Flywheels: Kinetic into Potential Energy Kinetic into Potential Energy.
-
Upload
reynold-morgan -
Category
Documents
-
view
234 -
download
1
Transcript of Flywheels: Kinetic into Potential Energy Kinetic into Potential Energy.
Flywheels:Flywheels: Kinetic into Potential Kinetic into Potential
EnergyEnergy
• Ultracapacitors: – Stores energy as a charge across two plates– High power, low energy
• Flywheels:– Energy stored in a high velocity composite wheel. When
desired, energy is transferred to the axle via clutch • Batteries:
– Electrochemical reaction creates electricity as long as reactants exist in closed containers (closed system)
• Fuel Cells:– Electrochemical reaction creates electricity as long as fuel
and oxidant are supplied (open system)
Alternative Vehicle Energy Storage
Vehicle Power RequirementsPower (W,J/s) = Energy (mass*velocity2) (J, Ws) /Time (s)
• Small passenger vehicles = 70-90hp (50-65kW)
• SUV or truck = 120-180hp (90-135kW)
• Only 10-25hp when cruising (I.e. not accelerating)
• Electric Vehicles (EV’s) must store-release ALL this power/energy
• Hybrid Vehicles (HEV’s) only need recoup-release small portion of this power/energy to supplement IC engine
Flywheel: Electromechanical System
Motor/Generator• Supply and remove energy via electricity
Housing• Containment (for safety in case of burst)• Vacuum (prevent heating, reduce losses)
Bearing(s)• Allow free rotation of rotor• Maintain orientation of rotor
Rotor (complete rotating assy.)• Rim (primary spinning mass)• Hub (connects rim and shaft)• Shaft (connects m/g to bearings, hub & rim)
Suspension• Shock & vibration isolation• Anchorage
Ball Bearings
Source: The Barden Corp.
Ball
Outer RaceInner Race
Cage
Groove
StatorRotor
Source: Revolve, Inc. http://www.revolve.com
Magnetic Bearings
Bearings
Rotor DesignObjective: Maximize energy per unit mass
Assume: Thin rim flywheel of radius r and mass m
Energy: K = ½ I2, where = rotational velocity (rad/s) and polar moment of inertia I = mr2
K = ½ mv2 = ½ mr22
where rim velocity v = r
•Want high strength, low density & high velocity
Flywheel Pros & Cons
Pros• High round-trip efficiency in short-
term use (80-95%)
• Potentially long product life (measured in tens of years)
• Low toxicity of constituents • High power per unit mass (fast,
equal charge & discharge times)
• Easy to determine state of charge
Cons• Developing technology
• Currently expensive
• Potentially low energy per unit mass (due to bulky containment)
• Uncertain safety in a burst event:– fragmentation & ejection of
material– sudden release of energy
Source: T. Michaelis, NASA GRC, 10/99
Speed ofSound in
air (1 atm,20°C)
Concorde AssaultWeapon
KalashnikovAK-102
Carbon FiberRotor
344 m/s 688 m/s 850 m/s @muzzle
1000 m/s @rim OD
Mach 1 Mach 2.0 Mach 2.5 Mach 2.9
Perspectives
• High speed flywheel must spin in vacuum
University of Texas Center for Electromechanics
• High speed fossil-fuel powered train w/ comparable acceleration as all-electric train
• 3 MW turbine-alternator to overcome rolling and aerodynamic losses at 150 mph
• 600 MJ (165 kWh) flywheel capable of delivering an additional 3 MW for acceleration, speed maintenance on grades, and recovery of braking energy