The big talk around the museum lately has been the weather for obvious reasons! Being cold got me thinking about the physics of heat loss, so for this month’s BWOM post I thought I would talk about evaporative cooling. When water changes from one state to another energy is either released or absorbed; as water moves from solid -> liquid ->gas energy input is required at each transition.
You might think of evaporative cooling as an issue for the summer time. Our sweat glands release moisture onto our skin’s surface, which then evaporates and takes away heat energy. This process can be life saving in the summer but threatens our survival in the winter. Even though we don’t feel like we are sweating, our skin is still releasing some water. Any exposed skin is chilled not only by the cold air but also by the evaporation of water. We also lose heat as we breathe cold air in and out of our lungs. The moist linings of our respiratory tract are an effective evaporative cooling mechanism just like our skin.
Of course, if you get really wet then you might be in big trouble. Heat from your body will be sucked away as the water evaporates from your clothing and you could quickly enter hypothermia. As our body temperature drops, our brain acts to save itself and shuts down blood flow to our extremities. As our fingertips, toes, ears, and nose lose blood flow they can become so cold that we experience frostbite.
Stay dry and warm out there and enjoy the winter weather as much as possible!