Amazing Heat Pack
June 25th, 2008 by free2share
Last Saturday I was in Genting for a concert (The Osmonds 50th Annivesary Tour…and their absolute last show together!) and my back was hurting badly. I found a stall there selling heat packs which I think is amazing and would like to share with you.
It is a clear liquid-gel (sorry…for the oxymoron) in a clear thick plastic bag, about 6″ x 4″. Inside the liquid-gel is a small thin metallic piece, about a 10-sen size. By merely pressing firmly on the metallic piece for a brief moment, the clear liquid-gel starts solidifying into a white solid, and gives off heat at about 50-60 deg C. I placed the heat-pack on my lower back throughout the concert, and it was great…relieved my back-ache somewhat. I found that the heat was released for about an hour.
As if that is not amazing enough, the heat-pack is re-usable! Just immerse the solidified pack into boiling water for about 5-10 minutes and presto! the clear liquid gel is back and you can then cool down the pack to store until you need to use again the next time. Very convenient…for only RM37 each.
I think the liquid-gel (I have to use this oxymoron as it aptly describes the substance) will change to solid if the molecules are agitated (by pressing the metallic piece) and thereby gives off heat; the reverse of freezing. Anyone knows what it is? The box does not tell its composition.
Update:
OK, I googled on “heat pack” and found the answer…
http://www.howstuffworks.com/question290.htm
It turns out that the stuff is sodium acetate + water.
“… heat pack like the one you are describing contains sodium acetate and water. It turns out that sodium acetate is very good at supercooling. It “freezes” at 130 degrees F (54 degrees C), but it is happy to exist as a liquid at a much lower temperature and is extremely stable. Clicking the disk, however, has the ability to force a few molecules to flip to the solid state, and the rest of the liquid then rushes to solidify as well. The temperature of the solidifying liquid jumps up to 130 degrees F in the process.
When you boil the solid, you melt it back to the liquid state. You have to completely melt every crystal, by the way, or the liquid will quickly re-solidify. You can repeat this cycle forever, theoretically, just as you can freeze and melt water as many times as you like. The plastic pouch eventually wears out and leaks, though (since sodium acetate is a food additive, it is non-toxic).”
Read the interesting full article at http://www.howstuffworks.com/question290.htm