19 ms·
A new heat engine with no moving parts is as efficient as a steam turbine
- megaman821 5y agoIs there some sort of physical property when you are that hot (2400C) that you begin glowing? Then just open a slot in the insulation so the photons cell whenever you need electricity.
- tialaramex 5y agoIf your question is "wait, do all hot things glow?" then the answer is Yes.
- jacquesm 5y agoEverything above absolute zero emits infrared photons, as something gets hotter it will also start to emit in the visible range because some of the photons are more energetic resulting in a shorter wavelength. That's why you see the progression from barely visible red to red to orange, yellow and eventually white when you make something hot enough. But it will always continue to output photons at lower energy levels as well, though not in equal proportion (and that's why a hot object is white and not blue, and why a hot gas flame can be blue).
- robotresearcher 5y agoThat’s what the article says. “The heat engine is a thermophotovoltaic (TPV) cell, similar to a solar panel’s photovoltaic cells, that passively captures high-energy photons from a white-hot heat source and converts them into electricity.” One detail is that objects radiate at all temperatures. The trick is to choose the temperature so that you get a lot of emission in the band that matches the best performance of the PV component.
- scythe 5y agohttps://en.wikipedia.org/wiki/Black-body_radiation https://en.wikipedia.org/wiki/Black-body_radiation
- kitd 5y agoMinor quibble: a heat engine converts heat to mechanical energy. So is a heat engine with no moving parts a contradiction in terms?
- yetihehe 5y agoYeah, this is a thermophotovoltaic cell, which uses heat apart from light. But because it uses heat, they called it heat engine.
- BlueTemplar 5y agoYou can just combine it with an electric motor. (Those are typically 95+% efficient.)
- arc-in-space 5y ago0 comments after 20 minutes on an energy post? How am I supposed to know why this won't work, won't be useful, won't be cost effective, won't scale, and that it's just a fad? Jokes aside, this seems impressive, I have no idea what the best applications would be but wikipedia claims that current similar devices have fairly bad efficiency(https://en.wikipedia.org/wiki/Thermoelectric_generator https://en.wikipedia.org/wiki/Thermoelectric_generator).
- smrtinsert 5y agoExactly why I clicked in, but man this technology sounds like a serious gamechanger.
- willhinsa 5y agoThanks for the laugh! So true.
- yetihehe 5y ago> won't be useful, won't be cost effective > The team’s design can generate electricity from a heat source of between 1,900 to 2,400 degrees Celsius Pretty high temperature for me, copper melts at 1800C.
- wishawa 5y agoHigh temperature is the point. The efficiency of heat engines depend on the temperature difference (relative to ambient). The hotter you can go, the better. (granted this thing isn’t really an “engine”, but the trend still applies)
- dv_dt 5y agoBut for practical applications, the availability and cost of materials to survive the operating temperature is also relevant.
- diarrhea 5y agoA Carnot heat engine operating between, say, 2600K and 400K can reach almost 85% efficiency. The higher the temperature, the higher the share of exergy in the heat flux. At high enough temperatures, it’s no longer a feat to convert to electricity at high efficiencies.
- tinco 5y agoIf you point concentrated solar at a vantablack object, heatsinked to this 40% efficient TPV, do you get an easy 39.94% efficiency, easily outpacing mass produced photovoltaic or am I missing a loss?
- rosetremiere 5y agoThe article says, if I'm not mistaken, that the heat source must be between 1900 and 2400 degrees (Celcius), and I would bet that Vantablack loses its blackness at such temperatures?
- chucksta 5y agoWikipedia indicates the melting point of vantablack being 3000C. I would think a black coloring is pretty heat resistant. It looks like it needs to be 500-750C to create it as well
- sbierwagen 5y agoIn vacuum, maybe. Vantablack is made of carbon nanotubes, and those oxidize away in atmosphere above 750C.
- VBprogrammer 5y agoOne minor issue is diffusion due to clouds, similar to all concentrated solar power systems it needs direct sunlight. Normal solar panels can produce some power even under a thin cloud layer.
- voakbasda 5y agoI’m guessing the vantablack would be destroyed by the concentrated heat or UV. Or is there an industrial formulation that could withstand the high temperatures?
- dioxide 5y agoYou'd need the solar to heat something white hot.
- 5y ago
- falcolas 5y agoI'm not well enough versed in these kinds of devices - how does this differ from a traditional thermocouple device?
- inetknght 5y agoSo does this mean I can attach one of these things to my CPU and get back some of the power used?
- lazyier 5y agoOnly if your CPU is producing around 1,900 to 2,400 degrees Celsius
- ziffusion 5y agoMy soup then.
