Waste Heat to Electricity? 330
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."
Hmmm... (Score:4, Interesting)
less power required= less pollution
Nice but not the end of entropy (Score:5, Interesting)
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.
Re:Neat Idea, but not terribly useful... (Score:3, Interesting)
IANAS, but I believe that today's newest and most efficient coal, oil, and even nuclear power plants can at some point be looked at as a simple heat -> steam -> turbine system, the same concept that's powered locomotives for over one-hundred years! As you'd imagine, such a system is terribly inefficient.
Thermionics, as I understand it, eliminates the "middleman" of the equation by translating heat directly to electricity. It certainly will be interesting to see how this develops on a commerical and thus much larger scale.
Portable devices (Score:2, Interesting)
Use on Hybrid cars? (Score:5, Interesting)
Another thing is how do these "thermal diodes" compare to a Peltier Element in heat conversion to electricity?
Re:Neat Idea, but not terribly useful... (Score:2, Interesting)
Chrysler has a diesel hybrid in development, a prototype called the ESX3, that currently is getting around 72 mpg. The main problem for them is *cost*. As time passes, this will go down. I don't know if they reclaim engine heat, but I doubt it.
Ford *does* have an all electric prototype but it, and any early all-electric cars would be primarily designed for the folks who want a strictly "in-town" car. This notion is already catching on in the form of NEV's (Neighborhood Electric Vehicles).
But, yes, this sort of technology will be probably be pointless within 20 years, at least for automobiles. May have some other uses, however.
Heatsinks for Power (Score:1, Interesting)
Especially in laptops, this could be great, and hypothetically could power the device indefinetely, assuming an initial charge to start everything up.
It could be especially useful with devices like new graphics chipsets to alleviate them from having to draw additional current from the rest of the system (Voodoo 5, anybody?).
Fortunately, computers don't generate quite the level of heat they're talking about, but given an improvement of the technology, this could really take off. Of course, the downside would be that if these conditions were true, it's not unreasonable to assume IC designs would get sloppier instead of less power-consuming and more efficient. I suppose it's a tradeoff. *Sigh*
is it more efficient than turbines? (Score:5, Interesting)
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.
There are other ways to use waste heat. (Score:2, Interesting)
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.
CPU heat == inefficiencies (Score:2, Interesting)
Re:thermodynamics, and entropy, and all that (Score:2, Interesting)
You don't need an expert for this one, you just need to think about it for a minute.
The way we use heat to generate electricity is by converting linear motion into rotational motion in a generator. We don't create the linear motion, really... You make water hot and give it only one place to go, and when it expands it goes there. Same deal with geothermal energy, even wind energy (though heat isn't involved in creating the linear motion, there).
So, if you want to just randomly generate electricity from a warm room, all you have to do is provide one exit for the warm air from the room, and have it lead to a colder room. You put a turbine in that passage, and you'll be able to convert the linear motion of the warm air moving into the cold room into rotational motion and turn a generator.
Problem is, you have to come up with a "cold room" that does not enter equilibrium with the warm room, and even if you come up with one of those, you're really not going to see particularly fast linear motion, unless the temperature difference is very great.
On the other hand, I really sucked at physics in school, so I could be wrong. :)
You'll still have a net loss... (Score:3, Interesting)
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
Re:You'll still have a net loss... (Score:2, Interesting)
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
Re:You'll still have a net loss... (Score:3, Interesting)
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.
This really isn't new (Score:2, Interesting)
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!
Cheaper and more efficient solar power? (Score:3, Interesting)
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.h
http://acre.murdoch.edu.au/refiles/pv/text.html
Re:This would be useless in automotive.. (Score:4, Interesting)
If the heat is being converted to electricity then there will be less heat. Lower heat in the exhaust alone means lower engine temperatures because the exhaust sytem radiates the most heat near the engine at the headers (the part where the exhaust comes off of each cylinder for you non-car types). Since thats where the exhaust is hottest thats where the devices would be mounted. A lower exhaust temperature means a lower overall engine temperature.
Secondly, the big step is going from 1000 degrees down to 250 degrees. Taking that 250 down to 180 or 160 would likely allow these devices to draw heat from the engine itself. Having these devices draw energy would reduce the work a typical liquid cooling system needs to do, allowing it to be reduced in size.
Newer cars and performance cars are replacing belt driven components with ones powered electrically, most notably fans and water/coolant pumps. Elimiating belts allows the engine to put more power to the wheels rather than turning an accesory. The catch is that these devices need more power from the battery and alternator. Alternators are presently limited to about 150-200 amps, enough for a stripped race machine to run its accesories, but not enough for a street driven car with lights, music systems, and long continuous driving. These thermocouples would add more electrical power to the system and use more of the energy produced by the combustion.
The automotive example is a bit advanced for the time, but in todays science community a potential commercial use is the best way to get money for new ideas.
Sorry if that went on too long, or was too automotive for you slashdot geeks.
Peter L. Hagelstein (Re:Cold Fusion Redux) (Score:2, Interesting)
I thought that name was familiar! Gary Taubes' excellent book on the genesis of "Cold Fusion", Bad Science [amazon.com], gives a thorough and not particularly kind account of Prof. Hagelstein's role in those events.
Re:is it more efficient than turbines? (Score:2, Interesting)
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 :-)
Replacing or augmenting cooling towers (Score:3, Interesting)
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)
Re:Hmmm... (Score:3, Interesting)
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..
A good thing for gas turbine supporters? (Score:2, Interesting)
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