Decipher the mysterious hot water faster than cold water?

Photo: physicalgeography An American scientist discovered the mechanism of the Mpemba effect - known after a Tanzanian student named Erasto Mpemba found that the sugar milk he used to make the ice cream would freeze faster if he gave it. Its head is hot milk.

According to him, the so-called "Mpemba effect" is only a common phenomenon, occurring with all solutes.

Jonathan Katz, of the University of Washington, who studied the Mpemba effect in detail, said these solvents are calcium and magnesium bicarbonate - two components that make most drinking water "hard water" - and when water is heated hot, these ingredients will precipitate to form a solid deposit in warm.

Katz said that if water has never been heated, it still contains these solutes, and when it freezes, ice crystals form, causing the solute concentration in the remaining water to become much higher - up to 50 times compared to normal - therefore, lowered the freezing point of water. In other words, water will freeze at lower temperatures.

According to Katz, a second effect also hampers the freezing of water that has never been heated. Lowering the freezing point reduced the temperature difference between the liquid and the frozen parts around it. " Because the heat loss rate of water depends on this temperature difference, the water that has not been heated will lose heat much harder, and therefore will slow down ."

Katz said the combination of the two effects could be a complete explanation for the phenomenon of heated water solidifying faster than water that has not passed fire. Katz is waiting for someone willing to do experiments to verify her hypothesis.

T. An