We know that water placed under normal pressure in an environment below zero degrees Celsius will freeze; if we keep stirring a basin of water, it will affect the freezing speed of the water. Whether the water can freeze completely at this time will depend on the strength of the agitation and the ambient temperature.
Under standard atmospheric pressure, the freezing point of water is zero degrees Celsius. If a basin of water is placed in an environment below zero degrees Celsius, the heat energy of the water will gradually disappear, and then a condensation nucleus begins to form inside the water. The water molecules around condensation nucleus gather on the condensation nucleus, causing the condensation nucleus to gradually grow and spread, ultimately resulting in the whole basin of water being "ice".
From the principle of water freezing, we will find that forming condensate nuclei and diffusion in water is the key to water freezing. If pure water is slowly reduced to below 0℃, although the temperature of the entire basin of water is lower than 0℃, because the water does not contain impurities, it makes it difficult to form condensate nuclei, thus obtaining unstable supercooled water. Once there is a slight vibration, condensate nuclei will form, causing supercooled water to instantly condense.
If we put water in an environment of minus 50℃ and stir, the heat energy of the water will disappear quickly, and the condensation nucleus will form in water, but stirring will affect the diffusion speed of the condensation nucleus, thereby affecting the freezing speed of the water. There are two influencing factors at this time;
1. Condensation nucleus continues to grow and spread in water. The lower the ambient temperature, the faster the growth rate of the condensation nucleus will grow in water. The lower the ambient temperature, the faster the growth rate of the condensation nucleus will grow in water. ;
2. Agitation will destroy the growth and diffusion of condensate nucleus. The greater the agitation force (or speed), the more serious the damage to condensate nucleus;
Situation 1: If the growth rate of condensate nucleus is greater than the rate of destruction of condensate nucleus by stirring, then more and more ice in the water will become greater and greater, and the stirring resistance will become completely unable to stir, and the whole basin of water will become "ice ice".
Scenario 2: The destruction rate of the condensation nucleus by stirring is greater than the growth rate, so the condensation nucleus cannot continue to grow. The whole basin of water exists in the form of an ice-water mixture. If the stirring force is strong enough, we cannot even see ice in the macroscopic state.
Someone may have questions. Water is constantly dissipating heat energy into the environment. So what should I do if the temperature is below zero?
The essence of temperature is the thermal movement of microscopic particles (here is water molecules). When we stir liquid water, we need to consume energy because the water itself has a viscous force. When the stirring process overcomes the viscous force to do work, this part of the energy will eventually be converted into the internal energy of water. Therefore, the above two situations can also be understood as:
1: The heat loss power of water is greater than the power of stirring work, and the water temperature continues to decrease, which eventually leads to the whole basin of water freezing.
Scenario 2: The heat loss power of water is less than or equal to the power of stirring work, the water temperature remains unchanged or rises, and the water temperature will not be much lower than the freezing point, and the whole basin will not completely freeze.
For example, in the cold winter, the outdoor temperature is lower than zero degrees Celsius, and the pond without flowing is easy to freeze on the surface, while the strong flowing stream water is "ice-cold", it will not completely freeze.
In fact, the microscopic mechanism of water icing is still an open question in science. Physicist Osterwald proposed the phase change mechanism in 1897.
Water and silicon have a similar coordination mechanism. When silicon crystallizes, it will gradually convert from the liquid state of tetrahedral coordination to the crystal state of tetrahedral coordination. However, water has at least 18 crystal structures . The crystallization process is very complicated. The microscopic details of water crystallization still need to be studied.
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