Have you ever heard of the assertion that ” hot water freezes faster than cold water “? Although it may sound strange, scientists have observed this phenomenon defying the laws of thermodynamics on several occasions. Moreover, this strange phenomenon bears the name of ” Mpemba effect “.
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What is the Mpemba effect?
The Mpemba effect is the phenomenon that causes hot water to freeze faster than cold water under the same cooling conditions. The name of this effect was given by a Tanzanian student who reported the existence of this phenomenon in the 1960s.
Although this effect is recognized, scientists are struggling to lay down the experimental conditions that make it possible to trigger this phenomenon, which complicates its study and creates many theories around it.
Mpemba effect: hot water thrown into the cold air
Several theories are put forward to explain the Mbempa effect
There is no shortage of hypotheses to explain the Mbempa effect. Some argue that it is the evaporation that hot water undergoes that is the cause of its rapid reduction compared to cold water. So, the Mbempa effect would have something to do with evaporation? Researchers have examined this trail.
Note that the Mbempa effect indeed allows the water to remain liquid below 0 ° C. Hot water is less sensitive to it and that could explain why it seems to freeze faster than cold water.
Another researcher, who won a competition organized by the Royal Society of Chemistry in 2012, explained the Mpemba effect by the convection effect. The latter designates the transfer of thermal energy within a moving fluid or between a moving fluid and a solid wall.
It would suffice to place a container of hot water in a cold environment to observe movements that will transport heat by convection and allow the water to cool more quickly. However, it would be enough just to stir the water regularly during the cooling to cancel the Mpemba effect.
In any case, the Mpemba effect is not yet unanimous in the scientific community. Some even think that this effect does not exist. Case to be continued …