1963 Mpamba, a Tanzanian middle school student, found that hot milk often freezes before cold milk when making ice cream. 1969, he and Dr. Denis G. Osborne)*** wrote a paper on this phenomenon, so the phenomenon was named after it.

The cooling rate of liquid is not determined by the average temperature of liquid, but by the temperature gradient of liquid. When hot liquid is cooled, the gradient is large. In the cooling process before freezing, the temperature difference of hot liquid is always greater than that of cold liquid. This is because the higher the temperature of the upper surface, the more heat the upper surface emits and the faster the temperature decreases.

The explanation behind the Mpumba effect.

Water Vapor Evaporation Theory: Some scholars believe that the higher the temperature of hot water, the faster the water evaporates, which is the primary reason for the Mbamba effect, because evaporation reduces the number of water molecules and correspondingly reduces the number of water molecules to be frozen, thus accelerating the freezing speed of hot water. However, some scientists measured the quality of water before and after freezing and found that the quality difference never exceeded 3%. Although the evaporated water is reduced, 3% water molecules can not significantly affect the time required for water to freeze.

At the same time, the heat consumed in the process of steam evaporation can not be ignored. Unfortunately, the control test of heat consumption is not easy to achieve, because it needs to measure open containers and closed containers, but in a closed environment, water vapor evaporation and heat conduction will be hindered, and it is impossible to measure the influence of a single variable.

People's Daily Online-Scientists are puzzled about who freezes first, hot water or cold water.