- disqard 5y agoIt requires "a heat source of between 1,900 to 2,400 degrees Celsius, or up to about 4,300 degrees Fahrenheit" -- so your Nvidia gpu should work great for this purpose :)
- sfink 5y agoSure, if you're running your CPU at 1900°C.
- zionic 5y agoSure, you get ~40% back once you hit 1,900 to 2,400C
- jotm 5y agoNo, but you could realistically make a small Stirling engine that would act as a heatsink for your processor while generating electricity. Would be noisy as hell, but quite a cool project haha
- driverdan 5y agoWhile this is far away from being a production device it's pretty exciting to see 40% efficiency. How would you go about converting the energy stored in a thermal battery to a high enough temp for this to work? Some kind of heat pump? It has never been clear to me how to concentrate heat like that.
- jandrese 5y agoI think they're planning to heat up big chunks of graphite to thousands of degrees C with electric heaters powered by the grid and then attach these thermocouples when the renewable sources start to flag (windless nights) to cover the gap.
- diarrhea 5y agoHeat radiation losses (scaling with the fourth power of the temperatures) would obliterate such a storage solution. I could only imagine it as very short-term, at which point heating using electricity and converting back shortly after quickly becomes pointless.
- danans 5y agoI don't know how they mitigate the radiation losses (huge amounts of insulation?), but it appears that graphite has some interesting properties when heated, like it gets stronger 1000-2500C and doesn't expand much when heated [1]. Perhaps those properties help it to store heat effectively at those extreme temps. 1. https://nucleus.iaea.org/sites/graphiteknowledgebase/wiki/Guide_to_Graphite/What%20is%20Graphite.aspx#:~:text=Graphite%20has%20a%20melting%20point,it%20sublimes%20rather%20than%20melting https://nucleus.iaea.org/sites/graphiteknowledgebase/wiki/Gu....
- lazyier 5y ago> I don't know how they mitigate the radiation losses (huge amounts of insulation?) My guess is a vacuum flask made of tungsten. Tungsten sheet metal is a thing and it has the second highest melting point of currently known elements, which is 3,422C. Then for the 'battery' you will want to find a material that has a phase change around the temperature required for this heat engine to operate. The energy required for water to go from 100c water to 100c steam is considerably more significant than the energy required to go from 0c water to 100c water. Graphite will likely come into play because you need to have electrodes to heat the material up to storage temperature. Graphite is a good for this sort of thing. Although gradual erosion will likely limit the life of the battery.
- frankus 5y agoThe university where I did a post-bacc had a research project back in the late 1990s to build a TPV-powered hybrid electric car that used compressed natural gas to heat an emitter surrounded by water-cooled PV cells. With the technology at the time they weren't able to get the efficiency to be competitive with an internal combustion engine, but something like this probably could've made it competitive. I'm not sure if there's any need for it with today's battery performance/price, but maybe as a range extender or something. https://vri.wwu.edu/viking-series-cars-history/ https://vri.wwu.edu/viking-series-cars-history/ (scroll down to Viking 29) https://www.sae.org/publications/technical-papers/content/972650/ https://www.sae.org/publications/technical-papers/content/97... (technical paper)
- jacquesm 5y agoThose are all amazing vehicles. I played a bit with water cooled solar cells, I found that the hard part wasn't the cooling but to be able to draw that much current from a single cell, the attachment points for the wiring typically really weren't up to the job and having multiple attachment points became a necessity. You also need a pretty beefy pump and radiator to get rid of the excess heat, though I guess in a vehicle you would use an active system with a fan. What I don't understand about the Viking 29 article is how an 8 KW generator is going to power a 75 KW motor, is there something I'm missing?
- opwieurposiu 5y agoThere was a battery used for peak acceleration power. 8KW is enough to cruise at highway speeds if you have an aerodynamic enough body. More details: http://fennetic.net/pub/viking_29_thermophotovoltaic_electric_car.pdf http://fennetic.net/pub/viking_29_thermophotovoltaic_electri...
- jacquesm 5y agoThank you! Very interesting design this.
- KennyBlanken 5y ago
- nicoburns 5y ago> The researchers plan to incorporate the TPV cell into a grid-scale thermal battery. The system would absorb excess energy from renewable sources such as the sun and store that energy in heavily insulated banks of hot graphite. It's clearly not ready for production yet, but storing energy as concentrated heat seems like one of the plausible proposed grid-scale storage solutions to me. I'm interested to see where this goes.
- diarrhea 5y agoConcentrated energy is not a technical term. But high-temperature internal energy storage (aka heat storage) is terrible because of the losses. For example, low temperature floor heating is very efficient. You don’t want high temperature deltas because of the associated exergy losses.
- CSSer 5y agoDoes anyone know if we already use things like this to increase the efficiency of existing energy usage in applications which require high degrees of heat output by recycling energy that is otherwise lost as excess thermal output? The example that springs to mind for me is a steel mill. The temperatures required there easily meet and exceed what is required to generate and store energy with this device.
