Why hot water freezes faster than cold water

From the physical aspect, there are four mechanisms of coexistence of cooling: radiation, conduction, vaporization, and convection, through experimental observation, the results are compared, and it is found that the reason for the freezing of hot water before cold water is mainly the comprehensive result of the interaction of conduction, vaporization and convection. The heat inside the liquid is difficult to rely on conduction to effectively transfer to the surface, the water in the cup due to the temperature drop, volume expansion, density becomes smaller, and gathers on the surface, so it freezes first at the surface of the water, followed by the bottom and around, forming a closed "ice shell", at this time, the water in the inner layer is isolated from the air, and can only rely on conduction and radiation to dissipate heat, so the cooling rate is very small, preventing the normal progress of the inner layer water temperature from continuing to drop, and because the volume of water freezes to expand, the "ice shell" plays a role in inhibition.

The cup with 100 cups of hot water takes much less time to freeze, and the phenomenon is that the ice on the surface is not connected to form an ice sheet, and the phenomenon of "ice shell" is not visible, and needle-like ice crystals grow into the liquid along the interface of the ice water (this phenomenon is not visible when the initial temperature is below 12). With the passage of time, the ice crystals change from fine to coarse, this is because the hot water with high initial temperature, the density of the upper water becomes larger after cooling, and the downward flow is formed, forming a convection flow inside the liquid, so that the water molecules form ice around their respective crystal centers, the higher the initial temperature, the more intense this convection, and the greater the loss of energy. It is this convection that makes the water in the upper layer not easy to form an ice sheet, due to the heat transfer and the latent heat of phase change, the internal energy loss per unit time is larger, the cooling rate is larger, when the water surface temperature drops below 0 and there is enough low temperature, ice crystals begin to appear on the water surface.

Water with higher initial temperature has a greater growth rate of ice crystals, which is due to the fact that the ice sheet is not formed and the convection is violent, and finally we observe that the ice sheet is still formed, and the cooling rate becomes smaller, but because the ice crystals in the water have grown and are coarse, with a large surface energy, the growth rate of ice crystals is proportional to the unit surface energy, so the growth rate is still much faster than that of water with low initial temperature.

From the perspective of biological action, in order for water to form ice, many crystallization centers are needed in water, and biological experiments have found that microorganisms in water are often "crystallization centers". And some microorganisms in hot water (water temperature below 100 a little) multiply faster than cold water, in this way, the "crystal center" in the hot water is much more than in the cold water, accelerating the synergistic effect of hot water freezing, around the "crystal center" to grow out of the daughter crystal, the daughter crystal is the crystal nucleus of epitaxial crystal, convection makes the molecules of various orientations flow through the daughter crystal, relying on the molecular force on the surface of the crystal, grasp the water molecules with suitable orientation, and extend the molecules to make many grains arranged in an orderly manner, suspended in the water, The energy released by the crystallization is released through the reflux, and the adjacent ice particles are linked together to freeze until the water freezes completely.

Hot water and cold water are not only changing their temperature under the same quality and quantity and external ambient temperature, but also their respective density, volume, mass and air pressure under the sealed state are changing, so that the cooling rate of water with high initial temperature is always faster than that of water with low initial temperature, as long as the external ambient temperature continues to drop, the water temperature with high initial temperature will eventually be lower.

Hot water is hot, but why freeze faster than cold water.

The reason why hot water freezes before cold water is mainly the combined result of the interaction of conduction, vaporization and convection.

From the perspective of biological action, in order for water to form ice, many crystallization centers are needed in water, and biological experiments have found that microorganisms in water are often "crystallization centers".

And some microorganisms in hot water (water temperature below 100 a little) multiply faster than cold water, in this way, the "crystal center" in the hot water is much more than in the cold water, accelerating the synergistic effect of hot water freezing, around the "crystal center" to grow out of the daughter crystal, the daughter crystal is the crystal nucleus of epitaxial crystal, convection makes the molecules of various orientations flow through the daughter crystal, relying on the molecular force on the surface of the crystal, grasp the water molecules with suitable orientation, and extend the molecules to make many grains arranged in an orderly manner, suspended in the water, The energy released by the crystallization is released through the reflux, and the adjacent ice particles are linked together to freeze until the water freezes completely.

This phenomenon is known as the Mupainmubar effect, also known as the Mpemba effect, which refers to the phenomenon that a slightly warmer liquid freezes before a slightly cooler liquid with the same volume, the same mass and the same cooling.

1. Evaporation. During the process of cooling the hot water to the initial temperature of the cold water, the hot water loses some of its water due to evaporation. Less mass makes water easier to cool and freeze. In this way, the hot water may freeze earlier than the cold water.

2. Dissolved gases. Hot water retains fewer dissolved gases than cold water, and as it boils, a large amount of gas escapes from the water. Dissolved gases can change the properties of water.

Either make it easier to form convection (and therefore cooler), or reduce the amount of heat required to freeze per unit mass of water, or change the boiling point.

3, to He Sun Liu. As a result of cooling, water can form convection currents, and uneven temperature distribution. As the temperature rises, the density of the water decreases, so the surface of the water is hotter than the bottom of the water"Hot top"。

If the water loses heat mainly through the surface, then,"Hot top"The water loses heat faster than the temperature is uniform.

4. Things around you. The last difference between the two glasses of water has nothing to do with themselves, but with the environment around which they are buried. Water with a higher initial temperature may change its surroundings in complex ways, thus affecting the cooling process.

Hot water and cold water are not only changing their temperature under the same quality and quantity and external ambient temperature, but also their respective density, volume, mass and air pressure under the sealed state are changing, so that the cooling rate of water with high initial temperature is always faster than that of water with low initial temperature, as long as the external ambient temperature continues to drop, the water temperature with high initial temperature will eventually be lower.

Hot water is hot, but why freeze faster than cold water.

Hot water is hot, but why freeze faster than cold water.

Hot water and cold water are not only changing their temperature under the same quality and quantity and external ambient temperature, but also their respective density, volume, mass and air pressure under the sealed state are changing, so that the cooling rate of water with high initial temperature is always faster than that of water with low initial temperature, as long as the external ambient temperature continues to drop, the water temperature with high initial temperature will eventually be lower.