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Capturing Waste Heat with Quantum Mechanics
TheMatt writes: "There is a summary of a Phys.Rev.Lett. article up at Nature Science Update that describes a design for a 'quantum afterburner' that would improve the efficiency of an Otto engine. It improves the efficiency by using a laser and maser to extract energy from the hot exhaust of the engine. In fact, the process could enhance performance beyond that of the "ideal" Otto engine."
I used a laser and a maser to extract energy from the waste heat generated by my Athlon. I've been running everything in my house but my computer off that exhaust tap!
They that would sacrifice their
So I get that you convert waste heat into light, first with the maser to get microwaves, and then with the laser to get some other wavelength. What then?
Why not simply use an adsorption type "refrigeration" (ammonium hydroxide & water) system to cool the air/fuel intake charge to make it more dense and get some more efficiency out of the internal combustion engine? The waste heat going out the exhaust and radiator could run the adsorption-cycle cooling system.
The hot gases belching out of your car's exhaust are not just useless waste. They are a laser waiting to happen, says physicist Marlan Scully
I sure hope this doesn't change the global warming going on or all that beachfront-after-the polar-icecaps-melt property I bought will remain high and dry (scuba diving in downtown LA whoohooooo)
I Am My Own Worst Enemy
I think this idea is genial, but the cost/effeciency on a car would be "hard" to achieve. What I find interesting, is that this duo laser/maser only require heat from an exaust : nearly the same thing as evaporated water from nuclear reactor. This could lead to a better efficiency of nuclear reactor, and the cost of such laser/maser would be minimal compared to electricity generated by that system.
Ideally, if the excess heat was converted back into electricity, I wouldn't need to waste electricity on the fan, and I could substantially extend my battery life. Oh well, I can still dream.
My first thought when reading this title (nothing to do with the article:
"Producing Hot Air with Quantum Mechanics."
-Paul Komarek
Can be found here (in PDF form), for all those who like reading physicists physics.
There's no reason for a sig here.
After reading the article, its not as far fetched as it sounds, atleast at a low efficiency.
The problem as I see it though is this, what is the engine going to do with the laser light anyway? Laser light isnt that usefull in a car as an energy source. And I cant see the intensity of light being enough to do something cool, like dissasociate water to H2 and O. This is probably in the "neat-things" file for quite some time. Though maybe they can use this technology for fixed poer generation (coal, nuclear) where the gasses temperatures are higher and there is more volume.
Anyone who considers arithmetical methods of producing random numbers is, of course, in a state of sin.-John von Neumann
Do Quantum Mechanics work for Maxtor now?
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
a frickin' laser, was that too much to ask?
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
Well, the university I went to had its own electrical power station. They used the waste heat to generate steam that was sent all over campus for heating. Even the dorms' clothes dryers used steam heat exchangers.
They seemed to have so much heat capacity available that they didn't think that proper thermostats were a priority. A lot of people had to regulate the heat on subzero days by opening the windows.
...The Fast and the Furious? I mean they had everything else: NOS stickers, neon lights on the undercarriage, ad naseum. Why not a laser in the engine?
-- ;-)
Kuro5hin.org: where the good times never end.
Could the exhaust gas heat be used to make a car heater that doesn't take so long to fire up?
But MIRACL is using a far more reactive fuel at far higher temperatures than anything you find in auto exhaust.
If this makes it into your average car, would you have to take it to a normal mechanic AND a quantum mechanic? The price of the devices used in research had better come down before it happens.
I can see it now...
QM: (Wipes hands on oily rag) Well, if you lookee here, yer muffler wall is causing the maser beam to create destructive interference.
Car owner: uhuh.
QM: That, combined with the alignment of the quantum magnetic dipole is causing yer car to stall.
Car owner: But how much will it cost?
QM: Yer salary fer the next two years.
Quantum Mechanics has been known to be a time-trasnlation invariant theory. In layman's term, it means that you can run the clock backwards and everything is fine. There is no "irreversible" process. (For the jargon-empowered, QM does not have a natural "arrow of time").
However, we know the Thermodynamics 2nd law tells us that even *ideal* processes are essentially irreversible if we do work, i.e. waste heat is inevitable.
