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Power Science

Turning Heat Into Sound Into Electricity 257

Posted by ScuttleMonkey from the sounds-like-a-hot-idea dept.
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."
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Turning Heat Into Sound Into Electricity More

Turning Heat Into Sound Into Electricity

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  • But.... (Score:5, Funny)

    by a.phoenicis ( 1026040 ) on Monday June 04, 2007 @01:44PM (#19384345)

    But does it change waste heat into electricity? I'm not quite sure based on that write-up...

  • Sound to electricity. (Score:5, Funny)

    by snowraver1 ( 1052510 ) on Monday June 04, 2007 @01:45PM (#19384355)
    Now they need to refine this to 100% effiecency and attach one to my wife.

  • Efficiency as opposed to thermoelectric? (Score:5, Interesting)

    by Anonymous Coward on Monday June 04, 2007 @01:45PM (#19384359)
    I just skimmed the article, but I didn't see mention of the efficiency of this process. What are the advantages to converting the heat to sound first, rather than directly to electricity via thermoelectric processes?

    • Re: (Score:3, Insightful)

      by LWATCDR ( 28044 )
      I think cost is more important the efficiency. If it was cheap enough and if you could say get 10% out of it it could be very useful.
      Imagine replacing a car radiator with it?

    • Re:Efficiency as opposed to thermoelectric? (Score:4, Informative)

      by dch24 ( 904899 ) on Monday June 04, 2007 @02:16PM (#19384833) Journal
      You want to read the Original Article [utah.edu]. Although the link above is almost an exact copy, there's some interesting stuff at the bottom of the original:

      Physicist Orest Symko's graduate students will present their studies during an Acoustical Society of America technical session from 8 a.m. to 10:05 a.m. MDT Friday, June 8 in Parlor B of the Hilton Salt Lake City Center hotel, 255 S. West Temple.
      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.

      • Re: (Score:3, Interesting)

        by Dan Ost ( 415913 )
        Carnot's Theorem applies to heat engines that use a gas to do work.

        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?
        • What do you thing that sound is?

          Just another way to adiabatically compress a working gas...

        • 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.

          • Re: (Score:2)

            by Dan Ost ( 415913 )
            Carnot's theorem applies to any thermal machine. The actual implementation doesn't matter.

            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)

              by wsherman ( 154283 ) * on Monday June 04, 2007 @06:05PM (#19387995)

              This is demonstrably false. Beating Carnot's theorem does not imply 100 percent (or greater) efficiency. The 2nd law would still be preserved.

              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).

        • Carnot's Theorem applies to heat engines that use a gas to do work.

          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

    • Re: (Score:2, Insightful)

      by ScentCone ( 795499 )
      but I didn't see mention of the efficiency of this process

      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...

      • Re: (Score:2)

        by Altus ( 1034 )

        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.
      • The sun produces heat. If solar and biodiesal are considered renewable, so should this.

      • Re:Efficiency as opposed to thermoelectric? (Score:4, Insightful)

        by Phisbut ( 761268 ) on Monday June 04, 2007 @03:56PM (#19386201)

        Never mind the hair splitting over "efficiency." How about the absurdity of using the word "renewable?"

        Wow, you woke up in a pedantic mood this morning...

        Solar energy isn't renewable... it's continually available from the sun. [...] Wind isn't renewable - it's just generally, mostly available...

        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.

        Taking the meaning away from words dumbs all communication down, and erodes our culture's ability to do intellectually challenging things.

        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 :

        Relating to or being a commodity or resource, such as solar energy or firewood, that is inexhaustible or replaceable by new growth.

        Or maybe you would prefer WordNet® 3.0© 2006 Princeton University

        capable of being renewed; replaceable; "renewable energy such as solar energy is theoretically inexhaustible"

        Here's a last one from The American Heritage® Science Dictionary

        Relating to a natural resource, such as solar energy, water, or wood, that is never used up or that can be replaced by new growth. Resources that are dependent on regrowth can sometimes be depleted beyond the point of renewability, as when the deforestation of land leads to desertification or when a commercially valuable species is harvested to extinction. Pollution can also make a renewable resource such as water unusable in a particular location.

