From: steinly@topaz.ucsc.edu (Steinn Sigurdsson)
Newsgroups: sci.energy
Subject: Re: Flywheel batteries as EV power source
Date: 22 Dec 92 22:44:21 GMT
	<51697@seismo.CSS.GOV>
Followup-To: sci.energy
Organization: Lick Observatory/UCO
NNTP-Posting-Host: topaz.ucsc.edu
In-reply-to: stead@skadi.CSS.GOV's message of 22 Dec 92 22:09:59 GMT

In article <51697@seismo.CSS.GOV> stead@skadi.CSS.GOV (Richard Stead) writes:

   In article <olsen.42.725052409@vetmed.cvm.uiuc.edu>, olsen@vetmed.cvm.uiuc.edu (Aart_Olsen) writes:
   > In article <77846@ncratl.AtlantaGA.NCR.COM> mwilson@ncratl.AtlantaGA.NCR.COM
   > >In <olsen.32.724613003@vetmed.cvm.uiuc.edu> olsen@
   > >|In article <BzEsw7.57B@cs.uiuc.edu> morrison@cs.uiuc.edu
   > >|>1) Slow down the rate of energy dumping. ...

   > >|This is what laboratory ultracentrifuges do.  Usually the rotor housing
   > >|is contained in a thick bronze casing which "slowly" absorbs the kinetic 
   > >|energy.  I once heard an ultracentrifuge blow, and it sounded like a freight
   > >|train for maybe five minutes.  Lab centrifuges contain a surprising
   > >|amount of energy--even though they have relatively small rotors and big 

   > >Do you happen to know how much one of the little beasties weighs.

   > Ultracentrifuge rotors weigh about 2-4 Kg.  They are maybe 15 cm diameter, 
   > spin at 60-80KRPM.  I think the best of them these days develop 800 kilo-
   > gravities at the tube ends (the tubes fit in the rotor).  They are the best 
   > technology around, by the way; they are about as massive and rotate as fast 
   > as current metallurgy reliably allows.

   Ok now the energy -

   so T = 0.5 * 0.4 * 4 kg * 0.15 m * 0.15 m * (2 * pi * 80000 * 60 1/s)^2
      T = 1.26 MJ

   This is the limit of metallurgical technology, and now someone is claiming
   400 times this energy?  I doubt it.  (400 MJ minimum is required to
   satisfy the claims of the flywheel battery people).

   Also, the bronze casing only has to absorb 1/400 th the energy.  take them
   2 gallons of gasoline for the 400 MJ fuel air bomb, 1/400th is about 1/2 oz
   of gasoline - about a teaspoon.  It'll make a good bang (the freight train?)
   but can be contained.  To look at it another way, this energy is only
   sufficient to melt less than a pound of steel.  I'm sure that centrifuge
   is quite warm when you open it up after such a failure, but there is
   so much mass (8 pounds in the rotor alone) that you won't come close to
   melting anything.

Actually, I think housing failure is not uncommon in ultracentrifuges,
it kills grad students with some regularity. Apparently you can often
hear them go wobbly though and run for it... of course they ain't cheap
either. (Hey, can you imagine quality control at the flywheel factory!
Make them spin each wheel up to 110% of rated spin, through several
cycles...  ;-)

Now, I've asked this several times before, does anyone know
the claimed Q for these beasties? If they're are as good as
the best mesoscopic physical systems I know of they should discharge
significantly over a weekend - somewhat of a problem for a family
commuter car, puts a pretty steep overhead on keeping the tank full.

*  Steinn Sigurdsson   			Lick Observatory      	*
*  steinly@lick.ucsc.edu		"standard disclaimer"  	*
*  Some people think they're really clever			*
*  Smash your head against the wall            Specials, 1979	* 
Xref: sparky sci.energy:6462 sci.electronics:21643 rec.autos:30596