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Science

MIT Scientists Invent a Better Way to Boil Water (mit.edu) 55

MIT News has an announcement: The boiling of water or other fluids is an energy-intensive step 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. Improving the efficiency of systems that heat and evaporate water could significantly reduce their energy use. Now, researchers at MIT have found a way to do just that, with a specially tailored surface treatment for the materials used in these systems. The improved efficiency comes from a combination of three different kinds of surface modifications, at different size scales. The new findings are described in the journal Advanced Materials in a paper by recent MIT graduate Youngsup Song PhD '21, Ford Professor of Engineering Evelyn Wang, and four others at MIT..... "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," Song says. 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 critical heat flux 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 these experiments, the cavities were made in the centers of a series of pillars on the material's surface. These pillars, combined with nanostructures, promote wicking of liquid from the base to their tops, and this enhances the boiling process by providing more surface area exposed to the water. In combination, the three "tiers" of the surface texture — the cavity separation, the posts, and the nanoscale texturing — provide a greatly enhanced efficiency for the boiling process, Song says... The nanostructures promote evaporation under the bubbles, and the capillary action induced by the pillars supplies liquid to the bubble base. That maintains a layer of liquid water between the boiling surface and the bubbles of vapor, which enhances the maximum heat flux.
While the article stresses it's still a laboratory-scale process (needing more work to become a practical "industry-scale" process), "There may be some significant small-scale applications that could use this process in its present form, such as the thermal management of electronic devices, an area that is becoming more important as semiconductor devices get smaller and managing their heat output becomes ever more important." Wang says in the announcement, "There's definitely a space there where this is really important." The article includes a bizarre-looking video showing how water now boils on their specially treated surface.

Thanks to Slashdot reader joshuark for sharing the link!
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MIT Scientists Invent a Better Way to Boil Water

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  • by backslashdot ( 95548 ) on Sunday July 17, 2022 @02:25PM (#62710208)

    Youngsup found a way to make soup while he was still young.

  • by FrankSchwab ( 675585 ) on Sunday July 17, 2022 @02:34PM (#62710226) Journal

    This doesn't improve boiling, it does improve heat transfer from the hot surface to the water. So something like a liquid cooler for a CPU would see an improvement - more heat transferred (or the same heat transferred at a lower delta-T), keeping the CPU cooler.

    • This doesn't appear to be any ground-breaking work. The phase-change immersion cooling people have been looking at this problem for at least a decade. https://www.sciencedirect.com/... [sciencedirect.com] The "best" surface was determined by sintering different sizes of particles and measuring the final performance.
    • Improved heat transfer during the process of boiling water results in more efficient boiling. The title seems fine as it is.
      • It should be made clear here that "efficient" refers to the size of the vessel, NOT the energy efficiency. The amount of power required to heat a certain amount of water I'd unaffected. In fact, that's actually the definition of power, of watts - how much it heats water.

        • The article specified that it does require less energy to boil water with the texturing. The increased surface area of the contact between the vessel and the water is a result of the introduction of three scales of texturing texturing features on the inside surface of the vessel, thus increasing the number of bubbles, reducing the size of the bubbles and providing better heat transfer between the vessel and the water. This means less of the applied heat is lost, the water boils faster, and the process requi
          • by mtm10 ( 1530769 )

            The savings is due to more of the applied heat is absorbed by the water in its liquid phase than is absorbed by the water in its gaseous phase.
            The large bubble of steam getting more heat than needed is where the wasted energy is getting 'lost'..

          • > This means less of the applied heat is lost

            Lost to what? If the heating element is in the water, such as a typical home water heater, 100% of the heat (and power) goes into the water. There is simply no way for the heat to go anywhere BUT into the water.

            If you have a water vessel of *fixed volume*, maybe inside a chimney,. increasing the surface area within that volume can increase heat transfer from the exterior of the vessel to the interior.

            • There is simply no way for the heat to go anywhere BUT into the water.

              Yes there is, it can go into the phase change. The issue is about heating water vs. creating water vapor: if more of your energy goes to creating water vapor then that rises to the surface and the liquid water doesn't increase in temperature by the same amount.

