Here is a closeup of how well a frio works in a humid environment. High relative humidity means that the air can’t absorb much more moisture— which means that there’s no tendency for liquid to evaporate into the air. (As a side note, warm air can hold more moisture than cool air that’s why dew forms in the morning when the air has cooled off and can’t hold as much moisture, it’s also why clouds form in the sky and all sorts of other cool things) The thermometer on the right here is draped in a wet cotton tube… if moisture were evaporating into the air from the tube it would be cooling the thermometer in the process. However, it is raining outside so the relative humidity is at or near 100%… and the moisture can’t evaporate into the air, so both thermometers are the same temp. This is exactly how the frio works (or in this particular example; doesn’t work)
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