Self-Heating Cans

Self-Heating Cans Self heating cans actually started around 1900 for the use by mountaineers and explorers. During World War II (1939-1945), some food cans had wicks on them, like candles have. The wicks were attached to an inside tube. When soldiers lit the wick, the tube heated the food. It relied on the burning of cordite (a smokeless propellant consisting of 65% gun cotton, 30% nitroglycerin and 5% mineral jelly) to provide thermal energy, a design that could hardly be considered safe in untrained hand. 

Newer self heating cans are easier to use. Just push a button. The button breaks a seal inside a heating cone. 

Water and limestone combine in the cone, releasing heat. Three minutes later your food or drink is hot. 

The recent designs have all relied on an exothermic chemical reaction to generate heat; in most cases; the reaction is between CaO (quicklylime) a water based solution, although armed forces tend to use the more expensive MgO because it heats more quickly. 

Giant company, Nestle launched self heating Nescafe Instant in 2001. However, they terminated the project due to the temperature increase is not sufficient in cold weather. The optimum temperature for storing is room temperature (approximately 20 degree C) which results in a final temperature of the coffee, once the can is activated of around 60 degree C. 

Self heating cans have been commercially available for decades and are particularly popular in Japan for sake, coffee, tea and ready meals. Several self-heating cans have been developed, which all use the same basic heating mechanism but in more convenient and efficient form. One is a three pieces, welded, retortable, steel container coated in both side with PET and with a conventional ring–pull top. The can has an internal volume of 330 mL, but to make room for the heat-generating chamber the can holds just 210 mL. 

In 2001, Ontro Inc. was making self-heating systems using the heat generated by the reaction of calcium oxide with water to heat coffee, tea, soup and hot chocolate. Before calcium oxide and water are mixed, they are separated in adjacent chambers within the can. Consumers are required to invert the can to rigger the puck that breaks the internal aluminum foil seal to release the water. The external polypropylene layer can resists boiling water temperature and can maintain the elevated temperature for about 20 minutes. Self-Heating Cans