This is so awesome. A group of scientists at the Fraunhofer Institute have created the ideal coffee mug. The mug receives your hot coffee, cools it to the “perfect” drinking temperature and then keeps it at that constant temperature while you sip the coffee. And does it all using passive heat transfer. (No plugs!)
“The key for this magic trick is physics and PCM—phase change material—an extraordinary substance used in construction and winter clothing. PCM is capable of storing and releasing heat or cold.
In its original state it is a solid. Then, when it receives heat, it absorbs it like a sponge liquifying into a gooey wax. As the PCM solidifies it releases the energy at a steady pace, keeping any liquid or room at the perfect temperature. In houses, they achieve this by filling hollow walls with PCM, which absorbs heat from the sun, and then releases it as the atmosphere cools down, keeping the room at a perfect temperature.”
Read the full article here.
See, the cool thing is that as a substance goes through a phase transition, the temperature of the substance stays exactly constant. The temperature of boiling water on the stove (at sea-level) is pretty much a constant 212 F – no matter how high the heat is on the stove. More heat just makes the water boil faster (which speeds up the phase transition from liquid to gas) but it doesn’t raise the temperature of the system. Same thing with ice and water in a glass. After a while, the ice water maintains at 32 F – until the ice is melted. Adding more ice doesn’t make the water colder than 32 F.
So this cool mug owes its magic to figuring out what the perfect temp is for coffee and then fine tuning the PCM insulation to go through a phase transition (solid-liquid) at that perfect temp. As you pour the hot coffee into the mug, the excess heat in the coffee causes the insulation to melt – which effectively stores heat energy in the increased entropy of the liquid. As the coffee cools, the entropy in the disordered liquid is extracted by the cooling coffee as the insulation goes back to a more ordered, solid state. That heat is transferred back to the coffee, keeping it at a constant temp.
I’m SO getting one of these.