What Is Evaporative Cooling in Biology?

Written by christine lehman
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What Is Evaporative Cooling in Biology?
This dog is using evaporative cooling. (puppy panting image by Paul Retherford from Fotolia.com)

Cooling adaptations allow animals to withstand a greater range of environmental temperatures than would otherwise be possible. Animals have a number of mechanisms by which they cool themselves in warm climates, including radiation, convection and conduction. Evaporative cooling is another efficient means by which animals can withstand high heat by releasing it into the environment; this process is achieved in a number of ways.

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How Evaporation Works

Evaporation occurs when warm liquid (in the case of an animal, sweat) comes in contact with cooler air. In evaporation, the liquid heats up and generates enough movement of the molecules to cause them to become gaseous. The greater the temperature difference, the higher the rate of evaporation. The rate of evaporation from a cooling object will also increase with increasing surface area and with the rate of airflow over the surface.

How Evaporative Cooling Works

As the liquid forms a gas, the remaining liquid contains less energy (in other words, the molecules are moving more slowly), which means it is cooler. This can cool the skin and, therefore, the blood supply under the skin.

Uses of Evaporative Cooling

By panting, dogs (and other animals such as gazelles and birds) use evaporative cooling to lower their body temperature. Some saliva on the tongue evaporates, while some cools. The saliva comes into contact with blood vessels in the tongue, which effectively cools the blood. This cooler blood then travels and cools vital organs.

Optimisation of Evaporative Cooling

Because the rate of evaporative cooling depends on air flow, panting blows air over the tongue more quickly than just opening the mouth would. By flattening and widening the tongue, there is a greater surface area from which to cool, which increases the evaporative cooling effect of panting.

Other Examples of Evaporative Cooling

A vulture can urinate on itself, thereby increasing the moisture on its legs. The vulture is cooled as the urine evaporates. Birds can flutter their gular (neck) region to bring air quickly in and out of the mouth, which increases evaporative cooling. Animals such as elephants can also increase evaporative cooling by getting their bodies wet.

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