The Super-Heater 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 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 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
5-15 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.
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