How Refrigerators Work

Cold Packs

Speaking of refrigeration and coldness, have you ever used one of those "instant cold packs" that looks like a plastic bag filled with liquid. You hit it, shake it up and it gets extremely cold. What's going on here?

The liquid inside the cold pack is water. In the water is another plastic bag or tube containing ammonium-nitrate fertilizer. When you hit the cold pack, it breaks the tube so that the water mixes with the fertilizer. This mixture creates an endothermic reaction -- it absorbs heat. The temperature of the solution falls to about 35 F for 10 to 15 minutes.


For more information on refrigeration and related topics, check out the links below.

Related Articles
More Great Links
  • Casiday, Rachel and Regina Frey. "Phase Changes and Refrigeration: Thermochemistry of Heat Engines." Washington University. 1/2007. (6/13/11).
  • Castleden, Rodney. "Inventions that Changed the World." Chartwell Books, Inc. 2007
  • "Fundamentals of Refrigeration: Common Refrigerants." (6/14/11).
  • Half a Handy. "How Your Refrigerator Works." 1/31/09.
  • Repair Clinic. "Refrigerator - How Things Work." (6/14/11).
  • Time Magazine, "Great Inventions - Geniuses and Gizmos: Innovations in Our Time." Time Books: New York. 2003. (6/14/11)
  • Woodford, Chris, Luke Collins, Clint Witchalls, Ben Morgan and James Flint. "Cool Stuff and How it Works. Korling Kindersley Limited. 2005.
  • Woodford, Chris. "Refrigerators." Explain that Stuff. 5/18/11. (6/14/11).