Principle of the Mpemba effect: Under the same mass and the same cooling environment, the molecules of a liquid with a slightly higher temperature that are in direct contact with the cooling environment will drop faster than those with a slightly lower temperature.

If the cooling environment can always maintain a consistent (temperature constant) cooling capacity, the liquid with a high temperature will first drop to the cooling environment temperature. If the temperature is lower than the freezing point of the liquid, the high-temperature liquid will freeze first. .

The speed of liquid cooling is not determined by the average temperature of the liquid, but by the liquid temperature gradient. When the hot liquid cools, the gradient is larger, and during the cooling process before freezing, the heat The temperature difference of cold liquids is always greater than the temperature difference of cold liquids. This is because the higher the temperature of the upper surface, the more heat is dissipated from the upper surface, so the temperature drops faster.

Extended information:

Experimental verification

In 2012, the Royal Society of Chemistry held a competition to explain the Mpemba phenomenon. More than 22,000 people took part, and in the end Erasto Mpemba himself announced Nikola Bregovivic as the winner.

Bregovi? proposed two reasons for this effect - colder samples supercool rather than freeze, and enhanced convection in warmer samples accelerates cooling by maintaining a thermal gradient across the container walls. .

Reference: Baidu Encyclopedia-Mpemba Phenomenon