Slashdot Mirror
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.
It's still a mecanical conversion of a compounds to energy, with all the inefficiencies that go with it, including disposal of waste heat. Where's these fuel cells I keep hearing about?
10 props for neat, anyway.
also, can it do this?
A feeling of having made the same mistake before: Deja Foobar
Do not shake.
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?
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.
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.
Give a man a fish and you have fed him for today. Teach a man to fish, and he'll say "WHERE'S MY FISH, YOU IDIOT?"
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?
think before you write, it'll save me moderator points.
Refillable butane lighters have been around for quite a while, I'd imagine this technology would have a similar refueling mechanism.
Will these devices come with ear plugs or noise blocking head phones?
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.
Deleted
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.
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?)
Is it just my observation, or are there way too many stupid people in the world?
I read the internet for the articles.
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.
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.
Never ask for directions from a two-headed tourist! -Big Bird
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.
Simple Unexpected Concrete Credible Emotional Stories
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.
What did you eat today? http://www.atetoday.com/
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.
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.
New battery? Must be for laptops!!
'Cmon? Does everything have to be "a new way to power your laptop"? First, who the hell wants a 500,000 RPM anything sitting in their lap? The high squeal resonant frequencies will be hell once it is about two weeks old. I'll pass, and I'll ask the stewardess to shut down the guy trying to use one next to me. Second, what happens when the enterprize standardizes on this thing, and you have a cubicle farm of laptops spew CO2 (and a small component of CO) into the closed office atmosphere. I'll pass, and I'll use the Worker's Compensation claim to its max if I survive the asphixiation.
The guy says that he was surprised that designing the combustion chamber turned out to be easy, but the bearings were hard. He expected it to be the other way around. Well, no shit, Sherlock? Stationary components are easy and moving parts are hard. That applies to all mechanical systems. Duh? Someone else justified the high RPM in a previous post, noting how small the rotor will be. The gyroscopic forces trying to pull the laptop from your hands when the taxi rounds the corner will indeed be small, but the forces on the rotor bearings in relation to their size will be huge. The laptop may not rip from your hands, but it will get quiet (which the taxi driver will appreciate).
How about putting one of these in a container the size of a breadbox, and mounting it above a septic tank in a small village or country farm. Have it charge a battery as it feeds off the methane produced?
Aah, change is good. -- Rafiki
Yeah, but it ain't easy. -- Simba
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).
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.
Don't mess with The Phone Company. Piss them off and you'll be using two tin cans and a piece of string.
I would love to see something like this on a small cleaning droid like the iRobot if the C02 output was minimal.
I d=2475131
http://store.irobot.com/product/index.jsp?product
It would be pretty cool to run a laptop for hours on a gas engine, but will I be allowed to take it with me when I fly? I can't imagine that TSA is going to allow me a small quantity of flamible liquid so I can run my laptop on the plane. What about the emissions in a closed environment?
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.
Apocalypse Cancelled, Sorry, No Ticket Refunds
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.