        • I would argue that the definitions you've cited are just examples of the cognitive battle already having been lost on this one. It doesn't make the word any more precise or actually meaningful.

          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

          • Re: (Score:3, Interesting)

            by It'sYerMam ( 762418 )

            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).

            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

            • Re: (Score:3, Interesting)

              by ScentCone ( 795499 )
              Meaning is determined not by what one person thinks - not even by what the dictionary says - it is determined by how it is used in a particular context.

              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

          • I would argue that the definitions you've cited are just examples of the cognitive battle already having been lost on this one. It doesn't make the word any more precise or actually meaningful.

            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)

      by Ungrounded Lightning ( 62228 ) on Monday June 04, 2007 @04:07PM (#19386337) Journal
      What are the advantages to converting the heat to sound first, rather than directly to electricity via thermoelectric processes?

      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.

  • Can it really be this good? (Score:4, Interesting)

    by Nom du Keyboard ( 633989 ) on Monday June 04, 2007 @01:46PM (#19384381)
    This would seem to say that I can take waste heat from my A/C heat-exchangers making them more efficient, and create electricity to drive said system and fans in the process. Given that it's about 100 degrees outside at this moment, this would be sweet!

    • Re: (Score:3, Informative)

      by Lumpy ( 12016 )
      you need a significant heat differential as well as the fact that AC needs fast dissipation to work.

      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.

      • Re: (Score:2, Interesting)

        by Steendor ( 917855 )
        Maybe it wouldn't work very well in the A/C, but I bet it could be used externally. For a while, my parents had a large thru-wall unit exhausting into an enclosed space, and that space got very warm.

  • Massive /. potential (Score:4, Funny)

    by u-bend ( 1095729 ) on Monday June 04, 2007 @01:48PM (#19384405) Homepage Journal
    There's so much waste heat here (Star Wars, Linux, browser, KDE/Gnome debates), that we could power a city and rock out at the same time.

    • that we could power a city and rock out at the same time.
      Yeah!! Rock out with our overclocks out!

      ...or something like that I once heard at a punk show.

  • Cool idea! (Score:4, Funny)

    by thewiz ( 24994 ) * on Monday June 04, 2007 @01:49PM (#19384417)
    Er, hot idea!

    Um, maybe I should stop now.

  • No efficiency ratings (Score:5, Insightful)

    by denis-The-menace ( 471988 ) on Monday June 04, 2007 @01:49PM (#19384419)
    How efficient is it?

    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_effect [wikipedia.org])

    • Re:No efficiency ratings (Score:5, Insightful)

      by drinkypoo ( 153816 ) <drink@hyperlogos.org> on Monday June 04, 2007 @01:59PM (#19384589) Homepage Journal

      Why not convert heat into electricity DIRECTLY using a peltier device?

      Because peltier junctions are themselves horribly inefficient?

    • Well theoritically, this could be better. If the efficiency of converting from heat to sound was 80%, and the efficiency of converting from sound to electricity was 80%, then it would be more efficient than a thermoelectric device that was only %50 efficient. It doesn't matter how many processes you go through, it's how efficient those processes are. For instance, you can use solar panels to create electricity. And some have an efficiency of somewhere around %5. Now you could also use Coal power to crea

      • Re: (Score:2)

        by SQLGuru ( 980662 )
        Why not take some of these "heat to sound to electricity" tubes and put the solar concentrators on that instead of on the solar cells? Or better yet, use the cells to get their 5%, then use the remaining "95%" heat to drive the tubes......

        Layne
        • This is an interesting idea relative to Stirling engines.

          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?

