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."
Re:Thermionics? Environmentally friendly?! (Score:2, Informative)
Re:Neat Idea, but not terribly useful... (Score:2, Informative)
Granted that people talk about how combustion engines waste heat, but no one ever seems to adress how that very heat is neccesary for many parts of the world. I suppose with vehicles, electic cars are a good idea for those in cities that mainly would just need to drive across town, but lets face it; many people use vehicles like an SUV just to drive across town.
Re:Heatsinks for Power (Score:3, Informative)
You *might* extend battery life for a small length of time (measured in tens of minutes at the most) by recycling some of the waste heat, but entropy still rules. You cannot recycle all of the waste heat, so you will be unable to run your device for anything close to indefinitely.
-Legion
More info (Score:3, Informative)
EXTREMELY Useful (Score:3, Informative)
To date, combustion based systems have the highest energy density of any portable energy source (barring fission reactions). Therefore, there will always be a use for it.
Perhaps automobiles won't necessarily need them - we can afford to carry additional weight - the fuel/weight ratio for automobiles is evidence of this - you can carry a LOT with a small amount of fuel for a car - and you can then drive for a long time.
But what about flying vehicles? Fuel/weight ratio is EXTREMELY important. The more efficiency that we can get the better. The best part about this is that it might remove the need for an alternator, which drains the power and adds weight to any flying device (which is significant for the small vehicles, such as the automonous surveyor helicopters used by the U.S. military). Improvements in fuel usage can mean a big deal for the aircraft industry.
Of course that's not the only industry that will benefit. Heat-differential technology is used as a power source for some areas...have you heard of geothermal and solar power plants? Know how those work? What if they could double their output? That would be significant.
Re:Use on Hybrid cars? (Score:2, Informative)
Re:Hmmm... (Score:4, Informative)
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.
Re:thermodynamics, and entropy, and all that (Score:5, Informative)
At a fundemental level, entropy is a measure of the number of accesible states of a system for a given energy distribution. Presumably you know that temperature is really just a statistical measure of average kinetic energy in a substance. In the simple case of a uniform temperature gas, it's possible to compute the entropy directly, by (a process analogous to) counting the possible ways to arrange the molecules and distribute their kinetic energy such that you still have the same temperature. (Okay it's not really counting cause there is [usually] a continuum of positions and energy values, but the idea is there, only with more integrals.)
Roughly speaking a system is "ordered" or "disordered" based on how much freedom it has in distributing the energy in it's heat. For instance, in highly complicated and stable configurations (e.g. DNA) you can infer that the heat gets distributed only in ways that don't break down the basic structure. Of course with enough heat it will no longer be stable, but that's a different case.
While the number of accesible internal configurations for the heat energy is the basis for entropy, very few people actually use this. What is actually used is a set of laws mathematically derived from this which can be directly applied to macroscopicly measurable quantities. Chemists know more about these areas than I do, but I'll cover a few of the basics.
The most important is known as the Second Law of Thermodynamics, stated simply "Entropy always increases (or stays the same)." Whenever you do anything that moves energy (such as heat) around, the net entropy will increase (except in those rare cases when it stays the same). It is possible to locally decrease the entropy of one system, but you are guaranteed to increase the entropy of everything else by at least the difference.
There is another important trick about entropy. It tells you that it's impossible to transfer energy from heat to any other form with 100% efficiency. Not only that but you can't even do it with arbitrarily close of 100% efficiency unless you have something who's initial temprature is arbitrarily close to 0 degrees Kelvin. Heat engines, any device that changes heat into other forms of energy, depend on having a difference in temperatures available (for instance, cool river water versus hot steam pipe). If you just have a box sitting at room temperature, it can't work.
There is an interesting caveat here. The Second "Law" and most of how we typically apply entropy are based upon something called the Fundemental Assumption of Thermodynamics. Roughly stated: "All possible energy configurations are equally likely". As it turns out this is rarely ever exactly true, but it is so nearly true in almost every concievable macroscopic situation that it makes no difference. Entropy always increases is a mathematically certain law derived from the fundemental assumption and mathematical definitions of temperature, etc, but it is still concievable that their might be systems where the fundemental assumption doesn't apply and entropy might decrease. Over the years there have been a few suggestions for how to build such a thing (mostly at a quantum mechanical level), but no one has ever succeeded.
If someone does build a box that sits on a desk and converts ambient heat into energy output, then they are almost certainly guaranteed a Nobel prize. On the other hand there may be something better than the fundemental assumption, which is exactly true and excludes all possibility of such a wonderful, energy giving black box.
Re:is it more efficient than turbines? (Score:2, Informative)
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).
Re:Desert? (Score:3, Informative)
Using something like this requires a temperature GRADIANT... i.e., you could be in a desert that is 5000 degrees, and could NOT use that temperature (i.e. ambient air energy) to generate energy with a junction like this without some form of lower temperature location.
You must have two areas with a temp. gradiate difference bewtween the two that you can place this device across... in this case, the gradient can be lower (250 degrees) and is more efficient. This gradient comes from the difference in termperature between the exhaust and the surronding air.
It's all based upon the tech of peltier junctions.
Re:Hmmm... - might ruin smokestack effect (Score:5, Informative)
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.
Thermodynamic efficiency limits (Score:5, Informative)
- (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.
Re:More info (Score:4, Informative)
Re:Nice but not the end of entropy (Score:4, Informative)
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?
Re:Use on Hybrid cars? (Score:3, Informative)
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]:
Thermal diode := Peltier Element (Score:4, Informative)
Re:is it more efficient than turbines? (Score:4, Informative)
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.