Forgot your password?
typodupeerror
Science Technology

Waste Heat to Electricity? 330

Posted by michael
from the negative-entropy dept.
Darwin_Frog writes: "Recent advances in thermionics at MIT lets waste heat generate electricity, thus pushing entropy one step further down the chain. These devices work at a temperature around 250 deg. C, instead of around 1000, so cars can augment the alternator by using the waste heat in the exhaust system to produce power for onboard electronics and A/C."
This discussion has been archived. No new comments can be posted.

Waste Heat to Electricity?

Comments Filter:
  • by King of Caffiene (517266) <CmdrTaco.aol@com> on Saturday December 01, 2001 @09:54PM (#2642719) Homepage
    soon they'll be able to use excess heat from humans...matrix style.
  • Hmmm... (Score:4, Interesting)

    by caseydk (203763) on Saturday December 01, 2001 @09:58PM (#2642728) Homepage Journal
    I think it might make the EPA happy if companies had these in their smokestacks... maybe reduce their power draw a bit...

    less power required= less pollution

    • by victim (30647) on Sunday December 02, 2001 @01:26AM (#2643080)
      Sapping heat from the smokestack contents will probably cause it to not work correctly.

      The goal of a smokestack is to get the harmful exhaust away from the ground long enough that it disperses sufficiently before touching down.

      This is done with convection. The hot gas in the tall stack creates the draw that powers it and blows the plume up after it leaves the stack, the hot plume continues to lift itself until it bleeds off too much heat, then it starts coming back down, but presumably dispersed enough to not be too noxious.

      The smoke stack was designed with a known gas temperature and dispersal requirement and a desire to minimize masonry. If you take away heat from the gas you will reduce your plume altitude and cause it to come down in a more concentrated region.

      I doubt you can use the thermo-generated electricty to run blowers to compensate. The `no free lunch' law of thermodynamics will probably forbid that. (Unless blowers are much more efficient than convection.)

      Now, if you are just bleeding off waste steam then it would work, but most of the energy in steam is the expansion from water to steam, there is relatively little left in the puffy clouds.

      Mostly unrelated note: I used to live in Pittsburg in a community where all the houses were required to have slate roofs, stone or brick exteriors and no wood trim. Even the window frames were metal. It was a fire-proof community from the days when the steel mills spewed lots of solids including hot cinders. The plume was powerful enough to carry those large distances fast enough that they were still hot enough to start a fire.
    • Re:Hmmm... (Score:3, Interesting)

      by Knobby (71829)

      Agreed!

      Now, for all the naysayers and trolls out there who can't see how this could possibly work I want you to stop and think for a second!!.. You're not going to glue these things onto the outside of your stock exhaust system. You're going to design a new exhaust system that incorporates this technology AND hopefully optimizes the waste heat recovery without increasing the accoustic and chemical emmissions or reducing performance. How would that be done?

      Well you want to begin by increasing the surface roughness on the inside of the exhaust piping to increase the surface area and thin the boundary layer which will increase the convective heat transfer coefficient. Okay, so now we have a heat exchanger that should remove heat from the exhaust stream at a greater rate than previously, however, the penalty for this is an increased pressure drop and a non-optimal inlet temperature for the catalytic converter. So, you reduce the length of the piping prior to the catalytic converter and possible increase the diameter of the piping.. Better yet, because the typical catalytic converter sold by Corning produces a huge pressure drop, why not design a nice smooth diffuser with some internal fins that trades the separation induced pressure drop developed within Corning's catalytic converter for one that results in improved heat recovery.. The point to all this is that there are a lot of design changes that will probably need to be made, but there's no reason why recoverying waste heat to improve efficiency should be considered impossible or even difficult.. Given a particular TEG, the design optimization problem is something a senior mechanical engineering student should be able to sort out in a week or two..

  • by Iamthefallen (523816) <Gmail name: Iamthefallen> on Saturday December 01, 2001 @10:04PM (#2642736) Homepage Journal
    Introducing Athlon XP 5000 - Now self powered!
  • by SysKoll (48967) on Saturday December 01, 2001 @10:04PM (#2642739)

    According to the article, this "breakthrough" is a reverse Peltier junction with about twice the efficiency of current semiconductor thermoconverters. Nice, but nothing revolutionary.

    I think it's quite excessive to claim this will reduce entropy. Although I agree that if it's economically deployed in, say, cars, it will supplement the alternator.

    Could this new junction actually replace the alternator for producing electricity in a car? Let's see: assume a car has a 100 HP internal combustion engine. That's 75 kW. Two third of this is wasted in heat. Typically, the radiator gets about half of this heat (the other half is dissipated away in radiant heat or through the exhaust. Assume further that 20 percent of this can be recovered and converted to electricity (for a really efficient semicon pile). That's 75 * 2/3 * 0.50 * 0.20, or 5 kW. That's more than a good SUV alternator. So this could actually work, provided it's reliable and not too expensive.

