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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 ...
Hydrogen is hardly a fossil fuel; it's abundant, and the combustion byproduct of hydrogen and oxygen (the two fuels used in this case) is none other than water. Pure water, at that.
This is why hydrogen is being looked at so heavily as an "alternative" fuel source -- it's abundant, clean, and very inexpensive.
--
I Hit the Karma Cap, and All I Got Was This Lousy
Its quite simple...
2.4million revolutions per minute
Divide by 60 to get revolutions per second
revolutions per second is analogous to frequency(Hz)
"When I grow up, I want to be a weirdo"
Umm, Hertz equals cycles(or rotations) per second.
(2.4E+06RPM (Rotations / Minute) / (60 Seconds / Minute) == 40000 Hertz
Or 40KHz
H2 in gaseous form is NOT explosive unless it's in a mixture with O2 where it is about 4% to 85% of the mixture. Pure H2 is perfectly safe. And even if the H2 tank ruptures there is not going to be enough H2 to do anything. It might burn for a second or two and thats about it, most likely not enough H2 mass there to really do any damage (beyond the device it's in). Certainly not enough to cause an explosive misture in a large enough volume of air to matter.
And since this tank is gonna be small, it can be made really freakin tough. Think about how tough a good quality propane cigarette lighter tank is.
Most micromotors demonstrated to date have simply succeeded to overcome the viscous drag on the rotor, leaving no power to drive other com-ponents and limiting their use for low-load actuation.
Luc Frechette just published ASSESSMENT OF VISCOUS FLOWS IN HIGH-SPEED MICRO ROTATING MACHINERY FOR ENERGY CONVERSION APPLICATIONS in which he lays out the constraints of micro-motors and how he hopes to overcome them.
Liquid hydrogen is cold at 1 atmosphere of pressure. You can make it as hot as you want, if your container can handle the increased pressure.
Gaseous hydrogen isn't really any more explosive than the butane in your lighter or the natural gas piped all over your house.
You prefer children playing with toys powered by batteries that are packed with lithium, mercury, etc?
"Prefiero morir de pie que vivir siempre arrodillado!"
to all those asking seriously whether whatever animal will go crazy at that frequency, i'd like to remind them that 40khz is NOT the frequency of the SOUND WAVE, but the frequency of rotation.
You've got it backwards. The stresses do go down by something like the square of the sizes. But the power output decreases by something like the cube of the sizes. The rub (pun intended) is that while power is decreasing by cubes, friction is only decreasing by squares. So as you get smaller, the poweroutput/friction ratio is getting smaller.
http://www.sciam.com/news/101101/3.html
As penance, I'll plagiarize some text for my honorable master, the slashdot audience:
Novel Semiconductor Device Heats and Cools on a Dime
[...] Rama Venkatasubramanian and co-workers, publishing in today's Nature, built a faster and more powerful than ordinary thermoelectric device, which converts heat and electricity back and forth, by alternating very thin layers of two semiconducing materials. This film-made of bismuth, antimony and tellurium-is 2.4 times more efficient than conventional bulk devices, 23,000 times faster, and can be applied in tiny dots for pinpoint refrigeration. "This marks a major advance in a field that has stagnated for 30 years," says John Pazik of the Office of Naval Research, which provided funding for the research.
Thermoelectric devices are longer lasting and tougher than mechanical refrigerators. Their high cost and low efficiency, though, have generally confined them to niche markets: powering deep-space probes, cooling infrared detectors, and, lately, heating and cooling luxury car seats. Cheaper, more convenient thermoelectrics could speed up microprocessors and fiber-optic lines, make possible miniature biotech tools capable of stopping and starting small biochemical reactions, or running a car's air conditioner with waste heat from the engine.
-Pimproot, betting his transplantable head on the Promised Land of scientific salvation
You wish. Actually, burning hydrogen in air generates some NOx emissions. Hydrogen in air is a complicated combustion system. NASA has been working on scramjet designs that burn hydrogen in air, so this problem is gettimg some attention. It's the subject of some big number-crunching simulations.
If you want a totally clean burn, you have to burn hydrogen in pure oxygen.
You are wrong. A gas can be liquified by compression only below a certain temperature. For H2, that temperature is something like 20 or 30 kelvin. That's really, really cold, requiring quite special refrigeration equipment, and AFAIK that's not portable, or even movable without a large forklift. Rocket fuel tanks are cooled by venting off the evaporating gasses, and pumping more in until the hoses have to be unhooked just before ignition. (I don't know if they vacuum the escaping hydrogen back to the liquifier plant, or just let the wind carry it away and watch that the concentration doesn't reach the explosive level...)