What if water could be boiled faster and more efficiently? It would benefit many industrial processes by reducing energy consumption, including most power plants, many chemical production systems and even cooling systems for electronics.
Improving HTC and CHF
Now, MIT scientists have devised a method to achieve this, according to a press release from the institution published on Tuesday. The researchers found a way to simultaneously improve the two key parameters that promote the boiling process, the heat transfer coefficient (HTC) and the critical heat flux (CHF).
This is quite a development as there is usually a trade off between the two, so anything that improves one tends to worsen the other.
“Both parameters are important,” said study co-author and recent Youngsup Song Ph.D. ’21 graduate, “but improving both parameters together is a bit tricky because they have an inherent trade-off.”
“If we have a lot of bubbles on the boiling surface, it means the boiling is very efficient, but if we have too many bubbles on the surface, they may coalesce, which may form a vapor film on the surface. boiling.”
This film introduces resistance to heat transfer from the hot surface to the water. “If we have steam between the surface and the water, it impedes the efficiency of heat transfer and lowers the value of CHF,” added the researcher.
Microscopic cavities at work
So how did the researchers achieve a more efficient and faster boiling process? By adding a series of microscopic cavities, or bumps, to a surface, controlling how bubbles form on that surface. This kept the bubbles effectively pinned to the dent locations and prevented them from spreading into a heat resistant film.
The microcavities were then positioned at the ideal length to optimize this process.
“These micro-cavities define the position where the bubbles appear,” Song explained. “But by separating these cavities by 2 millimeters, we separate the bubbles and minimize bubble coalescence.”
The work so far has shown promise, but study co-author MIT Engineering professor Evelyn Wang, argued that it took place in small-scale laboratory conditions that could not easily be scaled up for practical application in modern devices.
“These kinds of structures that we make are not meant to be scaled up in their current form,” she explained, but rather were used to prove that such a system can work.
Now the team is focused on finding additional ways to create these types of surface textures that can be used in practical dimensions.
“Showing that we can control the surface in this way to achieve improvement is the first step,” she concluded. “Then the next step is to think about more scalable approaches.”