    You'll need a battery for the short runs, though.

    --SysKoll
    • I think it's quite excessive to claim this will reduce entropy.

      I think they meant reduce the delta of entropy.
    • by GMwrench (211439) on Saturday December 01, 2001 @11:02PM (#2642854)
      I don't think so. First your 100 HP engine will only produce 25-35 HP most of the time. Peak power is only produced during hard accerlation during cruse it's much lower and at iddle almost nonexistant. This is 99% of the time. Also an alternator only produses 1-1.5 KW. And the battery cannot be replaced it's needed to start the engine and supply power at low speed when your charging device is insufficent.
      • by ZxCv (6138) on Sunday December 02, 2001 @05:31AM (#2643325) Homepage
        Even at 25-35 HP, according to his math, that still makes 1.6-2.3 KW. More than an alternator, according to you.

        Also, there was no mention of replacing the battery. In fact, I believe it was: You'll need a battery for the short runs, though.

        Maybe read the post a little harder next time before responding in a such a know-it-all tone?
      • by Spamalamadingdong (323207) on Monday December 03, 2001 @10:09AM (#2647642) Homepage Journal
        First your 100 HP engine will only produce 25-35 HP most of the time. Peak power is only produced during hard accerlation during cruse it's much lower and at iddle almost nonexistant.
        Which doesn't make much difference, because the engine's waste-heat output doesn't change nearly as fast with throttle opening as the crankshaft output does. Even at idle (zero power) you are still burning fuel and still pumping heat out the exhaust pipe. If you can force that waste heat to do some work for you instead of just being diluted to uselessness in the atmosphere, you've accomplished something.

        A hybrid vehicle would probably shut down the engine at idle and eliminate that waste-heat stream, so the thermal converter would be more useful as a way to increase the general efficiency level of the powertrain. If you can get an extra 10% off the 40% of the heat which is rejected through the exhaust, that's 4% of your fuel value; added to a 30% engine thermal efficiency, you've gained 13%. That's nothing to sneeze at.

    • Engine manufacturers don't rate their engines based on BTU input (like a water heater or furnace), but on mechanical output (regardless of waste heat output).

      Doesn't a 100HP (75kW) internal combustion engine actually consume 300HP of chemical energy to make its 100HP of mechanical energy if it's 33% efficient? So the waste heat would be 200HP or 150kW.

    • *nods*

      It's not by any means an end of entropy *fright*, but it is a solid-state heatpump (alternately, to some degree, heat->electrical transducer) with an efficiency rivalling that more efficient mechanical systems.

      An earlier /. article expounded on the opposite use (for cooling ala peltier) mentioning that the new material was about as efficient at cooling (running the cycle backwards heat-electrical) as the gas-compression cooling of a standard kitchen's fridge.

      While that's still not very efficient, it is good enough to use on 'recycling' waste heat. Do something economical and plate car-radiators with this material, bleeding off the heat to give back electricity and you've already won a tiny battle.

      Mostly, however, it seems likely that this material will be used as a pretty efficient way to turn electricity into cold. Not as cool perhaps as recycling waste heat, but still pretty chilly....

  • Portable devices (Score:2, Interesting)

    by elixx (242653)
    With the increasingly hot processor temperatures as clockspeeds rise, and the heat generated by laptop's power supplies, etc, could this technology be used to improve the battery life of portable devices?
  • Use on Hybrid cars? (Score:5, Interesting)

    by BlueJay465 (216717) on Saturday December 01, 2001 @10:07PM (#2642746)
    My question is how much more gas mileage could this technology squeeze forth given an array of these attached to the heat producers of a vehicle, like the engine or the brake pads.

    Another thing is how do these "thermal diodes" compare to a Peltier Element in heat conversion to electricity?
    • Yeah, when i saw this, i immediately thought of the honda insight. It does just about everything to conserve what gas energy it does burn, it would be consistant with their design (not to mention really neat) to encorporate something like this in. I do wonder how much more mpg they could squeeze out of it.
      • The Toyota Prius actually *does* reclaim heat. It does so while braking, converting the energy that normally would be transferred to the brake pads, to aid in charging up the half of the engine that is electric. So this theory is useful, and is currently in practice. I saw a report on TechTV about it. The car employs a process called "regenerative braking, which reclaims up to 30% of this waste heat, and helps charge up the batteries of the car. http://www.techtv.com/freshgear/story/0,23158,3357 682,00. html
        • by Graff (532189)

          It doesn't do this by converting the heat into electricity however. What it does is effectively act as an alternator, converting the kinetic energy into electricity. The loss of kinetic energy slows the vehicle to a stop while charging a series of batteries. Thus, no heat from brake pads in the first place.