So the idea to use QM to improve this "ideal"-ness (classically speaking) is an intersting step towards understanding the *other* big issue in science : which is how the 2nd Law fits into the grand scheme of things. (Grand Unified Theories do not incorporate 2nd law since microscopically are processes are essentially reversible. The 2nd law drove many people nuts, including Roger Penrose.)
So the point of the paper is not "get more $$$" for you engine. It's an interesting gedenken-experiment (sp?) that proves a point.
Mode (3) smart-aleck mode. Press * to return to main menu.
Joshu answered, "Mu!" (No)
I think you mistranslated 'Woof' ;)
Reboot macht Frei.
It actually has a big point.
:).
Although what you say may be correct, you have to remember that either using this to cool the intake or even better using it as a below-ambient intercooler on turbos increases the power-to-weight ratio of the engine because you can obviosly get more charge in a cylinder.
Thus you can create a lighter car with the same power and overall the efficiency increases because you have that much less mass to accelerate and that much less rolling resistance on the tires. Granted the efficiciency of the *engine* does not increase, but the efficiency of the entire system [car] does -- and that's the thing in the end that truly matters.
What I'm waiting for is efficient low-temperature thermo-couples to become cheap. That way electricity can be generated from the wasted exhaust heat getting rid of the need for an alternator.
Combine that with regenerative breaking and a few bucks on gas can definately be saved
if you could route the laser back to the combustion chamber, you could use it in turn to burn extra fuel (similar to the way nos affects combustion). the increased fuel being burned would create more exhaust. wash, rinse, repeat until nearly 100% of the fuel in the chamber is being burned and the car reaches maximum feasible efficiency. probably not all that feasible though, since routing lasers is expensive at best.
.cig - what you do after winning a good flame war
Something similar to this was posted a bit ago on Slashdot, but what the hell.
With a turbine engine, kinetic energy is extracted by hot-air through turbines, which in turn suck in air, compress it, combust it, etc. Cyclic compression and expulsion creates thrust, or rotational energy on the turbine shaft (which is what turbo-prop airplanes, APU's, helicopters and generators use).
This technology might have applicability for turbines which use rotational energy from the shaft. For instance, the APU on a 777 is a fairly large turbine engine. Would it be possible to lower its running RPM by using converted heat from the exaust stream as a secondary source of power? This would of course lower fuel consumption while the APU is running, as well as extend the time between overhaul for it.
Anyhow, essentially: this technology, if viable, could have serious use within turbine engines, since they waste a significant amount of heat in operation.
So, what's stopping you?
Home Power magazine is a good place to start for ideas and things.
And if you come up with something that runs a net surplus, sell the power back to your local government mandated utility. Most government grants of monopoly for electrical power include a requirement that the utility buy back what you as a private individual produce.
Not all, you can be sure, but HomePower has good information sources on that.
You could, of course, spend a decade lobying governments and buying influence with the politicians, but that would just make you another Enron. It's much more efficient to just build it yourself.
Bob-
The Ludwig von Mises Institute. The reasoning individuals economics
The whole idea seems like a good way to write a paper, get published and generate hot air, but not a good way to increase energy efficiency. Kinda like our current projects to build a fusion reactor ("We've already got one, fer Christ's sake! It's called the sun.").
There is no trap so deadly as the trap you set for yourself
-Raymond Chandler, The Long Goodbye
What you are refering to is VE(Volumetric Efficiency). VE is a major factor in the specific output(PS/Liter or HP/Cubic Inch). Regardless of VE, what we really are looking at is raising BSFC. That is Brake Specific Fuel Consumption. This number shows how much gasoline is required to produce horsepower. New electronically-actuated valves will do much to raise this. On a 4-valve cylinder, over 20% of the engine output is used soley to spin the camshafts and plunge the valves up and down quickly.
Turbocharged engines help by absorbing some of this engine's exhaust and 'reinvest' this kinetic and thermal engergy in the intake. However, it is a losing proposition; even with an intercooler, the more boost you pump, the hotter the intake charge gets. You quickly develop a cycle where you must retard timing to reduce preignition and detonation thus raising exhaust temp's even more. The retardation of the ignition severely reduces power output thus nullifying any boost pressure you are running anyways.