- 323 5y agoProbably not in a steel mill, because otherwise you could have just heat water to steam and use it to run a generator. Since this is not done, there is a catch. An example where this idea works is a condensing boiler where the burned gases heat is used to increase efficiency by 10-30%.
- Simon_O_Rourke 5y agoThis is great, but all of this feels like it's coming 15 to 20 years too late. I worked with a guy in Berlin who had previously worked in PV energy. He predicted that unless the costs were reduced by a factor of half the price point of fossil fuels that it would go nowhere. We're addicted to cheap, no hassle sources of energy right now, and it's depressing.
- nynx 5y agoThankfully, the price of PV has dropped by far more than a half over the past ten years.
- andrepd 5y agoMillions of people already die yearly from pollution. It's definitely not hassle free.
- Maursault 5y agoYou have to wonder what PV would cost if even a tenth of the resources invested in developing nuclear energy were instead invested in solar energy development. I expect by 1980, solar energy would have been the cheapest way to generate electricity, President Carter would have been reelected, no Iran-Contra affair, and no deregulation of banks leading to the 2008 recession, and likely would have avoided 911, both Iraq wars and the one in Afghanistan. We could have saved all kinds of money, had cheap energy, still had plenty of nuclear power, and it wouldn't be so damn hot all the time.
- TSiege 5y agoThis is a great timeline to imagine :)
- outworlder 5y ago> You have to wonder what PV would cost if even a tenth of the resources invested in developing nuclear energy were instead invested in solar energy development. Not enough was invested in nuclear. Fossil fuels received massive funding (and subsidies). Had we deployed more nuclear power for baseline and industry, we would have been in a far better place. The Cold War also messed up things, and caused the reactors that were deployed to be the ones better suited for weapons first, energy second. Note that our solar panels are similar to computer chips. Investing more money would have sped up the development but not in time for it to be viable in the 80s.
- k__ 5y agoCan it also absorb excess heat from me?
- outworlder 5y agoUnless you are a member of the Fantastic Four, no.
- danans 5y ago> The researchers plan to incorporate the TPV cell into a grid-scale thermal battery. The system would absorb excess energy from renewable sources such as the sun and store that energy in heavily insulated banks of hot graphite. The article doesn't provide the efficiency of this insulated hot graphite battery. Given that this device is meant to be paired pretty exclusively with such a battery, it seems like a narrowly applicable solution. Or are there other renewable sources of heat between 1900C and 2400C that could be used for this purpose?
- kragen 5y agoThe efficiency of heating things up is pretty much 100%. The efficiency of insulation can be arbitrarily high (up to 100%) or arbitrarily low; heat loss is proportional to surface area and storage time and inversely proportional to insulation thickness. If your heat engine is only 40% efficient you might as well design your insulation to be 80% efficient or so over the expected time span, which would be a few hours for grid storage systems.
- danans 5y agoI was thinking more about the efficiency of the mechanism that transfers the heat from battery to the TPV engine. The article said that the device has to be exposed to photons coming off a white-hot source. I suppose that if the TPV devices are closely coupled with the white-hot source this should be minimal but it's not clear from the article whether there is an intermediary step, or how they plan to control the TPV's exposure to the heat source to discharge the battery. Given that this works via radiation (vs convection like a traditional heat engine), the path between the heat source and the TPV would have to be fairly direct, and not lose much heat to any adjacent non-TPV material. Maybe they have some kind of massively insulated opening/closing heat shield that they can use in a manner similar to the gates used to control water in hydroelectric plants.
- gysfjiutedgj 5y agoYou are correct. There is a shutter over the eye of Sauron.
- wayfarer1291 5y agoThere's a silicon-valley based company that's building a combined thermal storage and TPV system: https://www.antoraenergy.com https://www.antoraenergy.com So these ideas may be get to market sooner than a typical university press release. https://www.nrel.gov/news/features/2021/new-projects-move-thermophotovoltaic-technology-closer-to-commercialization.html https://www.nrel.gov/news/features/2021/new-projects-move-th... (some of the same people involved in this paper at NREL seem to also be collaborating with Antra, which is great to see)
- lapinot 5y agorelevant lowtechmag article: https://solar.lowtechmagazine.com/2020/05/thermoelectric-stoves-ditch-the-solar-panels.html https://solar.lowtechmagazine.com/2020/05/thermoelectric-sto... tldr: thermoelectric generators don't have great efficiencies, but by cogenerating heat and electricity they can get viable (if you need heat and electricity, make a bit more heat than you need and put a thermoelectric generator, the non-converted heat will just end up as useful heat). This would be adapted to households, which typically need a lot of heating.