          Relevant quote from that article on techtv [techtv.com]:

          When decelerating or braking, the electric motor turns into a generator to charge the batteries automatically. It's a unique hybrid feature called regenerative braking. Normally when you brake, all that energy is converted into heat into the brakes. Toyota's Prius actually recaptures about 30 percent of that energy to recharge the nickel-medal-hydride batteries in the back
    • by wowbagger (69688) on Sunday December 02, 2001 @10:15AM (#2643598) Homepage Journal
      A thermal diode IS a Peltier element. This has been covered in EE Times among other trade journals. All they've done is take the standard BiTe diode, which is very thick, and thinned it down by creating the layers with standard chipmaking techniques. So, instead of one diode junction being about 1mm thick, they make a device that is 0.1mm thick consisting of many tens of layers.
  • by argoff (142580) on Saturday December 01, 2001 @10:10PM (#2642755)

    It'd be great if we could use this for cheap solar cells. Regular solar cells are pretty expensive. (I'm almost convinced that other industries are screwing with the market to make them cost so much). Anyhow, does anyone know how much this new stuff would cost? PS: nuclear's my favorite, but it's too easy for the govt to regulate.

    • by autopr0n (534291)
      I don't know about you, but where I live the sun dosn't head surfaces to 480 degrees Fahrenheit...
      • by autopr0n (534291)
        I mean "heat surfaces."
      • by Moofie (22272)
        Then you don't have a good enough reflector set up.

        Honestly, didn't you ever burn your name into leaves with a magnifying glass? Concentrating solar energy is pretty easy...just use a curved mirror or a lens. 480 degrees would be no problem at all.
  • by StandardDeviant (122674) on Saturday December 01, 2001 @10:18PM (#2642775) Homepage Journal
    here's the layman's formulation of the things that give chemistry students the cold sweats, the rules of the game as it were:
    1. You can't win.
    2. You can't break even.
    3. You have no choice about playing.
    Any closed system ends up in the state of most disorder, and all systems are closed if you look at the boundaries carefully. No matter how hard you try, no matter what ingenous things you do, in the end, the dealer wins and everything is dust. Cold dust, at that. The more energy you expend enforcing order, the more chaos you cause. There are no wins in technology, only a prolonging of the inevitable loss. So while I'm sure this new doohickey is neat, somewhere, Carnot is laughing and his cycle is tapping you on the shoulder snickering to itself.
    • While that's all very true, it's not tremendously *relevant* here. While you can't break even, you *can* get arbitrarily close to breaking even. Nobody's claiming that thermionics allows you to build an over-unity device, or violate the 2nd law.

      What this does do is allow us to design more efficient processes than before. That's a cost savings, a resources savings, and quite allowed by Carnot.
  • Hmmm... (Score:4, Offtopic)

    by jimhill (7277) on Saturday December 01, 2001 @10:28PM (#2642791) Homepage
    I couldn't help noticing that within a few paragraphs the writeup mentioned that (1) the research was partly sponsored by DARPA and (2) patents have been applied for with one already issued. Color me bitter, but as one of the taxpayers who funded the research I can't say I'm overjoyed at the prospect of paying licensing fees to MIT through the eventual commercial implementors.

    I'm all in favor of government-sponsored research. They have the resources to investigate stuff with great benefits but staggering R&D costs. I'm all in favor of universities conducting the sponsored research. Grad students are cheap (I know, I was one for many years) and the brainpower is not less than one finds in industry. However, when the government pays a university to do something new, the university's benefits should be the equipment bought for the research and the prestige that comes from doing it first/best/cheapest.
    • Well, the trick is that corporate sponsors also pay for a lot of academic research. Rather a lot of research wouldn't get done if the funds couldn't be cobbled together from both the government and the private sector.

      Giving the private-sector sponsors some real incentive to keep it up only makes sense.

      Chances are that you won't be paying licensing fees through those commercial implementors, because their funding of research at MIT has gained them access to the license already.

    • Re:Hmmm... (Score:4, Informative)

      by wass (72082) on Saturday December 01, 2001 @11:42PM (#2642934)
      I used to work at an MIT laboratory that was sponsored with DARPA funding. I left 2 years ago to go back to school to get my PhD in physics. I'm not sure of the exact details, but here's the basic scoop as far as I see it.

      DARPA essentially funds research laboratories to perform research projects that will further advance technology related to DARPA interests. In my case, the research was unclassified, and our group was able to colloborate with other groups and colleages, present our research at conferences, as well as publish our methods/systems/data in scientific journals.

      The laboratories that DARPA funds are either university laboratories, FFRDCs (Federally-Funded Research and Development Centers), and commercial laboratories (ie, IBM or Motorola research labs, for instance). It is usually standard practice for employees of all the above labs, upon the beginning of employment, to sign contracts handing over patent rights to the employer (ie, the FFRDC or the company). Actually, I'm not sure about students, as I haven't signed any patent forms yet. But did when I was an employee of MIT. So did Richard Feynman when he worked for Los Alamos (FFRDC).