              The purpose of the paper seems to be greater efficiency in boiling, i.e.: creating water vapor. This would reduce the temperature of the water, so that's bad if you need hot water for making tea or cooking food, but it could be useful for something

    • by e3m4n ( 947977 ) on Sunday July 17, 2022 @04:51PM (#62710482)
      I hate to break it to MIT but this was discussed at length in my nuclear power training back in the 80s. For the longest time no boiling what so ever was permitted in the core for these reasons. Reducing heat transfer leads to runaway temps. Later the discovery that nucleate boiling was actually more efficient and increased heat transfer drove designs where the cooling channels in the core were structured to promote nucleate boiling while the core still ran at 2000psi and 480F.
      • The MIT process sounds considerably more refined that what you describe, assuming it can be scaled up. It seems likely that the Navy will be in touch with them to see if it can improve reactor efficiency.
    • That does bring up a point. I'll bet this helps at a specific temperature range for any heat transfer system. Where the gas and liquid layers coexist often.

      Seems like an optimization for edge cases where typical solutions get worse or breakdown. I'd love numbers to compare the improvement, but I'm not a heat transfer scientist and probably wouldn't follow the paper well.

    • by BBF_BBF ( 812493 )

      The research is for heat sources that are hot enough to vaporize water, so at 100 degrees celcius or higher, that cause vapor bubbles to form on the heating surface that reduce heat transfer.

      Most heat sinks in computer systems don't get that hot, so this research is not applicable to consumer liquid coolers for CPUs and GPUs since the point is to keep the temperature of the chip under 100 degrees Celcius. If you've hit 100 degrees, the CPU/GPU will already be throttling itself.

  • Instead of transferring heat through the container to the water, just heat the water directly by, say, microwave absorption. Or, if you want a cheap alternative, steel wool your metal pots- that should reduce bubble coalescence and increase the effective surface area.

    • What is the conversion efficiency for microwave generators vs. thermal from electricity? I know thermal creation can be close to 100% with simple power resisters (reliable for a long time, cheap to make, etc).

      Thought I read home microwave magnetrons often last about 10 years, and replacements weren't super cheap ($100 installed?). Also the worry about frying yourself if you do it wrong meant people usually suggested buying a new microwave instead of repair. And super heated water seems more common in mic

      • by parker9 ( 60593 )

        Regardless, the net heat flow into the water determines how quickly it boils (i.e. Q = latent heat). Liquid water has a broad absorption spectrum in the microwave region. To calculate "thermal from electricity" one could start by assuming all electrical power turns to thermal and use the new impressive values they quote, but you need to assume some efficiency of your electrical heater and its coupling to the water container.

        If you want to do boiling of water w/ microwaves, you won't use a consumer microwave

  • Quickest cup-o-joe in the universe.

  • by jfdavis668 ( 1414919 ) on Sunday July 17, 2022 @02:52PM (#62710264)
    The water boils instantly.
    • by ls671 ( 1122017 )

      Air pressure is also replaced with steam pressure instantly. Granted, you boil a very little quantity of water faster but just for an instant.

      Also, if you manage to somehow keep air pressure and steam pressure down, things don't cook. It is very hard to cook an egg by boiling it in an open container on top of the highest mountains, if not impossible.

    • by dfm3 ( 830843 )
      I do this as a classic demonstration for my first year chemistry students. Put a beaker of water in a vacuum chamber and let it boil for a few minutes, and the students express surprise at the fact that the water gets colder as it boils (due to evaporative cooling). Then I perform the demonstration again with refrigerated water at 4C, and get ice to form in the water as it boils due to the water being at the triple point in low pressure.
  • I had a dimpled cooking pot 20 years ago that advertised faster boiling because of the dimples. Not sure how unique this innovation is.
    • Seems like it's micro-dimples.
      • Micro dimples happen over time with cookware as utensils bang and stir, so we should be all set on the cooking front.

