Mechanical Steel vs. Magnetic Levitation Composite Flywheels?

[BasketDaN]

Spinning at their respective maximum velocities, approximately how much more energy will an ideal composite flywheel (magnetically levitated in a vaccum) be able to store than an ideal ball bearing steel alloy flywheel of the same size and shape? Thanks.

 

[BasketDaN]

Anybody? ..

 

[Danger]

Isn't it purely dependent upon the rotating mass (and distribution thereof) as opposed to what material is used?

 

[berkeman]

I think he's asking about the difference that the support mechanism makes -- maglev versus bearings with physical contact. It seems like the maglev approach will still burn energy, because it will likely take some active feedback to keep the flywheel balanced while it spins, especially at high velocities. To the OP -- were you thinking of some passive maglev scheme to try to minimize the extra energy needed? Is passive maglev going to be sufficient? Do you have examples of maglev flywheels that you can point us to for reference?

 

[Danger]

I see. I thought that the phrase 'ball bearing steel alloy flywheel' meant that the wheel was made out of bearing metal, not that it was supported by ball bearings.

 

[pervect]

Spinning at their respective maximum velocities, approximately how much more energy will an ideal composite flywheel (magnetically levitated in a vaccum) be able to store than an ideal ball bearing steel alloy flywheel of the same size and shape? Thanks.

Looks to be about 8x more energy / unit mass for composites from the figures at

http://www.aspes.ch/faq.html#Why%20composite%20materials

(CFRP, some sort of carbon fiber composite, I guess, having the highest rating).

 

[BasketDaN]

The difference only exists because composite flywheels are able to withstand far greater rotational velocities than are steel flywheel.s

Yeah, I found that site too,, do you think the specific strength is directly proportional to the maximum speed it can withstand?

 

[pervect]

Nope, velocity goes as the square-root of the specific strength, energy density goes directly as the specific strength.