      So, essentially, DARPA has certain technological goals it wants to achieve, and funds a variety of sources to help achieve them. Usually for each specific project, DARPA funds a variety of research labs, and has them compete for further funding. The research labs in turn present their results at least annually for funding renewal. Eventually, DARPA gets it's results (or lack of them), and gets what it needs in terms of advanced technology, and then cna use that technology within more advanced systems.

      I do not know specifically what kind of strings come attached with DARPA funding. However, I would imagine that most likely the research labs themselves get some significant percentage of patent rights as a bonus for conducting DARPA research. Otherwise there is no incentive for, say, Boeing to research a new type of stealth aerofoil if DARPA holds on to all patent rights. I know my boss at MIT had his share of patents, but of course, MIT essentially owns said patents.

      Note that DARPA's ultimate purpose is to get better technology into Defense-related projects. They advocate using COTS (Commercial Off-The-Shelf) hardware/devices whenever possible. That is, don't waste $$$ designing your own op-amp if Analog-Devices has one that's within your specifications. Of course, you must roll your own if the COTS op-amps don't meet your bandwidth/linearity/bias/power/etc requirements. So, DARPA doesn't care about who gets the patent rights for that op-amp, they want the research that makes use the op-amp. So, in this example, your tax dollars are already going to Analog Devices and helping their own patent processes.

      Your concerns about tax dollars funding university patents are either too narrow or too broad. Realize DARPA funds commercial entities as well as FFRDS too, which have similar patent processes. However, DARPA's fundamental purpose is to fund advanced research projects to further American defense interests. That's what it does, and it will support commercial, government, or university research labs to achieve this goal. It's a government agency, so obviously it is funded with tax dollars. I don't think DARPA cares about patents, as long as it can utilize the fruits of the research.

      • Let me give an example to how the system probobably works in the big picture. (Disclaimer - I might be wrong).

        Some defense guys somewhere in the US government decide that, after running into many difficulties trying to find hidden Taliban hideouts, that the armed forces need better heat-vision technology. Specifically, higher sensitivity and resolution are required.

        DARPA comes forward with the Super-Cool-Heat-Vision (SCHV) program to fund research specifically aimed to advance heat-vision technology. The SCHV program is allocated $20 million dollars annually, for 4 years.

        DARPA puts out Announcement of Opportunity describing the SCHV program, and invites research labs to participate. The research labs, in turn, submit proposals describing how their specific laboratory can further the technology, and gives specific goals that they believe they can achieve within the allotted time frame.

        DARPA chooses the best programs, based on attempted goals as well as quality of research (ie, if the goals are grand but, as is often the case, depend on "magical non-existent devices" it's basically ignored).

        DARPA allocates the $20 million to the different projects. Annually, DARPA checks each group's status to determine the next year's funding to that group. Sometimes groups are not funded the next year due to lack of beneficial results.

        Eventually, the SCHV program is finished. Some groups have come up with useful heat-vision devices and prototypes.

        Here I'm not sure of the details regarding patents and IP issues. I don't know if Company XYZ has to pay licensing fees to the research groups if it uses the technology. But eventually, company XYZ offers commercially-available heat-vision goggles that are far more useful than the previously-availably heat-vision devices. The US Army will then order 100,000 units from company XYZ. Company XYZ makes $$$.

        DARPA's purpose was to further the progression from concept to obtainable entity.

  • by Pyromage (19360) on Saturday December 01, 2001 @10:47PM (#2642827) Homepage
    this truly is the fundamental question: can this be made to be more efficient than a turbine/generator combo?

    If this can be more efficient than a turbine, we can have solid-state power plants. Nukes are nothing more than a complex method of boiling water to push a turbine: if we can replace the water, we have an order of magnitude less waste! Not to mention that the core stuff is much easier to deal with than heavy water. Plus, with no pumps or pipes to break, it becomes even safer than it already is.

    Or other things, say laptops? PDAs? Naturally all these kinds of applications are XYZ years off, but just imagine what would happen when we get the effiency of these things up? I'd bet that boiling water to turn a turbine is real low efficiency: if we cut out the turbine step alone, that should increase effiency by a whole lot.

    This is truly cool shit.
    • Ehhrm...

      1. In a light water reactor you got two circuits. The water of the inner circuit comes into contact with radioactive material and can get slightly radioactive itself. The inner circuit is completely closed.
      The outer circuit is coupled to the inner one via a heat exchanger. It drives the turbine and is closed, too.
      Then after the turbine, the water of the outer circuit is further cooled down with an heat exchanger and river water.

      So where is the waste produced? Even the water of the inner circuit becomes only slightly radioactive and is not replaced.

      2. Graphite core reactors do not use water as a moderator. But it is still used for cooling. If there is an emergency, something like a peltier element will not be able to reduce the heat fast enough.