        If you have a new pot or pan maybe it's time to stir those foods a little more for a few weeks until it breaks in :D
    • by necro81 ( 917438 )
      Exactly, I put a bunch of speed holes in my car years ago, because I saw it on TV. [ref [youtube.com]]
  • MIT not covering all the bases here

  • by ffkom ( 3519199 ) on Sunday July 17, 2022 @04:29PM (#62710420)
    A cheap immersion heater already transfers practically all the heat it generates into he surrounding medium. It does not "significantly reduce energy use" if the heat-transfer through the immersion heater surface is somewhat quicker.
    • I couldn't find a paper to dig deeper than the article (didn't try hard), but yeah... Faster thermal flux could be called "more efficient", but that doesn't lower the power cost to heat water...just the time cost to transfer energy. Which should make smaller surfaces as good as larger ones (same overall amount of energy), or increase the maximum transfer rate for the same area.

      It pays to be specific when communicating. "I don't think that means what you think it means. And I think you did that on purpos

    • A cheap immersion heater already transfers practically all the heat it generates into he surrounding medium.

      It does. A fully insulated heating element does too. That doesn't mean both are equally effective at boiling water. Rate of heat transfer is a factor in many applications that require heat transfer, not just efficiency.

    • by BBF_BBF ( 812493 )

      It's strange that the summary in the MIT article doesn't state HOW much more efficient the new heating elements are.

  • Maybe this is useful to make gas/nuclear power plants more efficient?

    • by Skapare ( 16644 )

      or railroad steam engines. maybe they can make a comeback.

      • by Z80a ( 971949 )

        I vaguely remember modern trains using the combustion engine just to generate power to power it's electric motors.
        You probably can use some sort of steam engine to do the same job, like a nuclear steam engine.

  • I suspect those microcavities will fill up with lime scale, etc pretty quick
    • I suspect those microcavities will fill up with lime scale, etc pretty quick

      Which is why we have scientists and engineers.

  • by Twisted64 ( 837490 ) on Sunday July 17, 2022 @06:36PM (#62710702) Homepage

    Look, if it improves heat transfer from the surface into the water, that's something being more efficient.

    If it decreases the time taken to boil water with the same energy input, that's also more energy efficient. Not because the energy required to boil the water is different, but because the water loses less energy to the air over a shorter time.

    Since this appears to be known, I'm curious as to why I've never really seen a (non-immersion) kettle with a bumpy bottom. Presumably the gains are too minimal to justify the increased cost of R&D, manufacture/production?

    • You have, you just didn't notice it. People have been coming up with novel ways to better utilize heating surface area for ages. For example, the Jetboil stoves. I've also seen (on slashdot I think) designs for pots with fancy fins on the outside. I'd wager that you'll find that over the thousands of years humans made pots by hand, they discovered similar properties by chance.

      The main issue I see with this idea is fouling. In a completely closed system you can start with extremely clean surfaces and high pu

    • I'm curious as to why I've never really seen a (non-immersion) kettle with a bumpy bottom.

      Because cleaning efficiency is more important than heat transfer speed for this use case. If you make it hard to remove tea stains, hard water scale, or whatever then you have a worse kettle even if the theoretical efficiency of boiling is higher. Nobody with a hot watter kettle is crying over 13c a year in wasted electricity due to slightly lower heat transfer properties.

  • Will it let me brew a pot of coffee faster?!

    • The best coffee is brewed with water a bit less than boiling, i.e. between 195F and 205F.

      +1 for making me chuckle :-)
  • They want to improve boiling by not letting the liquid form a vapor film over the heating element. Increasing the surface area and provoking nucleation in specific places is sort of an obvious approach that you abandon once you figure out that it's not necessary.

    The entire issue can be sidestepped by heating the liquid under pressure so that there is no vapor at all, then releasing the pressure to provoke the phase change. It's standard practice to the extent that it's got an acronym and everything: PABP

  • Nano structures would not survive contact with London hard water.

    The quest for a faster cuppa must sadly go on.

The 11 is for people with the pride of a 10 and the pocketbook of an 8. -- R.B. Greenberg [referring to PDPs?]

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