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Hydrogen Micro Turbine Only 4mm In Diameter
savaget writes: "Luc G. Frchette of the Columbia University Microsystem Engineering Laboratory has developed a 20W electrical generator powered by a hydrogen turbine just 4mm in diameter. For more details, read the Wired
article or an older Popular Science
article. The tiny generator is more efficient than any battery and is expected to find military and commercial uses including robotics." Imagine the uses ...
Both articles say the engine is powered by fuel, but what fuel are we talking about? Regualar old gasoline/octane? Am I supposed to stop by the local gas station and top off my laptop battery each day on my drive to work? The Popular Science article mentions hydrogen being burned...maybe this means that they are looking for "alternative" fuels as opposed to fossil fuels. Then again, the Wired article hints at fossil fuels as the energy source. Someone shed some light on this please.
greg
"But where does the exhaust go?" - well, out, that is rather the definition of exhaust. The exhaust is water vapor, unused combustion air, and heat. That shouldn't be a problem. Well, you won't want 20W to 40W of heat running in your pocket, but other than that it should be fine.
"And isn't this kind of a step back in our attempt to stop using fossil fuels..." - I am an American. My goverment has no such policy. All your oil are belong to us. For those of you in conservation minded countries, hyrdrogen is not a fossil fuel. It is a theoretically handy way to store electrical energy. There are technical hurdles. Not insurmountable, just insurmounted. Once there is a demand, there will be a way of distributing and storing the hydrogen.
The contaminants in gasoline would be far too great for a machine this tiny. Cars have huge engines that still get clogged up...
Hydrogen should be what fuels this nation and we should make that move as soon as possible. We have everything to gain and absolutely nothing to lose.
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There's efficiency and there's power output.
The problem with fuel cells is that they're BIG for the power that they produce. A turbine is small for the power that it produces. So this dime-sized turbine supposedly generates 20W of power. How big of a fuel cell do you need in order to get 20W out of hydrogen?
I don't know the numbers myself. It could very well be that a fuel cell's power-to-volume ratio is good enough that you could still manage to power a laptop off of one. But since it's not as good as a turbine, that means that the turbine-powered "battery" pack would have more space available for fuel.
Even better, a turbine's efficiency (potentially) increases as you get it smaller. The major stumbling block for turbines is making the fan strong enough to handle the huge stresses that are put on it by the awesome speeds at which it rotates. But as a turbine gets smaller, its strength increases: mass decreases as the cube, but the various strength measurements (torsional, tensile, etc.) decrease by the square of the size. Silicon is far too weak for full-sized turbines, but (apparently) it works just fine for these submini turbines.
-- Nolite audere delere orbiculum rigidum meum.
Yes, hydrogen is abundant. But it is mostly tied up in covalent bonds with other elements, such as oxygen, in water, or some other such bound form.
To burn the stuff, you first have to split it from whatever it is bound to, and that takes some deltaE.
In fact, it takes as much deltaE to split the hudrogen off as you get back by burning it and puttign the bonds back together (first order calcs).
Hydrogen is a *storage* fuel. It is simply a new way to take energy from one place and move it to elsewhere, where it might be more convenient to use it.
If you plan on using hydrogen to create a lot of usable energy storage, as in to replace some of our curent fossil fuel dependency, you have to get the energy from somewhere. Like say, fossil fuel.
Or nukes, or some such thing.
The point is, it can't reduce our curent dependency on our current fuel sources (well, it might add some efficiency at sa few points, like al.owing us to use excess generating capacity at off-peak hours. The laws of thermo-goddamnics still apply.
Hydrogen technology doesn't create any new energy reserves, it simply allows us to store some of our energy reserves in a different (H2) and potentially differently-useful form.
Fuel cells will win in efficiency. Probably by a large margin.
Perhaps turbines have other advantages...
So what happens when you spill some liquid hydrogen into your expensive laptop? Doesn't liquid hydrogen need/exist at a cetrain (cold) temperature?
I'm no expert, but I think the fuel itself could pose some problems. Anyone have more info?
