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Waste Heat to Electricity?
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."
less power required= less pollution
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.
--
Mad science! Robots! Underwear! Cute girls! Full comic online! http://www.girlgeniusonline.com/
It's true, the applications for automobiles seem rather limited, but thermionics could stand to revolutionize the nature of power plants.
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.
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?
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.
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
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.
t ml
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
I beg to differ. Being an ex-geek, now a car guy, I'd love to use the heat my engine throws off.
;-)
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.
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.