- XorNot 5y agoI'm struggling to figure out what this is. If you can capture heat from a "white hot" object, why is it not just a good solar cell? The sun is easily in this range.
- BlueTemplar 5y agoThe sun is much less available.
- icodestuff 5y agoIf I'm reading this right, this actually has a larger usable band gap range than traditional photovoltaics -- the article talks about capturing the high-energy photons -- in the first pass. This means that the cell can actually capture the electrons knocked out by those high-energy photons, which is something we haven't been able to do. Silicon's band gap (1.11 eV) corresponds to 1110 nm (NIR), and any photons with more than 3 eV energy (413 nm) are lost (and all the excess energy in photons in between is lost as heat). Newer cells are around 0.6-0.7 eV, but I don't know their maximum capture energy. That's all the violet light and UV. There's a startup that makes a polymer film that can create two lower energy photons in the band gap from a high-energy photon to capture some of that wasted light. This would seem to be a cell that could capture it directly. Very very cool; that's a lot more energy captured per photon. What I'm unclear on is why you need to heat it up so much to get to those efficiency levels, and it wouldn't just work as an ordinary solar cell.
- raxxorraxor 5y agoI understood it that the efficiency of the TPV depends on the photons wavelength which is determined by temperature on emission. So the band gap probably has an efficiency curve.
- MatteoFrigo 5y agoThe article is confusing, but I read it the same way as you: these guys have figured out a way to capture a larger part of the blackbody spectrum than a normal photovoltaic cell. I don't think they are saying that the cell needs to be heated up. I think they are saying that they capture 40% of the power of a blackbody at 2000K. I am not sure why they don't mention what happens for a blackbody at 5600K such as the Sun.
- MatteoFrigo 5y agoReplying to myself and GP, I found the answers to our questions in the Nature paper linked from the article. The TPV is distinct from a solar cell because the TPV is meant to reflect energy back to the source. A solar cell also reflects some energy back to the sun, but that energy is effectively lost. In the TPV case, the reflected power helps keeping the source hot, thus effectively recycling photons in a feedback loop involving the source and the TPV. Some of the energy incident to the TPV is transformed into electricity, some is reflected, and some is dissipated as heat in the TPV. The 40% efficiency is measured as (electricity+reflected)/incident. Thus, it is not true that the TPV converts 40% of its input into electricity. Instead, the TPV converts some fraction, reflects (40%-fraction) to be recycled later, and dissipates 60% into heat. Using the TPV as a solar cell would reduce the efficiency because the reflected energy is wasted. Part of the magic of the TPV is to design a really good mirror that reflects energy back to the source, which is not a concern for solar cells. The current design operates best for a blackbody source around 2000K and there is probably no point in using it at 5600K. Cool stuff.
- tenthirtyam 5y agoWell now. We can have a heat pump with a COP of 3.5 or so. Let's say we put in 1kW of electricity, and take out 3.5kW of heat energy. Now let's take 2.5kW of that heat energy, push it through this gadget at 40% efficiency to get 1kW electricity out. Push that back into the heat pump and, violà, 1kW of free heat left over! What am I missing?
- syntaxing 5y agoEntropy. You cannot look at a system purely from an energy conservation stand point. Take Carnot efficiency for instance. That’s the extreme case where it teeters on the fully recoverable entropy. For your example, the entropy price has to be paid somewhere in the system (usually in the heat to work ratio).
- audunw 5y ago> What am I missing? Just guessing, but a heat pump that can actually output at least 1900°C of heat? If we had those kinds of heat pumps I guess we'd use them in all kinds of industrial processes
- danans 5y ago> We can have a heat pump with a COP of 3.5 or so. Let's say we put in 1kW of electricity, and take out 3.5kW of heat energy. A heat pump COP of 3.5 or higher or happens only at relatively low delta-T between the source and destination temps of the heat pump [1] - like the delta-T typical for space or water heating. The COP degrades exponentially with increasing delta T as it has to work ever harder to pump heat against an ever higher temperature/pressure (assuming thermal storage with a fixed volume with few losses). The refrigeration cycle can't raise temperatures even hundreds (much less thousands) of degrees C - otherwise we'd already have heat pump stoves and ovens. This is coincidentally also one reason why all else equal, heat pump clothes dryers (which are great) take a bit longer than conventional technologies to dry clothes: they only reach about 50C (vs 70C-75C for standard gas or electric resistance dryers). > Push that back into the heat pump and, violà, 1kW of free heat left over! Because the COP degrades with the delta-T, it bottoms out at 1 (an electrical resistance heater), and in your scenario, you end up with 1kWH in, and 400Wh out, so a theoretically 40% efficient battery. Minus the electrical generation, and at much lower temperatures, your scenario with a heat pump + thermal storage does however describe how the new domestic thermal heat batteries can work with heat pumps [2]. 1. https://www.engineeringtoolbox.com/heat-pump-efficiency-ratings-d_1117.html https://www.engineeringtoolbox.com/heat-pump-efficiency-rati... 2. https://sunamp.com/ https://sunamp.com/
- omgJustTest 5y agoThe Carnot efficiency of a heat engine favors large delta T! This is the theoretical limit of efficiency. For steam turbines this efficiency should be around 60-70%, theoretically. While cool (1,900 to 2,400 degrees C cool) the Carnot effiencies should be closer to 86%. The idea that heat engines get more efficient as you increase delta T has been around for a while. The problem is constructing a delta work extraction loop that doesn't have more losses as a result of the delta T increase, ie the practicalities of extracting work energy. Warning: I am assuming they are working with an approximately room temperature cold side, as article doesn't say. The practicalities of allowing for the delta-t is usually where the efficiency losses are made. source: I am an electrical / chemical engineer.
