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In this case, no chemical reaction occurs, instead the heat of solution is generated. Commercial heat sources for self-heating food packaging use an exothermic (heat releasing) reaction, for which there are several common formulations. These include: Quicklime aka calcium oxide, and water.
A warm compress is a method of applying heat to the body. [1] Heating sources can include warm water, microwaveable pads, wheat packs and electrical or chemical pads. Some unorthodox methods can include warmed potatoes, uncooked rice, and hard-boiled eggs. The most common warm compress is a warm, wet washcloth. [2]
The hand and foot warmer was first patented by Jonathan T. Ellis of New Jersey in 1891, [1] though no evidence exists that it was ever produced. [2]The first commercially produced hand warmer was created by Japanese inventor Niichi Matoba.
To heat a meal, the bag is first torn open, and a sealed food pouch is placed inside. About 1 US fluid ounce (30 mL) of water is then added to the bag, using the line printed on the bag as a marker. The chemical reaction begins immediately, and takes about 12 to 15 minutes to heat a food pouch to about 60 °C (140 °F).
Unlike some types of heat packs, such as those dependent upon irreversible chemical reactions, a sodium acetate heat pack can be easily reused by immersing the pack in boiling water for a few minutes, until the crystals are completely dissolved, and allowing the pack to slowly cool to room temperature. [15]
The pack is put inside a hot furnace for a variable length of time. Time and temperature determines how deep into the surface the hardening extends. However, the depth of hardening is ultimately limited by the inability of carbon to diffuse deeply into solid steel, and a typical depth of surface hardening with this method is up to 1.5 mm.
Heating packs can also be made by filling a container with a material that has a high specific heat capacity, which then gradually releases the heat over time. A hot water bottle is the most familiar example of this type of heating pad. A microwavable heating pad is a heating pad that is warmed by placing it in a microwave oven before use.
There are numerous methods used to sterilize the containers, the most commonly used methods include: heat, hot water, chemical sterilants (hydrogen peroxide or peracetic acid), and radiation or a combination of methods. [7] [8] UHT food products can be sterilized using either direct or indirect methods of heat transfer.