      • Re: (Score:2)

        by ArwynH ( 883499 )
        I won't argue that theoretically it is possible for a process with more stages to be more efficient than one with less stages, but practically that is rarely the case. Take your example for instance, where you are comparing apples to pears. A more accurate comparison of the efficiency of the generation of electricity from the sun would take into account the fact that coal is produced over 1000s of years from plant life, which in turn obtained it's energy via photosynthesis from the sun. As such I suspect th
    • Also, I believe that part of what they are going for here is the cooling effect provided by the heat engine. While a Thermoelectric effect provides electricity, it doesn't do so as part of a heat sink. Also, I think the "renewable" reference refers to the fact that this could potentially replace solar electric cells, to convert solar energy into electricity, if they can make it efficient enough or cheap enough.

  • I wonder (Score:2, Interesting)

    by Normal Dan ( 1053064 )
    If it could be used to practically and economically extract the rest of the energy from nuclear waste, which still produces quite a bit of heat. 'Free' power for thousands of years.

  • Maxwell's Daemon Rides Again? (Score:5, Informative)

    by overshoot ( 39700 ) on Monday June 04, 2007 @01:50PM (#19384441)
    Unless they're claiming to have found a way around the Second Law, the efficiency of any such conversion is going to utterly suck. My CPUs run less than 10C above ambient, so the absolute Carnot limit on any converter recovering that heat is going to be about 3%.

    Why bother?

    [1] Thermodynamics, not Robotics

    • Re: (Score:2)

      by swilver ( 617741 )
      Your CPU's run at less than 10C above ambient because it has a huge cooler sitting on top -- the CPU may be cool, but only bacause a lot of heat is extracted from it and pumped out of the system.

      • Your CPU's run at less than 10C above ambient because it has a huge cooler sitting on top -- the CPU may be cool, but only bacause a lot of heat is extracted from it and pumped out of the system.
        That's kind of the idea, no?

        I'm really not interested in running my CPU at 100C so that the heat recovery efficiency goes from 3% to 19%, thank you.

        • Re: (Score:2, Informative)

          by byron036 ( 178130 )
          If the device extracts energy, then the temperature of your CPU will be lowered. Thus replacing the heatsink.

        • Re: (Score:2)

          by spun ( 1352 )
          Yes, but you don't measure the heat difference AFTER the heat has been removed! The Carnot efficiency depends on the heat differential BEFORE the heat has been pumped, yes?

          • Yes, but you don't measure the heat difference AFTER the heat has been removed! The Carnot efficiency depends on the heat differential BEFORE the heat has been pumped, yes?

            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]

            • 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.

              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

              • 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 somewhere around 10C above ambient and instead of spreading the additional 90C worth of heat (assuming that your processor would hit 100C without heat sink) into the surrounding air, you're using it to generate electricity.

                And if all I had was a totally passive system, I

    • Even if the efficiency is low, it still might pay off to potentially eliminate the need for a fan, no? Your point is well taken, however. This isn't going to save us from our fossil fuel overlords, merely help reduce power use (or increase generation) on the margins.

      • Re: (Score:2)

        by Phisbut ( 761268 )

        Even if the efficiency is low, it still might pay off to potentially eliminate the need for a fan, no?

        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!

    • I believe the key point about the device is the lack of moving parts. A steam turbine for instance has a shit load of highly expensive moving parts to make it work.

       

  • Link to main site. (Score:3, Informative)

    by Anonymous Coward on Monday June 04, 2007 @01:50PM (#19384445)
    http://www.physics.utah.edu/~woolf/acoustics/ [utah.edu]

  • Good for comps (Score:4, Insightful)

    by eebra82 ( 907996 ) on Monday June 04, 2007 @01:51PM (#19384457) Homepage
    I realize this could be a great thing for computers - especially portable computers. However, I am more interested in how large portion of the heat that turns into sound and eventually into electricity. My stationary computer is fine without all that extra power. What I want is to know if this will kill the need for huge fans and actually remove some of the heat, or if it will just suck a small portion of it.

  • Use in autos? (Score:3, Funny)

    by evildarkdeathclicheo ( 978593 ) on Monday June 04, 2007 @01:51PM (#19384467)
    Since the internal combustion engine is really a noisy heat pump, wouldn't this be of use in hybrids, or perhaps as an alternative alternator? (alternatator? alternatatoe?) Perhaps in the cubicle farms of tomorrow, we'll all be sitting on these heat-powered piezo tubes and fed a diet of beans to power our own workstations.

