Turning Heat Into Sound Into Electricity 257
WrongSizeGlass writes "Science Daily is reporting on work by physicists at the University of Utah who have developed small devices that turn heat into sound and then into electricity. 'We are converting waste heat to electricity in an efficient, simple way by using sound [...] It is a new source of renewable energy from waste heat.' They report that technology holds promise for changing waste heat into electricity, harnessing solar energy and cooling computers and radars."
But.... (Score:5, Funny)
But does it change waste heat into electricity? I'm not quite sure based on that write-up...
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Cold Fusion (Score:2, Funny)
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Sound to electricity. (Score:5, Funny)
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Wait a minute...
Ack! Stupid Second Law of Thermodynamics.
Heat to Sound to electricity. (Score:5, Funny)
Re:Heat to Sound to electricity. (Score:4, Funny)
Re:Heat to Sound to electricity. (Score:5, Funny)
Re:Heat to Sound to electricity. (Score:5, Funny)
Efficiency as opposed to thermoelectric? (Score:5, Interesting)
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Imagine replacing a car radiator with it?
Re:Efficiency as opposed to thermoelectric? (Score:4, Informative)
It would be interesting to hear all the questions there. I imagine yours will be handled pretty well.
Obviously the conversion to sound can't beat Carnot's Theorem [wikipedia.org], and it says in the article it doesn't start until there's a temperature gradient of at least 90 degrees F. In other words, it's not very efficient.
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It's not clear to me that Carnot's Theorem applies to this technique.
Anybody want to chime in with some insightful comment on this?
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Just another way to adiabatically compress a working gas...
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Carnot's theorem applies to any thermal machine. The actual implementation doesn't matter.
If not, one would break 2nd law by putting a thermal machine feeding a thermal pump.
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Is that true? I thought it only applied to engines that used gas expansion/contraction to extract work from a heat gradient. Are, for instance, thermopiles limited by Carnot's theorem?
If not, one would break 2nd law by putting a thermal machine feeding a thermal pump.
This is demonstrably false. Beating Carnot's theorem does not imply 100 percent (or greater) efficiency. The 2nd law would still be preserved.
Re:Efficiency as opposed to thermoelectric? (Score:5, Informative)
Let's say you have a heat reservoir (e.g. a coal fire) and a cold reservoir (e.g. a cooling tower). You could just let the heat from the hot reservoir flow to the cold reservoir with nothing else happening. You could also set up a steam engine so that the flow of heat from the hot reservoir to the cold reservoir caused some of the heat to be "converted" to mechanical energy (or electrical energy or something equivalent). Now, ideally you would want as little heat as possible to flow between the reservoirs with as much heat as possible being converted to mechanical energy. Carnot's Theorem places an upper limit on how "efficient" this process can be. Basically, the smaller the difference in temperature between the two reservoirs the more heat will flow between the reservoirs and the less heat will be converted to mechanical energy.
Let's now consider a different scenario. Suppose you have some mechnical energy (e.g. some electricity) and you want to create a temperature difference between two heat reservoirs (e.g. you want to air condition your apartment). In this case, you want to do as little work as possible (keep the electric bill low) while moving as much heat from the cooler reservoir up to the hotter reservoir (moving the heat out of your apartment). Basically, you want to minimize the "conversion" of mechanical work to heat while maximizing the flow of heat between the reservoirs. Carnot's Theorem also applies here. You have to do less work to move heat between reservoirs that are at almost the same temperature and you have to do more work to move heat between reservoirs that are at very different temperatures.
For the second part of Carnot's Theorem, imagine that you found one (reversible) process where there was a lot of heat flow between the reservoirs for a given amount heat-work conversion and another (reversible) process where there was very little heat flow for a given amount of heat-work conversion - assuming the same temperature difference between heat reservoirs for both processes. You could hook these two processes together and have a perpetual motion machine of the second kind.
To put it another way, if you could find either an air conditioner or a power plant that was not limited by the Carnot Theorem then you could use your air conditioner to generate the temperature difference to run your power plant and you could use the electricity from your power plant to run your air conditioner all while having electricity left over to power your television (i.e. you'd get free energy from your power plant - no more having to burn coal).
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The "proof" of Carnot's Theorem actually has two parts. First, for the case of heat engines based on compressing ideal gasses, one calculates how much heat has to flow between two different reservoirs in order to do a certain amount of useful work (i.e. the "efficiency"). Second, one shows that if any other heat engine ever had a different "efficiency" then one would be able to construct a perpetual motion device of the second kind.
The argu
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Never mind the hair splitting over "efficiency." How about the absurdity of using the word "renewable?" Where is the heat coming from? Is THAT source of energy renewable (meaning, something that grows back or becomes re-available after it's been used, with less energy required to make it that way than you get out of it? It's maddening to see presumably technical discussions about something as important as energy and its practical applications...
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I caught that too, but really it would not be advised to explain where this "free" electricity comes from to someone writing an article like that.
