Wednesday, September 8, 2010

The Seagull’s Leg

seagull leg, bird leg, bird withe, bird ice
A seagull does not freeze even while standing on ice with bare feet. How does this creature conserve its body heat? Part of the secret is in what are called countercurrent heat exchangers.

A countercurrent heat exchanger consists of a tube carrying a warm fluid that runs in close proximity to a tube carrying a cool fluid. If the fluids run in the same direction, only half of the heat is transmitted, at best. But if the fluids run in opposite directions, nearly 100 percent of the heat is transmitted.

seagull leg, bird leg, leg ice
The heat exchangers in a seagull’s legs cool the blood on its way to the feet to near freezing and then rewarm the blood as it returns. Concerning birds in cold environments, ornithologist Gary Ritchison writes: “The principle of countercurrent heat exchange is so effective and ingenious that it has also been adapted in human engineering projects to avoid energy waste.”


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