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Two Tiny Gas Turbines

Posted by ryuzaki0 on from the burn-a-hole-in-your-pocket dept.

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.

5 of 202 comments (clear)

  1. Re:Inefficiencies? by Colin+Smith · · Score: 4, Informative

    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.

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  2. 6000C combustion? by Overzeetop · · Score: 3, Informative

    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?)

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    Is it just my observation, or are there way too many stupid people in the world?
    1. Re:6000C combustion? by Overzeetop · · Score: 3, Informative

      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.

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      Is it just my observation, or are there way too many stupid people in the world?
  3. Re:Inefficiencies? by jandrese · · Score: 4, Informative
    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?
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    I read the internet for the articles.
  4. Article close to pure crapola! by Ancient_Hacker · · Score: 4, Informative
    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.