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Flywheel Kinetic Energy
Kinetic energy and moment of inertia of a flywheel
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A flywheel is used to smooth the energy fluctuations in combustion engines and make the energy flow uniform. The flywheels store energy mechanically as kinetic energy.
Kinetic Energy
The kinetic energy of a flywheel can be expressed as
Ef = 1/2 I ω2 (1)
where
Ef = flywheel kinetic energy (Nm (Joule), ft lb)
I = moment of inertia (kg m2, lb ft2)
ω = angular velocity (rad/s)
Angular velocity converting units
- 1 rad = 360o / 2 π =~ 57.29578o
- 1 rad/s = 9.55 r/min (rpm) = 0.159 r/s (rps)
Moment of Inertia
Moment of inertia quantifies the rotational inertia of a rigid body and can be expressed as
I = k m r2 (2)
where
k = inertial constant - depends on the shape of the flywheel
m = mass of flywheel (kg, lb)
r = radius (m, ft)
Inertial constants of some common types of flywheels
- wheel loaded at rim like a bicycle tire - k =1
- flat solid disk of uniform thickness - k = 0.606
- flat disk with center hole - k = ~0.3
- solid sphere - k = 2/5
- thin rim - k = 0.5
- radial rod - k = 1/3
- circular brush - k = 1/3
- thin-walled hollow sphere - k = 2/3
- thin rectangular rod - k = 1/2
Moment of Inertia Converting Units
- 1 kg m2 = 10000 kg cm2 = 54675 ounce in2 = 3417.2 lb in2 = 23.73 lb ft2
Flywheel Rotor Materials
| Material | Density (kg/m3) |
Design Stress (MN/m2) |
Specific Energy (kWh/kg) |
| Aluminum alloy | 2700 | ||
| Birch plywood | 700 | 30 | |
| Composite carbon fiber - 40% epoxy | 1550 | 750 | 0.052 |
| E-glass fiber - 40% epoxy | 1900 | 250 | 0.014 |
| Kevlar fiber - 40% epoxy | 1400 | 1000 | 0.076 |
| Maraging steel | 8000 | 900 | 0.024 |
| Titanium Alloy | 4500 | 650 | 0.031 |
| "Super paper" | 1100 | ||
| S-glass fiber/epoxy | 1900 | 350 | 0.020 |
- Maraging steel is an iron alloy with a large percentage of nickel and superior strength
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Related Topics
- Dynamics - Dynamics Motion - velocity and acceleration
- Mechanics - Kinematics, forces, vectors, motion, momentum, energy and the dynamics of objects
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Related Documents
- Angular Motion - Power and Torque - Angular velocity and acceleration - power and torque
- Energy - Energy is the capacity to do work
- Formulas of Motion - Linear and angular acceleration, velocity and displacement
- Kinetic Energy - The kinetic energy of a rigid body is the energy possessed by the body motion
