Flywheel Stored Energy

[Don]

How much energy in Kilowatts are present in a spinning mass weighing 2 tons (4,400 lbs) and spinning at 8,000 RPMs?

[swansont]

We're not here to do your homework for you.

 

What are the relevant equations that apply?

[insane_alien]

i don't think any kilowatts are present. you might choose to measure the energy in kilowatt·hrs.

[Don]

We're not here to do your homework for you.

 

What are the relevant equations that apply?

Being back in school would be nice. I'm just trying to determine what potential this new approach to energy storage this website has:

 

http://elanetics.com/turbinearray.html

 

So if the answer is in kilowatt-hrs then I'd like to know the answer to that. Thanks in advance to any assistance with this.

 

don

[swansont]

Ah, now I remember you. It looked like a HW question.

 

KE is [math]\frac{1}{2}I\omega^2[/math] and the moment of inertia (I) of a uniform spinning disc (around the symmetry axis) is [math]\frac{1}{2}mr^2[/math]

 

So you need the radius of the disc. [math]\omega[/math] is the radial speed, in radians/sec

 

Incidentally, the moment of inertia of a uniform rod, spinning around one end (like a fan blade) is [math]\frac{1}{3}mr^2[/math]

[Don]

Each blade is 6 feet long which would also be the radius, correct? Also wouldn't the moment of inertia be 1/3 ML squared not MR? I don't really know. Ok, with that information do you know the answer? Thanks again For the assist.

[John Cuthber]

Q

How much energy in Kilowatts are present in a spinning mass weighing 2 tons (4,400 lbs) and spinning at 8,000 RPMs?

A

Provided that the mass is a very long thin wire spinning on its long axis, the answer can be made as close to zero as you like. OTOH, if it's spinning round an axis other than the long one then the answer can be as high as you like.

[swansont]

I get ~390 kWh, using 2m for the disc radius

 

(L and r both refer to the relevant length for the rotating rod)

[Don]

Q

How much energy in Kilowatts are present in a spinning mass weighing 2 tons (4,400 lbs) and spinning at 8,000 RPMs?

A

Provided that the mass is a very long thin wire spinning on its long axis, the answer can be made as close to zero as you like. OTOH, if it's spinning round an axis other than the long one then the answer can be as high as you like.

What's the answer if it's configured like the illustration in the link above?

[Don]

I get ~390 kWh, using 2m for the disc radius

 

(L and r both refer to the relevant length for the rotating rod)

 

Thanks for the response Swansont!

[Don]

Since kinetic energy increases with the square of the speed if I double the speed would I quadruple the Kw-hrs?

[J.C.MacSwell]

Since kinetic energy increases with the square of the speed if I double the speed would I quadruple the Kw-hrs?

 

yes

[swansont]

Also note that since it depends on the mass distribution (i.e on ^{[math]r^2[/math]}), concentrating more mass on the rim is a win as well

[Don]

Also note that since it depends on the mass distribution (i.e on ^{[math]r^2[/math]}), concentrating more mass on the rim is a win as well

Swansont, I take it this is what you mean:

 

http://elanetics.com/magflywheels.html

 

Thanks for the input!!

[swansont]

Swansont, I take it this is what you mean:

 

http://elanetics.com/magflywheels.html

 

Thanks for the input!!

 

Yes, exactly.