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.

Warning

[Supersonic1425]

Do not shake.

gyroscope?

[Burlap]

at half a million RPMs, what kind of damage would happen to this thing if it was put in, say, an MP3 player for a jogger?

Dupe with no more info

[ryanov]

Two postings now and the obvious question is still not answered... where the hell are you supposed to get the fuel for these things? How are they supposed to be refilled? Still nothing.

Actuallly should be pretty tough

[wsanders]

If the trend is anything like hard disk drives, the device should get tougher as the dimensions get smaller.

I'd hate to see one of these things throw off a blade while it's powering your iPod on the subway, though.

Power generation

[harryk]

I think it's neat that it can output upto 100watts of energy, but at what Amperage and Volt? Could I use a couple of these things to say... act as a battery charger for an electric car?

Re:Power generation

[Overzeetop]

At 95% efficiency (a dubious claim, imho, given that the cold sink temp is presumably room temp), it would be a good source for constant charging and potential peaking current. You'd need a good number, though, at roughly 8 to the horsepower.

I think the future might be in portable power and backup devices - having a refillable, continuous 7-15kW power supply in a breadbox. With the right gear ratios, it could put out sinusoidal 60hz power for AC backup, though synchronizing the signals and preventing drift across the array would be a task in itself.

Reversal of use

[LParks]

So our portable energy used to come from batteries, and now its becoming gas-powered. And our large vehicle engines used to all be gas powered, and now it comes from batteries. Interesting reversal.

None have run yet?

[sidles]

It takes a lot of reading to realize that none of these sub-centimeter turbines has actually run yet. Perhaps the laws of combustion physics prevent this? There's a reason why candle flames are the size they are ... see Michael Faraday's classic lecture The Chemical History of a Candle [bartleby.com].

Material fatigue?

[qwertphobia]

What happens after one of these has been used off and on for a few years and the materials start to fatigue? Have we all seen the videos of the CD-Roms spun on a Dremmel tool until they explode? Hint: convert 500k (or 1M) rpms into linear velocity at the outside radius of the turbine.

Would you buy one?

[bmetz]

I honestly wonder who these are for. I wouldn't use a cell phone or a laptop with a gas turbine in them. The noise, the vibration, the fumes, the refill process; even in the most ideal circumstances I am too spoiled by 'good enough' battery technology.

I'd like to see more work on battery technology and more pervasive conductive surfaces so every place I set my laptop and cell phone down helps charge it.

Re:Uncontained turbine failure = bad Ju Ju

[dschuetz]

Ever seen the results of an uncontained turbine failure on a jet engine?

Have you ever seen the results of a *contained* failure? A while back, as the Boeing 777 was just coming into commercial use, PBS ran a long special (or maybe a series of episodes, I forget) about the plane. They showed how they wrapped the engine in some kind of special kevlar blanket, then tested it by shooting something into a fully spun-up engine.

The outsides of the engine (the whole chamber) sort of bulged out maybe 6-12", then compressed back down to normal size. And that was it. It looked like something out of a cartoon, where (say) Bugs Bunny might swallow a lit stick of dynamite, then his stomach would bulge suddenly as it exploded, then he'd burp out a small puff smoke and be done with it. Really very cool, actually.

Anyway, I'd expect they could do something similar with this, too. Plus, even though it's spinning faster, the mass of the spinning parts is probably pretty infinitessimal, so even a total catastrophic failure at 1 million RPM might not be cause for concern. (as compared to the mass of the fan blades in a massive jet engine).

Does it twist your arm?

[cohomology]

The rotor of the Swiss turbine must be pretty beefy. How much angular momentum does it have at 500,000 RPM? If you've ever played with a large gyroscope, or twirled a bicycle wheel while holding onto its axle, you can see the problem. If you try to change the direction of its angular momentum vector, the thing will twist around an axis perpendicular to both its angular momentum vector, and the direction of the torque you apply. If this thing is in a laptop, spinning around an axis parallel to the floor, and you walk around a corner, the laptop could flip in a very surprising way.

Re:Article close to pure crapola!

[Big_Breaker]

Efficiency is often quoted as a % of Carnot efficiency, which is the efficiency limit for a pure heat engine and it's around 35%-40% depending on temperature. I think turbines are subject to a lower limit which happens to be around 90-95% below Carnot.

Anyway - who cares? Efficiency in small devices is MEANINGLESS. What matters is power and energy density by volume and weight. This has both in spades.

Batteries are incredibly efficient, but you need to generate the power to charge them somehow. They also (generally) have very poor power and energy density by weight and volume. Supercaps are great with power density and some press releases claim enormous increases in energy density but we haven't seen it yet.

These turbines are shrunken versions of proven technology. It seems very credible and promising. At small sizes and high RPM things like air bearings work BETTER. And those RPM records are for large rotating masses. These are tiny and easy to hold together. Translate 500k RPM into a linear m/s measure for a cm diameter turbine and you'll understand better. The edge doesn't even break the sound barrier (though it does approach it).

house droid power?

[wonkknows]

I would love to see something like this on a small cleaning droid like the iRobot if the C02 output was minimal.

http://store.irobot.com/product/index.jsp?productI d=2475131 [irobot.com]

6000C past temp limit of combustion gases

[Latent Heat]

The National Aerospaceplane (NASP) was supposed to burn hydrogen in a "scramjet" to propel and airplane-like vehicle to Mach 20 and into orbit. The funding got pulled on it, and there was some speculation that it was cover for "black" programs.

Anyway, the scramjet is the ultimate exercize in drinking from the firehose. A normal turbo or ram jet engine has a diffuser to slow the incoming airstream to some managable subsonic value, burn fuel, and drive the turbines. Trouble is that if you are going fast enough, the diffuser gives you so much compression and inlet temperature that nothing burns -- if you go much above the flame temperature of your fuel, your combustion gases (mainly water vapor for the hydrogen-powered NASP) disassociate back into hydrogen and oxygen.

The trick to the scramjet is to only slow the incoming airstream a little bit, somehow burn fuel in a supersonic airstream, and expand the burnt gases to get more thrust than the drag created by this arrangement.

I am not a physical chemist, but I would bet that 6000 C is past the disassociation temperature of combustion of whatever fuel and air, and you are not going to operate a gas turbine at 6000 C inlet temperature regardless of what miracle materials.

Furthermore, efficient use of a 6000 C turbine inlet temperature requires very high pressure ratios -- doubt you get that in miniature.

100 watts of output power sounds goofy -- that is of the same range of my gas engine weedwacker that generates a lot of heat and burns through a good amount of fuel.