How do sodium-acetate heat pads work?
How do sodium-acetate heat pads work? These heat pads are extremely cool to watch. If you would like to see the process and have the time, you can download this 1.2-megabyte MPEG file and see it happen. Bending the metal disk starts the crystallization process, and you can see the crystallization proceed through the liquid. What is happening here is strange, but the process can be understood if you think about water freezing. Water freezes at 32 degrees Fahrenheit (0 degrees C). If you were to stick a thermometer in a cup of water and put the cup in the freezer, you would find that the temperature of the water falls to 32 degrees F and then hangs there until all of the water is completely frozen. Then the temperature of the solid water falls to the temperature of the freezer. What if you could somehow supercool the water? That is, say that you could get the water’s temperature to 10 degrees below the fr
