold replacement filters for $5-10 I would feel much more comfortable using it and I'd absolutely recommend it to others.
evaCHILL is on Amazon:
(Amazon US) https://amzn.to/2S9JbVY
(Amazon UK) https://amzn.to/36Vv3no