No, turbochargers are good for increasing VE , but do little to alter the fundamental(thermal) efficiency of an engine.
We need a revolution.
You can't legislate goodness. Let each to his own destiny, by will of his freely made choices.
and it is a pretty interesting idea. I'm not sure about the practical feasibility of the concept for reasons I'll get into below. But, it shows that quantum effects might be usefully exploited to make better engines and will probably prompt a fair amount of thought and experiment into the matter.
... thanks lameness filter ... less than signs could never be useful).
... more molecules must be in one of the upper states than in the lower states. However, in a gas at thermal equilibrium, this is usually not the case ... the probabiliy of finding a given quantum state in state with energy E is proportional to exp(-E / kT ). Here, k is Boltmann's constant and T is the ambient temperature. At low temperatures, the ground state will be where most of the molecules are.
... "b" molecules to preferentially transistion into the ground state (state "c"). However, the "a" population won't be able to come to equilbrium that fast (provided the spontaneous emission rate is sufficiently low and the maser cavity isn't tuned to enhance the transition rate out of "a" state). This net impact of the maser is to create a population inversion between the "a" and "b" states. By passing the non-thermal maser cooled gas into a laser cavity tuned to the "a"-"b" transition, this inversion can be extracted as laser energy. This is the quantum afterburner part.
... involving passing the gas back and forth through two pistons. I'm pretty sure that materials and a simplified engine design could be made to validate the claims though.
Warning: Ph.D. punditry follows.
Suppose a molecule has three possible states ("a", "b" and "c") with energies E_c, E_b, E_a respectively (E_c is the ground state and E_b is the between E_a and E_c
Suppose further, microwave (maser) energy transitions are possible from state "b" to "c". Optical (laser) transitions are possible from "a" to "b".
For lasing to occur, you must have a population inversion
If the hot exhaust gas is first passed through a maser cavity tuned to the "b"-"c" transition containing a radiation field at the temperature of the cold reservior, the "b" and "c" populations will quickly come to thermal equilibrium with the low temperature radiation field
From a quantum standpoint, nothing is particularly new here. Using rapid cooling of a selective population to create inversion is pretty unique but nothing that can't be explained with the standard laser rate equations.
From a purely statistical mechanics standpoint, the net effect is to extract extra useful work from internal degrees of freedom of the working fluid. Statistical mechanics is not my forte so I can't really say if this is particularly out there.
From a practical standpoint, it might be hard to find gases at engine temperatures and gas pressures where the low spontaneous emission lifetimes necessary to sustain the inversion is possible. My intuition says that collisional de-excitation (high temp and pressures) would wipe out the inversion. Also, the exact scheme discussed in the paper is more complicated
As a thought experiment, though, this shows that it may be possible to improve the efficiency of an Otto engine. (By the way, the paper notes that a Carnot cycle efficiency doesn't get a boost from the technique.)
Kevin
Every time I see that Ben Franklin quote, I'm reminded that while many Americans risked (and lost) their lives to throw off British rule, Franklin "suffered" by staying in France during the revolution. I guess he didn't mind his own safety being secure while other people fought. Hypocrite.
-jon
Remember Amalek.
Same with classical mechanics, and more so, as QM has the "destructive measurement" hypothesis, that by merely measuring that an object is in a given state, you collapse any state superposition in which it might have been. Besides, Statistical Physics and Thermodynamics have borrowed quite a lot from QM (particles being in given states among a number of possible ones, etc.)
Yes, this comes from the fact that there exists a great many more possibilities that waste heat will be irrecoverably produced. It might stay in a usable form, just as you might open a bottle of ink under water, and the ink might flow out and then all crawl back into said bottle. It is just highly unlikely.
There is no need for an arrow of time at the microscopic level for that.
As for the paper itself, if I understand the summary correctly, it is ingenious but I'd look for a catch, such as the maser requiring at least as much power to function as that you can extract from the waste heat... Wouldn't that be annoying?
(And many thanks to all the scientists who publish on arXiv).
"Ya see, we're kinda afraid that if we observe the problem it might alter the system and give you a totally different problem..."
