In winter, mineral water freezes instantly. What is the principle?

In winter, I put a bottle of mineral water in the car. I left it overnight, but it didn't freeze the next morning, but I picked up the bottle with my hand and shook it gently, and the water in it froze instantly! In fact, this kind of water is called "supercooled water" because the water quality is too pure, lacking the condensation nuclei needed for freezing, or for other reasons, resulting in water still not freezing below zero.

The state of supercooled water is very unstable. A slight disturbance will freeze instantly. This unstable state is called metastable state. If a small amount of solid matter is put in at this time, or shaken gently, or the ambient temperature is raised, the water will crystallize and solidify immediately. The purer the water quality, the more obvious the supercooling phenomenon. If it is pure water, it will not freeze at MINUS 40℃.

There was once an animated film "Haier Brothers", in which there was a clip about supercooled water. The two brothers met a pond that was not frozen below 0℃. My brother threw a stone into the water, and the whole pond soon froze! Of course, this is only a theoretical situation, which can't happen in reality, because the water quality of the pond is not so good, and there will definitely be all kinds of impurities and plankton in it, which can be used as condensation nuclei, and there will be no supercooling phenomenon.

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There are many water droplets in the cloud that will not freeze when the temperature is below 0℃. This kind of water drop is called supercooled water drop. Supercooled water droplets are unstable. As long as they are shaken a little, they will freeze into ice particles at once.

When supercooled water droplets collide with graupel particles, they will freeze immediately, which is called collision freezing. When the collision occurs, the outside of the supercooled water droplets immediately freezes into an ice shell, but the inside of the supercooled water droplets temporarily remains liquid. Because the latent heat released by the external freezing is transferred to the inside, the temperature of the liquid supercooled water inside is higher than that of the external ice shell. The temperature difference makes the frozen supercooled water droplets positively charged outside and negatively charged inside.

When the inside also freezes, the cloud drops expand and split, and the outer skin breaks into many small positively charged ice chips, which fly to the upper part of the cloud with the airflow. The core of the negatively charged frozen drops adheres to the heavier graupel particles, so that the graupel particles are negatively charged and stay in the middle and lower part of the cloud.

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