MIT Engineers Find a Way To Save Energy and Make Water Boil More Efficiently:
At the heart of a wide range of industrial processes, including most electricity generating plants, many chemical production systems, and even cooling systems for electronics, is an energy-intensive step with the boiling of water or other fluids.
They could significantly reduce their energy use by improving the efficiency of systems that heat and evaporate water. [R]esearchers have now found a way to do just that, with a specially designed surface treatment for the materials used in these systems.
Three different kinds of surface modifications, at different size scales, together account for the increased efficiency. The new findings are described in a paper published in the journal Advanced Materials by recent MIT graduate Youngsup Song PhD '21, Ford Professor of Engineering Evelyn Wang, and four others at MIT. The scientists caution that this initial finding is still at a laboratory scale, and more effort is required to develop a practical, industrial-scale process.
High-speed video of the researchers' test setup shows water boiling on a specially treated surface, which causes bubbles to form at specific separate points rather than spreading out in a film across the surface, thus leading to more efficient boiling. The video has been slowed down by 100 times to show more detail.
The heat transfer coefficient (HTC) and the critical heat flux (CHF) are two key parameters that describe the boiling process. There's generally a tradeoff between the two in materials design, so anything that improves one of these parameters tends to make the other worse. But both are crucial for the efficiency of the system, and now, after years of work, through their combination of different textures added to a material's surface, the team of scientists achieved a way of significantly improving both properties at the same time.
"Both parameters are important," Song says, "but enhancing both parameters together is kind of tricky because they have intrinsic trade-offs." The reason for that, he explains, is "because if we have lots of bubbles on the boiling surface, that means boiling is very efficient, but if we have too many bubbles on the surface, they can coalesce together, which can form a vapor film over the boiling surface." That film introduces resistance to the heat transfer from the hot surface to the water. "If we have vapor in between the surface and water, that prevents the heat transfer efficiency and lowers the CHF value," he says.
[...] Adding a series of microscale cavities, or dents, to a surface is a way of controlling the way bubbles form on that surface, keeping them effectively pinned to the locations of the dents and preventing them from spreading out into a heat-resisting film. In this work, the researchers created an array of 10-micrometer-wide dents separated by about 2 millimeters to prevent film formation. But that separation also reduces the concentration of bubbles at the surface, which can reduce the boiling efficiency. To compensate for that, the team introduced a much smaller-scale surface treatment, creating tiny bumps and ridges at the nanometer scale, which increases the surface area and promotes the rate of evaporation under the bubbles.
Journal Reference: "Three-Tier Hierarchical Structures for Extreme Pool Boiling Heat Transfer Performance" by Youngsup Song, Carlos D. Díaz-Marín, Lenan Zhang, Hyeongyun Cha, Yajing Zhao and Evelyn N. Wang, 20 June 2022, Advanced Materials., (DOI: 10.1002/adma.202200899)
(Score: 2) by Rosco P. Coltrane on Thursday July 21 2022, @08:42PM
out of my Doble steam car [wikipedia.org]!
(Score: 2) by mhajicek on Thursday July 21 2022, @09:31PM (1 child)
Boil anything but distilled water with that and it will be immediately covered in mineral deposits or other crud and stop working.
The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek
(Score: 0) by Anonymous Coward on Thursday July 21 2022, @10:02PM
Boiler water usually contains anti-corrosion additives, but they start with highly purified water for exactly that reason.
(Score: 2) by JoeMerchant on Thursday July 21 2022, @09:43PM (1 child)
Contaminants are often a challenge in the real world, and given the billions of dollars spent boiling water each year in very controlled circumstances (e.g. for electric power), I suspect such things as surface roughness have been considered before. At least in most power plant situations, heat that doesn't reach the water for boiling isn't going much of anywhere, just raising the temperature on the hot side of the boiler a bit more.
There is, of course, plenty of similar prior art:
https://www.nature.com/articles/srep13145 [nature.com]
https://core.ac.uk/download/pdf/10238306.pdf [core.ac.uk]
https://search.proquest.com/openview/3fc5ee1b04afb42bc044ecfdb6744b75/1%3Fpq-origsite%3Dgscholar%26cbl%3D18750&ved=2ahUKEwi_lN70-Ir5AhW8STABHRPRDcI4FBAWegQIGBAB&usg=AOvVaw2bYWHNMmUeNCyDbtoGs4r1 [proquest.com]
Україна досі не є частиною Росії Слава Україні🌻 https://news.stanford.edu/2023/02/17/will-russia-ukraine-war-end
(Score: 0) by Anonymous Coward on Friday July 22 2022, @10:01AM
Depends on the type of power plant . If the "boiler" you are talking about is actually a light water reactor, and the "hot side" is a fuel rod, you don't want the hot side to become too hot....
(Score: 3, Interesting) by ElizabethGreene on Thursday July 21 2022, @11:13PM
I wonder if this could be useful as a surface treatment in collectors for heat pipes.