    • Re: (Score:2)

      by SQLGuru ( 980662 )
      If you put these things in the cubes of the sales force, you'd get a lot of hot air *AND* sound.......you could power the whole world. And then there's always the fertilizer/bio-fuel that is coming out of their mouths.

      Layne
  • if they can actually do this, then set up massive arrays of it on top of active volcanoes and other natural heat sources. As the claim is they end up with electricity, that means there is less heat, and we have this maybe/maybe not global warming thing going on. Seems we can reduce a lot of the natural warming of the earth's atmosphere with something that can do this, if it really can...

    • Re: (Score:3, Funny)

      by woolio ( 927141 )
      if they can actually do this, then set up massive arrays of it on top of active volcanoes and other natural heat sources. As the claim is they end up with electricity, that means there is less heat, and we have this maybe/maybe not global warming thing going on. Seems we can reduce a lot of the natural warming of the earth's atmosphere with something that can do this, if it really can...

      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)

    by Apocalypse111 ( 597674 ) on Monday June 04, 2007 @01:55PM (#19384535) Journal

    Symko says the devices won't create noise pollution. First, as smaller devices are developed, they will convert heat to ultrasonic frequencies people cannot hear.
    So now we've turned my car into a mobile dog-whistle, causing even the well-behaved dogs to bark at me.

    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.

  • Diaphragms? (Score:5, Interesting)

    by bigattichouse ( 527527 ) on Monday June 04, 2007 @01:55PM (#19384537) Homepage
    would it be possible to do something with a speaker? (as an experiment). I understand TFA about the piezeo devices being compressed/released by the plates vibrating like a flute, but I started wondering about the image that immediately popped into my head, of tuned diaphragms responding to air pressure differences to vibrate a coil... I guess if you did the flute thing, you could just put a piezo crystal between a tuning fork and a solid surface... every note at that frequency, especially if sustained, would then make power.... So, how about making great huge "moaning towers" out in the middle of nowhere that do the same thing? I'll call it "BULLROAR"(tm) technology. Hell.. I wonder if the forces involved on a bullroar spinning aroud your head might generate power (say, with a couterweight like thos rechargable watches). This idea is kinda fun.

  • cooling computers? (Score:3, Insightful)

    by gEvil (beta) ( 945888 ) on Monday June 04, 2007 @01:59PM (#19384581)
    I'm not sure about you, but when I spec parts for computer cooling, I'm looking for something that's cool AND quiet. I don't want whatever device to be creating extra sound in it's quest to cool more efficiently.
  • More stages of energy conversion = more waste. That is all.
    • More stages of energy conversion = more waste.

      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
    • Shesh. I was afraid I would never find an article touching the second law in this discussion. C'mon. In easy terms: You can't win! If you want to use waste heat, you need to cool something else in order to heat it up again with that same waste heat. This costs you energy that you need to take from somewhere. Even if you would use part of that waste heat, efficiency would go by the board. You cannot turn heat completely into mechanical energy (sound) your efficiency drops well below 100%. If you turn sound i
    • Uh unless you can take advantage of more efficient conversions resulting in an overall reduction in waste of course. You know, if the efficiency of heat->sound times sound->electricity is more efficient than heat->electricity, then you win. A single conversion of 1% efficiency is worse than a hundred consecutive conversions of 99% efficiency.

      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
  • AFAICT the "power" production is related to the fact that they have created a way to get vibration from a temperature rise at a given "resonant" frequency in a tube. Cool but there still has to be a heat rise -- and the power out is limited by the Carnot law to 1-(Temp Low/Temp High) in absolute temp units. So with a 90 degree fahrenheit heat rise, for example, the maximum efficiency (using room temp as t low) of about 14% -- the actual output is probably lower. Or about the same as current generation
    • Don't necessarily discount solar sources. Solar can produce quite a bit of heat, and being able to produce power from a 500-700F element could feasibly produce 30-40% efficient devices if the acoustic conversion is highly efficient. One poster mentioned poor output, with high voltages and small current, but a parallel set of such devices might deliver a net current that is into the useful range. Even 30% of 1200W/m is a nice return. I suppose it depends on the longevity of the components at higher temps an
  • This is from the same institution that brought you cold fusion (not the markup language) a few years back.

