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Nature always moves towards a state of equilibrium. So when a cooler region and a warmer area come into contact, the two temperatures will move towards every other and try to equal out. As warm, dry air passes over a body of water, it evaporates some of the water and is cooled by it.
wheeled cooler
This same idea is reproduced in a swamp evaporative cooler. Hot, dry air from outside is pulled to the cooler by a fan. That air is pulled by means of a series of damp pads, where it absorbs water that has the effect of reducing the air’s temperature. As an added benefit, the pads also filter or clean the air as it passes through. Then the cooler, cleaner air is blown by way of to the room or office which you are cooling. In reality, the cooler keeps the air circulating in a room, meaning that you feel even cooler due to the slight breeze that the swamp evaporative cooler creates.