Two Tiny Gas Turbines

Turbines are in the news this morning. bobtheimpossible writes to point out a BBC article on a Swiss turbine that runs at half a million RPM and generates 100 watts. It's the size of a matchbook. And af_robot alerts us to an even more diminuitive gas turbine on a chip, developed at MIT, that generates 10 watts — plenty for portable electronics — and should run 10 times as long as a battery of comparable weight and cost. A commercial version is 3 to 5 years away.

Comments

Re:Warning

[Anonymous Coward]

You would have a hard time shaking it as the 500,000rpm turbine would act like a Gyroscope.
I would worry about dust, sand, bugs and other small bits getting pass the air inet.

http://en.wikipedia.org/wiki/Gyroscope

Re:Inefficiencies?

[Colin Smith]

Sorry, but bollocks it is. A gas turbine is a heat engine, the efficiency is determined by difference between the temperature at combustion and the exhaust gases. 50% would be excellent for a gas turbine.

6000C combustion?

[Overzeetop]

That's what it would take for a carnot cycle to be 95% efficient (give or take) with a room temperature heat sink. Is it really burning this hot, or is the article full of shit? (or is my thermo just that rusty?)

Re:6000C combustion?

[Overzeetop]

That's true, but my (poor) memory seems to recall that no thermodynamic cycle can exceed the Carnot efficiency - it is the theoretical limit. A turbine does have a cycle, though I can't remember the name offhand - it's been almost two decades, and I don't do any thermo in my line of work. ...Okay, google is my friend. The answer is the Brayton cycle, and the effeciency appears to be 1-T1/T2, which is identical to the effiency of the Carnot cycle, presuming theoretical gasses and adiabatic conditions (neither of which exist in turbines). So the answer is still about 6000 Kelvin (not celcius, and extra , which is a good bit above the melting point of most materials. From Wikipaedia: The chemical element with the highest melting point is tungsten, at 3695 K (3422 C, 6192 F). The often-cited carbon does not melt at ambient pressure but sublimates at about 4000 K; a liquid phase only exists above pressures of 10 MPa and estimated 4300-4700 K. Tantalum hafnium carbide (Ta4HfC5) is a refractory compound with a very high melting point of 4488 K (4215 C, 7619 F) I'm banking that this isn't running at 6000K.

Re:Inefficiencies?

[jandrese]

What's 5% of 100 watts?

Um, about 5 watts? That's pretty low heat dissipation all told. Exaust and mechanical stress are definatly a concern though, although with components that small at least the masses will be tiny, even if the RPM is exceedingly high. I wonder about the sound though, is it going to drive dogs insane everytime you turn on your Laptop?

Re:Inefficiencies?

[syphax]

RTF Textbook Unless I'm missing something, this turbine is a heat engine, just like any other turbine. Heat engines' max. efficiency is 1 - T(cold)/T(hot), where T = absolute temperature (Kelvin or Rankine). At T(cold) is likely room temp (~300K), if this thing is 95% efficient, T(hot) must be around 6000K. That's... hot.

Re:Power generation

[Lumpy]

it generates 100 watts. 20 amps at 5 volts. 10 amps at 10 volts 1 amp at 100 volts or .1 amp at 1000 volts.

Take ypur pick, you can generate from 0.001 volts at insane amps or millions of volts at nearly no amps.

Watts are universal and translate to all voltages.. anyone with a very basic background in electricity or electronics knows this.

Article close to pure crapola!

[Ancient_Hacker]

An efficiency of 95% ! ?

The best large gas turbines do about 35%.

And efficiency drops very quickly with size-- you see friction goes down as the square of the size, while power goes down as the cube. Somewhere between the size of a sausage and a hot dog, all the turbine power is going into overcoming friction.

And the biz about 1 million RPM is pure hokum-- the worlds record is a bit below that, and that was with a tungsten alloy rotor in a vacuum chamber.

Methinks some press agent was drinking while on duty.

Re:Article close to pure crapola!

[John Hasler]

> Methinks some press agent was drinking while on duty.

Methinks some slashdotters have reading comprehension problems. The BBC article which mentions 95% is about a Swiss generator, not a turbine. 95% is quite reasonable for a small generator. The article only mentions turbines in passing, noting that one could be used to drive the generator.

This is a DARPA spinoff

[Animats]

DARPA has been funding this kind of thing for years. Small turbines have resulted. DARPA was originally trying to develop bird-sized unmanned aerial vehicles. That R&D program produced some flyable devices, but they didn't have the low cost and 2-hour endurance DARPA wanted.

DARPA-funded work at MIT resulted in some microturbine parts back in 1997. Progress has been slower than expected, but it's happening.

The microgenerator thing was intended as a military application. The idea is to have something small, maybe even wearable, a soldier can use to recharge all the battery-operated gear. Battery recharging in the field, where power outlets are rare, is getting to be a huge hassle in the US military. Current technology is to put power outlets on everything with wheels and an engine, but that creates its own headaches.

Re:Uncontained turbine failure = bad Ju Ju

[budgenator]

well i've got a 150K RPM turbine in my hand right now, from a dental High-speed handpiece, I'd feels about half the weight of a nickel so that 2.5 grams, and I'd estimate 3/4 the weight is bearings and shell so the rotating portion would be about 0.75 grams for the actual turbine, the shaft and the 1 mm press to release chuck.