Why I love my wetsuit, or living in the second law of thermodynamics
By Su Wild-River
Snorkeling in an Australian South Coast Autumn can be a chilly business. But last weekend wasn’t so bad. Our best estimate for the water temperature was 18ºC, and so Tim, who has better underwater staying power than the rest of us, decided not to wear his wetsuit. Armed with my thermal imaging camera, I decided to see what difference a wetsuit makes.
A thermal imaging camera is really a heat sensor, not a camera which shows what you see with your eyes. In these photos, the hottest areas are shown in white, and a rainbow spectrum going through red, to yellow, green and finally blue, show colder areas. The photos are calibrated so that the same colour has the same temperature in each of the pictures.
First, I photographed Kath and Tim before they went into the water. Tim is on the left, without a wetsuit, and Kath on the right in her full body suit, or ‘steamer’. Bare skin is showing up hottest in these photos, and you can see it on both faces, hands and feet, but only on Tim’s arms and torso. The highest temperatures here are reading 31ºC. (You can’t see to the top of the scale in this picture because I have calibrated it lower, for consistency with the cold pictures below).
Next, we all went snorkeling, and saw the most wonderful fish, sting-rays, crays and an octopus. After shivering for a while, we got out. The next photo shows Tim and Kath after they got out. Now they both look the same colour as one another all over, and are now thermally camouflaged with the ambient temperature of 16-18ºC.
But hang on, did the wetsuit keep Kath warm or not? In fact, Kath is showing up as cool as Tim because all of her heat is trapped underneath the wetsuit. But she was too cold to take it off and pose again. I had to do it myself.
I had been wearing a ‘spring suit’, which ends above the knees. Here’s the photo of my legs with the wetsuit on. Like Kath, the colours are similar to background, and the same both above and below my knees, ie, with and without the wetsuit.
But now the wetsuit comes off and suddenly you see some warm skin. Underneath my wetsuit, my skin maintained about 22ºC, which is closer to my healthy body temperature of about 36.5-37.5ºC.
What’s going on here?
Our bodies our demonstrating the second law of thermodynamics, which covers the conservation of energy. This states that heat (and other energy) moves from hot areas to cold areas. Our bare skin was uselessly transferring the heat within our bodies into the ocean, and in the process it was making us all cold. But the parts of us under the wetsuits weren’t transferring nearly as much heat, and so they stayed warmer. The outside of our wetsuits, and all of our skin that touched the water, ended up as cold as the ocean but the rest of us stayed a bit warmer. Our subcutaneous fat and skin were also insulating us against the elements, slowing the transfer of heat to the world and making our skin cooler than our blood, even before we went in the water.
How cold were we? Not cold enough for a brain freeze. But all of our toes and fingers were pretty chilly.
It took over an hour for my feet to warm back up.
Adventures are great. But one of the pleasures is getting comfortable afterwards.
When we got back in the car, my fingers absolutely loved the heater vent.
How do you experience the second law?