A common chemical process may explain how hot water can freeze more quickly than cold, a report on the web site of New Scientist said on Thursday.
A scientist of the University of Washington at St Louis found that what is behind the so-called "Mpemba effect is that the phenomenon is all to do with solutes," the report said.
The Mpemba effect came to be known after a Tanzanian school student named Erasto Mpemba noticed that the sugared milk he used to make ice cream froze more quickly if it started out hot.
Jonathan Katz, of the University of Washington, who worked out the details of the Mpemba effect, said the solutes are calcium and magnesium bicarbonate, which make most drinking water "hard" and when the water is heated, these elements precipitate to form the solid scale that "furs" up the inside of a kettle.
Katz said water that has never been heated still contains these solutes and as it freezes, ice crystals form, and the concentration of solutes in the remaining water becomes ever higher - up to 50 times as high as normal, thus lowering the freezing point of the water.
According to Katz, there is a second, related effect that hampers the freezing of water that has never been heated. The lowering of the freezing point reduces the temperature difference between the liquid and its freezing surroundings. "Since the rate at which heat is lost from the water depends on this temperature difference, water that has not been heated has greater difficulty losing heat," Katz was quoted as saying.
Katz said the two effects combined could perfectly explain why water that has been heated freezes more quickly than water that has not.
Katz is waiting for someone to do experiments to test his theory, New Scientist said.
中文翻譯：
一個普通的化學(xué)操作將揭示為什么熱水能比冷水更為迅速地結(jié)冰，星期四，一項來自新科學(xué)家的網(wǎng)站的報告稱。
該報道稱，一位來自位于圣路易斯的華盛頓大學(xué)的科學(xué)家，發(fā)現(xiàn)了隱藏在所謂的姆潘巴現(xiàn)象的實質(zhì)，姆潘巴現(xiàn)象就是該現(xiàn)象的產(chǎn)生和溶質(zhì)有關(guān)。
來自華盛頓大學(xué)的Jonathan Katz，發(fā)現(xiàn)了姆潘巴現(xiàn)象的細節(jié)。他說，溶質(zhì)是鈣和鎂的重碳酸鹽，這些物質(zhì)使很多飲用水變得很“硬”，當(dāng)水被加熱后，這些物質(zhì)沉淀生成了固體物質(zhì)，并在水壺內(nèi)壁形成水垢。
Katz表示，沒有被加熱過的水仍然含有這些溶質(zhì)，當(dāng)它被冷凍，冰晶形成的時候，這些仍保存在水中的溶質(zhì)濃度變得更高了，大概高出正常的50倍，這樣就降低了水的冰點。
據(jù)Katz稱，還有另外一個原因阻止未被加熱的水結(jié)冰。低冰點縮小了固體和其結(jié)冰環(huán)境下的氣溫差異?！耙驗闊崃繌乃辛魇У乃俣热Q于溫差。沒有被加熱過的水更難流失熱量?！?BR> Katz說這兩個原因結(jié)合在一起就可以很好地揭示為什么熱水比冷水更容易結(jié)冰了。
Katz正等待有人能通過實驗來證實他的理論。新科學(xué)家稱。
A scientist of the University of Washington at St Louis found that what is behind the so-called "Mpemba effect is that the phenomenon is all to do with solutes," the report said.
The Mpemba effect came to be known after a Tanzanian school student named Erasto Mpemba noticed that the sugared milk he used to make ice cream froze more quickly if it started out hot.
Jonathan Katz, of the University of Washington, who worked out the details of the Mpemba effect, said the solutes are calcium and magnesium bicarbonate, which make most drinking water "hard" and when the water is heated, these elements precipitate to form the solid scale that "furs" up the inside of a kettle.
Katz said water that has never been heated still contains these solutes and as it freezes, ice crystals form, and the concentration of solutes in the remaining water becomes ever higher - up to 50 times as high as normal, thus lowering the freezing point of the water.
According to Katz, there is a second, related effect that hampers the freezing of water that has never been heated. The lowering of the freezing point reduces the temperature difference between the liquid and its freezing surroundings. "Since the rate at which heat is lost from the water depends on this temperature difference, water that has not been heated has greater difficulty losing heat," Katz was quoted as saying.
Katz said the two effects combined could perfectly explain why water that has been heated freezes more quickly than water that has not.
Katz is waiting for someone to do experiments to test his theory, New Scientist said.
中文翻譯：
一個普通的化學(xué)操作將揭示為什么熱水能比冷水更為迅速地結(jié)冰，星期四，一項來自新科學(xué)家的網(wǎng)站的報告稱。
該報道稱，一位來自位于圣路易斯的華盛頓大學(xué)的科學(xué)家，發(fā)現(xiàn)了隱藏在所謂的姆潘巴現(xiàn)象的實質(zhì)，姆潘巴現(xiàn)象就是該現(xiàn)象的產(chǎn)生和溶質(zhì)有關(guān)。
來自華盛頓大學(xué)的Jonathan Katz，發(fā)現(xiàn)了姆潘巴現(xiàn)象的細節(jié)。他說，溶質(zhì)是鈣和鎂的重碳酸鹽，這些物質(zhì)使很多飲用水變得很“硬”，當(dāng)水被加熱后，這些物質(zhì)沉淀生成了固體物質(zhì)，并在水壺內(nèi)壁形成水垢。
Katz表示，沒有被加熱過的水仍然含有這些溶質(zhì)，當(dāng)它被冷凍，冰晶形成的時候，這些仍保存在水中的溶質(zhì)濃度變得更高了，大概高出正常的50倍，這樣就降低了水的冰點。
據(jù)Katz稱，還有另外一個原因阻止未被加熱的水結(jié)冰。低冰點縮小了固體和其結(jié)冰環(huán)境下的氣溫差異?！耙驗闊崃繌乃辛魇У乃俣热Q于溫差。沒有被加熱過的水更難流失熱量?！?BR> Katz說這兩個原因結(jié)合在一起就可以很好地揭示為什么熱水比冷水更容易結(jié)冰了。
Katz正等待有人能通過實驗來證實他的理論。新科學(xué)家稱。