Early Milk Cooler

Evaporative Cooling

How to keep the milk cool when camping? (Hint from early camping tips). Place the bottles in a suitable container with water in it. Cover with an absorbent cloth ensuring that the cloth reaches down into the water.

Does it work? Yes, the water soaks through the material, and evaporates from the surface. This is called Evaporative Cooling. It is responsible for the chill you feel when a breeze strikes your skin — the air evaporates the water on your skin, with your body heat providing the energy. The ancient Egyptians used Evaporative Cooling. They hung wet mats in their doors and windows, and wind blowing through the mats cooled the air—the first form of air conditioning.

How cold can we cool with Evaporative Cooling? The tendency for water to evaporate into the air around us is dependent on the amount of water vapour already in the air. This is termed "humidity". If a thermometer is covered with a wet cloth and placed outside, the temperature shown will be the "wet bulb temperature", and this is lowest temperature that can be achieved.

This simple example shows how cooling can be done by just taking advantage of atmospheric conditions, No electricity or other man-made power source is needed. Modern Evaporative Coolers are used for air conditioning where the climate is suitable, and they use fans to circulate the air.

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