      It would be more interesting to use the new system with something like MRTs (hope that's the word - those thingies used in sattelites).
      • the warm water is a waste product - not a big deal if it is going into the pacific, but when it goes into a river it can change things enough to alter the ecosystem

        or so I've heard.
        • the warm water is a waste product - not a big deal if it is going into the pacific, but when it goes into a river it can change things enough to alter the ecosystem

          That depends on a lot of factors.

          How hot is the water being discharged? How big and how fast is the river receiving the discharge? And what ecosystem is already present?

          Raising a stream temperature two degrees farenheit won't make a huge difference. Maybe a slight increase in plant productivity and a slight decrease in dissolved oxygen. That increases biological oxygen demand and at the same time decreases the available oxygen to meet that demand. I know what you're saying-increased plant productivity should increase dO2, but the oxygen tends to outgas once the water is saturated or close to it. And gases are less soluble in warmer water than cold. That's why trout don't live in warm water.

          Anyway, two degrees isn't likely to be a huge whammy. Ten degrees would probably be very significant.

          FWIW, a slight increase can often improve fisheries. Wolf Creek Reservoir in Kansas is the cooling pond for a nuclear power plant. The slight warming effect from the plant has done wonders for the fishery present. And then the stories are legion about prime fisheries being destroyed by warmer water-pacific anchovies, for instance. You really can't generalize too much when it comes to ecology.

          And yes, I am a fisheries biologist/acquatic ecologist. Either I have some experience or I've managed to fool a lot of professors and the hiring officer at the state DNR :-)

      • by leucadiadude (68989) on Sunday December 02, 2001 @10:32AM (#2643617) Homepage
        You are confusing reactor waste with waste heat.

        The waste comes from the approximately 65% of the original heat pumped into the primary circuit being lost to the river. You have to condense the steam coming out of the turbine so you can pump it. It takes a *lot* of energy to condense this steam back to water. You may not be raising a particular gallon of river(or ocean) water by more than a few degrees (usually less than 5-8F) but you are moving a whole pisspot full of cooling water through your condenser. So the total energy rejected to the environment is quite large. Real world example, the plant where I work is 34.2% efficient, which is actually pretty good for a large steam cycle power plant. The reactor core pumps about 3400MW of heat into the primary circuit and we get about 1175MW of electricity out of the turbine generator, the vast majority of the rest (2225MW) is transferred to the 1,000,000 GPM of ocean water used to cool that pesky steam back into water so it can be pumped.

        Now if you could design an economical steam pump (or better yet a two phase pump - steam in and water at higher pressure out) your billions of $'s would be waiting for you. You would be able to knock the stuffing out of the Rankine Cycle and increase plant efficiency into the 50-60% range overnight.
    • I highly doubt its more efficient than turbines. Turbines run at about 40-60 % eifficiency. Since these junctions are using low grade heat, their efficiency woud be significanly lower. However, they could be used to augment the efficiency of turbines. Put these at the condenser and you may be able to boost overall turbine efficiency by 10% which is significant.

  • And it came to pass that AC learned how to reverse the direction of entropy.

    But there was no one to whom AC might give the answer of the last question. No matter. The answer---by demonstration---would take care of that, too.

    For another timeless interval, AC thought how best to do this. Carefully, AC organized the program.

    The consciousness of AC encompassed all of what had once been a Universe and brooded over what was now Chaos. Step by step, it must be done.

    And AC said, "Let there be light!"
    And there was light---


    Isaac Asimov, The Last Question

  • by vscjoe (537452) on Saturday December 01, 2001 @10:58PM (#2642846)
    That's nice, but it seems like a lot of effort for something that, in many cases, has a much simpler solution: use waste heat for heating. A lot of waste heat could be used for heating homes and water for domestic use, and this is largely untapped in the US. (A lot of low-level waste heat could also be avoided entirely if people gave up on their inefficient water heaters and insulated their pipes.)

    It's nice when people come up with better technology, but the inefficient use of energy in the US right now is not a technological problem, it's a political problem. Let's hope that we'll eventually be doing well enough that it will really become a technological problem.

  • The 1st problem with this technology is the high temprature 400C is a material science problem.

    The next is the poor overall efficiency. MIT says they get 2X times the efficiency. From Photonpower.com [photonpower.com] I remember a 5% efficiency, so lets be generous and claim 15% efficiency.

    Yet, with the use of stirling engine technology A $90 750Watt engine [omachron.com] or the mystical Ginger [dekaresearch.com] or IT [jedstar.com] you can use waste heat and get power. Stirlings will move with as little as a 2C temprature difference. 90% as a CHP is possible [whipsergen.com]

    If you want to get excited about the idea of heat/electricity, then go take a look at some Naval research [sciencedaily.com] that could provide room grade AC w/o state change presently used.

