he Sodium Acetate Heat Packs contain a saturated solution of Sodium Acetate and one small stainless steel concave discs.
It is possible to "super cool" water and keep it in its liquid form well below its freezing temperature, but this is difficult as the water must be totally pure (distilled) and the container must be completely smooth to ensure that there are no blemishes to give the first ice crystal an opportunity to form. Even then it is very hard to achieve as even the slightest tremor will set the freezing process in motion (like the vibration of the compressor in a domestic refrigerator).
Regardless of how cold we managed to get our container of water when it freezes it will return to 32 degrees Fahrenheit until completely frozen. This sudden gain in temperature results in it heating its immediate environment by shedding the unwanted energy in the form of heat.Sodium acetate freezes at 130 degrees Fahrenheit (54 degrees Celsius).
Sodium acetate forms a very stable liquid making it easy to cool it way below its freezing point while remaining in its liquid form. In its liquid form it can tolerate very low relative temperatures before it freezes spontaneously and is also reasonably immune to movement, which is why it is the ideal substance for use in reusable heat packs. Sodium acetate reusable heat packs can safely be stored in liquid form at room temperature for prolonged periods.
Clicking the small stainless steel disc in the heat pack causes one or more crystals to form in its immediate proximity, which is then followed rapidly by all of the contents of the heat pack crystallizing. The heat pack's temperature will immediately rise to 130 degrees F (approximately the temperature produced by domestic hot water systems) and will remain at 130 degrees F until the entire contents of the sodium acetate heat pack has crystallized. Depending on the size of the heat pack and the insulation of the reusable heat pack it will then gradually lose warmth until it reaches the ambient temperature.
Bend the metal disc in the liquid a few times to activate heating if the product is liquid state,or else read the following step.The second time you use it,Please put the solid hot pack into the boiling water staying for 5-10 minutes. It will turn to liquid again. Different sizes/weights may take different time, please control the time.