Flameless ration heater

A flameless ration heater, or FRH, is a water-activated exothermic chemical heater included with Meals, Ready-to-Eat (MREs), used to heat the food. US military specifications for the heater require that it be capable of raising the temperature of an eight-ounce entree by 100° F in twelve minutes, and that it display no visible flame.

Chemical reaction

Here is the balanced chemical reaction:

Mg + 2H₂O ----> Mg(OH)₂ + H₂ + Heat

The exothermic chemical reaction works by the process of oxidation-reduction, which is similar to the process of rusting metals. When iron metal rusts, it is oxidized by the oxygen present in the air. In the case of the flameless ration heater, the metal used is magnesium. Magnesium is chosen because it is readily oxidized, which is due to its having only two electrons in its valence shell. The magnesium metal is mixed together with a small amount of iron in a pouch. To activate the reaction, a small amount of water is added, and the boiling point of water is quickly reached as the reaction proceeds. The role of iron in the heater is most likely as a catalyst, since it is used in a small amount. In this case, the iron is initially oxidized, and then reduced back to its elemental form as the magnesium is oxidized and sends its two valence electrons to iron.

Confined space hazard

The release of hydrogen gas from these flameless ration heaters is of a sufficient quantity to pose a potential hazard on board a passenger aircraft.

Notes

References

• HowStuffWorks article on MREs

See also

• Self-heating can

External links

• Flameless stoves from zenstoves.net - details chemical reaction