    But this technology? Not that exciting, and that is ONLY because of the high temprature.
  • Meteor? (Score:2, Offtopic)

    by 0000 0111 (141160)
    I know this is way off topic, but I had to post it somewhere. About ten minutes ago (9:16 MSDT) I happened to see something explode over West Texas crossing the sky. Not like anyone really gives a rip, but it was cool! Looks like it was heading a little north of east and I would guess it's near Arkansas by now. Main object flamed yellow and four smaller objects below flaming red. Spooky!
    • Re:Meteor? (Score:3, Funny)

      by dattaway (3088)
      How many kilowatts can we reclaim from this meteor?

      Four smaller ones? Imagine reclaiming the heat from a cluster of these...
  • Many of the comments posted make the connection of generating electricity from the heat that the CPU produces, However, the heat being produced is actually caused because of inefficiencies in transistor switching. So if transistors became more efficient they would would waste less electricity and generate less heat thus needing less electricity leading to less heat leading to needing less electricity until we are actually generating electricity from the lack of heat.
    • Years ago the informatics crowd I hung with was working on the relationship between computation and power.

      It turns out that because you need to represent state in a stable mechanism, and you can't change the stable state without using energy that there is a lower bound on the energy required to perform a given calculation.

      I have forgetten everything else, and I suspect it is many orders of magnitude smaller than current cpu power usage, but it is enough to break the '==' operator on the parent's title.
  • by Animats (122034) on Saturday December 01, 2001 @11:56PM (#2642956) Homepage
    Not too much info yet. In particular, there's no indication of how much such devices will cost per watt. This is a basic problem with things like Peltier-effect devices and solar cells; they work fine, but you need an awful lot of them to get serious power levels. If this requires something like a wafer fab to make, it will be a niche device for years to come.
  • Yeah, you know me!

    For the unintiated, MC Hawking [mchawking.com] lyrics follow.

    MC Hawking is Stephen Hawking, physicist and gangsta rapper. Despite three critically acclaimed albums and nearly ten years on the mic, Stephen Hawking remains virtually unknown as a musician. mchawking.com [mchawking.com] is devoted to Stephen Hawking's career as a lyrical terrorist [ampcast.com].

    Harm me with harmony.
    Doomsday, drop a load on 'em.

    Entropy, how can I explain it? I'll take it frame by frame it,
    to have you all jumping, shouting saying it.
    Let's just say that it's a measure of disorder,
    in a system that is closed, like with a border.
    It's sorta, like a, well a measurement of randomness,
    proposed in 1850 by a German, but wait I digress.
    "What the fuck is entropy?", I here the people still exclaiming,
    it seems I gotta start the explaining.

    You ever drop an egg and on the floor you see it break?
    You go and get a mop so you can clean up your mistake.
    But did you ever stop to ponder why we know it's true,
    if you drop a broken egg you will not get an egg that's new.

    That's entropy or E-N-T-R-O to the P to the Y,
    the reason why the sun will one day all burn out and die.
    Order from disorder is a scientific rarity,
    allow me to explain it with a little bit more clarity.
    Did I say rarity? I meant impossibility,
    at least in a closed system there will always be more entropy.
    That's entropy and I hope that you're all down with it,
    if you are here's your membership.

    Chorus
    You down with entropy?
    Yeah, you know me! (x3)
    Who's down with entropy?
    Every last homey!

    Defining entropy as disorder's not complete,
    'cause disorder as a definition doesn't cover heat.
    So my first definition I would now like to withdraw,
    and offer one that fits thermodynamics second law.
    First we need to understand that entropy is energy,
    energy that can't be used to state it more specifically.
    In a closed system entropy always goes up,
    that's the second law, now you know what's up.

    You can't win, you can't break even, you can't leave the game,
    'cause entropy will take it all 'though it seems a shame.
    The second law, as we now know, is quite clear to state,
    that entropy must increase and not dissipate.

    Creationists always try to use the second law,
    to disprove evolution, but their theory has a flaw.
    The second law is quite precise about where it applies,
    only in a closed system must the entropy count rise.
    The earth's not a closed system' it's powered by the sun,
    so fuck the damn creationists, Doomsday get my gun!
    That, in a nutshell, is what entropy's about,
    you're now down with a discount.

    Chorus

    Hit it!
    Doomsday, kick it in!

  • Cold Fusion Redux (Score:4, Flamebait)

    by Baldrson (78598) on Sunday December 02, 2001 @12:31AM (#2643003) Homepage Journal
    Peter L. Hagelstein was the guy at MIT who had MIT's lawyers churning out cold fusion patents like there was no tomorrow [mit.edu] at the same time that MIT's official position was that cold fusion was an illusion -- and making official recommendations against its funding.
  • by MarkusQ (450076) on Sunday December 02, 2001 @12:41AM (#2643018) Journal
    This has the same problem as the things that generate electricity from your body heat/motion/whatever. By adding such a device to the system you make the original system harder to cool (because your gizzmo acts as an insulator) or harder to move (because your gizzmo has mass) or whatever (details vary depending on how you're trying to get energy out of the system) and in the end you will reduce the efficiency by an amount that will require you to put more fuel/power/food/whatever into the original system. If your parasitic gizzmo were 100% efficient you still wouldn't gain anything, and in any real case you'll face a net loss.