- lacrosse_tannin 5y agoWhat is it made of?
- synalx 5y agoI love that the article talks about realizing a "decarbonized grid" by storing energy in literal chunks of carbon.
- after_care 5y agoThat's funny wordplay, but atmospheric carbo is clearly the intended implication.
- mwattsun 5y agoSometimes I like to take a step back and imagine a world with nearly free energy. Converting sea water to fresh water to irrigate the deserts is always the first thing that comes to mind, but that's mundane compared to the changes nearly free energy will bring, which is the direction we seem to be heading.
- civilized 5y agoIt will be unimaginable. I truly hope it is closer than I think it is.
- BlueTemplar 5y agoWe would literally boil the Earth in 450 years ! https://dothemath.ucsd.edu/2011/07/galactic-scale-energy/ https://dothemath.ucsd.edu/2011/07/galactic-scale-energy/
- kibwen 5y agoAs long as proof-of-work cryptocurrencies exist, free energy is impossible. Any time the price of energy falls below a certain point, the energy consumption of the network will increase to compensate. PoW is a floor on the price of energy.
- petermcneeley 5y agoKeep in mind that Carnot efficiency at this temperature is nearly 90% https://en.wikipedia.org/wiki/Carnot_cycle https://en.wikipedia.org/wiki/Carnot_cycle 1 - Tc/Th = 1 - 295k/2000k
- SnowHill9902 5y agoYeah but heat losses grow with the 4th power (!).
- klysm 5y agoThat sounds like O(bad)
- BlueTemplar 5y agoYeah, not to mention that these semiconductors are probably not particularly transparent ? (Not counting the photoelectric photons.) And you're going to have to cool them "before" and "after" the light hits the mirror behind them.
- HPsquared 5y agoIt's not really fair to compare this, which takes heat at 2000°C, to a steam turbine that takes heat at say 550°C. A turbine system would have much better efficiency than 40% if its heat was available at that temperature. For example a closed Brayton cycle gas turbine + steam turbine system. Certainly complex and expensive, but could get much better than 40% efficiency.
- lovemenot 5y agoIf a steam turbine could operate at those higher temperatures it would be more efficient. But it cannot do so under any reasonable condition. If you want the higher efficiency from storing high grade heat energy, it's not feasible to use a steam turbine. Think of the steam turbine as a baseline. Like rating a vehicle in horse power.
- cormacrelf 5y agoAlso I wonder if, using similar principles to a heat pump's operation, you could still get juice out of stored heat at lower temperatures. Surely you can have this hot graphite sitting at under 2000°C, heat some fluid/gas to say 1000°C, and then compress the gas to increase its temperature? Surely that would be the ideal solution anyway, since you don't want your hot graphite to become a chunk of useless heat simply for dropping below temp briefly. On the topic of heat pumps, you could also use a TPV for geothermal power. Since there are no moving parts and presumably no huge steam engine installation, it would be more feasible to have one of these in your back yard. The grid powers a heat pump, you compress the fluid till it hits 2000°C, and your TPV extracts power. The heat pump itself is >100% efficient, so overall you can steal a fair bit of electricity from the ground. Right?
- ok_computer 5y agoI just want to point out that compressing gas takes a non-zero amount of work. Compressing gas to increase temperature to use temperature to make energy would be better spent using the compressing work directly to make electricity.
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- bigcat123 5y ago
- jvanderbot 5y agoOK, so perhaps it's not the de-carbonization future we all wanted, but this could be an absolute game changer for planetary exploration, where RTG (nuclear-decay-driven thermal engines) are common. The existing efficiency for those is abysmal, which is actually OK since heat is such a useful product in itself. I'm looking at Dragonfly, specifically, where an RTG provides the electricity and heat to keep everything alive. Imagine what 10x longer flights would do for that mission.
- nautilius 5y agoDo RTG reach the >2170K necessary for this?