That said, everyone is focused on using these for waste heat conversion which is great and may improve the efficency of many of our electrical and mechanical systems (including power generation systems), but the other use for this would be harnessing solar power which could be pretty cool if it significantly beats the efficiency of photo voltaic cells.
Heat is renewable (Score:2)
Re:Efficiency as opposed to thermoelectric? (Score:4, Insightful)
Wow, you woke up in a pedantic mood this morning...
We call "renewable" energy a form of energy that we're not exhausting by using up. Harvesting solar energy today won't make less sun energy available tomorrow. The sun will not expire faster if we use its energy to produce electricity. Hydro is the same. Water will flow from the top of the mountain to the bottom whether we build a dam or not, so while we are harvesting the water's potential energy, we are not the cause of its exhaustion (gravity is, damn you gravity!).
When you do something "from scratch", do you start by creating a whole universe from a Big Bang instead of using what's already there (thus, not starting really from scratch)? People do stuff from scratch without creating universes, and the sun provides renewable energy.
Words have accepted meanings, and that is how we communicate. Agreed upon meanings are usually recorded in big books we call dictionaries. You should get one, they're really good.
May I recommend The American Heritage® Dictionary of the English Language, Fourth Edition, which defines renewable as :
Or maybe you would prefer WordNet® 3.0© 2006 Princeton University
Here's a last one from The American Heritage® Science Dictionary
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Why not call gravity-powered electricity generation (say, the Hoover Dam) just that: gravity-powered. That means something, especially if you mention the hydro part of it in conjunction. As opposed to "tidal power" (also hydro, but a different beast).
It's not pedantic, though, to mention that there is NOTHING "r
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Refer to Wittgenstein; meaning is use, and renewable is used to mean the definition that has been explained to you. I can imagine the scene at Bletchley park, now:
"But these encrypted messages are just a bunch of characters! They don't mean anything!"
Mea
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Right! So, consider my post and this thread to be an attempt to encourage people to use that word (and the others that are thus required) in a more meaningful way. If a single word is used to represent lots of substantially different things (in this case, "renewable" interchangeably meaning the same thing when referring to a marginally better way to burn
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I understand what you're saying, but if you want to play the "strict definition" game, you have to play it all the way. How can you possibly refer to "the cognitive battle" while demanding such restrictions on the use of language? Where are the weapons? Where is the blood? There are none, of course. Somehow, everyone
Current thermopiles are pretty low efficiency. (Score:4, Informative)
Current thermopiles are pretty inefficient. The main problem is that they unavoidably leak heat from the hot to the cold side. In peltier cells (the ones in those cheap "coolers" and CPU heatsinks) leak several times as much heat as they make use of when running as generators (and leak most of the heat they pump, so they have to pump it several times to get it dumped). There's a more efficient one in the labs, which doesn't have a lot of charge (and thus heat) carriers in the hot/cold bridge. But it's still far from perfect.
They also have to operate at temperatures that don't destroy their materials - typically semiconductors. That limits how hot the hot end can get, and thus how much energy you can get out of the heat (since they can't break the carnot cycle rules).
These devices are gas-working-fluid heat engines, with the gas (and the piezo power takeoff) as the only moving part(s). In principle the gas "prime mover" should be able to approach carnot cycle efficiency (which is as good as you CAN get) - and that's what this group is trying for. Being made of gas and metal, the "hot end" can get very hot, too, so you aren't as limited as with semiconductor heat converteres. Meanwhile, piezos are extremely efficient as well - and some (like quartz) can also handle very high temperatures.
As simple mechanical systems they should also be easier to fabricate than semiconductors, making them a garage-shop item that doesn't require your garage to be a clean-room in silicon valley with 100 megabux of specialized equipment.
Re:Efficiency as opposed to thermoelectric? (Score:5, Funny)
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Music that is nonsensical is considered "Brilliantly Artistic". Science that is nonsensical isn't - mostly it's useless.
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Can it really be this good? (Score:4, Interesting)
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Ac coils need to shed that heat fast, even faster when the ambient temperature is up there like 100degF (I hope you mean 100F and not 100C) This process relies on a wider temperature differential and not shedding it fast.
so it will not work in most places where waste heat energy recovery would be a benefit.
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Massive /. potential (Score:4, Funny)
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...or something like that I once heard at a punk show.
Cool idea! (Score:4, Funny)
Um, maybe I should stop now.
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No efficiency ratings (Score:5, Insightful)
With double conversions it couldn't be much.
Why not convert heat into electricity DIRECTLY using a peltier device?
(aka Seebeck effect http://en.wikipedia.org/wiki/Thermoelectric_effec
Re:No efficiency ratings (Score:5, Insightful)
Because peltier junctions are themselves horribly inefficient?
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Layne
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I wonder if it would be as efficient with less moving parts?
Picture a thousand mirrors, creating a 500 degree hot spot (~400 degree difference) which creates a monster sound that creates a lot of electricity. Would the sound at that intensity destroy the converting object?