    Example: You put a heat-based gizzmo on your car's exhaust pipe. The temerature (and thus pressure) in the exhaust system goes up, making the engine less efficient and making you use more fuel to go the same distance.

    Example: You put one on your CPU. Same deal, except your cooling system now has to work harder to keep it at a reasonable temperature, and thus uses more power.

    Example: You wear a swatch. It takes a little bit more energy each time you move your arm. If you want to power a computer the same way, you'll soon be too tired to type.

    The key point is in every case you will have to put more energy in than you get back out. That's why perpetual motion machines do not and can not work.

    -- MarkusQ

    • Well, the majority of the energy generated in a gasoline engine is simply wasted as heat. Putting therocouples into the engine block, say, would not make the engine work harder at all. There is an abundance of wasted energy ready to tap at many points.

      It's not perpetual motion, but an attempt to retain energy that is now simply radiated away.
      • There is an abundance of wasted energy ready to tap at many points. ... It's not perpetual motion, but an attempt to retain energy that is now simply radiated away.

        But heat isn't free energy (free in the physics sense, not in the open source sense). True, you can get energy from a difference in temperature, but only by slowing the flow of heat that would have otherwise taken place (just like damming a river) and thus raising the entropy (in this case, temperature). Now, doing so will make your engine run hotter, and thus less efficient, and you have a net loss.

        Suppose you do something to cool the heat sink to make up for this. Then you have two cases to consider: either 1) you are using energy to do this, or 2) you have a passive way to do it. In case 1 you are still at a net loss, but in case 2 you might well be doing better than the original system. But you've then changed the base case--if you used the passive cooling trick (a heat sink or whatever) on the original system, you would have gotten a greater gain, so your gizzmo is still costing you.

        -- MarkusQ

    • Example: You put a heat-based gizzmo on your car's exhaust pipe. The temerature (and thus pressure) in the exhaust system goes up, making the engine less efficient and making you use more fuel to go the same distance.

      Um, the catalytic convert is already there, and it gets rather hot. Bolting a few of these gadgets there, and on the engine block and in the radiator, won't make the temperature go up any, nor will it impede the flow of exhaust.

      Mind you, I doubt it'd fully replace an alternator, but it'd help. The alternator robs horsepower, too, and if these gadgets are "free" (as in do not take more work to run), the net effect should be to increase fuel economy.

      This says nothing about the cost and complexity, however. I'm not sure that making these cheap, robust and able to run along with an alternator will be a trivial exercise.
    • Example: You put a heat-based gizzmo on your car's exhaust pipe. The temerature (and thus pressure) in the exhaust system goes up, making the engine less efficient and making you use more fuel to go the same distance.

      Example: You put one on your CPU. Same deal, except your cooling system now has to work harder to keep it at a reasonable temperature, and thus uses more power.

      Your thinking here is slightly askew. Consider your CPU example. The device is converting heat energy into electrical potential. That means there is LESS heat energy in the CPU. That means the cooling system needs to work LESS to keep the CPU at a reasonable temperature. Your first example is similarly broken: removing energy from the system cannot possibly increase the temperature. Placement of the device might influence exhaust flow, but only if you place the device in a stupid place.

      The cost or mass of the device might be important, but your arguments about the device creating more heat in the system seem to be missing the entire point of what the device does. I suspect you're thinking along the lines of "the gizmo must contact the hot surface, therefore the cooling systems have less contact, therefore it's like a constricted pipe holding back the flow of heat, therefore the cooling system has to work harder". This isn't how it works. You can make the surface area as large as you like (think of radiators).

  • by Animats (122034) on Sunday December 02, 2001 @01:42AM (#2643104) Homepage
    The law of thermodynamics that's relevant here is that the maximum efficiency of any heat engine is
    • (T1 - T2)/T2
    where T1 is the temperature at the hot side, and T2 is the temperature at the cold side. Both of these temperatures are measured from absolute zero.

    This is why extracting energy from something that's just a little warmer than its environment is very inefficient. With the hot side at 100C and the cold side at 20C, you're limited to about 20% efficiency in theory, and will be lucky to get half that. Power plants generate steam at upwards of 600C, not just above the boiling point, for exactly this reason. Gas turbines run even hotter. Solar plants for power production typically focus enough energy on a target to reach the 600C level, as Solar Two in Mojave does.

    You just can't extract much power from things that are merely warm. They have to be really hot.