"Well, we're not quite sure where your car is, but we do know exactly how fast it's moving... Would you prefer the other way around? 'Cause I can do that instead if you want..."
--
Damn the Emperor!
... you can always run SETI@Home.
--
"By the way if anyone here is in advertising or marketing... kill yourself." -- Bill Hicks
That's what I thought. An ideal machine has no waste energy whatsoever; the useful work you get out of it is equal to the energy you put into it in the first place. "Better than ideal" would violate the 1st Law of Thermodynamics. This just brings it a bit closer to the ideal.
Dyolf Knip
On a related note, heat engines are much less efficient that 100% you seem to imply with "it should give same amount blah blah." The reason is second law of thermodynamics. You can convert all heat energy you put in the engine to work, since doing so would require heat transfer with no temperature gradient.
Gentlemen, you can't fight in here, this is the War Room!
Doesn't anybody else find it at least slightly funny that someone is proposing putting a Quantum Afterburner (TM) on a piston engine, the essential design of which is 125 years old? After all, there are other ways to recover waste heat in the exhaust that we could be using now, but aren't. Peltier junctions could be used to generate electricity to supplement or replace the function of the alternator once the engine was hot. Someone else here mentioned stirling engines. Maybe that'd be another way to increase the efficiency. Again, maybe you could drive the alternator with it. Of course, the alternator only uses maybe 1 or 2 horsepower anyway, so even eliminating that drag on the engine is only going to be a small improvement.
Than again... how many horsepower does a car use when cruising? Maybe eliminating 1 or 2 horsepower would make a difference. I would assume that this Quantum Afterburner (TM) would be able to recover a much greater amount of the waste heat, too, so maybe it would make quite a difference.
P.S. -- before anybody starts to rant on me for using horsepower, remember, there are metric horsepower too! According to my unit converter, one horsepower equals 1.01387 metric horsepower. Guess the French have different sized horses than the English! Cheers!
just otto. Infact in "Science" it is reported that the device is coupled with a carnot engine to check for an experimental fluke. The device, as expected/hoped, did not work at all.
Gentlemen, you can't fight in here, this is the War Room!
I'm no engine expert, but doesn't anything that impedes the flow of exhaust gasses interfere with the internal combustion process, making the engine less efficient? The two-poston contraption these guys are using would certainly seem to fall into that category, if they tacked it into the car's tailpipe.
Patrick Doyle
I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....
Alas *this* paper has nothing to do with violating 2nd law. It is not a gedanken experiment either, its a real device. I guess you should read the article from time to time.
Gentlemen, you can't fight in here, this is the War Room!
Sort of on topic, considering the number of comments being posted about heatsink fans (even though the article has little to do with it): why noone ever figured out a way to use the hot air being expelled by the system fan to turn something that would generate electricity. Can't some of it be recycled back to power the system?
Read some of the posts higher up for an explanation of why this is okay. Or do this simple experiment: Clean your house. Or room. Or sock drawer. Hey presto! Less entropy.
Ack! The story summary is misleaded. An ideal Otto engine DOES NOT ACHIEVE the maximum efficiency possible for a heat engine (so improving it doesn't violate anything). A Carnot engine is the engine with max efficiency which you are thinking of. Exceeding the efficiency of a Carnot engine (which is still less than one) is equivalent to breaking the Second Law of Thermodynamics.
The Second Law is really a statement about probabilities and how you count macrostates and microstates, and so doesn't have to be present in microscopic physical laws because it doesn't mean much there anyway.
I'm not impressed, especially since the point of the quote is that we need to never give up a single freedom, lest we start down the slippery slope towards dictatorship. This is usually used as an excuse to pirate MP3s. Or, right now, it's used as an excuse as to why we can't have racial profiling or face scans or background checks.
Meanwhile, the person who originated the quote decided to spend the Revolutionary War, not fighting for freedom, but living in a beautiful guilded cage in a repressive dictatorship (England in the 1780s was far more democratic than 1780's France). Seems like Franklin, given the choice, chose comfort.
-jon
Remember Amalek.
Well thought-out shot ... cheap shot, bit insightful ...
utter rubbish