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Being perfect to the last atom or so, there should be no vibration at the fundamental frequency. I counted 20 blades in the Popular Science picture, so the actual noise peak should be at 800kHz. Easily damped, and out of pet hearing frequency range.
No, one can also consult reference materials, but this requires initiative.
(And sometimes one wants to learn something that nobody else knows. This requires even more effort. Imagine the state of human knowledge if the only way to learn were to ask someone else.)
The exhaust is water vapor, unused combustion air, and heat. That shouldn't be a problem. Well, you won't want 20W to 40W of heat running in your pocket, but other than that it should be fine.
The 20-40 watts is the power delivered by the device to the laptop and eventually (except for a miniscule amount leaving as light, radio waves, telephone modem signals, etc.) disipated as heat by the laptop's circuitry.
But the generator is a HEAT ENGINE and this one runs at 10% efficiency. So to generate 40 watts it burns fuel at a 400 watt rate. 40 watts to the laptop, 400-40 = 360 watts of heat in the exhaust.
And you CAN'T improve it very much. It's a heat engine. Perfect efficiency for a heat engine is the carnot cycle limit: 100% * (Th - Tc)/Th.
Call that about 30% for a fuel-burning engine at room temperature, and you're still talking 133 watts of heat sitting on your lap for a 40 watt load. But you can't get anywhere near carnot cycle in a practical device, and the smaller and faster the device the more you'll fall short - you need something like a power-plant to approach it. So back to 10% and 400 watts.
What gets me about the Scientific American article is the apparent claim that the efficiency of batteries is ten times worse. Batteries and fuel cells can approach 100% efficiency.
I think what happened is they confused efficiency with energy density. A battery contains both its fuel and its oxidizer - and oxidizers tend to be heavy, due to heavy atoms and extra atoms to hold them down. Heat engines and fuel cells, on the other hand, can get their oxidizer from the ambient air, and expell the combustion products. So they only need the engine/cell proper plus the fuel tankage. Yes a heat engine would probably beat a battery by a factor of ten on energy density. But a fuel cell, if it can be adequately miniaturized, might do still better.
Nevertheless this engine looks like a good solution (if you're willing to put up with the waste heat), at least until fuel cell technology approaches it in power density.
The use of hydrogen is curious. Handling it is a real bitch. It crawls right through steel and burns with an invisible, super-hot, ultraviolet flame. Very dangerous.
They are probably using it, rather than a liquid hydrocarbon like butane, to simplify the design and to get the maximum energy-density numbers for the engine/tank system. With butane/air you need to do emission control for NOx, CO, and unburned hydrocarbon. With hydrogen/air you only need to sweat NOx. Hydrogen's energy/ounce of fuel is higher and it's easier to light. Liquid hydrocarbons - especially impure and "odorized" formulations - produce a number of combustion products that can potentially foul the engine or its exhaust as well. You don't need fancy controls for a hydrogen engine, while a butane engine might need a catalytic converter and some serious compute power.
What I'd like to know is whatever happened to the ceramic oxygen-concentration fuel cell - the one that uses the same basic cycle as the exhaust-gas oxygen sensor in a car?
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The way I interpreted the Wired article, this thing is still theoretical. They didn't even mention a working prototype. I refuse to read anything real into a Popular Electronics/Mechanics/Science article. That's all complete crap.
/. will instead be discussing the latest vapor being hyped.
I'm sure a couple years will pass and we'll all wonder what happened to that "micro turbine thing". We won't be discussing it much, though, because
Why are you letting these clowns ruin our country?
It's not PC to note this but did you realize that all the fuel from 40 years of operation of a nuclear plant will fit into the same volume as a large semi-trailer?
That's incredible really.
Imagine, all the electricity needs of a family of four for 40 years generate about 3 pounds of fuel waste.
It was in New scientist (no link available, sorry). Engines like these are needed in joints of exosceleton. Other solutions (backbag engine or batteries) are not viable.
Anyway, it is not fruitful to shootdown good research just because nobody can't come up with application in a second. The question why anyone wants tiny hydrogen-powered turbine generator will be definetly ansered in future.
-- Nyri