MIT researchers study heat transfer for better understanding of boiling crisis

Researchers at MIT have studied heat transfer in an effort to help predict and prevent a boiling crisis at nuclear power facilities and others that rely on heat transfer. In a recent MIT News article titled “Getting to the bottom of the ‘boiling crisis,’” David L. Chandler explains that nuclear plants operate well below the levels that could cause a boiling crisis, but the new understanding gained by these researchers could allow plants to operate at higher output levels.

Due t o the risk of overheating or a potential meltdown, regulations require operations to run at no more than 75% of the critical heat flux (CHF), but CHF has been poorly understood and conservatively estimated, Chandler reports. However, small changes can have a big effect on boiling and CHF and this has been difficult to measure and study until now, assistant professor and lead author Matteo Bucci said in the article.

“We have been able to actually measure and chart the phenomenon with the required spatial and temporal resolution,” he said. This has provided an understanding of how a boiling crisis begins.

Through this research, the team found that as bubbles build up on a heated surface, they behave like a traffic jam, crowding together and merging, and eventually forming an insulating layer on the surface, Chandler reports.

“The boiling crisis is essentially the result of an accumulation of bubbles that merge and coalesce with each other, which leads to failure of the surface,” Bucci said in the article.

Now, with the information collected from their experiments and using mathematical analysis, the researchers can quantify the incident to pinpoint when bubble merging will occur.

Chandler reports that surface texture, among other factors, play significant roles in heat transfer, and small adjustments could allow CHF to be raised, leading to more reliable heat transfer.

“We can use this information not only to predict the boiling crisis, but also to explore solutions, by changing the boiling surface, to minimize the interaction between bubbles. We’re using this understanding to improve the surface, so we can control and avoid the ‘bubble jam,’” Bucci said. “… If you can show that by manipulating the surface, you can increase the critical heat flux by 10 to 20%, then you increase the power produced by the same amount, on a global scale, by making better use of the fuel and resources that are already there.”

The research results were published in the journal Physical Review Letters in a paper written by assistant professor of nuclear engineering Matteo Bucci and graduate students Limiao Zhang and Jee Hyun Seong.