Mechanical Steel vs. Magnetic Levitation Composite Flywheels?

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Discussion Overview

The discussion centers around the energy storage capabilities of composite flywheels, specifically those that are magnetically levitated in a vacuum, compared to traditional ball bearing steel alloy flywheels of the same size and shape. Participants explore the implications of material properties and support mechanisms on energy storage and performance.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about the energy storage difference between an ideal composite flywheel and a steel alloy flywheel, suggesting a significant advantage for composites.
  • Another participant questions whether the energy storage capacity is primarily dependent on the rotating mass and its distribution rather than the material used.
  • A different viewpoint emphasizes the role of the support mechanism, noting that maglev systems may consume energy for active balancing, especially at high speeds.
  • Clarification is provided regarding the terminology used, with one participant interpreting "ball bearing steel alloy flywheel" as a flywheel made from bearing metal rather than one supported by ball bearings.
  • One participant cites a source suggesting that composite materials can store approximately eight times more energy per unit mass compared to steel, attributing this to their ability to withstand higher rotational velocities.
  • Another participant discusses the relationship between specific strength and maximum rotational speed, questioning if specific strength is directly proportional to maximum speed capability.
  • A later reply asserts that while velocity is related to the square root of specific strength, energy density is directly proportional to specific strength.

Areas of Agreement / Disagreement

Participants express differing views on the factors influencing energy storage in flywheels, particularly regarding the impact of material properties versus support mechanisms. There is no consensus on the primary determinants of energy storage capabilities.

Contextual Notes

Some assumptions about the definitions of terms used in the discussion may not be fully clarified, and the relationship between specific strength and energy storage remains unresolved.

BasketDaN
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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.
 
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Isn't it purely dependent upon the rotating mass (and distribution thereof) as opposed to what material is used?
 
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?
 
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.
 
BasketDaN said:
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).
 
Last edited by a moderator:
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?
 
Nope, velocity goes as the square-root of the specific strength, energy density goes directly as the specific strength.
 

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