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!
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!
Better title (Score:3)
Youngsup found a way to make soup while he was still young.
Now if only (Score:1)
Now if only those MIT scientists could invent better ways to summarise.
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Funniest comment in a week, Score: 0.
Sloshdut is broken.
Improved heat transfer, not improved boiling (Score:5, Insightful)
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.
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From the summary: "Improving the efficiency of systems that heat and evaporate water could significantly reduce their energy use."
It is not clear how efficiency is defined here nor is it clear how this improvement "could significantly reduce ... energy use". It would seem that water could be heated faster but that doesn't mean more efficient.
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It would seem that water could be heated faster but that doesn't mean more efficient.
That's exactly what it means. If it takes 5 minutes on an electric burner to boil a given volume of water, and these changes allow the same volume of water to be boiled in 4 minutes on the same burner, does that not represent an increase in efficiency? The same amount of heat is transferred to the water, but less electricity is used to do so.
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I see a few ways it could work.
It's extremely non-intuitive, but if you measure the temperature of boiling water it can vary significantly depending on the shape and surface finish of the container its boiling in. Decreasing the temperature required for boiling decreases the specific heat input required to reach that boiling point and the heat lost from the boiler to the environment. Normally the specific heat required to reach that boiling point is, for water, a rounding error compared to the latent heat
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Efficient for surface area, NOT for energy (Score:3)
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.
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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'..
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> 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.
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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
Re: Improved heat transfer, not improved boiling (Score:4, Informative)
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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.
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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.
or just use microwaves (Score:2)
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.
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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
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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
Yes! Espresso on the double! (Score:1)
Quickest cup-o-joe in the universe.
I just remove all air pressure (Score:3)
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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.
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Dimpled Pots (Score:2)
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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
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How efficient is cracking your joints? (Score:1)
MIT not covering all the bases here
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"could significantly reduce their energy use"? No! (Score:4, Informative)
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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
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but if the heat-loss to ambient air is a constant over time, reducing the time reduces the total loss and thus improving "efficiency" to the drones over in the marketing department.
Re: "could significantly reduce their energy use"? (Score:2)
You are correct, except for the significant part of the MIT claim, at least as portrayed in the article.
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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.
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It's strange that the summary in the MIT article doesn't state HOW much more efficient the new heating elements are.
Given we boil water for power in many cases.. (Score:2)
Maybe this is useful to make gas/nuclear power plants more efficient?
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or railroad steam engines. maybe they can make a comeback.
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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.
minerals in water... (Score:1)
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I suspect those microcavities will fill up with lime scale, etc pretty quick
Which is why we have scientists and engineers.
You pedants (Score:3)
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?
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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
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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.
The one true application for this new tech (Score:2)
Will it let me brew a pot of coffee faster?!
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+1 for making me chuckle
Unnecessary, but also obvious (Score:2)
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
Kettle (Score:2)
Nano structures would not survive contact with London hard water.
The quest for a faster cuppa must sadly go on.