    • The amount of practical power you extract has little if anything to do with theoretical efficiency. The efficiency is based on an arbitrary equation, the power is actual energy per unit time.

      For instance, what about a Stirling engine? It has a low "efficiency" according to your definition--but it uses literally any heat source at extremely low temperature differentials. Which engine is more efficient in a practical sense, the one that uses barrel after barrel of precious oil or the one that produces household current from sunshine and snow?
  • It seems so far that most of this discussion focuses on this technology's application to automotives, which are, obviously, an enormous source of fuel consumption. But what about more fundamental wastes of heat?

    Quite nearly every home contains dozens of devices that let off lots of energy while in use. Think of your oven, dryer, toaster, refrigerator, furnace... dare I say woodstove?!? Lining these heat-driven devices with such a product could prove valuable.

    Consider the open flame of a gas range literally belching heat, much of which escapes into the air or is absorbed by the metal around it. What if the oven and catch-plates below each burner were lined with a hard-coated version of the device? Maybe in the common home this would prove impractical, but surely in commercial kitchens where ovens and stoves are perpetually fired such an implementation would drastically cut down on the total electricity used.

    In older homes where radiators are the norm, this might even provide an economical way to prevent burns from leaning up against those pesky pipes!!!

    .
  • by tidavis (219267)
    ASPX annouced a device like this a couple of months ago. Includes pictures. Power output is not too impressive but with all the MEMS work these days maybe 10uW aint so bad.

    http://www.adsx.com/images/Generator1.html

    But the really interesting part is how this company plans to use it. They want to use it along side their digital angel product. Wireless biomonitoring that never runs out of batteries!
  • by Ogerman (136333) on Sunday December 02, 2001 @02:59AM (#2643212)
    By careful selection of materials, ENECO scientists are creating highly efficient, solid state conversion devices, called "thermal diodes," that will operate from 200 to 450 Celsius -- typical temperatures for waste heat and for concentrated solar radiation.

    The very best commercial solar cells today are about 18-20% efficient. The best (research) cell on record, was 32% efficient. It's really too bad they don't give any more specifics on this semi-conductor based device, because it wouldn't be too hard to figure a rough solar cell efficiency equivalent (based on the area of a concentrating lens or mirror)

    Now perhaps a more interesting use of such a device would be to increase the efficiency of fuel cells, which themselves are not so efficient and produce lots of waste heat. In a residential setting, this heat can be used for hot water and during winter months. But in a vehicle, I can't think of much use otherwise. Powering headlights, A/C, etc. would be great. Especially if they were white LED headlights of course.. (-;

    For your reading pleasure:
    http://www.nrel.gov/hot-stuff/press/5399world.ht ml
    http://acre.murdoch.edu.au/refiles/pv/text.html
  • "All your waste are reduce by us!!"

    *groan*
  • by JordanH (75307) on Sunday December 02, 2001 @08:33AM (#2643483) Homepage Journal

    I've always been struck with how much energy is thrown away in cooling towers at turbine-based electric generating plants.

    Just a little background for people who don't understand the function of a cooling tower. A turbine plant turns it's turbines by converting a liquid (typically water) to a gas (steam). Once you have the steam, you have to cool it down if you want to use it again or if you want to efficiently discard it. Some plants are designed to cool it down to the point where very little additional heat will boil it again, but this can be tricky. Some plants have been designed such that the waste steam is cooled in heating buildings through steam radiators, but it can be problematic finding customers for this steam, especially year round.

    If we have an efficient way to convert this steam to energy as we cool it, then the efficiency of these plants could go way up.

    On a related note, I wish the politicians were seriously working towards about energy efficiency, alternate fuels and new oil exploration now. I only hear half measures and partisan wrangling. It's like the politicians seem to believe that we can't have BOTH more energy efficiency and new energy sources. I'd like to be less dependent on some of the foreign oil now. Some of those areas just aren't looking too stable these days.

  • Wind Generators (Score:2, Interesting)

    by GooberToo (74388)
    Is there enough heat generated by the generators used in wind generators to allow these to further augment their power output? Seems to me that having these on a wind turbine would be excellent as you have a ready source of air to create a large temp. delta.
  • "... and A/C" (Score:2, Insightful)

    by Kymermosst (33885)

    Except the air conditioning cooling system in a car runs directly off the drive system, and not on electricity. The heater runs directly off of heat in the car's cooling system. Consequently, this development really has no impact on vehicle air conditioning or internal environment, with the exception of running a couple relays and a control circuit.

  • A question for someone more knowledgable in physics. Would this technology make it smarter to use gas-turbines in hybrid cars rather than reciprocating engines, since the waste heat is at a much higher temperature?

    And could this be used to augment power used with gas turbine generators at hospitals, on ships and oil platforms or even APU's in airplanes?

    Ethan

For every bloke who makes his mark, there's half a dozen waiting to rub it out. -- Andy Capp

Working...