- jvanderbot 5y agoApparently not, as someone below pointed out. Oh well, I was briefly excited but there's a big enough gap that it probably won't work as is
- paledot 5y agoBear in mind that, according to TFA, this work is noteworthy specifically because of the high temperature - past work has achieved the same results, albeit with lower efficiency, at lower temperatures.
- perihelions 5y agoApparently not. This 1991 document [0] says the GPHS [1] heat source's iridium cladding has an upper operating temperature limit of 1,300 °C (1,573 K). There's a suggestion this could be safely raised to 1,500 °C. (This is the structural part that contains the Pu-238 fuel; the plutonium itself could be hotter than this, and the thermoelectric junction is much colder). (Note the reason given for this limit is to guarantee that, if this capsule accidentally falls to Earth, the cladding has the mechanical performance to stay intact on impact. If iridium gets too hot, its strength is permanently degraded (so it says). I suspect if you voided this requirement -- if you created a separate of class of spacecraft "no longer capable of impacting earth" -- the limit could be raised much higher). [0, pdf] https://ntrs.nasa.gov/api/citations/19910015359/downloads/19910015359.pdf https://ntrs.nasa.gov/api/citations/19910015359/downloads/19... (2.2 "Temperature Constraints") [1] https://en.wikipedia.org/wiki/GPHS-RTG https://en.wikipedia.org/wiki/GPHS-RTG
- mfrieswyk 5y agoCould something like this directly harvest the heat from a traditional nuclear plant? Or would it degrade from the radiation?
- philipkglass 5y agoThis thermophotovoltaic cell is tuned to operate with radiant energy from a body heated to between 1900 and 2400 degrees Celsius. That is much hotter than any current reactor core. It wouldn't work with a traditional nuclear plant; it would require (at a minimum) developing reactors that operate at a much higher temperature. The most common power reactor design, the pressurized light water reactor, heats water to around 315 degrees Celsius: https://en.wikipedia.org/wiki/Pressurized_water_reactor#Coolant https://en.wikipedia.org/wiki/Pressurized_water_reactor#Cool...
- runeks 5y ago> The most common power reactor design, the pressurized light water reactor, heats water to around 315 degrees Celsius Can’t it just heat something else than water? E.g. something that’s liquid at 2000C?
- worldsayshi 5y agoCould this maybe be used as part of a fusion reactor?
- short_sells_poo 5y agoI think the problem isn't that we can't achieve 2000 degrees with fission, but the entire design would need to be re-thought to handle such temperatures. You need a completely different sort of materials and need to consider new types of risks for a reactor that's supposed to operate at such temperatures.
- aidenn0 5y agoMost semiconductors don't like ionizing radiation. In addition, the bottom-end of the operating range for this (1900C) is well above what google suggests is the typical coolant temperature (300C).
- aidenn0 5y agoTFA says turbines can't operate for heat sources around 2000C. I'd believe they can't operate with steam at 2000C, but can't you decrease the temperature of the steam relative to the heat source by increasing the flow rate?
- caf 5y agoThat reduces your efficiency. The same amount of total heat energy is "worth less" at 500C than at 2000C.
- aidenn0 5y agoBut you can get 36-40% efficiency with a steam turbine in a fossil-fuel plant, and IIRC coal flame temperatures can exceed 1000C (presumably the steam is much cooler; 500C sounds like a reasonable guess; I could only find that nuclear plants have a relatively low steam temperature of around 280C). [edit] Efficiencies of over 40% in steam turbines with temperatures between 500 and 600C from an article in 2002: https://www.power-eng.com/news/new-benchmarks-for-steam-turbine-efficiency/ https://www.power-eng.com/news/new-benchmarks-for-steam-turb...
- gene-h 5y agoThis would be interesting for powering spacecraft because it doesn't have any moving parts. For the most part, spacecraft are not serviced ever, so it's best to minimize things that can break. Nuclear powered spacecraft have been hard to develop because of the need for moving parts. NASA's cancelled Advanced Stirling Radioisotope Generator, which was supposed to be a more efficient radioisotope powered generator than the thermoelectric generators previously used, had trouble because the moving part based generator wasn't very reliable.[0] In addition to eliminating moving parts this is also interesting for nuclear powered spacecraft because it may be possible to pass light through a radiation shield to prevent damage to the converter. The problem is that the reactor would need operate at extremely high temperatures. While this probably isn't high enough to melt the fuel, the fuel might not be structurally stable. Although liquid uranium nuclear rockets are being considered[1]. [0]https://en.wikipedia.org/wiki/Advanced_Stirling_radioisotope_generator#Development https://en.wikipedia.org/wiki/Advanced_Stirling_radioisotope... [1]https://www.uah.edu/news/items/bubble-through-nuclear-engine-might-be-a-future-nasa-workhorse https://www.uah.edu/news/items/bubble-through-nuclear-engine...
