On Wed, 26 Aug 2009 23:26:34 -0400 Allan Streib <str...@cs.indiana.edu>
wrote:
> Craig McCluskey <diese...@pisquared.net> writes:
>
> > Jim's comment about how much momentum a moving freight train has is
> > indicative of the size of flywheel you would need. It wouldn't fit on
> > the train and couldn't fit through tunnels and across bridges.
>
> I'm imagining some kind of giant, box-car sized capacitors that would
> absorb energy during braking and release it back to the motors during
> acceleration. Again, probably impractical or they'd be doing it.
Well, there have been recent improvements in capacitors that allow them to
store more energy, but I don't remember the energy storage density.
To get an idea of how much energy one would need to store, consider a
locomotive accelerating a train from stop to some speed. Say, for example,
we have a 4000 horsepower locomotive that runs for 10 minutes to get the
train moving. That's
746 watt 60 seconds
4000 horsepower x ---------- x 10 minutes x ------------
horsepower minute
= 1.79 x 10^9 watt-seconds = 1.79 x 10^9 Joules = 1.79 x 10^6 kiloJoules
If the energy storage density is 10 kJ / cubic foot (not too far off, I
think) the volume of the capacitor would be 100,000 cubic feet. If the
energy storage density is 100 kJ / cubic foot, the volume of the capacitor
would be only 10,000 cubic feet.
Craig
_______________________________________
http://www.okiebenz.com
For new and used parts go to www.okiebenz.com
To search list archives http://www.okiebenz.com/archive/
To Unsubscribe or change delivery options go to:
http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
