Water can exist in three states: solid, liquid and gas. When a frozen solid is heated, it becomes a liquid. When a liquid is heated, it becomes steam.
When the heat source is hot enough, the behavior of water has changed greatly. According to scientists, when water droplets deposited on aluminum plates are heated to 150 degrees Celsius or above, they will no longer boil. On the contrary, the steam to be formed will be trapped under the water drops to form a buffer to prevent the liquid from directly contacting the surface of the aluminum plate. The trapped steam suspends the liquid and jumps on the aluminum surface. This phenomenon is called Leiden Frost Effect, named after the German doctor and theologian who first described it in the publication 175 1.
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Ice is slowly melting: Leiden frost effect. Ice melts into liquid, and then the liquid floats above the heating surface and is suspended by the steam layer below.
This generally accepted scientific principle applies to water as a liquid. The scientific team thinks that ice will do the same? Is it possible to have Leiden frost effect of solid, liquid and vapor?
About five years ago, curiosity prompted Breco's laboratory to conduct the first survey. At that time, researchers observed that even if aluminum was heated above 150 degrees Celsius, ice would not be suspended in water vapor like a liquid. As the researchers continued to raise the temperature, they observed the behavior of ice as the temperature increased. They found that the temperature of suspension was significantly higher: 550 degrees Celsius (1022 degrees Fahrenheit) instead of 150 degrees Celsius.
What happened under the ice to prolong the boiling time? The research team cooperated to develop a new heat conduction method and applied this knowledge to solve this problem. They found that the answer was the temperature difference of the meltwater layer under the ice. The meltwater layer has two different extremes: its bottom is boiling, which makes the temperature fixed at about 100 degrees Celsius; But its top is attached to the ice, which makes it fixed at about 0 degrees Celsius.
The researchers explained that the unique temperature difference created by the ice layer on the water layer changed the condition of the water itself, because most of the heat of the hot aluminum plate had to pass through the water surface to maintain this extreme temperature difference. So only a tiny part of energy can be used to produce water vapor.
"Floating ice is much more difficult than water droplets," the researcher continued. "Once suspended, the heat transfer will drop sharply, because when the liquid is suspended, it no longer boils. At this time, it jumps on the surface instead of direct contact, and contact is the reason for its boiling. Therefore, suspension is not conducive to heat transfer, and boiling is even more incredible. "
For application scenarios, researchers said that heat transfer plays a huge role in cooling objects such as computer servers or automobile engines. Because they need a substance or mechanism that can remove energy from hot surfaces and quickly redistribute heat to reduce the wear of metal parts.
At the same time, in nuclear power plants, ice can also be used as a coolant to induce rapid cooling. It is possible to avoid the problems encountered in cooling nuclear reactors after the Fukushima nuclear power plant disaster.
The Leiden frost effect caused by rapid evaporation of liquid undoubtedly interferes with the efficiency of cooling nuclear reactors after the Fukushima nuclear disaster, but ice coolant may avoid this. In addition, ice coolant also has potential applications in metallurgy. This is because if the cooling rate of metal is too slow after molding, metal tools will become brittle. Therefore, in order to make the metal stronger and less fragile, it is necessary to quench the heat of the metal in a short time.
This research paper, entitled "Boiling water with ice: Researchers found18th century expansion in principle", has been published in the journal Physical Review Fluid.
Source: China Nuclear Power Network