- beambot 5y agoI was under the impression that NASA RTGs relied on solid-state Peltier / Seebeck thermocouples that had no moving parts: https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...
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- blamazon 5y agoThose thermocouples are less than 10% efficient, usually less than 5%. This means you have to dissipate more than 10 times more energy as heat than the energy you actually want to use as electricity. Dissipating heat in space is not easy because unlike earth there is no surrounding fluid to dissipate heat into through convection. This means you have to spend precious mass budget on huge (compared to your energy budget) direct heat radiation systems that cannot leverage convection efficiencies. Thus, a significant energy efficiency increase would be a big deal for RTG powered spacecraft design. It is curious that the article above does not consider this. Bonus thought: consider what this lack of convection problem means for "Hyperloop" type vehicle systems that operate in a vacuum tunnel, as most conventional trains dissipate excess braking energy through convection from resistive heating elements atop the roof.
- mrfusion 5y agoWe could drastically shrink coal, and nuclear power plants if we can do away with the steam turbine portion.
- tomxor 5y ago> can generate electricity from a heat source of between 1,900 to 2,400 degrees Celsius [...] plan to incorporate the TPV cell into a grid-scale thermal battery. The system would absorb excess energy from renewable sources such as the sun and store that energy in heavily insulated banks of hot graphite. When the energy is needed, such as on overcast days, TPV cells would convert the heat into electricity, and dispatch the energy to a power grid. Heating graphite based thermal batteries to >1900C using the Sun for long term storage? I'm not sure why the article is refraining from being explicit, but i'm guessing the intended application here is to replace the steam turbine usually found at the centre of high temperature solar thermal collectors. I wonder how feasible and cost effective it is to insulate a battery well enough to maintain over 2000C for multi day periods without substantial loss? The heat storage strategies used for steam turbines doesn't require such high temperatures.
- wrycoder 5y agoI attended a paper given at MIT around 1980 which discussed using photovoltaic cells collecting energy from incandescent graphite in a solar collector. There is not really any advance here. The paper discussed using multiple bandgap stacked PV with backside gold reflectors, as discussed in the linked Nature paper. One of the difficulties is keeping the semiconductors cool. They definitely don't operate at 2000 degrees. One envisions a solar power tower[1] with this technology, but with more graphite mass at the collector. So, not much progress in 40 years. [1] https://en.wikipedia.org/wiki/Solar_power_tower https://en.wikipedia.org/wiki/Solar_power_tower
- jillesvangurp 5y agoIt's not that hard. All you need is a lot of mass surrounded by a good insulator. The heat has nowhere to go and leaks out at a rate controlled by how efficient the insulator is. But only at the surface area of the mass which relative to the volume is quite small. There's a basalt based thermal storage system in the Netherlands that is used for seasonal storage. It's heated up over the summer using solar energy and during the winter they pump water through it for heating. It's Basalt in a metal box surrounded by wool and it stays warm through the winter. The temperatures for this system are much lower (500 degrees) but the principle is about the same. https://materialdistrict.com/article/battery-natural-stone/ https://materialdistrict.com/article/battery-natural-stone/ So, if you can heat the mass to the desired temperature, keeping it there is relatively easy. It would slowly cool over time but not at a rate that is problematic and only very slowly. A large enough system might store heat for months/years.
- usrusr 5y agoIf the stored heat is on the level of getting the emitter into the white-hot, how is the "battery" turned off, to hold the "charge"? The article mentions a mirror layer as part of the cell, for retaining the energy of out of band photons. Would that be the "off" solution, just bounce them back when they are not needed? Cell moved out of the path? Somehow that triggers "too simple to be true" heuristics in me, but on the other hand... yeah, mirrors (or just very white surfaces, precise direction is not needed) can be quite capable of not getting heated by incoming photons, and that must mean bouncing them back.
- karamazov 5y agoYou have a heat reservoir, i.e. a well-insulated and very hot object, that stores energy as heat. If you insulate it with mirrors, that can look like bouncing photons back into the reservoir. When you want to generate energy, you open the insulation and let heat out to hit this chip. It’s like opening an oven door to let some hot air out.
- BlueTemplar 5y agoBut the chips are placed on the gold mirror here - more likely is that they just sit idle until you connect the circuit ?
- pooloo 5y agoDyson sphere, maybe?
- SnowHill9902 5y agoTo everyone in this thread commenting about the Carnot efficiency: yes, the Carnot efficiency grows with T, but you must use a Carnot engine for that! The Carnot theorem is an upper bound not a property of a given engine. It’s trivial to build a heat engine whose real efficiency (measured efficiency / Carnot efficiency) approaches 0.
