Heat Packs - How They Work
How it works: The SnapHeat Heat Pack contains sodium acetate, a form of salt, which under normal conditions in an open container will change from a liquid to a solid (freeze) at 130ºF (54ºC). By placing this solution in a sealed container, the solution can be cooled well below this temperature (as low as 14ºF) (-10ºC). Flexing the patented stainless steel "trigger" within the sealed container causes a single molecule of liquid to crystallize which starts a chain reaction causing the entire solution to change from a liquid to a solid. This phase change causes the pack to heat to approximately 130ºF.
To understand super-cooling, imagine a glass of water at 32ºF. It should turn into ice. This phase change, from one state (liquid) to another, (solid or crystals) occurs with a change in temperature. If the water dropped below 31ºF and no phase changed occurred, the water would be considered a super-cooled liquid.
When the SnapHeat Heat Pack is triggered, the solution is "taught" how to crystallize, and the temperature immediately jumps back to its "freezing" point. Much in the same way the water crystals produce "heat" at 31ºF, the heat pack produces an even heat flow with the crystals it produces at higher temperatures.
It is the physical restriction of various crystals that allows for such strict temperature tolerances that in effect controls the maximum heat produced. What this simply means is that once the system is manufactured, the temperature limits are built in and can not be exceeded, and this limit is not effected by most ambient temperature.
This super-cooled solution has been stored for extended periods of time and has still crystallized on demand. This capacity to be stored at low temperatures also allows the product to be useful as a cold weather product.
The SnapHeat Heat Pack is unique because it is the first time super-cooled fluids have been made stable and predictable.
By being able to control super-cooled fluids, the system can produce heat for two to three hours (or longer) depending on the size of the bag and the insulation used. Duration of time and temperature of the packs can be varied to meet many application demands.
Once the unit has given off all of its heat, it is then recycled by heating it up. The easiest method is by boiling in water for six to thirty minutes, depending on the product size. The product is heated, melting the crystals back to a liquid state and then is allowed to cool below its freezing temperature. It is then ready to be activated again.