Types of hand warmers, principles of hand warmers

Hand warmers are a common heating product. Because they are developed using physical and chemical principles, they are a health care product that helps the human body keep warm. The hand warmer generates heat automatically and is fun to use. It is practical and has novel and unique styles. Therefore, such products are very popular among people. In order to help us correctly understand and use hand warmers, let's learn about the relevant knowledge about hand warmers.

There are three main types of hand warmers that are commonly seen :

One that uses hot water to generate heat, which is what we usually call a hot water bag. Unlike some practical traditional hot water bags, electric hot water bags save the trouble of adding water. Just plug in the power and wait for a while to generate heat. In fact, it boils the water inside, so the temperature is generally very high.

One type generates heat through chemical reactions. The hot packs on the market are of this type. The heat generated by the contact of the chemical substances inside is about 40°C. The other is to use the lithium battery function, with an internal heating plate to generate heat and a USB connector for charging and discharging, similar to a hand warming mouse pad. Due to the charge and discharge function of the lithium battery, it can generally also be used as a mobile power source. It is small in size and easy to carry around, and the temperature can reach around 50°C.

To understand the principle of hand warmer, we must first know what a supersaturated solution is. At a certain temperature, the solubility of a solute in a solvent remains unchanged. For example, the solubility of table salt (sodium chloride) in water is 36 g/100 mL of water at room temperature. When the concentration of a solution is equal to its solubility, the solution is called a saturated solution; when the solubility of a solution is higher than its solubility, the solution is called a supersaturated solution. The liquid in the hand warmer is a supersaturated solution of sodium acetate (CH3COONa).

Since the concentration of a supersaturated solution is too high, it is not stable. When the metal is twisted, the slight vibrations are enough to cause the solute to crystallize into a more stable solid. However, this process is exothermic, so the hand warmer starts to warm up.

The above introduction to the knowledge of hand warmers makes us clear about the working principles of hand warmers, and at this time we must understand one thing, that is, when using hand warmers, we must know how to use them. Only by using hand warmers correctly will they not cause harm to the human body. We have to understand this.