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It has long occurred to me that (chemical energy released) = (kinetic energy produced in engine) + (heat produced), under the law of conservation of energy, and that (initial momentum) = (momentum of moving components) + (momentum of particles) under the law of conservation of momentum. This means that the system as a whole m
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This is a small gas turbine engine (you forgot that engine type) combined with a CVT transmission. I believe Volvo has been looking into the exact idea you are thinking of. It died in the early 90's, but as an idea it has always sounded pretty good to me too..
I wonder (Score:2, Interesting)
Maxwell's Daemon Rides Again? (Score:5, Informative)
Why bother?
[1] Thermodynamics, not Robotics
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I'm really not interested in running my CPU at 100C so that the heat recovery efficiency goes from 3% to 19%, thank you.
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You measure the heat difference between the hot side and the cold side of the transfer. In the case of a CPU, between the CPU and ambient.
For more, you really need to understand the Second Law of Thermodynamics and Carnot engines. [wikipedia.org]
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Yes, but unless you start VIOLATING laws of thermodynamics, converting heat to electricity actually removes heat from the system. That means (as was mentioned) that you basically replace the heat sink and fan on the CPU with the heat-to-sound-to-electricity conversion device. The net effect (as far as your CPU is concerned) is that the temperature is maintained at somew
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And if all I had was a totally passive system, I
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Right... so instead of having a light fan noise coming from my box, I should put amounts to be a whistle on the CPU... that'll help!
Depends how you define waste (Score:2)
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Link to main site. (Score:3, Informative)
Good for comps (Score:4, Insightful)
Use in autos? (Score:3, Funny)
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Layne
to heck with "waste" heat... (Score:2)
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Yes, but can you imagine the environmental effects caused by cooling a volcano at "Faster-Than-Nature-Indended" rate?
The e
Dog Whistle (Score:5, Funny)
Ooh, on the other hand, maybe we could get the sound into the frequency range at which various crystal wine glasses shatter... I've got some asshole neighbors who could do without those particular bits of glasswear.
I bet it could do infrasound too (Score:2)
Diaphragms? (Score:5, Interesting)
cooling computers? (Score:3, Insightful)
Hype - Second Law has not been repealed. (Score:2)
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Well, where I live most electricity is generated as follows:
1. Energy stored in coal->heat energy through combustion
2. Heat energy->mechanical energy through use of steam to drive a turbine
3. mechanical energy->electrical energy through the use of a generator attached to the steam turbine
There is also natural gas, which simply takes the place of coal and uses the same number of energy conversions, and nuclear power, in which step one is simply changed t
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All the Second Law tells you is that no stage of conversion can be 100% efficient. It does not say that any particular conversion path is more or less effic
Interesting but low on power production? (Score:2)
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Slow down everyone (Score:2)
I'm just sayin' . . .
In Related News... (Score:2)
Less heat is good... (Score:3, Funny)
amount of electricity per heat unit? (Score:2)
Just a little prob with the numbers.... (Score:5, Insightful)
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How much acoustic power did you generate? Well a loud whistle is about 100dbA, about a hundredth of a watt.
From the article:
When heated, the device generated sound at 120 decibels -- the level produced by a siren or a rock concert.
Assumming many devices can be put to work in parallel, it might not be a wild goose chase after all. Just imagine how much waste heat ALREADY GENERATED (i.e. in car engines) could be reused into electricity. That would make your car more energy-efficient, since you wouldn
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Well whoopee-ding.
So they get one watt of sound power.
Now how many watts of heat did it take to generate that one acoustic watt? Deponent sayeth not.
General Carnot principles suggest a whole spitload of watts.
In general converting random motion, the lowest quality of energy, into periodic sound waves, a MUCH higher quality of energy, never happens by chance or with any notable effici
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Well, given that the USA is spending about $10 million an hour on the war in Iraq and considering that the USA's interest in the Middle East is mostly about energy (specifically oil), I'd have to conclude that solving the USA's energy problems is rather important.
Compared to the cost of the Iraq war, $2 million for some obscure research into energy technology doesn't sound too bad.
This ars article might be something similar? (Score:2, Informative)
http://arstechnica.com/news.ars/post/20070527-new
this thing also uses thermoacoustic technology.
Free energy via the folks at University of Utah? (Score:2)
Seems easier to just put the sound > em units on every street corner in every major city.
And strapped to every 4 year old.
Why not use a solid-state Pelier instead? (Score:2, Interesting)
Prime Real Estate (Score:2)
Now we only have to install two in the US. One in the Capital Building (where Congress meets), and the White House (where Bush lives). All the hot air and excess sound should surely power the US for years to come.
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I've always wanted to try using the thermal dissipation of the processor to power its own cooling system. That is, create a pressurized case, and have an intake compressor that brings in cool air, which is heated by the processor(s), which is then sent out through a power-tapping device (turbine or piston) to power the compressor and keep things going.
Basically a Brayton-cycle cooling system. You could actually move a lot of air with 300W power dissipation! (way more than you can with a little 15 W cooling
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- Petaris
"The World is Open. Are You?"
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Don't we already have those? Most cars that I see parked on the street require some sort of secret key in order to operate properly, and it seems to be a crime to try and start the engine by circumventing the need for a key...
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