    I'm just sayin' . . .
  • Sources in Washington DC claim to have found a way to power 73% of the nation's capitol while nearly completely reducing the greenhouse emissions from the capitol building. Within a few years, planners expect this new energy source to power the entire city as well as the capacity to sell energy to surrounding areas.

  • Less heat is good... (Score:3, Funny)

    by FlyByPC ( 841016 ) on Monday June 04, 2007 @02:13PM (#19384793) Homepage
    ...as long as the sound-conversion part doesn't leak too much. My workstation already sounds like a jet engine.
  • It doesn't indicate what amounts of electricity could be retrieved, from what I read, but it almost wouldn't matter if it was cheap enough to build. You could blanket death valley with these things, and at least on summer days generate enough electricity to offset grid saturation by excess a/c units in some large area (hopefully large enough to justify the cost).

  • Just a little prob with the numbers.... (Score:5, Insightful)

    by Ancient_Hacker ( 751168 ) on Monday June 04, 2007 @02:18PM (#19384869)
    Nothing to see here. It's just a Prof that's spent $2 million on a wild goose chase. Now with the great smell of fish! The rub is multi-fold:
    • Good old Carnot's law. The efficiency is limited by the temperature drop across the device compared to the absolute temperature. Now take two thermometers, stick one up your butt and fart. compute the temperature difference. Divide by 483. That's your efficiency in converting heated gas into sound. Prolly about 0.005% as a rough approx.
    • For a less gross example, pucker your lips and blow. Do this for five minutes or until you pass out. You probably feel warm-- that's the heat. How much acoustic power did you generate? Well a loud whistle is about 100dbA, about a hundredth of a watt. Efficiency, 0.004% at best.
    • Piezoelectic efficiency. Well, it's really high-- for an acoustic transducer. The Interwebs seem to reveal no figures for this, and in general a high level of coyness is a way of hiding embarrasing numbers. Let's assume a best-case number of say 40%.
    • The impedances. Crystals are very high impedance devices, putting out LOTS of volts at vanishingly small amps, which is bad news for us, as most of our power sinks are low impedance. Getting a few milliamps at 40KV is not very compatible with powering your laptop, which is about a million times lower in impedance. It's particularly inconcvenient converting tens of kilovolts downwards with economy and efficiency.
    So sorry, probably much less than nothing to see here, just another bundle of our taxpayer's money spent on a totally pointless technical exercise.
    • You said:

      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
      • >When heated, the device generated sound at 120 decibels -- the level produced by a siren or a rock concert.

        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

    • Re: (Score:2, Informative)

      by jbeaupre ( 752124 )
      Just read about piezo efficiency the other day. 60% is pretty common for polycrystalline. 90+% for single crystal. I'll hunt down the link if you're dieing to read about it yourself.

    • It's just a Prof that's spent $2 million on a wild goose chase.

      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.

      Good old Carnot's law. The efficiency is limited by the temperat

  • I was trying to figure out where I had seen something like this recently:

    http://arstechnica.com/news.ars/post/20070527-new- stove-generator-refrigerator-combo-aimed-at-develo ping-nations.html [arstechnica.com]

    this thing also uses thermoacoustic technology.
  • Pardon my skepticism.

    Seems easier to just put the sound > em units on every street corner in every major city.

    And strapped to every 4 year old.

  • Some Slashdotters have doubtless use Peltier devices to try to chill their massively overclocked PCs, but that's only one application of them: they can also be used in reverse to generate electricity from a thermal differential. I don't know how the efficiency would compare to this - an actual efficiency wasn't mentioned in TFA and I've never used a Peltier in this fashion - but I suspect it might be comparable. There's also the absence of moving parts to consider, too.

  • 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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