Boiling water, this seemingly simple behavior is one of the ancient inventions of mankind, and it is also the prototype of the evolution of many science and technology today, whether it is a coffee machine or a nuclear power plant, it is inseparable from it. However, this seemingly simple process actually makes it difficult for people to understand deeply because of its complexity.
Recently, Matteo Bucci, assistant professor of nuclear engineering at the Massachusetts Institute of Technology, and graduate students Limiao Zhang and Jee Hyun Seong published a paper in the Physics Review Letters, introducing their research results. By studying how boiling phenomenon plays its core role in heat exchange technology, they predict the potential danger caused by a phenomenon called "boiling crisis". This phenomenon occurs when too many high heat flow bubbles form on the surface of hot water, they will merge with each other into a layer of steam, which hinders the normal heat transfer from inside.
As computer chips become smaller and more powerful, some high-performance processors may require liquid cooling to dissipate heat. Most power plants in the world, whether they are fossil fuels, solar power or nuclear power plants, mainly generate steam to drive turbines to generate electricity.
In nuclear power plants, the water is heated by fuel rods, which are heated by nuclear reactions, and the heat diffused into the water through the metal surface is responsible for transferring energy from the fuel to the power generation turbine, but this is also the key to preventing fuel overheating and possible meltdown. In the boiling crisis, the formation of a vapor layer that separates the liquid from the metal can prevent heat transfer and possible rapid overheating.
Because of this risk, the relevant regulations require that the heat flux of a nuclear power plant cannot exceed 75% of the critical heat flux, and the critical heat flux may cause a boiling crisis and damage key equipment components of the nuclear power plant. However, because people do not know much about the theoretical basis of critical heat flux, the estimation of its level is very conservative. Bucci said that if there is a greater grasp of this phenomenon, then these nuclear power plants are likely to operate at a higher thermal level, thereby using the same nuclear fuel to produce more electricity.
Bucci said: "Better understanding of boiling and critical heat flux is a very difficult problem because it is nonlinear, and small changes in material or surface texture can have a great impact. But now, thanks to the ability to With better instruments that capture the details of this process in our experiments, we have been able to understand how a boiling crisis has occurred. "
Facts have proved that this phenomenon is closely related to the city's traffic flow, or the way in which diseases are spread among people. Essentially, this is a matter of how things get together.
When the number of cars in a city reaches a certain threshold, they may get together in some places, causing traffic jams. Moreover, when disease carriers enter crowded places such as airports or auditoriums, the probability of an epidemic increases. The researchers found that the number of bubbles on the heated surface is similar. Above a certain bubble density, the possibility of bubbles gathering and merging and forming an insulating layer on the surface will increase. He said: "The boiling crisis is essentially the result of the accumulation of bubbles. These bubbles merge and merge with each other, causing the surface to break."
Taking into account these similarities, Bucci said: "We can draw inspiration and adopt the same method to simulate boiling, just like the same method to simulate traffic jams." These models have conducted a lot of research and exploration, and now based on experiments and mathematical analysis, Bucci and his colleagues were able to quantify this phenomenon and find a better way to determine when such a bubble merger will occur. "We proved that with this model, we can predict when a boiling crisis will occur based on the pattern and density of bubbles that are forming."
Bucci said, "We can not only use this information to predict the boiling crisis, we can also explore solutions by changing the boiling surface to minimize the interaction between the bubbles. Following this idea to improve the surface, we can control and Avoid 'bubble block'. "
If this research can bring about some changes that enable nuclear power plants to operate at a higher heat flux, that is, the heat dissipation rate exceeds the currently allowed speed, the impact may be significant. Bucci said, "If you can prove that by manipulating the surface, you can increase the critical heat flux by 10% to 20%, you can make better use of existing fuels and resources, thereby increasing power generation globally." (Liu Yiyang )
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