- waynecochran 5y agoHow long/well can "insulated banks of hot graphite" hold heat?
- Szpadel 5y agoI wonder if there is a way to include some lower temperature variant in eg. car engine to increase efficiency in hybrids
- basicplus2 5y agoIt is incorrect to say a steam turbine is less than 40% efficient as they are in fact up to 50% efficient https://www.linquip.com/blog/steam-turbine-efficiency-complete-explanation/ https://www.linquip.com/blog/steam-turbine-efficiency-comple...
- deleted 5y ago[deleted]
- robbrown451 5y agoIs "engine" the right word for this? I'd call it a generator if anything. I thought an engine took in power and output mechanical energy. I understand there are other kinds of engine, such as a gaming engine etc, but in this context it seems like there are better descriptors. "Heat to electricity converter"?
- wrycoder 5y agoIt's like calling an LED array for space lighting a "light engine". Which they do.
- limaoscarjuliet 5y agoThe title is somewhat overstatement, EPA says turbines have efficiencies up to 90%: "Multistage (moderate to high pressure ratio) steam turbines have thermodynamic efficiencies that vary from 65 percent for very small (under 1,000 kW) units to over 90 percent for large industrial and utility sized units. Small, single stage steam turbines can have efficiencies as low as 40 percent."
- wrycoder 5y agoTypical steam turbines have efficiency up to around 50%. I think the EPA is referring to isentropic efficiency[0], which is "efficiency" compared to the theoretical maximum for the delta T involved. [0] https://en.wikipedia.org/wiki/Steam_turbine#Thermodynamics_of_steam_turbines https://en.wikipedia.org/wiki/Steam_turbine#Thermodynamics_o...
- franciscop 5y agoYes, it's comparing apples to oranges, or the efficiency of the whole steam turbine plant (electricity/fuel) vs just a single component (electricity/heat). Is the comparison fair? Well it's tricky but I'd say yes, the generation of just heat from fuel is normally highly efficient so electricity/heat should be similar to electricity/fuel in the second case. However in a turbine generating plant it's not plain heat but it needs to be converted to steam and moved around, so there are many more loses. That paragraph in [1] is referring to: "Isentropic steam turbine efficiency refers to the ratio of power actually generated from the turbine to what would be generated by a perfect turbine with no internal flowpath losses using steam at the same inlet conditions and discharging to the same downstream pressure." It specifically says not to confuse them: "Turbine efficiency is not to be confused with electrical generating efficiency, which is the ratio of net power generated to total fuel input to the cycle." [1] https://www.epa.gov/sites/default/files/2015-07/documents/catalog_of_chp_technologies_section_4._technology_characterization_-_steam_turbines.pdf https://www.epa.gov/sites/default/files/2015-07/documents/ca...
- stevespang 5y ago
- littlestymaar 5y agoAs others have pointed out, 40% at this temperature isn't really an impressive in itself. Combined cycle power plant have a yield over 60%, while still operating at a much lower temperature. That doesn't means it's useless (it can improve yields for thermodynamic solar) but it means there's a really wide margin of improvement: the theoretical maximum for such temperature is 87%, and if it could be made as effective as a combined cycle[1], you could a yield up to 70-75%. [1] by that I means being as close as a combined cycle from the Carnot cycle at the same temperature.
- iandanforth 5y agoHere's the main Prof going over the full system plan briefly (2019): https://www.youtube.com/watch?v=xwCakHZTejs https://www.youtube.com/watch?v=xwCakHZTejs
- dgb23 5y agoAside: This website is very well made. Snappy, nice design, good discoverability and information architecture. There aren't many web (-designs) I really like. Most of them feel off in some way or another. Another good one would be MDN. Does anyone with design competency know what it is I like about the design? Are there some known principles at hand here that I can learn more about?
- jrwoodruff 5y agoYou might be keying on the absence of any advertising whatsoever. So many media sites are so bogged down by advertising that it would be funny if it wasn't so sad. Beyond that, it does have good fundamental design. Hierarchy of typography is simple and clear, they font used for the article copy is legible and sized nicely. And, because of he lack of advertisements and attempts to pull you further into the site, there's enough white space to give it a more relaxed feeling. If you want to learn the fundamentals of design, pick up the Non-Designers Design Book. Quick read with great explanations of the core principles of good information design.
- dgb23 5y agoThank you for the suggestion. It might be a nice way to start with a book like this.
- wrycoder 5y agoBe sure to get the paperback. The design doesn't carry over into the Kindle version. I found this amusing bio on the Amazon author's page: Robin Williams spent twenty-five years writing computer and design books and was one of the top three best-selling computer book authors in the world. But the world changed and no one bought computer books anymore, so she went to London and formalized her long study of Shakespeare with an M.A. and Ph.D. in Shakespeare studies.